Pillared clays can be tailored to give high surface areas and porosities with different degrees of acidity. These materials often show better hydrothermal stability than zeolites. Al-PILC based Rh catalysts were tested in the selective catalytic reduction of NO by methane in presence of excess oxygen. The catalysts were prepared by two methods: incipient wetness impregnation (IMP) and wet ion exchange (IEX). The Rh3+ ion exchanged PILCs showed better performances than their homologues prepared by IMP. On IEX samples the effect of temperature and O-2 concentration in SCR-CH4 activity was analyzed. Different activation degrees detected in the catalysts after 25 vol.% O-2 and 450 degrees C reaction conditions, were related to the various Rh species present in the catalysts as a consequence of the exchange degree of the support in contact with the active phase solutions. From the results, a reaction mechanism is proposed by which exchanged Rh3+ in the Al-PILC matrix and oxidized Rh2Ox in combination with the supports acid sites contribute to form oxygenated species as the process-determining step. The results from XPS and O-2 adsorption isotherms were used to support the proposed mechanism. (c) 2005 Elsevier B.V. All rights reserved.