Selective NH 3 oxidation to N 2 in a wet stream

Abstract

Al 2O 3 and ZSM-5 supported Pd, Rh and Pt catalysts were studied for NH 3 oxidation at 200–350°C in comparison with V 2O 5/TiO 2 and Co-ZSM-5 catalysts at 250–400°C. The precious metal catalysts are very active for NH 3 oxidation in this temperature range. With the addition of 5% H 2O vapor, the NH 3 conversion is not affected at high temperatures but decreases at 200–250°C. Generally, the ion exchanged ZSM-5 catalysts are more active than the Al 2O 3 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 Rh and Pd catalysts and low on Pt catalysts, where high levels of N 2O 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 NH 3 destruction in a wet stream. As a comparison V 2O 5/TiO 2 is quite selective for N 2 formation at T < 300°C but is much less active compared to the precious metal catalysts. In addition, water has a dramatic effect on the NH 3 conversion over the V 2O 5/TiO 2 catalyst. Co-ZSM-5, on the other hand, is the least active catalyst and produces relatively high levels of NO.