(305c) Microkinetic Model for the Water Gas Shift Reaction on Supported Copper Catalyst

Catalytic pathways (mechanisms) of the water gas shift (WGS) reaction have stimulated extensive research because of their enormous theoretical and practical significance; notable among the research efforts are those by Fishtik and his collaborators. At the outset, they have exhaustively identified stoichiometrically feasible reaction routes (RR_is), i.e., independent pathways (IP_is), by resorting to a linear algebraic approach through the formulation of the stoichiometric matrix of a set of plausible elementary reactions. This is followed by the selection of those RRis (IP_is) whose energy diagrams span the moderate range between -25 and 10 kcal/mole as the energetically favorable RRis (IP_is). Finally, the RR_i (IP_i) giving rise to the highest simulated rate of the WGS reaction in idealized CSTR and PFR is claimed to be dominant. The work of Fishtik and collaborators is scrutinized by our graph-theoretic method based on P-graphs (process graphs). It has identified with dispatch and ease on a PC 116 stoichiometrically feasible RR_is (IP_is), which substantially exceed the the 70 identified by them; moreover, these 116 RR_is (IP_is) have yielded 5 energetically favorable RR_is (IP_is). It is indeed the case that the dominant one should be searched among the 5 instead of the 3 RRis (IP_is) obtained by Fishtik and his collaborators. The results imply that an efficient and robust approach for determining the potentially dominant RR_i (IP_i) should involve the exhaustive identification of the stoichiometrically feasible RRis (IP_is) with our graph-theoretic method at the outset.