Specific selectivity of simple oxides towards CH4 activation

Abstract

Simple metal oxides exhibit noticeable catalytic activity in methane conversion reactions. However, their catalytic role in the selective activation of CH4 to more valuable products (CO, H2, olefins) is often masked by the highly oxidative reaction conditions and by complex catalyst formulations. Transient studies of the direct interaction of CH4 with simple catalytic systems, including rare-earth (La2O3, Nd2O3, Y2O3), alkali-earth (MgO) and reducible (TiO2), reveal peculiar selectivity for different monometallic oxides. Rare-earth metal oxides show high initial activity towards partial oxidation products (CO, H2), while MgO possesses unique selectivity towards coupling products (C2H6 and C2H4) with remarkable activity in dehydrogenation reactions. A continuous supply of lattice oxygen species for the selective oxidation of CH4 to CO is provided by TiO2, which can effectively prevent accumulation of C deposits. The results indicate the roles played by the metal oxide materials and provide a basis for rational design of catalysts and reaction conditions for the selective conversion of CH4.