Fast Selective Catalytic Reduction Reaction Research Articles

Uncovering the Dinuclear Mechanism of NO2-Involved NH3-SCR over Supported V2O5/TiO2 Catalysts.

Commercial vanadium oxide catalysts exhibit high efficiency for the selective catalytic reduction (SCR) of NO with NH3, especially in the presence of NO2 (i.e., occurrence of fast NH3-SCR). The high-activity sites and their working principle for the fast NH3-SCR reaction, however, remain elusive. Here, by combining in situ spectroscopy, isotopic labeling experiments, and density functional theory (DFT) calculations, we demonstrate that polymeric vanadyl species act as the main active sites in the fast SCR reaction because the coupling effect of the polymeric structure alters the elementary reaction step and effectively avoids the high energy barrier of the rate-determining step over monomeric vanadyl species. This study unveils the high-activity dinuclear mechanism of the NO2-involved SCR reaction over vanadia-based catalysts and provides a fundamental basis for developing high-efficiency and low V2O5-loading SCR catalysts.

Nitration-Promoted Vanadate Catalysts for Low-Temperature Selective Catalytic Reduction of NOX with NH3.

Vanadium-based catalysts have been commercially used in selective catalytic reduction (SCR), owing to their high catalytic activity and effectiveness across a wide temperature range; however, their catalytic efficiency decreases at lower temperatures under exposure to SOX. This decrease is largely due to ammonium sulfate generation on the catalyst surface. To overcome this limitation, we added ammonium nitrate to the V2O5-WO3/TiO2 catalyst, producing a V2O5-WO3/TiO2 catalyst with nitrate functional groups. With this approach, we found that it was possible to adjust the amount of these functional groups by varying the amount of ammonium nitrate. Overall, the resultant nitrate V2O5-WO3/TiO2 catalyst has large quantities of NO3- and chemisorbed oxygen, which improves the density of Brønsted and Lewis acid sites on the catalyst surface. Furthermore, the nitrated V2O5-WO3/TiO2 catalyst has a high NOX removal efficiency and N2 selectivity at low temperatures (i.e., 300 °C); this is because NO3- and chemisorbed oxygen, generated by nitrate treatment, facilitated the occurrence of a fast SCR reaction. The approach outlined in this study can be applied to a wide range of SCR catalysts, allowing for the development of more, low-temperature SCR catalysts.

Mechanism study of Na poisoning on Ce/TiO2(001) surface based on adsorption of reaction species and elementary reaction pathways

The presence of alkali metal Na in flue gas can significantly impair the reactivity of Ce/TiO2 (CT) SCR (Selective Catalytic Reduction) catalyst. This study investigates the deactivation mechanism of Na on the Ce/TiO2 catalyst using Density Functional Theory (DFT) calculations, focusing on the adsorption of surface species and the pathway of elementary reaction. Due to the high affinity between Na atom and the catalyst surface, Na poisoning readily occurs on Ce/TiO2 (001) surface. The presence of Na on the catalyst surface hampers hydrogenation, oxygen vacancy formation, and NH3 adsorption, while also reducing the catalyst's acidity and reducibility. Additionally, Na impedes the NH3 dehydrogenation reaction, as well as the formation and decomposition of NH2NO and the dissociation of O2 on the catalyst surface, thereby inhibiting the NH3-SCR reaction. The inhibition of NO2 formation further affects the fast SCR reaction, which may explain the low-temperature deactivation of the catalyst.

Performance characterization of a selective catalytic reduction on filter aftertreatment system in a heavy-duty diesel engine tested on a laboratory dynamometer

Increasingly stringent emission regulations call for improvement in the current emissions control technology in heavy-duty diesel engines. In the existing aftertreatment system utilized in diesel engines, there is already a challenge with space and volume, and an attempt to add more components would lead to the consumption of more space and impracticable. The Selective Catalytic Reduction on Filter (SCRF)-an integration of Selective Catalytic Reduction (SCR) and Diesel Particulate Filter (DPF) in a single component, offers space saving and favorable thermal inertia opportunities. However, literatures are conflicting on the effect of the SCR and DPF activities on the operations of the SCRF, as both require NO2 for fast SCR reaction, and passive soot oxidation respectively. This paper presents a detailed experimental characterization of a Silicon-Carbide (Si–C) coated with Copper-Zeolite (Cu-Ze) catalyst SCRF after-treatment component in a heavy-duty diesel engine, evaluated on a laboratory dynamometer. The effect of particulate matter loading on the SCRF activities in steady state, and transient operations was investigated, with emphasis on the simultaneous utilization of NO2 between the passive soot oxidation activities and SCR reactions-which is a determinant of the NOx conversion efficiency. The SCRF was loaded from 0 g/L up to 5 g/L while passive regeneration and NOx conversion activities were investigated over steady and transient cycles. The investigation has shown that both NOx conversion efficiency and passive soot oxidation increase with particulate matter loading in the SCRF system of a heavy-duty diesel engine.

