NOx Removal Performance Research Articles

A novel solar-aided NOx removal system in peaking power plants

Solar–coal hybrid power generation achieves the production of efficient, clean, and low-carbon electricity. The association between solar heat and selective catalytic reduction NOx removal (SCR de-NOx) can lead to the development of a novel solar-aided NOx removal system for peaking power plants. In this study, a novel system was proposed, in which large amount of flat-plate and small amount of trough solar energies were integrated to optimise the SCR de-NOx and energy utilisation in the boiler tail. Thermodynamic, NOx removal, and economic analyses were performed. For a typical peaking unit, the proposed system produced 14.6 MWe of solar-generated electric power and exhibited a high solar-to-electricity efficiency of 30.15 %. The integrated solar heat significantly increased the SCR de-NOx temperature and NOx removal efficiency. Based on its outstanding solar conversion performance, the proposed system achieved a net annual benefit (NAB) of 24.01 million Chinese yuan (CNY) and maintained a low cost of solar-generated electricity (COEs) of 0.56 CNY/kWh. Based on cascade utilisation of solar thermal energy, the proposed system achieved high performance under all loads and significantly improved the NOx removal performance under low and medium loads, especially for peaking power plants.

Bifunctional Photocatalysis Toward Efficient NOx Removal Performance and Water Splitting Activity: A Case of TiO2/g-C3N4

Bifunctional Photocatalysis Toward Efficient NOx Removal Performance and Water Splitting Activity: A Case of TiO2/g-C3N4

Distinct effect of preparation methods on reaction efficiency of Mn-Ce/Al2O3 catalysts in low-temperature NH3-SCR

In this study, a series of Mn-Ce/Al2O3 catalysts was prepared by different methods of deposition-precipitation (MnCeAl-DP), impregnation (MnCeAl-IM) and citric acid (MnCeAl-CA), and the distinct effect of preparation methods on NOx removal performance at low temperature was explored. Results show that MnCeAl-DP exhibits not only the best activity but also the highest resistance against SO2/H2O. With the assistance of comprehensive characterizations from scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), NH3-temperature programmed desorption (NH3-TPD), and X-ray photoelectron spectroscopy (XPS), it is revealed that the MnCeAl-DP sample owns admired features of large surface area and pore volume, enriched Mn4+ and chemisorbed oxygen species originating from enhanced interaction between MnOx and CeO2, as well as improved adsorption capacity to NH3 and NO. All these factors contribute to activity enhancement. Further in-situ DRIFTS studies reveal that the improvement of NH3-SCR performance over MnCeAl-DP is related to the formation of abundant nitrate species, which is beneficial to the “NH4NO3” reaction pathway and thus enhances low-temperature activity.

Super-strong adhesion of Fe-ZSM5 catalyst on metal substrate using ceramic powder spray coating for selective catalytic reduction of NOx with NH3

Fe-ZSM5 catalyst coating on stainless steel foil sheets for NOx removal NH3-SCR reaction was prepared using special ceramic powder spray coating (PSC) and conventional wash-coating methods. Super-strong catalyst adhesion on the substrates was obtained using PSC without any binder addition. The conventional slurry coating samples showed much lower adhesion strength than the PSC samples for all catalyst coating layer thicknesses. Honeycomb-shaped monolith catalyst prepared using PSC showed high NOx removal performance comparable to the wash-coated catalyst for both standard and fast NH3-SCR reactions. The PSC catalysts having strong adhesion to metal substrates with good catalytic performance can be a promising candidate for exhaust gas after-treatment exposed to harsh mechanical conditions such as pre-turbocharger applications under very high flow rates of exhaust gas and engine vibration. The excellent catalyst adhesion property can highly enhance long-term mechanical stability of monolith catalysts.

