Dissertationen: „The heterogeneous catalyst“

1

Guo, Chris. „Alkane Oxidation Catalysis by Homogeneous and Heterogeneous Catalyst“. Thesis, The University of Sydney, 2005. http://hdl.handle.net/2123/622.

Der volle Inhalt der Quelle

Annotation:

Abstract Cobalt-based complexes are widely used in industry and organic synthesis as catalysts for the oxidation of hydrocarbons. The Co/Mn/Br (known as "CAB system") catalyst system is effective for the oxidation of toluene. The Co/Mn/Br/Zr catalyst system is powerful for the oxidation of p-xylene, but not for the oxidation of toluene. [Co3O(OAc)5(OH)(py)3][PF6] (Co 3+ trimer 5) is more effective than [Co3O(OAc)6(py)3][PF6] (Co 3+ trimer 6) as a catalyst in the CAB catalyst system. Higher temperatures favour the oxidation of toluene. Zr 4+ does not enhance the oxidation of toluene. Zr 4+ could inhibit the oxidation of toluene in the combination of Co/Br/Zr, Co/Mn/Zr or Co/Zr. NHPI enhances the formation of benzyl alcohol, but the formation of other by-products is a problem for industrial processes. Complex(es) between cobalt, manganese and zirconium might be formed during the catalytic reaction. However, attempts at the preparation of complexes consisting of Co/Zr or Mn/Zr or Co3ZrP or Co8Zr4 clusters failed. The oxidation of cyclohexane to cyclohexanone and cyclohexanol is of great industrial significance. For the homogeneous catalysis at 50 o C and 3 bar N2 pressure, the activity order is: Mn(OAc)3 �2H2O > Mn12O12 cluster > Co 3+ trimer 6 > [Co3O(OAc)3(OH)2(py)5][PF6]2 (Co 3+ trimer 3) > Co 3+ trimer 5 > Co(OAc)2 �4H2O > [Co2(OAc)3(OH)2(py)4][PF6]-asym (Co dimerasym) > [Co2(OAc)3(OH)2(py)4][PF6]-sym (Co dimersym); whereas [Mn2CoO(OAc)6(py)3]�HOAc (Mn2Co complex) and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. But at 120 o C and 3 bar N2 pressure, the activity order is changed to: Co dimerasym > Co(OAc)2 �4H2O > Co trimer 3 and Mn(OAc)3 �2H2O > Co 3+ trimer 6 > Mn2Co complex > Co 3+ trimer 5 > Co dimersym > Mn12O12 cluster. The molar ratio of the products was close to cyclohexanol/cyclohexanone=2/1. Mn(II) acetate and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. Among those cobalt dimers and trimers, only the cobalt dimerasym survived after the stability tests, this means that [Co2(OAc)3(OH)2(py)4][PF6]-asym might be the active form for cobalt(II) acetate in the CAB system. Metal-substituted (silico)aluminophosphate-5 molecular sieves (MeAPO-5 and MeSAPO-5) are important heterogeneous catalysts for the oxidation of cyclohexane. The preparation of MeAPO-5 and MeSAPO-5 and their catalytic activities were studied. Pure MeAPO-5 and MeSAPO-5 are obtained and characterised. Four new pairs of bimetal-substituted MeAPO-5 and MeSAPO-5(CoZr, MnZr, CrZr and MnCo) were prepared successfully. Two novel trimetal-subtituted MeAPO-5 and MeSAPO-5 (MnCoZr) are reported here. Improved methods for the preparation of four monometal-substituted MeAPO-5 (Cr, Co, Mn and Zr) and for CoCe(S)APO-5 and CrCe(S)APO-5 are reported. Novel combinational mixing conditions for the formation of gel mixtures for Me(S)APO-5 syntheses have been developed. For the oxidation of cyclohexane by TBHP catalysed by MeAPO-5 and MeSAPO-5 materials, CrZrSAPO-5 is the only active MeSAPO-5 catalyst among those materials tested under conditions of refluxing in cyclohexane. Of the MeAPO-5 materials tested, whereas CrCeSAPO-5 has very little activity, CrZrAPO-5 and CrCeAPO-5 are very active catalysts under conditions of refluxing in cyclohexane. MnCoAPO-5, MnZrAPO-5 and CrAPO-5 are also active. When Cr is in the catalyst system, the product distribution is always cyclohexanone/cyclohexanol equals 2-3)/1, compared with 1/2 for other catalysts. For MeAPO-5, the activity at 150 o C and 10 bar N2 pressure is: CrZrAPO-5 > CrCeAPO-5 > CoZrAPO-5. For MeAPO-5 and MeSAPO-5, at 150 o C and 13 bar N2 pressure, the selectivity towards cyclohexanone is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5; and the selectivity towards cyclohexanol is: MnZrAPO-5 > CrZrAPO-5 > MnCoAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5. Overall the selectivity towards the oxidation of cyclohexane is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5. The amount of water in the system can affect the performance of CrCeAPO-5, but has almost no effect on CrZrAPO-5. Metal leaching is another concern in potential industrial applications of MeAPO-5 and MeSAPO-5 catalysts. The heterogeneous catalysts prepared in the present work showed very little metal leaching. This feature, coupled with the good selectivities and effectivities, makes them potentially very useful.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

2

Guo, Chris. „Alkane Oxidation Catalysis by Homogeneous and Heterogeneous Catalyst“. University of Sydney. Chemistry, 2005. http://hdl.handle.net/2123/622.

Der volle Inhalt der Quelle

Annotation:

Abstract Cobalt-based complexes are widely used in industry and organic synthesis as catalysts for the oxidation of hydrocarbons. The Co/Mn/Br (known as "CAB system") catalyst system is effective for the oxidation of toluene. The Co/Mn/Br/Zr catalyst system is powerful for the oxidation of p-xylene, but not for the oxidation of toluene. [Co3O(OAc)5(OH)(py)3][PF6] (Co 3+ trimer 5) is more effective than [Co3O(OAc)6(py)3][PF6] (Co 3+ trimer 6) as a catalyst in the CAB catalyst system. Higher temperatures favour the oxidation of toluene. Zr 4+ does not enhance the oxidation of toluene. Zr 4+ could inhibit the oxidation of toluene in the combination of Co/Br/Zr, Co/Mn/Zr or Co/Zr. NHPI enhances the formation of benzyl alcohol, but the formation of other by-products is a problem for industrial processes. Complex(es) between cobalt, manganese and zirconium might be formed during the catalytic reaction. However, attempts at the preparation of complexes consisting of Co/Zr or Mn/Zr or Co3ZrP or Co8Zr4 clusters failed. The oxidation of cyclohexane to cyclohexanone and cyclohexanol is of great industrial significance. For the homogeneous catalysis at 50 o C and 3 bar N2 pressure, the activity order is: Mn(OAc)3 �2H2O > Mn12O12 cluster > Co 3+ trimer 6 > [Co3O(OAc)3(OH)2(py)5][PF6]2 (Co 3+ trimer 3) > Co 3+ trimer 5 > Co(OAc)2 �4H2O > [Co2(OAc)3(OH)2(py)4][PF6]-asym (Co dimerasym) > [Co2(OAc)3(OH)2(py)4][PF6]-sym (Co dimersym); whereas [Mn2CoO(OAc)6(py)3]�HOAc (Mn2Co complex) and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. But at 120 o C and 3 bar N2 pressure, the activity order is changed to: Co dimerasym > Co(OAc)2 �4H2O > Co trimer 3 and Mn(OAc)3 �2H2O > Co 3+ trimer 6 > Mn2Co complex > Co 3+ trimer 5 > Co dimersym > Mn12O12 cluster. The molar ratio of the products was close to cyclohexanol/cyclohexanone=2/1. Mn(II) acetate and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. Among those cobalt dimers and trimers, only the cobalt dimerasym survived after the stability tests, this means that [Co2(OAc)3(OH)2(py)4][PF6]-asym might be the active form for cobalt(II) acetate in the CAB system. Metal-substituted (silico)aluminophosphate-5 molecular sieves (MeAPO-5 and MeSAPO-5) are important heterogeneous catalysts for the oxidation of cyclohexane. The preparation of MeAPO-5 and MeSAPO-5 and their catalytic activities were studied. Pure MeAPO-5 and MeSAPO-5 are obtained and characterised. Four new pairs of bimetal-substituted MeAPO-5 and MeSAPO-5(CoZr, MnZr, CrZr and MnCo) were prepared successfully. Two novel trimetal-subtituted MeAPO-5 and MeSAPO-5 (MnCoZr) are reported here. Improved methods for the preparation of four monometal-substituted MeAPO-5 (Cr, Co, Mn and Zr) and for CoCe(S)APO-5 and CrCe(S)APO-5 are reported. Novel combinational mixing conditions for the formation of gel mixtures for Me(S)APO-5 syntheses have been developed. For the oxidation of cyclohexane by TBHP catalysed by MeAPO-5 and MeSAPO-5 materials, CrZrSAPO-5 is the only active MeSAPO-5 catalyst among those materials tested under conditions of refluxing in cyclohexane. Of the MeAPO-5 materials tested, whereas CrCeSAPO-5 has very little activity, CrZrAPO-5 and CrCeAPO-5 are very active catalysts under conditions of refluxing in cyclohexane. MnCoAPO-5, MnZrAPO-5 and CrAPO-5 are also active. When Cr is in the catalyst system, the product distribution is always cyclohexanone/cyclohexanol equals 2-3)/1, compared with 1/2 for other catalysts. For MeAPO-5, the activity at 150 o C and 10 bar N2 pressure is: CrZrAPO-5 > CrCeAPO-5 > CoZrAPO-5. For MeAPO-5 and MeSAPO-5, at 150 o C and 13 bar N2 pressure, the selectivity towards cyclohexanone is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5; and the selectivity towards cyclohexanol is: MnZrAPO-5 > CrZrAPO-5 > MnCoAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5. Overall the selectivity towards the oxidation of cyclohexane is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5. The amount of water in the system can affect the performance of CrCeAPO-5, but has almost no effect on CrZrAPO-5. Metal leaching is another concern in potential industrial applications of MeAPO-5 and MeSAPO-5 catalysts. The heterogeneous catalysts prepared in the present work showed very little metal leaching. This feature, coupled with the good selectivities and effectivities, makes them potentially very useful.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

3

El, Solh Tarek. „Heterogeneous catalyst for methane reforming“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0007/MQ30748.pdf.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

4

Khurshid, Samir Najem Aldeen. „Biodiesel production by using heterogeneous catalyst“. Thesis, KTH, Skolan för kemivetenskap (CHE), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145953.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

5

Weller, Suzanne Catherine. „Electron microscopy of heterogeneous catalyst particles“. Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396431.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

6

Elhage, Ayda. „Palladium-based Catalyst for Heterogeneous Photocatalysis“. Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39388.

Der volle Inhalt der Quelle

Annotation:

Over the past decade, heterogeneous photocatalysis have gained lots of interest and attention among the organic chemistry community due to its applicability as an alternative to its homogeneous counterpart. Heterogeneous catalysis offers the advantages of easy separation and reusability of the catalyst. Several studies showed that under optimized conditions, efficient and highly selective catalytic systems could be developed using supported metal/metal oxide nanoparticles. In this dissertation, we summarize the progress in the development of supported palladium nanoparticles for different types of organic reactions. Palladium-decorated TiO2 is a moisture, air-tolerant, and versatile catalyst. The direct excitation of Pd nanoparticles selectively isomerized the benzyl-substituted alkenes to phenyl-substituted alkenes (E-isomer) with complete conversion over Pd@TiO2 under H2-free conditions. Likewise, light excited Pd nanoparticles catalyzed Sonogashira coupling, a C-C coupling reaction between different aryl iodides and acetylenes under very mild conditions in short reaction times. On the other hand, UV irradiation of Pd@TiO2 in alcoholic solutions promotes alkenes hydrogenation at room temperature under Argon. Thus, The photocatalytic activity of Pd@TiO2 can be easily tuned by changing the irradiation wavelength. Nevertheless, some of these systems suffer from catalyst deactivation, one of the main challenges faced in heterogeneous catalysis that decreases the reusability potential of the materials. In order to overcome this problem, we developed an innovative method called “Catalytic Farming”. Our reactivation strategy is based on the crop rotation system used in agriculture. Thus, alternating different catalytic reactions using the same catalyst can reactivate the catalyst surface by restoring its oxidation states and extend the catalyst lifetime along with its selectivity and efficiency. In this work, the rotation strategy is illustrated by Sonogashira coupling –problem reaction that depletes the catalyst– and Ullmann homocoupling –plausible recovery reaction that restores the oxidation state of the catalyst (Pd@TiO2). The selection of the reactions in this approach is based on mechanistic studies that include the role of the solvent and evaluation of the palladium oxidation state after each reaction. In a more exploratory analysis, we successfully demonstrated that Pd nanoparticles could be supported in a wide range of materials, including inert ones such as nanodiamonds or glass fibers. The study of the action spectrum shows that direct excitation of the Pd nanoparticles is a requisite for Sonogashira coupling reactions. The main advantages of heterogeneous catalysis compared to its homogeneous counterpart are easy separation and reusability of the catalyst. Finally in order to facilitate catalyst separation from batch reaction and develop a suitable catalytic system for continuous flow chemistry, we employed glass fibers as catalyst support for a wide variety of thermal and photochemical organic reactions including C-C coupling, dehalogenation and cycloaddition. Different metal/metal oxide nanoparticles, namely Pd, Co, Cu, Au, and Ru were deposited on glass wool and fully characterized. As a proof of concept, Pd decorated glass fibers were employed in heterogeneous flow photocatalysis for Sonogashira coupling and reductive de-halogenation of aryl iodides.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

