NO Oxidation Research Articles

Enhancement of photocatalytic NO oxidation by Ag-sulfide on TiO2 mixed with Na-ZSM-5

Enhancing NO oxidation performance is pivotal for integrating photocatalysts with wet scrubbers in continuous flow systems. Despite the recent development of various catalysts, such as MOFs, our goal was to simplify the composition by using photocatalyst + zeolite catalyst, bringing us closer to a catalyst that can be practically applied. In this study, we have utilized Ag2S doping and Na-ZSM-5 mixing to improve the photocatalytic NO oxidation performance. Results showed that Ag2S doping improved visible light absorbance and NO oxidation, despite the observed fluctuations in NO conversion being attributable to mass transfer limitations. Mixing with Na-ZSM-5 compensated for the mass transfer limitations and improved its average NO conversion from 19 to 34 %. The Na-ZSM-5 increased the NO adsorption capacity considerably to 0.67 mmol g−1, which reduced the fluctuations in the catalytic performance; subsequently, the diffusion of NO led to its oxidation. Detailed analyses using NO-TPD and DRIFTS further elucidated these improvements, highlighting the significance of optimizing both oxidation reaction and mass transfer rates in the photocatalytic process. We believed that the composite of Ag2S-TiO2 + Na-ZSM-5 could simplify the ways to improve the photocatalytic NO oxidation performance and make it closer to practical applications.

Optimizing Carbon Structures in Laser-Induced Graphene Electrodes Using Design of Experiments for Enhanced Electrochemical Sensing Characteristics.

In this study, we explored the morphological and electrochemical properties of carbon-based electrodes derived from laser-induced graphene (LIG) and compared them to commercially available graphene-sheet screen-printed electrodes (GS-SPEs). By optimizing the laser parameters (average laser power, speed, and focus) using a design of experiments response surface (DoE-RS) approach, binder-free LIG electrodes were achieved in a single-step process. Traditional trial-and-error methods can be time-consuming and may not capture the interactions between all variables effectively. To address this, we focused on linear resistance and substrate delamination to streamline the DoE-RS optimization process. Two LIGs, designated LIG A and LIG B, were fabricated using distinct and optimized laser settings, which resulted in a sheet resistance of 25 ± 2 Ω/sq and 21 ± 1 Ω/sq, respectively. These LIGs, characterized by scanning electron microscopy, Raman spectroscopy, and contact angle analysis, exhibited a highly porous morphology with 13% pore coverage and a contact angle <50°, which significantly increased their hydrophilicity when compared to the GS-SPE. For the electrochemical studies, the oxidation of NO2- ion by the graphene-based working electrodes was investigated, as it allowed for the direct comparison of the LIGs to the GS-SPE. These included cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulsed voltammetry studies, which revealed that LIG electrodes displayed a remarkable 500% increase in peak current during NO2- oxidation compared to the GS-SPE. The LIGs also demonstrated improved stability and sensitivity (420 ± 30 and 570 ± 10 nAμM-1 cm-2) compared to the GS-SPE (73 ± 4 nAμM-1 cm-2) in the oxidation of NO2- ions; however, LIG B was more susceptible to ionic interference than LIG A. These findings highlight the value of applying statistical approaches such as DoE-RS to systematically improve the LIG fabrication process, enabling the rapid production of optimized LIGs that outperform conventional carbon-based electrodes.

Achieving High Photocatalytic NOx Removal Activity Using a Bi/BiOBr/TiO2 Composite Photocatalyst.

