Glycerol hydrogenolysis to 1,2-propanediol with Cu/γ-Al2O3: Effect of the activation process

We have used Cu/γ-Al2O3 catalysts submitted to different activation protocols (calcination, reduction in H2/Ar, and reoxidation in N2O/N2) in order to investigate the role of the different copper surface species and acid properties in glycerol hydrogenolysis to 1,2-propanediol (1,2-PDO) under mild reaction conditions (493 K, 2.4 MPa H2). The activated catalysts have been characterized by temperature-programmed reduction (TPR), temperature-programmed desorption of NH3 (TPD-NH3), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO (DRIFT-CO). The significant different catalytic performance obtained with the Cu/γ-Al2O3 solids is not integrally related to their acid properties, surface Cu species also participate in the glycerol conversion. Partially reduced copper species (Cu+) promotes glycerol conversion rates. Activated catalysts follow the sequence: reoxidation > reduction > calcination, when glycerol conversion is compared. Moreover, Cu species are mostly responsible for the observed 1,2-PDO selectivity values. It is strongly dependent on the Cu0/Cu+ atomic ratio and on the surface concentration of both Cu0 and Cu+ species. Accordingly, 10CuAl-c-r catalyst showed the best behavior in glycerol hydrogenolysis to 1,2-PDO.