7

Ishtchenko, Vera. „Novel heterogeneous oxidation catalyst for organic compounds“. Thesis, De Montfort University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422594.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

8

Ahmad, Mushtaq. „Characterization of promoted supported platinum catalyst“. Thesis, University of Edinburgh, 1990. http://hdl.handle.net/1842/13273.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

9

Meyer, Simon [Verfasser]. „Carbide Materials as Catalysts and Catalyst Supports for Applications in Water Electrolysis and in Heterogeneous Catalysis / Simon Meyer“. München : Verlag Dr. Hut, 2014. http://d-nb.info/1058284967/34.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

10

Tangale, N. P. „Zeolite based micro-mesoporous composites: synthesis, characterization and catalytic performance as heterogeneous catalyst for valorization of sugar“. Thesis(Ph.D.), CSIR- National Chemical Laboratory, Pune, 2018. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/4576.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

11

Richardson, John Michael. „Distinguishing between surface and solution catalysis for palladium catalyzed C-C coupling reactions: use of selective poisons“. Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22704.

Der volle Inhalt der Quelle

Annotation:

This work focuses on understanding the heterogeneous/homogeneous nature of the catalytic species for a variety of immobilized metal precatalysts used for C-C coupling reactions. These precatalysts include: (i) tethered organometallic palladium pincer complexes, (ii) an encapsulated small molecule palladium complex in a polymer matrix, (iii) mercapto-modified mesoporous silica metalated with palladium acetate, and (iv) amino-functionalized mesoporous silicas metalated with Ni(II). As part of this investigation, the use of metal scavengers as selective poisons of homogeneous catalysis is introduced and investigated as a test for distinguishing heterogeneous from homogeneous catalysis. The premise of this test is that insoluble materials functionalized with metal binding sites can be used to selectively remove soluble metal, but will not interfere with catalysis from immobilized metal. In this way the test can definitely distinguish between surface and solution catalysis of immobilized metal precatalysts. This work investigates three different C-C coupling reactions catalyzed by the immobilized metal precatalysts mentioned above. These reactions include the Heck, Suzuki, and Kumada reactions. In all cases it is found that catalysis is solely from leached metal. Three different metal scavenging materials are presented as selective poisons that can be used to determine solution vs. surface catalysis. These selective poisons include poly(vinylpyridine), QuadrapureTM TU, and thiol-functionalized mesoporous silica. The results are contrasted against the current understanding of this field of research and subtleties of tests for distinguishing homogeneous from heterogeneous catalysis are presented and discussed.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

12

Galarraga, Carmen E. „Heterogeneous catalyst for the synthesis of middle distillate hydrocarbons“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0035/MQ30763.pdf.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

13

Baines, Nicholas John. „Synthesis of heterogeneous palladium catalyst assemblies by molecular imprinting“. Thesis, University of East Anglia, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249774.

Der volle Inhalt der Quelle

Annotation:

Heterogeneous palladium catalysts for use in Suzuki-type reactions have been prepared using the molecular imprinting technique. Using this technique allows the preparation of a heterogeneous catalyst with uniform active sites which have a metal complex configuration that favours processes in the catalytic cycle, thus enhancing the rate of reaction. It was reasoned, from the general catalytic cycle for palladium cross-couplings, that a bisphosphine complex with a cis ligand geometry would be beneficial. Polymerisable phosphines were synthesised and the cis bisphosphine palladium complexes prepared. The geometry of the complexes was fixed by addition of a bidentate ligand (catechol). The resulting complexes were incorporated into a macroporous polymer framework using the molecular imprinting technique. This produced the heterogeneous palladium catalysts with uniform active sites and known palladium content. The catalysts were ~ested in model Suzuki reactions and were shown to give far superior yields to the homogeneous catalyst and control heterogeneous catalyst (derived from commercial ligand). The favoured square-planar cis-geometry was likely to increase the rate of reductive elimination, which takes place from that conformation. It is also reasonable to imply that the catalytically active palladium(O) species would be strained, being tetrahedral not square-planar, and so the rate of oxidative addition (the slow step in some cases) could also be accelerated. The improved yields shown by the imprinted catalysts for the Suzuki reactions suggest that this is the case.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

14

Deepa, A. K. „Depolymerization of lignin over heterogeneous catalyst having acidic functionality“. Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2014. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/1979.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

15

Singh, D. „Investigation on the valorization of lignin: Base catalyzed lignin depolymerization to aromatic monomers and their further functionalization and defunctionalization using heterogeneous catalysts“. Thesis(Ph.D.), CSIR NCL, 2021. https://dspace.ncl.res.in/xmlui/handle/20.500.12252/5946.

Der volle Inhalt der Quelle

Annotation:

The high consumption rate of fossil feedstock throughout the world is responsible for decrease in its availability. Moreover, geo-political reasons and fluctuating prices are also playing crucial role in its utilization. At the same time, demand is increasing for the renewable, environment friendly resource for generating energy. Biomass, a sustainable and renewable resource has the potential to synthesize fuels and chemicals instead from fossil feedstock. Lignocellulosic biomass is readily available throughout the world at a lower cost.
AcSIR

APA, Harvard, Vancouver, ISO und andere Zitierweisen

16

Nguyen, Joseph Vu. „Design, synthesis, and optimization of recoverable and recyclable silica-immobilized atom transfer radical polymerization catalysts“. Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6860.

Der volle Inhalt der Quelle

Annotation:

Despite the growing interest in heterogeneous polymerization catalysis, the majority of the polymerization catalysts used industrially are single-use entities that are left in the polymer product. Recoverable and recyclable polymerization catalysts have not reached the industrial utility of single-use catalysts because the catalyst and product separation have not become economical. The successful development of recyclable transition metal polymerization catalysts must take a rational design approach, hence academic and industrial researchers need to further expand the fundamental science and engineering of recyclable polymerization catalysis to gain an understanding of critical parameters that allow for the design of economically viable, recoverable solid polymerization catalysts. Unfortunately, the rapid development of Atom Transfer Radical Polymerization over the past 10 years has not resulted in its wide spread industrial practice. Numerous reports regarding the immobilization of transition metal ATRP catalysts, in attempts to increase its applicability, have extended the fundamentals of recyclable polymerization catalysis. However, for industrial viability, more research is required in the area of how the catalyst complex immobilization methodology and support structure affect the catalyst polymerization performance, regeneration, and recyclability. A comprehensive rational catalyst design approach of silica-immobilized ATRP catalyst was undertaken to answer these questions and are discussed here.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

17

Zheng, Run. „Towards heterogeneous catalysis and catalyst design :a density functional theory study on Fischer-Tropsch synthesis“. Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492328.

Der volle Inhalt der Quelle

Annotation:

Fischer-Tropsch (FT) synthesis, which converts CO and H2 to a large range of hydrocarbons, is of paramount significance in utilizing natural resources, such as natural gas and coal. In this thesis, density functional theory (DFT) calculations together with kinetic analysis are introduced to study this important process. Our work shows that this combination is a good way to investigate chemical reactions occurring on surfaces, which are important in the area of heterogeneous catalysis. First of all, we study chain growth mechanism. With consideration of both coupling barriers and reactant stability, the reaction rates of all possible coupling channels are .evaluated and compared. By this means, the major coupling pathways are identified on the Co surface. We Furthennore extend this approach to the mechanisms on the Rh, Ru, Fe and Re surfaces. We also study a-olefin selectivity. A simple expression of the paraffin/olefin ratio is obtained based on a kinetic model. Combining the expression of the paraffin/olefin ratio and our calculation results, experimental findings are satisfactorily explained. Based on the understanding obtained from previous work, we further examine the a value, namely chain growth probability, one of the most important parameters in FT synthesis. A general expressIOn of chain growth probability is derived, and the relationship between the ex value and chain length observed experimentally IS satisfactorily explained. Attempting to understand the promotion effects of transition metals in Co-based catalysts, we examine two processes pertinent to reactivity and selectivity in FT synthesis, namely CO dissociation and ethylene chemisorption. Some suggestions are raised to modify Co catalysts to improve reactivity and selectivity in FT synthesis. Supplied by The British Library - 'The world's knowledge' Supplied by The British Library - 'The world's knowledge'

APA, Harvard, Vancouver, ISO und andere Zitierweisen

18

Yiu, Humphrey Hak Ping. „The application of MCM-41 type mesoporous molecular sieves as heterogeneous acid catalysts and catalyst supports“. Thesis, University of Huddersfield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285629.

Der volle Inhalt der Quelle

Annotation:

Two types of mesoporous molecular sieves, MCM-41 and MMS, were prepared, fully characterised and tested as solid acid catalysts and catalyst support materials. Three different methods for characterising the surface acidity of these solid acids were examined and compared. These methods were 1. Fourier Transform infrared (FTIR) spectroscopy of adsorbed pyridine, 2. Pulsed ammonia adsorption using a combination of thermogravimetry and differential scanning calorimetry (TG/DSC), and 3. Temperature-programmed desorption of amines. The acidity results of these molecular sieves were compared with zeolites and acid-treated clays. The Lewis and Br0nsted acid catalytic activities of the ion-exchanged aluminosilicate mesoporous molecular sieves were investigated in liquid phase Friedel-Crafts alkylations. Three model reactions were used to examine the Lewis and Br0nsted acid catalytic activities of the catalysts and the results were compared with acid-treated clays. Generally, the two aluminosilicate molecular sieves showed similar Br0nsted and Lewis acid catalytic activities. The Fe3+ exchanged catalysts showed high Lewis acid catalytic activities while H+ and AI3+ exchanged catalysts showed high Br0nsted acid catalytic activities. In addition to liquid phase Friedel-Crafts reactions, a new technique was developed to monitor the acid catalytic activity of catalysts. The use of temperature programmed-solid insertion probe-mass spectrometry (TP-SIPMS) for this application was investigated. The results were compared with zeolites. The catalytic results from this technique were found to have good correlation with the liquid phase Br0nsted acid catalytic test. Finally, the mesoporous molecular sieves were used as support materials for Lewis acid catalysts. Again, the catalytic activities of these catalysts were studied using a Friedel-Crafts alkylation reaction. The results were compared with some commercially available supported catalysts. Among these catalysts, FeCl) supported on MCM-41 was found to be very active while ZnCb supported on MCM-41 exhibited milder Lewis acid catalyitc activity. However, ZnCb was found to be more dependent on the nature of support.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

19

HOANG, ANH VIET DUNG. „Synthesis of biodiesel via supercritical ethanol condition with heterogeneous catalyst“. Doctoral thesis, Politecnico di Torino, 2016. http://hdl.handle.net/11583/2640032.

Der volle Inhalt der Quelle

Annotation:

This Ph.D. thesis aims to gain a better understanding of non-catalytic and catalytic supercritical fluid (SCF) transesterification between ethanol and rapeseed oil to produce biodiesel mainly consisting of fatty acid ethyl esters (FAEE) for future reactor scale-up and process design. Another goal was to develop a new analytical approach employ high performance liquid chromatograph (HPLC) with the potential for in-line reaction monitoring to determine the compositions of liquid products such as FAEEs, triglyceride (TG), diglyceride (DG) and monoglyceride (MG).

APA, Harvard, Vancouver, ISO und andere Zitierweisen

20

Wang, Xia. „Artificial Photosynthesis : Carbon dioxide photoreduction and catalyst heterogenization within solid materials“. Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLET025/document.