Fossil fuel combustion generates nitrogen oxides (NO + NO2 = NOx), which pose threats to the environment and human health. Although commercial products containing titanium dioxide (TiO2) can remedy NOx pollution by photocatalysis, they only function in the ultraviolet (UV). On the other hand, bismuth oxybromide (BiOBr) is active in the visible. BiOBr is stable, affordable, and non-toxic, making it an appealing alternative. In addition, nanoparticulate Bi metal can further enhance visible light absorption through its surface plasmon properties and charge carrier lifetime by spatially separating charge. In this study, to enhance the visible-light activity of TiO2-based photocatalysts for NOx pollution, a composite of Bi-decorated BiOBr/TiO2 was synthesized using a solvothermal method across varying the Ti/Bi atomic ratio (0.2, 2.2, 4.4, and 6.6), and synthesis duration (6h, 12h, and 18h). The photocatalytic performance of the synthesised composites for NO gas removal was investigated using an adapted ISO method (22197-1:2016). Analysis showed that the preferential growth of the (010) crystal facet in BiOBr and the presence of Bi metal both play an important role in the superior photocatalytic activity seen in our Bi-decorated BiOBr/TiO2 composite. The composites were characterised using X-ray diffraction (XRD), attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR), high-resolution scanning electron microscopy (HRSEM), UV-Vis diffuse reflectance (DRS) spectroscopy, transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Brunauer-Emmett-Teller (BET) analysis, thermogravimetric analysis (TGA), and diffuse reflectance transient absorption spectroscopy (DR-TAS). Our research shows that the Bi/BiOBr-TiO2 composite synthesised through the 12-hour solvothermal method with a Ti/Bi atomic ratio of 4.4 exhibits the highest photocatalytic performance towards both NO and NO2 oxidation; with 32.8% and 54.9% NO removal and 15.1% and 29.5% NO2 under visible and UV lamps, respectively.

Enhanced Photocatalytic Activity of Nickel(II)‐Doped Bi2O2CO3 Nanosheets for Efficient Nitric Oxide Removal

AbstractBi2O2CO3 is a typical bismuth‐based semiconductor photocatalyst that has attracted much attention because of layered structure and polarization characteristics. However, the wide bandgap of Bi2O2CO3 limits its practical applications in photocatalysis. In this study, the nickel (II)‐doped Bi2O2CO3 (Ni2+‐Bi2O2CO3) with oxygen vacancies was prepared by adding a controllable amount of nickel ions. The photocatalytic efficiency of the optimized sample for ppb‐grade NO under visible light irradiation is 59.4 %, which is 2.8 times than that of its counterpart, Bi2O2CO3 (21.2 %). Based on experiments and characterizations, Introduction of nickel ions and oxygen vacancies improves the photocatalytic performance of Ni2+‐Bi2O2CO3, which not only lowered the bandgap from 3.25 eV to 2.92 eV, but also reduced the recombination of photogenerated carriers by formation of the impurity level. Furthermore, the adsorption and photocatalytic conversion pathway of NO was explored by in situ DRIFTS, the principal byproducts of photocatalytic oxidation of NO are NO3− and NO2−. This work offers a new perspective to improve the photocatalytic activity by doping mothed for air purification.

Methanol-assisted NO oxidation under an oxygen atmosphere for efficient denitration: Experiments and ReaxFF-MD simulations

The development of selective catalytic reduction technologies for controlling nitrogen oxides (NOx) emissions in flue gas is hampered by high equipment and catalyst costs. In this study, a catalyst-free and efficient denitration process using methanol and oxygen as reactants was developed. Various gas atmospheres with differing concentrations were investigated to remove NO without catalysts. The addition of methanol significantly enhanced NO removal efficiency, reaching 94.6 % at 550 °C, with 55.1 % of NO converted to NO2, which can be absorbed by downstream alkali solutions. Reactive force field molecular dynamics (ReaxFF-MD) simulations were employed to analyze the atomic level NO oxidation mechanism in the CH3OH/NO/O2/H2O homogeneous reaction system. The simulation revealed the generation pathway of three key oxidizing intermediates (OH, HO2, and H2O2) and their roles in NO oxidation. This study offers critical insights into developing a cost-effective denitration process, highlighting the potential for improved NOx emission control.

The Activation of Oxygen Species on the Pt/CeO2 Catalyst by H2 for NO Oxidation

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.

