Al2O3 and ZSM-5 supported Pd, Rh and Pt catalysts were studied for NH3 oxidation at 200-350 degrees C in comparison with V2O5/TiO2 and Co-ZSM-5 catalysts at 250-400 degrees C. The precious metal catalysts are very active for NH3 oxidation in this temperature range. With the addition of 5% H2O vapor, the NH3 conversion is not affected at high temperatures but decreases at 200-250 degrees C. Generally, the ion exchanged ZSM-5 catalysts are more active than the Al2O3 supported catalysts with an identical metal loading and less affected by water vapor. However, for the supported precious metal catalysts the catalytic selectivity is not significantly affected by catalyst support. The selectivity to N-2 is relatively high on Ph and Pd catalysts and low on Pt catalysts, where high levels of N2O were produced on Pt. Some of the catalysts reported here, for example, Pd-ZSM-5, may be quite suitable as a practical catalyst for low temperature NH3 destruction in a wet stream. As a comparison, V2O5/TiO2 is quite selective for N-2 formation at T < 300 degrees C but is much less active compared to the precious metal catalysts. In addition, water has a dramatic effect on the NH3 conversion over the V2O5/TiO2 catalyst. Co-ZSM-5, on the other hand, is the least active catalyst and produces relatively high levels of NO.