Desorption Of NO Research Articles

Residue analysis of nitric oxide fumigation in nine stored grain and nut products

Nitric oxide (NO) is a recently discovered fumigant for postharvest pest control on fresh and stored products. Nitric oxide fumigation also does not leave residues on fresh fruit and vegetables when conducted properly. In this study, we analyzed nitrate (NO3−) and nitrite (NO2−) levels in liquid extracts and nitrogen dioxide (NO2) desorption rates as residues of NO fumigation at various times after fumigation on nine stored grain and nut products. Each product was fumigated separately with 3.0% NO for 24 h in two treatments: one treatment (NO–N2) was terminated with nitrogen gas (N2) flush and the other (NO-Air) was terminated with normal air flush. For NO–N2, NO3− concentrations of all fumigated products were not significantly higher than those of untreated controls at 1, 7, and 14 d after fumigation. NO2− concentrations of all fumigated products from N2 gas flush were not significantly higher than those of control products at 14 d after fumigation. NO2 desorption rates for most products from NO–N2 treatment showed no significant difference from those for the controls 1 d after NO fumigation, except for beans and wheat, which showed no significant difference at ≥7 d after fumigation. All products from NO-Air treatment, however, had significant higher NO3− and NO2− ion concentrations in liquid extracts at 14 d after fumigation than those from NO–N2 treatment and the control. NO2 desorption rates in all products from NO-Air treatment were also significantly higher than those from NO–N2 treatment and the control at 21 d after fumigation. Therefore, when terminated properly with N2 flush, NO fumigation did not result in significant increases of NO3−, NO2−, or NO2 as residue in nut and grain products.

Growth of cobalt films at room temperature using sequential exposures of cobalt tricarbonyl nitrosyl and low energy electrons

Cobalt thin films were grown at room temperature using sequential exposures of cobalt tricarbonyl nitrosyl (CTN, Co(CO)3NO) and low energy (75–175 eV) electrons. During this cyclic growth process, the CTN molecules were first adsorbed on the substrate. The electrons then induced the desorption of the carbonyl and nitrosyl ligands from the adsorbed CTN. The removal of CO and NO ligands produced new adsorption sites. Subsequent CTN exposures allowed CTN to react with these new adsorption sites on the substrate. In situ ellipsometry was utilized to monitor the film thickness during the electron enhanced growth. Co growth rates as high as 1.3 Å/cycle were observed by in situ ellipsometry depending on the reaction conditions. The in situ ellipsometry also observed the CTN adsorption and the removal of the carbonyl and nitrosyl ligands. Quadrupole mass spectrometer measurements confirmed the desorption of CO and NO during electron exposures. X-ray photoelectron spectroscopy (XPS) measured N XPS signals from the Co films deposited using electron exposures at 200 eV. The N/Co XPS signal ratio was consistent with the dissociation of 13% of the nitrosyl ligands on the CTN precursors that lead to Co deposition. In contrast, the negligible C XPS signals from the Co films indicated that the CO ligands were desorbed completely from CTN by the electron exposures at 200 eV. Under identical reaction conditions at lower incident electron currents, the maximum growth rate was obtained at an electron energy of 125 eV. Because the Co growth depends on the electron flux, the Co films were deposited only on the surface area irradiated by the electron beam. The spatial profile of the Co film deposited using long electron exposure times was mapped by ex situ spectroscopic ellipsometry. This spatial profile displayed a pronounced flat top that was consistent with the electron flux desorbing nearly all the CO and NO surface coverage in the central area of the electron beam during each reaction cycle. The spatial profile was used to calculate an electron induced desorption cross section of σ = 2 × 10−17 cm2 at 200 eV. This cross section was in approximate agreement with the cross sections for the electron impact dissociation of CTN in the gas phase.

Dissipative quantum dynamics using the stochastic surrogate Hamiltonian approach.

