A New Approach to Decomposition of Nitric Oxide Using Sorbent/Catalyst without Reducing Gas: Use of Heteropoly Compounds

Effective decomposition of NO to N₂ in flue gas can be accomplished by a two-step approach using sorbent/catalyst. No reducing gas is needed. A heteropoly compound, H₃PW₁₂O₄₀·6H₂O, is used as the sorbent/catalyst in this study. At a space velocity of 5000 h^-1,70% of NO in a simulated flue gas is absorbed in the fixed bed at 150 °C. Upon heating the NO-saturated bed to 450 °C (at 150 °C/min), 68.3% of the absorbed NO is decomposed into N₂. Based on the results of fixed-bed NO absorption and TGA and IR analyses, the absorption of NO is a bulk reaction where the six H₂O linkages in the secondary structure are substituted by three NO linkages, and the Keggin structure (primary structure) is preserved. X-ray diffraction data show that the spatial arrangement in the secondary structure is also preserved with a 5% reduction in the lattice constant. O₂ and H₂O are needed for NO absorption. SO₂ and CO₂ have no effects on either absorption or decomposition. The basic rationale for the two-step approach is to concentrate NO from flue gas concentrations (hundreds of ppm) into a bulk solid phase (where the NO partial pressure is of the order of 1 atm) thereby taking advantage of the kinetic law of catalyzed NO decomposition (which is either first or second order with respect to NO partial pressure).