Hydrogen-assisted transformation of CO2 on nickel: the role of formate and carbon monoxide

The nanoscale description of the reaction pathways and of the role of the intermediate species involved in a chemical process is a crucial milestone for tailoring more active, stable, and cheaper catalysts, thus providing "reaction engineering" capabilities. This level of insight has not been achieved yet for the catalytic hydrogenation of CO 2 on Ni catalysts, a reaction of enormous environmental relevance. We present a thorough atomic-scale description of the mechanisms of this reaction, studied under controlled conditions on a model Ni catalyst, thus clarifying the long-standing debate on the actual reaction path followed by the reactants. Remarkably, formate, which is always observed under standard conditions, is found to be just a "deadend" spectator molecule, formed via a Langmuir-Hinshelwood process, whereas the reaction proceeds through parallel Eley-Rideal channels, where hydrogen-assisted C-O bond cleavage in CO 2 yields CO already at liquid nitrogen temperature