Hydrogenolysis of glycerol to propylene glycol in continuous system without hydrogen addition over Cu-Ni catalysts

•Cu, Ni and Cu-Ni catalysts on ZSM-5 and Al2O3 evaluated on glycerol hydrogenolysis.•Under inert atmosphere only bimetallic catalysts showed formation of propylene glycol.•Glycerol reforming is the dominant reaction for Ni monometallic catalysts.•When H2 is added Cu monometallic catalysts presented higher propylene glycol yield.

A series of Cu, Ni and Cu-Ni catalysts with 20 wt% of each metal, supported on Al2O3 and ZSM-5, was prepared by wet impregnation method and tested in glycerol hydrogenolysis to 1,2-propanediol (propylene glycol) using a WHSV of 2 h−1 at 250 °C, and pressure of 40 bar for 6 h. Without external hydrogen, the reaction pathway involves glycerol dehydration to acetol, with simultaneous reforming to H2 and CO2; this hydrogen generated in situ is used for the hydrogenation of acetol to propylene glycol. Under these conditions, the CuNi/Al2O3 and CuNi/ZSM-5 catalysts exhibited the highest glycerol conversion, 80% and 85%, respectively, with propylene glycol yield around 25%. With external hydrogen, all catalysts showed higher glycerol conversion (>90%) and the monometallic Cu catalysts presented higher conversion to liquid and propylene glycol yield than the bimetallic ones; the Cu/Al2O3 showed the highest yield to propylene glycol (70%). The activity of the catalysts was correlated with their metallic dispersion and also the support acidity.

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