NOx Reduction Research Articles

The Impacts of COVID-19 Lockdowns on Road Transport Air Pollution in London: A State-Space Modelling Approach.

The emergence of the COVID-19 pandemic in 2020 led to the implementation of legal restrictions on individual activities, significantly impacting traffic and air pollution levels in urban areas. This study employs a state-space intervention method to investigate the effects of three major COVID-19 lockdowns in March 2020, November 2020, and January 2021 on London's air quality. Data were collected from 20 monitoring stations across London (central, ultra-low emission zone, and greater London), with daily measurements of NOx, PM10, and PM2.5 for four years (January 2019-December 2022). Furthermore, the developed model was adjusted for seasonal effects, ambient temperature, and relative humidity. This study found significant reductions in the NOx levels during the first lockdown: 49% in central London, 33% in the ultra-low emission zone (ULEZ), and 37% in greater London. Although reductions in NOx were also observed during the second and third lockdowns, they were less than the first lockdown. In contrast, PM10 and PM2.5 increased by 12% and 1%, respectively, during the first lockdown, possibly due to higher residential energy consumption. However, during the second lockdown, PM10 and PM2.5 levels decreased by 11% and 13%, respectively, and remained unchanged during the third lockdown. These findings highlight the complex dynamics of urban air quality and underscore the need for targeted interventions to address specific pollution sources, particularly those related to road transport. The study provides valuable insights into the effectiveness of lockdown measures and informs future air quality management strategies.

Ultra-low temperature selective catalytic reduction of NOx into N2 by micron spherical CeMnOx in high-humidity atmospheres containing SO2

The solvothermal synthesis of optimized micron-sized spherical Ce1Mn7Ox-350 yields remarkable results in ultra-low temperature NH3-SCR of NOx, with over 91 % NOx conversion achieved between 59 and 255 ℃. Notably, under 5 vol% H2O and 50 ppm SO2, the Ce1Mn7Ox maintains NOx conversion >99 % at 127 ℃ for extended periods, surpassing current ultra-low temperature deNOx standards. This superior performance is attributed to the material's unique characteristics: the regular and porous surface morphology enhances exposure to active sites, particularly Mn3O4(112) facets crucial for ultra-low temperature deNOx, while the rough and loose surface and high Mn2O3(222) exposure mitigate water vapor and SO2 poisoning. Furthermore, the thermal storage effect of the Mn2O3/Mn3O4 system within Ce1Mn7Ox facilitates rapid thermal dissipation and ammonium sulfite decomposition. This process is further augmented by the pores, which aid in the confinement of deNOx reaction heat and facilitate the flushing of flowing flue gas, thereby impeding the formation of ammonium bisulfate.

Efficient natural gas combustion and NOx reduction: A novel application of simultaneous over-fire air (OFA) and flue gas recirculation (FGR) in a 250 MW opposed firing steam power plant boiler

OFAGR, as a new controllable technology, combines over-fire air (OFA) and flue gas recirculation (FGR) systems for modifying combustion characteristics and enhancing boiler efficiency. It also reduces NOx generation considerably. The effects of OFA and FGR on the combustion are reported for coal-fired boilers, however, no reference was found for the application of OFAGR, especially in boilers with natural gas fuel so far. Furthermore, the method of adjusting the ratio of OFA and FGR in OFAGR nozzles to achieve the required combustion modification is not investigated and this fact should be even covered for different types of boilers. For analysis of complicated combustive mixed fuel (natural gas) and air in furnace, computational fluid dynamics (CFD) simulated the flow by the use of Eddy-Dissipation Concept (EDC) and developing reactions by Jones-Lindstedt mechanism. Simulation results are validated by the measured boiler operation data for a 250 MW steam power plant boiler. The staged combustion in each burner is modeled by considering three inlet air flows (primary, secondary, and tertiary) with swirl. The effects of different ratios of OFA and FGR streams on characteristics of combustion and NOx production are investigated. The combustion efficiency, temperature profile, distribution of species, and the transferred heat flux to water-walls are computed, and analyzed. Results showed injecting only OFA from OFAGR nozzles, reduced NOx generation up to 55.4 % but lowered the furnace efficiency from 95.3 % to 93.1 %. When the OFAGR stream contained 25 % FGR and 75 % OFA (case study 2), an ideal state existed for increasing the combustion efficiency from 95.3 % to 96.0 % and NOx reduction by 58 %. Increasing the share of FGR in the OFAGR stream by more than 25 % improved the NOx reduction but reduced the combustion efficiency from 95.3 % due to the drop in the usable absorption heat of the boiler. Calculations showed that the OFAGR injection stream containing 64.1 % OFA and 35.9 % FGR reduced NOx formation from 274 to 112 ppm without losing furnace efficiency.