Deep oxidation of NO via catalytic ozonation

ABSTRACT In addition to selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) which are available to remove NOx from flue gas, oxidation method is receiving more and more attention because this method makes it possible to remove NOx and SO2 from flue gas simultaneously by wet scrubbing. O3 as a strong oxidant has a high oxidation capacity and it can oxide NO to N2O5 which has a higher water solubility compared with NO2. However, it needs a long reaction time and the escape of unreacted ozone may cause secondary pollution. In this study, FeMnCo/Al2O3 catalyst and FeMnCe/Al2O3 catalyst were prepared and applied to enhance the deep oxidation of NOx with ozone and reduce O3 slip. Effects of various operating parameters such as O3/NO ratio, gas residence time, and operating temperature were evaluated, and the results demonstrate that N2O5 began to generate when O3/NO ratio was higher than 1.0 and increased with increasing O3/NO ratio. Little residual O3 was formed in the presence of catalyst, while 350 ppm O3 was measured at the outlet gas when O3/NO ratio was controlled at 2.0. The N2O5 conversion efficiency increased with increasing gas residence time and operating temperature, and the highest N2O5 conversion efficiency was achieved at 100°C. Furthermore, the conversion efficiency remained around 90% during 20 h operation over FeMnCe/Al2O3 catalyst with an O3/NO ratio of 1.73, a gas residence time of 1.2 s, and a temperature of 100°C. On the other hand, the N2O5 conversion efficiency remained around 80% during 3 h operation over FeMnCo/Al2O3 catalyst. Overall, FeMnCe/Al2O3 catalyst reveals good potential for deep oxidation of NO by O3 and can be further developed as a viable catalyst for reducing NO emission from industries. Implications: In this study, FeMnCo/Al2O3 catalyst and FeMnCe/Al2O3 catalyst were applied to enhance the deep oxidation of NO into N2O5 with O3. The catalysts can improve the conversion of NO into N2O5, shorten the reaction time and reduce the unreacted O3 slip, which are beneficial to reduce the size of the reactor required and cost of APCDs (air pollution control devices) in practical application. This method can make it possible to simultaneously remove NOx and SO2 from flue gas by wet scrubbing for reducing NO emissions from industries, especially small and medium scaled industries, to meet increasingly stringent emission standards.

Tracking the electrocatalytic activity of Au@Ag core–shell nanoparticles for nitrite oxidation via single-entity electrochemistry

Single-entity electrochemistry (SEE) has been extensively utilized for analyzing various substances, elucidating their mechanisms, and predicting particle behavior on electrode surfaces. In this paper, we propose a novel method for analyzing the electrochemical reactions between core–shell nanoparticles (NPs) and nitrite ions at the single-particle level. This method employs single Au@Ag core–shell NPs, nitrite ions (NO2-), and a carbon ultramicroelectrode (C-UME), utilizing the electrochemical oxidation of NO2- ions upon collision with individual core–shell nanoparticles on the C-UME surface. Au@Ag core–shell NPs with different ratios were synthesized to achieve the effective oxidation of NO2- ions, and their electrochemical properties were analyzed. Various parameters, such as applied potential and NO2- ion concentration, were adjusted in chronoamperometric experiments to analyze the resulting signals. This study is expected to significantly contribute to the analysis of oxidation/reduction, dispersion, and catalytic properties of various NPs, particularly core–shell NPs.

Influence of flue gas components on SO2 adsorption by activated carbon at low temperature

Activated carbon can adsorb SO2 in flue gas, whose performance is significantly enhanced when lowering the adsorption temperature; however, the characteristics and mechanism of SO2 adsorption under the action of complex flue gas components at low temperatures remain unclear. In this study, adsorption experiments were conducted to investigate the characteristics of SO2 adsorption on activated carbon and the impact of O2, H2O, and NO within −20 to 20 °C. The saturated adsorption of SO2 showed a 2.21-fold increase when the temperature was lowered from 20 °C to −20 °C. Within this temperature range, physical adsorption was dominant, accounting for 73.7–91.0 %. O2 and H2O inhibited the physical adsorption of SO2 and promoted its chemical adsorption. As the temperature was lowered, the promoting effect of O2 increased, while the influence of H2O shifted from promotion to inhibition. NO affects SO2 adsorption only when co-existing with O2. As the temperature decreased, the promoting effect of NO on both physical and chemical adsorption strengthened and was significantly higher than that of O2 and H2O. Based on desorption experiments and quantum chemical calculations, the mechanisms by which H2O and NO affect SO2 adsorption were proposed·H2O and SO2 share the same physical adsorption sites, with H2O being more strongly adsorbed, thus significantly inhibiting the SO2 physical adsorption. When NO coexists with O2, gaseous SO2 reacts with the NOx adsorption configurations to form C-SO3 and C-HSO3. Active atoms near C-SO3 and C-HSO3 can adsorb NO2, forming a co-adsorption configuration, which in turn enhances the nearby physical adsorption of SO2. Enhancing the catalytic oxidation and adsorption of NO through surface modification of activated carbon can improve the low-temperature adsorption performance of SO2.

