Reduction Of NO Research Articles

Greenhouse gas emissions from rotating biological contactors combined with hybrid constructed wetlands treating polluted river

The rotating biological contactors combined with hybrid constructed wetlands (R-HCWs) has promising treatment performance, however, concerns persisted regarding greenhouse gases (GHGs) emissions. In this study, GHGs in the R-HCWs was evaluated, and results revealed that R-HCWs facilitated nitrogen conversion and provided alternating oxygen environments, thereby promoting the reduction of N2O and CH4 emissions. Therefore, the comprehensive global warming potential (8.7±2.7 g CO2-eq·m-3·d-1) for handling unit volume of river water was low, thus, greater ecological benefits were achieved. The relative abundance of functional microorganisms such as Bacillus, Acinetobacter, Nitrospira and norank_f__norank_o__SBR1031, increased due to warm season, which promoted the nitrogen cycle and N2O emission reduction. Anammox and denitrifying bacteria showed significantly correlated with N2O and CH4 emissions (p < 0.01). This study provides valuable insights for the potential adoption of biological and ecological integrated treatment approach optimized for improving water and mitigating GHGs emissions.

Combined metabolomic and microbial community analyses reveal that biochar and organic manure alter soil C-N metabolism and greenhouse gas emissions

The use of biochar to reduce the gas emissions from paddy soils is a promising approach. However, the manner in which biochar and soil microbial communities interact to affect CO2, CH4, and N2O emissions is not clearly understood, particularly when compared with other amendments. In this study, high-throughput sequencing, soil metabolomics, and quantitative real-time PCR were utilized to compare the effects of biochar (BC) and organic manure (OM) on soil microbial community structure, metabolomic profiles and functional genes, and ultimately CO2, CH4, and N2O emissions. Results indicated that BC and OM had opposite effects on soil CO2 and N2O emissions, with BC resulting in lower emissions and OM resulting in higher emissions, whereas BC, OM, and their combined amendments increased cumulative CH4 emissions by 19.5 %, 31.6 %, and 49.1 %, respectively. BC amendment increased the abundance of methanogens (Methanobacterium and Methanocella) and denitrifying bacteria (Anaerolinea and Gemmatimonas), resulting in an increase in the abundance of mcrA, amoA, amoB, and nosZ genes and the secretion of a flavonoid (chrysosplenetin), which caused the generation of CH4 and the reduction of N2O to N2, thereby accelerating CH4 emissions while reducing N2O emissions. Simultaneously, OM amendment increased the abundance of the methanogen Caldicoprobacter and denitrifying Acinetobacter, resulting in increased abundance of mcrA, amoA, amoB, nirK, and nirS genes and the catabolism of carbohydrates [maltotriose, D-(+)-melezitose, D-(+)-cellobiose, and maltotetraose], thereby enhancing CH4 and N2O emissions. Moreover, puerarin produced by Bacillus metabolism may contribute to the reduction in CO2 emissions by BC amendment, but increase in CO2 emissions by OM amendment. These findings reveal how BC and OM affect greenhouse gas emissions by modulating soil microbial communities, functional genes, and metabolomic profiles.

Revisit the role of hydroxylamine in sulfur-driven autotrophic denitrification

Through dedicated batch tests using the enriched sludge dominated by sulfur-oxidizing bacteria (SOB), the potential transformation of hydroxylamine (NH2OH) by SOB and the effects of NH2OH on the rate-limiting sequential reduction processes of sulfur-driven autotrophic denitrification (SDAD) were systematically explored in this study. The results indicated that NH2OH might be first converted to NO by SOB and then participate in the SDAD process, thus accelerating the utilization of S2- and contributing to the formation of N2O. Up to 3.5 mg-N/L NH2OH didn't affect the NO3- or NO2- reduction of SDAD, during which no significant changes were observed for the NH2OH concentration. Comparatively, even though NH2OH had no direct impact on the N2O reduction of SDAD, it could be consumed and therefore affect the depletion of N2O indirectly by regulating the toxic effect and electron supply of S2-. These findings provide novel implications for applying NH2OH to SDAD-based integrated processes for biological nitrogen removal.

