NOx Conversion Rate Research Articles

Preparation and Performance of Modified Red Mud-Based Catalysts for Selective Catalytic Reduction of NOx with NH3

Bayer red mud was selected, and the NH3-SCR activity was tested in a fixed bed in which the typical flue gas atmosphere was simulated. Combined with XRF, XRD, BET, SEM, TG and NH3-Temperature Programmed Desorption (TPD) characterization, the denitration characteristics of Ce-doped red mud catalysts were studied on the basis of alkali-removed red mud. The results showed that typical red mud was a feasible material for denitration catalyst. Acid washing and calcining comprised the best treatment process for raw red mud, which reduced the content of alkaline substances, cleared the catalyst pore and optimized the particle morphology with dispersion. In the temperature range of 300–400 °C, the denitrification efficiency of calcined acid washing of red mud catalyst (ARM) was more than 70%. The doping of Ce significantly enhanced NH3 adsorption from weak, medium and strong acid sites, reduced the crystallinity of α-Fe2O3 in ARM, optimized the specific surface area and broadened the active temperature window, which increased the NOx conversion rate by an average of nearly 20% points from 250–350 °C. The denitration efficiency of Ce0.3/ARM at 300 °C was as high as 88%. The optimum conditions for the denitration reaction of the Ce0.3/ARM catalyst were controlled as follows: Gas Hourly Space Velocity (GHSV) of 30,000 h−1, O2 volume fraction of 3.5–4% and the NH3/NO molar ratio ([NH3/NO]) of 1.0. The presence of SO2 in the feed had an irreversible negative effect on the activity of the Ce0.3/ARM catalyst.

Analysis of composite sorbents for ammonia storage to eliminate NOx emission at low temperatures

A new type of composite sorbent-SCR system has been designed for NOx elimination of diesel vehicles to promote the NOx conversion rate at low temperatures (50–250°C), with the sorption reaction temperature of 50–100°C for safety reason. NH3 is sorbed by composite sorbents with expanded natural graphite treated with sulfuric acid (ENG-TSA) matrix at room temperature, and released from composite sorbents by heating phase, which is driven by both electricity and exhaust waste heat. The composite sorbent is a porous composite of 80% chemical sorbents and 20% ENG-TSA. The NH3 sorption capacity of chemical sorbents (NH4Cl, NaBr, BaCl2, CaCl2 and SrCl2) have been evaluated and compared with traditional urea-SCR system with AdBlue, and the results are analyzed. NH3 cannot be pyrolyzed from AdBlue below 160°C, and the NOx conversion rate of the composite sorbent-SCR system is about 45% higher than the urea-SCR system (0%) at 50°C. NH4Cl and NaBr are not suitable for composite sorbent-SCR system for that the pressure is too high even at the environmental temperature. According to the NH3 sorption capacity, composite of CaCl2 with ENG-TSA and composite of SrCl2 with ENG-TSA are both optimal solid sorbents, and between them CaCl2 with ENG-TSA as matrix is the best choice for the small mass required and the low cost.

Next Generation Diesel Engine Potential of Highly Integrated Exhaust Gas Aftertreatment

