Дисертації з теми "Mixed Oxide Catalyst"
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Meshesha, Beteley Tekola. "Hydrodechlorination of chlorinated organic wastes over pd supported mixed oxide catalysts." Doctoral thesis, Universitat Rovira i Virgili, 2011. http://hdl.handle.net/10803/37352.
Повний текст джерелаАнотація:
Environmental pollution by polychlorinated chlorinated organic wastes is of great concern. Catalytic hydrodechlorination is considered clean and efficient methodology for safe disposal of chlorinated organic wastes. This work aims at studying the catalytic hydrodechlorination reaction for the removal of environmentally polluting chlorinated organic wastes: 1,2,4-trichlorobenzene (1,2,4-TCB) and Trichloroethylene (TCE). The research has focused on evaluation of the activity, selectivity and stability of newly synthesized Pd based catalysts for hydrodechlorination of 1,2,4-trichlorobenzene and trichloroethylene. The first part, related to the HDC of 1,2,4-TCB, is to obtain active and stable catalyst for the hydrodechlorination of C-Cl bond of aromatic compounds to non chlorinated organic aromatic compound (benzene). While the second part aims at obtaining catalysts that allow high selectivity to ethylene formation during the HDC Trichloroethylene. Pd based hydrotalcite derived mixed oxides with different surface property were explored as catalysts for hydrodechlorination reaction. In addition, bimetallic and monometallic heterogeneous catalytic systems were investigated for selective hydrodechlorination reaction. Detailed characterization of the active centers of the newly synthesized catalysts by different techniques was achieved. This work presents original ideas, which could find a practical application, for the treatment of organo-halogenated pollutants.La contaminación ambiental mediante compuestos policlorados aromáticos y alifáticos es de gran preocupación. La reacción de hidrodecloración catalítica selectiva (HDC) se presenta como una nueva tecnología eficaz para una eliminación segura de estos tipos de compuestos orgánicos clorados. Es por ello, que este trabajo de investigación se ha enfocado en el estudio de nuevos catalizadores activos, selectivos y estables en diferentes reacciones de hidrodecloración de dos familias de compuestos orgánicos clorados: 1,2,4-triclorobenceno (1,2,4-TCB-compuestos aromáticos clorados) y el tricloroetileno (representativo de un compuesto clorado alifático). La primera parte de la tesis relacionadas con el HDC de 1,2,4-TCB, tiene como objetivo la obtención de catalizadores activos y estables para la hidrogenación del enlace C-Cl en compuestos aromáticos y la obtención final del compuesto aromático orgánico declorado. Mientras que la segunda parte tiene por objeto la obtención de catalizadores que permitan una gran selectividad a etileno y no hacia etano (hidrogenación profunda del tricloroetileno) durante la HDC de tricloroetileno. Por otra parte se ha realizado un estudio profundo en la síntesis de estos nuevos catalizadores, así como en la caracterización de los centros activos de dichos catalizadores, para su correlación con la actividad, selectividad y estabilidad de dichos catalizadores. Presenta ideas originales, lo que podría encontrar una aplicación práctica, para el tratamiento de compuestos órgano-halogenados contaminantes.
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Romano, Esteban Javier. "A surface science approach to understanding emission control catalyst deactivation due to sulfation of ceria-zirconia mixed-metal oxides." Master's thesis, Mississippi State : Mississippi State University, 2004. http://library.msstate.edu/etd/show.asp?etd=etd-03252004-162922.
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Rico, Francés Soledad. "Pt/TixCe(1-x)O2 catalysts for PROX reaction." Doctoral thesis, Universidad de Alicante, 2015. http://hdl.handle.net/10045/50208.
Повний текст джерелаАнотація:
The main objective of this Thesis is the synthesis, characterization and application in the PROX reaction of several series of catalysts synthesized using different methods, in order to find efficient materials with high catalytic activity. This work has been divided in six chapters. Chapter I presents an introduction about current energy problems and hydrogen (energy carrier) as a solution, with its limitations and advances on its use: storage, transport and security. Finally, its use as a fuel in PEMFC (Proton Exchange Membrane Fuel Cells) and the advantages comparing other existent fuel cells has been discussed. A brief summary was done about the catalytic systems studied in literature for PROX reaction and their characteristics. Following, Chapter 2 describes all the characterization techniques which were used to study the properties of the synthesized supports and catalysts, together with the experimental system employed for the catalytic tests. Most of these equipments belong to SSTTI of University of Alicante or are hand-made systems in the LMA group. DRIFTs and DTP were done at TUDelft, Catalysis Engineering Section. Next chapters contain the most important results obtained during the complete research work; they have been divided in two parts. On one hand, Chapter 3 describes the synthesis of pure TiO2 using five different methods, and its use as platinum support for PROX catalysts. On the other hand, taking into account the obtained results, three synthesis methods were chosen, and the study was centered in the addition of CeO2 to TiO2. Chapter 4 discusses the TixCe(1-x)O2 series synthesized using the sol-gel method. In Chapter 5 a solvothermal procedure was employed for the synthesis of supports with similar composition and, finally, impregnation of cerium over commercial P25 titania was compared in Chapter 6. Each chapter contains a complete study of characterization of both supports and catalysts. Synthesis parameters, pretreatment and reaction conditions were also modified for the best catalyst of the three series. Analyzing the catalysts’ behavior, a reaction mechanism was proposed. Finally, general conclusions summarize the most relevant results obtained in each chapter.
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Whittle, David Mark. "The structural characterisation of mixed-oxide catalyst systems by high resolution- and scanning transmission microscopy techniques." Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263767.
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Karslioglu, Osman. "Structural and chemical characterizations of Mo–Ti mixed oxide layers." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16767.
Повний текст джерелаАнотація:
In dieser Arbeit wurde ein Modell-Katalysator-Ansatz angewandt um Mischoxide mit Molybdän und Titan zu untersuchen. Die Schichten wurden auf TiO2(110) Einkristallen durch Verdampfen der Metalle in einer O2 Atmosphäre und in UHV und Nachbehandlung der Filme vorbereitet. Verschiedene Präparationen wurden in der Studie untersucht und diese werden in sechs Kategorien dargestellt. Wenn Mo und Ti in O2 gemeinsam aufgedampft wurden, wurde das meiste Mo an der Oberfläche abgeschieden mit einer nur geringen Mo-Konzentration in tieferen Schichten. Eine Mischung von Mo in TiO2 war sehr begrenzt, und die stimmt mit dem Phasendiagramm MoO2 und TiO2 überein. Mo6+ und Mo4+ sind die dominierenden Oxidationsstufen in den meisten der Schichten, wobei Mo6+ stets näher an der Oberfläche war als Mo4+. Schichten, in denen Mo vollständig in TiO2 gelöst ist, konnten durch Abscheidung von Metallen in UHV und Post-Oxidation der Filme erstellt werden. Im Inneren des TiO2 Gitters hat Mo die Oxidationsstufe 4+. Aufdampfen von Mo in O2 bei Raumtemperatur und anschließendes Tempern in UHV führte zur Bildung zweier Arten von Merkmalen in den STM-Bildern. Diese waren im UHV stabil bis mindestens 1000 K. Die Schichten mit hoher Mo-Konzentrationen erschienen uneinheitlich in den STM-Bildern aber sie zeigte das TiO2(110)-(1x1) LEED-Muster. Der Anstieg in der Mo-Konzentration führte zur Blockierung der Überbrückung Sauerstoffleerstellen (BOVs), was durch STM und Wasser-TPD nachgewiesen wurde. Die Reaktivitäten der Schichten wurden mit Methanol- und Ethanol-TPD getestet. Eine unerwartete Formaldehyd/Methanbildung bei hohen Temperaturen (~650 K) wurde bei der Methanol-TPD von reinem TiO2(110) beobachtet und mit BOVs in Verbindung gebracht. Der Anstieg der Mo-Konzentration unterdrückte diesen Effekt sowie die Ethylenbildung (~600 K) beim Durchführen von Ethanol-TPD. Sowohl in Ethanol als auch Methanol-TPD wurden neue Reaktionswege zu Ethylen und Methan-Bildung bei ~500 K beobachtet.In this work, a model-catalyst approach has been taken to study oxide mixtures containing molybdenum and titanium. The layers were prepared on TiO2(110) single crystals by evaporating the metals in an O2 atmosphere or in UHV and post treating the deposited material. Different preparation procedures were employed in the study and these are presented in six categories. When Mo and Ti were co-deposited in O2, most of the molybdenum stayed at the surface with only a small Mo concentration in deeper layers. Mixing of Mo into TiO2 was very limited, consistent with the phase diagram of MoO2 and TiO2. Mo6+ and Mo4+ were the dominant oxidation states in most of the layers and Mo6+ was always nearer to the surface than Mo4+. Layers where Mo was completely mixed into TiO2 could be prepared by depositing metals in UHV and post-oxidizing the deposited material. Inside the TiO2 lattice, Mo had an oxidation state of 4+. Depositing Mo in O2 at room temperature and post annealing in UHV led to the formation of two types of features in the STM images. These features were stable in UHV up to at least 1000 K. The layers with high Mo concentrations appeared patchy in the STM images but they still exhibited the TiO2(110)-(1x1) LEED pattern. The increase in Mo concentration led to the blocking of the bridging oxygen vacancies (BOVs) as evidenced by STM and water TPD. The reactivities of the layers were tested by methanol and ethanol TPD. An unprecedented high temperature (~650 K) formaldehyde/methane formation channel was observed in the methanol TPD of clean TiO2(110) and was associated with BOVs. The increase in the Mo concentration led to the vanishing of this channel as well as the ethylene formation channel (~600 K) in the case of ethanol TPD. In both ethanol and methanol TPD, new reaction channels towards ethylene and methane formation at ~500 K appeared.
