题名：Oxidative Coupling of Methane: Examining the Inactivity of the MnO_x-Na₂WO₄/SiO₂ Catalyst at Low Temperature

来源：Angewandte Chemie International Edition

发表年代：2022年

作者：Jiaqi Si, Guofeng Zhao,* Weidong Sun, Jincun Liu, Cairu Guan, Yong Yang, Xue-Rong Shi, Yong Lu*

Abstract: Oxidative coupling of methane (OCM) cata-lyzed by MnO_x-Na₂WO₄/SiO₂ has great industrial prom-ise to convert methane directly to C_2–3 products, but itshigh light-off temperature is the most challengingobstacle to commercialization and its working mecha-nism is still a mystery. We report the discovery of a low-temperature active and selective MnO_x-Na₂WO₄/SiO₂ catalyst enriched with Q² units in the SiO₂ carrier, beingcapable of converting 23 % CH₄ with 72 % C_2–3 selectiv-ity at 660 °C. From experiments and theoretical calcu-lations, a large number of Q₂ units in the MnO_x-Na₂WO₄/SiO₂ catalyst is a trigger for markedly loweringthe light-off temperature of the Mn³⁺  Mn²⁺ redoxcycle involved in the OCM reaction because of the easyformation of MnSiO₃. Notably, the MnSiO₃ formationproceeds merely through the SiO₂-involved reaction inthe presence of Na₂WO₄: Mn₇SiO₁₂ + 6 SiO₂  7 MnSiO₃+ 1.5 O₂. The Na₂WO₄ not only drives the light-off ofthis cycle but also gets it working with substantialselectivity toward C_2–3 products. Our findings shine alight on the rational design of more advanced MnO_x-Na₂WO₄ based OCM catalysts through establishing newMn³⁺  Mn²⁺ redox cycles with lowered light-off tem-perature.