Oxidative coupling of methane: MOx-modified (M = Ti, Mg, Ga, Zr) Mn2O3-Na2WO4/SiO2 catalysts and effect of MOx modification

Abstract

Mn2O3-Na2WO4/SiO2 is considered as the most promising catalyst for the oxidative coupling of methane (OCM) process; however, it only has a better catalytic performance over 800 °C. To improve its low-temperature performance, an attempt has been made to modify the Mn2O3-Na2WO4/SiO2 catalyst using TiO2, MgO, Ga2O3, and ZrO2. Among the synthesized catalysts, the TiO2-modified Mn2O3-Na2WO4/SiO2 catalyst shows markedly improved low-temperature OCM performance, achieving a high CH4 conversion of ~23% and a good C2-C3 selectivity of ~73% at 700 °C (the catalyst bed temperature), along with promising stability for at least 300 h without signs of deactivation. In comparison with the unmodified Mn2O3-Na2WO4/SiO2 catalyst, the TiO2 modification results in significant improvement in the low-temperature activity/selectivity, whereas the MgO modification has almost no impact and the Ga2O3 and ZrO2 modifications have a negative effect. The X-ray diffraction (XRD) and Raman results reveal that the formation of a MnTiO3 phase and a MnTiO3-dominated catalyst surface is crucial for the improvement of the low-temperature activity/selectivity in the OCM process.