Sub-nanometer-thick AI2O3 Overcoat Remarkably Enhancing Thermal Stability of Supported Gold Catalysts

Abstract

Supported gold nanoparticle catalysts show extraordinarily high activity in many reactions. While the relative poor thermal stability of Au nanoparticles against sintering at elevated temperatures severely limits their practical applications. Here atomic layer deposition (ALD) of TiO2 and Al2O3 was performed to deposit an Au/TiO2 catalyst with precise thickness control, and the thermal stability was investigated. We surprisingly found that sub-nanometer-thick Al2O3 overcoat can sufficiently inhibit the aggregation of Au particles up to 600 °C in oxygen. On the other hand, the enhancement of Au nanoparticle stability by TiO2 overcoat is very limited. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of CO chemisorption and X-ray photoelectron spectroscopy measurements both confirmed the ALD overcoat on Au particles surface and suggested that the presence of TiO2 and Al2O3 ALD overcoat on Au nanoparticles does not considerably change the electronic properties of Au nanoparticles. The catalytic activities of the Al2O3 overcoated Au/TiO2 catalysts in CO oxidation increased as increasing calcination temperature, which suggests that the embedded Au nanoparticles become more accessible for catalytic function after high temperature treatment, consistent with our DRIFTS CO chemisorption results.