Stable TiO2-P25@n-TiO2 nanocoating was prepared based of grafted size selected 5 nm Titanium-oxo-alkoxo (n-TiO2) nanoparticles on P25-TiO2 nanoparticles surface and their immobilization on Aluminium substrate. The 5-nm oxo-TiO2 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 with number of the deposited layers until a sursaturation regime. By modeling the photocatalytic activity of the composite, a death layer of electron-hole pairs excitation of 20 nm, corresponding of the film thickness, was found. Furthermore, the estimation of the TiO2 absorption coefficient (k=2 .104 cm-1) indicates a strong porosity of the deposited films.