New strategy to control distribution of acid sites in zeolites

New strategy to control distribution of acid sites in zeolites
Graphical abstract. Credit: ACS Catalysis (2022). DOI: 10.1021/acscatal.1c05896

Zeolites are one of the shape-selective catalysts. The characteristics of zeolites, which come from the structural confinement on the molecular dimensions, are crucial for shape-selective catalysis.

The catalytical acid sites at different positions of show a distinct confinement effect for reactant molecules, especially reflected in mordenite (MOR) zeolite catalyzing dimethyl ether (DME) carbonylation reaction.

Recently, a research team led by Prof. Liu Zhongmin from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences (CAS) developed a new strategy to preferentially remove the acid sites in the 12-membered ring (12-MR) channels of MOR zeolite by a trimethylchlorosilane (TMCS) silylation treatment, which could improve the performance of DME carbonylation.

This study was published in ACS Catalysis on April 1.

The 8-membered ring (8-MR) channels of MOR zeolite are preferred for the selective carbonylation of DME, while the larger 12-MR channels can accommodate more reaction routes, which will cause rapid deactivation of the MOR zeolite. Therefore, it is necessary to selectively remove the acid sites in 12-MR channels of MOR to improve its in the DME carbonylation reaction.

The researchers used in situ diffuse reflectance infrared Fourier transform (DRIFT) and 29Si cross-polarization (CP) Nuclear Magnetic Resonance (NMR) spectroscopic techniques to investigate the interaction of TMCS molecules with the bridging hydroxyl groups within different positions of the H-mordenite (HMOR) zeolite.

They found that TMCS molecules bridged the HMOR framework via a hydrolysis reaction between chloro groups and Brønsted H+ atoms to cover the acid sites. Due to the space limitation, the silylation treatment selectively retained most of the acid sites (80%) in the desired position by TMCS replacing the Brønsted H+ atoms within 12-MR channels in the HMOR zeolite, leading to better selectivity and a much longer lifetime in the DME carbonylation reaction.


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More information: Rongsheng Liu et al, Selective Removal of Acid Sites in Mordenite Zeolite by Trimethylchlorosilane Silylation to Improve Dimethyl Ether Carbonylation Stability, ACS Catalysis (2022). DOI: 10.1021/acscatal.1c05896
Journal information: ACS Catalysis

Citation: New strategy to control distribution of acid sites in zeolites (2022, April 7) retrieved 26 June 2022 from https://phys.org/news/2022-04-strategy-acid-sites-zeolites.html
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