Possibilities to selectively oxidize NH3 in gasification gas to N2 have been investigated. Either O2 or NO or both oxidizers simultaneously were added to the hot synthetic gasification gas, which was led through a catalyst bed positioned in the electrically heated furnace. In the empty reactor and in the nonporous quartz bed, only a slight NH3 reduction was achieved. When dolomite or iron sinter was used as catalyst, the added NO formed more NH3. The reactions of H2 with NO in fact may limit the use of certain catalysts in gasification atmosphere. In the experiments with silicon carbide, the silicon carbide surface was oxidized to porous oxide layer, which catalyzed the selective oxidation of NH3 to N2 at the temperature of 700−800 °C. Even with O2 addition alone large NH3 reduction was achieved. At the same time, significant NO formation was, however, noticed. The reason for the different behavior of the porous silicon dioxide layer, and dolomite and iron sinter, is probably their different capability to adsorb various gas species on their surface.