Selective Catalytic Reduction Technology Research Articles

Preparation and NOx Reduction Performance of Ag-Ni-TiO2/Cordierite Catalyst for HC-SCR System

Selective catalytic reduction (SCR) technology in diesel engines is an exhaust after treatment system used for abatement of nitrogen oxide (NOx) emissions. In order to synthesize Ag-Ni-TiO2/Cordierite catalyst in the conducted study, a solution including silver nitrate (AgNO3), titanium dioxide (TiO2), and nickel (II) nitrate hexahydrate (Ni(NO3)2·6H2O) were used in the coating of the cordierite (2Al2O3-5SiO2-2MgO) main carrier structure. The prepared catalyst was characterized for morphological characteristics via scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analysis. The NOx reduction measurements as catalytic was carried out at 20 °C intervals in the temperature range from 190 to 270°C at 1 kW and 3 kW motor loads and under 30000 h−1 space velocity (SV). Ethanol was used as a reductant during the experiments. As a results of the measurements, it was seen that the Ag-Ni-TiO2/Cordierite catalyst exhibited a good NOx conversion efficiency with 93.8 % at 270°C at 3 kW.

Promotional effects of Fe2O3 additive on the NH3-SCR activity and alkali resistance of MoTiOx catalysts

Catalyst is the core of selective catalytic reduction (SCR) technology, and an ideal SCR technology requires that the catalyst should have high activity and resistance to alkali metal poisoning. Therefore, in this paper, the influence of Na poisoning on the catalytic performance of Fe2O3-MoTiOx catalysts in the selective catalytic reduction (SCR) reaction was investigated, and the anti-alkali mechanism was revealed. The Fe2O3-MoTiOx catalyst demonstrated the NO conversion was 90 % at a broad temperature range of 225-400 °C when the Fe2O3 loading ratio was 20 wt%. Besides, 80 % NO conversion rate of the Fe2O3-MoTiOx catalyst at 320 °C was still achieved even at a Na+ concentration of 300 μmol g-1. The phenomenon was attributed to the interaction between Fe and Ti species, which could generate more Lewis acid centers and facilitate the adsorption activation of NH3. During the Na poisoning process, Na ions predominantly adsorbed on the Fe2O3, effectively safeguarding the MoTiOx catalyst. Additionally, although the Brønsted acid sites were deteriorated because of Na poisoning, the abundant Lewis acid sites were preserved for NHx adsorption. Therefore, the Na-poisoned Fe2O3-MoTiOx catalyst maintained efficient NH3 adsorption and NO activation. The work provided theoretical guidance and data support for the development of novel alkali-resistant SCR catalysts.

Potential Strategy to Control the Organic Components of Condensable Particulate Matter: A Critical Review.

More and more attention has been paid to condensable particulate matter (CPM) since its emissions have surpassed that of filterable particulate matter (FPM) with the large-scale application of ultralow-emission reform. CPM is a gaseous material in the flue stack but instantly turns into particles after leaving the stack. It is composed of inorganic and organic components. Organic components are an important part of CPM, and they are an irritant, teratogenic, and carcinogenic, which triggers photochemical smog, urban haze, and acid deposition. CPM organic components can aggravate air pollution and climate change; therefore, consideration should be given to them. Based on existing methods for removing atmospheric organic pollutants and combined with the characteristics of CPM organic components, we provide a critical overview from the aspects of (i) fundamental cognition of CPM, (ii) common methods to control CPM organic components, and (iii) catalytic oxidation of CPM organic components. As one of the most encouraging methods, catalytic oxidation is discussed in detail, especially in combination with selective catalytic reduction (SCR) technology, to meet the growing demands for multipollutant control (MPC). We believe that this review is inspiring for a fuller understanding and deeper exploration of promising approaches to control CPM organic components.

