Low-Temperature Light-off MnOx -Na2 WO4 -Based Catalysts: A Step Forward to OCM Process Industrialization

Abstract

Oxidative coupling of methane (OCM) catalyzed by MnO_x -Na₂ WO₄ -based catalysts has great industrial potential to convert CH₄ directly to C_2-3 products, but the high light-off temperature is a big challenge to OCM commercialization. The reaction mechanism studies disclosed that O₂ /CH₄ -activation relevant "Mn²⁺ ↔Mn³⁺ " redox cycle is tightly linked with the catalyst light-off. One concept is thus put forward that the OCM light-off temperature could be lowered once a "Mn²⁺ ↔Mn³⁺ " redox cycle was established to be triggered at low temperature over MnO_x -Na₂ WO₄ -based catalysts. The relevant studies in recent years are reviewed, showing that the establishment of low-temperature light-off "Mn²⁺ ↔Mn³⁺ " redox cycle over the MnO_x -Na₂ WO₄ -based catalysts indeed works effectively toward a low-temperature light-off OCM process. Moreover, three perspectives for the OCM industrialization are discussed based on this concept, including monolithic catalyst, fluidized-bed method and chemical-looping process.

Keywords: chemical looping; heterogeneous catalysis; oxidative coupling of methane; reaction mechanism; redox cycle.