Selective Catalytic Reduction Applications Research Articles

Design of assembled composite of Mn3O4@Graphitic carbon porous nano-dandelions: A catalyst for Low–temperature selective catalytic reduction of NOx with remarkable SO2 resistance

The biggest challenge for selective catalytic reduction (SCR) of NO by NH3 at low temperatures is to develop robust catalysts with high resistance to SO2. Mn-based catalysts have attracted great attention for their excellent activity, but the poor SO2 resistance limits their application. Herein, we report a novel assembled composite featuring Mn3O4 nanoparticles embedded in defect-abundant graphitic carbon frame (Mn3O4@G-A) via a confinement–pyrolysis–oxidation strategy derived from MOF. The Mn3O4@G-A exhibits excellent activity (reaching over 90 % NO conversion in 100, 000 h−1 GHSV at 160 °C) and significantly improved SO2 resistance in comparison to pristine Mn3O4, and all the performance tests were conducted with 5.6 vol.% water vapor. By combining synchrotron radiation-based X-ray absorption spectroscopy and density functional theory calculation, we further discovered the positive role and the origin of graphitic carbon for improving SO2 resistance. Over the Mn3O4@G-A sample, the electrons can be transferred from graphitic carbon to Mn3O4 nanoparticles, which can regulate the electronic properties and oxidizing ability of Mn3O4 nanoparticles. The proper oxidizing ability of Mn3O4@G-A can inhibit the oxidation of SO2 to SO3, thus further avoid the formation of NH4HSO4 and improve the SO2 resistance. Our work here not only solves the current problem of poor SO2 resistance of Mn-based catalysts, but also provides new insights into the design and synthesis of MOF-derived graphitic carbon-containing catalysts for SCR applications.

The Interaction of NH4HSO4 with Vanadium–Titanium Catalysts Modified with Molybdenum and Tungsten

With the wide application of selective catalytic reduction (SCR) systems in power plants for the control of NOx emission in China, a serious problem of catalyst deactivation due to the channel blockage by NH4HSO4 has drawn extensive attention. In this work, a combined experimental and simulation method was utilized to study the interaction between NH4HSO4 and a vanadium–titanium-based catalyst. Initially, the adsorption characteristics of NH4HSO4 onto TiO2, V2O5/TiO2, V2O5-WO3/TiO2, and V2O5-MoO3/TiO2 were simulated following density functional theory. The simulation revealed that during reaction, the NH4HSO4 loaded onto TiO2 can be dissociated into NH4+ and SO42–. The existence of V2O5, WO3, and MoO3 can form a protective layer to inhibit the adsorption of NH4HSO4 onto TiO2, to promote the reduction of sulfur-containing compounds, and to accelerate the reaction of NH4+ with NO. Thermogravimetric analysis also showed the positive effect of V, W, and Mo on NH4HSO4 decomposition. Fixed-bed experiments were then conducted to compare the performance of the studied catalysts and the effect of NH4HSO4 on their performance. It was proven that the V-5Mo/TiO2 catalyst showed better performance at low temperatures. On the V-5Mo/TiO2 catalyst, ∼78 wt % NH4+ in NH4HSO4 was attached onto Lewis acid sites, which can accelerate the reduction reaction of NO by NH4+. Meanwhile, SO42– can comparatively be easily decomposed at lower temperatures.

Deposition of Selective Catalytic Reduction Coating on Wire-Mesh Structure by Atmospheric Plasma Spraying.

A series of catalytic coatings consisting of MnOx-CeO2 and TiO2 support were prepared by atmospheric plasma spraying, which was aimed at the application of selective catalytic reduction (SCR) of NOx. The effect of the load of active component on the coating was firstly studied. The results showed that all the coating presented the highest catalytic activity at approximately 350 °C and the coating with the composition of 20MnOx/5CeO2/TiO2 (wt%) achieved the most powerful performance. The coating was then prepared on a wire-mesh structure substrate, which can be easily assembled as a gas filter. The results showed that the specific surface area was greatly increased resulting in the significant improvement of the catalytic activity of the coating. This strategy offered a promising possibility of removing NOx and particulate fliting simultaneously in industrial applications.

