A C-14 RADIOTRACER STUDY OF THE HYDROGENATION OF ETHYNE OVER EUROPT-1

The adsorption and hydrogenation of ethyne over EUROPT-1 has been stud ied using C-14-ethyne and C-14-ethene as tracers at 295 K. Adsorption of both ethyne and ethene show typical primary and secondary regions. Only a fraction of the initially adsorbed radioactivity can be removed evacuation, treatment in hydrogen or under ethyne hydrogenation condi tions at the adsorption temperature. Ethene cannot be adsorbed on an e thyne precovered surface, although ethyne will displace only 68% pread sorbed ethene. In the hydrogenation of ethyne, evidence has been obtai ned to show that the surface coverage by hydrocarbon progressively inc reases during the course of the reaction up to the acceleration point in the pressure-time curves. The initial selectivity for ethene format ion is ca. 0.25. Hydrogenation of C-12-ethyne/C-14-ethene mixtures sho ws that the further hydrogenation of ethene to ethane is of only minor importance in determining the selectivity. A reaction scheme is propo sed in which three types of surface site are identified as being respo nsible for the hydrogenation of (a) ethyne to ethene; (b) ethyne to et hane and (c) ethene to ethane.