Selective Catalytic Reduction Of NOx Research Articles

Simultaneously achieving selective catalytic reduction of NOx with NH3 and catalytic oxidation of CO with O2 over one finely optimized bifunctional catalyst Mn2Cu1Al1Ox at low temperatures

For coke oven flue gases, the simultaneous removal of NOx and CO pollutants is highly demanded but still remains a big challenge. So far there isn't a single efficient catalyst that can simultaneously achieve selective catalytic reduction of NOx by NH3 and the catalytic oxidation of CO to CO2 in the presence of excessive O2 at low temperatures (180–220 °C). Here, we report a bifunctional catalyst Mn2Cu1Al1Ox that possesses dual active sites and is highly active for both NH3-SCR and CO oxidation reactions under the above mentioned conditions. By tuning the redox properties and surface oxygen vacancies, the optimized Mn2Cu1Al1Ox catalyst achieved high conversions of both NOx and CO in the NH3-NO-CO-O2 system, with a NOx conversion of 86.8% and a CO conversion of 100% at 200 °C. The active reaction sites and the interaction principal between NH3-SCR and CO oxidation reactions were thoroughly investigated by well-designed experiments, in-situ DRIFTS and DFT calculations. It was revealed that NH3 and CO competed for the same active sites, which significantly influenced the catalytic performance of Mn3Al1Ox and Cu3Al1Ox for CO oxidation reactions. For the bifunctional Mn2Cu1Al1Ox catalyst, CO is more easily adsorbed on the Cu sites, while NH3 is more inclined to adsorb on the Mn sites, which enables both NH3-SCR and CO oxidation reactions to proceed simultaneously on one catalyst. The improvement of CO oxidation performance on Mn2Cu1Al1Ox catalyst is mainly attributed to the reduced Jahn-Teller effect of Cu atoms by doping into Mn3O4, which leads to the lift of d-band center and finally enhances the CO adsorption.

Encapsulation of ultra-small Cu–Fe into ZSM-5 zeolites for NH3-SCR with broad reaction-temperature ranges

A direct hydrothermal synthesis strategy is developed to prepare the Cu–Fe-ZSM-5 zeolites by using the ethylenediaminetetraacetic acid disodium dihydrate (EDTA-2Na·2H2O) chelated Cu2+ and Fe3+ precursors as metal sources. During the crystallization, the metal chelates were spontaneously embedded into the ZSM-5 crystals and subsequently transformed to the zeolites encapsulated copper and iron species after removing the chelating agent via the high-temperature calcination. Rigorous characterizations indicate that the resulted Cu2+/Cu+ and Fe3+/Fe2+ species are formed ultra-small nano-composites with an average diameter of ∼2.2 nm and highly dispersed in the ZSM-5 zeolite crystals. The acidity of the ZSM-5 zeolites is subtly modulated by the encapsulated Cu–Fe nano-composite. As expected, the as-prepared Cu–Fe-ZSM-5 exhibits outstanding catalytic performance for the selective catalytic reduction of NOx with ammonia (NH3-SCR) in the broad reaction temperature ranges of 220–480 °C, which is much better than the Cu–Fe/ZSM-5 prepared with the conventional wetness impregnation method. Furthermore, the resultant zeolites show high stability and good tolerance to H2O and SO2, and it is very competitive for practical application to eliminate NOx. The developed one-pot hydrothermal synthesis route by using EDTA-2Na·2H2O as chelating agent is very convenient and easily reproducible, providing a general guideline to design and fabricate the superior transition metal modified zeolite catalysts for NH3-SCR and the related reactions.

Multi-stage ammonia production for sorption selective catalytic reduction of NOx

Multi-stage ammonia production for sorption selective catalytic reduction of NOx

Recent progress of low-temperature selective catalytic reduction of NOx with NH3 over manganese oxide-based catalysts.

Selective catalytic reduction with NH3 (NH3-SCR) was the most efficient approach to mitigate the emission of nitrogen oxides (NOx). Although the conventional manganese oxide-based catalyst had gradually become a kind of principal catalyst for the low-temperature NH3-SCR reaction, there were still numerous defects. The growing demands for extensive operation temperature scope, strong SO2 tolerance, and excellent catalytic activity had boosted the development of novel manganese oxide-based catalysts. In this review, three forms of manganese oxide-based catalysts were introduced in detail, including single manganese oxide catalysts, composite manganese oxide-based catalysts, and supported manganese oxide-based catalysts. The surface acidity and redox properties of manganese oxide-based catalysts could be strengthened by optimizing the preparation methods, exposing specific crystal planes, and constructing multiple active centers and sacrificial sites, which improved the SCR performance and anti-poisoning properties of catalysts. Secondly, we briefly summarized the NH3-SCR reaction mechanism of manganese oxide-based catalysts, including the Eley-Rideal (E-R) mechanism and the Langmuir-Hinshelwood (L-H) mechanism. Finally, several overtures were proposed for the future research directions of manganese oxide-based catalysts for NH3-SCR reaction, hoping to narrow the gap between the novel manganese oxide-based catalysts and the actual demands and realize commercialized application in the nearest future.

