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

On hydroxyapatite of stoichiometric composition (Ca/P = 1.65), methanol decomposes at 600 degrees 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 H-2.