Decomposition Of Nitrite Research Articles

Mechanistic insights and application potentials for CeO2-Al2O3 passive NOx adsorber (PNA) materials

A series of CeO2/Al2O3 with Ce loading from 0.5 to 5.0 wt% were studied as PNA materials for low temperature NOx abatement. Via XRD, TEM imaging and UV–vis spectroscopy studies, it was demonstrated that CeO2 is present as nanoparticles on the Al2O3 support, and the particle size increases with increasing Ce loading. PNA performance of these materials was investigated by NOx trapping followed by TPD. The PNA chemistry was further probed with in situ NO-DRIFT spectroscopy. PNA chemistry involves a rapid direct NO trapping route that leads to surface nitrite formation, and a slower NO2 trapping route that leads to surface nitrate species. Surface nitrite decomposition releases NO at 200–300 °C, suitable for PNA application. Based on NO yields during TPD, the atomic efficiency of surface Ce was calculated, which demonstrates that dispersing CeO2 on high surface area supports is a viable strategy for improving PNA efficiency of CeO2-based materials.

Spectrophotometric Analysis of Nitrite in Gunshot Recentness Examinations from Non Toxic Ammunitions: Expanding the Frontiers of Forensic Chemistry

Nitrite ions consist on an important chemical clue related to gunshot examination, concerning to estimation of the time since discharge. Current forensic laboratory methods for nitrite analysis in gunshot residues are well established for investigating conventional ammunition residues. However, the use of these methods to analyze the so-called ecological or “non-toxic” ammunition has been less studied. Here, we have developed a spectrophotometric flow injection analysis method to test nitrite in samples of “non-toxic” ammunition residues. The ammunition used in these experiments was the NTA (non-toxic ammunition) model, .38 caliber, We also investigated the kinetics of nitrite decomposition for this type of ammunition over time. Sulfanilic acid and 1-naphthylethylenediamine in acetic acid were used as colorimetric reagents. The linear dependence of the spectrophotometric signal on the nitrite concentration was as follows: A = 2.07 x 104 µmol-1 L [NO2-] + 6.78 x 10-3 with a correlation coefficient (r) of 0.9994. The standard deviation (SD) of the analytical curve was 3.17 x 10-3 resulting in a limit of detection (LOD) = 0.46 µmol L-1 and a limit of quantification (LOQ) = 1.56 µmol L-1. The proposed instrumental method was more sensitive than conventional colorimetric tests and permitted the detection window to be extended to 32 days while ensuring the safety and reliability required for forensic analysis, in comparison to 7-10 days usually proposed for conventional ammunition. Therefore, the proposed method can be safely employed in forensic laboratories for routine analysis of nitrite ions in GSR samples from ecological or “non-toxic” ammunition.

Effects of platinum high-temperature redispersion on Pt/Al2O3 diesel oxidation catalyst for nitric oxide oxidation and its reaction pathway

High-temperature redispersion of platinum nanoparticle is inevitable for Pt/Al2O3 diesel oxidation catalyst (DOC), yet its effects on NO catalytic oxidation and its reaction mechanism are still indeterminate. Results of this work indicate that high-temperature redispersion not only decrease the nano-size of platinum particle, but also increase the crystallinity. The smaller size of platinum nanoparticle is beneficial for the reduction of high valence Ptδ+ species to form Pt0 active phase and hence improving NO oxidation performance. The higher crystallinity of platinum particle is beneficial to maintaining Pt0 state but adverse to the reduction of Ptδ+ species during long-time use. In-situ Fourier transform infrared spectroscopy results prove that NO oxidation on Pt/Al2O3 catalyst is mainly through the intermediates of nitrite and bridging nitrate. It will convert to chelated nitrates if the decomposition of nitrite and bridging nitrate intermediates are not able to occur promptly. Chelated nitrates are stable and hard to decompose which therefore will restrain NO oxidation reaction. The smaller Pt nano-size is conducive to the decomposition of nitrite/nitrate intermediates and therefore boost NO oxidation reaction, simultaneously the higher Pt crystallinity will lead to the generation and accumulation of chelated nitrates consequently cover the active sites and restrain NO oxidation reaction.

