Catalysts For Selective Reduction Research Articles

Performance evaluation of low heat rejection diesel engine operated with biofuels under-selective catalytic reduction

Vehicle emissions are responsible for about 30% of all air pollution in the world. Vehicle emissions can be significantly reduced through the use of selective catalyst reduction (SCR). The present work emphasizes the impact of thermal barrier-coated pistons on diesel engine performance as well as emission qualities. A Ni–Cr–Al–Y bond coat was applied to the tested engine piston that was 50 microns thick and a top coat that was 250 microns thick. These coatings were applied using the plasma spray technique to a combination of 2 mol. % of Gadolinium oxide (Gd2O3), 2 mol. % of Neodymium oxide (Nd2O3), 3 mol. % of Yttria (Y2O3), and continuing 93 mol. % of Zirconia (ZrO2). In a 4-stroke, 1-cylinder diesel engine, the testing was carried out utilizing diesel, Mahua, and Jatropha fuels with and without coating. The selective catalytic reduction technique was employed in the current test to reduce NOx emissions. The findings of this analysis indicate that the brake thermal efficiency of an insulated piston engine improved by 3.9%, and when JB 100 was chosen as the fuel, the insulated piston reduced brake-specific fuel consumption by 3.5% in comparison to the normal piston. In engines coated with SCR, hydrocarbon emissions were lowered by 20.1%, while carbon monoxide emissions were dropped by 13.4%. In comparison to the baseline engine, the oxide of nitrogen emissions were reduced by 39.1%.

Recovery and reuse of spent lithium-ion batteries as catalysts for low-temperature NH3-SCR

The wide application of lithium-ion batteries (LIBs) for electric vehicles forebodes the decommissioning tide of spent LIBs. Therefore, recycling valuable element from spent LIBs are becoming urgent to minimize the impact on the environment and supply chain of battery manufacturers. In this work, we propose to extract valuable elements from the cathode materials of spent ternary lithium-ion batteries and synthesize NiCoMnOx catalysts for low-temperature NH3 selective catalyst reduction (NH3-SCR) reactions. The oxalic acid is used as a precipitant and reducing agent and prepared as NiCoMnOx catalyst by hydrothermal process and heat treatment. The as-prepared catalyst presents a porous fluffy foam structure with abundant oxygen defects, ensuring sufficient catalytic active sites. As a result, the NiCoMnOx catalyst exhibits optimal catalytic activity with over 90% NOx conversion in the temperature range of 110 ∼ 230 °C, which is wider than the temperature range of 155 ∼ 210 °C for the catalysts prepared from metal salts. Meanwhile, the NiCoMnOx catalyst also shows better catalytic stability and resistance to H2O and SO2. This work provides a promising strategy to recycle spent LIBs to low-temperature NH3-SCR catalysts.

Thermal Management of Diesel Engine Aftertreatment System Based on Ultra-Low Nitrogen Oxides Emission

To achieve diesel engine ultra-low nitrogen oxide emission, light-off selective catalyst reduction (LO-SCR) has been suggested for better performance with lower exhaust temperature. An electric heater upstream of the exhaust aftertreatment system was applied to significantly decrease the NOx emission at a low exhaust temperature. With a 7.2 kW electric heater coupled with LO-SCR, the NOx emission during 200~500 s of the world harmonized transient cycle (WHTC) decreased from 282.6 ppm to 61.5 ppm, which is a decrease of 45%. Application of an upstream diesel oxidation catalyst (DOC) decreased the NOx emission by 63% at the same interval at the cost of worse cold-start performance. The urea input was also adjusted to avoid NOx emission during the latter part of the WHTC.

