TiO2-doped Mn2O3-Na2WO4/SiO2 catalyst for oxidative coupling of methane: Solution combustion synthesis and MnTiO3-dependent low-temperature activity improvement

Abstract

The Mn2O3-Na2WO4/SiO2 catalyst is the most promising one among the enormous catalysts for the oxidative coupling of methane (OCM) but only at above 800°C. No doubt that lowering temperature of the OCM process is at the forefront of this catalysis field. A promising low-temperature active and selective TiO2-doped Mn2O3 Na2WO4/SiO2 catalyst, consisting of 6wt% TiO2, 6wt% Mn2O3, 10wt% Na2WO4 and SiO2 in balance, is developed by solution combustion synthesis (SCS) method. This catalyst is capable of converting 20% CH4 with 70% selectivity to C2-C3 hydrocarbons even at 700°C (catalyst bed temperature) and is stable for at least 250h without deactivation sign, for a feed gas of 50% CH4 in air using a gas hourly space velocity of 8000mLgcat.−1h−1. In contrast, the non-TiO2-doped SCS catalyst is almost inactive at 700°C whereas it can achieve reactivity (∼24% CH4 conversion and ∼74% C2-C3 selectivity) comparable to the TiO2-doped one at 800°C. XRD and Raman results evidently reveal that the formation of MnTiO3 during the OCM process appears to be important for the low-temperature OCM activity improvement by TiO2-doping.