NH3-SCR Performance Research Articles

Migration behavior of heavy metals in coal fly ash-derived Cu-SSZ-13 during synthesis and NH3-SCR application

The hazardous heavy metals in coal fly ash (CFA) restrict the recycling, utilization, and application of CFA and its derived products, especially for the CFA-fabricated zeolite that is applied to environmental catalysis. To clarify the migration behavior of the heavy metals during the synthesis process of target zeolite and its application, we prepared zeolite SSZ-13 using a two-step hydrothermal strategy and evaluated the migration and residual rates of the heavy metals including Hg, As, Se, Pb, Cr, and Cd in these processes. The NH3-SCR of NO performance and its effects on the existence of heavy metals were also examined. A modified Community Bureau of Reference (BCR) sequential extraction procedure was used to extract the heavy metals. Pb, Cr, and Cd remain in the SSZ-13, while Hg, As, and Se reside in the leachate during the hydrothermal reaction. The former three elements existed mainly as residuals in zeolite SSZ-13. The latter moved to the leachates. The SSZ-13 after ion-exchanged with Cu2+ shows high NH3-SCR performance, and the residual minim heavy metals rarely moved into the environment, indicating a harmless utilization process. This work contributed to the harmlessness and recycling of CFA and the development of high-value CFA-derived zeolite catalysts applied to environmental catalysis.

Insight into the remarkable enhancement of NH3-SCR performance of Ce-Sn oxide catalyst by tungsten modification

A series of W-modified Ce-Sn catalysts were fabricated and investigated for the selective catalytic reduction (SCR) of NOx (NO and NO2) by NH3. All the prepared Ce-W-Sn ternary oxide catalysts showed higher deNOx efficiency than the Ce-Sn catalysts, among which the Ce1W0.24Sn2Ox catalyst prepared by the coprecipitation method showed the highest NOx conversion. The mechanism by which W modification improved the structure and function of the Ce1Sn2Oy catalyst was systematically investigated by various methods. The corresponding results suggested that Ce-doped tetragonal SnO2 (t-Sn(Ce)O2) was the main active phase in the Ce1Sn2Oy catalyst for the NH3-SCR reaction. The W species regulated the structure by promoting the formation of the t-Sn(Ce)O2 active phase while preventing the generation of the Sn-doped cubic CeO2 (c-Ce(Sn)O2) phase. In addition, the highly dispersed W species on the surface of the Ce1W0.24Sn2Ox catalyst also coupled with Ce species to form new Ce-O-W active sites. The W modification also promoted the ability of the catalysts to oxidize NO to NO2 at 150–300 °C and suppressed the occurrence of excess NH3 oxidation especially at high temperature. The optimal structure and physico-chemical properties induced by W species contributed to superior NH3-SCR performance.

Structural control for inhibiting SO2 adsorption in porous MnCe nanowire aerogel catalysts for low-temperature NH3-SCR

The presence of SO2 in industrial flue gases will cause permanent deactivation of the catalyst active centre. Therefore, an effective method to improve the SO2 resistance of manganese-based catalysts at low temperatures is urgently needed. In this work, a hierarchical porous nanowire structure catalyst was designed by the in situ self-assembly method to inhibit SO2 adsorption. This hierarchical porous nanowire aerogel catalyst with great BET surface area and surface acidity exhibited NOx conversion above 90% at 100–400 °C. Notably, the NOx conversion of the MnCe-N catalyst was almost not inhibited by SO2 (250 ppm) compared to the 33% decrease of the MnCe-P catalyst. On the MnCe-P catalyst, SO2 has strong competitive adsorption with NH3 and NO, and the stronger adsorption capacity of SO2 inhibits the adsorption activation of the reaction gas and hinders the reaction proceeding through the L-H mechanism. Meanwhile, a large quantity of sulfate is formed on the catalyst surface, which prevents the active centre to participate in the redox reaction. The structure of nanowires enhances the number of acid sites, facilitates the adsorption and activation of NH3, and effectively inhibits the adsorption of SO2 on the MnCe-N catalyst. Fewer sulfate species are generated and difficult to deposit and aggregate on the catalyst surface, as a result, the active centre is less affected by sulfate species. The stable adsorption of NH3-related species ensures reliable reaction on MnCe-N through the E-R mechanism. This work emphasizes the importance of hierarchically porous structures in improving the NH3-SCR performance and SO2 resistance of monolithic catalysts, and provides new insights into the design of highly efficient and stable catalytic materials.

