(629e) Hydrodeoxygenation over Ptwox Catalysts: Isotopic Labeling

Hydrodeoxygenation of platform molecules derived from biomass is critical to enabling biorenewable products. Hydrodeoxygenation has been investigated in the literature for conversion of glycerol to propylene glycol and 1,3-propanediol, hydroxymethylfurfural to 1,6-hexanediol and for upgrading of lignin. The use of PtWOx catalysts for 1,6-hexanediol production has been invented by DuPont.¹ We present the results of a mechanism investigation for the hydrodeoxygenation model compound, 1.2-pentanediol over this catalyst.

Three potential mechanisms were evaluated: 1) acid catalyzed dehydration and reduction,² 2) direct reduction of the secondary hydroxyl via hydride attack,³ and 3) a reverse Mars van Krevelen mechanism at WOx defect sites.^4-5 Deuterium incorporation into the product using either D₂ or D₂O has been characterized using nuclear magnetic resonance techniques. In neither case was a primary kinetic isotope effect observed, suggesting direct reduction of the C-O bond is not involved in the rate-limiting step. Utilization of aprotic solvents showed a significant decrease in the reaction rate suggesting the solvent has a major role in the reaction mechanism. The significance of these observations upon mechanism evaluation will be discussed.

1. Allgeier, A. M.; De Silva, W. I. N.; Menning, C. A.; Ritter, J. C.; Sengupta, S. K. Production of alpha, omega-diols. US9018423, April 28, 2015, 2014.
2. He, J.; Burt, S. P.; Ball, M.; Zhao, D.; Hermans, I.; Dumesic, J. A.; Huber, G. W., Synthesis of 1,6-Hexanediol from Cellulose Derived Tetrahydrofuran-Dimethanol with Pt-WOx/TiO2 Catalysts. ACS Catalysis 2018, 8 (2), 1427-1439.
3. Koso, S.; Nakagawa, Y.; Tomishige, K., Mechanism of the hydrogenolysis of ethers over silica-supported rhodium catalyst modified with rhenium oxide. Journal of Catalysis 2011, 280 (2), 221-229.
4. Prasomsri, T.; Nimmanwudipong, T.; Roman-Leshkov, Y., Effective hydrodeoxygenation of biomass-derived oxygenates into unsaturated hydrocarbons by MoO3 using low H2 pressures. Energy & Environmental Science 2013, 6 (6), 1732-1738.
5. Mironenko, A. V.; Vlachos, D. G., Conjugation-Driven “Reverse Mars–van Krevelen”-Type Radical Mechanism for Low-Temperature C–O Bond Activation. Journal of the American Chemical Society 2016, 138 (26), 8104-8113.