High resolution measurements reveal abiotic and biotic mechanisms of elevated nitric oxide emission after wetting dry soil

Wetting dry soil triggers emission of nitric oxide (NO), which can harm air quality and influence ecosystem N balance. NO released after wetting may be derived from two primary mechanisms: (1) abiotic decomposition of nitrite (NO2−) present in the dry soil and (2) biologically-mediated production of NO. The relative contributions of these mechanisms to NO emission are challenging to partition. To differentiate the two mechanisms, we made continuous observations of NO emission from a range of soils that varied in texture, pH, and exchangeable cations. We coupled NO gas exchange measurements with automated, non-destructive high-resolution sampling of inorganic N species via microdialysis. We identified two distinct phases of NO production (1) an initial phase that reached its maximum less than 30 min after rewetting; and (2) a second phase lasting up to 36 h. The magnitude of the initial phase of NO production was correlated with the initial nitrous acid concentration (calculated from NO2− concentrations and soil pH) and soil exchangeable calcium. The second phase of NO emission coincided with a peak in NO2− that preceded NO3− accumulation. Together, these results suggest that NO emissions following wetting are defined by an initial pulse of abiotic NO formation mediated by soil acidity at mineral surfaces, followed by a prolonged pulse of NO emission driven by a lag between the biological processes of ammonia oxidation and nitrite oxidation. These results can inform mechanistic models of NO emissions from soils to improve predictions of the terrestrial N cycle and atmospheric chemistry.

A modular, multi-diagnostic, automated shock tube for gas-phase chemistry.

A new shock tube has been constructed for investigations of high-temperature chemical kinetics with an emphasis on combustion chemistry. This instrument includes a diaphragmless driver and electrical control of valving. A diaphragmless design significantly improves repeatability of experimental conditions vs the use of diaphragms and leads to an approximate order of magnitude reduction in turnaround time between experiments. Electrical control of valves, combined with diaphragmless operation, also enables remote and automated operation of the shock tube. The design allows for both incident and reflected shock experiments with multiple diagnostics. The performance of the shock tube is demonstrated by reproducing previous literature measurements on the unimolecular decomposition of isobutyl nitrite and cyclohexene.

Evaluation of H2 Influence on the Evolution Mechanism of NO Storage and Reduction over Pt–Ba–Ce/γ-Al2O3 Catalysts

Abstract In this investigation, Pt–Ba–Ce/γ-Al2O3 catalysts were prepared by incipient wetness impregnation and experiments were performed to evaluate the influence of H2 on the evolution mechanism of nitrogen oxides (NOx) storage and reduction (NSR). The physical and chemical properties of the Pt–Ba–Ce/γ-Al2O3 catalysts were studied using a combination of characterization techniques, which showed that PtOx, CeO2, and BaCO3, whose peaks were observed in X-ray diffraction (XRD) spectra, dispersed well on the γ-Al2O3, as shown by transmission electron microscope (TEM), and that the difference between Ce3+ and Ce4+, as detected by X-ray photoelectron spectroscopy (XPS), facilitated the migration of active oxygen over the catalyst. In the process of a complete NSR experiment, the NOx storage capability was greatly enhanced in the temperature range of 250–350 °C, and reached a maximum value of 315.3 μmol·gcat−1 at 350 °C, which was ascribed to the increase in NO2 yield. In a lean and rich cycling experiment, the results showed that NOx storage efficiency and conversion were increased when the time of H2 exposure (i.e., 30, 45, and 60 s) was extended. The maximum NOx conversion of the catalyst reached 83.5% when the duration of the lean and rich phases was 240 and 60 s, respectively. The results revealed that increasing the content of H2 by an appropriate amount was favorable to the NSR mechanism due to increased decomposition of nitrate or nitrite, and the refreshing of trapping sites for the next cycle of NSR.