Exploring the role of Cu/Mn-BTC catalyst in the selective catalytic reduction of NOx by C3H6: Synthesis to in-situ DRIFTS study

The choice of reducing agents and their impact on catalytic performance are important aspects of selective catalytic reduction (SCR) technology. Marking the inaugural use of C3H6 as a reducing agent with the BTC catalyst, a bimetallic organic framework (xCu-Mn-BTC) was prepared and tested as a catalyst for NOx reduction under oxygen-enriched conditions. The results showed that NO conversion was influenced by the ratio of Cu and Mn metals, among which 3.2Cu-Mn-BTC exhibited the highest denitrification performance (80 % NOx conversion and 94 % N2 selectivity) at 300 °C. From the characterization results, Cu was successfully incorporated into the BTC framework and 3.2Cu-Mn-BTC became spherical grains with smaller particle sizes. The high catalytic activity of 3.2Cu-Mn-BTC was due to the presence of more adsorbed oxygen Oα (89.7 %) and Cu2+ (63 %) species than in the other catalysts. The TPR peak of xCu-Mn-BTC shifted to a lower temperature and showed better reducibility. The Py-FTIR study shows that xCu-Mn-BTC contained more Lewis acid but no Brønsted acid, because Cu increased the concentration of Lewis acid on the catalytic surface (42 to 46 mmol/g), and Lewis acid plays an important role in the C3H6-SCR of NOx.

Simultaneous Removal of Gas-Phase Pollutants CO and NO Using Ni-Fe Bimetallic Oxides Catalyst

Many studies have been conducted on methods to remove air pollutants. Among them, a representative commercial technology for reducing nitrogen oxides (NO<sub>X</sub>) is selective catalytic reduction (SCR) using NH<sub>3</sub> as a reductant. However, the NH<sub>3</sub>-SCR technology has problems, such as the need for additional NH<sub>3</sub> gas (Active-SCR), the fact that unreacted NH<sub>3</sub> (slipped-NH<sub>3</sub>) in the reaction process can be re-oxidized to NO<sub>X</sub>, and the facility system cost according to the added NH<sub>3</sub> gas. In order to solve these problems, CO gas that is naturally generated in industrial processes can be used, and NO and CO can be removed at the same time using passive-SCR technology that does not require a separate injection of a reductant. In this study, transition metals Ni and Fe were used as catalytic materials to replace expensive precious metals. The results confirmed that both NO<sub>X</sub> and CO removal efficiencies were about 90% or more in the catalyst with combined Ni-Fe, compared to the single catalyst. The addition of Ni to the Fe catalyst increased the catalytic reducing power, which also affected the increase in acid sites. Therefore, it is expected that this catalyst can simultaneously remove NO and CO without the use of NH<sub>3</sub> gas. These results could be explained through XRD, FT-IR, TEM, BET, H<sub>2</sub>-TPR and CO-TPD analyses, and compared to single catalysts, it was confirmed that the catalyst had higher low-temperature desorption ability for CO as a reductant and reducing capability.

Unexpected Promotion Effect of H2O on the Selective Catalytic Reduction of NOx with NH3 over Cu-SSZ-39 Catalysts.

Water molecules commonly inhibit the selective catalytic reduction (SCR) of NOx with NH3 on most catalysts, and water resistance is a long-standing challenge for SCR technology. Herein, by combining experimental measurements and density functional theory (DFT) calculations, we found that water molecules do not inhibit and even promote the NOx conversion to some extent over the Cu-SSZ-39 zeolites, a promising SCR catalyst. Water acting as a ligand on active Cu sites and as a reactant in the SCR reaction significantly improves the O2 activation performance and reduces the overall energy barrier of the catalytic cycle. This work unveils the mechanism of the unexpected promotion effect of water on the NH3-SCR reaction over Cu-SSZ-39 and provides fundamental insight into the development of zeolite-based SCR catalysts with excellent activity and water resistance.

Coverage-sensitive mechanism of electrochemical NO reduction on the SrTiO3(001) surface: a DFT investigation.

Due to its adverse environmental and human health hazards, addressing the elimination of nitric oxide (NO) has become a pressing concern for modern society. Currently, electrochemical NO reduction provides a new alternative to traditional selective catalytic reduction technology under mild reaction conditions. However, the complexity and variability of products make the coverage of NO an influencing factor that needs to be investigated. Hence, this study delves into the coverage-sensitive mechanism of electrochemical NO reduction on cost-effective perovskite catalysts, using SrTiO3 as an example, through density functional theory calculations. Phase diagrams analysis reveals that the coverage range from 0.25 to 1.00 monolayer (ML) coverage is favorable for NO adsorption. Gibbs free energy results indicate that the selectivity is significantly influenced by NO coverage. NH3 is likely to be generated at low coverage, while N2O and N2 are more likely to be produced at high coverage through a dimer mechanism. Charge analysis suggests that the charge transfer and Ti-O bond strength between reactants and catalysts are crucial factors. This work not only provides deep insights into coverage-sensitive reaction mechanisms but also is a guideline towards further rational design of high-performance perovskite catalysts.

