Directional Activation of Oxygen by the Au-Loaded ZnAl-LDH with Defect Structure for Highly Efficient Photocatalytic Oxidative Coupling of Methane.

Photocatalytic oxidative coupling of CH 4 (OCM) is a promising CH 4 conversion process that can achieve efficient methane conversion with the assistance of O 2 . It remains to be highly challenging to improve the photocatalytic OCM activity from catalyst design and to deepen the understanding of the reactant activation in the OCM process. In this work, the Au-loaded ZnAl-layered double hydroxides (LDHs) with and without oxygen vacancy are constructed (denoted as Au/ZnAl and Au/ZnAl-v), respectively. When applied for photocatalytic OCM, the Au/ZnAl-v shows a CH 4 conversion rate of 8.5 mmol g -1 h -1 with 92% selectivity of C 2 H 6 at 40 °C, outperforming most reported photocatalytic OCM systems at low temperature reported in the literature. Furthermore, the catalytic performance of Au/ZnAl-v can be stable for 100 h. In contrast, the An/ZnAl exhibits a CH 4 conversion rate of 0.8 mmol g -1 h -1 with 46% selectivity of C 2 H 6 . Detailed characterizations and DFT calculation studies reveal that the introduced Ov sites on Au/ZnAl-v are able to activate O 2 , and the resulting superoxide radical O 2 · - greatly promotes the activation of CH 4 . The coupling of CH 3 · groups with the assistance of Au cocatalyst leads to the formation of C 2 H 6 with high photocatalytic activity.