Oxidative Coupling of CH4 on Supported Na2WO4 Promoted with Transition Metals (M = Co, Mn, Mo).

Oxidative coupling of methane (OCM) is a promising process of direct transformation of CH4 to ethylene instead of a complicated two-step process in terms of first forming syngas through reforming or partial oxidation and then producing ethylene with Fischer–Tropsch synthesis (FTS). Na2WO4 has been one of the most studied catalysts of OCM. Here we investigated how the introduced transition metal elements Co, Mn, or Mo to Na2WO4 could influence the catalytic performance of OCM on the supported Na2WO4. It is found that Co, Mn and Mo can obviously promote catalytic activity of transforming CH4 and selectivity for producing ethylene and ethane in OCM performed on Na2WO4 supported on microporous silicate-1 (S-1). A similar promotion of Co, Mn and Mo to the catalytic activity and selectivity in OCM performed on Na2WO4 was found when the Na2WO4 was supported on Matériaux de l′Institut Lavoisier-53(Al) [MIL-53(Al)]. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy studies of these catalysts with added transition metal Co, Mn or Mo show that these metals diffused into the lattice of Na2WO4, further suggesting that the promotional effect likely arises from modification of the active phase of the supported Na2WO4 during OCM. [ABSTRACT FROM AUTHOR]