碳氧化反应速率常数与温度特殊关系的理论解释

Theoretical Explanation of the Special Temperature Dependence of Rate Constant for Oxidation of Carbon

对于碳氧化反应,在不同温度范围内,温度对反应速率常数的影响呈现不同规律的现象进行了讨论。指出第一阶段主要由氧气在碳表面化学吸附平衡受温度的影响决定。第二阶段则由碳在二氧化碳中发生气化反应,特别是其中的酮基脱附步骤决定。对已有的反应机理进行了比较,提出了新的简化机理,并采用速率控制步骤近似和平衡近似对机理进行了近似处理,得出的第二阶段动力学方程可以较好地解释相关实验规律。

For oxidation of carbon in different temperature ranges, there is different temperaturedependence of rate constant. The temperature dependence can be divided into two sections. The firstsection is mainly determined by the chemical adsorption of oxygen on the carbon surface, forming oxygencontainingsurface complexes. The effect of temperature on adsorption equilibrium of oxygen results inthe first increase and then decrease of rate constant with increasing temperature. For the second section,it is mainly influenced by gasification of carbon in carbon dioxide, in which desorption of the carboxylgroup is the rate-determining step (r.d.s.). In this paper, a comparison among the formerly establishedmechanisms for carbon oxidation at high temperature was made and a simplified mechanism was putforward. The rate equation for the second section was deduced based on this new mechanism usingr.d.s. approximation and pre-equilibrium approximation treatments. The deduced rate equation is in goodaccordance with the main experimental facts. Therefore, a satisfactory explanation is given for the unusualbehavior of carbon oxidation.