NOx Reduction Research Articles

Selective Catalytic Reduction of Nitrogen Oxides with Hydrogen (H2‐SCR‐DeNO x ) over Platinum‐Based Catalysts

Selective catalytic reduction of NOx with hydrogen (H2‐SCR‐DeNOx) is applied among other techniques (i.e., SCR‐DeNOx by applying NH3 or hydrocarbons as reducing agents) to control nitrogen oxides from mobile and stationary sources. As a zero carbon technology, which efficiently reduces NOx below 200 °C, H2‐SCR‐DeNOx has gained attention in installations and plants with H2 availability. The catalytic properties and reaction mechanism of platinum‐based catalysts are given in detail. Also, Pd‐based catalysts are briefly reviewed. It is expected that the review will provide broad insights into the design and optimization of catalysts in the H2‐SCR‐DeNOx.

Essential features of weak current for excellent enhancement of NOx reduction over monoatomic V-based catalyst

Human society is facing increasingly serious problems of environmental pollution and energy shortage, and up to now, achieving high NH3-SCR activity at ultra-low temperatures (<150 °C) remains challenging for the V-based catalysts with V content below 2%. In this study, the monoatomic V-based catalyst under the weak current-assisted strategy can completely convert NOx into N2 at ultra-low temperature with V content of 1.36%, which shows the preeminent turnover frequencies (TOF145 °C = 1.97×10−3 s−1). The improvement of catalytic performance is mainly attributed to the enhancement catalysis of weak current (ECWC) rather than electric field, which significantly reduce the energy consumption of the catalytic system by more than 90%. The further mechanism research for the ECWC based on a series of weak current-assisted characterization means and DFT calculations confirms that migrated electrons mainly concentrate around the V single atoms and increase the proportion of antibonding orbitals, which make the V-O chemical bond weaker (electron scissors effect) and thus accelerate oxygen circulation. The novel current-assisted catalysis in the present work can potentially apply to other environmental and energy fields.

Enhanced activity and water resistance of SiO2-coated Co/In-SSZ-13 catalysts in the selective catalytic reduction of NOx with CH4

CH4 selective catalytic reduction of NOx (CH4-SCR) is a promising technology to synergistic control of CH4 and NOx emission from LNG-powered vehicles and ships, while its insufficient catalytic activity and H2O resistance are key barriers for application. In this work, SiO2 coated Co3O4/In-SSZ-13 catalysts (Co/In-Z@Si) were prepared to simultaneously improve the CH4-SCR activity and H2O tolerance. The proper Co3O4 introduction enhanced the catalytic performance of the In-SSZ-13, while excessive amount of Co3O4 addition led to more CH4 being oxidized and insufficient CH4 participating in the CH4-SCR reaction. There was a “seesaw effect” between NO oxidation and CH4 oxidation performance of the catalysts. The H2O resistance of the Co/In-Z catalysts significantly enhanced via ultrathin SiO2 coating. The NOx and CH4 conversion maintained 81 % and 90 % in the presence of H2O at 500 °C for the Co/In-Z@Si catalyst, respectively. The in situ DRIFTS confirmed that the SiO2 coating could adsorb H2O molecules, prevent H2O from contacting the active sites, and limit the competitive adsorption between H2O and CH4 on the catalyst. This work provides a good candidate with superior catalytic performance and H2O resistance for removal of NOx and CH4 from LNG-powered vehicles and ships simultaneously.