Low-temperature selective catalytic reduction of N2O by CO over Fe-ZSM-5 catalysts in the presence of O2

Nitrous oxide (N2O) is an important ozone-depletion substance and greenhouse gas. Selective catalytic reduction (SCR) of N2O by CO is considered an effective method for N2O elimination. However, O2 exhibited a significant inhibition effect on the catalytic performance of N2O reduction by CO. A series of iron-based catalysts were prepared to investigate the effect of O2 in SCR of N2O by CO. The Fe-Z-pH2 (Fe-ZSM-5 ion-exchanged under pH of 2) catalyst manifested superior activity at low temperature and excellent O2 resistance in N2O reduction process. The characterization results from UV–vis DR spectra and XPS indicated that α-sites are the main active sites in Fe-Z-pH2, and they were inert to O2 but highly active to N2O. It could be concluded that the competition effect between N2O and O2 was very important over different catalysts. O2 is more prevalent over α-Fe2O3 catalyst, while N2O dominates over Fe-Z-pH2 catalyst. Moreover, in the presence of O2, Fe-Z-pH2 exhibited better performance for N2O removal than non-noble mixed oxide catalysts, which might broaden the application of low-temperature SCR of N2O by CO.

Simultaneous reduction of NOx and smoke emissions with low viscous biofuel in low heat rejection engine using selective catalytic reduction technique

The present work offered a comprehensive investigation on engine characteristics of single cylinder Direct Injection (DI) diesel engine fuelled with Lemon oil (LO) biofuel. LO was obtained from the peels of lemon using steam distillation process. The physio-chemical properties of LO were analysed based ASTM biodiesel standard and compared with diesel. The chemical composition of LO was observed with Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography and Mass Spectrometry (GC–MS). In-order to enhance the properties of LO, a cetane enhancer namely Pyrogallol (PY) was added. The engine combustion chamber components namely piston head, cylinder head and intake and exhaust valves were thermally coated with Partially Stabilized Zirconia (PSZ) which converted the conventional engine into low heat rejection engine. In the PSZ coated engine, enhanced performance and combustion characteristics were observed with LO and PY blend. Declined carbon monoxide (CO), hydrocarbon (HC) and smoke emissions were observed with LO and PY blend in coated engine. Further, the work was extended with the application of Selective catalytic reduction (SCR) and Catalytic Converter (CC) as post treatment system for the reduction of NOx emission. With post treatment, LO and pyrogallol in PSZ coated engine showed lower NOx emission than diesel and LO. Consequently, LO and pyrogallol in PSZ coated engine with post treatment was considered as more advantageous than other fuel samples on account of its performance, combustion and emission characteristics.

Synthesis of Bimetallic MOF-74-CoMn Catalyst and Its Application in Selective Catalytic Reduction of NO with CO

Synthesis of Bimetallic MOF-74-CoMn Catalyst and Its Application in Selective Catalytic Reduction of NO with CO

The Role of Impregnated Sodium Ions in Cu/SSZ-13 NH3-SCR Catalysts

To reveal the role of impregnated sodium (Na) ions in Cu/SSZ-13 catalysts, Cu/SSZ-13 catalysts with four Na-loading contents were prepared using an incipient wetness impregnation method and hydrothermally treated at 600 °C for 16 h. The physicochemical property and selective catalytic reduction (SCR) activity of these catalysts were studied to probe the deactivation mechanism. The impregnated Na exists as Na+ on catalysts and results in the loss of both Brönsted acid sites and Cu2+ ions. Moreover, the high loading of Na ions destroy the framework structure of Cu/SSZ-13 and forms new phases (SiO2/NaSiO3 and amorphous species) when Na loading was higher than 1.0 mmol/g. The decreased Cu2+ ions finally transformed into CuxO, CuO, and CuAlOx species. The inferior SCR activity of Na impregnated catalysts was mainly due to the reduced contents of Cu2+ ions at kinetic temperature region. The reduction in the amount of acid sites and Cu2+ ions, as well as copper oxide species (CuxO and CuO) formation, led to low SCR performance at high temperature. Our study also revealed that the existing problem of the Na ions’ effect should be well-considered, especially at high hydrothermal aging when diesel particulate filter (DPF) is applied in upstream of the SCR applications.

