DeNOx removal

Ag on alumina is an effiicient catalyst for deNOx removal but the drawback is die simultaneous formation of CO, requiring an oxidation catalyst behind a bed of silver on alumina. The activity depends on the distance between the catalysts, e.g. residence time between Ag/alumina and oxidation catalyst. When the Pt-oxidation catalyst is placed immediately behind the Ag/alumina bed, a significant drop in the NO to N2 activity is observed in comparison with the single Ag/alumina bed. As expected the oxidation catalyst removes completely the produced CO. However, when the distance between the two catalysts is extended, the conversion of NO to N2 improves to levels close to those recorded over the single Ag/alumina bed (Figure 7.15). 

Thus zeolite ZSM-5 can be grown (ref. 15) onto a stainless steel metal gauze as shown in Figure 6. Presumably the zeolite crystals are chemically bonded to the (chromium-) oxide surface layer of the gauze. After template removal by calcination and ion exchange with Cu(II) a structured catalyst is obtained with excellent performance (ref. 15) in DeNOx reactions using ammonia as the reductant. 

Denox A generic name for processes for removing nitrogen oxides from flue-gases by catalyzed reaction with ammonia. 

DeNOx (1) A Denox process for removing nitrogen oxides from the gaseous effluents from nitric acid plants. The oxides are reduced with ammonia, over a catalyst containing potassium chromate and ferric oxide. Developed by Didier Werke in the 1980s. 

Monolithic catalyst carriers are state-of-the-art in exhaust gas cleaning, for example in automobiles, DeNOx or removal of VOCs. To minimize diffusion length and to increase the geometric surface area, monoliths with small-diameter channels have been developed which can be produced easily by extrusion, followed by calcination. In the past few years the application of monoliths in gas-liquid operation has been investigated intensively [10-13]. 

Thermal DeNOx Process Costs and Requirements in Application to Boilers and Furnaces With a modest 1.5 to 1 excess of NH3 over NO t he Thermal DeNOx reaction is capable of reducing NOx to levels which in an ideal case would be very low. For NFf at 290/ ton this corresponds to a cost of 161/ton of NOx removed. In some applications hydrogen is not needed but in others it is. For some of the latter applications it is readily available and inexpensive. In others hydrogen must be generated by NHg decomposition. For a situation in which H2 at 2/1 ratio to NF is needed, the NFf thus used would cost 214/ton of NOx removed. 

Hydrothermal Durability of HC-SCR DeNO Catalysts. - Among numerous HC-SCR deNOx catalysts examined, some of the catalysts exhibiting reasonable water tolerance are of particular interest for their commercial use their practical engine applications subsequently require essentially strong hydrothermal stability of the catalyst, particularly zeolite type catalyst. None of the potential SCR catalysts containing appropriate hydrothermal stability for removing NOx from mobile sources have been reported yet. This section will concentrate mainly on the time on-stream stability of potential catalysts for HC-SCR reaction. 

Overexchanged Fe-MFI catalysts via an oxalate method offer high performance and hydrothermal durability for NOx reduction with iso-butane even in the presence of significant amounts of H2O and SO2 for high temperature deNOx application to the ICEs. However, this approach has hardly been reproducible. On the other hand, the CVD method can prepare such Fe-MFI catalysts on which somewhat lower NOx removal efficiency but still high durability can be achieved for the present reaction system. Not only could the technique be reproducible for the catalyst preparation, but it also depends strongly on the... 

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