Synergistic approaches to NOx reduction: Fuel innovations and engine modifications in biomass waste-fueled CI engines

Achieving low nitric oxide emissions in biomass fuel combustion remains a challenge. This study aims at enhancement of NOx reduction by employing a sequence of strategies to arrive at the optimal combination of techniques. This work explores the role of nano particle emulsion, change in profile of combustion chamber geometry, exhaust gas recirculation rates and contribution of selective catalytic reduction (SCR) in the combustion and emission phenomena of CI engine. Cerium oxide and zinc oxide nanoparticles are added in emulsion form at 50 ppm and 100 ppm dosage to grapeseed oil biodiesel. Furthermore, combustion chamber geometry is modified to shallow depth and toroidal shape and tested with ZnO 100 nano blend of grapeseed oil biodiesel (GSBD). EGR at 5 %, 10 %, 15 % and 20 % rates are included in the toroidal shape after concluding that profile as the best performing geometry. A customized model of SCR is implemented to the above combination of ZnO fuel blend, toroidal combustion chamber geometry and 5 % EGR to further reduce NOx emission. SCR device is fabricated with suitable flow and injection parameters with dual type mixers to enhance its NOx conversion efficiency. Overall, this research work gives useful insights for development of NOx reduction strategies in biomass fuel combustion in CI engines. A comprehensive reduction of NOx from 9.3 g/kWh to 2.05 g/kWh is noticed at the end of cumulative set of experiments.

Selective Catalytic Reduction of NOx with NH3 Over Fe Modified MOF-Derived MnOx Catalyst

Selective Catalytic Reduction of NOx with NH3 Over Fe Modified MOF-Derived MnOx Catalyst

Impact of varying injection pressure on CI engine characteristics fuelled with Ceiba pentandra biodiesel and NOx reduction strategy

Impact of varying injection pressure on CI engine characteristics fuelled with <i>Ceiba pentandra</i> biodiesel and NOx reduction strategy

Numerical analysis of NOx reduction in large-scale MSW grate furnace through in-bed combustion optimization using multi-section fuel bed model with thermally thick treatment

This study focuses on reducing NOx emissions in large-scale municipal solid waste (MSW) grate furnaces through in-bed combustion control. A multi-section fuel bed model with thermally thick treatment is developed to accommodate the configurations of large-scale MSW grate furnaces. The model incorporates detailed sub-grid models to simulate the intraparticle gradient, and the stochastic mixing is accounted to deal with the multi-section fuel beds with vertical drop-offs. The influences of primary air distribution and average grate velocity on combustion status and NOx emissions are investigated numerically and validated in a 600 t/d MSW grate boiler. The results indicate that combining a relatively low primary air ratio with a thickened fuel bed ensures both reduced NOx emissions and high burnout efficiency. By reducing the excess air ratio of primary air from 1.2 to 0.9 and distributing it through a rear-enhanced air mode, the overall NOx emission decreased from 398.50 mg/Nm3 to 215.05 mg/Nm3, although at the expense of an increased unburned carbon content from 1.995 wt% to 3.063 wt%. Further lowering the grate velocity to thicken the fuel bed allowed for leveraging the heterogeneous reduction effect of the char layer, reducing the NOx emissions to 184.95 mg/Nm3. Additionally, the unburned carbon content was also remarkably reduced to 1.560 wt%. The proposed strategies of delaying the primary air supply and thickening the fuel bed offer a cost-effective alternative to post-combustion measures, with which the MSW grate boilers can achieve lower NOx emissions while maintaining efficient and stable combustion.

Revealing the boosting roles of sulfate groups on NOx selective catalytic reduction over V2O5/CeO2 catalyst

Ceria-supported vanadia (VOx/CeO2) catalyst has been extensively investigated in the field of NOx selective catalytic reduction with NH3 (NH3-SCR) but is limited in practical application owing to its poor sulfur resistance and high-temperature activity. Herein, a series of SO42− modified V2O5/CeO2 catalysts were fabricated to improve the overall catalytic performance. The 2 %SO42−-V2O5/CeO2 catalyst exhibited above 95 % NOx conversion, 90 % N2 selectivity in the temperature range of 225–400 °C and excellent SO2 + H2O tolerance, which was much better than V2O5/CeO2 catalyst. Characterization results showed that the introduction of SO42− over V2O5/CeO2 increased the Ce3+/(Ce3++ Ce4+) ratio to promote the formation of oxygen vacancies and promoted the generation of more conducive polymeric vanadyl species. The synergistic effect of the redox sites and acid centers provided moderate redox property and enhanced surface acidity, thus improving the adsorption of NH3 and inhibiting the over-oxidation of NH3 that occurs on V2O5/CeO2. In-situ DRIFTS indicated that the NOx reduction over V2O5/CeO2 and 2 %SO42−-V2O5/CeO2 followed the Langmuir-Hinshelwood and Eley-Rideal routes concurrently. This study can expound the reasonable design of vanadium-based catalysts for efficient NOx reduction in industry.

