Tuning CO 2 hydrogenation selectivity on Ni/TiO 2 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 molCO2 molNi-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.