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The Pt/CeO2 catalyst has attracted significant attention due to its exceptional performance in NO oxidation. This study comprehensively examines the effects of calcination temperature and H2 pretreatment on the structure and activity of the Pt/CeO2 catalyst. Experimental findings indicate that the calcination temperature significantly affects the catalyst's redox performance, thereby modulating its efficacy in NO oxidation reactions. H2 pretreatment facilitates the creation of oxygen vacancies on the catalyst, assisted by the reduction in PtOx to Pt, enhancing the formation of activated oxygen and thereby improving NO oxidation. This study offers valuable insights into the design and optimization of Pt/CeO2 catalysts for environmental applications, particularly in the development of exhaust gas after-treatment technologies. [ABSTRACT FROM AUTHOR]

[Display omitted] 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 Cs 2 SnBr 6 /C 3 N 4 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 Cs 2 SnBr 6 /C 3 N 4 heterogeneous system can reach 86.8 %, which is approximately 3-fold and 18-fold that of pristine C 3 N 4 and Cs 2 SnBr 6 , respectively. The comprehensive understanding of the electron transfer between heterojunction atomic interfaces will provide a novel perspective on efficient environmental photocatalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] Nitric oxide (NO) oxidation is an integral part of the nitrogen chemical cycle, but competitive activation of NO/O 2 over single platinum (Pt)-based catalysts result in inadequate low temperature performance. Here, we constructed catalysts with BiMn 2 O 5 /CeO 2 and Pt/BiMn 2 O 5 defective interfaces (sufficient activation of NO/O 2). The constructed catalyst achieved 95 % NO conversion at 260 °C in NO/O 2 atmosphere, superior to most known catalysts. Even after aging (800 °C for 16 h), the NO conversion was up to 76 %. Further, the catalyst can be applied to actual diesel exhaust. Detailed oxygen vacancies (O v) characterization reveals that BiMn 2 O 5 /CeO 2 defective interface created by Ce3+-O v + Mn4+-O ↔ Ce4+-O + Mn3+-O v promote the activation of NO (on Mn3+ sites) and O 2 (on Mn3+-O v sites). Besides, the O v on Pt/BiMn 2 O 5 defective interface compensate for the loss of Pt sites ensuring hydrothermal stability. And this construction of multiple defective interfaces develops a pathway for boosting catalytic reactions. [ABSTRACT FROM AUTHOR]

Abstract The contamination of nitric oxide presents a significant environmental challenge, necessitating the development of efficient photocatalysts for remediation. Conventional heterojunctions encounter obstacles such as large contact barriers, sluggish charge transport, and compromised redox capacity. Here, we introduce an innovative S‐type heterostructure photocatalyst, UiO‐66‐NH2/ZnS(en)0.5, designed specifically to overcome these challenges. The synthesis, employing a unique microwave solvothermal method, strategically aligns the lowest unoccupied molecular orbital of UiO‐66‐NH2 with the highest occupied molecular orbital of ZnS(en)0.5, fostering the formation of a stepped heterojunction. The resulting intimate interface contact generates a built‐in electric field, facilitating charge separation and migration, as evidenced by time‐resolved photoluminescence spectroscopy and photoelectrochemical tests. The abundant active sites in the porous UiO‐66‐NH2 counterpart provide adsorption and activation sites for nitrogen monoxide (NO) oxidation. Performance evaluation reveals exceptional photocatalytic NO removal, achieving 70% efficiency and 99% selectivity toward nitrates under simulated solar illumination. Evidence from X‐ray photoelectron spectroscopy and trapping experiments supports the effectiveness of the S‐type heterostructure, showcasing refined reactive oxygen species, particularly superoxide. Thus, this study introduces a new perspective on advanced NO oxidation and unlocks the potential of S‐scheme heterojunctions to refine reactive oxygen species for NO remediation.

TiO2 was loaded on the porous nickel foam from the suspended ethanol solution and used for the photocatalytic removal of NOx. Such prepared material was heat-treated at various temperatures (400–600 °C) to increase the adhesion of TiO2 with the support. Obtained TiO2/nickel foam samples were characterized by XRD, UV–Vis/DR, FTIR, XPS, AFM, SEM, and nitrogen adsorption at 77 K. Photocatalytic tests of NO abatement were performed in the rectangular shape quartz reactor, irradiated from the top by UV LED light with an intensity of 10 W/m2. For these studies, a laminar flow of NO in the air (1 ppm) was applied under a relative humidity of 50% and a temperature of 28 °C. Concentrations of both NO and NO2 were monitored by a chemiluminescence NO analyzer. The adsorption of nitrogen species on the TiO2 surface was determined by FTIR spectroscopy. Performed studies revealed that increased temperature of heat treatment improves adhesion of TiO2 to the nickel foam substrate, decreases surface porosity, and causes removal of hydroxyl and alcohol groups from the titania surface. The less hydroxylated surface of TiO2 is more vulnerable to the adsorption of NO2 species, whereas the presence of OH groups on TiO2 enhances the adsorption of nitrate ions. Adsorbed nitrate species upon UV irradiation and moisture undergo photolysis to NO2. As a consequence, NO2 is released into the atmosphere, and the efficiency of NOx removal is decreasing. Photocatalytic conversion of NO to NO2 was higher for the sample heated at 400 °C than for that at 600 °C, although coverage of nickel foam by TiO2 was lower for the former one. It is stated that the presence of titania defects (Ti3+) at low temperatures of its heating enhances the adsorption of hydroxyl groups and the formation of hydroxyl radicals, which take part in NO oxidation. Contrary to that, the presence of titania defects in TiO2 through the formation of ilmenite structure (NiTiO3) in TiO2/nickel foam heated at 600 °C inhibits its photocatalytic activity. No less, the sample obtained at 600 °C indicated the highest abatement of NOx due to the high and stable adsorption of NO2 species on its surface. [ABSTRACT FROM AUTHOR]

The oxidation rate of NO to NO2 is a critical parameter in the removal of NOx within selective catalytic reduction (SCR) systems. LaCoO3-δ is a kind of potential catalyst to enhance the oxidation of NO to NO2, it may offers an economic and stable alternative to noble metal catalysts, particularly at elevated temperatures. This study aimed to enhance the catalytic efficiency of LaCoO3-δ through strontium (Sr) doping. La1-xSrxCoO3-δ (with varying x values of 0.1, 0.2, 0.3, 0.4) was synthesized using a sol-gel method. La1-xSrxCoO3-δ exhibited superior NO oxidation catalytic activity compared to LaCoO3-δ, with the most notable enhancement observed at x = 0.3 (84 % conversion). This improvement can be attributed to the substitution of La3+ with Sr2+, which induces lattice distortion and charge imbalance, thereby creating more oxygen vacancies that enhance the catalytic oxidation capability of La1-xSrxCoO3-δ. However, it's important to note that an excessive amount of Sr can result in the formation of SrCO3 deposits on the surface of La1-xSrxCoO3-δ, thereby diminishing its catalytic oxidation performance. The catalytic oxidation reaction behavior adhered most closely to the O2-adsorbed E-R model, the surface defects in La1-xSrxCoO3-δ playing a pivotal role in the catalytic reaction.

