High-Efficiency Electrocatalytic Reduction of N2O with Single-Atom Cu Supported on Nitrogen-Doped Carbon.

Nitrous oxide (N2O) is a potent greenhouse gas with a high global warming potential, emphasizing the critical need to develop efficient elimination methods. Electrocatalytic N2O reduction reaction (N2ORR) stands out as a promising approach, offering room temperature conversion of N2O to N2 without the production of NOx byproducts. In this study, we present the synthesis of a copper-based single-atom catalyst featuring atomic Cu on nitrogen-doped carbon black (Cu1-NCB). Attributed to the highly dispersed single-atom Cu sites and the effective suppression of the hydrogen evolution reaction, Cu1-NCB demonstrated an optimal N2 faradaic efficiency (82.1%) and yield rate (3.53 mmol h-1 mgmetal-1) at -0.2 and -0.5 V vs RHE, respectively, outperforming previously reported N2ORR electrocatalysts. Further, a gas diffusion electrode cell was employed to improve mass transfer and achieved a 28.6% conversion rate of 30% N2O with only a 14 s residence time, demonstrating the potential for practical application. Density functional theory calculations identified Cu-N4 as the crucial active site for N2ORR, highlighting the significance of the unsaturated coordination and metal-support electronic structure. O-terminal adsorption of N2O was favored, and the dissociative adsorption (*ON2 → *O + N2) was the rate-determining step. These findings reveal the broad prospects of N2O decomposition via electrocatalysis.

Core Soil Microorganisms and Abiotic Properties as Key Mechanisms of Complementary Nanoscale Zerovalent Iron and Nitrification Inhibitors in Decreasing Paclobutrazol Residues and Nitrous Oxide Emissions.

Agrochemical residues and nitrous oxide (N2O) emissions have caused considerable threats to agricultural soil ecology. Nanoscale zerovalent iron (nZVI) and nitrification inhibitors might be complementary to each other to diminish soil agrochemical residues and N2O emissions and enhance soil bacterial community diversities. Compared to the control, the nZVI application declined soil paclobutrazol residues by 5.9% but also decreased the bacterial community co-occurrence network node. Combined nZVI and Dicyandiamide applications significantly decreased soil N2O emission rates and paclobutrazol residues but promoted Shannon diversity of the bacterial community. The increased soil pH, ammonium nitrogen, and Actinobacteriota could promote soil paclobutrazol dissipation. The nZVI generated double-edged sword effects of positively decreasing paclobutrazol residues and N2O emissions but negatively influencing soil multifunctionalities. The nZVI and Dicyandiamide could be complementary to each other in diminishing soil agrochemical residues and N2O emission rates but promoting soil bacterial community diversities simultaneously.

Metagenomic insights into carbon and nitrogen cycling in the water-land transition zone of inland alkaline wetlands.

Inland alkaline wetlands play a crucial role in maintaining ecological functions. However, these wetlands are becoming more vulnerable to the effects of water level fluctuations caused by global climate change, especially concerning carbon (C) and nitrogen (N) cycling. Here, metagenomics sequencing was used to investigate microorganism diversity, C and N cycling gene abundance at three water level types (D (dry), MF (middle flooded), HF (high flooded)) along an inland alkaline wetland. Our findings reveal that water level was the most important factor in regulating the microbial communities. Distinct shifts in community composition were found along the water level increases, without fundamentally altering their composition. With the increase of water level, the relative abundance of pmoA decreased from 2.5 × 10-5 to 5.1 × 10-6. The C cycling processes shift from predominantly CO2-generated processes under low water levels to CO2 and CH4 co-generated processes under high water levels. The relative abundance of nosZ reached 4.9 × 10-5 in HF, while in D and MF, it is recorded at 4.5 × 10-5 and 3.4 × 10-5, respectively. Water levels accelerate N cycling and generating N2O intermediates. Furthermore, our study highlights the dynamic competition and cooperation between C and N cycling processes. This research provides a comprehensive biological understanding of the influence of varying water levels on soil C and N cycling processes in wetland.

