Involvement of solid acid on Al- and Ga-doped porous silica in the Diels-Alder reaction
Involvement of solid acid on Al- and Ga-doped porous silica in the Diels-Alder reaction
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DOI：
10.1016/j.apcata.2003.12.045
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发表时间：
2004-06-25
影响因子：
5.5
通讯作者：
Hattori, T
中科院分区：
文献类型：
--
作者：
Satsuma, A;Segawa, Y;Hattori, T
考察了固体酸催化剂的种类、强度、酸中心数量和孔径等因素对2，3-二甲基丁二烯和对苯二酚在Al和Ga掺杂的多孔硅胶(MCM-41、沸石和无定形二氧化硅)上的Diels-Alder反应。MCM-41和无定形二氧化硅催化剂对Diels-Alder反应表现出较高的活性，而沸石则表现出较低的活性。与吸附吡啶的红外光谱对比表明，固体Lewis酸中心对反应是有效的。根据NH3程序升温脱附(NH3-TPD)测定的总酸中心数，比较了每种催化剂的循环次数。Al-MCM-41和Ga-MCM-41催化剂的转化率高于典型的均相Lewis酸催化剂AlCl3。酸性中心越强的催化剂在Diels-Alder反应中的转化率越高。通过比较在973K抽空的Ga-MCM-41和H型丝光沸石(H-MoR)，考察了孔径的影响。通过973K抽空H-MoR脱水，H-MoR的Bronsted酸中心被转化为酸强度与Ga-MCM-41相当的Lewis酸中心。根据Lewis酸位的数量，在973K抽空后的Ga-MCM-41和H-MoR具有相同的翻转数，尽管它们具有不同的孔尺寸。这些结果清楚地表明，催化剂的催化活性依赖于Lewis酸位的强度和数量，而孔径对2，3-二甲基丁二烯与对苯二酚的Diels-Alder反应的催化活性影响不大。(C)2004爱思唯尔B.V.保留所有权利。
The Diels-Alder reaction of 2,3-dimethylbutadiene with p-benzoquinone using Al- and Ga-doped porous silica, i.e., MCM-41, zeolite, and amorphous silica, was studied focusing on individual effects of types, strength, and amount of acid sites and pore size of solid acid catalysts. MCM-41 and amorphous silica-based catalysts exhibited high activity for the Diels-Alder reaction, while zeolites only showed low activity. Comparison with IR spectra of adsorbed pyridine clearly indicates that solid Lewis acid sites are effective for the reaction. Turnover numbers of each catalyst were compared based on the number of total acid sites measured by NH3-temperature programmed desorption (NH3-TPD). Al-MCM-41 and Ga-MCM-41 showed higher turnover numbers than that of AlCl3, which is a typical homogeneous Lewis acid catalyst. The catalysts having stronger acid sites basically showed higher turnover numbers in the Diels-Alder reaction. The effect of pore size was examined by comparison of Ga-MCM-41 and H-type mordenite (H-MOR) evacuated at 973 K. Through dehydration of H-MOR by evacuation at 973 K, Bronsted acid sites of H-MOR were converted to Lewis acid sites of which acid strength is comparable to Ga-MCM-41. Based on the number of Lewis acid sites, Ga-MCM-41 and H-MOR after evacuation at 973 K showed the same turnover number, although they have different pore sizes. These results clearly demonstrate that the catalytic activity depends on strength and amount of Lewis acid sites, while there is not much effect of pore size on the catalytic activities of the Diels-Alder reaction of 2,3-dimethylbutadiene with p-benzoquinone. (C) 2004 Elsevier B.V. All rights reserved.