MnTiO(3)-driven low-temperature oxidative coupling of methane over TiO(2)-doped Mn(2)O(3)-Na(2)WO(4)/SiO(2) catalyst

Oxidative coupling of methane (OCM) is a promising method for the direct conversion of methane to ethene and ethane (C(2) products). Among the catalysts reported previously, Mn(2)O(3)-Na(2)WO(4)/SiO(2) showed the highest conversion and selectivity, but only at 800° to 900°C, which represents a substantial challenge for commercialization. We report a TiO(2)-doped Mn(2)O(3)-Na(2)WO(4)/SiO(2) catalyst by using Ti-MWW zeolite as TiO(2) dopant as well as SiO(2) support, enabling OCM with 26% conversion and 76% C(2)-C(3) selectivity at 720°C because of MnTiO(3) formation. MnTiO(3) triggers the low-temperature Mn(2+)↔Mn(3+) cycle for O(2) activation while working synergistically with Na(2)WO(4) to selectively convert methane to C(2)-C(3). We also prepared a practical Mn(2)O(3)-TiO(2)-Na(2)WO(4)/SiO(2) catalyst in a ball mill. This catalyst can be transformed in situ into MnTiO(3)-Na(2)WO(4)/SiO(2), yielding 22% conversion and 62% selectivity at 650°C. Our results will stimulate attempts to understand more fully the chemistry of MnTiO(3)-governed low-temperature activity, which might lead to commercial exploitation of a low-temperature OCM process.