A Novel Superior Fe-Ce-V Catalyst with High Performance for Selective Catalytic Reduction of Nox with Nh3

A Novel Superior Fe-Ce-V Catalyst with High Performance for Selective Catalytic Reduction of Nox with Nh3

Improved Hydrothermal Stability of Cu-Sapo-18 by Sm Modification in the Selective Catalytic Reduction of Nox with Nh3

Improved Hydrothermal Stability of Cu-Sapo-18 by Sm Modification in the Selective Catalytic Reduction of Nox with Nh3

Influence of Coke Deposition by Propene Poisoning on Cu-Ssz-13 Catalyst for Selective Catalytic Reduction of Nox with Nh3

Influence of Coke Deposition by Propene Poisoning on Cu-Ssz-13 Catalyst for Selective Catalytic Reduction of Nox with Nh3

Application of Fenton Sludge Coupled Selective Acid Leaching in Selective Catalytic Reduction of Nox: Performance and Mechanisms

Application of Fenton Sludge Coupled Selective Acid Leaching in Selective Catalytic Reduction of Nox: Performance and Mechanisms

A Novel Superior Fe-Ce-V Catalyst with High Performance for Selective Catalytic Reduction of Nox with Nh3

A Novel Superior Fe-Ce-V Catalyst with High Performance for Selective Catalytic Reduction of Nox with Nh3

The Enhanced Performance of Ce-Cu/Tio2 Catalyst Synthesized by Ice Melting Method for Selective Catalytic Reduction of Nox with Nh3

The Enhanced Performance of Ce-Cu/Tio2 Catalyst Synthesized by Ice Melting Method for Selective Catalytic Reduction of Nox with Nh3

DeNO x performance enhancement of Cu-based oxides via employing a TiO2 phase to modify LDH precursors.

CuAl-LDO, CuAl-LDO/TiO2 and CuAl-LDO/TiO2NTs catalysts were obtained from TiO2 modified LDHs precursor which were prepared by in situ assembly method. Then catalysts were evaluated in the selective catalytic reduction of NOx with NH3(NH3-SCR), and the results showed that the CuAl-LDO/TiO2NTs catalyst exhibited preferable deNOx performance (more than 80% NOx conversion and higher than 90% N2 selectivity at a temperature range of 210–330 °C) as well as good SO2 resistance. With the aid of series of characterizations such as XRD, N2 adsorption/desorption, XPS, NH3-TPD, H2-TPR, and in situ DRIFTS, it could be concluded that, doping TiO2NTs afforded the catalyst larger specific surface area, more abundant surface chemisorption oxygen species and more excellent redox performance. Meanwhile, In situ DRIFTS evidenced that CuAl-LDO/TiO2NTs catalyst has a strong adsorption capacity for the reaction gas, which is more conducive to the progress of the SCR reaction.

Comparative Analysis of NOx Emission Reduction in Engines Using NiCo2O4 Nanoparticles without External Reductant at Low Temperatures: An Experimental Investigation

Due to increasingly stringent rules, eliminating pollutants (NOx) emitted by diesel engines in the automobile sector remains an intriguing scientific and technological problem. To meet the strict NOx emission restrictions, a catalytic system with a high level of complexity, unit size, and quantity, as well as higher fuel consumption, is required. As a result, for a reduction in individual exhaust gas emissions, an after‐treatment system for a diesel vehicle must employ integrated catalyst technology. For selective catalytic reduction of NOx without any external reductant, a highly effective catalyst “spinel nickel cobaltite” (NiCo2O4) was produced using a polymeric precursor technique. In this work, an exhaust gas treatment system without external reductants using nano‐NiCo2O4 as catalyst was designed and fabricated, for NOx control in diesel and petrol engines at low temperature. In order to determine the NOx conversion efficiency in the selective catalytic reduction system, tests were carried out at different engine loads. The system was supposed to be cost‐effective due to the nano‐NiCo2O4 catalyst’s ability to work at low temperatures. The findings proved the developed SCR system’s potential to reduce NOx emissions. At a high load, the nitric oxide (NO) emissions were reduced by 54 and 96 percent, respectively, without increasing HC, CO, and CO2 emissions or compromising efficiency.

