Reduction Of NO Research Articles

Chemical kinetic study of gasoline surrogate with ammonia on combustion: Iso-octane modeling

To facilitate the transition towards a carbon–neutral society, it is necessary to undertake comprehensive research on the utilization of ammonia in gasoline engine applications. In the present work, a new chemical kinetic mechanism for iso-octane/ammonia (iC8H18/NH3) was proposed and widely validated with the experiment data of ignition delay time (IDT) and laminar burning velocity (SL). The iC8H18 model of Cai [Combust. Flame, 162, 2015] and NH3 model of Zhang [Combust. Flame, 234, 2021] was chosen as the based model, and they connected through the chemical coupling between the iC8H18 and the NH2 chemistry. In addition, the influence of C-N interaction on the prediction ability of iC8H18/NH3 model was also analyzed and found that the H-abstraction reaction between NH2 and iC8H18 is the key reaction affecting the IDT and SL of mixture. Present work was also focused on the chemistry kinetic of iC8H18/NH3 mixture. The reaction pathway analysis shows that the addition of NH3 slightly enhanced the H-abstraction reaction of iC8H18 in tertiary site (cC8H17) and slightly inhibited the H-abstraction reaction of primary site (aC8H17, bC8H17, and dC8H17). In the end, the mole fraction of NO in iC8H18/NH3 flames is analyzed. The results show that NH3 addition increased the concentration of NO, but with the gradual increase of equivalence ratio, the increasing trend of NO concentration gradually decreases. A higher equivalence ratio can be selected to effectively control the increase of NOx concentration. Through the analysis of NO formation and reduction reaction pathway, it was found that NH3 addition increases the mole fraction of NH2 radical, the NO formation pathway was stronger than NO reduction pathway due to the sufficient OH radical, and finally leading to the increase of NO concentration. However, with the increase of equivalence ratio, the concentration of NH2 radical exceeds OH, and the number of OH is insufficient in satisfying the NH3-related NO reaction pathway, resulting in a decrease of the influence of NH3 addition on NO concentration.

Electrochemical reduction of NO3− to NH3 using defect-rich TiO2 support loaded with CuNi catalysts: differential electrochemical mass spectrometry insights

A promising approach for reducing nitrate (NO3−) in water waste is NO3− reutilization to ammonia (NH3). This work investigates the synergistic effect of Cu40Ni60 catalyst on a defect-rich TiO2 (TNSD) carbon vulcan composite (C-TNSD). The study starts with CuNi metallic content pre-screened over carbon vulcan (C) to identify the most promising CuNi ratios for nitrate reduction reaction (NO3-RR) to NH3. This is the case of Cu 20 wt% and Ni 80 wt% (Cu20Ni80), Cu 40 wt% and Ni 60 wt% (Cu40Ni60), Cu 60 wt% and Ni 40 wt% (Cu60Ni40), and Cu 80 wt%, Ni 20 wt% (Cu80Ni20) and Cu/Ni monometallic catalysts. Among these ratios, Cu40Ni60 resulted in the most promising electrocatalyst when loaded over C-TNSD, whose functionality has been assessed using in situ differential electrochemical mass spectrometry (DEMS). The results indicate that Cu40Ni60/C-TNSD attains a similar NH3 selectivity to Cu40Ni60 supported on TiO2-carbon vulcan composites. However, Cu40Ni60/C-TNSD does not hinder charge transport, making it the most suitable electrocatalyst for NH3 production. A synergistic interaction between Cu40Ni60 and C-TNSD is proposed. The results are supported by structural, (electro)chemical, and morphological characterization. From a broader perspective, defective-rich catalysts can be developed to control the electrochemical reaction sequence during NO3-RR.