Influence of Co3O4-based catalysts on N2O catalytic decomposition and NO conversion.

This study investigated the effect of different Co3O4-based catalysts on the catalytic decomposition of nitrous oxide (N2O) and on nitric oxide (NO) conversion. The experiments were carried out using various reaction temperatures, alkaline solutions, pH, mixing conditions, aging times, space velocities, impregnation loads, and compounds. The results showed that Co3O4 catalysts prepared by precipitation methods have the highest catalytic activity and N2O conversion, even at low reaction temperatures, while the commercial nano and powder forms of Co3O4 (CS) have the lowest performance. The catalysts become inactive at temperatures below 400 °C, and their activity is strongly influenced by the mixing temperature. Samples without stirring during the aging process have higher catalytic activity than those with stirring, even at low reaction temperatures (200-300 °C). The catalytic activity of Co3O4 PM1 decreases with low W/F values and low reaction temperatures. Additionally, the catalyst's performance tends to increase with the reduction process. The study suggests that cobalt-oxide-based catalysts are effective in N2O catalytic decomposition and NO conversion. The findings may be useful in the design and optimization of catalytic systems for N2O and NO control. The results obtained provide important insights into the development of highly efficient, low-cost, and sustainable catalysts for environmental protection.

In situ 15 N-N2 O site preference and O2 concentration dynamics disclose the complexity of N2 O production processes in agricultural soil.

Arable soil continues to be the dominant anthropogenic source of nitrous oxide (N2 O) emissions owing to application of nitrogen (N) fertilizers and manures across the world. Using laboratory and in situ studies to elucidate the key factors controlling soil N2 O emissions remains challenging due to the potential importance of multiple complex processes. We examined soil surface N2 O fluxes in an arable soil, combined with in situ high-frequency measurements of soil matrix oxygen (O2 ) and N2 O concentrations, in situ 15 N labeling, and N2 O 15 N site preference (SP). The in situ O2 concentration and further microcosm visualized spatiotemporal distribution of O2 both suggested that O2 dynamics were the proximal determining factor to matrix N2 O concentration and fluxes due to quick O2 depletion after N fertilization. Further SP analysis and in situ 15 N labeling experiment revealed that the main source for N2 O emissions was bacterial denitrification during the hot-wet summer with lower soil O2 concentration, while nitrification or fungal denitrification contributed about 50.0% to total emissions during the cold-dry winter with higher soil O2 concentration. The robust positive correlation between O2 concentration and SP values underpinned that the O2 dynamics were the key factor to differentiate the composite processes of N2 O production in in situ structured soil. Our findings deciphered the complexity of N2 O production processes in real field conditions, and suggest that O2 dynamics rather than stimulation of functional gene abundances play a key role in controlling soil N2 O production processes in undisturbed structure soils. Our results help to develop targeted N2 O mitigation measures and to improve process models for constraining global N2 O budget.

Sulfide-driven nitrous oxide recovery during the mixotrophic denitrification process.

We propose a novel sulfide-driven process to recover N2O during the traditional denitrification process. The optimum initial sulfide concentration was 120 mg/L, and the N2O percentage in the gaseous products (N2O+N2) was up to 82.9%. Moreover, sulfide involved in denitrification processes could substitute for organic carbon as an electron donor, e.g., 1 g sulfide was equivalent to 0.5-2 g COD when sulfide was oxidized to sulfur and sulfate. The accumulation of N2O was mainly due to the inhibiting effect of sulfide on nitrous oxide reductase (N2OR), which was induced by the supply insufficiency of electrons from cytochrome c (cyt c) to N2OR. When the initial sulfide concentration was 120 mg/L, the N2OR activity was only 36.8% of its original level. According to the results of cyclic voltammetry, circular dichroism spectra and fluorescence spectra, significant changes in the conformations and protein structures of cyt c were caused by sulfide, and cyt c completely lost its electron transport capacity. This study provides a new concept for N2O recovery driven by sulfide in the denitrification process. In addition, the findings regarding the mechanism of the inhibition of N2OR activity have important implications both for reducing emissions of N2O and recovering N2O in the sulfide-driven denitrification process.

