Quasicatalytic and catalytic oxidation of methane to methanol by nitrous oxide over FeZSM-5 zeolite

• CH4 oxidation by N2O was studied in quasicatalytic and catalytic modes.
• The reaction in both modes proceeds with participation of α-oxygen.
• In quasicatalytic mode methanol and dimethyl ether are extracted from the surface.
• In catalytic reaction mode, water strongly increases selectivity for methanol.
• Quasicatalytic study provides valuable information on the mechanism of catalysis.

Methane oxidation by N2O at 200 °C and below was shown to proceed in a quasicatalytic mode resulting in product accumulation on FeZSM-5 surface. Methanol that formed via methane oxidation by α-oxygen, CH4 + (FeIII–O−)α, migrated from α-sites, initiating new reaction cycles. At 200 °C, a 4-h run provided turnover number close to 7. Methanol and dimethyl ether (DME) were the products extracted from the surface.At above 200 °C, the reaction moved to conventional catalytic mode with product desorption into gas phase. Water strongly increased methanol selectivity, which attained 62% at 275 °C (accounting coke). Contrary to expectations, DME was not detected among the gas-phase products being converted to coke.Comparison of quasicatalytic and catalytic data can provide new information on the reaction mechanism including a possibility of identifying potential intermediates invisible under catalytic conditions. Mechanistic scheme presenting main steps of both reaction modes was suggested.

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