Conditions for higher methanol selectivity for partial CH4 oxidation over Fe-MOR using N2O as the oxidant and comparison to Fe-SSZ-13, Fe-SSZ-39, Fe-FER, and Fe-ZSM-5

Abstract

Continuous catalytic conversion of methane to methanol was investigated on Fe-MOR at atmospheric pressure and moderate temperatures (270–300 °C) with an emphasis on improving the methanol selectivity. Results showed a relation between the methanol selectivity, iron content and mesopore addition on Fe-MOR as well as H2O concentration in the feed. Decreasing the iron content of Fe-MOR, adding mesopores to MOR or increasing water vapor pressure from 3 to 21 kPa gave higher methanol selectivity. Addition of mesopores suppressed the over-oxidation products (CO and CO2) and coke formation significantly, resulting in an increased catalyst lifetime as well as higher methanol turnover frequency (2.0 vs. 3.9 h−1 at 320 °C). Using DFT methods several active site candidates were analyzed regarding their formation energies, UV–Vis spectra and methanol formation pathways. DFT studies suggest that [Fe2O2]2+ or [HOFe(μ-O)FeOH]2+ sites on the 8 member rings are active for direct methane to methanol conversion.