Catalysts for clean-up of NO{sub X}, NH{sub 3}, and CO from nuclear waste processing
- Brigham Young Univ., Provo, UT (United States)
During radioactive waste processing NO{sub X} and CO pollutants are discharged at levels of 1-3% to a waste gas stream also containing about 20% H{sub 2}O and 14% O2. NO{sub X} is removed in two primary reactors to a level of 300-1,000 ppm by selective reduction with NH{sub 3} over a commercial mordenite catalyst at 300-500{degrees}C; NH{sub 3} slip from these reactors is about 100-500 ppm, while only 10-20% of the CO is converted on the mordenite beds. Pt/Al{sub 2}O{sub 3} and Cu-ZSM-5 catalysts under consideration for use in a third reactor for final cleanup of NO{sub x}, NH{sub 3} and CO were studied on laboratory scale over a range of anticipated process conditions using gas mixtures containing 500-1000 ppm NO, 500-1000 ppm NH{sub 3}, 1-2% CO, 14%, O2, 20% steam, and the remainder N{sub 2} or combination of these gases. Both catalysts have useful temperature windows in which simple oxidation of CO or NH{sub 3} occurs readily. Although significantly more active for either of these oxidation reactions, the Pt/Al{sub 2}O{sub 3} catalyst suffers from selectivity limitations in complex reactant mixtures and at higher reaction temperatures, a large fraction of an NO, NH{sub 3}, O{sub 2} mixture is converted to N{sub 2}O while in a mixture of NO, NH{sub 3}, CO, and O{sub 2} much of the nitrogen is oxidized to NO{sub x} at higher reaction temperatures. CU/ZSM-5, on the other hand, selectively reduces all of the reactant NO with NH{sub 3} to N{sub 2} over the temperature range of 260-450{degrees}C(in a reactant mix of No, NH{sub 3} CO, O{sub 2} and H{sub 2}O); stoichiometric amounts of NH{sub 3} completely removed about 350{degrees}C, while in a mixture of NH{sub 3}/NO=2, complete conversion of NH{sub 3} occurs at 475{degrees}C. The only drawback of the Cu/ZSM-5 catalyst is that only 20-40% of the CO in this reactant mix is oxidized to CO{sub 2} in the temperature range of 300-500{degrees}C.
- OSTI ID:
- 141999
- Report Number(s):
- CONF-930304--
- Country of Publication:
- United States
- Language:
- English
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