Der volle Inhalt der Quelle

Annotation:

Dans le contexte du réchauffement climatique et de l’usage abusif de combustibles fossiles, la recherche de sources d’énergie propres et durables est l’un des défis les plus importants de notre époque. Récemment, le stockage d’énergie solaire par la réduction de CO2 a fait l’objet d’un nouvel intérêt. Bien que la réduction de CO2 en carburants liquides ou gazeux soit une question à la fois fascinante et fondamentale, sa mise en œuvre dans les dispositifs technologiques reste très difficile à cause de la grande stabilité de CO2 et du caractère endergonique de sa transformation. On outre, les réactions impliquent multiples électrons et protons et ainsi demandent des catalyseurs efficaces et stables pour diminuer les barrières cinétiques importantes.Cette comprend deux parties. Après une introduction, la première partie décrit des études sur des catalyseurs homogènes en combinaison avec un photosensibilisateur, soit séparément soit connecté par liaison covalente. Grâce à la possibilité de les modifier par synthèse et à leur facile caractérisation, les photosystèmes moléculaires homogènes sont plus modulables et peuvent permettre un meilleur contrôle de la sélectivité des réactions et l’étude des mécanismes réactionnels.Cependant, les catalyseurs moléculaires ne peuvent être facilement transposés pour des applications à plus large échelle dans un contexte industriel. En effet, les catalyseurs homogènes sont moins stables et plus difficilement recyclables que les catalyseurs hétérogènes. Dans ce contexte, l’intégration de catalyseurs moléculaires au sein d’un support solide a l’avantage de maintenir leur activité catalytique tout en permettant une séparation et un recyclage plus faciles. La deuxième partie de cette thèse porte donc sur l’immobilisation de catalyseurs moléculaires dans les matériaux. Le but ultime de cette thèse est d’incorporer à la fois le catalyseur et le photosensibilisateur dans le support solide
In the context of global warming and the necessary substitution of renewable energies (solar and wind energy) for fossil fuels, efficient energy-storage technologies need to be urgently developed. Recently, energy storage via the reduction of CO2 has seen renewed interest. Although reduction of CO2 into energy-dense liquid or gaseous fuels is a fascinating fundamental issue, its practical implementation in technological devices is highly challenging due to the high stability of CO2 and thus the endergonic nature of its transformation. Furthermore, the reactions involve multiple electrons and protons and thus require efficient catalysts to mediate these transformations.The objective of this thesis is to investigate different strategies for the storage of solar energy in chemical compounds, through visible-light-driven CO2 reduction. This thesis comprises of two main parts. After an introduction, the first part describes the investigation of homogeneous catalysts in combination with a photosensitizer, either separately or connected covalently. Due to the easily-tunable synthesis and facile characterization of molecular catalysts, homogeneous photosystems are more controllable and can give deep insight into product selectivity and mechanistic issues.With regards to future applicability, however, homogeneous catalysis often suffers from additional costs associated with solvents, product isolation and catalyst recovery, amongst other factors. The integration of molecular catalysts into solid platforms offers the possibility to maintain the advantageous properties of homogeneous catalysts while moving towards practical system designs afforded by heterogeneous catalysis. The second part of this thesis is therefore the immobilization of molecular catalysts within solid materials, namely MOFs and PMO. The ultimate goal of this thesis is to incorporate both catalyst and photosensitizer into the solid support

APA, Harvard, Vancouver, ISO und andere Zitierweisen

21

Hamoudi, Safia. „Heterogeneous catalytic oxidation of aqueous phenol, degradation kinetics and catalyst deactivation“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0001/NQ39357.pdf.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

22

Kruger, Dawid. „Gas phase heterogeneous catalyst performance testing in laboratory fixed-bed reactors“. Master's thesis, Faculty of Engineering and the Built Environment, 2019. http://hdl.handle.net/11427/31115.

Der volle Inhalt der Quelle

Annotation:

Activity, selectivity and stability are invariably among the key factors of the performance of a catalyst. In the development of catalysts these properties are often screened for a range of materials and formulations. Interpretation of these key performance indicators are prone to various confounding effects. Here, performance testing of solid, porous catalysts for gas phase reactions in tubular fixed bed reactors is considered. Transport limitations and particularly internal mass transfer limitations are often cited in this case. Many have given general discussions and guides for effective catalyst performance testing, reviewed or put forward theoretical descriptions for transport phenomena and have measured and correlated associated transport coefficients. Some quantitative requirements and the relative importance of different effects have been found to remain unclear. Here, some of these aspects are addressed by the development of 3 catalyst testing criteria. Specifically, an upper limit is derived for the chemical conversion in a firstorder reaction such that differential rate conditions are established, a lower limit on the chemical conversion is applied to limit the loss of precision in conversion measurements, and an expression is derived to limit the effect of pressure drop across a catalyst bed on the observed rate of a first-order reaction. The prevalence and sensitivity of these and other transport limitation criteria were investigated theoretically in the context of the low-temperature (LT) water-gas shift (WGS) reaction over a Cu/ZnO/Al2O3 catalyst in a laboratory scale performance test. Factorial combination of some commonly manipulated experimental parameters (reactant feed rate, temperature, catalyst particle size, catalyst loading, dilution fraction and reactor tube size) was employed in this regard. The upper conversion limit, the internal mass transfer criterion and the radial heat transfer criterion were found to be particularly severe. So too, to a lesser extent, were the axial dispersion and pressure drop criteria, and the lower conversion limit. The sensitivity analysis indicated optima in the varied experimental parameters and yielded insights into effective control of different effects by selection of process conditions. Application of the set of criteria in an experimental performance test was demonstrated using a proprietary medium-temperature (MT), WGS catalyst under reaction at temperatures of 275 °C, 300 °C and 375 °C, 1 atm total pressure, dry feed composition of 10% CO, 10% CO2, 70% H2, 10% N2, steam-to-dry gas ratio of 0.5 and 158 h-1 weight hourly space velocity (WHSV). The catalyst was found to have near total selectivity towards the WGS reaction with activities of 12.2 ± 1.1, 17.1 ± 0.5 and 24.9 ± 1.5 µmol/s.gcat at 275 °C, 300 °C and 375 °C respectively. This corresponds to an activation energy of 39 ± 2 kJ/mol; a value within range of what is reported in literature for similar catalysts. This experiment also served to compare experimental and predicted internal mass transfer limitations by testing catalyst particles of different mean sizes. This catalyst as well as a CuO/ZnO/Al2O3 catalyst precursor was characterised in respect of their pore size distributions (N2 physisorption and mercury intrusion porosimetry (MIP)), particle size distributions (by photo- and microscopic analysis), bulk and particle densities and product gas compositions (by gas chromatography) to enable evaluation of the various criteria employed. Evaluation of the various criteria indicated that, theoretically, the considered confounding effects had a negligible effect on the measured catalytic activities for the catalyst sample with the smallest mean particle size, while the larger particles experienced only internal mass transfer limitations. Different models considered for effective diffusivities all under-predicted values when compared to the effective diffusivities inferred from the reaction-diffusion experiments. Predictions ranged to within factors of 3 – 20 of the experimental values, depending on whether pore size distribution data were derived from MIP or physisorption data. Here, the lack of characterisation of the macro-porosity by N2 physisorption resulted in more severe under-estimations of the effective diffusivities than the equivalent estimations made with MIP data. The best prediction was made by the ‘parallel-path pore’ model by Johnson & Stewart (1965) using MIP data. Predictions of internal mass transfer limitations varied in a similar manner. It is noted that the simplifications of the highly complex porous catalyst by these model combinations introduce large sources of error in the prediction of internal mass transfer limitations.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

23

Lopes, Ingridy Santos. „Estudo de catalisadores Pt-In/Nb2O5 na conversão de hidrocarbonetos“. Universidade Federal Fluminense, 2003. http://www.bdtd.ndc.uff.br/tde_busca/arquivo.php?codArquivo=216.

Der volle Inhalt der Quelle

Annotation:

Fundação de Amparo a Pesquisa do Estado do Rio de Janeiro
A desidrogenação de hidrocarbonetos é um importante processo industrial, devido à grande demanda de hidrocarbonetos insaturados para produtos e processos industriais. Hidrocarbonetos insaturados são utilizados na manufatura de vários produtos, tais como detergentes, gasolina de alta octanagem, produtos farmacêuticos e borrachas sintéticas. Na desidrogenação de hidrocarbonetos, o catalisador comercial utilizado é à base de platina suportado em alumina. A acidez intrínseca do suporte é neutralizada por um metal alcalino ou alcalino terroso, geralmente lítio. Índio e estanho são utilizados como promotores da fase metálica. O presente trabalho teve como objetivo principal o estudo das propriedades de catalisadores de Pt modificados com adição de In e suportados em nióbia, óxido redutível sujeito ao efeito da forte interação metal-suporte (SMSI). Catalisadores Pt/Nb2O5 foram testados recentemente na desidrogenação de alcanos e apresentaram resultados promissores. Catalisadores Pt/Nb2O5 e Pt-In/Nb2O5 foram preparados por impregnação seca e caracterizados por redução à temperatura programada (TPR), espectroscopia no UV-Visível com reflectância difusa (DRS), quimissorção de H2 e CO, dessorção à temperatura programada de H2 e CO (TPD), além de oxidação à temperatura programada (TPO). A atividade catalítica desses catalisadores foi avaliada na desidrogenação do cicloexano, na hidrogenólise do metilciclopentano, na conversão do n-heptano e na reforma do metilciclopentano. A análise dos perfis de TPR permitiu concluir que há uma interação entre Pt e In nos catalisadores bimetálicos, que foi confirmada pelo decréscimo na capacidade de adsorção, medidas pelos consumos de H2 e CO. A adição de In também inibiu o efeito da forte interação metal-suporte (SMSI) entre a platina e a nióbia. A desidrogenação do cicloexano para o catalisador Pt/Nb2O5 mostrou a criação de novos sítios interfaciais. As reações de hidrogenólise foram suprimidas pela presença do efeito SMSI e pela presença do In, como foi observado na hidrogenólise do metilciclopentano. Na conversão do n-heptano, todos os catalisadores suportados em nióbia mostraram uma alta seletividade para a formação de olefinas. A presença do In suprimiu reações de hidrogenólise e favoreceu a atividade e a estabilidade do catalisador. Na reforma do metilciclopentano todos os catalisadores apresentaram boa seletividade para produtos de desidrogenação.
Hydrocarbon dehydrogenation is an important industrial process, due to the high demand of unsatured hydrocarbons for industrial processes and products. Unsatured hydrocarbons are used in the manufacture of several products, such as detergents, high octanage gasoline, pharmaceutical products and synthetic rubber. The commercial catalysts employed in the hydrocarbon dehydrogenation process is based on platinum supported on alumina. The intrinsic acidity of the support is neutralized by an alkaline or alkali earth metal, usually lithium. Indium and tin are used as promoters of the metallic phase. The present work aimed to study the property of niobia supported Pt catalysts modified by In. Nióbia is a reductible oxide, able to promote a strong metal support interaction effect (SMSI). Pt/Nb2O5 catalysts were investigated recently in the dehydrogenation of alkanes and they presented promissing results. Pt/Nb2O5 and Pt-In/Nb2O5 were prepared by incipient wetness and characterized by temperature-programmed reduction (TPR), UV-Vis diffuse reflectance spectroscopy (DRS), H2 and CO chemisorption, H2 and CO temperature-programmed desorption (TPD), besides temperature-programmed oxidation (TPO). The catalytic activity of these catalysts was evaluated in the cyclohexane dehydrogenation, methylcyclopentane hydrogenolysis, n-heptane conversion and methylcyclopentane reforming. The analysis of TPR profiles allowed to conclude that there is an interaction between Pt and In in the bimetallic catalysis, which was confirmed by the decrease in the adsorption capacity measured by the H2 and CO uptakes. In addition it also inhibited the metal support effect (SMSI) between platinum and niobia. Cyclohexane dehydrogenation results demonstrated the creation of new interfacial sites for Pt/Nb2O5 catalysts. Hydrogenolysis reactions were suppressed by the presence of the SMSI effect and by the presence of In, as observed in the methylcyclopentane hydrogenolysis. In the n-heptane conversion, all the niobia-supported catalysts displayed a high selectivity for the olefin formation. The presence of In decreased the formation of hydrogenolysis products and increased the stability of the catalyst. In the reforming methylcyclopentane all the catalysts displayed a high selectivity for the dehydrogenation products.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

24

Mirza, Amin Ruhul. „Developments in supported aqueous-phase catalysis“. Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311179.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

25

Cheng, Lei. „FIRST-PRINCIPLES DENSITY FUNCTIONAL THEORY STUDIES OF REACTIVITIES OF HETEROGENEOUS CATALYSTS DETERMINED BY STRUCTURE AND SUBSTRATE“. OpenSIUC, 2009. https://opensiuc.lib.siu.edu/dissertations/99.

