Reduction Of NO Research Articles

Revealing the origin of activity and selectivity in nitrate to ammonia conversion on single transition metal atom catalysts supported by a Ti2NO2 monolayer.

In recent years, the issue of nitrate (NO3-) contamination has become an increasingly severe problem for human life. Electrocatalytic nitrate reduction to ammonia (NH3) is one of the promising strategies to eliminate nitrate contamination. However, the reduction of NO3- to NH3 is a multi-electron process and is susceptible to interference from by-products and competing hydrogen evolution reactions (HER). Introducing a single transition metal (TM) atom onto MXene-based surfaces can alter MXenes' electronic configuration, enhancing their catalytic performance and the Faraday efficiency of the nitrate reduction reaction (NO3RR). In this work, we investigated the initial activation mechanisms of nitrate on various TM-modified Ti2NO2 (TM@Ti2NO2) catalysts and their NO3RR performance using first-principles calculations, aiming to select effective NO3RR electrocatalysts. The results indicated that both V@Ti2NO2 and Cr@Ti2NO2 were viable catalysts for NO3RR, showing particular promise for the efficient conversion of NO3- to NH3 at the most favorable limiting potentials of -0.41 V and -0.52 V, respectively. Further electronic structure analysis (density of states, COHP, and the descriptor ψ) confirmed that the single TM atom supported the boost in product selectivity and efficiency of NH3 by acting as an electron "bridge" to strengthen the interaction between NO3- and MXenes. AIMD simulations indicated that V@Ti2NO2 and Cr@Ti2NO2 maintained dynamical stability at the reaction temperature. These findings lay the foundation for a deeper understanding of the initial activation mechanisms and provide fresh theoretical insights into the design of MXene-based electrocatalysts with high NO3RR performance.

In-tandem Electrochemical Reduction of Nitrate to Ammonia on Ultrathin-Sheet-Assembled Iron-Nickel Alloy Nanoflowers.

The development of alternative routes for ammonia (NH3) synthesis with high Faradaic efficiency (FE) is crucial for energy conservation and to achieve zero carbon emissions. Electrocatalytic nitrate (NO3-) reduction to NH3 (e-NO3RRA) is a promising alternative to the energy-intensive, fossil-fuel-driven Haber-Bosch process. The implementation of this innovative NH3 synthesis technique requires an efficient electrocatalyst and in-depth mechanistic understanding of e-NO3RRA. In this study, we developed an ultrathin sheet (µm) iron-nickel nanoflower alloy through electrodeposition and used it for e-NO3RRA under alkaline conditions. The prepared Fe-Ni alloy exhibited an FE of 97.28 ± 1.36% at -238 mVRHE with an NH3 yield rate of 3999.1 ± 242.59 mg h-1 cm-2. Experimental electrolysis, in-situ Raman spectroscopy, and density functional theory calculations showed that the adsorption and reduction of NO3- to NO2- occurred on the Fe surface, whereas subsequent hydrogenation of NO2- to NH3 occurred preferentially on the Ni surface. The catalysts exhibited comparable FE for at least 10 cycles, with a long-term stability of 216 h. Electron paramagnetic resonance results confirmed that adsorbed hydrogen was consumed during e-NO3RRA. This work introduces a sustainable, robust, and efficient Fe-Ni alloy electrocatalyst, offering an environmentally friendly approach for synthesizing NH3 from NO3--contaminated water.

Comparative Evaluation of the Effect of Exhaust Gas Recirculation Usage on the Performance Characteristics and Emissions of a Natural Gas/Diesel Compression-Ignition Engine Operating at Part-Load Conditions

The use of natural gas as an alternative fuel in dual-fuel compression-ignition engines can lead to a substantial reduction in the majority of pollutant emissions compared to fossil fuels, while the thermal efficiency of the engine can be maintained at adequate levels. Its usage has increased widely in recent years, and significant efforts have been made to investigate the inherent physical and chemical processes that take place during this engine’s combustion, as well as the parameters that affect the operation of the engine and use natural gas as energy source. The scope of this study is to investigate the effect of EGR temperature (cold and hot) and rate (10% and 20%) on the performance characteristics and emissions of a dual-fuel compression-ignition engine operating at a specific engine operating point under dual-fuel (diesel–natural gas) conditions. For this reason, a phenomenological two-zone combustion model was developed. The results of the model were validated against the experimental data obtained from a single-cylinder direct-injection, turbocharged compression-ignition dual-fuel research engine operated under part-load conditions (IMEP = 0.52 Mpa and engine speed = 1500 rpm) and at various replacement percentages of diesel using methane (which was treated as a natural gas surrogate). The model results were in good agreement with the experimental results, revealing the ability of the model to be used in the aforementioned EGR analysis. The results of the study revealed that engine operation with 10% cold EGR does not significantly affect the engine performance characteristics, and combined with the addition of 80% gaseous fuel energy, can lead to a substantial reduction in NO and soot emissions, with a moderate increase in CO emissions. On the other hand, a significant finding of the present work is that engine operation with hot EGR under the investigated operating conditions, even though it had a beneficial effect on NO-specific emissions, led to a reduction in engine efficiency and may raise issues regarding the mechanical strength of the engine.

