BET, XRD, XPS, and TPR by hydrogen were used for investigation of supported Mn-Bi oxide catalysts for ammonia oxidation into nitrous oxide. The catalysts were synthesized by impregnation of gamma-, alpha-Al2O3 and SiO2 with solutions of manganese and bismuth nitrates. The character of phase transformations, surface concentration, and state of the active component were shown to depend on the nature of the support. The sequence stabilization of active constituents of the Mn-Bi-O/alpha-Al2O3 catalyst and types of the stabilized species were determined. The activity of the Mn-Bi-O supported catalysts calcined at 400 degreesC was established to equal 95-97% and to be practically independent of the support nature, while the activity decreased with elevation of the calcination temperature. The Mn-Bi-O/alpha-Al2O3 catalysts exhibited the highest selectivity to N2O (84.4%) under identical conditions. The correlation between the Mn3+/Mndelta+ (2 < delta < 3) ratio in the catalyst and the selectivity to N2O was revealed. (C) 2003 Published by Elsevier Inc.