MnTiO-driven low-temperature oxidative coupling of methane over TiO-doped MnO-NaWO/SiO catalyst.

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