Enhanced SO2 and H2O resistance of MnTiSnOy composite oxide for NH3-SCR through Sm modification

NOx is one of the main sources of air pollution, and the abatement of NOx emission has aroused increasing attention. The NH3-SCR technology is mature and widely used for controlling NOx emissions from fixed sources. In this work, SmxMnTiSnOy was synthesized by a mixed solvothermal synthesis. The NH3-SCR performance of SmxMnTiSnOy was tested and the H2O and SO2 resistance of Sm0MnTiSnOy, Sm0.1MnTiSnOy, and Sm0.2MnTiSnOy catalysts (5 %H2O, 25 ppm SO2) were tested at 250 °C. The physicochemical properties of SmxMnTiSnOy were studied by XRD, FESEM, TEM, BET, XPS, H2-TPR, NH3-TPD and In-situ DRIFTS. The experimental results reveal that Sm0.2MnTiSnOy has a better low-temperature NH3-SCR performance and splendid H2O and SO2 durability. Moreover, appropriate Sm doping increases the specific area and enhances the acidity of the catalyst’s surface. The In-situ DRIFTS results suggest that the adsorption and activation of NH3 are of primary importance in the NH3-SCR reaction. Besides, a large number of weak acid sites on Sm0.2MnTiSnOy are conducive to adsorb and activate NH3 and good redox ability facilitates the activation of bidentate nitrate, respectively. Meanwhile, Sm doping could transfer electrons from the Sm species to the Mn species, which inhibits the formation of Mn sulfate.

Electrothermal alloy embedded V2O5-WO3/TiO2 catalyst for NH3-SCR with promising wide operating temperature window

Vanadia-based catalysts are widely used in selective catalytic reduction (SCR) reaction for reducing nitrogen oxides emissions, however, they only exhibit sufficient DeNOx efficiency within a narrow temperature window. In this study, a catalyst embedded with electrothermal alloy was prepared. The catalyst surface temperature could be heated using the electrothermal alloy, in order to widen the operating temperature window of the V2O5-WO3/TiO2 catalyst. Experimental results revealed that the electrothermal alloy embedded V2O5-WO3/TiO2 catalyst can maintain superior NH3-SCR performance and high resistance to H2O in a wide gas temperature range of 100–400 °C by controlling the surface temperature. In the meantime, the NH4HSO4 poisoned catalyst could be efficiently regenerated through electric heating, and NOx conversion can be restored to the level of fresh samples. Additionally, the effect of additives including methylcellulose and glass fiber, on the physicochemical properties of the plate-type catalyst was also investigated, and the catalyst samples were characterized by means of BET, XRD, NH3-TPD, H2-TPR, TG and SEM-EDS. This study proves the electric heating strategy is a promising way to enhance the performance of the V2O5-WO3/TiO2 during wide temperature SCR applications.

TiO2-modified CeVO4 catalyst for the selective catalytic reduction of NOx with NH3

A facile and efficient strategy was applied for doping Ti into CeVO4 to improve its NH3-SCR performance, and the obtained Ce–V–Ti catalyst exhibited excellent catalytic activity and high resistance to SO2 and H2O poisoning.