Effect of pre-injection strategy on the reduction of exhaust emissions from n-pentanol/biodiesel engine

N-pentanol can be used as an additive component of biodiesel to achieve NOx and soot emission reductions while improving the low-temperature fluidity of biodiesel. This paper investigates the mechanism of pre-injection strategies (pre-main injection interval and pre-injection ratio) on the emission characteristics of n-pentanol/biodiesel engines. It extends the study to investigate the effect pattern of pre-injection strategies on formaldehyde emissions. The results show that the emission characteristics of the n-pentanol/biodiesel engine can be effectively improved by using a pre-injection strategy compared to a single injection. With the pre-main injection interval increase, the in-cylinder combustion stability was improved, and the generation of NOx and soot was effectively suppressed. Compared to a single injection, a pre-main injection interval of 15 °CA resulted in a 15.38 % decrease in CA50 and an 18.32 % increase in IMEP. Meanwhile, the increase of the pre-main spray interval broke the trade-off relationship between NOx and soot, and when the main pre-spray interval was increased from 15 °CA to 30 °CA, Soot and NOx generation were reduced by 27.46 % and 21.30 %, respectively. As the proportion of pre-injection increases, the center of gravity of combustion is shifted forward, the combustion exotherm is more concentrated, and the soot emission is significantly reduced. When the percentage of pre-spray was increased from 0 % to 20 %, CA50 decreased by 19.23 %, IMEP increased by 1.32 %, and soot generation decreased by 61.02 %. When the proportion of pre-spray was increased from 15 % to 20 %, CH2O emissions were reduced by 14.81 %.

Unraveling the NH3-SCR-DeNOx Mechanism of Cu-SSZ-13 Variants by Spectroscopic and Transient Techniques.

Commercial SSZ-13 zeolite with different n(Si)/n(Al) ratios and from different suppliers were subjected to a post-synthetic treatment in order to create mesopores of up to 15 nm. Furthermore, the materials were modified with copper ions and thoroughly physico-chemically characterized. The modified textural properties varied the nature of copper species, and thus, activity in the selective catalytic reduction of NOx with ammonia (NH3-SCR-DeNOx). Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) studies with hexane as probe liquid revealed improved intracrystalline diffusion for some Cu-containing SSZ-13 materials. The NH3-SCR-DeNOx pathways are verified via in situ DR UV-Vis, in situ FT-IR and EPR, temperature-programmed studies as well as SSITKA studies that provide a mechanistic understanding of the reaction. Kinetic modelling results demonstrate the highest NH3-SCR-DeNOx reaction rates and up to 20 % lower energy barriers with n(Si)/n(Al) ratio of 6.5 for all modified forms (i. e., (NH4)Cu-SSZ-13_6.5 and Cu-SSZ-13_6.5_NaOH/0.1) and cause only negligible parasitic ammonia oxidation. The modelling of the stop-flow experiments further demonstrates that the SCR pathway via the HONO surface intermediate is present but barely contributes to the overall NO conversion compared to the dominant path between adsorbed NH3 and NO from the gas phase.

