Bridging the Gap between CO Adsorption Studies on Gold Model Surfaces and Supported Nanoparticles

A happy medium: Volumetric adsorption of carbon monoxide at 308 K and UHR-HAADF-STEM, HREM, and computer modeling techniques were compared. Experimental CO/Au ratios at saturation coverage for two supported gold catalysts were shown to fit very well the predictions of a nanostructural model that considers CO adsorption on gold sites with coordination numbers of less than eight.

Aqueous phase reforming of xylitol over Pt-Re bimetallic catalyst: Effect of the Re addition

The aqueous phase reforming (APR) of xylitol was studied in a continuous fixed bed reactor over three catalysts: Pt/Al2O3, Pt/TiO2 and Pt-Re/TiO2. The data obtained in the case of the monometallic Pt catalysts was compared to the bimetallic Pt-Re sample. The effect of Re addition on the catalyst stability, activity, product formation and selectivity toward hydrogen and alkanes was studied. The bimetallic catalyst demonstrated a higher selectivity to alkanes compared to the monometallic samples. The monometallic catalyst was more selective toward hydrogen formation. A plausible reaction scheme explaining differences in selectivity toward hydrogen and alkanes was proposed and discussed.

Studies on Catalysis by Vanadia Supported On Metal Oxides

Catalysis is an essential technology in manufacturing industries. The investigation based on supported vanadia catalysts and it’s sulfated analogues. Vanadia is a transition metal oxide and is used in oxidation reactions in chemical industry. It is more active and selective catalysts on suitable supports. The work deals with preparation of vanadia incorporated tin oxide and zirconia systems by wet impregnation. Physico-chemical characterization using instrumental techniques like BET etc. The surface acidic properties were determined by the ammonia TPD studies, Perylene absorption studies and Cumene conversion reaction. The catalytic activities of the prepared systems are tested by Friedel-Crafts benzylation of arenes and Bechmann rearrangement of Cyclohexanol oxime. Here the rector reactions are relatively rare. So to test the application of the catalyst systems for the selective oxidation of cyclohexanol to cyclohexanone and finally evaluate the catalytic activity of the systems for the vapour phase oxidative dehydrogenation of Ethylbenzene, which leads to the formation of Industrially important compound ‘styrene’ is another objective of this work

Structural and catalytic investigation of vanadia supported on ceria promoted with high surface area rice husk silica

Rice husk silica was utilized as the promoter of ceria for preparing supported vanadia catalysts. Effect of vanadium content was investigated with 2–10 wt.% V2O5 loading over the support. Structural characterization of the catalysts was done by various techniques like energy dispersive X-ray (EDX), X-ray diffraction (XRD), BET surface area, thermal analysis (TGA/DTA), FT-infrared spectroscopy (FT-IR), UV–vis diffused reflectance spectroscopy (DR UV–vis), electron paramagnetic spectroscopy (EPR) and solid state magnetic resonance spectroscopies (29Si and 51V MASNMR). Catalytic activity was studied towards liquid-phase oxidation of benzene. Surface area of ceria enhanced upon rice husk silica promotion, thus makes dispersion of the active sites of vanadia easier. Highly dispersed vanadia was found for low V2O5 loading and formation of cerium orthovanadate (CeVO4) occurs as the loading increases. Spectroscopic investigation clearly confirms the formation of CeVO4 phase at higher loadings of V2O5. The oxidation activity increases with vanadia loading up to 8 wt.% V2O5, and further increase reduces the conversion rate. Selective formation of phenol can be attributed to the presence of highly dispersed active sites of vanadia over the support.

Influence of surface and acid properties of vanadia supported on ceria promoted with rice husk silica on cyclohexanol decomposition

Cyclohexanol decomposition activity of supported vanadia catalysts is ascribed to the high surface area, total acidity and interaction between supported vanadia and the amorphous support. Among the supported catalysts, the effect of vanadia over various wt% V2O5 (2–10) loading indicates that the catalyst comprising of 6 wt% V2O5 exhibits higher acidity and decomposition activity. Structural characterization of the catalysts has been done by techniques like energy dispersive X-ray analysis, X-ray diffraction and BET surface area. Acidity of the catalysts has been measured by temperature programmed desorption using ammonia as a probe molecule and the results have been correlated with the activity of catalysts.