Cu docking-activated Nb incorporation in multivariate CuO-Nb2O5/CeO2 catalysts for selective reduction of NOx with NH3

Improving the low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR) meanwhile maintaining N2 selectivity are challenging in the field of catalysis. Herein, we showcase the fabrication of the synergistic catalytic sites in the CuO-Nb2O5/CeO2 catalysts. Impressively, the CuO-Nb2O5/CeO2 is characteristic with abundant oxygen vacancies at the interfacial regions, which facilitate the redox reaction between Ce3+, Nb5+ and Cu2+ with the assistance of surface oxygen, exhibiting high NH3-SCR activity, N2 selectivity and wide temperature window at a gas hourly space velocity of 150,000 h−1. Contrast experiments, EXAFS analysis, in situ infrared and Raman spectroscopy, and theoretical calculations indicate that the introduction of proper copper ions in the CeO2 lattice induces the structure distortion of surface CeO2, improving more niobium ions incorporation into the CeO2. The embedded Nb synergizes Cu and Ce to evoke the generation of newly adsorptive sites for NOx and NH3, thus contributing to the NH3-SCR reaction.

Comprehensive recovery of W, V, and Ti from spent selective reduction catalysts

Comprehensive recovery of W, V, and Ti from spent selective reduction catalysts

Pollutant emission characteristics of the close-coupled selective catalytic reduction system for diesel engines under low exhaust temperature conditions

The selective catalyst reduction system is an effective method for reducing pollutant emissions from diesel engines. To meet the increasingly strict requirements of pollutant emission regulations and further reduce the pollutant emissions of heavy diesel engines at low exhaust gas temperatures, a close-coupled selective catalyst reduction (ccSCR) system based on a corrugated substrate was proposed. Based on the corrugated substrate with V2O5-WO3/TiO2 catalysts, the pollutant emission characteristics of the ccSCR system were compared with those of a conventional selective catalyst reduction (SCR) system under the World Harmonized Transient Cycle at the exhaust gas temperature of 165 °C. Additionally, the effects of the volume ratio of ammonia to nitrogen (α) and the catalyst volume to engine gas capacity ratio (γ) on pollutant emissions of the ccSCR system were investigated. Results showed that pollutant emissions exhausted from the ccSCR system were significantly lower than those from the conventional SCR system. With the increase of α from 0.3 to 0.7 and γ from 0.33 to 0.76 in the ccSCR module, the NOx emission and NH3 slip of the ccSCR system decreased, and α had a larger effect on reducing pollutant emissions from the ccSCR system. The minimum values of NOx emission and NH3 slip were 0.22 g/kW·h and 2.33 ppm, respectively, at α = 0.7 and γ = 0.76 of the ccSCR module. The proposed ccSCR system was conducive to reducing the pollutant emission of diesel engines and its pollutant emission characteristics outperformed the conventional SCR system.

Iterative Approach of Experiment-Machine Learning for Efficient Optimization of Environmental Catalysts: An Example of NOx Selective Reduction Catalysts.

An iterative approach between machine learning (ML) and laboratory experiments was developed to accelerate the design and synthesis of environmental catalysts (ECs) using selective catalytic reduction (SCR) of nitrogen oxides (NOx) as an example. The main steps in the approach include training a ML model using the relevant data collected from the literature, screening candidate catalysts from the trained model, experimentally synthesizing and characterizing the candidates, updating the ML model by incorporating the new experimental results, and screening promising catalysts again with the updated model. This process is iterated with a goal to obtain an optimized catalyst. Using the iterative approach in this study, a novel SCR NOx catalyst with low cost, high activity, and a wide range of application temperatures was found and successfully synthesized after four iterations. The approach is general enough that it can be readily extended for screening and optimizing the design of other environmental catalysts and has strong implications for the discovery of other environmental materials.