Different driving scenarios produce different challenges in respect of reducing journey-specific pollutant emission, as shown in Figure 1 using the example of the temperature level in the exhaust gas aftertreatment system. The following requirements can be derived: Open image in new window Figure 1 Vehicle speed profiles and exhaust gas temperature curves in the SCRF for journey profiles under review (© IAV) NOx conversion at low temperatures in low-load cycles NOx engine-out emission control at high loads [2] large spread of space velocity in the SCR catalyst [3, 4] constantly high NOx conversion rate at rising temperatures in the SCR on filter (SCRF) [3, 4]. While controlling emissions from high-load cycles is more of a dimensioning matter, controlling them in the low- temperature range is always more complex [3, 4]. At extremely low average driving speeds (down to stop-and-go in congestion situations), exhaust gas aftertreatment temperature can fall below light-off. If this is immediately followed by rapid acceleration, the high levels of engine-out emissions are not treated adequately. To avoid such situations, the exhaust gas aftertreatment system must be kept at a constant temperature. This requires the application of additional exhaust gas temperature management measures like calibration-based measures, strategies for variable valve timing (VVT), hybridisation and exhaust gas aftertreatment (EAT) positioning: With regard to the CO2 advantages, which must be maintained compared to the gasoline engine, typical calibration-based measures in relevant heating modes (e.g. retarding the start of injection, throttling, post-injection) are detrimental to fuel consumption and therefore not ideal [3, 4]. Regarding VVT strategies discussion focuses in particular on secondary exhaust valve lift and cylinder shutoff as these strategies can be implemented more or less without increases in consumption. Moderate temperature advantages can be achieved and HC and CO emissions reduced during low-load operation [5]. Hybridisation can have an adverse effect on exhaust gas temperature as the average power output in the driving cycle is reduced by the higher efficiency achieved in the powertrain. Measures, such as avoiding trailing throttle and low torque levels as well as active load control, are capable of providing significant temperature and emission-related advantages. Depending on the hybrid powertrain's topology, the engine operating point could be decoupled completely from the driving situation [1]. Avoiding temperature losses as well as minimising the light-off time is a primary criterion in designing the powertrain. Particularly in hybridised concepts, this produces degrees of freedom in positioning the turbocharging (TC) and EAT components. Positioning EAT upstream of the TC provides the optimum in relation to temperature losses and light-off behaviour, but also with regard to the efficiency of any heating and operating strategy measures.

Comparative investigation of NOx emission characteristics from a Euro 6-compliant diesel passenger car over the NEDC and WLTC at various ambient temperatures

Euro 6-compliant diesel passenger cars have tended to feature lean NOx traps (LNTs) to satisfy the increasingly stringent NOx regulations. This paper focused on NOx emission characteristics by the NOx sensors installed at both before and after LNT from a Euro 6 diesel vehicle on a chassis dynamometer. The vehicle was repeatedly driven according to the new European driving cycle (NEDC) and the world-harmonized light-duty vehicle test cycle (WLTC) at various ambient temperatures (23, 14 and −5°C). LNT regeneration was detected twice in the NEDC but 5 times in the WLTC due to the longer period, increased mileage and more frequent acceleration in the WLTC. Accordingly, the NOx conversion rate was higher, and the NOx emission factor was lower for the NEDC than for the WLTC. Additionally, as the ambient temperature decreased, the NOx concentration increased considerably. Because of the poor mixing of fuel and air and the reduced combustion efficiency and stability, the exhaust gas recirculation (EGR) rates decreased. Because the LNT did not reach the light-off temperature (LOT) in the cold start phase, the chemical reactions in the LNT did not occur, and only NO was detected. For the LNT regeneration process, the EGR rates decreased, and the fuel rates increased to release the stored NOx in the LNT. The emissions characteristics of the products, such as NO, NO2, N2O and NH3, during regeneration varied depending on the stored NOx, the after-treatment temperature, and the vehicle driving condition. The results from this comparative study can contribute to monitoring the NOx emission characteristics and optimizing the engine management system to meet future emission regulations including WLTC and low ambient temperature conditions.

Research of copper contained SAPO-34 zeolite for NH3-SCR DeNOx by solvent-free synthesis with Cu-TEPA

With the introduction of solvent-free method, copper-contained SAPO-34 zeolite was synthesized by mixing, grinding and heating the raw materials with Cu-TEPA added in the precursor. Compared to conventional method of hydrothermal synthesis along with ion-exchange, the direct synthesis with the absence of solvent has effectively reduced the waste production, increased the yield and accelerated the crystallization period as well. The so-prepared sample exhibited absolute symmetry of isolated Cu2+ by incorporating into the cativy of SAPO-34. The ion-exchange process produced some bulk CuO on zeolite surface, and it might affect the crystallinity of zeolite. The addition of copper led to changes in surface area, pore structure, redox performance and acid sites for SAPO-34. The exchanged sample show wide active temperature and excellent low temperature NOx conversion, but the activity and selectivity decreased significantly at a high temperature. The direct synthesized sample exhibited remarkable NOx conversion rate and high N2 selectivity with a more efficient preparation, it also retained the excellent hydrothermal stability of chabazite structure.