Enhanced SO2 resistance of NiFe/CeO2 catalyst by adding WS2 for CO-assisted selective catalytic reduction reaction

Selective catalytic reduction (SCR) is an effective NOx reduction method. Recently, research has been conducted on simultaneously removing NOx and CO using passive SCR technology that consumes CO gas that is normally generated in industrial combustion processes (designated as CO-SCR). SO2 gas in industrial flue gas can compete with NOx and CO, leading to catalyst deactivation and a shortened lifespan. Catalysts with resistance to the sulfur present in industrial processes are crucial for CO-SCR. Therefore, this study aimed to develop a catalyst resistant to the SO2 present in exhaust gas; specifically, WS2 which has excellent chemical stability, was added to a transition metal-based catalyst NiFe/CeO2 and the CO-SCR activity of the unmodified and WS2-incorporated catalysts (NiFe/CeO2 and NiFe/WS2-CeO2, respectively) were examined. NiFe/WS2-CeO2 (1 wt% WS2 content) exhibited a high NOx conversion rate of more than 80% in a sulfur atmosphere. The addition of WS2 to NiFe/CeO2 improved its CO adsorption capacity and catalytic reduction properties by 1.63 and 1.28 times, respectively, thereby promoting the catalytic performance. Fourier-transform infrared analysis revealed that NiFe/WS2-CeO2 was more resistant to sulfur poisoning than NiFe/CeO2. These findings can be leveraged to develop sulfur-resistant catalysts for eliminating NOx and CO from industrial flue gas.

Potential Risk of Significant N2O Emission without Changing NOx Conversion on Commercial V2O5/TiO2 Catalyst under Working Conditions.

Vanadium-based catalysts play a pivotal role in the emission control of industrial NOx via selective catalytic reduction (SCR) technology. However, little attention has been paid to the potential emission of greenhouse gas N2O under complex working conditions. This work reports that a commercial V2O5/TiO2 catalyst may lead to significant N2O emission without greatly changing the outlet NOx concentration after chromium (Cr) deposition. With a Cr loading of 2 wt %, N2O concentration increased from 27.8 to 199.2 ppm at 350 °C with the value of outlet N2O/(N2O+N2) from 2.5% to 19.4%. Experimental results combined with DFT+U calculations suggest that nonselective catalytic reduction (NSCR) is the main route for N2O formation in a wide temperature range of 250 ∼ 400 °C. It is stemmed from the fact that the covalent interaction between Cr and V species on the V2O5/TiO2 surface accelerates the conversion of V4+ + Cr6+ → V5+ + Cr3+, leading to a larger proportion of surface V5+. More importantly, surface V5+ is highly related to the redox property of the V2O5/TiO2 catalyst, which is beneficial to NSCR reaction rather than the standard SCR process. The work suggests that to better inhibit the emission of greenhouse gases during the NH3-SCR process, monitoring N2O emission should be included along with the NOx concentrations, especially in complex flue gases.

Exhaust gas aftertreatment to minimize NOX emissions from hydrogen-fueled internal combustion engines

Hydrogen-fueled internal combustion engines are a promising CO2-free and zero-impact emission alternative to battery or fuel cell electric powertrains. Advantages include long service life, robustness against fuel impurities and a strong infrastructural base with existing production lines and workshop stations. In order to make hydrogen engines harmless in terms of pollutant emissions as well, NOX emissions at the tailpipe must be reduced as low as the zero-impact emission level. Here, the application of selective catalytic reduction (SCR) catalysts is a promising solution that can be rapidly adopted from conventional diesel engines.This paper therefore investigates the influences of the hydrogen concentration in the raw exhaust gas, of the NO2/NOX ratio and of the space velocity on the performance of two different SCR technologies. The results show that both types of SCR, copper-zeolite and vanadium-based, have their advantages and drawbacks. Copper-based SCR catalysts have an early light-off temperature and reach maximum efficiencies of up to >99%. On the other hand, vanadium systems promise almost no secondary N2O emissions. As a result, we combined both approaches to create a superior solution with high efficiency and lowest secondary emissions.

