Dispersion and reduction of copper oxide supported on WO3-modified Ce0.5Zr0.5O2 solid solution
ABSTRACT XRD (X-ray diffraction), BET (Brunauer-Emmett-Teller), LRS (laser Raman spectra), XPS (X-ray photoelectron spectroscopy), and TPR (temperature-programmed reduction) are used to investigate the surface properties of CuO/WO3/Ce(0.5)Zr(0.5)O2 samples. The results indicate that (1) tungsten oxide can be highly dispersed on Ce(0.5)Zr(0.5)O2 (denoted as CZ hereafter) solid solution, with a dispersion capacity of about 0.8 mmol WO(3)/(100 m2 CZ), and comparatively, the supported tungsten oxide species are preferentially interacted with ceria component on the surface of CZ; (2) for CuO/WO3/CZ samples with a half-monolayer WO3 loading, i.e., xCu-0.4W-CZ series, the surface of CZ is only partially covered by the preloaded WO3) and the supported copper oxide species are dispersed on the remaining surface vacant sites on CZ as well as on top of the preloaded tungsten oxide, while for the samples preloaded with a full-monolayer WO3, i.e., xCu-0.8W-CZ series, only dispersed on the top of the preloaded tungsten oxide monolayer; (3) the effect of the loading amount of WO3 on the reduction property of Cu2+ ions in a series of CuO/WO3/CZ samples has been observed and tentatively attributed to the formation of WO3 monolayer on CZ and the different coordination environments of the dispersed Cu2+ ions are discussed on the basis of the consideration of the incorporation model proposed previously (Chen, Y.; Zhang, L. Catal. Lett. 1992, 12, 51).
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ABSTRACT: Nanocrystalline (4–5 nm) Ce1−xRuxO2 mixed oxides (x = 0.03–0.16) were synthesized using water in oil microemulsion method. Morphology, microstructure and a phase composition of the samples subjected to heat treatment in oxidizing and reducing atmosphere were investigated by TEM, SEM-EDS-EBSD, XRD and XPS. Oxide with x = 0.11 was structurally stable in oxidizing atmosphere up to 550 °C but above this temperature it decomposed into Ru deficient, nanosized Ce1−xRuxO2 and large (few μm) RuO2 crystals. No phase separation was observed for Ce0.97Ru0.03O2 even after heating at 800 °C. Doping with Ru decreases the size of ceria particles and strongly hinders their sintering at high temperatures. In hydrogen atmosphere a segregation of small (∼1 nm) Ru crystallites occurred at the surface of the Ce0.89Ru0.11O2 mixed oxide. Only small increase of the mean crystallite size of Ru (to 2 nm) occurred after reduction at 1000 °C. The unique resistance of Ru to sintering is assigned to a special epitaxial orientation Ru (0 0 2)∥CeO2 (1 1 1), which persisted up to the highest temperature of reduction, due to very strong surface bonding. Contrary to a situation in oxidizing atmosphere, doping with Ru had no significant effect on the sintering of ceria in hydrogen. Partial substitution of Ru for Ce strongly enhances the reducibility of ceria at low temperatures and its activity in catalytic combustion of CO and soot.Applied Catalysis B Environmental 04/2014; s 148–149:123–135. DOI:10.1016/j.apcatb.2013.10.047 · 6.01 Impact Factor
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ABSTRACT: WO3/CexZr1–xO2 materials were evaluated as a possible NH3-selective catalytic reduction (SCR) active catalyst in a NOx storage reduction (NSR) + SCR combined system. The effect of the support composition was investigated at a constant WO3 loading (9.1 wt % of WO3). The impact of WO3 promotion over textural, structural, acid–base, and redox properties of SCR samples was characterized by means of nitrogen adsorption–desorption isotherms, XRD, NOx storage capacity, NH3 temperature programmed desporption, pyridine adsorption followed by FTIR, and H2-TPR. Catalytic activities in NH3-SCR and NH3-SCO reactions as well as corresponding kinetics parameters are also discussed. All WO3/Ce–Zr materials are active and fully selective in N2 for NOx reduction by NH3 and ammonia oxidation by O2. For the SCR reaction, the rate of NO conversion is found approximately half-order with respect to NO, and negative to nearly zero-order with respect to NH3. Tungstated ceria–zirconia materials were then associated downstream with a model Pt–Ba/Al NSR catalyst. Whatever the WO3–Ce/Zr catalyst, the global NOx conversion and N2 yield are significantly enhanced by the addition of the SCR catalyst. Special attention is paid to the influence of the ceria content of the SCR catalyst on the ammonia reactivity in the combined NSR + SCR system. It is demonstrated that NH3 produced during the regeneration step of Pt–Ba/Al catalyst can react either with NOx (NH3-SCR) or with O2 (NH3-SCO). This reactivity depends both on the Ce/Zr ratio of support and on the temperature. Finally, it is demonstrated that at high temperature (i.e., 400 °C), the strength of the acid sites of the WO3–Ce/Zr catalysts is not sufficient to ensure no ammonia slip.ACS Catalysis 04/2013; 3(6):1120–1132. DOI:10.1021/cs3008329 · 7.57 Impact Factor
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ABSTRACT: Noble metals-promoted tungstated oxides have been shown to be profitable in a wide variety of catalytic reactions of environmental interest but to be detrimental in the hydrogenation of aromatics. The origin of the deleterious effect of tungstates on the hydrogenation performance of noble metals is still being debated. To provide further insights into this, the location and the oxidation state of Rh were investigated as a function of the W surface density (0–10 W/nm2) of Rh/WOx–Ce0.62Zr0.38O2 (Rh/W–CZ) catalysts after high-temperature reduction. For that purpose, a thorough characterization of the oxide phases was performed through N2-sorption, X-ray diffraction, Raman spectroscopy, NOx temperature-programmed desorption, and X-ray photoelectron spectroscopy (XPS), whereas the metallic phases were characterized by low-temperature H2 chemisorption, XPS, N2 Fourier transform infrared spectroscopy and benzene hydrogenation. It was found that Rh deposited on both tungstates and CZ, and did not sinter with increasing W surface densities. The observed linear decrease in the Rh hydrogenation performance of the WOx-promoted Ce0.62Zr0.38O2 below pseudo monolayer coverage of CZ (4.8 W/nm2CZ) was assigned to a strong metal support interaction effect between the Rh particles and the nonreducible underlying WOx phase, resulting in the formation of electron-deficient Rh species (Rhδ+).The Journal of Physical Chemistry C 03/2014; 118(14):7386–7397. DOI:10.1021/jp410848f · 4.84 Impact Factor