Nitric Oxide Abatement Research Articles

S-Scheme heterojunction of Cs2SnBr6/C3N4 with interfacial electron exchange toward efficient photocatalytic NO abatement

Photocatalytic technology is of great significance in environmental purification due to its eco-friendly and cost-effective operations. However, low charge-transfer efficiency restricts the photocatalytic activity of the catalyst. Herein, we report Cs2SnBr6/C3N4 composite catalysts that exhibit a robust interfacial electron exchange thereby enhancing photocatalytic nitric oxide (NO) oxidation. A comprehensive study has demonstrated the S-scheme electron transfer mechanism. Benefiting from the interfacial internal electric field, the C-Br bond serves as a direct electron transfer channel, resulting in enhanced charge separation. Furthermore, the S-scheme heterojunction effectively traps high redox potential electrons and holes, leading to the production of abundant reactive oxygen radicals that enhance photocatalytic NO abatement. The NO removal rate of the Cs2SnBr6/C3N4 heterogeneous system can reach 86.8 %, which is approximately 3-fold and 18-fold that of pristine C3N4 and Cs2SnBr6, respectively. The comprehensive understanding of the electron transfer between heterojunction atomic interfaces will provide a novel perspective on efficient environmental photocatalysis.

Enhancing coking resistance of nickel-based catalysts for dry reforming of methane via nitric oxide abatement: a support study

How to enhance DRM and NO carbon-assisted coupling using a support?

Photocatalytic performance evaluation of flame‐sprayed and polymeric suspension coatings from TiO2 nanoparticles

AbstractBACKGROUNDHeterogeneous photocatalysis offers an interesting alternative to mitigate air pollution by using materials capable of reacting with toxic gases under ultraviolet light. One of these materials is titanium dioxide (TiO2), and thus it is necessary to analyze and improve its photocatalytic response for air depollution, in order to facilitate its use in surface applications.RESULTSThe photocatalytic ability of the synthesized TiO2 particles to remove nitric oxide (NO) was tested, and it was found that both the anatase and rutile phases present in the samples led to a NO abatement capacity of ≈60% η NO. Two different methods to coat surfaces with TiO2 particles were evaluated: thermal spray by oxyacetylene flame and dripping of polymeric suspensions of TiO2. A more detrimental effect on photocatalytic efficiencies was found using polymeric suspension rather than flame‐spraying as coating method. This was despite the anatase transformation to rutile and Ti7O13 that TiO2 particles undergo using the latter process as a consequence of heat transfer from the flame to the particles during the coating formation.CONCLUSIONResults obtained in this research demonstrate that polymeric suspensions inhibit the photocatalytic activity of TiO2 nanoparticles, probably due to the formation of a polymeric matrix on samples that constrains the action of pollutant and testing factors on samples. However, the thermal method can help retain part of the photocatalytic capability to abate NOx, despite depletion in the anatase content resulting from the heat transfer to the TiO2 raw particles sprayed to form coatings. © 2023 Society of Chemical Industry (SCI).

Hydrogen-Bond-Assisted Adsorption of Nitric Oxide on Various Metal-Loaded ZSM-5 Zeolites.

