NOx Removal Research Articles

Preparation and performance of aluminosilicate fibrous porous ceramics-supported catalyst for NOx removal

In this study, we report a new aluminosilicate fibrous porous ceramics-supported catalyst for the removal of [Formula: see text]. The influence of raw materials and sintering process on the structure and properties of aluminosilicate fibrous porous ceramics was studied. The composition and the structure of the catalysts were characterized by XRF, XRD, SEM-EDS, and XPS analysis, and the experiments of denitrification were performed to determine the influence of the porous structure and the calcination process on the denitrification efficiency. The results indicated that the glass fibers facilitate the formation of a uniform porous network structure within aluminosilicate fibrous porous ceramics, and that the optimal sintering temperature is 1000∘C. Under the condition, the loaded catalysts were highly dispersed on the surface of aluminosilicate fibrous porous ceramics, which possessed high porosity and large average pore sizes. The aluminosilicate fibrous porous ceramics-supported catalyst exhibited excellent denitrification efficiency and catalytic stability, which is expected to be used for the treatment of [Formula: see text] in flue gas.

Promotion effect of Ce and Ta co-doping on the NH3-SCR performance over V2O5/TiO2 catalyst

NH3-SCR (SCR: Selective catalytic reduction) is an effective technology for the de-NOx process from both mobile and stationary pollution sources, and the most commonly used catalysts are the vanadia-based catalysts. An innovative V2O5-CeO2/TaTiOx catalyst for NOx removal was prepared in this study. The influences of Ce and Ta in the V2O5-CeO2/TaTiOx catalyst on the SCR performance and physicochemical properties were investigated. The V2O5-CeO2/TaTiOx catalyst not only exhibited excellent SCR activity in a wide temperature window, but also presented strong resistance to H2O and SO2 at 275 ℃. A series of characterization methods was used to study the catalysts, including H2-temperature programmed reduction, X-ray photoelectron spectroscopy, NH3-temperature programmed desorption, etc. It was discovered that a synergistic effect existed between Ce and Ta species. The introduction of Ce and Ta enlarged the specific surface area, increased the amount of acid sites and the ratio of Ce3+, (V3++V4+) and Oα, and strengthened the redox capability which were related to synergistic effect between Ce and Ta species, significantly improving the NH3-SCR activity.

Establishing Z-scheme Bi2WO6/g-C3N4 interfaces toward efficient photocatalytic performance of NOx under visible light

NOx gas is released from automobile emissions and fossil fuel combustion. The photocatalytic method was applied to address environmental issues, notably NOx air pollution because of environmentally friendly, low cost, and utilized solar light irradiation. In this work, a Z-scheme Bi2WO6/g-C3N4 heterojunction photocatalyst was successfully synthesized by a hydrothermal method at 180 °C for 12 h. Combining g-C3N4 with Bi2WO6 promoted two oxidation (over Bi2WO6) and reduction (over g-C3N4) sites, enhancing the photocatalytic activity of the g-C3N4 single-component system. The sample contains 20 wt% of Bi2WO6, becoming the best excellent photocatalytic activity at approximately 43.45% in 30 minutes of visible light irradiation. In addition, the photogenerated electron (e−) and hole (h+) were determined as primary agents. The high stability of Bi2WO6/g-C3N4 photocatalysts was demonstrated by little change in photocatalytic performance over five cycles of photocatalytic measurements. The NOx removal mechanism and the intermediate generation were proposed to understand the reaction process better.

