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.