Understanding the characteristics of nitric oxide (NO) adsorption on metal-loaded zeolites is a prerequisite for developing efficient catalysts for NO abatement reactions. In this study, we probed the effect of the hydrogen bond that exists between adsorbed NO and Brønsted acid sites (BAS) in various metal-loaded ZSM-5 zeolites (M-ZSM-5, wherein M = Fe, Co, Ni, Cu, Zn, Pd, Ag, and Au) by using density functional theory calculations. The presence of a hydrogen bond has altered the NO adsorption energies significantly; appreciable stabilization via hydrogen bonding is noted for NO complexes of Zn, Fe, and Co, and reasonable stabilization is obtained for Ni and Cu complexes, whereas an anomalous effect of a hydrogen bond is identified in Ag, Pd, and Au species. Moderate weakening of the N-O bond in all NO-adsorbed complexes primarily due to a hydrogen bond has been realized in terms of Mayer bond order and quantum theory of atoms in molecules topological analyses; N-O bond activation follows the order Ag < Pd < Au < Ni < Cu < Co < Fe < Zn. We obtained a good correlation between hydrogen bond distance and molecular electrostatic potential at the O atom (VO) of NO adsorbed on BAS-free M-ZSM-5; which suggests that VO can be considered as a key descriptor to infer the strength of a hydrogen bond between the adsorbed NO and M-ZSM-5 with BAS. Finally, the energy decomposition analysis in combination with natural orbitals for chemical valence has provided the qualitative aspects of electron back-donation from the metal to the antibonding molecular orbital of NO; this back-donation is quite impressive in hydrogen-bond-assisted NO adsorption. We expect that the findings of this study will open up the possibility of the design of BAS-containing metal-loaded zeolites for the catalytic mitigation of NO.

Doping and facet effects synergistically mediated interfacial reaction mechanism and selectivity in photocatalytic NO abatement

The surface atomic coordination and arrangement largely determine photocatalytic properties. Whereas, the intrinsic impact of surface microstructures on the reaction mechanism and pathway is still unclear. Herein, via constructing N-doped Bi2O2CO3 photocatalysts with diverse exposed facets, (1 1 0) and (0 0 1) facet, we testify that the pivotal roles of crystal facet and doping effect on the intermediate production and reactivity for photocatalytic nitric oxide (NO) abatement. The photoreactivity of N-doped Bi2O2CO3 is documented to be higher than that of the pure samples because of the enhanced light absorption and charge transfer. Further in situ probing experiments and theoretical calculations verify that the unique adsorption patterns and activated intermediates on the (1 1 0) facet facilitate the formation of final products and inhibit the generation of toxic NO2 by-product in terms of thermodynamics. More importantly, we found that the selective and nonselective oxidation processes are emerged over (1 1 0) and (0 0 1) facets of Bi2O2CO3, respectively.

Improved NO removal from flue gas by hydrazine and its mechanism analysis

AbstractBACKGROUNDSelective non‐catalytic reduction (SNCR) is a proven technique to lessen nitric oxide (NO) emissions from stationary sources. However, the process using ammonia or urea as a reducing agent is only effective in a narrow and high temperature window, with the maximum NO abatement declining when increasing the oxygen (O2) content. Large industrial boilers may be often under a variable load and an excess of O2, which could decrease the effectiveness of the de‐NOx process. This study investigated hydrazine (N2H4) as a reagent to improve SNCR performance.RESULTSNO reduction by N2H4 was experimentally investigated in a pilot‐scale flow reactor. The effect of reaction temperature, molar ratio of NH2 to NO (normalized stoichiometric ratio, NSR), initial NO level and O2 concentration on the NO reduction in flue gas containing 7.4–17.4% (v/v) O2 at temperatures between 450 and 1100 °C was determined. The experimental results indicated that NO reduction by N2H4 was possible in dual temperature ranges, and the optimum reaction temperatures were about 580 and 1060 °C at NSR = 2.0. Moreover, the N2H4–NO reaction is less O2‐sensitive. A chemical kinetic model was developed to correctly describe the non‐catalytic reduction of NO by N2H4 in the presence of O2.CONCLUSIONHydrazine‐based SNCR is an alternative method for NO reduction occurring in dual temperature ranges and excess O2. The present model provided a satisfactory prediction of the experimental results, offering an effective tool for process simulation over a wide range of operating conditions. © 2019 Society of Chemical Industry

