(670h) Linking Zeolite Structure to Catalytic Behavior in the Carbonylation of Dimethyl Ether

The carbonylation of dimethyl ether (DME) into methyl acetate offers a promising route for converting syngas from non-petroleum sources into valuable chemicals like acetic acid, acetate esters, and related polymer products. This reaction primarily takes place at Brønsted acid sites on the 8-ring pores of zeolites, crucial for the stabilization of transition state. However, the relationship between the zeolite topology and catalytic activity remains partially understood, despite extensive research on high-performance zeolite frameworks such as MOR and FER. Addressing this gap, we synthesized various zeolites with 8-ring pores, including FER, CHA, ERI, AEI, STI, and LTA, having Si/Al ratios within 5–50. The carbonylation runs were conducted at 165 °C, and the turnover frequencies (TOFs) were estimated based on the acid site density characterization via the NH3-temperature programmed desorption. Highest TOFs were found at Si/Al ~10 regardless of the framework, with the TOF order being FER > STI ≈ CHA ≈ AEI > ERI > LTA. The conventional computation on the rate-determining CO addition step suggested LTA 8-rings have higher reactivity than CHA, based on the calculated CO addition activation energy order LTA < STI < ERI < CHA ≈ AEI < FER, conflicting with the experimental findings. This discrepancy highlights the limitations of relying solely on the CO addition activation energies on 8-ring pores as a kinetic descriptor and the importance of considering materials factors like Brønsted acid strength and true proton sitings over frameworks. For instance, the LTA zeolites showed the weakest acid strength, with preferred proton locations outside the 8-rings. We also calculated the methylation and water adsorption energies for the studied frameworks to provide a bird-eye view for the reaction, aiming to demystify the correlation between zeolite structures and catalytic performance and to contribute to the design of superior catalysts for DME carbonylation.