Catalytic Hydrogenolysis Of Glycerol To 1,2-Propanediol Over Cu-based Catalysts Derived From Hydrotalcite-Type Precursors

Cu-Zn-Al and Cu-Mg-Al catalysts were prepared from the hydrotalcite-like precursors. The effect of M²⁺ kinds, M²⁺/Al³⁺ ratios and Cu contents on the strcture and performance of the catalysts for the hydrogenolysis of glycerol was investigated by means of H2-TPR, XRD, H2-TPD, N2-adsorption, NH3-TPD and CO₂-TPD and activity test.After calcination at 450℃, the hydrotalcite-like precursors were transformed to the mixed oxides without hydrotalcite-like structure, in which Cu species dispersed well except Cu(1)Zn(2)Al(1) sample. After reduction at 270℃, the mixed oxides were converted to Cu-based catalysts. Compared with the Cu-Mg-Al catalysts, there were more amounts of hydrogen adsorbed on the Cu-Zn-Al catalysts. This may be related to the contribution of Zn species to H2 adsorption.With increasing Al2O3 contnets, i.e., decreasing M²⁺/Al³⁺ ratios, the specific surface areas and acid amounts of the catalysts increased. The catalyst acidity may mainly be atrributed to Al2O3. The Cu-Mg-Al catalysts had more and stronger basic sites than the Cu-Zn-Al catalysts.In the hydrogenolysis of glycerol, Cu(1)Zn(1)Al(4) showed higher activity and 1,2-propanediol selectivity than the Cu-Mg-Al catalysts. This is attributed to its larger specific surface area, more amounts of H2 absorbed and acid amounts. The Cu-Mg-Al catalysts with stronger basic sites may promote the dissociation of C-C bond, leading to higher selectivities of methnol, ethanol, and glycol. Moreover, stronger basic sites also promoted the polymerization of the reactant and products.For the Cu-Zn-Al (M²⁺/Al³⁺ = 1/2) catalysts, as the Cu contents increased, the dispersion of Cu and H2 adsorption amount decreased, and the activity in the hydrogenolysis of glycerol increased at first and then decreased. The catalyst containing 18 wt.% Cu possessed the best activity.