Impact of diesel-hythane dual-fuel combustion on engine performance and emissions in a heavy-duty engine at low-load condition

Heavy-duty diesel vehicles are currently a significant part of the transportation sector, as well as one of the major sources of carbon dioxide (CO2) emissions. International commitments to reduce greenhouse gas (GHG) emissions, particularly CO2 and methane (CH4) highlight the need to diversify towards cleaner and more sustainable fuels. Hythane, a 20% hydrogen and 80% methane mixture, can be a potential solution to this problem in the near future. This research was focused on an experimental evaluation of partially replacing diesel with hythane fuel in a single-cylinder 2.0 L heavy-duty diesel engine operating in the diesel-gas dual fuel combustion mode. The study investigated different gas substitution fractions (0%, 38% and 76%) of hythane provided by port fuel injections at 0.6 MPa indicated mean effective pressure (IMEP) and a fixed engine speed of 1200 rpm. Various engine control strategies, such as diesel injection timing optimisation, intake air pressure and exhaust gas recirculation (EGR) were investigated in order to optimise the dual-fuel combustion mode. The results indicated that by using hythane energy fraction (HEF) of 76% combined with 125 kPa intake air boost and 25% EGR dilution, CO2 emissions could be decreased by up to 23%, while indicated thermal efficiency (ITE) was compromised by 1.5 percentage points, equivalent to a 3% reduction. Furthermore, soot was maintained below Euro VI limit and nitrogen oxides (NOx) level was held below the Euro VI regulation limit of 8.5 g/kWh assuming a NOx conversion efficiency of 95% in a selective catalyst reduction (SCR) system. Nevertheless, carbon monoxide (CO), unburned hydrocarbon (HC) and methane slip levels were considerably higher, compared to the diesel-only baseline. The use of a pre-injection prior to the diesel main injection was essential to control the heat release and pressure rise rates under such conditions.

Development of Machine Learning Algorithms for Application in Major Performance Enhancement in the Selective Catalytic Reduction (SCR) System

Machine learning is used in this study to deal with the reduction in the design period and major performance improvement of the selective catalyst reduction system. The selective catalyst reduction system helps in the reduction in NOx emission in the diesel engine. The existing methods for the design and performance improvement of selective catalyst reduction systems tend to be inefficient, due to layout changes that require modification when mounting a vehicle based on previously designed models. There are some factors that can affect the design of the diesel engine selective catalyst reduction system that can be identified by applying an optimized design. The Taguchi orthogonal array design is used with the eight factors and three levels of the main design factors. The distance of the urea injector, the distance of the mixer, the inflow angle of the exhaust gas, the angle of the urea injector, the angle of the mixer, the mounting angle in the direction of rotation of the mixer inside the selective catalyst reduction pipe, the number of mixer blades, the and bending angle of the mixer blade are identified as the eight major factors involved. These factors can also be considered manufacturing factors and can be established through machine learning. Machine learning has the advantage of being more efficient compared to other methods in determining the relationship between the data for each mutual factor. Machine learning can help in reducing processing time, which can further decrease the cost of the design analysis and improve the performance of the selective catalyst reduction system. This study shows that the results are statistically significant as the p values of the mixer blade number and cone length are lower than 0.05.

Response of axial nitrogen coordination engineering to cobalt based molecular environmental catalysts for selective reduction of CO2

It is of practical significance to use appropriate catalysts to reduce CO2 into useful products by reasonably consuming a certain amount of electrical energy. Heterogeneous cobalt phthalocyanine/carbon nanotube (CoPc/CNT) catalyst can achieve efficient catalytic reduction performance. It has been proved that the introduction of axial coordination N atoms can effectively adjust the electronic structure of CoPc, thus regulating its activity. However, there is still a lack of systematic research on the axial coordination bond modulation CO2RR process provided by N sources on the surface of carbon materials. In this work, pydridine with C=N-C (Py), cyanobenzene with C≡N (Cy), and aminobenzene with C-N-H (Am) were grafted onto CNT through diazotization reaction, and CoPc was loaded to form axially coordinated Co-N5 configuration catalysts (i.e., CoPc-Py-CNT, CoPc-Cm-CNT, and CoPc-Am-CNT), and their catalytic activities were compared. CoPc-Am-CNT with Am ligand had the strongest coordination bond energy and achieved outstanding CO2RR activity (the turnover frequency (TOF) value was 5.3 s−1), which was attributed to its impaired CO2RR energy barrier, excellent CO2 affinity, and low mass transfer resistance. While the CO Faraday efficiency of CoPc-Am-CNT at the potential below −0.75 V vs RHE was lower than those of CoPc-Cy-CNT and CoPc-Py-CNT. This was due to the fact that the electron-donating group property of Am moved the CoPc/[CoPc].- couple potential of CoPc-Am-CNT more negative, so the maximum CO Faraday efficiency of CoPc-Am-CNT could only be achieved at higher potentials (＞ −0.75 V vs RHE). This work provides new insights for the design of axial ligand catalysts and their application in eleccatalytic reduction of CO2.

