N2O Generation Research Articles

Modulating the acidity and reducibility of FeMn/TiO2 to boost the low-temperature selective catalytic reduction of NOx

The design and fabrication of selective catalytic reduction (SCR) catalyst with ultra-low-temperature activity is diligent, however, remains challenging hitherto. Herein, a variety of TiO2-based catalysts with various Fe/Mn ratios were fabricated using a coprecipitation technique and tested for SCR of NOx with ammonia. The experimental results demonstrate that the Fe/Mn ratio considerably affects the acidity, redox property and thereafter the NH3-SCR behavior of FeMn/TiO2 catalysts. Therein, Fe0.3Mn0.7/TiO2 exhibits the broadest activity temperature window from 75 to 210 °C because of its more reactive oxygen species and higher Mn4+ ratio on the catalyst surface, leading to improved oxidation performance and surface acidity, thereby promoting the generation of active NO2 and HONO intermediates, and thereafter enabling the catalyst to adsorb more NH3 to generate active nitrate species and increasing the NH3-SCR performance. Further increasing or decreasing the Fe/Mn ratio would downgrade the SCR performances of corresponding catalysts due to the mismatch between acidity and redox ability, which inhibits the formation of active NO2 and HONO intermediates. In-situ DRIFTS results further illustrate that the SCR of NOx over FeMn/TiO2 catalysts follow both the L-H and E-R mechanisms at the low temperature, however, the types of active nitrates flourish at high temperatures, primarily via the E-R mechanism.

Dynamics of NO, N2O, and ONOOH in atmospheric-pressure air dielectric barrier discharge: decoupling energy density and gas temperature effects varying with discharge voltage

The dose regulation of reactive nitrogen species is crucial for biomedical applications. In this study, we develop a global chemical kinetics model comprising 92 species and 1018 reactions to investigate the regulatory dynamics of three types of reactive nitrogen species, i.e. NO, N2O, and ONOOH, which vary with the discharge voltage in an air coaxial dielectric barrier discharge. Based on the experimental results, the model can describe the density variations of NO, N2O, and ONOOH. The simulation results indicate that the O, NO3− , NO2− , and O3 are essential intermediate species related to NO generation; N, NO2, O-, N2*, and O(1D) are essential intermediate species related to N2O generation; and O2− , NO, NO2, OH, O4− , and O3 are essential intermediate species related to ONOOH generation. The individual and comprehensive effects of the energy density and gas temperature on the densities of NO, N2O, and ONOOH and the corresponding intermediate species are quantified under increasing discharge voltages. The simulation results indicate that the energy density is the primary factor affecting the number density of NO, N2O, and ONOOH, whereas the gas temperature exerts a completely different effect on these three species. These insights are valuable for plasma applications in biomedicine, where the selective and controlled production of reactive nitrogen species is key for achieving the desired plasma performance.

Impact and Emission of Greenhouse Gases from Paddy Fields and their Mitigation Techniques

Agricultural soil functions as both a supplier and absorber of significant greenhouse gases (GHGs) such as methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2). The scientific community has expressed significant concern regarding rice paddies, as they are responsible for the production of greenhouse gases (GHGs) that pose a long-lasting threat. The primary GHGs emitted from these fields are CH4 and N2O, accounting for approximately 30% and 11% of global agricultural emissions, respectively. Consequently, there is an urgent need to accurately measure the fluxes of CH4 and N2O in order to enhance our comprehension of these gases originating from rice fields. This understanding will enable the development of effective mitigation tactics to combat future climate change. This review aims to exclusively focus on the emission of CH4 and N2O in poddy fields, while also examining the impact of field and crop management activities on these emissions. Modifying traditional crop management practices could yield substantial results in mitigating greenhouse gas (GHG) emissions in poddy fields. By implementing effective management techniques, both environmental and agricultural aspects pertaining to soil can be readily adjusted. Therefore, comprehending the process of CH4 and N2O generation and release in poddy fields, as well as the factors governing these emissions, is crucial for devising efficient strategies to minimize emissions from poddy fields. This will assist regulatory bodies and policymakers in developing appropriate policies for agricultural farmers to enhance the reduction of GHG emissions and mitigate global climate change.

