Highly efficient photocatalytic NO removal and in situ DRIFTS investigation on SrSn（OH）6

A novel SrSn（OH）₆ photocatalyst with large plate and particle size were synthesized via a facile chemical precipitation method.The photocatalytic activity of the SrSn（OH）₆ was evaluated by the removal of NO at ppb level under UV light irradiation.Based on the ESR measurements,SrSn（OH）₆ photocatalyst was found to have the ability to generate the main active species of O₂^·-,^·OH and ¹ O₂ during the photocatalyti...     

Electron beam treatment of high NOx concentration off-gases

High concentration of NO_x removal from simulated off-gases was investigated using electron beam (EB) technology. Simulated off-gases were prepared by combusting Polish light oil or nature gas with addition of NO from a NO gas cylinder. Irradiation was carried out under a ILU-6 accelerator. It was found that removal efficiency of NO_x was influenced by inlet concentration of NO, temperature, SO₂ concentration, absorbed dose and irradiation dose rate. Methods of enhancing NO_x removal efficiency with additives using EB were also discussed.     

臭氧氧化结合湿法喷淋对玻璃窑炉烟气同时脱硫脱硝实验研究

采用臭氧氧化结合湿法喷淋对模拟玻璃窑炉烟气开展了同时脱硫脱硝实验研究.采用不同溶液(NaOH、Na₂S)进行了喷淋实验.结果表明,保证溶液pH值在10以上,NaOH浓度对NO_x脱除效率无影响,SO₂的存在促进了NO_x吸收.当O₃/NO物质的量比为1.6、溶液NaOH浓度为0.5%时,NO_x脱除效率可达70%,SO₂脱除效率在99%以上.往喷淋液中添加Na₂S,NO_x脱除效率随Na₂S浓度增加而提高,SO₂的存在对NO_x脱除效率无影响.当O₃/NO物质的量比为1.2、溶液中NaOH浓度为0.5%、添加剂Na₂S浓度为0.6%时,NO_x脱除效率可达70%,SO₂脱除效率在95%以上.60 min长时间运行实验证明,模拟烟气中的NO_x经碱液和添加剂吸收后主要以NO^-₂的形式存在于喷淋液中,且NO_x脱除效率不随溶液pH值的变化而变化.     

Boosted photocatalytic efficiency of GQDs sensitized (BiO)2CO3/β-Bi2O3 heterojunction via enhanced interfacial charge transfer

The NO gas is easily oxidized to form toxic by-products (NO₂) during the oxidation process, which are adsorbed on the catalyst surface and inhibit the subsequent reaction. For photocatalytic NO removal, a significant challenge is to achieve catalytic stability while maintaining high conversion efficiency. Here, we fabricated a (BiO)₂CO₃/β-Bi₂O₃ heterostructure that enables efficient charge transfer and promotes the NO removal. We propose that the catalytic stability depends on the heterojunction structure, which is able to generate interfacial charge transfer channels. In addition, we further introduce graphene quantum dots on the heterojunction structure, which further strengthens the interfacial charge transfer dynamics and finally realizes that the NO₂ byproduct could gain electrons and convert to the final product (nitrite or nitrate). This composite structure not only exhibits high activity for NO removal but also maintains long-term stability under visible light.     

Production of Reactive Oxygen Species and Application for NOx Control

Current gas ionization discharge techniques used in the removal of NOx from waste gases require large plasma sources, have high energy consumption, and may feature low NOx removal rates. We develop a system to generate reactive oxygen species through a strong ionization discharge, which is injected into a flow of simulated waste gas. The relative proportions and temperatures of input gases were controlled and the rate of consumption by reactive species was monitored. HNO₃ oxidization products of NOx were also collected and measured. The molar ratio of reactive oxygen species to NO was optimized to improve the rate of NOx removal. A input gas temperature of 58–60 °C was also found to be optimal. The O₂ volume fraction has almost no influence on NOx removal, while H₂O volume fractions above 6 %, gave rise to NOx removal rates of 97.2 %. The present study addresses disadvantages of current gas ionization discharge and requires no catalyst, reducing agent or oxidant.     

