NO Removal Efficiency Research Articles

EVALUATION OF THE EFFECTIVENESS OF NO REMOVAL USING THE PHOTOCATALYTIC ACTIVATED MATERIAL S-TiO2/DIATOMITE

S-TiO2 typically exhibits high photocatalytic activity, but its powdered form makes it difficult to apply practically in environmental pollution treatment. Diatomite from different locations varies in purity and integrity of the diatomaceous earth, making it a suitable catalyst support for synthesizing mixed-phase S-TiO2 catalysts using the sol-gel technique. The synthesized photocatalyst exhibits photocatalytic activity similar to that of S-TiO2. The NO removal efficiency under the same conditions with different catalyst supports only decreases by approximately 3% within 30 minutes at a reaction rate of 0.0950 min-1, with an optimal mass ratio of 70:30 for S-TiO2 and diatomite. This composite material holds promise for addressing the application of photocatalytic materials in practical environmental treatment, including NO removal and the treatment of other environmental pollutants, as diatomite is a naturally available and environmentally friendly material.

The reduction of copper in LaFeO3, La2CuO4 and CuO three-phase system improves the efficiency of NO removal: Experimental and density functional theory calculation

Hollow spherical LaCu0.5Fe0.5O3 (LCF) and La0.8Ce0.1Cu0.5Fe0.5O3 (LCCF) catalysts are synthesized by solvothermal method, and CuO is reduced in two samples, so that the two corresponding multiphase catalysts (R-LCF and R-LCCF) were prepared and used for the selective catalytic reduction of NO with CO (CO-SCR). The results show that the balance of Ce3++Cu2+↔Cu++Ce4+ between Ce and Cu ions promotes the reduction of CuO in the Ce-doped LCCF catalyst more obviously. In addition, the reduction of Ce and Cu in R-LCCF generates more oxygen vacancies, which leads to more surface adsorbed oxygen species, thus facilitating the conversion of more NO to NOx species. Besides, the presence of reduced Cu is highly active and can inhibit the production of carbonates occupying the active site. The ability to activate both CO and NO after the evolution of Cu0 to the key species Cu+ leads to a rapid reaction between Cu+-CO and NOx species. These are the key factors for the significant increase in catalytic activity at low temperatures. It is worth noting that the CO-SCR reaction on the R-LCCF catalyst corresponds to the Langmuir-Hinshlwood (L-H) and Eley-Rideal (E-R) mechanisms at different temperature windows, respectively.

Experimental study on integrated desulfurization and denitrification of low-temperature flue gas by oxidation method

In this paper, TiO2 catalysts doped with different Fe contents (Fe-TiO2 catalysts) were prepared by coprecipitation method and the Fe loading capacity was optimized, and then the integrated pollutant removal experiment was conducted, in which TiO2 doped with Fe as catalyst and H2O2 as oxidant. The results show that under the condition of constant H2O2/(SO2 + NO) molar ratio, low concentration of SO2 can promote the oxidation and removal efficiency of NO, while high concentration of SO2 can inhibit the removal of NOx. The pollutant removal efficiency is proportional to the amount of catalyst, liquid–gas ratio and pH value of the absorbing solution. The optimal experimental conditions are H2O2/(SO2 + NO) molar ratio 1.5, space velocity ratio 10,000 h−1, H2O2 mass fraction 10 wt%, liquid gas ratio 10, pH 10. Correspondingly, NO oxidation efficiency reaches 88%, NOx removal efficiency 85.6%, and SO2 is almost completely removed. The microstructure of the catalyst before and after the reaction was characterized, and the crystal structure did not change obviously. However, with the deepening of the reaction, the specific surface area of the catalyst decreases, and the catalytic effect decreases slightly.

