Exhaustive Identification of Feasible Pathways of the Reaction Catalyzed by a Catalyst with Multiactive Sites via a Highly Effective Graph-Theoretic Algorithm: Application to Ethylene Hydrogenation

Hitherto, no attempt has been made to identify exhaustively feasible pathways for any mechanism of a given reaction catalyzed by a catalyst with multiactive sites. Two stoichiometically exact and definitely feasible mechanisms have been proposed to date for the hydrogenation of ethylene to ethane on biactive-site or triactive-site platinum catalysts. One comprises seven elementary reactions, and the other comprises eight elementary reactions; nevertheless, both mechanisms involve competitive as well as noncompetitive adsorption. Any of these mechanisms gives rise to a multitude of feasible catalytic pathways. The present work exhaustively identifies such feasible pathways by resorting to the inordinately efficient graph- theoretic algorithm based on P-graphs (process graphs). The efficacy of this algorithm has been amply demonstrated by successfully deploying it for several catalysts with single-active sites, but has never been deployed for catalysts with multiactive sites as in the current work. The availability of exhaustively identified feasible pathways for both mechanisms renders it possible to stipulate that the hydrogenation of chemisorbed chemisorbed C2H5 is the rate-controlling step: This step is contained in either mechanism.

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