Dissertations / Theses: 'Zeolites as catalysts'

1

Sonqishe, Thantaswa Millecent. "Treatment of brines using commercial zeolites and zeolites synthesized from fly ash derivative." Thesis, University of the Western Cape, 2008. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_6127_1297842299.

Full text

Abstract:

The objectives of this project was to ameroliate two waste materials, namely Acid Mine Drainage and Fly Ash and recover the solid residues for conversion into an adsorbent to treat brine. The solid residues were then converted into zeolite P through low temperature hydrothermal treatment. The adsorption capacity of the solid residues, zeolite P derived from the solid residues was compared to the commercial zeolite Y and fresh Arnot fly ash. The quality of the resulting water was assessed using different analytical methods before the reaction with adsorbents and after the reaction and a comparison was done based on the removal efficiency of elements Zeolite P from solid residues was successfully synthesized as confirmed by XRD, BET and FTIR. Brine treatment with fly ash, solid residues, zeolite P and commercial zeolite Y adsorbents was done concentration on the following major elements Na, K, Mg, Ca and Si. Zeolite P had higher or similar removal efficiency that the commercial zeolite Y for the following elements K, Ca and Mg. Fly ash is the only adsorbent that managed to reduce the concentration of Na in brine and also had a good removal efficiency of Mg. Si leached out of all the adsorbents which could be ascribed to Si being the major component of these adsorbents which could indicate some dissolution of these adsorbents under the conditions tested. Overall, zeolite P did not completely remove the major elements, especially for Na, but did result in a cleaner waste stream which would improve brine processing.

APA, Harvard, Vancouver, ISO, and other styles

2

Huang, Wei. "Selective hydrogenation on zeolite-supported bimetallic catalysts." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 0.90 Mb., p. 76, 2005. http://proquest.umi.com/pqdlink?did=1037889271&Fmt=7&clientId=8331&RQT=309&VName=PQD.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Uçar, Şule Yılmaz Selahattin. "Investigation Of Catalytic Activity And Selectivity Of Pd and Ni Loaded Clinoptilolite Rich Natural Zeolite For Citral Hydrogenation/." [s.l.]: [s.n.], 2002. http://library.iyte.edu.tr/tezler/master/kimyamuh/T000122.doc.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Monama, Winnie. "Hierarchical zeolites: novel supports for hydrocracking catalysts." Thesis, University of Limpopo, 2016. http://hdl.handle.net/10386/1565.

Full text

Abstract:

Thesis (M. Sc. (Chemistry)) -- University of Limpopo, 2016
In this study, the use of synthetic hierarchical MFI zeolites as supports for palladium hydrocracking catalysts was investigated. Hierarchical zeolites were synthesised through two different routes, viz., (i) the indirect and (ii) direct routes. In (i) pristine ZSM-5 zeolites with different SiO2/Al2O3 ratios (SARs) were synthesised hydrothermally using tetrapropylammonium bromide as structure-directing agent (SDA), followed by a brief desilication of its calcined form in 0.2 M NaOH solution at 65 °C for 0.5 h. Procedure (ii) involved prior synthesis of three polyquaternary ammonium surfactants (containing 2 - 4 ammonium centres), followed by their use as SDAs in the hydrothermal synthesis of hierarchical MFI zeolites. The resulting materials were characterised by XRD, FT-IR, SEM and N2 adsorption isotherms (including BET surface area measurements). Successful synthesis of different classes of the hierarchical MFI zeolites was confirmed by XRD patterns, while successful synthesis of polyquaternary ammonium surfactants was confirmed by both their 1H NMR spectra and their ability to direct the MFI structure. On the basis of IR, peak intensities in the OH region between 3500 and 3800 cm-1, the surfactant-templated zeolites were inferred to be more acidic than zeolites prepared through the desilication route. Significant changes in crystal morphology were observed upon desilication of ZSM-5(50), while the ZSM-5(77) and ZSM-5(100) retained their agglomerated morphology upon a similar treatment. The micrograph pristine of ZSM-5(50) showed a predominant morphology of large and small spheroids, together with some ill-defined cubic shapes. After desilication, the zeolite did not retain the original morphology entirely, showing hexagonal prismatic crystals with twinning occurring in other areas and large spheroids “hatching” to reveal their contents upon treatment. Desilicated zeolites exhibited improved textural properties (i.e., increased SBET, pore volumes and pore diameters) and minor structural readjustments compared to their pristine counterparts. Textural properties of surfactant-templated zeolites were superior to those of desilicated zeolites, and improved with increasing number of quaternary ammonium centres in the surfactant template. These materials were generally more crystalline than the conventional zeolites. Hydrocracking catalysts containing 0.9 wt.% Pd loading on different MFI supports were prepared by the incipient wetness impregnation method. The n- v hexadecane hydrocracking conditions used were typical of LTFT process (i.e., Temperature = 215 - 310 °C, WHSV = 1 h-1, Pressure = 20 bar, in addition to the H2 /n-C16 ratio of 10). The catalytic activity in all catalyst systems increased with increasing reactor temperature and displayed C4/C12 ratios ≠ 1, evidence of the occurrence of secondary cracking (i.e., a non-ideal hydrocracking behaviour). This was also supported by the shapes of their product distribution profiles, which showed dominant C3 - C7 n-paraffins. Co-feeding H2O with n-C16 into the reactor was found to be detrimental to n-C16 conversion, but promoted the selectivity to iso-paraffins in the product spectrum. Simultaneous introduction of CO and H2O aggravated secondary cracking. Amongst the pristine ZSM-5 zeolite-based catalysts, Pd/P-ZSM-5(77) showed the best catalytic performance. Upon desilication, the performance order changed to favour Pd/D-ZSM-5(50*). For the surfactant-templated supports, Pd/HSZ(N4) showed the most superior hydrocracking performance. Comparison of catalytic activities of the best performing catalyst systems derived from the conventional and surfactant-templated zeolites in the hydrocracking of n-hexadecane, follow the order Pd/D-ZSM-5(50*) > Pd/P-ZSM-5(77) > Pd/HSZ(N4). That is, the pristine and desilicated zeolite-based catalysts performed better than their surfactant-templated zeolite-based counterparts. Therefore, the post-synthesis generation of mesoporosity through desilicating ZSM-5 with a SAR of 50 has proven beneficial for the resulting catalyst system. One of the possible reasons for the relatively inferior hydrocracking performance of the Pd/HSZ(N4) catalyst may be the aluminium-richness of the support (SAR = 40) compared to the conventional ZSM-5-based supports. In summary, catalysts Pd/D-ZSM-5(50*), Pd/P-ZSM-5(77) and Pd/HSZ(N4) are promising for diesel-selective catalysis and need further refinements and exploration.

APA, Harvard, Vancouver, ISO, and other styles

5

Woods, Gary B. "Computer simulation of fluids in zeolites." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.237831.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Seyedeyn-Azad, Fakhry. "Nitrogen monoxide reduction over ZSM-5 zeolite-supported catalysts /." Title page, summary and contents only, 1999. http://web4.library.adelaide.edu.au/theses/09PH/09phs519.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Panpranot, Joongjai. "Hydrothermal aging of zeolite-based catalysts." Morgantown, W. Va. : [West Virginia University Libraries], 1998. http://etd.wvu.edu/templates/showETD.cfm?recnum=274.

Full text

Abstract:

Thesis (M.S.)--West Virginia University, 1998.
Title from document title page. Document formatted into pages; contains xi, 84 p. : ill. Includes abstract. Includes bibliographical references (p. 64-67).

APA, Harvard, Vancouver, ISO, and other styles

8

Folifac, Leo. "Performance of zeolite ZSM-5 synthesised from South African fly ash in the conversion of methanol to hydrocarbons." Thesis, Cape Peninsula University of Technology, 2018. http://hdl.handle.net/20.500.11838/2751.

Full text

Abstract:

Thesis (Master of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2018.
Zeolites have found applications as heterogeneous or solid catalyst in the petrochemical and refining industries. Zeolite ZSM-5 in particular is a highly siliceous solid catalyst with a porous network that consists of medium pore structure (pore openings 5-5.5 A). The solid catalyst (ZSM-5) is well known for its high temperature stability and strong acidity, which makes it an established catalyst used for different petrochemical processes such as Methanol-To-Gasoline (MTG), isomerisation, disproportionation, and cracking. Unlike in the past, the synthesis of zeolite ZSM-5 from other sources that contains silica (Si) and alumina (Al) with the addition of a template (TPBr) as a structure-directing agent is eminent. Its synthesis can be achievable from coal fly ash that is a waste material and a cheap source of Si and Al. Coal fly ash is a waste material that is produced during the combustion of coal to generate electricity. The elemental composition of coal fly ash consists of mostly SiO2 and Al2O3 together with other significant and trace elements. Zeolite ZSM-5 catalyst synthesised from coal fly ash by previous authors required an excessive amount of additional source of silica even though the XRD spectra still show the presence of quartz and mullite phase in the final products. These phases prevented the use of fly ash (solid) as a precursor to synthesise zeolite ZSM-5 products. However, the synthesis of high purity zeolite ZSM-5 products by extracting silica and alumina from South African fly ash and then using it with small amounts of fumed silica was investigated This aim was achieved by fusing fly ash (FA) with sodium hydroxide (NaOH) under hydrothermal condition set at 550 oC for 1 hour 30 minutes. The quartz and mullite phase observed by previous authors was digested by the fusion process. Thereafter, the treatment of fused fly ash filtrate (FFAF) with concentrated H2SO4 (98-99%), precipitated silica and removed Al that therefore increased the Si/Al ratio from 1.97 in fly ash (FA) to 9.5 in the silica extract (named fused fly ash extract). This route was designed to improve the quality of the final products and reduced the amount of fumed silica added to the synthesis mixture prior to hydrothermal synthesis. In this line of investigation, the process of adding fumed silica to the hydrothermal gel was optimised. H-FF1 with a Si/Al ratio of 9.5 was synthesised using the silica extract without the addition of fumed silica. Its XRD, SEM and relative crystallinity results proved that H-FF1 was inactive and hence was not further characterised and utilised in the conversion of methanol to hydrocarbons (MTH). Purer phase zeolite ZSM-5 products (H-FF2 and H-FF3) that were synthesised from silica extract with the addition of small amounts of fumed silica were characterised and successfully used in the methanol to hydrocarbons (MTH) reaction. The synthesised ZSM-5 products had different Si/Al ratio, different morphology, crystal size, BET surface area, and relative crystallinity as well as different trends in the MTH reaction. It was also observed that H-FF2 and H-FF3 (pure phase) solid catalyst deactivated faster than the commercial H-ZSM-5 in the MTH reaction. However, the MTH conversion over H-FF2 competed with that of the commercial H-ZSM-5 within 3 hours of time on stream (TOS) but later deactivated at a faster rate. This was caused by the large crystal size and reduced BET surface area of H-FF2 when compared to the commercial H-ZSM-5. However, H-FF2 performed better than H-FF3 on stream (MTH reaction) due to its smaller crystal size and higher BET. This study has successfully utilised a route that synthesised high purity zeolite ZSM-5 products from the South African fused fly ash extract (FFAE) with the addition of small amounts of fumed silica. The properties of the synthesised zeolite ZSM-5 products (H-FF2 and H-FF3) were similar to that of the commercial H-ZSM-5 as well as active in the MTH reaction. This promoted the utilisation of a waste material (coal fly ash) to synthesise highly siliceous zeolite ZSM-5 products that avoided the presence of mineral phases from fly ash in the final products.

APA, Harvard, Vancouver, ISO, and other styles

9

Axon, Sean Alexander. "MFI-type zeolites synthesized in non-alkaline media." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240100.

Full text

APA, Harvard, Vancouver, ISO, and other styles

10

Güneş, Alev Bayraktar Oğuz. "The production of thymoquinone from thymol and carvacrol by using zeolite catalysts/." [s.n.]: [s.l.], 2005. http://library.iyte.edu.tr/tezler/master/kimyamuh/T000391.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

11

Birsoy, Öniz Yılmaz Selahattin. "Effects of metal cation on the skeletal isomerization of n-Butene over ZSM-5 and ferrierite/." [s.l.]: [s.n.], 2005. http://library.iyte.edu.tr/tezler/master/kimyamuh/T000432.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Dillon, Christopher J. "Zeolites as catalysts for fine chemicals synthesis : Friedel-Crafts acetylation." Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343865.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Suwardiyanto. "Novel molybdenum/zeolite catalysts for methane dehydroaromatization." Thesis, University of Aberdeen, 2015. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=228007.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

O'Connor, James Francis. "The removal of lead pollutants from effluents using zeolites." Thesis, City University London, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304673.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Güleç, Hilal Yılmaz Selahattin. "Liquid phase hydrogenation of citral on zeolite supported monometallic (Ni,Pt) and bimetallic (ni-Sn.Pt-Sn) catalysts/." [s.l.]: [s.n.], 2005. http://library.iyte.edu.tr/tezler/master/kimyamuh/T000398.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Al-Nayili, Abbas. "Novel Lewis acidic zeolites as heterogeneous catalysts for liquid phase chemistry." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/107295/.