NOx degradation by cement mortar containing B-TiO2/MgAl-CLDH under visible light: Experimental and modeling

In this paper, an advanced photocatalyst, B-TiO2/MgAl-CLDH, was synthesized and applied in cement mortar. The photocatalytic NOx degradation ability of cement mortar containing B-TiO2/MgAl-CLDH under different initial NOx concentrations and flow rates was investigated. The results show that B-TiO2/MgAl-CLDH has stronger visible light absorption, lower recombination rate of electron-hole pairs and narrower optical band gap than commercial nano-TiO2 (P25), resulting in enhanced NOx removal efficiency. Specifically, the maximum NOx degradation ratio of B-TiO2/MgAl-CLDH is 23.4% within 30 min, which is about 5 times that of P25. For photocatalytic mortar, the initial NOx concentration (from 1.0 ppm to 2.0 ppm) and flow rate (from 1 L/min to 3 L/min) were positively correlated with NOx removal amount, while negatively correlated with NOx removal ratio. Based on the internal molecular diffusion properties of NOx, Langmuir-Hinshelwood and the power law kinetic models were used to predict the NOx degradation ability of photocatalytic mortar. The modeling of NOx degradation process presents a reliable prediction of the NOx removal ability of photocatalytic mortar, serving as a valuable tool for assessing the mortar’s NOx removal effectiveness for policymakers and engineers.

A new integrated approach for NOx removal by absorption and anaerobic digestion of wasted activated sludge

Urban waste treatment and utilization are facing mounting demands, necessitating cities to evolve their infrastructure towards more efficient, affordable, and sustainable solutions. Achieving sustainable waste management in urban ecosystems is an intricate endeavor that spans multiple disciplines. Nitrogen oxides (NOx) from waste combustion and sludge from wastewater plant exemplify challenging urban secondary wastes with both environmental and energy implications. This study introduces a novel method for NOx removal, harnessing an integrated system of absorption and biological reduction through waste activated sludge (WAS) anaerobic digestion. Findings reveal that microbial adsorption amplified NO removal efficiency by an impressive 125.8%. A significant correlation emerged between pH, temperature, and NOx removal efficiency, with greatest removal (78.9%) occurring at pH 6.5 and 30 °C. On the other hand, concentrations of NOx and O2 exerted little influence on NOx removal. The presence of SO2 significantly enhanced the NOx removal efficiency, suggesting potential for concurrent SO2 and NOx extraction. The NOx removal mechanism was elucidated as a two-step reaction pathway comprising NOx absorption and subsequent conversion. This process integrates both the chemical absorption of NOx and microbial denitrification. Concurrently, nitrite accumulation was found to boost the hydrolysis rate and the methanogenic potential of anaerobic digestion. This innovative NOx removal strategy, which is devoid of chemicals, produces no secondary waste, and facilitates energy recovery, holds substantial promise for future applications in urban waste-to-energy initiatives.

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.

A Novel Activated Vanadium Extraction Tailing Catalyst for NOX Removal in NH3-SCR

A Novel Activated Vanadium Extraction Tailing Catalyst for NOX Removal in NH3-SCR

Tunable Highly Dispersed Nia-xMnxAlOy Catalysts Derived from Layered Double Oxide for Low Temperature NOx Removal

Tunable Highly Dispersed Nia-xMnxAlOy Catalysts Derived from Layered Double Oxide for Low Temperature NOx Removal

Advanced nitrogen removal from municipal wastewater by autotrophy-heterotrophy coupled anammox system in a novel simultaneous microaerobic/limited-oxygen SBR: Interspecific correlation network

Nowadays, autotrophic nitrogen removal of mainstream municipal wastewater by anammox is highly promising. However, due to the lack of a long-term stable nitrite-oxidizing bacteria (NOB) inhibition strategy, the accumulation of NO3−-N byproducts severely affects the nitrogen removal efficiency (NRE). In this study, a simultaneous autotrophy-heterotrophy coupled anammox system was developed in a microaerobic/oxygen-limited SBR through the co-induction of the regulation of aeration intensity and limited organics to achieve the optimization of the mainstream Partial nitrification-anammox (PN/A) processes. The nitrogen removal system constructed by anammox and denitrification achieved the high NRE of 90.77 ± 1.82 %. Under the autotrophic-heterotrophic multiple induction of nitrite supply (PN, partial denitrification and endogenous partial denitrification), the contribution of the nitrogen removal by anammox increased to 57.93 %. The high-throughput sequencing analysis showed that the relative abundance of AnAOB increased from 0.40 % to 0.67 %. In-situ tests assay further demonstrated that the realization of multi-channel nitrite supply facilitated the enrichment of anammox bacteria (AnAOB). The endogenous denitrifying bacterial genus Candidatus (Ca.) Competibacter was significantly enriched in the system (7.98 %, P ≤ 0.001), which enhanced the deep removal of NOX−-N and organics. Correlation network analysis indicated that closer and more balanced interspecies interactions were the key to the high efficiency and stability of the autotrophy-heterotrophy coupled anammox system. Based on the nitrite recirculation and denitrification performance, the simultaneous autotrophy-heterotrophy coupled anammox system established by the novel SBR provides a potential strategy for mainstream anammox applications.

