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Co-precipitated NiAl and NiMgAl layered double hydroxides (LDHs) were prepared at M2+/Al3+ molar ratio of 2.5/1 and subsequently promoted with gold targeting to be studied as catalysts and supports of gold particles in the hydrogen production via water-gas shift (WGS) reaction. Powder X-ray diffraction and N2 physisorption before and after WGS tests were applied to investigate the impacts of Mg and Au on the structure and catalytic behavior of the systems. Partial replacement of Ni by Mg resulted in moderate activity of NiMgAl and Au/NiMgAl catalysts than NiAl analogues due to: (i) smaller Ni amount that could not supply sufficient number catalytically active sites; (ii) higher thermal stability leading to the creation of the active Ni species at higher temperatures, and (iii) partial regeneration of the layered structure with the assistance of small Au particles, Mg, and the reaction medium as well. Favorable role of gold on Au/NiAl WGS activity was elucidated.

The demands for high-purity hydrogen required in fuel-cell applications impose new goals and challenges for design of well performing water-gas shift (WGS) catalysts. Gold-based catalysts have exhibited high activity in the WGS reaction at low temperature. Preparation of appropriate and economically viable supports with complex composition by various synthesis procedures is an attractive approach to WGS performance improvement. The effect of two different preparation methods (wet impregnation or mechanical mixing) and ceria content (10, 20 or 30 wt%) on textural, structural, surface and reductive properties and WGS activity of gold catalysts was studied. Additionally, the role of Y2O3 as a promoter of ceria was examined. Long-term stability test was carried out at 260 °C over the most active catalyst. The composition of the best performing sample (composed of about 70 wt% alumina), prepared by mechanical mixing, was considered promising in case of practical applications because of its cost efficiency. The combination of gold nanoparticles and alumina supported Y-doped ceria proved an advantageous approach for developing new catalytic formulations with high effectiveness in clean hydrogen production.

Three samples of NiAl layered double hydroxides with takovite-like structure were prepared by a co-precipitation method at Ni2+/Al3+ molar ratios of 1.5, 2.5 and 4.0. The samples were investigated as catalysts for hydrogen production by means of water–gas shift reaction (WGSR). The properties and catalytic behavior of the unmodified as-synthesized materials are compared with those of the same materials used as a support on which gold particles have been deposited. All samples were characterized by N2 physisorption, Powder X-ray diffraction (PXRD), and X-ray photoelectron spectroscopy (XPS) techniques. Catalytic activity of all materials was studied towards conversion of CO at atmospheric pressure within the temperature interval 140–300 °C. The dependence of WGS activity on the Ni2+/Al3+ molar ratio and the presence of gold were investigated. The promotional role of Au on the WGS performance was clearly demonstrated by Au–NiAl2.5 catalyst, which reached equilibrium conversion value of 97.6% at 240 °C. The stability test of the most active Au–NiAl2.5 catalyst resulted in the same CO conversion degree within 32 h under stream at 260 °C. A plausible scheme for the reaction mechanism, including the redox Ni2+ ↔ Ni3+ transition on the catalyst surface as well as adsorption and activation of the CO molecule on the Au particles, is proposed.

Supported gold on co-precipitated nanosized NiAl layered double hydroxides (LDHs) was studied as an effective catalyst for medium-temperature water–gas shift (WGS) reaction, an industrial catalytic process traditionally applied for the reduction in the amount of CO in the synthesis gas and production of pure hydrogen. The motivation of the present study was to improve the performance of the Au/NiAl catalyst via modification by CeO2. An innovative approach for the direct deposition of ceria (1, 3 or 5 wt.%) on NiAl-LDH, based on the precipitation of Ce3+ ions with 1M NaOH, was developed. The proposed method allows us to obtain the CeO2 phase and to preserve the NiAl layered structure by avoiding the calcination treatment. The synthesis of Au-containing samples was performed through the deposition–precipitation method. The as-prepared and WGS-tested samples were characterized by X-ray powder diffraction, N2-physisorption and X-ray photoelectron spectroscopy in order to clarify the effects of Au and CeO2 loading on the structure, phase composition, textural and electronic properties and activity of the catalysts. The reduction behavior of the studied samples was evaluated by temperature-programmed reduction. The WGS performance of Au/NiAl catalysts was significantly affected by the addition of CeO2. A favorable role of ceria was revealed by comparison of CO conversion degree at 220 °C reached by 3 wt.% CeO2-modified and ceria-free Au/NiAl samples (98.8 and 83.4%, respectively). It can be stated that tuning the properties of Au/NiAl LDH via CeO2 addition offers catalysts with possibilities for practical application owing to innovative synthesis and improved WGS performance.

