(560h) Kinetics Study of the Simultaneous Hydrodeoxygenation of Xylitol over a ReOx-Pd/CeO2 Catalyst

Xylitol is a sugar alcohol derived from the hemicellulose portion of lignocellulosic biomass, and is mass produced and commonly used as a sugar substitute. However, xylitol can be chemically upgraded into value added platform chemicals such as 1,2-dideoxypentitol and 1,2,5-pentanetriol via a simultaneous hydrodeoxygenation (S-HDO). 1,2-dideoxypentitol and 1,2,5-pentanetriol are 300-5000 times more valuable than the initial cost of xylitol. The S-HDO removes two vicinal hydroxyl groups by undergoing a deoxydehydration to form a double bond and then is hydrogenated to a single bond¹. The ReO_x-Pd/CeO₂ catalyst was determined to be the best catalyst tested in literature for the S-HDO of sugar alcohols². The S-HDO of xylitol has been previously studied at 160°C and 80bar H₂¹ and our previous works have found that the pressure of this reaction has little effect on the yield down to 10bar H₂. However, the kinetics of this reaction have not been previously studied or reported. A kinetic study of the xylitol S-HDO was conducted at 10bar H₂ with temperatures ranging from 120-170°C. The reaction order, rate constant, and activation energy were elucidated. The effects of varying the xylitol concentration within the solvent were studied to determine the optimum conditions in which to conduct the xylitol S-HDO. Optimal conditions for the xylitol S-HDO with respect to temperature and concentration were elucidated.

References

(1) Ota, N.; Tamura, M.; Nakagawa, Y.; Okumura, K.; Tomishige, K. Hydrodeoxygenation of Vicinal OH Groups over Heterogeneous Rhenium Catalyst Promoted by Palladium and Ceria Support. Angew. Chemie - Int. Ed. 2015, 54 (6), 1897–1900.

(2) Ota, N.; Tamura, M.; Nakagawa, Y.; Okumura, K.; Tomishige, K. Performance, Structure, and Mechanism of ReO X –Pd/CeO 2 Catalyst for Simultaneous Removal of Vicinal OH Groups with H 2. ACS Catal. 2016, 6 (5), 3213–3226.