Ammonia Selective Catalytic Reduction Research Articles

Investigation of CNT and Zn doped Cu-SSZ-13 zeolite catalyst for ammonia selective catalytic reduction activity of NOx

Hybrid Cu-SSZ-13 zeolite catalyst are prepared and analyzed for NH3-SCR activity with different topologies in the present investigation. Cu-SSZ-13 was synthesized by ionexchange method, and hybrid Cu-SSZ-13 was synthesized by wet-impregnation method with three different molar ratios between Znx-CNTy as 1:5, 1:10, & 1:15 and maintained as 1:5 mass ratio between Znx-CNTy/Cu-SSZ-13 hybrid zeolite catalysts. The catalytic activity measured at a temperature window of 100˚C to 550˚C concludes hybrid Zn1- CNT10/Cu-SSZ-13 catalyst exhibits high NH3-SCR performance (100%) at a temperature of 180˚C to 475˚C and by anti-sulfur activity, it exhibits 80% NOx at 300˚C for 8hrs in the presence of SO2 gas in feed aid that addition of Zn species and CNTs influence Cu-SSZ13 in NH3-SCR activity finding them to be a better catalyst for NOx reduction.

Study on the Performance of the Zr-Modified Cu-SSZ-13 Catalyst for Low-Temperature NH3-SCR.

Cu-SSZ-13 and Zr-modified Cu-SSZ-13 catalysts with different Zr/Cu mass ratios were prepared by ion-exchange and impregnation methods, respectively. The NH3-SCR performance tests were performed using the catalyst performance evaluation device to investigate the effects of different Zr/Cu mass ratios on the catalyst ammonia-selective catalytic reduction (NH3-SCR) performance. X-ray diffraction, ICP-OES, BET, NH3 temperature-programed desorption (NH3-TPD), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectrometry, and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) were used to characterize the catalysts. The results show that the prepared Cu-SSZ-13 catalyst had good catalytic activity. Zr introduction was carried out on this basis. The results showed that proper Zr doping improved the catalytic activity at low temperatures and widened the high-temperature stage, with an optimal activity stage at a Zr/Cu mass ratio of 0.2. The NO x conversion efficiency was close to 100% at 200 °C and over 80% at 450 °C. The active species were well dispersed on the catalyst surface, and the metal modification did not change the crystal structure of the zeolite. The NH3-TPD results showed that the Zr-modified catalyst had more abundant acid sites, and the H2-TPR results indicated that the Cu species on the catalyst had excellent reducibility at low temperatures. The interaction between Cu and Zr could regulate the Cu+ and Cu2+ proportion on the catalyst surface, which facilitated the increase in the Cu+ for fast SCR reaction at low temperatures. With abundant acid sites and both SCR reactions following the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanism on the catalyst surface at a low temperature of 150 °C, more abundant acid sites and reaction paths created favorable conditions for NH3-SCR reactions at low temperatures.

A review on zeolite catalyst for deNOx performance in ammonia–selective catalytic reduction

Internal combustion (IC) engines rely heavily on NOx emissions. Various studies are being conducted to lower NOx emission in order to achieve the BS-VI norms. This review examines a zeolite catalyst using metal substitutes, primarily copper Cu, and iron Fe, and compares it to a commercial vanadium catalyst in terms of deNOx efficiency and deactivation process. Based on the size of pores of zeolite, it has been classified into large size, medium size and small size zeolites. At low temperature, small pore zeolite with Cu substituted has better deNOx efficiency with higher thermal stability with high-temperature reaction conditions. Whereas, Cu-SSZ-13 & Cu-SAPO-34 exhibits wider temperature window and also exhibits good thermal stability even below 350 °C. Si/Al ratio (SAR) plays a vital role in deNOx efficiency.

The Effect of Iron Content on the Ammonia Selective Catalytic Reduction Reaction (NH3-SCR) Catalytic Performance of FeOx/SAPO-34.

