Ab Initio Simulation of Lewis Sites in Mordenite and Comparative Study of the Strength of Active Sites via CO Adsorption
Ab Initio Simulation of Lewis Sites in Mordenite and Comparative Study of the Strength of Active Sites via CO Adsorption
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DOI：
10.1021/jp048056t
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发表时间：
2004-08
影响因子：
3.3
通讯作者：
L. Benco;T. Bučko;J. Hafner;H. Toulhoat
中科院分区：
文献类型：
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作者：
L. Benco;T. Bučko;J. Hafner;H. Toulhoat
采用从头算密度泛函方法研究了丝光沸石分子筛内活性中心的结构。我们调查的结构和性质的裸Al 3+阳离子绑定到框架和源自框架外的Al（H2O）63+阳离子脱水在严重的热处理的沸石。沸石中裸露的Al 3+阳离子导致有限的局部弛豫或被捕获在沸石结构的小环中而没有骨架的实质性弛豫。这样的阳离子表现为强刘易斯中心。捕获的Al 3+的强度通过CO的吸附进行评估，并比较各种沸石活性中心，如布朗斯台德网站，Na-抗衡离子，和表面硅烷醇。观察到CO伸缩频率的实验位移和计算位移之间总体一致。裸和水合Al 3+和Ga 3+阳离子的比较表明，伸缩频率蓝移到2230 cm-1可以只源于裸阳离子上的吸附。在不含.
Ab initio density-functional investigations of intrazeolite active centers have been performed for mordenite. We investigate the structure and properties of bare Al3+ cations bound to the framework and originating from extra-framework Al(H2O)63+ cations dehydrated at severe thermal treatment of the zeolite. A bare Al3+ cation in the zeolite causes either a limited local relaxation or is trapped in a small ring of the zeolite structure without substantial relaxation of the framework. Such a cation behaves as a strong Lewis site. The strength of trapped Al3+ is evaluated via the adsorption of CO and compared to a variety of zeolite active centers such as Bronsted sites, Na-counterions, and surface silanols. An overall agreement between experimental and calculated shifts of the CO stretching frequency is observed. The comparison of bare and hydrated Al3+ and Ga3+ cations shows that stretching frequencies blue-shifted to ∼2230 cm-1 can originate only from adsorption on bare cations. In zeolites not containing...