Based on the original Stochastic Surrogate Hamiltonian approach for the simulation of open quantum system dynamics, we present a modified algorithm for the swap procedure. The implementation is tested with nuclear relaxation dynamics of model systems known from literature, i.e., the harmonic oscillator and the Morse oscillator. Finally, the stochastic surrogate Hamiltonian is applied to simulate the dynamical electronic excitation and relaxation of a photodesorption process. This is the first application of the stochastic surrogate Hamiltonian in an ab initio context. A comparison to a surrogate Hamiltonian benchmark allows us to evaluate the results obtained. For this purpose, the well-studied laser-induced desorption of NO from NiO(100) is chosen.

Effect of N-doping on NO2 adsorption and reduction over activated carbon: An experimental and computational study

Due to high adsorption capacity, NO2 adsorption using activated carbon has become a potential denitration technology. A correlation between N-doping and NO2 adsorption process on activated carbon is pointed out by previous studies but lacks a clear explanation. The main objective of this work is to clarify the influencing mechanism of N-doping on NO2 adsorption and reduction over activated carbon. N-doped activated carbons were synthesized by melamine impregnation followed by calcination and tested as NO2 adsorbents. Experimental results showed that AC600 with highest N content possessed highest NO2 adsorption capacity and lowest NO release percentage. NO2 adsorption on activated carbon is a complex process, including NO2 adsorption, NO2 reduction to NO, and NO release. Density functional theory calculations results showed that N-doping affected all steps mentioned above. Firstly, N-doping increased NO2 physisorption energies, meaning that NO2 was easier to be adsorbed. Thus, NO2 adsorption capacities increased with the increase of N content experimentally. Secondly, N-doping increased the energy barrier of the rate-determining step of NO2 reduction. Thus, the reduction of NO2 to NO was harder. Thirdly, N-doping increased NO desorption energies, implying that the release of generated NO was harder. The inhibition of NO2 reduction and NO desorption results in the decrease of NO release percentage due to N-doping jointly. This work elucidates the influencing mechanism of N-doping on NO2 adsorption and NO2 reduction on theoretical level, which fills up the research gap and guides the design of activated carbon for efficient NO2 adsorption.

Influence of Ce doping on catalytic oxidation of NO on LaCoO3 (011) surface: A DFT study

The catalytic oxidation of NO on the undoped and Ce-doped LaCoO3 (011) surfaces has been systematically studied by utilizing the density functional theory (DFT) method. The extra-lattice oxygen and Mars−van Krevelen (MvK) mechanisms of NO oxidation are considered. According to our calculations, the extra-lattice oxygen mechanism is more likely to occur on the undoped and Ce-doped LaO-terminated LaCoO3 (011) surfaces, while the MvK mechanism is more suitable for the undoped and Ce-doped CoO2-terminated LaCoO3 (011) surfaces. By comparing and analyzing the same NO oxidation pathway on the undoped and Ce-doped surfaces, it is proved that the Ce doping is favorable for the LaO-terminated LaCoO3 (011) surface, but harmful for the CoO2-terminated LaCoO3 (011) surface. In our research on NO oxidation, the addition of Ce dopant contributes to the LaO-terminated LaCoO3 (011) surface by reducing the energy barriers of O2 dissociation and NO2 desorption.

Adsorption performance of CMK-3 and C-FDU-15 in NO removal at low temperature

CMK-3 and C-FDU-15 samples were synthesized using hard-templating and evaporation-induced self-assembly (EISA) methods, respectively. The pore structures of CMK-3 and C-FDU-15 as well as commercial activated carbon were characterized by means of X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and N2 adsorption-desorption. Adsorption of NO was investigated by means of thermogravimetric analysis, temperature-programmed desorption of NO + O2, and in situ diffuse reflectance Fourier transform infrared spectroscopy. The results show that the CMK-3 and C-FDU-15 materials possessed ordered and uniform structures. The co-adsorption capacity of NO and O2 decreased in the sequence CMK-3 (88.6 mg/g) > C-FDU-15 (71.7 mg/g) > AC (25.3 mg/g). There were two main adsorption species on CMK-3 and C-FDU-15: nitrite and nitrate. Nitrite is converted to nitrate easily. However, the adsorption species were more complex on AC, with nitrite being the main species. Moreover, CMK-3 and C-FDU-15 exhibit excellent regeneration efficiency compared with AC. The excellent NO adsorption performance of CMK-3 and C-FDU-15 was associated with their ordered mesoporous structures and high surface areas. The research provides more options for NO adsorption in the future.