Interaction of Coal with Sodium Nitrite

A mechanism is proposed for the interaction of coal with paramagnetic nitrogen oxides produced in the decomposition of sodium nitrite. The main role in the self-oxidation of coal is played by quinoid structures with high redox potential. Four basic periods are identified in the thermooxidative transformation of coal. These periods differ in the rate of the processes, the quantity of gaseous oxidative products, and their composition. The decomposition products of the coal react most vigorously with the oxidant in the fourth period. That leads rapidly to self-heating of the reaction mixture, culminating in explosive gas liberation.

Application of Si/SiC ceramic filters as support for structural palladium catalysts for the reductive decomposition of aqueous nitrite

A Si/SiC ceramic filter was used to support a structural palladium catalyst in a continuous fixed-bed flow reactor during a reductive decomposition of nitrite. A previous report described the use of non-porous alumina spheres coated with Pd/C, a carbon monolith impregnated with Pd or a structural catalyst consisting of a polyurethane sponge skeleton impregnated with Pd resulted either in negligible activity or a complete stoppage of the flow by increasing the pressure drop in the flow system. The use of a Si/SiC filter impregnated with palladium, however, overcame the demerits and resulted in an 11% conversion of nitrite in 60 min. The use of a Si/SiC filter coated with a char intermediate followed by impregnation with Pd (Pd/C/Si/SiC) resulted in a structural catalyst that enhanced the activity to yield a 33% conversion of nitrite in 60 min. When five Pd/C/Si/SiC structural catalysts were used, however, the complete decomposition was achieved in the same amount of time. Although improvement was previously observed by using an alumina intermediate, use of the char intermediate resulted in a new factor for activity improvement. The characterization results show that it was the affinity between aqueous nitrite and the intermediate rather than palladium dispersion that contributed the most to the improvement of activity.

Nitrite kinetics during anoxia: The role of abiotic reactions versus microbial reduction

Anoxic spells in soil induce denitrification, i.e. the sequential reduction NO3−→NO2−→NO→N2O→N2, catalysed by the four enzymes NAR, NIR, NOR and NOS, respectively. Transient accumulation of all intermediates is inevitable, but the concentrations depend on the regulation of gene expression and the physical/chemical properties of the soil. Nitrite is chemically unstable at low pH, decomposing via a conglomerate of abiotic reactions with metals and organic compounds which can result in production of NO, N2O, N2 and nitrosated organic compounds (R-NO). There is evidence that acidic soils accumulate less nitrite than neutral soils, but it is unclear if this is due to high abiotic decomposition rate (VADEC) or fast enzymatic reduction of nitrite (VNIR) at low pH. To investigate this, we monitored the kinetics of NO2−, NO, N2O and N2 during anoxic incubations of three organic soils with pHCaCl2 ranging from 3.4 to 7.2, taken from a long-term liming experiment. In parallel, we determined the rate of abiotic nitrite decay (VADEC) and its product stoichiometry (NO, N2O and R-NO) in gamma-irradiated soils. VADEC was clearly first-order with respect to HNO2 (kHNO2 = 1.4 h−1), N-gas production (NO, N2O and N2) accounted for only ∼50% of VADEC, the rest was ascribed to nitrosation (R-NO). During denitrification (live soil incubation), the nitrite concentrations reached 2–3 mM in the soils with pH 4.9 and 7.2, while the soil with pH 3.4 kept nitrite concentrations at 20–50 μM, except for a short spike reaching 160 μM after 40 h. Estimated rates of nitrite scavenging by the two competing sinks (NIR and ADEC) showed that NIR was the strongst nitrite sink in soil with pH 3.4 (VNIR > VADEC), while VNIR ≈ VADEC in the soil with pH 5.9. In the soil with pH 7.2, VADEC was insignificant. Thus, the regulation of denitrification (high VNIR relative to VNAR) played a crucial role in determining nitrite kinetics, hence the fate of nitrite in acid soils. High nitrite reductase activity effectively minimized abiotic nitrite decomposition and nitrosation of soil organic matter. The results shed light on regulation of denitrification in acid soils, and its implications for the fate of nitrogen during denitrification events.