Nitrogen oxides in industrial flue gas are an important cause of environmental pollution. Non-thermal plasma technology is widely used to remove pollutants in flue gas, based on the oxidation of active particles. In this paper, a dielectric barrier discharge plasma generation system was designed and the oxidation of NO by non-thermal plasma was investigated, focusing on the effects of specific energy density (SED) and oxygen content. The results showed that when SED increased from 960 J/ L to 1920 J/L, the conversion efficiency of NO decreased. At the same time, the decrease of oxygen concentration promoted the conversion of NO. In combination with the oxidation catalyst, NO conversion could be dramatically promoted. A 500 m^3/h pilot-scale device was designed according to the laboratory results. The test was carried out in an industrial silicon submerged arc furnace. The results showed that NO could be completely converted with inlet NO volume fraction of 0~0.005%. The generated NO_2 was adsorbed on the surface of the catalytic material initially and gradually desorbed with the proceeding of the reaction. For inlet NO volume fraction of 0.005%~0.025%, the average outlet NO concentration was 0.001%(volume fraction). The above results confirmed the feasibility of NO conversion employing non-thermal plasma coupled with the catalyst.

BiOCl photocatalysis shows great promise for molecular oxygen activation and NO oxidation, but its selective transformation of NO to immobilized nitrate without toxic NO2 emission is still a great challenge, because of uncontrollable reaction intermediates and pathways. In this study, we demonstrate that the introduction of triangle Cl−Ag1−Cl sites on a Cl‐terminated, (001) facet‐exposed BiOCl can selectively promote one‐electron activation of reactant molecular oxygen to intermediate superoxide radicals (⋅O2−), and also shift the adsorption configuration of product NO3− from the weak monodentate binding mode to a strong bidentate mode to avoid unfavorable photolysis. By simultaneously tuning intermediates and products, the Cl−Ag1−Cl‐landen BiOCl achieved >90 % NO conversion to favorable NO3− of high selectivity (>97 %) in 10 min under visible light, with the undesired NO2 concentration below 20 ppb. Both the activity and the selectivity of Cl−Ag1−Cl sites surpass those of BiOCl surface sites (38 % NO conversion, 67 % NO3− selectivity) or control O−Ag1−O sites on a benchmark photocatalyst P25 (67 % NO conversion and 87 % NO3− selectivity). This study develops new single‐atom sites for the performance enhancement of semiconductor photocatalysts, and also provides a facile pathway to manipulate the reactive oxygen species production for efficient pollutant removal. [ABSTRACT FROM AUTHOR]

• A facile method for sludge char preparation with good de-NOx activity was proposed. • Urea doping enhanced NO conversion from 47.3% to 54.7%. • Urea doping markedly increased S BET and amorphousness of sludge char. • Urea doped nitrogen primarily existed in the form of Pyrr‑N which increased basicity of NSC. Catalytic oxidation of NO at room temperature was carried out over nitrogen (N)-doped sludge char (SC) prepared from pyrolysis of municipal sewage sludge, and urea was adopted as nitrogen source. The effects of different N-doping methods (one-step and two-step method), dried sludge (DS)/urea mass ratios (5:1, 4:1, 3:1, 2:1, and 1:1), SC preparation procedures (pyrolysis only, pyrolysis with acid washing, and pyrolysis with KOH activation and acid washing), and different pyrolysis temperatures (500, 600, 700, and 800°C) on the catalytic oxidation of NO were compared to optimize the procedure for SC preparation. The results indicated that N-doping could obviously promote the catalytic performance of SC. The one-step method with simultaneous sludge pyrolysis (at 700°C), KOH activation, and N-doping (DS/urea of 3:1) was the optimal procedure for preparing the N-doped SC with the NO conversion rate of 54.7%, whereas the optimal NO conversion rate of SC without N-doping was only 47.3%. Urea worked both as carbon and nitrogen source, which could increase about 2.9%-16.5% of carbon and 24.8%-42.7% of nitrogen content in SC pyrolyzed at 700°C. N-doping significantly promoted microporosity of SC. The optimal N-doped SC showed specific surface areas of 571.38 m2/g, much higher than 374.34 m2/g of the optimal SC without N-doping. In addition, N-doping also increased amorphousness and surface basicity of SC through the formation of N-containing groups. Finally, three reaction paths, i.e. microporous reactor, active sites, and basic site control path, were proposed to explain the mechanism of N-doping on promoting the catalytic performance of NO. [Display omitted] [ABSTRACT FROM AUTHOR]

TiO2 was loaded on the porous nickel foam from the suspended ethanol solution and used for the photocatalytic removal of NOx. Such prepared material was heat-treated at various temperatures (400–600 °C) to increase the adhesion of TiO2 with the support. Obtained TiO2/nickel foam samples were characterized by XRD, UV–Vis/DR, FTIR, XPS, AFM, SEM, and nitrogen adsorption at 77 K. Photocatalytic tests of NO abatement were performed in the rectangular shape quartz reactor, irradiated from the top by UV LED light with an intensity of 10 W/m2. For these studies, a laminar flow of NO in the air (1 ppm) was applied under a relative humidity of 50% and a temperature of 28 °C. Concentrations of both NO and NO2 were monitored by a chemiluminescence NO analyzer. The adsorption of nitrogen species on the TiO2 surface was determined by FTIR spectroscopy. Performed studies revealed that increased temperature of heat treatment improves adhesion of TiO2 to the nickel foam substrate, decreases surface porosity, and causes removal of hydroxyl and alcohol groups from the titania surface. The less hydroxylated surface of TiO2 is more vulnerable to the adsorption of NO2 species, whereas the presence of OH groups on TiO2 enhances the adsorption of nitrate ions. Adsorbed nitrate species upon UV irradiation and moisture undergo photolysis to NO2. As a consequence, NO2 is released into the atmosphere, and the efficiency of NOx removal is decreasing. Photocatalytic conversion of NO to NO2 was higher for the sample heated at 400 °C than for that at 600 °C, although coverage of nickel foam by TiO2 was lower for the former one. It is stated that the presence of titania defects (Ti3+) at low temperatures of its heating enhances the adsorption of hydroxyl groups and the formation of hydroxyl radicals, which take part in NO oxidation. Contrary to that, the presence of titania defects in TiO2 through the formation of ilmenite structure (NiTiO3) in TiO2/nickel foam heated at 600 °C inhibits its photocatalytic activity. No less, the sample obtained at 600 °C indicated the highest abatement of NOx due to the high and stable adsorption of NO2 species on its surface.