Simultaneous abatement of NOx and CO using tandem catalyst system via reactant- and energy- Co-promoting effect

Although selective catalytic reduction (SCR) of NOx with NH3, CO catalytic oxidation, and selective catalytic reduction of NOx with CO have been used to control NOx and CO from mobile and industrial sources, the simultaneous removal of NOx and CO at low temperatures remains a great challenge due to the specificity of each catalytic reaction. Here, we achieve the simultaneous abatement of NOx and CO at low temperatures by skillfully utilizing a tandem catalyst system (e.g., Cu1/MnO2 and Ce-W/TiO2 as oxidation-SCR tandem catalysts). Through a series of catalytic activity evaluations and structural characterizations, we report that NO can promote the oxidation of CO due to the easier decomposition of the intermediates formed by the combination of adsorbed NO species and gaseous CO, and the faster supply of O* required for CO oxidation in CO+O2+NO2/NO atmosphere. Meanwhile, the heat released from the oxidation of CO not only accelerates the oxidation of NO in the oxidation system, but also contributes to the high reaction rate of subsequent fast NH3-SCR. Eventually, 100 % conversion of CO and 80 % conversion of NO appear at 128 and 186 °C, respectively. This work provides a new strategy for the simultaneous and efficient removal of CO and NOx at lower temperatures.

Pilot-scale Validation of the Modeling of NOx Reactive Absorption Process Using Aqueous Solutions Containing Nitric Acid and Hydrogen Peroxide

NOx are harmful pollutants emitted by many industries and must be removed before the gases are released into the atmosphere. Among the various techniques used for NOx removal, reactive absorption by hydrogen peroxide in a packed column has the advantage of being able to transform NOx into nitric acid which can be recycled and reused in the plants. This work aimed at modeling the NOx absorption by means of aqueous solutions of hydrogen peroxide and nitric acid, applied in a packed column operating under different representative conditions. The model established using the Aspen software considers the equilibrium and the kinetics of the reactions taking place both in the gas phase and in the liquid phase as well as the thermodynamic properties of the chemical (molecular and ionic) components estimated using the Electrolyte NRTL model. It allows predicting NOx absorption performances in terms of efficiency and selectivity. The model was validated by comparing simulation results with experimental ones obtained in a pilot-scale absorption column and published previously. The predicted values are in satisfactory agreement with the experimental data showing a deviation between 5 and 8%. Therefore, the model developed in this work could be advantageously used to design industrial-scale reactive NOx absorption columns.

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

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

Catalytic Oxidation of Chlorobenzene over HSiW/CeO2 as a Co-Benefit of NOx Reduction: Remarkable Inhibition of Chlorobenzene Oxidation by NH3.

