Fan Benhan, Zhang Wenna, Gao Pan, Hou Guangjin, Liu Rongsheng, Xu Shutao, Wei Yingxu, Liu Zhongmin
National Engineering Research Center of Lower-Carbon Catalysis Technology, Dalian National Laboratory for Clean Energy, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China.
University of Chinese Academy of Sciences, Beijing 100049, P. R. China.
J Phys Chem Lett. 2022 Jun 6:5186-5194. doi: 10.1021/acs.jpclett.2c00932.
It is of great significance to accurately quantify the Brønsted acid sites (BASs) at different positions of mordenite (MOR) zeolite. However, H-MOR obtained from Na-MOR can hardly avoid dealumination under hydrothermal conditions, which causes difficulty in the acid characterization. Herein, Na-Al -HMQC was performed combined with high-field Na MQ MAS NMR and DFT calculation, which provided an unambiguous attribution of the Na chemical shifts and further helped to improve the resolution of Al MAS NMR. By fitting the Na and H MAS NMR spectra of Na/H-MOR, the intrinsic BAS contents in different T-sites were measured by characterizing the location and content of sodium ions. These Na/H-MOR zeolites with various acid distributions were used for DME carbonylation and showed that the amount of BASs in the T3 site was proportional to the activity of carbonylation. This study provides a new method for investigating the intrinsic acid properties of zeolites.
准确量化丝光沸石（MOR）不同位置的布朗斯特酸位点（BASs）具有重要意义。然而，由钠型丝光沸石（Na-MOR）得到的氢型丝光沸石（H-MOR）在水热条件下难以避免脱铝，这给酸性质表征带来困难。在此，结合高场钠魔角旋转核磁共振（Na MQ MAS NMR）和密度泛函理论（DFT）计算进行了钠-铝-高分辨魔角旋转核磁共振（Na-Al -HMQC），这对钠化学位移进行了明确归属，并进一步有助于提高铝魔角旋转核磁共振（Al MAS NMR）的分辨率。通过拟合钠型/氢型丝光沸石（Na/H-MOR）的钠和氢魔角旋转核磁共振谱，通过表征钠离子的位置和含量来测量不同T位的本征BAS含量。这些具有不同酸分布的Na/H-MOR沸石用于二甲醚羰基化反应，结果表明T3位的BAS数量与羰基化活性成正比。该研究为研究沸石的本征酸性质提供了一种新方法。