Cu/BEA catalysts for the selective catalytic reduction of engine-out NOx emissions: Experimental and kinetic investigations

Selective catalytic reduction (SCR) technology using NH3 has shown to be the most promising method in the curbing of NOx and zeolite catalysts impregnated with copper has shown excellent SCR activity below 350 °C. However, most of the investigations are carried out with the artificial mixing combination of exhaust gases. The effect of real-time engine-out exhaust gas on NH3-SCR activity has been scantily reported. In this paper, Cu/BEA zeolite with varying copper loading from 0.83 to 4.31 wt% has been used and the effect of engine-out exhaust emissions has been investigated. The catalysts were prepared using ion-exchange method and characterized using SEM, XRD, and BET analyses. The highest NOx reduction efficiency of 62.5 % was observed for 1.77 wt% Cu for which the Cu/Al ratio was close to unity. The kinetic modeling of the SCR activity was also carried out to validate the experimental results with an average error of 3.85 %.

Combined removal experiment of NOx, SO2 and PM from marine diesel exhaust gas with SCR-DryEGCS system

Pollutants such as nitrogen oxides (NOx), sulfur oxides (SO2), and particulate matter (PM) in ship exhaust have a great impact on human health, environment and climate conditions. Combined selective catalytic reduction technology and dry exhaust gas cleaning technology, a test rig (SCR-DryEGCS system) for WD10C195-15 marine four-stroke high speed diesel engine was established to analyse the removal effect of NOx, SO2, and PM from exhaust gas. The SCR-DryEGCS system removed 89.03%, 99%, and 96% of NOx, SO2, and PM respectively. And also compared with low sulfur oil combined SCR method to verify the feasibility of the SCR-DryEGCS method. It shows that the SCR-DryEGCS system has its own advantages and has a good effect on the removal of NOx, SOx, and PM at the same time.

An improved control strategy for a denitrification system using cooperative control of NH3 injection and flue gas temperature for coal-fired power plants

Selective catalytic reduction (SCR) technology is widely applied for flue gas denitrification in coal-fired power plants. Given the high penetration of renewable power, coal-fired power plants should operate flexibly to support power grid peak regulation. However, the flexible operation of coal-fired power plants often causes transient overshoot of the NOx outlet concentration and NH3 slip, and restricting the clean and reliable operation of coal-fired power plants is a difficult issue. In this study, a dynamic model of the coal-fired power plant is developed, and the characteristics of a denitrification system during load cycling transient processes were evaluated. Then, an improved control strategy for the denitrification system using cooperative control of NH3 injection and flue gas temperature is proposed. Moreover, the control targets of NH3 injection and flue gas temperature are analytically derived. The NOx outlet concentration exceeds the standard value by 14.22 and 6.80 mg m−3, respectively, during the loading down processes and loading up processes with the original control strategy. When the improved control strategy is adopted, the NOx outlet concentration can be controlled to be smaller than the standard value, and the NH3 slip can be controlled well.

Investigation on the applicability of parameters identification of marine diesel engine SCR kinetic model based on Discrete-Grid algorithm