NOx-Sorbing Metal Oxides, MnOx–CeO2. Oxidative NO Adsorption and NOx–H2 Reaction

(n)MnO_x–(1?n)CeO₂ binary oxides have been studied for the sorptive NO removal and subsequent reduction of NO_x sorbed to N₂ at low temperatures (≤150 °C). The solid solution with a fluorite-type structure was found to be effective for oxidative NO adsorption, which yielded nitrate (NO^? ₃) and/or nitrite (NO^? ₂) species on the surface depending on temperature, O₂ concentration in the gas feed, and composition of the binary oxide (n). A surface reaction model was derived on the basis of XPS, TPD, and DRIFTS analyses. Redox of Mn accompanied by simultaneous oxygen equilibration between the surface and the gas phase promoted the oxidative NO adsorption. The reactivity of the adsorbed NO_x toward H₂ was examined for MnO_x–CeO₂ impregnated with Pd, which is known as a nonselective catalyst toward NO–H₂ reaction in the presence of excess oxygen. The Pd/MnO_x–CeO₂ catalyst after saturated by the NO uptake could be regenerated by micropulse injections of H₂ at 150 °C. Evidence was presented to show that the role of Pd is to generate reactive hydrogen atoms, which spillover onto the MnO_x–CeO₂ surface and reduce nitrite/nitrate adsorbing thereon. Because of the lower reducibility of nitrate and the competitive H₂–O₂ combustion, H₂–NO reaction was suppressed to a certain extent in the presence of O₂. Nevertheless, Pd/MnO_x–CeO₂ attained 65% NO-conversion in a steady stream of 0.08% NO, 2% H₂, and 6% O₂ in He at as low as 150 °C, compared to ca. 30% conversion for Pd/γ–Al₂O₃ at the same temperature. The combination of NO_x-sorbing materials and H₂-activation catalysts is expected to pave the way to development of novel NO_x-sorbing catalysts for selective deNO_x at very low temperatures.     

Oxygen vacancies on the BiOCl surface promoted photocatalytic complete NO oxidation via superoxide radicals

One of the core issues in the photocatalytic oxidation of nitric oxide is the effective conversion of NO into the final product (nitrate). More than just improving the visible light photocatalytic performance of BiOCl, we aim to inhibit the generation of toxic by-product NO₂ during this process. In this study, we demonstrate that the oxygen vacancies (OVs) modulate its surface photogenerated carrier transfer to inflect the NO conversion pathway by a facile mixed solvent method to induce OVs on the surface of BiOCl. The photocatalytic NO removal efficiency under visible light increased from 5.6% to 36.4%. In addition, the production rate of NO₂ is effectively controlled. The effects of OVs on the generation of reactive oxygen species, electronic transfer, optical properties, and photocatalytic NO oxidation are investigated by combining density functional theory (DFT) theoretical calculations, the in situ FTIR spectra and experimental characterization. The OVs on the surface of BiOCl speed the trapping and transfer of localized electrons to activate the O₂, producing O₂⁻, which avoid NO₂ formation, resulting in complete oxidation of NO (NO + O₂⁻ → NO₃⁻). These findings can serve as the basis for controlling and blocking the generation of highly toxic intermediates through regulating the reactive species during the NO oxidation. It also can help us to understand the role of OV on the BiOCl surface and application of photocatalytic technology for safe air purification.     

Direct catalytic nitrogen oxide removal using thermal,electrical or solar energy

Considering the significant importance in both ecological and environmental fields, converting nitrogen oxide(NOx, especially NO) into value-added NH3or harmless N2lies in the core of research over the past decades. Exploring catalyst for related gas molecular activation and highly efficient reaction systems operated under low temperature or even mild conditions are the key issues. Enormous efforts have been devoted to NO removal by utilizing various driving forces, such as thermal, electrical o...     

