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In the present study a series of Au–transition metal oxides supported on a clay mineral such as sepiolite were tested in the preferential oxidation of CO in an excess of H2 under simulated solar light irradiation and in the absence of light, at 30 °C and atmospheric pressure. Transition metal oxides (ZnO, Fe2O3, NiO, MnO2, and Co3O4) were dispersed over the sepiolite surface where, subsequently, Au nanoparticles with an average particle size between 2 and 3 nm were successfully deposited–precipitated. The obtained photocatalysts were characterized by XRD, XRF, DRUV-Vis, N2 adsorption–desorption and HRTEM in order to evaluate the optical, structural and chemical properties of the prepared samples. Despite the low amount of gold (nominal 1.0 wt%), the catalysts exhibited an outstanding behavior under light irradiation, with reaction rates between 4.5 and 5.2 mmol COox gcat−1 h−1 for the Au–NiSep, Au–CoSep and Au–ZnSep samples. These photocatalysts exhibited a high dispersion of the respective transition metal oxides over the sepiolite support and the presence of low-coordinated hemispherical gold nanoparticles. The superior photocatalytic efficiency of these samples was ascribed to the reduction of the electron–hole pair recombination of photogenerated charge carriers by the excitation of the localized surface plasmon resonance of the Au nanoparticles. The BET surface area and the gold particle size seemed to be relevant factors affecting the catalytic performance.

Gold nanoparticles precipitated-deposited on titania nanostructures (1.0 wt% nominal loading) were studied in the preferential CO oxidation in excess of H2 at room temperature and atmospheric pressure, both in dark and under simulated solar light irradiation. Titania supports were synthesized by means of two hydrothermal methods markedly acid and basic, giving rise to rutile nanorods and anatase deformed nanorods structures, respectively. Characterization techniques such as N2 physisorption, XRD, XPS, DRUV-vis, HRTEM and XRF were performed in order to study the chemical, structural and optical properties of the catalysts. Well defined rutile nanorods structures were obtained from the acidic treatment allowing a regular distribution of gold nanoparticles and resulting quite active in the CO-PROX reaction. In particular the sample from the acidic synthetic approach calcined at 700 °C displayed the best results as it was highly selective to CO2 under both dark and simulated solar light irradiation.

In this study the photo-response behaviour of Au/TiO2 systems in the preferential CO oxidation in a H2-rich stream (CO-PROX) was investigated by the first time under simulated solar light irradiation at room temperature and atmospheric pressure. Au nanoparticles, with an average size of 2–5 nm, were precipitated-deposited on a mesoporous TiO2, previously synthesized by sol-gel type procedure and thermally treated at different temperatures to obtain anatase/rutile mixed phases. Structural, chemical and optical properties were studied by means of AAS, N2 physisorption, XRD, HR-TEM, DRUV–vis and XPS, investigating the effects of TiO2 polymorphs (anatase, rutile and combination thereof). All samples, containing a very low amount of noble metal (0.5 wt%), resulted very active in the photocatalytic CO-PROX at ambient conditions, attaining very high CO conversion and CO2 selectivity values. The Au/TiO2 sample containing both anatase/rutile polymorphs in the support displayed the highest activity, both in dark and under simulated solar light, due to the simultaneous presence of these two titania crystalline phases, capable to lower the effective band gap of the composite system (2.90 eV) and improving the photocatalytic activity in the studied reaction. This kind of materials may provide a sustainable and feasible approach to selectively oxidize CO in H2-rich stream under solar light irradiation and ambient conditions.

A study was conducted to investigate the effect of the preparation route of ZrO2 in CuO–CeO2/ZrO2 catalysts for the oxidation of carbon monoxide at low temperature (COX). Four ZrO2 supports were synthetized via either type sol-gel methodology or precipitation. The final Cu-Ce-Zr oxide catalysts were prepared by incipient wetness co-impregnation with copper and cerium solutions (with a loading of 6 wt% of CuO and 20 wt% of CeO2). The catalyst crystalline phases, texture and active species reducibility were determined by XRD, N2 physisorption at −196 °C and H2-TPR, respectively; meanwhile the surface composition and copper-cerium electronic states were studied by XPS. The catalytic activity was evaluated in the oxidation of CO to CO2, in the 40–215 °C temperature range. Catalytic results evidenced that the samples prepared by a sol-gel methodology showed, after the impregnation, a severe decrease of specific surface area and pore volume attributable to a wide degree of pore blockage caused by the presence of metal oxide particles and a collapse of the structure partially burying the active sites. A simple co-impregnation of a zirconia support, obtained through facile and fast precipitation, provided instead a catalyst with very good redox properties and high dispersion of the active phases, which completely oxidizes CO in the range 115–215 °C with T50 of 65 °C. This higher observed activity was ascribed to the formation of a larger fraction of highly dispersed and easily reducible Cu species and ceria nanocrystallites, mainly present as Ce(IV), with an average size of 5 nm.