Considerable efforts to reduce the harmful emissions of volatile organic compounds (VOCs) have been directed towards the development of highly active and economically viable catalytic materials for complete hydrocarbon oxidation. The present study is focused on the complete benzene oxidation as a probe reaction for VOCs abatement over Co3O4-CeO2 mixed oxides (20, 30, and 40 wt.% of ceria) synthesized by the more sustainable, in terms of less waste, less energy and less hazard, mechanochemical mixing of cerium hydroxide and cobalt hydroxycarbonate precursors. The catalysts were characterized by BET, powder XRD, H2-TPR, UV resonance Raman spectroscopy, and XPS techniques. The mixed oxides exhibited superior catalytic activity in comparison with Co3O4, thus, confirming the promotional role of ceria. The close interaction between Co3O4 and CeO2 phases, induced by mechanochemical treatment, led to strained Co3O4 and CeO2 surface structures. The most significant surface defectiveness was attained for 70 wt.% Co3O4-30 wt.% CeO2. A trend of the highest surface amount of Co3+, Ce3+ and adsorbed oxygen species was evidenced for the sample with this optimal composition. The catalyst exhibited the best performance and 100% benzene conversion was reached at 200 °C (relatively low temperature for noble metal-free oxide catalysts). The catalytic activity at 200 °C was stable without any products of incomplete benzene oxidation. The results showed promising catalytic properties for effective VOCs elimination over low-cost Co3O4-CeO2 mixed oxides synthesized by simple and eco-friendly mechanochemical mixing.

The protection of environment and human health stimulates intensive research for abatement of volatile organic compounds (VOCs) in the atmosphere. Complete catalytic oxidation is an efficient, environmentally friendly and economically feasible method for elimination of VOCs. This study aims to design high performing and cost-effective catalytic formulations by exploration of appropriate and economically viable supports. Alumina-supported ceria (30 wt.%) and Y2O3 (1 wt.%)-doped ceria were prepared by mechanical mixing and were used as support of mono Au (2 wt.%) and Pd (1 wt.%) and bimetallic Pd-Au catalysts. The characterization by textural measurements, X-ray powder diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), EPR (electron paramagnetic resonance) and temperature-programmed reduction (TPR) was carried out in order to clarify the relationship between catalyst composition, textural, structural and surface properties, reducibility and catalytic performance for complete benzene oxidation. Among all studied catalysts, Pd-based catalysts exhibited the best combustion activity. In particular, monometallic Pd on alumina supported Y-doped ceria attained 100% of complete benzene conversion at 180 &deg, C. These catalytic materials have potential to meet stringent emission regulations in an economical and effective way.

The present work investigates the photocatalytical abatement of trichlorethylene (TCE) under simulated solar irradiation (AM 1.5). The employed catalytic materials, Au and Pd–Au nanoparticles supported on TiO2, were prepared by incipient wetness and by deposition–precipitation methods. It is found out that TCE is converted efficiently (>80%) to Cl− and CO2 over all scrutinized catalysts. Typically, the metal addition enhances to some extent the photooxidation activity of TiO2 via photogenerated OH radicals, electrons, and holes. The photocatalytic abatement of TCE over the same catalytic materials was examined in the presence of small amount of methanol. The idea was to convert TCE to Cl− and C2 (ethane and ethylene) over Au and Pd–Au/TiO2 catalysts by the H2 generated photocatalytically in situ. The experimental results evidenced that, over Pd–Au/TiO2 catalysts, hydrodechlorination (HDC) and photomineralization reactions of TCE occurs simultaneously. In contrast, Au/TiO2 is inactive to catalyze the hydrogenation of TCE. The results of TCE abatement by combined photooxidation/HDC reactions in presence of methanol are corroborated with H2 photocatalytic generation results, over the same catalytic materials, from water/methanol mixture. A reaction mechanism is advanced in light of experimental results. The photogenerated OH radicals, electrons, and holes participate in a complex reaction pathway to formation of oxygenated organic intermediates, Cl−, CO2, and H2.

