Low‐Temperature De‐NO_x by Selective Catalytic Reduction Based on Iron‐Based Catalysts

Abstract

Low-temperature De-NO x technology is a new topic in the area of flue gas treatment. This paper presents experimental studies on selective catalytic reduction (SCR) of NO x from synthetic flue gas over iron-based catalysts with ammonia in a fluidized reactor. The iron-based catalysts used in the experiments are particles of Fe 3 O 4 and c-Fe 2 O 3 , and they are analyzed by X-ray diffraction (XRD) and Mössbauer spectroscopy, before and after reaction. It is observed that the efficiency of De-NO x with c-Fe 2 O 3 catalyst is high at temperatures from 200-290°C and the maximum efficiency is seen to exceed 90 % at 250°C. The effects of magnetic fields on SCR De-NO x using c-Fe 2 O 3 particles as catalysts are also studied by applying uniform and coaxial magnetic fields to the fluidized bed. The results suggest that SCR De-NO x on c-Fe 2 O 3 catalyst is fit for operation below 200°C in the fluidized reactor in conjunction with the effects of magnetic fields. IntroductionSelective catalytic reduction (SCR) of NO x is an effective flue gas cleaning technology, which can reduce NO x with high efficiency [1][2][3]. Currently, SCR De-NO x is normally undertaken at medium to high temperatures varying from 350-450°C. However, the temperature of the flue gas discharged from the boiler is reduced to 200°C, since the flue gas cools down when it passes through the boiler economizer and the air preheater. Therefore, it is difficult for the tail end configurations to apply SCR De-NO x technologies developed under middle to high temperature conditions in practical situations. Moreover, the De-NO x catalysts can be poisoned by SO 2 , and thus, one should remove SO 2 in the flue gas before the De-NO x process proceeds. Unfortunately, the temperature of the flue gas after desulfurization is normally below 200°C. In such instances, if the operation temperatures of De-NO x catalysts are in the medium to high temperature range, the flue gas must be reheated by heat exchange, and this results in even further energy consumption. Hence, it is important to develop a low temperature De-NO x technology and determine the catalysts that can be used in such low temperature De-NO x processes. However, most of the suitable catalysts currently available are expensive metal oxides, e.g., Mn-based [4-8], Cu-based [9][10][11][12], and Cebased [3,13] catalysts. In addition to the high costs involved in applying these metal-based catalysts to industry, the heavy metal-based catalysts will cause further pollution to the environment if their disposal is not undertaken properly.Therefore, in the current context, the SCR De-NO x from synthetic flue gas is investigated in a fluidized reactor based on magnetic iron-based catalysts, such as Fe 3 O 4 and Fe 2 O 3 . These iron-based catalysts are fairly cheap and less hazardous compared to the above-mentioned metal oxide catalysts. Furthermore, a magnetically fluidized bed is configured by applying uniform and axial magnetic fields to the fluidized bed, and the effects of magnetic fields on SCR De-NO x are rese...

NO reduction by CO over iron‐based catalysts supported by activated semi‐coke

“…However, further increases of the precursor concentration led to a decrease of the Fe loading content. As Yao et al reported, Fe 2 O 3 provided a much higher deNO x efficiency than the other FeO x species. Thus, we speculate that the excellent deNO x performance for Fe20/ASC may be ascribed to the larger quantity of surface Fe 3+ ions.…”

Rod‐Shaped Fe2O3 as an Efficient Catalyst for the Selective Reduction of Nitrogen Oxide by Ammonia

“…This mature system displays adequate activity typically at 300-400 8C, but it is still not satisfactory with respect to the volatility and toxicity of VO x and the easy deactivation. [1][2][3] Attracted by the inherently environmentally benign character and the prominent thermal stability, ferric oxides have long been explored to catalyze selective reduction of NO x with ammonia, [3][4][5][6][7][8] but no significant progress has been achieved so far. Ferric oxides commonly suffer from the insufficient activity at low temperatures and the severe deactivation induced by H 2 O and SO 2 that are permanently and abundantly present in the exhaust.…”

Stäbchenförmiges Fe2O3 als effektiver Katalysator für die selektive katalytische Reduktion von NO mit NH3

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Die selektive katalytische Reduktion (SCR) von Stickstoffoxiden (NO x ) mit NH 3 ist heutzutage die aussichtsreichste Technik zur Beseitigung derartiger Verbindungen, die bei der Verbrennung fossiler Brennstoffe entstehen. [1][2][3] Begünstigt durch ihre Umweltverträglichkeit und ausgeprägte thermische Stabilität wurden Eisenoxide seit Langem für die SCR von NO x mit NH 3 untersucht, [3][4][5][6][7][8] bislang konnte jedoch kein Durchbruch erzielt werden, da Eisenoxide bei niedrigen Temperaturen üblicherweise eine unzureichende Aktivität aufweisen und stark durch H 2 O und SO 2 , die permanent und allgegenwärtig im Abgas vorhanden sind, desaktiviert werden. Das ausgereifte System zeigt typischerweise bei 300-400 8C eine hinreichende Aktivität, ist aber wegen der Flüchtigkeit und Giftigkeit von VO x und der raschen Desaktivierung nicht zufriedenstellend.

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