Abstract:
Atomically adsorbed hydrogen is a prerequisite for acrolein hydrogenation over silver particles. With density functional models, the dissociative adsorption of H2 on silver was calculated endothermic, with an activation barrier of ~120 kJ/mol. Oxygen binds strongly on silver and the dissociative adsorption of H2 on oxygen-modified surfaces, like p(nx1)O/Ag(110), Ooss/Ag(111) and O/Ag(110), is highly exothermic, with calculated barriers from ~70 kJ/mol to as low as 10 kJ/mol. The most efficient mechanism for hydrogen activation found, identified by the model studies, is near isolated O atoms at Ag(110) where each oxygen produces two adsorbed H atoms while oxygen is removed as water. The mechanism of acrolein hydrogenation to propenol or propanal was modelled on O/Ag(110) and Ooss/Ag(111). The calculated barriers suggest that the model with subsurface oxygen yields a high selectivity to allyl alcohol, as found in experiment.