A DFT Study of CO Hydrogenation on Faujasite-Supported Ir Clusters: on the Role of Water for Selectivity Control.

Reaction mechanisms for the catalytic hydrogenation of CO by faujasite-supported Ir clusters were studied by periodic DFT calculations. The reaction can proceed through two alternative paths. The thermodynamically favoured path results in the reduction of CO to CO, whereas the other, kinetically preferred channel involves CO 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 Ir cluster by opening low-energy reaction channels for CO conversion.