(630h) Understanding and Manipulating the Solvent Microenvironment for Selective, Catalytic Amination of Renewable Oxygenates

Catalytic upgrading of biomass to commodity chemicals and fuels is pivotal to a more sustainable chemical industry. Due to their low vapor pressure, biomass feedstocks are typically processed in liquid solvents giving rise to a complex environment that remains inadequately understood. In this study, we considered the Ru catalyzed reductive amination of 3-hydroxybutyrolcatone (3HBL) to 3-aminotetrahydrofuran (3A-THF) and 2-amino-3-hydroxytetrahydrofuran (2A-3H-THF) using ammonia and hydrogen.

We performed Density Functional Theory (DFT) calculations using VASP 5.4.4. Electron-core interactions were treated using the Projector Augmented Wave method (PAW), while exchange-correlation effects were accounted for using the PBE-D3 functional. The energy cut-off was set to 420 eV. A 444 slab was used to model the Ru(0001) surface. We performed condensed phase simulations using the iSMS method¹.

Under all reaction conditions, we exclusively observe 3A-THF as the main product. We predict a limited overall TOF (Table 1) at moderate temperatures in all reaction environments. Only at elevated temperatures, we observe an appreciable activity. The high apparent activation barrier can be explained by both a high intrinsic activation barrier and a relatively crowded Ru surface. Implicit solvation models predict only a limited impact of a condensed-phase environment on the TOF; however, Ru is well-known to exhibit a significant increase in activity for aqueous phase reduction reactions.² To overcome the limitations of implicit solvation models, we developed a neural network potential for the water-ruthenium inaction that can be used together with free energy perturbation calculations to predict solvation effects on free energies of the most critical steps in the reaction network of the reductive amination of 3HBL.

References.

(1) Faheem, M.; Suthirakun, S.; Heyden, A. J. Phys. Chem. C 2012, 116 (42), 22458–22462.

(2) Michel, C.; Gallezot, P. ACS Catal. 2015, 5 (7), 4130–4132.