Oxidation state of copper species rather than ammonium nitrate decomposition determines the N2O generation during NO reduction with NH3 on Cu-AEI catalyst

Cu-based zeolite has excellent performance for nitrogen oxide removal from diesel vehicle exhaust, but a small amount of N2O is still generated in the selective catalytic reduction (SCR) process, and N2O has a strong greenhouse effect, which promotes the policy formulation of strictly regulating N2O emissions. This work systematically investigated the formation mechanism of low temperature N2O on Cu-AEI catalyst during SCR process. Under both steady and transient state test, the bimodal emission distribution and instantaneous generation behavior of N2O were observed. In addition, the contribution of NH4NO3 pathway to N2O formation at low temperature in standard SCR (SSCR) was demonstrated by temperature programmed desorption experiment, Thermogravimetric analysis and in situ diffuse fourier transform infrared spectroscopy experiment. NO + NH3 titration experiment, Raman and density functional theory calculation showed the role of Cu species in low temperature N2O generation. These results indicate that N2O formation during SSCR process on Cu-AEI at 200 ℃ is not generated through the decomposition path of NH4NO3, but due to the oxidation state of copper species, that is, the side reaction on Cu-peroxo.

Optimization of diesel oxidation catalyst for enhanced emission reduction in engines

With tightening emission regulations and the advent of Zero-Carbon targets, curbing emissions from engines has become imperative. To enhance the emissions reduction of engines, a diesel oxidation catalyst (DOC) inserted within a three-layer porous media is proposed. Effects of Pd/Pt blended ratios, porous media settings, and boundary conditions on pollutant conversion are simulated and analyzed. The results indicate that increasing the Pd/Pt blended ratio and reducing the porosity favor the conversion of CO and C3H6 but hinder the generation of NO2, and there exists a balancing effect of porosity and multi-layer porous media on emission conversion. With mean porosity augment from 0.4 to 0.6, NO conversion rate is improved by 2.1 % in the DOC with incremental porous media setting at Vin = 10 m/s, Tin = 550 K, and 100 % Pt. Moreover, the differences in conversion rates are enlarged with an increased Pd catalyst content, by 3.2 %, 5.9 %, 9.6 %, and 10.6 % respectively. Besides, 50 sets of DOCs are simulated, using orthogonal experiment analysis to optimize the boundary conditions and DOC setting. The maximum conversion rate is achieved when Vin = 10 m/s, Tin = 600 K, mO2 = 0.04, and Pd/Pt catalyst blended ratio and porosity is 100%Pt+1/4 + 1/4 and 0.5 + 0.4+0.4 in porous media.

Enhanced low-temperature H2-selective catalytic reduction performance and selectivity of Pt/ZSM-5–TiO2 washcoated monolithic catalysts for NOx reduction

Hydrogen-selective catalytic reduction (H2-SCR) is a promising technology for reducing nitrogen oxide (NOx) emissions at low temperatures, but the selectivity of this process is limited by the generation of N2O. To achieve enhanced denitrification (deNOx) performance, H2-SCR catalysts with mixed zeolite and TiO2 supports washcoated on monolithic cordierite were developed. The catalyst support, active metal type and content, and monolithic cordierite cell density significantly influenced the H2-SCR performance. The xPt/TiO2 catalysts (where x is the metal content, wt.%) achieved >90% NOx conversion 135–180 °C, whereas the xPd/TiO2 catalysts exhibited poor H2-SCR activity, with <30% NOx conversion. In contrast to 0.5Pt/TiO2, the 0.5Pt/zeolite catalysts achieved high NOx conversion at 140–150 °C (91% at 140 °C for 0.5Pt/ZSM-5 > 89% at 140 °C for 0.5Pt/BETA >85% at 150 °C for 0.5Pt/SSZ-13), suggesting that zeolite supports significantly promote H2-SCR activity at low reaction temperatures. For the 0.5Pt/ZSM-5 washcoated monolithic catalyst, increasing the cell density from 400 to 900 cpsi significantly improved the NOx conversion from 52% to 90% at 100 °C owing to the increased geometric surface area and open frontal area of monolithic cordierite. For catalyst with mixed supports (0.5Pt/yZSM-5zTiO2) changing the ZSM-5/TiO2 ratio (y:z) from 25:75 to 90:10 increased the low-temperature NOx conversion from 39% to 89% at 100 °C, indicating that the deNOx characteristics can be tuned. With NO as the reactant, the 0.5Pt/90Z10T catalyst produced the lowest N2O share (8–17%) within the temperature window of maximum NOx conversion, resulting in an increased N2 share (83–88%). Thus, the synergetic effect of mixed ZSM-5/TiO2 catalyst supports can enhance low-temperature NOx conversion and mitigate N2O formation.

