Selective Hydrogenolysis of Glycerol over Acid-Modified Co–Al Catalysts in a Fixed-Bed Flow Reactor

In this study, different acid-modified Co–Al catalysts were prepared and employed for glycerol hydrogenolysis by the addition of B, Ce, Zr, and heteropolyacids (HSiW, HPW, HPMo) to Co–Al catalysts. The catalysts prepared in this work were thoroughly examined by various characterization methods such as BET, ICP, SEM, H2 chemisorption, TEM, XRD, H2-TPR, NH3-TPD, XPS, and FTIR. The results showed an increase in the acid strength and Co dispersion on the catalytic surface for the modified Co–Al catalysts. This facilitated the conversion of glycerol. When ethanol was used as a solvent, the selectivity of 1,2-propanediol (1,2-PDO) by the acid-modified Co–Al catalysts decreased slightly, attributable to the enhanced etherification activity of glycerol with ethanol. However, when water was used as a solvent, the modified Co–Al catalyst with the B, Ce, and Zr species increased the selectivity of 1,2-PDO. Addition of heteropolyacids to the Co–Al catalyst enhanced the selectivity of 1,3-propanediol (1,3-PDO) as compared to 1,2-PDO selectivity which was relatively low due to its association with Brønsted acid sites on the modified Co–Al catalysts. The optimal HSiW/Co–Al catalyst (in terms of both 1,2- and 1,3-PDO selectivity) showed 76.3% glycerol conversion and 18.3% 1,3-PDO selectivity with a good stability. This could be attributed to the existence of well-dispersed Co particles with strong interaction between Co and W species.