NO x storage properties of hollandite-type K x Ga x Sn8−x O16

The interaction of NO, NO+O₂ and NO₂ with K _x Ga _x Sn_8?x O₁₆ powder, including potassium ions, has been investigated by temperature-programmed desorption. In the case of NO+O₂, NO _x storage rapidly increased with increasing concentration of O₂ and the main peak has high intensity with a maximum around 600°C. These results indicate that K _x Ga _x Sn_8?x O₁₆ has NO _x storage ability with high thermal stability and is one of the promising catalysts for NO _x storage reduction.     

Development of the bifunctional catalyst Mn-Fe-Beta for selective catalytic reduction of nitrogen oxides

The catalytic properties of the Mn-Fe-Beta system with Mn contents in the range 0.1–16 wt.% were studied in the selective catalytic reduction (SCR) of NO _x with ammonia. The catalyst structure was investigated using IR spectra of adsorbed NO, temperature-programmed reduction with hydrogen (H₂-TPR), X-ray diffraction analysis, and ESR. The use of manganese as a promoter substantially increases the activity of iron-containing catalysts in the SCR of NO _x with ammonia. At low contents (<2 wt.%), Mn exists in the cation form and the catalytic activity of the Mn-Fe-Beta system does not increase. At a higher content of Mn, clusters MnO _x begin to form, which are highly active in the oxidation of NO to NO₂ and the low-temperature catalytic activity of the Mn-Fe-Beta system increases. The observed increase in the low-temperature catalytic activity in the process of SCR of NO _x with ammonia is related to a change in the reaction route. The MnO _x clusters favor the oxidation of NO and the iron cations facilitate the reaction of “fast” SCR.     

Photocatalytic removal of nitrogen oxides from air on TiO<Subscript>2</Subscript> modified with bases and platinum

The efficiency of TiO₂ (Degussa P-25) modified with an alkaline admixture (urea, BaO), sulfuric acid, or platinum in the photocatalytic oxidation of NO (50 ppm) with a flowing 7% O₂ + N₂ mixture under UV irradiation in a flow reactor at room temperature and atmospheric pressure is reported. Because of the progressive blocking of active sites of the photocatalyst by the reaction products (NO₂, NO₃⁻), it is impossible to realize prolonged continuous removal of NO _x (NO + NO₂) from air without catalyst regeneration at elevated temperatures. The efficiency of the photocatalysts is characterized by specific photoadsorption capacity (SPC) calculated from the total amount of NO _x adsorbed during 2-h-long irradiation. Modification of TiO₂ with 5% BaO or 5% urea raises the SPC of the catalyst by a factor of 2–3. Presumably, this promoting effect is due to the basic properties of these dopants, which readily sorb NO₂ and NO₃⁻. A considerable favorable effect on SPC is also attained by adding 0.5% Pt to (5% BaO)/TiO₂. The SPC of the (0.5% Pt)/TiO₂ catalyst depends on the state of the platinum. The samples calcined in air at 500°C, which contain Pt⁺ and Pt²⁺, have an approximately 2 times higher SPC than unpromoted TiO₂ and ensure a much larger NO₂/NO ratio at the reactor outlet. Conversely, the samples reduced in an H₂ atmosphere at 200°C, whose platinum is in the Pt0 state, show a lower SPC than the initial TiO₂ and cause no significant change in the NO₂/NO ratio.     

Self-doped Br in Bi5O7Br ultrathin nanotubes: Efficient photocatalytic NO purification and mechanism investigation

Bismuth-rich Bi₅O₇Br is a promising photocatalyst for pollutant removal owing to its stability and appropriate band structure in comparison with bismuth oxybromide.However,bulk-phase Bi₅O₇Br suffers from poor light absorption and high charge recombination rates resulting in poor activity.Elemental doping is a powerful strategy to enhance photocatalytic activity.In this study,we prepared a series of Br autodoped ultrathin Bi₅O₇Br n...     