NO, NO2 and N2O emissions over a SCR using DOC and DPF systems with Pt reduction

A Pt-reduced diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) combination was used to evaluate the influences of Pt reduction on the oxidation performance in a nonroad diesel engine. For the Pt-reduced combination, a mass fraction of 1.5% Pt in the DOC was lower than a DOC of a non-reduction combination. These DOCs were composed of Pt only. The DPF in the Pt-reduced combination was composed of Pt and Pd with a 2:1 ratio, i.e., Pd was substituted for Pt. Whereas the DPF in the non-reduction combination was Pt only. The oxidation performance in the DOC and DPF systems of the Pt-reduced combination was relatively consistent with the non-reduction combination. The behavior of the undesirable oxidation of nitric oxide (NO) to nitrogen dioxide (NO2) occurred in both combinations. The selective catalytic reduction (SCR) system was also installed for NO and NO2 abatement, and NO and NO2 were evaluated based on the conversion efficiency. The fast SCR reaction, which involves both NO and NO2, was dominantly activated at the SCR inlet temperature of 380 °C because the NO2/NOX ratio is approximately 60%. The fast SCR reaction competed with the standard SCR reaction above 380 °C, and then the standard SCR reaction became the prevailing reaction as the temperatures increased. Nitrous oxide (N2O), which has 298 times more global warming potential than carbon dioxide, was also investigated mainly over the SCR. N2O has increased dozens of times over the SCR, and a lower ratio of N2O emission after the SCR to the NOX at the SCR inlet was obtained in the Pt-reduced combination than in the non-reduction combination.

Catalytic oxidation of nitric oxide (NO) with carbonaceous materials

This paper reviewed recent progress in catalytic oxidation of nitric oxide (NO) over various carbonaceous materials, such as activated carbon, carbon nanofibers with the aim of NO abatement.

Highly efficient and stable Au/CeO2-TiO2 photocatalyst for nitric oxide abatement: potential application in flue gas treatment.

In the present work, highly efficient and stable Au/CeO2-TiO2 photocatalysts were prepared by a microwave-assisted solution approach. The Au/CeO2-TiO2 composites with optimal molar ratio of Au/Ce/Ti of 0.004:0.1:1 delivered a remarkably high and stable NO conversion rate of 85% in a continuous flow reactor system under simulated solar light irradiation, which far exceeded the rate of 48% over pure TiO2. The tiny Au nanocrystals (∼1.1 nm) were well stabilized by CeO2 via strong metal-support bonding even it was subjected to calcinations at 550 °C for 6 h. These Au nanocrystals served as the very active sites for activating the molecule of nitric oxide and reducing the transmission time of the photogenerated electrons to accelerate O2 transforming to reactive oxygen species. Moreover, the Au-Ce(3+) interface formed and served as an anchoring site of O2 molecule. Then more adsorbed oxygen could react with photogenerated electrons on TiO2 surfaces to produce more superoxide radicals for NO oxidation, resulting in the improved efficiency. Meanwhile, O2 was also captured at the Au/TiO2 perimeter site and the NO molecules on TiO2 sites were initially delivered to the active perimeter site via diffusion on the TiO2 surface, where they assisted O-O bond dissociation and reacted with oxygen at these perimeter sites. Therefore, these finite Au nanocrystals can consecutively expose active sites for oxidizing NO. These synergistic effects created an efficient and stable system for breaking down NO pollutants. Furthermore, the excellent antisintering property of the catalyst will allow them for the potential application in photocatalytic treatment of high-temperature flue gas from power plant.

Green synthesis of Pt and Ag nanoparticles and their use towards nitric oxide abatement

Pt and Ag nanoparticles (NPs) were synthesized by eco-friendly room-temperature chemical reduction routes based on trisodium citrate and L-ascorbic acid (for Pt NPs) and on gelatin and trisodium citrate (for Ag NPs). The as-prepared NPs were characterized by UV-visible absorption spectroscopy and transmission electron microscopy analyses, which confirmed the formation of sub-10 nm metal particles. Then, the colloidal solutions were used to obtain activated carbon-supported catalysts (metal/AC) for direct NO decomposition. X-ray photoelectron spectroscopy and x-ray diffraction measurements proved that the NPs hosted on the support surface were present in the metallic chemical state. In situ infrared absorption spectroscopy investigations during NO reduction catalytic reactions showed that the Pt/AC and Ag/AC catalysts were highly active at 373 K. At 573 K, we observed different behaviors for each catalyst. While Ag/AC performed similarly to the reaction at 373 K, Pt/AC was found to participate in a redox mechanism, where the catalyst’s active sites were oxidized by NO and reduced by carbon, thus emitting CO2 and enhancing its catalytic activity, an effect that we have also observed in carbon-supported Pd NPs.