In‐tandem Electrochemical Reduction of Nitrate to Ammonia on Ultrathin‐Sheet‐Assembled Iron–Nickel Alloy Nanoflowers

The development of alternative routes for ammonia (NH3) synthesis with high Faradaic efficiency (FE) is crucial for energy conservation and to achieve zero carbon emissions. Electrocatalytic nitrate (NO3−) reduction to NH3 (e‐NO3RRA) is a promising alternative to the energy‐intensive, fossil‐fuel‐driven Haber–Bosch process. The implementation of this innovative NH3 synthesis technique requires an efficient electrocatalyst and in‐depth mechanistic understanding of e‐NO3RRA. In this study, we developed an ultrathin sheet (µm) iron–nickel nanoflower alloy through electrodeposition and used it for e‐NO3RRA under alkaline conditions. The prepared Fe–Ni alloy exhibited an FE of 97.28 ± 1.36% at −238 mVRHE with an NH3 yield rate of 3999.1 ± 242.59 mg h−1 cm−2. Experimental electrolysis, in‐situ Raman spectroscopy, and density functional theory calculations showed that the adsorption and reduction of NO3− to NO2− occurred on the Fe surface, whereas subsequent hydrogenation of NO2− to NH3 occurred preferentially on the Ni surface. The catalysts exhibited comparable FE for at least 10 cycles, with a long‐term stability of 216 h. Electron paramagnetic resonance results confirmed that adsorbed hydrogen was consumed during e‐NO3RRA. This work introduces a sustainable, robust, and efficient Fe–Ni alloy electrocatalyst, offering an environmentally friendly approach for synthesizing NH3 from NO3−‐contaminated water.

Processes and microorganisms driving nitrous oxide production in the Benguela Upwelling System

AbstractUpwelling systems and their associated oxygen deficient zones (ODZs) are hotspots of nitrous oxide (N2O) production in the ocean. The Benguela Upwelling System (BUS) is a highly productive region and an important, yet variable source of N2O to the atmosphere. This study examined underlying processes and microbial key players governing N2O production in the BUS during the austral winter. 15N‐tracer incubation experiments were conducted to track N2O production from NH4+ oxidation and denitrification. N2O production and consumption mechanisms over a longer temporal scale were determined through natural‐abundance isotope analyses. Metagenomics and 16S rRNA gene amplicon sequencing were used to identify potential key prokaryotes driving N2O production. Our results showed that, compared with permanent ODZs, the BUS is characterized by a higher oxidative and a lower reductive N2O production, both of which exhibit substantial spatial variability. N2O production peaked in low‐oxygen (O2) waters, with nearly equal contributions of oxidative and reductive processes, suggesting their co‐occurrence across an O2 concentration range broader than previously thought. However, the observed N2O isotope signatures implied a legacy of recent and extensive N2O reduction to N2. Metagenomic and 16S rRNA gene data identified denitrifiers belonging to Thioglobaceae and the archaeal ammonia‐oxidizers Nitrosopumilaceae among the potential key drivers of N2O production. Our study provides a comprehensive picture of N2O production in the BUS, revealing significant variability in the N‐cycling regime and underlying N2O production mechanisms, and demonstrating the value of combining direct rate measurements with more integrative approaches, such as molecular omics and natural‐abundance stable isotope tracers.

Rapid start-up and metabolic evolution of partial denitrification/anammox process by hydroxylamine stimulation: Nitrogen removal performance, biofilm characteristics and microbial community.

Enhanced nitrogen removal by hydroxylamine (NH2OH) on anammox-related process recently received attention. This study investigated the impact of NH2OH on the partial-denitrification/anammox (PDA) biosystem. Results show that NH2OH (≤10mg N/L) immediately induced nitrite accumulation and provided sufficient NO2- to anammox, achieving a 18.1±4.3% increase of nitrogen removal efficiency compared to the absence of NH2OH. Long-term exposure to NH2OH accelerated the functional microbial community transformation to PDA. Thauera was highly enriched (6.1%→26.9%) along with Candidatus Brocadia increased in the biofilms, which mainly favor the coupling process of nitrate reduction and anammox. Although the migration mechanism of anammox and denitrifier revealed by CLSM-FISH alleviates the adverse effects of NH2OH, the anammox was inhibited when NH2OH exceeding 15mg N/L through destroying the inner reduction of NO2-. These results suggested appropriate NH2OH addition favors the synergy between denitrifying and anammox bacteria, providing a promising option for wastewater treatment.