Point and Multipoint to Plane Barrier Discharge Process for Removal of NOx from Engine Exhaust Gases: Understanding of the Reactional Mechanism by Isotopic Labeling

An experimental study on the removal of NO_x in a simulated vehicle exhaust gas has been carried out using point to plane and multipoint to plane DBD corona reactors. Hydrocarbon (C₃H₆) and NO_x by-products were systematically investigated with a Gas Chromatography coupled to a Mass Spectrometry (GC/MS). NO_x (NO and NO₂) and CO output were also monitored with a gas analyzer in order to complete the mass balance. ¹⁸O tracer technique analyzes is applied to investigate the mechanism of propylene decomposition. From the plasma chemical reaction pathway proposed, it is apparent that the oxygen activation is one of the important steps for initiating the oxidation processes and the R-NO_x formation. We present data for the reaction of the (N₂/O₂/C₃H₆/CO₂NO/H₂O system in the corona discharge reactors mentioned above. This system has been shown to generate a significant amount of aldehyde. CH₃NO₂ and CH₃ONO₂ are the main R-NO_x compounds produced. Reactant composition and discharge energy densities (controlled by a numerical oscilloscope) were the operating parameters under study in wet and dry air mixture. Water vapors played an important role in NO_x removal (especially in NO₂ removal) via the reaction forming HNO₃. Therefore, in wet-gas mixture supplied reactors the highest removal rates of NO_x were as high as 30%, while in dry-gas only 15%. Different dielectric materials such as Al₂O₃/SiO₂ and TiO₂ on Al₂O₃/SiO₂ support have been used.     

Potentiometric NOx sensor based on stabilized zirconia and NiCr2O4 sensing electrode operating at high temperatures

The two types of electrochemical sensors using stabilized zirconia and the oxide sensing electrode (SE) were developed for NO_x detection at high temperatures. For the mixed-potential-type sensor, NiCr₂O₄ was found to give fairly excellent NO_x sensing characteristics in air among several spinel-type oxides tested. This NO_x sensor provided a linear correlation between EMF and the logarithm of NO or NO₂ concentration in the range 25–436 ppm and in the temperature range 550–650°C. With fixed bias voltage being applied between the SE (oxide) and the counter (Pt) electrode (CE), the EMF between SE and the reference (Pt) electrode (RE) was measured as a sensing signal. The NiCr₂O₄-attached tubular device was found to provide selective response to NO over NO₂ if SE was polarized at +175 mV versus RE. It was also found that this device gave selective response to NO₂ over NO, if SE was polarized at −250 mV versus CE. The new design of the planar device was proposed to avoid the cross-sensitivities to the others gases usually coexisting in car exhausts.     

Supported catalysts for simultaneous removal of SO2, NOx,and Hg0 from industrial exhaust gases: A review

The simultaneous removal of SO₂, NO_x and Hg⁰ from industrial exhaust flue gas has drawn worldwide attention in recent years. A particularly attractive technique is selective catalytic reduction, which effectively removes SO₂, NO_x and Hg⁰ at low temperatures. This paper first reviews the simultaneous removal of SO₂, NO_x and Hg⁰ by unsupported and supported catalysts. It then describes and compares the research progress of various carriers, eg., carbon-based materials, metal oxides, silica, molecular sieves, metal-organic frameworks, and pillared interlayered clays, in the simultaneous removal of SO₂, NO_x and Hg⁰. The effects of flue-gas components (such as O₂, NH₃, HCl, H₂O, SO₂, NO, and Hg⁰) on the removal of SO₂, NO_x, and Hg⁰ are discussed comprehensively and systematically. After summarizing the pollutant-removal mechanism, the review discusses future developments in the simultaneous removal of SO₂, NO_x and Hg⁰ by catalysts.     

