Effect of Calcination Temperature on the Characteristics and Performance of Solid Acid WO3/TiO2-Supported Lithium-Manganese Catalysts for the Oxidative Coupling of Methane

A series of solid acid WO3/TiO2-supported lithium-manganese oxide (Li-Mn/WO3/TiO2) catalysts for the oxidative coupling of methane (OCM) were prepared by the impregnation method. The XRD and XPS analyses showed that increasing the calcination temperature could promote the generation of Mn2+ and Mn3+ species and the anatase-to-rutile phase transformation of TiO2, which are beneficial to the OCM reaction. It was revealed by CO2-TPD, O-2-TPD, H-2-TPR, XPS, and CH4-TPSR that Li-Mn/WO3/TiO2 with higher calcination temperature possessed much stronger surface basicity, lower lattice oxygen mobility, and more abundant lattice oxygen, which are favorable for the selectivity to C-2 hydrocarbons. The catalytic, structural, and spectroscopic results showed that the catalytic performance, structure, and properties of catalysts were little influenced by the calcination temperature of the WO3/TiO2 support. The optimized calcination temperature of the support and the catalyst is 800 degrees C, on which the highest C-2 yield of 16.3 % was achieved at a reaction temperature of 750 degrees C.