Effect of the Hydrothermal Aging on the Nh3-Scr Performance and N2o Selectivity of Cu-Ssz-39 and Cu-Ssz-13

Effect of the Hydrothermal Aging on the Nh3-Scr Performance and N2o Selectivity of Cu-Ssz-39 and Cu-Ssz-13

Effect of the Hydrothermal Aging on the Nh3-Scr Performance and N2o Selectivity of Cu-Ssz-39 and Cu-Ssz-13

Effect of the Hydrothermal Aging on the Nh3-Scr Performance and N2o Selectivity of Cu-Ssz-39 and Cu-Ssz-13

Redistributing Cu species in Cu-SSZ-13 zeolite as NH3-SCR catalyst via a simple ion-exchange

The nature and distribution of Cu species in Cu-SSZ-13 play a vital role in selective catalytic reduction of NO by NH3 (NH3-SCR), but existing methods for adjusting the Cu distribution are complex and difficult to control. Herein, we report a simple and effective ion-exchange approach to regulate the Cu distribution in the one-pot synthesized Cu-SSZ-13 that possesses sufficient initial Cu species and thus provides a “natural environment” for adjusting Cu distribution precisely. By using this proposed strategy, a series of Cu-SSZ-13x zeolites with different Cu contents and distributions were obtained. It is shown that the dealumination of the as-synthesized Cu-SSZ-13 during the ion-exchange generates abundant vacant sites in the double six-membered-rings of the SSZ-13 zeolite for relocating Cu2+ species and thus allows the redistribution of the Cu species. The catalytic results showed that the ion-exchanged Cu-SSZ-13 zeolites exhibit quite different catalytic performance in NH3-SCR reaction but superior to the parent counterpart. The structure–activity relationship analysis indicates that the redistribution of Cu species rather than other factors (e.g., crystallinity, chemical composition, and porous structure) is responsible for the improved NH3-SCR performance and SO2 and H2O resistance. Our work offers an effective method to precisely adjust the Cu distribution in preparing the industrial SCR catalysts.

Oxygen-Functionalized Activated Carbon Supported Vanadia Catalysts: Unexpected Improvement in Low-Temperature Nh3-Scr Performance

Oxygen-Functionalized Activated Carbon Supported Vanadia Catalysts: Unexpected Improvement in Low-Temperature Nh3-Scr Performance

Trace Co Doping Improved Nh3-Scr Performance and Poisoning Resistance of Ce-Mn-Based Catalysts

Trace Co Doping Improved Nh3-Scr Performance and Poisoning Resistance of Ce-Mn-Based Catalysts

Synthesis of W-modified CeO2/ZrO2 catalysts for selective catalytic reduction of NO with NH3.

In this paper, a series of tungsten–zirconium mixed binary oxides (denoted as WmZrOx) were synthesized via co-precipitation as supports to prepare Ce0.4/WmZrOx catalysts through an impregnation method. The promoting effect of W doping in ZrO2 on selective catalytic reduction (SCR) performance of Ce0.4/ZrO2 catalysts was investigated. The results demonstrated that addition of W in ZrO2 could remarkably enhance the catalytic performance of Ce0.4/ZrO2 catalysts in a broad temperature range. Especially when the W/Zr molar ratio was 0.1, the Ce0.4/W0.1ZrOx catalyst exhibited the widest active temperature window of 226–446 °C (NOx conversion rate > 80%) and its N2 selectivity was almost 100% in the temperature of 150–450 °C. Moreover, the Ce0.4/W0.1ZrOx catalyst also exhibited good SO2 tolerance, which could maintain more than 94% of NOx conversion efficiency after being exposed to a 100 ppm SO2 atmosphere for 18 h. Various characterization results manifested that a proper amount of W doping in ZrO2 was not only beneficial to enlarge the specific surface area of the catalyst, but also inhibited the growth of fluorite structure CeO2, which were in favor of CeO2 dispersion on the support. The presence of W was conducive to the growth of a stable tetragonal phase crystal of ZrO2 support, and a part of W and Zr combined to form W–Zr–Ox solid super acid. Both of them resulted in abundant Lewis acid sites and Brønsted acid sites, enhancing the total surface acidity, thus significantly improving NH3 species adsorption on the surface of the Ce0.4/W0.1ZrOx catalyst. Furthermore, the promoting effect of adding W on SCR performance was also related to the improved redox capability, higher Ce3+/(Ce3+ + Ce4+) ratio and abundant surface chemisorbed oxygen species. The in situ DRIFTS results indicated that nitrate species adsorbed on the surface of the Ce0.4/W0.1ZrOx catalyst could react with NH3 due to the activation of W. Therefore, the reaction pathway over the Ce0.4/W0.1ZrOx catalyst followed both Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) mechanisms at 250 °C.