Mixed ceria–zirconia oxide (CZ91, Ce:Zr = 9:1) has been used to support Nickel (CZ91Ni), Cobalt (CZ91Co) and bimetallic Nickel/Cobalt active phases (CZ91NiCo) to be tested in Ethanol Steam Reforming reaction (ESR). H 2 -TPR analyses and IR studies of adsorbed probe molecules suggest that ceria/zirconia actually favors the reduction of supported metal oxide phases. Moreover, characterization results point out that the co-presence of Nickel and Cobalt, as in the CZ91NiCo material, enhances the reducibility of both the metal oxide phases, in comparison with monometallic formulations, thus suggesting a synergetic effect between Cobalt and Nickel species. Correspondingly, bimetallic CZ91NiCo catalyst shows the best results in ESR in terms of ethanol conversion, hydrogen yield and selectivity to CO 2 above 500 °C, which should be explained by the high reducibility of this sample. Ethene formation was not detected in significant amount during catalytic tests. Indeed, the basicity of ceria component is mainly characterizing the surface of this family of catalysts.

CuO supported on CeO2, Ce0.8Zr0.2O2 and Ce0.8Al0.2O2 based catalysts (6%wt Cu) were synthesized and tested in the preferential oxidation of CO in a H2-rich stream (CO-PROX). Nanocrystalline supports, CeO2 and solid solutions of modified CeO2 with zirconium and aluminum were prepared by a freeze-drying method. CuO was supported by incipient wetness impregnation and calcination at 400 � C. All catalysts exhibit high activity in the CO-PROX reaction and selectivity to CO2 at low reaction temperature, being the catalyst supported on CeO2 the more active and stable. The influence of the presence of CO2 and H2O was also studied.

The application of the catalytic system CuO/CeO2 supported on Zr doped SBA-15 mesoporous silica to the preferential oxidation of CO on hydrogen streams (CO-PROX) suitable to be used to feed PEM fuel cells, has been studied. A loading of 20% (wt.) Ce and 6% (wt.) Cu was found optimal for the CO-PROX reaction. The influence of the presence of CO2 and H2O in the gas feed was also studied in order to simulate the real operation conditions of a PEMFC feed stream generated by alcohol steam reforming. The catalysts were characterized by XRD, adsorption–desorption of N2 at −196 ◦ C, TEM, –H2-TPR and XPS. The system reducibility was found modified by the incorporation of zirconium in the support, with improvement of both the conversion and selectivity of the catalytic system, compared to the same material without Zr. © 2010 Elsevier B.V. All rights reserved.

Nanostructured Au/Al(2)O(3)-CeO(2) catalysts with a low content of precious metal (0.9% wt.) were prepared immobilizing two different stabilized Au sols on a high surface area Al(2)O(3)-CeO(2) mixed oxide with a uniform pore size distribution, synthesized by a one-pot methodology. The samples were characterized by elemental analysis, N(2) physisorption, XRPD, TEM and (27)Al-MAS NMR techniques. The catalytic activity of the two samples in the preferential oxidation of CO in excess of H(2) (CO-PROX) was comparatively evaluated in the 35-110 degrees C temperature range. The Au-THPS/AlCe20 sample, prepared immobilizing a sol obtained reducing an aqueous solution of gold tetrachloroaurate salt with bis[tetrakis(hydroxymethyl)phosphonium sulfate], resulted very active and selective at low temperatures and its catalytic activity was correlated with the structural characteristics of the metal particles and of the ordered mesoporous support.

Natural kaolin was treated at 850 or 950 degrees C in air flow to give respectively the metakaolin samples MK8 and MK9. The obtained materials were successively treated at 90 degrees C with a 1 M solution of H(2)SO(4), for various time lengths. The acid treatment of MK8 was found to give a high surface area microporous material with good catalytic properties related to the high density of acid sites, while MK9 gave an ordered mesoporous material with a low density of acid sites. The materials were characterized by several techniques, X-ray powder diffraction, thermogravimetric analysis, N(2) physisorption, scanning electron microscopy, and temperature-programmed desorption of ammonia. The 1-butene isomerization was used as test reaction to evaluate the acidity of the samples.