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Elfaki, Hind Omer Elsheikh. "Hydrogen production through sorption-enhanced steam reforming of ethanol using CaO-based sorbent mixed with iron oxide catalyst." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/31789/.
Повний текст джерелаАнотація:
Novel synthetic CaO-based sorbents for carbon dioxide (CO2) capture in sorption-enhanced steam reforming (SESR) were prepared by the co-precipitation method. Magnesium oxide (MgO) and cerium oxide (CeO2) were mixed with calcium oxide (CaO) in different molar percentages in order to obtain the optimum percentage, which provide high CO2 uptake capacity and cyclic stability. The TGA results for CO2 uptake, revealed that for the molar ratio of CaO, MgO and CeO2 of (6:2:1) and (4:2:1), the sorbents had CO2 capture capacity of 29 and 25 wt.%, respectively. The fresh sorbents were characterized using X-ray diffraction, mercury porosimetry, N2 physisorption and scanning electron microscopy. It was found that the sorbents with higher CO2 uptake capacities had relatively high porous surface structure with porosity percentage (>66%). Modelling of CO2 uptake kinetics showed that JMA (Johnson-Mehl-Avrami) fits best the first and second stages except for the molar ratio of CaO, MgO and CeO2 of (4:2:1) sample where, surface chemisorption (SC) fits the initial stage and JMA fits the second stage. While the contracting volume model (CV2/3) fits the final stages of all the studied sorbents. The stability of sorbents at high temperatures was examined over multiple cycles of carbonation/de-carbonation reactions. After 45 cycles, the sample with a molar ratio of CaO, MgO and CeO2 of (6:2:1) remained as high as 25 wt.% (0.43g CO2 /1g CaO) with only 25% decrease from its CO2 uptake capacity as a fresh sample. Therefore, the latter sample was selected to be mixed with iron oxide catalyst and used for the SESR. The study of ethanol steam reforming employing an iron oxide as a catalyst, with and without in-situ CO2 removal, has been investigated. The results confirmed that iron oxide exhibited catalytic activity for hydrogen (H2) production from ethanol steam reforming/decomposition reactions. Furthermore, the CaO-based sorbent had sucessfully decrease the amount of CO2 produced during ethanol reforming reaction up to 70 min of reaction time. Ethanol reformation with in-situ CO2 removal was investigated at 550-700 °C. The maximum H2 yield achieved was 3.5 mol (H2) /mol (EtOH) at 600°C. GC results revealed that there was no evidence of CO and C across the studied temperature range. The results showed an enhancement in reaction reactivity by increasing the gas hourly space velocities (GHSVs). The amount of H2 produced remained stable within 10 cycles, which is equivalent to 30 hours of reaction time.
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Min, Byoung Koun. "Scanning tunneling microscopic studies of SiO2 thin film supported metal nano-clusters." Diss., Texas A&M University, 2004. http://hdl.handle.net/1969.1/2737.
Повний текст джерелаАнотація:
This dissertation is focused on understanding heterogeneous metal catalysts supported on oxides using a model catalyst system of SiO2 thin film supported metal nano-clusters. The primary technique applied to this study is scanning tunneling microscopy (STM). The most important constituent of this model catalyst system is the SiO2 thin film, as it must be thin and homogeneous enough to apply electron or ion based surface science techniques as well as STM. Ultra-thin SiO2 films were successfully synthesized on a Mo(112) single crystal. The electronic and geometric structure of the SiO2 thin film was investigated by STM combined with LEED, Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). The relationship between defects on the SiO2 thin film and the nucleation and growth of metal nano-clusters was also investigated. By monitoring morphology changes during thermal annealing, it was found that the metal-support interaction is strongly dependent on the type of metal as well as on the defect density of the SiO2 thin film. Especially, it was found that oxygen vacancies and Si impurities play an important role in the formation of Pd-silicide. By substituting Ti atoms into the SiO2 thin film network, an atomically mixed TiO2-SiO2 thin film was synthesized. Furthermore, these Ti atoms play a role as heterogeneous defects, resulting in the creation of nucleation sites for Au nano-clusters. A marked increase in Au cluster density due to Ti defects was observed in STM. A TiO2-SiO2 thin film consisting of atomic Ti as well as TiOx islands was also synthesized by using higher amounts of Ti (17 %). More importantly, this oxide surface was found to have sinter resistant properties for Au nano-clusters, which are desirable in order to make highly active Au nano-clusters more stable under reaction conditions.
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Beppu, Kosuke. "Studies on Sr-Fe Mixed Oxides for Purifying Automotive Exhaust Gas." Kyoto University, 2018. http://hdl.handle.net/2433/232055.
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Beckler, Robert Kendall. "Polynuclear metal complexes as model mixed oxide catalysts." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/11897.
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Zheng, Zhanfeng. "Synthesis and modifications of metal oxide nanostructures and their applications." Thesis, Queensland University of Technology, 2009. https://eprints.qut.edu.au/31728/1/Zhanfeng_Zheng_Thesis.pdf.
Повний текст джерелаАнотація:
Transition metal oxides are functional materials that have advanced applications in many areas, because of their diverse properties (optical, electrical, magnetic, etc.), hardness, thermal stability and chemical resistance. Novel applications of the nanostructures of these oxides are attracting significant interest as new synthesis methods are developed and new structures are reported. Hydrothermal synthesis is an effective process to prepare various delicate structures of metal oxides on the scales from a few to tens of nanometres, specifically, the highly dispersed intermediate structures which are hardly obtained through pyro-synthesis. In this thesis, a range of new metal oxide (stable and metastable titanate, niobate) nanostructures, namely nanotubes and nanofibres, were synthesised via a hydrothermal process. Further structure modifications were conducted and potential applications in catalysis, photocatalysis, adsorption and construction of ceramic membrane were studied. The morphology evolution during the hydrothermal reaction between Nb2O5 particles and concentrated NaOH was monitored. The study demonstrates that by optimising the reaction parameters (temperature, amount of reactants), one can obtain a variety of nanostructured solids, from intermediate phases niobate bars and fibres to the stable phase cubes. Trititanate (Na2Ti3O7) nanofibres and nanotubes were obtained by the hydrothermal reaction between TiO2 powders or a titanium compound (e.g. TiOSO4·xH2O) and concentrated NaOH solution by controlling the reaction temperature and NaOH concentration. The trititanate possesses a layered structure, and the Na ions that exist between the negative charged titanate layers are exchangeable with other metal ions or H+ ions. The ion-exchange has crucial influence on the phase transition of the exchanged products. The exchange of the sodium ions in the titanate with H+ ions yields protonated titanate (H-titanate) and subsequent phase transformation of the H-titanate enable various TiO2 structures with retained morphology. H-titanate, either nanofibres or tubes, can be converted to pure TiO2(B), pure anatase, mixed TiO2(B) and anatase phases by controlled calcination and by a two-step process of acid-treatment and subsequent calcination. While the controlled calcination of the sodium titanate yield new titanate structures (metastable titanate with formula Na1.5H0.5Ti3O7, with retained fibril morphology) that can be used for removal of radioactive ions and heavy metal ions from water. The structures and morphologies of the metal oxides were characterised by advanced techniques. Titania nanofibres of mixed anatase and TiO2(B) phases, pure anatase and pure TiO2(B) were obtained by calcining H-titanate nanofibres at different temperatures between 300 and 700 °C. The fibril morphology was retained after calcination, which is suitable for transmission electron microscopy (TEM) analysis. It has been found by TEM analysis that in mixed-phase structure the interfaces between anatase and TiO2(B) phases are not random contacts between the engaged crystals of the two phases, but form from the well matched lattice planes of the two phases. For instance, (101) planes in anatase and (101) planes of TiO2(B) are similar in d spaces (~0.18 nm), and they join together to form a stable interface. The interfaces between the two phases act as an one-way valve that permit the transfer of photogenerated charge from anatase to TiO2(B). This reduces the recombination of photogenerated electrons and holes in anatase, enhancing the activity for photocatalytic oxidation. Therefore, the mixed-phase nanofibres exhibited higher photocatalytic activity for degradation of sulforhodamine B (SRB) dye under ultraviolet (UV) light than the nanofibres of either pure phase alone, or the mechanical mixtures (which have no interfaces) of the two pure phase nanofibres with a similar phase composition. This verifies the theory that the difference between the conduction band edges of the two phases may result in charge transfer from one phase to the other, which results in effectively the photogenerated charge separation and thus facilitates the redox reaction involving these charges. Such an interface structure facilitates charge transfer crossing the interfaces. The knowledge acquired in this study is important not only for design of efficient TiO2 photocatalysts but also for understanding the photocatalysis process. Moreover, the