An Operando Spectroscopic Investigation of the NO/H2 Reaction on LaCoO3 and Pd-modified LaCoO3 — Influence of O2 on Catalyst Performances and Structure of Adsorbed Species

The catalytic reduction of NO by hydrogen has been studied over palladium-based catalysts supported on LaCoO 3 . Particular attention has been paid to the observation of chemisorbed N-containing species from operando infrared spectroscopic experiments during the NO/H 2 reaction in the presence and in the absence of excess oxygen. X-ray photoelectron spectroscopy coupled to a catalytic chamber was used to examine parallel changes in oxidation state and chemical environments of Co and Pd after exposure to various reactive conditions. Complementary atomic information were obtained from the examination of the N 1s photopeak and compared to those obtained from IR observations. Dinitrosyl species adsorbed on oxidic cobalt species were observed at low temperature, whereas nitrate/nitrite species and NH x species predominate at high temperature. The presence of dinitrosyl species has been discussed for elucidating surface changes in the presence of oxygen and related modifications in the selectivity behavior of prereduced Pd/LaCoO 3 . The formation of adsorbed N-atoms and NH 2 species as intermediate was observed correlatively to ammonia formation on LaCoO 3 and on Pd/LaCoO 3 catalysts in the absence of oxygen. Monodentate nitrates were characterized and could be involved in the selective reduction of NO by hydrogen on Pd/LaCoO 3 in excess O 2 .