Structure and UV-Vis spectroscopy of nitrosylthiolatoferrate mononuclear complexes

Density functional calculations for the [(RS)_xFe(NO)_4−x]⁻ (R=CH₃) compounds are carried out using the DFT method with the B3LYP functional. The results can be verified by the experimental data only in the case of the [(RS)₂Fe(NO)₂]⁻ complex. The experimentally characterised molecular structure of [(RS)₂Fe(NO)₂]⁻ (where (RS)₂=(SCH₂CH₂NMeCH₂CH₂CH₂NMeCH₂CH₂S) is properly reproduced by the RB3LYP method. The discrepancy between the calculated spin densities with the integral spin observed experimentally is interpreted in terms of antiferromagnetic coupling between the Fe(III) centre and the NO⁻ ligands. The theoretical analysis gives a good account of some properties observed in these compounds. In particular, the electronic spectrum calculated by the TDDFT method for [(CH₃S)₂Fe(NO)₂]⁻ is similar in shape to the experimental one, although is hypsochromically shifted. The LLCT (S_π→π^*_NO), LMCT (S_π→d) or (π^*_NO→d+S_π→d) and MLCT (d→π^*_NO) transitions are mostly responsible for absorption of the [(RS)_xFe(NO)_4−x]⁻ complexes within UV-Vis. The chemical reactivity of [(RS)₂Fe(NO)₂]⁻ is interpreted basing on the calculated effect of a polar solvent on the ligand polarity and on the character of the HOMO and LUMO orbitals.     

Kinetics of nitric oxide oxidation

Nitrogen oxides are nowadays a subject of global concern. Several types of nitrogen oxides exist in the environment: N₂O, NO, NO₂, N₂O₃, N₂O₄, N₂O₅. The abbreviation NO _x usually relates to nitric oxide NO, nitrogen dioxide NO₂, and nitrous oxide N₂O. The first two are harmful pollutants for both environment and human health, whereas the third is one of the greenhouse gases. Implementation of stringent NO _x emission regulations requires the development of new NO _x removal technologies from exhaust gases. One of many proposals for NO _x emission reduction is the application of an oxidizing agent which would transform NO _x to higher nitrogen oxides with higher solubility in water. The main objective of the paper was to present the rate constant of nitric oxide oxidation, determined in our studies.     

Comparison of passive and active sampling methods for the determination of nitrogen dioxide in urban air

Three different methods for sampling and determination of nitrogen dioxide in urban air are compared: an NO/NO_x-monitor and an active (pumped) and a passive sampling method. For the latter two methods, sodium iodide is used as absorbent. For weekly averages the results from the passive sampler are within 10–20% of the results for the two other methods in the concentration range 15–30 μg NO₂/m³. The detection limit for the passive sampler is 1 μg NO₂/m³ (7 days), the precision is 5% and the accuracy is estimated to 20%. The active iodide method agrees very well with the NO/NO_x-monitor. Compared on 24 h basis for a period of 3 months, covering a concentration range of 5–45 μg NO₂/m³, the deviation between the two methods is within 5%, and the absorption capacity of the iodide reagent is excellent as the breakthrough is below 1%.     

Nb and N co-doped TiO2 for a high-performance deNO x photocatalyst under visible LED light irradiation

By a facile and rapid microwave-assisted hydrothermal reaction at 190 °C for 30 min, niobium and nitrogen co-doping TiO₂ nanoparticles were prepared. The obtained samples were characterized by XRD, UV–Vis spectroscopy, EDX analysis, and BET measurements. To evaluate the photocatalytic activity, destruction of NO _x gas under the irradiation of several LED lamps with various wavelengths were carried out. Although co-doping of Nb with N into TiO₂ resulted in the decrement of the specific surface area, it was useful to improve the photocatalytic activity for the oxidative destruction of NO, probably due to the effective reduction of the anion vacancy in the lattice which acts as the recombination center of the photo-induced electrons and holes.