Selective-detection NO at room temperature on porous ZnO nanostructure by solid-state synthesis method

High sensitivity and selectivity detection of NO at room temperature has always been full of challenges. In this work, a kind of porous ZnO with coralline-like nanostructure was prepared by a rapid and simple solid-state synthesis strategy, using zinc acetate and oxalic acid as precursors. Structural analysis and morphological investigations of the ZnO powder showed that it has a large specific surface area (32.75 m2 g−1) and many nanometer-sized channels between ZnO nanoparticles. This is beneficial to the adsorption and desorption of NO, which is an important reason for the selective detection of NO by the ZnO powder at room temperature. So based on the ZnO powder, a gas sensor was fabricated and its gas-sensing properties were investigated. It exhibited outstanding response (23.59) and fast response time (331 s) to 40 ppm of NO at room temperature (21 ± 2 °C). As the relative humidity study changed from 17% to 80% at 10 ppm of NO, the sensitivity of the sensor changed little, only decreased from 1.43 to 1.12. The stability study was also carried out. Under the concentration of 5 ppm of NO, the relative standard deviation was 0.33% within 8 days, which indicates that the obtained sensor is suitable for practical application.

Adsorption and Desorption of NO and NO2 Molecules on Gold Cluster Anions Observed by Thermal Desorption Spectrometry

The adsorption and thermal desorption of NO and NO2 molecules on gold cluster anions, Au4–, were experimentally observed using gas-phase thermal desorption spectrometry. Multiple collisions of NO molecules with Au4– at 300 K generated Au4(NO)k– (k = 1–3). The NO molecules desorbed from the clusters in a stepwise manner when the clusters were heated, and finally Au4– was regenerated above 600 K. For NO2, Au4N2O4– was found to be thermally unstable. Hence, two NO2 molecules were sequentially released from Au4N3O6–, when Au4N3O6– was heated at 500–800 K, forming Au4NO2–. A gold oxide cluster, Au4O2–, was produced as a result of the decomposition of NO2 to NO and O on Au4–, and the NO molecules were released above 900 K.

Mn‐Fe‐Ce Coating onto Cordierite Monoliths as Structured Catalysts for NO Catalytic Oxidation

AbstractA series of Mn‐Fe−X (X=Ce, W, Cu, Co) mixed oxides doped on cordierite monoliths as structured catalysts based monolithic for NO oxidation has been investigated. The results showed that Mn−Fe‐Ce/Al2O3/CC sample exhibited the best activity, for which a maximal NO conversion (72%) could be attained at 250 °C with the GHSV of 5971 h−1. The effects of the preparation parameters including the catalyst preparation methods and the coating material on the catalytic performance for NO catalytic oxidation was also investigated. The XRD and SEM‐EDS also indicated the coating material had a significant influence on specific surface area, surface morphology, which resulted in differences in the catalytic activity of NO catalytic oxidation. The NO+O2‐TPD results indicated that different general procedures to prepare Mn−Fe‐Ce based monolithic catalysts had a great influence on the catalytic oxidation activity of NO and Mn−Fe‐Ce/Al2O3/CC catalyst was beneficial to NO adsorption and NO2 desorption, which increased activity of catalytic oxidation of NO. The physisorption of N2 revealed that the catalyst synthesized with Al2O3 presented a higher BET specific surface area, more abundant pore structure, and better dispersion of catalysts’ active components which were favorable for catalytic oxidation reaction of NO.

