(97d) Activity of PtxCoy Alloys for Phenol Hydrogenation in the Aqueous Phase

Understanding the adsorption of reactants and intermediates on metal surfaces is a key step in designing active and selective catalysts relevant to bio-oil catalysis, e.g., hydrogenation of bio-oil model compounds in the aqueous phase. Electrocatalytic (ECH) and thermocatalytic hydrogenation of phenol are important aqueous-phase reactions that have low turnover frequency (<1 s^−1). To increase the rate, a catalyst must both maintain high coverages of adsorbed H (H*) and phenol, and have a low barrier for the addition of H* to phenol. Weakening the hydrogen binding energy has been proposed as a method to increase the rate of phenol hydrogenation on Pt,¹ and alloying has been used to this effect for hydrogenation of benzene and cyclohexene.² We hypothesize that by synthesizing Pt alloy catalysts with weaker hydrogen binding energies than pure Pt we can increase the turnover frequency of phenol ECH. Co content has been reported to weaken the H binding energy,³ supported by our density functional theory calculations, and so we choose Pt_xCo_y alloys for the study here.

Herein we synthesized Pt and Pt_xCo_y alloy nanoparticles directly on carbon felt supports via chemical reduction with borohydride. We characterized these catalysts using X-ray diffraction and X-ray absorption spectroscopy to determine particle sizes and alloy composition. We perform phenol ECH on these catalysts having varying Co content (0-10 mol%) but similar nanoparticle sizes (8-10 nm) to determine their ECH activity and current efficiency, and compare to the predicted H binding energy to understand the influence of hydrogen adsorption on kinetics.

(1) Singh, N.; Lee, M.; Akhade, S. A.; et al. ACS Catal. 2019, 9 (2), 1120–1128.

(2) Lu, S.; Lonergan, W.; Bosco, J.; et al. J. Catal. 2008, 259 (2), 260–268.

(3) Wakisaka, M.; Morishima, S.; Hyuga, Y.; et al. Electrochem. commun. 2012, 18 (1), 55–57.