NO Oxidation Research Articles

NO Oxidation States in Nonheme Iron Nitrosyls: A DMRG-CASSCF Study of {FeNO}6-10 Complexes.

Building upon an earlier study of heme-nitrosyl complexes (Inorg. Chem. 2023, 62, 20496-20505), we examined a wide range of nonheme {FeNO}6-10 complexes (the superscript represents the Enemark-Feltham count) and two dinitrosyl iron complexes using DMRG-CASSCF calculations. Analysis of the wave functions in terms of resonance forms with different [π*(NO)]i occupancies (where i = 0-4 for mononitrosyl complexes) identified the dominant electronic configurations of {FeNO}6 and {FeNO}7 complexes as FeIII-NO0 and FeII-NO0, respectively, mirroring our previous findings on heme-nitrosyl complexes. A trigonal-bipyramidal S = 1 {FeNO}8 complex with an equatorial triscarbene ligand set appears best described as a resonance hybrid of FeI-NO0 and FeII-NO-. Reduction to the corresponding S = 1/2 {FeNO}9 state was found to involve both the metal and the NO, leading to an essentially FeI-NO- complex. Further reduction to the {FeNO}10 state was found to be primarily metal-centered, leading to a predominantly Fe0-NO- configuration. Based on the weights wi of the [π*(NO)]i resonance forms, an overall DMRG-CASSCF-based π*(NO) occupation number could be derived, which was found to exhibit a linear correlation with both the NO bond distance and NO stretching frequency, allowing a readout of the NO oxidation state from the NO bond distance.

Chemical Insights Into Nitrogen Oxidation Via Surface Dielectric Barrier Discharge Plasma Driven By Different Power Supplies

ABSTRACTDischarge modes of surface dielectric barrier discharge are influenced by various factors, with its underlying mechanisms still unclear. This study explores the effects of power input and N2/O2 ratios on NOx yield and selectivity using Fourier Transform Infrared Spectroscopy and analyzes the spatiotemporal evolution of discharges under alternating current (AC) and pulsed power sources. Results show that NO2 selectivity is higher under pulsed power compared to AC, with a peak of 56.2% at 30% N2 content. Increased power enhances NO2 selectivity to 49.6% in the pulsed‐driven system, while no significant change is observed with AC. The lower rotational temperature in pulsed power systems facilitates the O generation for further NO oxidation. These findings may provide new chemical insights into plasma‐enabled nitrogen oxidation.

Ostwald Process Intensification by Catalytic Oxidation of Nitric Oxide.

The Ostwald process is one of the commercial pathways for the production of nitric acid (HNO3), a key component in the production of nitrate fertilizers. The Ostwald process is a mature, extensively studied, and highly optimized process, and there is still room for further intensification. The process can be further intensified by catalyzing the homogeneous oxidation of nitric oxide to nitrogen dioxide. In this work, we explore the NO to NO2 oxidation capacity of ruthenium on γ-Al2O3 support wash-coated on to a cordierite monolith. In a lab-scale setup with simulated feed comprising 10% NO, 6% O2, 15% H2O and rest Ar, and 8% NO, 2% NO2 5% O2, 15% H2O and rest Ar, the ruthenium and γ-Al2O3 wash-coated monoliths attained a steady conversion of 72 and 56%, respectively. A remarkable steady conversion of 20% more than the gas phase for 65 h over 4 days was presented by the RuWc,γ-Al2O3,Cordierite catalyst in one of the pilot plants at Yara, a Norwegian fertilizer company. The results presented in this work clearly provide evidence to support the idea that ruthenium on a gamma-alumina catalyst support can oxidize NO to NO2 under industrial nitric acid production conditions and mark an important step in the intensification of the Ostwald process.

Enhancing Catalytic Removal of Autoexhaust Soot Particles via the Modulation of Interfacial Oxygen Vacancies in Cu/CeO2 Catalysts.

