Formation and influence of surface hydroxyls on product selectivity during CO2 hydrogenation by Ni/SiO2 catalysts

Hydroxyl formation on metallic Ni sites and Ni-SiO2 interfacial region of Ni/SiO2 during CO2 hydrogenation is characterized for the first time with the aid of H2-TPR, CO-TPR, quasi in situ XPS and in situ DRIFTS of adsorbed CO. These reaction-generated hydroxyl groups are distinct from those existing on SiO2 surfaces and can decrease the binding strength of CO, hampering its further hydrogenation, particularly for smaller nickel nanoparticles, as evidence by the DFT calculations. This fact contributes to the product selectivity of CO2 hydrogenation over nickel nanoparticles with different sizes. The experimental and theoretical observations shed lights on the characterization of surface hydroxyls and rational design of heterogeneous catalysis through fine tuning of surface reaction intermediates by optimization of particle size.