Full text

Abstract:

Porous Lewis acids are rapidly emerging heterogeneous catalysts, particularly for the upgrading of biorenewable feedstocks, due to their ability to coordinate lone-electron pairs from oxygen atom, hence inducing molecular rearrangements and cleavage. As such, this study tackles one of the most important challenges in liquid phase catalytic chemistry, namely the design of novel Lewis acidic zeolites to act as heterogeneous catalysts for liquid phase applications. Lewis acidic (Sn-BEA) zeolites are typically synthesised by highly complicated hydrothermal synthesis procedures, which have significant downsides preventing industrial application. In addition to technical difficulties, some drawbacks minimize the effectiveness of Sn-BEA in industrial interest. Amongst these limitations are 1) long crystallization time (40 days), 2) the large crystallite sizes obtained via typical hydrothermal synthesis, resulting in mass-transfer issues, and 3) the low Sn amount (typically < 2 wt.%), resulting in low space-time yield. Furthermore, a relatively amount of undesirable HF is required to induce crystallisation. Therefore, much academic and industrial research is currently devoted to the development of new methodologies for preparing Lewis-acid zeolite catalysts with higher or similar activity. The broad context at this doctoral dissertation is to investigate the potential of acid leaching (i.e., demetallation) of commercial (Al-containing) BEA zeolite as a simple, versatile, and scalable method to introduce different amounts of active centers (Sn) in zeolites, using solid-state incorporation (SSI). To evaluate the activity of the synthesized catalysts, the study focused firstly on the Meerwein-Ponndorf-Verley (MPV) transfer hydrogenation of carbonyl compounds and isomerization of glucose. Owing to the low activity of Sn-BEA micropores catalyst for the activation of bulky molecules, mesopores are subsequently created via top-down alkaline treatment to synthesis hierarchical Lewis-acid porous zeolite (Sn-h*-BEA), by employing the post-synthetic demetallation route. This catalyst, was evaluated in reactions that involve bulky molecules, such as cyclooctanone (C8) and cyclododecanone (C12). Sn-h*-BEA was found to be active, selective and more stable for continuous operation than its purely microporous analogue. Subsequent work focused on the catalytic valorisation of bio-renewable feedstock, which often relies upon multi-stage processing of highly-functionalised substrates, resulting in selectivity and process engineering challengers. Later parts of this thesis therefore report the synthesis of a novel acid-base bifunctional catalyst [Sn-Al] BEA which contains Sn-related Lewis acid sites and Al-related BrØnsted acid sites. This bifunctional catalyst has been tested, as a catalyst for the cascade catalytic transfer hydrogenation and etherification of furfural, under batch as well as continuous flow reaction condition. With this catalyst, furfural was first converted by Lewis acid Sn(Ⅳ) framework sites to form furfural alcohol via transfer hydrogenation from the solvent. Subsequently, furfuryl alcohol etherification with the solvent is catalysed by the BrØnsted acid (Al) framework to produce corresponding alkyl furfuryl ether. Such ethers are highly desirable as bio renewable fuel additives.

APA, Harvard, Vancouver, ISO, and other styles

17

Schnitzer, Jill. "Liquid phase hydroformylation by zeolite supported rhodium." Thesis, Virginia Tech, 1985. http://hdl.handle.net/10919/45732.

Full text

Abstract:

The purpose of this research was to directly compare the behavior of zeolites containing rhodium with that of homogeneous rhodium species as catalysts for liquid phase hydroformylation of 1-hexene in order to study the effects of zeolite immobilization. NaX zeolite was cation exchanged with several rhodium salts and used as hydroformylation catalysts at 50°C and 125°C in the presence of: triphenylphosphine (PPh₃), dimethylphenylphosphine (PMe₂Ph), and the poison for zeolite surface and solution rhodium: triphenylmethylmercaptan (Ph₃CSH). The results of these experiments were compared with those of several homogeneous catalysts under similar conditions. It was found that previously reported results of intrazeolitic activity with RhNaX at 50°C were probably incorrect, since, the addition of PMe₂Ph, Ph₃CSH, or both, virtually halted all reactivity of RhNax. The catalytic results at 125°C did not conclusively indicate the location of the active rhodium. Thus, intrazeolitic activity at 125°C may or may not have been observed, and needs further investigation. Reaction profiles were obtained for several of the catalyst systems, using an automatic sampling system. From these profiles, it was found that the addition of excess PMe₂Ph halted isomerization of 1-hexene to 2-hexenes for the zeolite-supported rhodium, and hindered, but did not stop isomerization for the homogeneous catalysts. Also, as expected, it was observed that the homogeneous catalysts reacted to completion faster than the heterogeneous catalyst. In addition, the effects of such treatments as preheating in air and precarbonylation of the heterogeneous catalysts were studied. Pretreatments had no effect upon the catalysis. Also, no activity was observed from the heterogeneous catalysts at 125°C unless phosphines were present. Finally, the hydrogenation of 1-hexene was studied. Heterogeneous and homogeneous rhodium catalysts showed hydrogenation activity which was accompanied by isomerization at 60°C and 125°C.
Master of Science

APA, Harvard, Vancouver, ISO, and other styles

18

Connaway, Melissa Clare. "Design and characterization of zeolite supported cobalt carbonyl catalysts." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/82894.

Full text

Abstract:

Transition metal compounds such as Co₂(CO)₈ have often been used to catalyze various organic reactions. Severe difficulties may be encountered when attempts are made to recover and separate the soluble catalysts. A heterogeneous system consisting of Co₂(CO)₈ impregnated on zeolites with faujasitic structure has been designed and investigated using a variety of techniques. In situ FTIR spectroscopy and carbon monoxide evolution were used to identify the major products generated, namely Co₄(CO)₁₂ and Co(CO)_4^-. Disproportionation may be induced thus forming Co(CO)_4^- and an associated cation from the supported subcarbonyls by addition of various ligands such as methanol. The location of the supported cobalt carbonyls is determined by their reactivity toward various phosphines with various kinetic diameters. The materials prepared in this manner were found to be active in catalyzing the methanol carbonylation reaction and following thermolysis were also found to be active Fischer-Tropsch catalysts. Major products observed in the carbonylation of methanol were methyl acetate and an acetaldehyde dimethyl acetal. The supported cobalt catalyst displays greater activity than Co₂(CO)₈ in solution for the carbonylation reaction when conducted under similar conditions. In the Fischer-Tropsch process, selectivity is seen for the production of linear, short-chain hydrocarbons.
Ph. D.

APA, Harvard, Vancouver, ISO, and other styles

19

Wang, Yi. "Synthesis and catalytic performance of hierarchical Zeolites supported Nickel-Tungsten hydrodesulfurization catalysts." Thesis, Lille 1, 2015. http://www.theses.fr/2015LIL10124/document.

Full text

Abstract:

Des règles environnementales de plus en plus strictes imposent une concentration en soufre dans les carburants en-dessous de 10 à 15 ppm. Donc, des catalyseurs plus efficaces doivent être développés. Dans ce travail, des catalyseurs nickel-tungsten supportés sur zéolites Beta et Mordenite hiérarchisées ont été préparés et évaluées en hydrodésulfuration (HDS).Tout d'abord, des zéolites Beta hiérarchisées ont été obtenues par post-traitement et caractérisées par DRX, N2-sorption, SEM, TEM et RMN. En conséquence, la zéolite Beta hiérarchisée préparée par post-traitement base-acide présente une excellente activité dans les réactions en catalyse acide, en particulier pour la conversion de grosses molécules.Des catalyseurs NiW supportés sur Al2O3 (NiW/Al2O3), zéolite Beta commerciale et hierarchisée (NiW/HB et NiW/HB-M), zéolite Mordenite commerciale et hierarchisée (NiW/HM et NiW/HM-M) ont été préparés et caractérisés par XRD, N2-sorption, IR, TEM et XPS. L'activité en HDS du 4,6-DMDBT sur NiW/HM-M et NiW/HB-M est plus du double de celle du catalyseur à base d’alumine NiW/Al2O3. La désactivation de catalyseurs supportés sur zéolite Beta a été étudiée dans la réaction d’HDS du thiophène. Les résultats indiquent que le mélange des solides NiW/HB ou NiW/HB-M avec NiW/Al2O3 et l'utilisation de zéolite Beta après échange avec des ions Na+ comme support (NiW/NaB-M) améliorent remarquablement la capacité anti-désactivation des catalyseurs. En conséquence, les catalyseurs NiW/NaB-M et catalyseur mélangé conduisent à une activité catalytique supérieure à celle de NiW/HB-M et NiW/Al2O3
More and more strict regulations were drawn up in many countries to limit the concentration of sulfur below 10 ppm or 15 ppm in transportation fuel oil. Therefore, more efficient catalysts have to be developed. In this work, hierarchical Beta and Mordenite zeolite supported nickel-tungsten catalysts were prepared and evaluated in hydrodesulfurization (HDS) reactions.Firstly, hierarchical Beta zeolite was prepared by post-treatment and characterized by XRD, N2-sorption, SEM/TEM and NMR techniques. As a result, hierarchical zeolite Beta prepared by base-acid treatment exhibited excellent catalytic activity in acid-catalytic reactions, especially towards large molecules. NiW catalysts supported on Al2O3, commercial Beta and Mordenite zeolites (HB and HM), and hierarchical Beta and Mordenite prepared by post treatment (HB-M and HM-M) were characterized by XRD, N2 sorption, IR, TEM and XPS. Zeolite supported catalysts exhibited higher catalytic performance in the HDS of 4,6-DMDBT, due to the strong acidity of the zeolitic support that supplied an additional isomerization reaction route. The use of hierarchical zeolite could further improve the isomerization ability of catalyst. As a result, the HDS activity of 4,6-DMDBT over NiW/HM-M and NiW/HB-M was more than twice as that of NiW/Al2O3. The deactivation of hierarchical Beta zeolite supported catalysts was studied in the HDS of thiophene. Interestingly, mixing NiW/HB or NiW/HB-M with NiW/Al2O3 and the utilization of Na+-exchanged Beta as support (NiW/NaB) improved remarkably the anti-deactivation ability of the catalysts. As a result, NiW/NaB-M and mixture catalyst gave superior catalytic activity than NiW/HB-M and NiW/Al2O3

APA, Harvard, Vancouver, ISO, and other styles

20

Pillinger, Martyn. "EXAFS studies of polyoxometalates and polyoxometalate-pillared layered double hydroxides." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240624.

Full text

APA, Harvard, Vancouver, ISO, and other styles

21

Nada, Majid H. "Mechanochemically assisted synthesis of zeolite catalysts for biomass conversion." Diss., University of Iowa, 2019. https://ir.uiowa.edu/etd/6997.

Full text

Abstract:

Recently, there has been growing interest in the green synthesis of zeolite (aluminosilicate) materials using solvent-free synthesis methods. Solid starting materials are typically ground for a period of time followed by thermal heating to synthesize crystalline ZSM-5 zeolite. These studies generally have focused on products formed after the thermal heating. However, very little is known about the reaction intermediates formed during the mechanochemical pre-reaction grinding step and how the pre-reaction impacts the subsequent synthetic success. In this study, the mechanochemical approach used to synthesize ZSM-5 and mordenite zeolite was investigated. Two types of solvent-free synthesis methods were investigated; templated solvent-free synthesis, and template-free and solvent-free synthesis. The effect of grinding time was investigated first to find the optimal grinding time that initiates pre-reactions between the starting materials. Controlled experiments were used to monitor chemical and physical changes occuring during the grinding step. Subsequently, the effect of different synthesis conditions such as time, temperature, template, SiO2/Al2O3, and Na2O/Al2O3 ratios, and different precursors were studied using the optimal grinding time. Both manual (mortar and pestle) and ball mill (FTS 1000) grinding were used in this study. The synthesized products were characterized using XRD, BET nitrogen adsorption, SEM, and ICP-OES. Finally, selected single-phase synthesized zeolite materials were evaluated for their catalytic performance in biomass conversion process of cellulose and glucose to useful chemicals such as hydroxymethylfurfural (HMF).

APA, Harvard, Vancouver, ISO, and other styles

22

Marin-Rosas, Celia. "Middle distillate hydrotreatment zeolite catalysts containing Pt/Pd or Ni." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1066.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

Fox, Jack David. "Infrared vibrational spectra of tert-butyl halides in dehydrated NA-X and low-aluminum H-Y faujasites vibrational excitation exchange and other effects of guest-host interactions /." Diss., Online access via UMI:, 2006.

Find full text

APA, Harvard, Vancouver, ISO, and other styles

24

Bräuer, Pierre. "A multi-technique approach to characterise acidic surface properties of microporous catalysts." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/278651.

Full text

Abstract:

Microporous catalysts belong to a class of materials that exhibit pore networks in the molecular dimension, that is, channel diameters less than 2 nm. The industrially most important microporous catalysts are zeolites, which are crystalline aluminosilicates and consist of interlinked alumina (AlO4) and silica (SiO4) tetrahedra forming pores and cavities of molecular dimensions. Zeolites can act as very strong solid acids and function as heterogeneous catalysts in various industrial processes used to obtain polyethylene terephthalate (PET) or polyvinyl chloride (PVC). They are crucial for products with a significant market demand such as plastics used in bottles, packaging materials and household consumable goods as well as for coatings of pharmaceutical pills and detergents. Recently, zeolites have been found to have increased applications in aqueous and biphasic reactions that use reactants derived from biomass to arrive at petrochemical products. Thus, surface acidity in zeolites is crucial to understand to tune parameters such as activity and selectivity of zeolite catalysts to optimize product distributions. The objective of this dissertation was to validate the use of non-invasive nuclear magnetic resonance (NMR) techniques to characterise surface acidity in zeolites by benchmarking the NMR results to various more established zeolite characterisation techniques, such as Fourier transform infrared (FTIR) spectroscopy and temperature-programmed desorption (TPD). Furthermore, the use of the tapered element oscillating microbalance (TEOM) to characterise internal and external acidity in zeolites was explored. IR and TPD techniques were used to assess important acidity parameters such as type, number, location and strength of acid sites of ZSM-5 zeolites with varying silica-alumina ratio (SAR = SiO2/Al2O3). The use of NMR relaxation time analysis of pyridine adsorbed in ZSM-5 was then explored as a model system to study surface acidity in microporous materials. Correlation with pyridine TPD results suggested that NMR relaxation time analysis probes the effective strength of pyridine adsorption sites, which varies with SAR. NMR relaxation time analysis was then further shown to be applicable to characterise non-acidic surface properties such as the hydrophilic and hydrophobic surface character. Lastly, the NMR techniques developed at high magnetic field strength (300 MHz) were transferred to a portable, low-cost benchtop low-field (43 MHz) magnet and shown to be applicable for base probe molecules other than pyridine, that is, ammonia (NH3) as well as zeolite framework types other than ZSM-5, that is, chabazite (CHA).

