Synergistic Active Sites on SiO2−Al2O3−TiO2 Photocatalysts for Direct Methane Coupling

Abstract

The SiO2−Al2O3−TiO2 ternary oxide system exhibited high photocatalytic activity in the photoinduced direct methane coupling at room temperature to produce hydrogen and hydrocarbons such as ethane. The best SiO2−Al2O3−TiO2 sample containing 10 mol % of Al and 0.5 mol % of Ti marked about 20 times higher photocatalytic activity than the SiO2−Al2O3 system reported previously. Al K-edge and Ti K-edge X-ray absorption near-edge structure (XANES) of the active SiO2−Al2O3−TiO2 samples indicated that both Al and Ti oxide species have a tetrahedral local structure in the active ternary samples. In the diffuse reflectance UV−vis spectra, the active samples showed additional absorption at 220−300 nm centered at 245 nm, which would be due to the interaction between the Al and Ti oxide species. The effective excitation wavelength of this photocatalyst for the photoinduced direct methane coupling was in good agreement with this additional photoabsorption. These results suggest that the pair sites consisting of the disp...