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Preparation and characterization of Ce(1-x)PrxO2 supports and their catalytic activities

Journal of Rare Earths 2017年第12期35卷 1197-1205页

作者： Kingkaew Chayakul Chanapattharapol Somkiat Krachuamram ammarika makdee Preeya Unwiset Sirihathai Srikwanjai Materials Chemistry Research Center Department of Chemistry and Center of Excellence for Innovation in ChemistryFaculty of ScienceKhon Kaen University Center of Alternative Energy Research and Development Khon Kaen University Department of Chemistry Mahidol Wittayanusorn School

In this work, the addition of praseodymium（Pr） into ceria as a mixed oxide support in a form of Ce（1-x）PrxO2（x = 0.01,0.025, 0.050, 0.075 and 0.10） was prepared using a co-precipitation method. The structural and textural properties of the synthesized supports were characterized by X-ray diffraction（XRD）, N2 adsorption-desorption, Raman spectroscopy, H2-temperature programmed reduction（H2-TPR） and H2-chemisorption. Upon addition of Pr, XRD patterns and Raman spectra indicated an enlargement of ceria unit cell and the characteristics Raman broad peak at 570 cm^（-1） which was attributed to the existence of oxygen vacancies in the ceria lattice. This indicated that some Ce^（4＋） ions in ceria were replaced by larger Pr^（3＋） cations. To evidence the incorporation of Pr^（3＋） cations into ceria lattice,X-ray absorption near edge structure（XANES） was employed. The results showed that the oxidation states of Ce in mixed oxide supports were slightly lower than 4＋ while those of Pr were still the same as a precursor salt. Therefore, the incorporation of Pr^（3＋） into ceria lattice would lead to strain and unbalanced charge and result in oxygen vacancies. The reducibility of Ce（1-x）PrxO2 mixed oxide supports was investigated by H2-TPR and temperature-resolved X-ray absorption spectroscopy experiment under reduction conditions. XANES spectra of Ce L3 edges showed a lower surface reduction temperature（Ce^（4＋）to Ce^（3＋）） of Ce（0.925）Pr（0.075）O2 than that of CeO2 which agreed with H2-TPR results. H2-chemisorption indicated that Pr promoted the dispersion of the metal catalyst on the mixed oxide support and increased the adsorption site for CO. For WGS reaction, 1% Pd/mixed oxide support had higher WGS activity than 1%Pd/ceria. The increase of WGS activity was due to the increase of Pd dispersion on the support and the existence of oxygen vacancies produced from incorporation of Pr into the ceria lattice.

关键词： Ce(1-x)PrxO2 mixed oxide support Oxygen vacancies Temperature-resolved in-situ H2 reduction

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