The first non-precious metal passive NOx adsorber for cold-start applications

Co-SSZ-13 served as a non-PM passive NOx adsorber (PNA) was adopted for the first time, to the best of our knowledge, as a promising alternative to platinum-based NOx adsorbers. This Co-based catalyst has a NOx storage capacity of 27.3 μmol/gcat, which is 77% of that of Pd-SSZ-13. NOx is desorbed above 250 °C, which is appropriate for use downstream of the NH3-SCR catalyst. NO adsorption on Co-SSZ-13 resulted in the formation of dinitrosyl species, which are further converted into NO+ on the zeolite framework and nitrate species on Co2+. The strong interaction between Co2+ and NO is responsible for the high NOx storage capacity. In addition, conversion among the adsorbed species increases the NO desorption temperatures, which is important for the correct operation of PNA.

All-carbon fiber-based chemical sensor: Improved reversible NO2 reaction kinetics

All-carbon fiber-based chemiresistor is fabricated by assembling reduced graphene oxide (RGO) fiber and carbon nanotube (CNT) fiber as reversible NO2 sensing layer and flexible heater, respectively. Both graphene oxide (GO) and CNT fibers were synthesized by wet-spinning technique facilitating lyotropic nematic liquid crystal (LC) property. Randomly entangled CNT fiber-based heater, which is embedded in one surface of colorless polyimide (cPI) film with thickness of ˜200 μm, exhibits high bending stability and heating property up to 100 °C. Single reduced graphene oxide (RGO) fiber obtained after heat treatment at 900 °C in H2/N2 ambient was integrated on the CNT fiber-embedded cPI heater, thereby establishing a new type of all-carbon fiber sensing platform. As a result, accelerated NO2 adsorption and desorption kinetics were achieved with RGO fiber at an elevated temperature. In particular, a 9.22-fold enhancement in desorption kinetic (kdes = 8.85 × 10–3 s–1) was observed at 100 °C compared with the desorption kinetic (kdes = 0.96 × 10–3 s–1) at 50 °C, which was attributed to the effective heating by CNT fiber networks. This work pioneered a research on the use of emerging carbonaceous fibers for potential application in wearable chemical detectors.

The Influence of Si/Al Ratios on Adsorption and Desorption Characterizations of Pd/Beta Served as Cold-Start Catalysts.

The majority of NOx is exhausted during the cold-start period for the low temperature of vehicle emissions, which can be solved by using Pd/zeolite catalysts to trap NOx at low temperature and release NOx at a high temperature that must be higher than the operating temperature of selective catalytic reduction catalysts (SCR). In this work, several Pd/Beta catalysts were prepared to identify the influence of Si/Al ratios on NO and C3H6 adsorption and desorption characterizations. The physicochemical properties were identified using N2 physical adsorption, Fourier Transform Infrared Spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photo electron spectroscopy (XPS), and Na+ titration, while the adsorption and desorption characterizations were investigated by catalyst evaluation. The results indicated that the amount of dispersed Pd ions, the main active sites for NO and C3H6 adsorption, decreased with the increase of Si/Al ratios. Besides this, the intensity of Brønsted and Lewis acid decreased with the increase of Si/Al ratios, which also led to the decrease of NO and C3H6 adsorption amounts. Therefore, Pd dispersion and the acidic properties of Pd/Beta together determined the adsorption ability of NO and C3H6. Moreover, lower Si/Al ratios resulted in the formation of an additional dispersed Pd cationic species, Pd(OH)+, from which adsorbed NO released at a much lower temperature. Finally, an optimum Si/Al ratio of Pd/Beta was found at around 55 due to the balanced performance between the adsorption amounts and desorption temperature.

