Preparation and characterization of Ce1−xPrxO2 supports and their catalytic activities

Abstract

In this work, the addition of praseodymium (Pr) into ceria as a mixed oxide support in a form of Ce1−xPrxO2 (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 Ce4+ ions in ceria were replaced by larger Pr3+ cations. To evidence the incorporation of Pr3+ 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 Pr3+ into ceria lattice would lead to strain and unbalanced charge and result in oxygen vacancies. The reducibility of Ce1−xPrxO2 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 (Ce4+ to Ce3+) of Ce0.925Pr0.075O2 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.