(756e) Promotion of Cross-Coupling Reactions in the Liquid-Phase Oxidation of Alcohols over Nanoporous Au

The selective semi-hydrogenation of alkynes to alkenes without over-hydrogenation to alkanes is an important class of reaction in the industrial synthesis of many bulk and specialty chemicals. Catalysts based on Pd are used most consistently for such transformations, although obtaining high selectivities without the addition of organic promotors remains challenging. One general approach for improving the selectivity of highly-reactive metals is dilution by a less reactive, but more selective, metal such as Au. When diluted to the limit where the minority metal is surrounded only by host metal atoms, a “single-atom alloy” is produced which possesses sites with unique geometric and electronic structures that have been shown to be capable of breaking scaling relations and thus enable new opportunities for selective catalysis. This approach has been recently used to synthesize PdAu catalysts which demonstrate improved reactivity and selectivity for the hydrogenation of 1-hexyne to 1-hexene.

In this work, dilution in Au is shown to be an effective method for improving the selectivity of Ni-catalyzed 1-hexyne hydrogenation. This is shown experimentally through the comparison of kinetic data collected with supported NiAu nanoparticles wherein Ni in Au is diluted to ratios below 1:100. Studies of single-crystal analogues through surface science and density functional theory provide additional insights into the performance of this catalyst in comparison with its PdAu counterpart. While conventional strategies for improving alkene selectivity revolve around synthesizing alloys for which the alkene possesses a higher barrier for hydrogenation than for desorption, the improved performance with these catalysts is instead attributed to differences in H-addition kinetics. By breaking conventional wisdom in alloy design, these findings provide new directions for the design of catalysts capable of selective semi-hydrogenations.