Effect of Tourmaline Addition on the Anti-Poisoning Performance of MnCeOx@TiO2 Catalyst for Low-Temperature Selective Catalytic Reduction of NOx.

In view of the flue gas characteristics of cement kilns in China, the development of low-temperature denitrification catalysts with excellent anti-poisoning performance has important theoretical and practical significance. In this work, a series of MnCeOx@TiO2 and tourmaline-containing MnCeOx@TiO2-T catalysts was prepared using a chemical pre-deposition method. It was found that the MnCeOx@TiO2-T2 catalyst (containing 2% tourmaline) exhibited the best low-temperature NH3-selective catalytic reduction (NH3-SCR) performance, yielding 100% NOx conversion at 110 °C and above. When 100-300 ppm SO2 and 10 vol.% H2O were introduced to the reaction, the NOx conversion of the MnCeOx@TiO2-T2 catalyst was still higher than 90% at 170 °C, indicating good anti-poisoning performance. The addition of appropriate amounts of tourmaline can not only preferably expose the active {001} facets of TiO2 but also introduce the acidic SiO2 and Al2O3 components and increase the content of Mn4+ and Oα on the surface of the catalyst, all of which contribute to the enhancement of reaction activity of NH3-SCR and anti-poisoning performance. However, excess amounts of tourmaline led to the formation of dense surface of catalysts that suppressed the exposure of catalytic active sites, giving rise to the decrease in catalytic activity and anti-poisoning capability. Through an in situ DRIFTS study, it was found that the addition of appropriate amounts of tourmaline increased the number of Brønsted acid sites on the catalyst surface, which suppressed the adsorption of SO2 and thus inhibited the deposition of NH4HSO4 and (NH4)2HSO4 on the surface of the catalyst, thereby improving the NH3-SCR performance and anti-poisoning ability of the catalyst.

Evaluation of performance, emissions and combustion attributes of diesel engines powered by Palmyra biodiesel blends with distinct injection pressures and EGR rates

The present work explores the viability of Palmyra oil methyl ester (POME) as a renewable biodiesel. Initially, oil is extracted from the Palmyra fruit and the oil is transesterified to produce Palmyra oil methyl ester. Preliminary tests were conducted with blends of Palmyra oil methyl esters. From the test results, it was found that the POME20 blend performed better than other blends and was considered as an optimised blend. Secondly, analysis was carried out with POME20 on the CI engine at three injection pressures (210bar, 230bar and 250bar). POME20 at 230bar was shown to have improved thermal efficiency and reduced emissions of CO, HC and CO2 except NOX emissions. Finally, the tests were repeated for optimal conditions of 230bar injection pressure along with 6% and 12% EGR rates. The experimental results revealed that POME20 operated at 230bar 6% EGR rate observed a drastic reduction of NOX by 32.08% and 57.49% compared to diesel and POME20.

