Kinetics and catalysis: Direct mechanisms, autonomous reaction pathways, and the constitutive rate function

Rate functions of catalytic reactions are derived from direct mechanisms based on an adsorption theory and a kinetic mathematical model. Often, more than one direct mechanism corresponds to an overall chemical reaction. Since each direct mechanism can potentially produce a distinct rate function, it is likely that more than one independent rate function describes the rate of an overall reaction. This appears to be a fundamental property of the structure of the kinetics of heterogeneous catalysis and this article addresses this possibility via an examination of the independent direct mechanisms of the steam methane reforming and ammonia synthesis.