Hydrochars derived from real organic wastes as carbonaceous precursors of activated carbons for the removal of NO from contaminated gas streams.

The improvement of air quality in densely-populated urban regions constitutes an environmental challenge of increasing concern. In this respect, the abatement of NO emissions, primarily emanating from combustion processes associated with motor-vehicles, along with industrial/domestic combustion systems, represents one of the main problems. Here, three hydrochars from diverse organic residues were used as activated carbon precursors for their evaluation in the NO removal in two potential application scenarios. Hydrochars were physically activated at 800 °C with pure-CO2 or diluted-O2. These materials were tested in a lab-scale biofilter at different conditions (NO concentration, temperature, relative humidity, NO-containing gas and carbon particle size) and in a larger-scale biofilter to evaluate the long-term NO removal capacity. Hydrochar-derived carbons present a relatively well-developed micro- and mesoporous structure, with BET areas of up to 421 m2/g, and a variety of oxygen surface functionalities (carboxylic, lactone, carbonyl and quinone groups), especially concerning CO2-activated carbons. These exhibited an excellent behaviour at low NO concentration (5 ppmv) between 25 and 75 °C with removal capacities of ≈97 % and > 82 %, respectively; and still good-performance (≈66 %) in a more concentrated gas (120 ppmv). Whilst, carbons obtained by diluted-O2 activation from the same hydrochars, evidenced a higher removal capacity loss at high NO concentration. The O2 presence in the gas stream was confirmed as a crucial factor in the NO elimination, since both co-adsorb on the carbon surface favouring NO oxidation to NO2. Besides, the humidity in the airstream diminished the NO removal capacity from 0.88 to 0.51 mgNO/gcarbon, but still remained at 0.54 mgNO/gcarbon, when the carbon (in pellet) was operated at larger-scale biofilter in 9-fold longer test under humid air. Therefore, this study highlights the potential of renewable carbons to serve as cost-effective component in urban biofilters, to mitigate NO emissions from exhaust gases in biomass boilers and urban semi-close areas.

NOx removal capacity and compressive strength of photocatalytic cementitious materials with various color properties.

The photocatalytic cementitious materials (PCM) are expected to alleviate air pollution due to the direct utilization of natural solar energy. However, the color properties of cementitious materials have significant effect on the photocatalytic performance of PCM. In the present study, the colorful PCM is prepared using various colorants. The effect of color properties of cementitious materials on the NOx removal capacity of PCM is researched, and the related mechanism is analyzed by optical analysis. Furthermore, the effect of colorants on the compressive strength of PCM is studied. Results showed that the NOx removal capacity of PCM is decreased by the presence of colorants. As the 5% of black, yellow, red, and blue colorants are used, the NOx removal capacity of PCM is reduced by 73%, 48%, 21%, and 19%, respectively. Both the nano-TiO2 and cement in the PCM can absorb UV light. Colorants could enhance the UV light absorption capacity of cement, leading to a decrease in the UV light absorption of nano-TiO2, which is harmful to the generation of electron-hole pairs. Moreover, the Fe-phase in colorants could improve the surface charge separation resistance of nano-TiO2, limiting the efficiently separated electron-hole pairs. Therefore, the photocatalytic performance of PCM is weakened by the presence of colorants. The compressive strength of PCM is decreased by using colorants, but the reduction ratio at 28 d is no more than 10%, with the content of colorants within 5%. This research can guide the color design of PCM in practical applications.

Selective Synergistic Catalytic Elimination of NOx and CH3SH via Engineering Deep Oxidation Sites against Toxic Byproducts Formation.

NOx and CH3SH as two typical air pollutants widely coexist in various energy and industrial processes; hence, it is urgent to develop highly efficient catalysts to synergistically eliminate NOx and CH3SH. However, the catalytic system for synergistically eliminating NOx and CH3SH is seldom investigated to date. Meanwhile, the deactivation effects of CH3SH on catalysts and the formation mechanism of toxic byproducts emitted from the synergistic catalytic elimination reaction are still vague. Herein, selective synergistic catalytic elimination (SSCE) of NOx and CH3SH via engineering deep oxidation sites over Cu-modified Nb-Fe composite oxides supported on TiO2 catalyst against toxic CO and HCN byproducts formation has been originally demonstrated. Various spectroscopic and microscopic characterizations demonstrate that the sufficient chemisorbed oxygen species induced by the persistent electron transfer from Nb-Fe composite oxides to copper oxides can deeply oxidize HCOOH to CO2 for avoiding highly toxic byproducts formation. This work is of significance in designing superior catalysts employed in more complex working conditions and sheds light on the progress in the SSCE of NOx and sulfur-containing volatile organic compounds.