TiO2-Supported Catalysts in Low-Temperature Selective Reduction of NOx with NH3: A Review of Recent Progress

Selective catalytic reduction (SCR) stands out as a pivotal method for curbing NOx emissions from flue gas. The support, crucially, for SCR efficacy, loads and interacts with the active components within the catalyst. The catalysts could be amplified by the denitration performance of the catalyst by enhancements in support pore structure, acidity, and mechanical robustness. These improvements ensure efficient interaction between the support and active materials, thereby optimizing the structure and property of the catalysts. TiO2 is the most commonly used support of the NH3-SCR catalyst. The catalyst with TiO2 support has poor thermal stability and a narrow temperature range, which can be improved. This paper reviews the research progress on the effects of various aspects of TiO2 support on the NH3-SCR catalyst’s performance, focusing on the TiO2 crystal type, TiO2 crystal surface, different TiO2 structures, TiO2 support preparation methods, and the effects of TiO2-X composite support on the NH3-SCR catalyst’s performance. The reaction mechanism, denitrification performance, and anti-SO2/H2O poisoning performance and mechanism of TiO2 support with different characteristics were described. At the same time, the development trend of the NH3-SCR catalyst using TiO2 as the support is prospected. It is hoped that this work can provide optimization ideas for SCR catalyst research.

A comparative study of gas temperature determination in non-thermal atmospheric pressure plasma jet by spectral analysis and scattering technique for plasma-catalyst measurements

Comparison and validation of different methods for the measurements of plasma gas temperature were studied. The investigations depend on optical emission spectroscopy OES, laser scattering technique, and line-broadening mechanisms. The rotational temperature of the second positive system SPS (C3 ∏+ u - B3 ∏+ g) around 380 nm, second positive system SPS at 337.1 nm of nitrogen molecule (C3 ∏+ u - B3 ∏+ g), and first negative system FNS at 391.4 nm of nitrogen ion (B2Σu +→X2Σg +) were investigated. Moreover, Raman scattering spectra at 532 nm were used to measure the gas temperature in the plasma jet. Gas temperature from the emission line broadening method was also calculated. The role of non-thermal plasma in assisting NOx reduction over an Ag/Al2O3 catalyst at low temperatures using simulated diesel fuels (toluene) was confirmed. Importantly, a significant activity of both NOx and hydrocarbons oxidation was observed and obtained at low gas temperatures. It was found that there is a clear correlation between the gas temperature and the conversion efficiency of the catalyst under different operating conditions of the plasma reactor. The main objective of this investigation was to confirm the important role of the non-thermal plasma in catalyst activation at low gas temperatures compared to traditional thermal activation.

A new insight on surface chemistry and redox species of transition metal (Fe, Mn) doped CeO2-SnO2/Al2O3 nanocomposites for automobile emission control

The ceria-tin/alumina mixed metal oxides (Ce/Sn =1) with different proportions of Fe & Mn dopants were synthesized and investigated in detailed approach for diesel emission reduction. The dopants created structural defects enhancing the oxygen ion mobility for exhaust treatment. The existence of surface-active oxygen sites and oxygen ion vacancy sites generated for charge compensation due to reduction of Ce4+, Sn4+ and dopants incorporation evidenced from XPS analysis. The Mn doped sample holds better physicochemical properties than Fe doped sample. The Mn doped sample with higher surface area of about 101.32 m2 g−1 exhibits greater active sites for better catalytic activity. The redox couples in the Mn-doped sample Ce4+/Ce3+, Sn4+/Sn2+, and Mn3+/Mn2+ helps in oxygen regeneration to contribute to exhaust treatment by oxygen ion conduction from bulk to the surface. This sample exhibited the 92 % of NOx reduction and proved to be a dynamic candidate for diesel emission reduction.

Benchmarking of primary measures to achieve lowest NOx emissions in small-scale biomass grate furnaces

Despite recent progress, NOx is still a major problem in biomass combustion, especially when using fuels with high nitrogen contents. The aim of this work was to determine the minimum NOx emissions achievable by applying primary measures in small-scale biomass grate furnaces. For this purpose, a new benchmark for furnaces using double air staging was defined on the basis of three different plants. An experimental study with different biomass fuels was conducted in two of these plants to systematically improve this benchmark.The results show that the new NOx benchmark using double air staging is up to 39 % lower than values achieved with conventional single air staging. Furthermore, this new benchmark was improved by extending the reduction zone, additionally reducing the NOx by up to 30 %. Secondary flue gas recirculation and partial load further reduced the NOx emissions.By combining the primary measures investigated in the 70-kW furnace, NOx emissions were achieved that were up to 70 % lower than those from other small-scale furnaces described in the literature. This efficiency also applies to fuels with a high nitrogen content, so that secondary NOx reduction measures can be avoided in most cases in furnaces in the future by taking this approach.