Electrocatalytic Co‐Upcycling of Nitrite and Ethylene Glycol over Cobalt–Copper Oxides

AbstractElectrocatalytic nitrite (NO2−) reduction reaction (NO2−RR) for ammonia (NH3) synthesis is a promising alternative for NO2− resource utilization. Herein, a dual‐site copper‐cobalt oxide catalyst is reported for the efficient electrocatalytic reduction of NO2− to NH3, exhibiting NH3 Faradaic efficiency that remained above 95% (0.1 m NaNO2) over a wide potential window (−0.1 to −0.6 V vs reversible hydrogen electrode, vs RHE). More importantly, the high NH3 Faradaic efficiency maintains an over 85% (−0.1 to −0.3 V vs RHE) at a low concentration of NaNO2 (0.01 m). Theoretical calculations demonstrate that CuO serves the *NO2 to *NO and is subsequently converted to NH3 on Co3O4. Coupled anodic ethylene glycol (EG) oxidation reaction endows low cell voltage (ΔU = 480 mV, 10 mA cm−2) and energy consumption saving (>23%) in a two‐electrode system. This work provides a reference for a co‐upcycling electrolyzer for NO2− and EG.

Dynamics of N2O production and reduction processes in a soybean field revealed by isotopocule analyses

Agricultural soils are the largest anthropogenic source of atmospheric nitrous oxide (N2O) that causes global warming and stratospheric ozone depletion. In addition to the well-known emission associated with fertilization, significant N2O emission during the harvest season has been reported for soybean fields. Because soybean production is increasing, it is important to understand the production and consumption mechanisms of N2O in soybean fields. This study aimed to identify the microbial production processes using the ratios of isotopically substituted molecules, isotopocules. We also investigated the effectiveness of inoculating soybean with symbiotic nitrogen-fixing soil bacteria (rhizobia) with a high N2O-reducing ability, which was suggested as a mitigation option for N2O emission from soybean fields, on the basis of the characteristic isotope effect during N2O reduction.Along with semi-continuous flux measurements, weekly sampling and analysis of soil-emitted gas and soils were conducted in an experimental soybean field for two periods, after fertilization and before harvest, in two successive years. The isotopocule ratios of N2O emitted after fertilization suggested that it was produced by bacterial denitrification and nitrifier denitrification with smaller contributions from nitrification and fungal denitrification. Those for preharvest emission showed that N2O was produced by bacterial denitrification, including the process mediated by nodule rhizobia, with little progress of N2O reduction. We could not detect any difference between soybeans inoculated with rhizobia with different N2O reducing activity (nosZ− dominant, nosZ+, and nosZ++) because of the weak N2O reduction, probably due to relatively aerobic soil conditions. Since temporal changes in the N2O isotopocule ratios further implied that the rate of N2O reduction decreased in the later phase of autumn emission, suitable soil conditions are crucial for effective N2O reduction by inoculation of high nosZ-expressing rhizobia.

Sustainable conversion of alkaline nitrate to ammonia at activities greater than 2 A cm−2

Nitrate (NO3‒) pollution poses significant threats to water quality and global nitrogen cycles. Alkaline electrocatalytic NO3‒ reduction reaction (NO3RR) emerges as an attractive route for enabling NO3‒ removal and sustainable ammonia (NH3) synthesis. However, it suffers from insufficient proton (H+) supply in high pH conditions, restricting NO3‒-to-NH3 activity. Herein, we propose a halogen-mediated H+ feeding strategy to enhance the alkaline NO3RR performance. Our platform achieves near-100% NH3 Faradaic efficiency (pH = 14) with a current density of 2 A cm–2 and enables an over 99% NO3–-to-NH3 conversion efficiency. We also convert NO3‒ to high-purity NH4Cl with near-unity efficiency, suggesting a practical approach to valorizing pollutants into valuable ammonia products. Theoretical simulations and in situ experiments reveal that Cl-coordination endows a shifted d-band center of Pd atoms to construct local H+-abundant environments, through arousing dangling O-H water dissociation and fast *H desorption, for *NO intermediate hydrogenation and finally effective NO3‒-to-NH3 conversion.