Porous washcoat structure in CeO2 modified Cu‐SSZ‐13 monolith catalyst for NH3‐SCR with improved catalytic performance

AbstractA series of CeO2 modified Cu‐SSZ‐13 monolith catalysts were prepared by embedding CeO2 into the washcoat of Cu‐SSZ‐13 monolith catalyst through solvent combustion method. These CexCu‐SSZ‐13 catalysts were studied in the selective catalytic reduction (SCR) of NO with NH3, among which the Ce2Cu‐SSZ‐13 catalyst exhibited the best low‐temperature activity, hydrothermal stability, and sulfur resistance. The physicochemical properties of the catalysts were characterized using multiple methods. Results showed that the acidity, redox capacity, and ammonia adsorption capacity significantly enhanced after CeO2 modification, thus leading to the high performance of Ce2Cu‐SSZ‐13 catalyst. Furthermore, the introduction of CeO2 induced the fast SCR reaction by promoting the oxidation of NO to NO2. Analog calculation suggested that the porous structure generated via solvent combustion in the washcoat effectively increased the diffusion rate of reaction. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFT) analysis showed that Brønsted acid sites were the main active center and the reaction followed Eley–Rideal mechanism.

Recent advances in selective catalytic oxidation of nitric oxide (NO-SCO) in emissions with excess oxygen: a review on catalysts and mechanisms.

Nitric oxides (NOx, which mainly include more than 90% NO) are one of the major air pollutants leading to a series of environmental problems, such as acid rain, haze, photochemical smog, etc. The selective catalytic oxidation of NO to NO2 (NO-SCO) is regarded as a key process for the development of selective catalytic reduction of NOx by ammonia (via fast selective catalytic reduction reaction) and also the simultaneous removal of multipollutant (pre-oxidation and post-absorption). Until now, scholars have developed various types of NO-SCO catalysts, dividing the main groups into noble metals (Pt, Pd, Ru, etc.), metal oxides (Mn-, Co-, Cr-, Ce-based, etc.), perovskite-type oxides (LaMnO3, LaCoO3, LaCeCoO3, etc.), carbon materials (activated carbon, carbon fiber, carbon nanotube, graphene, etc.), and zeolites (ion-exchanged ZSM-5, CHA, SAPO, MCM-41, etc.) in this review. This paper summarizes the recent progress of the above typical catalysts and mostly analyzes the catalytic performance for NO oxidation in terms of the H2O and/or SO2 resistances and also the influencing factors, and their reaction mechanisms are described in detail. Finally, this review points out the key problems and possible solutions of the current researches and presents the application prospects and future development directions of NO-SCO technology using the above typical catalysts.

Sulfur and Water Resistance and Activity of Ru-Ce-Zr-O x Catalysts for Nitric Oxide Catalytic Oxidation

Most mobile pollution sources have narrow space. Due to its small occupation area, fast selective catalytic reduction (SCR) is more suitable for controlling oxynitride (NO x ) in exhausted gas in mobile pollution sources such as vessels. The fast SCR reaction can be divided into two stages: nitric oxide (NO) catalytic oxidation stage and NO x removal stage. This paper focused on the study of NO oxidation catalysts consists of ruthenium-cerium-zirconium (Ru-Ce-Zr) metal-oxides. It was found that the doping of ruthenium (Ru) which is the precious metal, greatly improved the catalytic activity. The NO oxidation rate of catalyst doped with 0.5% Ru at 300 °C was about 15% higher than that without Ru. However, with the increasing content of ruthenium, the sulfur and water resistance of catalysts decreased and the activity of the catalysts was only partially restored after regeneration. The results showed that Ru increased the activity of the catalysts while Ce and Zr improved the resistance of SO2 and H2O. Our work provided a solution to the space problem of mobile pollution sources such as vessels.

