One‐step synthesis of methylal via methanol oxidation: Reaction kinetics, mechanism, thermodynamics, and product analysis

Abstract

Summary The recent abundance of methanol has made it an attractive raw material for chemical synthesis. This study conducts a thermodynamic analysis of the main and side reactions in a system where methanol is oxidized to methylal. A relationship between the thermodynamics and product distribution of this system is proposed. By studying the effect of reaction temperature on the catalytic activity of a Mo‐Fe/HZSM‐5 (80‐80) catalyst, the relationship between thermodynamic parameters and product distribution was further verified. Kinetic analysis of the one‐step process shows that a lower activation energy is one of the reasons for the higher catalytic activity of the iron‐molybdenum‐based bifunctional catalyst. Accordingly, it is proposed that all main and side reactions in this process are driven by two chemical adsorption reactions. The first occurs at active sites of iron and molybdenum oxidation on the catalyst surface. The adsorbed methanol and O2 obtain hydroxyl and methoxy groups linked to the iron molybdate. Subsequently, desorbed formaldehyde and methanol undergo a second chemical adsorption on the acidic active centres of the catalyst with surface carbonyl and hydroxyl groups, respectively. Formaldehyde and the adsorbed methoxy group are catalysed by the acidic sites to generate intermediates similar to the methoxy and methylene group structures. This study provides complete information on the thermodynamics, kinetics, and reaction mechanism of a one‐step process of producing methylal from methanol, thereby allowing optimization of this process.