Splashing characteristics of diesel exhaust fluid (AdBlue) droplets impacting on urea-water solution films

The rapid implementation of Selective-Catalytic-Reduction (SCR) technologies into light passenger and commercial vehicles, led to the omission of fundamental research creating several reliability issues that are largely related to the research field of droplet dynamics. In this study, the splashing behaviour of an AdBlue droplet impacting onto thin urea-water solution films is experimentally investigated over a range of impact parameters. In particular, the crown-type splashing threshold, the number of fingers and the characteristics of the ejected secondary droplets are evaluated for various drop impact velocities, wall-film thicknesses and urea concentrations in the liquid film. The results show that impact parameters that are able to enhance the energy dissipation in the wall-film, e.g. film thickness and viscosity, influence negatively the intensity of splashing. On the other hand, as the droplet kinetic energy increases or the wall-film thickness decreases, more energy is available to intensify the splashing outcome, and consequently, the upward ejected secondary droplet volume. The obtained trends are correlated in simple empirical expressions providing a remarkable industrial design tool, and they are also compared to the state-of-the-art literature of single- and binary-droplet/wall-film interactions aiming to draw generalised theories and paradigms that will support the connection between SCR applications and academic research.

A Perspective on the Selective Catalytic Reduction (SCR) of NO with NH3 by Supported V2O5–WO3/TiO2 Catalysts

The selective catalytic reduction (SCR) of NOx with NH3 to harmless N2 and H2O plays a crucial role in reducing highly undesirable NOx acid gas emissions from large utility boilers, industrial boilers, municipal waste plants, and incinerators. The supported V2O5–WO3/TiO2 catalysts have become the most widely used industrial catalysts for these SCR applications since introduction of this technology in the early 1970s. This Perspective examines the current fundamental understanding and recent advances of the supported V2O5–WO3/TiO2 catalyst system: (i) catalyst synthesis, (ii) molecular structures of titania-supported vanadium and tungsten oxide species, (iii) surface acidity, (iv) catalytic active sites, (v) surface reaction intermediates, (vi) reaction mechanism, (vii) rate-determining-step, and (viii) reaction kinetics.

Modeling Approach for a Hydrolysis Reactor for the Ammonia Production in Maritime Selective Catalytic Reduction Applications

The catalytic generation of ammonia from a liquid urea solution is a critical process determining the performance of selective catalytic reduction (SCR) systems. Solid deposits on the catalyst surface from the decomposition of urea have to be avoided, as this leads to reduced system performance or even failure. At present, reactor design is often empirical, which poses a risk for costly iterations due to insufficient system performance. The presented research project proposed a performance prediction and modeling approach for SCR hydrolysis reactors generating ammonia from urea. Different configurations of hydrolysis reactors were investigated experimentally. Ammonia concentration measurements provided information about parameters influencing the decomposition of urea and the system performance. The evaporation of urea between injection and interaction with the catalyst was identified as the critical process driving the susceptibility to deposit formation. The spray of urea solution was characterized in terms of velocity distribution by means of particle-image velocimetry. Results were compared with theoretical predictions and calculation options for processes in the reactor were determined. Numerical simulation was used as an additional design and optimization tool of the proposed model. The modeling approach is presented by a step-by-step method, which takes into account design constraints and operating conditions for hydrolysis reactors.