There is an urgent need to develop novel and high-performance catalysts for chlorinated volatile organic compound oxidation as a co-benefit of NOx. In this work, HSiW/CeO2 was used for chlorobenzene (CB) oxidation as a co-benefit of NOx reduction and the inhibition mechanism of NH3 was explored. CB oxidation over HSiW/CeO2 primarily followed the Mars-van-Krevelen mechanism and the Eley-Rideal mechanism, and the CB oxidation rate was influenced by the concentrations of surface adsorbed CB, Ce4+ ions, lattice oxygen species, gaseous CB, and surface adsorbed oxygen species. NH3 not only strongly inhibited CB adsorption onto HSiW/CeO2, but also noticeably decreased the amount of lattice oxygen species; hence, NH3 had a detrimental effect on the Mars-van-Krevelen mechanism. Meanwhile, NH3 caused a decrease in the amount of oxygen species adsorbed on HSiW/CeO2, which hindered the Eley-Rideal mechanism of CB oxidation. Hence, NH3 significantly hindered CB oxidation over HSiW/CeO2. This suggests that the removal of NOx and CB over this catalyst operated more like a two-stage process rather than a synergistic one. Therefore, to achieve simultaneous NOx and CB removal, it would be more meaningful to focus on improving the performances of HSiW/CeO2 for NOx reduction and CB oxidation separately.

Modulation of acidic and redox properties of Mn-based catalysts by Co doping: Application to the synergistic removal of NOx and chlorinated organics

The synergistic catalytic removal of nitrogen oxides (NOx) and chlorinated volatile organic compounds (CVOCs) mainly depends on the redox properties (RP) and surface acidity (SA) of the catalyst. Striking the right balance between these factors is the key to ensuring both the high efficacy of synergistic removal and the exceptional selectivity of N2 and CO2. This study aims to regulate the RP and SA of catalysts by adjusting the Co/Mn ratio, with the goal of exploring their impact on NOx/chlorobenzene (CB) synergistic removal performance. The results showed that after Co doping, some Co entered the Mn cells to form MnCo2O4 which together with the residual Co and Mn regulated the PR and SA of the catalyst. The RP of the catalysts increased with the increase of Co doping, and the SA showed a tendency to increase and then decrease. When the Co doping amount was 40 %, the RP and SA reached a good balance, which made the Mn6Co4Ox catalyst show outstanding catalytic activity. The NOx conversion was higher than 90 % in the temperature range of 104–275 °C, and 90 % CB conversion was achieved at 181 °C. These observations are anticipated to serve as a valuable reference for practical applications of NOx/CB synergistic removal.

Improvement of NH3-SCR Performance by Exposing Different Active Components in a VCeMn/Ti Catalytic System

The physicochemical properties of active components play a key role in enhancing catalytic performance. In multi-component catalysts, different components offer a wide range of structural possibilities and catalytic potential. However, determining the role of specific components in enhancing efficiency may be blurry. This study synthetized a range of catalysts with various metal compositions on their external surfaces to investigate their catalytic activity on NH3-SCR. The V/CeMn/Ti catalysts exhibited exceptional catalytic efficiency and strong tolerance to SO2 during the SCR process. In the system, Mn and Ce facilitated electron transfer during the catalytic removal of NOx. As an assisting agent, increased the number of active species and acidic sites, playing a crucial role in oxidizing NO to NO2 and facilitating the denitrogenation reaction process at low temperatures. Further studies showed that the three ingredients exhibited unique adsorbent behaviors on the reacting gases, which provided different catalytic possibilities. This work modeled the particular catalysis of V and Ce (Mn) species, respectively, and offers experimental instruction for improving the activity and excellent tolerance to SO2 by controlling active ingredients.

Heteroatoms doped iron oxide-based catalyst prepared from zinc slag for efficient selective catalytic reduction of NOx with NH3

