MoO3/CeO2 and MxOy/MoO3/CeO2 (M = Fe, Cu, Ni) catalysts had been characterized by XRD, TPR, LRS, NH3-adsorbed in situ FT-IR and activity test for selective catalytic reduction (SCR) of NO by NH3. The results suggested that the addition of NiO, CuO and Fe2O3 to MoO3/CeO2 catalysts had led to the different structures of surface molybdena species, i.e., isolated regular tetrahedral, highly distorted tetrahedral and polymerized octahedral molybdena species, revealing that the intensities of interaction between molybdena species and these metal oxides could be listed as: NiO/MoO3/CeO2 > CuO/MoO3/CeO2 > Fe2O3/MoO3/CeO2. Furthermore, it exhibited the same order for the surface acid intensities of the Lewis acid sites of these samples. The reactivity of "NO + NH3 + O-2" reaction is tightly related to acid properties of the catalysts (no matter Brensted or Lewis acid sites): At low temperature, a weak Lewis acid site (L1) is the main active site for "NO + NH3 + O-2" reaction: at middle temperature range, the Bronsted acid site is the primary active site: while at high temperature, another strong Lewis acid site (L2) can also promote the reaction. (C) 2009 Elsevier B.V. All rights reserved.