Efficient photocatalytic NO removal with inhibited NO2 formation and catalyst loss over sponge-supported and functionalized g-C3N4

Though photocatalytic purification of NO has been widely studied, how to avoid secondary pollution during gas-solid reaction is still a challenge, especially in inhibiting the formation of toxic intermediates (NO2) and avoiding the blow away of powdery photocatalyst. Herein, we proposed a one-step solvothermal method to prepare melamine sponge (MS) supported and functionalized g-C3N4 (CN), which simultaneously realizes the inhibition of NO2 formation and catalyst loss. Sodium hydroxide, which plays a dual role, has been introduced during the preparation of supported photocatalyst. Specifically, sodium atom, as the modifier of performance, could facilitate the randomly distributed charge of pristine CN to be converged, which accelerates the adsorption/activation of reactants for efficient and deep NO oxidation. Hydroxyl group, as the binder between CN and MS, induces the interaction by forming hydrogen bonds, which contributes to the firm immobilization of powdery photocatalyst. The supported sample exhibits outstanding NO removal rate (58.90%) and extremely low NO2 generation rate (1.41%), and the mass loss rate of photocatalyst before and after reaction is less than 1%. The promotion mechanism of performance also has been elaborated. This work takes environmental risks as a prerequisite to propose a feasible strategy for perfecting the practical application of photocatalytic technology.

Computational Exploration of Minimum Energy Reaction Pathway of N2O Formation from Intermediate I of P450nor Using an Active Center Model.

P450nor is a heme-containing enzyme that catalyzes the conversion of nitric oxide (NO) to nitrous oxide (N2O). Its catalytic mechanism has attracted attention in chemistry, biology, and environmental engineering. The catalytic cycle of P450nor is proposed to consist of three major steps. The reaction mechanism for the last step, N2O generation, remains unknown. In this study, the reaction pathway of the N2O generation from the intermediate I was explored with the B3LYP calculations using an active center model after the examination of the validity of the model. In the validation, we compared the heme distortions between P450nor and other oxidoreductases, suggesting a small effect of protein environment on the N2O generation reaction in P450nor. We then evaluated the electrostatic environment effect of P450nor on the hydride affinity to the active site with quantum mechanics/molecular mechanics (QM/MM) calculations, confirming that the affinity was unchanged with or without the protein environment. The active center model for P450nor showed that the N2O generation process in the enzymatic reaction undergoes a reasonable barrier height without protein environment. Consequently, our findings strongly suggest that the N2O generation reaction from the intermediate I depends sorely on the intrinsic reactivity of the heme cofactor bound on cysteine residue.

Cyano/Hydroxyl Groups Co-Functionalized g-C3N4 for Photocatalytic NO Removal: A Synergistic Strategy towards Inhibition of Toxic Intermediate NO2

Photocatalytic NO removal is usually accompanied by the generation of NO2, an intermediate with a higher toxicity than NO. Therefore, it is critically important to develop new photocatalysts capable of NO selective conversion. Herein, we report on the synergistic roles of cyano and hydroxyl functional groups in photocatalytic NO removal. According to the results, the NO2 production efficiencies on cyano/hydroxyl-group-modified g-C3N4 (DCN-O-R) was limited to 4.8%, which was lower than that of cyano-group-modified g-C3N4 (DCN, 38.6%) and pure g-C3N4 (CN, 50.0%). Meanwhile, the photocatalytic NO conversion efficiency over DCN-O-R was higher than that of DCN and g-C3N4. It was found that the insertion of cyano groups favorably changes the energy band of g-C3N4 towards the generation of •O2−. NO can only be oxidized to NO2 by the photogenerated holes. When NO2 is adsorbed on the surface of hydroxyl groups, it can be further oxidized to the product NO3− by •O2−. The synergistic effect of bifunctional groups regulates the conversion pathway from NO→NO2 to NO→NO2→NO3−. This work provides a strategy to abate toxic intermediates during the NO removal process, underlining the importance of surface/interface molecular engineering in regulating catalytic reaction pathways.