Production of hydrogen via steam reforming of biofuels on Ni/CeO(2)-Al(2)O(3) catalysts promoted by noble metals

The catalytic activity of Ni/CeO(2)-Al(2)O(3) catalysts modified with noble metals (Pt, Ir, Pd and Ru) was investigated for the steam reform of ethanol and glycerol. The catalysts were characterized by the following techniques: Energy-dispersive X-ray, BET, X-ray diffraction, temperature-programmed reduction, UV-vis diffuse reflectance spectroscopy and X-ray absorption near edge structure (XANES). The results showed that the formation of inactive nickel aluminate was prevented by the presence of CeO(2) dispersed on alumina. The promoting effect of noble metals included a decrease in the reduction temperatures of NiO species interacting with the support, due to the hydrogen spillover effect. It was seen that the addition of noble metal stabilized the Ni sites in the reduced state along the reforming reaction, increasing the ethanol and glycerol conversions and decreasing the coke formation. The higher catalytic performance for the ethanol steam reforming at 600 degrees C and glycerol steam reforming was obtained for the NiPd and NiPt catalysts, respectively, which presented an effluent gaseous mixture with the highest H(2) yield with reasonably low amounts of CO. (c) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Production of hydrogen by ethanol steam reforming on Co/Al2O3 catalysts: Effect of addition of small quantities of noble metals

The catalytic performance of Co/Al2O3 catalysts promoted with small amounts noble metals (Pt, Pd, Ru, Ir) for steam reforming of ethanol (SRE) has been investigated. The catalysts were characterized by the energy dispersive X-ray, X-ray diffraction, BET surface area, X-ray absorption fine structure and temperature reduction programmed techniques. The results showed that the promoting effect of noble metals included a marked decrease of the reduction temperatures of both Co3O4 and cobalt surface species interacting with the support due to the hydrogen spillover effect, leading to a significant increase of the reducibilities of the promoted catalysts. The better catalytic performance for the ethanol steam reforming at 400 degrees C was obtained for the CoRu/Al2O3 catalyst, which presented an effluent gaseous mixture with the highest H, selectivity and the reasonable low CO formation. (C) 2007 Published by Elsevier B.V.

Reduction of NO by CO on Cu/ZrO(2)/Al(2)O(3) catalysts: Characterization and catalytic activities

ZrO(2), gamma-Al(2)O(3) and ZrO(2)/gamma-Al(2)O(3)-supported copper catalysts have been prepared, each with three different copper loads (1, 2 and 5 wt%), by the impregnation method. The catalysts were characterized by nitrogen adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) with H(2), Raman spectroscopy and electronic paramagnetic resonance (EPR). The reduction of NO by CO was studied in a fixed-bed reactor packed with these catalysts and fed with a mixture of 1% CO and 1% NO in helium. The catalyst with 5 wt% copper supported on the ZrO(2)/gamma-Al(2)O(3) matrix achieved 80% reduction of NO. Approximately the same rate of conversion was obtained on the catalyst with 2 wt% copper on ZrO(2). Characterization of these catalysts indicated that the active copper species for the reduction of NO are those in direct contact with the oxygen vacancies found in ZrO(2). (C) 2009 Published by Elsevier Ltd.

Carbon dioxide reforming of ethanol over Ni/Y(2)O(3)-ZrO(2) catalysts

Supported nickel catalysts of composition Ni/Y(2)O(3)-ZrO(2) were synthesized in one step by the polymerization method and compared with a nickel catalyst prepared by wet impregnation. Stronger interactions were observed in the formed catalysts between NiO species and the oxygen vacancies of the Y(2)O(3)-ZrO(2) in the catalysts made by polymerization, and these were attributed to less agglomeration of the NiO during the synthesis of the catalysts in one step. The dry reforming of ethanol was catalyzed with a maximum CO(2) conversion of 61% on the 5NiYZ catalyst at 800 degrees C, representing a better response than for the catalyst of the same composition prepared by wet impregnation. (C) 2009 Published by Elsevier B.V.