fibril titania photocatalysts are of great advantage when they are separated from a liquid for reuse by filtration, sedimentation, or centrifugation, compared to nanoparticles of the same scale. The surface structure of TiO2 also plays a significant role in catalysis and photocatalysis. Four types of large surface area TiO2 nanotubes with different phase compositions (labelled as NTA, NTBA, NTMA and NTM) were synthesised from calcination and acid treatment of the H-titanate nanotubes. Using the in situ FTIR emission spectrescopy (IES), desorption and re-adsorption process of surface OH-groups on oxide surface can be trailed. In this work, the surface OH-group regeneration ability of the TiO2 nanotubes was investigated. The ability of the four samples distinctively different, having the order: NTA > NTBA > NTMA > NTM. The same order was observed for the catalytic when the samples served as photocatalysts for the decomposition of synthetic dye SRB under UV light, as the supports of gold (Au) catalysts (where gold particles were loaded by a colloid-based method) for photodecomposition of formaldehyde under visible light and for catalytic oxidation of CO at low temperatures. Therefore, the ability of TiO2 nanotubes to generate surface OH-groups is an indicator of the catalytic activity. The reason behind the correlation is that the oxygen vacancies at bridging O2- sites of TiO2 surface can generate surface OH-groups and these groups facilitate adsorption and activation of O2 molecules, which is the key step of the oxidation reactions. The structure of the oxygen vacancies at bridging O2- sites is proposed. Also a new mechanism for the photocatalytic formaldehyde decomposition with the Au-TiO2 catalysts is proposed: The visible light absorbed by the gold nanoparticles, due to surface plasmon resonance effect, induces transition of the 6sp electrons of gold to high energy levels. These energetic electrons can migrate to the conduction band of TiO2 and are seized by oxygen molecules. Meanwhile, the gold nanoparticles capture electrons from the formaldehyde molecules adsorbed on them because of gold’s high electronegativity. O2 adsorbed on the TiO2 supports surface are the major electron acceptor. The more O2 adsorbed, the higher the oxidation activity of the photocatalyst will exhibit. The last part of this thesis demonstrates two innovative applications of the titanate nanostructures. Firstly, trititanate and metastable titanate (Na1.5H0.5Ti3O7) nanofibres are used as intelligent absorbents for removal of radioactive cations and heavy metal ions, utilizing the properties of the ion exchange ability, deformable layered structure, and fibril morphology. Environmental contamination with radioactive ions and heavy metal ions can cause a serious threat to the health of a large part of the population. Treatment of the wastes is needed to produce a waste product suitable for long-term storage and disposal. The ion-exchange ability of layered titanate structure permitted adsorption of bivalence toxic cations (Sr2+, Ra2+, Pb2+) from aqueous solution. More importantly, the adsorption is irreversible, due to the deformation of the structure induced by the strong interaction between the adsorbed bivalent cations and negatively charged TiO6 octahedra, and results in permanent entrapment of the toxic bivalent cations in the fibres so that the toxic ions can be safely deposited. Compared to conventional clay and zeolite sorbents, the fibril absorbents are of great advantage as they can be readily dispersed into and separated from a liquid. Secondly, new generation membranes were constructed by using large titanate and small ã-alumina nanofibres as intermediate and top layers, respectively, on a porous alumina substrate via a spin-coating process. Compared to conventional ceramic membranes constructed by spherical particles, the ceramic membrane constructed by the fibres permits high flux because of the large porosity of their separation layers. The voids in the separation layer determine the selectivity and flux of a separation membrane. When the sizes of the voids are similar (which means a similar selectivity of the separation layer), the flux passing through the membrane increases with the volume of the voids which are filtration passages. For the ideal and simplest texture, a mesh constructed with the nanofibres 10 nm thick and having a uniform pore size of 60 nm, the porosity is greater than 73.5 %. In contrast, the porosity of the separation layer that possesses the same pore size but is constructed with metal oxide spherical particles, as in conventional ceramic membranes, is 36% or less. The membrane constructed by titanate nanofibres and a layer of randomly oriented alumina nanofibres was able to filter out 96.8% of latex spheres of 60 nm size, while maintaining a high flux rate between 600 and 900 Lm–2 h–1, more than 15 times higher than the conventional membrane reported in the most recent study.
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Cau, Camille. "Influence de la méthode de synthèse sur les propriétés structurales et catalytiques d'oxydes mixtes cérium-zirconium." Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20192/document.
Повний текст джерелаАнотація:
Les oxydes mixtes de cérium-zirconium sont au cœur de nombreux sujets de recherche. En effet, ces matériaux sont utilisés dans différents domaines d'application, et tout particulièrement en catalyse, dans les catalyseurs trois voies en automobile ou pour l'oxydation de polluants organiques. L'intérêt pour ce composé réside dans ses propriétés remarquables d'oxydoréduction, sa capacité de stockage de l'oxygène et sa résistance au frittage. En conséquence, un nombre important de méthodes de synthèse ont été mises au point et soulignent la grande sensibilité de cet oxyde mixte à la voie de préparation employée. Dans le cadre de ce travail deux grandes voies de synthèses ont été utilisées, la co-précipitation (milieu aqueux) et la dégradation des -dicétonates métalliques (milieu non aqueux). Ces synthèses ont été réalisées à l'aide de plusieurs techniques que sont (i) le chauffage à pression atmosphérique, (ii) le traitement hydrothermal, (iii) la sonolyse et (iv) la combinaison de la sonolyse et du traitement hydrothermal, de façon successive ou en simultané. Afin de pouvoir réaliser cette dernière méthode de synthèse innovante, un réacteur permettant de réaliser un traitement sonochimique en température et sous pression a été développé (réacteur sonothermal). L'activité chimique des ultrasons dans ces conditions a pu être mise en évidence lors de la sonolyse de l'eau (légère ou lourde) et de celle d'un hydrocarbure. Au cours de la préparation de (Ce,Zr)O2, des paramètres autres que le dispositif de synthèse ont été étudiés, comme la présence d'un surfactant ou la longueur de chaine du solvant. Ainsi, il a pu être démontré que, dans le cas de la voie aqueuse, l'utilisation du réacteur sonothermal a une réelle incidence sur la surface spécifique du matériau final en comparaison de la réalisation successive des traitements sonochimique et hydrothermal. Les oxydes présentant les propriétés structurales les plus intéressantes ont été sélectionnés afin d'être employé en tant que support de métal noble dans des catalyseurs de type Pt/(Ce,Zr)O2. L'évaluation de l'activité catalytique de ces matériaux, lors de l'oxydation catalytique à l'air humide de l'acide formique, a montré que celle-ci dépend non seulement du mode de synthèse de l'oxyde mixte, mais également de la voie de dépôt du platine et du couple méthode de dépôt du platine/méthode de synthèse du supportCerium-zirconium mixed oxides are at the heart of numerous research subjects. Indeed, these materials are used in different fields of application, and particularly in catalysis in three-way catalyst for automobile or for organic pollutant oxidation. The interest for this compound resides in its remarkable oxidoreduction properties, its oxygen storage capacity and its resistance to sintering. Consequently, numerous preparation methods have been developed and underline the high sensitivity of these oxides to the synthesis way. In the present work, two main synthesis have been employed, coprecipitation (aqueous medium) and diketonate degradation (non-aqueous medium). These syntheses have been realized with several techniques which are (i) heating at atmospheric pressure, (ii) hydrothermal treatment, (iii) sonolysis and (iv) combination of sonolysis and hydrothermal treatments, in a successive or simultaneous way. In order to realize this last and innovative method, a reactor allowing sonochemical treatment under high temperature and pressure has been developed. Under these conditions, the ultrasounds chemical activity has been proved during light or heavy water or hydrocarbon sonolysis. During the (Ce,Zr)O2 preparation, other parameters than the synthesis technique have been studied such as the surfactant presence or the solvent chain length. Thus, it has been shown that, in the case of aqueous synthesis, the use of the sonothermal reactor has a real effect on the specific surface area of the material in comparison of successive realization of sonochemical and hydrothermal treatments. Oxides with the more interesting structural properties have been selected for being used as supports of noble metal in the Pt/(Ce,Zr)O2 catalysts. The evaluation of the catalytic activity of these materials, during the catalytic wet air oxidation of formic acid, showed that it not only depends on the synthesis method, but also on the platinum deposition method and the pair platinum deposition method/support synthesis method
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Romano, Esteban Javier. "In-situ surface science studies of the interaction between sulfur dioxide and two-dimensional palladium loaded-cerium/zirconium mixed metal oxide model catalysts." Diss., Mississippi State : Mississippi State University, 2005. http://library.msstate.edu/etd/show.asp?etd=etd-04062005-093500.