Spatiotemporal Analysis of Complex Emission Dynamics in Port Areas Using High-Density Air Sensor Network.

Cargo terminals, as pivotal hubs of mechanical activities, maritime shipping, and land transportation, are significant sources of air pollutants, exhibiting considerable spatiotemporal heterogeneity due to the complex and irregular nature of emissions. This study employed a high-density air sensor network with 17 sites across four functional zones in two Shanghai cargo terminals to monitor NO and NO2 concentrations with high spatiotemporal resolution post sensor data validation against regulatory monitoring stations. Notably, NO and NO2 concentrations within the terminal surged during the night, peaking at 06:00 h, likely due to local regulations on heavy-duty diesel trucks. Spatial analysis revealed the highest NO concentrations in the core operational areas and adjacent roads, with significantly lower levels in the outer ring, indicating strong emission sources and limited dispersion. Employing the lowest percentile method for baseline extraction from high-resolution data, this study identified local emissions as the primary source of NO, constituting over 80% of total emissions. Elevated background concentrations of NO2 suggested a gradual oxidation of NO into NO2, with local emissions contributing to 32-70% of the total NO2 concentration. These findings provide valuable insights into the NO and NO2 emission characteristics across different terminal areas, aiding decision-makers in developing targeted emission control policies.

The enhanced SO2 resistance of Fe-Ti catalyst by W/SO42− co-modification for NH3-SCR: A combined experimental and DFT study

It remains a great challenge to improve the low-temperature SO2 resistance of catalysts applied for selective catalytic reduction of NOx with NH3 (NH3-SCR). This work develops an outstanding SO2-tolerant Fe-Ti (FT) catalyst by W/SO42− co-modification via a sol–gel method using Fe(NO3)3·9H2O, tetrabutyl titanate, ammonium tungstate and thiourea as raw materials. The physicochemical characterizations, in-situ diffuse reflectance infrared Fourier transform (DRIFT) measurements and density functional theory (DFT) calculations were combined to reveal the underlying mechanisms. Although W doping can effectively enhance the surface acidity, NH3 adsorption on Lewis acid sites can still be restrained by competitive adsorption of SO2, whereas SO42− modification can enhance the adsorption stability of NH3 without being affected by SO2. Simultaneously, the NO adsorption ability on Fe sites can be significantly enhanced by W/SO42− co-modification. Furthermore, the W doping or SO42− modification can induce conversion of Fe3+ to Fe2+ to affect the redox property of Fe species. A proper amount of Fe2+ suppressed the oxidizability of FT catalyst to inhibit NH3 overoxidation to enhance N2 selectivity, and created more oxygen vacancies to generate larger amount of chemisorbed oxygen to facilitate NH3 dehydrogenation and NO oxidation. More importantly, the inhibition effect of SO2 adsorption on Fe sites was strengthened by W/SO42− co-modification. Consequently, the W/SO42− co-modified FT catalyst exhibited high activity with >90 % of NO conversion and >95 % of N2 selectivity within a broad window of 275–450 °C and possessed superior SO2 + H2O tolerance at 275 °C.

