Conversion Of Nitric Oxide Research Articles

Preparation of Aluminum-Molybdenum Alloy Thin Film Oxide and Study of Molecular CO + NO Conversion on Its Surface.

Adsorption and interaction of carbon monoxide (CO) and nitric oxide (NO) molecules on the surface of bare Al-Mo(110) system and on that obtained by its in situ oxidation have been studied in ultra-high vacuum (base pressure: ca. 10−8 Pa) by means of Auger and X-ray photoelectron spectroscopy (AES, XPS), low energy electron diffraction (LEED), reflection–absorption infrared and thermal desorption spectroscopy (RAIRS, TDS), and by the work function measurements. In order to achieve the Al-Mo(110) alloy the thin aluminum film of a few monolayers thick was in situ deposited onto the Mo(110) crystal and then annealed at 800 K. As a result of Al atoms diffusion into the Mo(110) subsurface region and the chemical reaction, the surface alloy of a hexagonal atomic symmetry corresponding to Al2Mo alloy is formed. The feature of thus formed surface alloy regarding molecular adsorption is that, unlike the bare Mo(110) and Al(111) substrates, on which both CO and NO dissociate, adsorption on the alloy surface is non-dissociative. Moreover, adsorption of carbon monoxide dramatically changes the state of pre-adsorbed NO molecules, displacing them to higher-coordinated adsorption sites and simultaneously tilting their molecular axis closer to the surface plane. After annealing of this coadsorbed system up to 320 K the (CO + NO → CO2 + N) reaction takes place resulting in carbon dioxide desorption into the gas phase and nitriding of the substrate. Such an enhancement of catalytic activity of Mo(110) upon alloying with Al is attributed to surface reconstruction resulting in appearance of new adsorption/reaction centers at the Al/Mo interface (steric effect), as well as to the Mo d-band filling upon alloying (electronic effect). Catalytic activity mounts further when the Al-Mo(110) is in situ oxidized. The obtained Al-Mo(110)-O ternary system is a prototype of a metal/oxide model catalysts featuring the metal oxides and the metal/oxide perimeter interfaces as a the most active reaction sites. As such, this type of low-cost metal alloy oxide models precious metal containing catalysts and can be viewed as a potential substitute to them.

The effect of the addition of nitrogen oxides on the oxidation of ethane: An experimental and modelling study

This study reports new ignition delay time (IDT) measurements of ethane (C2H6)/‘air’ mixtures with NOx (nitric oxide (NO), nitrogen dioxide (NO2), and nitrous oxide (N2O)) addition in the range 0 – 1000 ppm at stoichiometric fuel to air (φ) ratios, at compressed temperatures (TC) of 851 – 1390 K and at compressed pressures (pC) of 20 – 30 bar. In addition, new IDT measurements of three highly diluted C2H6/NO2 mixtures at φ = 0.5, TC = 805 – 1038 K, and pC = 20 – 30 bar are also studied. These new experimental data, together with data already available in the literature, are used to validate NUIGMech1.2 with an updated NOx sub-mechanism. Although the addition of 200 ppm of NO or NO2 to ethane shows a minimal promoting effect, the addition of 1000 ppm significantly promotes its reactivity. The similarity of the effect of the addition of both NO and NO2 addition is due to the fast conversion of NO into NO2 in the presence of molecular oxygen. However, the 1000 ppm NO doped ethane mixtures exhibit ∼20% shorter IDTs compared to the NO2 blended ones. The addition of 1000 ppm of N2O exhibits no effect on ethane oxidation at the conditions studied. The NUIGMech1.2 predictions can reproduce the sensitisation effect of NOx on ethane with good agreement over a wide range of pressure, temperature, equivalence ratio, and percentage dilution. Sensitivity and flux analyses of C2H6/NOx are performed to highlight the key reactions controlling ignition over the different temperature regimes studied. The analyses show that there is a competition between the reactions Ṙ + NO2 ↔ RȮ + NO and Ṙ + NO2 (+M) ↔ RNO2 (+M). This governs NOx sensitization on C2H6 ignition.