Direct measurements of dissolved N2 and N2O highlight the strong nitrogen (N) removal potential of riverine wetlands in a headwater stream.

Increasing levels of nitrogen (N) in aquatic ecosystems due to intensified human activities is focusing attention on N removal mechanisms as a means to mitigate environmental damage. Important N removal processes such as denitrification can resolve this issue by converting N to gaseous emissions. Here, the spatiotemporal variability of N removal rates in China's Zhongtian River, a headwater stream that contains wetlands, was investigated by quantifying gaseous emissions of the main end products, N2 and N2O, using the water-air exchange model. Excess concentrations of these gases relative to their saturations in the water column generally varied within 1.4-8.7 µmol L-1 and 8.7-20.3 nmol L-1, with mean values of 4.5 µmol L-1 and 13.7 nmol L-1, respectively, demonstrating significant N removal in the river. The reach with wetlands was characterized by higher in-stream N2 production than the non-wetland reach, especially in July, when aquatic vegetation is most abundant. High N2O emissions during the same period in the non-wetland reach indicate that environmental conditions associated with vegetation are conducive to N2 production and likely constrain N2O emission. Changes in dissolved oxygen, pH, temperature, and carbon to nitrogen ratios are correlated with the observed spatiotemporal variabilities in gaseous N production. The mean N removal rate in the wetland reach was roughly twice that in the non-wetland reach, i.e., 22.4 vs. 10.3 mmol N m-2 d-1, while the corresponding efficiency was about five times as high, i.e., 15 % vs. 3 %. This study reveals the spatiotemporal patterns of in-stream N removal in a headwater stream and highlights the efficacy of wetlands in N removal. The data provide a strong rationale for constructing artificial wetlands as a means to mitigate N pollution and thereby optimize riverine environmental conditions.

Mechanistic study on reduction of nitric oxide to nitrous oxide using a dicopper complex.

A density functional theory study was carried out to investigate the reduction mechanisms of NO to N2O using a dicopper complex reported by Zhang and coworkers (J. Am. Chem. Soc., 2019, 141, 10159-10164). The reaction mechanism consists of three steps: N-N bond formation, isomerization of the resultant N2O2 moiety, and cleavage of the N-O bond.

Effects of nitrogen and phosphorus enrichment on soil N2O emission from natural ecosystems: A global meta-analysis.

Nitrogen (N) and phosphorous (P) enrichment play an important role in regulating soil N2O emission, but their interactive effect remains elusive (i.e. whether the effect of P or N enrichment on soil N2O emission varies between ambient and elevated soil N or P conditions). Here, we conducted a Bayesian meta-analysis across the global natural ecosystems to determine this effect. Our results showed that P enrichment significantly decreased soil N2O emission by 13.9% at ambient soil N condition. This N2O mitigation is likely due to the decreased soil NO3--N content (-17.6%) derived by the enhanced plant uptake when the P limitation was alleviated by P enrichment. However, this P-induced N2O (and NO3--N) mitigation was not found at elevated soil N condition. Additionally, N enrichment significantly increased soil N2O emission by 101.4%, which was associated with the increased soil NH4+-N (+41.0%) and NO3--N (+82.3%). However, the effect of N enrichment on soil N2O emission did not differ between ambient and elevated soil P subgroups, indicating that the P-derived N2O mitigation could be masked by N enrichment. Further analysis showed that manipulated N rate, soil texture, soil dissolved organic nitrogen, soil total nitrogen, soil organic carbon, soil pH, aboveground plant biomass, belowground plant biomass, and plant biomass nitrogen were the main factors affecting soil N2O emission under N enrichment. Taken together, our study provides evidence that P enrichment has the potential to reduce soil N2O emission from natural ecosystems, but this mitigation effect could be masked by N enrichment.

Nitrous oxide emissions from agricultural soils challenge climate sustainability in the US Corn Belt.