Nitrogen Oxide Removal by Coal-Based Activated Carbon for a Marine Diesel Engine

Vanadium-based catalysts are mainly used for marine diesel exhaust denitration. However, their poor catalytic ability at low temperature and poor sulfur tolerance, as well as high toxicity and cost, are big turnoffs. AC (Activated carbon) exhibits good adsorption capacity and catalytic ability in denitration because of its high specific surface area and chemical activity. In this paper, coal-based AC was used for simulating diesel exhaust denitration in different conditions. The results show that the NO removal ability of AC is poor in an NO/N2 system. The NO2 removal ability is excellent in an NO2/N2 system, where NO is desorbed. The NOx removal efficiency is 95% when the temperature is higher than 200 °C in an NO2/NH3/N2 system. When the temperature is lower than 100 °C, AC can catalytically oxidize NO to NO2 in an NO2/O2/N2 system. The near-stable catalytic efficiencies of AC for a slow SCR (Selective Catalytic Reduction) reaction, a standard SCR reaction, and a fast SCR reaction at 300 °C are 12.1%, 31.6%, and 70.8%, respectively. When ships use a high-sulfur fuel, AC can be used after wet scrubber desulfurization to catalytically oxidize NO to NO2 at a low temperature. When ships use a low-sulfur fuel, AC can be used as a denitration catalyst at high temperatures.

NO, NO2 and N2O emissions over a SCR using DOC and DPF systems with Pt reduction

A Pt-reduced diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) combination was used to evaluate the influences of Pt reduction on the oxidation performance in a nonroad diesel engine. For the Pt-reduced combination, a mass fraction of 1.5% Pt in the DOC was lower than a DOC of a non-reduction combination. These DOCs were composed of Pt only. The DPF in the Pt-reduced combination was composed of Pt and Pd with a 2:1 ratio, i.e., Pd was substituted for Pt. Whereas the DPF in the non-reduction combination was Pt only. The oxidation performance in the DOC and DPF systems of the Pt-reduced combination was relatively consistent with the non-reduction combination. The behavior of the undesirable oxidation of nitric oxide (NO) to nitrogen dioxide (NO2) occurred in both combinations. The selective catalytic reduction (SCR) system was also installed for NO and NO2 abatement, and NO and NO2 were evaluated based on the conversion efficiency. The fast SCR reaction, which involves both NO and NO2, was dominantly activated at the SCR inlet temperature of 380 °C because the NO2/NOX ratio is approximately 60%. The fast SCR reaction competed with the standard SCR reaction above 380 °C, and then the standard SCR reaction became the prevailing reaction as the temperatures increased. Nitrous oxide (N2O), which has 298 times more global warming potential than carbon dioxide, was also investigated mainly over the SCR. N2O has increased dozens of times over the SCR, and a lower ratio of N2O emission after the SCR to the NOX at the SCR inlet was obtained in the Pt-reduced combination than in the non-reduction combination.

Ammonium-Salt Formation and Catalyst Deactivation in the SCR System for a Marine Diesel Engine

Due to the low temperature and complex composition of the exhaust gas of the marine diesel engine, the working requirements of the selective catalytic reduction (SCR) catalyst cannot be met directly. Moreover, ammonium sulfate, ammonium nitrate, and other ammonium deposits are formed at low temperatures, which block the surface or the pore channels of the SCR catalyst, thereby resulting in its reduction or even its loss of activity. Considering the difficulty of the marine diesel engine bench test and the limitation of the catalyst sample test, a one-dimensional simulation model of the SCR system was built in this paper. In addition, the deactivation reaction process of the ammonium salt in the SCR system and its influencing factors were studied. Based on the gas phase and the surface reaction kinetics, the models of the urea decomposition, the surface denitrification, the nitrate deactivation, and the sulfate deactivation were both constructed and verified in terms of accuracy. Moreover, the formation/decomposition reaction pathway and the catalytic deactivation of ammonium nitrate and ammonium bisulfate, as well as the composition concentration and the exhaust gas temperature range were correspondingly clarified. The results showed that within a certain range, the increase of the NO2/NOx ratio was conducive to the fast SCR reaction and the NH4NO3 formation’s reaction. Increasing the exhaust gas temperature also raised the NO2/NOx ratio, which was beneficial to both the fast SCR reaction and the NH4NO3 decomposition reaction, respectively. Furthermore, the influence of the SO2 concentration on the denitrification efficiency decreased with the increase of the exhaust gas temperature because of increasing SCR reaction rate and reversibility of ammonia sulfate formation, and when the temperature of the exhaust gas was higher than 350 °C, the activity of the catalyst was almost unaffected by ammonia sulfate.