Gold catalysts on CeO/AlO and Y-doped CeO/AlO supports (20 wt.% CeO and 1 wt.% YO) were synthesized. The mixed oxide supports were prepared by impregnation (IM) or by mechanical mixing (MM). The samples were characterised by BET, XRD and HRTEM/HAADF measurements. The catalytic properties in the preferential CO oxidation in hydrogen rich stream (PROX) using gas feed composition: 60% H+ 1% CO + 1% O (He as balance) were estimated. The effect of supports preparation on the gold loading and its dispersion, supports features and catalytic performance was commented. The positive effect of yttrium for catalysts stability was evidenced during long run tests in PROX with CO and water addition to gas stream. The obtained results could be useful for the design of catalysts for CO-free hydrogen production with good PROX performance at reasonable price.

The utilization of pure hydrogen as an energy source in fuel cells gave rise to renewed interest in developing active and stable water-gas shift catalysts. Gold catalysts have proven to be very efficient for water-gas shift reaction at low temperature. The aim of the present study was to investigate the effect of: (i) different preparation methods (impregnation and coprecipitation) to obtain a modified ceria support, and (ii) the amount of Y2O3 (1.0 wt%, 2.5 wt%, 5.0 wt% and 7.5 wt%) as dopant on the water-gas shift activity of Au/CeO2 catalysts. An extended characterization by means of SBET, XRD, HRTEM/HAADF, FTIR, H2-TPR and CO-TPR measurements in combination with careful evaluation of the catalyst behavior allowed to shed light on the parameters governing the water-gas shift activity. The catalysts show very high activity (>90% CO conversion) in the temperature range 180–220 °C, with a slightly better performance of the gold catalysts on supports prepared by impregnation. The decreased activity with increasing Y2O3 concentration is related to the hindering of oxygen mobility due to ordering of surface oxygen vacancies in vicinity of segregated Y3+. The effect of catalyst pre-treatments and the stability of the best performing samples were examined as well.

Alumina supported Cu–Mn mixed oxide with Cu/Mn molar ratio 2:1 was used as a support of gold and silver catalysts for oxidation of CO, methanol and dimethylether. Different techniques (XRD, HRTEM, XPS, FTIR, EPR, and TPR) were used to investigate structure–reactivity relationship. A strong effect of the nature of the promoters on the catalytic behaviour was observed. Superior catalytic activity in oxidation of CO was measured after addition of Au, while modification by Ag affected very slightly the CO oxidation activity of Cu/Mn 2:1 sample. Both Au and Ag have beneficial effect on CH3OH oxidation activity of Cu–Mn mixed oxides. The combination of the good redox properties of Cu–Mn mixed oxides and gold nanoparticles has proved to be an advantageous approach for developing new catalytic formulations with high effectiveness to eliminate different type pollutants in waste gases from formaldehyde production. The use of high surface area support is beneficial for the stabilization of gold particles in a highly dispersed state and contributes for economic viability in case of practical applications, because of the composition of this catalytic system, that is mostly alumina (80 %).

Herein, a series of highly efficient gold based catalysts supported on mesoporous CeO2-Fe2O3 mixed oxides for CO elimination reactions have been developed. The materials have been fully characterized by means of XRD, Raman and UV-Vis spectroscopies among other techniques. We identify the Ce-Fe synergism as a fundamental factor controlling the catalytic performance. Our data clearly reveal that the CO oxidation activity is maximized when the electronic and structural properties of the support are carefully controlled. In this situation, fairly good catalysts for environmental applications as for example H2 streams purification for fuel cell goals or CO abatement at room temperature can be designed

