化学
催化作用
酸强度
芳构化
反应速率
活化能
选择性
反应机理
光化学
碳离子
催化裂化
反作用坐标
过渡状态
计算化学
有机化学
沸石
作者
Dongdong Chen,Dongyang Liu,Jun Wei,Yuen Bai,Liang Zhao,Jinsen Gao,Chunming Xu
标识
DOI:10.1016/j.apcata.2023.119389
摘要
Acid strength is an important factor affecting the reaction mechanism. The influences of different Brønsted acid strengths on the cracking path of n-hexane were systematically investigated using the density functional theory. Most of the hexane activation cracking transition states are carbenium ions with no intermediate products of five-coordinate hexanium due to the weak Brønsted acid sites were not conducive to the stabilization of hexanium ions. With increasing acid strength, the protonated cracking reaction (the rate-controlling steps of monomolecular paths) energy barrier was reduced by 38.0% and the β-scission reaction (the rate-controlling steps of bimolecular paths) energy barrier was reduced by 27.15%, where enhanced the selectivity of E&P by changing the ratio of monomolecular and bimolecular cracking. However, the optimal reaction paths, the rate-controlling steps and the order of the various reaction energy barriers haven’t been changed. In addition, decreasing the acid strength increased the energy barriers of aromatization reaction and inhibited the reaction. The effect of molecular size on aromatization was further explored. The intermolecular hydrogen transfer reaction between 2-propoxide and 3-ethylcyclohexene is the rate controlling step and the larger the cycloalkane molecule, the higher the reaction energy barrier. The catalyst design requires a reduced pore size to prevent the formation of cycloalkanes and thus inhibit side reactions to improve the selectivity of E&P.
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