Enhancement of Pt-O Synergistic Sites through Titanium Vacancies for Low-Temperature Nitrogen Oxide Reduction.

Improving the reaction rate of each step is significant for accelerating the multistep reaction of NO reduction by H2. However, simultaneously enhancing the activation of different gaseous reactants using single-atom catalysts remains a challenge to maximize the activity. Herein, we propose a strategy that utilizes titanium-vacancy-regulated electronic properties of single atoms and defective support (Pt1/d-TiO2) to facilitate electron transfer from edge-share O atoms (OTi) to adjacent Pt single atoms. This leads to the formation of low-valence Pt and unsaturated-charge OTi sites, which causes the catalytic reaction to follow a synergistic mechanism. Specifically, experimental and theoretical analyses demonstrate that low-valence Pt sites finely tune the adsorption of H2 molecules, consequently lowering the dissociation energy from 0.15 to as low as 0.01 eV. Moreover, using quasi-in situ spectroscopy, we clearly observe NO molecules being adsorbed on interfacial oxygen sites of a defective support. Then, the bond energy of the N-O bond is weakened through an electron acceptance-donation mechanism between unsaturated-charge OTi sites and NO, thereby facilitating NO activation. The designed single-atom catalysts with synergistic sites exhibit unmatched activity at low temperatures (above 90% NOx conversion at 100 °C), along with higher turnover frequency value (0.74 s-1) and superior stability, making them potentially suitable for industrial applications.

Unique κ-Ce2Zr2O8 Superstructure Promoting the NOx Adsorption-Selective Catalytic Reduction (AdSCR) Performance of the WO3/CeZrOx Catalyst.

Selective catalytic reduction of NOx by NH3 (NH3-SCR) for diesel emission control at low temperatures is still a great challenge due to the limit of the urea injection threshold and inferior SCR activity of state-of-the-art catalyst systems below 200 °C. Fabricating bifunctional catalysts with both low temperature NOx adsorption-storage capacity and medium-high temperature NOx reduction activity is an effective strategy to solve the issues mentioned above but is rarely investigated. Herein, the WO3/Ce0.68Zr0.32Ox (W/CZ) catalyst containing the κ-Ce2Zr2O8 pyrochlore structure was successfully developed by a simple H2 reduction method, not only showing superior NOx adsorption-storage ability below 180 °C but also exhibiting excellent NH3-SCR activity above 180 °C. The presence of the pyrochlore structure effectively increased the oxygen vacancies on the κ-Ce2Zr2O8-containing W/CZ catalyst with enhanced redox property, which significantly promoted the NOx adsorption-storage as active nitrate species below 180 °C. Upon NH3 introduction above 180 °C, the κ-Ce2Zr2O8-containing W/CZ catalyst showed greatly improved NOx reduction performance, suggesting that the pyrochlore structure played a vital role in improving the NOx adsorption-selective catalytic reduction (AdSCR) performance. This work provides a new perspective for designing bifunctional CeZrOx-based catalysts to efficiently control the NOx emissions from diesel engines during the cold-start process.

Research landscape and hotspots of selective catalytic reduction (SCR) for NOx removal: insights from a comprehensive bibliometric analysis.

Selective catalytic reduction (SCR) has been one of the most efficient and widely used technologies to remove nitrogen oxides (NOx). SCR research has developed rapidly in recent years, which can be reflected by the dramatic increase of related academic publications. Herein, based on the 10,627 documents from 2001 to 2020 in Web of Science, the global research landscape and hotspots in SCR are investigated based on a comprehensive bibliometric analysis. The results show that SCR research has developed positively; the annul number of articles increase sharply from 246 in 2001 to 1092 in 2020. People's Republic of China and Chinese Academy of Sciences are the most productive country and institution, respectively. The global collaboration is extensive and frequent, while People's Republic of China and USA have the most frequent research cooperation. Applied Catalysis B-Environmental is the leading publication source with 711 records. Five major research areas on SCR are identified and elaborated, including catalyst, reductant, deactivation, mechanism, and others. Zeolite is the most widely studied SCR catalyst, while copper, silver, platinum, and iron are the most popular metal elements in catalyst. Ammonia (NH3) is dominated among various SCR reductants, while hydrocarbon reductant has gained more attention. Sulfur dioxide (SO2) and vapor are the two most concerned factors leading to catalyst deactivation, and catalyst regeneration is also an important research topic. Density functional theory (DFT), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and kinetics are the most widely used methods to conduct mechanism study. The studies on "low temperature," "atomic-scale insight," "elemental mercury," "situ DIRFTS investigation," "arsenic poisoning," "SPOA-34," "Cu-CHA catalyst," "TiO2 catalyst," and "Ce catalyst" have been the hotspots in recent years.