The tightening emission regulations have led to the development of commercial DOCs with zoned or layered formulations allowing to cover a wide range of functionalities (i.e. CO, HC and NO oxidation as well as HC or NOx trap). Aging phenomena in such complex formulations are not well understood. To shed light on material deactivation, this study compares phosphorus poisoning and thermal sintering of two DOC monoliths with related formulations: (1) a commercial monolith comprising two catalytic layers where the top layer is rich in Pt, and (2) a model monolith containing only the top layer of the commercial monolith. The activity and characterisation (elemental analysis, microscopy and N2-physisorption) results are used to deconvolute the deactivation process of the two layers and should serve to rationalize the aging in layered catalyst formulations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Doped Pt/mullite has excellent performance for NO oxidation. • The radius and valence differences of dopant ions induce oxygen vacancies. • Low temperature activity linked to oxygen vacancies and oxygen migration capacity. • The Pt/mullite interface are the key to the hydrothermal stability. • This simple doping method is also applicable to other mullite. Deep catalytic removal of nitrogen oxides is one of the widespread research topics, mainly limited by the low temperature activity and hydrothermal stability of the first step for NO oxidation. Oxygen vacancies (O v) and oxygen migration capacity play a crucial role in this challenge. Particularly, tuning the Mn-O coordination environment according to the radius and valence differences of dopant ions can increase O v , while accelerate oxygen migration by constructing Pt/mullite interfaces. Here, based on the hydrothermal stability of Pt/mullite to NO oxidation, we designed Mg2+- and Ba2+-doped catalysts. And the NO oxidation performance of the Mg2+-doped catalyst was significantly enhanced compared to the undoped catalysts (After hydrothermal aging, turnover frequency = 1.9 s−1 at 150 °C and activation energy = 21 kJ/mol). Meanwhile, all catalysts tested with simulated diesel exhaust and the NO oxidation performance showed essentially no decrease after 16 h of hydrothermal aging at 800 °C. Furthermore, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) demonstrated the O v content of doped catalysts increased significantly. In addition, O 2 temperature programmed desorption (O 2 -TPD) and Thermogravimetry (TG) proved that the oxygen migration capacity of doped catalysts was enhanced by several times. Notably, the simple doping method is general for the modification of other mullites and worthy of industrial application. [ABSTRACT FROM AUTHOR]

The present work aims to assess the impact of morphology and reducibility on lanthanum-doped ceria nanocatalysts with controlled morphology on the NO oxidation reaction. Specifically, samples were prepared using a hydrothermal method incorporating lanthanum at varying molar concentrations (0, 5, 10, and 15 mol.%) into ceria with a controlled morphology (nanocubes and nanorods). The structural, compositional, and redox characterization of these catalysts has been performed via scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (X-EDS), inductively coupled plasma (ICP), hydrogen temperature-programmed reduction (H2-TPR), and oxygen storage capacity (OSC). NO oxidation catalytic tests were conducted, and the results were compared with estimated curves (obtained by considering the proportions of the corresponding components), which revealed the presence of a synergistic effect between lanthanum and ceria. The degree of enhancement was found to depend on both the morphology and the amount of lanthanum incorporated into CeO2. These findings may facilitate the optimization of features concerning ceria-based nanocatalysts for the removal of NOx emissions from exhaust gases. [ABSTRACT FROM AUTHOR]

Selective catalytic reduction (SCR) is an effective system for treating nitrogen oxides (NOx; mainly NO), and fast SCR requires the equimolar reactants of NO and NO2. This study focused on catalysts for oxidizing 50% of NO to NO2. A series of catalysts composed of a variety of components, such as mesoporous mMnO2-nCeO2 as carrier catalysts (m:n = 9:1 and 7:3) and transition metals (e.g., Fe, Co, Ni, Cu, and Cr), were synthesized and characterized using N2 adsorption, in situ XRD, TEM, and XPS. All samples had a mesoporous structure with pore size around 8 nm. XPS results demonstrated that addition of cerium ion increased the surface area and provided oxygen vacancy due to the formation of Ce3+ within the structure. NO oxidation activity was tested using a feed (205~300 ppm NO and 6% O2) that simulated typical flue gas conditions. Doped mesoporous mMnO2–nCeO2 has higher NO oxidation activity than pristine mMnO2–nCeO2. The doped mMnO2-nCeO2 catalyzed 50% of NO to NO2 at between 140 and 200 °C resulting in an equivalent amount of NO and NO2. Among the transition metals, Cu, Ni, Co, Fe, and Cr have the highest to lowest oxidation activity, respectively. The precatalytic oxidation of NO can potentially be combined with the current SCR system without changes to existing equipment and can be applied to the exhaust gas treatment for de-NOx. [ABSTRACT FROM AUTHOR]

One step fabrication of SiC catalytic filter is currently limited by the mismatched calcination temperature between SiC filter (>1700°C) and the catalysts (<800°C), and the difficulty in the chemical immobilization of catalysts. Here, a SrTi1−xCoxO3‐SiC (STC‐SiC) catalytic filter was directly fabricated from raw SiC grains and STC precursor oxides (SrCO3, TiO2, and Co3O4) via a single‐step reactive thermal processing (SRTP) approach, which significantly reduced energy consumption and sintering time over 50%. Acid etching enables the active TiO2 and Co3O4 nanoparticles spontaneously formed on STC catalysts in STC‐SiC catalytic filter (STC‐SiC‐A), which induces the generation of oxygen vacancies and facilitates the adsorption and activation of O2 and NO. The STC‐SiC‐A catalytic filter exhibits highly competitive NO oxidation of 60% and complete dust interception (100%) at 360°C. This work demonstrates an efficient and rapid processing technique of SiC based catalytic filters, which can also be implemented on other ceramic‐based catalytic filters. [ABSTRACT FROM AUTHOR]