NO Reduction with CO on Low‐loaded Platinum‐group Metals (Rh, Ru, Pd, Pt, and Ir) Atomically Dispersed on Ceria

AbstractLow‐loaded platinum‐group single‐atom catalysts on CeO2 (M1/CeO2) were synthesized via high‐temperature atom trapping (AT) and tested for the NO+CO reaction under dry and wet conditions. The activity of these catalysts for NO+CO reaction follows the order Rh>Pd≈Ru>Pt>Ir. For Rh, Ru, and Pd single‐atom catalysts, the N2O byproduct is formed but not clearly observed in Ir and Pt cases, which may result from the higher reaction temperature (>200 °C) required for Pt and Ir catalysts. The presence of water can promote the activity of these M1/CeO2 catalysts for the NO+CO reaction. Under wet conditions, significant NH3 formation occurred during the reaction, which is due to the co‐existence of water‐gas‐shift reaction on these catalysts. Compared with Pt, Pd and Ir, the Rh and Ru single‐atom catalysts show higher selectivity to NH3 species, resulting from the hydride species on the surface. Among all tested catalysts, Ru1/CeO2 shows the highest production of ammonia and highest CO conversion due to excellent water‐gas‐shift activity, whereas Pd1/CeO2 shows lowest ammonia production. Rh1/CeO2 shows the best low temperature NO reduction activity among all tested catalysts.

Copper-based catalysts supported on novel Metal-Organic Framework MIL-125(Ti) for selective catalytic reduction of NO with CO

A type of novel copper-based catalysts supported on MIL-125(Ti), a kind of metal–organic frameworks (MOFs), noted as Cu-MIL-125(Ti), was synthesized for the selective catalytic reduction (SCR) of NO with CO. The reactivity of Cu-MIL-125 catalysts for selective catalytic reduction of NO by CO (SCR-CO) was evaluated in a fixed bed reactor. A number of characterization techniques were used to explore the basic physical–chemical properties and the reaction mechanism. The results showed that the large specific surface area and micro-mesopores of the MIL-125 carrier promoted the high dispersion of Cu species, leading to the outstanding SCR-CO performance. Among the results, 90 % NO conversion and 92 % N2 selectivity were proved for the 6.2Cu-MIL-125 catalyst at 325 °C in oxygen-rich environment. XRD results showed that the metal organic frame structure and TiO2 structure coexisted in the catalysts, which was the major factor to influence the NO reduction efficiency. XPS characterization and H2-TPR reduction results showed that the catalytic performance of the catalyst was mainly determined by the path of Cu2+ reduction to Cu+ and then Cu+ to Cu0. Lewis acid on the catalyst surface played an important role in the CO-SCR reaction. In situ DRIFTS study proved that NO was first adsorbed on the surface of the catalyst to form different nitrate, NCO and isocyanate species. Then the adsorbed NO and the intermediates reacted with gaseous CO, which is a typical interaction between adsorbed molecules and gas molecules. Oxygen vacancies on the catalyst surface was involved in the reaction of CO to CO2. The whole reaction follows the M–K mechanism and the E-R mechanism. A preliminary reaction pathway was proposed based on the in situ DRIFTS results.

Effects of Biochar Application Two Years Later on N2O and CH4 Emissions from RiceVegetable Rotation in a Tropical Region of China

