NO Removal Activity Research Articles

Mechanism of CO + NH3-coupled removal of NO from Fe/AC catalysts at medium and low temperatures

Catalysts with different mass ratios (Fe: AC = 7.5, 10.0, and 12.5) were prepared using the equal-volume impregnation method. The 12.5Fe/AC catalyst exhibited the highest NO removal activity and best N2 selectivity at any given temperature. Furthermore, NO removal was mediated by redox reactions between Fe2+ and Fe3+ and dominantly occurred at the Fe2+ active sites. As the loading amount of active metal (Fe) increased, the diffraction ring gradually diffused, and the number of Fe oxide crystals, number of oxygen-containing functional groups, and content of chemically adsorbed oxygen increased. Chemically adsorbed oxygen plays a major role in NO removal. The NO removal mechanism of the Fe/AC catalyst is dominated by physical adsorption and the Langmuir–Hinshelwood mechanism at low temperatures and by the Eley–Rideal mechanism at medium and low temperatures.

In-situ fabrication of TiO2/NH2−MIL-125(Ti) via MOF-driven strategy to promote efficient interfacial effects for enhancing photocatalytic NO removal activity

In-situ fabrication of TiO2/NH2−MIL-125(Ti) via MOF-driven strategy to promote efficient interfacial effects for enhancing photocatalytic NO removal activity

Promoting NO removal performance of Fenton-like enhanced SCR reactions via modulating V/Fe in Fe-V oxides

Low-temperature NO removal technology was critical for tail gas purification. Our previous work has proposed an efficient Fenton-like enhanced SCR reaction over monoclinic FeVO4. This work modulates the V to Fe ratio (V/Fe) in Fe-V oxides to enhance the NO removal activity. The textual characterization and NO removal of FeV0.82Ox, FeV1.31Ox, FeV1.52Ox, and FeV1.96Ox were carried out to investigate the structure–activity relationships. For the Fenton-like enhanced SCR reactions, the NO removal efficiency was affected by catalysts with different V/Fe. Based on XPS, NH3-TPD, and •OH annihilation tests, it could be deduced that the NO removal in Fenton-like enhanced SCR reactions was simultaneously affected by the performance of SCR reactions and Fenton-like reactions. The density functional theory calculation indicated that the H2O2 was more likely adsorbed on Fe sites of Fe2V4O13, and the adsorption of NH3 was conducive to the oxidized V sites of FeVO4. The research elucidated the modulation strategy for NO removal via Fenton-like enhanced SCR reactions over Fe-V oxides.

Visible light photocatalytic NOx removal with suppressed poisonous NO2 byproduct generation over simply synthesized triangular silver nanoparticles coupled with tin dioxide.

The treatment or conversion of air pollutants with a low generation of secondary toxic substances has become a hot topic in indoor air pollution abatement. Herein, we used triangle-shaped Ag nanoparticles coupled with SnO2 for efficient photocatalytic NO removal. Ag triangular nanoparticles (TNPs) were synthesized by the photoreduction method and SnO2 was coupled by a simple chemical impregnation process. The photocatalytic NO removal activity results show that the modification with Ag TNPs significantly boosted the removal performance up to 3.4 times higher than pristine SnO2. The underlying roles of Ag TNPs in NO removal activity improvement are due to some advantages of Ag TNPs. Moreover, the Ag TNPs contributed photogenerated holes as the main active species toward enhancing the NO oxidation reaction. In particular, the selectivity toward green products significantly improved from 52.78% (SnO2) to 86.99% (Ag TNPs/SnO2). The formation of reactive radicals under light irradiation was also verified by DMPO spin-trapping experiments. This work provides a potential candidate for visible-light photocatalytic NO removal with low toxic byproduct generation.

