Beta分子筛中Al的分布和Brφnsted酸的酸性强度

Location of Al and Acid Strength of Brφnsted Acid in Beta Zeolite

基于量子化学中的密度泛函理论(DFT),研究了Beta分子筛中骨架Al在9个不同T位的分布和Brφnsted酸的分布及其强度.计算采用8T簇模型和B3LYP/6-31G(d,p)方法,得到了不同T位的Al/Si替代能、(Al,H)/Si替代能和质子亲和势,以及碱性探针分子NH3在Beta分子筛酸性位的吸附能.结果表明,骨架Al和Brφnsted酸优生位于Beta分子筛的T5和T6位;其中酸性最强的位置是Al5-O14-Si9,最弱的位置是Al7-O3-Si1.

Density functional theory （DFT） was applied to study the distribution of framework aluminum atoms at nine inequivalent T sites and the acidity of Brφnsted acid sites in Beta zeolite. The calculation was carried out at B3LYP/6-31G （d,p） level based on the 8T cluster model According to the calculated AI/Si substitution energies, （Al, H）/Si substitution energies, proton affinities and the adsorption energies of ammonia （NH3）, we propose that the most favorable sites for A1 substitution and Brφnsted acid sites are at the T5 and T6 sites. The acidity of A15-O14-Si9 is the highest among the preferred Brφnsted acid sites and the A17-O3-Sil site is the lowest.