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首页> 外文期刊>ACS catalysis >Carbonylation of Dimethyl Ether to Methyl Acetate over SSZ-13
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Carbonylation of Dimethyl Ether to Methyl Acetate over SSZ-13

机译：二甲醚在SSZ-13上乙酸甲酯的羰基化

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摘要

The small-pore zeolite with the chabazite framework topology, SSZ-13, is found to be an active catalyst in the carbonylation of dimethyl ether to methyl acetate (MA). The production of MA over SSZ-13 after 24 h on stream at 165 degrees C and 1 bar approaches that obtained from mordenite and is significantly higher than from ferrierite at comparable Si/Al of ca. 10. To understand the origin of the activity, SSZ-13 materials are synthesized with variable Si/Al, characterized via several techniques including multinuclear magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and evaluated for their carbonylation activity. While MA production rates increase with decreasing Si/Al, the correlation is nonlinear due to the effect of Si/Al on the acid site distribution within different confining environments, and the associated impact of the latter on the rate-determining transition state barrier. Enhanced MA production rates trend with acid sites located at the eight-membered ring (8MR) that are increasingly populated as framework Al content increases. Density functional theory analyses of transition state energies as a function of active site location support the experimental findings, where the lowest apparent barriers are associated with the methoxy groups that orient within the plane of the 8MR window. This is due to an optimal charge stabilization of the cationic transition states with the negatively charged oxygens within the 8MR window. The effects of catalyst chemical composition, separate from framework topology, are also investigated using SAPO-34 (the silicoaluminophosphate analog of SSZ-13). Analyses of the H-1 MAS NMR signals and carbonylation activity suggest that the higher acid site strength of SSZ-13 compared to that of the SAPO material is required for effective Bronsted acid catalysis of Koch-type carbonylation pathways.
机译：发现具有Chabazite框架拓扑的小孔沸石SS​​Z-13，是在二甲醚的羰基化至乙酸甲酯（MA）中的活性催化剂。在165摄氏度的165摄氏度上的溪流上产生MA通过SSZ-13和从丝光沸石获得的1巴接近，并且显着高于CA的比较Si / Al的Ferrierate。为了了解活动的来源，通过可变Si / Al合成SSZ-13材料，其特征在于，通过多核魔法角旋转核磁共振（MAS NMR）光谱，并评估其羰基化活性。虽然MA生产率随着Si / Al的降低而增加，但由于Si / Al对不同限制环境中的酸部位分布的影响，因此相关性是非线性，以及后者对速率确定过渡状态屏障的相关影响。增强的MA生产率与位于八元环（8MR）的酸部位潮湿，越来越多地填充为框架Al含量增加。作为活动位点位置的功能的过渡状态能量的密度函数理论分析支持实验结果，其中最低表观屏障与定向在8MR窗口的平面内的甲氧基有关。这是由于阳离子过渡状态的最佳电荷稳定状态，在8MR窗口内具有带负电的氧气。使用SAPO-34（SSZ-13的硅铝磷酸硅磷酸硅磷酸硅磷酸硅基磷酸硅基）还研究了催化剂化学组合物的影响。 H-1MAS NMR信号和羰基化活性的分析表明，与SAPO材料相比，SSZ-13的较高酸部位强度是Koch型羰基化途径的有效桥接酸催化。

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