Reduction of nitrogen oxides with ammonia

Ammonia is sometimes used as a reducing agent for the selective reduction of NOE in emissions from industrial installations, but unreacted ammonia creates a secondary air pollution problem because it is itself hazardous. Consequently, selective catalytic oxidation (SCO) is required to convert traces of ammonia to nitrogen downstream of the reactor 134 

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S. Matsuda, T. Kamo, A. Kato, F. Nakajima, Deposition of ammonium bisulfate in the selective catalytic reduction of nitrogen oxides with ammonia, Ind, Eng, Chem. Prod, Res, Develop, 2I A% (1982). 

Kotter M., Lintz H.-G. and Turek T., Selective catalytic reduction of nitrogen oxide by use of the Ljungstroe air heater as reactor A case study, Chem. Eng. Sci. 47 (9/11) 2763 (1992). Lintz H.-G. and Turek T, The selective catalytic reduction of nitrogen oxides with ammonia in a catalytically active LJungstroem heat exchanger, in New Frontiers in Catalysis, Guezi et al., eds, Elsevier. Amsterdam (1993). 

Vanadium plays an important role in many industrial catalysts used extensively in a variety of applications including the production of SO3 from SO2, selective oxidation of hydrocarbons, reduction of nitrogen oxides with ammonia, and in the manufacture of many chemicals and chemical intermediates. Such catalysts typically consist of vanadium compounds supported on oxides such as silica, alumina, titania, etc., and their activity depends on factors such as the chemical form and crystalline environment... 

Bayer operates a number of. similarly engineered waste combustion units. At the Dormagen plant, a further combustor for solid and liquid wastes has been placed in service. It consists of a rotary furnace, afterburner, waste-heat boiler, and gas scrubber. The plant incorporates a condensation-type electrostatic filter specially developed by Bayer [259] and an SCR unit for selective catalytic reduction of nitrogen oxides (with ammonia) and for degradation of dioxins in the tail gas (see Fig. 115). 

VANADIUM EXCHANGED TITANIUM PHOSPHATES AS CATALYSTS FOR THE SELECTIVE REDUCTION OF NITROGEN OXIDE WITH AMMONIA... 

Matsuda S, Kamo T, Kato A, Nakajima F, Kumura T, Kuroda H (1982) Deposition of Ammonium Bisulfate in the Selective Catalytic Reduction of Nitrogen Oxides with Ammonia. Ind. Eng. Chem. Prod. Res. Dev. 21(l) 48-52... 

Grzybek T, Klinik J, Rogoz M, Papp H (1998) Manganese supported catalysts for selective catalytic reduction of nitrogen oxides with ammonia - Part 1 - Characterization. J Chem Soc-Faraday Trans 94 (18) 2843-2850... 

Grzybek T, Pasel J, Papp H (1999) Supported manganese catalysts for the selective catalytic reduction of nitrogen oxides with ammonia 11. Catalytic experiments. Phys Chem Chem Phys 1 (2) 341-348... 

Briiggemann TC, Vlachos DG, Kell FJ (2011) Microkinetic modeling of the fast selective catalytic reduction of nitrogen oxide with ammonia on H-ZSM-5 based on first principles. J. Catal. 283 178-191... 

Devadas, M. (2006) Selective catalytic reduction (SCR) of nitrogen oxides with ammonia over Fe-ZSM5, PhD. Thesis No. 16524, ETH Zurich. 

An interesting variant of selective oxidation catalysis is the catal)hic reduction of nitrogen oxides by ammonia or hydrocarbons. In this case the reducing molecule should specifically react with NO or NO2, that are present in very low concentrations, rather than become oxidized to CO2 + H2O by reacting with O2 that is present in much higher concentration. The distinction between oxo-ions and oxide particle is most convenient if these entities are present on a zeolite support. Techniques have been developed to study the interconversion by IR spectroscopy ... 

A modification of the SFGD process just described is the Shell flue gas treating process, which not only removes sulfur oxides from flue gas, but can also effect a substantial reduction of the nitrogen oxides content. This is based on the activity of copper, whether in the oxidic or sulfate form, to catalyze the reaction of nitrogen oxides with ammonia according to the reactions... 

The PPR and LFR are also applied in a more recently developed dedicated process for NOx removal from off-gases. The Shell low-temperature NO reduction process is based on the reaction of nitrogen oxides with ammonia (reactions iv and v), catalyzed by a highly active and selective catalyst, consisting of vanadium and titania on a silica carrier [18]. The high activity of this catalyst allows the reaction of NO with ammonia (known as selective catalytic reduction) to be carried out not only at the usual temperatures around 300°C, but at substantially lower temperatures down to 130°C. The catalyst is commercially manufactured and applied in the form of spheres (S-995) or as granules (S-095) [19]. 

Process of selective catalytic reduction of nitrogen oxides by ammonia (SCR) involves injection of ammonia into a gas stream containing nitrogen oxides, then reduction of NOx by ammonia on the surface of a catalyst typically containing vanadium oxide on titania. The reactions involved are mildly exothermic (additional heat is required in most cases). Limits of the optimal process temperature, usually from 200 to 350°C, are dictated by catalyst activity at low temperatures and by the reaction selectivity at high temperatures. The NOj-containing gas flows often have low temperature and variable flow rates and concentrations. This combination of factors makes application of an RFR to NO reduction advantageous. One industrial unit for NO selective catalytic reduction was reported to operate in Russia [44], with ammonia water injection between two catalyst beds. 

Other reactions of small inorganic molecules are the oxidation of chloride ion at a Nafion electrode impregnated with a ruthenium 0x0 complex and the reduction of nitrogen monoxide to ammonia at a Co phthalocyanine modified electrode... 

Voorhoeve, RJH Remeika, JP Johnson, DWJr. Rare-earth manganites catalysts with low ammonia yield in the reduction of nitrogen oxides. Science, 1973, Volume 180, 62-64. 

Nitrogen (IV) oxide, 6 87 Nitrogen (V) oxide, 3 78 Nitrogen selenide, as explosive product in reduction of strontium selenite with ammonia, 3 21 N itropentamminechromium (III) nitrate, 5 133... 

The operability and reliability of processes using ammonia must also be studied. With the potential for increased ammonia use in these systems (in the selective catalytic reduction of nitrogen oxides and as an absorbent), research documenting ammonia emissions and the effects of ammonia on process equipment should be conducted. Furthermore, additional investigations should be performed to determine whether ammonium salts are formed and to document their effects on both the environment and the flue gas treatment system. 

Second, there appear to be a variety of enzymes (in the general, EC 1.7 reductase rubric) with more or less well-defined structures that reduce a variety of other oxides of nitrogen. However, the real challenge, given the composition of the earth s atmosphere, is the reduction of nitrogen (N2) to ammonia (NH3), and, to that end, there appear to be a number of different enzymes in the generalized rubric nitro-genase as found in the PDB. 

If the irradiated water was, however, saturated with hydrogen or carbon monoxide instead of oxygen then no oxides were formed [35]. Under these conditions reduction of nitrogen occurred to afford ammonia [36]. Interestingly, HCN is also observed when carbon monoxide is replaced by methane [37].Thus the result of a sonochemical reaction, in water, depends largely on the nature of the dissolved gases and their concentration. 

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