The direct conversion of methane into methanol is an ideal, auspicious process; however, its application remains challenging. Herein, a systematic study was carried out on the continuous gas-phase oxidation of methane into methanol with steam in the absence and presence of O2 over Cu-mordenite (Cu-MOR) with various Cu loadings. The methanol productivity was found to depend on the Cu/Al ratio and selecting the optimum Cu/Al ratio was crucial in maximizing methanol productivity. Methanol productivity increased with the O2 concentration up to a certain point, after which methanol selectivity decreased. The stability of the catalyst improved with increasing Cu/Al ratio. Methanol selectivity was found to be 100% under anaerobic conditions, indicating the effectiveness of steam in activating methane and preventing further oxidation of the methoxy group. However, under aerobic conditions, methanol selectivity decreased due to the oxidation of the methoxy group by O2. The developed catalysts achieved stable methanol production rates, and the dominant Cu species changed with the Cu/Al ratio. Overall, the results suggest that optimizing the Cu/Al ratio and carefully controlling the O2 concentration in the feed can improve the conversion of methane into methanol using Cu-MOR catalysts.