Using periodic density functional calculations, we studied the local structure and preferred locations of yttrium cations and oxygen vacancies in Y-doped cerium dioxide. We employed three kinds of models – a slab of the CeO2(111) surface and two ceria nanoparticles of different sizes and shapes. In the slab models, which represent the (111) surface of ceria and the corresponding extended terraces on the facets of its nanoparticles, Y3+ cation dopants were calculated to be preferentially located close to each other. They tend to surround a subsurface oxygen vacancy that forms to maintain the charge balance. Such general behavior was not found for the nanoparticle models, in which structural flexibility and the presence of various low-coordinated surface centers seem to be crucial and suppress most of the trends. Configurations with four Y3+ cations were calculated to be particularly stable when they combined two of the most stable configurations with two Y3+ cations. However, no clear trend was found regarding the preferential spatial distribution of the Y3+ pairs – they can be stable both in isolation and close to each other. In general, doping by yttrium does not notably change the reducibility of ceria systems but selectively facilitates the formation of oxygen vacancies at the ceria surface in comparison with pristine ceria. Yttrium cations also slightly increase the basicity of the nearby oxygen centers with respect to a stoichiometric ceria surface.

Mono metallic and bimetallic Pd (1 wt. %)&ndash, Au (3 wt. %) catalysts were prepared using two ceria supports doped with 1 wt. % Y2O3. Yttrium was added by impregnation or co-precipitation. The catalyst synthesis was carried out by deposition&ndash, precipitation method, with sequential deposition&ndash, precipitation of palladium over previously loaded gold in the case of the bimetallic samples. The obtained materials, characterized by X-ray powder diffraction (XRD), High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR) techniques, were tested in the complete benzene oxidation (CBO). The results of the characterization analyses and the catalytic performance pointed to a close relationship between structural, redox, and catalytic properties of mono and bimetallic catalysts. Among the monometallic systems, Pd catalysts were more active as compared to the corresponding Au catalysts. The bimetallic systems exhibited the best combustion activity. In particular, over Pd&ndash, Au supported on Y-impregnated ceria, 100% of benzene conversion towards total oxidation at the temperature of 150 &deg, C was obtained. Comparison of surface sensitive XPS results of fresh and spent catalysts ascertained the redox character of the reaction.

Mesoporous oxides TiO2 and ZrO2, synthesized by surfactant templating via a neutral C13(EO)6–Zr(OC3H7)4 assembly pathway, and ceria-modified TiO2 and ZrO2, prepared by a deposition–precipitation (DP) method, featuring high surface areas and uniform pore size distributions were used as supports for gold catalysts. The supported gold catalysts were assessed for the catalytic abatement of air pollutants, i.e., CO, CH3OH, and (CH3)2O. The gold was supported on the mesoporous oxides by a DP method. The supports and catalysts were characterized by powder X-ray diffraction, high-resolution transmission electron microscopy, N2 adsorption–desorption analysis, and temperature-programmed reduction technique. A high degree of synergistic interaction between ceria and mesoporous ZrO2 and TiO2 as well as a positive modification of the structural and catalytic properties by ceria was observed. The ceria additive interacts with the mesoporous oxides and induces a strong effect on the reducibility of the supports. The catalytic behavior of the catalysts was discussed to determine the role of the ceria modifying additive and possible interaction between the gold nanoparticles and ceria-mesoporous oxide supports. The gold catalysts supported on ceria-modified mesoporous ZrO2 displayed superior catalytic activity (∼100% conversion of CO at 10 °C and CH3OH at 60 °C). The high catalytic activity can be attributed to the ability of the support to assist oxygen vacancies formation. The studies indicate that the ceria-modified mesoporous oxide supports have potential as supports for gold-based catalysts.

a b s t r a c t Gold catalysts supported on ceria doped by different metal oxides (Me = Fe, Mn, Sn) were synthesized by two different methods: coprecipitation (CP) and mechanochemical activation (MA). Samples were characterized by means of XRD, HRTEM, TPR and XPS. Both XRD and HRTEM analyses reveal differences in the average size of the gold and ceria particles. As shown by TPR data, ceria doping improves oxygen mobility, i.e. a higher oxygen capacity was observed while compared with gold catalyst on undoped ceria. The method of preparation and the nature of dopant applied influence the catalytic performance in the water-gas shift (WGS) reaction. The differences in WGS activity between the MA and CP samples were significant. The MA catalysts, doped by Fe and Mn, manifested higher WGS activity than the undoped Au/ceria sample and the sample doped by Sn. A high concentration of Ce3+ ions in the highly active catalysts containing Fe or Mn was registered by XPS and found consistent with an earlier proposed model of the active sites for the WGS reaction.

