Catalysts For NOx Removal Research Articles

Mesh-supported V2O5-WO3/TiO2 nanosheet array catalysts for efficient removal of NOx

Mesh-supported V2O5-WO3/TiO2 nanosheet array catalysts for efficient removal of NOx

New insights and reaction mechanisms in the design of catalysts for the synergistic removal of NOx and VOCs from coke oven flue gas: Dual regulation of oxidative properties and acidic sites

The acid and redox sites of the MnCo catalysts are simultaneously fine-tuned by the addition of V. A dual-function catalyst, designated as V0.5Mn5Co5, has been constructed for the synergistic removal of NOx and volatile organic compounds under coke-oven flue gas conditions, which exhibits > 95 % NOx conversion and > 80 % N2 selectivity at 180–300 °C. Meanwhile, it removes 70 % of ethylene at 240 °C. Besides it has excellent sulfur and water resistance. The characterization results indicate that this acid-redox dual sites modulation strategy appropriately weakens the oxidation capacity of the catalysts while increasing the surface acidity of the catalysts. The catalyst mainly performs SCR reaction through the E-R mechanism, and N2O is generated through the transition dehydrogenation of NH3 and NSCR reaction. Ethylene is first adsorbed on the catalyst surface then oxidized to form carbonate species, and finally decomposed to CO2. Ethylene oxidation follows the MvK mechanism. There is a competitive adsorption between NH3 and C2H4, and a mutual inhibition between the SCR reaction and the ethylene oxidation reaction. V0.5Mn5Co5 exhibits excellent synergistic removal of NOx and VOCs in coke oven flue gas compared with commercial VWTi catalysts, which indicates great promise for industrial application.

Elucidating the electron confinement effect on CeFeW/ZrO2 catalysts to enhance SO2 resistance in the low temperature NH3-SCR reaction

Currently, the inefficiency of the catalysts for NOx removal in the presence of SO2 in NH3-SCR reaction still prevalent. The problem of how to improve the SO2 tolerance at low temperature is still a common direction for researchers to work together. In this work, the CeFeW/ZrO2 catalyst prepared by a two-step hydrothermal method exhibited excellent SO2 resistance and SO2 had basically no impact on the CeFeW/ZrO2 catalyst activity. The superior catalytic performance and SO2 tolerance of CeFeW/ZrO2 catalyst mainly originated from that Ce acted as a functional site to form Ce-O-Fe, which altered the local electronic environment through electron confinement effect, increased the proportion of Fe3+/(Fe2+ + Fe3+) and surface chemisorption oxygen as well as the formation of oxygen vacancies on one hand. On the other hand, Fe sites exhibited excellent SO2 capacity and preferentially reacted with SO2, the metal sulfates Fe2(SO4)3 and FeSO4 restrained the formation and deposition of NH4HSO4 and (NH4)2SO4 on the catalyst surface. Simultaneously, the Ce-O-Fe-SO42− species ensured the electron transfer between Ce and Fe, and the redox properties of the catalyst were remained, thus the L-H mechanism on the CeFeW/ZrO2 catalyst could still be carried out smoothly under the conditions of the presence of SO2. Moreover, DFT calculation confirmed that the adsorption ability of NO, NH3 and O2 was enhanced over CeFeW/ZrO2 catalyst, which resulted in an excellent SO2 tolerance.

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.

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

The chemical nature of SO2 poisoning of Cu-CHA-based SCR catalysts for NOx removal in diesel exhausts

Unveiling how the chemistry of the reaction of [Cu2II(NH3)4O2]2+ with NO changes upon exposure to SO2. The important stage of the NH3-SCR cycle in the Cu-CHA deNOx catalyst is investigated with temperature-programmed reaction with NO, XAS and DRIFTS.

Modification of Recycled Industrial Solid Waste Incineration Fly Ash as a Low-cost Catalyst for NOx Removal

Modification of Recycled Industrial Solid Waste Incineration Fly Ash as a Low-cost Catalyst for NOx Removal

Enhanced Low-Temperature Activity and Hydrothermal Stability of Ce-Mn Oxide-Modified Cu-SSZ-39 Catalysts for NH3-SCR of NOx

