NiO/CeO2-Sm2O3 nanocomposites for partial oxidation of methane: In-situ experiments by dispersive X-ray absorption spectroscopy

In this work, we analyze Sm2O3-doped CeO2 (SDC) nanopowders and NiO/SDC nanocomposites in terms of sample reducibility and catalytic activity for partial oxidation of methane. We assess the role of the average crystallite size and specific surface area in Ni and Ce reduction kinetics by in-situ X-ray absorption spectroscopy experiments in diluted H2 and CH4/O2 mixtures. Our results indicate that crystallite size and surface area play a key role in CH4 activation through modification of the sample redox behavior. The oxidation of the metallic phase is the main cause of sample deactivation. A clear relationship is established between the temperature of maximum Ni oxidation rate and grain size. An interplay between Ce atoms from the support and Ni from the active phase was observed during the experiments, evidencing a complex relationship between oxygen vacancy concentration and catalytic activity. A high Ce3+ content in catalyst support was detrimental to catalytic activity [Display omitted] •Redox behavior significantly depends on grain size and surface area.•Sample deactivation occurs due to re-oxidation of metallic phase.•Temperature of maximum rate of Ni oxidation is directly correlated to grain size.•Ce reduction is enhanced by H2 spillover mechanism over metallic Ni particle•An excessive concentration of oxygen vacancies is detrimental to catalytic activity.