Simultaneous removal of NO and N2O in the coexistence of NH3 and CH4 on Ion-exchanged zeolites

In this work, a series of ion exchanged Me-MFI zeolites (Me = Al, K, Ca, Mn, Fe, Co, Ni, Cu, Zn, Ga, Pd, Ag, In, Ir, Pt) was adopted as catalysts for the removal of NO and N2O by selective catalytic reduction (SCR) with NH3 and CH4. MFI zeolite structure was maintained after the ion-exchange. Fe3+ exchanged MFI zeolite had the highest catalytic activities for N2O removal and relatively higher activities for NO removal by NH3 and CH4. In this way, Fe-MFI can be a good candidate for the aftertreatment of natural gas NH3 co-firing exhaust.

A novel defect reassembly strategy for NH2-MIL-125(Ti) to enhance the photocatalytic NO removal activity

Photocatalysis technology has been widely used to eliminate typical air pollutants, but its further application is limited by the finite visible light response and severe charge carrier recombination. In this study, through a simple defect reassembly strategy, the carboxyl group of highly photosensitive eosin Y is successfully coordinated with the exposed Ti clusters in the defective NH2-MIL-125(Ti) to improve photocatalytic activity. The results demonstrate that the NO removal rate of the optimal sample (named D-NM-125/EY) is about 62.05%, which is 1.62 times that of the original NH2-MIL-125(Ti). The UV–Vis, PL, and photochemical characterization analysis confirm that the incorporation of eosin Y significantly can enhance the visible light absorption capacity and promote the photogenerated carriers separation, which may be due to that eosin Y can more easily absorb and utilize visible light to produce more photogenerated electron-hole pairs. Combining ESR with in-situ DRIFTS analysis, the possible photocatalytic mechanism is revealed, in which the reactive oxygen species generated in the photocatalytic process are the key factors for the successful degradation of NO into less toxic substances. This study will provide a new strategy for modifying MOFs photocatalysts to solve typical air pollution problems.

The defective NH2-MIL-125(Ti) was adjusted by a simple nitric acid etching method for switching on photocatalytic NO removal

In this paper, the photocatalytic properties of NH2-MIL-125(Ti) is enhanced by using a simple nitric acid etching method to form a ligand defect strategy. The structures and properties of the samples are characterized by XRD, SEM, XPS, BET, TG, and UV–vis etc. The results display that the yield of modified NH2-MIL-125(Ti) photocatalytic NO removal experiment is significantly improved based on excellent photoresponse capacity. The optimal sample (0.1 mol/L HNO3-NH2-MIL-125(Ti)) shows excellent photocatalytic activity for NO removal under visible light irradiation (42.69%), which was 1.84 times higher than that of the original NH2-MIL-125(Ti).

Synergetic effect of CQD and oxygen vacancy to TiO2 photocatalyst for boosting visible photocatalytic NO removal

The wide band gap of TiO2 photocatalyst material limits its application in the field of visible photocatalysis. In this paper, oxygen vacancies and carbon quantum dots (CQD) with up-conversion character were proposed to improve the photocatalytic activity for NO removal of TiO2 under visible light irradiation. The one-dimensional TiO2 nanotube (TNs), TNs containing oxygen vacancies (OVTNs), TNs of composite CQD (CQD-TNs) and OVTNs of composite CQD (CQD-OVTNs) were prepared, respectively. Furthermore, the influence of oxygen vacancies and CQD on the removal of NOx by photocatalysis were explored. It is found that CQD-OVTNs exhibits the conspicuous synergetic effect of CQD and oxygen vacancy to boost visible photocatalytic NO removal, the NO removal efficiency was about 12, 2, and 2.6 times to TNs, OVTNs and CQD-TNs. Also, CQD-OVTNs exhibits the NO2-inhibited property during the process of photocatalytic NO removal. Finally, the synergetic mechanism of CQD and oxygen vacancies to TNs for boosting visible photocatalytic NO removal was revealed.

