The work is related to the fundamental research of the process of ammonia neutralization using catalytic oxidation over Pt/Al2O3 catalysts in an excess of oxygen. The catalysts are synthesized using nitrate precursors on the supports prepared from Pural SCF-55 aluminum hydroxide by the calcination in air at 550°C or 750°C for 4 h. A number of physicochemical methods are used to study morphology, dispersion, structure, and electronic state of the catalyst active component before and after the reduction in hydrogen. It is shown that the synthesized Pt/Al2O3 catalysts are characterized by high dispersion of the active component: the size of deposited platinum particles is in the range from 0.5 nm to 2.0 nm, while the proportion of oxidized and reduced Pt forms varies. Based on the results of kinetic measurements, the catalyst activity and the selectivity to all major products (N2, N2O, NO, NO2) are determined depending on the reaction temperature. The results of the catalytic testing are discussed in relation to the data on dispersion and oxidation state of platinum.