Der volle Inhalt der Quelle

Annotation:

In this dissertation, density functional theory (DFT) calculations were used to investigate (1)NO2 adsorption on BaO in NOx Storage Reduction (NSR) catalyst affected by the morphology of BaO and the γ-Al2O3 support, (2) energy barrier of H2 dissociative adsorption over Mg clusters affected by its electronic structure, and (3) comparison of the activities of CeO2 clusters affected by two different supports--monoclinic ZrO2 and non-spinel γ-Al2O3. Our results showed that the electronic effect caused by the non-stoichiometry of the bare BaO clusters and surfaces improves their reactivities toward NO2 adsorption greatly, whereas the geometric structure of the catalyst has only minor effect on the activity; we also found that the γ-Al2O3 substrate improves the reactivities of the supported BaO clusters and at the same time the interface between BaO and γ-Al2O3 provided a unique and highly reactive environment for NO2 adsorption. Hydrogen dissociation barrier over pure Mg clusters is greatly affected by the electronic structure of the clusters--closed shell clusters such as Mg10 and Mg92- have higher energy barrier toward H2 dissociation; however, H2 dissociation over clusters that are two electrons shy from the closed electronic shell are relatively easier. As substrates, neither ZrO2(111) nor γ-Al2O3(100) affects the reactivity of the supported Ce2O4 toward CO2 adsorption and CO physisorption significantly; whereas the reactivity of Ce2O4 toward CO reactive adsorption were found to be affected by the two substrates very differently.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

26

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.

Der volle Inhalt der Quelle

Annotation:

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 und andere Zitierweisen

27

Kong, Pei San. „A novel hydrophobic ZRO2-SIO2 based heterogeneous acid catalyst for the esterification of glycerol with oleic acid“. Thesis, Toulouse, INPT, 2018. http://www.theses.fr/2018INPT0042.

Der volle Inhalt der Quelle

Annotation:

Le faible coût du glycérol sur le marché a conduit à des études approfondies sur la conversion du glycérol en dérivés à valeur ajoutée. Ce travail se concentre sur l'estérification catalytique du glycérol, avec l'acide oléique, réaction d’intérêt industriel en raison de la grande valeur commerciale des produits obtenus. Dans ce travail, un nouveau catalyseur acide hétérogène présentant une surface hydrophobe a été développé sur le support ZrO2-SiO2 car un catalyseur acide solide tolérant à l'eau est essentiel pour les réactions d'estérification en milieu biphasique produisant de l'eau. Le catalyseur synthétisé (ZrO2-SiO2-Me&Et-PhSO3H) a été préparé par silication et modification de surface en utilisant du triméthoxyméthylsilane (TMMS) et du 2-(4- chlorosulfonylphényl) éthyltriméthoxysilane. La morphologie de surface, les propriétés physicochimiques et texturales, l'acidité et l'hydrophobicité ont été caractérisées. Le mécanisme de modification de la surface du catalyseur est proposé en fonction des résultats de caractérisation complets. Une nouvelle technique pour contrôler le niveau d'acidité et d'hydrophobicité du catalyseur conçu est décrite dans ce travail. L'acidité et l'hydrophobicité du catalyseur ont été réglées en contrôlant la quantité d'agents de modification de surface. Il a pu être montré que l'hydrophobicité du catalyseur était diminuée à mesure que son acidité augmentait. Le catalyseur ZrO2-SiO2-Me & Et-PhSO3H_70 avec 70% molaire de TMMS et 0,62 mmol/g d'acidité est le catalyseur optimal pour l'estérification du glycérol avec l'acide oléique. Enoutre, le rôle de l'hydrophobicité dans la réaction catalytique a été étudié ici. Ce travail a montré qu'à acidité constante du catalyseur, le catalyseur le plus hydrophobe présentait un meilleur rendement. La conversion en utilisant le catalyseur préparé (ZrO2-SiO2-Me et EtPhSO3H_70) est de 88,2% avec une sélectivité en monooléate de glycérol de 53,5% et une sélectivité en dioléate de glycérol de 40,0% (sélectivité combinée de 94% en monooléate et dioléate de glycérol) pour un rapport équimolaire d'acide oléique/glycérol, une température de réaction de 160°C, une concentration massique du catalyseur de 5% par rapport à la masse d’acide oléique introduit, en conditions de réaction sans solvant et avec un temps de réaction de 8 h. Ce travail révèle que l'hydrophobicité et le volume des pores du catalyseur conçu affectent significativement la sélectivité en produit. De plus, les performances du catalyseur hydrophobe ZrO2-SiO2-Me&Et- PhSO3H_70, ont été comparées à celles de la zircone sulfatée (SO42-/ZrO2) et des catalyseurs commerciaux (Amberlyst 15 et Aquivion). Les résultats de corrélation ont montré que le volume moyen des pores (taille des pores) influençait la sélectivité du produit lorsque le catalyseur ZrO2- SiO2-Me&Et-PhSO3H_70 était comparé à trois catalyseurs SO42-/ZrO2 développés à partir de différents précurseurs de zirconium. Ainsi, le catalyseur à volume de pores le plus élevé est favorable à la production de dioléate de glycérol dans des conditions réactionnelles identiques. On peut conclure que le volume et la taille des pores peuvent être utilisés pour contrôler la sélectivité en produit. En outre, cette étude a également révélé que la propriété d'hydrophobicité améliorait la vitesse de réaction initiale
The low market value of glycerol has led to extensive investigations on glycerol conversion to value-added derivatives. This work focuses on industrially important catalytic esterification of glycerol with oleic acid due to the high commercial value of the resulting products. In this work, a novel heterogeneous acid catalyst featuring hydrophobic surface was developed on ZrO2-SiO2 support as water tolerant solid acid catalyst is vital for biphasic esterification reactions producing water. The synthesized catalyst (ZrO2-SiO2-Me&Et-PhSO3H) was prepared through silication and surface modification using trimethoxymethylsilane (TMMS) and 2-(4-chlorosulfonylphenyl) ethyltrimethoxysilane. The surface morphology, physiochemical and textural properties, acidity and hydrophobicity were characterized. The mechanism of the catalyst surface modification is thereof proposed according to comprehensive characterization results. A novel technique to control acidity and hydrophobicity level of the designed catalyst is disclosed in this work. The acidity and hydrophobicity of the catalyst were tuned by controlling the amount of surface modification agents. It was found that the hydrophobicity of the catalyst decreased as its acidity increased. ZrO2-SiO2-Me&Et-PhSO3H_70 catalyst with 70 mol% of TMMS and 0.62 mmol/g acidity is the optimal catalyst for glycerol esterification with oleic acid. Furthermore, the role of hydrophobicity in catalytic reaction was investigated herein. It was found that at constant catalyst acidity, the more hydrophobic catalyst showed better yield. The conversion using the designed catalyst (ZrO2-SiO2-Me&EtPhSO3H_70) is 88.2% with 53.5% glycerol monooleate selectivity and 40.0% glycerol dioleate selectivity (combined 94% selectivity of glycerol monooleate and dioleate) at equimolar oleic acid-to-glycerol ratio, 160 oC, reaction temperature, 5 wt% catalyst concentration with respect to weight of oleic acid, solvent-less reaction conditions and 8 h reaction time. This work reveals that the hydrophobicity and the pore volume of the designed catalyst significantly affect the product selectivity. In addition, the performance of the hydrophobic designed ZrO2-SiO2-Me&Et-PhSO3H_70 catalyst was used to benchmark with catalytic activity of sulfated zirconia (SO42-/ZrO2) and commercial catalysts (Amberlyst 15 and Aquivion). The correlation results showed that the average pore volume (pore size) influenced the product selectivity when ZrO2-SiO2-Me&Et-PhSO3H_70 catalyst was compared to three SO42-/ZrO2 catalysts that were developed from different zirconium precursors. Whereby, the higher pore volume catalyst is favourable to glycerol dioleate production at identical reaction conditions. It can be concluded that pore volume and size can be used to control the product selectivity. In addition, this study also revealed that hydrophobicity characteristic facilitated initial reaction rate effectively

APA, Harvard, Vancouver, ISO und andere Zitierweisen

28

Shi, Fan. „NMR/MRI SIGNAL ENHANCEMENT BY REVERSIBLE EXCHANGE (SABRE) AND HETEROGENEOUS SABRE (HET-SABRE)“. OpenSIUC, 2015. https://opensiuc.lib.siu.edu/dissertations/994.

Der volle Inhalt der Quelle

Annotation:

Signal Amplification by Reversible Exchange, or SABRE, is a type of PHIP (ParaHydrogen Induced Polarization) pioneered by Duckett, Green, and co-workers where an organometallic catalyst is used to co-locate parahydrogen (pH2) and a molecular substrate to be hyperpolarized. Like traditional PHIP, SABRE is of interest because it is cost-effective, potentially continuous, scalable, and rapid (achieving polarization enhancement in seconds). However unlike traditional PHIP, SABRE does not require permanent alteration of the substrate to hyperpolarize it. In addition to achieving 1H polarizations of several percent, SABRE in microTesla fields has enabled the creation of ~10% polarization for heteronuclear (15N) spins. I will discuss on a series of novel catalysts that I developed in my Ph.D program. Firstly of all, a heterogeneous SABRE ("HET-SABRE") catalyst where catalytic moieties were tethered to solid supports. Although NMR enhancements were modest (5), this initial work showed the feasibility of the approach. Next, two types of nanoscale catalysts were created to explore SABRE at the interface between heterogeneous and homogeneous conditions. Nanoparticle and polymer comb variants were synthesized by covalently tethering Ir-based catalysts to support materials comprised of TiO2/PMAA (poly methacrylic acid) and PVP (polyvinyl pyridine), respectively, and characterized by AAS, NMR, and DLS. Following pH2 delivery to mixtures containing one type of "nano-SABRE" catalyst, a target substrate, and ethanol, up to ~(-)40-fold and ~(-)7-fold 1H NMR signal enhancements were observed for pyridine using the nanoparticle and polymer comb catalysts, respectively, following transfer to high field (9.4 T). These enhancements appear to result from intact particles and not from any catalyst molecules leaching from their supports. Unlike the case with homogeneous SABRE catalysts, high-field (in situ) SABRE effects were generally not observed with the nanoscale catalysts. The potential for separation and reuse of such catalyst particles is also demonstrated. Besides the effort on green chemistry of SABRE catalyst, I have been investigating the preparation of different variants of the "standard" SABRE catalyst--[IrCl(COD)(IMes)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; COD=cyclooctadiene)]--for performing SABRE in otherwise "pure" aqueous environments. Because of the poor aqueous solubility of SABRE catalysts, previous promising efforts have used co-solvents to achieve SABRE in aqueous/organic mixtures. However, I have found that the chemical changes that accompany this catalyst's activation also endow it with water solubility. Complete removal of the organic solvent following activation and subsequent re-constitution of the activated structure in deuterated water allowed up to ~(-)33-fold 1H signal enhancements to be obtained for nicotinamide. Additionally, I have investigated chemical alteration of the structure of the pre-activated catalyst to endow greater water solubility. PEGylation of the aromatic carbine moiety provided much greater aqueous solubility, but while SABRE-active in organic solutions, the catalyst lost activity in >50% water (an effect under ongoing study). As an alternative approach, synthesis of a di-Ir complex precursor where the COD rings have been replaced by CODDA (1,2-dihydroxy-3,7-cyclooctadiene) permits creation of a water-soluble catalyst [IrCl(CODDA)IMes] that enables aqueous SABRE in a single step without need for any organic co-solvent; the potential utility of the catalyst is demonstrated with the ~(-)32-fold enhancement of 1H signals of pyridine in water with only 1 atm of pH2. Taken together, these results support the utility of rational design for improving SABRE and HET-SABRE for applications varying from fundamental studies of catalysis to biomedical imaging. In the following, I also investigate different aspects of how catalyst structure can affect resulting SABRE enhancements, including the interplay of catalyst structure and temperature for optimal SABRE, as well as the confounding effects on catalyst activation. Results from the "standard" Ir SABRE catalyst (1)--[IrCl(COD)(IMes)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; COD=cyclooctadiene)]--are compared with those obtained with variants respectively created by synthetically replacing the -Cl moiety with 4-amino-pyridine (4AP, 2), (diphenylphosphino)ethylamine (DPPA, 3), triphenyl phosphine (TPP, 4), and tribenzyl phosphine (TBP, 5); a sixth variant (6) was serendipitously created by an alternate synthetic route for (1) that appears to result in a polymorph according to x-ray crystallography. Studies of activation rate found that (4) and (5) activated the fastest under pH2 exposure (~20 s, an order of magnitude faster than (1)); activation rate was inversely correlated with SABRE enhancement, with peak 1H polarization enhancement ( ranging from only ~(-)44 for (4) to nearly ~(-)1900 for (1) (or PH~6%) for pyridine at 9.4 T, and ~(-)240 for nicotinamide. Although (1) gave the overall highest  values as expected, other catalysts gave rise to better SABRE performance in other temperature regimes: Optimal temperatures varied significantly, e.g. ~273 K for (2) to ~310-320 K for (1); the optimal temperature for (6) was considerably lower (<273 K) than that for (1), despite the apparent structural similarity. Taken together, these results show that full optimization of SABRE enhancement for a given experiment (with respect to substrate, target nucleus, etc.) may require systematic variation of parameters including catalyst ligand choice and temperature (to modulate binding affinities and off rates with respect to relevant spin-spin couplings), in addition to pH2 partial pressure, flow rate, and magnetic field. Finally, some research on an ssNMR will be represented, to show the potential application of ssNMR on the coating detection.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

29

Sun, Xiaojiao. „Single molecule studies of acidity in heterogeneous catalysts“. Diss., Kansas State University, 2013. http://hdl.handle.net/2097/16423.