Gold (3 wt. %) catalysts on Y-doped (1, 2.5, 5 and 7.5 wt. % Y2O3) ceria supports prepared by coprecipitation (CP) or impregnation (IM) were studied in complete benzene oxidation (CBO). A low-extent Y modification was chosen to avoid ordering of oxygen vacancies. The samples were characterized by XRD, TGA, XPS and TPR techniques. A positive role of air pretreatment at 350 °C as compared to 200 °C was established for all Y-containing catalysts and it was explained by cleaning the active sites from carbonates. The oxygen supply cannot be considered as a limiting step for benzene oxidation except for the high 7.5%-doped samples, as suggested by TGA and TPR data. On the basis of XPS results of fresh and used in CBO catalysts, the presence of cationic gold species does not seem important for high CBO activity. The gold catalyst on an IM support with 1% Y-doping exhibited the best performance. A 100% benzene conversion was achieved only over this catalyst and Au/ceria, while it was not reached even at 300 °C over all other studied catalysts. Gold and ceria particle agglomeration or coke formation should be excluded as a possible reason, and the most probable explanation could be associated with the importance of the benzene activation stage.

Gold catalysts supported on ceria doped with different metal oxides (Fe, Mn, Co and Sn) were synthesized using two techniques: CP and mechanochemical activation. The catalytic activity in complete benzene oxidation (CBO) was studied. The samples were characterized by means of XRD and high resolution transmission electron microscopy, and non-significant differences in the average size and the distribution of gold particles were observed. This means that the main reason for the different catalytic behavior in CBO has to be searched in the composition and structure of the supports. In spite of the higher hydrogen consumption (e.g., higher oxygen mobility) estimated by means of TPR, the gold catalysts on ceria doped with transition metal oxides generally are less active than gold/ceria catalyst. This observation could be explained taking into consideration that the key factor for the high oxidation activity is not the oxygen supplying but the activation of the very stable benzene molecule. The higher catalytic activity in comparison with that of the gold/ceria catalyst was observed only using a mixed ceria–CoOx support mechanochemically prepared. Very high and stable catalytic activity in CBO was obtained over this sample.

New gold catalytic system prepared on ceria-modified mesoporous titania (CeMTi) used as water-gas shift (WGS) reaction catalyst is reported. Mesoporous titania (MTi) was synthesized using surfactant templating method through a neutral [C 13 (EO) 6 –Ti(OC 3 H 7 ) 4 ] assembly pathway. Ceria modifying additive was deposited on MTi by deposition precipitation (DP) method. Gold-based catalysts with different gold content (1–5 wt.%) were synthesized by DP of gold hydroxide on mixed metal oxide support. The supports and the catalysts were characterized by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N 2 adsorption analysis and temperature-programmed reduction (TPR). The catalytic behavior of the gold-based catalysts was evaluated in WGS reaction in a wide temperature range (140–300 °C) and at different space velocities and H 2 O/CO ratios. The influence of gold content and particle size on the catalytic performance was investigated. The WGS activity of the new gold/ceria-modified mesoporous titania catalysts was compared with that of gold catalysts supported on simple oxides CeO 2 and mesoporous TiO 2 , as well as gold/ceria-modified titania and reference catalyst Au/TiO 2 type A (World Gold Council). A high degree of synergistic interaction between ceria and mesoporous titania and a positive modification of structural and catalytic properties by ceria has been achieved. It is clearly revealed that the ceria-modified mesoporous titania is of much interest as potential support for gold-based catalyst. The Au/ceria-modified mesoporous titania catalytic system is found to be efficient catalyst for WGSR.