Investigating the Impact of Steam Enhancement on Combustion in a Swirl-Assisted Jet-Stabilized Gas Turbine Combustor

Abstract A newly developed gas turbine combustor system based on the swirl-assisted jet-stabilized concept using Jet A-1 and natural gas as reference fuel is tested under wet conditions to evaluate its combustion characteristics in the presence of steam. The effect of steam injection into the gas turbine combustor under both spray and superheated liquid fuel injection conditions is studied experimentally on an atmospheric test rig. To evaluate the effect of steam injection on combustion performance, the water-to-gas ratio (WGR) is varied from 0 to 32%. With increasing WGR = 0 to 16% and at stoichiometric condition, NOx reductions of -82% to -100% were observed during Jet A-1 and natural gas combustion, respectively. It is shown that the reduction of the combustion zone temperature due to the steam acting as a heat sink is the main cause of the NOx decrease. The operating range of the burner remained fairly constant for Jet A-1 until WGR = 20%, while it decreased significantly with increasing WGR for natural gas combustion. While the effect of the WGR on CO was modest, the greatest effect of the WGR was on the heat release zone intensity at a constant air to fuel ratio. In reducing the NOx levels of Jet A-1 and natural gas combustion, both thermal and chemical effects of steam injection were observed. However, steam acting as a heat sink and lowering the flame temperature, thereby reducing the thermal NO formation rate, was the dominant factor in NOx reduction.

Excellent performance of Ce doped CoMn2O4/TiO2 catalyst in NH3-SCR of NOx under H2O&SO2 conditions

Mn-based catalysts have become a research hotspot for low-temperature NH3-SCR, and the improvement of anti-SO2 poisoning performance is crucial to promote their industrial application for NH3 selective catalytic reduction of NOx. In this work, the CoMn2O4/Ce-TiO2 catalyst was able to maintain 95 % NOx conversion even in the presence of 10 vol% H2O+50 ppm SO2 for 24 h at 250 °C.The excellent performance was attributed to the large mesoporous structure, specific surface area, and the enhancement of acid and redox properties associated with the catalysts. The Ce doped CoMn2O4/Ce-TiO2 catalyst maintained Mn3+, Mn4+ and Co3+ in high concentrations on the surface, which improved the lattice oxygen mobility, and the electron transfer and interaction. The presence of more Ce4+ provided higher SCR activity due to the strong oxygen storage migration and also release ability. The reaction process of NH3-SCR for NOx removal on the surface of CoMn2O4/Ce-TiO2 catalyst mainly followed the Eley-Rideal (E-R) mechanism. The NH3 adsorbed on the catalyst surface reacted mainly with NO/NO2 species, even under H2O&SO2. The E-R reaction mechanism on the surface of CoMn2O4/Ce-TiO2 catalyst was less restricted by the inhibition of H2O&SO2. This is one of the primary reasons for the superior anti-sulfur toxicity performance of the catalyst. This work opens a new avenue for the design of efficient and environmentally friendly NH3-SCR catalysts with good application prospects.

Changing ozone sensitivity in Fujian Province, China, during 2012–2021: Importance of controlling VOC emissions

