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

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.