Influence of catalyst composition on NOx storage and reduction characteristics of Ag catalyst supported on MgO-doped alumina

A novel material (Ag/MgO-Al2O3) for storage of NOx under cold-start conditions and its reduction in the high-temperature stabilized phase is synthesized, and the influence of MgO and Ag loading on its NOx removal performance is investigated. A high MgO loading increases the NOx storage capacity but also decreases the stability of adsorbed NOx. Moreover, it decreases the adsorption rate at early times since NOx spillover is inhibited. The catalysts with the lowest Ag and MgO loading exhibit the highest NO oxidation activity. The amount of NOx storage increases with a decrease in Ag loading and is attributed to enhanced spillover of NOx to the support. Increasing the Ag and MgO content leads to an enhanced NH3 and C3H6 oxidation activity, which is explained by the presence of Ag metallic clusters. Further, the NH3-SCR and C3H6-SCR activity decrease with Ag and MgO loading. Thus, the catalyst composition can be tuned to obtain the desired activity for various oxidation and reduction reactions.

Removal of NOx from flue gas using different agricultural wastes as carbon sources: Performance and microbial communities

To solve the problem of high cost caused by continuous supply of carbon sources to industrial flue gas denitrification, this study investigated the feasibility of agricultural wastes as carbon sources. In this study, the carbon/nitrogen release from different agricultural wastes was compared by short-effect leaching tests, and the results showed that banana peel and bagasse had a higher carbon release capacity, with chemical oxygen demand (COD) of 1850.58 mg/L and 1022.46 mg/L, respectively. Subsequently, the NOx removal performance of a biotrickling filter-anaerobic baffled reactor (BTF-ABR) integrated system with glucose, banana peel leaching solution, and bagasse leaching solution as carbon sources was investigated under thermophilic (50 ± 3 ℃) micro-oxygen (3% O2) condition. The findings revealed that the maximum NOx removal efficiency from all the carbon sources reached more than 97%, with almost no NO3--N and NO2--N accumulation during the entire process. However, using agricultural wastes as carbon sources resulted in higher NH4+-N accumulation than glucose. Illumina high-throughput sequencing indicated that Actinobacteriota, Patescibacteria, and Firmicutes were the dominant members. In addition, bacterial function analysis showed that agricultural wastes as carbon sources had more abundant carbon metabolism function. These results provide new insights into using agricultural wastes as carbon sources for removing NOx from flue gas.

Simultaneous polarization engineering and selectivity regulation achieved using polymeric carbon nitride for promoting NOx photo-oxidation

Sluggish charge kinetics and high NO2 selectivity are still the bottleneck issues that restrict the efficient NOx photo-oxidation and removal using polymeric carbon nitride (PCN). Herein, approximately 2 times higher NOx-removal performance and almost complete NO2-inhibition can be synchronously achieved by maximizing the versatility of the coupled hydroxyl groups. The experimental and computational results reveal the roles of different types of coupled-hydroxyl groups in PCN in the enhancement of photocatalytic activity in terms of NOx removal and product selectivity. The spontaneous polarization effect caused by the introduction of the structural hydroxyl into the C6N7 framework accounts for the improved separation efficiency of the carriers. The mediated role of product selectivity was attributed to the process of surface hydroxyl grafting. Different conversion pathways for NOx photo-oxidation over pristine and hydroxylated-PCN were proposed. These findings provide molecular-level insight into the multiple roles of the coupled hydroxyls and can help design efficient NOx-removal photocatalysts.

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.

Boosting the catalytic performance of Cu-SAPO-34 in NOx removal via hydrothermal treatment