Enhanced Low-Temperature Behavior of Selective Catalytic Reduction of Nox by Co on Fe-Based Catalyst with Looping Oxygen Vacancy

Enhanced Low-Temperature Behavior of Selective Catalytic Reduction of Nox by Co on Fe-Based Catalyst with Looping Oxygen Vacancy

Preferential Chemical Vapor Deposition for the Synthesis of the Catalysts for Co Mediated Nox Selective Catalytic Reduction

Preferential Chemical Vapor Deposition for the Synthesis of the Catalysts for Co Mediated Nox Selective Catalytic Reduction

Low-cost Mn–Fe/SAPO-34 catalyst from natural ferromanganese ore and lithium-silicon-powder waste for efficient low-temperature NH3-SCR removal of NOx

The development of low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR) catalysts is desirable but still challenging. Herein, a low-cost Mn–Fe/SAPO-34 catalyst was successfully synthesized using natural ferromanganese ore (FO) and industrial waste lithium-silicon-powder (LSP) by solid-state ion exchange (SSIE) method, and showed high NH3-SCR activity at low temperature range (150–200 °C) with high N2 selectivity. After loading FO, Mn–O and Fe–O bonds on Mn–Fe/SAPO-34 were weakened, which were beneficial to electron transfer and the oxidation-reduction cycle of SCR. The coexisting of Mn and Fe promoted the dispersion of Fe, resulted in high amounts of Oa, Mn4+ and Fe3+ which facilitated the adsorption and activization of NH3 over Mn–Fe/SAPO-34 catalyst. The Brønsted and Lewis acid sites participate in NH3-SCR, and the adsorbed nitrate species could quickly react with the adsorbed NH3 species via the Langmuir–Hinshelwood (L-H) mechanism. The Mn–Fe/SAPO-34 integrated the advantages of low-cost, resource saving and environment friendly, giving a low-carbon and sustainable choice for the industrial application of NOx abatement.

Phosphate on ceria with controlled active sites distribution for wide temperature NH3-SCR

Practical catalysts that work well at a wide operation window for selective catalytic reduction of NOx by NH3 (NH3-SCR) are essential for the purification of non-isothermal emission such as vehicle exhaust. However, NH3-SCR catalyst with high low-temperature performance has excellent NO activation and oxidation ability, leading inevitably to NH3-intermediates over-oxidation and N2 selectivity deterioration at high operation temperatures. By far the best performance ceria-based catalyst with a super-wide temperature window of 175–400 oC for 90% NOx conversion in ideal environment and 225–475 oC for 90% NOx conversion by addition of 50 ppm SO2 and 5% H2O is obtained via distributing phosphate over the outer of ceria. NH3 protection strategy is the key for keeping high-temperature activity. Brønsted acidity surged as the formation of P-OH network via a charge compensatory mechanism of phosphate. NH3 was prone to be captured by the surface P-OH network, forming NH4+ species, avoiding being oxidized and contributing to both low and high temperature activity. NO can also be readily absorbed and oxidized to the absorbed NO2(ad) species over phosphate as reflected by in situ DRIFTS and DFT calculation, providing a facile pathway for ‘fast SCR’ by reacting with NH4+ species to form N2 and H2O. The reaction followed the L-H mechanism and contributed to catalytic activity under 300 oC. This directional structure fabricate strategy helps to increases the NOx conversion and N2 selectivity under a broaden temperature window. The enriched Brønsted acid sites over phosphate treated ceria were also demonstrated to have largely suppressed SO2 adsorption, which significantly slowed down the catalyst poisoning. A dynamic equilibrium between the poisoning and regeneration process can be achieved according to the shrinking-core model for each nanosphere, leading to the excellent resistance.

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.

Enhanced SO2 resistance of V2O5/WO3-TiO2 catalyst physically mixed with alumina for the selective catalytic reduction of NOx with NH3

Selective catalytic reduction with NH3 (NH3-SCR) is an effective NOx removal technology in the industry. Vanadia supported on tungsten titania (V2O5/WO3-TiO2) is most widely utilized for NH3-SCR because of its high tolerance to sulfur. Although it exhibits stable performance under SO2 in the stream, there are still unsolved sulfur poisoning issues under low-temperature operations due to the accumulation of ammonium bisulfate (ABS). In this study, we introduce a hybrid catalyst comprising V2O5/WO3-TiO2 physically mixed with alumina (VWTi + Al), which exhibited superior stability during SO2 aging compared to conventional vanadia catalysts. The improved sulfur tolerance originates from the direct migration of in-situ formed ABS from the vanadia domain to the alumina domain through physical contact rather than gas-phase SO2 adsorption on alumina. Interestingly, the mixed alumina maintains superior affinity to ABS as well as reusability after repetitive SO2 aging and regeneration. In addition, the protection ability, i.e. affinity to ABS, of mixed alumina closely related to its surface properties including acidity and pore size. The present study suggests that the hybrid catalyst can be an applicable catalyst to NOx removal process in stationary sources and a breakthrough for the decrease of pollutants emission.

Cobalt doped Fe-Mn@CNTs catalysts with highly stability for low-temperature selective catalytic reduction of NOx

Cobalt doped Fe-Mn@CNTs catalysts with highly stability for low-temperature selective catalytic reduction of NOx

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.