Experimental and kinetic modeling investigation of NOx control in coal combustion by ammonia reburning

The carbon peaking and carbon neutrality goals present urgent demands for the green low-carbon transformation of the energy system. As a potential alternative energy, ammonia (NH3) used as reburning fuel in the coal-fired boilers will achieve both low-carbon and low-NOx emissions. To investigate ammonia reburning, experimental and chemical kinetic modeling were conducted in a tube flow reactor at 1023–1573 K under both ammonia and coal combustion conditions. Factors are researched including the combustion atmospheres of NH3/N2/O2 (PM-NH3) and coal/N2/O2 (PM-Coal), different inlet CO concentrations, reburning temperatures and reburning fuel ratios. The results indicate that ammonia reburning can effectively reduce NO emissions by about 95 %. The C-N reaction exhibits a positive effect on NO reduction at low temperature and a negative effect at high temperatures. As the CCO increases from 0 % to 4 % at 1573 K, the optimum temperature window size increases from 225 K to 413 K, and NO reduction rises from 31.25 % to 97.5 %. The whole ammonia reburning process includes NO rapid reduction stage (NRS), NO oxidation stage (NOS), and NO slowly re-reduction stage (NRRS) at high temperature. The chemical kinetic modeling indicates that the C-N reaction obviously shortens the residence time of the NRS and increases the ROP in the NOS, which together undercut NO reduction compared to PM-NH3 case. The promotion of the oxidation path of NH3-NH2-HNO-NO results in the NOS appearance and NRS ending. Moreover, this path affected by C-N reaction is primarily responsible for NO reduction cutoff in the PM-coal case.

Cause of nocturnal surface ozone enhancement in the North China Plain

The North China Plain (NCP), known for its dense population, extensive urbanization, and developed industry and agriculture, faces one of the foremost ozone (O3) pollution issues nationwide and even globally. Currently, most studies focus on daytime peak O3 levels, with insufficient understanding of the increase in nighttime O3 concentrations. Based on data from 204 national atmospheric composition monitoring sites in the NCP from 2015 to 2023, we investigated the characteristics of nocturnal surface O3 enhancement (NSOE) events and explored potential formation mechanisms. The mean annual frequencies of single-site and regional NSOE event in the NCP between 2015 and 2023 are 42 % and 21 %, respectively. The daytime peak O3 concentrations before and after NSOE events exceeded those during the corresponding periods of non-NSOE events by 84 ± 19 and 32 ± 15 μg/m3, respectively. The overall effect of the NSOE events was to decelerate the rate of decline in nighttime O3 concentrations and resulted in a reduction of NO2 and CO concentrations from 22:00 onwards. Low level jet (LLJ) and vertical mixing were the main factors affecting NSOE events in the NCP. The proportion of NSOE events affected by LLJ in four representative cities ranged from 57.6 % to 79.5 %. Furthermore, the high concentration of O3 in the residual layer before the NSOE event and the reduction of atmospheric stability during the NSOE event favored downward mixing of upper layer O3. The primary weather systems influencing the four most severe regional NSOE events were LLJ, typhoon, and cold fronts. The first two events were dominated by vertical mixing of O3, while the latter two events were mainly affected by horizontal transport. Our findings provide the first overview of NSOE events in the NCP from characteristics to mechanisms, emphasizing the necessity for future detailed studies based on nocturnal vertical O3 observations.

Protective Effects of Wild Sulla coronaria (Fabaceae) Flowers Phytocomplex in Human Dermal Fibroblasts Stimulated with Interleukin-1β