CO2 Reduction Mechanism on the Cu2 O(110) Surface: A First-Principles Study.

Cu2 O is an attractive catalyst for the selective reduction of CO2 to methanol. However, the mechanism of the reaction and the role of the Cu species in different oxidation states are not well understood yet. In this work, by first-principles calculations, we investigate the mechanism of the reaction on the Cu2 O(110) surface, which is the most selective for methanol, in different degrees of reduction: ideal surface, slightly reduced surface (SRS), and partially reduced surface (PRS). The most favorable reaction pathways on the three surfaces were identified. We found that Cu(I) on the ideal surface is not capable of chemisorbing CO2 , but surface oxygen serves as the active site which selectively converts CO2 to CH3 OH with a limiting potential of -0.77 V. The Cu(0) on the SRS and PRS promotes the adsorption and reduction of CO2 , while the removal of the residue O* becomes potential/rate limiting with a more negative limiting potential than the ideal surface. The SRS is selective to methanol while the PRS becomes selective to methane. The result suggests that the key to high methanol selectivity is to avoid the reduction of Cu(I), which provides a new strategy for the design of more efficient catalysts for selective CO2 reduction to methanol.

High-Performance Low-Vanadium V2O5/Al2O3 Catalysts for Selective Reduction of NOx: I. Catalytic Properties

High-Performance Low-Vanadium V2O5/Al2O3 Catalysts for Selective Reduction of NOx: I. Catalytic Properties

MOx@VOx‐Pd‐type Nanorods and Nanotubes as Catalysts for Selective Reduction of NO

AbstractVanadium oxide (VOx‐Pd) nanotubes as well as VOx‐coated ZnO nanorods (ZnO@VOx‐Pd) and VOx‐coated, layered‐titania nanotubes (l‐TiO2@VOx‐Pd) are decorated with Pd nanoparticles and evaluated for selective catalytic reduction with hydrogen (H2‐SCR) for the first time. The nanostructures exhibit lengths of 300 to 700 nm, diameters of 20–100 nm and, in the case of the nanotubes, an inner tube diameter of about 10 nm. Pd nanoparticles (14±5 nm) are well‐dispersed over the respective nanorod/nanotube nanostructure. Structure and composition are characterized by SEM, TEM, EDXS with element mapping, XPS, FT‐IR, XRD, and sorption analysis. Thermal analysis indicates the nanostructures to be thermally stabile up to 350 °C (VOx), and 500 °C (ZnO@VOx, l‐TiO2@VOx). All catalysts are tested for their activity in regard of the selective catalytic reduction of NO with H2, revealing a significant impact of the catalyst support on both activity and selectivity. Specifically, l‐TiO2@VOx nanotubes show promising properties with an activity up to 70 % and a selectivity up to 80 % N2.

Analysis of the pollution emission system of large-scale combustion of biomass briquette fuel in China

In order to realize the sustainable development strategy and reduce the air pollution caused by biomass boiler emissions, the current study added a Selective Catalyst Reduction (SCR) external denitration system and a wet electrostatic precipitator to the original “three-stage” dust removal system for biomass briquetting fuel boiler emissions and completed the upgrading of the “five-stage” dust removal system. Taking the soot concentration, Sulfur dioxide (SO2) concentration, and Nitrogen oxides (NOX) concentration in the flue gas as the evaluation indicators, real-time online monitoring of the operating conditions of the system is carried out. The results show that the average concentration of smoke and dust in the flue gas discharged from the “five-stage” dust removal system is 3.47 mg/m3, with 2.49 mg/m3 for the average concentration of SO2, and 25.48 mg/m3 for the average concentration of NOX. The removal rates of soot, SO2, and NOX have increased by 5.8%, 4%, and 48.5%, respectively, which are much lower than the emission standards of biomass boiler flue gas pollutants. The innovation of this system is unprecedented for the large-scale combustion of biomass briquettes in China, which greatly reduces the emission of harmful gases. This upgrading will not only make a certain contribution to environmental protection but also provide a theoretical basis to the biomass briquette fuel industry.