Combination of Nonthermal Plasma and Low Temperature-C3H8-Selective Catalytic Reduction over Co-In/H-beta Catalyst for Nitric Oxide Abatement

Abstract Nitric oxide (NOx) abatement by a two-stage system composed of nonthermal plasma (NTP) followed by the selective catalytic reduction with C3H8 (C3H8-SCR) over the Co-In/H-beta catalyst was investigated at a relativity low temperature range from 548 to 598 K. The combination system shows better synergy at low temperature. Optimum active temperature of Co-In/H-beta in the complex system is shifted from 648 to 598 K compared with that in C3H8-SCR. The highest NOx conversion is over 98%. In contrast to treatment by the NTP, the two-stage system converts mostly NO to nitrogen; without NO2, nitrogen-containing and organic components formed. The synergetic effect of the combination system is enhanced with the C3H8 concentration and O2 content.

A dynamic optimization procedure for non-catalytic nitric oxide reduction in waste incineration plants

Reduced chemical kinetic models are often used to simulate the kinetics of full-scale DeNO x systems because of the computational expense of combining a detailed description of fluid dynamics and a complete mechanism of reaction. In particular, these simplified models might be useful when complete combustion minimizes the influence of CO and hydrocarbon fuels on the kinetic mechanism of thermal DeNO x , such as that occur in large-scale systems for non-catalytic nitrogen oxides reduction installed in hazardous waste incineration plants. In this work, a lumped mechanism is involved in a dynamic optimization procedure to reach a maximum efficiency of NO abatement in such devices, by handling the inlet ratio of H 2 or CH 4 to inlet NH 3 . As a consequence, a simplified chemical kinetic model reported in the literature was modified to reproduce the influence of hydrogen and methane addition on the selective non-catalytic reduction of nitric oxide with ammonia. The consistency of the lumped mechanism, which involves only two global reactions to describe the NO / NH 3 / O 2 and H 2 or CH 4 gas phase reaction system, was verified by using a large set of experimental results obtained at stationary conditions in tubular reactors. The dynamic optimization procedure aims to compensate the effect of the main kinetic disturbances on nitrogen oxides reduction, as variation in the flue-gas temperature in NH 3 injection zones and in the flue-gas residence time, which are typically found in incinerators due to the heterogeneity of the waste composition. Calculated results of NO abatement by assuming typical fluctuations in the kinetic characteristics of exhausts in incineration plants evidence an increase of nitric oxide abatement from 5% to approximately 40–50% when involving the suggested dynamic optimization strategy.

Hydrothermal Synthesis of New Compounds with the Pyrochlore Structure and Its Application to Nitric Oxide Abatement.

Several new compounds with a pyrochlore-type crystal structure have been synthesized by a low-temperature hydrothermal process under N2 atmosphere using a mixture of nitrate salts. The chemical compositions of the new pyrochlores are represented as (a) Y2Sn1.8Cr0.2O7, (b) Y1.8Sm0.2Sn1.8Cr0.2O7, (c) Y1.8Ce0.2Sn1.8Cr0.2O7, (d) Y1.8Eu0.2Sn1.8Cr0.2O7, (e) Y2Zr1.8Co0.2O7, (f) Ba0.8Y1.2Sn1.8Cr0.2O7, (g) Ba0.6Y1.2Sm0.2Sn1.8Cr0.2O7 and (h) Ca0.8Sm1.2Sn1.8Ni0.2O7. The Ba- and Ca-containing pyrochlores exhibited excellent spherical morphology with a pure pyrochlore phase structure and were composed of nanometer-sized particles. A- and B-sitedoped pyrochlores maintained a fully ordered crystal structure over a wide temperature range. The pyrochlore oxide powders were tested as catalysts for NOx absorption and reduction by CH4. NO could be almost completely converted into N2 using hydrothermally derived pyrochlore oxide catalysts in the absence of oxygen at high temperatures. Rapid absorption of NO into alkali-substituted pyrochlores was effective for NO removal from the gas phase, absorption being significantly accelerated by the presence of oxygen.

