Determination of Acid Site Location in Dealuminated MCM-68 by 27Al MQMAS NMR and FT-IR Spectroscopy with Probe Molecules
Determination of Acid Site Location in Dealuminated MCM-68 by 27Al MQMAS NMR and FT-IR Spectroscopy with Probe Molecules
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使用探针分子通过 27Al MQMAS NMR 和 FT-IR 光谱测定脱铝 MCM-68 中的酸位位置
DOI：
10.1021/acs.jpcc.7b09576
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
Yokoi Toshiyuki
中科院分区：
文献类型：
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作者：
Otomo Ryoichi;Nishitoba Toshiki;Osuga Ryota;Kunitake Yusuke;Kamiya Yuichi;Tatsumi Takashi;Yokoi Toshiyuki
采用硝酸处理法制备了一系列不同硅铝比的MCM-68分子筛，并与β分子筛进行了比较。铝的形态和酸中心的位置随硅铝比的不同而变化。以吡啶和2，6-二叔丁基吡啶为探针分子，通过傅里叶变换红外光谱对MCM-68分子筛样品中的布朗斯特酸中心位置进行了分类，并根据位置确定了布朗斯特酸中心的数量。对于高铝MCM-68，布朗斯特酸中心广泛分布在12环通道和10环窗口以及超级笼内。酸处理容易去除12环通道中的Brnsted酸中心，因此，高硅MCM-68的Brnsted酸中心主要位于10环窗口和超笼内部。高硅MCM-68的27Al MQMAS核磁共振谱显示两个特定的峰可分配给T6和T7位，这两个峰不面向12环通道，形成了对酸处理高度耐受的Brnsted酸中心。在山梨醇脱水反应中，MCM-68催化剂表现出比β、丝光沸石和ZSM-5更好的催化性能。MCM-68分子筛在12环和10环通道的交叉处和超笼内部存在较大的空隙，使得山梨醇脱水时容易出现大体积的过渡态，从而使其具有较高的催化性能。
A series of MCM-68 zeolites with different Si/Al ratios were prepared by treatment with nitric acid and compared with beta zeolites. Speciation of aluminum and location of acid sites changed depending on the Si/Al ratio. The location of Brønsted acid sites in MCM-68 samples was able to be classified by FT-IR measurements with pyridine and 2,6-di-tert-butylpyridine as probe molecules, and the number of Brønsted acid sites was quantified according to the locations. For high-aluminum MCM-68, Brønsted acid sites were broadly distributed in both the 12-ring channel and 10-ring windows as well as inside the supercage. The Brønsted acid sites in the 12-ring channel were easily removed by the acid treatment, and consequently, high-silica MCM-68 had Brønsted acid sites predominantly in the 10-ring windows and inside the supercage.27Al MQMAS NMR spectra of high-silica MCM-68 showed two specific peaks assignable to T6 and T7 sites, which did not face the 12-ring channel, forming the Brønsted acid sites highly tolerant to the acid treatment. MCM-68 catalysts showed better catalytic performance in dehydration of sorbitol than beta, mordenite, and ZSM-5. Large void spaces at the intersection of 12- and 10-ring channels and inside the supercage for MCM-68 made it easy to take bulky transition states in the dehydration of sorbitol, resulting in its high catalytic performance.