Mechanism of NO removal in selective catalytic reduction based on γ‐Fe2O3 catalyst doped with Mg element

AbstractThe doping of different elements will make the Fe2O3 catalyst show different catalytic characteristics and improve the activity of the Fe2O3 catalyst in selective catalytic reduction (SCR), mainly by increasing the types of reactive oxygen species and the specific surface area of the catalyst. In this paper, density functional theory (DFT) was used to reveal the reaction path and adsorption behaviour of the Mg‐doped γ‐Fe2O3 catalyst. The results show that the doping of Mg ions can contribute electrons and lead to electron migration on the catalyst surface, which changes the acidity of some sites on the catalyst surface. The adsorption energy of NH3 is related to the binding sites of N atoms on the catalyst surface, and different adsorption sites will be enhanced or weakened due to Mg doping. NH2 reacts with NO to form N2 and H2O, so the dehydrogenation of NH3 to the NH2 radical is a key step in SCR. With doping, this process becomes more likely to occur. In addition, the activation energy barrier of NH2 formation in the aerobic environment is lower than that in the anaerobic condition, which contributes to NH3 dehydrogenation. Therefore, doping Mg on the surface of γ‐Fe2O3 catalyst can improve the catalytic activity of NO removal.

2D/3D g-C3N4/BiOI heterostructure catalyst for efficient and robust photocatalytic NO removal

Developing visible light responsive photocatalysts with strong light capture ability for catalytic NO removal is of great significance. In this work, we coupled the narrow-gap semiconductor BiOI with graphite-like carbon nitride (g-C3N4) to construct 2D/3D heterostructure and applied it for efficient photocatalytic elimination of NO under visible light irradiation. At relative humidity (RH) of 15 %, g-C3N4/BiOI achieves remarkable NO removal activity (80.5 %) under a gas hourly space velocity (GHSV) of 1,740,000 mL h−1 g−1. Outstanding durability was realized that the NO removal efficiency of g-C3N4/BiOI after 6 consecutive runs. Even at high RH of 50 % and 80 %, g-C3N4/BiOI still exhibited excellent NO removal performances of 80.3 % and 78.5 %, respectively. The heterostructure of g-C3N4/BiOI endowed the enhanced light harvesting, efficient charge separation and rapid charge transfer, which enables sufficient superoxide radicals (O2−) production to improve the efficiency and strengthen the durability of photocatalytic NO removal. This work provides insights into the rational design of heterostructure photocatalyst toward air purification.

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.

Modulation of photocatalytic activity of SrBi2Ta2O9 nanosheets in NO removal by tuning facets exposure

• The (2 0 0) facet of SrBi 2 Ta 2 O 9 photocatalyst tends to accumulate electrons while (0 0 1) facet favors the accumulation of photogenerated holes. • High surface facet exposure of (2 0 0) plane in SrBi 2 Ta 2 O 9 benifits photocatalytic NO removal. • Superoxide radicals play a vital role in photocatalytic NO removal by SrBi 2 Ta 2 O 9 . Photocatalysts with exposure of different crystal facets often show great differences in their photocatalytic activities due to differences in surface atomic arrangement and coordination. Thus, the actual photoreaction mechanism of a specific crystal facet in photocatalysis deserves to be explored. In this paper, as a case study, SrBi 2 Ta 2 O 9 photocatalyst with preferential facet exposure was explored for the photocatalytic removal of NO at a ppb level. The efficiency of NO removal was remarkably improved by tuning the crystal exposure facet with high (2 0 0) facet exposure ratio. Optimized exposure of (2 0 0) crystal facet in SrBi 2 Ta 2 O 9 (SBT) by thermal calcination at 800 °C (SBT-800) leads to the highest NO removal activity of 51% under a 300 W Xe lamp for 20 min; under visible light, SBT 800 achieves a 5-fold enhancement in NO removal efficiency compared to its counterpart, SBT-900. Active species capture experiments prove that the superoxide radical ·O 2 − is the main active species for the photocatalytic removal of NO, and surface selective deposition experiments conclude that (2 0 0) is the main electron-rich crystal plane, based on which the results of density functional theory (DFT) computation reveal the BiO terminated nature of (0 0 1) crystal plane, where the models with both BiO and TaO terminated (0 0 1) planes were created and computated. Mechanistic study reveals that SrBi 2 Ta 2 O 9 with a larger exposure of (2 0 0) facet provides more active reduction sites, thereby reducing more O 2 to ·O 2 − , which further oxidizes the adsorbed NO to NO 2 − /NO 3 − . The present work underlines the role of facet tuning in the photoactivity modulation for NO removal photocatalytically.