Agricultural landscapes are the largest source of anthropogenic nitrous oxide (N2O) emissions, but their specific sources and magnitudes remain contested. In the US Corn Belt, a globally important N2O source, in-field soil emissions were reportedly too small to account for N2O measured in the regional atmosphere, and disproportionately high N2O emissions from intermittent streams have been invoked to explain the discrepancy. We collected 3 y of high-frequency (4-h) measurements across a topographic gradient, including a very poorly drained (intermittently flooded) depression and adjacent upland soils. Mean annual N2O emissions from this corn-soybean rotation (7.8 kg of N2O-N ha-1⋅y-1) were similar to a previous regional top-down estimate, regardless of landscape position. Synthesizing other Corn Belt studies, we found mean emissions of 5.6 kg of N2O-N ha-1⋅y-1 from soils with similar drainage to our transect (moderately well-drained to very poorly drained), which collectively comprise 60% of corn-soybean-cultivated soils. In contrast, strictly well-drained soils averaged only 2.3 kg of N2O-N ha-1⋅y-1 Our results imply that in-field N2O emissions from soils with moderately to severely impaired drainage are similar to regional mean values and that N2O emissions from well-drained soils are not representative of the broader Corn Belt. On the basis of carbon dioxide equivalents, the warming effect of direct N2O emissions from our transect was twofold greater than optimistic soil carbon gains achievable from agricultural practice changes. Despite the recent focus on soil carbon sequestration, addressing N2O emissions from wet Corn Belt soils may have greater leverage in achieving climate sustainability.

A Nonheme Mononuclear {FeNO}7 Complex that Produces N2 O in the Absence of an Exogenous Reductant.

A new nonheme iron(II) complex, FeII (Me3 TACN)((OSiPh2 )2 O) (1), is reported. Reaction of 1 with NO(g) gives a stable mononitrosyl complex Fe(NO)(Me3 TACN)((OSiPh2 )2 O) (2), which was characterized by Mössbauer (δ=0.52 mm s-1 , |ΔEQ |=0.80 mm s-1 ), EPR (S=3/2), resonance Raman (RR) and Fe K-edge X-ray absorption spectroscopies. The data show that 2 is an {FeNO}7 complex with an S=3/2 spin ground state. The RR spectrum (λexc =458 nm) of 2 combined with isotopic labeling (15 N, 18 O) reveals ν(N-O)=1680 cm-1 , which is highly activated, and is a nearly identical match to that seen for the reactive mononitrosyl intermediate in the nonheme iron enzyme FDPnor (ν(NO)=1681 cm-1 ). Complex 2 reacts rapidly with H2 O in THF to produce the N-N coupled product N2 O, providing the first example of a mononuclear nonheme iron complex that is capable of converting NO to N2 O in the absence of an exogenous reductant.

Comprehensive evaluation of manganese oxides and iron oxides as metal substrate materials for constructed wetlands from the perspective of water quality and greenhouse effect.

Manganese oxides and iron oxides have been widely introduced in constructed wetlands (CWs) for sewage treatment due to their extensiveness in nature and their ability to participate in various reactions, but their effects on greenhouse gas (GHG) emissions remain unclear. Here, a set of vertical subsurface-flow CWs (Control, Fe-VSSCWs, and Mn-VSSCWs) was established to comprehensively evaluate which are the better metal substrate materials for CWs, iron oxides or manganese oxides, through water quality and the global warming potential (GWP) of nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2). The results revealed that the removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in Mn-VSSCWs were all higher than that in Fe-VSSCWs, and manganese oxides could almost completely suppress the CH4 production and reduce GWP (from 8.15 CO2-eq/m2/h to 7.17 mg CO2-eq/m2/h), however, iron oxides promoted GWP (from 8.15 CO2-eq/m2/h to 10.84 mg CO2-eq/m2/h), so manganese oxides are the better CW substrate materials to achieve effective sewage treatment while reducing the greenhouse gas effect.

Short-lived intermediate in N2O generation by P450 NO reductase captured by time-resolved IR spectroscopy and XFEL crystallography.

