School of Natural and Applied Sciences, Northwestern Polytechnical University, Xi'an, Shaanxi 710072, People's Republic of China.
J Comput Chem. 2010 May;31(7):1421-42. doi: 10.1002/jcc.21427.
The gas-phase reaction pathways in preparing pyrolytic carbon with propene pyrolysis have been investigated in detail with a total number of 110 transition states and 50 intermediates. The structure of the species was determined with density functional theory at B3PW91/6-311G(d,p) level. The transition states and their linked intermediates were confirmed with frequency and the intrinsic reaction coordinates analyses. The elementary reactions were explored in the pathways of both direct and the radical attacking decompositions. The energy barriers and the reaction energies were determined with accurate model chemistry method at G3(MP2) level after an examination of the nondynamic electronic correlations. The heat capacities and entropies were obtained with statistical thermodynamics. The Gibbs free energies at 298.15 K for all the reaction steps were reported. Those at any temperature can be developed with classical thermodynamics by using the fitted (as a function of temperature) heat capacities. It was found that the most favorable paths are mainly in the radical attacking chain reactions. The chain was proposed with 26 reaction steps including two steps of the initialization of the chain to produce H and CH(3) radicals. For a typical temperature (1200 K) adopted in the experiments, the highest energy barriers were found in the production of C(3) to be 203.4 and 193.7 kJ/mol. The highest energy barriers for the production of C(2) and C were found 174.1 and 181.4 kJ/mol, respectively. These results are comparable with the most recent experimental observation of the apparent activation energy 201.9 +/- 0.6 or 137 +/- 25 kJ/mol.
在丙烯热解制备热解炭的气相反应途径中，共涉及 110 个过渡态和 50 个中间体，详细研究了气相反应途径。采用密度泛函理论在 B3PW91/6-311G(d,p)水平下确定了各物种的结构。通过频率和内禀反应坐标分析验证了过渡态及其连接的中间体。在直接和自由基进攻分解的途径中探索了基本反应。在考察非动态电子相关后，采用精确模型化学方法在 G3(MP2)水平上确定了能量势垒和反应能。用统计热力学法得到热容和熵。报道了所有反应步骤在 298.15 K 下的吉布斯自由能。任何温度下的吉布斯自由能都可以通过使用拟合的热容（作为温度的函数）用经典热力学来开发。结果表明，最有利的途径主要是在自由基进攻的链式反应中。提出了一条由 26 个反应步骤组成的链，包括两条引发链产生 H 和 CH(3)自由基的步骤。对于实验中采用的典型温度（1200 K），生成 C(3)的最高能垒为 203.4 和 193.7 kJ/mol。生成 C(2)和 C 的最高能垒分别为 174.1 和 181.4 kJ/mol。这些结果与最近的实验观察到的表观活化能 201.9 +/- 0.6 或 137 +/- 25 kJ/mol 相当。
