Synthesis of Direct Mechanisms for Chemical Systems
Mavrovouniotis, Micheal L.
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A chemical system consists of intermediate species, terminal species, and mechanism steps. Understanding the behavior of a chemical system can be significantly aided by the identification of mechanisms responsible for overall reactions which do not involve net consumption or production of reaction intermediates. Issues arising in the definition and identification of direct mechanisms, which are the shortest possible mechanisms, are discussed. In the context of examples of catalytic synthesis of ammonia and methanol, an alternative approach for the construction of mechanisms from steps is presented. An algorithm for the construction of direct mechanisms is then formally stated; the algorithm is based on successive processing and elimination of reaction intermediates which should not appear in the overall stoichiometry of the reactions accomplished by the mechanisms. Throughout the operation of the algorithm, irreversible steps are used only in their permitted direction. The basic algorithm may construct indirect or duplicate mechanisms, but variations of the algorithm are proposed which discard such redundant mechanisms. A number of hypothetical chemical systems illustrate the differences between the proposed algorithm and other approaches.