Li Ying, Yu Man, Cai Kai, Wang Meiyan, Lv Jing, Howe Russell F, Huang Shouying, Ma Xinbin
Key Laboratory for Green Chemical Technology of Ministry of Education, Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300350, China.
Phys Chem Chem Phys. 2020 May 28;22(20):11374-11381. doi: 10.1039/d0cp00850h. Epub 2020 May 6.
As the activity of dimethyl ether (DME) carbonylation over mordenite proportionally correlates with the Brønsted acid sites (BAS) in 8-membered ring (8-MR), enhancing the concentration of BAS in the 8-MR of MOR is important to improve the efficiency of the reaction. Herein, we report that the distribution of the BAS in the zeolite catalyst H-MOR can be altered by the synthesis of H-MOR with different cyclic amine structure-directing templates, several of which have not been reported previously for MOR synthesis. By combining FTIR, ICP, TG analysis and DFT calculations, it is verified that the strength of the interaction between amine or sodium cations and [AlO] in the zeolite framework plays a decisive role in Al distribution, owing to the competitive effect between Na and the cyclic amine compensating negative charges from the framework [AlO]. Quantitative analysis of the BAS in the 12-MR and 8-MR identifies the optimum template for maximizing the BAS in the 8-MR. It is shown that the enhanced activity of the H-MOR for the DME carbonylation to methyl acetate correlates with the increase in the BAS in the 8-MR. Our finding thus provides a facile strategy to direct Al location within different channels of the zeolite, which must benefit spatially confined reaction systems.
由于丝光沸石上二甲醚（DME）羰基化活性与八元环（8-MR）中的布朗斯台德酸位（BAS）成正比，提高丝光沸石8-MR中BAS的浓度对于提高反应效率至关重要。在此，我们报道通过使用具有不同环状胺结构导向模板合成H-MOR，可以改变沸石催化剂H-MOR中BAS的分布，其中几种模板此前尚未见用于MOR合成的报道。通过结合傅里叶变换红外光谱（FTIR）、电感耦合等离子体（ICP）、热重（TG）分析和密度泛函理论（DFT）计算，证实了由于Na与环状胺之间存在竞争效应，二者对沸石骨架中[AlO]负电荷的补偿作用不同，导致胺或钠离子与沸石骨架中[AlO]之间相互作用的强度对Al的分布起决定性作用。对12-MR和8-MR中BAS的定量分析确定了使8-MR中BAS最大化的最佳模板。结果表明，H-MOR对DME羰基化生成乙酸甲酯活性的增强与8-MR中BAS的增加相关。因此，我们的发现提供了一种简便策略来指导Al在沸石不同通道内的定位，这必将有利于空间受限的反应体系。
