ZSM-5分子筛中相邻酸性位的酸性强度及其对乙烯质子化反应影响的理论计算  

Theoretical Study on the Acidity of Neighboring Acid Sites in ZSM-5 Zeolite and Its Effect on Ethylene Protonation

作　　者：王善鹏[1] 王伊蕾[1] 曹亮[1] 邢双英[1] 周丹红[1] 

机构地区：[1]辽宁师范大学化学化工学院功能材料化学研究所,辽宁大连116029

出　　处：《催化学报》2009年第4期305-311,共7页

基　　金：国家自然科学基金(20773058);辽宁省教育厅高等学校科学研究项目(A类05L211)

摘　　要：应用量子力学与分子力学联合的ONIOM2(B3LYP/6-31G(d,p):UFF)方法,对ZSM-5分子筛中与T6,T9和T12位相邻的骨架铝的落位稳定性以及酸性强度进行了理论计算.根据Si/Al替代能确定了最稳定的相邻酸性位在Al6-Al6位,其次是Al6-Al9位,通过(Si/Al,H)替代能计算确定了氢质子的落位.计算结果证明了相邻骨架铝会导致酸性强度降低,而且Al6-Al9位的酸性低于Al6-Al6位.应用密度泛函理论方法进一步考察了相邻酸性位对乙烯分子吸附和质子化反应历程的影响.结果表明,-Al-O-Si-O-Al-结构的相邻酸性位对乙烯分子的吸附以及质子化反应历程有明显影响,尤其是使乙醇盐产物更不稳定.By the QM/MM hydride ONIOM2 （B3LYP/6-31G（d,p）：UFF） method, the substitution of framework Al pairs at T6, T9, and T12 sites in ZSM-5 was calculated, and the stability and acidity of the neighboring acid sites were theoretically studied. According to the calcu-lated Si/Al substitution energy, the most stable acid site is located at Al6-Al6, and the more stable acid site is at Al6-Al9. The localization of acidic proton was explored by calculating （Si/Al,H） substitution energy, and the acid strength was evaluated with the calculated deprotona-tion energy. The results indicated that the neighboring framework Al leads to the decrease in acid strength, and the acidity is in the order Al6-Al9 〈 Al6-Al6. The adsorption property of ethylene molecule on the neighboring acid sites was also explored. It was found that the -Al-O-Si-O-Al- structure neighboring acid sites have strong effect on the adsorption and the protonation of ethylene and especially lead to very low stability of ethoxide product.

关 键 词：ZSM-5分子筛 相邻酸性位 乙烯质子化 ONIOM方法 

分 类 号：O643.36[理学—物理化学]