High‐Performance Mn2O3‐Na2WO4/SiO2‐TiO2 Catalyst for the Oxidative Coupling of Methane: TiO2‐Modulated MnTiO3 Formation for Enhanced Low‐Temperature Performance

Abstract

AbstractAs a direct conversion route for the production of ethylene from methane, the oxidative coupling of methane (OCM) is highly promising. The Mn2O3‐Na2WO4/SiO2 catalyst doped with 44 μm anatase‐TiO2, consisting of 5 wt% TiO2, 5 wt% Mn2O3, 8 wt% Na2WO4 and balance SiO2 was prepared, achieving ∼22 % CH4 conversion with ∼72 % selectivity towards C2−C3 hydrocarbons even at the relatively low temperature of 700 °C. This catalyst was found to run stably for at least 300 h without signs of deactivation, which provides promising and comparable low‐temperature activity and selectivity but a more cost‐effective alternative to the previously‐reported Mn2O3‐Na2WO4/Ti‐MWW catalyst containing expensive Ti‐MWW zeolite. XRD and Raman analyses revealed that the in situ formation of MnTiO3 in the TiO2‐doped catalyst is responsible for the gains in low‐temperature OCM activity. In addition, TPR and TPO results also indicated that MnTiO3 activates O2 more readily at ∼650 °C, while three‐step switchover experiments clearly demonstrated that MnTiO3 could trigger facile redox behavior at low reaction temperatures. Thus, the MnTiO3‐induced redox cycle for O2 activation enables this TiO2‐doped catalyst to provide superior CH4 conversion at 700 °C.