Influence of temperature and H2 adsorption on the structure of silica-supported gold subnanometer clusters

The structure of selected gold subnanometer clusters (AuN, N = 6–7) deposited onto a silicon oxide (silica) surface is studied as a function of temperature and background hydrogen pressure via first-principles calculations. It is predicted that, in the absence of hydrogen, heating above 400 °C leads to the desorption of a water molecule, and correspondingly to a flip of the Au clusters from vertical to horizontal configurations to better adhere to the dehydroxylated silica surface. In the presence of hydrogen, instead, the gold clusters are predicted to dissociate hydrogen molecules and at high temperature to finally detach from the surface and start sintering. These results elucidate the importance of Au–H interactions for very small gold clusters, and their possible role on the structure and chemistry of these nano-catalytic systems.