Polarisation enhanced 13C magnetic resonance studies of the hydrogenation of pentene over Pd/Al2O3 catalysts

This paper reports the first demonstration of 13C distortionless enhancement by polarisation transfer (DEPT) NMR spectroscopy at natural abundance to study the hydrogenation and isomerisation of pentenes over a 1 wt% Pd/Al2O3 catalyst. Single component C5 hydrocarbons and binary mixtures of hydrocarbon and hydrogen have been adsorbed on both a pure alumina support and the Pd/Al2O3 catalyst derived from it. The pentene species studied were 1-, cis-2- and trans-2-pentene. No isomerisation or hydrogenation was observed when single component pentene isomers or binary mixtures of 1-pentene and hydrogen, and cis-2-pentene and hydrogen were adsorbed onto the pure alumina support. However, when trans-2-pentene and hydrogen were both adsorbed onto the support, partial hydrogenation to n-pentane was observed in addition to the presence of both cis-2- and trans-2-pentenes. All pentene isomers hydrogenate over the Pd/Al2O3 catalyst to give predominantly n-pentane and a small amount of the trans-2-pentene isomer. For the parameters chosen here these studies show that trans-2-pentene appears to be the active isomer for hydrogenation over the pure support alone.