(64f) Investigation of Chabazite and Other Small-Pore Zeolites in the DME Carbonylation Reaction

Carbon-carbon bond formation via carbonylation reactions constitutes an important step in upgrading low-value feedstocks derived from syngas and biomass into useful chemical intermediates. The carbonylation of dimethyl ether (DME) is one such reaction, that occurs in the presence of acid catalysts to yield methyl acetate (MA), an industrially important solvent and platform chemical. MA production activity in mordenite (MOR) and ferrierite (FER) zeolites is attributed to the 8-membered ring (8MR) side pockets of these topologies, that facilitate the rate-limiting attack of CO onto the methoxy intermediate due to an optimized geometry.

In this work, we investigated the activity and location of the active site of a small-pore, 8MR-containing zeolite topology, chabazite (CHA). We found that the activity towards MA production orders MOR > CHA > FER for comparable Si/Al (~10), and that CHA-type zeolites (SSZ-13s) synthesized with 5 < Si/Al < 70 exhibit an activity maximum centered near Si/Al = 10 that does not scale with total acid site density. To understand this, we conducted high-spin ¹H MAS NMR analyses on dehydrated SSZ-13s and divalent cation-exchange experiments to develop a structure-activity model for the active site in the CHA framework. The promising activity of CHA motivated the investigation of other small-pore, 8MR-containing topologies (e.g., LEV, AEI) as catalysts in the carbonylation of DME. Understanding the origin of activity in these types of frameworks may lead to applications in other carbonylation chemistries of interest.