Design of an intelligent system for modeling and optimization of perovskite-type catalysts for catalytic reduction of NO with CO

Design of an intelligent system for modeling and optimization of perovskite-type catalysts for catalytic reduction of NO with CO

Mechanism of HCN formation from NO reduction by biomass-char in CO2/H2O atmosphere for oxy-fuel combustion – A combined experimental and DFT study

Mechanism of HCN formation from NO reduction by biomass-char in CO2/H2O atmosphere for oxy-fuel combustion – A combined experimental and DFT study

Electrosynthesis of NH3 from NO with ampere-level current density in a pressurized electrolyzer

Electrocatalytic NO reduction reaction (NORR) offers a promising route for sustainable NH3 synthesis along with removal of NO pollutant. However, it remains a great challenge to accomplish both high NH3 production rate and long duration to satisfy industrial application demands. Here, we report an in situ-formed hierarchical porous Cu nanowire array monolithic electrode ensembled in a pressurized electrolyzer to regulate NORR reaction kinetics and thermodynamics, which delivers an industrial-level NH3 partial current density of 1007 mA cm–2 with Faradaic efficiency of 96.1% and remains stable at 1000 mA cm–2 for 100 hours. Integrating the Cu nanowire array monolithic electrode with pressurized electrolyzer boosts the NH3 production rate to 10.5 mmol h–1 cm–2, which is over tenfold that using commercial Cu foam at 1 atm. The NORR performance can be attributed to the promoted NO mass transfer to the enriched Cu surface, which could increase the NO coverage on Cu and then destabilize adsorbed NO and weaken hydrogen adsorption, thereby facilitating NO hydrogenation to NH3 while suppressing the competing hydrogen evolution.

Key reaction pathways for NO reduction by NH3 in the reduction zone during ammonia-coal co-firing: A combined experimental and DFT study

Key reaction pathways for NO reduction by NH3 in the reduction zone during ammonia-coal co-firing: A combined experimental and DFT study

Substrate Engineering of Single Atom Catalysts Enabled Next-Generation Electrocatalysis to Power a More Sustainable Future

Single-atom catalysts (SACs) are presently recognized as cutting-edge heterogeneous catalysts for electrochemical applications because of their nearly 100% utilization of active metal atoms and having well-defined active sites. In this regard, SACs are considered renowned electrocatalysts for electrocatalytic O2 reduction reaction (ORR), O2 evolution reaction (OER), H2 evolution reaction (HER), water splitting, CO2 reduction reaction (CO2RR), N2 reduction reaction (NRR), and NO3 reduction reaction (NO3RR). Extensive research has been carried out to strategically design and produce affordable, efficient, and durable SACs for electrocatalysis. Meanwhile, persistent efforts have been conducted to acquire insights into the structural and electronic properties of SACs when stabilized on an adequate matrix for electrocatalytic reactions. We present a thorough and evaluative review that begins with a comprehensive analysis of the various substrates, such as carbon substrate, metal oxide substrate, alloy-based substrate, transition metal dichalcogenides (TMD)-based substrate, MXenes substrate, and MOF substrate, along with their metal-support interaction (MSI), stabilization, and coordination environment (CE), highlighting the notable contribution of support, which influences their electrocatalytic performance. We discuss a variety of synthetic methods, including bottom-up strategies like impregnation, pyrolysis, ion exchange, atomic layer deposition (ALD), and electrochemical deposition, as well as top-down strategies like host-guest, atom trapping, ball milling, chemical vapor deposition (CVD), and abrasion. We also discuss how diverse regulatory strategies, including morphology and vacancy engineering, heteroatom doping, facet engineering, and crystallinity management, affect various electrocatalytic reactions in these supports. Lastly, the pivotal obstacles and opportunities in using SACs for electrocatalytic processes, along with fundamental principles for developing fascinating SACs with outstanding reactivity, selectivity, and stability, have been highlighted.

Membrane-covered aerobic composting mitigated nitrous oxide emission through improved micro-aerobic state and enhanced carbon source utilization.

