Rational Catalyst Design for Higher Propene Partial Electro-oxidation Activity by Alloying Pd with Au

Selective partial oxidation of hydrocarbons to oxygenates plays a large role in the chemical industry, while falling prices for electricity from renewable sources make electrification of such industrial chemical processes relevant. The oxidation of propene is an interesting model system as propene can be oxidized in two different positions, allowing for insights into the reaction mechanism. On Pd, a layer of adsorbates formed in situ governs the reaction by steering reactant adsorption to achieve high selectivity for allyl oxidation, albeit largely inhibiting the reaction rate. Through rational catalyst design, we demonstrate that alloying reactive Pd with inert Au influences the adsorbate layer formation, enhancing activity while maintaining high selectivity toward allyl oxidation. We obtain mechanistic insights with a combination of ab initio computational modeling and electrochemical measurements with ex situ product quantification and online mass spectrometry. Using a statistical approach, we explore the correlation of the Au:Pd ratio with Pd surface cluster size and density, which determine the properties of the adsorbate layer and thus the reaction outcome. We report an activity enhancement by a factor 2.4 with 10% Au in Pd and propose that (i) activity is maximized at potentials just before Pd cluster oxidation and (ii) the optimal catalyst surface contains approximately one Au every six Pd atoms, statistically most frequent at the nominal alloy composition Au14Pd86.