Selective catalytic reduction (SCR) technology is the most widely used denitrification method in industry. However, the calibration of its kinetic model is very problematic due to the large number of parameters involved and the nonlinear characteristics, especially for the undesired reactions such as formation-decomposition of ammonium nitrate (AN), ammonium sulfate (AS), ammonium bisulfate (ABS), etc. In this paper, the synthetic gas test bench and the SCR system of WD10 marine diesel engine burning high-sulfur fuel oil (HSFO) and low-sulfur fuel oil (LSFO) are taken as the research objects. Firstly, based on the experimental data obtained from the synthetic gas test bench, the pre-exponential multiplier and activation energy of each reaction were identified using the Discrete-Grid algorithm. In this work, considering that the production of N2O, SO3, AN, AS, and ABS in the undesired reactions is very low, not on the same order of magnitude as that of NO and NH3, it is easy to overlook their reaction characteristics in the optimization process. We have adopted an approach that amplifies the error between the predicted concentration and the observed concentration of the species to solve this problem. Secondly, a detailed and complete SCR kinetic model was constructed. Finally, with the parameter identification results obtained from the synthesis gas bench as initial values, all the kinetic parameters of the WD10 marine engine SCR model was calibrated simultaneously using the Discrete-Grid algorithm. The results showed that the SCR kinetic model derived from the synthetic gas test bench was suitable for the real marine engine SCR system when the range of temperature and space velocity (SV) of the synthetic gas bench test is similar to that of the marine SCR system.

A Research of Selective Catalytic Reduction of NOx with NH3 by Using Novel Catalysts

Nitrogen oxides are one of the most important industrial pollutants, which have many harmful effects on the human body and the environment. In this paper, the formation mechanism of nitrogen oxides was studied, and the selective catalytic reduction of nitrogen oxides was carried out by selective catalytic reduction technology. This paper also reviews the low-temperature denitration performance of molecular sieve catalysts, manganese oxide and ceria-based catalysts, and expounds on the influence of catalysts on denitration activity under different active components. It is found that ceria-based catalytic materials have better structural properties and catalytic performance, the methods to improve the performance of ceria-based catalysts are discussed, and the future development of ceria-based catalysts has been prospected.

Sequential Capture of Gaseous Hg0 in Flue Gas and Aqueous Hg2+ in Desulfurization Solution by Cu–ZnS: Mechanisms, Kinetics, and Its Application in Hg Recovery as a Supplement of Selective Catalytic Reduction + Wet Flue Gas Desulfurization

The combined technology of selective catalytic reduction and wet flue gas desulfurization (SCR + WFGD) to control Hg0 emissions from coal-fired flue gas is often unsatisfactory due to the undesired Hg0 oxidation efficiency of SCR, the re-emission of Hg0 from WFGD, and the potential secondary pollution. To offset the shortcomings of SCR + WFGD, Cu–ZnS that resulted from Cu2+ activation of natural sphalerite was developed as a difunctional sorbent to sequentially capture gaseous Hg0 in flue gas and aqueous Hg2+ in desulfurization solution. Not only did Cu–ZnS exhibit significant performance in capturing the gaseous Hg0 downstream of an electrostatic precipitator, but it also displayed a superior ability in capturing aqueous Hg2+. Hg0 re-emission from WFGD, which resulted from the reduction of aqueous Hg2+ by SO2, was completely suppressed because Cu–ZnS could adsorb both aqueous Hg2+ and re-emitted Hg0 in desulfurization solution. Spent Cu–ZnS containing Hg can be separated from the desulfurization slurry via flotation for Zn smelting, and adsorbed Hg can be at last recovered as mainly liquid Hg0 in modern smelters for centralized control. Therefore, the sequential capture of gaseous Hg0 and aqueous Hg2+ by Cu–ZnS may be an economically viable and eco-friendly technology to control Hg pollution of coal-fired power plants.

Simulation study of De-NO x and ammonia slip with two-stage selective catalytic reduction for diesel engine

ABSTRACT Selective catalytic reduction (SCR) technology has several benefits for reducing NO x . It offers significant NO x removal efficiency, often greater than 90%. Due to increasingly strict pollution rules, SCR catalysts have lately been installed in diesel engines all over the world. The dynamics and economy of the original diesel engine are examined in this work concerning the addition of various SCR catalyst after-treatment methods, including a one-stage vanadium-based SCR catalyst (V-I), a two-stage vanadium-based SCR catalyst (V/V-II), and a two-stage vanadium-based-copper-based SCR catalyst (V/Cu-II). A complete engine model of a marine diesel engine is built on this model. The findings indicate that each of the three layouts decreases diesel engine power and raises fuel consumption rates. The V/Cu-II is the best configuration for this kind of marine machine because the V-I satisfies the most recent Tier III NO x emission limits only at 100% load, the V/V-II satisfies them at 75% to 100% load, and the V/Cu-II satisfies them at 50% to 100% load. For all three arrangements, ammonia slip reduces with increasing load, with the V/Cu-II having the lowest ammonia slip. In the end, it was determined for the V/Cu-II how different ammonia-to-nitrogen ratios affected ammonia slip and NO x conversion. The results revealed that with an ammonia-to-nitrogen ratio of 0.7, both the ammonia slip and NO x emission limits could be reached at 50% to 100% load, saving urea expenditures.