Der volle Inhalt der Quelle

Annotation:

Doctor of Philosophy
Department of Chemical Engineering
Keith L. Hohn
Amorphous silica-alumina is widely used as a solid acid catalyst for various reactions in oil refining and the petrochemical industry. The strength and the number of the acid sites in the material are most often believed to arise from the alumina atoms inserted into the silica lattice. The existence of the acidity distribution across the framework is a result of the local composition or the short-range interactions on the silica-alumina surface. Conventional techniques used to characterize silica-alumina provide effective information on the average acidity, but may not reflect the heterogeneity of surface acidity within the material. Recently, it is possible to study individual catalytic sites on solid catalysts by single molecule fluorescence microscopy with high time and space resolution. Fluorophores can be chosen that emit at different wavelengths depending on the properties of the local environment. By doping these fluorophores into a solid matrix at nanomolar concentrations, individual probe molecules can be imaged. Valuable information can be extracted by analyzing changes in the fluorescence spectrum of the guest molecules within a host matrix. In this research, silica-alumina thin films were studied with single molecule fluorescence microscopy. The samples were prepared by a sol-gel method and a wide-field fluorescence microscope was used to locate and characterize the fluorescent behaviors of pH sensitive probes. In mesoporous thin films, the ratio of the dye emission at two wavelengths provides an effective means to sense the effective pH of the microenvironment in which each molecule resides. The goal of this work was to develop methods to quantify the acidity of individual micro-environments in heterogeneous networks. Pure silica films treated with external phosphate solutions of different pH values were used to provide references of the fluorescence signals from individual dye molecules. SM emission data were obtained from mesoporous Al-Si films as a function of Al content in films ranging from 0% to 20% alumina. Histograms of the emission ratio revealed that films became more acidic with increasing Al content. The acidity on interior surfaces in zeolite pores was also of interest in this work. A microfluidic device was built to isolate the interior surface from the exterior surface. Some preliminary results showed the potential of using SM fluorescence method to study the acidic properties inside the pores of zeolite crystals.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

30

Xu, Chunli. „Preparation and characterisation of MgO : a heterogeneous basic catalyst for liquid phase reactions“. Thesis, Cardiff University, 2006. http://orca.cf.ac.uk/55646/.

Der volle Inhalt der Quelle

Annotation:

We systematically studied the preparation method of magnesium oxide as cheap heterogeneous basic catalysts, and found a very simple method to obtain MgO with high surface area and high catalytic activity. Furthermore, the structure of MgO was characterized using many techniques, such as BET, TGA, XRD and SEM. The relationship of catalytic activity and structure of MgO has been investigated in detail. At last, the obtained MgO was used in the liquid phase reactions, including Meerwein-Pondorf-Verley reaction, Michael addition, Knoevenagel condensation, transesterification of vegetable oil to biodiesel and synthesis of P-Keto 1,3-dithianes. The prepared magnesium oxide catalyst was used in the liquid phase Meerwein-Pondorf-Verley reaction of benzaldehyde with alcohol. Effect of preparation method on the catalytic activity and structure of MgO has been investigated in detail. The experimental result showed that the optimal calcination temperature was 450 °C. Lithium supported magnesium oxide was also studied. Magnesium oxide obtained using a novel but simple procedure was systematically investigated as a heterogeneous base catalyst for the Michael addition and Knoevenagel condensation. The activity of MgO was studied in detail, together with the effects of solvent and of substrate on the catalytic activity for each type of reaction. A key finding is that the formation of enols affected the activity of MgO. The preparation method and activity of MgO was determined and compared with CaO. MgO was used for the first time as a heterogeneous basic catalyst to synthesis P-keto-1,3-dithianes from conjugated ynones and ynoates. It was found that MgO is an active catalyst with activity better than or comparable with previously identified homogeneous or heterogeneous catalysts for this reaction. The effect of preparation methods on the activity of MgO is described. Transesterification of vegetable oil to biodiesel with MgO as catalyst was studied at 60 °C and 200 °C, respectively. Effect of methanol-to-oil molar ratio, catalyst loading, reaction temperature and calcination temperature was investigated. 90% yield can be obtained at 60 °C for 3h, and 80% at 200 °C for 15min. The results showed that the prepared MgO was active for the synthesis of biodiesel.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

31

Zhan, Xiaotong. „Heterogeneous catalysis in microreactors : study of the performance of various supports“. Thesis, Ecole centrale de Marseille, 2018. http://www.theses.fr/2018ECDM0007/document.

Der volle Inhalt der Quelle

Annotation:

Cette étude présente la préparation et l’évaluation de l’activité d’un nouveau catalyseur monolithique en microréacteur. La réaction d’hydrogénation du p-nitrophénol par transfert d’hydrogène avec l’acide formique a été choisie comme réaction modèle pour comparer les performances du monolithe à celles d’un catalyseur commercial en lit fixe.Cette thèse comporte une partie expérimentale importante. D’un côté, un montage expérimental et des protocoles d’analyse en ligne ont été mis au point pour faire une étude quantitative précise de la réaction modèle. De l’autre côté, les conditions de préparation d’un monolithe de silice fonctionnalisée dans le tube-réacteur en acier chemisé de verre ont été optimisées. Il a été chargé en nanoparticules de Pd par une méthode en écoulement. Le monolithe comporte un réseau de macropores pour l’écoulement et une organisation hexagonale typique de mésopores et micropores, et cela presque sans retrait au séchage. L’activité des 2 types de catalyseurs dans la réaction modèle a été comparée par leur cinétique de réaction et leur comportement dynamique dans la phase de mise en régime du microréacteur. Une partie théorique présente la modélisation du microréacteur en régime stationnaire pour l’établissement des cinétiques et en régime transitoire pour rationaliser les observations expérimentales. Le monolithe Pd@silice et le catalyseur commercial Pd@alumine ont des comportements différents et obéissent à des lois cinétiques différentes. Un modèle réactionnel impliquant un changement de propriétés de la surface catalytique pourrait expliquer le profil de concentration inhabituel observé avec le catalyseur commercial. La comparaison démontre la supériorité du nouveau catalyseur monolithe, et lui ouvre de bonnes perspectives industrielles
This study presents the preparation and the evaluation of performance of a new monolithic catalyst in microreactor. The transfer hydrogenation of p-nitrophenol by formic acid is chosen as the model reaction for the comparison of the monolith with a traditional packed-bed microreactor containing commercial catalyst.This thesis includes an important experimental part. On the one hand, experimental set-up and protocols involving on-line analysis have been developed in order to study quantitatively the model reaction; On the other hand, the conditions of preparation of functionalized silica monolith in a stainless steel tube with the inner wall pre-coated by glass were optimized, and the palladium nanoparticles were immobilized by a continuous flow method. The monolith possesses the flow-through macropores, typical hexagonal organization of mesopores and micropores, and scarcely any shrinkage. The comparison of the two types of catalysts mainly focuses on the activity of catalysts in the model reaction, their kinetic model and their dynamic behavior in the start-up phase of the flow microreactor. In the theoretical part, the modelisation of reactor has been investigated both under stationary conditions for kinetics determination and under transient conditions for the rationalization of experimental observations. Pd@silica monolith and commercial Pd@alumina powder have different behavior and gives different kinetic laws. A reaction model with change in the catalytic surface properties could explain the unusual profile of concentrations observed with commercial catalyst. The superior performance of monolithic catalyst is demonstrated, which also exhibits particular industrial interests

APA, Harvard, Vancouver, ISO und andere Zitierweisen

32

PIZZOLITTO, CRISTINA. „Development of heterogeneous catalysts for fuel and chemicals production“. Doctoral thesis, Università degli Studi di Trieste, 2020. http://hdl.handle.net/11368/2963761.

Der volle Inhalt der Quelle

Annotation:

Substitution of a fossil sources-based society to renewable one is the main challenge of 21 century. This Ph.D. work is focused on the development of heterogeneous catalysts for biomass valorisation, concerning both fuel and chemical production. Thanks to their promising properties, H2 and Levulinic acid (LA) were selected. The common denominator of this thesis is the study and the optimization of the most suitable catalyst for each process. The ideal catalyst for H2 production must be robust and resistant to coke deposition, for this reason, optimisation of nickel-ceria and nickel-zirconia based catalyst was performed. In the case of LA, the best catalyst must be sufficiently acid to direct the conversion of glucose to the main product and suppress unwanted reactions. In this case, SBA-15, a silica mesoporous material, was properly modified introducing acid functionalities via grafting approach and by the addition of a promoter. Considering H2 production, it was demonstrated how support synthesis strongly influences the catalyst features and consequently, the catalytic activity. For ceria support, it was determined how the precipitation method allows obtaining a good catalyst with high surface area, a high degree of crystallinity and with a wide distribution of active phase. Moreover, these properties were successfully implemented introducing a promoter as lanthanum. It was found that lanthanum increases the redox ability of the Ni-ceria catalyst, guaranteeing higher stability in ESR conditions. Moreover, these properties were widely enhanced when the lanthanum was added by co-precipitation. The effect of lanthanum was also investigated in nickel zirconia-based catalyst. In this case, its influence is completely different from the ceria case. Indeed, for zirconia, lanthanum properly modulates the acidic/basic features. Moreover, in this case, the best result was obtained with the catalyst prepared via the impregnation of the promoter on the support. Thanks to this study, it was possible to enormously implement the properties of the individual support, tuning its preparation method and introducing a promoter. Considering LA production via hydrolysis, implementation of SBA-15 acidity was achieved with the introduction of aluminium and sulfonic groups. It was found a new environmentally friendly and cost-effective method to graft sulfonic acid groups over silica surface and increase its Brønsted acidity. To implement the Lewis one, it was demonstrated that the addition of alumina via evaporation-impregnation increases the number of medium and strong Lewis sites preserving the SBA-15 morphological features. Therefore, this new material has promising properties to be used in converting more complex carbohydrate substrates.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

33

Anshuman, Aashu. „Development of a microwave-assisted catalytic reactor for wastewater treatment : simulation and experiments“. Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/34231.

Der volle Inhalt der Quelle

Annotation:

The global population is constantly rising and with the consequent increase in demand for clean water, the planet is facing a looming freshwater shortage. At the current rate, cities around the globe could lose as much as two thirds of their freshwater supply by 2050. To tackle this, there has been a huge surge on the investigation of novel wastewater treatment technologies. Advanced oxidation processes (AOPs) have shown great promise in this regard. Recently using microwaves with AOPs has been proven to exhibit improved reaction rates and thus there is a push towards developing processes involving microwaves and AOPs to achieve high water treatment efficiencies. However no methodical studies have been conducted to the best of our knowledge, to take the lab scale improvements successfully on to the pilot scale wastewater treatment system. To design such a system by coupling microwaves with Fenton process is the objective of this microwave assisted catalytic treatment of wastewater (MICROCAT) research project. Multiphysics simulation was used for cavity design optimisation and common pesticides found in agricultural wastewater were used as candidate impurities. A heterogeneous Fenton catalyst was prepared by a multi-stage thermal and chemical treatment of polyacrylonitrile (PAN) mesh on polypropylene support structure in collaboration with De Montfort University (DMU). The PAN meshes, after each stage of the treatment process, have been characterised using the field emission gun scanning electron microscope (FEGSEM) and electron dispersive X-ray spectroscopy (EDX) for microstructure and composition. The catalyst was used to study the decomposition of a model compound (e.g., carbetamide) using microwave radiation as well as conventional heating. Two kinds of trials were carried out constant power and constant temperature to observe the effect of variation of process parameters on the reaction rates. It was seen that the use of microwave heating enhanced the rate of decomposition compared to conventional heating in both scenarios. Attempts were also made to modify the composition of the catalyst and the support structure using polyvinylidene fluoride (PVDF) and carbon based additives (graphite and carbon black) to improve the microwave absorption characteristics. The combination of additive and PAN/PVDF mixtures has the potential to help in designing a suitable fabric support for catalyst that could be more receptive to microwaves, thereby helping to improve the energy efficiency of the process. Thorough investigation of dielectric properties and microwave absorption characteristics of the catalyst and support materials were performed independently. The heating rates of the meshes were monitored using an infrared thermal imaging camera. The absorption efficiencies of materials commonly used to build water treatment reactors such as polypropylene (PP), Fibreglass reinforced plastic (FRP), polyvinyl chloride (PVC), glass, PTFE, and fused quartz were assessed by subjecting them to constant microwave power experiments to ascertain their utility for making the reactor parts To take the successful lab scale results (100 ml) to scalable levels (80000 ml) for field trails, a new microwave reactor system was designed and tested. The cavity design was aided by multiphysics simulation of the electromagnetic field and temperature distribution inside the cavity. The model was created using COMSOL and provided valuable insight in making several design choices and improvements. The material data used in the model was determined both from our characterisation results and from corroborative literature data. The cavity itself was fully constructed using aluminium and the internal components were made using polypropylene and PTFE within the project timeline. The cavity was commissioned and initial testing at end user sites involved experiments measuring the rate of decomposition of carbetamide and other pesticides the results again emphasising that microwave treatment improves the reaction rates both from lab scale and in pilot scale water treatment situations in comparison to conventional treatment systems. This augers well for the generic applicability of the microwave assisted catalytic reactor system and its potential for the efficient treatment of contaminated water from hard to treat agricultural. Industrial, medical and defence waste/pollutants in future. An added advantage is that the developed microwave treatment system is mobile (on an ISO-container) and hence can reach the remote, contaminated site and treat it then and there rather than transporting the contaminated fluid to the treatment plant in a faraway location.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

34

Lovon, Quintana Juan Jose. „Oxidação total de metano sobre catalisadores de paladio e estanho suportados em zirconia“. [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/267204.