The H2O2 evaporation rate directly affected the oxidation of NO by H2O2. Green zeolite and synthetic mordenite were selected to promote H2O2 thermal decomposition and NO oxidation. The effects of different zeolites, evaporation conditions, temperatures, and reactant concentrations on the NO oxidation ratio were explored. The promotion mechanism of zeolite on NO oxidation by H2O2 thermal decomposition was explained. The results show that the zeolite surface can significantly accelerate the H2O2 evaporation rate to obtain a high NO oxidation ratio. The hydrophilicity and rich pore structure of zeolite enable the rapid diffusion and evaporation of droplets on the zeolite surface. Compared with the green zeolite with the mesoporous structure, the synthetic mordenite with the hierarchical pore structure has a more obvious promotion effect on the NO oxidation by H2O2 thermal decomposition. The reason is that the synthetic mordenite contains micropores, resulting in a larger specific surface area, and the mesoporous structure is conducive to the mass transfer and diffusion of H2O2 on its surface. The product of NO oxidation is mainly NO2, which proves that ·OH plays a major role in the process. [ABSTRACT FROM AUTHOR]

The effective oxidation of NO is the key to the catalytic treatment of diesel vehicle exhaust. Improving the NO oxidation ability is mainly to optimize the chemical state of the active site (Pt), followed by increasing the number of active centers. Considering that the atoms with electronegativity weaker than Pt can provide electrons to change the chemical state of Pt, rare earth elements with weak electronegativity are selected as additives to obtain Pt/M-SiO 2 -Al 2 O 3 (M = Sc, Y, La, Ce, Pr, Nd, Sm, Eu) catalysts by co-impregnation method. Among them, the Pt/La-SiO 2 -Al 2 O 3 catalyst has the best NO oxidation performance, compared with the Pt-SiO 2 -Al 2 O 3 , the NO conversion rate increased by 28 %. Due to the special outer electron arrangement of La, its electronegativity is the smallest in rare earth, which makes its outer electrons easy to transfer to Pt atoms, and has the strongest electron interaction. Thus, the highest content of Pt0 was detected in CO diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS) and X-ray photoelectron spectroscopy (XPS). In addition, CO chemisorption and transmission electron microscopy (TEM) confirmed that the introduction of La in the catalyst can significantly improve the dispersion of precious metals. Notably, this simple approach of affecting electron interaction by introducing weakly electronegative elements provides a reference for the design of noble metal catalysts with different valence states to solve complex problems. [Display omitted] • The electronegativity of added elements affects the valence state of Pt. • The electronegativity of elements decreases, easier the outer electrons transfer. • Reducing the electronegativity of added elements increases the content of Pt0. • The increase of Pt0 content improves the NO oxidation performance of the catalyst. [ABSTRACT FROM AUTHOR]

Semiconducting SnO2 photocatalyst nanomaterials are extensively used in energy and environmental research because of their outstanding physical and chemical properties. In recent years, nitrogen oxide (NOx) pollutants have received particular attention from the scientific community. The photocatalytic NOx oxidation will be an important contribution to mitigate climate change in the future. Existing review papers mainly focus on applying SnO2 materials for photocatalytic oxidation of pollutants in the water, while studies on the decomposition of gas pollutants are still being developed. In addition, previous studies have shown that the photocatalytic activity regarding NOx decomposition of SnO2 and other materials depends on many factors, such as physical structure and band energies, surface and defect states, and morphology. Recent studies have been focused on the modification of properties of SnO2 to increase the photocatalytic efficiency of SnO2, including bandgap engineering, defect regulation, surface engineering, heterojunction construction, and using co-catalysts, which will be thoroughly highlighted in this review.

Two Mn0.15Ce0.85O2−δ mixed oxides were synthesized by a co-precipitation method using Mn(NO3)2 and KMnO4 as the manganese precursors, respectively. Structural analyses by X-ray powder diffraction and Raman spectroscopy reveal the formation of MnOx-CeO2 solid solutions. The Mn0.15Ce0.85O2−δ catalyst prepared from the high-valent manganese precursor exhibits higher activity for the catalytic oxidation of NO. The advantage of KMnO4 is related to the improved redox property of the catalyst as supported by H2 temperature-programmed reduction (TPR) and O2 temperature-programmed desorption (TPD). The Mn-Ce interactions create more Mn4+, Ce3+ and oxygen vacancies on the KMnO4-synthesized mixed oxides based on the Raman and X-ray photoelectron spectra (XPS). [ABSTRACT FROM AUTHOR]

The positive effects of SO 2 on NO oxidation with H 2 O 2 vapor over a Fe 2 O 3 /SiO 2 catalyst were investigated. In well-designed experiments, the pretreatment of S-contained gaseous species and NO oxidation were carried out. The results indicated that the sulfate species from the oxidation of SO 2 could significantly promote NO oxidation. In the radical scavenger and ESR tests, the H 2 O 2 decomposition over SO 2 -pretreated Fe 2 O 3 /SiO 2 produced •OH and •SO 4 -. The •OH was dominant for NO oxidation. The XPS tests verified the Fe(III) reduction and the surface SO 4 2- species formation on Fe 2 O 3 /SiO 2. According to the kinetic studies, the NO adsorbed Eley-Rideal model gave the best fit, indicating that the adsorbed NO over SO 2 -pretreated Fe 2 O 3 /SiO 2 was oxidized by H 2 O 2. The systematic research revealed that the generation of •OH from H 2 O 2 decomposition over adsorbed H 2 SO 4 was faster than that over Fe 2 O 3 /SiO 2. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Monomeric Cu ions (Z 2 Cu and ZCuOH) do not catalyze dry NO oxidation. • Dehydrated ZCuOH can dimerize to Cu-oxo if diffusion radii of at most 0.50 nm overlap. • Cu-oxo cations come in three pools and catalyze dry NO oxidation at different rates. • Nitrates detected during in situ FTIR are a spectator species. The identification and quantification of multinuclear Cu-oxo cations in Cu-zeolites is a challenge amidst the dynamic nature of Cu ions in Cu-zeolites. Herein, we synthesized Cu-SSZ-13 zeolites containing varying densities of monomeric Cu cations (Z 2 Cu and ZCuOH, where Z represents an anionic site on the z eolite framework). The number of Cu-oxo cations, quantified using carbon monoxide temperature programmed reduction (CO-TPR), quadratically increased with increasing ZCuOH density, evidencing that proximal ZCuOH sites are precursors to Cu-oxo dimers. We also find that dehydrated proximal ZCuOH with overlapping diffusion radii of at most 0.5 nm can form Cu-oxo dimers. CO-TPR also revealed the presence of three distinct pools (i.e types) of Cu-oxo dimers; these pools catalyze dry NO oxidation at different turnover rates, with the fastest pool 2 to 30 times faster than the slowest pool. From reaction kinetics and rate law analysis, we also proposed a cohesive dry NO oxidation mechanism and demonstrated that nitrates detected by in situ FTIR are a spectator species. [ABSTRACT FROM AUTHOR]