Structure–Activity Relationship Study of Mn/Fe Ratio Effects on Mn−Fe−Ce−Ox/γ-Al2O3 Nanocatalyst for NO Oxidation and Fast SCR Reaction

A series of Mn−Fe−Ce−Ox/γ-Al2O3 nanocatalysts were synthesized with different Mn/Fe ratios for the catalytic oxidation of NO into NO2 and the catalytic elimination of NOx via fast selective catalytic reduction (SCR) reaction. The effects of Mn/Fe ratio on the physicochemical properties of the samples were analyzed by means of various techniques including N2 adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H2-temperature-programmed reduction (TPR), NH3-temperature-programmed desorption (TPD) and NO-TPD, meanwhile, their catalytic performance was also evaluated and compared. Multiple characterizations revealed that the catalytic performance was highly dependent on the phase composition. The Mn15Fe15−Ce/Al sample with the Mn/Fe molar ratio of 1.0 presented the optimal structure characteristic among all tested samples, with the largest surface area, increased active components distributions, the reduced crystallinity and diminished particle sizes. In the meantime, the ratios of Mn4+/Mnn+, Fe2+/Fen+ and Ce3+/Cen+ in Mn15Fe15−Ce/Al samples were improved, which could enhance the redox capacity and increase the quantity of chemisorbed oxygen and oxygen vacancy, thus facilitating NO oxidation into NO2 and eventually promoting the fast SCR reaction. In accord with the structure results, the Mn15Fe15−Ce/Al sample exhibited the highest NO oxidation rate of 64.2% at 350 °C and the broadest temperature window of 75–350 °C with the NOx conversion >90%. Based on the structure–activity relationship discussion, the catalytic mechanism over the Mn−Fe−Ce ternary components supported by γ-Al2O3 were proposed. Overall, it was believed that the optimization of Mn/Fe ratio in Mn−Fe−Ce/Al nanocatalyst was an extremely effective method to improve the structure–activity relationships for NO pre-oxidation and the fast SCR reaction.

The promotional effects of cerium on the catalytic properties of Al2O3-supported MnFeOx for NO oxidation and fast SCR reaction

To reveal the cooperative effects of cerium with manganese and iron on the catalytic oxidation of NO to NO2 and the catalytic activity in the fast selective catalytic reduction (SCR) reaction, Ce–MnFeOx/Al2O3 catalysts were prepared with different amounts of cerium doping. The results showed that the oxidation rate of NO to NO2 achieved by MnFeOx/Al2O3 was obviously improved with cerium doping. The highest catalytic activity, corresponding to NOx conversion >95.5% within the range of 100–350 °C and NO oxidation rate of 55.1% at 350 °C, was obtained when using Ce1.0–MnFeOx/Al2O3 (Ce:Fe:Mn = 1:2:16), Furthermore, according to characterization by scanning electron microscopy (SEM), X-ray diffraction (XRD), H2-temperature-programmed reduction (TPR), NH3-temperature-programmed desorption (TPD), NO-TPD, and X-ray photoelectron spectroscopy (XPS) techniques, the active element dispersion and combination of iron and manganese were both enhanced with cerium doping, while the metal oxide crystallinity was reduced. Cerium doping improved the Mn4+/(Mn2+ + Mn3+ + Mn4+) and Fe3+/(Fe2+ + Fe3+) ratios, while increasing the amounts of lattice oxygen and oxygen vacancies, thereby promoting the oxidation rate of NO to NO2 and ultimately facilitating the fast SCR reaction. However, excess cerium doping led to crystallization of ceria. This study revealed that Ce1.0–MnFeOx/Al2O3 has potential for application as an excellent catalyst with efficient catalytic activity in NO preoxidation and the fast SCR reaction.

Development and Validation of a Two-Site Kinetic Model for NH3-SCR over Cu-SSZ-13. Part 1. Detailed Global Kinetics Development Based on Mechanistic Considerations