Theoretical Study of the NO Reduction Mechanism on Biochar Surfaces Modified by Li and Na Single Adsorption and OH Co-Adsorption

Theoretical and experimental investigations have shown that biochar, following KOH activation, enhances the efficiency of NO removal. Similarly, NaOH activation also improves NO removal efficiency, although the underlying mechanism remains unclear. In this study, zigzag configurations were employed as biochar models. Density functional theory (DFT) was utilized to examine how Li and Na single adsorption and OH co-adsorption affect the reaction pathways of NO reduction on the biochar surface. The rate constants for all reaction-determining steps (RDSs) within a temperature range of 200 to 1000 K were calculated using conventional transition state theory (TST). The results indicate a decrease in the activation energy for NO reduction reactions on biochar when activated by Li and Na adsorption, thus highlighting their beneficial role in NO reduction. Compared to the case with Na activation, Li-activated biochar exhibited superior performance in terms of the NO elimination rate. Furthermore, upon the adsorption of the OH functional group onto the Li-decorated and Na-decorated biochar models (LiOH-decorated and NaOH-decorated chars), the RDS energy barriers were higher than those of Li and Na single adsorption but easily overcome, suggesting effective NO reduction. In conclusion, Li-decorated biochar showed the highest reactivity due to its low RDS barrier and exothermic reaction on the surface.

S-scheme Bi12TiO20/Bi4Ti3O12 heterojunction immobilized on 3D-printed support as a monolithic photocatalyst for NO removal

Photocatalysis is recognized as one of the most promising techniques for environment purification. However, the inconvenient recovery of powder photocatalysts significantly impeded their practical applications. Immobilization of the photocatalysts on supports to form monolithic photocatalysts is an effective method to solve this problem. Herein, a monolithic photocatalyst Bi12TiO20/Bi4Ti3O12/SiOC is fabricated by growing optimal Bi12TiO20/Bi4Ti3O12 S-scheme heterojunction onto 3D-printed porous SiOC support. On one side, S-scheme heterojunction facilitates the separation of photoinduced electrons and holes while retaining their strong redox ability. On the other side, the porous structure favors mass transport and improves light harvesting by reflecting the light several times. Under simulated solar light irradiation, the NO removal efficiency of the monolithic photocatalyst Bi12TiO20/Bi4Ti3O12/SiOC is 16.4 %. Furthermore, the composite has good stability and reusability, suggesting its great potential in practical application. The possible photocatalytic mechanism is proposed according to systematic experiments and density functional theory (DFT). This work provides a rational reference for constructing efficient photocatalysts for environmental purification.

Franckeite-derived van der Waals heterostructure with highly efficient photocatalytic NOx abatement: Theoretical insights and experimental evidences

Addressing the pressing issue of nitrogen oxides (NOx) pollution requires the identification and optimization of efficient materials for NOx removal. This study rigorously explores franckeite, a naturally occurring van-der-Waals heterostructure, for its photocatalytic potential in NOx elimination. Employing ab-initio calculations underpinned by density functional theory (DFT) and the many-body BerkeleyGW (GW) plus Bethe-Salpeter (GW-BSE) approach, we analyze franckeite’s structural, electronic, and optical characteristics, including its absorption spectra. Our experimental data indicate a substantial improvement in NO removal efficiency, ranging from 30% to a remarkable 100% under specific conditions. We find a direct correlation between removal efficiency and gas flow rate; higher rates reduce catalyst-NO interaction time. Additionally, we identify radical species responsible for oxidizing NO to nitrates/nitrites. Franckeite demonstrated both stability and reusability, achieving an average efficiency of 95% during three continuous hours of testing. These findings open new avenues for scaling up the use of Franckeite in environmental applications.

Enhanced photocatalytic NO removal over AgCu alloy modified UiO-66-NH2 promoting charge transfer