Bimetallic MnO2-supported catalysts for selective reduction of NO with NH3. Operando IR studies

Bimetallic shaped catalysts were prepared by wet equilibrium impregnation. MnO2 was the main component and a second metal oxide (Co, Fe and Ce oxides) was added. The highest catalytic activity in the selective reduction of NOx with NH3 of the Ce-promoted catalyst (88 % of NO was converted at 170 °C) may be related to its capacity to adsorb NOx even in presence of water. It is demonstrated that NO adsorbs and oxidizes on CeOx and MnOx and then reacts with NH3 via a Langmuir-Hinshelwood mechanism. However, in presence of water, the surface of Fe-promoted catalyst during NH3-SCR was only covered by NH3 adsorbed species and NOx conversion was lower (65 % of NO was converted at 170 °C). NOx adsorbed species were not observed, which suggests that the reaction of ammonia with gaseous NOx was much faster than that of nitrites/nitrates formation. Elay-Riedel seems to be the predominant mechanism over this catalyst.

Comprehensive Control Strategy of Fuel Consumption and Emissions Incorporating the Catalyst Temperature for PHEVs Based on DRL

PHEVs (plug-in hybrid electric vehicles) equipped with diesel engines have multiple model transitions in the driving cycle for their particular structure. The high frequency of start–stop of a diesel engine will increase fuel consumption and reduce the catalytic efficiency of SCR (Selective Catalyst Reduction) catalysts, which will increase cold start emissions. For comprehensive optimization of fuel consumption and emissions, an optimal control strategy of PHEVs that originated from the PER-TD3 algorithm based on DRL (deep reinforcement learning) is proposed in this paper. The priority of samples is assigned with greater sampling weight for high learning efficiency. Experimental results are compared with those of the DP (dynamic programming)-based strategy in HIL (hardware in loop) equipment. The engine fuel consumption and NOX emissions were 2.477 L/100 km and 0.2008 g/km, nearly 94.1% and 90.1% of those of the DP-based control strategy. By contrast, the fuel consumption and NOx of DDPG (Deep Deterministic Policy Gradient)-based and TD3(Twin Delayed Deep Deterministic Policy Gradient) -based control strategy were 2.557, 0.2078, 2.509, and 0.2023, respectively. By comparative results, we can see that the comprehensive control strategy of PHEVs based on the PER-TD3 algorithm we proposed can achieve better performance with comparison to TD3-based and DDPG-based, which is the state-of-the-art strategy in DRL. The HIL-based experimental results prove the effectiveness and real-time potential of the proposed control strategy.

Effects of high cetane diesel on combustion, performance, and emissions of heavy-duty diesel engine.

Fuel economy improvement and reducing exhaust emissions are drivers for advancement in engine technology and fuel quality enhancement. The latest generation diesel engine uses a high pressure common rail fuel injection system and after-treatment devices such as selective catalyst reduction (SCR) and diesel particulate filters (DPF) to meet the stringent emission norms. The performance of engine can be further improved by using better quality fuel than the minimum requirement. Fuel quality improvement can be achieved through modifying blending components and/ or using additives. This study investigates the effect of high cetane diesel on the performance and emission behavior of SCR fitted heavy-duty engines. Normal diesel is doped with diesel multi-functional additives containing cetane improver, and thereby cetane number enhanced to 55 from 52. Fuel consumption and exhaust emission were evaluated over the European stationary cycle (ESC) under the controlled test cell conditions. The fuel consumption with the high cetane diesel was 0.5% lower; CO, HC, and NOx emissions were lower by 12%, 6%, and 8% respectively over the ESC. This paper also highlights mode-wise engine performance, emissions, noise, and combustion behavior of the engine while using a cetane improver in diesel over the ESC cycle. Noise level reduced by 1dB in the wide-open throttle performance tests when the cetane number increased by 3 units.

