Selective Hydrogenation of 1,3-Butadiene over a Pd/Cu(111) Single Atom Alloy Surface

The hydrogenation of 1,3-butadiene (BD, C4H6) to 1-butene (C4H8) over a Pd/Cu(111) single-atom alloy (SAA) was studied under ambient pressure conditions with reflection absorption infrared spectroscopy (RAIRS). The gas-phase reactants and products were monitored with RAIRS using s-polarized light, while p-polarization was used to search for adsorbed species present during the reaction. The formation of gas-phase 1-butene was revealed by the growth of a distinct infrared peak at 2878 cm-1, whereas the consumption of gas-phase BD was measured by the decrease of a peak at 1587 cm-1. The reaction rate was found to be first-order (1.12 +/- 0.04) with respect to H2 and zero-order (-0.12 +/- 0.01) with respect to BD and corresponded to a turnover frequency of 36 s-1 at 380 K. From the temperature dependence of the rate constant, an activation energy of 63 +/- 3 kJ/mol was obtained. Complete conversion of 1,3-butadiene was observed with a high selectivity of 84% toward 1-butene without any production of butane. No surface species were detected with RAIRS during the reaction. Post-reaction analysis with Auger electron spectroscopy revealed carbon deposition, indicating that some dissociation accompanied hydrogenation.