Der volle Inhalt der Quelle

Annotation:

Orientador: Gustavo Paim Valença
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
Made available in DSpace on 2018-08-12T09:16:19Z (GMT). No. of bitstreams: 1 LovonQuintana_JuanJose_D.pdf: 3240261 bytes, checksum: ad92f4d1100edab50342a486f6808682 (MD5) Previous issue date: 2008
Resumo: Pd e Sn foram suportados sobre ZrO2 por impregnação incipiente usando Pd(NO3)2.XH2O e SnC4H4O6.XH2O como precursores. Os sólidos foram secados e calcinados a 800, 1100 e 1400 K e caracterizados por ICP-AES, TEM, XRD, TPR, adsorção de H2, O2 e CO e por titulação de oxigênio adsorvido com H2. Nos sólidos contendo Pd ou Pd-Sn calcinados a 800 K as partículas de Pd foram completamente oxidadas formando fases com baixo grau de cristalinidade e os sólidos calcinados a 1400 K a fase ativa foi decomposta a Pd° e sinterizada, formando partículas de Pd com planos cristalinos expostos de baixa densidade Pd(200). A quantidade de O2 adsorvido sobre Pd-Sn ou Sn suportado sobre ZrO2 foi maior que nos sólidos contendo Pd suportado sobre ZrO2. O tamanho das partículas metálicas de Pd determinadas por adsorção de H2 foi maior que nos sólidos contendo Sn. Os testes de reação da oxidação de CH4 sobre catalisadores de Pd e Sn suportados sobre a ZrO2 foram realizados em um reator de fluxo contínuo a pressão atmosférica, na faixa de temperaturas de 450 até 750 K. A atividade catalítica dos sólidos foi dependente das condições de preparação dos catalisadores. Os sólidos Pd-Sn/ZrO2 calcinados a temperaturas = 1100 K mostraram valores de TOR de 2 a 4 vezes maiores do que para Pd/ZrO2 devido à alta capacidade de armazenamento de O2 nos sólidos contendo Pd e Sn. No entanto, com o aumento da temperatura de calcinação a contribuição do Sn diminuiu, sendo praticamente zero a 1400 K.
Abstract: Pd and Sn were supported on ZrO2 by incipient wetness using Pd(NO3)2.XH2O and SnC4H4O6.XH2O as precursors. The solids were dried and calcined at 800, 1100 and 1400K. The solids were characterized by ICP- AES, TEM, XRD, TPR, adsorption of H2, O2, and CO and by titration of adsorbed oxygen with H2. In the solids containing Pd or Pd-Sn calcined at 800 K the Pd particles were made of fully oxidized low crystalline phases and the solids calcined at 1400 K the active phase was decomposed to Pdº and sinterized, with the formation of particles with exposed low density planes such as Pd(200). The amount of adsorbed O2 on Pd-Sn or Sn supported on ZrO2 was higher than that on Pd supported on ZrO2. The size of the Pd particles determined by adsorption of H2 was larger for the Sn-containing samples. The methane catalytic combustion on palladium and tin catalysts supported on ZrO2 was carried out in a flow reactor at atmospheric pressure at the temperatures range of 450 to 750 K. The catalytic activity of the solids was strongly dependent on the preparation conditions. The solids Pd-Sn/ZrO2 calcined at temperatures = 1100K showed values of TOR twice to four times higher than the Pd/ZrO2 due to the high O2 storage capacity of the catalysts containing Pd and Sn. However, with the increase of the calcination temperature the Sn contribution decrease and was null at 1400 K.
Doutorado
Desenvolvimento de Processos Químicos
Doutor em Engenharia Química

APA, Harvard, Vancouver, ISO und andere Zitierweisen

35

Odura, William Owusu. „Towards ultra-selective hydrogenation and hydrogenolysis : A nano engineering approach to heterogeneous catalyst design“. Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531995.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

36

Fuss, Botti Renata. „Development of Structured Porous Heterogeneous Catalyst for Biodiesel Production by Transesterification of Vegetable Oil“. Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3426343.

Der volle Inhalt der Quelle

Annotation:

Many environmental problems are caused when fossil fuels are used in engines. Biodiesel is a promising option to substitute these fuels because it is renewable, biodegradable and not toxic. The most used process to prepare biodiesel is by homogeneous transesterification of vegetable oils, using NaOH or KOH, but it produces a high concentration of impurities in the product. To overcome this, the use of heterogeneous catalysts is being increasingly studied. Geopolymer (GP) is an inorganic material with a chemical composition similar to zeolite and a variable microstructure, obtained by the reaction of aluminosilicates with a highly alkaline medium forming a continuous 3D network. It can be used as a heterogeneous catalyst, due to the high content of metals such as Na and/or K, as well as high basicity and specific surface area. The great advantage of using heterogeneous catalysts is that they can be recovered by filtration and reused in the process, making the biodiesel production more economical and generating fewer effluents to be treated. This work investigated GP acting as heterogeneous catalysts to produce biodiesel by transesterification reaction of soybean oil with methanol. Three types of GP powder were produced mixing metakaolin with an activating alkaline solution: Na-based, K-based GP and a mixture between them; they were treated at 110, 300, 500 and 700 °C, then lattice-shaped GPs were designed and produced by DIW, adding PEG and filler in the previous formulation and then, they were dried at 110 °C. Porous structures with Ø ~24 mm x 9,6 mm height and unsupported parts were produced. All materials were characterized. The transesterification reaction was carried out using all the samples as a heterogeneous catalyst to evaluate the yield of biodiesel concerning the GP composition, reaction conditions and morphology of samples. According to the results obtained in this study, it was verified that using GP both in powder and structure as catalyst, it was possible to obtain biodiesel from the transesterification of soybean oil. Comparing the materials with the same molar ratios, Na.K_GP treated at 500°C (powder) achieved the highest conversion (~98%). For the 3D structure tested in the reaction (3D_Na_GP1, 110 °C) a conversion was observed, but lower (~41%) compared to Na.K_GP, even in its powdered version (~53%). To verify the conversion efficiency of the other structures (3D_K_GP1, Na.K_GP) further studies are needed.
Molti problemi ambientali sono causati dall'uso dei combustibili fossili nei motori. Il biodiesel è un'opzione promettente per sostituire questi carburanti perché è rinnovabile, biodegradabile e non tossico. Il processo più utilizzato per preparare il biodiesel è la transesterificazione omogenea degli oli vegetali, utilizzando NaOH o KOH, ma produce un'alta concentrazione di impurità nel prodotto. Per superare questo, l'uso di catalizzatori eterogenei viene sempre più studiato. Geopolymer (GP) è un materiale inorganico con una composizione chimica simile alla zeolite e una microstruttura variabile, ottenuta dalla reazione di alluminosilicati con un mezzo altamente alcalino che forma una rete 3D continua. Può essere usato come catalizzatore eterogeneo, a causa dell'elevato contenuto di metalli come Na e/o K, nonché di un'elevata basicità e di una superficie specifica. Il grande vantaggio dell'utilizzo di catalizzatori eterogenei è che possono essere recuperati mediante filtrazione e riutilizzati nel processo, rendendo la produzione di biodiesel più economica e generando meno effluenti da trattare. Questo lavoro ha indagato su GP che agisce come catalizzatori eterogenei per produrre biodiesel mediante la reazione di transesterificazione dell'olio di soia con metanolo. Sono stati prodotti tre tipi di polvere GP miscelando metacaolino con una soluzione alcalina attivante: GP a base di Na, a base di K e una miscela tra loro; sono stati trattati a 110, 300, 500 e 700 °C, quindi i GP a forma di reticolo sono stati progettati e prodotti da DIW, aggiungendo PEG e filler nella precedente formulazione e quindi, sono stati essiccati a 110 °C. Sono state prodotte strutture porose con Ø ~ 24 mm x 9,6 mm di altezza e parti non supportate. Tutti i materiali sono stati caratterizzati. La reazione di transesterificazione è stata effettuata utilizzando tutti i campioni come catalizzatore eterogeneo per valutare la resa di biodiesel riguardante la composizione GP, le condizioni di reazione e la morfologia dei campioni. In base ai risultati ottenuti in questo studio, è stato verificato che l'utilizzo di GP sia in polvere sia nella struttura come catalizzatore, è stato possibile ottenere biodiesel dalla transesterificazione dell'olio di soia. Confrontando i materiali con gli stessi rapporti molari, Na.K_GP trattato a 500 °C (polvere) ha ottenuto la conversione più alta (~98%). Per la struttura 3D testata nella reazione (3D_Na_GP1, 110 °C) è stata osservata una conversione, ma inferiore (~41%) rispetto a Na.K_GP, anche nella sua versione in polvere (~53%). Per verificare l'efficienza di conversione delle altre strutture (3D_K_GP1, Na.K_GP) sono necessari ulteriori studi.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

37

Mgedle, Nande. „The use of bimetallic heterogeneous oxide catalysts for the Fenton reaction“. Thesis, Vaal University of Technology, 2019. http://hdl.handle.net/10352/460.

Der volle Inhalt der Quelle

Annotation:

M.Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology
Water contaminated with non-biodegradable organics is becoming increasing problematic as it has a hazardous effect on human health and the aquatic environment. Therefore, the removal of organic contaminants is of importance and an active heterogeneous Fenton catalyst is thus required. The literature indicates that a bimetallic oxide Fenton catalyst is more active than an iron oxide catalyst. This study focused on increasing the activity of iron-based Fenton catalysts with the addition of transition metals such as manganese, cobalt and copper and optimizing the preparation method. In this study, bimetallic oxide (Fe-Cu, Fe-Mn, Fe-Co) and monometallic oxide (Fe, Cu, Mn,Co) catalysts supported on silica SiO2 where prepared by incipient wetness impregnation. The total metal oxide contents were kept constant. The catalysts where calcined in two different ways, in a conventional oven and in a microwave. These catalysts were characterized with XRD, XPS and CV and were tested for the degradation of methylene blue dye at 27°C. The catalysts calcined in a microwave oven had a higher catalytic activity than those prepared in a conventional oven. The bimetallic oxide catalysts outperformed the mono- metallic oxide catalysts in the degradation of methylene blue. The Fe2MnOx prepared by microwave energy were the most active catalyst yielding the highest percentage of degradation of methylene blue dye (89.6%) after 60 minutes. The relative amounts of manganese and iron oxide were varied while keeping the total metal content in the catalyst the same. The optimum ratio of Fe to Mn was 1:7.5 since it yielded the most active catalyst. A 96.6 % removal of methylene blue was achieved after 1 hour of degradation. Lastly this ratio 1Fe:7.5Mn was prepared by varying different microwave power (600, 700 and 800 W) and irradiation time (10, 20 and 30 min). The optimum microwave power and irradiation time was 800W and 10 min with the methylene blue percentage removal of 96.6 % after 1 hour of degradation.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

38

Angelo, Laetitia. „Développement de catalyseurs pour la synthèse de méthanol produit par hydrogénation du dioxyde de carbone“. Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAF051/document.

