Nitric oxide reduction with ammonia

2 Nitric oxide reduction with ammonia. Lintz and co-workers78,79 have studied the platinum catalysed reduction of nitric oxide by ammonia in the region 

It was found that when the partial pressure of nitric oxide was more than 1.5 times greater than the partial pressure of ammonia, the platinum surface remained in a relatively oxidised state and the selectivity to nitrogen was poor. When the partial pressure of nitric oxide was less than 1.5 times the partial pressure of ammonia, the platinum surface remained in a relatively reduced state and the selectivity to nitrogen approached unity. 

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S. Kasaoka and H. Nanba, "Effect of Alkali Earth Metal Salt Deposition on Catalytic Activity of Vanadium Pentoxide/Titanium Dioxide in Nitric Oxide Reduction with Ammonia", Nenryo Kvokaiski. Japan, 1984, i(6), 403-412. 

Williamson WB, Lunsford JH (1976) Nitric oxide reduction with ammonia over copper(II) Y zeolites. J Phys Chem 80 (24) 2664-2671... 

Postformation nitrogen oxide emission control measures include selective catalytic and noncatalytic reduction with ammonia, which between them are used by some 900 power station installations worldwide [51]. The catalytic removal methods are 70-90% efficient at NOx removal, but are more expensive to operate than the noncatalytic methods which are 30-80% efficient. Ammonia or methane noncatalytic reduction of NOx to elemental nitrogen is also an effective method which is cost-effective for high concentration sources such as nitric acid plants (Chap. 11). NOx capture in packed beds is less expensive, but this method is not particularly effective [23]. It is also not a very practical method either for utilities or for transportation sources. Two-stage scrubbing has also been proposed as an effective end-of-pipe NOx control measure. The first stage uses water alone and the second uses aqueous urea. 

Hydroxylamine sulfate is produced by direct hydrogen reduction of nitric oxide over platinum catalyst in the presence of sulfuric acid. Only 0.9 kg ammonium sulfate is produced per kilogram of caprolactam, but at the expense of hydrogen consumption (11). A concentrated nitric oxide stream is obtained by catalytic oxidation of ammonia with oxygen. Steam is used as a diluent in order to avoid operating within the explosive limits for the system. The oxidation is followed by condensation of the steam. The net reaction is... 

Nitric oxide is made commercially by oxidation of ammonia above 500°C in the presence of platinum, or by reduction of nitrous acid with ferrous sulphate or feiTous halides. The physical ... 

Nitric oxide is the simplest thermally stable odd-electron molecule known and, accordingly, its electronic structure and reaction chemistry have been very extensively studied. The compound is an intermediate in the production of nitric acid and is prepared industrially by the catalytic oxidation of ammonia (p. 466). On the laboratory scale it can be synthesized from aqueous solution by the mild reduction of acidified nitrites with iodide or ferrocyanide or by the disproportionation of nitrous acid in the presence of dilute sulfuric acid ... 

Water soluble iron porphyrins [Fem(TPPS)(H20) ]3-330 and [Fem(TMPy)(H20)2]5+ 331 332 (TPPS = maso-tetrakis(/ -sulfonatophenyl)porphyrin, TMPyP = / /e.vo-tetrakis(7V-methyl-4-pyridi-nium)porphyrin331 or maso-tetrakis (A -methyl-2-pyridinium)porphyrin332 dications) act as effective electrocatalysts for the reduction of nitrite to ammonia in aqueous electrolytes (Equation (64) Ei/2= 0.103 V vs. SCE at pH 7), with NH2OH or N20 also appearing as products depending on the reaction conditions. Nitric oxide then ligates to the iron(III) porphyrin to form a nitrosyl complex [Fen(P)(NO+)] (P = porphyrin) as intermediate. 

Wiehterlova, B Sobalik, Z Vondrova, A. Differences in the strueture of eopper aetive sites for deeomposition and seleetive reduction of nitric oxide with hydroearbons and ammonia, Catal. Today, 1996, Volume 29, Issues 1-4, 149-153, Seeond Japan-EC Joint Workshop on the Frontiers of Catalytic Science and Technology for Energy, Environment and Risk Prevention... 

It was found that the electrocatalytic activity strongly depends on the nature of the electrode it decreases in the order Rh > Ru > Ir > Pd and Pt for the transition-metal electrodes and in the order Cu > Ag > Au for the coinage metals. It was concluded that the rate-determining step on Ru, Rh, Ir, Pt, Cu, and Ag is the reduction of nitrate to nitrite. It was assumed that chemisorbed nitric oxide is the key surface intermediate in the nitrate reduction. It was suggested that ammonia and hydroxylamine are the main products on transition-metal electrodes. This is in agreement with the known mechanism for NO reduction, which forms N2O or N2 only if NO is present in the solution. On Cu the production of gaseous NO was found, which was explained by the weaker binding of NO to Cu as compared to the transition metals. 

Fig. 13.6 Laboratory flow reactor experiments on selective noncatalytic reduction of nitric oxide by ammonia, with and without hydrogen addition [251]. Inlet composition NO = 225 ppm, NH3 = 450 ppm, O2 = 1.23% balance inert. Residence time 0.075 s atmospheric pressure.

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