Phosphate ions promoted Cu-SAPO-34 (P-Cu-SAPO-34) were prepared using bulk CuO particles as Cu2+ precursor by a solid-state ion exchange technique for the selective catalytic reduction of NOx with NH3 (NH3-SCR). The effects of high temperature (H-T) hydrothermal aging on the NOx removal (de-NOx) performance of Cu-SAPO-34 with and without phosphate ions were systematically investigated at atomic level. The results displayed that both Cu-SAPO-34 and P-Cu-SAPO-34 presented relatively poor NOx removal activity with a low conversion (< 30%) at 250-500°C. However, after H-T hydrothermal treatment (800°C for 10 hr at 10% H2O), these two samples showed significantly satisfied NOx elimination performance with a quite high conversion (70%-90%) at 250-500°C. Additionally, phosphate ions decoration can further enhance the catalytic performance of Cu-SAPO-34 after hydrothermal treatment (Cu-SAPO-34H). The textural properties, morphologies, structural feature, acidity, redox characteristic, and surface-active species of the fresh and hydrothermally aged samples were analyzed using various characterization methods. The systematical characterization results revealed that increases of 28% of the isolated Cu2+ active species (Cu2+-2Z, Cu (OH)+-Z) mainly from bulk CuO and 50% of the Brønsted acid sites, the high dispersion of isolated Cu2+ active component as well as the Brønsted acid sites were mainly responsible for the accepted catalytic activity of these two hydrothermally aged samples, especially for P-Cu-SAPO-34H.

Photocatalytic NOx degradation performance of TiO2-nanofiber-spray-coated foam composite according to saturated conditions

We investigated the photocatalytic NOx degradation performance of foam composites using various TiO2 application methods and saturated conditions. TiO2 powder (TP) and TiO2 nanofiber (TF) were used. TF was fabricated using polyvinyl pyrrolidone, ethanol, acetylacetone, and titanium 4-isopropoxide via electrospinning. TF mixed with an inorganic coating material was sprayed on cementitious materials once. The NOx degradation performance of the TF-spray-coated specimen was higher than that of specimens with TP. The NOx removal performance of the form composite decreased with increasing specimen water content. The TF-spray-coated foam composite with activated carbon yielded the highest NOx removal performance.

Superior CuMgFe mixed oxide catalysts engineered by tuning the redox cycle for enhancing NOx removal performance

In this work, the CuMgFe layered double hydroxides (CuMgFe-LDH) with different Cu/Mg/Fe molar ratios were fabricated, and derived catalysts (CuMgFe-LDO) were tested in the removal of NOx by selective catalytic reduction with NH3 (NH3-SCR). Cu/Mg/Fe molar ratios of LDH precursors were systematically identified to achieve optimal catalytic performance. The results showed that the denitration performances of the as-acquired catalysts were vulnerable to the Cu/Mg/Fe molar ratios. The Cu0.5Mg2.5Fe1-LDO catalyst displayed the superior activity (the NOx conversion was 80% at the range of 180–250 °C) and SO2 resistance (the NOx conversion was decreased by 18% in 8 h when 100 ppm SO2 was introduced at 210 °C). Multiple characterization techniques revealed that superior catalytic performance of Cu0.5Mg2.5Fe1-LDO could be attributed to the well dispersed active ingredients and the electron transfer between copper and iron species (Cu++Fe3+↔Fe2++Cu2+), consequently resulting in higher specific surface area, enhanced acidity, increased redox capacity, and improved cycle reactions of Cu++Fe3+↔Fe2++Cu2+. This work provides a fundamental understanding on Cu++Fe3+↔Fe2++Cu2+ synergistic effect of NH3-SCR and expand the applications of LDH in the field of low-temperature de-NOx.

Evaluation of NOx removal performance of foam composites with titanium dioxide and active carbon

• Activated carbon (AC) and titanium dioxide (TiO 2 ) foam composites were fabricated. • The NO X removal performances and micropore structures of the composites were studied. • The TiO 2 and AC replacement ratios and specimen thickness and density were varied. • NO X removal improved with increasing TiO 2 replacement but decreased with density. • The NO X removal was the highest with 15% AC replacement and varied with UV intensity. In this study, the nitrogen oxide (NO X ) removal performances and micropore structures of foam composites with activated carbon (AC) and titanium dioxide (TiO 2 ) powder were investigated. AC was used to increase the NO X removal efficiency through TiO 2 powder by increasing the specific surface areas of the foam composites. The foam composites were fabricated with the replacement ratios of TiO 2 powder and AC, as well as the specimen thickness and density, as variables. The NO X removal performance was evaluated according to the test method presented in ISO-22197. The specific surface area of the foam composite tended to increase with increasing AC content but decreased by AC content more than 15 %. The NO X removal efficiency was the highest when the AC replacement ratio was 15 %. The NO X removal efficiency improved as the replacement ratio of TiO 2 powder increased but decreased as the density of the foam composite increased. The NO X removal efficiency was the highest when the thickness of the specimen was 20 mm and was greatly affected by the ultraviolet light intensity.