Enhanced NOx removal performance of amorphous Ce-Ti catalyst by hydrogen pretreatment

Hydrogen pretreatment was processed on the amorphous Ce-Ti catalyst which notably enhanced its NH3-SCR performance. We concluded that 3-h and 400°C were the most suitable and efficient pretreatment conditions, whereas the NOx conversion rate was above 95% from 210°C to 360°C for such pretreated catalyst. XRD, PL, H2-TPR, XPS and Raman analyses found that the enhancement was attributed to the effects generated by the pretreatment: Ce4+ reduced to active Ce3+, the incerase of the oxygen vacancies, the chemisorbed oxygen, and the formation of superoxide ions. The NO adsorption oxidation capability, and the acid sites were also promoted by the pretreatment, which were favorable for the SCR reaction. The reaction among NO, O2 and NH3 on catalysts were studied by in-situ DRIFT. The adsorption of NH3 was dominant under the SCR reaction conditions The enhancement demonstrated good durability. The stability of catalyst under water vapor and sulfur dioxide were also tested.

Study on MnOx–FeOy composite oxide catalysts prepared by supercritical antisolvent process for low-temperature selective catalytic reduction of NOx

Abstract

단기통 디젤엔진에서 LNT/DPF + SCR/DPF 하이브리드 시스템의 NOx 및 PM 동시저감 특성

The market demand for diesel engine tends to increase in general passenger cars as well as commercial vehicles because of its advantages. However, to meet the vehicle emissions regulation which will be more stringent in the future, it is necessary to plurally apply all after-treatment technologies such as diesel oxidation catalyst (DOC), catalyzed diesel particulate filter (CDPF), lean NOx trap (LNT) and selective catalytic reduction (SCR), and so on. Accordingly, the exhaust after-treatment system for diesel vehicle requires the technology of minimizing the numbers of catalysts by integrating every individual catalysts. The purposes of this study is to develop hybrid exhaust after-treatment device system which simultaneously uses LNT/DPF and SCR/DPF catalyst concurrently reducing NOx and particulate matter (PM). As the results, the hybrid system with <TEX>$NH_3$</TEX> generated at LNT/DPF working as a reducing agent of SCR/DPF catalyst, improving NOx conversion rate, was found to be more excellent in de-NOx performance than that in LNT/DPF alone system.

Modeling urea-selective catalyst reduction with vanadium catalyst based on NH3 temperature programming desorption experiment

The selective catalyst reaction technology was stipulated under the IMO Tier 3 regulation for controlling NOx emissions from marine diesel engines. This paper presents a steady kinetic model of urea-SCR with a vanadium-based catalyst. Simulation was carried out using a commercial one-dimensional aftertreatment code coupled with an optimizer. Optimization was performed using experimental NH3 temperature programming desorption (TPD) data. The simulated data and trends in NH3 and NOx reactions under different temperatures, NO/NO2 ratios, space velocities and NH3/NOx ratios produced generally good agreement with experimental measurements. At increased space velocities, the NOx and NH3 reaction rates decreased, but this had no effect on the NOx conversion rate until over 400°C. Over 450°C, the NH3 oxidation of ammonia was equal to the NOx conversion rate due to NH3 oxidation. Based on these results, an optimal condition was proposed for urea-SCR in terms of NH3/NOx ratio and temperature. In the case of NH3/NOx=0.8, the NOx conversion rate was 80% and NH3 slip was no occur over 200°C. The optimal NOx conversion condition for these two performance indicators is estimated to be NH3/NOx=0.8–1.0 at 300°C.