APA, Harvard, Vancouver, ISO, and other styles

25

Rode, Edward James. "Rhodium-zeolite hydroformylation of propylene." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/71252.

Full text

Abstract:

The purpose of this research was to characterize the rhodium exchanged NaX and NaY zeolites as propylene hydroformylation catalysts. Catalytic activity was measured in a differential bed reactor. Flow in situ infrared spectroscopy was used to probe the coordination chemistry of the zeolite modified rhodium carbonyls. The catalytic activity of rhodium zeolites at atmospheric pressure and between 100-150ºC was measured. The rate of n-butyraldehyde production was approximately 5x10⁻³ moles/g- Rh hr at 150°C. Regioselectivity was dependent upon pretreatment. Precarbonylation with carbon monoxide, drying with air, and heating with N₂ prior to hydroformylation conditions produced a straight to branched isomer ratio (n/i) of 1.9-2.3. Partial reduction with 10% H₂ in N₂ at 127°C lowered n/i to 1.3. Hydrogenation to propane was 3-10 times faster than the hydroformylation rate at 150°C. Catalytic activity was sensitive to cation exchange conditions. Rhodium form, pH, temperature, and salt concentration altered catalyst behavior. Only RhCl₃•3H₂O preparations on NaY zeolite produced above 80ºC, a pH above 4, and a salt concentration of 0.1N NaCl were required in order to produce an active hydroformylation catalyst. Ammine complexes did not activate under any circumstances. It was found that the degree of hydration controlled the formation of rhodium carbonyls. On NaY, the hydrated rhodium zeolite reacted with CO at 120ºC to form Rh₆(CO)₁₆. By drying the zeolite in air at 190ºC, two rhodium dicarbonyls, Rh(CO)₂(O_z)₂-NaY and Rh(CO)₂(O_z)(H₂O)-NaY, were formed. The rhodium carbonyls were reacted with n-hexyl diphenylphosphine to determine rhodium locations. Rh(CO)₂(O_z)₂-NaY was located at the surface while the other two species were located within the zeolite cages. One dicarbonyl species, Rh(CO)₂(O_z)₂-NaX, was observed on NaX. It was determined by reactions with phosphines that this species resides in the zeolite cages. Reaction intermediates identified by FTIR under hydroformylation conditions suggested that the heterogeneous catalyst proceeds through a mechanism similar to that occurring in solution. Heterogeneous reaction orders also agreed with those reported for homogeneous hydroformylations. Addition of dimethylphenylphosphine (DMP) to the rhodium zeolites significantly increased regioselectivity. Rates were slightly less than those from the unmodified rhodium carbonyls. However, the phosphine modified rhodium zeolites deactivated within 16 hours. Continuous exposure to DMP decreased the rate of deactivation.
Ph. D.

APA, Harvard, Vancouver, ISO, and other styles

26

Gubellini, Federico. "Designing heterogeneous catalysts for naphthalene isopropylation." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20659/.

Full text

Abstract:

2,6 di-isopropylnaphthalene is a plant growth regulator and it is used for the manufacturing of products intended to prevent sprouting of stored potatoes; despite that in the last decades it has been mainly produced as a precursor of the corresponding dicarboxylic acid (2,6-naphthalene dicarboxylic acid) which is, with ethylene glycol, the monomer for polyethylene naphthalate (PEN) polymerization. PEN results appealing for many uses for which PET is more commonly utilized; the most relevant, higher glass transition temperature (PEN 122°C, PET 80°C), higher Young’s modulus (PEN 5200 MPa, PET 3900 MPa), lower oxygen permeability (PEN 20 cm3/[m2*day*atm], PET 56 cm3/[m2*day*atm]) and lower thermal shrinkage (PEN 0,6%, PET 1,3%). This thesis reports of the study of the alkylation reaction of naphthalene with propylene, to get 2,6 di-isopropylnaphthalene. Operative conditions such as temperature and feed composition were optimized. The effect of parameters, such as catalyst size and inlet flow rate, on catalytic performance were studied. Part of the work was aimed at checking the presence of internal and external diffusion limitations. Several commercial catalysts have been tried on the bench-scale plant, both zeolites and amorphous silica-alumina materials. Desilicated zeolites were synthesized and tested as well, resulting in interesting catalysts for such reaction, with the need of further optimization of the synthesis procedure. ASA materials, as main catalysts of this project, were synthesized by means of wet impregnation and tested on the bench-scale plant. From the results is possible to hypothesize the presence of species like PBS-Al and PBS-Si within the ASA framework, that provide the catalyst with Brønsted acid sites with a zeolite-alike strength. The synthesized ASA catalysts show promising results, with high activity, but selectivity needs to be improved. Catalysts were characterized by means of XRD, n-butylamine titration and TGA (on used samples).

APA, Harvard, Vancouver, ISO, and other styles

27

Lemoine, Gaetan. "Comparison of different types of Zeolites used as Solid Acid Catalysts in the Transesterification reaction of Jatropha-type oil for Biodiesel production." Digital WPI, 2013. https://digitalcommons.wpi.edu/etd-theses/268.

Full text

Abstract:

Sustainable energy management has become a high priority for many countries. A great majority of our energy stocks comes from non-renewable fossil fuels, which are currently dwindling. Biofuels are one of the most promising solutions being researched to address this urgent problem. In particular, using transesterified Jatropha curcas L. oil appears to be a promising method of producing biofuels due to several properties of the plant, such as the high oil yield of its seeds and the fact that it does not compete with food crops. The literature mentions many attempts of using zeolites as solid acid catalysts in transesterification reactions of vegetable oils with high free fatty acid (FFA) content. The acid catalysis prevents soap formation and emulsification, which can be observed in the basic process. The use of a solid catalyst makes the separation and purification of the final products steps easier to implement in comparison to catalysis in homogeneous conditions. However, the efficiency of the zeolite in the heterogeneous transesterification reaction of vegetable oil is not well-known yet and varies on the structure of the catalyst used. This project aims at better understanding the relationship between the type of zeolite used and the yield of this particular reaction using reconstituted Jatropha oil from Sesame seed oil, which has a similar composition. Five different types of zeolites were compared: Y, X, Beta, Mordenite & ZSM-5. Non-catalyzed reactions as well as homogeneously catalyzed - with H2SO4 - reactions were also implemented. Since we take advantage of the catalytic properties of different zeolites, the one that were not already in hydrogen form were ion-exchanged and the ion-exchanged species were then analyzed by Energy-Dispersive X-Ray spectroscopy (EDX). Three alcohol-to-oil ratios were tested at atmospheric pressure and at T=115Â°C for each catalyst in order to determine the influence of this ratio. All experiments were conducted in an airtight autoclave with butan-1-ol in order to obtain a biofuel whose cetane index is higher than regular petroleum-based diesels.

APA, Harvard, Vancouver, ISO, and other styles

28

Faisal, Abrar. "Zeolite adsorbents and catalysts for the recovery and production of biochemicals." Doctoral thesis, Luleå tekniska universitet, Kemiteknik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-60137.

Full text

Abstract:

Fossil based energy resources are dominating the world’s primary energy consumption for the last century. However, with decreasing crude oil reservoirs and the role they play in global warming by emitting greenhouse gases, the focus has been turned towards improved utilization of renewable resources and the need for new, sustainable fuels and chemicals is more urgent than ever. Biomass is a carbon neutral resource that can be used to produce biofuels and other useful chemicals. One such chemical is 1-butanol (or simply butanol), which has great potential as a gasoline substitute because of its favorable fuel properties. Butanol can be produced from acetone, butanol and ethanol (ABE) fermentation using e.g. Clostridium acetobutylicum. However, the concentration of butanol in fermentation in the resulting broth is limited to ca. 20 g/L due to its toxicity for microorganisms. Butyric acid is a precursor to butanol, which is produced prior to butanol in ABE fermentation. Butyric acid is an important industrial chemical, which can be further converted into a number of commercial compounds e.g. acetate butyrate, butyl acetate and butanol. Arginine is a semi-essential amino acid that has vast applications in the field of pharmaceutical and food industry. In addition, arginine can replace inorganic nitrogen as nitrogen source in fertilizers. It can be produced via fermentation of sugars using engineered microorganism like E. Coli, but like butanol its concentration is restricted to approximately 12 g/L. Due to low concentration of these useful chemicals in the resulting fermentation broths recovery of these chemicals remain challenging with today’s options and therefore novel recovery process should be developed. In this study, zeolite adsorbents were used to recover butanol, butyric acid and arginine from model and real fermentation broths. Zeolite MFI adsorbent efficiently adsorbed butanol from model solutions with a saturation loading of 0.11 g/g- zeolite. On the other hand, adsorption of butyric acid was found to be strongly pH dependent, with high adsorption below and little adsorption above the pKa value of the acid. A structured adsorbent in the form of steel monolith coated with a silicalite-1 film was also used and performance was evaluated by performing breakthrough experiments at room temperature using model ABE fermentation broths and the results were compared with those obtained using traditional adsorbent sin the form of beads. Desorption studies showed that a high quality butanol product with purity up to 95.2% for butanol-water system and 88.5% for the ABE system can be recovered with the structured silicalite-1 adsorbent. Further, zeolite X adsorbents in the form of powder and extrudates was used to recover arginine from a real fermentation broth and also from aqueous model solutions. To the best of our knowledge, this is the first time recovery of arginine from real fermentation broths using any type of adsorbent is reported. Arginine loading of 0.15 g/g was observed at pH 11 using zeolite X powder. The selectivity for arginine over ammonia and alanine from the fermentation broth at pH 11 was 1.9 and 8.3, respectively, for powder and 1.0 and 4.1, respectively, for extrudates. Synthesis gas (CO + H2) can be produced e.g.by gasification of lignocellulose biomass. This synthesis gas can be used to produce methanol, which subsequently may be converted into gasoline using zeolite ZSM-5 catalyst. However, during Methanol to Gasoline (MTG) process, undesirable carbon residue (coke) is formed that gradually reduces the activity of catalyst. It was hypothesized that intracrystalline defects in the zeolite formed during conventional synthesis may accelerate the deactivation rate by coke formation. In this work, a novel ZSM-5 zeolite catalyst essentially free of intracrystalline defects was synthesized and evaluated in the MTG reaction,. The novel catalyst showed significantly higher resistance towards deactivation by coke formation as compared to a reference catalyst containing defects.

APA, Harvard, Vancouver, ISO, and other styles

29

Najfach, Aaron Jacob. "EFFECT OF MANGANESE AND ZEOLITE COMPOSITION ON ZEOLITE-SUPPORTED NICKEL CATALYSTS FOR DRY REFORMING OF METHANE." Miami University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=miami1501673873019245.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

VENNESTROM, PETER NICOLAI RAVNBORG. "Selective catalytic reduction of nitrogen oxides with ammonia over microporous zeolite catalysts." Doctoral thesis, Universitat Politècnica de València, 2014. http://hdl.handle.net/10251/43217.