Removal of NO at low concentration from air in urban built environments by activated miscanthus biochar.

This work presents an innovative and sustainable approach to remove NO emissions from urban ambient air in confined areas (underground parking areas or tunnels) using low-cost activated carbons obtained from Miscanthus biochar (MSP700) by physical activation (with CO2 or steam) at temperatures ranging from 800 to 900 °C. The NO removal capacity of the activated biochars was evaluated under different conditions (temperature, humidity and oxygen concentration) and compared against a commercial activated carbon. This last material showed a clear dependence on oxygen concentration and temperature, exhibiting a maximum capacity of 72.6% in air at 20 °C, whilst, its capacity notably decreased at higher temperatures, revealing that physical NO adsorption is the limiting step for the commercial sample that presents limited oxygen surface functionalities. In contrast, MSP700-activated biochars reached nearly complete NO removal (99.9%) at all tested temperatures in air ambient. Those MSP700-derived carbons only required low oxygen concentration (4 vol%) in the gas stream to achieve the full NO removal at 20 °C. Moreover, they also showed an excellent performance in the presence of H2O, reaching NO removal higher than 96%. This remarkable activity results from the abundance of basic oxygenated surface groups, which act as active sites for NO/O2 adsorption, along with the presence of a homogeneous microporosity of 6 Å, which enables intimate contact between NO and O2. These features promote the oxidation of NO to NO2, which is further retained over the carbon surface. Therefore, the activated biochars studied here could be considered promising materials for the efficient removal of NO at low concentrations from air at moderate temperatures, thus closely approaching real-life conditions in confined spaces.

Effects of various COD/NO ratios on NOx removal performance and microbial communities in a BTF-ABR integrated system.

In this study, we investigated the removal performance of NOx and stability of the biotrickling filter-anaerobic baffled reactor (BTF-ABR) integrated system at various chemical oxygen demand (COD)/NO ratios (12.18, 6.71, and 4.63 in stages 1, 2, and 3, respectively) under 3.5% O2 and 50 ± 0.5 °C conditions for the first time. The results showed that the maximum elimination capacity of NOx was 4.46, 8.16, and 11.58 g/(m3·h) in stages 1, 2, and 3, respectively. The minimum operating cost in terms of glucose was 4.79 g of glucose/g of NO. However, a COD/NO ratio of 12.18 resulted in a wastage of carbon sources, while a COD/NO ratio of 4.63 led to about 20 mg/m3 N2O emission at the end of the study. Highly bacteria diversity and positive co-occurrence networks at the COD/NO ratio of 6.71 were the main reasons for no intermediate accumulation or N2O emission. Analysis of real-time polymerase chain reaction (PCR) indicated that nirS and norB were more sensitive to the changes in the COD/NO ratios than other denitrifying genes, and the denitrifiers with nirS filled more ecological niches as the NOx increased. Furthermore, although the decrease in COD/NO ratio significantly impacted the microbial community structure, the NOx RE was stabilized at over 90% because the micro-aerobic environment produced by ABR combined highly diverse microbes and functions in BTF, as well as the coordinated expression of denitrifying genes. Achieving efficient, stable, and low-cost denitrification is feasible in this BTF-ABR integrated system.

Synergistic effect of cyano defects and CaCO3 in graphitic carbon nitride nanosheets for efficient visible-light-driven photocatalytic NO removal.

Photo-oxidation with semiconductor photocatalysts provides a sustainable and green solution for NOx elimination. Nevertheless, the utilization of traditional photocatalysts in efficient and safe photocatalytic NOx removal is still a challenge due to the slow charge kinetic process and insufficient optical absorption. In this paper, we report a novel porous g-C3N4 nanosheet photocatalyst modified with cyano defects and CaCO3 (xCa-CN). The best performing sample (0.5Ca-CN) exhibits an enhanced photo-oxidation NO removal rate (51.18 %) under visible light irradiation, largely surpassing the value of pristine g-C3N4 nanosheets (34.05 %). Such an enhancement is mainly derived from an extended visible-light response, improved electron excitation and transfer, which are associated with the synergy of cyano defects and CaCO3, as evidenced by a series of spectroscopic analyses. More importantly, in-situ DRIFTS and density functional theory (DFT) results suggest that the introduction of cyano defects and CaCO3 enables control over NO adsorption and activation processes, making it possible to implement a preference pathway (NO → NO+ → NO3¯) and reduce the emission of toxic intermediate NO2. This work demonstrates the potential of integrating defect engineering and insulator modification to design highly efficient g-C3N4-based photocatalysts for air purification.

