Catalytic oxidation of carbon monoxide over stoichiometric and non-stoichiometric hydroxyapatites

Abstract

Calcium hydroxyapatites [Ca_10−z(PO₄)_6−z(HPO₄)_z(OH)_2−z; (0 ⩽ z ⩽ 1)] catalyze the oxidation of CO at 600 °C. O₂⁻ radical oxygen species can be formed on the sample of approximately stoichiometric form (z = 0.10). It is believed that oxygen molecules are activated with O²⁻ produced by the dehydration of the hydroxy groups in the structure. No radical oxygen species can be detected with the nonstoichiometric form (z = 0.34) on which the disproportionation of CO to CO₂ and carbon takes place at 600 °C.