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Motshweni, Jim Sipho. "Synthesis of mixed metal oxides for use as selective oxidation catalysts." Thesis, Link to the online version, 2007. http://hdl.handle.net/10019/445.
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Wetwatana, Unalome. "Light Hydrocarbon conversion over mixed oxide catalysts." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504936.
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Rowbotham, Elizabeth Jane. "Propene oxidation on mixed metal oxide catalysts." Thesis, University of Reading, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299302.
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Väliheikki, A. (Ari). "Resistance of catalytic materials towards chemical impurities:the effect of sulphur and biomaterial-based compounds on the performance of DOC and SCR catalysts." Doctoral thesis, Oulun yliopisto, 2016. http://urn.fi/urn:isbn:9789526212845.
Повний текст джерелаАнотація:
Abstract Exhaust gas emissions, e.g. nitrogen oxides (NOx), hydrocarbons (HCs) and carbon monoxide (CO), are harmful to human health and the environment. Catalysis is an efficient method to decrease these emissions. Unfortunately, the fuels and lubricant oils may contain chemical impurities that are also present in exhaust gases. Thus, catalytic materials with high activity and chemical resistance towards impurities are needed in the abatement of exhaust gas emission. In this thesis, the aim was to gain new knowledge about the effects of chemical impurities on the behaviour and activity of the catalysts. To find out these effects, the impurities existing in the exhaust gas particulate matter after combustion of biofuels and fossil fuels were analysed. The studied zeolite (ZSM-5), cerium-zirconium mixed oxides (CeZr and ZrCe) and silicon-zirconium oxide (SiZr) based catalysts were also treated with impurities to simulate the poisoning of the catalysts by, e.g. potassium, sodium, phosphorus and sulphur, using gas or liquid phase treatments. Several characterization techniques were applied to find out the effects of impurities on catalysts’ properties. The activity of catalysts was tested in laboratory-scale measurements in CO and HC oxidation and NOx reduction using ammonia (NH3) and hydrogen (H2) as reductants. The results revealed that the CeZr based catalysts had a high activity in NOx reduction by NH3 and moderate activity by H2. Sulphur was proven to enhance the activity of CeZr catalysts in NOx reduction. This is due to an increase in chemisorbed oxygen after the sulphur treatment on the catalyst surface. Instead, in HC and CO oxidation reactions, sulphur had a negligible impact on the activity of the SiZr based diesel oxidation catalyst. Thus, both CeZr and SiZr based catalysts can be utilized in exhaust gas purification when sulphur is present. ZSM-5 based catalysts were proven to be resistant to potassium and sodium. Alternatively, the activity of SiZr based catalysts decreased due to phosphorus. Thus, the removal of biomaterial-based impurities from the exhaust gases is needed to retain high catalyst activity in the exhaust gas after-treatment systemTiivistelmä Pakokaasupäästöissä olevat typen oksidit (NOx), hiilivedyt (HCs) ja hiilimonoksidi (CO) ovat haitallisia ihmisten terveydelle ja ympäristölle. Katalyysi on tehokas menetelmä vähentää näitä päästökomponentteja. Polttoaineet ja voiteluöljyt sisältävät epäpuhtauksia, jotka siirtyvät myös pakokaasuihin. Tästä johtuen pakokaasupäästöjen hallinnassa tarvitaan katalyyttimateriaaleja, joilla on hyvä vastustuskyky myrkyttymistä vastaan. Tavoitteena oli saada uutta tietoa kemiallisten epäpuhtauksien vaikutuksesta katalyyttien toimintaan. Biopolttoaineiden sisältämät mahdolliset epäpuhtaudet selvitettiin analysoimalla fossiilisen ja biopolttoaineen palamisessa muodostuvia partikkeleita ja vertaamalla niitä polttoaineiden hivenaineanalyysiin. Tutkimuksessa käytetyt zeoliitti (ZSM-5), cerium-zirkonium-sekaoksidi (CeZr) ja pii-zirkonium-oksidipohjaiset (SiZr) katalyytit käsiteltiin epäpuhtauksilla (kalium, natrium, fosfori ja rikki) kaasu- ja nestefaasissa. Tutkimuksessa käytettiin useita karakterisointitekniikoita, joiden avulla selvitettiin epäpuhtauksien vaikutuksia katalyyttien ominaisuuksiin. Katalyyttien toimintaa testattiin laboratoriomittakaavan kokeissa CO:n ja HC-yhdisteiden hapetuksessa sekä NOx:ien pelkistyksessä käyttäen ammoniakkia (NH3) tai vetyä (H2) pelkistimenä. Tulokset osoittavat, että CeZr-pohjaisten katalyyttien aktiivisuus NOx:ien pelkistyksessä oli hyvä käytettäessä pelkistimenä NH3:a ja kohtalainen käytettäessä vetyä. Rikki paransi CeZr-katalyyttien aktiivisuutta NOx:ien pelkistyksessä, mikä johtui kemiallisesti sitoutuneen hapen osuudesta katalyyttien pinnoilla. Vastaavasti hiilivetyjen ja CO:n hapetusreaktioissa rikki ei vaikuttanut SiZr-pohjaisten dieselhapetuskatalyyttien aktiivisuuteen. Sekä CeZr- ja SiZr-pohjaisia katalyytteja voidaan siten käyttää rikkiä sisältävien pakokaasujen puhdistuksessa. SiZr-pohjaisten katalyyttien aktiivisuus laski fosforin vuoksi. ZSM-5-pohjaiset katalyytit olivat vastustuskykyisiä kaliumille ja natriumille. Kestäviä katalyyttejä on siten kehitettävä, mikäli biopolttoaineiden sisältämien epäpuhtauksien poistaminen polttoaineista ei ole mahdollista
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Yaseneva, Polina. "Selective oxidation of methanol on mixed oxide catalysts." Thesis, Cardiff University, 2011. http://orca.cf.ac.uk/54464/.
Повний текст джерелаАнотація:
In the present work selective oxidation of methanol over the model Mo/Fe2O3 and Mo/Co(Zn) Fe2O4 systems has been investigated. It was shown that pure iron oxide and cobalt ferrite combust methanol to carbon dioxide and water. When molybdenum is loaded on the surface of iron oxide and calcined at 500 C, this leads to the formation of iron molybdate surface layer over Fe2C>3 core, which significantly changes selectivity in methanol oxidation towards partial oxidation products. The neighbouring Fe-Mo and Mo-Mo pairs of iron molybdate layer are responsible for the formation of carbon monoxide and formaldehyde respectively. According to XRD, Raman and XPS data, dosing of molybdenum onto the cobalt ferrite surface results in the formation of a mixed layer consisting of cobalt molybdate, iron molybdate and molybdena phases. Oxidation of methanol over Mo/CoFe2O4 results in the formation of a mixture of CO and CO2 with small traces of formaldehyde. CO is produced on mixed Fe-Mo and Co-Mo sites at temperatures above 220 C, whereas CO2 is mainly produced at lower temperatures and low oxygen conversion due to oxidation of CO by highly reactive traces of pure cobalt ferrite or cobalt molybdate present on the surface. Methanol oxidation was used as a model reaction to establish whether there is a relationship between catalytic activity and selectivity, and magnetic properties of catalysts. The catalytic behaviour of the pure and Mo impregnated ZnxCoi-xFe2O4 systems in the vicinity of Curie point was studied. Curie temperature of the material and the nature of Curie transition were adjusted varying Zn content and sample calcination temperature.
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James, David William. "Selective propene oxidation on mixed metal oxide catalysts." Thesis, University of Reading, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252228.
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Waldvogel, Audrey. "Mise au point d'un catalyseur performant pour la chaîne de procédé Power-to-Methane et étude cinétique." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAF077/document.
