A DFT study of CO2 hydrogenation on faujasite supported Ir4 clusters: on the role of water for selectivity control

Reaction mechanisms for the catalytic hydrogenation of CO2 by faujasite-supported Ir4 clusters were studied by periodic DFT calculations. The reaction can proceed through two alternative paths. The thermodynamically favoured path results in the reduction of CO2 to CO, whereas the other, kinetically preferred channel involves CO2 hydrogenation to formic acid under water-free conditions. Both paths are promoted by catalytic amounts of water confined inside the zeolite micropores with a stronger promotion effect for the reduction path. Co-adsorbed water facilitates the cooperation between the zeolite Brønsted acid sites and Ir4 cluster by opening low-energy reaction channels for CO2 conversion.