The Strengthened Photocatalytic NOx Removal of Composites Bi4O5Br2/BiPO4: The Efficient Regulation of Interface Carriers by Integrating a Wide-Bandgap Ornament.

A series of binary composites Bi4O5Br2/BiPO4 (PBX) was fabricated through a simple mechanical ball milling protocol. Relevant microstructural, morphological, and optical properties were thoroughly analyzed via various techniques. The integration of both components was confirmed to produce heterojunction domains at the phase boundaries. Upon exposure to visible light irradiation, the as-achieved PBX series possessed the reinforced photocatalytic NOx removal efficiencies and the weakened generation of toxic intermediate NO2 in comparison to both bare components, chiefly attributed to the efficient transport and separation of carriers and boosted production of superoxide radicals (·O2-) through the combination of a wide-bandgap ornament BiPO4 as an electron acceptor. In particular, the composite PB5 with the optimal phase composition exhibited the highest NOx removal of 40% with the lowest NO2 formation of 40 ppb among all tested candidates. According to the band structures' estimation and reactive species' detection, a reasonable mechanism was ultimately proposed to describe the migration of charge carriers and the enhancement of photocatalytic performance.

Recent trends in vanadium-based SCR catalysts for NOx reduction in industrial applications: stationary sources.

Vanadium-based catalysts have been used for several decades in ammonia-based selective catalytic reduction (NH3-SCR) processes for reducing NOx emissions from various stationary sources (power plants, chemical plants, incinerators, steel mills, etc.) and mobile sources (large ships, automobiles, etc.). Vanadium-based catalysts containing various vanadium species have a high NOx reduction efficiency at temperatures of 350-400 °C, even if the vanadium species are added in small amounts. However, the strengthening of NOx emission regulations has necessitated the development of catalysts with higher NOx reduction efficiencies. Furthermore, there are several different requirements for the catalysts depending on the target industry and application. In general, the composition of SCR catalyst is determined by the components of the fuel and flue gas for a particular application. It is necessary to optimize the catalyst with regard to the reaction temperature, thermal and chemical durability, shape, and other relevant factors. This review comprehensively analyzes the properties that are required for SCR catalysts in different industries and the development strategies of high-performance and low-temperature vanadium-based catalysts. To analyze the recent research trends, the catalysts employed in power plants, incinerators, as well as cement and steel industries, that emit the highest amount of nitrogen oxides, are presented in detail along with their limitations. The recent developments in catalyst composition, structure, dispersion, and side reaction suppression technology to develop a high-efficiency catalyst are also summarized. As the composition of the vanadium-based catalyst depends mostly on the usage in stationary sources, various promoters and supports that improve the catalyst activity and suppress side reactions, along with the studies on the oxidation state of vanadium, are presented. Furthermore, the research trends related to the nano-dispersion of catalytically active materials using various supports, and controlling the side reactions using the structure of shaped catalysts are summarized. The review concludes with a discussion of the development direction and future prospects for high-efficiency SCR catalysts in different industrial fields.

Boosting SO2-Resistant NOx Reduction by Modulating Electronic Interaction of Short-Range Fe-O Coordination over Fe2O3/TiO2 Catalysts.

SO2-resistant selective catalytic reduction (SCR) of NOx remains a grand challenge for eliminating NOx generated from stationary combustion processes. Herein, SO2-resistant NOx reduction has been boosted by modulating electronic interaction of short-range Fe-O coordination over Fe2O3/TiO2 catalysts. We report a remarkable SO2-tolerant Fe2O3/TiO2 catalyst using sulfur-doped TiO2 as the support. Via an array of spectroscopic and microscopic characterizations and DFT theoretical calculations, the active form of the dopant is demonstrated as SO42- residing at subsurface TiO6 locations. Sulfur doping exerts strong electronic perturbation to TiO2, causing a net charge transfer from Fe2O3 to TiO2 via increased short-range Fe-O coordination. This electronic effect simultaneously weakens charge transfer from Fe2O3 to SO2 and enhances that from NO/NH3 to Fe2O3, resulting in a remarkable "killing two birds with one stone" scenario, that is, improving NO/NH3 adsorption that benefits SCR reaction and inhibiting SO2 poisoning that benefits catalyst long-term stability.