Graphene quantum dots/carbon nitride heterojunction with enhanced visible-light driven photocatalysis of nitric oxide: An experimental and DFT study

Visible light-driven photocatalysis for the degradation of nitric oxide (NO) has attracted considerable attention. Graphene quantum dots/graphite phase carbon nitride (GQDs/CN) heterojunctions were proposed as efficient visible-light responsive photocatalysts for NO treatment under the guidance of density function theory (DFT) simulation. Then, the GQDs/CN was synthesized via hydrothermal combination of GQDs and g-C3N4 (CN) produced from pyrolysis of citric acid (CA) and melamine, respectively. Afterwards, the GQDs/CN composite samples were characterized using XRD, XPS, FE-SEM, TEM, HR-TEM, BET, UV–Vis DRS, PL, photocurrent tests, and EIS. Later, the photocatalytic activity of the prepared GQDs/CN composites was evaluated by degrading NO at ppm level under visible light irradiation at conditions of 20 ppm of NO, 5% of O2, and 50% of relative humidity. Results show that 9GQDs/CN outperforms its counterparts. Compared to CN, the 9GQDs/CN increases the NO conversion rate from 61% to 90%, the selectivity of nitrate formation from 53% to 74%, and the value of DeNOx index from −0.25 to 0.19. The enhanced performance results from the inclusion of GQDs, which increases the specific surface area, promotes the absorption of light, boosts the separation of photogenerated electrons and holes, and inhibits their recombination. Furthermore, we used active species detection experiment, IC, in-situ DRIFTS, ESR measurement, XPS VB, Mott-Schottky, and DFT calculations to systematically explore the mechanism behind the degradation of NO using GQDs/CN, and confirmed the formation of Type-Ⅱ heterojunction between GQDs and g-C3N4. In addition, 9GQDs/CN maintains a high NO conversion rate after 5 cycles of experiments, indicating its potential in industrial applications.

Nitric Oxide Turnover Under Hypoxia Results in the Rapid Increased Expression of the Plastid-Localized Phosphorylated Pathway of Serine Biosynthesis.

The plant mitochondrial electron transport chain influences carbon and nitrogen metabolism under near anoxic conditions through its involvement in the phytoglobin-nitric oxide cycle, where the respiratory chain reduces nitrite to nitric oxide (NO), followed by NO conversion to nitrate by class 1 phytoglobin. Wild type (WT) and transgenic tobacco (Nicotiana tabacum L.) with differing amounts of alternative oxidase (AOX) were used to manipulate NO generation under hypoxia, and to examine whether this in turn influenced the gene expression of two stress-related amino acid biosynthetic pathways, the plastid-localized phosphorylated pathway of serine biosynthesis (PPSB), and the γ-aminobutyric acid (GABA) shunt. Under hypoxia, leaf NO emission rate was highest in AOX overexpressors and lowest in AOX knockdowns, with WT showing an intermediate rate. In turn, the rate of NO emission correlated with the degree to which amino acids accumulated. This amino acid accumulation was associated with the increased expression of the enzymes of the stress-related amino acid biosynthetic pathways. However, induction of the PPSB occurred much earlier than the GABA shunt. This work shows that high rates of NO turnover associate with rapid gene induction of the PPSB, establishing a clear link between this pathway and the maintenance of carbon, nitrogen and energy metabolism under hypoxia.

Hydrodynamic zones and the influence of microorganisms on nitrogen transformation in the diverging area of branched rivers

Diverging area is widespread in river networks, and understanding its biogeochemical process characteristics is of great significance to river ecological restoration and environmental quality improvement. Microbial communities affected by hydrodynamics play an important role in biogeochemical processes, but their relationship in diverging area is little known. Here, the composition of microbial community and its feedback to hydrodynamics and nitrogen conversion in the diverging area of river networks were first studied by coupling ecological theory, biogeochemical theory, microbial DNA sequencing and mathematical model of water environment. The results showed that there were five hydrodynamic zones with significant velocity differences in the diverging area, namely low velocity zone, maximum velocity zone, stagnant zone, separation zone, and deflection zone. According to the flow velocity grouping, there were significant differences in the microbial diversity and abundance among low velocity group, maximum velocity group and stagnant group had significant differences (p < 0.05, stress = 0.1207). In the low velocity group, Firmicutes was the dominant phylum which had a highest abundance and may promot the conversion of organic nitrogen into ammonia nitrogen. In the maximum velocity group, Bdellovibrionota was the dominant phylum which had a highest abundance and may promot the conversion of nitrate and nitric oxide to nitrogen. In the stagnant zone, Methylomirabilota was the dominant phylum which had a highest abundance and may promot the conversion of nitrogen into nitrate and ammonium. In addition, dissolved oxygen was the most sensitive environmental factor for shaping microorganisms and nitrogen conversion in the diverging area of the river networks by canonical correlation analysis. The denitrifying bacteria Rhodocyclaceae, was shown to negatively correlated with the flow velocity. This research improves the scientific basis for the study of the ecosystem in river networks, which will guide the construction of river ecological projects.