Photocatalytic NOx Removal in Bismuth-Oxyhalide (BiOX, X = I, Cl) Cement-Based Materials Exposed to Outdoor Conditions

Cement-based materials modified with 3D BiOX (X = I, Cl) microspheres at different percentages (1, 5 and 10% by weight of the cement binder) were prepared to investigate the durability of the photocatalytic NOx removal under outdoor conditions. Weathering—corresponding to a period of 13 months outdoors—was studied in terms of NO removal efficiency under visible and UVA light irradiation for BiOI and BiOCl mortars, respectively. Following this period, the samples were protected from the environment for four years, and NOx removal and selectivity to nitrates were assessed. BiOI and BiOCl mortar samples were initially photocatalytically active; NOx removal performance increased as BiOX content increased. There was good photocatalyst dispersion, and compressive strength was not significantly impacted. The BiOI mortars had nearly completely lost their activity after 5 years from casting, whereas mortars containing 10% BiOCl had maintained about 7% of initial performance. The results suggest that mortar deactivation is due to surface dirt and nitrates accumulation from NOx oxidation on the surface rather than carbonation. An internal self-deactivation mechanism that affects BiOI in mortar matrix has also been postulated.

CFD modeling for NOx absorption accompanying with SO2 in wet flue gas desulfurization scrubber based on gas-phase ozone oxidation

NOx removal performance accompanying with SO2 is investigated in a two-step process containing O3 pre-oxidation of NO and NOx post-absorption in the scrubber of wet flue gas desulfurization (WFGD) unit. Based on EulerianLagrangian framework, a comprehensive CFD model is established to describe the reactions of NO2 and N2O5 with S(IV) in droplets coupled with NOx transfer process and hydrodynamics in the scrubber. Taking the WFGD scrubber of 330 MW coal-fired power unit as case study, the results indicate NOx absorption efficiency in scrubber is increased by increasing O3/NO molar ratio from 1.0 to 2.2 and decreasing reaction temperature from 423 K to 363 K in O3 pre-oxidation process. The obtained highest removal efficiency is 85.79% for pH of 5.5 or 96.32% for pH of 9.0 in droplets. NO2 absorption is much slower than N2O5 and more sensitive to chemical compositions in droplets or hydrodynamics in scrubber. The overall mass transfer coefficient (KG) for NO2 is mainly determined by pH and S(IV) concentration in droplets, while the specific interfacial area (a) is largely influenced by gasdroplet hydrodynamics in scrubber. Finally, a correlation is proposed to predict the volumetric mass transfer coefficient (KGa) for NO2 absorption accompanying with SO2 in WFGD scrubber.

A novel integrated rotary reactor for NOx reduction by CO and air preheating: NOx removal performance and mechanism

AbstractA novel integrated rotary reactor for NOx reduction by CO and air preheating (iNA reactor) was proposed. NOx removal performance was investigated in a fixed‐bed reactor, which was used to simulate the working conditions change in the iNA reactor. Lab‐synthesized Cu/FeCeOx were used as the catalyst. Two different modes were tested with the iNA reactor: short cycles and long cycles. Excellent NOx removal efficiencies of over 95% and 90% for short cycles and long cycles, respectively, were observed in the iNA reactor. Moreover, compared with the constant‐temperature rotary reactor, better H2O and SO2 resistances were also found in the iNA reactor. The reaction mechanism was proposed based on in situ diffuse reflectance infrared Fourier transform study. In the iNA process, NOx was stored as nitrates in the adsorption zone, and then decomposed rapidly by both high temperatures and CO, leading to the deep catalyst regeneration. Therefore, temperature swinging and the feed of CO were key to having high iNA reactor performance for NOx removal.