A Cu/CeO2/Al2O3 catalyst prepared by a single-step sol–gel method was studied for methanol steam reforming (SRM) to gain information on the oxidation state of Cu and the role of oxidized Cu species. The catalyst was tested in a new laboratory-made flow apparatus that allowed on-line analysis of the products and measurement of the oxidation state and dispersion of Cu in situ. The catalyst pre-reduced in H2 was more active and selective than the not pre-reduced one. The oxidation state, evaluated after SRM tests, suggested the presence of a layer of oxygen atoms on the metallic Cu surface. Treating the pre-reduced catalyst with H2O vapour at 250 °C caused dissociative H2O chemisorption and led to a partial oxidation of Cu. The H2O oxidized sample reacted with CH3OH producing CO2 and H2 as long as oxygen was present on the Cu surface. The results support an oxidation–reduction mechanism.

Ce–Zr–Cu mixed oxide systems, with different contents of ZrO2 and CuO, were prepared by slow co-precipitation method, leading to the formation of materials with a flower-like morphology. It was evaluated both the role of CuO loading (3–7 wt%), by maintaining constant the amount of ZrO2 (7 wt%), and the role of ZrO2 (2–10 wt%) with a fixed amount of CuO (7 wt%). The prepared catalysts were characterized by means of ICP-OES, SEM, N2 physisorption, quantitative XRD, H2-TPR, and XPS. Their catalytic performances in the preferential oxidation of CO in excess of H2 (CO-PROX) were evaluated, in the 40–190 °C temperature range. Characterization and catalytic results showed that an optimum Zr/Ce molar ratio and CuO loading are required to attain the best catalytic performance over the studied nanostructured Ce/Zr/Cu oxide system. Characterization results revealed that, regardless of the sample composition, all of them presented similar flower-like morphology and textural properties. Instead, the catalyst composition determined the crystalline phases formed, their reducibility and surface distribution. The catalyst containing an intermediate ZrO2 loading (7 wt%) and the highest studied CuO amount (7 wt%), FCZCu77, showed the higher fraction of undetectable CuO from XRD, that is the highest proportion of highly dispersed Cu species also observed from H2-TPR. These characteristics justify how FCZCu77 catalyst exhibited a quite higher catalytic activity than the others samples.

The liquid phase hydrogenation of acetophenone was studied over a series of silica supported bimetallic catalysts with various Ru/Cr atomic ratios. The catalysts were prepared by reduction of the metal salts with NaBH4 aqueous solutions and were characterised by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) (ESCA). The hydrogenation reaction was carried out in batch at a hydrogen pressure of 9 bar. The selectivity towards reduction of the carbonyl function increases with the increasing amount of Cr ions added. © 2002 Elsevier Science B.V. All rights reserved.

a b s t r a c t Nanocrystalline CeO2 with a regular size of 9.5 nm was prepared by a freeze-drying method, and subse- quent impregnated with a Cu(II) acetate solution, varying the loading of Cu (3, 6, 12 wt.%). The resulting CuO/CeO2 materials were characterized by N2 physisorption at −196 ◦ C, HRTEM, H2-TPR, X-ray diffrac- tion, Raman spectroscopy and XPS and tested as catalysts in the preferential CO oxidation in a H2-rich stream (CO-PROX) in the temperature range 40-190 ◦ C. In spite of their low specific surface areas the cat- alysts exhibited a good catalytic performance, resulting active and selective in the CO-PROX reaction at low temperatures. The inhibiting effect of the simultaneous presence of CO2 (15 vol.%) and H2O (10 vol.%) in the reaction mixture on the performance of CuO-CeO2 catalysts was also investigated. The addition of CO2 and water in the gas stream depressed CO oxidation up to 160 ◦ C, its effect being negligible at higher temperatures. Nevertheless, despite these expected deactivation phenomena, a CO conversion value higher than 90% and a CO2 selectivity of about 90% was achieved for all the samples at 160 ◦C. The excellent performance, especially shown by the catalyst with 6 wt%. of copper, has been related to the wide dispersion of the copper active sites associated with the high amount of Ce4+ species before reaction.

