Effects of surfactant on morphology, chemical properties and catalytic activity of hydroxyapatite

Hydroxyapatite (HAP) was synthesised in the presence of surfactants and tested as a catalyst in CO oxidation. XRD confirmed that the characteristic HAP crystal phase was practically unaffected by the addition of surfactant. The surfactant altered both the Ca/P ratio and particle size of HAP. Catalyst tests showed that the activity of HAP increased for preparations using TWEEN, PEG and PVA. The temperature for 50% conversion, T-50, values decreased from 340 degrees C for unmodified HAP, to 320 degrees C for TWEEN and to 315 degrees C for both PEG and PVA. This enhanced activity is rationalised by the higher BET surface areas and acid site densities in the surfactant-modified preparations: these increased from 52 m(2) g(-1) for HAP to 69, 76 and 68 m(2) g(-1), and from 101 mu mol g(-1) for HAP to 110, 170 and 126 mu mol g(-1) for TWEEN, PEG and PVA, respectively. These findings demonstrate that HAP i.e. without the addition of precious metals to either the surface or framework, is an active CO catalyst and that the straightforward inclusion of surfactant during preparation can optimise the catalytic performance.