MnTiO₃-driven low-temperature oxidative coupling of methane over TiO₂-doped Mn₂O₃-Na₂WO₄/SiO₂ catalyst

Oxidative coupling of methane (OCM) is a promising method for the direct conversion of methane to ethene and ethane (C₂ products). Among the catalysts reported previously, Mn₂O₃-Na₂WO₄/SiO₂ showed the highest conversion and selectivity, but only at 800° to 900°C, which represents a substantial challenge for commercialization. We report a TiO₂-doped Mn₂O₃-Na₂WO₄/SiO₂ catalyst by using Ti-MWW zeolite as TiO₂ dopant as well as SiO₂ support, enabling OCM with 26% conversion and 76% C₂-C₃ selectivity at 720°C because of MnTiO₃ formation. MnTiO₃ triggers the low-temperature Mn²⁺?Mn³⁺ cycle for O₂ activation while working synergistically with Na₂WO₄ to selectively convert methane to C₂-C₃. We also prepared a practical Mn₂O₃-TiO₂-Na₂WO₄/SiO₂ catalyst in a ball mill. This catalyst can be transformed in situ into MnTiO₃-Na₂WO₄/SiO₂, yielding 22% conversion and 62% selectivity at 650°C. Our results will stimulate attempts to understand more fully the chemistry of MnTiO₃-governed low-temperature activity, which might lead to commercial exploitation of a low-temperature OCM process.