The prediction of nitric oxide conversion by dielectric barrier discharge using an artificial neural network model

NO conversion to NO2 by DBD (Dielectric Barrier Discharge) was investigated in the N2/O2/NO system. Since NO2 could be generated from NO oxidation by O species, the increase of specific energy input (SEI), function of discharge power and residence time, facilitated the production of O radicals, promoting NO2 production. However, high temperature accomplished by DBD inhibit the NO2 generation to some extent. Also, the conversion is affected by stoichiometric ratio, i.e., oxygen content and inlet NO concentration, which makes a challenge to characterize and predict the products using traditional methods, such as chemical kinetic model. To address above problem, an artificial neural network (ANN) model was developed to predict NO conversion by DBD in the N2/O2/NO system. The experimental data was adopted to train the proposed ANN model in order to simulate and predict the concentrations of NO, NO2, N2O and NOx during reactions. Good agreement was observed between the simulated results and the validated tests. The ANN model showed that inlet NO concentration plays a dominant role in NO2 generation, accounting for 36.22%, followed by residence time and discharge power, which were 26.25% and 23.52%, respectively. O2 content has marginal effect, taking 14.01%. As a byproduct, N2O was much more affected by stoichiometric ratio, which accounted for 64.75%, compared to 35.25%, belonging to discharge power and residence time.

Autotrophic denitrification of NO for effectively recovering N2O through using thiosulfate as sole electron donor

To reclaim nitrous oxide (N2O) as an energy resource economically, this study developed an autotrophic denitrification-based system with thiosulfate (S2O32-) and nitric oxide (NO) as electron donor and acceptor, respectively. NO from flue gases is absorbed on Fe(II)EDTA to overcome its low solubility in liquid phase by forming Fe(II)EDTA-NO. Short-term batch tests and long-term continuous experiments were conducted to investigate the N2O production profile and NO conversion efficiency from thiosulfate-based denitrification under varied Fe (II)EDTA-NO conditions (5–20 mM). Up to 39% of NO was converted to gaseous N2O at 20 mM Fe(II)EDTA-NO amid batch test due to the inhibition of key enzymatic activities by NO and the acidic conditions following thiosulfate oxidation. Higher Fe(II)EDTA-NO levels induced lower enzymatic activities with N2OR being suppressed harder than NOR. Microbial diversity was reduced in the continuous thiosulfate-driven Fe(II)EDTA-NO-based denitrification system. NO-resistant bacteria and sulfide-tolerant denitrifiers were enriched, facilitating NO conversion to N2O thereafter.

Repurposing of Hydroxyurea Against COVID-19: A Promising Immunomodulatory Role.

Cytokine release syndrome, a prominent mechanism of morbidity and mortality in patients with coronavirus disease 2019 (COVID-19), can cause multiple bodily reactions, including excessive release of proinflammatory mediators, with tumor necrosis factor-α (TNF-α) being the most prevalent cytokine combined with persistently elevated D-dimer levels that are indicative of potential thrombotic events, low levels of endogenous nitric oxide (NO) generation, and progressive decrease in hemoglobin production. In our argument, the conceptual repurposing of hydroxyurea (HU) for managing COVID-19 can provide a promising therapeutic option originating from a rich history of investigational antiviral activity. HU as a proposed supportive therapeutic agent for treating COVID-19 can exemplify a successful remedial choice through its anti-inflammatory activity along with an intrinsic propensity to control the circulatory levels of key cytokines including TNF-α. HU has the ability to undergo in vivo NO conversion acting as NO donor together with being a prominent inducer of fetal hemoglobin (HbF) production. The combination of the mentioned two properties allows HU to possess evident capability of protecting against thrombotic events by controlling D-dimer levels. The implication of our hypothetical argument sheds light on the curative potential of HU, which can be strategically harnessed against COVID-19.

