Brønsted Acidity of Isomorphously Substituted ZSM-5 by B, Al, Ga, and Fe. Density Functional Investigations
Brønsted Acidity of Isomorphously Substituted ZSM-5 by B, Al, Ga, and Fe. Density Functional Investigations
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DOI：
10.1021/jp025792t
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发表时间：
2002-08
影响因子：
2.9
通讯作者：
S. Yuan;J. G. Wang;Y. W. Li;H. Jiao
中科院分区：
文献类型：
--
作者：
S. Yuan;J. G. Wang;Y. W. Li;H. Jiao
在密度泛函B3 LYP水平上研究了B、Al、Ga和Fe同晶取代ZSM-5分子筛的Bronsted酸性.根据计算的质子亲合能、酸性质子上的自然电荷和NH3的吸附能，布朗斯台德酸度按以下顺序增加：B-（OH）-Si < Fe-（OH）-Si < Ga-（OH）-Si < Al-（OH）-Si，与实验一致。在Al和Ga改性的团簇中，吸附的NH3变成由两个N−H···O氢键稳定的铵（NH 4+），而在Fe和B取代的团簇中，物理吸附的NH3由一个N···H−O氢键稳定。NH_3吸附改变了B配位球。
The Bronsted acidity of isomorphously substituted ZSM-5 by B, Al, Ga, and Fe has been studied at the B3LYP level of density functional theory. On the basis of the calculated proton affinity, natural charge on the acidic proton, and the adsorption energy of NH3, the Bronsted acidity increases in the order: B−(OH)−Si < Fe−(OH)−Si < Ga−(OH)−Si < Al−(OH)−Si, in agreement with the experiment. In both Al and Ga modified clusters, the adsorbed NH3 becomes ammonium (NH4+) stabilized by two N−H···O hydrogen bonds, while the physisorbed NH3 is stabilized by one N···H−O hydrogen bond in Fe and B substituted clusters. It is also found that NH3 adsorption changes the B coordination sphere.