ANALYSIS OF THE THERMOCHEMISTRY OF C-2 HYDROCARBONS ON TRANSITION-METAL SURFACES USING A REFINED BOC-MP APPROACH

A refined version of the BOC-MP (bond-order-conservation Morse-potential) approach has been used to calculate the heats of adsorption and the activation barriers for dissociation and recombination of C2Hx species on transition metal surfaces, such as Fe/W(110), Ni(111), and Pt(111). The calculations reveal distinct periodic patterns of C2Hx transformations. In particular, it is found that most of the decomposition routes of ethylene and acetylene are strongly exothermic on Fe and W, but are mildly endothermic on Pt. Accordingly, the calculations predict that C-H and C-C bond cleavage from the gas phase occurs practically without activation on Fe and W, but with finite activation barriers on Ni and especially Pt. The conceivable pathways of C2Hx decompositions are discussed in detail. The projections of the refined BOC-MP approach are in much better agreement with experiment, as compared with our previous calculations. © 1990.