We report on an elaboration of new composite photocatalysts (TiO 2-P 25 @ n-TiO 2 @HAP) based of grafted size-selected 5nm titanium-oxo-alkoxo nanoparticles on P25-TiO 2 nanoparticles and HAP obtained by co-precipitation of salts. The 5-nm oxo-TiO 2 particles were prepared in a sol-gel reactor with rapid reagents micromixing. The photocatalytic test of ethylene degradation, in a continuous-flow fixed bed reactor, showed an increase of the photocatalytic yield for the composite photocatalysts with an addition of HAP. This result was interpreted by a synergy between adsorption and photooxidation.