The purification efficiency of autoexhaust carbon strongly depends on the heterogeneous interface structure between active metal and oxide, which can modulate the local electronic structure of defect sites to promote the activation of reactant molecules. Herein, the high-dispersion CuO clusters supported on the well-defined CeO2 nanorods were prepared using the complex deposition slow method. The formation of heteroatomic Cu+-Ov-Ce3+ interfacial structural units as active sites can capture electrons to achieve activation of the NO and O2 molecules. Among all of the synthesized catalysts, the Cu10/CeO2 catalyst exhibits superior catalytic performance (T50 = 351 °C) along with remarkable tolerance to H2O and SO2 in the removal of soot particles. Through a combination of comprehensive characterizations and density functional theory calculations, it is proposed that the interfacial Cu+-Ov-Ce3+ site, acting as an electron enrichment center, can capture electrons from the Cu d-band and Ce d/f-band to obtain high delocalized electron density, and then enhance the oxidation of NO to NO2, which plays a crucial role in the NOx-assisted catalytic mechanism for soot oxidation. This study presents a novel strategy for developing highly efficient catalysts that exhibit resistance to H2O and SO2, aimed at enhancing the removal of soot particles.

Photocatalytic NO Removal by Ternary Composites Bi12GeO20/BiOCl/W18O49 Using a Waste Reutilization Strategy

Heterojunction creation is demonstrated as an effective strategy to enhance the transfer and separation of charge carriers, which is beneficial for subsequent photocatalytic reactions. In this study, “sea urchin-like” W18O49 was in situ-grown on the surface of Bi12GeO20 through a hydrothermal process, and the released Cl− anions tended to produce BiOCl simultaneously. Systematical characterizations confirmed the construction of ternary composites Bi12GeO20/BiOCl/W18O49 (GBW), in which Type I and Z-scheme models were integrated to promote charge carrier migration and separation by combining the structural merits of both models. Under UV–visible light, the catalytic performance of the as-synthesized samples was tested in terms of NO oxidation removal. Compared to pure Bi12GeO20, the composite GBW5 showed the highest NO photocatalytic removal efficiency of 42%, which was nearly four times that of pure Bi12GeO20. These improvements were mainly due to enhanced light absorption, suitable morphological features, effective separation of charge carriers, and the boosted generation of reactive species in the GBW series. This study paves the way for the construction of Bi12GeO20-based ternary composites using a comprehensive utilization of waste method and the employment of the composites for the photocatalytic removal of low concentrations of NO at the ppb level.

Employing Triphenylene-Based, Layered, Conductive Metal-Organic Framework Materials as Electrochemical Sensors for Nitric Oxide in Aqueous Media.

This paper describes the first use of conductive metal-organic frameworks as the active material in the electrochemical detection of nitric oxide in aqueous solution. Four hexahydroxytriphenylene (HHTP)-based MOFs linked with first-row transition metal nodes (M = Co, Ni, Cu, Zn) were compared as thin-film working electrodes for promoting oxidation of NO using voltammetric and amperometric techniques. Cu- and Ni-linked MOF analogs provided signal enhancement of 5- to 7-fold over a control glassy carbon electrode (SANO = 6.7 ± 1.2 and 5.7 ± 1.1 for Ni3(HHTP)2 and Cu3(HHTP)2, respectively) for detecting micromolar concentrations of NO. Zinc-based MOF electrodes offered more limited enhancement (SANO = 3.1 ± 0.5), while the cobalt-based MOF analog had intrinsic redox activity at potentials close to NO oxidation, which interfered with sensing. Combining MOFs with a conductive polymer improved electrode stability under repeated electrochemical scanning (14 ± 3% decrease in signal over 10 scans). The stabilized Ni3(HHTP)2@polymer-coated electrodes were able to detect NO at physiologically relevant concentrations (LOD = 9.0 ± 4.8 nM) in amperometric sensing experiments, and exhibited moderate selectivity against ascorbic acid and nitrite (log kj,NO = -1.3 ± 0.3 and -0.83 ± 0.68 for ascorbic acid and nitrite, respectively). This study demonstrates that layered, conductive 2D MOFs have promising applicability for NO detection in aqueous environments.

