(509bm) Tunable Catalytic Performance of Palladium Nanoparticles for H2O2 Direct Synthesis Via Surface-Bound Ligands

Global demand for hydrogen peroxide (H₂O₂) has increased significantly in recent years because of its importance as an oxidant in a number of industrial processes.^1-3 Direct synthesis of H₂O₂ from molecular hydrogen and oxygen at (sub)ambient temperatures using unmodified supported Pd catalysts has attracted significant attention due to the limitations associated with the current process of H₂O₂ production by the sequential hydrogenation and oxidation of anthraquinones in a mixture of organic solvents. Supported Pd catalysts have shown promise for direct synthesis of H₂O₂¹, however they are often limited by low selectivity. In this presentation, we show that the Pd surface functionality controlled through surface-bound ligands can be tuned for enhancing the selectivity of supported Pd catalysts for direct synthesis of H₂O₂. A wide range of surface-bound ligands with varying functionalities was used to gain an understanding of the ligand characteristics that governed the modulation of Pd catalyst performance for direct H₂O₂ synthesis.² We showed that, in general, ligands improved selectivity of supported Pd catalysts, with the ones containing H-bonding groups resulting in the highest selectivities (75-80%). These ligands were hypothesized to interact via hydrogen bonding with key reaction intermediates (i.e., OOH and adsorbed H₂O₂)³, favoring the energetics associated with the desired path leading to H₂O₂ production. For a subset of ligand-modified Pd catalysts, we also showed that the ones characterized by H-bonding groups led to PdH_x formation when exposed to H₂ at room temperature, uncovering another feature that potentially played a role in selectivity enhancement. The insights obtained from these studies set the basis for designing optimal surface-bound ligands on Pd catalysts to maximize their performance for direct H₂O₂ synthesis.

References

(1) Angew. Chem., Int. Ed. 2017, 56, 1775– 1779.

(2) ACS Catal. 2020, 10 (9), 5202–5207.

(3) J. Am. Chem. Soc. 2016, 138, 574−586.