Influence of Alkali and Alkaline Earth Cations on the Brønsted Acidity of Zeolites
Influence of Alkali and Alkaline Earth Cations on the Brønsted Acidity of Zeolites
复制标题
碱金属和碱土金属阳离子对沸石布朗斯台德酸度的影响
DOI：
10.1021/jp0041048
复制
发表时间：
2001
影响因子：
3.3
通讯作者：
N. Rösch
中科院分区：
文献类型：
--
作者：
†‡§ and Georgi N. Vayssilov;N. Rösch
我们报告了一个关于碱和碱土金属阳离子如何影响其附近桥接OH基团的Bronsted酸度的计算研究。沸石碎片被建模为含有两个或三个铝中心的六环faujasite结构。计算结果表明，碱或碱土金属阳离子的电荷补偿使桥接羟基的去质子化能（DE）相对于完全质子形式的团簇有所降低；也就是说，混合形式的沸石含有质子和金属阳离子用于电荷补偿，其表现出比相应的纯质子形式更酸的位点。钙和钠交换模型簇的DE下降幅度最大。对桥接羟基性质和计算DE值趋势的分析表明，金属阳离子对团簇去质子化形式的稳定的贡献对于降低所考虑的桥接羟基的DE是重要的。
We report a computational study on how alkali and alkaline earth metal cations affect the Bronsted acidity of a bridging OH group in their close vicinity. The zeolite fragment is modeled as a six-ring of faujasite structure which contains two or three aluminum centers. The calculations show that charge compensation by alkali or alkaline earth metal cations decreases the deprotonation energy (DE) of the bridging OH group relative to the completely protonic forms of the clusters; i.e., mixed forms of zeolites which contain both protons and metal cations for charge compensation exhibit sites that are more acidic than the corresponding pure protonic forms. The strongest decrease in DE is found for calcium and sodium exchanged model clusters. An analysis of the properties of the bridging OH groups and the trends in calculated DE values reveals that the contribution of the metal cation to the stabilization of the deprotonated form of the cluster is important for the reduction of DE of the considered bridging OH...