Spectroscopic characterization and reactivity study of ceria-supported nickel catalysts

Abstract

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 Ni⁰/CeO₂ samples with regard to Ni⁰/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 enhanced the migration of hydrogen dissociated on the metal towards ceria.