Does H2O improve the catalytic activity of Au1-4/MgO towards CO oxidation?

TL;DR

This study uses density functional theory to investigate how water affects the catalytic activity of small gold clusters on MgO for CO oxidation, finding that water does not significantly influence the activity.

Contribution

It provides new insights into the role of water in gold-catalyzed CO oxidation, especially regarding different gold cluster sizes and the formation of reactive complexes.

Findings

Water presence does not alter catalytic activity of Au1-4/MgO.

Formation of hydroperoxyl-hydroxyl complex on Au1,3/MgO.

Water-mediated catalytic cycle unlikely on Au1,3/MgO.

Abstract

The present density functional theory study addresses the question whether the presence of H2O influences the catalytic activity of small gold clusters, Au1-4/MgO(100), towards the oxidation of carbon monoxide. To this end, we studied the (co-)adsorption of H2O and CO/O2 on these gold clusters. The ground state structures in the presence of all three molecular species, that we found, are Au1O2/MgO and Au2-4CO/MgO with H2O adsorbed on the surface in the proximity of the clusters-molecule complex. In this configuration the catalytic activity of Au1-4/MgO is indifferent to the presence of H2O. We also found that a stable, highly activated hydroperoxyl-hydroxyl complex, O2H\dot\dot OH, can be formed on Au1,3/MgO. For the catalytic active system Au8/MgO, it has been predicted that this complex opens an alternative catalytic reaction pathway towards CO oxidation. Our results suggest that this water mediated catalytic cycle is unlikely to occur on Au1,3/MgO. In the case of Au1/MgO the cycle is interrupted by the dissociation of the remaining (OH)2 complex after forming the first CO2 molecule. On Au3 /MgO the O2 H\dot\dot OH complex is likely to decompose upon the impact of a CO molecule, since three of its bond dissociation energies are comparable to the reaction barrier of the CO to CO2 oxidation.