Selective catalytic reduction of NOx with NH3 on Mn, Co-BTC-derived catalysts: Influence of thermal treatment temperature

The paper presented facile method for preparing Mn, Co-BTC (BTC ​= ​1,3,5-benzenetricarboxylic acid) derived catalyst with honeycomb structure through direct decomposition of Mn and Co based metal-organic framework (MOF) Mn, Co-BTC in air. Also, the correlation between catalytic performance of MOF (metal organic framework) derivatives for the selective catalytic reduction (SCR) of NOx with ammonia and annealing temperature have been investigated. The catalytic activity test results indicated that annealing temperature had the clear promoting effects on catalytic performance. The X-ray photoelectron spectroscopic (XPS), X-ray diffraction (XRD), Thermogravimetric (TG), Scanning electron microscopy (SEM), Temperature programmed reduction of H2 (H2-TPR) and Fourier-transform infrared (FTIR) spectra were employed to characterize Mn, Co-BTC and its derived catalysts. Based on SEM, FTIR and XRD analytical results, Mn, Co-BTC with nanoneedle structure turned into (Co, Mn) (Co, Mn)2O4 spinel compound with honeycomb structure accompanied by decomposition of organic linkers through direct annealing process. The XPS and H2-TPR results showed that Mn, Co-BTC-500 (Mn, Co-BTC annealed at 500 ​°C) had the greatest interaction between Mn and Co, resulting in high catalytic performance for NH3-SCR of NOx, which were consistent with catalytic performance test results. Finally, based on the in-situ DRIFT experiments, it was suggested that the SCR process of NOx with NH3 over Mn, Co-BTC-500 followed both Langmuir–Hinshelwood (L–H) mechanism and Eley-Rideal (E-R) mechanism.

Promoting effect of post-synthesis treatment strategy on NH3-SCR performance and hydrothermal stability of Cu-SAPO-18

The influence of post-synthesis treatment with MnSO4, (NH4)2SO4 and (NH4)2S2O8 blended solution on NH3-SCR activity and hydrothermal stability of Cu-SAPO-18 (Cu-18) was investigated. Via adjusting the mixed solution concentration, the optimal Mn/Cu-18-Ⅲ with higher deNOx activity and hydrothermal stability was acquired. Based on the optimal Mn/Cu-18-Ⅲ, diverse metal cations such as La3+, Ce3+, Sm3+ or Zr4+ were simultaneously doped into Cu-18 during Mn2+ and NH4+ blended solution treatment to further promote its catalytic performance before and after hydrothermal treatment. The doping with Sm could improve the NH3 activity and hydrothermal stability of Mn/Cu-18-Ⅲ to the greatest extent. The elevation of acid sites content and the disappearance of CuO species in Mn/Cu-18-Ⅲ caused the enhancement of its NH3-SCR activity. More Cu2+ and acid sites in SmMn/Cu-18-Ⅲ were responsible for its higher NH3-SCR activity than Mn/Cu-18-Ⅲ. The decline of vulnerable Brønsted acid sites by substituting Mn2+ or Sm3+ for H+ could restrain the hydrolysis of Cu-18 and enhance the hydrothermal stability of Cu-18 during hydrothermal treatment. The mechanism analysis demonstrates that the fresh and aged Cu-18, Mn/Cu-18-Ⅲ and SmMn/Cu-18-Ⅲ follow both Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) mechanism in NH3-SCR reaction, with the L–H mechanism being more dominated.