In the troposphere, ozone (O3) formation can be limited by NOx, VOCs, or both, complicating efforts to reduce O3 by controlling its precursors. This study used formaldehyde (HCHO) data and nitrogen dioxide (NO2) data from the Ozone Monitoring Instrument (OMI) to analyze O3 formation sensitivity in Fujian from 2012 to 2021. Over the past decade, an 8.7% reduction in NO2 VCDs and a 9.91% increase in HCHO VCDs were observed. Due to differences in the primary driving factors, HCHO VCDs exhibit a characteristic seasonal pattern with higher in summer and lower in winter, whereas NO2 VCDs show the opposite trend. O3 formation chemistry was accurately diagnosed by combining satellite-based data and ground-based O3 data. A new threshold value (3.3–4.6) was derived to determine the transition from VOC-limited to NOx-limited O3 formation regimes. Results showed that O3 sensitivity exhibited pronounced seasonal variations. The VOC-limited regime predominates throughout the entire Fujian region in winter, whereas it occupies only 5% of the area in summer. A VOC-limited region was found widely across Fujian on an annual average, but it decreased by 24% over 10 years. Transitional areas experienced a 19% increase. In two natural emission reduction cases (reductions during the Chinese Lunar New Year holiday and reductions in weekend traffic emissions compared to weekdays), ground-level O3 effectively captured the impacts of sensitivity changes. The impact suggests that when Fujian is in the VOC control region, a significant reduction in NOx, without effective VOC control, might lead to an O3 increase. The importance of controlling VOC emissions is highlighted in Fujian. This study enhances the understanding of O3 formation regimes in southeastern China, which is crucial for developing O3 prevention and control strategies.

Low-silica chabazite zeolites for NOx reduction: Tailoring the active center of Cu2+-2Z and [Cu(OH)]+-Z through the regulation of CHA-cages opening

Low-silica chabazite (CHA) catalysts with varying configurations of Cu2+-2Z and [Cu(OH)]+-Z active centers are developed through the regulation of the opening of CHA-cages. The catalysts are subsequently applied to the selective catalytic reduction of NOx by NH3 (NH3-SCR) reactions. A series of characterizations and performance evaluations indicate that the density of [Cu(OH)]+-Z in eight-member rings (8MRs) is positively correlated with low-temperature performance. Moreover, the presence of partial Cu2+-2Z in six-member rings (6MRs) enhances activity and tolerance at high temperatures. The residual K+ ions in the CHA-cages after NH4+ exchange are retained in the 6MRs. Density functional theory calculations demonstrate that the residual K+ ions stabilize the 6MRs structure, ensuring the entry and stable presence of the active Cu2+-2Z centers. In situ analysis reveals the reaction intermediates involved in the NH3-SCR process on representative catalysts. These findings can further elucidate the active centers of CHA-type catalysts and guide the design of commercial catalysts.

Studies on NOx formation and reduction characteristics in high-ash, low-volatile coal combustion by mechanism experiments and industrial-scale trials

Mechanism experiments were performed to investigate NOx formation and reduction during the combustion of high-ash, low-volatile coal. Additionally, industrial-scale trials were conducted to study the effects of air-staging degree on the combustion and NOx emission characteristics of high-ash coal on a 350 MW supercritical down-fired boiler. The results showed that the total BET specific surface area, total pore volume and porosity values of high-ash coal (HAC) and ultra-high-ash coal (UHAC) were all larger than those of normal-ash coal (NAC), whereas NAC contained more N-5 and N-6 than HAC and UHAC. The carbon layer structure of HAC char was less ordered and the content of hydroxyl group was relatively high. The overall NO reduction ratio obtained using the HAC char was higher than the value for the UHAC char. However, in the high temperature range of 1300–1400 °C, NO reduction associated with UHAC char was accelerated because of catalysis by ash. On increasing the excess oxygen ratio λ from 1.0 to 1.2, the char-N conversion shown by the UHAC char slowly increased and remained the lowest among the three chars. When burning UHAC, as the ratio of secondary to tertiary air fluxes, Rst, was decreased from 1.56 to 0.57, heating of the fuel-rich coal/air flow slowed and pulverized coal combustion was inhibited. The situation associated with HAC was different. At the Rst of 1.11, the ignition distance of fuel-rich flow was the shortest at 1.50 m, and the overall temperature in the furnace was the highest. However the NOx emissions at the furnace exit were as high as 715 mg/m3 (6 % O2) in this condition. Decreasing Rst to 0.57 reduced this value to 634 mg/m3 (6 % O2) with carbon levels in the fly ash and slag of 5.17 % and 3.67 %, respectively. Air-staging combustion is evidently a reasonable approach to controlling NOx emissions when burning HAC. While for UHAC, it was necessary to appropriately reduce the air-staging degree to enhance combustion and maintain low NOx emissions.