Cu-SSZ-39 zeolite with an AEI structure exhibits excellent hydrothermal stability and can be a potential alternative to Cu-SSZ-13 zeolite SCR catalysts for NOx removal in diesel vehicles. However, the inferior low-temperature performance of Cu-SSZ-39 leads to substantial NOx emissions during the cold-start period, impeding its practical application. In this study, Ce-Mn oxide-modified Cu-SSZ-39 catalysts (CeMnOx/Cu-SSZ-39) and references (CeO2/Cu-SSZ-39 and MnOx/Cu-SSZ-39) were prepared by the ion-exchange of Cu ions followed by impregnation of the oxide precursors, with the aim of enhancing the NH3-SCR performance at low temperatures. The modified catalysts exhibited improved low-temperature activity and hydrothermal stability compared to the unmodified counterpart. In particular, CeMnOx/Cu-SSZ-39 showed the highest activity among the three catalysts and achieved NOx conversions above 90% within the temperature range of 180 °C to 600 °C, even after undergoing hydrothermal aging at 800 °C. Experimental results indicated that the synergistic effect between Ce and Mn in CeMnOx improves the redox properties and acidity of the catalyst due to the presence of Ce3+, Mn4+, and abundant adsorbed oxygen species, which facilitate low-temperature SCR reactions. Furthermore, the interaction of CeMnOx with Cu-SSZ-39 stabilizes the zeolite framework and hinders the agglomeration of Cu species during the hydrothermal aging process, contributing to its exceptional hydrothermal stability. The kinetics and NO oxidation experiments demonstrated that CeMnOx provides access to fast SCR reaction pathways by oxidizing NO to NO2, resulting in a significant increase in low-temperature activity. This study provides novel guidelines for the design and preparation of Cu-SSZ-39 zeolite with outstanding SCR performance over a wide temperature range.

Revealing the mechanism of K-enhanced Cu-SSZ-13 catalysts against hydrothermal aging and P-poisoning for NOx reduction by NH3-SCR

Cu-SSZ-13 (Cu-Z) has been commercialized as an efficient catalyst for NOx removal in mobile sources. However, in practical applications, the catalyst faces problems of poisoning (K and P) and hydrothermal aging. Therefore, in this work, we investigated the effects of K on P poisoning and hydrothermal aging in Al-rich Cu2/Z (2 wt% Cu). The presence of 1 wt% K could not only improve the high-temperature activity, which could reach above 99% at 225–600 °C on the K1/Cu2/Z, but also enhanced the hydrothermal stability and the resistance of P poisoning. Combing with a series of characterizations, K was mainly present in the Brӧnsted acid sites in the CHA cage, which led to the transformation of part of Z-[Cu(OH)]+ to Z2-Cu2+, reducing dealumination and the formation of CuOx and CuAl2O4 species during hydrothermal aging. Moreover, the presence of K could inhibit the formation of Cu-PO3-/PO43- species by P poisoning of Z-[Cu(OH)]+ species. In-situ DRIFTS results showed that the catalysts followed both E-R and L-H mechanism at 150 ℃. K doping could promote the formation of nitrate species and thus favoring the L-H mechanism, which probably enhanced the NH3-SCR activity.

Unveiling the SO2 Resistance Mechanism of a Nanostructured SiO2(x)@Mn Catalyst for Low-Temperature NH3-SCR of NO.

Low N2 selectivity and SO2 resistance of Mn-based catalysts for removal of NOx at low temperatures by NH3-SCR (selective catalytic reduction) technology are the two main intractable problems. Herein, a novel core-shell-structured SiO2@Mn catalyst with greatly improved N2 selectivity and SO2 resistance was synthesized by using manganese carbonate tailings as raw materials. The specific surface area of the SiO2@Mn catalyst increased from 30.7 to 428.2 m2/g, resulting in a significant enhancement in NH3 adsorption capacity due to the interaction between Mn and Si. Moreover, the N2O formation mechanism, the anti-SO2 poisoning mechanism, and the SCR reaction mechanism were proposed. N2O originated from the reaction of NH3 with O2 and the SCR reaction, as well as from the reaction of NH3 with the chemical oxygen of the catalyst. Regarding improving the SO2 resistance, DFT calculations showed that SO2 was observed to preferentially adsorb onto the surface of SiO2, thus preventing the erosion of active sites. Adding amorphous SiO2 can transform the reaction mechanism from Langmuir-Hinshelwood (L-H) to Eley-Rideal (E-R) by adjusting the formation of nitrate species to produce gaseous NO2. This strategy is expected to assist in designing an effective Mn-based catalyst for low-temperature NH3-SCR of NO.

