Hydrogenation of olefins. Part 6.—Reaction of n-butenes with hydrogen and with deuterium over alumina- supported palladium

The reactions of each of the three n-butene isomers with hydrogen and with deuterium over a palladium on α-alumina catalyst have been studied in the temperature range 0–70°C: the hydrocarbon products have been analyzed, and where appropriate each component was separated by gas-liquid chromatography and examined by mass-spectrometry. Kinetics of hydrogenation (h) and of olefin isomerization (i) are reported for each isomer: orders with respect to hydrogen are 0.3–0.5 for hydrogenation and zero-0.1 for isomerization. For 1-butene Eh exceeds Ei by about 23 kJ mol–1. The mean deuterium contents x of isomerized olefins are generally small, being about 0.5 at 17–20°C for both the 2-butenes formed from 1-butene and only about 0.2 for isomers formed from each of the 2-butenes. The results are interpreted in terms of a conventional scheme involving only 1- and 2-butyl radicals besides the adsorbed olefins: the surface concentration of H and D atoms is thought to be low and dissolved atoms are believed important. Probable rate-controlling steps are, for hydrogenation, formation of butyl radicals from adsorbed butene and dissolved H or D atoms, and for isomerization, butene desorption.