Abstract: Copper-based catalysts exhibit high activity and selectivity in the oxidation and carbonylation of methanol to dimethyl carbonate (DMC), however, the presence of water as a byproduct can significantly affect the catalytic performance. This study investigated the effect of water in the methanol feedstock on the conversion of methanol to DMC using a copper-based catalyst supported on carbon material (Cu/C) catalyst. The results indicate that, as the water content in the methanol feedstock increases, the initial catalytic activity decreases significantly, the water content has no apparent effect on the selectivity of DMC; however, the CO2 content in the gas-phase products increases remarkably as the water content increases. Under different water content conditions, the catalyst exhibits identical patterns of reactivity variation. Methanol conversion reaches its maximum value at 15 hours into the reaction. As reaction time progresses, activity gradually declines and stabilizes between 150 and 250 hours. Increasing water content significantly reduces the initial catalytic activity. This is mainly due to that the competitive adsorption of water molecules on the Cu/C catalyst with reactant methanol molecules, which reduces contact between active Cu species and reactant methanol. Under the reaction conditions with a constant water content, the active Cu reacts with the reactant O2 and the by-products water and CO2, and thus converted into Cu2(OH)2CO3. Moreover, the acidic environment created by CO2 dissolving in water promotes the dissolution and loss of Cu2(OH)2CO3, which reduces the content of active Cu species in the catalyst and leads to the decrease in catalytic activity and stability. Furthermore, the oxidation and agglomeration of Cu species, induced by water, exacerbate the catalyst deactivation. This work may inform the design of Cu-based catalysts for oxidative carbonylation reactions and provide a theoretical basis for understanding the impact of by-product water on Cu/C catalysts.

Key words: Cu-based catalyst, water, activity, stability, methanol oxidative carbonylation; dimethyl carbonate