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

Methane oxidation by N2O at 200 degrees 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 alpha-oxygen, CH4 + (Fe-III-O center dot-)(alpha), migrated from alpha-sites, initiating new reaction cycles. At 200 degrees 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 degrees C, the reaction moved to conventional catalytic mode with product desorption into gas phase. Water strongly increased methanol selectivity, which attained 62% at 275 degrees 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. (C) 2014 Elsevier Inc. All rights reserved.