High NH3-SCR Activity Research Articles

Unveiling the Promoting Effects of Zr and the Hydrothermal Treatment on the NH3-SCR Activity of the Cu-SAPO-18 Catalyst.

Selective catalytic reduction of NOx by NH3(NH3-SCR) remains challenging for diesel vehicles due to the complex exhaust condition. Cu-SAPO-18 zeolite has emerged as an efficient catalyst for the NH3-SCR process, attributed to its unique small pore configuration and high NH3-SCR activity. Herein, Zr-modified Cu-SAPO-18 has been fabricated and evaluated for the reduction of NOx. The addition of Zr to Cu-SAPO-18 led to enhanced activity, with the 0.05 wt % Zr-doped Cu-SAPO-18 catalyst achieving more than 90% NOx conversion across a temperature span of 230 to 470 °C. More importantly, hydrothermal aging at 750 °C further enhanced the activity significantly, achieving nearly 100% NOx conversion at 175 °C. The presence of Zr led to an increased amount of Cu2+ species and acid sites, while the hydrothermal treatment promoted a significant increase in acidity and facilitated the conversion of some Cu2+ to CuxOy species, which is crucial for the enhanced activity. The present research provides insights into the development of high-efficiency small-pore zeolite-based NH3-SCR catalysts, offering valuable implications for both fundamental research and industrial catalysis.

Iron-containing tailings catalyst modified by Mn for SCR of NO with NH3 at low temperature: Study of carrier treatment and calcination temperature

The development of cost-effective low temperature selective catalytic reduction (NH3-SCR) catalysts for nitrogen oxides is a major challenge. To this end, a low-cost rare earth tailings catalyst modified by Mn was successfully synthesized by the impregnation method using rare earth tailings as raw materials. The iron-containing tailings catalyst modified by Mn exhibited high NH3 SCR activity with high N2 selectivity at low temperature range (150–200 ℃). The H2SO4 modification resulted in the weakening of the Fe-O bonds on the catalyst, thereby producing the active component, iron sulfate salt. The coordination occupancy of Brønsted acid sites is increased, thereby facilitating electron transfer and redox cycling of SCR. Furthermore, by modulating the calcination temperature, the synergistic effect of Fe and Mn is augmented, resulting in the generation of a substantial number of Mn-Fe composite oxides, which is conducive to the enhancement of NH3 adsorption and activation on the catalyst. The formation of additional Brønsted acids was identified as a primary factor influencing the enhancement of N2 selectivity in the catalyst. The catalytic process followed both the E-R and L-H mechanisms on the catalyst. The Iron-containing tailings catalyst modified by Mn represents a cost-effective and resource-conserving alternative. The provision of high denitrification efficiency, coupled with the capacity to address the issue of low N2 selectivity, offers a sustainable and low-carbon solution for the industrial reduction of NOx.

Essential features of weak current for excellent enhancement of NOx reduction over monoatomic V-based catalyst

Human society is facing increasingly serious problems of environmental pollution and energy shortage, and up to now, achieving high NH3-SCR activity at ultra-low temperatures (<150 °C) remains challenging for the V-based catalysts with V content below 2%. In this study, the monoatomic V-based catalyst under the weak current-assisted strategy can completely convert NOx into N2 at ultra-low temperature with V content of 1.36%, which shows the preeminent turnover frequencies (TOF145 °C = 1.97×10−3 s−1). The improvement of catalytic performance is mainly attributed to the enhancement catalysis of weak current (ECWC) rather than electric field, which significantly reduce the energy consumption of the catalytic system by more than 90%. The further mechanism research for the ECWC based on a series of weak current-assisted characterization means and DFT calculations confirms that migrated electrons mainly concentrate around the V single atoms and increase the proportion of antibonding orbitals, which make the V-O chemical bond weaker (electron scissors effect) and thus accelerate oxygen circulation. The novel current-assisted catalysis in the present work can potentially apply to other environmental and energy fields.

