Effect of MgO addition to Cu-Ni/Al2O3 catalysts on glycerol hydrogenolysis in continuous reactor without external hydrogen

Abstract

Cu-Ni/xMgO-Al2O3 catalysts with x = 0, 10, 20 and 30 wt% were prepared and evaluated in glycerol hydrogenolysis to 1,2-propanediol (1,2-PDO) at 250 oC, pressure of 40 bar for 30 h, without addition of external hydrogen. The addition of MgO to alumina decreased the surface area, increased the Cu/Ni dispersion and the number of basic sites. The highest 1,2-PDO yield was achieved by Cu-Ni/30%MgO-Al2O3 catalyst: 50% after 6 h of reaction; it decreases to 25% after 30 h. The decrease in 1,2-PDO yield is accompanied by an increase in acetol yield, showing that the rate limiting step for MgO-Al2O3 catalysts is the hydrogenation of acetol to 1,2-PDO because there is not enough hydrogen in reaction medium. For Cu-Ni/MgO catalyst, the reaction pathway changed to the basic route, with preferential formation of lactic acid (50% of lactic acid yield in the first hours of reaction).