Catalytic hydrogenolysis of xylose into diols with high yields over the Ru-Re/CZO catalysts

Ethylene glycol (EG) and 1,2-propylene glycol (1,2-PG) are very important chemicals that are produced mainly from fossil resources at present. Catalytic hydrogenolysis of biomass (such as cellulose and sugar alcohols) to diols has attracted much attention in recent years. However, compared to sugar alcohols, sugars such as xylose have been scarcely used for the production of EG and PG until now due to their instability and low selectivity of diols. Xylose is an abundant and readily available bio-chemicals that can be produced from the hydrolysis of hemicellulose, but its catalytic hydrogenolysis into diols with high yields remains a great challenge. Herein, bimetallic Ru-Re/CZO(Ce 0.7 Zr 0.3 O 2 ) catalysts were synthesized and used to catalyze the hydrogenolysis of xylose to EG and PG. The nature of the catalysts is thoroughly characterized by XRD, XPS, BET, TEM, etc. It is found that Ru and Re nanoparticles are uniformly distributed on CZO alloy support formed by Ce and Zr. A very high total yield (65.0 %) of EG and 1,2-PG was achieved on the 4 %Ru-1 %Re/CZO catalyst under optimal conditions. Recycling experiments demonstrate that high xylose conversion and diol yields are maintained over four successive cycles under optimal conditions, despite a slight increase in Ru nanoparticle size observed via TEM analysis. The mechanistic study shows that xylose is first isomerized into xylulose, which undergoes retro-aldol cleavage to generate the intermediates, followed by further hydrogenation to EG and 1,2-PG. This work provides a new research avenue for the efficient preparation of diols from xylose.