SSZ-13分子筛在二甲醚羰基化反应中的机理研究和空间限域效应  

Mechanistic insights and the role of spatial confinement in catalytic dimethyl ether carbonylation over SSZ-13 zeolite

作　　者：张晓敏 蔡凯[1,3] 李媖 戚暨 王悦 刘云铎[1,2] 王美岩 黄守莹 马新宾[1] Xiaomin Zhang;Kai Cai;Ying Li;Ji Qi;Yue Wang;Yunduo Liu;Mei-Yan Wang;Shouying Huang;Xinbin Ma(Key Laboratory for Green Chemical Technology of Ministry of Education,Haihe Laboratory of Sustainable Chemical Transformations,School of Chemical Engineering and Technology,Tianjin University,Tianjin 300350,China;Zhejiang Institute of Tianjin University,Ningbo 315201,Zhejiang,China;Research Institute of Petroleum Processing,SINOPEC,Beijing 100083,China;College of Chemical Engineering,Inner Mongolia University of Technology,Hohhot 010051,Inner Mongolia,China;Institute of Molecular Plus,Tianjin University,Tianjin 300072,China)

机构地区：[1]天津大学化工学院,绿色合成与转化教育部重点实验室,物质绿色创造与制造海河实验室,天津300350 [2]天津大学浙江研究院,浙江宁波315201 [3]中石化石油化工科学研究院有限公司,北京100083 [4]内蒙古工业大学化工学院,内蒙古呼和浩特010051 [5]天津大学分子+研究院,天津300350

出　　处：《Chinese Journal of Catalysis》2024年第6期301-311,共11页催化学报（英文）

基　　金：国家重点研发计划(2023YFB4103600);国家自然科学基金(21978209,22008177).

摘　　要：乙醇作为一种绿色清洁的燃料替代品和油品添加剂,在全球有广泛的市场需求.利用合成气经乙酸甲酯(MA)合成乙醇的工艺路线,因其原子经济性、产品选择性高、反应条件温和等优势而备受关注.其中,二甲醚(DME)羰基化是该路线的关键步骤之一.研究证实,具有8元环(8-MR)孔道结构的硅铝酸盐微孔分子筛可以在较低的反应温度下高选择性催化二甲醚羰基化反应.目前,研究者已经对丝光沸石(MOR)、镁碱沸石(FER)等分子筛进行了全面深入的分析,但对SSZ-13等菱沸石(CHA型)的研究有限,缺乏SSZ-13上主、副反应催化机理的阐释,并且忽略了沸石独特的笼状结构在反应中的空间限域效应.本文结合实验和理论计算确定了SSZ-13分子筛催化DME羰基化的活性位点,并探究了孔道的限域效应.通过负载具有不同尺寸的Na^(+)和Cs^(+)实现了对不同通道中Brönsted酸位点(BAS)的选择性屏蔽.酸性质表征和密度泛函理论(DFT)计算结果表明,在较低的负载量下,Na^(+)优先取代SSZ-13的6元环(6-MR)中的BAS,而Cs^(+)由于其较大的离子半径只能与8-MR中的BAS发生交换,从而实现了对SSZ-13不同孔道中酸分布的调控.负载不同金属量以及金属种类的样品活性研究表明,当6-MR中BAS减少时,DME转化率基本不变;而当8-MR中BAS被离子交换时,DME转化率明显下降.随后,将未经金属改性的、具有不同硅铝比的母体SSZ-13样品的MA生成速率与其8-MR中BAS的数量相关联,发现两者呈较好的线性关系,说明SSZ-13的8-MR中BAS为DME羰基化的活性中心.同时,DFT计算了DME在不同孔道BAS上的解离能,结果表明DME更容易在8-MR的BAS上解离从而进行后续反应.随后,探究了SSZ-13笼的空间限域效应对主副反应的影响机制.通过比较金属负载量相近的Na/H-SSZ-13和Cs/H-SSZ-13上CO插入甲氧基形成烯酮的反应势垒,证实了较大尺寸金属离子的引入增加了主反应速控步的能垒.为�The SSZ-13 zeolite,which exhibits typical CHA topology characterized by 8-membered ring(8-MR)channels,has shown potential for catalyzing dimethyl ether(DME)carbonylation.However,current studies have yet to provide a comprehensive analysis of its catalytic mechanisms.In this study,we investigated the mechanism of SSZ-13-catalyzed DME carbonylation and the role of spatial confinement in this reaction.By exploiting the differences in the radii of the metal ions,we selectively replaced Brønsted acid sites(BAS)within specific channels,as confirmed by quantitative acidity analysis.Combining the activity data and the dissociation energies of the reactants on the BAS within different rings,we found that both the main and side reactions of DME carbonylation occurred on the 8-MR BAS of SSZ-13.Furthermore,the exchange of ions of different radii highlighted the confinement effect of the pore space in the SSZ-13 zeolite.Characterization of the deposits in spent catalysts,along with theoretical insights,revealed that the reduced cage space adversely affects the stabilization of side reaction intermediates,which in turn mitigates side reactions and improves the selectivity toward methyl acetate.This study presents an effective approach to modulate the acid site distribution and spatial confinement and provides critical insights into the determinants of the catalytic performance of SSZ-13.These findings offer valuable guidance for the future design and optimization of zeolites,aiming to enhance their efficacy in catalytic applications.

关 键 词：二甲醚 羰基化 SSZ-13分子筛 酸位点 限域效应 

分 类 号：TQ223.122[化学工程—有机化工] O643.36[理学—物理化学]