Повний текст джерелаАнотація:
Le contexte environnemental (réchauffement climatique) et politique (augmentation du parc EnR) entraîne une mutation du paysage énergétique français. Le méthane de synthèse est présenté comme un vecteur énergétique permettant le stockage et le transport de l’électricité renouvelable en surproduction tout en recyclant le CO2 (Power-to-Methane). Un des objectifs de la thèse est de développer un catalyseur actif en co-méthanation d’un mélange post co-électrolyse H2/CO/CO2/H2O/CH4 (projet ANR CHOCHCO). Le catalyseur synthétisé est de type Ni/CZP. L’optimisation de la synthèse coprécipitation par l’utilisation combinée du sel précipitant (NH4)2CO3 et du tensioactif CTAB a mené à un catalyseur performant (absence de poison alcalin et augmentation de la surface spécifique) capable de produire du CH4 à basse température (250 °C) avec un rendement élevé. Le catalyseur a montré une résistance satisfaisante à la désactivation par dépôt de carbone et par frittage, indispensable pour le fonctionnement intermittent du procédé. Un modèle cinétique, de type Langmuir-Hinshelwood, a pour la première fois été développé sur un catalyseur de type Ni/CZPThe environmental (global warming) and political (increase of the renewable electric farm) context leads to a mutation of the French energy landscape. Synthetic methane is presented as a energy carrier for storing and transporting renewable electricity in overproduction while recycling CO2, a process called Power-to-Methane. One of the objectives of the thesis is to develop an active catalyst for the co-methanation of a post-co-electrolysis mixture H2/CO/CO2/H2O/CH4 (CHOCHCO ANR project). A Ni/CZP type catalyst was synthesized in this purpose. The optimization of the coprecipitation synthesis by the combination of the precipitating salt (NH4)2CO3 and the surfactant CTAB has led to a high performance catalyst (absence of alkaline poison and increase of the specific surface area) able to produce CH4 at low temperature (250 °C) with a high yield. The catalyst showed a satisfactory resistance to carbon deposition and sintering deactivation, which is a key point for the intermittent operating conditions of the process. A kinetic model, of the Langmuir-Hinshelwood type, was developed for the first time on a Ni/CZP type catalyst
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Ferguson, Jonathan. "Mixed metal oxide catalysts prepared using supercritical carbon dioxide." Thesis, Cardiff University, 2009. http://orca.cf.ac.uk/54914/.
Повний текст джерелаАнотація:
The use of nitrate precursors for the production of mixed oxide catalysts such as iron molybdates and copper manganese oxides has been well documented in the literature. Nitrates have been used because of their high solubility and the ease of removal of the nitrate anion during calcination. In the case of copper manganese oxides, the use of chlorides and sulphates leads to the retention of the anion on the surface of the catalyst, using nitrates leaves no residue on the catalyst. The use of nitrates, however, is unfavourable due to the environmental issues associated with them. The main aim of this project was to provide a nitrate free route for the production of iron molybdate and copper manganese oxide catalysts. Using supercritical antisolvent precipitation (SAS) provided an alternative preparative route for the production of these catalysts. The catalysts produced exhibited activity when tested in their respective reactions. Some catalysts produced were comparable to those currently prepared using the conventional preparation methods i.e. the use of nitrate precursors. The research performed focussed on the production of theses mixed metal oxides using supercritical carbon dioxide. Optimisation of the supercritical process by varying operational parameters was also investigated to determine their effect on the activity of the catalyst obtained. By utilising operating parameters and understanding the supercritical antisolvent process, the results obtained showed that it was possible to produce mixed metal oxides, and to tune their catalytic activity.
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Olcay, Hakan Onder. "Steam Reforming Of Ethanol Over Sol-gel-synthesized Mixed Oxide Catalysts." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606310/index.pdf.
Повний текст джерелаАнотація:
Depletion in the reserves of fossil fuels, inefficient energy production from these fuels and the negative effect of their usage on atmosphere, and thereby, on human health have accelerated researches on clean energy. Hydrogen produced from ethanol when used in fuel cells not only generates efficient energy but also creates a closed carbon cycle in nature.
ZnO and Cu/ZnO catalysts are known with their superior performance in alcohol synthesis. From the principle of microkinetic reversibility they are expected to be superior catalysts for the steam reforming reaction of ethanol as well. ZnO catalysts can be modified by precious, Pd, or non-precious, Cu, metals to enhance hydrogen desorption capability, and dispersed on SiO2 for high surface areas via sol-gel technique.
Steam reforming tests over ZnO catalysts revealed that they act only as ethanol dehydrogenation catalysts in the temperature range of 300-500C. Promotion with Pd or Cu decreased hydrogen selectivity due most probably to unreachable closed pores of the catalysts. Autothermal reforming tests over both ZnO/SiO2
and Co/SBA-15 catalysts, on the other hand, gave rise to the formation of several side products.
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Caglar, Basar. "Nox Storage And Reduction Over Ce-zr Mixed Oxide Supported Catalysts." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610418/index.pdf.
Повний текст джерелаАнотація:
NOx storage and reduction activities of Pt/BaO/CexZr1-xO2 (x= 1, 0.75, 0.5, 0.25, 0) catalysts were investigated by transient reaction analysis and Diffuse Reflectance Infrared Fourier Tramsform Spectroscopy (DRIFTS). Pt/BaO/Al2O3 catalyst was used as reference catalyst. Ce-Zr mixed oxides were synthesized by means of Pechini Method. Pechini method is a sol-gel like method based on mixing the related mixed oxide precursors with an α
-hydroxy carboxylic acid. 10% BaO (w/w) and 1% Pt (w/w) were deposited on synthesized mixed oxide and reference alumina support via incipient wetness impregnation. Prepared catalysts were characterized by BET, XRD and in-situ DRIFTS. Pt/BaO/CexZr1-xO2 catalysts (x= 0.75, 0.5, 0.25) exhibited higher surface than pure ceria and zirconia supported catalysts and highest surface was observed for Pt/BaO/Ce0.5Zr0.5O2. The reducibility of catalysts was tested by Temperature Programmed Reduction (TPR). It was observed that the reducibility of Pt/BaO/CexZr1-xO2 catalysts increases with incorporation of Zr into ceria lattice. Pt/BaO/Ce0.25Zr0.75O2 showed the highest reducibility. The Pt dispersions of catalysts were determined by CO chemisorption. The highest Pt disperison was observed in the presence of Pt/BaO/Ce0.5Zr0.5O2 catalyst. NOx storage and reduction efficiency of the catalysts were determined by transient reaction analysis in a home-built setup at 350oC. The reaction results revealed that all catalysts exhibit similar NOX storage and reduction performance. The NOX storage performances of all catalysts were differentiated via in-situ DRIFTS analysis. Pt/BaO/CexZr1-xO2 (x= 0.75, 0.5, 0.25) catalysts revealed higher performance than the ceria and zirconia supported catalysts. Pt/BaO/Ce0.5Zr0.5O2 catalyst absorbed highest amount of NO on the surface in the form of nitrate. The reduction behaviours of catalysts also were investigated by in-situ DRIFTS. It was observed that nitrates and nitrites were completely removed from the surface after reduction by H2 at 300oC.
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Hamid, Hamzah b. Abd. "Oxidative coupling of methane on samaria and on mixed oxide catalysts." Thesis, University of Hull, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335155.
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Joshi, Suvid. "MIXED SURFACTANT SYSTEMS: THERMODYNAMICS AND APPLICATIONS IN METAL OXIDE IMPRINTING." UKnowledge, 2014. http://uknowledge.uky.edu/cme_etds/29.
Повний текст джерелаАнотація:
In this work we study mixtures of cationic surfactant (CTAB) and sugar based surfactant(s) (octyl beta-D-glucopyranoside (C8G1), dodecyl maltoside (C12G2) and octyl beta-D-xylopyranoside (C8X1)) to understand the non-ideal thermodynamic behavior of the mixtures of cationic and non-ionic surfactants in water and synthesis of imprinted materials. The thermodynamics of micellization, mixing and dilution of these systems are studied using Isothermal Titration Calorimetry (ITC) and the experimental data obtained are modeled with a pseudo-phase separation model with non-ideal mixing described by regular solution theory. It is shown that a model accounting for enthalpy of demicellization and enthalpy of dilution based on McMillan-Mayer model is able to fit ITC data set for CTAB-C8G1 system with varying mole fractions.
In addition to measuring non-ideal mixing behavior, mixtures of cationic and saccharide-based surfactants are of interest for the molecular imprinting of oxide materials. Mixtures of CTAB and either C8G1 or C8X1 are utilized to prepare nonporous adsorbent materials which act as selective adsorbents towards the headgroup of the saccharide surfactant. The approach is based on the Stöber silica particle synthesis process in which surfactants are added to soft particles present at the onset of turbidity to imprint their surface. This approach is shown to yield particles displaying selective adsorption for sugars with different number of carbons, but also provide enantioselective adsorption of targeted saccharides. Enantioselectivity of D-glucose, D-xylose and D-maltose is demonstrated by imprinting with C8G1, C8X1 and C12G2, respectively. The imprinting technique provides the first example of selective adsorption based on non-covalent imprinting of silica for sugars.
The mixed surfactant are also used to synthesize templated porous materials incorporating titanium which are used for epoxidation catalysis. The porous materials obtained have high surface area, uniform pore sizes in the mesopore range, and provided high selectivity and activity towards epoxidation of styrene. Titanosilicate thin films are also synthesized using cationic and saccharide surfactant mixtures to understand the incorporation of the titanium into the porous material. It is demonstrated that large amounts of isolated, tetracoordinated titanium sites can be incorporated into mesoporous silica-based materials via the complexation of the titanium precursor with a saccharide-based surfactant.
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AL-SAEEDI, JAMAL N. "MOLECULAR STRUCTURE-REACTIVITY RELATIONSHIPS FOR PROPANE OXIDATION OVER MODEL MIXED OXIDE CATALYSTS." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1053698262.