Reductive Decomposition of Nitrite in a Continuous-Flow Reactor Using Fixed-Bed Structural Pd Catalysts

In order to decompose trace amounts of nitrite in drinking water under mild conditions, a fixed-bed filtering system that used structural catalysts was employed to filter recycled aqueous nitrite. High performance and continuous mass processing are generally accepted as requirements to catalyze the decomposition of aqueous nitrite. However, the use of a fixed-bed operation when recycling aqueous nitrite with palladium catalyst systems could result in either negligible activity when using a carbon monolith impregnated with Pd, or could stop the flow by enhancing the pressure drop when using non-porous alumina spheres coated with Pd/C or structured catalysts consisting of a polyurethane sponge skeleton impregnated with Pd. In the present paper, a Si/SiC ceramic filter was employed as a structured support to prevent pressure drop. When palladium was loaded onto the surface of the filter via electroless plating, continuous flow suitably continued, and the conversion of nitrite was 45% after 60 min. In contrast, when palladium was loaded after the coating of the filter with alumina, complete decomposition was achieved after 60 min under conditions corresponding to those used for the former system. X-ray diffraction, an N2 adsorption-desorption measurement, scanning-electron microscopy and energy-dispersive X-ray spectroscopy analyses revealed that a higher dispersion of palladium on the latter structured catalyst resulted in the greatest level of activity for the reductive decomposition of aqueous nitrite.

Effect of nitrate on residual nitrite decomposition rate in cooked cured pork

The effects of nitrate on the color stability of cooked cured pork were examined. Nitrate inhibited the nitrite decrement and discoloration in the cooked cured ham. Nitrate reduction and nitrite accumulation were observed in the uncooked sausage models, but were not detected in the sausage models cooked at 75°C. The kinetics of nitrite degradation was subsequently examined at various concentrations of nitric acid at constant acidity. The degradation rate of nitrite was clearly found to decrease with nitric acid content. Thus, nitrate does not appear to serve as a donor of nitrite, but rather inhibits nitrite reduction in cooked meat products, with consequent prolongation of color stability.

Selective electrochemical reduction of nitrogen oxides by covalent triazine frameworks modified with single Pt atoms

The present work demonstrates that a single platinum atom-modified covalent triazine framework hybridized with carbon nanoparticle (Pt-CTF/CP) exhibited selective activity for the electrochemical reduction of nitrogen oxides. Pt-CTF/CP had low nitrate reduction activity, but efficiently catalyzed the reduction of nitric oxide (NO) molecules derived from the decomposition of nitrite. In contrast, a bulk Pt surface exhibited high activity for both reactions. The selectivity of Pt-CTF/CP for NO is likely due to the unique adsorption behavior of hydrogen atoms and/or nitrate ions on the single Pt atoms.

Wheat fiber colored with a safflower (Carthamus tinctorius L.) red pigment as a natural colorant and antioxidant in cooked sausages

This study was conducted to evaluate the effects of nitrite and wheat fiber (WFC) colored with a safflower (Carthamus tinctorius L.) red pigment on the color characteristics and lipid oxidation of cooked sausages. The safflower red pigment (carthamin) was extracted at alkali condition, and wheat fiber was colored with the extracted safflower red pigment. Total six cooked sausage treatments were prepared with two nitrite levels (0 and 120 ppm) and three WFC levels (0, 1, and 2%). As the WFC level was increased, redness of cooked sausages increased, regardless of presence/absence of nitrite. Carthamin contained in WFC could promote a reaction and/or decomposition of nitrite, resulting in increased nitrosoheme pigment and decreased residual nitrite. In addition, WFC inhibited lipid oxidation of cooked sausages. Consequently, the addition of WFC resulted in positive effects on color formation, residual nitrite, and lipid oxidation, as well as the improvement cooking yield of cooked sausages. Therefore our result suggested that WFC could be possible to partially replace nitrite and coloring of dietary fiber with natural pigments is a useful technique to expand the purposeful use of dietary fiber.

