Performance of oxidative coupling of methane on LiMn₂O₄/TiO₂ catalysts

A series of LiMn₂O₄/TiO₂ catalysts with spinel crystal structure were prepared by solid state reaction method, and the catalytic performance of oxidative coupling of methane on the different catalysts, such as TiO₂, Li/TiO₂, Mn/TiO₂, LiMn₂O₄ as well as LiMn₂O₄/TiO₂, was evaluated. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, CO₂ temperature programmed desorption and H₂ temperature programmed reduction. It is found that LiMn₂O₄ with spinel structure has high catalytic activity in oxidative coupling of methane reaction. 25.8% of CH₄ conversion, 43.2% of C₂ selectivity was obtained under the reaction conditions of 775℃, 0.1MPa, 7200mL·h^-1·g^-1, CH₄:O₂(volume ratio)=2.5. The introduction of TiO₂ support can not only improve CH₄ conversion and C₂ selectivity, but also restrain the deep oxidation of methane to CO₂. The LiMn₂O₄/TiO₂ with 8% loading amount showed the best activity, on which 31.6% of CH₄ conversion, 52.4% of C₂ selectivity were obtained and CO₂ selectivity was decreased to 26.3%. The effect of calcination temperature on the activity of LiMn₂O₄/TiO₂ catalysts was investigated. 850℃ is the optimal calcination temperature.