Alx/HKUST-1 prepared by synthetic exchange as catalyst for reduction of NO by CO at low temperature

Alx/HKUST-1(x=1/24, 1/12, 1/6, 1/3), one of the bimetallic copper-based organic framework materials, was successfully prepared by the synthetic exchange method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area (BET), thermogravimetric analysis (TG), infrared spectra (IR), X-ray photoelectron spectroscopy (XPS), and H2-temperature programmed reduction (H2-TPR). The findings indicated that Alx/HKUST-1 maintained the octahedral morphology of its precursor (HKUST-1). The thermal stability and catalytic reduction ability of HKUST-1 skeleton were improved by doping aluminum (Al3+). Al1/12/HKUST-1 showed the best performance among all samples, with a nitric oxide (NO) conversion rate of 100% at 210 °C (50 °C lower than that of HKUST-1). The valence kind of Al, Cu, and O in Al1/12/HKUST-1 did not change after the catalytic reaction, but the contents of Al, Cu, and O in different forms changed significantly. The catalytic process of the Alx/HKUST-1 followed a Langmuir−Hinshelwood mechanism.

Rhenium-Mediated Conversion of Dinitrogen and Nitric Oxide to Nitrous Oxide.

Reductive splitting of N2 is an attractive strategy towards nitrogen fixation beyond ammonia at ambient conditions. However, the resulting nitride complexes often suffer from thermodynamic overstabilization hampering functionalization. Furthermore, oxidative nitrogen atom transfer of N2 derived nitrides remains unknown. We here report a ReIV pincer platform that mediates N2 splitting upon chemical reduction or electrolysis with unprecedented yield. The N2 derived ReV nitrides undergo facile nitrogen atom transfer to nitric oxide, giving nitrous oxide nearly quantitatively. Experimental and computational results indicate that outer‐sphere ReN/NO radical coupling is facilitated by the activation of the nitride via initial coordination of NO.

Rhenium‐Mediated Conversion of Dinitrogen and Nitric Oxide to Nitrous Oxide

AbstractReductive splitting of N2is an attractive strategy towards nitrogen fixation beyond ammonia at ambient conditions. However, the resulting nitride complexes often suffer from thermodynamic overstabilization hampering functionalization. Furthermore, oxidative nitrogen atom transfer of N2derived nitrides remains unknown. We here report a ReIVpincer platform that mediates N2splitting upon chemical reduction or electrolysis with unprecedented yield. The N2derived ReVnitrides undergo facile nitrogen atom transfer to nitric oxide, giving nitrous oxide nearly quantitatively. Experimental and computational results indicate that outer‐sphere ReN/NO radical coupling is facilitated by the activation of the nitride via initial coordination of NO.

Insights on copper, manganese, and Nickel/ZSM-5 catalytic mechanisms for nitric oxides selective reduction with ammonia