Der volle Inhalt der Quelle

Annotation:

De nombreuses mesures pour réduire les émissions anthropiques de gaz à effet de serre et plus particulièrement de CO2, existent déjà, elles restent cependant insuffisantes. C’est dans ce cadre qu’a vu le jour le projet ANR VItESSE2 visant à développer un procédé de conversion de CO2,issu de certaines industries, en méthanol par réduction à l’hydrogène produit par électrolyse de l’eau à partir d’électricité fournie par des énergies faiblement émettrices de CO2 (énergie nucléaire et les énergies renouvelables). Ce procédé permet aussi d’assurer, une fonction de gestion du système électrique en reliant la production d’hydrogène aux quantités d’électricités disponibles sur le réseau. Les principaux objectifs de la thèse sont la synthèse et la caractérisation de catalyseurs performants ainsi que la mise au point des conditions réactionnelles conduisant à la meilleure productivité en méthanol. L’optimisation des systèmes catalytiques a permis de développer un catalyseur de type CuO-ZnO-ZrO2 compétitif par rapport aux catalyseurs commerciaux actuellement sur le marché
Numerous measures to reduce anthropogenic emissions of greenhouse gases, especially CO2, already exist; however they are still insufficient. It is in this context that the ANR project VItESSE2 emerged to develop a method for converting CO2 produced by industries. The aim of this project is to transform CO2 into methanol, by reduction with hydrogen produced by water electrolysis using electricity provided by decarbonised energies (nuclear and renewable energies). This process also allows to secure a management function of the electrical grid by connecting the production of hydrogen to the available quantity of electricity in the network. The main objectives of this thesis are the synthesis and the characterization of efficient catalysts for CO2 hydrogenation into methanol and the development of reaction conditions leading to improved methanol productivity. The optimization of catalyst systems allowed to develop a CuO-ZnO-ZrO2 catalyst competitive in relation to commercial catalysts currently on the market

APA, Harvard, Vancouver, ISO und andere Zitierweisen

39

Ellis, Ieuan. „Interstitial modification of palladium for partial hydrogenation reactions“. Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:7c8c294c-0583-4a61-98e5-4c32d76cbf89.

Der volle Inhalt der Quelle

Annotation:

Heterogeneous catalysis is a key industrial process involved in the synthesis of nearly all chemicals currently produced. The environmental impact of these processes is huge so improvements must be made to current catalysts. Should a new material provide better yields at lower energy cost the benefits to both the industry and the planet are significant. There are many ways to change the behaviour of a catalyst, the addition of dopants, the selective blocking of active sites, and changing the strength of the support interaction to name a few. One technique that has become increasingly investigated is interstitial modification, the insertion of a light element into a metal lattice to change the metal's catalytic properties. The work presented in this thesis devises greener synthetic routes to the known Pd-^interstitialB/C catalyst and investigates potential routes to a novel interstitial material, Pd-^interstitialLi/C. Initially, successful verification of interstitial modification comes from the characteristic increase in palladium lattice parameter from 3.89 to 4.00 Å and the blocking of the β-hydride formation. Initial catalytic screening determines the synthetic route which yields the most active catalyst which subsequently undergoes thorough characterisation. The wealth of evidence generated confirms the interstitial location of lithium within the palladium lattice, as well as adding to the current understanding of the Pd-^interstitialB/C material. EELS analysis on Pd-^interstitialB is the closest to direct observation of boron within the palladium lattice to date. PDF on Pd-^interstitialLi shows 13.7 % of the palladium octahedral interstitial sites are occupied by lithium. This is the first report of interstitial lithium within palladium to date. The effect of the interstitial modification on catalytic hydrogenation by two elements that have opposite effects on the surface electronics of the host palladium gives intriguing results. The effect on catalysis varies depending on the conditions investigated. This bank of hydrogenation data allows an informed choice as to which interstitial material would be best suited to the gas or liquid phase catalytic hydrogenation under investigation.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

40

Lin, Andrew. „Metal-Organic Frameworks and Graphene-Based Support Materials for Heterogeneous Catalysis“. VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5574.

Der volle Inhalt der Quelle

Annotation:

Nanoparticles are involved in a broad range of applications, including heterogeneous catalysis. Nanoparticles tend to quickly lose their well-defined shapes and facets due to aggregation under duress such as heat. A series of highly studied materials are explored as support materials for nanoparticle supports. These supports include metal-organic frameworks (MOF), graphene oxide (GO), and a MOF-PRGO (partially reduced graphene oxide) hybrid. The inclusion of a support with the palladium increased lifespan of the catalyst by separation of nanoparticles. The choice of support material not only allowed for supporting of palladium nanoparticles, but allowed for rational catalyst synthesis in order to design catalysts with improved catalytic activity. CO oxidation, vanillin hydrogenation, and Suzuki cross coupling were studied. For the CO oxidation reaction, a cerium-based MOF, Ce-MOF, is shown to increase activity of palladium nanoparticles by capturing reactant gases and acting as an oxygen reservoir that cycles between (III) and (IV) states while transferring oxygen to palladium nanoparticles at the Pd/Ce-MOF interface. A hybrid Ce-MOF-PRGO was synthesized to increase the surface area and acidity of Ce-MOF materials and was shown to be active for vanillin hydrogenation. Smaller rod-like Ce-MOF crystals were observed, indicating intercalation of crystals on GO. Zirconium-based MOF UiO-66-NH2 was acidified via incorporation of tungstophosphoric acid (HPW), which increased the selectivity of products by adjusting the mechanistic pathway. GO was partially functionalized with aromatic amines to improve the coupling of bromobenzene and phenylboronic acid. Small amounts of aromatic amines increased the Pd(0) content and decreased nanoparticle size.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

41

Sum, Sze Nga. „Photo-fenton degradation of textile wastewater by a novel laponite clay based Fe nanocomposite as a heterogeneous catalyst /“. View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?EVNG%202004%20SUM.

Der volle Inhalt der Quelle

Annotation:

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.
Includes bibliographical references (leaves 125-135). Also available in electronic version. Access restricted to campus users.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

42

Keybl, Jaroslav. „A microreactor system for high-pressure, multiphase homogeneous and heterogeneous catalyst measurements under continuous flow“. Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/70399.

Der volle Inhalt der Quelle

Annotation:

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2011.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 194-206).
The shift towards biomass and lower quality fossil fuel feedstocks will require new conversion approaches. Catalysis will be critical in the processing of these new feedstocks. By studying catalysis at industrially relevant conditions, it may be possible to reduce the time and cost of developing new catalyst systems. Microreactors enable the study of multiphase catalyst systems at pressures that were previously difficult to attain on the laboratory scale. The reduced length scales, characteristic of microchemical systems, provide additional benefits such as enhanced heat and mass transfer and a reduction of hazardous waste. The improved heat and mass transfer allow for kinetics to be probed at isothermal conditions in the absence of complicating mass transfer effects. A high-pressure microreactor system for catalyst study was designed, fabricated, and tested. The system allows for the multiphase study of homogenously and heterogeneously catalyzed systems, with a unique reactor designed for each application. A multicomponent gas phase is delivered simultaneously with a liquid stream, resulting in regular segmented (slug) flow. The isobaric system is operated at pressures of up to 100 bar. Gas and liquid flow rates, and therefore residence time, are specified independently of pressure. The system is capable of being operated at temperatures of up to 350°C and residence times of up to 15 minutes. Inline analysis, using an attenuated total reflection FTIR flow cell, and sample collection for offline analysis can be performed simultaneously. Both homogeneous and heterogeneous catalysis were demonstrated in the high-pressure system. A kinetic expression was derived for the homogeneous hydroformylation of terminal alkenes, catalyzed by Wilkinson's catalyst. The empirical reaction orders for the dependence on catalyst, hydrogen, and carbon monoxide were determined, along with the activation energy and pre-exponential factor. These results were then reconciled with a mechanistic model. The hydrogenation of cyclohexene over platinum catalysts was chosen to demonstrate the performance of the heterogeneous reactor. This reaction proceeded rapidly allowing mass transfer to be characterized in the microreactor. Observed mass transfer rates were two orders of magnitude higher than in traditional systems.
by Jaroslav Keybl.
Ph.D.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

43

Abidli, Abdelnasser. „Design of novel well-defined organorhenium heterogeneous catalyst for unsaturated fatty acid derivatives self-metathesis“. Doctoral thesis, Université Laval, 2015. http://hdl.handle.net/20.500.11794/26473.

Der volle Inhalt der Quelle

Annotation:

La formation des liaisons C-C est parmi les cibles les plus élevés de la science et de la technologie de la catalyse. Dans ce cadre, la réaction de métathèse catalytique a gagné une importance considérable en raison de l'efficacité du processus de transformation. Par conséquent, un grand progrès a été réalisé dans ce domaine avec le développement de plusieurs catalyseurs homogènes et hétérogènes, ainsi que les différentes approches de métathèse. Cette formule a permis une conception plus facile et plus durable de diverses stratégies de synthèse dans différents domaines, y compris la synthèse organique, la science des polymères, etc. Cependant, le développement des catalyseurs de métathèse robustes pour les applications à grande échelle est encore une tâche difficile. Tenant compte de cela, les résultats de recherche présentés dans cette thèse de doctorat se concentrent sur la synthèse d'un nouveau catalyseur hétérogène de métathèse. Par conséquent, le méthyltrioxorhénium (MTO) a été supporté sur différents matériaux à base d'alumine. La performance des catalyseurs synthétisés a été étudié par l'auto-métathèse de l'oléate de méthyle, choisi comme substrat modèle; volumineux et fonctionnalisé, afin d'évaluer la tolérance des espèces actives aux groupements fonctionnels, ainsi que d'évaluer sa diffusion à l'intérieur des canaux mésoporeux. Tout d'abord, des supports très organisés à base alumine mésoporeux organisée modifiée avec le chlorure de zinc (ZnCl2-AMO) ont été préparés avec succès grâce à un procédé sol-gel puis une imprégnation post-synthèse. Le MTO supporté sur ces supports catalytiques est très actif pour l'auto-métathèse de l'oléate de méthyle, avec des vitesses de réaction plus élevées et une meilleure sélectivité par rapport aux catalyseurs à base d'alumine classiques. Cette amélioration est attribuée à des meilleurs phénomènes de transfert de masse à l'intérieur du réseau mésoporeux organisé. Ensuite, nous avons développé une voie de synthèse efficace en une seule étape pour la préparation des matériaux ZnCl2-AMO. Cette approche a permis l'accès à des supports ZnCl2-AMO très ordonnés avec de meilleurs rendements de synthèse ainsi que de meilleures propriétés physiques et de surface. En outre, ces fonctionnalités améliorées ont permis aux catalyseurs à base de MTO supportés sur ces matériaux préparés en une seule étape de manifester une meilleure performance catalytique par rapport à celle de ZnCl2-AMO préparé par le processus en plusieurs étapes. Toutefois, des études spectroscopiques ont révélé la formation d'espèces actives semblables sur la surface pour tous les supports catalytiques préparées. Ces caractérisations nous ont guidés pour étudier et proposer un mécanisme complet pour les voies de formation des produits de métathèse, ainsi que le cycle catalytique de métathèse, démontrant l'effet d'encombrement stérique sur l'interface de catalyseurs qui contrôle la sélectivité de la réaction. La synthèse des catalyseurs de métathèse MTO/ZnCl2-AMO nous a permis d'effectuer efficacement les transformations de métathèse utilisant des matières premières renouvelables (par exemple des acides gras estérifiés provenant des huiles végétales), offrant un accès à une variété de monomères fonctionnalisés, qui pourraient éventuellement être utilisés pour d'autres transformations telles que la synthèse des bio-polymères à valeur ajoutée à base (par exemple, les bioplastiques, biosurfactants).
Sustainable C-C bond forming reactions have been among the highest target of catalysis science and technology. In this scope, metathesis reaction has been gaining enormous attention due to the efficiency of the transformation process. Therefore, a great progress has been made in this area by developing several homogeneous and heterogeneous catalysts as well as distinct metathesis reaction approaches. This allows an easier and more sustainable design for various synthesis strategies in different fields including organic synthesis, polymer science, etc. However, the development of robust metathesis catalysts for large scale applications is still a challenging task. Taking this into account, this research presented in this doctoral dissertation is focusing on the synthesis of new heterogeneous metathesis catalysts. Therefore, methyltrioxorhenium (MTO) was supported on various alumina-based materials. The synthesized catalysts' performance was studied though methyl oleate self-metathesis, chosen as a model bulky functionalized substrate, in order to evaluate the active species tolerance to functional groups as well as to evaluate its diffusion inside the mesoporous channels. First, highly organized ZnCl2-modified OMA supports were successfully prepared through a sol-gel method followed by a post-synthesis modification via wet-impregnation process. MTO supported on these catalytic supports were found o be highly active for methyl oleate self-metathesis, displaying higher reaction rate and products selectivity compared to the conventional wormhole-like alumina-based catalysts. This improvement is ascribed to enhanced mass transfer phenomena inside the organized mesoporous network. Afterwards, we have developed efficient one-pot synthesis route ZnCl2-modified OMA supports. Interestingly, this approaches allowed access to numerous highly ordered ZnCl2-modified OMA supports with better synthesis yields and improved textural and surface properties. Moreover, these enhanced features allowed the MTO-based catalyst supported on these one-step prepared materials to exhibit higher metathesis reaction performance compared to ZnCl2-modified OMA supports prepared via the two-steps processes. However, spectroscopic investigations revealed the formation of similar surface active species for all the prepared catalytic supports. These characterizations guided us to study and propose a comprehensive mechanism of metathesis products formation pathways as well as the metathesis catalytic cycle, demonstrating the steric hindrance effect on the catalysts interface that governed the reaction selectivity. The synthesis of the 3 wt.% MTO/ZnCl2-OMA catalysts allowed us to efficiently perform metathesis reaction using renewable feedstock (e.g. fatty acid esters derived from vegetable oils), offering access to a variety of functionalized monomers which could be used for further transformations such as the synthesis of value-added bio-based polymers (e.g. bioplastics, biosurfactants).