Nitric oxide (NO) reductase from the fungus Fusarium oxysporum is a P450-type enzyme (P450nor) that catalyzes the reduction of NO to nitrous oxide (N2O) in the global nitrogen cycle. In this enzymatic reaction, the heme-bound NO is activated by the direct hydride transfer from NADH to generate a short-lived intermediate ( I ), a key state to promote N-N bond formation and N-O bond cleavage. This study applied time-resolved (TR) techniques in conjunction with photolabile-caged NO to gain direct experimental results for the characterization of the coordination and electronic structures of I TR freeze-trap crystallography using an X-ray free electron laser (XFEL) reveals highly bent Fe-NO coordination in I , with an elongated Fe-NO bond length (Fe-NO = 1.91 Å, Fe-N-O = 138°) in the absence of NAD+ TR-infrared (IR) spectroscopy detects the formation of I with an N-O stretching frequency of 1,290 cm-1 upon hydride transfer from NADH to the Fe3+-NO enzyme via the dissociation of NAD+ from a transient state, with an N-O stretching of 1,330 cm-1 and a lifetime of ca. 16 ms. Quantum mechanics/molecular mechanics calculations, based on these crystallographic and IR spectroscopic results, demonstrate that the electronic structure of I is characterized by a singly protonated Fe3+-NHO•- radical. The current findings provide conclusive evidence for the N2O generation mechanism via a radical-radical coupling of the heme nitroxyl complex with the second NO molecule.

Synthetic and natural MOR zeolites as high-capacity adsorbents for the removal of nitrous oxide.

N2O is typically present as a trace gas in chemical processes, but its emission causes serious environmental issues. We herein demonstrate that ion-exchanged mordenite zeolites (framework code: MOR) can exhibit high capacities for N2O adsorption under ambient conditions. In particular, a natural MOR zeolite gives an adsorption capacity as high as 0.34 mmol-N2O per g-zeolite (1 atm, 25 °C), representing the best performing material among all zeolite-based adsorbents reported so far. The results contribute toward a comprehensive understanding of the structure-activity relationship and offer insights to establishing a zeolite-based adsorption system for enriching or removing N2O.

Current understanding of the global cycling of carbon dioxide, methane, and nitrous oxide.

To address the climate change caused by anthropogenic emissions of greenhouse gases into the atmosphere, it is essential to understand and quantitatively elucidate their cycling on the Earth's surface. This paper first presents an overview of the global cycling of three greenhouse gases, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), followed by a description of their variations in the atmosphere. This paper then presents the recent global budgets of these greenhouse gases estimated using two different approaches, top-down and bottom-up. Discussions on our current knowledge regarding the global cycling of the three gases are also presented.

N2O Decomposition over Fe-ZSM-5: A Systematic Study in the Generation of Active Sites.

We have carried out a systematic investigation of the critical activation parameters (i.e., final temperature (673-1273 K), atmosphere (He vs. O2/He), and final isothermal hold (1 min-15 h) on the generation of "α-sites", responsible for the direct N2O decomposition over Fe-ZSM-5 (Fe content = 1200-2300 ppm). The concentration of α-sites was determined by (ia) transient response of N2O and (ib) CO at 523 K, and (ii) temperature programmed desorption (TPD) following nitrous oxide decomposition. Transient response analysis was consistent with decomposition of N2O to generate (i) "active" α-oxygen that participates in the low-temperature CO→CO2 oxidation and (ii) "non-active" oxygen strongly adsorbed that is not released during TPD. For the first time, we were able to quantify the formation of α-sites, which requires a high temperature (>973) treatment of Fe-ZSM-5 in He over a short period of time (<1 h). In contrast, prolonged high temperature treatment (1273 K) and the presence of O2 in the feed irreversibly reduced the amount of active sites.

Structural and functional shifts of soil prokaryotic community due to Eucalyptus plantation and rotation phase.

