(679b) Computational Studies of the Active Sites of Pt and PtxCoy Alloys for Phenol Hydrogenation

Electrocatalytic hydrogenation (ECH) is a promising strategy for upgrading distributed biomass-derived waste resources to value-added fuels and chemicals. However, ECH is capital- and energy-intensive due to low activity and high costs of the catalysts, which often are platinum group metals (PGMs). The activity and utilization of the catalysts can be increased by ensuring a high fraction of active sites are present at the surface and by decreasing the amount of PGMs required via alloying. Here, we identify the active site for Pt and investigate the effect of alloying with Co for the hydrogenation of phenol, a prototypical bio-oil constituent.

We study phenol hydrogenation on different facets of Pt and on Pt_xCo_y alloys using density functional theory (DFT) and compare to experimental rate measurements on Pt nanoparticles supported on carbon (Pt/C) and Pt_xCo_y/C to understand the active site and influence of alloying. We find that (111) terrace sites on Pt/C dominate catalytic activity because of lower activation barriers and weaker phenol adsorption energies compared to sites with lower coordination numbers (i.e., step sites).¹ Next, we model phenol hydrogenation on a series of Pt_xCo_y surfaces to elucidate how the modification of the electronic structure of the Pt due to Co alloying can tune adsorption energies and improve hydrogenation rates. We show that the adsorption energy of hydrogen is reduced with increasing Co content in the alloy subsurface, resulting in lower activation barriers for hydrogenation. We synthesize and characterize a set of Pt_xCo_y/C alloys and perform kinetic measurements to compare with our predictions. Ultimately, we show that alloying and synthesis methods to preferentially expose (111) sites may be used to improve utilization and performance of expensive PGMs.

(1) Barth, I.; Akinola, J.; Lee, J.; Gutiérrez, O. Y.; Sanyal, U.; Singh, N.; Goldsmith, B. R. J. Chem. Phys. 2022, 156 (10), 104703.