Electrospun YMn2O5 nanofibers: A highly catalytic activity for NO oxidation

Nanofiber catalysts are potentially promising to be equipped in the lean-burned vehicle exhaust emission system considering its facile synthesis, low-cost, long durability in contrast to the traditionally complicated powder based catalyst. Here, via electrospinning method, we synthesized YMn2O5 nanofibers (average diameter: ˜93 nm) including nanowire stacked with particles, and hollow tubes with or without inside nanowires. The morphologies remained even after hydrothermal aging at 800 ℃ for 10 h with 10% H2O stream. X-ray photoelectron spectrum revealed Mn4+/Mn3+ ratio 0.589 on the surface of YMn2O5 catalyst (YMO), indicating the existence of oxygen vacancies. The highest conversion of electrospun mullite fibers at 310 ℃ is ˜18% higher than powder-based YMO at 352 ℃ in the presence of 5% H2O at WHSV = 240,000 ml g−1 h−1. The extracted activation energy from NO-to-NO2 conversion curves of YMO nanofiber (61.68 kJ/mol) is slightly lower than that of powder-based mullite (91.45 kJ/mol), consistent with calculated 68.16 kJ/mol on the fiber YMO surface (121) with a rate-limiting step of the NO2 desorption. The catalytic activity can be attributed to the unit occupy of the eg (dz2 and dx2-y2) orbitals of Mn-dimer atoms around fermi level based on the combination of the theoretical calculations and DRIFTS spectra analysis. Importantly, after the hash hydrothermal-aging, the highest NO oxidation conversion of powder-based mullite is less than 50%, while the fiber maintains a conversion of 62%. Moreover, the fresh YMO fiber maintained superior oxidation stability for 12 h at its maximum conversion of 66%. This work provides the possibility for mullite oxide fibers to replace powder-based precious metal catalyst coating on monolith converter.

Phthalocyanine Photoregeneration for Low Power Consumption Chemiresistors.

It is well-known that the applicability of phthalocyanine chemiresistors suffers from long recovery time after NO2 exposure. This circumstance enforces the necessity to operate the sensors at elevated temperatures (150-200 °C), which shortens the sensor lifetime and increases its power consumption (regardless, a typical measurement period is longer than 15 min). In this paper, we propose a new method for fast and effective recovery by UV-vis illumination at a low temperature (55 °C). The method is based on short illumination following short NO2 exposure. To support and optimize the method, we investigated the effects of light in the wavelength and intensity ranges of 375-850 nm and 0.2-0.8 mW/mm2, respectively, on the rate of NO2 desorption from the phthalocyanine sensitive layer during the recovery period. This investigation was carried out for a set of phthalocyanine materials (ZnPc, CuPc, H2Pc, PbPc, and FePc) operating at slightly elevated temperatures (55-100 °C) and was further supported by the analysis of UV-vis and FTIR spectral changes. We found out that the light with the wavelength shorter than 550 nm significantly accelerates the NO2 desorption from ZnPc, CuPc, and FePc, and allows bringing the measurement period under 2 min and decreasing the sensor power consumption by 75%. Possible mechanisms of the light-stimulated desorption are discussed.

Influence of B-site transition metal on NO oxidation over LaBO3 (B=Mn, Fe and Co) perovskite catalysts

A comprehensive understanding of NO catalytic oxidation on different La-based perovskites LaBO3 (B=Mn, Fe, Co) enables to ultimately utilize the catalyst in the lean-burn NOx after treatment system. Here, we report a comparative study of the NO oxidation on LaBO3 (B = Mn, Fe and Co) surfaces by first-principles calculations though density functional theory (DFT). Based on the adsorption of NOx (x=1, 2 and 3) on the LaO and BO2 terminations of (001) surface, we find that the NOx adsorbates are bound stronger on the LaO terminations than BO2 ones. Infrared vibrational spectra and the NO oxidation reactions calculations suggest that BO2 surfaces are more active compared to LaO ones. The primary step for NO oxidation is the desorption of NO2* from the BO2 surfaces with a sequence of barrier 1.43eV, 1.60eV, 1.68 eV for CoO2, MnO2, and FeO2 terminations, respectively. Fundamentally, least charge transfer from CoO2 surface to NO2 ensures its smallest activation energy in contrast to the other two BO2 terminations. These findings provide insights into the influence of B-site transition metal and different terminations on NO oxidation activity of La-based perovskites which might be extended to design of other NO oxidation catalysts.