Exploration of effects of CO2 exposure on the NOx-removal performance of TiO2-incorporated Portland cement evaluated via microstructural and morphological investigation

Weathering carbonation is a crucial degradation phenomenon to Portland cement, potentially posing deleterious effects on the photocatalytic performance of cement during its service life. Therefore, the effects of CO2 exposure on the NOx-removal performance of TiO2-incorporated Portland cement were explored through microstructural and morphological investigations in this study. TiO2 was incorporated into cement samples at the levels of 0, 0.5, 1, 3, and 5% according to the mass of the cement. After 28 days of curing, the TiO2-incorporated samples were exposed to a 3% atmospheric CO2 concentration for an additional 28 days to simulate the weathering carbonation, investigating the microstructural and morphological alteration by means of the XRD, TG/DTG, compressive strength, SEM/EDS, and water contact angle test. Comparisons according to the content of TiO2 showed that the incorporation of TiO2 has no significant effect on the hydration process of the samples and that it enhanced the early strength development, whereas it does not ensure any notable strength enhancement at a later age. The NOx-removal performance of the samples was reduced upon exposure to CO2 due to the fact that the TiO2 particles on the surface of the samples were covered by the calcium carbonate that formed during carbonation.

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.

Empirical NOx Removal Analysis of Photocatalytic Construction Materials at Real-Scale.

The NOx removal performance of photocatalytic construction materials is demonstrated using two experiments under indoor and outdoor environments: (1) A photoreactor test was conducted to assess the NO removal performance of construction materials (e.g., coatings, paints and shotcrete) using a modified ISO 22197-1 method; (2) A water washing test was conducted using two specimens enlarged to the size of actual building materials and artificially exposed to NOx in a laboratory to analyze NOx removal performance. For (1), the UV irradiation of the outdoor environment was analyzed and the experiment was conducted in an indoor laboratory under UV irradiation identical to that of the outdoor condition. Photoreactor tests were conducted on construction materials applied to actual buildings located in Seoul, South Korea. In (2), the enlarged specimen was used for a field experiment by applying a modified method from the ISO 22197-1 standard. On sunny days, the NOx removal performance (3.12–4.76 μmol/150 cm2·5 h) was twice as much as that of the ISO 22197-1 standard specification (2.03 μmol/150 cm2·5 h) in the real-world. The washing water test results indicated that general aqueous paint achieved a NOx removal of 3.88 μmol, whereas photocatalytic paint was superior to 14.13 μmol.

Sound-absorption and NOx-removal performances of TiO2-incorporated porous concrete made with bottom ash aggregates

The sound-absorption and NOx-removal performances of TiO2-incorporated porous concrete made with bottom ash aggregates were investigated. Concrete samples made with bottom ash aggregates having different paste-to-aggregate volume ratios (i.e., 0.2, 0.3 and 0.4) and TiO2 contents (i.e., 0%, 1% and 3%) were fabricated. The correlation between the voids and the mechanical strength values of concretes made with bottom ash aggregates was investigated through void ratio measurement and compressive strength tests to derive a proper aggregate size. The influence of target void and TiO2 content on the void ratio, compressive strength, sound-absorption, and NOx-removal performances of the samples was explored through compressive strength, void ratio, sound-absorption, and NOx-removal performance tests. The test results indicated that the sound-absorption and NOx-removal performances of the concrete samples were greatly influenced by the total void ratio, and the NOx-removal efficiency of the concrete samples was further promoted with an increase in the TiO2 content. These coupled effects were possibly attributed to the fact that the photocatalytic reaction is surface-oriented and can be affected by an increase in the total void ratio, increasing the available number of TiO2 particles on the surface that can facilitate the photocatalytic reaction when exposed to light.

광촉매 제품의 NOx 저감 성능 현장 평가 사례 고찰

광촉매 제품의 NOx 저감 성능 현장 평가 사례 고찰