Improved catalytic NO oxidation over Pt supported on sulfuric acid treated TiO2

Promoting the formation of metallic Pt over the catalysts is the key to improving the NO reactivity. In general, TiO2 suppresses the oxidation of Pt by surface acidity and induces the formation of the metallic phase of Pt by Pt-Ti interaction. However, the limited number of acidic sites (–OH) contributes to the formation of large Pt particles, which may lead to the formation of Pt2+ or Pt4+, resulting in performance degradation. In this study, we further formulated the acidic sites of the TiO2 with sulfuric acid treatment (SA-TiO2) to improve catalytic NO oxidation. During the SA treatment, the TiO2 surface is positively charged by the low pH, providing an environment for well-distributed sulfate. In the subsequent introduction of Pt, the increase in acidic sites for Pt adsorption greatly enhanced the dispersion of Pt. During this process, Pt formed bonds with sulfate as [Pt(NH3)4]-SO4. The surface species combined with SO4 and NH3 were decomposed during the calcination process, thereby inhibiting the oxidation of Pt, which promotes the formation of metallic Pt. As a result, highly reactive Pt0 and Pt2+ were further formulated by increasing the acidic sites of SA-TiO2, where the low-temperature NO oxidation performance was improved, regardless of the Pt loading (0.3 to 3 wt.%).

Mechanistic investigation of the suppressed N2O formation during the low-temperature NH3-SCR over the Sb-modified Mn/Ti catalyst

The formation of N2O during the NH3-SCR reaction over the Mn-based is one of the crucial factors limiting the industrial application of Mn-based catalysts. In this work, the Sb-modified Mn/Ti catalyst was prepared by the ultrasonic assistance impregnation method to control the formation of N2O during the NH3-SCR reaction. The preferred Mn3Sb/Ti catalyst had over 80 % NOx conversion at 150–300 °C, and more than 80 % N2selectivity at 150–250 °C, which were higher than that of the Mn/Ti catalyst at the same temperature window. A series of performance experiments showed that the Sb modification inhibited the oxidation of NH3to N2O and suppressed the N2O produced by the E-R mechanism in the NSCR reaction, which is the main pathway for N2O generation. Moreover, the presence of NO inhibited the oxidation of NH3 to generate N2O over the Mn3Sb/Ti catalyst. Based on the physical–chemical characterizations and DFT calculations, it was revealed that the introduced Sb species achieves a trade-off between redox ability and surface acidity over the Mn3Sb/Ti catalyst, which is beneficial to enhance the NH3-SCR performance and simultaneously suppress the over-oxidation of NH3. The high content of Mn3+caused by the electron transfer through the redox cycle of Sb3++Mn4+→Sb5++Mn3+ was beneficial in decreasing the N2O formation.The formation of NH speciesis inhibited on the Mn3Sb/Ti catalyst with a higher energy barrier of the NH2* conversion to NH* species due to the Sb modification. Meanwhile, the energy barrier of NH3*→NH2* is decreased and the energy barrier of NH2*+NO → N2 + H2O is lower than that of NH2*→NH* over the Sb-modified catalyst, indicating that the NH3-SCR reaction is more favorable than the formation of N2O on the Mn3Sb/Ti catalyst.

Experimental and kinetic modeling investigation of NOx control in coal combustion by ammonia reburning

The carbon peaking and carbon neutrality goals present urgent demands for the green low-carbon transformation of the energy system. As a potential alternative energy, ammonia (NH3) used as reburning fuel in the coal-fired boilers will achieve both low-carbon and low-NOx emissions. To investigate ammonia reburning, experimental and chemical kinetic modeling were conducted in a tube flow reactor at 1023–1573 K under both ammonia and coal combustion conditions. Factors are researched including the combustion atmospheres of NH3/N2/O2 (PM-NH3) and coal/N2/O2 (PM-Coal), different inlet CO concentrations, reburning temperatures and reburning fuel ratios. The results indicate that ammonia reburning can effectively reduce NO emissions by about 95 %. The C-N reaction exhibits a positive effect on NO reduction at low temperature and a negative effect at high temperatures. As the CCO increases from 0 % to 4 % at 1573 K, the optimum temperature window size increases from 225 K to 413 K, and NO reduction rises from 31.25 % to 97.5 %. The whole ammonia reburning process includes NO rapid reduction stage (NRS), NO oxidation stage (NOS), and NO slowly re-reduction stage (NRRS) at high temperature. The chemical kinetic modeling indicates that the C-N reaction obviously shortens the residence time of the NRS and increases the ROP in the NOS, which together undercut NO reduction compared to PM-NH3 case. The promotion of the oxidation path of NH3-NH2-HNO-NO results in the NOS appearance and NRS ending. Moreover, this path affected by C-N reaction is primarily responsible for NO reduction cutoff in the PM-coal case.