Electrocatalysis on noble metal and noble metal alloys dispersed on high surface area carbon

In this work, a simple route to prepare carbon supported Pt/C, Pt:Ru/C, Pt:Mo/C and Pt:Ru:Mo/C catalysts is reported. The electrochemical properties of the several carbon materials used as substrates in the absence and in the presence of supported platinum and platinum alloys catalysts were investigated using cyclic voltammetry and employing the thin porous coating electrode technique. The activity of the dispersed catalysts composed of Pt/C with respect to the oxygen reduction and of alloy/C with respect to methanol oxidation was investigated using steady state polarization measurements. The performance with respect to the oxygen reduction reaction of the Pt/C catalyst prepared on heat-treated Vulcan carbon substrate is equivalent to that reported in the literature for the state-of-the-art electrocatysts. Pt:Ru:Mo/C samples prepared in this work presented the higher catalytic effect for methanol electro-oxidation.

Influence of support on catalytic behavior of nickel catalysts in the steam reforming of ethanol for hydrogen production

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Preparation, structural characterization and catalytic properties of Co/CeO2 catalysts for the steam reforming of ethanol and hydrogen production

In this paper, Co/CeO2 catalysts, with different cobalt contents were prepared by the polymeric precursor method and were evaluated for the steam reforming of ethanol. The catalysts were characterized by N-2 physisorption (BET method), X-ray diffraction (XRD), UV-visible diffuse reflectance, temperature programmed reduction analysis (TPR) and field emission scanning electron microscopy (FEG-SEM). It was observed that the catalytic behavior could be influenced by the experimental conditions and the nature of the catalyst employed. Physical-chemical characterizations revealed that the cobalt content of the catalyst influences the metal-support interaction which results in distinct catalyst performances. The catalyst with the highest cobalt content showed the best performance among the catalysts tested, exhibiting complete ethanol conversion, hydrogen selectivity close to 66% and good stability at a reaction temperature of 600 degrees C. (c) 2012 Elsevier B.V. All rights reserved.

EFFECTS OF ADDING LANTHANUM TO Ni/ZrO2 CATALYSTS ON ETHANOL STEAM REFORMING

EFFECTS OF ADDING LANTHANUM TO Ni/ZrO2 CATALYSTS ON ETHANOL STEAM REFORMING. The catalytic performance of Ni/ZrO2 catalysts loaded with different lanthanum content for steam reforming of ethanol was investigated. Catalysts were characterized by BET surface area, X-ray diffraction, UV-vis spectroscopy, temperature programmed reduction, and X-ray absorption fine structure techniques. Results showed that lanthanum addition led to an increase in the degree of reduction of both NiO and nickel surface species interacting; with the support, due to the higher dispersion effect. The best catalytic performance at 450 degrees C was found for the Ni/2LZ catalyst, which exhibited an effluent gaseous mixture with the highest H-2 yield.

Structural changes and dynamic behaviour of vanadium oxide-based catalysts for gas-phase selective oxidations

