Modification of Au/TiO₂ nanosystems by SiO₂ monolayers: Toward the control of the catalyst activity and stability

The activity and stability of Au/TiO₂ catalysts depend on several different factors such as the anchoring strength of the Au particles at the TiO₂ surface, the particle sintering, and the surface mobility of individual gold atoms and/or gold particles. Au/TiO₂ catalysts can be made resistant to sintering by atomic layer deposition (ALD) of a layer of SiO₂ onto the catalysts. In this study, first-principles density-functional calculations are used to investigate how the stability of Au nanoparticles is modified when a partial monolayer of SiO₂ is deposited on a Au/TiO₂ catalyst. We find that SiO₂ structures deposited on a pure TiO₂ substrate exhibit lattice-mismatch instabilities that result in the formation of additional strong anchoring sites for Au atoms/nanoparticles. An atomic-scale roughness introduced by a partial monolayer of SiO₂ can slow the atomic surface diffusion and inhibit Au nanoparticle growth/sintering, in agreement with previous experimental results.