Selective CO2 reduction to methane catalyzed by mesoporous Ru-Fe3O4/CeOx-SiO2 in a fixed bed flow reactor

Development of a robust catalyst for selective reduction of CO2 directly into hydrocarbon fuels is very challenging from both energy and environmental perspectives as it offers a renewable and green route for the production of fuels. Herein, we report a novel catalyst synthesized via excess solution impregnation of Ru and Fe3O4 nanoparticles (NPs) on ceria promoted mesoporous silica SBA-15 support. The selective catalytic reduction of CO2 to methane was carried out in the presence of H2 over novel Ru-Fe3O4/CeOx-SiO2 (Ce3+/Ce4+, x=1.64) catalyst in a fixed bed reactor. The CO2 conversion was found to be 82% at 0.25 wt% ruthenium loading, 2.5 wt% iron loading, 575 K temperature, 20 bar pressure, 3000 mLg−1h−1 gas hour space velocity and H2 to CO2 mole ratio of 5:1. The close contact between ruthenium and Fe3O4 nanoparticles facilitated the reduction of CO2 through hydrogen spill-over effect at lower temperature, whereas ceria NPs acted as a promoter for this reduction reaction. The catalysts were characterized thoroughly using physicochemical techniques such as CO chemisorption, BET, TPR, TPD, XRD, SEM, HR- TEM, ICP-AES and XPS analyses. High surface area and large mesopores of silica support facilitated the fine dispersion of the active catalytic sites and oxygen vacancy as supported from the DFT study on the catalytic activity. Optimal process conditions could render much higher CO2 conversion efficacy for selective methane synthesis in comparison with previous investigations.

Insight into SO2 poisoning and regeneration of one-pot synthesized Cu-SSZ-13 catalyst for selective reduction of NO by NH3

The effects of SO 2 on an one-pot synthesized Cu-SSZ-13 catalyst for selective reduction of NO x by NH 3 were examined. The addition of SO 2 inhibited NO x conversion significantly below 300 o C, while no effect on NO x conversion was observed above 300 o C. TGA, TPD, and XPS results showed that the deactivation was caused by the formation of (NH 4 ) 2 SO 4 , SO 2 chemisorption on the isolated Cu 2+ ion sites, as well as the formation of CuSO 4 -like species. Among them, the site-blocking effect of (NH 4 ) 2 SO 4 on Cu 2+ was the primary reason for deactivation. Fortunately, 89% of deNO x activity of the poisoned catalyst was recovered after thermal treatment at 500 o C in air, where (NH 4 ) 2 SO 4 was completely decomposed. The activity was further recovered with regeneration temperature increasing to 600 o C, removing the adsorbed SO 2 on the Cu 2+ sites. The regeneration at 600 o C could not recover the activity completely, because of the high stability of CuSO 4 -like species.

Progress in Metal-Organic Framework Catalysts for Selective Catalytic Reduction of NOx: A Mini-Review

Nitrogen oxides released from the combustion of fossil fuels are one of the main air pollutants. Selective catalytic reduction technology is the most widely used nitrogen oxide removal technology in the industry. With the development of nanomaterials science, more and more novel nanomaterials are being used as catalysts for the selective reduction of nitrogen oxides. In recent years, metal-organic frameworks (MOFs), with large specific surface areas and abundant acid and metal sites, have been extensively studied in the selective catalytic reduction of nitrogen oxides. This review summarizes recent progress in monometallic MOFs, bimetallic MOFs, and MOF-derived catalysts for the selective catalytic reduction of nitrogen oxides and compares the reaction mechanisms of different catalysts. This article also suggests the advantages and disadvantages of MOF-based catalysts compared with traditional catalysts and points out promising research directions in this field.