The effects of biochar application on soil nitrous oxide （N2O） and methane （CH4） emissions in a typical rice-vegetable rotation system in Hainan after two years were investigated. The aim was to clarify the long-term effects of biochar on greenhouse gas emissions under this model， and it provided a theoretical basis for N2O and CH4 emission reduction in rice-vegetable rotation systems in tropical regions of China. Four treatments were set up in the field experiment， including no nitrogen fertilizer control （CK）； nitrogen， phosphorus， and potassium fertilizer （CON）； nitrogen， phosphorus， and potassium fertilizer combined with 20 t·hm-2 biochar （B1）； and nitrogen， phosphorus， and potassium fertilizer combined with 40 t·hm-2 biochar （B2）. The results showed that： ① compared with that in the CON treatment， the B1 and B2 treatments significantly reduced N2O emissions by 32% and 54% in the early rice season （P < 0.05， the same below）， but the B1 and B2 treatments significantly increased N2O emissions by 31% and 81% in the late rice season. The cumulative emissions of N2O in the pepper season were significantly higher than those in the early and late rice seasons， and the B1 treatment significantly reduced N2O emissions by 35%. There was no significant difference between the B2 and CON treatments. ② Compared with that in the CON treatment， B1 and B2 significantly reduced CH4 emissions by 63% and 65% in the early rice season， and the B2 treatment significantly increased CH4 emissions by 41% in the late rice season. There was no significant difference between the B1 and CON treatments. There was no significant difference in cumulative CH4 emissions between treatments in the pepper season. ③ The late rice season contributed to the main global warming potential （GWP） of the rice-vegetable rotation system， and CH4 emissions determined the magnitude of GWP and greenhouse gas emission intensity （GHGI）. After two years of biochar application， B1 reduced the GHGI of the whole rice-vegetable rotation system， and B2 increased the GHGI and reached a significant level. However， the B1 and B2 treatments significantly reduced GHGI in the early rice season and pepper season， and only the B2 treatment increased GHGI in the late rice season. ④ Compared with that in the CON treatment， the B1 and B2 treatments significantly increased the yield of early rice by 33% and 51%， and the B1 and B2 treatments significantly increased the yield of pepper season by 53% and 81%. In the late rice season， there was no significant difference in yield except for in the CK treatment without nitrogen fertilizer. The results showed that the magnitude of greenhouse gas emissions in the tropical rice-vegetable rotation system was mainly determined by CH4 emissions in the late rice season. After two years of biochar application， only low biochar combined with nitrogen fertilizer had a significant emission reduction effect， but high and low biochar combined with nitrogen fertilizer increased the yield of early rice and pepper crops continuously.

Stability challenges and prospects for the industrial application of non‐noble catalysts for selective catalytic reduction of NOx by CO (CO‐SCR)

AbstractThe selective catalytic reduction of NOx by CO (CO‐SCR) holds considerable promise as a simple and cost‐effective technology capable of concurrently removing CO and NOx from mobile and stationary sources. This is especially pertinent for industry sectors with high CO emissions, such as the iron and steel industry, making CO‐SCR an attractive solution with significant industrial applicability. However, despite the promising industrial potential of CO‐SCR technology, its widespread adoption is hindered by several factors, most notably the impacts of SO2, H2O, and O2 on catalyst performance and stability. Current research on these limiting factors is not exhaustive, posing challenges for the comprehensive industrial implementation of CO‐SCR technology. Therefore, this review paper focuses on the variables impeding the industrial utilization of CO‐SCR, summarizing existing bottlenecks and emphasizing the urgent need to address the inhibitory effects of O2 on the CO‐SCR reaction, a critical issue in contemporary research. This review aims to clearly articulate the key challenges of CO‐SCR technology and provide direction for future research.

Oxidation state of copper species rather than ammonium nitrate decomposition determines the N2O generation during NO reduction with NH3 on Cu-AEI catalyst

Cu-based zeolite has excellent performance for nitrogen oxide removal from diesel vehicle exhaust, but a small amount of N2O is still generated in the selective catalytic reduction (SCR) process, and N2O has a strong greenhouse effect, which promotes the policy formulation of strictly regulating N2O emissions. This work systematically investigated the formation mechanism of low temperature N2O on Cu-AEI catalyst during SCR process. Under both steady and transient state test, the bimodal emission distribution and instantaneous generation behavior of N2O were observed. In addition, the contribution of NH4NO3 pathway to N2O formation at low temperature in standard SCR (SSCR) was demonstrated by temperature programmed desorption experiment, Thermogravimetric analysis and in situ diffuse fourier transform infrared spectroscopy experiment. NO + NH3 titration experiment, Raman and density functional theory calculation showed the role of Cu species in low temperature N2O generation. These results indicate that N2O formation during SSCR process on Cu-AEI at 200 ℃ is not generated through the decomposition path of NH4NO3, but due to the oxidation state of copper species, that is, the side reaction on Cu-peroxo.