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Yuan, Li. "Mesoporous and macroporous mixed metal oxide MoVTeNbOx catalysts for propane (amm) oxidation." Cincinnati, Ohio : University of Cincinnati, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1199297348.
Повний текст джерелаАнотація:
Thesis (Ph. D. )--University of Cincinnati, 2008.Advisor: Dr. Vadim V. Guliants Title from electronic thesis title page (viewed May 7, 2008). Includes abstract. Includes bibliographical references.
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Weightman, Gareth John. "The development of mixed oxide adsorbents and catalysts through continuous flow processes." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/81820/.
Повний текст джерелаАнотація:
The aim of this project was to produce solid adsorbents and catalysts in a continuous flow process. These materials are traditionally made in a batch process. The materials were made and the effect of the change in synthesis explored. When hydrotalcite was produced in a batch process it was found to yield material that was synthesised by a reaction governed by thermodynamic control. Contrary, solid formation in a continuous flow it was found to be governed by a kinetically controlled reaction. During the batch reaction the reactants had time and mobility to precipitate, dissolve and re-precipitate in order to arrive at the lowest energy configuration. This configuration resulted in aluminium from one meixnerite intermediate layer aligning with aluminium in the opposing layer (referred to as “in phase”). This allowed carbonate anions to join the layers together creating a crystalline structure by balancing its charge between the two aluminium atoms. In a continuous flow process the reactants were not afforded either the time or space to move. This resulted in aluminium being randomly located within the meixnerite intermediate. Due to the random placement of aluminium, the aluminium in opposing layers did not consistently align (referred to as “out of phase”). Carbonate anions bound to these out of phase aluminium atoms are unable to balance their charge by linking layers together. The anions compensated by taking up hydrogen and forming a bicarbonate anion. The remaining aluminium took up monovalent nitrate anions in the absence of any divalent anions. Hydroxide anions would have been more favourable but they were required in the formation of the lattice. It was also found that the kinetically controlled product could be converted to the thermodynamically controlled product by washing. Washing, however, degraded the lattice structure and washed away an amount of material. The hydrotalcites produced by continuous flow process were thermally decomposed to act as a carbon dioxide adsorbent. They decomposed much faster than their batch counterparts, suggesting the carbonate bridge provides thermal stability to the material. The decomposition also revealed that the magnesium/aluminium spinel recorded in other studies did not form for the materials produced in a continuous flow process. Instead the material decomposed to the separate metal oxides. This did not have an effect on the ability of the material to adsorb carbon dioxide and performed comparably to the batch process materials. The continuous flow process was used to create a Ni/Mg/Al hydrotalcite that could be used as a catalyst in ethanol steam reforming. The continuous flow process allowed three processes for introducing nickel into the system: the doping of the starting reagents, ion exchange during the washing process and the impregnation of the dry product. The doped samples produced material comparable to those produced in continuous flow without doping or washing. The ion exchange and the impregnation samples produced samples that are comparable to those produced in continuous flow with washing The doped samples exhibited a fourth region of weight loss in thermogravimetric analysis which is speculated to be the formation of nickel aluminide at high temperatures. The catalytic activity corroborated this idea with an increase in metallic behaviour. The doped sample was found to be the more active sample tested. In order to further test the effect of kinetic and thermodynamic control during the continuous flow process, an attempt to control the particle size of zirconium basic sulfate was made. It was found that the particle size could be altered in the batch process due the variable environment within the reactor. Inefficient mixing created concentration gradients and inefficient heating created temperature gradients. It was these gradients within the batch reactor that facilitated the thermodynamic product to be produced and the particle size to increase. In a continuous flow reactor these gradients did not exist. The advantage of the flow reactor was the ability to control the environment of the reactor in an even and uniform manner. The uniformity of the reactor environment eliminated any temperature or concentration gradients, keeping all the materials at similar chemical potentials, limiting particle growth.
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Hong, Won-Jong. "Direct Decomposition of NO over Ba-loaded Ce-based Mixed Oxide Catalysts." 京都大学 (Kyoto University), 2011. http://hdl.handle.net/2433/142237.
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Gonçalves, Alexandre Amormino Dos Santos. "Development of Nanostructured Ceramic Catalysts Based on Mixed Metal Oxides." Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1543412496976455.
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Patil, Aniket. "Simultaneous Fixed Bed Removal of Nitrogen Oxides and Mercury Using Manganese and Cerium Mixed Metal Oxide Catalysts at Low Temperature SCR." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1530266242697853.
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Cabrera, Navarrete Maria Elia. "Preparação, caracterização e propriedades cataliticas de hidrotalcitas MgAICr calcinadas na conversão de etanol." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/267173.
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Orientador: Renato SprungTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
Made available in DSpace on 2018-08-14T09:58:31Z (GMT). No. of bitstreams: 1 CabreraNavarrete_MariaElia_D.pdf: 13508491 bytes, checksum: ed8e83647aa4fc77ef26b506eee4e91a (MD5) Previous issue date: 2007
Resumo: Materiais do tipo hidrotalcita Mg1-x(Al,Cr)x(OH)2(CO3)x/2yH2O foram sintetizados por coprecipitação a partir de nitratos de magnésio, alumínio e cromo. Os sólidos foram calcinados, caracterizados e testados na conversão de etanol. Na preparação, alumínio foi substituído por cromo na hidrotalcita MgAl nas proporções de 0, 5, 10, 50, 80 e 100% e as frações de cátions trivalentes x foram de 0,20, 0,25 e 0,33. Os materiais mostraram difratogramas de raios-X característicos de hidrotalcitas. A calcinação a 650°C das hidrotalcitas com 0 a 80% de substituição de alumínio resultou em óxidos mistos com estrutura de MgO, e a de materiais com 100% de substituição, em cromita de magnésio. As áreas BET dos materiais calcinados diminuíram com os aumentos do teor de cromo e da fração x, variando entre 90 e 309 m²/g. Os materiais não contêm microporos. A adsorção de CO2 mostrou que a densidade de sítios básicos diminui com os aumentos do teor de cromo e de x. Os testes catalíticos foram realizados num reator de leito fixo, à pressão atmosférica e temperaturas de 300 a 375°C. Os principais produtos foram n-butanol, éter etílico, acetaldeído e etileno, além de quantidades menores de butiraldeído, crotonaldeído e acetato de etila. A substituição de alumínio por cromo inibiu a formação de éter etílico e favoreceu a formação de acetaldeído. A substituição de 5 a 10% de alumínio por cromo resultou nas maiores conversões de etanol e nos maiores rendimentos de n-butanol. A presença da água na alimentação de etanol diminuiu as conversões. A promoção de catalisadores com sódio inibiu as reações, especialmente as de desidratação.
Abstract: Hydrotalcite-type materials, Mg1-x(Al,Cr)x(OH)2(CO3)x/2yH2O, were synthesized by coprecipitation from solutions containing magnesium, aluminium and chromium nitrates, calcined, characterized and tested for the conversion of ethanol. Aluminum was substituted by chromium in MgAl-hydrotalcite in amounts of 0, 5, 10, 50, 80 and 100 mol% and x-values of 0,20, 0,25 and 0,33. Powder X-ray diffraction patterns of the synthesized materials were typical of hydrotalcites. Calcination at 650°C of materials with aluminum yielded mixed oxides with diffraction patterns typical of MgO, and of materials without aluminum, that of magnesium chromite. BET areas of calcined materials increased with increasing chromium contents as well as with increasing x-values, varying between 90 and 309 m²/g. No material contained micropores. CO2 adsorption showed decreasing base site density as either the chromium content or the x-value was increased. Catalysts were tested at atmospheric pressure and temperatures of 300 to 375°C in a fixed bed reactor. Diethyl ether, n-butanol, acetaldehyde and ethylene were the main reaction products; small amounts of crotonaldehyde, butyraldehyde and ethyl acetate were also present. The presence of chromium in the catalysts inhibited diethyl ether formation while favoring acetaldehyde formation. The substitution of 5-10 mol% of aluminum by chromium resulted in the highest ethanol conversions and the largest overall yields of n-butanol. Lower conversions were obtained when water was added into the ethanol feed. Promotion of catalysts with sodium decreased conversions, particularly of dehydration reactions.
Doutorado
Desenvolvimento de Processos Químicos
Doutor em Engenharia Química
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Buchneva, O. "NANOSTRUCTURED MIXED OXIDES CATALYSTS: RELATIONSHIPS BETWEEN PHYSICAL-CHEMICAL AND CATALYTIC PROPERTIES." Doctoral thesis, Università degli Studi di Milano, 2010. http://hdl.handle.net/2434/150140.
Повний текст джерелаАнотація:
Perovskitic catalysts showed satisfactory activity for the low temperature flameless combustion of methane. This process allows to decrease the emission of CO, NOx and partially unburnt hydrocarbons. Partial substitution in the composition of perovskites may improve catalytic activity and it can modulate their resistance to sulphur poisoning.