Effects of MOx modification (M = Mn, Ce, and Fe) on the SCR catalytic properties of the CrOx-WOx mixed oxide catalysts

In this study, a series of MOx-modified (M = Mn, Fe, and Ce) CrOx-WOx mixed oxides were synthesized via the sol-gel technique for the selective catalytic reduction of NOx with NH3. Given the addition of MnOx or CeOx, the availability of the catalyst surface acid sites tended to decline, which negatively affected the proceeding of the deNOx process. Moreover, the retention of oxidative ability by introducing MnOx also favored the over-oxidation of NH3, which accelerated the additional formation of NOx and created a crucial barrier for the increment in the higher-temperature deNOx activity. Apparently, <80 % of the NOx could be effectively eliminated from the working gas within the whole temperature range for the CrCeW and CrMnW samples. By contrast, doping FeOx was able to introduce ample acid sites onto the catalyst surfaces, which was beneficial for the adsorption of NH3 and subsequently the facilitation of the progression of the deNOx process. Furthermore, the weakened oxidizability suppressed the over-oxidation of NH3. Consequently, a broad operating temperature window was obtained for the FeOx-doped catalyst; >90 % NOx conversion efficiency was achieved in the temperature range of 230–450 °C. During the deNOx process, the Eley-Rideal mechanism dominated over the four investigated samples.

Mn-Based Catalysts in the Selective Reduction of NOx with CO: Current Status, Existing Challenges, and Future Perspectives

Mn-Based Catalysts in the Selective Reduction of NOx with CO: Current Status, Existing Challenges, and Future Perspectives

Unlocking the potential of novel ternary non-edible seed oil biodiesel: impact on diesel engine knock intensity, performance, combustion, and emissions

The escalating demand for sustainable energy sources amid dwindling fossil fuel reserves prompts an exploration into innovative biodiesel alternatives for automotive applications. This study investigates a unique ternary mixture comprising non-edible seed oils from Azadirachta indica (Neem), Argemone mexicana (Satyanashi), and Melia azedarach (Bakayan) for biodiesel production and its potential as an alternative to conventional diesel. The ternary blend, extracted using a mechanical oil press, achieved a raw oil yield of 32%. Optimising process parameters, including a 93% biodiesel yield, was attained with a methanol to oil molar ratio of 6:1, 0.6% NaOH by weight, and a temperature of 60°C for 60 min. Performance testing of blends in a computerised single-cylinder, 4-stroke CI engine revealed notable improvements in brake thermal efficiency, with the B80 blend demonstrating the most significant reduction in brake-specific fuel consumption by 8.5%. The B100 blend exhibited the highest brake thermal efficiency at 37.6%. Emission analyses demonstrated reductions in CO and CO2 emissions, with the NOx reduction percentages varying for different blends. Notably, all blends exhibited comparable in-cylinder pressure and ignition delays with diesel, indicating the potential of the ternary seed oil mixture biodiesel as a viable diesel fuel substitute in CI engines.

Summertime Ozone Production at Carlsbad Caverns National Park, New Mexico: Influence of Oil and Natural Gas Development

AbstractSoutheastern New Mexico's Carlsbad Caverns National Park (CAVE) has increasingly experienced summertime ozone (O3) exceeding an 8‐hr average of 70 parts per billion by volume (ppbv). The park is located in the western part of the Permian oil and natural gas (O&amp;G) basin, where production rates have increased fivefold in the last decade. We investigate O3–precursor relationships by constraining the F0AM box model to observations of nitrogen oxides (NOx = NO + NO2) and a suite of volatile organic compounds (VOCs) collected at CAVE during summer 2019. O&amp;G‐related VOCs dominated the calculated VOC reactivity with hydroxyl radicals (OH) on days when O3 concentrations were primarily controlled by local photochemistry. Radical budget analysis showed that NOx levels were high enough to impose VOC sensitivity on O3 production in the morning hours, while subsequent NOx loss through photochemical consumption led to NOx‐sensitive conditions in the afternoon. Maximum daily O3 was responsive to both NOx and O&amp;G‐related VOC reductions, with NOx reductions proving most effective. The model underestimated observed O3 during a 5‐day high O3 episode that was influenced by photochemically aged O&amp;G emissions, as indicated by back‐trajectory analysis, low i‐/n‐pentane ratios, enhanced secondary VOCs, and low ratios of NOx to total reactive oxidized nitrogen (NOy). Model‐observation agreement was improved by constraining model NOx with observed NOy, which approximates NOx at the time of emission, indicating that a large fraction of O3 during this episode was formed nonlocally.