Sulla coronaria is indigenous to the Mediterranean region. It is grown as fodder in southern Italy because it contains various secondary metabolites with beneficial activities on animals. Recently, its potential use in cosmeceutical treatments for skin problems was reported. In this scenario, to contribute to a possible cosmeceutical application, we characterized the phytochemical profile of Sulla coronaria flowers’ hydroalcoholic extract by HPLC-DAD, Folin-Ciocalteu, Aluminum Chloride methods, DPPH assay, and, for the first time, we evaluated the antioxidant and anti-inflammatory activities on dermal fibroblasts. The phytochemical analysis confirmed the significant content of phenolic compounds (TPC 69.8 ± 0.6 mg GAE/g extract, TFC 15.07 mg CE/g extract) and the remarkable presence of rutin, quercetin, and isorhamnetin derivatives that give to the phytocomplex a good antioxidant activity as highlighted by the DPPH assay (IC50 of 8.04 ± 0.5 µg/mL). Through the reduction in NO• and ROS levels in human dermal fibroblasts, the biological tests demonstrated both the safety of the extract and its ability to counteract the inflammatory state generated by Interleukin-1β exposure. Our findings indicate that the antioxidant activities of the phytocomplex are strictly related to the anti-inflammatory action of the Sulla coronaria flowers extract, confirming that this plant could be a valuable source of bioactive molecules for cosmeceutical and nutraceutical applications.

Economic and environmental benefits of optimized waste transportation routes in Khulna

Urban transportation is a big source of pollution and greenhouse gas emissions. Khulna City handles the waste of 1.23 million people daily, using Heavy Duty Diesel Vehicles (HDDV) that release major environmental pollutants. The current waste transportation routes lack proper planning, leading to extra fuel consumption and pollutant emissions. This study aims to reduce fuel consumption and socio-environmental costs by improving waste transportation routes. Present collection routes, collecting points, and the speed of 30 waste collector vehicles were tracked using GPS devices for ten months between July 2023 and April 2024. The network dataset was modified according to four types of waste collector vehicles. ArcGIS Pro was used to find the optimal paths and their lengths. Fuel usage and prices were estimated using simple fuel consumption rate calculations. The lengths of current and optimal routes were used in COPERT to measure pollutant emissions. The results show that improved routes lower fuel consumption costs by approximately USD 55.39 per day and CO2 emissions by about 38.242 tonnes per year. Reductions in CO, CH4, NMVOC, NO2, PM10, and PM2.5 were roughly 9.3%, 9.53%, 9.21%, 9.29%, 9.35%, and 9.3%, respectively. This study demonstrates a comprehensive approach for improving solid waste management covering both financial efficiency and environmental effects.

Effects of inhibitors and slit incorporation on NH3 and N2O emission processes after urea application

The use of urea fertilizers in agriculture is associated with many negative environmental impacts and is a source of ammonia (NH3) and nitrous oxide (N2O) emissions. Such losses from urea fertilizer can be avoided by different mitigation techniques. Three different mitigation principles, urease inhibitor (N-(2-Nitrophenyl) phosphoric triamide, 2-NPT) (UI) alone and urease inhibitor in combination with nitrification inhibitors (N-[3(5)-methyl-1 H-pyrazol-1-yl) methyl] acetamide, MPA) (NI) and closed slit incorporation of urea fertilizer into the soil, were compared on a sandy loam soil at a soil water level of 70 % water-holding capacity. An in vitro microcosm approach with open dynamic incubation chambers was used to monitor NH3 emissions over two weeks with NH3 sampling by washing bottles. N2O emissions were studied over ten weeks in slow throughflow mesocosms with continuous gas chromatographic (GC) measurements. To get insights into N2O production and consumption processes, gas samples were taken after six weeks and N2O isotopocules were analyzed by isotope ratio mass spectrometry (IRMS). Slit injection showed the greatest effect on NH3 emission reduction by 79.6 % (40.6 % by UI, and 46.7 % by UINI) compared to surface applied urea. Minor pollution swapping to N2O was observed at the beginning of the trial due to incorporation but not in the cumulative emissions over the entire incubation time. The reduction effect of UINI on N2O emissions decreased over time with no cumulative emission reduction at the end of experimentation. N2O isotopocules confirmed the high contribution of nitrification to N2O production. In contrast and bacterial denitrification, nitrifier denitrification and fungal denitrification were involved on a much lower level and N2O reduction to N2 was not pronounced. All NH3 mitigation measurements where effective to decrease NH3 emissions while their effects on N2O emission varied over time. Factors as crop N uptake and rainfall would further modify the overall effect on N2O emissions and need to be considered for final pollution swapping assessment. Further research on the impact of NI on non-target microbial communities is warranted to elucidate potential environmental consequences and long-term efficacy of inhibitor compounds.