The Influence of Titanium Dioxide Nanosheet on Water Permeability of Silicone Rubber after Nitrogen Dioxide Aging Treatment.

In this study, the aging process of a surface-functional titanium dioxide nanosheet (f-TNS) composited room-temperature-vulcanized silicone rubber (RTV) composite coating was simulated in a NO2 generation device, and then the electrochemical impedance spectroscopy (EIS) of the aged composite coating was tested in a 3.5% NaCl solution. The water permeation process was analyzed by the changes in the impedance modulus, porosity, and breakpoint frequency of the composite coating. The experimental results show that the water permeability of aged RTV decreases first and then increases with the increase in the composite proportion of f-TNS. When the composite proportion of TNS was 0.3 wt.%, the composite sample had the minimum water permeability and the best resistance to NO2 corrosion. The effect of TNS on the NO2 aging resistance of RTV composites and its mechanism were studied by SEM, FT-IR, and XPS. The impedance modulus and porosity of the aged 0.3% f-TNS/RTV, respectively, were 1.82 × 107 Ω cm2 and 0.91 × 10-4%, which increased by 2.23 times and decreased by 0.37 times, respectively, compared with the values of aged pure RTV sample. In addition, the breakpoint frequency of the aged 0.3% f-TNS/RTV also significantly reduced to 11.3 Hz, whereas it was 35 Hz in aged pure RTV.

Kinetic roles of excited state species in the oxidation of n-pentane/air assisted by nanosecond-pulsed discharge

Despite the significant advancement in plasma assisted combustion recently, many of the underlying plasma/combustion interaction mechanisms remain unknown. Critical data such as cross sections for large hydrocarbons and reaction rate constants involving excited species are still limited. To address these issues, a detailed plasma chemistry mechanism governing the oxidation processes in a n-pentane/air combustion mixture was proposed and studied by including a complete set of e-n-pentane cross section and excited state chemistry of n-pentane. The concentrations of alkane (CH4, C2H6, C3H8), alkene (C2H4, C3H6), methanol, NO2 and NH3 were measured by GC and a small amount of liquid products are qualitatively characterized by GC-MS. The electron-scattering cross sections of n-pentane were obtained by the R-matrix method. The rate constants of excited species of n-pentane which involved the chemical reactions were calculated via Fridman α-model and MMVT method. A linear increase in reactants consumption with increased voltages was observed experimentally, suggesting that n-pentane excitation by plasma was decoupled from the low-temperature chemistry. The kinetic mechanism accurately predicted the generation of alkane and hydrogen and captured the overall trend. However, it underestimated the generation of NH3 and NO2, indicating certain reaction pathways in NH3 and NO2 generation were missed. The results showed that because of the introduction nitrogen in the system, the excited states of the oxidant molecules O(1D), O(1S), N2(B) and N2(C) reacted with n-pentane to form fuel radicals via H-atom abstraction reactions RH + X* → R + XH. The excited species of n-pentane reacted with O, H, OH to form n-pentane radicals via RH* + X → R + XH, accordingly enhancing the chain initial reactions. Importantly, ammonia was produced in a n-pentane/air mixture with plasma assistance through the pathway of N2 → N(2D) → NH → NH2 → NH3. These results highlight strong roles of excited species in a complex n-pentane/air plasma chemistry system.