Thin film deposition of organic-inorganic quinoline-tin dioxide p-n junction for optoelectronic devices

Tin dioxide (SnO2) is an oxide semiconductor with n-type characteristics, with high transparency in the UV–Vis, where the donors are usually associated with oxygen vacancies and interstitial tin ions. Quinoline derivatives (QD) are usually p-type semiconductors with emission in the blue range. We report photo-induced properties of the QD 4-(6-(diethylamino)-4-phenylquinolin-2-yl)benzoic acid and the combination with the inorganic semiconductor oxide SnO2, both layers in the form of thin film, which forms a heterostructure. Thin film is a very convenient format for integration in optoelectronics. Emission of the QD takes place in blue range (470–485 nm) and depends on the solvent when in solution, being used acetone and tetrahydrofuran (THF). However, when in the form of thin film, it does not depend on the solvent. Concerning the heterostructure, it is explored under distinct device architecture: 1) combination in a transport profile perpendicular to the films (transverse contacts) leading to a rectifying behavior similar to a p-n junction, which is evidence of the p-type-like electrical behavior of the QD; 2) in parallel conduction profile, where there seems to exist some sort of interfacial phenomenon similar to a two-dimensional electron gas (2-DEG), a property that can be explored in transparent high-mobility transistors.

Type-II heterojunction In2O3/TiO2 with highly efficient charge separation for boosted photocatalytic NO abatement

Photocatalytic NO degradation often suffers from sluggish charge carrier separation and low selectivity. Herein, a series of In2O3/TiO2 (P25) composites were synthesized to enhance NO abatement. Benefiting from the conspicuous synergistic effect between In2O3 and P25, the In2O3/P25 catalysts demonstrated more than double the NO elimination performance compared to pure P25 and In2O3. The In2O3/P25 sample with 75 wt% In2O3 (In-P25-75) achieved a NO removal efficiency of 51.7 %, higher than reported catalysts (30.0–49.0 %). It was the successful formation of type-II heterostructure that enabled intimate interfacial contact and provided ample electron transfer channels. Moreover, photoluminescence spectra and photoelectrochemical measurement confirmed the improved separation and inhibited recombination of photogenerated charge carriers in In-P25-75, thereby boosting the NO photocatalytic efficiency. ·O2− and ·OH radicals generated by photoinduced electron transfer to the conduction band of P25, along with the induced holes confined to the valence band of In2O3, facilitated the targeted deep oxidation of trace NO into NO3− rather than harmful NO2. This work discloses a promising strategy for the efficient removal of NO from the atmosphere by reducing the emission of hazardous intermediate NO2.

Impact of metal oxides on the selectivity of NiBi/C catalysts for high-value C-3 products in glycerol electrooxidation reaction

Enhancing the catalytic efficiency and specificity of non-noble Nickel-based catalysts for glycerol electro-oxidation reaction (GEOR) is an ongoing challenge. Recently, metal oxides have attracted attention due to their unique physical properties, such as chemical stability at high anodic potentials, presence of oxygen vacancies, which can significantly influence reaction kinetics and pathways.In this study, we explored the impact of metal oxides CeO2, SnO2, and Sb2O3 • SnO2 (ATO) on the electrochemical performance and product selectivity of NiBi/C and Ni/C catalysts in glycerol electrooxidation (GEOR). The Ni/C-X and NiBi/C-X (X= CeO2, SnO2, and ATO) catalysts were synthesized through a sodium borohydride reduction method at room temperature and comprehensively characterized using various physiochemical and electrochemical techniques.Among the composite support catalysts, Ni and NiBi/C-X, Ni/C-ATO exhibited the highest peak current density, reaching 96 mA cm-2 at 1.50 V vs. RHE. To further assess the catalysts' performance, continuous electrolysis, coupled with HPLC analysis, was conducted to determine product selectivity. Notably, NiBi/C-ATO demonstrated remarkable selectivity, achieving 100 % lactate selectivity under mild conditions. These findings contribute valuable insights into optimizing non-noble Nickel-based catalysts for GEOR, particularly highlighting the promising performance of Ni/C-ATO in terms of selectivity towards valuable products. The DFT calculations provided insight into the synergistic interactions for GEOR over Ni-Ni and Bi-Bi nanoparticles.