Simple preparation of V2O5-WO3/TiO2/SiC catalytic membrane with highly efficient dust removal and NO reduction

Simplifing the preparation process is an efficient method to reduce process energy consumption and product costs. In this work, a one-step vacuum impregnation technology was developed for the preparation of V2O5-WO3/TiO2 catalyst modified SiC (VWTi/SiC) catalytic membranes. In comparison to VWTi/SiC (II) catalytic membrane prepared by the traditional two-step method, the VWTi/SiC (I-X) catalytic membrane prepared via one-step vacuum impregnation technology demonstrate significant advantages in terms of energy saving and consumption reduction. Owing to the strongest activation ability for O2 and NH3 induced by high V4+ species and strong V-W interaction, the optimal VWTi/SiC (I-500) can achieve 90 % ammonia selective catalytic reduction (NH3-SCR) denitrition efficiency at the temperature range from 200 °C to 350 °C, presenting a much higher NH3-SCR activity than VWTi/SiC (II-500). The evaluation of sulfur resistance, long-term stability and dust filtration performance proposed that VWTi/SiC (I-500) demonstrated excellent sulfur resistance and outstanding long-term stability and excellent dust filtration performance (particle interception rate exceeds 99.9 % for typical 2.5 μm silicon dioxide particles) at various condition. Therefore, the VWTi/SiC catalytic membrane prepared by one-step vacuum impregnation method holds great promise and development potential for high-temperature flue gas purification.

Reasonably designed CuSbTiOx series catalysts with high NH3-SCR activity and obviously improved SO2 tolerance

The mechanism for NOx reduction in CuSbTiOx-0.2 catalyst.

Cu docking-activated Nb incorporation in multivariate CuO-Nb2O5/CeO2 catalysts for selective reduction of NOx with NH3

Improving the low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR) meanwhile maintaining N2 selectivity are challenging in the field of catalysis. Herein, we showcase the fabrication of the synergistic catalytic sites in the CuO-Nb2O5/CeO2 catalysts. Impressively, the CuO-Nb2O5/CeO2 is characteristic with abundant oxygen vacancies at the interfacial regions, which facilitate the redox reaction between Ce3+, Nb5+ and Cu2+ with the assistance of surface oxygen, exhibiting high NH3-SCR activity, N2 selectivity and wide temperature window at a gas hourly space velocity of 150,000 h−1. Contrast experiments, EXAFS analysis, in situ infrared and Raman spectroscopy, and theoretical calculations indicate that the introduction of proper copper ions in the CeO2 lattice induces the structure distortion of surface CeO2, improving more niobium ions incorporation into the CeO2. The embedded Nb synergizes Cu and Ce to evoke the generation of newly adsorptive sites for NOx and NH3, thus contributing to the NH3-SCR reaction.

Dual improvement in acid and redox properties of the FeOx/OAC catalyst via APS oxygen-functionalization: High low-temperature NH3-SCR activity, SO2 and H2O tolerance

Carbon-based transition metal catalysts (CTCs) have shown tremendous potential within NOx abatement, while the improvement of low-temperature NH3-SCR activity and SO2 and H2O tolerance remains challenging. Herein, we report an easily-achievable strategy to regulate the active phases of the FeOx/AC catalyst via APS oxygen-functionalization for improving in acid and redox properties and facilitating NH3-SCR activity. For redox sites, APS oxygen-functionalization boosted the metal-support interaction, immobilized γ-Fe2O3 nanoparticles highly dispersed on FeOx/OAC1.5-60-3 surface. Meanwhile, Fe valence and oxygen vacancy of FeOx were tailored by APS oxygen-functionalization, resulting in the formation of active oxygen vacancy-coupled Fe2+. For acid sites, in situ DRIFTs further confirmed that APS oxygen-functionalization enhanced the adsorption and activation properties of NH3 over the oxygen-containing functional groups (OCFGs) on FeOx/OAC1.5-60-3. Due to the improvement of acid and redox properties, FeOx/OAC1.5-60-3 delivered superior NO conversion (>90 %) at 120–250 °C and SO2/H2O resistance in comparison with FeOx/AC. Therefore, this work sheds light on a robust and pragmatic strategy for the rational design of CTCs and provides a new insight in improving catalytic performance of CTCs.

Water in the ball-milling process affects the dispersion of vanadia species on V2O5/TiO2 catalysts for NH3-SCR

Water in the ball-milling process increased polymeric vanadyl species and enhanced the redox capability, resulting in high NH3-SCR activity of V2O5/TiO2.