Interface Induced by Hydrothermal Aging Boosts the Low-Temperature Activity of Cu-SSZ-13 for Selective Catalytic Reduction of NOx.

Hitherto, sulfur poisoning and hydrothermal aging have still been the challenges faced in practical applications of the Cu-SSZ-13 catalyst for the selective catalytic reduction (SCR) of NOx from diesel engine exhaust. Here, we elaborately design and conduct an in-depth investigation of the synthetic effects of hydrothermal aging and SO2 poisoning on pristine Cu-SSZ-13 and Cu-SSZ-13@Ce0.75Zr0.25O2 core@shell structure catalysts (Cu@CZ). It has been discovered that Cu@CZ susceptible to 750 °C with 5 vol % H2O followed by 200 ppm SO2 with 5 vol % H2O (Cu@CZ-A-S) could still maintain nearly 100% NOx conversion across the significantly wider temperature region of 200-425 °C, which is remarkably broader than that of the Cu-SSZ-13-A-S (300-400 °C) counterpart. The experimental results show that the hydrothermal aging process results in the migration of highly active Cu species within the cage of Cu-SSZ-13 to the CZ surface, forming CuO/CZ with abundant interfaces, which significantly enhances the adsorption and subsequent activation of NO, leading to the generation of reactive N2O3 and HONO intermediates. Moreover, density functional theory (DFT) calculations reveal that the H of the HONO* species can function as Brønsted acid sites, effectively adsorbing NH3 to generate the active NH4NO2* intermediate, which readily decomposes into N2 and H2O. Furthermore, this pathway is the rate-determining step with an energy barrier of 0.93 eV, notably lower than that of the "standard SCR" pathway (1.42 eV). Therefore, the formation of the new CuO/CZ interface profoundly boosts the low-temperature NH3-SCR activity and improves the coresistance of the Cu@CZ catalyst to sulfur poisoning and hydrothermal aging.

Unveiling the mechanistic insights into the potassium resistance of 3.5 W-V-1 %K NH3-SCR catalysts: The dual functionality of V-O-W structure as acid and redox sites

The poisoning effect of alkali metals over Vanadium-based catalysts still faced a significant challenge in the selective catalytic reduction of NOx with NH3 (NH3-SCR). In order to improve the alkali (mainly potassium resistance) resistance of the Vanadium-based catalysts, WO3 was introduced into the vanadium oxide catalysts. The obtained 3.5WO3-V2O5(3.5 W-V) catalyst exhibited the excellent low-temperature NH3-SCR performance owing to the formation of V-O-W structures. Noteworthily, when 1 wt% K was introduced into the 3.5 W-V catalyst, vanadium oxide (V-O, V=O) species preferentially bonded to alkali metal K as an acidic sacrifice site, prompting more active V-O-W species to remain. Thus, the 3.5 W-V catalyst also possessed excellent alkali resistance. The NH3-TPD results showed that the 3.5 W-V-1 %K catalyst had a considerable acid site to ensure the adsorption capacity of NH3, while the XPS results showed that the 3.5 W-V-1 %K catalyst had excellent redox performance to ensure the activation capacity of the reactant NH3. Moreover, in-situ DRIFTS transient experiments revealed that the 3.5 W-V and 3.5 W-V-1 %K catalysts were more capable of adsorbing and activating NH3 species to rapidly react with gaseous NO, obeying the Eley-Rideal (E-R) pathway in NH3-SCR reaction. This work provides new insights into poisoning resistant of vanadium-based catalysts.

