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Alumina-Supported Manganese Oxide Catalysts. Part 2. Surface Characterization and Adsorption of Ammonia and Nitric Oxide.-The title catalysts, prepared by impregnation with Mn acetate, are characterized by in situ IR spectroscopy and temp.-programmed reaction and desorption (TPRD) with regard to SCR of NO with NH3. On the catalyst, exhibiting two Lewis acid-type coordinatively unsaturated Mn ions on the surface, most likely in the +3 state, NH3 coordination is stable up to near 473 K. In the absence of O2 no NH3 oxidation is observed. The interaction with NO is very weak. Mn3+ species are probably able to bind both one NO and one NH3 molecule. In the absence of O2, reaction of NO with NH3 is observed in the IR cell in the range 300-423 K. The presence of oxygen has a strong effect on the rate of the SCR reaction. It plays a role in the catalyst reoxidation, promotion of NO absorption enables the abstraction of H from adsorbed NH3 and thus activates reaction with NO and it oxidizes gas-phase NO to NO2. -(KAPTEIJN, F.; SINGOREDJO, L.; VAN DRIEL, M.; AN-DREINI, A.; MOULIJN, J. A.; RAMIS, G.; BUSCA, G.; J. Catal. 150 (1994) 1, 105-116; Dep. Chem. Eng., Delft Univ. Technol., NL-2628 BL Delft, Neth.; EN)