A quantum chemical ONIOM [B3LYP/6-31G(d,p):UFF] method has been applied to study the distribution of BrΦnsted acid at nine inequivalent T sites and the acidity of Bransted acid in β-zeolite. In the calculation, the structure of β-zeolite is represented by 22T cluster model. According to the calculated (Al, H)/Si substitution and proton affinity, it was proposed that most favorable sites for BrΦnsted acid are Al(8)-O(11)-Si(4), Al(8)-O(4)-Si(1), Al(7)-O(7)-Si(2), and Al(9)-O(6)-Si(3). The acidity of Al(7)-O(7)-Si(2) is the most highest in the preferable BrΦnsted acid sites, and Al(8)-O(l1)-Si(4) site is the lowest. The order of acidity is Al(7)-O(7)-Si(2)>Al(9)-O(6)-Si(3)>Al(8)-O(4)-Si(1)>Al(8)-O(11)-Si(4).%基于量子化学ONIOM [B3LYP/6-31G(d,p):UFF]计算方法,研究了β分子筛中BrΦnsted酸的落位及其酸性强度.计算采用22T簇模型,得到了不同酸性位的(Al,H)/Si替代能和质子亲和势.研究结果表明,BrΦnsted酸最有可能落位在Al(8)-O(11).Si(4),Al(8)-O(4)-Si(1),Al(7)-O(7)-Si(2)和Al(9)-O(6)-Si(3)位置.根据去质化能的计算,Al(7)-O(7)-Si(2)位置的酸性最强,A1(8)-O(11)-Si(4)的酸性最弱.酸性的强弱顺序为Al(7)-O(7)-Si(2)＞Al(9)-O(6)-Si(3)＞Al(8)-0(4)-Si(1)＞Al(8)-O(11)-Si(4).
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