Current understanding of Oxidative Coupling of Methane (OCM) reaction over supported Mn-Na₂WO₄ catalysts

This perspective reviews the current understanding of the Oxidative Coupling of Methane (OCM) reaction over the supported Mn-Na₂WO₄/SiO₂ catalyst, with a focus on recent insights gained from state-of-the-art in-situ and operando spectroscopic characterization and chemical probe experiments under controlled environments. The supported Mn-Na₂WO₄/SiO₂ catalyst exhibits dynamic structural changes during the OCM reaction, involving multiple reactive lattice and adsorbed oxygen species, each associated with different oxide phases. These oxygen species play distinct roles in various steps of the OCM mechanism. The catalytic active sites for activation of CH₄ are associated with isolated surface Na-WO_x sites on the SiO₂ support and the role of surface MnO_x sites on SiO₂ is to oxidatively dehydrogenate C₂H₆ to C₂H₄. This paper provides a detailed discussion of these roles and also introduces new experimental data from Temporal Analysis of Products (TAP) studies to clarify the ongoing debate in the literature regarding the contributions of lattice versus adsorbed oxygen species in OCM reaction product formation. Additionally, recommendations are offered for optimizing the performance of supported Mn-Na₂WO₄/SiO₂ catalysts to enhance CH₄ activation and C₂ product selectivity.