Nutrient removal performance and the nitrogen-sulfur conversion pathways in sulfur-iron based biofilter under acidic/alkaline conditions

The nitrate and phosphate removal in sulfur based (Vp) and sulfur-iron based autotrophic denitrification systems (Sp) with sponge iron as the iron source was investigated under different pH (6–9). In this study, Sp (>98 %) and Vp (>97 %) had higher nitrate removal efficiency at pH 7–8 and the highest phosphate removal efficiency (94.9 % ± 3.57 %) at pH 6. The flow cytometry detection revealed that the cell integrity was damaged due to the formation of iron crusts at pH 6, which resulted in irreversible inhibition in Sp. Electron transfer and nitrogen transformation showed that compared with the sustained inhibition of denitrification at pH 6, the inhibition at pH 9 occurred mainly in the initial 0–2 h due to the enhanced flow of electrons toward the formation of biological element sulfur (Sbio0). Coupled sponge iron promoted the adsorption and reduction of NO2−/N2O and reduced N2O emissions. Metatranscriptomics analysis showed that significant upregulation of key gene expression for nitrogen and sulfur metabolism in Sp, with complex regulatory mechanisms enhancing system stability and performance. Acidic conditions reduced the abundance of denitrification and sulfur oxidation functional genes. However, alkaline conditions (pH of 9) mainly caused the decreased abundance of denitrification functional genes, which was favorable for accumulation of Sbio0. This study provides a theoretical basis for the stable operation and regulation of the sulfur-iron based autotrophic denitrification process.

Calcium-Poison-Resistant Cu/YCeO2-TiO2 Catalyst for the Selective Catalytic Reduction of NO with CO and Naphthalene in the Presence of Oxygen.

The pollution from industrial processes based on biomass combustion is still an ongoing problem. In the present contribution, the selective catalytic reduction of NO with CO and naphthalene is carried out in the presence of 10% oxygen. The accumulation of alkaline and alkaline earth metals during biomass combustion is here simulated by the addition of calcium to a Cu-impregnated YCeO2-TiO2 support. The results show that a high dispersion of copper is obtained, which is resistant to the accumulation of calcium. Full conversion of CO and naphthalene is achieved above 200 °C, whereas NO conversions of 80, 90, and 87% are obtained for the catalysts with Ca loadings of 2.6, 5.2, and 13%, respectively, at 350 °C. It is proposed that the high activity of the catalysts is ascribed to the formation of Cu-Ox-Ce species and that the accumulation of Ca acts as a barrier to avoid copper sintering. It was found that different forms of carbonate and nitrite/nitrate species form during reaction, coexisting as adsorbed species during the SCR reaction. The selectivity to N2 was almost 100% in all cases, due to the small presence of NO2 in the reactor outlet (no N2O was detected in any conditions).

Theoretical study on borophene as metal-free catalyst for selective conversion of NO

The electrocatalytic reduction of NO (NORR) and selective catalytic reduction of NO by CO (CO-SCR) are the two most attractive approaches for selective conversion of NO. Herein, a bifunctional metal-free catalyst 2-Pmmn borophene is reported that is effective for both NORR and CO-SCR. NO can form NH3 and N2 through NORR and CO-SCR respectively. The results show that NO chemically adsorbed on the surface of borophene through the NO terminal can be electrocatalytically reduced to NH3. The optimal reaction path for NO to generate NH3 is through the protonation process of *NHO instead of *NOH. The rate-determining step is the hydrogenation of *NH2O to *NH2OH, and the free energy increases by 0.41 eV. At the same time, NO can also react with CO on the surface of borophene to form N2 and CO2. First, NO can form chemically adsorbed ONNO intermediate through NN coupling, then ONNO can be denitrified to form N2 and residual oxygen, and finally residual oxygen and CO can generate CO2 through the LH mechanism. The rate-determining step of the reaction is the NN coupling process of NO, and activation energy barrier is 1.27 eV. The present work provides theoretical insights for the effective conversion of NO.