Selective oxidation is one of the simplest functionalization methods and essentially all monomers used in manufacturing artificial fibers and plastics are obtained by catalytic oxidation processes. Formally, oxidation is considered as an increase in the oxidation number of the carbon atoms, then reactions such as dehydrogenation, ammoxidation, cyclization or chlorination are all oxidation reactions. In this field, most of processes for the synthesis of important chemicals used vanadium oxide-based catalysts. These catalytic systems are used either in the form of multicomponent mixed oxides and oxysalts, e.g., in the oxidation of n-butane (V/P/O) and of benzene (supported V/Mo/O) to maleic anhydride, or in the form of supported metal oxide, e.g., in the manufacture of phthalic anhydride by o-xylene oxidation, of sulphuric acid by oxidation of SO2, in the reduction of NOx with ammonia and in the ammoxidation of alkyl aromatics. In addition, supported vanadia catalysts have also been investigated for the oxidative dehydrogenation of alkanes to olefins , oxidation of pentane to maleic anhydride and the selective oxidation of methanol to formaldehyde or methyl formate [1]. During my PhD I focused my work on two gas phase selective oxidation reactions. The work was done at the Department of Industrial Chemistry and Materials (University of Bologna) in collaboration with Polynt SpA. Polynt is a leader company in the development, production and marketing of catalysts for gas-phase oxidation. In particular, I studied the catalytic system for n-butane oxidation to maleic anhydride (fluid bed technology) and for o-xylene oxidation to phthalic anhydride. Both reactions are catalyzed by systems based on vanadium, but catalysts are completely different. Part A is dedicated to the study of V/P/O catalyst for n-butane selective oxidation, while in the Part B the results of an investigation on TiO2-supported V2O5, catalyst for o-xylene oxidation are showed. In Part A, a general introduction about the importance of maleic anhydride, its uses, the industrial processes and the catalytic system are reported. The reaction is the only industrial direct oxidation of paraffins to a chemical intermediate. It is produced by n-butane oxidation either using fixed bed and fluid bed technology; in both cases the catalyst is the vanadyl pyrophosphate (VPP). Notwithstanding the good performances, the yield value didn’t exceed 60% and the system is continuously studied to improve activity and selectivity. The main open problem is the understanding of the real active phase working under reaction conditions. Several articles deal with the role of different crystalline and/or amorphous vanadium/phosphorous (VPO) compounds. In all cases, bulk VPP is assumed to constitute the core of the active phase, while two different hypotheses have been formulated concerning the catalytic surface. In one case the development of surface amorphous layers that play a direct role in the reaction is described, in the second case specific planes of crystalline VPP are assumed to contribute to the reaction pattern, and the redox process occurs reversibly between VPP and VOPO4. Both hypotheses are supported also by in-situ characterization techniques, but the experiments were performed with different catalysts and probably under slightly different working conditions. Due to complexity of the system, these differences could be the cause of the contradictions present in literature. Supposing that a key role could be played by P/V ratio, I prepared, characterized and tested two samples with different P/V ratio. Transformation occurring on catalytic surfaces under different conditions of temperature and gas-phase composition were studied by means of in-situ Raman spectroscopy, trying to investigate the changes that VPP undergoes during reaction. The goal is to understand which kind of compound constituting the catalyst surface is the most active and selective for butane oxidation reaction, and also which features the catalyst should possess to ensure the development of this surface (e.g. catalyst composition). On the basis of results from this study, it could be possible to project a new catalyst more active and selective with respect to the present ones. In fact, the second topic investigated is the possibility to reproduce the surface active layer of VPP onto a support. In general, supportation is a way to improve mechanical features of the catalysts and to overcome problems such as possible development of local hot spot temperatures, which could cause a decrease of selectivity at high conversion, and high costs of catalyst. In literature it is possible to find different works dealing with the development of supported catalysts, but in general intrinsic characteristics of VPP are worsened due to the chemical interaction between active phase and support. Moreover all these works deal with the supportation of VPP; on the contrary, my work is an attempt to build-up a V/P/O active layer on the surface of a zirconia support by thermal treatment of a precursor obtained by impregnation of a V5+ salt and of H3PO4. In-situ Raman analysis during the thermal treatment, as well as reactivity tests are used to investigate the parameters that may influence the generation of the active phase. Part B is devoted to the study of o-xylene oxidation of phthalic anhydride; industrially, the reaction is carried out in gas-phase using as catalysts a supported system formed by V2O5 on TiO2. The V/Ti/O system is quite complex; different vanadium species could be present on the titania surface, as a function of the vanadium content and of the titania surface area: (i) V species which is chemically bound to the support via oxo bridges (isolated V in octahedral or tetrahedral coordination, depending on the hydration degree), (ii) a polymeric species spread over titania, and (iii) bulk vanadium oxide, either amorphous or crystalline. The different species could have different catalytic properties therefore changing the relative amount of V species can be a way to optimize the catalytic performances of the system. For this reason, samples containing increasing amount of vanadium were prepared and tested in the oxidation of o-xylene, with the aim of find a correlations between V/Ti/O catalytic activity and the amount of the different vanadium species. The second part deals with the role of a gas-phase promoter. Catalytic surface can change under working conditions; the high temperatures and a different gas-phase composition could have an effect also on the formation of different V species. Furthermore, in the industrial practice, the vanadium oxide-based catalysts need the addition of gas-phase promoters in the feed stream, that although do not have a direct role in the reaction stoichiometry, when present leads to considerable improvement of catalytic performance. Starting point of my investigation is the possibility that steam, a component always present in oxidation reactions environment, could cause changes in the nature of catalytic surface under reaction conditions. For this reason, the dynamic phenomena occurring at the surface of a 7wt% V2O5 on TiO2 catalyst in the presence of steam is investigated by means of Raman spectroscopy. Moreover a correlation between the amount of the different vanadium species and catalytic performances have been searched. Finally, the role of dopants has been studied. The industrial V/Ti/O system contains several dopants; the nature and the relative amount of promoters may vary depending on catalyst supplier and on the technology employed for the process, either a single-bed or a multi-layer catalytic fixed-bed. Promoters have a quite remarkable effect on both activity and selectivity to phthalic anhydride. Their role is crucial, and the proper control of the relative amount of each component is fundamental for the process performance. Furthermore, it can not be excluded that the same promoter may play different role depending on reaction conditions (T, composition of gas phase..). The reaction network of phthalic anhydride formation is very complex and includes several parallel and consecutive reactions; for this reason a proper understanding of the role of each dopant cannot be separated from the analysis of the reaction scheme. One of the most important promoters at industrial level, which is always present in the catalytic formulations is Cs. It is known that Cs plays an important role on selectivity to phthalic anhydride, but the reasons of this phenomenon are not really clear. Therefore the effect of Cs on the reaction scheme has been investigated at two different temperature with the aim of evidencing in which step of the reaction network this promoter plays its role.

