Hydrogenolysis of sorbitol over Ni supported on Ca- and Ca(Sr)-hydroxyapatites

Abstract

Ca-hydroxyapatite (HAP) was synthesized with different morphologies, in needle (N), sphere (S) and rod (R) shapes. A partially Sr-substituted sample (Ca(Sr)-hydroxyapatite) with the stoichiometric composition of Sr0.6Ca9.4(PO4)6(OH)2, and possessing a rod shaped morphology was also hydrothermally synthesized (SrHAP-R). The samples were characterized by X-ray diffraction, Fourier-Transform infra-red spectroscopy (FT-IR), scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS) and surface area measurement. Nickel (6 wt%) was loaded on the samples by an impregnation method. Rod-shaped hydroxyapatite (HAP-R) was more crystalline than the others. FT-IR results showed characteristic bands for (PO4)3− and OH vibrations. XPS results indicated Ni to be in the 2+ state, and O 1s satellite features revealed a phosphoric oxide environment in all the samples. The catalytic activities of the Ni-containing samples were tested in the hydrogenolysis of sorbitol into ethylene and propylene glycols in an aqueous medium in a stirred high pressure reactor at different process conditions. The most active catalyst was Ni/SrHAP-R. The catalyst was reusable many times with only a minor activity loss.