Regulation of Oxygen Activation Pathways to Optimize Photocatalytic Methane Oxidative Coupling Selectivity
Jiangjie Zhang, Junhui Zhang, Jinni Shen, Dongmiao Li, Jinlin Long, Wenxin Dai, Xuxu Wang, Zizhong Zhang
Abstract
Photocatalytic oxidative coupling of methane (POCM) is a direct way for the methane transformation into ≥C2 alkanes. However, the typical oxygen activation path often leads to the formation of strong oxidizing superoxide radical (O 2 – ) species, which makes the whole reaction face serious selectivity problems. Herein, we constructed N and oxygen vacancy dual active sites on TiO 2 {001} nanosheets (TiO 2 –NV o ) to regulate the oxygen activation pathway and achieve a high activity and selectivity of photocatalytic OCM. Compared with ordinary Au/TiO 2 {001} nanosheets, the alkane yields of Au/TiO 2 –NV o are increased from 16 μmol h –1 to 32 μmol h –1, and the selectivity of alkanes increased from 61% to 93%. The performance is superior when compared with the reported till date in photocatalytic OCM in batch reactors. The superior performance originates from the unique N–V o dual active sites for synergistically cleaving the detrimental O 2 – into desirable mono-oxygen active species (O ·– ) to suppress undesired overoxidation reaction. The formed O ·– species from O 2 – dissociation, in turn, is active for the selective H abstraction of CH 4 into •CH 3 to improve the subsequent C–C coupling reaction on the Au nanocluster surface. This work provides a new approach of O 2 dissociation to address the overoxidation of methane in an aerobic environment for achieving highly selective CH 4 conversion.