Water-Driven Surface Lattice Oxygen Activation in MnO2 for Promoted Low-Temperature NH3-SCR.

Water is ubiquitous in various heterogeneous catalytic reactions, where it can be easily adsorbed, chemically dissociated, and diffused on catalyst surfaces, inevitably influencing the catalytic process. However, the specific role of water in these reactions remains unclear. In this study, we innovatively propose that H2O-driven surface lattice oxygen activation in γ-MnO2 significantly enhances low-temperature NH3-SCR. The proton from water dissociation activates the surface lattice oxygen in γ-MnO2, giving rise to a doubling of catalytic activity (achieving 90% NO conversion at 100 °C) and remarkable stability. Comprehensive in situ characterizations and calculations reveal that spontaneous proton diffusion to the surface lattice oxygen reduces the orbital overlap between the protonated oxygen atom and its neighboring Mn atom. Consequently, the Mn-O bond is weakened and the surface lattice oxygen is effectively activated to provide excess oxygen vacancies available for converting O2 into O2-. Therefore, the redox property of Mn-H is improved, leading to enhanced NH3 oxidation-dehydrogenation and NO oxidation processes, which are crucial for low-temperature NH3-SCR. This work provides a deeper understanding and fresh perspectives on the water promotion mechanism in low-temperature NOx elimination.

Exploring the dynamic evolution of lattice oxygen on exsolved-Mn2O3@SmMn2O5 interfaces for NO Oxidation

Lattice oxygen in metal oxides plays an important role in the reaction of diesel oxidation catalysts, but the atomic-level understanding of structural evolution during the catalytic process remains elusive. Here, we develop a Mn2O3/SmMn2O5 catalyst using a non-stoichiometric exsolution method to explore the roles of lattice oxygen in NO oxidation. The enhanced covalency of Mn–O bond and increased electron density at Mn3+ sites, induced by the interface between exsolved Mn2O3 and mullite, lead to the formation of highly active lattice oxygen adjacent to Mn3+ sites. Near-ambient pressure X-ray photoelectron and absorption spectroscopies show that the activated lattice oxygen enables reversible changes in Mn valence states and Mn-O bond covalency during redox cycles, reducing energy barriers for NO oxidation and promoting NO2 desorption via the cooperative Mars-van Krevelen mechanism. Therefore, the Mn2O3/SmMn2O5 exhibits higher NO oxidation activity and better resistance to hydrothermal aging compared to a commercial Pt/Al2O3 catalyst.

The response of daytime nitrate formation to source emissions reduction based on chemical kinetic and thermodynamic model

Particulate nitrate is an important component of particulate matter and poses a significant threat to the ecosystem and human health. The gas-phase formation pathway of nitrate is extremely important, which mainly comprises the NO2 oxidation process triggered by OH radicals and the nitrate partitioning process. The response of nitrate to source emission reduction during different pollution periods remains unclear. Here, we applied the chemical kinetic and thermodynamics model to explore the importance oxidation process and partitioning process during different pollution periods based on high-time resolution observation data. The result indicated that with the aggravation of pollution, the partitioning process gradually ceases to be a limiting step in the formation of nitrates. The results of the influencing factor analysis indicate that NO2 concentration and aerosol pH values play a more significant role in the formation of nitrates. Specifically, during the clean period, nitrate formation is sensitive to both NO2 concentration and pH values, but during the pollution period, it becomes sensitive only to NO2 concentration. By combining source apportionment, we explored the response of nitrate formation to source emission reduction, and the results showed that the control of vehicle exhaust emissions and coal combustion sources is more effective in mitigating nitrate pollution. Additionally, this study also emphasized the importance of early prevention and control of pollution sources. This research provides scientific evidence for the precise management and control of nitrates.