Full text

Abstract:

With increasing legislative demands to remove nitrogen oxides (NOx) from automotive diesel exhaust, new catalyst systems are investigated and intensely studied in industry as well in academia. The most prevailing catalytic method of choice is the selective catalytic reduction (SCR) where non-toxic urea is used as a reductant for practical reasons. Usually urea is stored in a separate tank and once injected into the exhaust system it hydrolyses into the more aggressive reductant NH3 and CO2. 4 NH3 + 4 NO + O2 -> 4 N2 + 6 H2O (NH3-SCR reaction) In regions where vanadium is not banned cost effective V2O5/WO3/TiO2 NH3-SCR catalyst systems can be used. Vanadium based are well understood, but they do however not provide stability above ca. 550 °C for longer periods of time. In exhaust treatment systems where the temperature is either high or where high temperature excursions are experienced from e.g. regeneration of particulate filters, zeolite based catalysts are therefore today the most promising candidates as high-temperature stable and non-toxic catalysts for the NH3-SCR reaction. Among the most promising candidates are the Cu- and Fe-based zeolites. Usually Fe based zeolites show good performance in the temperature range 250-500 °C and reasonable stability, whereas Cu-based zeolites show good low-temperature activity in the 180-400 °C range. The presence of copper does however also lead to a lower stability of the catalyst material. Since the low-temperature activity is of paramount importance it is necessary to improve this behavior. Therefore the purpose of this project is to investigate: - The deactivation mechanism of copper based zeolites - The influence of the zeolite framework on stability and activity These investigations should mostly be carried out on model systems such as Cu-ZSM-5 and Cu-IM-5. Recently it was found that zeolite materials with the CHA-type structure show increased hydrothermal stability, most likely originating from the small 8-MR window openings in the structure. Part of the project should therefore also include investigations on this type and other similar structures, and therefore entail: - Synthesis, in-depth characterization and catalytic testing of Cu-SSZ-13 and Cu-SAPO-34 (both structures having the CHA-type framework) - Theoretical DFT calculations on relevant parameters found by the in-depth investigation of the afore-mentioned materials - Synthesis and testing of similar materials with 8-MR windows to elucidate the influence of the zeolite sub-structure i.e. if different ring sizes in the structure influences the catalytic performance Relevant characterization techniques include, besides conventional methods, in situ methods such as: high resolution (transmission) electron microscopy, infrared (and raman) spectroscopy together with X-ray absorption spectroscopy. These are all techniques that will complement each other to produce invaluable results. Zeolites are today applied in many and diverse applications both within automotive and environmental catalysis, but also within the petrochemical and renewable chemistry. The findings of this project are therefore also believed to contribute to a more comprehensive understanding of this class of materials, relevant to many areas of heterogeneous catalysis, and therefore have the potential, to create research and business with very high impact.
Vennestrom, PNR. (2014). Selective catalytic reduction of nitrogen oxides with ammonia over microporous zeolite catalysts [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/43217
TESIS

APA, Harvard, Vancouver, ISO, and other styles

31

Mthethwa, Londiwe Yvonne. "Synthesis of metal modified Mesoporous Zeolites catalysts: application in conversion of Olefins to Valuable liquid products." University of the Western Cape, 2016. http://hdl.handle.net/11394/5881.

Full text

Abstract:

Magister Scientiae - MSc (Chemistry)
The effects of temperature, synthesis duration and silica source were studied to obtain suitable conditions for our laboratory experiment concerned with the synthesis of MCM-41 catalyst. The transformation of 1-hexene was studied using modified mesoporous MCM-41as a catalyst. Catalysts were synthesised by co-precipitation and wet impregnation methods doped with aluminium, chromium and iron. Tetraethylorthosilane (TEOS) was used as silica source due to its ability to show improved results than sodium silicate sources. Catalysts were synthesised with single metal doping for the production of Al-MCM-41, Cr-MCM-41 and Fe- MCM-41. Double doped metal catalysts were also synthesised for the production of Cr/Al- MCM-41 and Fe/Al-MCM-41. Catalysts were hydrothermally synthesised at 150 ?C for 72 h then calcined at 560 ?C after drying. XRD, SEM, FTIR spectroscopy, BET surface area measurents, ammonia-TPD and NMR spectroscopy were used for characterisation of synthesised materials to understand the structural frame and interior as well as exterior surface.

APA, Harvard, Vancouver, ISO, and other styles

32

Ravenelle, Ryan M. "Heterogeneous catalysts in aqueous phase reforming environments: an investigation of material stability." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42921.

Full text

Abstract:

There are many problems associated with the use of fossil fuels to produce fuels and chemicals, and lignocellulosic biomass stands as a promising alternative fuel/chemical feedstock. Large scale processing of biomass will likely take place in high temperature liquid water due to the low vapor pressure and polar nature of carbohydrates. However, little is known about the material stability of these catalysts in high temperature aqueous phase environments. This dissertation aims to investigate the structural integrity of some common catalytic materials under typical biomass reforming conditions. There are 3 main objectives of this study: 1) identify potentially stable candidates from commonly used materials, 2) understand the mechanism(s) by which these catalysts degrade, 3) design/modify catalysts in an effort to increase their hydrothermal stability. The two main materials investigated in this work are zeolites (faujasite, ZSM-5) and γ-Al2O3 as these are commonly used as catalysts and catalyst supports. A number of physicochemical techniques were used to characterize the materials as a function of treatment time at conditions relevant for biomass reforming. For zeolites, the major findings are that ZSM-5 framework is highly stable whereas faujasite stability depends on the Si/Al ratio, where silicon rich materials are less stable. For γ-Al2O3 based catalysts, it was found that the alumina support hydrates and undergoes a phase transformation to form crystalline boehmite (AlOOH) with a subsequent loss in surface area and Lewis acid sites. When metal particles are present on the support, the phase change kinetics are slowed. The role of metal precursor on the stability of γ-Al2O3 supported catalysts was also explored, and it was found that the precursor used in catalyst synthesis changes the boehmite formation kinetics and also affects alumina support dissolution. The final thrust aims to stabilize a Pt/γ-Al2O3 catalyst by depositing silicon on the catalyst surface. The silicon modification is effective in protecting the catalyst from boehmite formation upon exposure to hot liquid water while also stabilizing metal particles against sintering. Additionally, an increase in turnover number for hydrogen production via aqueous phase reforming of sorbitol was observed.

APA, Harvard, Vancouver, ISO, and other styles

33

Morgan, David Rees. "In situ ¹³C NMR monitoring of the dehydration of 2-propanol over H-ZSM-5." Thesis, Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/52091.

Full text

Abstract:

The first in situ ¹³C NMR monitoring of zeolite catalyzed reaction is described. The dehydration of 2-propanol over H-ZSM-5 was observed using solution type techniques. Although this produces broad lines, several mechanistic details were elucidated. This study indicates that: 1) the dehydration does not proceed through a cyclopropyl carbenium ion intermediate, 2) propene oligomerizes on the catalyst and reaches a steady state concentration before propene is desorbed, and 3) the 2-propanol flowing over the catalyst does not react with the oligomerized propene.
Master of Science

APA, Harvard, Vancouver, ISO, and other styles

34

GOPAL, SRIKANT. "SYNTHESIS, MODIFICATION, CHARACTERIZATION AND CATALYTIC STUDIES OF ZEOLITE BASED BIFUNCTIONAL CATALYSTS FOR HYDROISOMERIZATION REACTION." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1061218813.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Casas, Fernández Carlos. "Synthesis of C10‐C16 linear symmetrical ethers from n‐alcohols over heterogeneous acid catalysts." Doctoral thesis, Universitat de Barcelona, 2013. http://hdl.handle.net/10803/307535.

Full text

Abstract:

Combustion of diesel fuel in a diesel engine is a complex process where several pollutants are emitted in the engine exhausts. To solve this problem and at the same time accomplish with the increasingly stringent regulations for diesel composition, diesel reformulation with oxygenate compounds is proposed. Linear symmetrical ethers with more than 9 carbon atoms represent a group of oxygenate compounds with excellent properties as diesel additives. Its addition in small quantities to diesel enhances the blending cetane number, improves cold start performance of diesel engine and dilutes undesired components. C10-C16 linear ethers such as di-n-pentyl ether (DNPE), di-n-hexyl ether (DNHE) and di-n-octyl ether (DNOE) are three linear symmetrical ethers with excellent properties to be added to commercial diesel. This work proves that the synthesis of DNOE from 1-octanol dehydration over acid catalysts (acidic zeolites and polystyrene-divinylbenzene (PS-DVB) ion exchange resins) is possible at 413-473 K. At the same time, the present work continues with the series of synthesis of linear symmetrical ethers from n-alcohols started with DNPE and DNHE in previous works. A catalyst screening of acidic PS-DVB ion exchange resins showed best performances to yield DNPE, DNHE and DNOE selectively on low-crosslinked macroreticular and geltype resins with high acid capacity. The ability to swell in the reaction media of lowcrosslinked and gel-type resins contributes to create porosity ,allowing the diffusion of alcohols and ethers almost equally regardless the length of the molecules. On medium and large pore zeolites synthesis of linear symmetrical ether was found to be strongly related to the zeolites mesoporous surface and the acid sites number. Selectivity to linear ether decreased as the chain length increased which revealed a great steric hindrance for bulky molecules. The large pore zeolite H-BEA-25 showed the best yield of linear ether due to the combination of high conversion of alcohol and high selectivity to linear ether. In this work, the thermodynamic equilibrium constant of 1-octanol dehydration to DNOE was determined, proving that dehydration of 1-octanol to DNOE is an exothermic reaction. The study, allowed at the same time improving current methods to estimate molar entropy of DNOE. A kinetic study of the alcohol dehydration to linear ether was performed over zeolites and the thermostable resin Amberlyst 70. Over Amberlyst 70 a series of kinetic equations based on LHHW-RE mechanisms were fitted to rate data of 1-octanol dehydration to DNOE. Pure 1-octanol experiments revealed that kinetic models where 1-octanol and water are the adsorbed compounds in the resin and the fraction of free active sites is negligible fit the best. Influence of products (water and DNOE) and solvent (1,4-dioxane) was evaluated which revealed a strong inhibition effect of water. Inhibition effect of water was quantified by means of correction factors which described the fraction of active sites not blocked by water according to different adsorption isotherms. Freundlich isotherm was found to better describe the water inhibition effect in an scenario where one molecule of 1-octanol adsorbed reacts with another molecule of 1-octanol of the liquid phase in a Rideal-Eley mechanism. Activation energy determined accounting water deactivation was 110 ± 5 kJ·mol-1. Over zeolites, LHHW-RE kinetic models were fitted to rate data for DNHE and DNOE synthesis showing that the best kinetic models assume that the fraction of active sites is negligible. Within these models, two type of equations were found to best represent rate data, one assumes that alcohol and linear ether are adsorbed in the zeolite surface. The other equation assumes that alcohol and water are preferably adsorbed through the reaction. Apparent activation energy of 100-120 kJ·mol-1 were estimated for the reactions on tested zeolites.
La reformulació del combustible dièsel amb compostos oxigenats com els èters lineals de més de 9 carbonis permet augmentar la qualitat ambiental del combustible als motors dièsel. Els èters lineals simètrics com el di-n-pentil èter (DNPE), di-n-hexil èter (DNHE) i di-n-octil èter (DNOE) es presenten com tres compostos amb propietats excel·lents com additius pel dièsel ja que n’augmenten l’índex de cetà i en milloren les propietats fluidodinàmiques del dièsel. Aquest treball demostra que la deshidratació de 1-octanol a DNOE és possible sobre catalitzadors sòlids àcids (resines de bescanvi iònic de poliestirè reticulades amb divinilbenzè (PE-DVB) i zeolites) i a la vegada continua amb la sèrie de síntesis d’èters lineals simètrics a partir de n-alcohols començada amb el DNPE i DNHE en treballs previs. Les resines de bescanvi iònic PE-DVB macroreticulars amb baixos continguts de DVB i les resines tipus gel foren les resines que mes rendiment a DNPE, DNHE i DNOE van obtenir. Amb zeolites es va observar que la obtenció d’èters lineals simètrics amb estava fortament lligada a la superfície mesoporosa i al nombre de centres àcids de la zeolita. En aquest treball es va determinar la constant d’equilibri de la reacció de deshidratació de 1-octanol a DNOE i es va demostrar que la reacció mencionada és una reacció exotèrmica. Fruit de l’estudi d’equilibri es van poder corregir els mètodes actuals per estimar l’entropia molar del DNOE, proposant-ne un valor nou. Finalment es va desenvolupar un estudi cinètic sobre la resina termoestable Amberlyst 70 i sobre zeolites. A l’estudi de la deshidratació de 1-octanol a DNOE sobre Amberlyst 70 es va proposar un model cinètic basat en un mecanisme Rideal-Eley (RE) on una molècula de 1-octanol adsorbida al catalitzador reacciona amb una altra molècula de 1-octanol de la fase líquida. Així mateix es va constatar que la presència d’aigua exercia un fort efecte desactivador de la reacció i es va quantificar al model cinètic mitjançant un terme corrector basat en la isoterma Freundlich. Sobre les zeolites es van proposar dos tipus de models cinètics basats en mecanismes Langmuir-Hinselwood-Hougen-Watson (LHHW) i RE per les síntesis de DNOE i DNHE.

APA, Harvard, Vancouver, ISO, and other styles

36

Burton, Robert M. "Oxidant concentration effects in the hydroxylation of phenol over titanium-based zeolites Al-free Ti-Beta and TS-1." Thesis, Stellenbosch : University of Stellenbosch, 2006. http://hdl.handle.net/10019.1/2366.

