密度泛函理论研究Y分子筛的Bronsted酸性

利用密度泛函理论(DFT),研究了Y分子筛骨架上4种O—H(Bronsted酸位)的酸性,计算基于以B酸位为中心的团簇模型,采用BLYP方法。结果表明,通过计算Y分子筛的团簇结构、去质子化能量以及NH3,C5H5N在B酸中心上的吸附能,得出Y分子筛4种O—H的酸性由强至弱顺序为:SOD笼内的O 2 H、超笼内的O 4 H、超笼内的O 1 H/六棱柱内的O 3 H,即Y分子筛中最强的B酸位在SOD笼内。4种酸性中心与碱性探针分子之间的吸附稳定性由强至弱的顺序为O 4,O 1,O 2/O 3,分子筛的空间位阻致使吸附稳定性顺序与酸性顺序不同。探针分子通常倾向于与B酸位在超笼内吸附。

Study on the Bronsted acidity of Y zeolite by density functional theory

The acidity of four kinds of O—H （Bronsted acid sites） in framework of Y zeolite was studied in terms of density functional theory （DFT）,and the corresponding calculations were performed by BLYP hydride functional on the basis of cluster models in which each of Bronsted acid sites was taken as center.The results showed that by calculating cluster structures,deprotonating energy and adsorption energy of ammonia and pyridine onto Bronsted acid sites,the order for acidity of four kinds of O—H in Y zeolite from strong to weak was obtained as follows：O 2 H in sodalite cage,O 4 H in super cage,O 1 H in super cage/O 3 H in hexagonal prism,indicating that the strongest Bronsted acid site was in sodalite cage.The order for stability of adsorption of probe molecules onto Bronsted acid sites from strong to weak was O 4,O 1,O 2/O 3,and the steric hindrance of Y zeolite led to the difference between the above-mentioned orders.In general,probe molecules tended to be adsorbed onto Bronsted acid sites in super cage.