Surface reactivity of zinc-modified hydroxyapatite

Surface reactivity of hydroxyapatite (Hap), Ca-10(PO4)(6)(OH)(2), and zinc-Hap was evaluated using temperature-programmed desorption (TPD) of ethanol and diffuse reflectance infrared spectroscopy (DRIFTS). Hap was prepared by the precipitation method and the Zn-based catalysts were prepared by the ionic exchange method (ZnHap(tac)) and by zinc oxide deposition (ZnHaP(dep)). X-ray diffraction (XRD) results have shown the Ca2+ substitution by Zn2+ ions for the catalyst prepared by ionic exchange method and a zinc oxide formation as a segregated phase after zinc deposition. TPD-ethanol analyses showed that Hap has catalytic activity to ethanol decomposition and low surface acidity. DRIFTS results showed ethoxide species formation at the surface of ZnHap(troc), which undergoes transformation into acetate and carbonate species with increasing temperature. The catalyst prepared through the ionic exchange method (ZnHaP(troc)) showed high selectivity to the ethanol dehydrogenation reaction. (C) 2007 Elsevier B.V. All rights reserved.