The importance of the choice of a suitable substrate as supporting material for photoactive TiO2, either in the form of powders or thin films or in photoactive paints, is frequently disregarded. In this paper four different supports (stainless steel, sand-blasted stainless steel, Teflon and glass) are object of investigation. The final aim is to verify the presence of interactions between the photocatalyst (AEROXIDE (R) TiO2 P25 by Evonik Degussa Corporation) and the support, directly involved in the photocatalytic activity in the NOx abatement. The characterization results have been correlated with the photoactivity of the different samples. In particular, a coating of about 6-9 mu m seems to allow a photocatalytic result free from any positive or negative interference with the supporting material, therefore giving reliable results about the photoactivity of the TiO2 under investigation. (c) 2011 Elsevier B.V. All rights reserved.