The elucidation of the selective catalytic reduction mechanisms over state-of-the-art metal-promoted zeolites is essential for nitric oxides removal in automobile and stationary source applications. In this work, H/ZSM-5 catalysts modified with transition metals, including copper, manganese, and nickel, were prepared by using an incipient wetness impregnation method and were evaluated for the selective reduction of nitric oxides with ammonia. Results indicate that copper/ZSM-5 exhibits the highest catalytic activity, with > 90% nitric oxide conversion at a broad operation temperature window (221–445 °C). The nitric oxide conversion profiles of nickel/ZSM-5 shows two peaks that correspond to weak activity among the catalysts; the low-temperature peak (290 °C) was induced by nickel clusters dispersed on the ZSM-5 surface, while the high-temperature peak (460 °C) was assigned to the bulk nickel oxides. The size of granular nickel monoxide crystallites with an exposed (2 0 2) plane is 2–30 nm, as confirmed by Scanning electron microscopy, X-ray diffraction, and Transmission electron microscope measurements. Temperature-programmed reductions with hydrogen results testified that the copper and nickel cations, as the main species contributing to selective catalytic reduction, were reduced via Cu2+/Cu+→Cu0 and Ni2+→Ni0 for copper/ZSM-5 and nickel/ZSM-5, respectively, while for the manganese/ZSM-5, the Mn3+ species in manganese clusters were reduced to Mn2+ by hydrogen. Particularly, temperature-programmed desorption coupled with mass spectrometer (TPD-MS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were comprehensively used to reveal the relationship between zeolite structure and catalysts’ properties for improving selective catalytic reduction. These results confirm that the ammonia is adsorbed and activated on both Brønsted and Lewis acid sites. The nitrous oxide desorbs in two stages during nitric oxide-TPD-MS measurements, corresponding to the desorption of nitric oxide bounded to amorphous clusters and the nitric oxide strongly bounded to bulk metal oxides, respectively. The selective catalytic reduction process follows the L-H mechanism at low temperatures, in which nitric oxide and ammonia molecules were adsorbed and activated on the catalyst surface. The selective catalytic reduction rates reached the maximum value of 1.8 × 108 (218 °C), 6.4 × 107 (227 °C), and 3.9 × 107 s−1 (235 °C) for copper, manganese, and nickel /ZSM-5, respectively.

A NO-Responsive Ratiometric Fluorescent Nanoprobe for Monitoring Drug-Induced Liver Injury in the Second Near-Infrared Window.

Currently, drug-induced liver injury (DILI) has become a huge concern for the majority of modern medicine, whereas the diagnosis of DILI is still in its infancy due to the lack of appropriate methods. Herein, based on the fact that nitric oxide (NO) has been recognized as an early unifying, direct, and vital biomarker for DILI, we rationally designed and developed a NO-responsive ratiometric fluorescent nanoprobe DCNP@MPS@IR NO to quantitatively detect NO and monitor DILI in the second near-infrared (NIR-II) window. In the presence of NO, due to the conversion of IR NO into IR RA and excellent stability of the downconversion nanoparticle (DCNP), DCNP@MPS@IR NO could present a "Turn-On" fluorescence signal at 1050 nm under 808 nm excitation (F1050Em,808Ex) and an "Always-On" fluorescence signal at 1550 nm under 980 nm excitation (F1550Em,980Ex), which led to a "Turn-On" ratiometric fluorescence signal F1050Em,808Ex/F1550Em,980Ex. DCNP@MPS@IR NO was then successfully applied in vitro to selectively detect NO, at a linear concentration range of 0-100 μM with a limit of detection of 0.61 μM. In vivo results revealed that DCNP@MPS@IR was available to quantify NO in acetaminophen (APAP)-induced liver injury, monitor DILI, and screen an antidote for APAP through NIR-II ratiometric fluorescence imaging. We envision that our nanoprobe DCNP@MPS@IR NO might become a really useful biotechnology tool for visualizing and early diagnosis of drug-induced liver injury and revealing the mechanism of drug hepatotoxicity in the clinic in the near future.

Reduction of Nitrogen Oxides by Hydrogen with Rhodium(I)-Platinum(II) Olefin Complexes as Catalysts.

The nitrogen oxides NO2, NO, and N2O are among the most potent air pollutants of the 21st century. A bimetallic RhI–PtII complex containing an especially designed multidentate phosphine olefin ligand is capable of catalytically detoxifying these nitrogen oxides in the presence of hydrogen to form water and dinitrogen as benign products. The catalytic reactions were performed at room temperature and low pressures (3–4 bar for combined nitrogen oxides and hydrogen gases). A turnover number (TON) of 587 for the reduction of nitrous oxide (N2O) to water and N2 was recorded, making these RhI–PtII complexes the best homogeneous catalysts for this reaction to date. Lower TONs were achieved in the conversion of nitric oxide (NO, TON=38) or nitrogen dioxide (NO2, TON of 8). These unprecedented homogeneously catalyzed hydrogenation reactions of NOx were investigated by a combination of multinuclear NMR techniques and DFT calculations, which provide insight into a possible reaction mechanism. The hydrogenation of NO2 proceeds stepwise, to first give NO and H2O, followed by the generation of N2O and H2O, which is then further converted to N2 and H2O. The nitrogen−nitrogen bond‐forming step takes place in the conversion from NO to N2O and involves reductive dimerization of NO at a rhodium center to give a hyponitrite (N2O2 2−) complex, which was detected as an intermediate.