Full text

Abstract:

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2006.
This work focuses on the effects of hydrogen peroxide concentration on the catalytic activity and product selectivity in the liquid-phase hydroxylation of phenol over titanium-substituted zeolites Al-free Ti-Beta and TS-1 in water and methanol solvents. Hydroquinone is typically the desired product, and these solvents employed have previously been shown to be of importance in controlling the selectivity of this reaction. Different volumetric quantities of an aqueous 30 wt-% peroxide solution were added to either water or methanol solutions containing the catalyst and phenol substrate, and the reaction monitored by withdrawing samples over a period of 6-8 hours. For Al-free Ti-Beta catalysed reactions, the peroxide concentration affects the selectivity and activity differently in water and methanol solvents. Using methanol solvent, the selectivity to hydroquinone formation is dominant for all peroxide concentrations (p/o-ratio > 1), and favoured by higher initial peroxide concentrations (> 1.27 vol-%), where p/o-ratios of up to can be reached; in water solvent, increasing the peroxide concentration above this level results in almost unchanging selectivity (p/o-ratio of ca. 0.35). For lower peroxide concentrations in water, the p/o-ratio increases slightly, but never exceeds the statistical distribution of ca. 0.5. Using water as a solvent, higher phenol conversion is obtained as the initial peroxide concentration increases; in methanol the phenol conversion is largely independent of peroxide concentration. As expected for the smaller pore TS-1, higher hydroquinone selectivity is obtained in methanol than for Al-free Ti-Beta, which is consistent with shape-selectivity effects enhanced by the use of this protic solvent. Interestingly, with TS-1 the p/o-ratio is higher at lower phenol conversions, and specifically when the initial peroxide concentration is low (p/o-ratio exceeding 3 were obtained at low phenol conversion), and decreases to a near constant value at higher conversions regardless of the starting peroxide concentration. Thus, low peroxide concentrations favour hydroquinone formation when TS-1 is used as the catalyst. Comparing the performance of the two catalysts using methanol solvent, the phenol conversion on TS-1 is more significantly influenced by higher hydrogen peroxide concentrations than Al-free Ti-Beta. However, with higher initial concentrations the unselective phenol conversion to tars is more severe since the hydroquinone selectivity is not higher at these high peroxide concentrations. The increased tar formation, expressed as tar deposition on the catalyst or as the tar formation rate constant, confirms that the greater amount of free-peroxide present is mainly responsible for the non-selective conversion of phenol. Kinetic modelling of the reaction data with an overall second-order kinetic model gave a good fit in both solvents, and the phenol rate constant is independent of changing hydrogen peroxide concentration for the hydroxylation over Al-free Ti-Beta using water as the solvent (kPhenol = 1.93 x 10-9 dm3/mmol.m2.s). This constant value suggests that the model developed to represent the experimental data is accurate. For TS-1 in methanol solvent the rate constant is also independent of peroxide concentration (kPhenol = 1.36 x 10-8 dm3/mmol.m2.s). The effect of the method of peroxide addition was also investigated by adding discrete amounts over a period of 4.5 hours, and was seen to improve hydroquinone selectivity for reaction on both catalysts, and most significantly for Al-free Ti-Beta in methanol solvent. With TS-1, the mode of peroxide addition had little influence on phenol conversion, but the initial selectivity to hydroquinone was ca. 1.6 times higher than for an equivalent single-portion addition (at a similar phenol conversion). Discrete peroxide addition for hydroxylation in methanol over Al-free Ti-Beta gave greatly improved hydroquinone selectivities compared to the equivalent single-dose addition. Compared to TS-1, the initial selectivity was not as high (p/o-ratios of 0.86 and 1.40 respectively at 10 mol-% phenol conversion), but this can be explained on the basis of geometric limitations in the micropores of TS-1 favouring hydroquinone formation. The final selectivity, however, is marginally higher (using the same mode of peroxide addition, and at the same phenol conversion). Discrete peroxide addition has an additional benefit in that it also reduces the quantity of free-peroxide available for product over-oxidation, and consequently reduces the amount of tars formed. Thus, the interaction of the effects of peroxide concentration and the solvent composition and polarity on the product selectivity and degree of tar formation is important. Particularly with TS-1, lower peroxide concentrations in bulk methanol solvent are highly beneficial for hydroquinone formation, because of the implicit geometric constraints in the micropores, the lower water concentration, and the decreased tar formation associated with high methanol concentrations. This could have significant reactor design implications, as the results obtained here suggest that the reaction should be terminated after approximately 30 minutes to maximise hydroquinone production (under the conditions evaluated in these experiments), even though the corresponding phenol conversions are low (ca. 10 mol-%). The higher hydroquinone selectivities reached at low phenol conversions for the discrete peroxide addition experiments also confirm this. Practically, to enhance the hydroquinone selectivity for reaction over TS-1, the initial phenol-peroxide molar ratio should be ca. 10, methanol should constitute not less than 90 vol-% of the reaction volume, and the peroxide should be added in discrete amounts. For reaction over Al-free Ti-Beta, methanol solvent also enhances the hydroquinone formation as expected. At low phenol conversions (ca. 10 mol-%) hydroquinone is still the preferred product, although in contrast to TS-1 the selectivity increases with phenol conversion, and is higher with higher initial peroxide concentrations. Under the best conditions evaluated here for optimal hydroquinone formation, the initial phenol-peroxide molar ratio should be ca. 2.5, with methanol making up at least 90 vol-% of the total volume. Discrete peroxide addition in methanol solvent for the Al-free Ti-Beta catalysed hydroxylation gives excellent improvements in hydroquinone selectivity (2.5 times higher than water solvent), and the addition in more discrete portions might further improve hydroquinone formation, and should therefore be examined.

APA, Harvard, Vancouver, ISO, and other styles

37

ARAÚJO, Alfredina dos Santos. "Desenvolvimento de catalisadores zeolíticos destinados à reforma do metano." Universidade Federal de Campina Grande, 2006. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/1828.

Full text

Abstract:

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-09-27T14:01:53Z No. of bitstreams: 1 ALFREDINA DOS SANTOS ARAÚJO - TESE (PPGEP) 2006.pdf: 1109435 bytes, checksum: 15b173725f8a1ad90eb4e7cbec8f6742 (MD5)
Made available in DSpace on 2018-09-27T14:01:53Z (GMT). No. of bitstreams: 1 ALFREDINA DOS SANTOS ARAÚJO - TESE (PPGEP) 2006.pdf: 1109435 bytes, checksum: 15b173725f8a1ad90eb4e7cbec8f6742 (MD5) Previous issue date: 2006-09
Nos últimos anos tem-se buscado rotas alternativas para a conversão do gás natural em gás de síntese, uma mistura de hidrogênio e monóxido de carbono, da qual pode ser obtido o H2. A tendência à formação de coque pode ser minimizada pelo desenvolvimento de novos materiais catalíticos. Essa reação requer o emprego de catalisadores metálicos. Portanto neste trabalho, a reforma a vapor do metano foi realizada sobre catalisadores monometálicos à base de níquel e platina com seguintes teores 0,5%, 1,0%, 1,5% e 2,0%, suportados na zeólita NaY. Os catalisadores metálicos foram preparados via impregnação por umidade incipiente e foram caracterizados pelas técnicas de difração de raios X (DRX), espectroscopia de infravermelho com transformada de Fourier (FTIR), redução a temperatura programada, área superficial específica, volumes de poros e a reação de deshidrogenação do ciclohexano. Os catalisadores foram avaliados na reação de reforma a vapor a 600ºC, 1 atm e CH4/H2O = 4 por 360 minutos. O DRX e FTIRs indicaram que os processos de impregnação dos metais não mudaram as estruturas das zeólitas Y. Os perfis de RTP dos metais nas zeólitas foi possível observar que a redução das espécies de níquel inicia-se em 198ºC e há um consumo máximo de hidrogênio em 483ºC, no caso da platina a redução se inicia em 203ºC. Na deshidrogenação do ciclohexano observou-se aumento da atividade da função catalítica que está relacionado com a maior densidade dos sítios catalíticos. Todos os catalisadores conduziram a atividades elevadas, relacionadas com a proximidade dos teores metálicos. No contexto geral, o catalisador platina-NaY mostrou atividades mais altas do que os catalisadores níquel-NaY.
In the last years, it has been an increasing interest for new alternatives to natural gas conversion to synthesis gas, a mixture of hydrogen and carbon monoxide from which hydrogen can be obtained. This reaction requires the use of metallic sites and the tendency to produce coke can be minimized by the use of new catalytic materials. In order to develop new catalysts to this reaction nickel and platinum supported on NaY zeolite (0.5%, 1.0%, 1.5% and 2.0%) were studied in this work. Samples were prepared by incipient wet impregnation and characterized by thermal differential analysis, thermogravimetry, X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIRs), temperature programmed reaction (TPR), specific surface area and porosity measurements and cyclohexane dehydrogenation. The catalysts were evaluated in steam reforming at 600 oC, 1 atm and CH4/H2O = 4 for 360 min. The XRD and FTIRs0,0 showed that metal impregnation did not change the structure of Y zeolite. From the TPR profiles, it was noted that the reduction of nickel began at 198ºC with a maximum at 483ºC. In the case of platinum the reduction began at 203ºC. From the cyclohexane dehydrogenation, it was observed an increase of activity, which is related to the higher amount of catalytic sites. All catalysts showed high activities, closely related to the metal charge. As a whole, the platinum-NaY catalyst showed higher activities that the nickel-NaY ones.

APA, Harvard, Vancouver, ISO, and other styles

38

Cheng, Kang. "Novel Fischer-Tropsch catalysts based on mesoporous zeolites and carbon materials for the production of gasoline-range hydrocarbons and lower olefins." Thesis, Lille 1, 2015. http://www.theses.fr/2015LIL10001/document.

Full text

Abstract:

Les catalyseurs Fischer-Tropsch bifonctionnels ont été mis en œuvre pour la production d’hydrocarbures C5-C11 à partir du gaz de synthèse. Ces catalyseurs ont été constitués de nanoparticules du ruthénium ou du cobalt, ainsi que de zéolithes mésoporeuses. Nos résultats démontrent que la synthèse d’hydrocarbures lourds implique des nanoparticules métalliques, tandis que les réactions d’hydrocraquage/isomérisation se produisent sur les sites acides Bronsted. La mésoporosité contribue à la suppression des hydrocarbures légers. La sélectivité en hydrocarbures C5-C11 atteint 65-70% avec un rapport iso-paraffines/n-paraffines très élevé.Les effets de la taille de pores, de la composition chimique du support et de l'ajout du sodium sur les performances des catalyseurs à base de fer pour la synthèse Fischer-Tropsch à haute température ont été aussi étudiés. Les grosses cristallites d’oxyde de fer situées dans les pores larges de silice sont beaucoup plus faciles à transformer en nanoparticules de carbures de fer que les petites cristallites Fe2O3 dans les pores étroits du support. Des vitesses de la réaction Fischer-Tropsch plus importantes, des meilleures sélectivités en oléfines ont été observées sur les catalyseurs à base de fer avec des pores plus larges. Les catalyseurs de fer supportés par les nanotubes de carbone et le charbon actif ont présenté des activités très élevées. Ce phénomène a été attribué à des nanocomposites de carbures de fer et de magnétite. L’interaction entre le sodium et le catalyseur dépend fortement du taux du promoteur et du support. Une interaction forte entre le fer et le sodium a permis d’obtenir des sélectivités plus importantes en oléfines
Novel bifunctional Fischer-Tropsch (FT) catalysts were developed for the selective production of gasoline-range (C5−C11) hydrocarbons from syngas. These catalysts are constituted by ruthenium or cobalt nanoparticles and mesoporous zeolites. Our results reveal that heavier hydrocarbons form on metal nanoparticles, while hydrocarbon hydrocracking/isomerization occurs on the Brønsted acid sites of the catalysts. The zeolite mesoporosity contributes to suppressing the formation of lighter (C1−C4) hydrocarbons. The selectivity of C5−C11 hydrocarbons could reach 65-70% with a high ratio of isoparaffins to n-paraffins, markedly higher than the maximum value (~45%) expected from the theory. The effects of pore size, support, chemical composition and sodium addition on the performance of iron catalysts in high temperature FT synthesis were also investigated in this thesis. It was found that larger iron oxide crystallites in large pore silicas were much easier to transform to iron carbides than smaller Fe2O3 crystallites in smaller pore supports. Higher FT reaction rates, better olefin selectivities were observed over iron catalysts supported by large pore silicas with higher concentration of iron carbide active phase. Iron catalysts supported on carbon nanotubes (CNT) and activated carbon showed very high activity in FT synthesis. This phenomenon was attributed to the formation of stable nanocomposites of iron carbide and magnetite. The interaction of Na with the catalysts strongly depends on the amount of added Na and type of the support. The strong interaction of Fe and Na promoter leads to higher olefin selectivity

APA, Harvard, Vancouver, ISO, and other styles

39

Kaminishikawahara, Katia Kaori. "PREPARAÇÃO DA ZEÓLITA SODALITA VIA TRATAMENTO TÉRMICO, SUA IMPREGNAÇÃO COM ÍONS Zn2+ E UMA AVALIAÇÃO PRELIMINAR DE SUA EFICIÊNCIA NA PRODUÇÃO DE BIODIESEL." UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2015. http://tede2.uepg.br/jspui/handle/prefix/185.