Generation mechanism and emission characteristics of N2O and NOx in ammonia-diesel dual-fuel engine

Ammonia, as a hydrogen-derived fuel, primarily emits N2O and NOx when burned in an engine. The emissions originate from ammonia fuel and nitrogen in the air. In this paper, the N of N2 was labeled by isotope labeling method, so that the nitrogen element in the formation path of the thermal N2O and NOx was labeled, and the chemical reaction path of the formation and evolution of the fuel and thermal nitrogen oxide was defined. In addition, the spatiotemporal distribution characteristics, generation and evolution rules of fuel and thermal nitrogen oxide in ammonia-diesel dual-fuel engine, as well as the influence of different ammonia energy ratios on the generation ratio of two types of N2O and NOx were studied by combining experiment and simulation. The ammonia energy ratio is defined as the proportion of energy provided by ammonia in a constant total lower calorific value. The results showed that when the ammonia energy ratio increased from 20 % to 60 %, the emissions of NO and NO2 decreased, but the proportion of fuel NO and NO2 increased. The proportion of N2O in nitrogen oxide emission increased from 7.3 % to 20 %. Fuel N2O accounts for about 90 % of N2O emission. Fuel N2O and NOx were mainly generated in ammonia-rich, low-temperature regions and thermal N2O and NOx were mainly generated in the high-temperature regions. Temperature significantly affected N2O generation.

Thermal decomposition and combustion behavior of the core-shell Al@AP composite embedded with CuO as a catalyst

Conventional solid propellants suffer from undesirable combustion performance due to the poor mass and heat transfer between metal fuels and oxidizers, as well as a lack of catalytic active sites between the catalyst and catalyzed objects. Embedding metal fuels and catalysts within the oxidizer has shown promise in improving the overall combustion performance of HTPB/AP/Al and HTPB/AP/RDX/Al composite solid propellants. However, the underlying mechanisms responsible for this enhancement remain to be further understood. In this study, we investigated the reactivities of core–shell Al@AP and Al@AP/CuO composites using thermal analysis and combustion diagnostic techniques. The results demonstrated that the decomposition of AP was promoted, as evidenced by a lower peak temperature (415.2–334.7 ℃), higher total heat release (116.4–720.8 J·g−1), a transition in the decomposition physical model from the random nucleation and 2D/3D growth of nuclei model to the auto-catalytic model, and increased generation of NO2. Furthermore, the Al@AP/CuO propellant pellet exhibited a more stable flame without agglomeration, and the condensed combustion products (CCPs) contained a lower amount of unreacted Al compared to that of conventional mixtures. These findings highlighted the potential of core–shell Al@AP and Al@AP/CuO composites as replacements for discrete ingredients of solid propellants, thereby offering improved performance for next-generation propulsion systems.

Microbiota and genetic potential for reducing nitrous oxide emissions by biochar in constructed wetlands

The denitrification process in constructed wetlands (CWs) is responsible for most of the nitrous oxide (N2O) emissions, which is an undesired impact on the ecology of sewage treatment systems. This study compared three types of CWs filled with gravel (CW-B), gravel mixed with natural pyrite (CW-BF), or biochar (CW-BC) to investigate their impact on microbiota and genetic potential for N2O generation during denitrification under varying chemical oxygen demand (COD) to nitrate (NO3−-N) ratios. The results showed that natural pyrite and biochar were superior in enhancing COD (90.6–91.2 %) and NO3−-N removal (90.0–93.5 %) in CWs with a COD/NO3−-N ratio of 9. The accumulation of NO2−-N during the denitrification process was the primary cause of N2O emission, with the fluxes ranging from 95.6–472.0 μg/(m2·h) in CW-B, 92.9–400 μg/(m2·h) in CW-BF, and 54.0–293.3 μg/(m2·h) in CW-BC. The addition of biochar significantly reduced N2O emissions during denitrification, while natural pyrite had a lesser inhibitory effect on N2O emissions. The three types of substrates also influenced the structure of microbiota in the biofilm, with natural pyrite enriched nitrogen transformation microorganisms, especially for denitrifiers. Notably, biochar significantly enhanced the abundance of nosZ and the ratio of nosZ/(norB + norC), which are critical factors in reducing N2O emissions from CWs. Overall, the results suggest that the biochar-induced changes in microbiota and genetic potential during denitrification play a significant role in preventing N2O production in CWs, especially when treating sewage with a relatively high COD/NO3−-N ratio.

