Microcalorimetric study of ethylene adsorption on the Pt{111} surface

The reaction of C2H4 on Pt{111} at 300 K has been investigated by single crystal adsorption calorimetry. The initial heats of adsorption and the initial sticking probability are 174 kJ/mol and 0.67 respectively. The adsorption heat versus coverage data shows a remarkable minimum which serves as a basis for a mechanism involving ethylidene (CHCH3) as an intermediate for the formation of ethylidyne (C2H2) on the Pt{III} surface. The coverage-dependent sticking probability strongly indicates that adsorption is precursor mediated and is well-fitted by the King and Wells expression. From the structure of the decomposition species known to form on the Pt{III} surface, the average C-Pt bond strength is found to be about 245 kJ/mol, although the actual value is found to be species-dependent.