Full text

Abstract:

Made available in DSpace on 2017-07-21T14:32:37Z (GMT). No. of bitstreams: 1 katia Kaori K.pdf: 5891591 bytes, checksum: 2785b5f69d4024535978fce1d58c20d2 (MD5) Previous issue date: 2015-01-28
Biodiesel has great commercial potential for being biodegradable, non toxic, presenting low carbon monoxide (CO) emission and solid particles. It can be produced from the transesterification reaction of vegetal oil or animal fat as raw material. The optimization of the reaction speed in the biodiesel production is possible with the use of zeolites as catalysts that can be recovered at the initial level in an economical way. A field study was carried out to collect natural zeolites and to produce synthetic zeolites varying the amount of colloidal silica and sodium aluminate. The methodology which resulted in a zeolite with a single zeolitic phase and low amount of amorphous material was submitted to different thermal treatments (8, 12, 24, and 30 hours). The 24-hour thermal treatment obtained a zeolite (Sodalite) with high basicity which was impregnated with Zn2+ ions. The zeolitic material was characterized with X-ray diffraction (XRD), Rietveld method, thermogravimetry analysis (TG/DTG), infrared absorption spectrophotometry (IV), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), nitrogen physisorption analysis and basicity qualitative and quantitative analyses. The preliminary test converting soybean oil in alkyl esters was carried out employing non impregnated, impregnated with 3% and 9% Zn2+ ions and natural Sodalite. The non impregnated Sodalite was the one presenting the highest conversion rate (40.7%) possibly due to the larger number of total basic sites it presented. The low conversion rate verified in other tests might be ascribed to the saponification reaction, possibly due to its highly hygroscopic property which reduces the transesterification reaction efficacy. That is, the presence of absorbed water in the structure or the existence of Na+ and OH- ions enables triglyceride saponification reactions by taking water to the reaction medium.
O biodiesel tem grande potencial para o mercado consumidor por ser biodegradável, atóxico, apresentar baixas emissões de monóxido de carbono (CO) e de partículas sólidas. Pode ser produzido na reação de transesterificação com óleos vegetais ou gordura de origem animal como matérias-primas. A otimização da velocidade de reação na produção de biodiesel, é possível a partir da utilização de zeólitas, como catalisadores que podem ser recuperados a nível inicial de forma econômica. Foi realizado um trabalho de campo para a coleta de zeólita natural e produção de zeólitas sintéticas variando a quantidade de sílica coloidal e aluminato de sódio. A metodologia que apresentou a zeólita com apenas uma fase zeolítica e com baixa quantidade de material amorfo foi submetida a diferentes tratamentos térmicos (8, 12, 24, e 30 horas). O tratamento térmico de 24 horas obteve uma zeólita (Sodalita) de elevada basicidade o qual foi impregnada com íons Zn2+. Os materiais zeolíticos foram caracterizados com difração de raios X (DRX), método de Rietveld, análise de termogravimetria (TG/DTG), espectrofotometria de absorção na região do infravermelho (IV), microscopia eletrônica de varredura (MEV), espectroscopia de energia dispersiva (EDS), análise de fisissorção de nitrogênio e análise qualitativa e quantitativa de basicidade. O teste preliminar de conversão de óleo de soja em ésteres alquílicos foi realizado utilizando a Sodalita sem impregnação, as impregnadas com 3% e 9% de íons Zn2+ e a natural. A que apresentou a maior taxa de conversão foi a Sodalita sem impregnação (40,7%) possivelmente devido a maior quantidade de sítios básicos totais que ela apresenta. A baixa taxa de conversão verificada em outros testes pode estar atrelada a reação de saponificação, possivelmente devido a sua propriedade altamente higroscópica que diminui a eficiência da reação de transesterificação. Ou seja, a presença de água adsorvida na estrutura ou a eixstência de íons Na+ e OH- propicia reações de saponificação do triglicerídeo ao levar água para o meio reacional.

APA, Harvard, Vancouver, ISO, and other styles

40

Catherin, Nelly. "Selective ring opening of naphthenes over bifunctional catalysts in the presence of H2S." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1246.

Full text

Abstract:

L'ouverture sélective de cycle (OSC) d'hydrocarbures polycycliques vise à augmenter le nombre de cétane des carburants diesel. OSC efficace peut être atteint par l'hydroconversion sur des catalyseurs bifonctionnels métal noble/fonction acide. La décaline et, à plus faible mesure, le perhydroindane, le butylcyclohexane et la tétraline, ont été utilisés comme molécules modèles pour l'étude des l'OSC de sulfures de métaux de transition (TMSs) supportés sur zéolithes ou silice-alumine amorphe dans un réacteur à lit fixe sous haute pression (5 MPa) avec une concentration élevée d'H2S dans la charge réactionnelle (1 %). Les nombreux produits d'hydroconversion ont été identifiés grâce à la chromatographie gazeuse bidimensionnelle, qui nous a permis de mieux comprendre les mécanismes de réaction. Ce travail a consisté à l'étude de la nature et la charge du SMT et la nature du support. Comparé à la zéolithe seule, le catalyseur RuSx/HY (qui sert de référence) est plus stable et dix fois plus actif avec une sélectivité en produits d'ouverture proche des 30% à 240 °C. Les produits les plus abondants restent les produits d'isomérisation, ce qui suggère que l'acidité du support domine le schéma réactionnel. Quant à l'ajout de TMS, leur rôle est d'activer l'hydrogène, de favoriser les réactions d'hydrogénation/déshydrogénation et limiter le cokage des sites acides. NiSx/HY est aussi performant que les catalyseurs à base de Ru, Ir ou Rh et un effet de synergie est observé pour les catalyseurs ternaires Ni-Ru et Ni-Rh. Toutefois, comparé aux métaux nobles comme l'Ir et le Ru étudiés sans H2S, les catalyseurs sulfures sont quasiment non-hydrogénolysants. Enfin, la zéolithe HY présente des performances proches a la H-Beta mais avec moins de craquage
The selective ring opening (SRO) of polycyclic hydrocarbons aims at increasing the cetane numbers of diesel fuels. Efficient SRO can be achieved through hydroconversion over bifunctional noble metal/acid catalysts. Decalin and, to lower extents, perhydroindan, butylcyclohexane and tetralin, have been used as model molecules to investigate the SRO performances of transition metal sulfides (TMSs) supported on zeolites or amorphous silica-alumina in a high-pressure (5 MPa) flow-fixed bed reactor with a high concentration of H2S in the reactant feed (1 %). The numerous hydroconversion products have been identified using comprehensive two-dimensional chromatography for various levels of reactant conversions, which allowed us to gain insight into the reaction mechanisms. The presence, loading and nature of the TMS, and the nature of the support, have been investigated. With respect to the bare HY zeolite, RuSx/HY (which served as our reference) is more stable and ten times more active, with a ring-opening selectivity of up to 30 % at 240 °C. The most abundant products are skeletal-isomerization ones, which suggests that the acidic support dominates the reaction scheme. The TMS role is to activate hydrogen, catalyze hydrogenation/ dehydrogenation and prevent the coking of acidic sites. NiSx/HY performs similarly to Ru, Ir and Rh-based catalysts, and a synergetic promoting effect is observed for Ni-Ru and Ni-Rh combinations. However, with respect to noble metals such as Ir and Ru under H2S-free conditions, the sulfide counterparts appear much less (if not) hydrogenolytic. As compared to HY, the H-Beta support shows similar performance but promotes cracking

APA, Harvard, Vancouver, ISO, and other styles

41

Laprune, David. "Application de catalyseurs encapsulés à base de nickel au réformage d’un gaz modèle issu de la gazéification de la biomasse." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1129/document.

Full text

Abstract:

L'Europe est confrontée à des défis climatiques et énergétiques et vise à accroître l'utilisation de la biomasse dans la production d'énergies renouvelables. De nombreuses difficultés technologiques persistent, par exemple, la gazéification de la biomasse produit un gaz de synthèse riche en goudrons et H2S qui peuvent conduire à une désactivation des catalyseurs dans les réacteurs en aval. Notre objectif a été de développer des catalyseurs stables qui peuvent réformer complètement ces hydrocarbures contenus dans le gaz de synthèse. Des nanoparticules de nickel encapsulées dans des monocristaux de silicalite-1 creusée formant une cavité unique ("single-hollow") ont été étudiées. L'encapsulation a pour but de limiter le frittage des particules et le cokage dans des conditions de reformage difficiles. Le frittage de ces particules au sein de chaque monocristal a cependant été observé. La synthèse d'une nouvelle structure creusée (c'est-à-dire un monocristal de zéolites avec de multiples cavités mésoporeuses, nommé "multi-hollow") a été développée. L'exclusion en taille de composés aromatiques larges par la membrane l'échantillon a été démontré. Ce matériau a également permis d'améliorer la dispersion initiale des nanoparticules métalliques. L'activité de l'échantillon a cependant été affectée par deux facteurs principaux associés aux étapes de préparation, c'està- dire la formation d'une couche de silice à la surface des particules et d'un empoisonnement au phosphore. Au cours du réformage d'un gaz de synthèse model riche en hydrocarbures, la membrane silicalite-1 n'a pu empêcher la désactivation due aux goudrons des particules de nickel encapsulées, car ceux-ci craquent aux températures typiques de reformage en composés aromatiques plus petits, susceptibles de se diffuser à travers la paroi de type MFI. La préparation de matériaux analogues à base de Rh n'a pas pu être réalisée. Des catalyseurs à base de Rh et de Ni supportés sur alumine ont ensuite été testés. Nous avons montré que le H2S induit une chute significative de l'activité en reformage et que les catalyseurs au Rh sont les moins influencés par le cokage et l'empoisonnement au S. L'activité en reformage du méthane était proportionnelle à la surface spécifique en Rh. Une température de réaction élevée (> 875 °C) a été jugée nécessaire pour limiter la désactivation par cokage
Europe is facing climate and energy challenges and aims at increasing the utilization of biomass in the production of renewable fuels. Many technological difficulties remain, for instance, biomass gasification produces a syngas rich in tars and H2S that can lead to catalyst poisoning in downstream reactors. Our goal was to develop stable catalysts that could fully reform producer gas. Nickel nanoparticles encapsulated inside hollow silicalite-1 single crystals were studied. The encapsulation was expected to limit particle sintering and coking under harsh reforming conditions. These particles could still sinter within each single crystal. The synthesis of a novel hollow structure ("multi-hollow", i.e. a single zeolite crystal with multiple mesoporous cavities) was developed. The size-exclusion of large aromatic compounds from the sample was demonstrated. This material also enabled improving the initial dispersion of metal nanoparticles. The sample activity was yet adversely affected by two main factors associated with the preparation steps, i.e. the formation of a silica over-layer and phosphorus-poisoning. During the reforming of a simulated producer gas, the silicalite-1 membrane could not prevent tar-related deactivation of embedded nickel particles, because those were cracked at typical reforming temperatures into smaller aromatic compounds, which could diffuse throughout the MFI-type layer. The preparation of Rh-based multi-hollow analogues could not be achieved. Alumina-supported Rh and Ni-based catalysts were then tested. H2S induced a large drop of the reforming activity and Rh catalysts were the least impacted by coking and S-poisoning. Methane reforming rate were proportional to the Rh metal surface area. The use of high reaction temperatures (>875Â°C) was shown to be necessary to limit deactivation by coking

APA, Harvard, Vancouver, ISO, and other styles

42

Bernardi, Junior Ernesto. "Catalise de oxido-redução via metalossilicatos zeoliticos." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/250131.

Full text

Abstract:

Orientador: Eduardo J. S. Vichi
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica
Made available in DSpace on 2018-08-06T15:46:01Z (GMT). No. of bitstreams: 1 BernardiJunior_Ernesto_D.pdf: 5488181 bytes, checksum: 9191e2a8912ede9a6844335070db1c20 (MD5) Previous issue date: 2005
Resumo: Foram preparados aproximadamente quarenta materiais entre cromiossilicatos zeolíticos tipo MFI e sílica com superfície modificada por zircônio e depois servindo de suporte ao metal crômio. Estes materiais foram denominados Cr-ZSM-5 e Cr-SSM e foram devidamente caracterizados, visando processos de conversão catalítica de monóxido de carbono a dióxido de carbono. As caracterizações envolveram técnicas de: Difração de Raios-X de Pó, Espectrometria de Infravermelho do Estado Sólido, Análises Elementares por Fluorescência de Raios-X, Ressonância Paramagnética Eletrônica, Espectroscopia Fotoacústica, Análise de Área Superficial BET. As reações de conversão foram realizadas através de um reator de vidro microcatalítico, inserido num forno tubular microprocessado. Os efluentes gasosos foram analisados por Espectrometria de Infravermelho com Transformada de Fourier, Cromatografia Gasosa e Análise de Gases com Célula Eletroquímica. Dos zeólitos obtidos por planejamento estatístico, três amostras foram testadas nas conversões, denominadas, ZS-1, ZF-2 e ZP-3. Quanto ao material de sílica, duas amostras foram preparadas e utilizadas nas conversões, denominadas, SF-1 e SF-2. Destes materiais, somente uma amostra de cromiossilicato revelou-se mais ativa para a reação e ambas as amostras de sílica. As conversões foram muito eficientes e revelaram turnover elevados. Os zeólitos desativados foram regenerados com sucesso e a conversão continuou com gradual perda de eficiência. Os materiais de sílica não desativaram após 49 horas de operação. Reações tipo: CO+NOCO2+1/2N2, foram investigadas sem alimentação de ar, com relativo êxito. Existem perspectivas de aplicação do material de sílica em processos de catálise automotiva. Está sendo estudado o registro de propriedade intelectual para estes materiais.
Abstract: About forty catalyst materials were prepared among MFI zeolitic chromiumsilicates type and silica grafted by zirconium oxides, and after serve as anchoring cromium species. These materials were named Cr-ZSM-5 and Cr-SSM and were characterized to drive at catalytic process to change carbon monoxide to carbon dioxide. The characterizations involved, Powder X-Ray Diffraction, Infrared Spectroscopy (MID-IR), Elemental Analysis by X-Ray Fluorescence, Electron Paramagnetic Resonance, Photoacoustic Spectroscopy, BET Superficial Area. The catalytic reactions were carried out on a microcatalytic glass reactor, inserted in a microprocessed cilindrical owen. The gaseous products were analyzed by a Fourier Transformed Infrared Spectroscopy, Gas Chromatography and a Gas Analyzer with Electrochemistry Cell. Synthesis applying statistical planning for zeolites, resulted in three catalysts to be tested in reactions. In respect to silica catalyst, two samples were prepared and applied in reactions. From these materials only a sample of chromiumsilicate revealed active to reaction and more two samples of a silica type. The reactions were most efficacious and revealed high turnover number. The zeolitic catalysts switches off and were renewed with sucessfull process and the reaction extends with gradual loss of efficacious. The silica catalysts did not switches off after 49 hours in action. Class of reactions like: CO + NO CO2 + 1/2N2 were experimented without feed of air, with restrained results. There are applicative perspectives of silica catalysts in automotive catalytic process. This work will generate a patent request for these materials.
Doutorado
Quimica Inorganica
Doutor em Ciências

APA, Harvard, Vancouver, ISO, and other styles

43

Huh, Seong. "Morphological Control of Multifunctional Mesoporous Silica Nanomaterials for Catalysis Applications." Ames, Iowa : Oak Ridge, Tenn. : Ames Laboratory ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2004. http://www.osti.gov/servlets/purl/837271-xREJ4t/webviewable/.

