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HZSM-5沸石分子筛硅铝骨架结构基本单元为五元环,它通过氧桥联接而得到单元为四元环、六元环。本文采用CNDO/2半经验量子化学的方法,对HZSM-5沸石基本结构单元—四、五、六元环的电荷分布进行计算。依据Mortier等人处理y型沸石分子筛酸性的基本思想,从而得到了HZSM-5沸石分子筛酸性结构参数α_0。Barthomeuf等认为沸石分子筛可作为一个多元酸的电解质溶液,因此其质子酸度应用活度来表示。a_(H~+)=[H~+]f_(H~+),而活度系数f_(H~+)为结构参数乘以一个常数,f_(H~+)=Kα_0,我们取K=32,[H~+]=nH~+αN_(A_1)/Z_(cat),从理论上求出HZSM-5沸石分子筛在不同硅铝比时的活度,其结果和实验值相一致。这为从理论上计算HZSM-5沸石分子筛的酸性提供了一个参考方法。
The basic unit of HZSM-5 zeolite molecular sieve framework is five-membered ring, which is connected by oxygen bridge to obtain four-membered ring, six-membered ring. In this paper, the CNDO / 2 semiempirical quantum chemical method was used to calculate the charge distributions of four, five and six membered rings of HZSM-5 zeolite. Based on the basic idea of treating the acidity of zeolite y zeolite by Mortier et al., The acid structure parameter α_0 of zeolite HZSM-5 was obtained. Barthomeuf, etc. that the zeolite can be used as a polybasic acid electrolyte solution, so its proton acidity is expressed by activity. The activity coefficient f_ (H ~ +) is the structural parameter multiplied by a constant, f_ (H ~ +) = Kα_0, we take K = 32, [H ~ +] = nH ~ + αN_ (A_1) / Z cat, the activity of HZSM-5 zeolite at different Si / Al ratios was calculated theoretically. The results are consistent with the experimental data. This provides a reference method for the theoretical calculation of the acidity of HZSM-5 zeolites.