Selective catalytic oxidation of NH₃ in gasification gas. 1: Effect of iron sinter and dolomite on the reactions of NH₃, NO, and O₂ in gasification gas

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.