Photocatalytic NO removal technology is considered as one of the most effective green methods for reducing atmospheric NO but there remains the problems of lower efficiency and poor stability of photocatalysts. Rapid recombination of photogenerated electron (e−) and holes (h+) is known as a key issue that causes low activity and poor stability of catalysts. Herein, we report a novel AgCu@UiO-66-NH2 photocatalyst (AgCu@UN) that is made up of AgCu alloy on the surface of Zr-MOF (UiO-66-NH2) by employing in-situ photodeposition method. The experimental results of photocatalytic NO removal indicated that the optimized 0.5Ag0.5Cu@UN sample with 0.5 mg of Ag and Cu exhibited the best NO removal efficiency of 63 % for ppb-level atmospheric NO, more higher than that of pure UiO-66-NH2 (38 %). The characterizations suggested that the excellent photocatalytic performance of 0.5Ag0.5Cu@UN can be ascribed to the efficient charge separation and transfer and the visible-light-harvesting ability due to benefiting electron migration process between AgCu alloys and UN. Moreover, the enriched electrons around AgCu could be transferred to O2 to generate more superoxide radicals (•O2−), which could oxidize NO to the final product, nitrate (NO3−). The present findings can provide some novel insights for the design of efficient MOF based photocatalysts to eliminate low concentrations of NOX.

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.

The temperature-controlled optimization of g-C3N4 structure significantly enhances the efficiency of photothermal catalytic NO removal

The efficiency of photocatalytic NO removal is often constrained by catalyst lifespan and secondary contamination from reaction products.

Enhanced simultaneous oxidation of Hg0 and NO with SO2 resistance by dual single-atom Co-Cu incorporated g-CN nanocomposites

The simultaneous catalytic oxidation of Hg0 and NO within coal-fired plants is crucial in abating diverse pollutants. Nevertheless, conventional catalysts often encounter challenges, such as diminished oxidation efficiency at lower temperatures and competitive adsorption with other gaseous components, particularly SO2, to remove Hg0 and NO. A nanocomposite catalyst, Co-Cu/g-CN, was developed to address these issues, featuring dual single-atom doping of Co and Cu in graphitized carbon nitride (g-CN). Surface characterization techniques and theoretical calculations confirmed that Co and Cu single atoms were successfully incorporated into the g-CN structure. Moreover, this innovative catalyst exhibited a strong metallic interaction between the dual single atoms, which led to an increased production number of superoxides (O2−), albeit with a slightly reduced oxidizing ability. The trade-off in the active centers of O2− ultimately enhanced the oxidation capability of Hg0 and NO owing to the augmented number of O2−. Co-Cu/g-CN demonstrated complete Hg0 removal efficiency and achieved 81.3% NO removal efficiency at 200–250 °C. Both theoretical analysis and DRIFTS investigation revealed that the competitive adsorption of SO2 over O2− was significantly weakened due to the reduced oxidizing ability of O2−. Additionally, the Cu single atoms acted as sacrificial sites for sulfate species, thereby preserving the catalytic activity of Co single atoms for NO oxidation. This research provides a valuable dual single-atom-catalyst fabrication strategy for addressing flue-gas NOx and Hg0 pollution.

Single-atom Pd anchored in the porphyrin-center of ultrathin 2D-MOFs as the active center to enhance photocatalytic hydrogen-evolution and NO-removal

Single-atom catalysts were widely used to treat atmospheric pollution and alleviate energy crises through photocatalysis. However, how to prevent the aggregation of single atoms during the preparation and catalytic processes remained a great challenge. Herein, a novel ultrathin two-dimensional porphyrin-based single-atom photocatalyst Ti-MOF (abbreviated as TMPd) obtained through a simple hydrothermal synthesis strategy was used for photocatalytic hydrogen evolution and NO removal, in which the single-atom Pd tightly anchored in the center of porphyrin to ensure single-atom Pd stable existence. Compared with most reported MOFs-based photocatalysts, the TMPd showed an excellent hydrogen evolution rate (1.32 mmol g−1 h−1) and the NO removal efficiency (62%) under visible light irradiation. Aberration-corrected high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) and synchrotron-radiation-based X-ray absorption fine-structure spectroscopy (XAFS) proved that pd in TMPd existed in an isolated state, and the atomic force microscope (AFM) proved the ultrathin morphology of TMPd. DFT calculations had demonstrated that single-atom Pd could serve as the active center and more effectively achieve electron transfer, indicating that single-atom Pd played a vital role in photocatalytic hydrogen evolution. In addition, a possible photocatalytic pathway of NO removal was proposed based on ESR and in-situ infrared spectra, in which the catalysts anchored with single-atom Pd could produce more active substances and more effectively oxidize NO to NO2− or NO3−. The results suggested that coordinating single-atom metal species as the active site in the center of porphyrin could be a feasible strategy to obtain various ultrathin porphyrin-based single-atom photocatalysts to acquire excellent photocatalytic performance further.