Alkaline earth metal enhancement of cerium‐manganese‐based three‐dimensional ordered macroporous catalysts for NO oxidation

Nitrogen oxides are an industrial and domestic waste gas, which pollutes the air and affects health. In this paper, we use the template method to achieve the doping of alkaline earth metals, and the alkaline earth metals are doped into cerium‐manganese‐based three‐dimensional ordered macroporous (3DOM) catalysts to detect NO oxidation. The introduction of alkaline earth metals can improve the stability and thickness of macroporous results, which increases the contact area between the catalyst and reactant gases. At the same time, alkaline earth metal doping can promote the formation of more oxygen vacancies and unsaturated structures, and improve the catalytic activity of NO oxidation. The NO conversion rate of CM‐3Mg doped with 3% Mg was 61.25% at 250°C, and the NO conversion rate was the highest at 303°C, which was 79.2%. This study provides a promising catalyst candidate for NO oxidation in practical applications.

Promotion mechanism of SO2 on the catalytic oxidation of NO by H2O2

Promotion mechanism of SO2 on the catalytic oxidation of NO by H2O2

In-situ confined up-conversion Pt/CQDs within linker-defective NH2-MIL-125 to integrate photosensitivity and conductivity for hydrogen production and NO oxidation

In-situ confined up-conversion Pt/CQDs within linker-defective NH2-MIL-125 to integrate photosensitivity and conductivity for hydrogen production and NO oxidation

An experimental and kinetic modeling study of NO oxidation over Pt/Al2O3 catalysts: Effects of co-fed propane and Pt particle size

An experimental and kinetic modeling study of NO oxidation over Pt/Al2O3 catalysts: Effects of co-fed propane and Pt particle size

Thirty years of global warming potential evolution for the Italian dairy cow sector measured by two different metrics

This study aimed to provide a comprehensive evaluation of the greenhouse gases (GHG) emission between 1991 and 2021 of both the entire Italian dairy cattle sector (ITA_POP) and the registered Holstein Friesian population only (HF). An attributional cradle-to-farm gate Life Cycle Assessment was performed, including emissions (methane–CH4, nitrous oxide–N2O, carbon dioxide–CO2) due to animal and manure management, feed production, and farm materials. The functional units were 1 year and 1 kg of fat- and protein-corrected milk. We applied 100-year global warming potential (GWP) metric. For 2011–2021 period, we also applied GWP star (GWP*). Data originated from Italian GHG accounting and official milk recording systems. From 1991 to 2021, annual GHG emission of ITA_POP decreased from 20.4 ± 2.7 to 15.5 ± 2.1 Mt CO2e and emission intensity (EI) from 1.90 ± 0.25 to 1.17 ± 0.16 kg CO2e/kg corrected milk. The share of officially registered HF cows in ITA_POP increased from 36 to 70%. The annual emission of HF increased by 32% to 12.2 ± 1.8 Mt CO2e, but its EI decreased by 34% to 1.09 ± 0.16 kg CO2e/kg corrected milk. The accumulation in GHGs in 2011–2021 period due to ITA_POP (100-year GWP) continuously increased. When considering the short lifetime of CH4 (GWP*), the rate of increase in the same years was quite lower, with a flat pattern in the last 5 years. The decrease in CH4 emission is compensating the accumulation of N2O and CO2 from fossil fuels, highlighting the need of considering GHGs lifetime in the estimation of dairy cow sector emissions.

The combination of hydrogen evolution, nitric oxide oxidation and Zn-nitrate battery for energy conversion and storage by an efficient nitrogen-dopped CoOX electrocatalyst with Turing structure.

