Catalytic oxidative decomposition of dimethyl methylphosphonate over cu-substituted hydroxyapatite

The oxidative decomposition of dimethyl methyiphosphonate (DMMP) has been studied over Cu-substituted hydroxyapatite catalysts in a flow reactor in the temperature range 373-773 K. By substitution of a portion of the Ca²⁺ by Cu²⁺ in the hydroxyapatite lattice, the catalytic activity was markedly increased. The composition Cu₂Ca₈(PO₄)₆(OH)₂, herein called Cu2-HA, had the highest activity among these catalysts. All the catalysts showed 100% conversion at the beginning of the reaction, but became deactivated after a period of time. Only CO₂ and H₂O were produced during the "protection period" of the 100% conversion. With deactivation, CO₂ formation decreased and methanol and dimethyl ether appeared as products. A phosphorus-containing product was not detected in the gas phase. Some condensate of phosphoric acid appeared in the outlet of the reactor after deactivation. Several analytical methods revealed that carbonaceous compounds did not remain on the surface after 773-K oxidative regeneration, but the phosphorus compounds that had accumulated during the reaction were not eliminated. The catalytic activity of Cu-substituted hydroxyapatite was compared to that of conventional supported Pt catalysts. This study suggested that easily made and cheap Cu-substituted hydroxyapatite catalysts could be used as successful alternatives to conventional adsorbents and catalytic systems based on supported noble metals devised for protection against nerve gases in warfare.