(704e) Catalyst Design for Selective Hydrogenations of Unsaturated Aldehydes through a Liquid-Phase Energy Scaling Approach

Catalytic hydrogenation is critical in industrial processes, with substantial importance in the transformation of biomass-derived molecules.¹ Attracting particular interest is the selective hydrogenation of α,β-unsaturated aldehydes.^2-3 While the role of solvents has been reported to be important in experimental hydrogenations, detailed mechanistic studies and generalization of the role of solvent on these hydrogenations are still lacking. This motivates a search for reactivity rules for selective hydrogenations, and determining the extent to which hydrogenations can be controlled by manipulating the solvation environment.

In this presentation, we share density functional theory (DFT) calculations of crotonaldehyde and cinnamaldehyde hydrogenations on model transition metal surfaces. We consider the energetics of C=C and C=O hydrogenations, both in the gas-phase contexts typical of DFT studies and in microsolvation environments more representative of the liquid-phase environment. We thereby establish an energy scaling relationship that efficiently accounts for the effect of solvent on reaction energetics. Our results demonstrate that the simple energy scaling relationships established in gas-phase contexts, such as those between adsorbed atomic species (C or O) and the molecular intermediates of this study, are still present in the microsolvated environment; this enables the use of simple solvent representations for catalyst screening and design. We find that the energy scaling is shifted based on the differential interactions between functional groups and the solvent environment. We additionally investigate the structure sensitivity of these reactions, determining that reaction energetics and selectivities are structure sensitive while the existence of solvent scaling is structure insensitive. These results suggest a strategy for the future design of materials for controlling the selectivity of C=C vs. C=O hydrogenations.

1. Li, A. Y. and Moores, A., ACS Sus. Chem. Engr. 7, 10182 (2019).
2. Falcone, D. D., Hack, J. H., Davis, R. J., ChemCatChem 8, 1074 (2016).
3. Ji, X. et al. ChemCatChem 6, 3246–3253 (2014).