The hydrogen spillover effect. A misunderstanding story
Mohammed M. Bettahar
Abstract
The hydrogen spillover effect (HSPE) on metal catalysts supported on non-reducible oxides is still controversial. Our investigation shows that the controversy comes from a misunderstanding about statements of pioneer works. Papers accepting or rejecting the HSPE and based on these statements were found both not pertinent. Factually, the oxide surface OH groups play an important role in the formation, extent, and reactivity of hydrogen spillover. We propose that hydrogen spillover would consist in H/OH pairs, produced by an interfacial dehydroxylation then diffusing over the support by a thermodynamically neutral H/OH exchange mechanism and not by an H atom hopping process, as generally believed. The hydrogen atoms of the H/OH pairs may be consumed chemically or desorb as H2, giving rise to □/O2- pairs (where □ denotes an oxygen vacancy) which, in turn, may further dissociate H2, renewing the H/OH active sites. H/OH and □/O2 constitute conjugated pairs in the hydrogen spillover effect.