SPECTROSCOPIC CHARACTERIZATION AND REACTIVITY STUDY OF CERIA-SUPPORTED NICKEL-CATALYSTS

A comparative study of the hydrogen chemisorption properties and catalytic activities for the CO-H2 reaction of two Ni/CeO2 catalysts has been carried out. These catalysts are obtained by reduction of Ni(OH)2 precipitated on ceria supports differing by their preparation. At the precursor state, a more intense interaction occurs between nickel hydroxide and the ceria support of sample C1, displaying better division state; this is shown by infrared spectroscopy by the bathochromic shift of the 1120 nm band characteristic of Ni2+ ions in an octahedral environment, and by X-ray photoelectron spectroscopy (XPS), from the higher Ni 2p binding energy. After reduction treatment under hydrogen, XP spectra of cerium ions in ceria show that the two supports are in a reduced state, peculiarly after the reduction process for sample C1. The high catalytic activity and selectivity changes in the CO-H2 reaction of both Ni(o)/CeO2 samples with regard to Ni(o)/SiO2, can be interpreted by the presence of active sites at the metal/support interface, involving oxygen vacancies and the neighbouring electron-enriched nickel atoms. The authors suggest that the high hydrogen adsorption capacity of sample C1 and, consequently, its higher activity in the CO-H2 reaction may originate from a better ceria division state and higher metallic dispersion, which could favour electronic metal-support interactions and enhance the migration of hydrogen dissociated on the metal towards ceria.