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

Abstract

Methane conversion strategies that protect methanol 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 μmol 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.

Fine-Tuning Electron–Donor Capability in the Basic Anion of Poly(ionic liquid) Frameworks for Revolutionizing Catalytic Synthesis of Ethyl Methyl Carbonate with Both Ultrahigh Catalytic Activity and Selectivity

“…Hot filtration testing was performed to understand the mechanism of the slight loss in the catalytic performance through the modified procedure reported. 40 No further reaction of the filtrate after hot filtration was detected compared to before the filtration, as shown in Figure 4(b), indicating that the loss in the catalytic performance was not caused by the leaching of active sites of ILs. Moreover, we performed the FTIR and SEM studies on [CPIL-CDI][MeOPhO] before and after the reactions.…”

High conversion of methane to methyl ester at 298 K

“…9 However, although a lot of progress in the functionalization of methane has been made for over five decades, 2,10,11 to break through the selectivity-conversion limit of the aerobic oxidation of methane, i.e., to obtain methanol or methyl ester with a high yield (over 80%), is still a great challenge, [12][13][14][15][16][17][18][19][20][21][22][23][24] especially at room temperature (293-298 K) [25][26][27][28][29] under normal or low pressure (0.1-1.6 MPa). [25][26][27]30 Although some reaction systems show a high catalytic efficiency, over-oxidation has not been avoided. 31,32 Normally, to establish effective oxidation of methane with dioxygen to give methanol or methyl ester with a high yield under ambient conditions, it is necessary to determine: 1) a more effective catalytic species to cleave an inert C-H bond of methane (BDE = 439 kJ mol −1 ), 1 2) a reasonable way to generate methyl-oxygen intermediates using dioxygen or dioxygen activation, and 3) a chemical environment to guarantee that the product survives completely.…”

“…, to obtain methanol or methyl ester with a high yield (over 80%), is still a great challenge, 12–24 especially at room temperature (293–298 K) 25–29 under normal or low pressure (0.1–1.6 MPa). 25–27,30 Although some reaction systems show a high catalytic efficiency, over-oxidation has not been avoided. 31,32…”

Pyridine N-Oxide-Promoted Cobalt-Catalyzed Dioxygen-Mediated Methane Oxidation

“…More recently, a photopromoted decatungstate-catalyzed methane oxidation with more than 350 turnovers was reported by the Gunnoe group . In addition to homogeneous catalysts, heterogeneous Co and Mn catalysts were also demonstrated to be effective in TFA/C 6 F 14 at 215 °C by the van Bokhoven group. , …”

“…19 In addition to homogeneous catalysts, heterogeneous Co and Mn catalysts were also demonstrated to be effective in TFA/C 6 F 14 at 215 °C by the van Bokhoven group. 18,20 We recently reported a NaCl-promoted cobalt-catalyzed methane oxidation with O 2 as the oxidant to form methylene bis(trifluoroacetate) (MBTFA), which could be isolated by distillation and used in the synthesis of triazinane and imidazole salt (Scheme 1B). 21 The reaction is very efficient with productivity around 90 mol ester mol metal −1 h −1 but became violent when the temperature reached 140 °C.…”