Utilizing MgAl₂O₄ as a support for Mn-doped K₂WO₄ catalysts to maintain high surface area under the harsh reaction conditions of OCM, to get high CH₄ conversion rata, compared with commonly used SiO₂ support.

Abstract

The oxidative coupling of methane (OCM) provides a direct route to transform methane into higher value products. The alkali metal tungstate catalysts have demonstrated high selectivity towards C₂ products, ethane (C₂H₆) and ethylene (C₂H₄). However, the severe sintering of the SiO₂ support limits the reaction rate requiring active site densification to compete with unselective gas phase combustion reaction especially at high pressure operations. This work studies alkaline earth metal oxides as supports for K₂WO₄ catalysts to maintain comparatively high surface area under OCM conditions. Among Mg, Ca, and Sr aluminates, the K₂WO₄/MgAl₂O₄ catalyst exhibited the highest C₂ yields. To achieve high C₂ product selectivity, a relatively large loading of K₂WO₄ (20 wt %) was required likely to cover the unselective surface sites of MgAl₂O₄ support. The catalyst further showed high levels of stability when utilized at high pressures (0.9 MPa) for over 60 h, without any change in product selectivity. The Mn/K₂WO₄/MgAl₂O₄ showed multifold higher CH₄ conversion rate, compared with the SiO₂ counterpart. The findings showcase the potential of the MgAl₂O₄ support as a viable candidate for alkali metal tungstate catalysts for OCM, which introduces high density of active components in given volume in the reactor, which induces high contribution of the catalyst relative to the pure gas phase oxidation.