Promoting Effect of Pt on CoZeolites upon the SCR of NOx

The promoting effect of Pt incorporated to Cozeolites (viz., mordenite, ferrierite, ZSM-5, and Y-zeolites) on the selective catalytic reduction (SCR) of NOxwith CH4was studied. The PtCo bimetallic zeolites showed higher NO to N2conversion and selectivity than the monometallic ones under all reaction conditions tested. The Y-zeolite based samples which were inactive both in the mono and bimetallic samples constituted an exception. The promoting effect was a function of the zeolite type and, for a given zeolite, of the pretreatment of the catalysts and Pt loading. The best results were obtained for a 0.5% Pt loading after reduction of the samples in H2flow for 1 h at 350°C. Under dry conditions Pt0.5Co2.0mordenite converted 60% of NO to N2at GHSV of 100,000 h−1with a CH4/NO ratio of 3 at 500°C and 2% oxygen in the feed stream. The specific activities given as molecules of NO converted per total metal atoms per second at 500°C were 16.5 10−4s−1for Pt0.5Co2.0Fer, 13 10−4s−1for Pt0.5Co2.0Mor, and 4.33 10−4s−1for Pt0.5Co2.0ZSM-5. The incorporation of Pt also shows a positive effect in the stability of the samples under wet reaction conditions. The XPS results revealed that in the calcined samples most of the Co2+and Pt2+was located at exchange positions. After reduction no changes in the binding energies (B.E.) were observed in samples with low Pt loading. For higher contents (viz., 1 to 5 wt%) the B.E. characteristics of Co° and Pt°, as well as Co2+and Pt2+, were detected. No evidence of alloy or intermetallic compounds at the surface level was observed. The incorporation of Pt also promoted the Co reducibility in the zeolitic matrix. The greater reducibility and a shift of the maxima in the temperature-programmed reduction profiles suggest a Pt-Co interaction inside of the zeolitic channels. The solid that the reacting mixture initially “sees” has Co° and Pt° metallic particles highly dispersed in the zeolitic matrix, together with Co2+. Some Pt2+and protons generated during reduction also appeared. Such species remained after reaction but some reorganization occurred. In order to get an efficient catalysts for nitric oxide abatement it is necessary for such species to be in intimate contact. A synergetic effect among the different sites could be responsible for the high activity of the bimetallic zeolites.

Field evaluation of nitric oxide abatement with ferrous chelates

AbstractThe absorption of nitric oxide from flue gas streams presents some unique problems due to its low solubility in conventional scrubbing solutions. A process is being developed that utilizes an electrolytic cell to reduce Fe(III) to Fe(II) and maintain the majority of the iron chelate in the active ferrous state. This process has been tested on an actual flue gas stream and achieved 80% nitric oxide abatement. Further reduction of nitric oxide is possible with increased stages.

Analysis of a proposal for nitric-oxide abatement in jet-aircraft engines

Modifications are reported to a conventional gas-kinetics computer program which allow for the continuous addition of chemical species to the flowing gas. This is necessary in modelling the gas flows in a jet engine where air is continuously entrained with the burnt or burning gases, and it also facilitates the investigation of introducing chemical additives into a flowing reaction mixture.The program is used to compare, under the same one-dimensional modelling approximations, the nitric-oxide emissions from a conventional jet engine and from a proposed lean-burning modification, and it is concluded that the lean-burning model has potential for reducing nitric-oxide emission by more than two orders of magnitude.