Hydrogenation of but-1-yne on platinum catalyst: Role of reversible adsorbed hydrocarbon deposit

By using rectangular pulses of but-1-yne carried by H₂ or H₂-He mixtures over a platinum catalyst, it was possible to visualize the build-up of an adsorbed hydrocarbon deposit which is a necessary condition for getting a selective catalyst (on platinum, but-1-ene selectivity is 90%). Such a deposit is reversibly adsorbed since it desorbs as hydrogenated butyne molecules when the butyne pressure drops at the end of the pulse. Moreover it was shown, during stationary phase, that the sudden fall in the selectivity at high but-1-yne conversion, is due to the desorption of such reversibly adsorbed molecules.