Samples with nominal composition La1-xA’xBO3, where A’= Sr, Ce, Ag, B=Co, Mn with x = 0; 0.05; 0.10, 0.20 and x%NB/LaBO3, where NB=Pt, Pd, Ag were prepared by flame spray pyrolysis (FP) and by the so-called sol-gel citrate method (SG). Temperature-programmed analysis, X-ray powder diffraction (XRD) and Electron Paramagnetic Resonance (EPR) spectroscopy were used as main characterisation tools. Almost all of the catalysts showed very active for the flameless combustion of methane. The activity of the FP-prepared catalysts was always higher than that of the SG-prepared ones with identical nominal composition.
Partial substitution didn’t lead to a significant change of activity, though an evident result was achieved in case of Sr-substituted manganites. Also activity may be increased by the addition of a small amount of Pt. Ag addition led to a complex change of activity and resistance to poisoning for Co-based perovskites. The activity of samples doped with a small amount of Ag (e.g. 5 mol%) was indeed even lower than that of the “pure” LaCoO3. By contrast, a further increase of Ag concentration led to increasing catalytic activity, mainly when extraframework Ag was present. Partial substitution of Ag for La in Mn-based perovskites led to increasing activity both for SG- and FP-prepared catalysts and the catalytic activity increased with increasing Ag substitution.
From the point of view of resistance against poisoning Sr and noble metals may be good protectors since they react more promptly with sulphur. Silver is not as effective from the point of view of protection against poisoning. The main advantage is the improved initial activity of some catalysts, which leads to satisfactory results even after more or less severe poisoning. A brief investigation of different poisoning agents (nitrogen-containing compounds) was also made. The transient response of the catalysts during the injection of poisons was also analyzed.
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Zhang, Hongxia. "Study of the effect of gold, platinum and vanadium oxide additives on the activity of TiO₂-ZrO₂ mixed oxide for the decomposition of CFC-22." HKBU Institutional Repository, 2002. http://repository.hkbu.edu.hk/etd_ra/367.
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Keenan, Matthew. "The influence of dopants on the surface properties of zirconia." Thesis, Nottingham Trent University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389703.
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Xu, Yin. "Preparation of noble metal free mixed oxides : applications to environmental catalysis." Thesis, Lille 1, 2019. http://www.theses.fr/2019LIL1R070.
Повний текст джерелаАнотація:
Dans un contexte politique et législatif favorisant l’utilisation de métaux abondants et non toxiques, différentes classes de catalyseurs à base de métaux de transition ont été développées puis évaluées pour deux réactions de dépollution : (i) l’ozonation catalytique pour l’élimination de polluants en phase aqueuse et (ii) l’oxydation catalytique de composés organiques volatils en phase gazeuse. Les oxydes de structure type spinel AB2O4 et les pérovskites possédant la formule générale ABO3 (où A et B sont des cations métalliques) sont des candidats intéressants de par leur innocuité et leur plus faible coût comparé aux métaux de la famille du platine. Par ailleurs, les propriétés versatiles de ces oxydes mixtes, telles que les nombreuses compositions possibles et leurs états de surface associés, ont démontré leur intérêt en catalyse hétérogène. Dans la première réaction concernant les procédés d’oxydation avancés, des oxydes mixtes de structure type spinel ont été étudiés pour agir comme catalyseur de dégradation de polluants organiques (AO7 et bisphénol A). Deux compositions, CuAl2O4 et CuFe2O4, ont été identifiés comme catalyseurs actifs pour l’activation de l’ozone et du peroxymonosulfate, précurseurs d’espèce radicalaires. La combinaison du cuivre avec l'aluminium ou avec le fer s’est révélée bénéfique pour former des radicaux réactifs à partir d’ozone ou de péroxymonosulfate, améliorant nettement la dégradation des polluants visés par rapport aux oxydes simples. Dans la seconde réaction impliquant l’oxydation catalytique du formaldéhyde en phase gazeuse, des pérovskites et des oxydes de manganèse ont été évalués. Une étude sur l’enrichissement en surface du métal de transition a été réalisée soit par traitement chimique via un lavage acide du précurseur pérovskite, soit par une approche de synthèse en sous-stœchiométrie employée lors de la préparation. Au regard des résultats expérimentaux, cet enrichissement permet d’exalter les propriétés catalytiques des solides pour l’élimination du formaldéhyde à basse température. Ces performances peuvent être reliées aux effets cumulés associés à la formation d’une morphologie contenant une porosité multiple suite au traitement chimique par voie acide, à l’augmentation significative de la surface spécifique et à l’augmentation de la densité des sites redox de surface mise en évidence par le suivi du couple Mn4+/Mn3+. Enfin, la promotion du support catalytique LaMnO3 par des métaux alcalins et alcalino-terreux a été réalisée (La0.8A0.2MnO3 avec A = K, Na, Sr, Ca). Basé sur les performances catalytiques à une température donnant une conversion de 50%, le dopage au potassium s’est révélé être le plus attractif (La0.8K0.2MnO3> La0.8Na0.2MnO3> La0.8Sr0.2MnO3> LaMnO3≈ La0.8Ca0.2MnO3≈ LMO-OH ≈ LMO-Na). Des vieillissements chimiques sous conditions humides et sèches ont par conséquent été réalisés sur les meilleurs catalyseurs afin d’évaluer leur robustesse. Malgré une conservation des propriétés texturales, une désactivation graduelle des pérovskites dopées (K, Na, Sr) a été observée et reliée à une perte d’espèces actives de surface et à une réduction du degré d’oxydation moyen du manganèseIn a political and legislative context promoting the use of abundant and non-toxic metals, different classes of transition metal catalysts have been developed and evaluated for two depollution reactions: (i) catalytic ozonation or activated persulfate for the elimination of pollutants containing nitrogen in the aqueous phase and (ii) the catalytic oxidation of volatile organic compounds in the gas phase. Structural spinel oxides AB2O4 and perovskites having the general formula ABO3 (where A and B are metal cations) are interesting candidates because of their safety and lower cost compared to platinum family metals. Moreover, the versatile properties of these mixed oxides, such as the numerous possible compositions and their associated surface states, have demonstrated their interest in heterogeneous catalysis. In the first reaction concerning advanced oxidation processes, spinel type mixed oxides have been studied to act as a degradation catalyst for organic pollutants (AO7 and bisphenol A). Two compositions, CuAl2O4 and CuFe2O4, have been isolated as active catalysts for the activation of ozone and peroxymonosulphate radical precursors. The combination of copper with aluminum or iron has been found to be beneficial in forming reactive radicals from ozone or peroxymonosulphate, significantly improving the degradation of targeted pollutants compared with simple oxides. In the second reaction involving the catalytic oxidation of formaldehyde in the gas phase, the perovskites and the manganese oxides were evaluated. A study dealing with the surface enrichment of the transition metal was carried out either by chemical treatment via acid washing of the perovskite precursor, or by a sub-stoechiometric approach used during the preparation. At the light of the experimental results, this enrichment improves drastically the elimination of formaldehyde towards low temperatures. These performances can be related to the cumulative effects associated with the formation of a morphology containing a multiple porosity following the acidic chemical treatment, the significant increase of the specific surface and the increase of the density of the surface redox sites highlighted by the Mn4 + / Mn3 + couple. Finally, the promotion of the catalytic support LaMnO3 by alkali and alkaline earth metals was carried out according to different conditions (La0.8A0.2MnO3 with A = K, Na, Sr, Ca). Based on the catalytic performances at a temperature giving a conversion of 50% of formaldehyde in CO2, potassium doping proved to be the most attractive doping agent (La0.8K0.2MnO3> La0.8Na0.2MnO3> La0.8Sr0.2MnO3> LaMnO3 = La0. 8Ca0.2MnO3= LMO-OH = LMO-Na). Chemical aging under wet and dry conditions has therefore been carried out on the best catalysts to evaluate their robustness. Despite a conservation of textural properties, a gradual deactivation of the doped perovskites (K, Na, Sr) was observed and related to a loss of surface active oxygen species and a reduction in the average degree of oxidation of manganese
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PENA, DONOVAN ALEXANDER. "DEVELOPMENT AND CHARACTERIZATION OF MIXED OXIDE CATALYSTS FOR THE SELECTIVE CATALYTIC REDUCTION OF NITRIC OXIDE FROM STATIONARY SOURCES USING AMMONIA." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1054307250.
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Pena, Donovan A. "Development and characterization of mixed oxide catalysts for the selective catlytic reduction of nitric oxide from stationary sources using amonnia." Cincinnati, Ohio : University of Cincinnati, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=1054307250.
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Penner, S., and H. Lorenz. "From Pure Oxides to Mixed Oxides: Model Systems for Structural and Catalytic Studies." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35049.