Reduction of Nitrogen Oxides by Hydrogen with Rhodium(I)–Platinum(II) Olefin Complexes as Catalysts

AbstractThe nitrogen oxides NO2, NO, and N2O are among the most potent air pollutants of the 21st century. A bimetallic RhI–PtII complex containing an especially designed multidentate phosphine olefin ligand is capable of catalytically detoxifying these nitrogen oxides in the presence of hydrogen to form water and dinitrogen as benign products. The catalytic reactions were performed at room temperature and low pressures (3–4 bar for combined nitrogen oxides and hydrogen gases). A turnover number (TON) of 587 for the reduction of nitrous oxide (N2O) to water and N2 was recorded, making these RhI–PtII complexes the best homogeneous catalysts for this reaction to date. Lower TONs were achieved in the conversion of nitric oxide (NO, TON=38) or nitrogen dioxide (NO2, TON of 8). These unprecedented homogeneously catalyzed hydrogenation reactions of NOx were investigated by a combination of multinuclear NMR techniques and DFT calculations, which provide insight into a possible reaction mechanism. The hydrogenation of NO2 proceeds stepwise, to first give NO and H2O, followed by the generation of N2O and H2O, which is then further converted to N2 and H2O. The nitrogen−nitrogen bond‐forming step takes place in the conversion from NO to N2O and involves reductive dimerization of NO at a rhodium center to give a hyponitrite (N2O22−) complex, which was detected as an intermediate.

Electro-Synthesis of Ammonia From Dilute Nitric Oxide on a Gas Diffusion Electrode

The electrochemical conversion of nitric oxide (NO) to ammonia (NH3) provides a sustainable route to transform an air pollutant into a value-added chemical. However, the development of NO electroreduction remains hindered by the poor solubility in aqueous electrolytes, requiring the use of concentrated NO. Here, we report a dilute NO reduction using a gas diffusion electrode (GDE) to circumvent the mass transport issue. Through the incorporation of nanoscale zero-valent iron into carbon on the GDE, 96% NH3 Faradaic efficiency was achieved with 1% NO, and the computational calculations revealed that the Fe catalyzed the breaking of the N–O bond in the H2NO intermediate. The NH3 production rate was accelerated by controlling the concentration of protons in the electrolyte and reached 1,239 µmol cm-2h-1 with 10% NO. Our findings show that the gas-phase electrolysis of dilute NO can offer a practical option for upcycling the waste nitrogen.

Monitoring a MOF Catalyzed Reaction Directly in Blood Plasma.

Herein, we establish a method to quantitatively monitor a metal-organic framework (MOF)-catalyzed, biomedically relevant reaction directly in blood plasma, specifically, the generation of nitric oxide (NO) from the endogenous substrate S-nitrosoglutathione (GSNO) catalyzed by H3[(Cu4Cl)3-(BTTri)8] (CuBTTri). The reaction monitoring method uses UV-vis and 1H NMR spectroscopies along with a nitric oxide analyzer (NOA) to yield the reaction stoichiometry and catalytic rate for GSNO to NO conversion catalyzed by CuBTTri in blood plasma. The results show 100% loss of GSNO within 16 h and production of 1 equiv. of glutathione disulfide (GSSG) per 2 equiv. of GSNO. Only 78 ± 10% recovery of NO(g) was observed, indicating that blood plasma can scavenge the generated NO before it can escape the reaction vessel. Significantly, to best apply and understand reaction systems with biomedical importance, such as NO release catalyzed by CuBTTri, methods to study the reaction directly in biological solvents must be developed.