Designing non-precious catalysts to synergistically expose high active sites and exhibit optimized NO oxidation activity still remains a big challenge. Herein, a low-cost and high-active CuOx/black-TiO2 catalyst was prepared by impregnation method for NO oxidation. The CuOx/black-TiO2 (molar ratio of Cu/Ti is 0.05) exhibited the highest NO oxidation efficiency (53.43%) at 350 °C, which was higher than that of corresponding CuOx/TiO2 (38.86%) catalyst. Moreover, the kinetics of NO conversion over CuOx/black-TiO2 and CuOx/TiO2 catalysts were also studied. Raman spectra results indicated that CuOx interacted strongly with oxygen vacancies on the surface of black-TiO2. XPS further proved that electrons transferred from black-TiO2 to CuOx, leading to a higher proportion of Cu+ on CuOx/black-TiO2 than that of CuOx/TiO2. In addition, CuOx/black-TiO2 exhibited better reduction property and bigger adsorption capacity of NO and O2 than those of CuO/TiO2, confirming by H2-TPR and NO (O2)-TPD, respectively. Finally, the possible mechanism of CuOx/black-TiO2 for NO oxidation was proposed. [ABSTRACT FROM AUTHOR]

This study investigated the reactive dissolution of nitric oxide (NO) and nitrogen dioxide (NO2) mixtures in deionized water. The dissolution study was carried out in a flat surface type gas–liquid reaction chamber utilizing a gas flow-pattern resembling plasma jets which are often used in biomedical applications. The concentration of NO and NO2 in the gas mixtures was varied in a broad range by oxidizing up to 800 ppm of nitric oxide in Ar carrier gas with variable amount of ozone. The production of nitrite (NO2−) and nitrate (NO3−) in the water was proportional to treatment time up to 50 min. The concentration of NO3− was a power function of gas phase NO2 while the concentration of NO2− increased approximately linearly with gas phase NO2. The formation of NO2− and NO3− could be described by reactions between dissolved NO2 and NO in the water while the production rate was determined by diffusion-limited mass transport of nitrogen oxides to the bulk of the liquid. At higher NO2 concentrations, the formation of dinitrogen tetraoxide (N2O4) increased the formation rate of NO2− and NO3−. The identified mass transport limitation by diffusion suggests that convection of water created by the gas jet is insufficient and dissolution of nitrogen oxides can be increased by additional mixing. In respect of practical applications, the ratio of NO2− /NO3− in water could be varied from 0.8 to 5.3 with treatment time and gas phase NO2 and NO concentrations. [ABSTRACT FROM AUTHOR]

[Display omitted] Establishing an ideal photocatalytic system with efficient reactive oxygen species (ROS) generation has been regarded as the linchpin for realizing efficient nitric oxide (NO) removal and unveiling the ROS-mediated mechanism. In this work, a novel oxygen-deficient 0D/1D Bi 3.64 Mo 0.36 O 6.55 /Bi 2 MoO 6 heterojunctions (BMO-12-H) were successfully synthesized under the enlightenment of clarified crystal growth mechanism of bismuth molybdates. Because of the synergies between defect-engineering and heterojunction-construction, BMO-12-H demonstrated improved photoelectrochemical properties and O 2 adsorption capacity, which in turn facilitated the ROS generation and conversion. The enhancement of •O 2 – and 1O 2 endowed BMO-12-H with strengthened NO removal efficiency (59%) with a rate constant of 12.6*10-2 min−1. A conceivable NO removal mechanism dominated by •O 2 – and 1O 2 was proposed and verified based on the theoretical calculations and in-situ infrared spectroscopy tests, where hazardous NO was oxidized following two different exothermic pathways: the •O 2 –-induced NO → NO 3 – process and the 1O 2 -induced NO → NO 2 → NO 3 – process. This work offers a basic guideline for accelerating ROS generation by integrating defect-engineering and heterojunction-construction, and provides new insights into the mechanism of efficient NO removal dominated by •O 2 – and 1O 2. [ABSTRACT FROM AUTHOR]