Kinetics of Sulfite Oxidation in the Simultaneous Desulfurization and Denitrification of the Oxidation‐Absorption Process

AbstractThe kinetics of sulfite oxidation in the simultaneous desulfurization and denitrification of the oxidation‐absorption process was investigated with a bubbling apparatus under the conditions of varying pH, sulfite concentration, nitrite concentration, temperature, and air flow. The results indicate that the oxidation of sulfite is promoted dramatically by mixing with nitrite, due to the decline of the apparent energy of activation and the initiation of nitric dioxide decomposition by nitrite. An increase of the nitrite concentration, the air flow, the reaction temperature, or the pH supports the decomposition of nitrite and the production of nitric dioxide, thus leading to an enhancement of the sulfite oxidation rate. A kinetic model is established according to the experimental results. A satisfactory agreement between the calculated and the experimental values is obtained.

A Signature of Roaming Dynamics in the Thermal Decomposition of Ethyl Nitrite: Chirped-Pulse Rotational Spectroscopy and Kinetic Modeling.

Chirped-pulse (CP) Fourier transform rotational spectroscopy is uniquely suited for near-universal quantitative detection and structural characterization of mixtures that contain multiple molecular and radical species. In this work, we employ CP spectroscopy to measure product branching and extract information about the reaction mechanism, guided by kinetic modeling. Pyrolysis of ethyl nitrite, CH3CH2ONO, is studied in a Chen type flash pyrolysis reactor at temperatures of 1000-1800 K. The branching between HNO, CH2O, and CH3CHO products is measured and compared to the kinetic models generated by the Reaction Mechanism Generator software. We find that roaming CH3CH2ONO → CH3CHO + HNO plays an important role in the thermal decomposition of ethyl nitrite, with its rate, at 1000 K, comparable to that of the radical elimination channel CH3CH2ONO → CH3CH2O + NO. HNO is a signature of roaming in this system.

Characterization of novel nitrite-based nitric oxide generating delivery systems for topical dermal application

Topical application of nitric oxide (NO) has been shown to exert beneficial effects in the therapy of chronic wounds, impaired microcirculation, and skin infections. Nitrite acidified by ascorbic acid has been widely used in many studies as NO-donor system, unfortunately with inflammatory and toxic effects on the treated skin due to unregulated excessive NO generation, low pH and possible toxic side products. Here we describe an essentially modified nitrite based NO generating system that avoid the mentioned unwanted side effects on human skin by using a pH-stable acetate/acetic acid buffer with a skin neutral pH of 5.5 and sodium ascorbate. In order to overcome the shortcoming of lower NO yields due to the higher pH-value and low nitrite concentrations, we have determined additionally the influence of copper ions. To investigate the influence of different NO release and penetration kinetics on NO-induced toxicity, we have developed a fibroblast assay using cell culture plates with gas permeable bottoms. The results show clearly that the donor system can achieve a sustained NO generation without generating high peaks.Furthermore, the presence of Cu2+ ions enhances manifold NO generation of pH/ascorbate-induced nitrite decomposition, a mechanism comprising the reduction of Cu2+ ions to Cu1+ by ascorbate. Finally, we have found that apart from the NO dose the NO release kinetics had a significant influence of cell toxicity. Thus, application of comparable NO amounts within a time interval of 600s led to the development of variable cell toxicities, which predominantly depended on the NO concentration values generated in the first 200s.In summary, we here describe a novel nitrite-based NO-donor system that can provide well defined NO concentrations at skin neutral pH-values for side effect poor topical dermal application, i.e. in the therapy of chronic wounds and impaired microcirculation.