Full text

Abstract:

Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US); 19 Dec 2004.
Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2397" Seong Huh. US Department of Energy 12/19/2004. Report is also available in paper and microfiche from NTIS.

APA, Harvard, Vancouver, ISO, and other styles

44

Durgun, Gülay Artok Levent. "Short-time suzuki reactions of arly halides catalyzed by palladium-loaded NaY zeolite under aerobic conditions/." [s.l.]: [s.n.], 2006. http://library.iyte.edu.tr/tezler/master/kimya/T000528.pdf.

Full text

Abstract:

Thesis (Master)--İzmir Institute of Technology, İzmir, 2006.
Keywords:Suzuki reactions, palladium, NaYzeolite, heterogeneous catalyst, C-C coupling. Includes bibliographical references (leaves. 71-81).

APA, Harvard, Vancouver, ISO, and other styles

45

Blair, Johanna Wendy. "Zeolite biomimetic catalysts." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388460.

Full text

APA, Harvard, Vancouver, ISO, and other styles

46

Krstic, Vesna. "Catalizadores de Rh-soportado y su aplicación en la hidrogenación de crotonaldehído." Doctoral thesis, Universidad de Cantabria, 2005. http://hdl.handle.net/10803/10685.

Full text

Abstract:

Este trabajo ha sido realizado en el contexto de los proyectos de MAT 2002-03808 y MAT 2002-02158, financiados por la Dirección General de Investigación del Ministerio de Ciencia y Tecnología (MCyT). Se han sintetizado y caracterizado catalizadores Rh-soportado (sólo o promovido con Sn) utilizando diferentes tipos de soportes. Como soportes de catalizadores se utilizaron tanto materiales microporosos, silicatos laminares (bentonitas) de distinta procedencia y bentonitas modificadas mediante la introducción de pilares (PILC's) o transformadas en productos zeolíticos; como materiales mesoporosos, MCM-41, con una o dos fuentes de Silicio. Los mencionados catalizadores han sido aplicados en la hidrogenación de crotonaldehído, en fase gaseosa y condiciones suaves, de alto interés tanto académico como industrial en química fina, farmacéutica y alimentaria. Se han analizado y discutido la actividad/selectividad en relación con las diferentes características de los soportes y las distintas condiciones de trabajo como: temperatura de reducción del Rh, temperaturas de reacción, y presencia de estaño como promotor. Se han caracterizado los soportes y catalizadores mediante diferentes técnicas instrumentales UV-Vis, espectroscopia IR, ATG/DTG, DRX, isotermas de adsorción-desorción de N2, quimisorción de O2/H2, quimisorción de NH3, adsorción-desorción de piridina mediante espectroscopia IR-TF, XPS y se utilizó la Cromatografia de gases para la hidrogenación de crotonaldehído. Los resultados obtenidos ponen de manifiesto que tanto las arcillas de partida como las modificadas (con pilares o bien transformada en zeolitas) y materiales MCM-41, han resultado soportes idóneos para la formación de catalizadores heterogéneos de Rh y de Rh promovido con Sn, habiéndose generado, por tanto, nuevos materiales de alto valor añadido para el caso de las arcillas modificadas y nuevos retos de aplicación para los nuevos nanomateriales MCM-41. Así mismo se constata que la adición de Sn como promotor, modifica la conversión a todas las temperaturas de reacción, obteniéndose para todos los catalizadores, mayor selectividad hacia alcohol crotílico que en ausencia de Sn. En resumen, a lo largo de este trabajo se han logrado preparar catalizadores metal soportados utilizando unos nuevos soportes de catalizadores que muestran, generalmente, alta selectividad hacia alcohol crotílico en la hidrogenación de crotonaldehído, en condiciones suaves y a presión atmosférica, condiciones usuales de trabajo en la industria de química fina, farmacéutica y alimentaria, donde time mayor repercusión la aplicación de la reacción estudiada.
This work has been performed within the projects MAT 2002-03808 and MAT 2002-02158, financed by the DGESIC (Dirección General de Enseñanza Superior e Investigación y Ciencia) and CICYT (Comisión de Investigación Científica y Técnica), respectively.An Rh-supported catalyst (alone or promoted with Sn) has been synthesized and characterized using different types of supports. Aluminum silicate (clay) of different origins and clay modified by introduction of pillars (PILC's) or transformed into zeolytic products were used as microporous materials. MCM-41 (with one or two Silicon sources) was used as mesoporous materials. The catalyst has been applied in the hydrogenation of cortonaldehyde in gaseous phase and mild conditions. These have high academic and industrial interest. Activity and selectivity of catalysts have been analyzed at different conditions of work like: temperature of reduction of the Rh, temperatures of reaction and tin presence as promoter.These supports (micro and mesoporous materials) and catalysts have been characterized using different technical instruments: UV-Vis, spectroscopy IR, ATG/DTG, XRD, isotherms of adsorption-desorption of N2, chemisorptions of O2/H2, chemisorptions of NH3, adsorption-desorption of pyridine by DRIFTS, XPS and hydrogenation of crotonaldehyde by Gas Chromatography. The results obtained show that the natural clay material, as modified (with incorporation of pillars or transformed into zeolites), and materials MCM-41, have been good supports to the formation of heterogeneous catalysts of Rh and Rh promoted with Sn, having generated new materials of high value in the case of modified clays and raises new challenges of application for nanomaterials MCM-41. Also observed is that the addition of Sn as promoter was modifying the conversion at all temperatures of reaction, obtaining for all the catalysts greater selectivity to crotyl alcohol than without tin (Sn).In summary, throughout this work, we have been able to prepare and obtain metal supported catalysts using new supports of catalysts that show great selectivity towards crotyl alcohol in the hydrogenation of crotonaldehyde in mild conditions and atmospheric pressure. This is a very important reaction in the production of many pharmaceutical, agrochemical and fragrance compounds, having great repurcussion on the application of the studied reaction and attracting much interest in fundamental research in catalysis.

APA, Harvard, Vancouver, ISO, and other styles

47

Lima, Dirléia dos Santos. "Obtenção de hidrocarbonetos superiores a partir da conversão do etanol utilizando catalisadores suportados em ZSM-5." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/116718.

Full text

Abstract:

O petróleo é a principal matéria-prima empregada para produzir combustíveis, lubrificantes e produtos petroquímicos. Atualmente, devido ao fato desta fonte não ser renovável e estimar-se a sua extinção, busca-se por fontes renováveis de energia que possam vir a substituí-la. Nesse contexto, o etanol vem sendo investigado por ser uma alternativa sustentável para a obtenção de hidrocarbonetos de maior valor agregado, tais como, eteno, propeno, benzeno, tolueno, entre outros, através de sua conversão catalítica em condições controladas. Este trabalho teve por finalidade avaliar o efeito de diferentes catalisadores metálicos suportados em zeólita HZSM-5 na reação de conversão do etanol em produtos de maior valor agregado. Para isso, prepararam-se catalisadores com 2,5 % em massa dos metais La, Ca, Li, Mg e Ni impregnados na zeólita HZSM-5 comercial. A seguir foram preparados catalisadores a partir da modificação da zeólita HZSM-5 com diferentes teores de Ni e, na sequência, amostras com diferente combinação de Ni e La. Posteriormente, a zeólita HZSM-5 foi sintetizada em laboratório e impregnada através da combinação entre os metais Ni e Zn. Os catalisadores antes do seu emprego nos ensaios catalíticos foram caracterizados por medidas de área específica SBET, DRX e TPD-NH3. As amostras após a reação foram caracterizadas por TPO. Os ensaios de atividade foram conduzidos em reator tubular de leito fixo, com carga de catalisador de 100 mg, na faixa de temperaturas entre 300 e 400 °C, utilizando-se uma vazão de alimentação de etanol na faixa de 0,2 a 1,2 mL.h-1. Foram realizados três tipos de ensaios: com diferentes temperaturas de reação, teste de influência do tempo de residência e teste de estabilidade dos catalisadores. Os testes de atividade catalítica da zeólita comercial modificada, conduzidos em diferentes temperaturas de reação, sugerem que o metal e sua quantidade, assim como a temperatura de reação, influenciam na seletividade para formação dos hidrocarbonetos superiores. Quanto aos catalisadores preparados a partir da modificação da zeólita sintetizada através da combinação de Ni e Zn, observou-se a influência do teor de cada metal e a necessidade de serem empregadas temperaturas de reação mais elevadas (400 °C) para obtenção dos hidrocarbonetos pesados. O teste de avaliação do tempo de residência mostrou que vazões menores (0,3-0,4 mL.h-1) favorecem a formação dos produtos pesados. Através do teste de estabilidade constatou-se que ao final de 10 horas de reação a conversão do etanol ainda foi de 100%, mas que a seletividade dos catalisadores para os hidrocarbonetos superiores foi diminuindo ao longo da reação devido à deposição de carbono sobre o catalisador.
The crude oil is the main raw material used to produce fuels, lubricants and petrochemicals. Currently, due to its increasing price some alternatives for petroleum replacement are being investigated. Among them, the renewable ones, such as ethanol, are receiving great attention. The catalytic conversion of ethanol is a potential source for obtaining liquid hydrocarbons, such as benzene, toluene, etc., that are of great interest in chemical industry. This work aim to evaluate the effect of different metals on HZSM-5 supported catalysts for the ethanol conversion into variable products. A series of catalysts containing 2.5 wt% of the metals La, Ca, Li, Mg and Ni were impregnated on commercial HZSM-5. Other series were prepared with different amounts of Ni, and with different combination of Ni and La on commercial HZSM-5. Subsequently, the HZSM-5 zeolite was synthesized in the laboratory and impregnated with Ni and/or Zn. Samples were characterized by specific area SBET, XRD and NH3-TPD. The spent catalysts were characterized by TPO. The catalyst activity was evaluated by catalytic conversion of ethanol experiments, carried out in a tubular fixed bed reactor with catalyst weight of 100 mg in the temperature range between 300 and 400 °C, using a feed rate of ethanol in the range of 0.2 to 1.2 mL.h-1. Three types of experiments were performed: with different reaction temperatures, different residence time and test of catalyst stability. The results with different reaction temperatures suggest that the type and the amount of metal used for the modification of commercial HZSM-5 zeolite influence the selectivity for the formation of higher hydrocarbons as well as the reaction temperature. For the catalysts prepared by modification of the synthesized HZSM-5 using Ni and/or Zn, the influence of the content of each metal and the reaction temperature can be observed. The residence time test showed that the lower flow rates favor the formation of heavy products. Total ethanol conversion was obtained during the 10 h reaction experiments for catalysts stability evaluation. However the catalysts selectivity for higher hydrocarbons decreased toward the end of the reaction due to the formation and deposition of coke on the catalyst surface.

APA, Harvard, Vancouver, ISO, and other styles

48

Chaves, Thiago Faheina. "Síntese e avaliação catalítica das zeólitas com estrutura BEA, MFI e MTW na reação de Knoevenagel." Universidade Federal de São Carlos, 2014. https://repositorio.ufscar.br/handle/ufscar/3955.