Agriculture, forestry and other land uses are currently the second highest source of anthropogenic greenhouse gases (GHGs) emissions. In soil, these gases derive from microbial activity, during carbon (C) and nitrogen (N) cycling. To investigate how Eucalyptus land use and growth period impact the microbial community, GHG fluxes and inorganic N levels, and if there is a link among these variables, we monitored three adjacent areas for 9 months: a recently planted Eucalyptus area, fully developed Eucalyptus forest (final of rotation) and native forest. We assessed the microbial community using 16S rRNA gene sequencing and qPCR of key genes involved in C and N cycles. No considerable differences in GHG flux were evident among the areas, but logging considerably increased inorganic N levels. Eucalyptus areas displayed richer and more diverse communities, with selection for specific groups. Land use influenced communities more extensively than the time of sampling or growth phase, although all were significant modulators. Several microbial groups and genes shifted temporally, and inorganic N levels shaped several of these changes. No correlations among microbial groups or genes and GHG were found, suggesting no link among these variables in this short-rotation Eucalyptus study.

Effects of Sulfamethoxazole and 2-Ethylhexyl-4-Methoxycinnamate on the Dissimilatory Nitrate Reduction Processes and N2O Release in Sediments in the Yarlung Zangbo River.

The nitrogen pollution of rivers as a global environmental problem has received great attentions in recent years. The occurrence of emerging pollutants in high-altitude rivers will inevitably affect the dissimilatory nitrate reduction processes. In this study, sediment slurry experiments combined with 15N tracer techniques were conducted to investigate the influence of pharmaceutical and personal care products (alone and in combination) on denitrification and the anaerobic ammonium oxidation (anammox) process and the resulting N2O release in the sediments of the Yarlung Zangbo River. The results showed that the denitrification rates were inhibited by sulfamethoxazole (SMX) treatments (1-100 µg L-1) and the anammox rates decreased as the SMX concentrations increased, which may be due to the inhibitory effect of this antibiotic on nitrate reducing microbes. 2-Ethylhexyl-4-methoxycinnamate (EHMC) impacted nitrogen transformation mainly though the inhibition of the anammox processes. SMX and EHMC showed a superposition effect on the denitrification processes. The expression levels of the denitrifying functional genes nirS and nosZ were decreased and N2O release was stimulated due to the presence of SMX and/or EHMC in the sediments. To the best of our knowledge, this study is the first to report the effects of EHMC and its mixtures on the dissimilatory nitrate reduction processes and N2O releases in river sediments. Our results indicated that the widespread occurrence of emerging pollutants in high-altitude rivers may disturb the nitrogen transformation processes and increase the pressure of global warming.

Biological and Bioinspired Inorganic N-N Bond-Forming Reactions.

The metallobiochemistry underlying the formation of the inorganic N-N-bond-containing molecules nitrous oxide (N2O), dinitrogen (N2), and hydrazine (N2H4) is essential to the lifestyles of diverse organisms. Similar reactions hold promise as means to use N-based fuels as alternative carbon-free energy sources. This review discusses research efforts to understand the mechanisms underlying biological N-N bond formation in primary metabolism and how the associated reactions are tied to energy transduction and organismal survival. These efforts comprise studies of both natural and engineered metalloenzymes as well as synthetic model complexes.

Quantification of denitrifier genes population size and its relationship with environmental factors.

The objectives of this study were to use real-time PCR for culture-independent quantification of the copy numbers of 16S rRNA and denitrification functional genes, and also the relationships between gene copy numbers and soil physicochemical properties. In this study, qPCR analysis of the soil samples showed 16S rRNA, nirS, nirK, nosZI and nosZII average densities of 3.0 × 108, 2.25 × 107, 2.9 × 105, 4.0 × 106 and 1.75 × 107 copies per gram of dry soil, respectively. In addition, the abundances of (nirS + nirK), nosZI and nosZII relative to 16S rRNA genes were 1.4-34.1%, 0.06-3.95% and 1.3-39%, respectively, confirming the low proportion of denitrifiers to total bacteria in soil. This showed that the non-denitrifying nosZII-type bacteria may contribute significantly to N2O consumption in the soil. Furthermore, the shifts in abundance and diversity of the total bacteria and denitrification functional gene copy numbers correlated significantly with the various soil factors. It is the first study in Turkey about the population size of denitrification functional genes in different soil samples. It also aims to draw attention to nitrous oxide-associated global warming.