Formation mechanisms of N2O and NH3 on Pd/ZrO2 and Pd/Al2O3 for NO reduction

Reducible and nonreducible supports usually display distinct properties on the size, valence, and coordination of Platinum group elements in supported metal oxide. However, there are few reports on the regulation of main and side reaction rates and inhibition of byproducts from the perspective of reaction kinetics. Here, we compare the N2O and NH3 formations of Pd supported on Al2O3 and ZrO2 in NO reductions. Pd/Al2O3 produces less N2O and NH3 in quantity than Pd/ZrO2, which could be due to the moderate metal-support interactions between Pd with higher average valence and Al2O3 with lower ability of electrons transfer. ZrO2 acted as an electron acceptor in NO reduction facilitating the formations of unstable nitrates and surface hydroxyls. In-situ DRIFTS and NAP-XPS results suggest that the N2O generation is directly related to nitrates with different stabilities: bridging, bidentate, and partial monodentate nitrates are active on Pd/ZrO2, whereas, only nitro and partial bridging nitrates are active on Pd/Al2O3. The NH3 is mainly originated from the reaction of nitrates to surface hydroxyls with different coordination numbers. This work clarifies the byproducts formation mechanism in NO reduction and opens up the research topics using in-situ spectroscopy methodology.

Facile construction of novel Z-scheme Bi4O5I2/CuFe2O4 heterojunctions for NO2-inhibited and robust photocatalytic removal of NO under visible light

Photocatalytic oxidation has been confirmed as a promising manner to control and treat low-concentration NO, during which the generation of hazardous intermediate NO2 is unavoidable, causing more severe health concerns and environmental pollution issues than NO itself. In this research, the photocatalytic removal of NO was studied over novel Bi4O5I2/CuFe2O4 (BCF) binary composites that were constructed by a straightforward solvothermal route. CuFe2O4 nanoparticles and Bi4O5I2 nanosheets were coexisted in composites and merged into heterojunction structures with compatible morphologies. Under visible light, these resultant composites exhibited reinforced photocatalytic NO removal efficiency in comparison to bare components. Specifically, the best sample BCF3, defined as the composite with the mass percent of CuFe2O4 to Bi4O5I2 as 3%, presented the toxic intermediate NO2 as 21 ppb (part per billion) and the largest photocatalytic NO removal of 44% that referred to the ratio of removal to initial concentration of NO. NO removal and NO2 generation of BCF3 improved 1.5 times and reduced by half in only 5 min compared to that of pristine Bi4O5I2, which could be attributed to the strengthened visible light harvesting, efficient transfer and separation of charge carriers through intimate interfaces, and the availability of sufficient reactive radicals. Through entrapping experiments and band structure estimation, a Z-scheme model was put forward for the photocatalysis mechanism of these robust n-p heterojunction composites.

Chemical Activity of Low Altitude (50 km) Sprite Streamers

AbstractA three‐stage simulation is used to explore the chemical influence of low altitude (50 km) sprite streamers on the atmosphere, including the chemical trail after the streamer has faded away. In the first stage (streamer phase) a 2D electrodynamical streamer model quantifies the generation of NOx and N2O, and the removal of ozone (O3) by a downward propagating streamer during Δtstreamer = 80 μs. This streamer propagation leads to a distinctive region in the streamer channel, the glow, where the electric field is enhanced. In the second stage (glow phase), the computed densities of the first stage are used as initial conditions for a 0D model to study the chemical evolution of the streamer channel, where we assume a remanent field of 100 Td for the glow and 0 Td elsewhere. This stage lasts Δtglow = 85 μs, the typical glow lifetime at 50 km. Finally, in the third stage (post‐streamer phase), we use the same 0D model, switch off the field in the glow region and let the whole streamer wake evolve roughly 100 s (100 s − Δtglow). Results show a key species such as O3 is mainly depleted during the streamer phase while NOx and N2O are predominantly produced during the same phase. We also compute the local increase of NO2 by sprite streamers at ∼50 km and find out that it could account for the measurable NO2 anomaly over thunderstorms reported from satellite‐based measurements.