Development of innovative catalysts for the hydrodechlorination to fluoroethers

In this work the hydrodechlorination of CF3OCFClCF2Cl to produce unsaturated CF3OCF=CF2 was studied over a series of supported metal catalysts. Currently this molecule is produced from the precursor CF3OCFClCF2Cl by dechlorination with zinc powder. An important cost on the economic and environmental balance is represents by the large amount of ZnCl2 produced and to be disposed of. A new approach, based on gas-phase hydrodechlorination over supported catalysts can lead to a new sustainable process. During the feasibility step of this project, substantially two kind of materials were studied: metals supported over activated carbon and Pd/Cu species supported over MCM-41 mesoporous silica. Observed catalytic performances were strongly dependent on the metal and support used. All carbon-supported Ru, Pd, and bimetallic catalysts are fairly active and yielded the target product CF3OCF=CF2, the higher selectivity being obtained with ruthenium- and palladium-based materials. Nevertheless, Ru-based catalysts showed poor stability and this deactivation may be attributed to the deposition of chlorinated organic species blocking the active sites. On the other hand, palladium-containing catalysts showed high stability. Ru/Pd and Pd/Cu bimetallic catalysts exhibited long-term selectivity and stability, highlighting the possibility for these materials to be employed in the CF3OCF=CF2 production process. During the second part of this thesis, a series of bimetallic meso-structured Pd/Cu MCM-41 catalysts were studies to overcome possible mass transfer limitations. The materials were obtained by different synthesis methods. The incorporation of Pd and Cu during MCM-41 synthesis, did not destroy the typical hexagonal array and ordered pore system of MCM-41. However, the calcination for the removal of the template provoked significant segregation of oxides. The impregnation leads to pore-occlusion and formation of Cu particles and large bimetallic PdCu species. Larger metal particles leads to lower CF3OCFClCF2Cl conversion, while the monometallic particles can decrease the selectivity to CF3OCF=CF2, fostering the dehalogenation to CF3OCH=CF2.