Physicochemical characteristics according to aging of Fe-zeolite and V2O5–WO3–TiO2 SCR for diesel engines

The purpose of this study is to investigate the physicochemical characteristics according to hydrothermal aging, sulfur poisoning and HCs co-existence of Fe-zeolite (1), (2) and V2O5–WO3–TiO2 SCR which are appropriate for diesel engines. Fe-zeolite (1) is a zeolite with low Fe content (∼1wt.%) while Fe-zeolite (2) is a zeolite with a high Fe content (1.8wt.%). The BET specific surface area of Fe-zeolite (2) was smaller than that of Fe-zeolite (1) but its NH3 storage capacity was larger than Fe-zeolite (1) because Fe-zeolite (2) has a large amount of Al content that can absorb NH3. In the case of Fe-zeolite (2), thermal durability was strong, When mildly set in hydrothermal aging for 12 and 24h at 600 and 700°C respectively, the NOx conversion rate was higher than the Fresh catalyst above 350°C. The active site of the catalyst, which is an Fe site, was damaged during the hydrothermal aging process, resulting in a decline in low-temperature performance. However, at higher temperatures, the NH3 oxidation was largely hindered by the damage to the Fe site. The highest degree of coking arose for Fe-zeolite (1). On the other hand, V2O5–WO3–TiO2 SCR, exhibited high durability against HCs, and experienced less coke deposition. Of the three catalysts V2O3–WO3–TiO2 SCR suffered the least sulfur poisoning (0.007g/L). Due to the effects of Brønsted acid site, its resistance to sulfur poisoning is sufficient for reduction catalysts for exhaust gases from ship engines.

Vanadia SCR의 열적 열화에 따른 조촉매의 영향

The purpose of the study is to investigate the effect of additive catalyst according to the thermal aging of vanadia SCR catalysts. At a fresh condition, the <TEX>$3V_2O_5-5WO_5-92TiO_2$</TEX> SCR showed the highest NOx conversion rate of about 30%, the performance of 5 kinds of SCR to which additive catalysts were added was not improved due to the insignificant effect of acid site control. For catalysts aged for 12h at <TEX>$700^{\circ}C$</TEX>, the SCR to which 3wt% Zeolite was added decreased in NOx conversion rate by 2.5% on average compared to the fresh SCR, it showed higher thermal durability than other additive catalyst. For 3Zeolite with high performance of NOx conversion rate during thermal aging, the Zeolite with stronger durability at a high temperature than other 5 kinds of SCR catalysts decreased the sintering of catalysts.

One-step hydrothermal synthesis of Cu-SAPO-34/cordierite and its catalytic performance on NOx removal from diesel vehicles

Cu-SAPO-34/cordierite catalysts were prepared via one-step hydrothermal synthesis method and their performances to remove NOx from the diesel vehicle exhaust were evaluated. The morphology, structure, Cu content and valence state were characterized by SEM, XRD, ICP and XPS, respectively. The experimental results show the active component Cu of the catalysts via in situ synthesis could significantly improve the selective catalytic reduction (SCR) activities of NOx and the optimal Cu content is in the range of 0.30%-0.40% (mass fraction). No N2O is detected by gas chromatograph (GC) during the evaluation process, which implies that NOx is almost entirely converted to N2 over Cu-SAPO-34/cordierite catalyst. The conversion rate of NOx to N2 by NH3 over catalyst could almost be up to 100% in the temperature range of 300–670 °C with a space velocity of 12000 h−1 and it is still more than 60% at 300–620 °C under 36000 h−1. The catalysts also show the good hydrothermal and chemical stability at the atmosphere with H2O.

Reduce NOx Emissions by Adsorber-Reduction Catalyst on Lean Burn Engine

The effect of a new catalyst system composed of traditional three way catalyst converter and adsorber-reduction catalysis converter on the emission characteristics and BSFC ( Breake Specific Fuel Consumption- BSFC ) of a lean burn gasoline engine operated were investigated in this paper under different schemes of catalyst converter arrangement and different speeds and loads. The results show that the position of Three Way Catalyst is before the NOx adsorber Catalyst was the best scheme of catalyst converter arrangement. Which has the highest converter efficiency of reduction NOx emission in lean burn gasoline engine. The effects of speed on the exhaust emission and BSFC were also related to the ratio of lean burn time to rich burn time and the absolute value of both time of the adsorber-reduction catalyst converter. The load of the engine was the main influential factor to the exhaust emission characteristics and BSFC of lean burn gasoline engine, and the more load of the engine was, the more NOx emission, the less NOx conversion rate (C NOx ) and the better BSFC were.