Selective catalytic reduction of NOx by NH3 at low temperature over Mn0.5Zr(0.5-x)Fex catalyst with different Fe/Zr ratios

ABSTRACT Through a basic co-precipitation technique, a series of Mn0.5Zr(0.5-x)Fex ternary oxide catalysts with different Fe/Zr ratios have been prepared and applied to the selective catalytic reduction of NOx. The results of catalytic activity test show that the Mn0.5Zr0.2Fe0.3 catalyst with a molar ratio of Fe/Zr of 3:2 has the most effective denitrification activity at low temperature and displays considerable tolerance to SO2 and H2O. The Mn0.5Zr0.2Fe0.3 catalyst exhibits a combination of physical and chemical attributes, including an elevated specific surface area and a homogeneously distributed active component, which collectively furnish additional points of interaction for the reacting gases, thus improving the catalytic performance. In addition, the high Mn4+/Mnn+ and Fe2+/Fen+ ratios, strong redox capacity, and more acidic sites on the surface of the catalyst also have positive effects on its denitrification performance. Meanwhile, the reaction process on Mn0.5Zr0.2Fe0.3 catalyst is driven by the Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms. This study provides an important reference for the design of Mn-based catalysts with high denitration performance and excellent resistance to SO2 and H2O.

Development of an Onboard Urea Electrolyser to Reduce NOx Emissions in Vehicles By Enhancing the Selective Catalytic Reduction with the Produced H2 and NH3

In the persistent pursuit of reducing nitrogen oxide emissions from diesel exhaust, challenges arise in achieving optimal performance at lower temperatures, especially in urban driving conditions. This research focuses on a pragmatic approach – development of an onboard urea electrolyser using diesel exhaust fluid (DEF) as the hydrogen-rich carrier. The primary goal is to enhance the NOx reduction efficiency at temperatures below 200oC by providing the electrolyser products – hydrogen and ammonia [1]. The reason behind this innovation lies in recognising DEF as a viable electrolyte, offering both safety and a promise of performance increase due to splitting of urea instead of water. Beyond the contribution to NOx reduction, this approach aligns with the broader societal and political imperatives of integrating cleaner energy solutions within the automotive sector. However, the development of a functional urea electrolyser involves certain complexities. The key considerations are the material stability under operating conditions, anode catalyst dissolution in DEF, mass transport limitations, and the reduction of relatively high cathode overpotentials. A notable aspect of our research involves addressing these challenges in scenarios both with and without potassium hydroxide alongside DEF, requiring a nuanced understanding of the electrochemical processes involved. Additionally, weight, packaging, and system integration play an important role in the development of an onboard urea electrolyser.This study systematically explores these challenges to devise a comprehensive understanding of the underlying electrochemical processes involved as well as the integration and operation strategy. The research methodology adopts single cell tests for which activation and measurement protocols have been established to achieve representative and comparable performance curve recordings and electrochemical impedance spectroscopy (EIS) data. Additionally, to various operating conditions of the electrolyte, the cell components screening adds to a considerable effort of this study. We explore the influence on the materials and design of the bipolar plates (BP) and porous transport layers (PTL); electrode performance and durability as well as the membrane selection. Within this study we consider anion exchange membranes (AEM) and bipolar membranes (BPM) for the performance comparison. Adopting both catalyst-coated membrane (CCM) and catalyst-coated substrate (CCS) approaches enables for examination of electrode preparation techniques and their influence on performance of the electrolysis cell. The initial results are promising, especially when employing 1 M KOH in the DEF electrolyte at 70oC, reaching 0.85 A cm-1 at 2 V. The respective performance curve is presented in Figure 1., together with a diagram of the electrolyser system integration into an existing Diesel exhaust line.This research represents a practical stride towards realising the denitrification of transportation sector especially in city cycle driving when the exhaust gases temperature is too low for the state-of-the-art SCR systems. By addressing identified challenges and optimising key parameters, our study lays a robust foundation for the scalable implementation of a functional urea electrolyser for transport applications and a basic understanding of the electrochemical processes behind the performance and stability of such a system.Figure 1.Depicts a recorded polarisation curve of a single cell using an anion exchange membrane (AEM) and nickel catalyst anode fed DEF and 1 M KOH as an electrolyte at 70oC. Below, the suggested integration of the electrolyser into latest generation Diesel exhaust aftertreatment system. It includes diesel oxidation catalyst (DOC), selective Diesel particulate filter (sDPF), hydrogen supported denitrification catalyst ‘H2-deNOx’ and finally a selective catalytic reduction (SCR) step.Reference: Esser, E., Kureti, S., Heckemüller, L., Todt, A. et al., "Low-Temperature NOx Reduction by H2 in Diesel Engine Exhaust," SAE Int. J. Adv. & Curr. Prac. in Mobility 4(5):1828-1845, 2022, https://doi.org/10.4271/2022-01-0538. Figure 1