Microspherical MnO2-CeO2-Al2O3 mixed oxide for monolithic honeycomb catalyst and application in selective catalytic reduction of NOx with NH3 at 50–150 °C

MnOx-CeO2-Al2O3 microspheres (MSs) were successfully designed and synthesized via spray drying (SD) and easily used for monolithic honeycomb catalyst (MHC). The as-obtained MnOx-CeO2-Al2O3 (SD) catalyst exhibited a great BET surface area of 201.4 m2/g, a pore volume of 0.29 cm3/g, and an average pore diameter of 5.8 nm. Furthermore, the MnOx-CeO2-Al2O3 (SD) MSs delivered much more Olatt sits resulting in enhanced catalytic activity at low temperature. The MnOx-CeO2-Al2O3 (SD) performed excellent NOx conversion of 97.4% and N2 selectivity of 94.5% at 150 °C with a gas hourly space velocity (GHSV) of 15,000 h−1, and NOx concentration of 500 ppm. Even at 50 °C and 100 °C, the titled product still exhibited great N2 selectivity of 95.5% and 96.1%, respectively, corresponding to the NOx conversion of 55% and 98.0%, respectively. The MnOx-CeO2-Al2O3 (SD) monolithic honeycomb catalyst (MHC) was prepared by vacuum-impregnation method. The MnOx-CeO2-Al2O3 (SD-MHC) delivered NOx conversion of 93% at 150 °C with a GHSV of 2000 h−1, and NOx concentration of 500 ppm. Even at 50 °C and 100 °C, the titled product still performed NOx conversion of 55% and 83%, respectively. The MnOx-CeO2-Al2O3 (MHC) performed great catalytic activity in the low temperature arrange from 50 to 150 °C and presented potential application in stationary industrial installations.

One-step synthesized SO42–-TiO2 with exposed (001) facets and its application in selective catalytic reduction of NO by NH3

A sample of sulfated anatase TiO2 with high-energy (001) facets (TiO2-001) was prepared by a simple one-step hydrothermal route using SO42– as a morphology-controlling agent. After doping ceria, Ce/TiO2-001 was used as the catalyst for selective catalytic reduction (SCR) of NO with NH3. Compared with Ce/P25 (Degussa P25 TiO2) and Ce/P25-S (sulfated P25) catalysts, Ce/TiO2-001 was more suitable for medium- and high-temperature SCR of NO due to the high surface area, sulfation, and the excellent properties of the active-energy (001) facets. All of these facilitated the generation of abundant acidity, chemisorbed oxygen, and activated NOx-adsorption species, which were the important factors for the SCR reaction.

Study on the poisoning effect-of non-vanadium catalysts by potassium

The poisoning effect of catalyst by alkali metals is one of the problems in the selective catalytic reduction (SCR) of NO by NH3. Serious deactivation by alkali poisoning have been proved to take place in the commercial vanadium catalyst. Recently, non-vanadium catalysts such as copper oxides, manganese oxides, chromium oxides and cerium oxides have attracted special attentions in SCR application. However, their tolerance in the presence of alkali metals is still doubtful. In this paper, copper oxides, manganese oxides, chromium oxides and cerium oxides supported on TiO2 nanoparticle was prepared by impregnating method. Potassium nitrate was chosen as the precursor of poisoner. Catalytic activities of these catalysts were evaluated before and after the addition of potassium. Some characterization methods including X-ray diffraction and temperature programmed desorption was utilized to reveal the main reason of alkali deactivation.

New insights into the mechanism of NH3-SCR over Cu- and Fe-zeolite catalyst: Apparent negative activation energy at high temperature and catalyst unit design consequences