Effect of Ions Substitution on Nanospace La-Fe-O Catalytic Properties for Simultaneous Removal of NO&lt;sub&gt;x&lt;/sub&gt; and Soot

The catalysts La0.8K0.2FeO3(LKFO), La0.8K0.2Fe0.7Mn0.3O3(LKFMO) and La0.8K0.2Fe0.67Mn0.3Pt0.03O3(LKFMPO) were prepared by the citrate-gel process and the catalyst-coated honeycomb ceramic devices were prepared by the citrate-gel assisted dip-coating method. All the catalysts have a high performance on the simultaneous removal of NOxand soot at a temperature range of 200 to 400°C under the practical diesel exhaust emission. The obvious catalytic improvement is largely due to the effects of ions substitution, pore structure and microstructural characteristics of the catalysts. The catalytic performance order is LKFMPO &gt; LKFMO &gt; LKFO. Among them the LKFMPO catalyst shows the best catalytic properties, especially in the removal of NOx, with a maximum conversion rate of NOx(21.2%).

Changes in the chemical composition of V2O5-loaded CVC-TiO2 materials with calcination temperatures for NH3-SCR of NOx

In this study, the aim was to evaluate the effect of calcinations temperature on the catalytic activity and chemical composition of V2O5/TiO2. We prepared V2O5-loaded CVC-TiO2 catalysts by a combination of chemical vapor condensation (CVC) and impregnation method at different calcination temperatures. These catalysts were analyzed for their ability to catalyze NH3-based selective catalytic reduction of NOx. Compared with V2O5 loaded P25-TiO2 (commercial). V2O5/CVC-TiO2 catalysts calcined above 200 °C exhibited better performance towards NOx conversion than that by a commercial catalyst prepared using P25-TiO2 (calcined at 500 °C). In addition, the NOx conversion rate obtained with the sample calcined at 500 °C gave the best result (90 %) at a reaction temperature of 200 °C. From the XPS results, we observed that the V4+/5+ ratio was well balanced when the V2O5 loaded CVC-TiO2 sample was calcined at 500 oC.

Preparation and Characterization of MnO&lt;sub&gt;X&lt;/sub&gt;-CeO&lt;sub&gt;2&lt;/sub&gt;/TiO&lt;sub&gt;2&lt;/sub&gt; Catalytic Material for SCR of NO&lt;sub&gt;X&lt;/sub&gt; with NH&lt;sub&gt;3&lt;/sub&gt; at Low Temperature

The MnOX-CeO2/TiO2 catalytic material for low temperature SCR of NOX with NH3 was prepared using aqueous solutions of three manganese salt as well as cerous nitrate and TiO2(anatase) powder by impregnation method. The properties of the catalytic materials were investigated by TG-DSC, XRF, XRD, XPS, BET and SEM. And the low temperature catalytic activity of the catalytic materials was measured. The results showed that, when manganese nitrate and manganese chloride and manganese acetate were used as precursors, respectively, the primary phases of catalytic materials were MnOx/MnO2, MnO2/Mn8O10Cl3 and Mn3O4/MnO2, the surface Mn/Ti molar ratio were 0.68, 0.19 and 0.88, the surface area were 45.1m2/g, 25.1 m2/g and 48.6 m2/g ,respectively. The optimum NOX conversion rate of catalytic material from manganese nitrate precursor and manganese chloride precursor and manganese acetate precursor were 97.9% at 483K, 86.6% at 513K, 97.2% at 423K, respectively. Consequently, the higher low-temperature activity of MnOX-CeO2/TiO2 from manganese acetate precursor may be attributed to higher surface and higher surface concentration of activity component.

Recent Developments of Electrochemical Promotion of Catalysis in the Techniques of DeNOx

Electrochemical promotion of catalysis reactions (EPOC) is one of the most significant discoveries in the field of catalytic and environmental protection. The work presented in this paper focuses on the aspects of reaction mechanism, influencing factors, and recent positive results. It has been shown with more than 80 different catalytic systems that the catalytic activity and selectivity of conductive catalysts deposited on solid electrolytes can be altered in the last 30 years. The active ingredient of catalyst can be activated by applying constant voltage or constant current to the catalysts/electrolyte interface. The effect of EPOC can improve greatly the conversion rate of NOx. And it can also improve the lifetime of catalyst by inhibiting its poisoning.

