Methanol adsorption and dehydrogenation over stoichiometric and non-stoichiometric hydroxyapatite catalysts

Abstract

On hydroxyapatite of stoichiometric composition (Ca/P = 1.65), methanol decomposes at 600 °C, in the absence of oxygen, to produce predominantly carbon monoxide. As the Ca/P ratio decreases, the selectivities to formaldehyde and dimethyl ether increase to ca. 80% at a value of Ca/P equal to 1.51. IR spectra show that methoxy groups are formed on the surface of both the stoichiometric and non-stoichiometric catalysts. Both IR and temperature-programmed desorption experiments suggest that for the decomposition of methanol, acidic sites are required for the dissociative adsorption whereas basic sites facilitate the C—H bond scission via carboxylate groups and the consequent formation of CO and H₂.