We demonstrate an unusual behavior of a practically-important reaction of selective catalytic reduction (SCR) of NOx with NH3 over a state-of-the-art Cu-SSZ-13 catalyst. In response to increasing temperature, the rate of SCR reaction increases initially, attains a maximum around 300 °C, and then declines, resulting in a negative apparent activation energy at higher temperatures. This behavior has never been previously reported because the side reaction of NH3 oxidation obfuscated the kinetic analysis of SCR reaction at high temperatures. We were able to discover this phenomenon by performing severe hydrothermal aging of the catalyst that suppressed the NH3 oxidation activity without a significant change in the SCR activity. Further, we show that the phenomenon is more general and also found in other Cu- and Fe-exchanged zeolite and V2O5-(WO3)/TiO2 catalysts. The behavior is explained based on the fact that the activation energy for NH3 desorption is higher than that for standard SCR reaction. Therefore, at higher temperatures, the increase in the SCR reaction rate constant with temperature gets outpaced by the decline in the NH3 coverage, resulting in the overall decline of the reaction rate.One of the implications of the finding is that the studied Cu-SSZ-13 SCR catalyst never operates in a purely external mass transfer limited regime, under the range of conditions relevant to the practical SCR applications. In other words, there is always a certain contribution of slower reaction rate to the performance of the SCR catalyst, even after increasing the reaction rates by increasing catalyst amount, using the “fast” SCR reaction, or operating at elevated temperatures. This has significant consequences for the design of practical SCR catalysts, in particular related to the choices of the active material loading and channel hydraulic diameter, as empirically and analytically demonstrated in this paper.

Empirical model to predict melt volume for different range of diesel exhaust fluid tank volumes used in selective catalytic reduction systems

Technologies such as Selective Catalytic Reduction (SCR) assists in complying with diesel emission limits for NOx. Diesel Exhaust Fluid (DEF) which is an aqueous urea solution plays an important role in SCR systems. DEF freezes at approximately −11 °C due to which it becomes a challenge to meet regulations which state that, NOx emissions must be under regulatory limits within 70 min of engine starting. Hence, it is important to ensure DEF melts within stipulated time so that the system is ready to reduce engine out NOx. Prediction of melt volume is an important performance parameter used to compare different DEF tank designs. In this paper, empirical models are identified from various studies done in the past and selection of suitable models for wide range of SCR applications is done. Models were selected which predicts melt volume w.r.t time for vertical heating arrangements for different tank sizes, aspect ratios and shapes i.e. rectangular and cylindrical enclosures used worldwide. This empirical model is compared with experiment data and also with previous literature to understand its robustness and feasibility for different geometries. New hybrid approach was also identified to predict melt volumes for helical heater arrangements within acceptable percentage error range.

Highly efficient and stable Ru/K-OMS-2 catalyst for NO oxidation

The influence of addition of a series of non noble and noble metals to a manganese oxide octahedral molecular sieve (OMS) with a cryptomelane structure (K-OMS-2) has been studied for NO oxidation in view of fast selective catalytic reduction applications. Fe, Cu, Zn, Pt, Pd, Ru and Ag were selected as dopant metals with a metal loading around 2wt.%. The catalysts were characterized in detail by ICP-OES, N2 adsorption/desorption at 77K, XRD, H2-TPR and HR-TEM. The highest NO conversion was obtained for a K-OMS-2 catalyst modified with ruthenium, showing a reaction rate up to 5.3μmolg−1s−1 at 584K. A markedly higher catalyst reducibility upon incorporation of ruthenium can be proposed as an underlying reason for the enhanced catalytic performance.

Numerical analysis of ammonia homogenization for selective catalytic reduction application

Selective catalytic reduction based on urea water solution as ammonia precursor is a promising method for the NOx abatement form exhaust gasses of mobile diesel engine units. It consists of injecting the urea-water solution in the hot flue gas stream and reaction of its products with the NOx over the catalyst surface. During this process flue gas enthalpy is used for the urea-water droplet heating and for the evaporation of water content. After water evaporates, thermolysis of urea occurs, during which ammonia, a known NOx reductant, and isocyanic acid are generated. The uniformity of the ammonia before the catalyst as well as ammonia slip to the environment are important counteracting design requirements, optimization of which is crucial for development of efficient deNOx systems.The aim of this paper is to show capabilities of the developed mathematical framework implemented in the commercial CFD code AVL FIRE®, to simulate physical processes of all relevant phenomena occurring during the SCR process including chemical reactions taking part in the catalyst. First, mathematical models for description of SCR process are presented and afterwards, models are used on the 3D geometry of a real SCR reactor in order to predict ammonia generation, NOx reduction and resulting ammonia slip. Influence of the injection direction and droplet sizes was also investigated on the same geometry. The performed study indicates importance of droplet sizes on the SCR process and shows that counterflow injection is beneficial, especially in terms of minimizing harmful ammonia slip to environment.