Fourier transform infrared spectra of CO adsorption from 120 K up to room temperature on two gold catalysts supported on different mixed ceria-titania oxides are discussed in comparison with those obtained on Au/TiO(2) and Au/Fe(2)O(3) reference catalysts provided by the World Gold Council. The spectra of adsorbed CO, run on the different samples before preliminary treatment, are shown and compared with those of the untreated catalysts and of the samples reduced either in CO or in hydrogen. Big differences have been found between the ceria-titania supported samples and the reference ones: unusual absorption bands, irreversible to outgassing, have been detected after CO interaction on the untreated and oxidized ceria containing samples. These absorptions are assigned to CO on Au(n)(+) small clusters stabilized at the ceria defects. By reduction in hydrogen, negatively charged Au(n)(-) species are produced on the same sample. Oxidized small particles are present on the reference catalysts, but only on the untreated samples; after treatment, only metallic step sites are evident.

Diesel soot oxidation over Au–VO x /TiO 2 and Au–VO x /ZrO 2 catalytic systems with different vanadia loadings were studied. The heavy-duty diesel soot was preliminarily analyzed. The composition of the catalysts was investigated by means of FT–Raman. Their activity toward the oxidation of diesel soot was assessed by thermogravimetrical analysis. The combustion onset temperature and the combustion peak maximum can be lowered to 361 and 419°C, respectively. Reaction rates R at certain temperature T r are calculated out of the first derivative from the mass loss in function of temperature (TGA plot). The results of the activity tests indicate a synergistic effect between Aunanoparticles and vanadia when VO x presents as a monolayer on the support. Catalysts with higher V loadings show a higher activity but no synergistic effects between Au and V could be observed.

The production of H2 pure enough for use in fuel cells requires the development of very efficient catalysts for the water-gas shift reaction. Herein, a series of gold catalysts supported on ZnO-promoted CeO 2-Al2O3 are presented as interesting systems for the purification of H2 streams through the water-gas shift reaction. The addition of ZnO remarkably promotes the activity of an Au/CeO 2/Al2O3 catalyst. This increase in activity is mainly associated with the enhanced oxygen storage capacity exhibited for the Zn-containing solids. High activity and good stability and resistance towards start-up-shut-down situations was found, which makes these catalysts a promising alternative for CO clean-up applications. Zinc booster: A series of gold catalysts supported on ZnO-promoted CeO2-Al2O3 are applied in the purification of H2 streams through the water-gas shift reaction. The addition of ZnO promotes the activity of an Au/CeO 2/Al2O3 catalyst. This increase in activity is mainly associated with the enhanced O2 storage capacity of the Zn-containing solids. The prepared catalysts tolerate start-stop cycles, showing potential for industrial application. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

This book presents the major developments in hydrogen-related catalytic and electrocatalytic reactions over gold-based materials over the last decade, including many of the advances made by academic and industrial researchers. Gold-based catalysts with potentially exciting new applications in hydrogen technology (e.g. purification of hydrogen, anode/cathode electrodes) are being investigated at a much higher rate than even before. A variety of techniques to synthesize, characterize and evaluate these materials is being employed. The book will be of interest to all those working in catalysis/green chemistry, in particular, to advanced level researchers in catalysis using gold-based materials. It is hoped that specialists in one reaction will read with interest the chapters on the neighbouring expertise. The book is also meant for PhD-students and advanced students interested in this area.

In this work the development of a series of gold catalysts, essentially based on g-alumina promoted with a small superficial fraction of Ce¿Fe mixed oxides, is reported. The catalytic behaviour is evaluated in the water gas shift reaction. The formation of a Ce¿Fe solid solution is evidenced by XRD and related to the catalytic activity where the importance of the Ce¿Fe interaction is demonstrated. The best catalyst reached CO conversions very close to the equilibrium limit. A long-term stability test is performed and the loss of activity is observed and attributed to reaction intermediates. Almost complete recovery of the initial conversion is achieved after oxidation treatment, suggesting that the problem of stability could be overcome by a suitable change in the reaction parameters thus leading to a highly efficient catalyst for future applications in H2 production and clean-up.