In this study, we present the first of two parts in the development and validation of a two-site detailed global kinetic model for NH3 Selective Catalytic Reduction (SCR) over a well-characterized Cu-SSZ-13 catalyst. Based on fundamental literature studies and experimental data for two distinct hydrothermal aging conditions, it was observed that at least two distinct sites were necessary to describe the storage, oxidation, and SCR behavior for this catalyst. The site definitions were allocated based on analysis of simulated net desorption rates during the NH3-TPD experiment. The S1 sites were associated with extra framework copper ions stabilized by -OH ligands (ZCuOH), likely located near the eight-membered ring CHA cages, along with Bronsted acid sites, while S2 sites were associated with copper ions attached directly to the repeating units (Z2Cu) near the six-membered rings, along with physisorbed NH3 sites and low temperature transient copper dimers. The selective NH3 oxidation and NO oxidation reactions were only modeled over S1, in line with the expected catalytic sites for these reactions. Standard, fast, and NO2 SCR reactions were modeled on both sites, with different activation energies. Finally, noticeable nitrate-based hysteresis effects were observed, in both N2O concentrations and fast SCR NO conversions. These were accounted for by explicitly modeling nitrate formation, titration by NO, and thermal decomposition to N2O. The developed SCR model was validated with additional reactor data at nominal inlet NH3-to-NOx ratios (ANRs) of 0.8 and 1.2. In general, the model showed good predictability in the temperature range of 150–550 °C for both hydrothermal ageing conditions and space velocities. Further full-scale engine dynamometer validation and development of a downstream NH3 slip catalyst (ASC) reaction-diffusion model will be reported in the second part of the paper.

A Computational Investigation of Industrial Selective Catalytic Reduction Systems for NOx Control

The selective catalytic reduction (SCR) is a promising NOx (a mixture of NO and NO2) reduction technology for various applications. The SCR process entails the conversion of NOx by the use of a reducing agent such as ammonia and a suitable catalyst. Due to increasingly stricter NOx emission regulations, the SCR technology for NOx control needs continuous improvement. The improvement requires better understanding of complex processes occurring in the SCR system. The current study employs a mathematical model to elucidate the effect of key operating and geometric parameters on the performance of SCR systems. The model considers both standard and fast SCR reaction processes. The model was used to investigate the effects of NH3/NOx and NO2/NOx ratios in the exhaust on the SCR performance and the effect of using a dual layer SCR system. Furthermore, the effect of different operating parameters and the interdependence of parameters is analyzed by using a factorial approach. The results show that the SCR performance is very sensitive to NH3/NOx ratio. The SCR performance is also affected by the NO2/NOx ratio particularly at low temperatures. The optimal NOx conversion performance requires a combination of NH3/NOx ratio of 1.0, NO2/NOx ratio of 0.5, low space velocities, and high inlet temperature. The results depict that adding a second catalyzed layer results in increased reaction activity especially when the concentration is still high after the first layer.

Recent Progress in Atomic-Level Understanding of Cu/SSZ-13 Selective Catalytic Reduction Catalysts

Cu/SSZ-13 Selective Catalytic Reduction (SCR) catalysts have been extensively studied for the past five-plus years. New and exciting fundamental and applied science has appeared in the literature quite frequently over this time. In this short review, a few topics specifically focused on a molecular-level understanding of this catalyst are summarized: (1) The nature of the active sites and, in particular, their transformations under varying reaction conditions that include dehydration, the presence of the various SCR reactants and hydrothermal aging; (2) Discussions of standard and fast SCR reaction mechanisms. Considerable progress has been made, especially in the last couple of years, on standard SCR mechanisms. In contrast, mechanisms for fast SCR are much less understood. Possible reaction paths are hypothesized for this latter case to stimulate further investigations; (3) Discussions of rational catalyst design based on new knowledge obtained regarding catalyst stability, overall catalytic performance and mechanistic catalytic chemistry.

Simultaneous soot combustion and NOx reduction over a vanadia-based selective catalytic reduction catalyst

Abstract Simultaneous NO x reduction and soot combustion over a commercial vanadia-based selective catalytic reduction (SCR) catalyst were investigated. Carbon black was used as model soot. The impact of the contact intensity between carbon and catalyst was studied. The experiments appeared as promising results for the utilization of vanadia-based SCR catalysts in SCR on filter system as, in the SCR operating temperature range (250–400 °C), no significant impact of the presence of carbon black on NO x reduction was observed. However, a decrease in the specific carbon oxidation rate was highlighted. This latter increases with the contact between carbon and catalyst and is attributed to a lack of NO 2 , consumed by the fast SCR reaction. At temperatures greater than 400 °C, the contact between carbon particles and the SCR catalyst partially inhibits the NO x reduction, whereas it exhibits a catalytic effect on the carbon oxidation rate. The tighter the contact between the two materials, the more significant is this behavior. A redox mechanism, which competes with the redox cycle of the SCR mechanism, was proposed. The impregnation of a V-based SCR catalyst with 2 wt % of calcium was also performed. A drastic loss of DeNO x activity was observed, whereas the effect of the contact between carbon and catalyst was reduced.

