We synthesize and evaluate a diverse range of Mn/TiO2 catalysts with varying physical and redox properties for the methane-to-methyl-ester reaction using molecular oxygen in a diluted acid medium (10 wt% trifluoroacetic acid). Despite initial differences in manganese distributions, nearly all catalysts are active under the reaction conditions, and the degree of activity is partially correlated to catalyst reducibility in hydrogen temperature programmed reduction and manganese K-edge X-ray absorption spectroscopy. Under methane-limited conditions, exceptionally high product yields of up to ca. 30% are obtained. Catalysts synthesized with a co-precipitation method demonstrate the highest productivity (up to 1440 μmol gcat-1 h-1) in methane-excess conditions and the full activity can be restored in a subsequent reaction cycle upon a mild thermal treatment. Under high conversion conditions, the co-precipitated catalyst can achieve methane-based product yields of ca. 15%. The performance of Mn/TiO2 catalysts using molecular oxygen under less corrosive conditions surpasses that of other heterogeneous catalysts.

中文翻译：

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Mn/TiO2 催化剂，用于将甲烷与分子氧高产率部分氧化成甲酯

我们合成并评估了各种具有不同物理和氧化还原特性的 Mn/TiO2 催化剂，用于在稀酸介质（10 wt% 三氟乙酸）中使用分子氧进行甲烷-甲酯反应。尽管锰分布最初存在差异，但几乎所有催化剂在反应条件下都是活性的，并且活性程度与氢程序升温还原和锰 K 边缘 X 射线吸收光谱中的催化剂还原性部分相关。在甲烷受限的条件下，可获得高达 30% 的极高产品产量。在甲烷过量条件下，用共沉淀法合成的催化剂表现出最高的生产率（高达 1440 μmol gcat-1 h-1），并且在温和的热处理后，可以在随后的反应循环中恢复全部活性。在高转化率条件下，共沉淀催化剂可实现约 15% 的甲烷基产品收率。在腐蚀性较小的条件下使用分子氧的 Mn/TiO2 催化剂的性能优于其他非均相催化剂。