Mordenite films were grown on FeCrAl alloy, CSi foam, and cordierite monoliths in order to study the influence of chemical and physical characteristics of the support on the structure of the coatings and its catalytic activity for the SCR of NO, with CH4 as test reaction, using In as the active ingredient. The method of secondary synthesis from nanometric seeds was selected because of the higher coating homogeneities achieved. The FeCrAl alloy and cordierite yielded ordered crystals growths, preferentially with the b-axis perpendicular to the metallic surface, and with the c-axis perpendicular to the cordierite support, respectively. While high crystal intergrowth was observed for the FeCrAl alloy, in the cordierite case it was limited to the interphase. The CSi foam yielded disordered film structures, forming a dense phase in the shape of cumulus laying at the top of mordenite crystals with high intergrowth. The differences are mainly attributed to chemical characteristics that originate different local environments in which the seeds are immersed and the growth takes place, the topography of the substrates not being so important. The order in maximum NOx conversions was InHMOR/FeCrAl > InHMOR/cordierite > InHMOR powder > InHMOR/CSi, and it can be related, among other factors, to the accessibility of the reactants to the active sites. (c) 2006 Elsevier B.V. All rights reserved.