Coupling CO2 utilization and NO reduction in chemical looping manner by surface carbon

Carbon deposits typically enforce shutdowns of chemical reactors to periodically regenerate their active materials, a continuous challenge for industry and scientists alike. This downside can however be turned to benefit by utilizing carbon’s reductive power. Here, we integrate dry reforming of methane (DRM) and selective reduction of nitric oxide (SRN) in a novel chemical looping process, coupled by the periodic deposition and removal of surface carbon, which participates in both reactions. Carbon formed on the catalyst during dry reforming is subsequently used as reductant for nitric oxide (NO) conversion into N2, hence not only achieves stable CO2 utilization and NO reduction with cyclic catalyst regeneration, but also reduces the consumption of valuable energy resources demanded by NO removal. In contrast to co-feeding all reactants in a single step, the inherent temporal-spatial separation of reactions in chemical looping allows for complete conversion of carbon and NO, ensuring a higher exergetic efficiency (70 % more efficient). Also, adaptation of the relative duration of the DRM and SRN steps to the conditions of the CO2 and NO industrial point sources allows to account for the differences in supply of carbon and NO, offering an attractive strategy for selective catalytic reduction of NO with greenhouse gases rather than NH3.

Effect of Gas Components and Particulate Matter on the Conversion of Nitric Oxide by Dielectric Barrier Discharge

The conversion of nitric oxide by dielectric barrier discharge (DBD) in different reaction gases (O2, H2O, Ar, and N2) was studied. In the N2/O2 system, N and O could react to form NO; consecutively, extra O would oxidize NO to form NO2. Increase of oxygen content would promote the generation of NO, and the highest concentration of NO2 could be obtained with different oxygen contents at specific energy inputs (SEIs) of 1200 or 1440 J/L. In the N2/O2/NO system, the oxidation and reduction of NO took place simultaneously to form NO2 and N2, and NO was mainly removed by reduction when the oxygen content was lower than 6 vol %. In comparison, in the Ar/O2/NO system, NO was mainly oxidized to NO2. However, when the oxygen content exceeded 12 vol %, the increase of the SEI between 960 and 1440 J/L will increase the temperature of the DBD reactor, resulting in the restrain of the NO oxidation rate. In the SO2/N2/O2/NO system, SO2 could be oxidized by O radicals in the discharge region, leading to the restrain of NOx generation. In the H2O/N2/O2/NO system, H2O could promote the oxidation of NO so that NO conversion could reach 100% at 18 vol % O2 content. In the system of particulate matter/N2/O2/NO, particles would change the parameters in the discharge region and promote the production of N and O radicals, leading to the concentrations of NO2 and NOx being higher than those in the N2/O2/NO system. When the oxygen content was lower than 6 vol %, the conversion of NO reached 100% at 960 J/L. N2O formed in all systems as a byproduct of NO conversion by DBD. With the increase of the SEI, part of N was oxidized, resulting in the increase of NOx in all the systems containing N2.

Interference from HONO in the measurement of ambient air NO2 via photolytic conversion and quantification of NO

The reference method to quantify mixing ratios of the criteria air pollutant nitrogen dioxide (NO2) is NO-O3 chemiluminescence (CL), in which mixing ratios of nitric oxide (NO) are measured by sampling ambient air directly, and mixing ratios of NOx (= sum of NO and NO2) are measured by converting NO2 to NO using, for example, heated molybdenum catalyst or, more selectively, photolytic conversion (P-CL). In this work, the nitrous acid (HONO) interference in the measurement of NO2 by P-CL was investigated. Results with two photolytic NO2 converters are presented. The first used radiation centered at 395 nm, a wavelength region commonly utilized in P-CL. The second used light at 415 nm, where the overlap with the HONO absorption spectrum and hence its photolysis rate are less. Mixing ratios of NO2, NOx and HONO entering and exiting the converters were quantified by Thermal Dissociation Cavity Ring-down Spectroscopy (TD-CRDS). Both converters exhibited high NO2 conversion efficiency (CFNO2; > 90%) and partial conversion of HONO. Plots of CF against flow rate were consistent with photolysis frequencies of 4.2 s-1 and 2.9 s-1 for NO2 and 0.25 s-1 and 0.10 s−1 for HONO at 395 nm and 415 nm, respectively. CFHONO was larger than predicted from the overlap of the emission and HONO absorption spectra. The results imply that measurements of NO2 by P-CL marginally but systematically overestimate true NO2 concentrations, and that this interference should be considered in environments with high HONO:NO2 ratios such as the marine boundary layer or in biomass burning plumes.