Jointly augmented photocatalytic NO removal by S-scheme Bi12SiO20/Ag2MoO4 heterojunctions with surface oxygen vacancies

The deep oxidation of NO molecules to NO3– species with the avoidance of toxic NO2 generation is a big and challengeable concern, which can be solved by the rational design and construction of catalytic systems with satisfactory structural and optical features. For such, in this investigation binary composites Bi12SiO20/Ag2MoO4 (BSO-XAM) were fabricated through a facile mechanical ball-milling route. From microstructural and morphological analyses, heterojunction structures with surface oxygen vacancies (OVs) were simultaneously created, contributing to the enhanced visible-light absorption, reinforced migration and separation of charge carries, and further boosted generation of reactive species such as superoxide radicals and singlet oxygen. Based on the density-functional theory (DFT) calculations, surface OVs induced the strengthened adsorption and activation of O2, H2O, and NO molecules and oxidation of NO to NO2, while heterojunction structures were beneficial for the continuous oxidation of NO2 to NO3– species. Thus, the heterojunction structures with surface OVs synergistically guaranteed the augmented photocatalytic NO removal and constrained NO2 generation of BSO-XAM through a typical S-scheme model. This study may provide scientific guidances for the photocatalytic control and removal of NO at ppb level by Bi12SiO20-based composites through the mechanical ball-milling protocol.

Surface Modification of TiO2 by Hyper-Cross-Linked Polymers for Efficient Visible-Light-Driven Photocatalytic NO Oxidation.

Solar-driven photocatalysis offers an environmentally friendly and sustainable approach for the removal of air pollutants such as nitric oxides without chemical addition. However, the low specific surface area and adsorption capacity of common photocatalysts restrict the surface reactions with NO at the ppb-level. In this study, imidazolium-based hyper-cross-linked polymer (IHP) was introduced to modify the surface of TiO2 to construct a porous TiO2/IHP composite photocatalyst. The as-prepared composite with hierarchical porous structure achieves a larger specific surface area as 309 m2/g than that of TiO2 (119 m2/g). Meanwhile, the wide light absorption range of the polymer has brought about the strong visible-light absorption of the TiO2/IHP composite. In consequence, the composite photocatalyst exhibits excellent performance toward NO oxidation at a low concentration of 600 ppb under visible-light irradiation, reaching a removal efficiency of 51.7%, while the generation of the toxic NO2 intermediate was suppressed to less than 1 ppb. The enhanced NO adsorption and the suppressed NO2 generation on the TiO2/IHP surface were confirmed by in situ monitoring technology. This work demonstrates that the construction of a porous structure is an effective approach for efficient NO adsorption and photocatalytic oxidation.

Redox on Mn-Ce interface and its effects on low temperature selective catalytic reduction for NOx removal

The objective of this work was to clearly elucidate the interactions on Mn-Ce interface and understand how they affect low temperature selective catalytic reduction (SCR) for NOx removal. In this work, three Mn-Ce catalysts in similar particle size and morphology with different Mn-Ce interface areas were prepared. MnO2@CeO2-F had the tightest and largest amount of Mn-Ce interfaces compared with MnO2@CeO2-P and MnO2-CeO2-M, and also exhibited the highest NO conversion degree at 100–150 °C as well as the strongest activity of Mn species and lowest generation of N2O. The TG-DTG, XPS and electrochemical impedance spectroscopy results proved the redox of Ce4+ + Mn3+ ↔ Ce3+ + Mn4+ on the Mn-Ce interface, and MnO2@CeO2-F had the highest Mn4+, Ce3+, Oα concentrations. The results of the study on the redox reactions during the NH3-SCR process provided powerful evidence of the Mn4+/Mn3+ and Ce3+/Ce4+ recycles that are important for low temperature NH3-SCR process. Moreover, the Mn-Ce interface was directly proved to benefit the surface acid sites, redox ability, and activity of the adsorbed intermediates. Both the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) reaction mechanisms were observed in the SCR reaction with prepared Mn-Ce materials, where “fast SCR” can be observed with MnO2@CeO2-F. Moreover, the Mn-Ce interface also lowers the activation energy of the low-temperature SCR process, with MnO2@CeO2-F having the lowest activation energy. The results from this work offered powerful evidences for the interactions of Mn/Ce redox at the Mn-Ce interface and elucidated clear understanding of the effects of Mn-Ce redox on low-temperature SCR process, which is expected to promote the NOx removal process.