Accurately Predicting Spatiotemporal Variations of Near-Surface Nitrous Acid (HONO) Based on a Deep Learning Approach.

Gaseous nitrous acid (HONO) is identified as a critical precursor of hydroxyl radicals (OH), influencing atmospheric oxidation capacity and the formation of secondary pollutants. However, large uncertainties persist regarding its formation and elimination mechanisms, impeding accurate simulation of HONO levels using chemical models. In this study, a deep neural network (DNN) model was established based on routine air quality data (O3, NO2, CO, and PM2.5) and meteorological parameters (temperature, relative humidity, solar zenith angle, and season) collected from four typical megacity clusters in China. The model exhibited robust performance on both the train sets [slope = 1.0, r2 = 0.94, root mean squared error (RMSE) = 0.29 ppbv] and two independent test sets (slope = 1.0, r2 = 0.79, and RMSE = 0.39 ppbv), demonstrated excellent capability in reproducing the spatiotemporal variations of HONO, and outperformed an observation-constrained box model incorporated with newly proposed HONO formation mechanisms. Nitrogen dioxide (NO2) was identified as the most impactful features for HONO prediction using the SHapely Additive exPlanation (SHAP) approach, highlighting the importance of NO2 conversion in HONO formation. The DNN model was further employed to predict the future change of HONO levels in different NOx abatement scenarios, which is expected to decrease 27-44% in summer as the result of 30-50% NOx reduction. These results suggest a dual effect brought by abatement of NOx emissions, leading to not only reduction of O3 and nitrate precursors but also decrease in HONO levels and hence primary radical production rates (PROx). In summary, this study demonstrates the feasibility of using deep learning approach to predict HONO concentrations, offering a promising supplement to traditional chemical models. Additionally, stringent NOx abatement would be beneficial for collaborative alleviation of O3 and secondary PM2.5.

Designing VWTi-based catalysts with K resistance via Ce-S modification for selective catalytic reduction of NOx

Selective catalytic reduction (SCR) with NH3 is the main reaction to eliminate nitrogen oxide, and the access of K+ to the catalyst surface severely deactivates the physicochemical properties. To inhibit the deactivation of the catalyst by potassium (K), we synthesized VWCeSTi. In the current study, the catalyst surface was functionalized with cerium sulfate (Ce-S) as a method to suppress K+ deactivation, and the physicochemical properties of the functionalized catalyst were explored. In VWCeSTi, Ce has a low electronegativity compared with V and W; hence, sulfated Ce has a relatively abundant electronic state. Therefore, the approach of the K+ ion in an electron-deficient state leads to the preferential binding of S with K, forming K2SO4 and inhibiting chemical deactivation. Additionally, the addition of Ce-S resulted in improved NH3 adsorption ability, the amount of defective metal species, and participating oxygen. Thus, the modified (Ce-S) catalyst showed improved SCR performance and increased resistance to K.

Sb-loaded MnOx/TiO2/CNTs catalysts for selective catalytic reduction of NOx: insight to the SO2 and H2O tolerance

