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Ni/CeO 2 /YSZ and Ni/Ce 0.15 Zr 0.85 O 2 have been investigated as catalysts for the dry reforming of methane at 750 °C. Ni was incorporated by the impregnation method. The supports were previously activated by using a thermo-chemical protocol consisting on a severe reduction (H 2 /Ar) at 950 °C followed by a mild oxidation (O 2 /He) at 500 °C. According to TPR results, this protocol leads to the development of unique redox properties in the case of the CeO 2 /YSZ oxide. Two types of CO 2 + CH 4 (1:1) mixtures (helium-diluted and undiluted) were used to feed the reactor. When using the Ni/Ce 0.15 Zr 0.85 O 2 catalyst with undiluted feed, the reactor became plugged by coke. By contrast, Ni/CeO 2 /YSZ behaved as an active and stable catalyst even under the most severe operation conditions. The characterization of the spent Ni/CeO 2 /YSZ using TGA, TEM, Raman and XPS spectroscopy revealed that only a limited amount of graphitic carbon, in form of nanotubes, was formed. No evidences of deactivating carbonaceous forms were obtained. The singular redox properties of the activated CeO 2 /YSZ oxides are proposed as a key for designing Ni catalysts highly stable in reforming processes. [ABSTRACT FROM AUTHOR]

Abstract: A new procedure to determine, with very high accuracy, the lattice parameter of individual supported nanoparticles of interest in catalytic system is presented, checked and applied to ceria supported Palladium catalysts. The procedure is based on the analysis of double diffraction effects present in High Resolution Electron Microscopy (HREM) images recorded in top view conditions. For nanoparticles about 5nm in diameter accuracies in the order of ±0.2% are demonstrated by using a method in which intensity profiles of Digital Diffraction Patterns obtained from experimental HREM images are fitted to a set of Lorentzian-type functions. The new method allows characterizing the distribution of lattice parameter of nanoparticles in systems which are out of range for XRD, as it is the case of catalysts with very low loadings or those in which the particle size distribution is dominated by very small (<5nm) nanoparticles. In the Pd/CeO2 catalysts investigated, evidences of phenomena of large interest to understand the catalytic behaviour like Pd–Ce alloying or Pd nanoparticle encapsulation have been evidenced by measurements of Pd lattice parameters performed using the new method on catalyst reduced at high temperatures (>773K). Likewise, in Pd/CeO2 catalysts reduced at low temperatures (<773K), structural accommodation phenomena of the metal nanoparticles on the ceria support have been revealed whose intensity depends both on the particle diameter and on reduction temperature. [Copyright &y& Elsevier]

Abstract: MnO x –CeO2 and Pt(2%)/MnO x –CeO2 catalysts were prepared and investigated in the catalytic wet oxidation (CWO) of phenol. The reaction was carried out in a high-pressure autoclave reactor operating at 140°C and oxygen partial pressure of 2MPa. The effect of a reduction pre-treatment at 350°C on the catalytic performance of both, the platinum catalyst and the bare oxide was studied. Higher activities were found for the reduced catalysts, independently of the presence or absence of Pt. Formation of carbonaceous deposits on the catalytic surface and leaching of manganese was confirmed as the two major deactivation mechanisms occurring in CWO of phenol. The amounts of deposits formed and manganese leached were higher in the case of reduced samples. Different techniques (XRD, HREM, HAADF, EDS, ICP) were used to characterise the chemical and structural changes experimented by the catalysts during reaction. The behaviour of reduced catalysts was found to be associated to the presence of MnO. The formation of this manganese oxide phase during the reduction pre-treatment significantly influenced the catalytic performance and stability of the catalysts under operation conditions. [ABSTRACT FROM AUTHOR]