Au Nanoparticles Loaded Bi5Ti3FeO15 Ferroelectric Nanosheets with Enhanced Photocatalytic Activity for NO Removal

Au Nanoparticles Loaded Bi5Ti3FeO15 Ferroelectric Nanosheets with Enhanced Photocatalytic Activity for NO Removal

Efficient photothermal-assisted photocatalytic NO removal on molecular cobalt phthalocyanine/Bi2WO6 Z-scheme heterojunctions by promoting charge transfer and oxygen activation

Developing a high-performance photocatalyst with an efficient charge transfer pathway and reasonable active sites for photocatalytic NO removal is a formidable challenge. Herein, a novel Z-scheme molecular cobalt phthalocyanine(CoPc)/Bi2WO6 photothermal-assisted photocatalyst was elaborately designed. The interfacial Co-O-W bond and built-in electric field(BIEF) between Bi2WO6 and CoPc promote a cascade Z-scheme charge transfer system from Bi2WO6 to CoPc, thereby facilitating the charge separation and retaining high redox potential. Meanwhile, the Co-N4(II) sites of CoPc can capture more photoexcited electrons migrating from Z-scheme of the CoPc/Bi2WO6 composite, which facilitates the electron transfer to O2 for the generation of •O2-. Moreover, the photothermal effect of CoPc can further improve the O2 activation efficiency. Consequently, the obtained photocatalysts exhibit superior photocatalytic activity for NO removal (74.9%) and lower generation of toxic NO2 (<6 ppb) by-products compared with pristine Bi2WO6. This work offers a new idea for constructing high-efficiency NO photo-oxidation systems.

The excellent photocatalytic NO removal performance relates to the synergistic effect between the prepositive NaOH solution and the g-C3N4 photocatalysis

Photocatalysis technology is used to remove the low concentration NO in recent years. However, the effect of this process is not very satisfactory. In this study, it was found that the prepositive NaOH solution could significantly improve the photocatalytic NO removal activity of g-C3N4. The apparent quantum yield of g-C3N4 in the NO removal process was increased 3.5 times by the prepositive NaOH solution. The reason is that there was a synergistic effect formed between the prepositive NaOH solution and the photocatalytic NO removal process. The prepositive NaOH solution not only could increase the humidity and pH value in the photocatalytic unit, but also could improve the adsorption ability of g-C3N4 for the H2O, NO, and O2. Moreover, the prepositive NaOH solution reduced the difficulty of the photogenerated carriers’ transport and the ·OH generation. This study provided a new idea for the removal of low-concentration NOx.

Manganese oxide nanorod catalysts for low-temperature selective catalytic reduction of NO with NH3.

MnOx nanorod catalysts were successfully synthesized by two different preparation methods using porous SiO2 nanorods as the template and investigated for the low-temperature selective catalytic reduction (SCR) of NO with NH3. The catalysts were characterized by scanning electron microscopy, transmission electron microscopy, nitrogen adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, and NH3 temperature-programmed desorption. The results show that the obtained MnOx-P nanorod catalyst prepared by redox precipitation method exhibits higher NO removal activity than that prepared by the solvent evaporation method in the low temperature range of 100–180 °C, where about 98% NO conversion is achieved over MnOx(0.36)-P nanorods. The reason is mainly attributed to MnOx(0.36)-P nanorods possessing unique flower-like morphology and mesoporous structures with high pore volume, which facilitates the exposure of more active sites of MnOx and the adsorption of reactant gas molecules. Furthermore, there is a lower crystallinity of MnOx, higher percentage of Mn4+ species and a large amount of strong acid sites on the surface. These factors contribute to the excellent low-temperature SCR activity of MnOx(0.36)-P nanorods.

