甲基环戊烷在Pt/SiO_2上开环的动力学模拟

KINETIC MODELING OF METHYLCYCLOPENTANE RING OPENING ON Pt/SiO 2

用动力学模拟的方法探索甲基环戊烷在铂催化剂上开环的反应机理。根据可能的Ｃ－Ｃ键断裂机理，导出了不同的竞争动力学模型。为了使实验数据与速率方程相符合，在反应机理中必须包含甲基环戊烷的吸附和脱氢两个平衡步骤。用模拟方法判别竞争的动力学模型是困难的，但根据速率方程中参数的物理意义，作者认为Ｃ－Ｃ键断裂很可能涉及一个氢分子。在生成正己烷和甲基戊烷的反应中没有发现Ｃ－Ｃ键断裂的活化能有显著差异。

Kinetic modeling was carried out to explore possible reaction mechanism of methylcyclopentane ring opening over a Pt/SiO 2. Different mechanisms were considered for the C-C bound rupture: involving a vacant site, an adsorbed hydrogen, a gaseous hydrogen molecule or a combined form of a H 2 plus a vacant site. Two equilibrium steps, methylcyclopentne adsorption and dehydrogenation, were found to be included in the reaction scheme in order to derive a rate equation consistent with the experimental data, indicating that the effect of the adsorbed methylcyclopentane on the reaction can not be neglected. A discrimination seems difficult between the competitive rate equations by model fitting. However with the significance of the parameters, it is preferred that the C-C bound rupture involves a molecule hydrogen. No significant difference in activation energy of the C-C bound rupture was found between the reactions forming methylpentanes and n-hexane, the value is about 93 kJ/mol. While there is a significant difference in the adsorption heat of methylcyclopentane for these two reactions, it is -111kJ/mol for n-hexane and -22 kJ/mol for methylpentanes.