(560y) Catalytic Transfer Hydrogenolysis of Xylitol over Bifunctional Pd-Based Catalysts

Authors: 
Xia, Q., State Key Laboratory of Heavy Oil Processing, China University of Petroleum
Yin, B., College of Chemical Engineering
Jin, X., State Key Laboratory of Heavy Oil Processing, China University of Petroleum
Xylitol is known as one of the key platform chemicals, which can be converted into renewable products, including ethylene glycol (EG), 1,2-propanediol (1,2-PDO) and other derivatives. They are widely used as antifreezes, solvents and pharmaceuticals.[1] Up to date, it has been reported that conversion of xylitol to those renewables have been carried out in the aqueous phase under harsh conditions with high temperature (T > 200 oC) and high H2 pressure (4 ~ 8 MPa), which cause several technological issues such as significant formation of gaseous by-products, fast catalyst deactivation as well as high capital cost and energy consumption.[2,3] It is still a great challenge to achieve high glycol yields at mild conditions, due to the complexity of the parallel and consecutive reactions in xylitol hydrogenolysis.[4] In this work, we proposed a unique process of catalytic transfer hydrogenolysis (CTH) in the absence of externally added H2 for facile conversion of xylitol to value-added glycols.

Taking xylitol as a model compound, in this work, we have designed a series of bimetallic Pd-Cu, Pd-Ni, Pd-Pt and Ni-Cu catalysts and confirmed their remarkable performances in CTH reactions to 1,2-PDO, EG and lactic acid. Based on experimental results, it is found that bimetallic Pd-Pt catalysts supported on TiO2 has obvious superior CTH performances by comparing the conversion and products distribution to monometallic Pd and Pt under identical conditions. In particular, at nearly 100% xylitol conversion, a selectivity of 41.1% to EG and 1,2-PDO was obtained on Pd-Pt/TiO2 at 220 oC, 1.0 MPa nitrogen atmosphere in absence of external H2. In contrast, the main product of hydrogenolysis of xylitol on monometallic Pd/TiO2 was lactic acid with the low conversion. Similarly, monometallic Pt/TiO2 catalyst shows strong tendency for C-C breaking. In our presentation, the structural properties including effect of particle size on catalytic activity and selectivity will be systematically studied, with the aim to establish structure-activity correlations for C-C and C-O cleavage of xylitol during CTH process.

Reference

[1] Sun, J. Y.; Liu, H. C. Green Chemistry 2011, 13 (1), 135-142.

[2] Riviere, M.; Perret, N.; Cabiac, A.; Delcroix, D.; Pinel, C.; Besson, M. Chemcatchem 2017, 9 (12), 2145-2159.

[3] Jin, X.; Shen, J.; Yan, W.; Zhao, M.; Thapa, P. S.; Subramaniam, B.; Chaudhari, R. V. ACS Catalysis 2015, 5 (11), 6545-6558.

[4] Liu, H. L.; Huang, Z. W.; Kang, H. X.; Li, X. M.; Xia, C. G.; Chen, J.; Liu, H. C. Applied Catalysis B-Environmental 2018, 220, 251-263.