NOx Reduction over Smart Catalysts with Self-Created Targeted Antipoisoning Sites.

Selective catalytic reduction of NOx in the presence of alkali (earth) metals and heavy metals is still a challenge due to the easy deactivation of catalysts. Herein, NOx reduction over smart catalysts with self-created targeted antipoisoning sites is originally demonstrated. The smart catalyst consisted of TiO2 pillared montmorillonite with abundant cation exchange sites to anchor poisoning substances and active components to catalyze NOx into N2. It was not deactivated during the NOx reduction process in the presence of alkali (earth) metals and heavy metals. The enhanced surface acidity, reducible active species, and active chemisorbed oxygen species of the smart catalyst accounted for the remarkable NOx reduction efficiency. More importantly, the self-created targeted antipoisoning sites expressed specific anchoring effects on poisoning substances and protected the active components from poisoning. It was demonstrated that the tetrahedrally coordinated aluminum species of the smart catalyst mainly acted as self-created targeted antipoisoning sites to stabilize the poisoning substances into the interlayers of montmorillonite. This work paves a new way for efficient reduction of NOx from the complex flue gas in practical applications.

Pilot-Scale Studies of WO3/S-Doped g-C3N4 Heterojunction toward Photocatalytic NOx Removal.

Due to the rising concentration of toxic nitrogen oxides (NOx) in the air, effective methods of NOx removal have been extensively studied recently. In the present study, the first developed WO3/S-doped g-C3N4 nanocomposite was synthesized using a facile method to remove NOx in air efficiently. The photocatalytic tests performed in a newly designed continuous-flow photoreactor with an LED array and online monitored NO2 and NO system allowed the investigation of photocatalyst layers at the pilot scale. The WO3/S-doped-g-C3N4 nanocomposite, as well as single components, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller surface area analysis (BET), X-ray fluorescence spectroscopy (XRF), X-ray photoemission spectroscopy method (XPS), UV-vis diffuse reflectance spectroscopy (DR/UV-vis), and photoluminescence spectroscopy with charge carriers' lifetime measurements. All materials exhibited high efficiency in photocatalytic NO2 conversion, and 100% was reached in less than 5 min of illumination under simulated solar light. The effect of process parameters in the experimental setup together with WO3/S-doped g-C3N4 photocatalysts was studied in detail. Finally, the stability of the composite was tested in five subsequent cycles of photocatalytic degradation. The WO3/S-doped g-C3N4 was stable in time and did not undergo deactivation due to the blocking of active sites on the photocatalyst's surface.

Reaction Mechanism for the Removal of NOx by Wet Scrubbing Using Urea Solution: Determination of Main and Side Reaction Paths.

Secondary problems, such as the occurrence of side reactions and the accumulation of by-products, are a major challenge in the application of wet denitrification technology through urea solution. We revealed the formation mechanism of urea nitrate and clarified the main and side reaction paths and key intermediates of denitrification. Urea nitrate would be separated from urea absorption solution only when the concentration product of [urea], [H+] and [NO3-] was greater than 0.87~1.22 mol3/L3. The effects of the urea concentration (5-20%) and reaction temperature (30-70 °C) on the denitrification efficiency could be ignored. Improving the oxidation degree of the flue gas promoted the removal of nitrogen oxides. The alkaline condition was beneficial to the dissolution process, while the acidic condition was beneficial to the reaction process. As a whole, the alkaline condition was the preferred process parameter. The research results could guide the optimization of process conditions in theory, improve the operation efficiency of the denitrification reactor and avoid the occurrence of side reactions.

Ammonium Ion Enhanced V2O5-WO3/TiO2 Catalysts for Selective Catalytic Reduction with Ammonia.

Selective catalytic reduction (SCR) is the most efficient NOX removal technology, and the vanadium-based catalyst is mainly used in SCR technology. The vanadium-based catalyst showed higher NOX removal performance in the high-temperature range but catalytic efficiency decreased at lower temperatures, following exposure to SOX because of the generation of ammonium sulfate on the catalyst surface. To overcome these limitations, we coated an NH4+ layer on a vanadium-based catalyst. After silane coating the V2O5-WO3/TiO2 catalyst by vapor evaporation, the silanized catalyst was heat treated under NH3 gas. By decomposing the silane on the surface, an NH4+ layer was formed on the catalyst surface through a substitution reaction. We observed high NOX removal efficiency over a wide temperature range by coating an NH4+ layer on a vanadium-based catalyst. This layer shows high proton conductivity, which leads to the reduction of vanadium oxides and tungsten oxide; additionally, the NOX removal performance was improved over a wide temperature range. These findings provide a new mothed to develop SCR catalyst with high efficiency at a wide temperature range.