Study on fuel-N conversion mechanism of ammonia-coal co-firing at different combustion stages

The co-combustion of ammonia and pulverized coal can effectively reduce the carbon emission of thermal power generation. However, ammonia, as a carbon-free fuel, is rich in large amounts of nitrogen, which increases the risk of high NOx emissions. Therefore, it is important to clarify the influence mechanism of ammonia on the NO formation of coal volatile-N and coal char-N in the co-combustion, and to reveal the N oxidation pathway in different combustion stages.In this study, simulations were carried out on the CHEMKIN software to investigate the generation characteristics of NO and the transformation mechanism of fuel-N at different combustion stages of ammonia-coal co-firing. The study showed that ammonia-blending combustion promoted the release of coal volatiles and the oxidation to NO. In the total NO generation during the ammonia-coal co-firing, the proportion of NO produced by ammonia-coupled coal char combustion was very low. Compared with ammonia-coupled coal combustion, the amount of NO produced in ammonia-coupled coal volatile combustion was significantly reduced. Sensitivity analysis and rate of production (ROP) analysis indicated that the increase of H, OH, and O free radicals promoted the NO formation, and that NHi free radicals played an important role in the NO reduction. By analyzing the elementary path of NO generated from ammonia-coupled pulverized coal, coal volatiles and coal char combustion at 1400 °C and 10 % ammonia ratio, it can be seen that the main path of NO formation during ammonia-coupled coal volatiles combustion is VOL→HCN→NCO→NO, CHAR→NO, NH2→HNO→NO, compared with ammonia-coupled coal combustion. The proportion of NH2→NH→NO reaction paths decreased, while the proportion of NH2→N2, NCN→NCO→N2, and NH2→NNH→N2 reaction paths increased respectively, indicating that separation combustion promoted the reduction of NO by NHi free radicals while inhibiting the oxidation of N-containing components.

Enhancing the nitrogen removal of anammox sludge by setting up novel redox mediators-mediated anammox process

Anaerobic ammonium oxidizing (anammox) bacteria have been proven weak-electroactive. However, the impact of exogenous anthraquinone-2,6-disulfonate (AQDS) on the anammox activity, although it usually plays essential roles in the life activities of many other electroactive microorganisms, is still unknown. Therefore, this study further explored the influences of AQDS on the anammox activity and the interaction mechanism with anammox bacteria, as well as the behaviors of NH4+, NO2−, and NO3−. The results showed that exogenous AQDS increased the ammonium and total nitrogen removal rates by 12.8% and 10.7%, respectively. Interestingly, the conversion from NO2− to NO3− was significantly reduced after adding AQDS, resulting in a 40.1% reduction in NO3− production of anammox process. In this study, we found for the first time that anammox bacteria could not only carry out the conventional anammox process but also perform a weak redox mediator-mediated anammox process, which could achieve the 1:1 consumption of NH4+ and NO2−. The redox mediator-mediated anammox process was related to an endogenous redox mediator (ERM) synthesized and secreted by anammox bacteria, whose redox midpoint potential was around −0.26 V (vs. Ag/AgCl). After adding AQDS, not only the ERM-mediated anammox process was enhanced, but also two novel redox mediator-mediated anammox processes were introduced, including the AQDS-mediated anammox process and ERM-AQDS-mediated anammox process. These three redox mediator-mediated anammox processes significantly improved the nitrogen removal performance of anammox bacteria and reduced energy consumption. These findings will help reduce the dependence of anammox technology on NO2−, reduce the cost of subsequent treatment of NO3−, and provide new visions for optimizing and applying anammox technology.

Unraveling the genetic potential of nitrous oxide reduction in wastewater treatment: insights from metagenome-assembled genomes.