Efficient NO reduction by CO on Cu/Ce co-modified CaO in calcium looping CO2 capture process

In the calcium looping CO2 capture process, using CO in the flue gas to reduce NO at a high molar ratio of CO to NO (e.g., above 10:1) can achieve efficient removal of NO. However, the lots of unreacted CO causes secondary pollution. In this study, a novel Cu/Ce co-modified CaO was proposed for cyclic CO2 capture and the catalytic NO reduction at a low CO:NO molar ratio (e.g., 2:1). The experimental findings indicate that Cu/Ce modification improves the performance of CaO in both catalytic NO reduction and carbonation. The Cu/Ce co-modified CaO contained the optimal Cu/Ce/Ca molar ratio of 1:5:100 possesses both NO removal and CO conversion efficiencies of above 99 %, along with CO2 removal efficiency exceeding 88%. Microscopic analysis determines that the electron transfer between Cu and Ce facilitates the conversion of lattice oxygen into surface oxygen, mitigating the competition between CO2 and CO for surface oxygen. Furthermore, density functional theory calculations demonstrate that CO/NO/CO2 exhibits non-competitive adsorption behavior on Cu/Ce co-modified CaO. Consequently, Cu/Ce-modified CaO possesses superior catalysis for efficient NO reduction by CO at low CO:NO molar ratio in calcium looping process.

Transient anoxic conditions boost N2O emissions by stimulating denitrification capacity and decreasing N2O reduction ratio in soils with different carbon substrates

Quantitative identification of the dominant N2O production and consumption processes following sudden shifts in soil aeration in well-aerated soils is limited, lagging the development of N2O mitigation strategies. Nitrous oxide emissions from agricultural soils, the largest source of anthropogenic N2O, are strongly influenced by low-molecular-weight organic carbons from root exudates (RootEx). In this study, we conducted a laboratory incubation experiment to investigate the mechanisms of N2O emissions regulated by transient anoxic conditions under the effects of different carbon substrates. Three common components in RootEx, oxalic acid, serine, and glucose were individually added as carbon sources every 24 h to the sandy loam soil. The contribution of microbial processes to N2O production (fungal denitrification, nitrification, bacterial denitrification) and consumption (N2O reduction) was evaluated using a dual isotope mapping approach (SP/δ18O MAP). The result indicated that transient anoxic conditions stimulated N2O production primarily through bacterial denitrification process facilitated by carbon substrates, and diminished the proportion of N2O reduction compared to oxic conditions. Among the three components of RootEx, serine and glucose induced higher N2O emissions and N2O reduction rates than oxalic acid during incubation. The differential effects of these three components on N2O emissions imply that the regulatory effect of carbon substrates on N2O reduction could not counterbalance the influence of transient anoxic conditions on N2O stimulation. Our findings provide a fundamental understanding of the effects of transient anoxic conditions and RootEx on N2O stimulation, facilitating the study of the spatial and temporal heterogeneity of N2O emissions in response to soil aeration changes in various upland soils.

Optimization of operating parameters and microbiological mechanism of a low C/N wastewater treatment system dominated by iron-dependent autotrophic denitrification

Ferrous iron (Fe2+) reduces the amount of external carbon source used for the denitrification of low-C/N wastewater. The effects of key operating parameters on the efficiency of ferrous-dependent autotrophic denitrification (FDAD) and the functioning mechanism of the microbiome can provide a regulatory strategy for improving the denitrification efficiency of low C/N wastewater. In this study, the response surface method (RSM) was used to explore the influence of four important parameters–the molar ratio of Fe2+ to NO3−-N (Fe/N), total organic carbon (TOC), the molar ratio of inorganic carbon to NO3−-N (IC/N) and sludge volume (SV, %)–on the FDAD efficiency. Functional prediction and molecular ecological networks based on high-throughputs sequencing techniques were used to explore changes in the structure, function, and biomarkers of the sludge microbial community. The results showed that Fe/N and TOC were the main parameters affecting FDAD efficiency. Higher concentrations of TOC and high Fe/N ratios provided more electron donors and improved denitrification efficiency, but weakened the importance of biomarkers (Rhodanobacter, Thermomonas, Comamonas, Thauera, Geothrix and unclassified genus of family Gallionellaceae) in the sludge ecological network. When Fe/N > 4, the denitrification efficiency fluctuated significantly. Functional prediction results indicated that genes that dominated N2O and NO reduction and the genes that dominated Fe2+ transport showed a slight decrease in abundance at high Fe/N levels. In light of these findings, we recommend the following optimization ranges of parameters: Fe/N (3.5–4); TOC/N (0.36–0.42); IC/N (3.5–4); and SV (approximately 35%).

