Photocatalytic Oxidative Coupling of Methane to Ethane Using Water and Oxygen on Ag₃PO₄-ZnO

Abstract

Photocatalytic oxidative coupling is an effective way of converting CH4 to high-value-added multi-carbon chemicals under mild conditions, where the breaking of the C–H bond is the main rate-limiting step. In this paper, the Ag3PO4-ZnO heterostructure photocatalyst was synthesized for photocatalytic oxidative coupling of methane (OCM) to C2H6. In addition, an excellent C2H6 yield (16.62 mmol g–1 h–1) and a remarkable apparent quantum yield (15.8% at 350 nm) at 49:1 CH4/Air and 20% RH are obtained, which is more than three times that of the state-of-the-art photocatalytic systems. Ag3PO4 improves the adsorption and dissociation ability of O2 and H2O, benefiting the formation of surface hydroxyl species. As a result, the C–H bond activation energy of CH4 on ZnO was obviously reduced. Meanwhile, the improved separation of photogenerated carriers on the Ag3PO4-ZnO heterostructure also accelerates the OCM process. Moreover, Ag nanoparticles (NPs) derived from Ag3PO4 reduction by photoelectrons promote the coupling of *CH3, which can inhibit the overoxidation of CH4 and increase C2H6 selectivity. This research provides a guide for the design of catalyst and reaction systems in the photocatalytic OCM process.

Regulation of Oxygen Activation Pathways to Optimize Photocatalytic Methane Oxidative Coupling Selectivity

“…Therefore, the effects of reaction temperature and Au plasmon resonance on the OCM reaction were excluded out for Au/TiO 2 –NV o catalysts. Numerous studies have also confirmed that the performance of OCM depends mainly on light irradiation rather than temperatures less than 150 °C. ,, We also tested the performance of the catalyst under simulated light conditions (AM 1.5G), the catalyst can also exhibit C 2 H 6 yields of 1.76 μmol h –1 (Figure S20a). The yield was significantly decreased due to the much smaller proportion of ultraviolet bands in the simulated 1sun as compared to the original xenon lamp (Figure S20b).…”

Recent Advances in the Conversion of Methane to Syngas and Chemicals via Photocatalysis

“…And the Ag nanoparticle supporting on the ZnO further increased the photoactivity due to the surface plasmon resonance. Wang et al [131] synthesized a Ag 3 PO 4 -ZnO hetero-structured photocatalyst for OCM reaction, which exhibited excellent C 2 H 6 yield (16.62 mmol•g À 1 •h À 1 ) and significant apparent quantum yield (15.8 % at 350 nm). It was suggested that Ag 3 PO 4 improved the adsorption and dissociation ability of O 2 and H 2 O, which were conducive to the formation of surface hydroxyl group.…”