In this study, the variables related to nitrous oxide (N2O) emissions and their interactions during membrane-covered aerobic composting (MCAC) and conventional aerobic composting were characterized at multiple scales. For the first time, it was quantified that the MCAC-created micro-positive pressure (50-500Pa) significantly increased compost particles aerobic layer thickness by 24%-27% (P<0.001). Pile-scale results demonstrated that MCAC decreased the abundance of key functional genes (nirS, nirK, cnorB, and nosZ) and microbes (norank_f__A4b, Halomonas, norank_f__norank_o__SBR1031, and norank_f__Xanthomonadaceae) associated with N2O emissions (P<0.001); MCAC significantly enhanced the microbial metabolic potential for carbohydrate-based, carboxylic acid-based, amino acid-based, lipid-based, organic phosphate-based, and amine-based carbon sources (P<0.05). Interaction analysis suggested that the improved micro-aerobic state inhibited the N2O generation pathway, while the increased microbial utilization of carbon facilitated the N2O reduction pathway. Consequently, MCAC decreased N2O emissions by 20%-27%. These findings offer valuable insights for optimizing MCAC strategies to mitigate N2O emissions.

Co0 and CoOx Nanoclusters Encapsulated in Carbon Microspheres for the Low‐Temperature Enhanced Reduction of NOx by CO

Co⁰ and CoO_x Nanoclusters Encapsulated in Carbon Microspheres for the Low‐Temperature Enhanced Reduction of NO_x by CO

Bilayer electrified-membrane with pair-atom tin catalysts for near-complete conversion of low concentration nitrate to dinitrogen

Discharge of wastewater containing nitrate (NO3−) disrupts aquatic ecosystems even at low concentrations. However, selective and rapid reduction of NO3− at low concentration to dinitrogen (N2) is technically challenging. Here, we present an electrified membrane (EM) loaded with Sn pair-atom catalysts for highly efficient NO3− reduction to N2 in a single-pass electrofiltration. The pair-atom design facilitates coupling of adsorbed N intermediates on adjacent Sn atoms to enhance N2 selectivity, which is challenging with conventional fully-isolated single-atom catalyst design. The EM ensures sufficient exposure of the catalysts and intensifies the catalyst interaction with NO3− through mass transfer enhancement to provide more N intermediates for N2 coupling. We further develop a reduced titanium dioxide EM as the anode to generate free chlorines for fully oxidizing the residual ammonia (<1 mg-N L−1) to N2. The sequential cathode-to-anode electrofiltration realizes near-complete removal of 10 mg-N L−1 NO3− and ~100% N2 selectivity with a water resident time on the order of seconds. Our findings advance the single-atom catalyst design for NO3− reduction and provide a practical solution for NO3− contamination at low concentrations.

Ce1-xMnxVO4 with Improved Activity for Low-Temperature Catalytic Reduction of NO with NH3.

Novel Ce1-xMnxVO4 catalysts prepared via modified hydrothermal synthesis were used in selective catalytic reduction of NO using NH3 (NH3-SCR). The Ce1-xMnxVO4 catalysts displayed optimum NO removal efficiency at 250 oC. Physicochemical properties including crystal type, morphology, particle size, elemental composition, BET surface area, chemical bond, and valence state were studied by XRD, TEM, EDS, N2 adsorption-desorption, Raman spectroscopy, and XPS. Specific properties such as reduction property and acid sites were studied by H2-TPR and NH3-TPD. The in-situ DRIFTS results revealed that NH3-SCR over Ce0.5Mn0.5VO4 follows the Eley-Rideal mechanism. The experimental results showed that doped "active manganese" replaces the Ce position in CeVO4. The Mn-O-Ce interaction may increase the contents of defective oxygen and Brønsted acid sites, thus leading to enhanced activity.

N2O Reduction on Surfaces of V-Si48, V-C48, V-B24N24, V-CNT(6, 0) and V-BNNT(6, 0)) as Catalysts

N2O Reduction on Surfaces of V-Si48, V-C48, V-B24N24, V-CNT(6, 0) and V-BNNT(6, 0)) as Catalysts

Synergetic effects of cerium and titanium on the catalytic performance of NiMn2O4 for selective catalytic reduction of NO by NH3.

In this work, NiMn2O4/TiO2-CeO2 (Ce = 1.15, 2.5, 5, 7.5%) nanocomposites were prepared by the co-precipitation method and evaluated for the selective catalytic reduction of NOx with NH3. The physical and chemical properties of the synthesized catalysts were examined using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), Brunauer-Emmett-Teller (BET), temperature programmed desorption (TPD), temperature-programmed reduction of H2 (H2-TPR), and inductively coupled plasma optical emission spectrometry (ICP). The activity of NiMn2O4 catalysts was greatly enhanced by the addition of TiO2 and CeO2 in the temperature window of 200 to 400°C and the space velocity of 10,000 to 40,000h-1; NiMn2O4/TiO2-CeO2 (Ce = 5%) demonstrated the highest catalytic activity.

