Acid Site's Shape Selectivity in Dimethyl Ether Carbonylation Reaction over 8-Membered Ring Zeolites : a First-principles Study

Zeolite is in the spotlight as an eco-friendly catalyst for various reactions. It can typically promote dimethyl ether (DME) carbonylation reaction to methyl acetate (MA). In this reaction, CO addition reaction to surface methyl group (SMG) is known as rate determining step (RDS). Stabilizing the cationic transition state of RDS can increases the reactivity, and zeolites which have eight-membered ring (8MR) is suitable. In this research, the DME carbonylation reaction mechanisms over 8MR zeolites, especially CO addition reaction, are studied using a First-principles calculation. Chabazite (CHA), erionite (ERI), ferrierite (FER), linde type A (LTA), stilbite (STI) are selected as 8MR zeolites. CHA, LTA has a symmetric circular shape 8MR, but ERI, FER, STI has an aliphatic shape 8MR. Circular 8MR zeolites have little difference in reaction energy and activation energy according to acid site because of highly symmetric ring shape. However, aliphatic 8MR zeolites differs in reaction energy and activation energy depending on the acid site. At the acid site with a large curvature, negatively charged oxygens within 8MR can stabilize the cationic transition state better compared to the small curvature acid site. Based on these results, the reactivity according to the shape of the zeolite and the site is compared, and the reaction conditions with optimal reactivity is explored.