This study provides critical insights into the genetic diversity of nitrous oxide reductase (nosZ) genes and the microorganisms harboring them in wastewater treatment plants (WWTPs) by exploring 1,083 high-quality metagenome-assembled genomes (MAGs) from 23 Danish full-scale WWTPs. Despite the pivotal role of nosZ-containing organisms, their diversity remains largely unexplored in WWTPs. Our custom pipeline for detecting nosZ provides near-full-length genes with detailed information on secretory pathways and accessory nos genes. Using these genes as templates, we developed taxonomically diverse clade-specific primers that generate nosZ amplicons for phylogenetic annotation and gene-to-MAG linkage. This approach improves detection and expands the discovery of novel sequences, highlighting the prevalence of non-denitrifying N2O reducers and their potential as N2O sinks. These findings have the potential to optimize nitrogen removal processes and mitigate greenhouse gas emissions from WWTPs by fully harnessing the capabilities of the microbial communities.

Highly-selective Electrocatalytic Reduction of NO to NH3 using Cu Embedded WS2 Monolayer as Single-atom Catalyst: A DFT Study.

Electrocatalytic nitric oxide reduction reaction (NORR) is a promising method for generating NH3. However, developing a NORR catalyst for NH3 synthesis with low cost and high efficiency is still challenging. We here report a series of single-atom catalysts (SACs), designed by embedding nine different transition metals from Sc to Cu in S-vacant WS2 monolayer (TM@WS2), and investigate the electrocatalytic performance for NORR process using the dispersion-corrected density functional theory (DFT) calculations. Among them, Cu-based SACshows a strong binding to the WS2 surface and high selectivity towards NORR process, and also it greatly inhibits the competing hydrogen evolution reaction (HER). Through ab initio molecular dynamics (AIMD) simulations, the thermal stability of SAC is assessed and found no structure deformation even at 500 K temperature. All possible reactive pathways including distal and alternating mode at both N- and O-end configurations for NH3 production were explored. We predicted that the Cu@WS2 SAC exhibits remarkable catalytic activity and selectivity with lowest limiting potential of -0.41 V via the N-alternating pathway. Our study emphasize that the transition metal dichalcogenide (TMDC) based SACs are potential candidates for converting NO to NH3, and this opens a new avenue in designing NORR catalysts with high catalytic performance.

Investigating drivers of N2 loss and N2O reducers in paddy soils across China

Denitrification plays a pivotal role in nitrogen (N) cycling in rice paddies, significantly impacting N loss and greenhouse gas emissions. Accurate quantification of net N2 emissions from paddy fields is therefore essential for improving fertilizer N use efficiency. However, challenges in directly measuring gaseous N2 hinder our understanding of microbially-mediated N loss in paddy soils at large scales. In this study, we investigated net N2 loss and its influencing factors in 45 paddy soils across China using membrane inlet mass spectrometry and N2/Ar technique, complemented by microbial community analysis via metagenomics. Potential N2 loss rates varied from 0.41 to 3.58 nmol N g−1 h−1, with no significant regional differences. However, soils from rice-upland rotation (1.72 ± 0.64 nmol N g−1 h−1) and mono-rice cropping systems (1.41 ± 0.53 nmol N g−1 h−1) exhibited higher N2 loss rates compared to double-rice cropping soils (1.13 ± 0.62 nmol N g−1 h−1). Our results revealed a unimodal relationship between soil N2 loss rates and soil pH, with N2O reducers and soil properties primarily regulating regional variations in N2 loss. Significant ecological differentiation was observed within both nosZ Clade I and Clade II, with soil pH emerging as the key factor shaping their community composition. Specifically, in rice-upland rotations, soil moisture and pH significantly influenced nosZ Clade I, while in double-rice cropping systems, soil texture and pH were the main factors affecting nosZ Clade II, thereby driving N2 loss. These findings enhance our understanding of N2 loss dynamics in paddy soil ecosystems, underscoring the critical role of N2O reducers on microbial-derived N2 loss and highlighting the importance of developing strategies to mitigate N2O emissions by balancing N2 loss through the manipulation of N2O-reducing and N2O-producing microbes.

Screening of Silver-Based Single-Atom Alloy Catalysts for NO Electroreduction to NH3 by DFT Calculations and Machine Learning.