New insight into vanadium phosphorus oxides (VPO/TiO2) catalysts for NOx removal with NH3-SCR at low temperature: Relationship between non-VOx phases and SO2&H2O resistance

Enhancing SO2&H2O resistance has important environmental implications for the NH3-selective catalytic reduction (NH3-SCR) catalysts in NOx removal. Herein, vanadium phosphorus oxides (VPO) were synthesized as active phases for NH3-SCR catalysts. Non-VOx phases containing (VO)2P2O7 and δ-VOPO4 were generated by adjusting the P/V molar ratio and the atmosphere properties of the activation and calcination. The NOx conversion of the VPO-1.5/TiO2 sample did not decrease (about 90%) after 6 h exposure to 180 °C, 500 ppm SO2 and 6% H2O. The abundant acid content (especially increased content of the weak Brønsted acids) corresponding to the non-VOx phases significantly inhibited stable SO2 adsorption on the catalyst surface. In-situ DRIFTS results showed that SO2 + O2 pre-adsorption on the catalyst surface had no significant influence on the adsorbed NH3 species. Density functional theory calculation also proves that SO2 has low competitive adsorption activity with NH3 and NO in the non-VOx phases. Under more severe conditions, the non-VOx phases still minimized the influence of SO2&H2O poisoning on surface acidity by inhibiting the accumulation of ammonium bisulfate. This work proposes a mechanism for enhancing SO2&H2O resistance with non-VOx phases, which is essential for extending the application of VPO/TiO2 catalysts from alkane selective oxidation to NH3-SCR.

Potassium poisoning impact on FeCu selective catalytic reduction catalyst: Structure and mechanism

Alkali metals bring great challenges to the elimination of NOx from stationary emissions in the selective catalytic reduction (SCR) reaction. The FeCu catalyst, as an eco-friendly and high-efficiency catalyst for NOx removal possesses wide application prospects. However, the poisoning effect of potassium is not clear. Therefore, the potassium poisoning catalyst was obtained by the wet impregnation means. The XRD, H2-TPR, NH3-TPD, XPS and DRIFT technologies were performed to study the influence of K poisoning. The results indicate that potassium causes damage to Cu-O-Fe construction. Then the Cu2+ in lattice of Fe2O3 separate out from Fe2O3 and form CuO which leads to the decline of acid sites and excessive NH3 oxidation. And it finally leads to the catalyst deactivation. After K poisoning, NO2, monodentate nitrates and nitrites cannot generate. Only bidentate nitrates can generate and then react with NH3 species on the Lewis acid sites to produce H2O and N2. Hence, the reaction rate has a slide.

Recent advance for NOx removal with carbonaceous material for low-temperature NH3-SCR reaction

The purification of gaseous pollutants, especially for nitrogen oxides, from the combustion of fossil fuels has become a concern matter at present. Selective catalytic reduction (SCR) technology is proved an effective method to remove nitrogen oxides. The performance of catalysts, such as the improvement of anti-poisoning ability and low-temperature catalytic efficiency, become the main direction of current extensive research. Carbonaceous materials were widely applied in low-temperature catalysts for removal of NOx due to their various structures and rich surface functional groups, and had potential to expand the function to remove multipollutant. Herein, different carbonaceous materials, activated methods and carbon-based NH3-SCR catalysts were concluded, and the corresponding reaction mechanisms were discussed. In addition, the removal of double or three contamination components with carbon-based catalysts were also summarized and discussed. Finally, further development directions for carbonaceous material in pollutants control were proposed.

In-situ DRIFTs study for synergistic removal of NOx and o-DCB over hydrotalcite-like structured Cr(x)/LDO catalysts

Developing efficient and stable catalysts for synergistic removal of NOx and dioxin has always been key for controlling air pollution.

Catalytic NO Reduction by NO Pre-Adsorbed RhCeO2 NO- Clusters.

A fundamental understanding on the dynamically structural evolution of catalysts induced by reactant gases under working conditions is challenging but pivotal in catalyst design. Herein, in combination with state-of-the-art mass spectrometry for cluster reactions, cryogenic photoelectron imaging spectroscopy, and quantum-chemical calculations, we identified that NO adsorption on rhodium-cerium bimetallic oxide cluster RhCeO2 - can create a Ce3+ ion in product RhCeO2 NO- that serves as the starting point to trigger the catalysis of NO reduction by CO. Theoretical calculations substantiated that the reduction of another two NO molecules into N2 O takes place exclusively on the Ce3+ ion while Rh behaves like a promoter to buffer electrons and cooperates with Ce3+ to drive NO reduction. Our finding demonstrates the importance of NO in regulating the catalytic behavior of Rh under reaction conditions and provides much-needed insights into the essence of NO reduction over Rh/CeO2 , one of the most efficient components in three-way catalysts for NOx removal.