Insights into samarium doping effects on catalytic activity and SO2 tolerance of MnFeOx catalyst for low-temperature NH3-SCR reaction

The development of catalysts with high NH3-SCR activity in the presence of SO2 was urgent for non-electric industries to control NOx emission at low temperature. Herein, a series of Sm-doping MnFeOx catalysts were synthesized through a typical PEG-assisted co-precipitation method and applied for low-temperature NH3-SCR process. SmMnFe-0.1 catalyst significantly broadened the activation temperature window and yielded almost 100% NO conversion from 75 to 200 °C, simultaneously, the NO removal efficiency still maintained at about 90% in the presence of SO2 and H2O. The characterization results confirmed that Sm could optimize the dispersity of active components and enlarge the surface area of catalyst. Furthermore, strong interaction among active ions facilitated more oxygen vacancies and accelerated NO oxidizing to NO2, further cooperating with abundant adsorbed NH3, leading to cause “Fast SCR” reaction. Both catalysts were dominated by the E-R mechanism despite MnFeOx catalyst also obeyed the L-H pathway. Particularly, the intense redox circles between Sm and Mn inhibited the electron transferring from SO2 to Mn ions, and induced Fe species serving as sacrificial sites along with Sm to preferentially react with SO2, resulting in an excellent SO2 tolerance, and the possible mechanism model was proposed.

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.

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.

Revealing active species of CePO4 catalyst for selective catalytic reduction of NOx with NH3

Revealing the active species of the catalyst is conducive to the design of more efficient catalyst. Herein, we tried to demonstrate the roles of amorphous and crystalline structures on CePO4 catalyst during selective catalytic reduction (SCR) of NOx by NH3. Higher calcination temperature promotes the transfer of amorphous structure to crystalline structure on the surface of CePO4. Both amorphous and crystalline CePO4 species on CePO-X samples can provide acid sites for NH3 adsorption, but the former can provide more acid sites. The superior redox property of surface amorphous CePO4 species contributes to its high NH3-SCR activity at low temperature, but it also leads to the decrease of high temperature (>350 °C) NH3-SCR activity due to the oxidation of NH3. In contrast, crystalline CePO4 species shows high activity only at high temperature because of its poor redox property. Therefore, it can be inferred that amorphous and crystalline structures on CePO4 catalyst can be the efficient active species of NH3-SCR at low and high temperature, respectively.

Promotional effect of phosphorus modification on improving the Na resistance of V2O5-MoO3/TiO2 catalyst for selective catalytic reduction of NO by NH3

Improving the resistance to alkali metals poisoning of commercial V2O5-TiO2 based catalyst could significantly enhance its service life. In this work, a simple method of incorporating P species was developed to enhance the resistance to Na species of commercial V2O5-MoO3/TiO2 (V-Mo/Ti) catalyst. XRD and N2-adsorption results proposed that P adding have no obvious influence on the structure of V-Mo/Ti. However, the results referred from the H2-TPR, XPS, NH3-TPD and NH3-DRIFTS suggested that Na species preferentially reacted with P species than V2O5 species, which preserved most of redox sites (V = O structure) and acid sites (V−OH structure) on V-Mo-P/Ti catalyst. Thus, V-Mo-P-Na/Ti presented a much higher NH3-SCR activity than V-Mo-Na/Ti. Finally, possible promotional mechanism of P modification on improving Na resistance of V-Mo/Ti catalyst was proposed. We expect this work could contributed to the studies on preparing high effective NH3-SCR catalysts.

Effect of gas composition on the NOx adsorption and reduction activity of a dual-function Ag/MgO/[formula omitted]-Al2O3 catalyst

An Ag/MgO/γ-Al2O3 catalyst is developed, which can perform the dual role of a passive NOx adsorber (PNA) at low temperatures and a NOx reduction catalyst at higher temperatures. The effect of H2O and CO2, as well as various reductants such as H2, NH3, and C3H6 on its deNOx performance is investigated. The NOx storage is comparable to that obtained by Pd-based PNAs, and occurs through a spillover mechanism. The presence of H2 remarkably increases the low-temperature NOx adsorption and binding strength, and is attributed to the significant formation of nitrates as opposed to the predominant formation of nitrites in the absence of H2. Moreover, the positive effect of H2 is not related to the H2-SCR activity of the catalyst or an enhancement in the NO oxidation activity. C3H6 inhibits NOx storage, but the presence of H2 promotes it considerably. A significantly high NH3-SCR activity with negligible N2O formation is measured at 150 °C, while C3H6-SCR activity is exhibited at higher temperatures. However, the presence of NH3 does not affect the binding of NOx on the various adsorption sites, which is primarily governed by the presence of H2.