Two different synthesis routes, in particular deposition-precipitation (DP) and modified deposition-precipitation (MDP) have been used for preparation of gold/ceria catalysts. The catalysts have exhibited significant differences in CO, CH3OH and (CH3)2O oxidation. The most pronounced effect of different preparation methods was registered in the CO oxidation reaction. DP-prepared catalyst showed high ability to oxidize CO at room temperature. Microscopic measurements have evidenced formation of very small gold particles (d below 1 nm) on the surface of DPprepared catalyst. In contrast, only large gold particles with average size about 15 nm were observed in MDP-prepared sample. A detailed characterization by FTIR spectroscopy after CO adsorption at 90 K and TPR measurements has been carried out with aim to unravel the impact of preparation method on the structural and catalytic properties of the catalysts. The catalytic behavior was explained with the large differences in the gold dispersion and in the number of active gold sites in intimate contact with ceria surface defects.

New gold catalysts supported on ceria modified by addition of ZrO 2 have been synthesized and tested in the water-gas shift reaction (WGSR) at low temperature, where they displayed better catalytic activity than gold supported on pure ceria, following the trend: AuCe50Zr50 > AuCe80Zr20 > AuCe. Morphologic, textural, structural and spectroscopic characterisation showed that the addition of zirconia to ceria leads to the formation of mixture of tetragonal ceria–zirconia phases. Moreover, depending on the zirconia amount, a different Au dispersion is observed. Au agglomerates (10–20 nm) and nanoparticles (about 2.5 nm) have been detected by HRTEM on AuCe80Zr20, while only nanoparticles have been found on AuCe50Zr50. FTIR spectroscopy of CO adsorbed at 120 K showed also the presence of Au clusters, more abundant on AuCe50Zr50 than on AuCe80Zr20. However, at low temperature the best catalytic activity of AuCe50Zr50 is correlated not only to the abundance of gold clusters and nanoparticles, but also to the effect of ZrO 2 addition that influences the acid/base surface properties of ceria, as successfully demonstrated by adsorption and surface reaction of acetone vapor at room temperature. FTIR measurements performed before and after reaction showed that the carbonate-like species have the lowest stability on the AuCe50Zr50 surface. This feature, along with the presence of a high gold dispersion, makes AuCe50Zr50 the best catalyst in terms of activity and stability.

Titanium oxide nanotubes (TNTs) have been synthesized via laboratory-made TiO2 A and commercial TiO2 P25. 1.5wt% gold or palladium were deposited on TNTA and TNTP25 supports and the catalytic activity was evaluated in propene, methyl ethyl ketone (MEK) and toluene total oxidation. The catalytic properties of supported TNT were correlated with the structural peculiarity and the nature of the TNT, but also with the nature of the noble metal and the kind of the VOC.

New gold catalysts supported on mixed CeO2-TiO2 with different ceria loading have been prepared. BET, HRTEM and FTIR characterization has been carried out to reveal the effect of ceria on the WGS and PROX activity.

The support of this new catalytic system concerns ceria-modified mesoporous titania (CeMTi). Mesoporous TiO 2 (MTiO 2 ) with high surface area and uniform pore size distribution was synthesized using surfactant templating method through a neutral [C 13 (EO) 6 -Ti(OC 3 H 7 ) 4 ] assembly pathway. Ceria modifying additive was deposited on suspended in water MTiO 2 by means of precipitation with Na 2 CO 3 . Gold-based catalysts with different gold loading were synthesized by deposition-precipitation of gold hydroxide on mixed metal oxide support. The support and the catalysts were characterized by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and N 2 adsorption analysis. The catalytic behavior of the gold-based catalysts was evaluated in water-gas shift reaction (WGSR) at a wide temperature range (140-300 °C). The influence of gold content and particle size on the catalytic performance was investigated. The CO conversion of the new catalysts was compared with that related to the gold catalysts supported on simple oxides CeO 2 and mesoporous TiO 2 as well as and to reference Au/TiO 2 type A (World Gold Council).

This paper gives a short account of results associated with the high catalytic activity of metallic gold, deposited on ferric oxide, in the water-gas shift (WGS) reaction. Until now there have been no literature data on the catalytic activity of gold in that important industrial reaction except some results for the hydrogenation of CO{sub 2}. 8 refs., 1 fig.