Preparation and performance of monolithic Pd-based catalyst for simultaneous removal of NOx and particulate matter

Preparation and performance of monolithic Pd-based catalyst for simultaneous removal of NOx and particulate matter

Insight into the dynamic behaviors of reactants with temperature over a TiOx-based catalyst for NOx removal via NH3-SCR

NH3-SCR has been an efficient technology for purifying NOx from industrial facilities. However, it is still a huge challenge to clearly understand the intrinsic mechanisms. Here, in situ DRIFTS was employed for elucidating the adsorption behaviors, active sites and reaction routes over the model catalyst of CuNbTiOx. The oxygen played a vital role in the reactant adsorption and reaction process, especially for NOx adsorbing, in which oxygen could promote monodentate and bidentate nitrates forming and bridged nitrate increasing. Then the correlation between DRIFTS peak locations and active sites for NH3 adsorption was further defined, thereinto, the bands at ca. 1604 cm−1 represented the coordinated NH3 species at Cu2+. Similar with most SCR catalysts, CuNbTiOx exhibited various catalytic activities among different temperature ranges. It was found that NH3-SCR reaction occurred mainly via Langmuir-Hinshelwood pathway at 200 °C, in which the relatively inert nitrates and NH3 adsorption species restricted the low temperature activity. Afterwards, the reaction mechanism transformed into Eley-Rideal when the temperature was elevating to a high temperature of 400 °C due to the weak adsorption of NOx. These new findings provide an innovative view for understanding the surface reaction on catalysts, further facilitate the development of NH3-SCR catalysts.

Effects of cerium and tungsten addition on acid–base properties of spindle-like α-Fe2O3 in low-temperature SCR of NOx with NH3

Low-temperature selective catalytic reduction (SCR) is important for the elimination of NOx from stationary sources. In the present study, the loading of Ce and W on α-Fe2O3 was achieved through the integration of single-mode microwave and incipient wetness impregnation (IWI) methods. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal that the structure of α-Fe2O3 is spindle-like, and the structure remains unchanged after the introduction of Ce and/or W. The results of NH3-SCR investigation demonstrate that NOx conversion over Ce–W/α-Fe2O3 is more than 85% at 300 °C, which is much higher than that over Ce/α-Fe2O3 and α-Fe2O3. Our studies illustrate that the addition of Ce can significantly increase the amount of surface oxygen vacancies as well as sites of moderate basicity. On the other hand, the addition of W can obviously decrease the amount of basic sites and increase the number of Brønsted acid sites. The synergistic effect of Ce and W addition on balancing acidity/basicity properties accounts for the high activity of Ce20W10/α-Fe2O3 for NOx removal at low temperatures. The study provides insight into the relationship between acidity/basicity properties and catalytic performance of Ce–W/α-Fe2O3 catalysts, which is beneficial to the design of high-performance NH3-SCR catalyst for NOx removal at low temperatures.

Interaction Mechanism for Simultaneous Elimination of Nitrogen Oxides and Toluene over the Bifunctional CeO2-TiO2 Mixed Oxide Catalyst.

Simultaneous catalytic elimination of nitrogen oxides (NOx, x = 1 and 2) and volatile organic compounds (VOCs) is of great importance for environmental preservation in China. In this work, the interactions of simultaneous removal of NOx and methylbenzene (PhCH3) were investigated on a CeO2-TiO2 mixed oxide catalyst, which demonstrated excellent bifunctional removal efficiencies for the two pollutants. The results indicated that NOx positively promotes PhCH3 oxidation, while NH3 negatively inhibits through competitive adsorption with PhCH3. The underlying mechanism is that a pseudo PhCH3-SCR reaction happened in this process is parallel to NH3-SCR. Combined with in situ diffuse reflectance infrared Fourier transform spectroscopy and quasi in situ X-ray photoelectron spectroscopy, the interaction mechanism between NOx and PhCH3 is proposed. Specifically, NOx is adsorbed on the catalyst surface to produce nitrate species, which reacts with the carboxylate generated during PhCH3 oxidation to form organic nitrogen intermediates that create N2 and CO2 in the following reactions. In the reaction process, the superoxide (O2-) generated by O2 activation on the catalyst surface is an important species for the propelling of oxidation reaction. This work could provide guidelines for the design of state-of-the-art catalysts for simultaneous catalytic removal of NOx and VOCs.