Polymeric carbon nitride (PCN) photocatalysts have the potential to remove NO from ambient air. However, the catalytic performance of PCN is limited by the lack of sufficient active sites to effectively activate molecular oxygen. Herein, we report the construction of photocatalysts consisting of defective-activated-carbon and PCN via amide bond formation. This photocatalyst not only significantly enhances the chemisorption of O 2 , but also accelerates the activation of molecular oxygen and oxidation of NO by creating a new electron transport pathway. This work provides a new strategy for polymer photocatalysts to promote molecular oxygen activation by constructing close-contact interfaces through amide bonding. [Display omitted] • Defective activate carbon confined polymeric carbon nitride (DAC/PCN) is fabricated by a facile amide bonded strategy. • The close contact interface of DAC/PCN creates a new electron transport pathway to inhibit the charge recombination. • The DAC/PCN composite promotes the chemisorption of O 2 , and accelerates the activation of O 2 and NO. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of Mn doping size over Al 2 O 3 on NO oxidation activity were elucidated. • Mn SACs/Cs -Al 2 O 3 exhibits a superior NO-NO 2 capacity compared with Mn NPs -Al 2 O 3. • The coordination environment of Mn species significantly affects the mobility of O sur. • Reducing Mn size from NPs to SACs/Cs promotes labile nitrate species formation. The exploitation of transitional metal catalysts for high-efficient conversion of NO to NO 2 still persists as an imperative issue due to the high cost of currently used Pt–based catalysts. Herein, we report a TEA-modification strategy to anchor Mn single atoms/clusters on Al 2 O 3 (Mn/Al 2 O 3 -T) for NO oxidation. Activity tests show that Mn/Al 2 O 3 -T (T 83 = 275 °C) displays a superior NO-to-NO 2 capacity compared with the unmodified Mn nanoparticle on Al 2 O 3 (Mn/Al 2 O 3 -B, T 66 = 300 °C) and Pt/Al 2 O 3 (T 43 = 350 °C) counterparts. Comprehensive characterization and DFT calculations discover that the effective adjustment of TEA can promote the generation of coordination unsaturated Mn sites with elongated Mn-O bonds, which can improve the mobility of surface lattice oxygen and facilitate the activation of molecular oxygen. Additionally, reducing Mn size from nanoparticles to single atoms/clusters favors the formation of labile nitrate species and facile desorption of NO 2 , thereby regenerating active sites and accelerating overall NO oxidation reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effective O 3 -assisted soot catalytic combustion was achieved at ≥ 200 °C. • The roles of O 3 included breeding NO 2 , SOCs and surface manganese oxides. • The nitrate/nitrite-SOC reactions went smoothly at ∼200–300 °C. • The surface manganese oxide-SOC reactions went effectively at ∼300–400 °C. • The reactions between O 2 and the NO 2 -induced SOCs went intensely at ∼400–500 °C. Catalytic diesel particulate filtration (CDPF) assisted by ozone is a promising strategy for soot elimination at exhaust temperatures. It is important yet challenging to utilize the strongly oxidizing ozone while prevent its escape. In this study, rod-like Mn 2 O 3 catalysts with high ozone decomposition ability were proved as an ideal tool for such a task. With thorough characterizations and temperature-programmed oxidation tests in selected atmospheres, triple low-temperature incubation effects were ascribed to the (catalytic) decomposition of ozone, including oxidizing NO to NO 2 , breeding surface oxygen complexes on soot and surface manganese species on the catalyst. Superior soot elimination efficiency (T 10 = 267 °C, T 50 = 392 °C, TOF Mn = 1.0 × 10−2 s−1) was achieved by the tandem work of NO 2 (at ∼200–500 °C), NO 2 -induced nitrates/nitrites (at ∼200–300 °C), surface manganese oxides (at ∼300–400 °C) and O 2 (at ∼400–500 °C), indicating the coupling of ozone and transition metal oxides may lead to reliable and cost-effective CDPF systems. [ABSTRACT FROM AUTHOR]

The synthesis of photocatalysts with rapid photogenerated electron transfer, strong reactant adsorption, and activation is urgent to promote photocatalytic NO oxidation. Herein, we construct a series of carbon nanotube (CNT)-threaded CeO2 mesocrystalline photocatalysts applying the microwave thermal method. The noncontinuous CNT-threaded structure provides two interfacial charge transport pathways for the efficient separation of photogenerated carriers. The introduction of CNTs induces mesocrystalline CeO2 with surface Ce3+ and oxygen vacancies, which is in favor of adsorption and activation for reactants, further facilitating a deep oxidation pathway for NO removal. The optimal photocatalyst exhibits a remarkable conversion ratio for NO oxidation and NO3 - selectivity in a recyclable way. [ABSTRACT FROM AUTHOR]

The oxidation rate of NO to NO 2 is a critical parameter in the removal of NO x within selective catalytic reduction (SCR) systems. LaCoO 3-δ is a kind of potential catalyst to enhance the oxidation of NO to NO 2 , it may offers an economic and stable alternative to noble metal catalysts, particularly at elevated temperatures. This study aimed to enhance the catalytic efficiency of LaCoO 3-δ through strontium (Sr) doping. La 1-x Sr x CoO 3-δ (with varying x values of 0.1, 0.2, 0.3, 0.4) was synthesized using a sol-gel method. La 1-x Sr x CoO 3-δ exhibited superior NO oxidation catalytic activity compared to LaCoO 3-δ , with the most notable enhancement observed at x = 0.3 (84 % conversion). This improvement can be attributed to the substitution of La 3+ with Sr 2+ , which induces lattice distortion and charge imbalance, thereby creating more oxygen vacancies that enhance the catalytic oxidation capability of La 1-x Sr x CoO 3-δ . However, it's important to note that an excessive amount of Sr can result in the formation of SrCO 3 deposits on the surface of La 1-x Sr x CoO 3-δ , thereby diminishing its catalytic oxidation performance. The catalytic oxidation reaction behavior adhered most closely to the O 2 -adsorbed E-R model, the surface defects in La 1-x Sr x CoO 3-δ playing a pivotal role in the catalytic reaction., Competing Interests: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Yige guo reports financial support was provided by 10.13039/501100001809National Natural Science Foundation of China. Yige guo reports financial support was provided by 10.13039/501100002858China Postdoctoral Science Foundation. Yige guo reports financial support was provided by 10.13039/501100004543China Scholarship Council. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

The NO and propane oxidation activities of a series of 1%Pt/TiO2–SiO2 catalysts show different underlying trends as the support composition changes. Surface characterisation of the catalysts indicates that the trend for NO conversion is consistent with the oxidation rate being dependent on the degree of metallic character of the Pt nanoparticles, rather than their morphology. Although a similar correlation is expected for the total oxidation of propane, it is masked by the effects of adventitious ions originating during manufacture of the support materials. When residual chloride is present in the support, most of the exposed Pt is stabilised in its low-activity ionic form; while support materials containing W or oxidised-S ions give rise to catalysts with much higher activity than expected from their measured Pt0 content. When a Cl-containing, but SiO2-free, TiO2 support material is pre-treated hydrothermally, the propane-oxidation activity of the resultant Pt/TiO2 catalyst is substantially improved, so that it matches the performance of highly-metallic Pt supported on TiO2 containing 16 wt% SiO2. The hydrothermal pre-treatment removes residual chloride from the support material, but it also leaves the catalyst in a hydrated state. We show that, by controlling the metallic content of Pt nanoparticles, understanding the promoting and inhibiting effects of adventitious ions, and optimising the degree of catalyst hydration, the activity of 1%Pt/TiO2–SiO2 catalysts can be made to exceed that of a benchmark 2%Pt/γ-Al2O3 formulation for both NO and propane oxidation. [ABSTRACT FROM AUTHOR]