Co-application of straw incorporation and biochar addition stimulated soil N2O and NH3 productions.

Nitrous oxide (N2O) and ammonia (NH3) volatilization (AV) are the major pathways of nitrogen (N) loss in soil, and recently, N2O and NH3 mitigation has become urgently needed in agricultural systems worldwide. However, the influence of straw incorporation (SI) and biochar addition (BC) on N2O and NH3 emissions are still unclear. To fill this knowledge gap, a soil column experiment was conducted with two management strategies using straw - straw incorporation (S1) and straw removal (S0) - and four biochar application rates (0 (C0), 15 (C1), 30 (C2), and 45 t ha-1 (C3)) to evaluate the impacts of their interactions on N2O and NH3 emissions. The results showed that NO3--N concentration and pH was the major contributors to affect the N2O and NH3 losses. Without biochar addition, N2O emissions was decreased by 59.6% (P<0.05) but AV was increased by 97.3% (P<0.05) under SI when compared to SR. Biochar was beneficial for N2O mitigation when straw was removed, but increased N2O emission by 39.4%-83.8% when straw was incorporated. Additionally, biochar stimulated AV by 27.9%-60.4% under S0 and 78.6%-170.3% under S1. Consequently, SI was found to significantly interact with BC in terms of affecting N2O (P<0.001) and NH3 (P<0.001) emissions; co-application of SI and BC promoted N2O emissions and offset the mitigation potential by SI or BC alone. The indirect N2O emissions caused by AV, however, might offset the reduction of direct N2O caused by SI or BC, thus leading to an increase in overall N2O emission. This paper recommended that SI combined BC at the amount of 8.2 t ha-1 for maintaining a lower overall N2O emission for future agriculture practices, but the long-term impacts of straw incorporation and biochar addition on the trade-off between N2O and NH3 emissions and reactive N losses should be further examined and assessed.

Introduction of soybean into maize field reduces N2O emission intensity via optimizing nitrogen source utilization

The application of synthetic nitrogen (N) fertilizer has increased anthropogenic N2O emission in global croplands. Due to the advantage of biological nitrogen fixation (BNF), the introduction of legume may lessen N2O emission intensity (emission/yield) in cereal field. Yet, this speculation lacks strong evidences and the relevant mechanistic explanations. A two-year field study was conducted using static chamber method (15N isotope labeling in fertilizer) in the mono- and inter-cropping fields with soybean introduced in maize field in semiarid rainfed Loess Plateau. The results indicated that maize-soybean intercropping showed 13 % lower N2O emission intensity than monocropping, attributed to 14 % and 20 % lower annually N2O emissions in intercropped zone than that of sole maize and soybean zones respectively. Also, a 15 % higher grain yield was observed in intercropped maize relative to that in sole maize. Particularly, during the peak time of emission following N fertilization and BNF within growing season, soybean introduction reduced 25 % and 24 % of N2O emissions in intercropped zone than sole maize and soybean zone respectively. It also favored maize plant with an additional 17 % more fertilizer-derived N, 21 % less soil-derived N and 30 kg N ha−1 soybean transferred-N from BNF. The contributions of N fertilization, BNF and soil initial organic N to N2O production were lessened in intercropping. In this case, the capacity of substrates N transformation into N2O emissions was lowered. Critically, soybean introduction reduced soil ammonia oxidation (as evidenced from amoA AOA and AOB gene abundance) in intercrops’ rhizosphere, and increased soil nitrite reduction (nirS and nirK gene abundance) in maize rhizosphere, and improved soil N2O reduction to N2 (nosZ gene abundance) in soybean rhizosphere. Therefore, soybean introduction optimized N source use for lower N2O emission intensity, via reducing the transformation of substrate N into N2O, and modifying the expression of nitrification and denitrification functional genes.

