A Critical Review of Recent Progress and Perspective in Practical Denitration Application

Abstract

Nitrogen oxides (NO x ) represent one of the main sources of haze and pollution of the atmosphere as well as the causes of photochemical smog and acid rain. Furthermore, it poses a serious threat to human health. With the increasing emission of NO x , it is urgent to control NO x . According to the different mechanisms of NO x removal methods, this paper elaborated on the adsorption method represented by activated carbon adsorption, analyzed the oxidation method represented by Fenton oxidation, discussed the reduction method represented by selective catalytic reduction, and summarized the plasma method represented by plasma-modified catalyst to remove NO x . At the same time, the current research status and existing problems of different NO x removal technologies were revealed and the future development prospects were forecasted.Catalysts 2019, 9, 771 2 of 39 adsorption, oxidation, reduction, and plasma methods. In view of these attentive findings, adsorption method uses recyclable solid adsorbent material to adsorb NO x from flue gas through microporous structure, remarkably, environmentally friendly, no secondary pollution, and energy-saving and -efficient features make it stand out [18][19][20]. The oxidation process is a method that oxidizes NO into NO 2 or N 2 O 3 with high solubility under the action of an oxidant that is then absorbed by water or alkali solution. The process is simple and cost-saving, and is widely used in the wet flue gas denitrification process with relatively low cost and high removal efficiency of NO x ; except that the oxidized NO and SO 2 can be removed simultaneously to produce high value-added products [21][22][23]. The reduction method has the characteristics of high efficiency, cleanliness, and mildness; NO x removal can be realized at low temperature at present [24][25][26]. The plasma method is used to modify the surface of the catalyst, the dispersion of active species can be improved by plasma treatment, and the stability and low temperature activity of catalyst can be improved [27,28].Seldom, if ever, does a comprehensive article to introduce the current situation and treatment methods of removing NO x . In this paper, we tried to renovate, classify, and summarize the significant perspectives and most relevant findings reported in recent research articles and earlier reviews generalizing the mechanism analysis and research progress of NO x removal by adsorption, oxidation, reduction, and plasma methods, which can provide means for promoting the technological progress of pollution prevention, maintaining healthy development of factories continuously, studying the methods of removing NO x deeply, and mastering different technologies of removing NO x , as well as providing guidance for controlling the emission of NO x from motor vehicles such as diesel, gasoline, and so on. In order to improve the environmental quality and save the ecological environment, this paper further provides a convenient, low-cost, efficient, and economic guidance line.

A Review of Recent Advances of Dielectric Barrier Discharge Plasma in Catalysis

“…The non-thermal plasma low-temperature catalytic conversion of NO x to valuable chemicals or harmless gases has been effectively done [109]. Our research group also conducted experiments and reviews on selective reduction and denitrification of MnO x -Fe 2 O 3 /vermiculite monolithic honeycomb catalysts and porous microspherical aggregates of Mn–Ce–Fe–Ti mixed oxide nanoparticles at low temperatures [110,111,112,113]. Yu et al [109] used non-thermal DBD plasma and H 2 O as external electrode to efficiently remove NO x .…”

Pilot Plant Evaluation of NOx Removal by Cobalt Ethylenediamine Solution

“…Although a variety of flue gas denitration technologies has been developed, each with its own characteristics [11][12][13]. At present, selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR) are still widely used NO x removal strategies in industry [14][15][16].…”

Experimental Investigation into NO Removal over Circulating Ash in Selective Noncatalytic Reduction during Circulating Fluidized Bed Combustion

“…The secondary measures are applied in the downstream of the combustion process, including NO x oxidation/adsorption, selective noncatalytic reduction (SNCR), selective catalytic reduction (SCR), and so on. 2,3 Among these techniques, SNCR is considered to be cost effective because of its superiorities in low investments, simple installation, and easy operation. 4 The basic principle of SNCR technique is to reduce NO x by using certain reductants in the absence of catalysts, such as ammonia (NH 3 ), urea (CO(NH 2 ) 2 ), and cyanuric acid (C 3 H 3 N 3 O 3 ), within the temperature ranging from 800 to 1000 °C.…”

“…The primary measures are techniques applied during fuel combustion, such as low-NO x combustion, air staging, fuel staging, and flue gas recycling. The secondary measures are applied in the downstream of the combustion process, including NO x oxidation/adsorption, selective noncatalytic reduction (SNCR), selective catalytic reduction (SCR), and so on. , Among these techniques, SNCR is considered to be cost effective because of its superiorities in low investments, simple installation, and easy operation …”