Effect of alkyl nitrite decomposition on catalytic performance of CO coupling reaction over supported palladium catalyst

The syntheses of dimethyl oxalate (DMO) and diethyl oxalate (DEO) by CO coupling reaction in gaseous phase were investigated in a fixed bed reactor over Pd-Fe/Al2O3 catalyst. The catalytic performance was characterized by CO conversion, space-time yield (STY) and selectivity of DMO (or DEO). The results showed that over Pd-Fe/Al2O3 catalyst, the STY of DMO was higher than that of DEO under the same reaction conditions. The optimum reaction temperatures for synthesizing DMO and DEO were 403 K and 393 K, respectively, at the molar ratio 1:1 of alkyl nitrite to CO. The difference in synthesizing DMO and DEO on the same catalyst was attributed to the decomposition performances of methyl nitrite (MN) and ethyl nitrite (EN), as density functional theory (DFT) calculation showed that EN decomposed more easily than MN.

Selective liquid phase oxidation of benzyl alcohol catalyzed by carbon nanotubes

A HNO3-promoted benzyl alcohol catalytic oxidation system was developed in the presence of carbon nanotubes (CNTs), using molecular oxygen as the terminal oxidant under the mild reaction conditions. The effects of solvent, reaction temperature, amount of HNO3, catalyst loading and surface structure of CNTs on the catalytic performances have been investigated. The CNTs showed excellent catalytic activity exhibiting benzyl alcohol conversion of 96.2% and benzaldehyde selectivity of 88.3% under optimal conditions. In particular, it had remarkable reusability without a significant loss in its activity and selectivity after six consecutive usages. The carbon catalysts were characterized by N2 adsorption–desorption, FT-IR (Fourier transform infrared spectroscopy), Raman, SEM (scanning electron microscopy) and TEM (transmission electron microscopy) techniques. A possible reaction pathway has been proposed, it is clarified that HNO2 attacks benzyl alcohol to generate benzyl nitrite, which is decomposed to benzaldehyde over the HNO3-promoted CNTs-catalyzed system, and electron transfer in graphene sheets plays an important role in the decomposition of benzyl nitrite. These results not only provide an attractive metal-free alternative to noble-metal-catalyzed systems but also come up with a better understanding of the mechanism of CNTs as a metal-free catalyst for the liquid-phase oxidation of benzyl alcohol.

Protonated Nitrosamide and Its Potential Role in the Release of HONO from Snow and Ice in the Dark

A joint Fourier transform reflection absorption infrared spectroscopy/thermal programmed desorption (RAIRS/TPD) study has provided good evidence for the existence of protonated nitrosamide (NH₃NO(+)) on surfaces at cold temperatures. This species has long been proposed to exist in studies of the DeNO(x) process and the decomposition of ammonium nitrite. In the context of the current experiments, performed at low-temperatures in the absence and presence of water-ice, the results provided a firm mechanistic basis for understanding the release of HONO from snowpack in a "dark" mechanism and also under alkaline surface conditions.

뽕잎발효차 제조에 따른 항산화 및 in vitro 항암활성

This study was conducted to compare and analyze the qualitative property of MLT (mulberry leaf tea) and FMLT (fermented mulberry leaf tea) based on the antioxidant, anticancer activities of various extracts. When the antioxidant activity of MLT and FMLT extracts was evaluated, the electron donating activity was found to increase proportionally as the concentration of each extract increased. In addition, the extract of FMLT showed a higher electron donating activity than that of MLT. Furthermore, the ethanol extracts showed the highest electron donating ability. When the SOD activity was evaluated, it was also found to increase proportionally with the concentration of each extract. Furthermore, the SOD activity of the ethanol extract group was the highest, whereas the SOD like activities of both MLT and FMLT were similar. When nitrite decomposition was evaluated for each pH, the highest value was observed at pH 1.2. Finally, the nitrite deleting ability was the highest for the ethanol extracts. When each extract of MLT and FMLT was analyzed in vitro for anticancer effects, they were found to decrease the number of cancer cells proportionally as the concentration of extract increased for both HeLa cells and MCF-7 cells. Furthermore, FMLT was found to exert a greater inhibition of cancer cells than MLT. Among the extract groups, the ethanol extract induced the greatest inhibition of the development of cancer cells, and these effects were greater against MCF-7 cells than HeLa cells.