Tuning CO2 hydrogenation selectivity on Ni/TiO2 catalysts via sulfur addition

Abstract

In the context of CO₂ valorization, the possibility of shifting the selectivity of Ni catalysts from CO₂ methanation to reverse water gas shift reaction could be economically attractive provided that the catalyst presents sufficient activity and stability. Remarkably, the addition of sulfur (0.2–0.8% w/w) to nickel on a Ni/TiO₂ catalyst induces a complete shift in the catalyst selectivity for CO₂ hydrogenation at 340 °C from 99.7% CH₄ to 99.7% CO. At an optimal Ni/S atomic ratio of 4.5, the productivity of the catalyst reaches 40.5 mol_CO2 mol_Ni⁻¹ h⁻¹ with a good stability. Density functional theory (DFT) calculations performed on various Ni surfaces reveal that the key descriptor of selectivity is the binding energy of the CO intermediate, which is related to the local electron density of surface Ni sites.