PurposeThis paper aims to synthesize and test Mn-Sb/TiO2-CNT catalysts with different Sb/Mn molar ratios to be used in NH3-SCR reaction.Design/methodology/approachA series of Sb-loaded carbon nanotubes (CNTs)-based Mn/TiO2 catalysts were prepared by the incipient wetness co-impregnation method and tested for the selective catalytic reduction (SCR) of NOx with NH3.FindingsThe Sb-loaded Mn/TiO2-CNTs catalyst outperformed other catalysts and presented the highest activity in the temperature regime of 100–400°C. The catalyst loaded with Sb also showed good SO2 and H2O resistance and exhibited better thermal stability. A stepwise study of SO2 addition evidenced that Mn-Sb/TiO2-CNTs catalyst exhibited better SO2 resistance than the base catalyst Mn/TiO2, where the Sb doping greatly inhibited the sulphating of active phase of the catalyst.Originality/valueIn Sb-loaded catalysts, the formed SOx species fused with SbOx instead of MnOx. This favoured interaction of SO2 with SbOx successfully prevents the MnOx from being sulphated by SO2 which substantially improves the SO2 tolerance of Sb-loaded catalysts.

Experimental study on combustion characteristics of a 40 MW pulverized coal boiler based on a new low NOx burner with preheating function

In this study, a novel low NOx burner is proposed and tested on a 40 MW pilot pulverized coal combustion system, aiming to experimentally investigate the impact of preheating temperature, air ratio distribution, and thermal power on furnace combustion characteristics. The experimental results demonstrate that the pulverized coal could be preheated stably above 700 °C in the designed burner. Furthermore, an increase in preheating temperature from 500 °C to 750 °C corresponds to a proportional rise in the total volume fraction of combustible pyrolysis gases released from pulverized coal, ranging from 18.34 % to 22.85 %. Consequently, the release and combustion of pyrolysis gases effectively improve the combustion characteristics within the boiler furnace and lead to reduced NOx emissions at the furnace outlet. When the thermal power is increased from 22.5 MW to 37.5 MW, the NOx emissions at the furnace output range from 46.8 mg/Nm3 to 98.3 mg/Nm3 (at 9 % O2). Under a specific thermal power of 25MWth, the boiler furnace output NOx emissions are reduced to 47.9 mg/Nm3 (@9 % O2) without any additional NOx reduction equipment. These findings offer valuable insights for advancing cleaner and more efficient low-NOx pulverized coal combustion technology.

Impact of sulfur exposure on high-temperature Cu speciation in SSZ-13 Zeolites

Metal active sites exchanged in zeolites dynamically change speciation under different reaction conditions, resulting in condition-dependent reactivity with gas molecules. This is of particular significance in chemical deactivation, such as sulfur poisoning of Cu-SSZ-13 zeolites used for NH3-assisted selective catalytic reduction (SCR) of NOx in diesel engine exhaust. Here, we employ computational techniques, combined with experiments and spectroscopies, to develop thermodynamic models for sulfur poisoning of zeolite framework-bound Cu dimers that form at high temperatures in Cu-SSZ-13 zeolites as a function of both the Al distribution and reaction conditions. Our results demonstrate that framework-bound Cu dimers that form under high temperature oxidative conditions are particularly susceptible to poisoning by SO2 and SO3. These Cu dimers react more exothermically with SOx species than Cu monomers, forming thermodynamically stable sulfur-containing Cu dimers that require high temperatures for catalyst regeneration.

Nitrogen oxides removal from hydrogen flue gas using corona discharge in marine boilers: Application perspective

This paper focuses on the combustion of hydrogen in boilers, as it appears to be a more effective method than using fuel cells for heating purposes due to higher boiler efficiency. One of the main disadvantages of hydrogen combustion in air is NOx formation. Therefore, the authors decided to introduce corona discharge as an innovative technique to clean hydrogen flue gas by effectively reducing NOx levels. The method involves generating positive plasma at atmospheric pressure by applying up to a 23 kV voltage difference between rod and ring-shaped electrodes. Experimental studies have shown that corona discharge can significantly lower the concentrations of NO and NOx in exhaust gases. The maximum DeNOx level was found to be 32.3%, while the plasma generator uses 17.5% of the power contained in burned hydrogen. The findings suggest that this technology holds potential for application in industrial hydrogen combustion systems, offering an environmentally friendly alternative to conventional NOx reduction methods.