Ce–Cu and Ce–Zr–Cu oxide systems with a flower-like morphology were prepared by slow co-precipitation in the absence of any structure directing agent. For the sake of comparison, Ce–Cu and Ce–Zr–Cu oxide samples were also prepared by a classic co-precipitation method. All the samples were calcined in air flow at 650 °C. The materials were characterized by SEM and TEM microscopy, quantitative X-ray diffraction, N2 physisorption, H2-TPR, O2-TPD and XPS. The catalytic activity of the prepared samples was evaluated in the preferential oxidation of CO in excess of H2 (CO-PROX), in the 40–190 °C temperature range., The authors wish to thank Martina Marchiori (Ca’ Foscari University – Venice) for N2 physisorption and TPR-TPO measurements and Dr. Davide Cristofori (Ca’Foscari University-Venice) for the HRTEM measurements.

In this article, the preparation and application of gold and cerium catalysts supported on zirconium-doped mesoporous silica SBA-15 was studied. These materials have been prepared by two different methods and characterized to investigate their textural properties, dispersion of the active phases and oxidation states. Both materials exhibit a marked catalytic activity. The size of the gold nanoparticles is directly related to the CO conversion rate and to the selectivity towards CO 2 exhibiting a strong temperature dependence. An X-ray photoelectron spectroscopic study of the composition and chemical state of the nanoparticles indicates the presence of Au in a metallic state. Transmission electron microscopic micrographs indicate that the best catalyst shows a higher dispersion of Au in spite of its lower gold surface content.

A Ce-Zr-Cu oxide system with a flower-like morphology was prepared by a slow co-precipitation method in the absence of any structure directing agent. Four portions of the oxide were thermally treated at four different temperatures (350°C, 450°C, 550°C, 650°C). The resulting materials samples were characterized by quantitative XRD, adsorption-desorption of N2 at-196°C, SEM and TEM microscopy, -H2-TPR, XPS and Operando-XANES. All samples were tested in the preferential CO oxidation (CO-PROX) in the 40-190°C temperature range. Thermal treatments were found to induce slight structural changes without altering the starting morphology of the samples. The samples treated at higher temperature 550-650°C showed a quite interesting CO-PROX activity and selectivity in a temperature range suitable for a practical use within the FEMFC technology. © 2011 Elsevier B.V.

A mesoporous Cu-Ce-Al-based material was prepared by a single-step synthesis, performed in n -propanol using aluminum sec -butoxide as Al precursor and metal stearates, both as Cu-Ce sources and structural directing agents. This type of synthetic approach appears to be very efficient for the preparation of highly dispersed Cu-Ce containing particles supported on a structurally ordered alumina with high surface area (>400 m 2 g −1 ) and quite narrow pore size distribution, as confirmed by X-ray powder diffraction, TPR and dispersion data and N 2 physisorption. The catalyst was also characterized by XPS and FT-IR measurements of adsorbed CO. The catalytic activity for the preferential oxidation of CO to CO 2 (PROX) in H 2 -rich streams was tested in the 75–200 °C temperature range.

A series of CuO-ZnO/TiO2 ternary catalysts was prepared by co-precipitation and characterized by X-ray powder diffraction (XRPD), N2 physisorption at 77 K, temperature-programmed reduction/oxidation (H2-TPR/TPO) and FT-IR measurements of low temperature adsorbed CO. The catalysts were tested and found active in the preferential oxidation of CO (CO-PROX) in hydrogen-rich gas streams and their catalytic performance was compared with that of the binary systems CuO/ZnO and CuO/TiO2. © 2008 Elsevier B.V. All rights reserved.

An Al/Ce/Mg=50.0/1.0/1.0 atomic ratio (a.r.) pillared montmorillonite was used to support 1.0 wt.% of the bimetallic species Pd/Pt=5.0 and Pd/Au=5.0 a.r. The resulting catalysts were characterized by XRPD, N2 physisorption, ammonia TPD and FT-IR spectroscopy. The catalytic activity in the hydrogenation and hydrogenolysis/ring-opening of naphthalene and thio-tolerance to dibenzothiophene were investigated at 6.0 MPa in a flow reactor. Both catalysts showed interesting performances. Of the two catalysts, the former showed higher productivities in hydrogenation and hydrogenolysis/ring-opening compounds together with lower losses in carbon balance and higher thio-tolerance. These results not only confirmed that Pd/Pt is one of the most suitable bimetallic pair for noble metal containing hydrotreating catalysts, but also that the Al/Ce/Mg PILC can be used as low cost support for noble-metal-containing active phases.

Synthetic smectites framework substituted with Ti, Fe, and Zn were synthetized in hydrothermal conditions. The materials were characterized by XRD, nitrogen adsorption, MAS-NMR. FT-IR spectroscopy of adsorbed pyridine and analysis of product distribution in the 1-butene isomerization was used to evaluate the surface acidity. Chemical properties were correlated to the nature and presumed lattice location of the framework substituents.