HY分子筛催化异丁烷/丁烯烷基化反应中加成反应的模拟研究

建立了120T HY分子筛模型，采用量子力学与分子力学（QM/MM）相结合的方法，揭示了叔丁基烷氧基团（TBA）〖JP〗与异丁烯/2 丁烯发生加成反应的细节，并比较了二者的异同。结果表明，叔丁基碳正离子是加成反应的过渡态，且TBA与2 丁烯分子发生加成反应的能垒值是与异丁烯反应的2倍左右。这是由于过渡态的碳正离子与异丁烯之间的电荷转移明显大于与2 丁烯的，二者之间的相互作用力更强，故过渡态能量更低。另外，由于TBA与2 丁烯发生加成反应后中心C原子稳定性降低，故需要首先生成“三角形结构”中间产物，再形成C8碳正离子，最终形成C8烷氧基团完成加成反应。

Multi-Scale Computational Study onthe Addition Reaction ofButene Alkylation With Isobutane Over HY Zeolite

The mechanism of addition reaction between t butyl alkoxide (TBA) and isobutene/2 butene〖JP〗 was calculated using an embedded QM/MM (quantum mechanics/molecular mechanics) method on the 120T HY zeolite model. It is confirmed that carbonium ion is the transition state of the two reactions, and the reaction barrier of addition reaction between TBA and 2 butene (290 kJ/mol) is 2 times than that of isobutene (149 kJ/mol). It is because the electron transfer from isobutene to t butyle carbonium is much easier than that from 2 butene. Moreover, with respect to 2 butene, to form C8 carbonium ion, the extra generation of triangle structured intermediate and its corresponding rotation are needed, but their reaction heat is ultra low, thus the formation of triangle structured intermediate is hard to occurr. Especially, the central C atom of C8+ is in the form of secondary carbonium, which is less stable than t butyle carbonium, owing to the endothermic pathway. Consequently, TBA preferentially reacts with isobutene, rather than 2 butene.