Study on photocatalytic performance of carbonated coating supported TiO2@SiO2

In recent years, photocatalytic cement-based materials have demonstrated a positive impact on reducing air pollutants. However, challenges arise from the aggregation of photocatalysts and the intricate internal environment of cement-based materials, resulting in diminished photocatalytic efficiency. To address these issues, the TiO2@SiO2 photocatalyst which reduced agglomeration and was easy to disperse was prepared by sol-gel method, and the TiO2@SiO2 photocatalyst was added into γ-C2S carbonated cementitious material system by surface loading and blending to prepare the photocatalytic carbonation coating. In this paper, the TiO2@SiO2 photocatalyst synthesized at solution pH 4.16 had the highest photocatalytic degradation efficiency of nitrogen oxides. The photocatalytic efficiency of the prepared carbonated coating was evaluated through the degradation efficiency of nitrogen oxide and rhodamine B. When the content of TiO2@SiO2 was 7%, the photocatalytic carbonation coating had the highest photon removal efficiency for NO (0.17%), and the degradation rate for rhodamine B was 32.94% after 7 h illumination. The photocatalytic effect of the photocatalytic carbonated coating prepared with surface loaded TiO2@SiO2 was better than that of the doped coating. When the surface loading was 1.5 g/m2, the photocatalytic efficiency of the coating on NO reached 0.81%, and the degradation rate of rhodamine B after 7 h illumination was 36.92%. This method introduced a novel concept for the future application of photocatalytic building materials, contributing to carbon sequestration and energy conservation efforts.

Boosting visible-light photocatalytic NO removal by non-intrinsic oxygen vacancies in graphitic carbon nitride

Modifying photocatalysts for effective NO removal has profound implications for environmental protection. In this work, a novel g-C3N4 containing non-intrinsic oxygen vacancies (VO-CN) is synthesized via a facile oxygen pre-doping followed by elimination. Compared to pristine g-C3N4, VO-CN exhibits remarkably enhanced visible-light photocatalytic activity, increasing NO removal by 54.3%, with high NO3- selectivity. This photocatalytic enhancement is attributed to the non-intrinsic oxygen vacancies introduced in Vo-CN. As comprehensively revealed by experimental characterizations coupled with density functional theory (DFT) calculations. The results show that the midgap state generated in the VO-CN electronic band structure accelerates photogenerated electron-hole separation. Additionally, the unique surface structure of VO-CN provides favorable channels for carrier migration while enhancing O2 and NO adsorption. Consequently, the markedly improved generation of reactive oxygen species by Vo-CN promotes highly efficient NO removal. This work provides novel insights into designing high-performance g-C3N4-based photocatalysts for eliminating hazardous NO pollutants.

Experimental study of Fe modified Mn/CeO2 catalyst for simultaneous removal of NO and toluene at low temperature

A series of Mn/CeO2 catalysts modified with different Fe contents were prepared by impregnation method and tested for their low-temperature performance for simultaneous de-nitrification and toluene removal. It was found that the Fe5Mn/CeO2 catalyst showed the best catalytic performance and the conversion efficiency of toluene reached 90% at 175 °C and NO conversion reached 90% at 95−300 °C. The physical and chemical properties of the catalysts were characterized by BET, SEM, XRD, XPS, H2-TPR, NH3-TPD and O2-TPD. XPS results showed that the increased content of Ce3+ and Mn4+ in the Fe5Mn/CeO2 catalyst promoted the formation of oxygen vacancies and unsaturated chemical bonds, providing more active sites, thus facilitating the efficient removal of NO and toluene at low temperatures. Compared with other catalysts, H2-TPR, NH3-TPD and O2-TPD indicate that Fe5Mn/CeO2 catalyst has great redox ability, stronger acidity and better oxygen migration ability. In addition, this paper explores the effects between selective catalytic reduction (NH3-SCR) and catalytic oxidation reaction of toluene over Fe5Mn/CeO2 catalyst. NH3 preferentially reacts with the active site on the catalyst to inhibit the toluene oxidation process, while NO promotes the toluene removal process. Toluene can promote the NH3-SCR process in a certain temperature range. While NO promotes the formation of NO2, NO2 effectively promotes the combination of toluene and active sites, which is conducive to the catalytic oxidation of toluene; The inhibition of toluene on the NH3-SCR process weakens with the increase of temperature. At 100 °C, the inhibition of toluene on the NH3-SCR process disappears. When the temperature exceeds 225 °C, toluene reacts with NO as a reducing agent and promotes the formation of NO2, thus promoting the NH3-SCR reaction.

