Title : The hydrogen spillover effect influencing parameters
Abstract:
Mechanisms of formation and diffusion, structure and role in hydrogenation reactions of hydrogen spillover are still debated. In this study we show how these issues are correlated to the nature and particle size [nanoparticles (NP), nanoclusters (NC), single atoms (SA)] of the metal phase, the nature of the oxide support, the nature of the reactant organic molecules. It is formed by reduction/dehydration or dehydroxylation processes. The H spilt-over species diffusion over the support proceeds by migration of pairs of H atoms, not by the hopping of H atoms from OH to OH surface groups, as generally believed. No correlation can exist between catalytic activity and concentration of hydrogen spillover or oxygen vacancies. The latter are active at the interface only. Activity orders in support effect studies are empirically useful but not pertinent from the fundamental point of view. Four hydrogenation mechanisms were identified.
