Nickel Dynamics Switches the Selectivity of CO2 Hydrogenation

Abstract

The Reverse Water Gas-Shift reaction (CO2+H2mathematical equation CO+H2O) allows to balance syn-gas under industrial conditions. Nickel has been suggested as a potential catalyst but the temperature required is too high, more than 800 °C, limiting practical implementation but when lowering the temperature methanation occurs. Simulations via Density Functional Theory on well-defined surfaces have systematically failed to reproduce these experimental results. But under reaction conditions, Ni surfaces are not static and DFT models coupled to microkinetics show that low temperatures (high CO coverages) drive the generation of Ni adatoms that are the active sites for methanation. At higher temperatures, the adatom population decreases, and the selectivity towards CO increases. Thus the mechanism behind the selectivity switch is driven by the dynamics induced by reaction intermediates. Our work contributes to the inclusion of dynamic aspects of materials under reaction conditions in the understanding of complex catalytic behaviour.