Full text

Abstract:

Made available in DSpace on 2016-06-02T19:55:40Z (GMT). No. of bitstreams: 1 6262.pdf: 12922381 bytes, checksum: d9847d4190f445fab3aa2cb28bd467a1 (MD5) Previous issue date: 2014-08-22
Universidade Federal de Minas Gerais
The use of zeolites in basic catalysis is small, especially when compared to the numerous applications of material in their acid form. Inside this context, are even smaller the number of studies on the use of as-synthesized zeolites as basic catalysts. Zeolites are crystalline hydrated aluminosilicates that have a pores size well-defined. Many of zeolite structures need organic compounds to be synthesized, these compounds are called structure directing agents. Zeolites containing organic cations (as-synthesized) have basic properties and can be used as catalysts in reactions that require this type of catalytic site. In this work were investigated three zeolites structures widely studied in the literature, BEA, MFI and MTW. Zeolites were synthesized with different compositions (ratio Si/Al) in the reaction mixture. Addition to the conventional synthesis were performed modifications using an organosilane (TPOAC - trimethoxysilyl-propyl-octadecylammonio chloride) in the synthesis of structures MFI and MTW. Were obtained, for the three structures, samples with different Si/Al ratios, some of them containing organosilane. The samples were characterized and used as catalysts in the Knoevenagel condensation. For all samples the increase of the Si/Al ratio increased the number of species [≡Si O ][TEA+]. The characterization and catalytic conversion show that for BEA zeolite only one portion of the species [≡Si O ][TEA+] were available for the reaction. The samples modified with organosilane (TPOAC) were the most active, especially with MTW structure. This increased activity is related to the modification that the organosilane promoted on the surface of the particles. The addition of organosilane favored the increase of the Si/Al ratio on the surface and this may be related to better conversion results. In this work, we propose new efficient catalysts, with zeolitic structure, for reactions involving basic sites.
O uso de zeólitas em catálise básica ainda é muito pequeno, principalmente quando comparado às inúmeras aplicações de material em sua forma ácida. Dentro desse contexto, é menor ainda o número de estudos sobre a utilização de zeólitas tal como sintetizadas como catalisadores básicos. Zeólitas são aluminosilicatos hidratados cristalinos que possuem um tamanho de poros muito bem definidos. Muitas das estruturas zeolíticas precisam de compostos orgânicos para serem sintetizadas, esses compostos são chamados de direcionadores de estrutura. Zeólitas contendo cátions orgânicos (tal como sintetizadas) possuem propriedades básicas e podem ser usadas como catalisadores em reação que necessitam esse tipo de sítio catalítico. Nesse trabalho foram investigadas 3 estruturas zeólitas bastante estudadas na literatura, BEA, MFI e MTW. As zeólitas foram sintetizadas com diferentes composições (razão Si/Al) na mistura reacional. Além da síntese convencional foram realizadas também modificações usando um organossilano (TPOAC Cloreto de Trimetoxisilil-propil-octadecilamônio) na síntese das estruturas MFI e MTW. Foram obtidas, para as 3 estruturas, amostras com diferentes razões Si/Al, algumas delas contendo organossilano. As amostras foram caraterizadas e usadas como catalisadores na reação de condensação de Knoevenagel. Para todas as amostras o aumento da razão Si/Al levou ao aumento da quantidade das espécies [≡Si O ][TEA+]. As caracterizações e os resultados de conversão catalítica mostram que para a zeólita BEA apenas parte das espécies [≡Si O ][TEA+] estavam na superfície disponíveis para a reação. As amostras modificadas com organossilano (TPOAC) foram as mais ativas, principalmente as com estrutura MTW. Essa maior atividade está relacionada a modificação que o organossilano promoveu na superfície das partículas. A adição de organossilano favoreceu o aumento da razão Si/Al na superfície e isso pode estar relacionado aos melhores resultados de conversão. Nesse trabalho, propomos novos catalisadores eficientes, a base de zeólitas, para reações que envolvam sítios básicos.

APA, Harvard, Vancouver, ISO, and other styles

49

Losch, Pit. "Synthesis and characterisation of zeolites, their application in catalysis and subsequent rationalisation : methanol-to-olefins (MTO) process with designed ZSM-5 zeolites." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAF035/document.

Full text

Abstract:

Cette thèse s'articule autour des zéolithes, plus particulièrement leur synthèse, leur caractérisation et leur application comme catalyseurs hétérogènes. Dans certains cas, la compréhension des phénomènes encontrés au cours de ce processus nécessitait un travail de rationalisation. Ce dernier ingrédient permet une réelle amélioration continue, ou une conception sur mesure d'un catalyseur pour une réaction. Les zéolithes sont des aluminosilicates, microporeux et cristallins, qui se définissent et se différencient de part leur arrangement 3D de tétraèdres (SiO4 et AlO4) . Il a été essayé d'utiliser des zéolithes conçues sur mesures en tant que catalyseurs pour des réactions faisant partie d'une chimie renouvelable. Ainsi, ces travaux s'inscrivent dans le cadre des concepts de la chimie verte et de l'addition graduelle de complexité moléculaire. Au cours de cette thèse, la boucle itéative de l'amélioration continue a mené à deux reprises à un catalyseur très adapté au processus catalytique en question: d'une part l'halogènation d'aromatiques a été effectuée en phase liquide, il s'agit d'un procédé liquide-solide pour lequel le meilleur catalyseur résulte en une zéolithe béta (H-*BEA) avec une porosité hiérarchisée. Au contraire, la réaction de la conversion du méthanol en oléfines (MTO) une réaction gas-solide semble avoir comme catalyse uroptimal des zéolithes de type ZSM-5 sans porosité hierarchisée, mais ayant des tailles cristallines élevées, une qualité cristalline proche de la perfection (sans défauts) et une densité de sites acides très disperses
This work revolved around the synthesis, characterisation and application of zeolites in heterogeneous catalysis. In some cases, counterintuitive observations and results needed a thorough rationalisation, which allowed a truly continuous improvement, or rational design of a catalyst for a given reaction. Zeolites are crystalline and microporous aluminosilicates, which are defined and differ one from another through their 3D arrangement of tetrahedra (SiO4 and AlO4).It has been aimed to design heterogeneous catalysts for reactions that fit in the concepts of a sustainable chemistry. Thus, this works describes and tried to respect the concepts of green chemistry and carbon upgrading. Remarkably, during this thesis the feedback looped continuous improvement approach has led twice to adapted catalysts for a catalytic chemical transformation: the liquid-solid continuous flow halogenation of aromatics was best performed with nanosized H-*BEA zeolites exhibiting a hierarchical porosity. In contrast, the gas-solid Methanol-to-Olefins (MTO) process needed an unusual catalyst. Indeed based on our study, large and perfectly crystalline H-ZSM-5 crystals with a disperse Brønsted acidity were the optimum catalyst

APA, Harvard, Vancouver, ISO, and other styles

50

Boruntea, Cristian-Renato. "Design, synthesis and characterization of small-pore zeolites for industrial environmental applications." Doctoral thesis, Universitat Politècnica de València, 2020. http://hdl.handle.net/10251/141094.

Full text

Abstract:

[ES] El Proyecto de investigación aquí descrito se estructura en dos partes. La primera parte se centra en la investigación fundamental con el objetivo de crear un protocolo para la síntesis de zeolitas. La segunda parte se refiere al diseño, síntesis y caracterización de nuevas zeolitas, particularmente utiles para aplicaciones DeNOx,, pero también podría ser útil para aplicaciones MTO. La investigación fundamental sugiere un Nuevo modelo de preparación de zeolitas utilizando otras zeolitas como simiente. Este proceso se llama transformación zeolita-zeolita o también conversión interzeolita. El alto rendimiento obtenido, la rápida cristalización y la mejor utilización y rendimiento de los materiales de partida se han tenido en cuenta para mejorar el proceso en base a un proyecto de doctorado financiado por una empresa. Este método se ha ilustrado utilizando varias zeolitas como semilla, entre otras FAU y CHA, para la preparación de las dos zeolitas objetivo: AEI y AFX. En la segunda parte, la investigación se centra en el diseño de nuevas zeolitas de poro medio. Se han seleccionado tres zeolitas hipotéticas de una base de datos de 933611 estructuras. Esta selección se ha realizado utilizando descriptores específicamente diseñados en base a la aplicabilidad de estas zeolitas en procesos DeNOx zeolitas. A continuación se han buscado los agentes directores de estructura (ADE) más apropiados, con la ayuda de métodos computacionales, algunos de los cuales se han sintetizado posteriormente. El uso de dichos ADE en el gel de síntesis ha permitido la obtención de una zeolita cuya topología (ERI) ha sido identificada mediante análisis por PXRD, y cuya morfología y tamaño de cristal (particularmente pequeño) la hacen muy adecuada para su uso como catalizador en algunos procesos. El trabajo de síntesis también reveló la aparición de una nueva zeolita de alta densidad, llamada 'paracelsio-K'. Este nuevo material se ha obtenido al explorar el espacio de fases que cristalizan al utilizar 1-methyl-DABCO como ADE. La síntesis de esta zeolita tiene un especial interés porque el ADE no se incorpora en los canales de la zeolita, pero más bien influyendo en la nucleación y cristalización. La caracterización reveló que la composición del material es próxima al mineral microcline, estructuralmente cercano al paracelsio, ambos feldespatos. A diferencia de los feldespatos el paracelsio-K contiene moléculas de agua en su interior (1 molécula por cavidad) y puede describirse como el material más simple de la familia de las zeolitas que contiene cadenas del tipo 'doble-cigüeñal'. Utilizando los elementos topológicos correspondientes a esta estructura es posible generar estructuras zeolíticas ya conocidas, como GIS, APC, MER, PHI, SIV y algunas otras zeolitas hipotéticas.
[CAT] El Projecte d'investigació aquí descrit s'estructura en dos parts. La primera part se centra en la investigació fonamental amb l'objectiu de crear un protocol per a la síntesis de zeolites. La segona part es refereix al disseny, síntesis i caracterització de noves zeolites, particularment útils per a aplicacions DeNOx , però també podria ser útil per a aplicacions MTO. La investigació fonamental suggereix un nou model de preparació de zeolites utilitzant altres zeolites com a llavor. Aquest procés s'anomena transformació zeolita-zeolita o també conversió interzeolita. L'alt rendiment obtingut, la ràpida cristal·lització i la millor utilització i rendiment dels materials de partida s'han tingut en compte per millorar el procés en base a un projecte de doctorat finançat per una empresa. Aquest mètode s'ha il·lustrat utilitzant diverses zeolites com a llavor, entre altres FAU i CHA, per a la preparació de les dues zeolites objectiu: AEI i AFX. A la segona part, la investigació se centra en el disseny de noves zeolites de porus mitjà. S'han seleccionat tres zeolites hipotètiques d'una base de dades de 933.611 estructures. Aquesta selecció s'ha realitzat utilitzant descriptors específicament dissenyats sobre la base de l'aplicabilitat d'aquestes zeolites en processos DeNOx zeolites. A continuació s'han buscat els agents directors d'estructura (ADE) més apropiats, amb l'ajuda de mètodes computacionals, alguns dels quals s'han sintetitzat posteriorment. L'ús d'aquests ADE al gel de síntesi ha permès l'obtenció d'una zeolita la topologia (ERI) ha estat identificada mitjançant anàlisi per PXRD, i la morfologia i mida de vidre (particularment petit) la fan molt adequada per al seu ús com a catalitzador en alguns processos. El treball de síntesi també va revelar l'aparició d'una nova zeolita d'alta densitat, anomenada 'paracelsio-K'. Aquest nou material s'ha obtingut a explorar l'espai de fases que cristal·litzen en utilitzar 1-methyl-DABCO com ADE. La síntesi d'aquesta zeolita té un especial interès perquè el ADE no s'incorpora en els canals de la zeolita, però més aviat influint en la nucleació i cristal·lització. La caracterització va revelar que la composició del material és propera al mineral microcline, estructuralment proper al paracelsio, tots dos feldspats. A diferència dels feldspats el paracelsio-K conté molècules d'aigua al seu interior (1 molècula per cavitat) i pot descriure com el material més simple de la família de les zeolites que conté cadenes del tipus 'doble-cigonyal'. Utilitzant els elements topològics corresponents a aquesta estructura és possible generar estructures zeolítiques ja conegudes, com GIS, APC, MER, PHI, SIV i algunes altres zeolites hipotètiques.
[EN] The research project described herein is structured in two parts. The first part is focused on the fundamental research with the aim of creating a toolbox for zeolite preparation. The second part deal with the design, synthesis and characterization of novel zeolites particular useful for DeNOx applications, but could be also useful for MTO applications. The fundamental research is addressing a novel approach of preparing zeolites by using other zeolites as raw materials. This process is known as zeolite-to-zeolite transformation or interzeolite conversion. The high yield obtained, fast crystallization time and the better utilization of the raw materials (e.g. parent zeolite, organic structure directing agent (OSDA)), are important benefits of interzeolite conversion technic, which answer the objectives formulated for an industrial PhD project. The method has been exemplified by using various raw materials as parent zeolites, such as FAU and CHA for the preparation of two target small pore zeolites AEI and AFX. In the second part the focus has been on the design of novel small pore zeolites. Three hypothetical frameworks have been selected by narrowing down a database containing 933611 structures. The selection has been performed by using the general descriptors for the state-of-the-art DeNOx zeolites (e.g. CHA). This was followed by finding suitable OSDAs for the selected frameworks, by using computational methods. The usage of the theoretically predicted OSDAs in synthesis gels made possible the synthesis of a novel high-silica zeolite. PXRD analysis, revealed that the zeolite has the ERI framework topology. The obtained material has a distinct particle morphology and smaller crystallites, which are key parameters for various catalytic processes. The synthesis work revealed also a novel dense zeolite, named K-paracelsian. The new material has been obtained while exploring the phase space using 1-methyl-DABCO as OSDA. The synthesis of this zeolite is especially interesting in the sense that the OSDA is not being incorporated into the zeolite channels, but rather influencing the nucleation and crystallization. Further characterization revealed a material compositionally closely related to the mineral microcline and structurally closely related to the mineral paracelsian, both of which are feldspars. In contrast to the feldspars, K-paracelsian contains intrazeolitic water corresponding to one molecule per cage and can be described as the simplest endmember of a family of dense double-crankshaft zeolite topologies. By applying the identified building principle, a number of known zeolite frameworks (e.g. GIS, APC, MER, PHI, SIV) and hypothetical zeolite topologies can be constructed.
The authors thank Haldor Topsoe A/S and Innovation Fund Denmark for financial support under the Industrial PhD programme (Case no. 1355-0174B). We thank MINECO of Spain for funding (SEV-2016- 0683 and RTI2018-101033-B-100) and ASIC-UPV for the use of computational facilities. We also thank Prof. M. M. J. Treacy for assistance with the Database of Prospective Zeolite Structures.
Boruntea, C. (2020). Design, synthesis and characterization of small-pore zeolites for industrial environmental applications [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/141094
TESIS

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Zeolites as catalysts'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles