Submonolayer Is Enough: Switching Reaction Channels on Pt/SiO₂by Atomic Layer Deposition

The reaction mechanism of CO2 with H2 is studied on platinum nanoparticles supported on fumed silica. It is found that platinum nanoparticle size, reaction temperature, and metal oxide promoters play important roles in determining the reaction rate and the mechanism of forming surface carbonyl species. Metal oxide promoters consist of submonolayer titanium oxide or aluminum oxide overcoated onto the catalysts by atomic layer deposition (ALD). These alter the CO formation rate, influence the adsorption and desorption behavior, and switch the surface reaction channel from the Eley-Rideal to Langmuir-Hinshelwood mechanism due to an enhancement of CO2 affinity to the metal-metal oxide interface. At the temperatures relevant for catalytic turnover, ALD overcoating significantly increases catalytic activity in CO2 hydrogenation to CH4 and CO, while the identity of the oxide overcoat helps control product selectivity.