Periodic Density Functional Calculation on the Brønsted Acidity of Modified Y-Type Zeolite
Periodic Density Functional Calculation on the Brønsted Acidity of Modified Y-Type Zeolite
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DOI：
10.1021/jp8104562
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发表时间：
2009-03
影响因子：
3.7
通讯作者：
Katsuki Suzuki;T. Noda;Germán Sastre;N. Katada;M. Niwa
中科院分区：
文献类型：
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作者：
Katsuki Suzuki;T. Noda;Germán Sastre;N. Katada;M. Niwa
对Ca2+-、Ba2+-和Al(OH)2+交换的y型沸石的Bronsted酸进行了周期性密度泛函计算。当二价阳离子稳定在6元环窗（I′，II′和II′位）时，氨的吸附能（Eads）增强，位于超笼中的酸性O1H基团（νOH）的振动频率降低。计算值与氨红外光谱/质谱-程序升温解吸（IRMS-TPD）方法得到的相应实验值一致。Al(OH)2+中的Al位于6元环上与周围3个氧原子配位的I ‘和II ’位点，这些位点被稳定为四配位的框架外Al（EFAL）。在高磁场（16 T）下的27Al MQ MAS NMR测量证实了EFAL物质的这种构型。钠盐笼处阳离子的高吸电子势增强了酸性O1H基团的强度。
Periodic density functional calculations on Bronsted acidities of Ca2+-, Ba2+-, and Al(OH)2+-exchanged Y-type zeolites were performed. When a divalent cation was stabilized in the 6-membered ring window (sites I′, II, and II′), the adsorption energy of ammonia (Eads) was enhanced and the vibrational frequency of the acidic O1H group (νOH) located in the supercage was decreased. Those calculated values agreed with the corresponding experimental values obtained by the ammonia infrared spectroscopy/mass spectroscopy-temperature programmed desorption (IRMS-TPD) method. Al in Al(OH)2+ is located in sites I′ and II′ coordinated to the surrounding three oxygen atoms in the 6-membered ring, and those were stabilized as tetracoordinated extra-framework Al (EFAL) species. This configuration of EFAL species has been supported by 27Al MQ MAS NMR measurement at a high magnetic field (16 T). High electron-withdrawing potentials of cations at the sodalite cage enhanced the strength of the acidic O1H group located in sup...