APPLICATION OF A SYSTEMATIC APPROACH FOR DETERMINING POSSIBLE REACTION MECHANISMS: METHANOL SYNTHESIS AND ANODIC OXIDATION OF ZINC

A systematic enumeration of possible reaction mechanisms consistent with a given set of chemical species and elementary steps is useful in guiding research in heterogeneous reaction systems which are encountered in catalysis and electrochemistry. In this paper, the synthesis of methanol by catalytic hydrogenation of carbon monoxide and the anoidic oxidation of zinc in alkaline solutions are presented as two examples of the usefulness of such an approach. The technique utilized to generate the reaction mechanisms is based upon combinatorial analysis, linear algebra and the principle of microscopic reversibility.

In the case of methanol synthesis, it is shown that in addition to the two currently proposed mechanisms, there exist two alternate reaction pathways each of which involves the hydrogenation of a formyl species to form a surface methoxide. One of these mechanisms has recently been proposed for a ZnO catalyst, however there remains an additional mechanism for consideration. For the case of anodic zinc oxidation, it is shown that mechanisms which involve cathodic elementary steps are also possible. To the authors knowledge, these mechanisms have not been previously discussed in the literature.