(52b) Mechanistic Studies of Selective Hydrogenation Reactions with Palladium Gold Alloy Catalysts

Selective hydrogenation of alkynes to alkenes is an important process to produce alkyne-free feedstocks for the polymer industry. Pd with lead additives has shown good reactivity and selectivity in partial hydrogenation of alkynes and is widely used in industry. To further improve the catalytic performance of Pd catalysts and avoid the use of lead, different additives including Ag, Rh, Au, Cu, Zn, Cr, Bi and V have been reported. One promising approach to achieve the optimal material efficiency and selectivity of Pd catalysts is to form the alloy of Pd and Au at the single atom limit, which we call single atom alloy (SAA). Previous reports have demonstrated that PdCu and PdAu SAA catalysts are highly selective in partial hydrogenation of phenylacetylene[1] and 1-hexyne[2], respectively.

We have investigated the selective hydrogenation of 1-hexyne over PdAu alloys with different Pd ensembles, namely single atoms, clusters and nanoparticles. The surface structures of Pd species were studied by ATR-IR of chemisorbed CO. Kinetics studies indicate the hydrogenation reaction pathway and rate limiting step on PdAu SAA is same as that of Au nanoparticles. In situ ATR-IR tests were run to follow the evolution of the reactants and intermediates over the course of the hydrogenation reaction. The structure/ function relationships of different Pd ensembles in hydrogenation reactions were elucidated with these studies. The reactivity and characterization of the PdAu alloy nanoparticles with ATR-IR, STEM and XAS will be presented.

Acknowledgments: This work was supported as part of the Integrated Mesoscale Architectures for Sustainable Catalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under award #DESC0012573.

References

1. M. B. Boucher, B. Zugic, G. Cladaras, J. Kammert, M. D. Marcinkowski, T. J. Lawton, E. C. H. Sykes and M. Flytzani-Stephanopoulos, Phys. Chem. Chem. Phys., 2013, 15, 12187–12196.
2. J. Liu,J. Shan, Felicia R. Lucci, S. Cao, E. C. H. Sykes, M. Flytzani-Stephanopoulos, 2017, In Submission.