Synchronous Achievement of Advanced Nitrogen Removal and N2O Reduction in the Anoxic Zone in the AOA Process for Low C/N Municipal Wastewater.

Continuous flow processes for the in situ determination of N2O emissions during low C/N municipal wastewater treatment have rarely been reported. The anaerobic/aerobic/anoxic (AOA) process has recently shown promising potential in energy savings and advanced nitrogen removal, but it still needs to be comprehensively explored in relation to N2O emissions for its carbon reduction advantages. In this study, a novel gas-collecting continuous flow reactor was designed to comprehensively evaluate the emissions of N2O from the gas and liquid phases of the AOA process. Additionally, the measures of enhancing endogenous denitrification (ED) and self-enriching anaerobic ammonium oxidation (Anammox) were employed to optimize nitrogen removal and achieve N2O reduction in the anoxic zone. The results showed that enhanced ED coupled with Anammox led to an increase in the nitrogen removal efficiency (NRE) from 67.65 to 81.96%, an enhancement of the NO3- removal rate from 1.76 mgN/(L h) to 3.99 mgN/(L h), and the N2O emission factor in the anoxic zone decreased from 0.28 to 0.06%. Impressively, ED eliminated 91.46 ± 2.47% of the dissolved N2O from the upstream aerobic zone, and the dissolved N2O in the effluent was reduced to less than 0.01 mg/L. This study provides valuable strategies for fully evaluating N2O emissions and N2O reduction from the AOA process.

Theoretical Study of the NO Reduction Mechanism on Biochar Surfaces Modified by Li and Na Single Adsorption and OH Co-Adsorption

Theoretical and experimental investigations have shown that biochar, following KOH activation, enhances the efficiency of NO removal. Similarly, NaOH activation also improves NO removal efficiency, although the underlying mechanism remains unclear. In this study, zigzag configurations were employed as biochar models. Density functional theory (DFT) was utilized to examine how Li and Na single adsorption and OH co-adsorption affect the reaction pathways of NO reduction on the biochar surface. The rate constants for all reaction-determining steps (RDSs) within a temperature range of 200 to 1000 K were calculated using conventional transition state theory (TST). The results indicate a decrease in the activation energy for NO reduction reactions on biochar when activated by Li and Na adsorption, thus highlighting their beneficial role in NO reduction. Compared to the case with Na activation, Li-activated biochar exhibited superior performance in terms of the NO elimination rate. Furthermore, upon the adsorption of the OH functional group onto the Li-decorated and Na-decorated biochar models (LiOH-decorated and NaOH-decorated chars), the RDS energy barriers were higher than those of Li and Na single adsorption but easily overcome, suggesting effective NO reduction. In conclusion, Li-decorated biochar showed the highest reactivity due to its low RDS barrier and exothermic reaction on the surface.

Does no-till crop management mitigate gaseous emissions and reduce yield disparities: An empirical US-China evaluation