A Study on Mn-Fe Catalysts Supported on Coal Fly Ash for Low-Temperature Selective Catalytic Reduction of NOX in Flue Gas

A series of Mn0.15Fe0.05/fly-ash catalysts have been synthesized by the co-precipitation method using coal fly ash (FA) as the catalyst carrier. The catalyst showed high catalytic activity for low-temperature selective catalytic reduction (LTSCR) of NO with NH3. The catalytic reaction experiments were carried out using a lab-scale fixed-bed reactor. De-NOx experimental results showed the use of optimum weight ratio of Mn/FA and Fe/FA, resulted in high NH3-SCR (selective catalytic reduction) activity with a broad operating temperature range (130–300 °C) under 50000 h−1. Various characterization methods were used to understand the role of the physicochemical structure of the synthesized catalysts on their De-NOx capability. The scanning electron microscopy, physical adsorption-desorption, and X-ray photoelectron spectroscopy showed the interaction among the MnOx, FeOx, and the substrate increased the surface area, the amount of high valence metal state (Mn4+, Mn3+, and Fe3+), and the surface adsorbed oxygen. Hence, redox cycles (Fe3+ + Mn2+ ↔ Mn3+ + Fe2+; Fe2+ + Mn4+ ↔ Mn3+ + Fe3+) were co-promoted over the catalyst. The balance between the adsorption ability of the reactants and the redox ability can promote the excellent NOx conversion ability of the catalyst at low temperatures. Furthermore, NH3/NO temperature-programmed desorption, NH3/NO- thermo gravimetric-mass spectrometry (NH3/NO-TG-MS), and in-situ DRIFTs (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) results showed the Mn0.15Fe0.05/FA has relatively high adsorption capacity and activation capability of reactants (NO, O2, and NH3) at low temperatures. These results also showed that the Langmuir–Hinshelwood (L–H) reaction mechanism is the main reaction mechanism through which NH3-SCR reactions took place. This work is important for synthesizing an efficient and environmentally-friendly catalyst and demonstrates a promising waste-utilization strategy.

Starch bio-template synthesis of W-doped CeO2 catalyst for selective catalytic reduction of NOx with NH3: influence of ignition temperature.

A novel tungsten-doped CeO2 catalyst was fabricated via the sweet potato starch bio-template spread self-combustion (SSC) method to secure a high NH3-SCR activity. The study focuses on the influence of ignition temperature on the physical structure and redox properties of the synthesized catalyst and the catalytic performance of NOx reduction with NH3. These were quantitatively examined by conducting TG-DSC measurements of the starch gel, XRD analysis for the crystallites, SEM and TEM assessments for the morphology of the catalyst, XPS and H2-TPR measurements for the distribution of cerium and tungsten, and NH3-TPD assessments for the acidity of the catalyst. It is found that the ignition temperature shows an important role in the interaction of cerium and tungsten species, and the optimal ignition temperature is 500 °C. The increase of ignition temperature from 150 °C is beneficial to the interactions of species in the catalyst, depresses the formation of WO3, and refines the cubic CeO2 crystallite. The sample ignited at 500 °C shows the biggest BET surface area, the highest surface concentration of Ce species and molar ratio of Ce3+/(Ce3++Ce4+), and the most abundant surface Brønsted acid sites, which are the possible reasons for the superiority of the NH3-SCR activity. With a high GHSV of 200,000 mL (g h)-1 and the optimal ignition temperature, Ce4W2Oz-500 can achieve a steadily high NOx reduction of 80% or more at a lowered reduction temperature in the range of 250~500 °C.