Electrochemical Nitric Oxide Reduction on Metal Surfaces.

Electrocatalytic denitrification is a promising technology for removing NOx species (NO3- , NO2- and NO). For NOx electroreduction (NOx RR), there is a desire for understanding the catalytic parameters that control the product distribution. Here, we elucidate selectivity and activity of catalyst for NOx RR. At low potential we classify metals by the binding of *NO versus *H. Analogous to classifying CO2 reduction by *CO vs. *H, Cu is able to bind *NO while not binding *H giving rise to a selective NH3 formation. Besides being selective, Cu is active for the reaction found by an activity-volcano. For metals that does not bind NO the reaction stops at NO, similar to CO2 -to-CO. At potential above 0.3 V vs. RHE, we speculate a low barrier for N coupling with NO causing N2 O formation. The work provides a clear strategy for selectivity and aims to inspire future research on NOx RR.

Yellow phosphorus and Potash for SOX and NOX removal.

Flue gases emitted from the industries and other emission sources are considered the main atmospheric issues. The main Flue gases emitted are sulfur oxides SOX and Nitrogen oxides NOX. The study was about methods of removing SOX and NOX from emitted gases and the possibility of deriving useful byproducts. The process for removing was investigated using different absorbers, process conditions, and phosphorus allotropes. The yellow phosphorus (P4) was applied for removal accompanied by Potash. The simultaneous removal achieved higher removing efficiency for SOX than NOX. Yellow phosphorus emulsion proved to be one of the effective SOX and NOX removal techniques. Byproducts produced from SOX and NOX proved to contain the complete fertiliser Nitrogen Phosphorus Potassium NPK. The obtained results showed that several useful byproducts can be derived from SOX and NOX removal process.

Evaluation of NOx removal from flue gas and Fe(II)EDTA regeneration using a novel BTF-ABR integrated system.

A promising process is under development for the removal of NOx and regeneration of Fe(II)EDTA in a novel biotrickling filter-anaerobic baffled reactor (BTF-ABR) integrated system at 50 ± 0.5 â„ƒ. In this work, we investigated the NOx removal capacity of a BTF under different O2 concentrations (7.0 vol%, 5.25 vol% and 3.5 vol%), and tested the effect of an ABR on NOx removal and regeneration of Fe(II)EDTA. The results showed that the NOx removal capacity was significantly increased with the O2 concentration reduced from 7.0% to 3.5%. The microoxygen environment produced by the BTF-ABR integrated system was more conducive to the removal of NOx and regeneration of Fe(II)EDTA compared with that in the BTF. Real-time polymerase chain reaction (PCR) analysis showed that the coordinated expression of denitrification genes was the major reason for no N2O emission, along with no nitrate and nitrite accumulation. The 16S rRNA gene amplicon sequencing analysis showed that the cooperation of denitrifying bacteria (Klebsiella, Petrimonas, Rhodococcus and Ochrobactium) and iron-reducing bacteria (Klebsiella, Geobacter and Petrimonas) in the system was the key to the stable and efficient removal of NOx and the regeneration of Fe(II)EDTA simultaneously.

Effect of Catalyst Crystallinity on V-Based Selective Catalytic Reduction with Ammonia.

In this study, we synthesized V2O5-WO3/TiO2 catalysts with different crystallinities via one-sided and isotropic heating methods. We then investigated the effects of the catalysts' crystallinity on their acidity, surface species, and catalytic performance through various analysis techniques and a fixed-bed reactor experiment. The isotropic heating method produced crystalline V2O5 and WO3, increasing the availability of both Brønsted and Lewis acid sites, while the one-sided method produced amorphous V2O5 and WO3. The crystalline structure of the two species significantly enhanced NO2 formation, causing more rapid selective catalytic reduction (SCR) reactions and greater catalyst reducibility for NOX decomposition. This improved NOX removal efficiency and N2 selectivity for a wider temperature range of 200 °C-450 °C. Additionally, the synthesized, crystalline catalysts exhibited good resistance to SO2, which is common in industrial flue gases. Through the results reported herein, this study may contribute to future studies on SCR catalysts and other catalyst systems.