NO is a harmful pollutant to the environment. The traditional removal of NO is hindered by the harsh operating conditions and sacrifice of value‐added chemicals. Efficient electrocatalytic oxidation of NO was achieved over plasma‐treated commercial carbon cloth, serving as a promising anode substitution reaction to couple with the hydrogen evolution reaction without consumption of hydrogen‐containing resources. The introduction of carboxyl groups onto the carbon cloth boosted the electrocatalytic activity via the enhancement of NO chemisorption. Only potentials of 1.39 V and 1.07 V were applied to reach the current density of 10 mA cm−2 in neutral and acidic conditions, respectively, which is superior to the state‐of‐the‐art electrocatalysts for oxygen evolution. Energy and environmental concerns on fossil‐fuel‐derived hydrogen production, ammonia manufacture and nitrate synthesis, are greatly alleviated. This work provides an original strategy to realize the resource utilization of NO, the sustainable nitrate synthesis and hydrogen production in a green and economical way. [ABSTRACT FROM AUTHOR]

Calcination conditions in the catalyst preparation process have a significant influence on catalyst performance. To explore the optimal calcination condition of MnOx/Al2O3 catalysts for NO oxidation, a series of samples was prepared using the same support and active compound but under different calcination conditions. The catalytic efficiency of the catalyst was tested, and through characterization [X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE SEM), Brunauer–Emmett–Teller analysis (BET), and Barrett–Joyner–Halenda analysis (BJH)], the effect of calcination conditions on the catalytic performance was analyzed and discussed. The results showed that the samples calcined at 600°C for 5 h had the best catalytic performance. At a reaction temperature of 450°C, the molar ratio of NO2/NO conversion was as much as 1.65. The high surface area, crystal phase, and crystallinity (the relative content of Mn2O3 is about 50%); the high content of lattice oxygen Oβ (about 20.4%); and high dispersion of active sites on the MnOx/Al2O3 catalyst calcined at 600°C for 5 h led to its relatively high catalytic activity. Compared with traditional noble metal catalysts, the MnOx/Al2O3 catalyst prepared by the impregnation method has good application prospects because of its low material cost, simple preparation process, and superior catalytic performance. [ABSTRACT FROM AUTHOR]

BACKGROUND: In this paper, Mn–Co binary oxides prepared by an (NH4)2CO3‐assisted co‐precipitation method were used for the catalytic oxidation of NO at low temperatures. RESULTS: Experimental results showed that the Mn–Co binary catalysts prepared with manganese acetate and cobalt nitrate exhibited the highest oxidation activity, obtaining a NO conversion of 76% at 200 °C and 80% at 250 °C. The passivation effect of SO2 was found to be irreversible in the examination of the resistance to SO2 or/and H2O(g). Furthermore, characterization by X‐ray Photoelectron Spectroscopy (XPS), Fourier Transform infrared spectroscopy (FTIR), and in situ Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs) revealed that the passivation effect was due to the bidentate and surface or bulk‐like sulfates generated on the surface of the catalyst. CONCLUSION: The analysis of intermediate species during the in situ DRIFTs characterization revealed that these sulfate species competed with nitrate/nitrite species for adsorption and affected the activity. Moreover, the poisoned catalysts could be regenerated to remove the majority of the bidentate and surface or bulk‐like sulfates from the surface and maintain the excellent NO catalytic oxidation activity. © 2021 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Two series of Cu/SSZ-13 catalysts were synthesized via aqueous solution and solid-state ion exchange using SSZ-13 supports of varying Si/Al ratios. The isolated and multinuclear Cu content of these catalysts were determined by H 2 temperature programmed reduction (H 2 -TPR). Multinuclear Cu in these catalysts, including in situ Cu-dimers formed from ZCuIIOH coupling and permanent CuO clusters, are active species for dry NO oxidation. NH 3 oxidation on these catalysts follows an internal SCR (i-SCR) mechanism, i.e., a portion of NH 3 is first oxidized to NO, then NO is selectively reduced by the remaining NH 3 to N 2. NH 3 oxidation displays distinct kinetic behavior below ∼300 °C and above ∼400 °C. At low temperature the results indicate that NH 3 -solvated mobile Cu-ions are the active centers. CuO clusters, when present, also contribute to the low temperature activity by catalyzing NH 3 oxidation to NO. At high temperature, in situ Cu-dimers and CuO clusters catalyze NH 3 oxidation to NO, and isolated Cu-ions catalyze SCR to realize the cascade turnovers. For both NO and NH 3 oxidation, Cu-dimers balanced by framework charges of close proximity appear to be more active than Cu-dimers balanced by distant framework charges. However, the former Cu-dimers are less stable than the latter and tend to split into monomers in the presence of vicinal Brønsted acid sites. Via density functional theory (DFT) calculations, the i-SCR mechanism for low temperature NH 3 oxidation, i.e., the energetic favorability for the involvement of the NO intermediate, is justified. The DFT results also agree with experimental data that the formation of Cu-dimers from ZCuIIOH dimerization is essential for NH 3 oxidation at high temperature. [Display omitted] • NO and NH 3 oxidation on Cu-SSZ-13 occurs on multinuclear Cu sites, including in situ Cu-dimers and permanent CuO clusters. • NH 3 oxidation follows an internal SCR mechanism, which displays distinct kinetic behavior below 300 °C and above 400 °C. • Solvated CuII(NH 3) 3 OH species oxidize NH 3 at low-temperature and catalyze further reduction of produced NO to N 2 and H 2 O. • Permanent CuO clusters catalyze NH 3 oxidation to NO at low temperatures, clarifying a synergy with isolated Cu-ions. • At high temperature, multinuclear Cu sites sustain NH 3 oxidation, and immobilized & isolated Cu-ions sustain NO reduction. [ABSTRACT FROM AUTHOR]

Photocatalysis has proven to be a green technology that possesses the synergy between addressing climate change and combating air pollution. Compared with traditional photocatalysts, Cerium oxide (CeO 2) holds distinct advantages such as low-cost, and high affinity for Ce3+/Ce4+ redox pair. This study presents a systematic investigation into the modification of CeO 2 morphologies via optimized one-step hydrothermal synthesis method with low-temperature control. The findings reveal that CeO 2 nanorods exhibited the notable photocatalytic performance, achieving 71.8% NO degradation while generating a mere 4.1% of toxic byproducts. Additionally, the promising CO and CH 4 yields from CO 2 conversion were 4.11 and 3.67 µmol g–1 h–1, respectively. The improvement in photocatalytic activity is attributed to the relationship between the specific surface area and the defects within the CeO 2 nanorods structure. Furthermore, CeO 2 nanorods also emerged as promising candidates for superior and sustainable photocatalytic CO 2 conversion, demonstrating high stability, with only 0.7% and 1.1% reduction in CO and CH 4 yields after four successive photocatalytic cycles. This study underscores the potential of CeO 2 nanorods in advancing green technologies for clean energy and contributes valuable insights to the field of practical zero emissions strategies. [Display omitted] • CeO2 morphologies were synthesized using optimized hydrothermal method. • Influencing factors for CeO2 morphologies were discussed. • Surface area and oxygen vacancies enhanced photocatalytic performance. • CeO 2 nanorods demonstrated highest performance for photocatalysis of NO and CO 2. • Plausible photocatalytic mechanism of CeO2 nanorods for NO and CO2 is presented. [ABSTRACT FROM AUTHOR]

