As the catalytic performance of zeolite catalysts is closelyrelated to the positions of Bronsted acid sites (BAS),identifying and controlling the distribution of BAS in zeolites are of great importance to regulate the catalytic reactions, which is also a widely concerned fundamental issue in the field of zeolite catalysis.A paradigmatic case is that the dimethyl ether (DME)carbonylation preferentially occurs in the 8- membered ring (8-MR) channels of mordenite zeolite, while the acid sites in 12-membered ring (12-MR) channel favor the methanol-to-hydrocarbons reactions and causethe deactivation. In order to design and develop the catalysts for the DME caronylation reaction, therefore, it is very important to identify and control the acid site distribution in zeolite.
Recently, a research group led byProf. Zhongmin Liu and Wenliang Zhu from Dalian Institute of Chemical Physics, Chinese Academy of Sciences reported that the acid site distribution of mordenite zeolite can be identified and controlled by the means of selective ion-exchange,which wasrealized by using tetramethylammonium (TMA+) ions.TMA+ionscan selectively remove the counter ions in the 12-MRchannels butwereinaccessible to the counter ions in 8-MRchannels due to the steric hindrance.The selective ion-exchangerevealedthat the relative amounts of acid sites in 12-MRchannels and 8-MRchannelswere68% and 32%, respectively. Interestingly, itwasfound that introducing TMA+intoH-MOR zeolites significantly improvedthecatalyticactivityand stabilityinDME carbonylation reactionas a result of depressingthemethanol-to-hydrocarbons reactions.TheTMA-modifiedcatalyst shows high stability for210 hours on stream.
This work was published inCatalysis Science & Technology.
The present workopensanewavenue fordesigning carbonylation catalysts with excellent stability in DME carbonylation reaction.
This work was supportedby theStrategic Priority Research Program of the Chinese Academy of Sciences: Transformational Technologies for Clean Energy and Demonstration(TEXT by Shiping Liu)
Identifying and controlling the acid sitedistributions in mordenite zeolite for dimethylether carbonylation reaction by means of selectiveion-exchange. Shiping Liu, Hongchao Liu, Xiangang Ma, Yong Liu,Wenliang Zhu* , Zhongmin Liu*, Catalysis Science & Technology, 10(14):4663-4672, 2020.