We tuned the morphology from the needle-like Co(CO3)0.5(OH)·0.11H2O to the unique Turing-structured CoCO3 through controlling the amount of glycerol in the solvothermal system, and then synthesized the Turing structure consisting of N-50%-CoOX hollow nanoparticles though the Kirkendall effect during nitriding process, which was applied as a novel bifunctional self-supporting electrode for efficient electrocatalytic hydrogen evolution reaction (HER) and electrocatalytic NO oxidation reaction (eNOOR). The eNOOR can be not only used as a substitution anode reaction of oxygen evolution reaction (OER) to couple with HER for efficient water splitting, but the production of nitrate from eNOOR also provides a strategy for the development of Zn-nitrate battery. The N-50%-CoOX electrode showed significant HER activity and excellent stability in 1M KOH electrolyte, with an overpotential of 30mV at a current density of 10mA cm-2. While the eNOOR performance of the N-50%-CoOX electrode showed significantly increased NO3- yield of 163.2mg cm-2h-1 with NO concentration of 10%, which was far more exceeding the most advanced nitrogen electro-oxidation. It is worth mentioning that the Zn-nitrate battery showed an open circuit voltage (OCV) of 1.36 V and a power density of 1.21 mW cm-2. Density function theory (DFT) and orbital theory results indicate that the doping of N in CoOX facilitates the electrons transfer, and greatly reduces free energy of the decision step in the eNOOR reaction path (the second step NO*→NOOH*), leading to excellent catalytic activity. This study provides a strategy of "Killing three birds with one arrow", which can achieve the effective hydrogen production, removal of NO pollutant, and chemical energy storage of nitrate for power generation.

Rapid charge transfer via anion bridge strategy for enhanced deep photocatalytic NO oxidation

Surface defect engineering and interfacial heterojunction construction can provide a promising strategy to achieving efficient reactant molecular activation and rapid charge transfer. However, traditional surface defect and interfacial heterojunction could often suffer from the potential space barrier, sluggish electron transfer, and weak reactant adsorption/activation, resulting in unsatisfactory pollutant removal effect. Herein, the anions (WO42−) bridged AgBr/Bi4O5Br2 heterojunction, involves the in situ growth of AgBr onto Bi4O5Br2 with the generation of bromine vacancies (BVs), is designed and synthesized by using a chemical deposition method. By establishing an electron-bridge into the interface of AgBr and Bi4O5Br2, a rapid charge carrier transfer channel is created, efficiently promoting the transport of photogenerated electrons from AgBr to Bi4O5Br2. Importantly, these spatially separated electrons of AgBr-WO42−-Bi4O5Br2 are captured by the active sites (BVs) in Bi4O5Br2to promote reactant activation, resulting in highly stable photocatalytic NO removal (67.7 %) and efficient inhibition of toxic NO2 formation (417.9 ppb → 30.6 ppb). The effective removal of NO2 by other anions, such as PO43-, demonstrates the broad applicability of this approach. This work introduces a synergistic mechanism of electron bridge, built-in electric field and vacancy engineering to create rapid charge carrier transfer channel and molecular activation strategy in designing highly efficient photocatalysts for deep photocatalytic NO oxidation.

Atomic behaviors in PdRu solid-solution nanoparticles on CeO2-ZrO2 support for the three-way catalytic reaction

Understanding the behavior of noble-metal catalysts is a key point of catalysis research aimed at reducing the environmental and economic costs associated with the increased use of automobiles. In this study, the atomic-behaviors of Ru and Pd atoms in PdRu solid-solution nanoparticles (NPs) supported on CeO2-ZrO2 (CZ) as a Rh-free three-way catalyst in a modeled three-way catalytic reaction (TWCR) were elucidated using a gas conversion analysis, transmission electron microscopy, and in-situ X-ray absorption fine structure spectroscopy. We found that the PdRu NPs enlarged by the annealing effect separated a smaller grain size with the Pd-rich and Ru-rich phase under TWCR. Most of the oxidation and reduction reactions under the modeled TWCR occurred on the Ru. However, the Pd metals acted as a major role of the reduction of NO gas and oxidation of CO and C3H6 gas. Ru atoms just is a minor role during the modeled TWCR. This study demonstrates the potential of PdRu NPs as a three-way catalyst and reveals the atomic-behavior and catalytic role under the modeled TWCR.

Unraveling the mechanism of CTAB-assisted in situ synthesis of CuAlOx-doped 0D CeO2 heterostructures for boosting simultaneous removal of NO, benzene, and toluene: The role of different active sites