Understanding the high hydrothermal stability and NH3-SCR activity of the fast-synthesized ERI zeolite

ERI zeolite is a small-pore zeolite that has been rarely explored as a catalyst in the selective catalytic reduction of NOx with ammonia (NH3-SCR) as the performance has been considered to be limited by its insufficient hydrothermal stability. We herein report that a fast-synthesized ERI zeolite, which can be synthesized in only 2 h at a high temperature (210 °C), shows much enhanced hydrothermal stability than the conventional ERI zeolite due to the presence of less silanol defects. The fast-synthesized ERI zeolite with an optimal copper loading (equaling a Cu/Al ratio of 0.20) is demonstrated to be highly active in the NH3-SCR, which even rivals Cu-SSZ-13 – the benchmark NH3-SCR catalyst. Various characterization techniques are employed to characterize the copper species in the fast-synthesized ERI zeolite in order to understand its high hydrothermal stability and NH3-SCR activity. The results indicate that the copper species sitting at different locations exhibit variant hydrothermal stability and NH3-SCR activity, suggesting the importance of the interplay between the copper species and the zeolite host. With a deep understanding into the structure-activity relationship, this work presents that the fast-synthesized ERI zeolite holds potential to emerge as a robust NH3-SCR catalyst for emission control.

Fabrication of Cu-CHA composites with enhanced NH3-SCR catalytic performances and hydrothermal stabilities

Cu-SSZ-13 and Cu-SAPO-34, both with CHA topology but different compositions, are highly active NH3-SCR catalysts for the abatement of harmful nitrogen oxides from the exhausts of lean-burn engines. However, the former suffers from high preparation cost and worse high-temperature hydrothermal stability, and the latter is limited by its poor low-temperature hydrothermal stability. Herein, a new Cu-CHA composite (named Cu-CHADNL) containing both microenvironments of SSZ-13 and SAPO-34 was synthesized by employing one-pot synthesized Cu-SSZ-13 as Cu source, seeds and part of Si/Al source. The resultant materials have cubic-like morphology, high Si contents, controllable Cu loadings and uniform Si/P/Al/Cu elemental distributions. Solid state MAS NMR, NH3-DRIFTS and H2-TPR demonstrate the coexistence of aluminosilicate and SAPO zones in the Cu-CHADNL crystals. Notably, Cu-CHADNL exhibits high NH3-SCR activity in wide temperature window and robust resistance against both steaming at 800 °C and soaking in 80 °C water. These advantages are owing to the unique composite microstructures of Cu-CHADNL and suggest the material has huge application potential in deNOx process.

A novel Cerium-Tin composite oxide catalyst with high SO2 tolerance for selective catalytic reduction of NOx with NH3

The selective catalytic reduction for reducing NOx with NH3 (NH3-SCR) has been widespread used in denitration. Considering the shortcomings of vanadium-based catalysts, a series of novel CeO2-SnO2 composite oxide catalysts with good SO2 tolerance were developed. The effects of preparation methods on the catalytic performance had been systematically studied by characterization methods, such as XRD, SEM, N2 adsorption–desorption, H2-TPR, NH3-TPD, XPS and in situ Fourier transform infrared spectroscopy (FTIR). Characterization results concluded that the catalytic performance was closely related to the different physicochemical property resulting from preparation methods. CeO2-SnO2 composite catalyst was prepared by coprecipitation method (CeSn-CP) that displayed high NH3-SCR activity and good SO2 tolerance. The coprecipitation method resulted in the high dispersion of SnO2 species and the formation of binary solid solution. Binary solid solution was beneficial to play the synergetic effect between CeO2 and SnO2, which had improved reduction ability and acidity, and thus an apparent promotion of activity was presented.

Nanosized Cu-SSZ-13 and Its Application in NH3-SCR

Nanosized SSZ-13 was synthesized hydrothermally by applying N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) as a structure-directing agent. In the next step, the quantity of TMAdaOH in the initial synthesis mixture of SSZ-13 was reduced by half. Furthermore, we varied the sodium hydroxide concentration. After ion-exchange with copper ions (Cu2+ and Cu+), the Cu-SSZ-13 catalysts were characterized to explore their framework composition (XRD, solid-state NMR, ICP-OES), texture (N2-sorption, SEM) and acid/redox properties (FT-IR, TPR-H2, DR UV-Vis, EPR). Finally, the materials were tested in the selective catalytic reduction of NOx with ammonia (NH3-SCR). The main difference between the Cu-SSZ-13 catalysts was the number of Cu2+ in the double six-membered ring (6MRs). Such copper species contribute to a high NH3-SCR activity. Nevertheless, all materials show comparable activity in NH3-SCR up to 350 °C. Above 350 °C, NO conversion decreased for Cu-SSZ-13(2–4) due to side reaction of NH3 oxidation.