Adsorption of Vanadium (V) from SCR Catalyst Leaching Solution and Application in Methyl Orange.

In this study, we explored an effective and low-cost catalyst and its adsorption capacity and catalytic capacity for Methyl Orange Fenton oxidation degradation were investigated. The catalyst was directly prepared by reuse of magnetic iron oxide (Fe3O4) after saturated adsorption of vanadium (V) from waste SCR (Selective Catalytic Reduction) catalyst. The obtained catalyst was characterized by FTIR, XPS and the results showed that vanadium (V) adsorption process of Fe3O4 nanoparticles was non-redox reaction. The effects of pH, adsorption kinetics and equilibrium isotherms of adsorption were assessed. Adsorption of vanadium (V) ions by Fe3O4 nanoparticles could be well described by the Sips isotherm model which controlled by the mixed surface reaction and diffusion (MSRDC) adsorption kinetic model. The results show that vanadium (V) was mainly adsorbed on external surface of the Fe3O4 nanoparticles. The separation-recovering tungsten (VI) and vanadium (V) from waste SCR catalyst alkaline solution through pH adjustment was also investigated in this study. The results obtained from the experiments indicated that tungsten (VI) was selectively adsorbed from vanadium (V)/tungsten (VI) mixed solution in certain acidic condition by Fe3O4 nanoparticle to realize their recovery. Tungsten (V) with some impurity can be obtained by releasing from adsorbent, which can be confirmed by ICP-AES. The Methyl Orange degradation catalytic performance illustrated that the catalyst could improve Fenton reaction effectively at pH = 3.0 compare to Fe3O4 nanoparticles alone. Therefore, Fe3O4 nanoparticle adsorbed vanadium (V) has a potential to be employed as a heterogeneous Fenton-like catalyst in the present contribution, and its catalytic activity was mainly evaluated in terms of the decoloration efficiency of Methyl Orange.

SCR 촉매의 공간속도 및 선속도가 NOx 제거 효율에 미치는 영향

Air pollutants nitrogen oxides are inevitably generated in the combustion reaction. Its amount trend is steadily increasing because the rapid modern industrialization and population growth. For this reason, NOx is controlled to reducing the harmful components in the exhaust gas. So Marine Environment Protection Committee (MEPC) take effect 'Tier I', 'Tier II' of air pollution regulation in 2005 and 2011 respectively. According to NOx emissions are strictly regulated management of the vessel through them. In addition, since 2016 the regulation enter into force in the next step 'Tier III' was confirmed by MEPC 66th committee. It's 80% enhanced emissions limits than the 'Tier I' Alternatively these emission regulation, research is actively being carried out about exhaust gas after-treatment methods through the vessel application of Selective Catalytic Reduction(SCR). Therefore depending on the basic specification of cell density according to the Area velocity, Space velocity, Linear velocity is studied the effects of NOx removal efficiency

Investigation on UWS evaporation for vehicle SCR applications

Urea water solution (UWS) droplet evaporation characteristics directly affect the conversion and distribution of NH3 in urea based selective catalytic reduction (SCR) system. The UWS droplet temperature is very difficult to be measured directly. Whereas, this piece of research work involves the measurement of droplet temperature by an Omega‐K type thermocouple of 127 µm diameter. According to the temperature changes of the droplet, the evaporation process can be divided into four steps. Droplets heat and mass transfer processes are derived theoretically at high exhaust temperature. The UWS droplet has been placed in a continuous observation test system to investigate its diameter and temperature variations in the aforementioned four steps. The results shown that, this unique method of four steps analysis has more explicitly and better described the UWS evaporation process, hence establishing the basis for the subsequent detailed simulation and monitoring. © 2015 American Institute of Chemical Engineers AIChE J, 62: 880–890, 2016