Vanadium-based catalytic fibers for selective reduction of NO by NH3 and their potential use on co-processing of dust and NOx

This work is dedicated to fabrication of catalytic fibers for the process of selective catalytic reduction of NOx by NH3 (NH3-SCR). By employing vanadium-titanium as main catalytic components, we investigated the effect of different inorganic supports (glass fiber, aluminum silicate fiber and quartz fiber), preparation methods (a sol–gel method and a hydrothermal method) and loading weight of V2O5 on the NH3-SCR performance of catalytic fibers. The catalytic aluminum silicate fiber with 5% vanadium/titanium ratio prepared by a sol–gel method (denoted as V5Ti/AF) showed the best SCR and mass transfer performance. Characterization results indicated that a relatively large surface area, strong acidity, well-dispersed catalyst particles, and good redox and desorption properties derived from the interaction between catalytic components and supports all contributed to the good performance of V5Ti/AF. The pressure drop of catalytic fibers were measured, and the total pressure drop of catalytic fibers and de-dust ceramic membranes was much lower than previously prepared catalytic ceramic membranes, indicating their potential use in the co-processing of dust and gaseous pollutants.

ZSM-5 core–shell structured catalyst for enhancing low-temperature NH3-SCR efficiency and poisoning resistance

By constructing core–shell ZSM-5@CeO2 support rather than bulk phase for loading copper, the enhanced NH3-SCR performance as well as H2O and SO2 tolerance was achieved. Cu/(ZSM-5@CeO2) catalyst exhibited the superior activity with the lowest T90 at 215 °C, which is due to the interaction between CeO2 shell and copper ions that promotes the redox properties as evidenced by oxygen isotopic exchange technique. The ZSM-5 core provides more acid sites to improve the ammonia adsorption. Thus, the highest activity of Cu/(ZSM-5@CeO2) catalyst can be ascribed to the synergistic effect of redox ability and acidity. The CeO2 shell can react with SO2 preferentially and lead to a high sulfur tolerance. This study provides a strategy for design and the practical applications of NH3-SCR zeolite catalysts.

Influence of CS2 pretreatment on the NH3-SCR activity of CeO2: Synergistic promotional effect of sulfation and reduction

Due to the promotional effect on the surface acidity, SO2 had been usually used to improve the selective catalytic reduction of NOx with NH3 (NH3-SCR) over cerium oxide/cerium-based catalyst via gas phase sulfation. However, CS2 and COS, largely existing in the coke oven or/and gasification flue gas, exhibit stronger reducibility and present the unique physicochemical properties in acidity and reduction property compared to SO2. To the best of my knowledge, the reductive CS2 and COS had not been used to increase the NH3-SCR activity of cerium oxide/cerium-based catalyst. Therefore, the influence of CS2 and COS gas phase sulfation pretreatment on the NH3-SCR performance of CeO2(w/o) had been investigated with SO2 as comparison herein. The results indicate that the promotional effect of the sulfur-containing species pretreatment on the NH3-SCR performance over CeO2(w/o) decrease as following: CS2>COS>SO2, which is in accordance with the intensity of their reducibility. Compared with SO2, the pretreatment with CS2 could induce more Ce4+ to reduce to Ce3+ and generate more surface defects due to its stronger reducibility, leading to more oxygen defects and chemisorbed oxygen formed on the surface of CeO2(w/o). And the sulfation treatment could slightly decrease the crystallinity of cubic CeO2. The characterization results also confirm that the pretreatment with CS2 contributes to the formation of more sulfate species, not only enhances the abundance and strength of Brønsted acid sites on the CeO2(w/o) surface, but also helps to the generation of low-temperature Lewis acid sites compared to SO2. All these should be the crucial reasons for the best de-nitration activity over CeO2-CS2-3 in the operating temperature range. We expected that this research could provide a new strategy for designing novel CeO2-based NH3-SCR catalyst.

