Studies of NO decomposition on Pd/gamma-Al2O3, Mo/gamma-Al2O3 and Pd-Mo/gamma-Al2O3 catalysts were made. The reaction was investigated at 400 degreesC using a reactant mixture of 1100 ppm NO in He. Adsorption and dissociation of NO, O-2 and N-2 on Pd(1 1 1), MoOx-Pd(1 1 1) and MoOx-gammaAl(2)O(3) surfaces have been investigated using a molecular orbital approach of the extended Huckel (EHMO) type, including repulsion terms. The catalytic tests have revealed that the binary catalyst present a different behavior for the NO decomposition, the main difference being a longer steady-state activity at low temperature. Characterization results by TPR and hydrogen chemisorption have indicated that palladium physicochemical properties are altered by an effective interaction with molybdenum. This interaction appears to be responsible for the observed modification in NO activity. Our results of EHMO have showed that the NO adsorption energy on MoOx-Pd(1 1 1) model is lower than the one for Pd(1 1 1) or MoOx-gammaAl(2)O(3). Also, adsorption and dissociation of N-2 and O-2 are notoriously modified when an interaction between the two metals exists. Those results would indicate the existence of a Pd-Mo interface with catalytic properties different to the metals. (C) 2002 Published by Elsevier Science B.V.