Noncatalytic Reduction of Nitrogen Oxide and Soot Inhibition during Cocombustion with Biotar: The Molecular Dynamics Modeling Approach.

Cocombustion with biomass tar is a potential method for NO reduction during fossil fuel combustion. In this work, the molecular dynamic method based on the reactive force field was used to study the NO reduction by phenol, which is a typical tar model compound. Results indicate that phenol undergoes significant decomposition at 3000 K, resulting in the formation of small molecular fragments accompanied by the generation of large molecular, network-structured soot particles. At higher temperatures (3500 K), the morphology of the soot produced from phenol decomposition undergoes a certain degree of change. It evolves from a two-dimensional network structure to a three-dimensional particulate structure. Soot particles are significant products of the thermal decomposition process of phenol. NO acts as an oxidant during the phenol decomposition process, significantly inhibiting the formation of soot particles during this process. Phenol also promotes the reduction of NO. The corresponding NO reduction ratios of NO are 52%, 76%, and 89% for 1500, 2000, and 2500 K respectively. CO, H2O, and N2 were the three most important reaction products during phenol-NO interaction. HNO is an important intermediate during the reduction of NO by phenol. The combination of the H radical and NO is the main route for HNO. It can be seen that HNO is quickly produced at the initial stage. The calculated activated energies for NO reduction and phenol oxidation are 30.47 and 50.85 kJ/mol, respectively.

A Density Functional Theory (DFT) Modeling Study of NO Reduction by CO over Graphene-Supported Single-Atom Ni Catalysts in the Presence of CO2, SO2, O2, and H2O.

The mechanisms of NO reduction by CO over nitrogen-doped graphene (N-graphene)-supported single-atom Ni catalysts in the presence of O2, H2O, CO2, and SO2 have been studied via density functional theory (DFT) modeling. The catalyst is represented by a single Ni atom bonded to four N atoms on N-graphene. Several alternative reaction pathways, including adsorption of NO on the Ni site, direct reduction of NO by CO, decomposition of NO to N2O followed by reduction of N2O to N2, formation of active oxygen radical O*, and reduction of O* by CO, were hypothesized and the energy barrier corresponding to each of the reaction steps was calculated using DFT. The most probable pathway was found to be that NO adsorbed on the Ni site decomposes via the Langmuir-Hinshelwood mechanism to form N2O and subsequently N2, leaving an active oxygen radical (O*) on the surface, which is then reduced by CO. The large adsorption energy of NO on the Ni site results in strong resistance to CO2, SO2, O2, and water vapor. The activation energy of N2O reduction to N2 was found to be larger than those of NO decomposition to N2O and active oxygen radical reduction by CO, illustrating that the step of N2O reduced to N2 is the rate-controlling step.

Catalytic Performance of Ti-MCM-22 Modified with Transition Metals (Cu, Fe, Mn) as NH3-SCR Catalysts

In the presented work, titanosilicate with the MWW structure (Ti-MWW) was hydrothermally synthesized using boron and titanium precursors, with piperidine as a structure-directing agent. The resulting layered zeolite precursor, with a Si/Ti molar ratio of 50, was treated in an HNO3 solution to remove extraframework Ti and B species. The acid-modified zeolite was functionalized with transition metal cations (Cu2+, Fe2+, Mn2+) and trinuclear oligocations (Fe(3) and Mn(3)). The application of this catalytic system is supported by the presence of titanium in the catalytic support structure—similar to a commercial system, V2O5–TiO2. The obtained samples were characterized with respect to their structure (P-XRD, DRIFT), textural parameters (low-temperature N2 sorption), surface acidity (NH3-TPD), transition metal content (ICP-OES) and form (UV–vis DRS) as well as catalyst’s reducibility (H2-TPR). Ti-MWW zeolite samples modified with transition metals were evaluated as catalysts for the selective catalytic reduction of NO with ammonia (NH3-SCR). The effective temperature range for the NO conversion varied depending on the type of active phase used to functionalize the porous support. The catalytic performance was influenced by transition metal content, its form, and accessibility for reactants as well as interactions between the active phase and titanium-containing support. Among the catalysts tested, the copper-modified Ti-MWW zeolite showed the most promising results, maintaining 90% NO conversion rates across a relatively broad temperature range from 200 to 325 °C. This catalyst meets the requirements of modern NH3-SCR installations, which aim to operate in the low-temperature region, below 250 °C.