Heterogeneous Mn-Based Catalysts for the Aerobic Conversion of Methane-to-Methyl Trifluoroacetate

Methane conversion strategies that protect meth-anol via in situ esterification achieve higher yields compared to direct methane conversion without product protection; however, most of these high-yield systems operate under unfavorable conditions. To date, there is very limited work in developing heterogeneous catalysts for methane-to-methyl-ester conversion, and studies demonstrating the activity of manganese for methane conversion are limited. We have prepared a series of silica-, titania-, and zirconia-supported manganese catalysts and measured the activity of these catalysts for the aerobic conversion of methane to methyl trifluoroacetate in diluted trifluoroacetate acid. The silica-supported catalyst exhibits high overall activity, but significant amounts of homogeneously active manganese are observed. Titania-and zirconia-supported manganese catalysts catalyze the reaction heterogeneously with activities up to 613 mu mol gcat-1 h-1 and show nondetectable leaching. Manganese oxide is poorly dispersed on titania and zirconia, whereas high dispersion is realized on silica. This work demonstrates a facilely synthesized supported manganese catalyst that converts methane heterogeneously in satisfactory yields under improved conditions in a diluted acid, compared to those of conventional methane-to-methyl-ester systems.