Influence of phosphorus on the NH3-SCR performance of CeO2-TiO2 catalyst for NOx removal from co-incineration flue gas of domestic waste and municipal sludge

Domestic waste and municipal sludge are two major solid hazardous substances generated from human daily life. Co-incineration technology is regarded as an effective method for the treatment of them. However, the emitted NOx-containing exhaust with high content of phosphorus should purified strictly. CeO2-TiO2 is a promising catalyst for removal of NOx by NH3-SCR technology, but the effect of phosphorous in the exhaust is ambiguous. Therefore, the effect of phosphorus on NH3-SCR performance and physicochemical properties of CeO2-TiO2 catalyst was investigated in our present work. It was found that phosphorus decreased the NH3-SCR activity below 300 °C. Interestingly, it suppressed the formation of NOx and N2O caused by NH3 over-oxidation above 300 °C. The reason might be that phosphorus induced Ti4+ to migrate from CeO2-TiO2 solid solution and form crystalline TiO2, which led to the destruction of Ti-O-Ce structure in the catalyst. So, the transfer of electrons between Ti and Ce ions, the relative contents of Ce3+, and surface adsorbed oxygen, as well as the redox performance were limited, which further inhibited the over-oxidation of NH3. In addition, phosphorus weakened the NH3 adsorption on Lewis acid sites and the adsorption performance of NO + O2, while increased the Brønsted acid sites. Finally, the reaction mechanism over CeO2-TiO2 catalyst did not change after introducing phosphorus, L-H and E-R mechanisms co-existed on the surface of the catalysts.

Significant promoting effect of La doping on the wide temperature NH3-SCR performance of Ce and Cu modified ZSM-5 catalysts

Different La doping Ce–Cu/Z5 catalysts were synthesized via ion-exchange way and then applied in the selective catalytic reduction of NOx via ammonia (NH3-SCR). The 2 ​wt% La doping Ce–Cu/ZSM-5 (CC-L2/Z5) catalyst exhibited better SCR activity compared to other catalyst in the wide reaction temperature window (200–500 ​°C). The addition of La can also enhance the SCR performance. It is because that the redox cycle Cu2++Ce3+↔Cu++Ce4+ facilitates the electron transfer, which further promotes the oxidation of NO into NO2 that could result in the “Fast SCR”. The La can also increase the good surface acidic and redox properties and is conducive to the generation of oxygen vacancy. Furthermore, the more content of Ce3+ can generate oxygen vacancy, leading to improving catalytic performance. The CC-L2/Z5 has excellent water and SO2 resistance. At the same time, it has the outstanding stability for repeating six cycles. In-situ DRIFTS results illustrated that L-H mechanism was the main reaction mechanism for CC-L2/Z5 over 250 ​°C.

High-temperature selective catalytic reduction of NO with NH3: Optimization of ZrO2 and WO3 complex oxides

The catalyst for selective catalytic reduction of NOx at high temperatures is significantly demanded by current gas-fired exhaust purification. In this work, the complex oxides composed of two different structures of ZrO2-WO3 and WO3/ZrO2 with zirconium as the main component were prepared for NH3-SCR of NO at high temperatures by blending method and equal volume impregnation method, respectively. Combined with XRD, NH3-TPD, FE-SEM, BET and in situ DRIFTS characterization, the effects of component optimization of two kinds of ZrO2 and WO3 complex oxides on the performance for NH3-SCR of NO were mainly studied. The optimal compatibility of ZrO2 and WO3 complex oxides was determined, and the corresponding N2 selectivity and anti-interference ability of water vapor and SO2 were further investigated. Results showed that the performance of ZrO2-WO3 prepared by blending method for NH3-SCR of NO was significantly better than that of WO3/ZrO2 prepared by impregnation method. The ZrO2-WO3 containing 20% WO3 has the best performance in NH3-SCR of NO with NO conversion higher than 90% and N2 selectivity higher than 90% at 450–650 °C, and the performance was not affected by SO2, slightly affected by competitive adsorption of water vapor at 450 °C and not disturbed by water vapor above 500 °C. Further investigation showed that the NH3-SCR of NO over the ZrO2-WO3 reaction followed both L-H and E-R mechanisms. Characterization analysis revealed that ZrO2-WO3 has finer microscopic particles, larger specific surface area, higher acid amount and stronger acid strength than WO3/ZrO2.