An active N-methylation ferrospinel catalyst, Cu1-xZnxFe2O4, is reported for the first time. A mechanistic approach to selective mono-N-methylation of aniline on Cu1-xZnxFe2O4 is Successfully explained by in situ temperature-dependent DRIFTS studies of reactants on the catalyst. Perpendicular orientation of aromatic rings of aniline, methyl group availability, an optimum metal-ion distribution on the catalyst surface, and a stable methyl group on Zn leads selectively to N-methylaniline (NMA) on Cu0.5Zn0.5Fe2O4. Desorption-limited kinetics is evident from NMA formation at low temperatures. (C) 2004 Elsevier Inc. All rights reserved.