Calcium-Deficient and Stoichiometric Hydroxyapatites Promoted by Cobalt for the Catalytic Removal of Oxygenated Volatile Organic Compounds

AbstractThree series of hydroxyapatites (Hap) promoted by cobalt, have been synthesized using co-precipitation or impregnation methods, characterized by various techniques (XRD, UV-visible, Raman, and H 2 -TPR), and their catalytic properties were tested in the total oxidation of methanol. Characterization of the Co-promoted Hap solids showed that some Co 2+ ions could incorporate the apatite structure and that bulk Co 3 O 4 entities could be formed outside the apatite grains. The activity for methanol oxidation of the cobalt-coprecipitated samples was low because structural cobalt ions are difficult to reduce, whereas the activity of the Co-impregnated samples was found to be very high since the methanol was totally converted at low temperature. This was related to the presence of Co 3 O 4 entities that are more easily reducible than structural Co ions and are found in higher quantity in the impregnated solids. This catalytic effect was highlighted using an Ca-deficient Hap as a support: cooperation of redox properties of Co 3 O 4 and acid properties of the apatite support led to a very efficient catalyst since the corresponding light-off temperature was lowered by 50 °C with a catalyst containing 5 wt% of cobalt.Graphical Abstract[IMAGE]