The urgent necessity persists for the development of catalysts resilient to SO2, capable of effectively removing NO, benzene, and toluene simultaneously, yet comprehensive understanding of the mechanisms is still challenging. Herein, the CuAlOx-CeO2-CTAB catalyst with 0D CeO2 heterostructures and uniform middle mesopores heterostructures was synthesized utilizing CTAB as a template-directing agent and evaluated their performance in the simultaneous removal of NO, benzene, and toluene within the temperature range of 180–420 °C. Remarkably, the CuAlOx-CeO2-CTAB catalyst demonstrated superior simultaneous removal efficiencies (>91.5 % denitrification efficiency and > 94.0 % C6H6/C7H8 conversion at 300–420 °C), coupled with high N2/CO2 selectivity (>90 % at 300–420 °C) and remarkable stability (>96.0 % denitrification efficiency and > 90.5 % C6H6/C7H8 conversion in 1000 ppm SO2 at 300–380 °C). Mechanistically, the Langmuir-Hinshelwood route predominated in NO removal, while NH3primarily adsorbed on Lewis acid sites. Density functional theory (DFT) calculations revealed Cu+ as the principal adsorption and activation site for NH3 and NO. Surface reactive oxygen species facilitated the rapid oxidation of benzene and toluene following the Mars-van Krevelen mechanism. Furthermore, surface sulphates indicated the dual functionality of Ce3+ and Cu+ as antitoxic sites for SO2 absorption. Notably, in situ deposition of 0D CeO2 significantly enhanced the Ce3+/Ce and Cu+/Cu ratio, generating abundant active centres that deterred the deposition of NH4HSO4 and (NH4)2SO4 on the catalyst surface.In situDRIFTs results demonstrated negligible impact of SO2 on NO oxidation to NO2 and limited influence on fast SCR, affirming the CuAlOx-CeO2-CTAB catalyst to maintain excellent simultaneous removal activity in the presence of SO2.

Sulfur-resistant catalytic NO oxidation over surface-disproportionated CaMnO3 perovskites

A highly active CaMnO3 perovskite catalyst (CMO-H) was fabricated for NO oxidation, a key reaction in the control of NOx emissions from mobile and stationary sources, by tuning the average oxidation state of Mn on the surface via acid-initiated Mn disproportionation. In-depth structure-performance investigations suggest that an increased abundance of surface Mn4+ on CMO-H is responsible for its high activity. Doping with a tiny amount of Pd promoted the formation of reactive oxygen species on the CMO-H surface, leading to a further increase of NO oxidation activity which was largely sustained even in the presence of CO and hydrocarbons. Strikingly, an increased SO2-resistance was achieved over the Pd-doped CMO-H, due to an alleviation of surface sulfate formation by Pd. Our study sheds new lights on the rational fabrication of active, poisoning-resistant and cost-effective oxide catalysts for NO oxidation, which is an important reaction in various environmental and industrial applications.

Enhancing reactive oxygen release-replenishment and Lewis acid acidity by Nb doping in NbmCeOx for simultaneous elimination of NOx and toluene

Multi-pollutant control (MPC) is a promising technology for the simultaneous removal of nitrogen oxidation (NOx) and volatile organic compounds (VOCs) in fossil and biomass fuel combustion. This study uses Nb doping CeO2 bimetallic oxide catalysts to meet low-temperature NH3-SCR de-NOx, catalytic toluene oxidation and simultaneous elimination of NOx and toluene. X-ray diffraction (XRD), Raman and transmission electron microscopy (TEM) are applied to confirm the Nb doping into the lattice of CeO2 for Nb0.034CeOx and Nb0.36CeOx, but excess Nb in polymeric state NbOx present in Nb0.36CeOx. The effects of Nb doping on surface adsorbed oxygen, surface lattice oxygen and bulk phase lattice oxygen were investigated by XPS, EPR, O2-TPD, H2-TPR and DFT calculations. Using in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), it is investigated that the surface reactive oxygen species (including surface adsorbed oxygen and surface lattice oxygen) participates in NO oxidation, NH3 activation and toluene oxidation process. The reaction mechanism of NH3-SCR de-NOx, toluene oxidation and multi-pollutant co-elimination processes, as well as interactions between multiple reactants in the MPC reaction, were also studied with in-situ DRIFTS. It is found that Nb doping contributes to the mobility of lattice oxygen, which favors the oxidation of NH3 to NH2 and the release and rapid replenishment of reactive oxygen species at temperature ≥ 210 °C. The strong Lewis acid sites (Nb5+) promote the adsorption of NH3 species and their stability. These facilitate the NH3-SCR de-NOx in a wide temperature range and achieve the elimination of multiple pollutants on Nb0.034CeOx. So, Nb0.034CeOx exhibits matching activity temperature window in 170–390 °C for MPC (100 ppm toluene and 1000 ppm NO) over 90 % NO and toluene conversion in wet condition. Polymeric NbOx inhibits the activity of surface adsorbed oxygen and surface lattice oxygen and weakens the acidity of Lewis acid, therefore leading Nb0.36CeOx to poor performance of toluene oxidation and NH3-SCR at low-temperature.

