正庚烷脱氢生成烯烃反应的分子模拟

Molecule Simulation of Dehydrogenation of n-Heptane to Produce Olefins

采用基于密度泛函理论的量子化学方法研究了催化重整过程中正庚烷脱氢生成烯烃的反应过程。结果表明,在无催化剂作用下,正庚烷分子的仲碳C—H键优先发生均裂,生成烷基自由基和氢自由基,均裂能在433.80～434.83kJ/mol范围;中间产物烷基自由基中,与自由基碳相邻的仲碳位的C—H键容易发生均裂生成烯烃,均裂能在187.11～209.18kJ/mol范围。正庚烷脱氢反应产物主要为2-庚烯和3-庚烯。在Pt催化剂作用下,正庚烷均裂仲碳位C—H键的反应能垒在75.90～78.51kJ/mol范围,中间产物烷基自由基中,与自由基碳相邻的仲碳位的C—H键均裂的反应能垒为99.63kJ/mol,说明Pt催化剂有效地降低了烷烃脱氢反应能垒。

Density functional theory （DFT） quantum chemical method was used to study the process of dehydrogenation of n-heptane to produce olefins. The results showed that, in the absence of catalyst, homolysis of the C-H bond on the secondary carbon atom in n-heptane occurred preferentially to generate alkyl radicals and hydrogen radicals, in which the homolysis energy was in the range of 433.80-434.83 kJ/mol. In the intermediate products of alkyl radicals, the C＆mdash;H bond on the secondary carbon atom, which adjacent to the free radical carbon atom, will give priority homolysis to generate olefin, in which the homolysis energy was in the range of 187.11-209.18 kJ/mol. The main reaction products of n-heptane dehydrogenation were 2-heptene and 3-heptene. In the presence of Pt catalyst, the reaction energy barrier for homolysis of the C-H bond on the secondary carbon atom in n-heptane was in the range of 7590-78.51 kJ/mol. For intermediate products of alkyl radicals, the reaction energy barrier for homolysis of the C-H bond on the secondary carbon atom, which adjacent to the free radical carbon atom was 99.63 kJ/mol,indicating that Pt catalyst has a good effect on reducing the reaction energy barrier of alkane dehydrogenation.