Structure of complex catalytic reactions: thermodynamic constraints in kinetic modeling and catalyst evaluation

The paper examlnes the thermodynamic constraints on chemical reaction trajectories. It shows how thermodynamic concepts can be used to organize and analyze the results of kinetic studies in complex reaction systems where several reactions can occur simultaneously. It defines rigorous criteria for setting up a set of stoichiometric relations to obtain an empirical kinetic model for the system. This can be done without any kinetic calculations by inspecting the measured trajectories in compositlon space. The paper also deflnes the concept of coupling between overall ostensible reactions and explains the thermodynamic advantages by using shape-selectlve catalysts. The concept of thermodynamic constraint is defined, and it is shown that the mechanism of the kinetic reactions has thermodynamic consequences far more restrictive than the Second Law itself. The results should be useful in the modeling of complex reactions systems as well as in the testing and evaluation of new catalysts.