Повний текст джерелаАнотація:
As pure oxides and mixed oxide systems play an ever-increasing role in a variety of research fields ranging from catalysis over electrochemical applications to microelectronics, the present contribution aims at introducing a straightforward concept for the easy and reproducible preparation of well-defined and well-structured thin film model systems both for pure and mixed oxide systems. Exploiting the special structural and surface properties of vacuum-cleaved NaCl (001) growth templates, the concept is exempli-fied for the formation of nano-spheres (Ga2O3), nano-pyramids (In2O3), plates and needles (V2O5) and den-dritic structures (Ga2O3-WO3). Careful tuning of the preparation conditions (substrate temperature, depo-sition rate, oxygen partial pressure or post-annealing temperature) allows the formation of special particle morphologies at much lower substrate temperatures (less than 400°C) than previously and usually applied.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35049
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Can, Mukaddes. "Hydrogen Generation From Conventional Fuels Over Mesoporous Mixed Oxide Catalysts Under Time Interrupted Reaction Conditions." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12614520/index.pdf.
Повний текст джерелаАнотація:
In this study, catalytic activity of the Co and/or Pb-SBA-15 mesoporous catalysts in methane partial oxidation reaction was investigated. By using sol-gel, incipient wetness impregnation and post grafting method, SBA-15 samples are incorporated with Co and/or Pb at different weight loadings to provide a controlled geometry in nanometer scale. The characterization of the synthesized samples was done by XRD, N2 adsorption isotherms, FTIR, TEM images, Raman and XPS analysis. In the present study also, gas phase methane partial oxidation modeling and the synthesizing of mesoporous SBA-15 silica with different pore sizes were investigated.
For the samples prepared by sol-gel method, XRD analysis showedthat cobalt exists in the form of Co3O4and Pb exist in the form of PbO. BET surface areas of the Co loaded catalysts are in the range of 479.5-640.1 m2/g. However, in Pb loaded samples, higher metal loading decrease the surface area up to 4.63 m2/g. Considering the both Co and Pb containing bi-metallic samples, TEM and BET results revealed that the ordered hexagonal mesostructure was fully destroyed.
The samples prepared by incipient wetness impregnation and post grafting method characterized by using BET, TEM, Raman and XPS analysis. According to the BET results all the samples show ordered mesostructure in agreement with TEM results for all Co and/or SBA-15 mesoporous samples. TEM results also revealed that, the Co(5%) Pb(5%)-SBA-15 catalyst prepared by incipient wetness impregnation method possess big cobalt and lead oxide crystallines on the mesoporous structure. Raman analysis results indicated that cobalt exist in Co3O4 form. According to XPS results all samples containing cobalt include Co3O4.
The partial oxidation of methane was carried out in a fixed bed flow-type reactor in a temperature range of 50&ndash850°
C under atmospheric pressure.According to the reaction test results, the 0.5%Rh-Co-SBA15 catalyst shows the highest methane conversion (82%) and H2 selectivity. The non-precious metal show lower reactivities, addition of Pb to the Co-SBA-15 catalyst increases the catalytic activity and decrease the H2 production temperature.
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YUAN, LI. "MESOPOROUS AND MACROPOROUS MIXED METAL OXIDE MoVTeNbO xCATALYSTS FOR PROPANE (amm) OXIDATION." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1199297348.
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ABOU, MRAD CHAFIC. "Synthese du methanol et d'alcools superieurs sur catalyseurs cuo-zno modifies." Université Louis Pasteur (Strasbourg) (1971-2008), 1987. http://www.theses.fr/1987STR13200.
Повний текст джерелаАнотація:
Mise au point sur la synthese du methanol en presence de cuo-zno et mise en evidence de l'influence du pretraitement et de l'effet benefique des promoteurs(cao,tho::(2),al::(2)o::(3), zro::(2),bao et sro)
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Rödel, Eva. "In situ bulk structural investigation of Mo5O14-type mixed metal oxide catalysts for partial oxidation reactions." [S.l.] : [s.n.], 2006. http://opus.kobv.de/tuberlin/volltexte/2007/1473.
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Ferrandon, Magali. "Mixed metal oxide - noble metal catalysts for total oxidation of volatile organic compounds and carbon monoxide." Doctoral thesis, Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3156.
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Kolli, T. (Tanja). "Pd/Al2O3 -based automotive exhaust gas catalysts:the effect of BaO and OSC material on NOx reduction." Doctoral thesis, University of Oulu, 2006. http://urn.fi/urn:isbn:9514280563.
Повний текст джерелаАнотація:
Abstract
The aim of the thesis was to find new information on the effect of BaO and oxygen storage capacity material on NOx reduction. A total of nine different kinds of Pd/Al2O3-based metallic monoliths were studied. Promoters such as oxygen storage capacity material (OSC material in our case Cex-1ZrxO2 mixed oxides) and stabilisers such as barium (BaO) were added into the catalyst alone or together to improve catalyst properties such as catalytic activity, selectivity, and thermal stability.
The key aspects in this thesis can be divided into four parts. First, the behaviour of NO reduction and CO as well as C2H4 oxidation over Pd/Al2O3-based catalysts in rich, stoichiometric and lean conditions were studied. Secondly, the effect of BaO and the OSC material in NO reduction was considered. Thirdly, the preparation procedure, i.e. the addition order of BaO, OSC material, and Pd on the catalyst was considered. Finally, the effect of ageing on the behaviour of catalysts was investigated.
Several characterization methods (in situ DRIFT, catalytic activity measurements, N2 physisorption, CO chemisorption, dynamic oxygen storage capacity measurements, and X-ray diffraction (XRD)) were utilised to find answers to the behaviour of these catalysts in the studied model reactions. The Rapid Ageing Hot in Laboratory (RAHLAB) method was used to age the catalyst.
First, it was demonstrated that the CO and hydrocarbon oxidation and NO reduction reactions over the Pd/Al2O3-based catalyst behave differently. NO reduction and CO and hydrocarbon oxidation reactions were dependent on the reaction conditions and temperatures. Secondly, the effect of OSC and BaO on NO reduction was studied separately. In the case of OSC material, it was observed that the OSC material has an effect on NO reduction as well as on CO and C2H4 oxidation. In the case of BaO, it was observed that BaO has a positive effect on NO reduction as well as CO and C2H4 oxidation especially in rich conditions. Thirdly, the effects of the addition order of OSC and BaO on the catalyst was studied separately. It was shown that these have an effect on NO reduction, especially after ageing. First, on the fresh Pd/Al2O3 catalyst it was observed that the addition order of OSC on the catalyst has not an influence on catalyst performance. The effect of the BaO addition order on the Pd/OSC/Al2O3-based catalyst is found to be insignificant, especially, after the ageing process. Furthermore, it is observed that the effect of RAHLAB ageing was that the catalyst lost its catalytic activity, stability, and selectivity.
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Baker, John Edward. "An investigation of the factors affecting Cu/Co/Zn/Al mixed oxide catalysts for the formation of higher alcohols from syngas." Thesis, University of Reading, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254181.
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Beale, Andrew Michael. "Novel low temperature preparation methods for mixed complex oxide catalysts and their characterisation via in situ SR techniques." Thesis, University College London (University of London), 2003. http://discovery.ucl.ac.uk/1453143/.
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Chen, Luqian. "High throughput preparation and testing of SbMoVNb mixed oxide catalysts for selective oxidation of propane to acrylic acid." Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250441.
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BHATT, SALIL R. "SYNTHESIS, CHARACTERIZATION AND KINETIC STUDIES OF MIXED METAL Mo-V-Nb-Te OXIDE CATALYSTS FOR PROPANE AMMOXIDATION TO ACRYLONITRILE." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1140626212.
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Novakova, Ekaterina Krasteva. "Catalytic studies of propane oxidation to acrylic acid on Mo-V-Sb-Nb mixed oxides catalysts." Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250417.
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Velasquez, Ochoa Juliana <1984>. "New Insights on the Mechanism of Interaction Between Light (bio) Alcohols and Metallic Mixed Oxides Catalysts." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7404/1/VelasquezOchoa_Juliana_Tesi.pdf.
Повний текст джерелаАнотація:
This research intends to explore the mechanism behind the transformation of ethanol over basic and acid/base catalysts. The approach used was first to explore in depth the role of the MgO which is a common component of both reactions (Lebedev and Guerbet) and then to study the incorporation of Si ion and the effect on the acid/base properties of the resulting materials. Moreover, the addition of a dopant with acid/dehydrogenating properties was also explored. Further on, several catalysts were tested under the usual conditions for this reaction and characterization was made in order to understand their particular behavior. An important tool in this research was the in-situ infrared diffuse reflectance spectroscopy (DRIFTS) coupled with mass spectrometry (MS) due to the possibility that it offers to study what occurs on the catalysts surface under real working conditions. This study allowed to gain new insights on the mechanism behind the catalytic upgrading of ethanol on basic and acid/base mixed oxides, giving an alternative view of the mechanism for the Lebedev and Guerbet reactions that permitted us to discard the key role of the generally accepted intermediates and helped to explain several experimental findings not clear before.