Identifying and controlling the acid site distributions in mordenite zeolite for dimethyl ether carbonylation reaction by means of selective ion-exchange

As Brønsted acid sites in different types of channels exhibit distinct catalytic behaviors in the dimethyl ether (DME) carbonylation reaction over acidic mordenite (H-MOR) zeolites ( e.g. acid sites in 8-membered ring channels for carbonylation reaction, acid sites in 12-membered ring channels for methanol-to-hydrocarbons reactions), the identification and regulation of acid site distribution in mordenite zeolites are of great importance to improve the catalytic performance. In this work, we employ the selective ion-exchange method to identify and control the acid site distribution in mordenite zeolites, and the chemical properties of acid sites in different channels are investigated by NH 3 -TPD and CD 3 CN FT-IR. Additionally, the effect of selective ion-exchange on the catalytic performance of DME carbonylation reaction is also discussed. The selective ion-exchange is realized by using tetramethylammonium (TMA + ) ions, which can selectively remove the counter ions in the 12-membered ring channels but are inaccessible to the counter ions in 8-membered ring channels due to the steric hindrance. The selective ion-exchange reveals that the relative amounts of acid sites in 12-membered ring channels and 8-membered ring channels are 68% and 32%, respectively. Interestingly, it is found that introducing TMA + into H-MOR zeolites significantly improves the catalytic activity and stability in DME carbonylation reaction as a result of depressing the methanol-to-hydrocarbons reactions. The 3TMA-H-MOR catalyst shows high stability for 210 hours on stream. The present work opens a new avenue for designing carbonylation catalysts with excellent stability in DME carbonylation reaction. The identification and regulation of acid site distributions in mordenite zeolites are accomplished by using tetramethylammonium ions to selectively exchange with the counter ions in 12-membered channels.