Conversion of Syngas to Methyl Acetate and Acetic Acid Using Tandem Catalysts Combining a Cu-based Methanol Synthesis Catalyst and a Cu-exchanged Mordenite Zeolite: Effect of Pyridine Pre-adsorption on Mordenite

Direct synthesis of methyl acetate (MA) and acetic acid (AA) from syngas using a tandem catalyst consisting of heterogeneous catalysts for methanol synthesis and dimethyl ether (DME) carbonylation has attracted considerable attention. In this system, syngas derived from the gasification of biomass and plastic waste can be converted into MA and AA via methanol and DME in a single step without using expensive noble metal catalysts or toxic and corrosive halogen cocatalysts. In this study, Cu ion-exchanged mordenite (Cu-MOR) zeolites pre-treated with pyridine at 150-400 °C were used as catalysts for DME carbonylation. The catalytic performance was evaluated at 230 °C, 5 MPa, and a gas hourly space velocity of 5.2 L g−1 h−1. Pyridine pre-adsorption modified the size and morphology of MOR particles, as well as the oxidation state and spatial distribution of ion-exchanged Cu species, thereby influencing the catalytic activity. Among the catalysts tested, Cu-MOR pre-treated with pyridine at 200 °C exhibited the highest total selectivity and space-time yield of MA and AA. This enhanced performance was attributed to an increased proportion of active Cu species. The structure-activity relationship of Cu-MOR catalysts was discussed.