Probing into the Catalytic Activity of Single-Atom Catalysts for NO Oxidation by H2O2 via the Tri-activity Volcano Plot

Probing into the Catalytic Activity of Single-Atom Catalysts for NO Oxidation by H₂O₂ via the Tri-activity Volcano Plot

Optimizing Carbon Structures in Laser-Induced Graphene Electrodes Using Design of Experiments for Enhanced Electrochemical Sensing Characteristics.

In this study, we explored the morphological and electrochemical properties of carbon-based electrodes derived from laser-induced graphene (LIG) and compared them to commercially available graphene-sheet screen-printed electrodes (GS-SPEs). By optimizing the laser parameters (average laser power, speed, and focus) using a design of experiments response surface (DoE-RS) approach, binder-free LIG electrodes were achieved in a single-step process. Traditional trial-and-error methods can be time-consuming and may not capture the interactions between all variables effectively. To address this, we focused on linear resistance and substrate delamination to streamline the DoE-RS optimization process. Two LIGs, designated LIG A and LIG B, were fabricated using distinct and optimized laser settings, which resulted in a sheet resistance of 25 ± 2 Ω/sq and 21 ± 1 Ω/sq, respectively. These LIGs, characterized by scanning electron microscopy, Raman spectroscopy, and contact angle analysis, exhibited a highly porous morphology with 13% pore coverage and a contact angle <50°, which significantly increased their hydrophilicity when compared to the GS-SPE. For the electrochemical studies, the oxidation of NO2- ion by the graphene-based working electrodes was investigated, as it allowed for the direct comparison of the LIGs to the GS-SPE. These included cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulsed voltammetry studies, which revealed that LIG electrodes displayed a remarkable 500% increase in peak current during NO2- oxidation compared to the GS-SPE. The LIGs also demonstrated improved stability and sensitivity (420 ± 30 and 570 ± 10 nAμM-1 cm-2) compared to the GS-SPE (73 ± 4 nAμM-1 cm-2) in the oxidation of NO2- ions; however, LIG B was more susceptible to ionic interference than LIG A. These findings highlight the value of applying statistical approaches such as DoE-RS to systematically improve the LIG fabrication process, enabling the rapid production of optimized LIGs that outperform conventional carbon-based electrodes.

Enhanced Photocatalytic Activity of Nickel(II)‐Doped Bi2O2CO3 Nanosheets for Efficient Nitric Oxide Removal

AbstractBi2O2CO3 is a typical bismuth‐based semiconductor photocatalyst that has attracted much attention because of layered structure and polarization characteristics. However, the wide bandgap of Bi2O2CO3 limits its practical applications in photocatalysis. In this study, the nickel (II)‐doped Bi2O2CO3 (Ni2+‐Bi2O2CO3) with oxygen vacancies was prepared by adding a controllable amount of nickel ions. The photocatalytic efficiency of the optimized sample for ppb‐grade NO under visible light irradiation is 59.4 %, which is 2.8 times than that of its counterpart, Bi2O2CO3 (21.2 %). Based on experiments and characterizations, Introduction of nickel ions and oxygen vacancies improves the photocatalytic performance of Ni2+‐Bi2O2CO3, which not only lowered the bandgap from 3.25 eV to 2.92 eV, but also reduced the recombination of photogenerated carriers by formation of the impurity level. Furthermore, the adsorption and photocatalytic conversion pathway of NO was explored by in situ DRIFTS, the principal byproducts of photocatalytic oxidation of NO are NO3− and NO2−. This work offers a new perspective to improve the photocatalytic activity by doping mothed for air purification.