Experimental study on the ash deposition and NO emission of high-alkali coal under the staged O2/CO2 and O2/RFG conditions

The oxy-fuel combustion contributes to carbon capture, while the recirculation of flue gas brings about high concentrations of SO2 and H2O, which can affect the transformation of minerals in high-alkali coal. The staged oxy-fuel combustion, as an effective method for NOx reduction, can also change the ash deposition behavior of high-alkali coal. Two kinds of diluting agents, including pure CO2 for O2/CO2 combustion and simulated “recycled flue gas” (CO2, SO2, and H2O) for O2/RFG combustion, were employed in the present work. The ash deposition and NO emission of high-alkali coal during the staged oxy-fuel combustion were simultaneously studied under O2/CO2 and O2/RFG conditions. The conversion ratios of fuel-nitrogen to NO (CNO) and ash deposition efficiencies (Ed) at different stoichiometric ratios in primary combustion zone (SR1) and different oxygen concentrations were obtained. Afterwards, a series of tests were performed to further analyze the ash deposits. The experimental results show that as SR1 increases from 0.6 to 1.2, CNO jumps from 2.0 % to 23.5 % (O2/CO2 combustion) and from 1.9 % to 19.9 % (O2/RFG combustion). The additions of SO2 and H2O can reduce the NO emission. With the rising SR1, Ed under the O2/CO2 and O2/RFG conditions decreases from 4.0 % to 2.6 % and from 4.8 % to 2.1 %, respectively. At high SR1, the CaSO4 amount declines and the iron contributes less to the ash deposition. In O2/RFG combustion, the small sticky particles of sodium aluminosilicates on large particle surfaces reduce, and the large particles of calcium aluminosilicates shrink because some calcium produces CaSO4. Moreover, the exposure of ferrous iron to H2O helps its oxidization so iron is harder to cause severe adhesion. As O2 concentration rises from 21 % to 40 %, CNO shows an upward trend. Meanwhile, Ed under the O2/CO2 and O2/RFG conditions increases from 2.6 % to 3.7 % and from 2.3 % to 2.7 %, respectively. The present work is expected to provide some conducive information for the clean utilization of high-alkali coal and secure operation of boiler, as well as large-scale CO2 capture.

Engineering In-Co3O4/H-SSZ-39(OA) Catalyst for CH4-SCR of NOx: Mild Oxalic Acid (OA) Leaching and Co3O4 Modification.

Zeolite-based catalysts efficiently catalyze the selective catalytic reduction of NOx with methane (CH4-SCR) for the environmentally friendly removal of nitrogen oxides, but suffer severe deactivation in high-temperature SO2- and H2O-containing flue gas. In this work, SSZ-39 zeolite (AEI topology) with high hydrothermal stability is reported for preparing CH4-SCR catalysts. Mild acid leaching with oxalic acid (OA) not only modulates the Si/Al ratio of commercial SSZ-39 to a suitable value, but also removes some extra-framework Al atoms, introducing a small number of mesopores into the zeolite that alleviate diffusion limitation. Additional Co3O4 modification during indium exchange further enhances the catalytic activity of the resulting In-Co3O4/H-SSZ-39(OA). The optimized sample exhibits remarkable performance in CH4-SCR under a gas hourly space velocity (GHSV) of 24,000 h-1 and in the presence of 5 vol% H2O. Even under harsh SO2- and H2O-containing high-temperature conditions, it shows satisfactory stability. Catalysts containing Co3O4 components demonstrate much higher CH4 conversion. The strong mutual interaction between Co3O4 and Brønsted acid sites, confirmed by the temperature-programmed desorption of NO (NO-TPD), enables more stable NxOy species to be retained in In-Co3O4/H-SSZ-39(OA) to supply further reactions at high temperatures.