A series of Co-ferrierite catalysts (Co-FERs) containing a variety of Co contents in the range 0.06 < Co/Al < 0.71 were prepared by wet ion exchange (WIE) and solid-state ion exchange (SSIE) methods. Their activities of NOx reduction to N-2 by CH4 over Co-FERs were examined over a fixed bed flow reactor in O-2-rich condition to illustrate the distinctions of NO removal activity with respect to the ion exchange methods and cobalt loadings of the catalyst. X-ray photoelectron spectroscopy was employed to analyze 2p(1/2) and 2p(3/2) binding energies of Co on the catalyst surface. As Co loading of Co-FERs prepared by WIE increases, Co oxide clusters begin to form due to the high possibility of Co agglomeration through the interaction of Co ions on the catalyst surface. For Co-FERs prepared by SSIE, the binding energies of Co 2p(3/2) are basically unchanged in the range of the cobalt loadings prepared, revealing that Co oxide clusters have already formed in the outer region of the catalyst surface, even at the rather low loading values of Co. XANES and EXAFS techniques were also employed to confirm that the Co-FERs by SSIE even with the low loadings of Co contain a small-sized Co3O4-like phase, which may promote CH4 activation and/or the oxidation of NO to NO2, and that the Co-FERs by WIE with high Co loadings comprise a small-sized Co(OH)(2)-like phase, which may enhance the amount of NO, adsorption on the surface of the catalyst. (C) 2004 Elsevier B.V. All rights reserved.