Catalytic activities of M (Fe, Cu, Co)-beta (BEA) zeolites for N2O direct decomposition were systematically investigated by employing both experimental and theoretical [density functional theory (DFT)] approaches. The activities of M-BEA determined by intrinsic kinetic evaluations are in good agreement with the DFT calculations and the microkinetic analyses, revealing that the distinguishing activities of M-BEA were mainly attributed to their distinct energy barriers for the O-2 desorption (Part 3). During the DFT calculations, a unique intermediate (IM) was generated only over Co-BEA, which was verified by the activity evaluation and N2O-TPD experiments, showing that the formation of IM reduced N2O decomposition rate of Co-BEA. The negative effect of the IM was thereafter investigated by the microkinetic analyses through which it was known that the second forward reaction rate constant of Co-BEA was lower than its reverse reaction rate constant, resulting in a final decline of the N2O decomposition rate. (C) 2012 Elsevier Inc. All rights reserved.