Excessive emissions of nitrogen oxides from flue gas have imposed various detrimental impacts on environment, and the development of deNOx catalysts with low-cost and high performance is an urgent requirement. Iron oxide-based material has been explored for promising deNOx catalysts. However, the unsatisfactory low-temperature activity limits their practical applications. In this study, a series of excellent low-temperature denitrification catalysts (Ha-FeOx/yZS) were prepared by acid treatment of zinc slag, and the mass ratios of Fe to impure ions was regulated by adjusting the acid concentrations. Ha-FeOx/yZS showed high denitrification performance (> 90%) in the range of 180–300 °C, and the optimal NO conversion and N2 selectivity were higher than 95% at 250 °C. Among them, the Ha-FeOx/2ZS synthesized with 2 mol/L HNO3 exhibited the widest temperature window (175–350 °C). The excellent denitrification performance of Ha-FeOx/yZS was mainly attributed to the strong interaction between Fe and impurity ions to inhibit the growth of crystals, making Ha-FeOx/yZS with amorphous structure, nice fine particles, large specific surface area, more surface acid sites and high chemisorbed oxygen. The in-situ DRIFT experiments confirmed that the SCR reaction on the Ha-FeOx/yZS followed both Langmuir-Hinshelwood (L-H) mechanism and Eley-Rideal (E-R) mechanism. The present work proposed a high value-added method for the preparation of cost-effective catalysts from zinc slag, which showed a promising application prospect in NOx removal by selective catalytic reduction with ammonia.

Synergistic Removal of NOx and VOCs from Flue Gas on Mn-Based Catalysts

Synergistic Removal of NOx and VOCs from Flue Gas on Mn-Based Catalysts

Enhancing the Precipitant and Calcination Process of Manganese-Iron Oxide Catalyst for Low-Temperature NH3-SCR

Catalysts containing manganese as the primary active component have emerged as promising candidates for ultra-low temperature NH3-SCR applications. To enhance the catalytic activity of these catalysts, a series of Mn-FeOX catalysts were prepared using the co-precipitation method. This study focuses on investigating the appropriate calcination process for catalyst preparation using different precipitants, namely NaOH, NH3-H2O and Na2CO3. The results revealed that catalysts prepared with Na2CO3 as the preferred precipitant and calcined at 330∘C exhibited exceptional NOx removal efficiency, exceeding 90% at a temperature of 60∘C and GHSV [Formula: see text] 30,000[Formula: see text]h[Formula: see text], which demonstrated this catalyst’s remarkable low-temperature reduction capability. Detailed characterization demonstrated that the MnOX catalysts synthesized through this process possessed an amorphous structure, superior pore structure and the highest Fe[Formula: see text] content. These findings offer valuable insights for optimizing the preparation conditions of Mn-FeOX catalysts in ultra-low temperature denitrification applications.

Effect of Oxidants in the Utilization of Polysulfone Hollow Fiber Membrane Module as Bubble Reactor for Simultaneously Removal of NOx and SO2

Effect of Oxidants in the Utilization of Polysulfone Hollow Fiber Membrane Module as Bubble Reactor for Simultaneously Removal of NOx and SO2

The simultaneous elimination of NOx and VOCs over industrial V-based catalytic filter: Reaction behaviors and catalyst structural evolutions

The effective elimination of multiple pollutants (e.g., SOx, NOx, VOCs, dusts) in a simple unit is a long-term goal in the field of flue gas purification. In this work, the simultaneous removal of NOx and toluene was explored over the industrial V2O5-MoO3/TiO2 catalytic filter. The catalytic evaluations show that two reactions may share the same type of active sites, and observed adverse interaction effects at low temperatures, which significantly weakened as the temperature increased. Water vapor plays an amazing role with almost 100% removal efficiency of both NOx and VOCs for long-term test under harsh conditions at 350 ℃. Multiple structural characterizations confirmed the great structure stability. Especially, the catalyst components can be sulfated by SO2 and become more dispersed and uniform owing to the formation of solid solution phase, which further improves the removal performance. Moreover, the mechanism over the dynamically balanced V5+/4+/3+-SO3/42- sites was proposed, and the main reaction pathway of toluene oxidation follows the route of benzaldehyde → benzoic acid → maleic anhydride → CO2. Particularly, the In-situ DFIRTS results further confirm the above reaction/interaction effects and sulfur/steam-resistance mechanisms during the simultaneous removal of both NOx and VOCs. The excellent sulfur/steam-resistance performance and special structure features of the industrial V-based catalytic filter foreshadow the promising industrial application prospect for the effective purification of flue gas containing VOCs.