Effects of Ce and Nb additives on the de-NOx performance of SCR/CDPF system based on Cu-beta zeolite for diesel vehicles

In this study, the de-NOx performance of the Cu-beta zeolite (BEA) selective catalytic reduction (SCR) catalyst with Ce and Nb as additives was investigated for the diesel catalytic reduction catalyzed diesel particulate filter (SCR/CDPF) system. The Cu-BEA catalyst with the Ce and Nb additives improved the NOx conversion, compared to the Cu-BEA catalyst without additives, under conditions of both standard and fast SCR reaction. This result is related to the strength of the intensity ratio as (Cu2p3 B peak)/(Cu2p3 A peak) for the Ce and Nb added catalysts. At the aging temperature of >650°C, the Cu-BEA-Nb catalyst showed better de-NOx performance than the other catalysts, because the Nb2O5 (Nb5+) of the aged Cu-BEA-Nb catalyst remained. The Cu-BEA-CeNb catalyst was most affected by HC, and the addition of Nb to the Cu-BEA catalyst improved the oxidation ability and inhibited the HC poison at a high temperature.

A complete reaction mechanism for standard and fast selective catalytic reduction of nitrogen oxides on low coverage VOx/TiO2(0 0 1) catalysts

We present a complete catalytic mechanism describing both the Standard and the Fast selective catalytic reduction (SCR) reactions in their correct stoichiometric form on a vanadia titania (anatase 001 facet) based catalyst model. It consists of two cycles, a NO-activation cycle and a Fast SCR cycle that share the same reduction part but use NO+O2 and NO2 respectively for the reoxidation. The stoichiometry of the Standard SCR reaction is obtained by coupling the two cycles and the stoichiometry of the Fast SCR reaction is represented by the Fast SCR cycle. We establish structures and energetics for each elementary reaction allowing us to calculate the rate for the two reactions by microkinetic modeling. We find at low temperatures the rate for the Standard SCR reaction is determined by H2O formation and desorption as neither NO nor O2 reacts exothermically with the reduced site prior to H2O desorption. On the contrary NO2 reacts directly with the reduced site resulting in higher rate for the Fast SCR reaction at low temperatures. The rate for the two reactions is the same at higher temperatures as the rate determining step is in the reduction part which is common to both reactions.

A plasma-assisted catalytic system for NO removal over CuCe/ZSM-5 catalysts at ambient temperature

A series of CuCe catalysts were prepared by an incipient-wetness impregnation method for selective catalytic reduction of NO in combination with dielectric barrier discharge plasma. The effect of the Cu/Ce mass ratio on NO and NOx (NO+NO2) removal efficiency has been studied as a function of energy density at ambient temperature. The catalyst samples were characterised by BET, XRD, XPS, H2-TPR and NH3-TPD. The results indicated that catalyst addition enhances NO and NOx removal based on only the plasma process. The CuCe catalysts exhibited higher reduction performance compared with the 4wt.% Cu or 4wt.% Ce catalysts, and the catalyst with 4wt.% Cu and 4wt.% Ce showed the best reduction performance with the highest NO and NOx removal efficiencies of 90.7% and 80.1%, respectively, at an energy density of 367J/L. The interactions between Cu and Ce increase oxygen migration to form oxygen vacancies, which facilitates the oxidation of NO to NO2, and NO2 favours NO removal via a fast selective catalytic reduction reaction at low temperature. In addition, the CuCe catalysts exhibited low thermal stability, thereby facilitating the catalytic reduction of NO at ambient temperature.

Effect of plasma-catalyst system on NO removal using M–Cu (M = Mn, Ce, Cr, Co, and Fe) catalysts

A series of M–Cu (M = Mn, Ce, Cr, Co, and Fe) bimetal oxide catalysts combined with plasma were prepared for NOx removal at various temperatures. All catalysts combined with plasma exhibited excellent deNOx activity. The Mn–Cu catalyst showed the highest selective catalytic reduction (SCR) activity; the NO removal efficiency of the Mn–Cu catalyst could reach 90% at a gas temperature of 25 °C. E/N increased as gas temperature increased; the mean electron energy and the proportion of high-energy electrons also increased considerably, producing more active radicals. Without any catalyst, the increase in temperature inhibited NO removal owing to O3 consumption. As the temperature increased, NO removal efficiency decreased below 100 °C; however, it increased in the range of 100–300 °C, and then decreased above 300 °C in the plasma-catalyst system. NO2 concentration decreased markedly at 150 °C via the fast SCR reaction.