Unveiling the SO2 Resistance Mechanism of a Nanostructured SiO2(x)@Mn Catalyst for Low-Temperature NH3-SCR of NO.

Low N2 selectivity and SO2 resistance of Mn-based catalysts for removal of NOx at low temperatures by NH3-SCR (selective catalytic reduction) technology are the two main intractable problems. Herein, a novel core-shell-structured SiO2@Mn catalyst with greatly improved N2 selectivity and SO2 resistance was synthesized by using manganese carbonate tailings as raw materials. The specific surface area of the SiO2@Mn catalyst increased from 30.7 to 428.2 m2/g, resulting in a significant enhancement in NH3 adsorption capacity due to the interaction between Mn and Si. Moreover, the N2O formation mechanism, the anti-SO2 poisoning mechanism, and the SCR reaction mechanism were proposed. N2O originated from the reaction of NH3 with O2 and the SCR reaction, as well as from the reaction of NH3 with the chemical oxygen of the catalyst. Regarding improving the SO2 resistance, DFT calculations showed that SO2 was observed to preferentially adsorb onto the surface of SiO2, thus preventing the erosion of active sites. Adding amorphous SiO2 can transform the reaction mechanism from Langmuir-Hinshelwood (L-H) to Eley-Rideal (E-R) by adjusting the formation of nitrate species to produce gaseous NO2. This strategy is expected to assist in designing an effective Mn-based catalyst for low-temperature NH3-SCR of NO.

Effect of additives on the compressive strength and denitrification performance of fly ash catalysts

AbstractFly ash is a massive industrial waste. Owing to the abundance of oxides, such as SiO2 and Al2O3, fly ash is considered a high value material. In this study, we assessed its application in the industrial deoxidation of nitrogen oxides, a major environmental pollutant, using the selective catalytic reduction technology. Fly ash was used as the main raw material and bentonite was used as an auxiliary material in the catalyst. Silica sol, starch, and glycerol were added to improve the compressive strength and denitrification performance of the catalyst. The use of silica sol as a binder improved the compressive strength of the catalyst due to the production of Si–O–Si. In addition, the availability of acidic functional groups could improve the denitrification performance of the catalyst. The optimal dosages of the additives were as follows: 6% silica sol, 6% starch, and 5% glycerol. Under these conditions, the catalyst formation was the easiest, the cracks were the least, the compressive strength of the catalyst reached 1434 kPa, and the denitrification performance improved. The findings presented here are relevant for the development of an economical and practicable solution for tackling environmental pollution caused by nitrogen oxides.

Beyond Purification: Highly Efficient and Selective Conversion of NO into Ammonia by Coupling Continuous Absorption and Photoreduction under Ambient Conditions.

Although the selective catalytic reduction technology has been confirmed to be effective for nitrogen oxide (NOx) removal, green and sustainable NOx re-utilization under ambient conditions is still a great challenge. Herein, we develop an on-site system by coupling the continuous chemical absorption and photocatalytic reduction of NO in simulated flue gas (CNO = 500 ppm, GHSV = 18,000 h-1), which accomplishes an exceptional NO conversion into value-added ammonia with competitive conversion efficiency (89.05 ± 0.71%), ammonia production selectivity (95.58 ± 0.95%), and ammonia recovery efficiency (>90%) under ambient conditions. The anti-poisoning capacities, including the resistance against factors of H2O, SO2, and alkali/alkaline/heavy metals, are also achieved, which presents strong environmental practicability for treating NOx in flue gas. In addition, the critical roles of corresponding chemical absorption and catalytic reduction components are also revealed by in situ characterizations. The emerging strategy herein not only achieves a milestone efficiency for sustainable NO purification but also opens a new route for contaminant resourcing in the near future of carbon neutrality.