APA, Harvard, Vancouver, ISO und andere Zitierweisen

44

Saboya, Rosana Maria Alves. „ProduÃÃo de biodiesel empregando catalisadores nanoestruturados do tipo SBA-15 modificada com lantÃnio“. Universidade Federal do CearÃ, 2012. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=7795.

Der volle Inhalt der Quelle

Annotation:

AgÃncia Nacional do PetrÃleo
O objetivo desta dissertaÃÃo foi estudar a aplicaÃÃo da sÃlica mesoporosa SBA-15 modificada com lantÃnio como catalisador heterogÃneo nas reaÃÃes de transesterificaÃÃo e esterificaÃÃo visando Ã produÃÃo de biodiesel. Para isso sintetizou-se o catalisador La-SBA-15 variando a razÃo molar Si/La em 25, 50 e 75. O catalisador heterogÃneo La-SBA-15 apresenta caracterÃsticas Ãcidas o qual pode ser mais tolerante a Ãgua e aos Ãcidos graxos livres presentes nos Ãleos e podem catalisar simultaneamente as reaÃÃes de transesterificaÃÃo e esterificaÃÃo. O catalisador foi caracterizado atravÃs das anÃlises de DRX, MEV e adsorÃÃo e dessorÃÃo de nitrogÃnio a 77 K. Para o estudo da aplicaÃÃo do catalisador La-SBA-15 na reaÃÃo de transesterificaÃÃo utilizou-se como matÃria-prima o Ãleo de soja e para a reaÃÃo de esterificaÃÃo o Ãcido olÃico. Ambas matÃrias-primas foram previamente caracterizadas quanto Ã composiÃÃo dos Ãcidos graxos por cromatografia gasosa, Ãndice de acidez, Ãndice de iodo, Ãndice de saponificaÃÃo, densidade a 20 ÂC, viscosidade cinemÃtica a 40 ÂC e teor de umidade. Primeiramente aplicou-se o catalisador La-SBA-15 com diferentes razÃes molares Si/La na reaÃÃo de esterificaÃÃo do Ãcido olÃico com etanol, verificando-se que o catalisador com razÃo molar Si/La igual a 50 apresentou a maior atividade catalÃtica na reaÃÃo com conversÃo de 91,14 %. Portanto, o catalisador La-SBA-15 com razÃo molar Si/La igual a 50 foi a melhor proporÃÃo para utilizaÃÃo da SBA-15 modificada com lantÃnio como catalisador. Em seguida utilizou-se o catalisador La-SBA-15 com razÃo molar Si/La igual a 50 na reaÃÃo de transesterificaÃÃo do Ãleo de soja com etanol obtendo-se conversÃo de 80,00 %. Com isso, verifica-se que o catalisador La-SBA-15 com razÃo molar Si/La igual a 50 pode catalisar ambas as reaÃÃes de esterificaÃÃo e transesterificaÃÃo, ou seja, catalisadores com propriedades Ãcidas podem agir sobre ambas as reaÃÃes.
The dissertation proposal to study the application of mesoporous silica SBA-15 modified with lanthanum as a heterogeneous catalyst in the esterification and transesterification reactions for biodiesel production. The catalyst lanthanum-incorporated SBA-15, La-SBA-15, with different Si/La molar ratios (75, 50, 25) were synthesized. The heterogeneous catalyst La-SBA-15 has acid characteristics which can be more tolerant of water and free fatty acids present in oils and can simultaneously catalyze the esterification and transesterification reactions. The catalyst was characterized by XRD, SEM and nitrogen isotherms at 77 K analysis. For study the application of La-SBA-15 catalyst in the transesterification reaction was used as feedstock the soybean oil and esterification reaction the oleic acid. Before the reaction, both raw materials were characterized as the fatty acid composition by gas chromatography, acid value, iodine value, saponification index, density, kinematic viscosity and water content. First applied the catalyst La-SBA-15 with different Si/La molar ratios in the esterification reaction of oleic acid with ethanol, verifying that the catalyst with Si/La = 50 molar ratio showed the highest catalytic activity in the reaction with conversion of 91,14%. Therefore, the La-SBA-15 catalyst with Si/La molar ratio of 50 was the best ratio for use of SBA-15 modified with lanthanum as a catalyst. Then used the La-SBA-15 catalyst with Si/La molar ratio of 50 in the transesterification reaction of soybean oil with ethanol resulting in conversion of 80.00%. So observed that the La-SBA-15 catalyst with Si/La molar ratio of 50 can catalyze both esterification and transesterification reactions.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

45

Zell, Elizabeth Theresa. „Synthesis and Support Shape Effects on the Catalytic Activities of CuOx/CeO2 Nanomaterials“. Youngstown State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1525699148756394.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

46

Spinozzi, Di Sante Lisa. „Heterogenization of an organic catalyst by adsorption on alginic acid gels“. Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14425/.

Der volle Inhalt der Quelle

Annotation:

A sustainable approach focused on the practice of green chemistry was used to develop a method which improved the performances of a catalyst system based on a natural and non-toxic substance. A benchmark Michael addition reaction was performed employing 9-amino(9-deoxy)epi quinine, adsorbed on alginic acid gels by hydrogen bonds, as catalyst. Compared to conventional heterogeneization of this organic catalyst, the present approach is more straightforward and employs as support a renewable biomaterial instead of oil-derived polymers. The optimization of the adsorption protocol was carried out to obtain an active and heterogeneous system able to work under different reaction temperatures. The Michael addition reaction rate, heterogeneity, enantiomeric excess and recyclability of the catalytic system were studied. The influence of temperature, additives and the presence of water were successfully investigated. The heterogeneity of the catalyst was perfectly preserved, therefore the catalyst could be easily recovered. Two optimal conditions were disclosed, differing in reaction temperature and catalyst pre-treatment. A scale-up is performed with good results for the first three reactions cycles (conversions: 100%, 87% and 55% respectively). The enantiomeric excess is determined as 98%. The results of this project demonstrated that a green catalytic system has a great potential to be competitive with more classic heterogeneous catalysts.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

47

Upreti, Pushpa Datta. „Remediation of textile and mining influenced effluents using novel heterogeneous PAN catalyst and modified PAN mesh“. Thesis, De Montfort University, 2018. http://hdl.handle.net/2086/16390.

Der volle Inhalt der Quelle

Annotation:

The effectiveness of a modified PAN catalyst and hydrogen peroxide system in the treatment of textile effluent and a modified ion exchange PAN mesh in the remediation of non-coal mine drainage was investigated. The results show a tremendous potential in the treatment of such wastewaters. The treatment process for textile effluent was optimized in batch mode of operation. The influence of pH and catalyst was more pronounced compared to that of H2O2. At optimum conditions, 99.5 % decolourization and 91.9 % loss of aromaticity and 70 % mineralization were achieved in 100 minutes. The sorption of dye onto the catalyst is favourable and can be best described by a Langmuir adsorption isotherm model. The model predicts a maximum adsorption capacity for the PAN catalyst as 0.68 mg of RO16 per gram of catalyst. A direct relationship between pH, temperature and iron leaching was established. The leached iron has no significant contribution, by means of homogeneous catalysis, in the removal of dye. The system was successful in treating a real dye-bath effluent that was much more concentrated than usual textile effluents. The continuous flow treatment in a prototype of a rotating discs contactor revealed that 99.2 %, 73 %, 64.4 % and 50 % removal efficiencies for decolourization, loss of aromaticity, COD and mineralization at optimum conditions. The breakthrough of the system occurred after 50 days. The system was successfully regenerated in-situ three times and the lifetime of the catalyst extended to 103 days in total, decolourizing 25.3 g of RO16 dye from 546.7 L solution. The deactivation of catalyst occurred mainly due to the loss of iron and partially due to loss of functional groups that ligate iron. Similar to the batch experiments, the leached iron, in continuos flow experiment, has insignificant contribution in removing dye through homogeneous catalysis. The ion exchange capacity of the modified PAN fibre was determined though acid-base titration. The sorption of zinc onto ion exchange mesh is favourable and can be best described by Langmuir adsorption isotherm model. The pH of the medium was found to be the most influential parameter with maximum sorption observed at pH ≥ 5.5 at contact time ≥ 4 hours in batch mode of operation. A pilot scale field trial was performed to remediate mine effluent with elevated concentration of zinc, cadmium and lead demonstrates a tremendous potential applicability. According to analyses by UKAS accredited laboratory, the 170 days long trial successfully removed 5.59 kg, 8.53 g and 18.18 g of zinc-total, cadmium-total and lead-total from 131.46 m3 of mine effluent. The system also removed suspended solids, iron, copper, arsenic, nickel, aluminium, boron, manganese and nitrate (NO3-N). The performance of the system was not affected by the in-situ regeneration and seasonal variation in temperature. The best performance of the system was observed when the contact time ≥ 1.33 hours. The metal removal mechanism was ion exchange initiated (co)precipitation / sorption of metals onto the surface of ion exchange mesh. This technology can be applied in the remediation of all type of mine waters though pre-treatment to adjust pH and alkalinity may be needed.

APA, Harvard, Vancouver, ISO und andere Zitierweisen

48

Tshizanga, Ngoya. „A study of biodiesel production from waste vegetable oil using eggshell ash as a heterogeneous catalyst“. Thesis, Cape Peninsula University of Technology, 2015. http://hdl.handle.net/20.500.11838/2153.

Der volle Inhalt der Quelle

Annotation:

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology.
While biodiesel has the potential to resolve the energy crisis, its production is hampered by both feedstock and catalyst availability. The aim of this current study is to investigate the production of biodiesel from waste vegetable oil (WVO) as feedstock under heterogeneous catalysis, mediated by calcined eggshell ash. WVO, characterised by 9% free fatty acid (FFA) and 0.17wt% water content, was employed as feedstock in the biodiesel production via transesterification reaction. The composition of WVO was determined using Gas chromatography (GC) analysis. The eggshell was washed with distilled water to remove impurities, dried in an oven at 105°C, and then crushed into fine particle of 75μm, and finally, calcined in a muffle furnace at 800°C. The chemical properties of the catalyst were assessed as follows: 1) using X-ray diffraction (XRD) to determine the major component phase of the element; 2) using X-ray fluorescent (XRF) to determine the elemental composition of the eggshell ash; 3) using Brunauer Emmet Teller (BET) to define the structure, the surface area, pore volume and pore diameter of the eggshell ash; and 4) using SEM to show the morphology structure of the element. The XRD analysis performed on eggshell ash showed 86% CaO as a major component in the catalyst; the remaining 14% was composed of MgO, SiO2, SO3, P2O5, Na2O, Al2O3, K2O and Fe2O3, as obtained from XRF. The BET result of the catalyst prepared was characterised by large pore diameter (91.2 Å) and high surface area (30.7m2/g), allowing reactants to diffuse easily into the interior of the catalyst used

APA, Harvard, Vancouver, ISO und andere Zitierweisen

49

Luo, Mingliang. „Heterogeneous catalytic oxidation of aqueous phenol using an iron-based catalyst and a magnetic titanium dioxide photocatalyst“. Thesis, University of East Anglia, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445198.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

50

Deshpande, Nitish. „Catalytic Material Design: Design Factors Affecting Catalyst Performance for Biomass and FineChemical Applications“. The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu154273906480973.

Der volle Inhalt der Quelle

APA, Harvard, Vancouver, ISO und andere Zitierweisen

Dissertationen zum Thema „The heterogeneous catalyst“

Geben Sie eine Quelle nach APA, MLA, Chicago, Harvard und anderen Zitierweisen an