[Display omitted] • Catalytic NO oxidation investigated at concentrations relevant for the Ostwald process. • Kinetics over a Pt/SiO 2 catalyst studied using steady state and SSITKA experiments. • The kinetically relevant step suggested to be the reaction between adsorbed NO and adsorbed molecular oxygen. The reaction mechanism of the oxidation of NO under conditions of high NO concentration over a 2 wt% Pt/SiO 2 was studied using both kinetic and transient isotopic tracing experiments. The reaction mechanism was found to involve both NO adsorption and oxygen adsorption, contrary to the situation under low NO concentration where NO reacts from the gas phase. The kinetic rate data could be fitted to the Langmuir-Hinshelwood model permitting the estimation of rate and equilibrium constants of elementary steps. These steps were investigated using transient responses following independent reactant gas isotopic switches for tracing the nitrogen path and the oxygen path during NO oxidation. These transients could be sufficiently described by a microkinetic model based on two pools of NO intermediates, one pool each for the adsorbed molecular oxygen and atomically adsorbed oxygen. Surface atomic oxygen was found to be formed by two different routes: via a direct dissociation of molecularly adsorbed oxygen and also via an assisted pathway that leads to NO 2 formation. The latter surface reaction between adsorbed NO and adsorbed molecular oxygen comprised the kinetically relevant step. Insights from the two experimental and model approaches were in good agreement and provided a coherent reaction mechanism for NO oxidation under high NO reactant concentration. [ABSTRACT FROM AUTHOR]

CrOx/black-TiO2 catalysts were prepared by ligand-assisted (citric acid, oxalic acid and ethylenediaminetetraacetic acid) impregnation method. These catalysts were characterized in detail by means of X-ray diffraction, Raman, BET, X-ray photoelectron spectroscopy, H2 and O2(NO) temperature programmed reduction or desorption and in-suit DFTIR spectra. The results indicated that ligands assistance was beneficial for CrOx interacted with oxygen vacancies and O–Ti–O structures. Among all the catalysts, CrOx/black-TiO2/CA (modified by citric acid) revealed excellent catalytic activity and stability for NO oxidation in the temperature range of 200–450 °C. The characterization results exhibited that the interaction existed between CrOx and oxygen vacancies resulting in more Cr6+. Moreover, the strong interaction between CrOx and O–Ti–O was attributed to the modification of carboxylic acid, which increased the content of Cr3+ and chemical adsorption oxygen. High content of chemical adsorption oxygen promoted the adsorption ability of O2, and Cr6+ enhanced the adsorption capacity of NO. Hence, chemical adsorption oxygen and Cr6+ synergistically promoted the NO oxidation. [ABSTRACT FROM AUTHOR]

Over the past several decades, much effort has been applied to atmospheric nitrogen oxide (NOx) abatement. The current techniques require high energy consumption and result in secondary pollution. Particularly, the removal of low dose (<200 ppm) of NOx has been very challenging. Though graphitic carbon nitride (g-CN), an eco-friendly and sustainable material was tried as a promising metal-free photocatalyst for NOx abatement. Herein, a one-step, energy efficient calcination approach is developed to prepare amorphous carbon nitride (ACN) with N3C-site vacancies. The visible-light responsive range is expanded and the activation barrier of N≡O triple bonds is sharply decreased by one order of magnitude; 0.19 eV when compared to the 2.22 eV of g-CN. These modifications allow the NOx removal efficiency of ACN to reach 57.1% which is among the highest in visible light. The unique N3C-site vacancies are well maintained after photocatalytic NO oxidation, which shows an exceptional structural stability. This boosts the generation of singlet oxygen (¹O2) and superoxide radical (•O2-) for complete NO removal. This study sheds light on the active site design and photocatalytic performance enhancement of g-CN based materials by vacancy engineering. [ABSTRACT FROM AUTHOR]

The study investigated the reactive dissolution of gas phase nitrogen-oxides and ozone in water. Mixtures with variable composition of nitrogen oxides were produced by mixing nitric oxide (NO) with ozone. Pure NO in Ar carrier gas resulted in the production of NO2− but its production rate was limited by low NO solubility. The presence of NO2 in the gas increased the production of NO2− while NO3− was also produced. The presence of N2O5 in the gas abruptly increased the production of NO3− due to higher solubility of N2O5. In the present configuration, about 8% of NO2 was dissolved in the water while for N2O5 the fraction was 78%. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C3N4, CN) as a popular photocatalyst has been investigated for the removal of air pollutants, but its photocatalytic efficiency and selectivity for ionic species (Si) can be enhanced through chemical or microstructural modification. The combinatorial study of six salts, Na+, K+, and NH4+ (per)-sulfate, as mediators in the melamine precursor for the CN synthesis indicates that the thermal decomposition behaviors of the salts affect the CN polymerization process and the functional groups on CN samples, though all of them are found to increase the surface area. The mediation with Na+ and K+ (per)-sulfate increases the dangling −CN bonds and surface moieties at a higher oxidation state. The sodium and ammonia salts caused an upward shift of the conduction band energy for the final photocatalyst, while K2SO4 and K2S2O8 induced a downward shift of the conduction band. The NO removal efficiency of CN with sodium persulfate and sulfate reached 80% and near 100%, respectively, much higher than that of the pristine CN (60%). Moreover, the samples with persulfates showed higher Si than those with sulfate salts. The high surface area and the keen hierarchical pores down to 2 nm in the salt-mediated CN samples increased the residence time of the gaseous species and the resultant NO removal efficiency, and Si. NO2 can still be produced in the dark for 15 min after the photocatalysis, indicating that there are long-lived species related to H2O2 produced in the prior illumination. The systematic investigation of the effects of inorganic salt addition was presented on CN in terms of the microstructure, band structure, and correlated photocatalytic oxidation efficiency, pathway, and product selectivity. [ABSTRACT FROM AUTHOR]