Global agricultural systems face one of the greatest sustainability challenges: meeting the growing demand for food without leaving a negative environmental footprint. United States (US) and China are the two largest economies and account for 39 % of total global greenhouse gases (GHG) emissions into the atmosphere. No-till is a promising land management option that allows agriculture to better adapt and mitigate climate change effects compared to traditional tillage. However, the efficacy of no-till for mitigating GHG is still debatable. In this meta-analysis, we comprehensively assess the impact of no-till (relative to traditional tillage) on GHG mitigation potential and crop productivity in different agroecological systems and management regimes in the US and China. Overall, no-till in China did not change crop yields, although soil CO2 (8 %) and N2O (12 %) emissions decreased significantly, while soil CH4 emissions increased by 12 %. In contrast to Chinese no-till, a significant improvement in crop yields (up to 12 %) was recorded on US cropland under no-till. Moreover, significant decreases in soil N2O (21 %) and CH4 (12 %) emissions were observed. Of the three cropping systems, only wheat showed significant reduction in CO2, N2O and CH4 emissions in the Chinese no-till system. In the case of US, no-till soybean-rice and maize cropping systems demonstrated significant emission reductions for N2O and CO2, respectively. Interestingly, yields of no-till maize in China and rice in US exceeded those of other no-till cereals. In China, no-till on medium-texture soils resulted in significant reductions in GHG emissions and higher crop yields compared to other soil types. In both countries, the relatively higher crop yields under irrigated versus non-irrigated no-till and the significant yield differences on fine textured soils under US no-till are likely due to the substantial N2O reductions. In summary, crop yield disparities from no-till between China and the US were related to the insignificant effects on controlling CH4 emissions and successfully mitigating N2O, respectively. This study comprehensively demonstrates how cropping system and pedoclimatic conditions influence the relative effectiveness of no-till in both countries.

Appropriate stoichiometric ratios of dissolved organic carbon and nitrate can trigger a transition in nitrate removal in groundwater around plateau lakes, Southwest China

Increasing dissolved organic carbon (DOC) in groundwater as a carbon source for microorganisms that stimulate nitrate attenuation is considered a sustainable strategy to mitigate nitrate pollution in groundwater. However, little is known on the stoichiometric ratio of DOC and nitrate required in groundwater nitrate reduction processes, which has become an obstacle for evaluating the current status of DOC limitations on nitrate reduction. Here, the NO3—-N and DOC concentrations in groundwater around 8 plateau lakes were investigated, and a microcosm experiment was performed to elucidate the effects of different DOC:NO3—-N levels in groundwater on NO3—-N reduction, and the current status of DOC limitations on groundwater NO3—-N reduction around 8 lakes was further evaluated. The results indicated that nearly 41 % of the groundwater NO3—-N concentrations exceeded the WHO threshold for drinking water (11.3 mg L−1) and 79 % of the groundwater DOC concentrations exceeded 5 mg L−1. The differences in groundwater NO3—-N and DOC concentrations among the 8 lakes were controlled by the intensity of agricultural and human activities and hydrogeological background. The stoichiometric ratio of DOC:NO3—-N regulated the NO3—-N reduction process, and groundwater NO3—-N accumulation rate appeared to become limited and sharply decreased when the DOC concentration was approximately 10 mg L−1 or when the DOC:NO3—-N ratio was close to 1:1, and the DOC:NO3—-N ratio threshold for limiting the NO3—-N reduction process was approximately 2.25. Based on this threshold, >33 %–86 % of the groundwater samples around the 8 plateau lakes were strongly limited in the reduction of groundwater NO3—-N due to a lack of sufficient DOC provides energy for heterotrophic microorganisms. Additionally, we highlight that the sustainable strategy of increasing DOC to stimulate groundwater NO3— attenuation should be combined with short-term strategies to jointly coordinate and control groundwater NO3— pollution.

Reactivity of Ni-modified MIL-100(Fe) catalysts for C3H6-SCR and reaction mechanism

Metal-organic frameworks (MOFs)-based carrier, MIL-100(Fe), was synthesized by hydrothermal method and Ni was supported on the MIL-100(Fe) by wet impregnation method to prepare the catalysts for selective catalytic reduction of NO with C3H6 (C3H6-SCR). The addition of Ni significantly improved the reactivity of C3H6-SCR. At 275 °C, the NO conversion of MIL-100(Fe) was 74.5%, whereas the NO conversion of 5.8%Ni/MIL-100(Fe) with 100% N2 selectivity was 100%. The in-situ DRIFTS prove that the interaction between NO2−/NO3− and CxHyOz substances generated intermediate isocyanates (R-NCO), and the reaction pathway was proposed based on the DRIFTS results to understand the mechanism.