Exploring NO reduction reaction (NORR) electrocatalysts with high activity and selectivity toward NH3 is essential for both NO removal and NH3 synthesis. Due to their superior electrocatalytic activities, single-atom alloy (SAA) catalysts have attracted considerable attention. However, the exploration of SAAs is hindered by a lack of fast yet reliable prediction of catalytic performance. To address this problem, we comprehensively screened a series of transition-metal atom doped Ag-based SAAs. This screening process involves regression machine learning (ML) algorithms and a compressed-sensing data-analytics approach parameterized with density-functional inputs. The results demonstrate that Cu/Ag and Zn/Ag can efficiently activate and hydrogenate NO with small Φmax(η), a grand-canonical adaptation of the Gmax(η) descriptor, and exhibit higher affinity to NO over H adatoms to suppress the competing hydrogen evolution reaction. The NH3 selectivity is mainly determined by the s orbitals of the doped single-atom near the Fermi level. The catalytic activity of SAAs is highly correlated with the local environment of the active site. We further quantified the relationship between the intrinsic features of these active sites and Φmax(η). Our work clarifies the mechanism of NORR to NH3 and offers a design principle to guide the screen of highly active SAA catalysts.

Efficient Tandem Electrocatalytic Nitrate Reduction to Ammonia on Bimodal Nanoporous Ag/Ag-Co across Broad Nitrate Concentrations.

Electrocatalytic nitrate (NO3-) reduction reaction (NO3-RR) represents a promising strategy for both wastewater treatment and ammonia (NH3) synthesis. However, it is difficult to achieve efficient NO3-RR on a single-component catalyst due to NO3-RR involving multiple reaction steps that rely on distinct catalyst properties. Here we report a facile alloying/dealloying-driven phase-separation strategy to construct a bimodal nanoporous Ag/Ag-Co tandem catalyst that exhibits a remarkable NO3-RR performance in a broad NO3- concentration range from 5 to 500 mM. In 10 and 50 mM NO3- electrolytes, the NH3 yield rates reach 3.4 and 25.1 mg h-1 mgcat.-1 with corresponding NH3 Faradaic efficiencies of 94.0% and 97.1%, respectively, outperforming most of the reported catalysts under the same NO3- concentration. The experimental results and density functional theory calculations demonstrate that Ag ligaments preferentially reduce NO3- to NO2-, while bimetallic Ag-Co ligaments catalyze the reduction of NO2- to NH3.

Electrocatalytic nitrite reduction to ammonia on isolated bismuth alloyed ruthenium

Electrochemical reduction of NO2− to NH3 (NO2−RR) is recognized as an appealing approach for achieving renewable NH3 synthesis and waste NO2− removal. Herein, we report isolated Bi alloyed Ru (Bi1Ru) as an efficient NO2−RR catalyst. Theoretical calculations and in situ electrochemical measurements reveal the creation of Bi1-Ru dual sites which can remarkably promote NO2− activation and suppress proton adsorption, while accelerating the NO2−RR protonation energetics to render a high NO2−-to-NH3 conversion efficiency. Remarkably, Bi1Ru assembled in a flow cell delivers an NH3 yield rate of 1901.4 μmol h−1 cm−2 and an NH3-Faradaic efficiency of 94.3% at an industrial-level current density of 324.3 mA cm−2. This study offers new perspectives for designing and constructing p-block single-atom alloys as robust and high-current-density NO2−RR catalysts toward the ammonia electrosynthesis.

Mechanistic studies on defective hBN-supported metal-nonmetal synergistic catalysis for urea electrosynthesis

This study explores electrocatalytic urea synthesis promoted by a newly-designed bimetallic-tricenter catalyst consisting of defective hexagonal boron nitride (hBN) and embedded dimerized 3d metal, by means of density functional theory calculations. Among all candidates, Mn was proved to be the most feasible catalytic center originating from its unique electronic structure and metal-support interactions. The metal-nonmetal synergistic effects of the Mn2N center effectively drive site-selective co-adsorption of CO and NO, spontaneous C-N coupling, low-energy-demand NO hydrogenation, and adequate protection of the carbonyl group, achieving highly active and selective urea production. The calculated limiting potential of urea formation is as low as −0.19 V, making it more favorable energetically compared to other competing reactions such as hydrogen evolution and NO reduction reactions.