Tuning visible light-driven photocatalytic NO removal: Insights from glucose-derived CQDs/ZnO nanorods composite

The potential of visible light photocatalysis in mitigating environmental pollutants has gained significant attention. In this study, we investigate the photocatalytic NO removal efficiency of oxygen defect-rich zinc oxide nanorods (ZnO NRs), facilitated by the incorporation of carbon quantum dots (CQDs) under mild conditions. The successful integration of CQDs with ZnO NRs represents a novel and sustainable approach for efficient NO removal under visible light irradiation. Notably, the CQDs/ZnO NRs shows a substantial increase in NO removal efficiency (71.9%), low toxicity (2.7%) and durability (only 7.7% efficiency reduction after five cycles). The synergetic effects of CQDs and oxygen defects within the ZnO NRs structure, which broadens the light absorption spectrum, facilitates electron separation, thus enhanced photocatalytic NO removal. Furthermore, photoluminescence, active species trapping experiments, and electron spin resonance analysis have confirmed the generation of hydroxyl radicals (•OH) and superoxide radicals (•O2–) during the excitation of electrons. Finally, the synergetic mechanism of CQDs and oxygen defects in ZnO NRs for amplifying visible-light-driven photocatalytic NO removal was elucidated.

Halogen (Cl, Br, I) regulation Cu-BTC for NH3-SCR: NO and Hg0 removal and mechanism analysis

Emissions of NOx and Hg0 in the atmosphere are primarily derived from coal-fired power plant flue gases. The control of these pollutants has emerged as a focal point of research in recent years. In this study, we synthesized a novel halogen-modified Cu-BTC catalyst designed for the synergistic removal of NO and Hg0. The results showed that: Cu-BTC catalyst maintained its original physicochemical properties even after being modified with different halogens (Cl, Br, I), and C-X (Cl, Br, I) bonds indicated the successful incorporation of halogens into the Cu-BTC. Furthermore, the catalytic performance was investigated through NH3-SCR method. Research indicated that halogens amplified the catalytic reduction of NO and the catalytic oxidation ability of Hg⁰. Furthermore, the effect of post-modification proved to be superior to pre-modification, following the order of Cl＞Br＞I. Under the conditions of 200 °C and 30000 h−1, the Cu-BTC-Cl catalyst exhibited the highest removal efficiency for both NO and Hg⁰, reaching 84.895 % and 76.841 %. While NO had a minor impact, NH₃ enhanced the removal of NO but inhibited the removal of Hg⁰. O2 significantly promoted pollutants removal, and the catalyst also showed strong resistance to both sulfur and water. The modified catalyst exhibited covalent C–Cl species, which effectively captured Hg0. Cu2+ participated in the removal of NO and Hg0, with partial transformation into Cu+.

The reaction characteristics and mechanism of polymer non-catalytic reduction (PNCR) for NOx removal