The influence on SCR activity of the atomic structure of V2O5/TiO2 catalysts prepared by a mechanochemical method

A catalyst prepared by a mechanochemical method enables changes in physico-chemical properties such as surface area, particle size and phase. Accordingly, after preparing the catalyst by synthesizing V2O5 and anatase TiO2 with the mechanochemical method, a study on the selective catalytic reduction (SCR) reactive properties of NH3 was performed. The dry ball milling method was shown to be compatible with the dry synthesis method of the SCR catalyst by combining V2O5 and TiO2. The properties of the catalyst were studied using physio-chemical analyses, including BET surface area, X-ray diffraction (XRD), Raman spectroscopy, H2 temperature programmed reduction (H2-TPR), diffuse reflectance UV–VIS spectroscopy and X-ray photoelectron spectroscopy (XPS). The V2O5 crystallite peak decreased with increased milling time, and the monomeric species was formed. The maximum reducing temperature (Tmax) decreased by H2-TPR. Improvements in the redox capacity were identified by experiments in which O2 was introduced and subsequently removed as well as by reoxidation analysis. Additionally, the presence of non-stoichiometric vanadium and an increased number of surface atoms were identified through the milling effect. A correlation was identified between the ratio of (V4++V3+)/V5+ and the catalyst NOx conversion rate.

In situ synthesis of CuSAPO-34/cordierite and its selective catalytic reduction of nitrogen oxides in vehicle exhaust: The effect of HF

CuSAPO-34/cordierite catalysts were prepared via in situ hydrothermal synthesis technique with and without HF. The morphology and structure of the synthesized samples were characterized in the present work. The NOx selective catalytic reduction (SCR) activities of the catalysts were evaluated with a fixed-bed reactor in simulated diesel vehicle exhaust. The results indicate that the addition of HF into the initial gel during the preparation of CuSAPO-34/cordierite can accelerate the crystallization and improve the relative crystallinity of CuSAPO-34, which lead to the compact morphology of the products. Furthermore, the existence of HF can increase the specific pore volume, BET surface area and CuSAPO-34 loading of the catalyst. For the crystallization time of 24h, the loading amounts of CuSAPO-34 are 20.3wt% and 13.6wt% for the samples prepared with and without HF, respectively. The obvious improvement of the catalytic activities for NOx removal has been obtained over the catalysts prepared with HF. The active temperature window (NOx conversion rate>95%) of the samples prepared with HF is wider (340–600°C) than the samples prepared without HF (440–540°C). The catalysts with HF present great endurance ability for the aging treatment at 650°C with 15vol.% H2O. The low temperature activity for NOx removal of the catalyst prepared with HF is not affected by the aging treatment and the maximum NOx conversion rate of the aging catalyst at the crystallization time of 12h is about 96%, but only 80% for the catalyst without HF. The roles of HF and the different performances of the samples prepared with and without HF were discussed with the aid of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques.

An investigation into the properties of V-based catalysts for Selective Catalytic Reduction of NO with NH3

Selective catalytic reduction (SCR) is the most potential method for removing marine NOx emissions by up to 95%. This paper presents the results of an investigation using vanadium (V) based catalysts doped by metals W (tungsten), Ce (cerium) and Ni (nickel) to improve the low temperature performance of an SCR for NOx reduction. The temperature range studied was between 100–450°C with intervals of 100°C. A honeycomb ceramic substrate was modified by composite sol and coated with the catalysts. The study also included preparation, characterisation and activity tests of the selected catalysts, including studying the activity of the catalysts in ammonia selective catalytic reduction reaction with an excess of oxygen concentration.The investigation verifies that a mixture of the above metallic catalysts exhibit high activity for selective catalytic reduction of NOx with ammonia. Among all the catalysts studied, the mixed catalyst of Ni-Ce-W-V is the most potential one, not only because of its higher NOx conversion rate at low temperature, but also because of its wider window of operation temperature.