Study of the reaction mechanism of oxygen to heterogeneous reduction of NO by char

Quantum chemistry theoretical calculations were carried out to investigate the influence mechanism of different oxygen concentrations on the heterogeneous reduction of NO by char. The results show that there are two reaction paths for the heterogeneous reduction of NO by char using the char edge model with one hydroxyl group (R1). One is to reduce the NO adsorbed on the surface of R1 to N2O, which can be decomposed on the surface of char or react with CO. Three stepwise reactions with the highest energy barrier of 274.2 kJ/mol are found responsible for the desorption of CO and production of new active sites, on which N2O desorption can occur barrierlessly. The other path with a moderate energy barrier (139.6 kJ/mol) takes place to reduce NO to N2. The rate-determining step in the heterogeneous reduction of NO by the char edge with two hydroxyl groups (R2), a ring opening reaction, with a higher-barrier (398.03 kJ/mol), is less effective to the reduction of NO. From the kinetic analysis it is known that the reaction rate constants increase with the increase of temperature, indicating that temperature has a great influence on the reduction of NO and a higher combustion temperature contributes to lower NO emission. At a high temperature (1800 K), the rate constant of rate-determining step of R1 is 103 times higher than that of R2, which shows that R1 is more beneficial to the reduction of NO. The results reveal that the mechanism of NO reduction by char is promoted by oxygen at the char surface.

Influence of loading QCMs with electrochemically-deposited ZnO on their NO2-sensing properties

This paper reports on ZnO layers’ sensitivity to NO2 exposure. ZnO layers were grown by electrochemical deposition on the surface of quartz crystal microbalances (QCMs) with Au electrodes; the sensitivity was estimated by the frequency-time characteristics (FTCs) of the QCM, namely, its resonance-frequency-shift response. The sorption process was investigated in NO2 test gas. The behavior was studied of three different sensors with ZnO layers deposited for different times – 30, 35 and 60 min. The change in the frequency, ΔF, of the QCM as a function of the loaded mass of NO2 was detected in different NO2 concentrations in the range of 250 – 5000 ppm and the value of the sorbed mass was calculated, together with the rate of the NO2 sorption and desorption. As the time of ZnO layers deposition was increased, the sorbed NO2 mass increased for all concentrations used in the experiment. This can be explained by changes in the ZnO layers’ structure with the time of deposition.

Desorption of NO and NO<sub>2</sub> from Mn-Cu Mixed Oxide by the Effect of Non-Thermal Plasma

Desorption of NO and NO<sub>2</sub> from Mn-Cu Mixed Oxide by the Effect of Non-Thermal Plasma

The effect of surface coverage on N2, NO and N2O formation over Pt(111).

The effect of surface coverage of species, θ, on the kinetic parameters of N2, NO and N2O formation in a system simulating ammonia oxidation over Pt(111) has been studied by using periodic density functional theory (DFT). The energy barriers for product formation decrease as θ increases, with the effect being more significant above 0.25 ML. The heat of surface reaction decreases as θ increases, making the dissociation of the products less favourable due to a weaker interaction of the intermediates with the surface. The effect of θ on the binding energy is stronger for N* than for either O* or NO*, but it is more apparent in the co-adsorption with O* and NO*. Similarly, the coverage of N* more strongly affects the activation energy of N2 and N2O desorption than does the coverage of O* for NO* and N2O formation.

Understanding the Effect of NO Adsorption on Potassium-Promoted Co3O4 for N2O Decomposition

Co3O4 and K/Co3O4 were tested in catalytic N2O decomposition. K/Co3O4 exhibited higher activity than Co3O4, which was drastically and irrecoverably decreased with added NO. Studies revealed that the Co2+ valence state changed after NO adsorption, and that potassium strengthened the Co–NO bond, impeding NO desorption, even above 400 °C.