The photocatalytic NO-removal activity of g-C3N4 significantly enhanced by the synergistic effect of Pd0 nanoparticles and N vacancies

Pd0 and N vacancy co-modified g-C3N4 displayed excellent NO-removal activity.

Fabrication of 1D/2D BiPO4/g-C3N4 heterostructured photocatalyst with enhanced photocatalytic efficiency for NO removal

The visible light photocatalytic removal of NO in air is a promising way. BiPO4 is restricted by its wide band gap and can only be responded to ultraviolet light. Herein, 1D BiPO4 nanorod/2D g-C3N4 heterostructured photocatalyst was successfully synthesized via a facile one-step hydrothermal process for efficient visible light photocatalytic removal of NO. With simulated sunlight irradiation, the photocatalytic NO removal activity of the BiPO4/g-C3N4 (64%) is much higher than that of the pure BiPO4 (7.2%) and g-C3N4 (50%). Its excellent photocatalytic performance was ascribed to broadening the light response range to visible light and boosting the separation and transfer of photogenerated electrons and holes. The NO photocatalytic removal mechanism was proposed by the free radical trapping experiment and in situ DRIFTS research. The present study might induce a new means to design BiPO4-based heterostructured photocatalysts for the removal of NO from air pollution under simulated solar light irradiation.

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 1O2 during the photocatalytic process. Moreover, SrSn(OH)6 photocatalyst not only exhibits high photocatalytic activity for NO removal (79.6%), but also has good stability after five cycles. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to investigate the NOx transfer pathway and the intermediate products distribution during the adsorption and photocatalytic NO oxidation process. The present work not only provides an efficient material for air pollutants purification at room temperature but also in-depth understanding of the mechanism involved in the photocatalytic NO removal process.

Oxygen vacancy defects-boosted deep oxidation of NO by β-Bi2O3/CeO2-δp-n heterojunction photocatalyst in situ synthesized from Bi/Ce(CO3)(OH) precursor

Flower-like n-type CeO2-δ is hybridized with p-type β-Bi2O3 nanoparticles to design a novel β-Bi2O3/CeO2-δp-n heterojunction photocatalyst via a thermal treatment process of Bi/Ce(CO3)(OH) precursor. The synthesized β-Bi2O3/CeO2-δ exhibits a remarkable enhancement in NO removal and significant suppression of toxic intermediates nitrogen dioxide (NO2) under visible light irradiation. The superior photocatalytic activity of β-Bi2O3/CeO2-δ for NO removal is mainly derived from the synergistic effects of the oxygen vacancies (OVs) and p-n heterojunction. The OVs not only enhance the visible light utilization and boost the separation of electron-hole pairs but also improve the adsorption and activation of NO and O2. Particularly, the p-n heterojunction is beneficial for the interfacial migration of photogenerated charge carriers. Electron spin resonance (ESR) and trapping experiment reveal that the synergistic effects of OVs and p-n heterojunction can induce the generation of more active species. The electrochemical measurements and density-functional theory (DFT) calculations in-depth confirm that both p-n heterojunction and OVs can accelerate the interfacial charge transfer, resulting in the deep oxidation of reactants. Therefore, the flower-like β-Bi2O3/CeO2-δp-n heterojunction photocatalyst exhibits an advanced photocatalytic activity for deep NO removal and a suppressed NO2 generation. In addition, monitoring the reaction products by in situ Fourier transform infrared spectrum (FTIR) further validates that the main products of nitrates are formed during the photocatalytic process. This work demonstrates a straightforward approach for construction of p-n heterojunction photocatalysts, which can enhance the effective photocatalytic activity and stability for NO removal.