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, H-2 chemisorption, TEM, XRD, H-2-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 Bronsted 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.