To overcome the defects of the traditional selective non-catalytic reduction (SNCR) process (e.g., low efficiency, narrow temperature range), a new modified SNCR technology based on the solid complex polymer reducing agents, also called polymer non-catalytic reduction (PNCR), was investigated both in the laboratory and pilot scale to reveal its reaction characteristics and mechanism. The PNCR process demonstrates excellent removal efficiency (about 90%) of NO in furnace in the wide temperature range (850–1150 °C), and possesses promising application feasibility with an average NOx emission concentration of 68.72 mg·m−3 even on unstable industrial operating conditions. The NO removal behaviors influenced by O2, temperature, or water steam illuminate the unique O2-independent and H2O-promoted reaction characteristics of PNCR in the wide temperature range. The thermogravimetric infrared spectra/mass spectrometry (TG-IR/MS) results further reveal a pyrolysis-assisted formation mechanism of active NH2/NH free radicals without the requirement of O2 and high temperature, which avoids the overoxidation of active radicals and accounts for the wide denitrification temperature window, low oxygen compliance and high denitrification efficiency of PNCR process. The excellent NO removal performance as well as the unique reaction characteristics/mechanism of PNCR forebode its broad industrial application prospect in the field of flue gas cleaning.

Engineering bifunctional Pd/CeNbTiOx catalyst for the simultaneous removal of NO and CO under oxygen-rich conditions at low temperature

The simultaneous elimination of CO and NO has practical significance for the control of air pollutants in the flue gas operating temperature range of 240–320 °C. CeNbTiOx catalyst was prepared by evaporation-induced self-assembly method (EISA), and the 0.3 % Pd/CeNbTiOx catalyst was obtained by appropriate Pd anchoring at the defects of CeNbTiOx. CO and NO removal efficiency were above 90 % from 240 to 320 °C, which exhibited satisfactory N2 selectivity. The CO and NO removal efficiency of the 0.3 % Pd/CeNbTiOx catalyst exceeded 92 % during stability and water resistance. Oα and Oβ were involved in the oxidation of NO and CO, respectively, promoting the fast SCR and CO oxidation reaction within the ordered mesoporous of the 0.3 % Pd/CeNbTiOx catalyst. In addition, the efficiency of CO and NO elimination had been further improved due to the enhancement of defects after resistance of H2O. Therefore, this work provided a new and efficient way to control CO and NO by the efficient using of oxygen species.

Oxygen vacancies-modified S-scheme heterojunction of Bi-doped La2Ti2O7 and La-doped Bi4Ti3O12 to improve the NO gas removal avoiding NO2 product

Monoclinic phase La2Ti2O7 and orthorhombic phase Bi4Ti3O12 with layered crystal structure constructed by the perovskite slab were widely used in photocatalysis. Their electronic structures are the most crucial factor in high photocatalytic activity. Bi-doped La2Ti2O7 gradually converts to La-doped Bi4Ti3O12 with the incorporation of bismuth ions, and the two phases build an S-scheme heterojunction. More oxygen vacancies were introduced into the S-scheme heterojunction after heat treatment in a nitrogen atmosphere. The 0.1BTO/LTO-OV sample exhibits the largest NO removal efficiency of 52% and only 5.6 ppb NO2 intermediate generation. The improved NO removal efficiency was ascribed to the synergistic effect of oxygen vacancies, doping and heterojunction, providing a new insight into the photocatalytic NO removal. The photocatalytic mechanism was eventually proposed on the basis of trapping experiments.

Flexible monolithic Pt/CuO-Fe2O3/TiO2 catalysts integrated on Ti mesh for efficient NO removal via CO-SCR reaction

This study reports on the development of highly-efficient Pt/CuO-Fe2O3/TiO2 monolithic catalysts for the low-temperature conversion of NO to N2 via CO-SCR. In this case, ultrathin TiO2 nanosheet arrays are designed to in situ grow on flexible Ti mesh to provide more spaces/areas for the loading of highly-dispersed Fe2O3 and CuO active components. Furthermore, Pt nanoparticles with an average size of 1.30 nm are effectively decorated on the surface of CuO-Fe2O3/TiO2. The H2-TPR and NO-TPD results demonstrate that the excellent synergistic effect between TiO2, CuO, Fe2O3 and trace amounts of Pt is conducive to enhance the adsorption of NO and finally promote the CO-SCR. The obtained Pt/CuO-Fe2O3/TiO2 catalysts exhibit excellent CO-SCR performance with 100 % NO conversion, and 100 % N2 selectivity at 250 °C, showing great potential of de-NOx application by using toxic CO as reductant in industry.