Iron-based catalysts are regarded as promising candidates for the ammonia selective catalytic reduction reaction (NH3-SCR) which show good catalytic activity at medium and high temperatures, whereas SAPO-34 molecular sieves have a micro-pore structure and are ideal catalyst carriers. In this paper, four FeOx/SAPO-34 molecular sieve catalysts with different iron contents (Fe = 1%, 2%, 3%, 4%) were prepared using an impregnation method. The effect of iron content on the surface properties and catalytic activity was investigated by a series of characterization techniques including XRD, SEM, BET, XPS, H2-TPR and NH3-TPD. Iron species in the FeOx/SAPO-34 catalysts exist in the form of isolated iron ions or well-dispersed small crystals and iron oxide species clusters. With the addition of iron content, the integrity of CHA (chabazite) zeolite structure remained, but the crystallinity was affected. The FeOx/SAPO-34 catalyst with 3% Fe loading showed a relatively flat surface with no large-diameter particles and strong oxidation-reduction ability. Meanwhile, more acidic sites are exposed, which accelerated the process of catalytic reaction. Thus, the FeOx/SAPO-34 catalyst with 3% Fe showed the best NO conversion performance among the four catalysts prepared and maintained more than 90% NO conversion efficiency in a wide temperature range from 310 °C to 450 °C.

A novel low-temperature Fe-Fe double-atom catalyst for a “fast SCR” reaction

Theoretically designing a catalyst with high catalytic activity for ammonia selective catalytic reduction (NH3-SCR) reaction at low temperature to guide the subsequent experimental synthesis, which is of great significance for controlling the emission of NOx. Herein, we examine for the first time Fe2-N6 catalysts as candidates for this application at a theoretical level. The adsorption behavior of various gases, catalytic mechanism of the NH3-SCR reaction, and turnover frequency were analyzed using density functional theory calculations (DFT) and microkinetic modeling. We found that a “fast SCR” reaction is the dominant path of the NH3-SCR reaction. The energy barrier for the rate-determining step (HONO formation) is 1.00 eV, much lower than that of other SCR catalysts. In addition, the Fe2-N6 catalyst exhibits outstanding low-temperature activities in the temperature window from 300 to 500 K.

Mesoporous–optimized BaMnO3 perovskite small-scale nanocrystals in SSZ-13 to enhance activity for the selective catalytic reduction reaction of NO

As one of the cores of ammonia-selective catalytic reduction technology (NH3-SCR), conventional microporous Cu-SSZ-13 has developed hierarchical pores in recent years. The reasonable use of newly mesoporous channels to improve catalytic activity has become a new challenge. We designed novel hierarchical Cu-SSZ-13 catalyst supported with BaMnO3 perovskite, which exhibited excellent low-temperature SCR activity. A series of characterizations illustrated that BaMnO3 was introduced into mesopores located in hierarchical Cu-SSZ-13 and form small-scale nanocrystals of 5–10 nm, which significantly improves the ability to oxidize NO to NO2. In addition, the synergistic effect caused by introduced BaMnO3 and Cu species makes BaMnO3-Cu-SSZ-13 have higher Mn4+ proportion and stronger redox ability. In situ DRIFTS experiments revealed that the introduced BaMnO3 enhanced the reactivity of ammonia and NOx species. Different from the monodentate nitrate observed on Cu-SSZ-13, the reaction intermediate bidentate nitrate and ads-NO2 appeared on BaMnO3-Cu-SSZ-13 in the reaction process, which is also a crucial reason for the higher low-temperature activity.

Influence of Fe–Cu-SSZ-13 and hybrid Fe–Cu-SSZ-13 zeolite catalyst in ammonia-selective catalytic reduction (NH3-SCR) of NOx

Influence of Fe–Cu-SSZ-13 and hybrid Fe–Cu-SSZ-13 zeolite catalyst in ammonia-selective catalytic reduction (NH3-SCR) of NOx

Fe-promoted V/W/TiO2 catalysts for enhanced low-temperature denitrification efficiency

Research on low-temperature ammonia selective catalytic reduction (NH3-SCR) is being actively conducted to reduce the operating costs of environmental facilities and fulfill stringent environmental regulations. The main limitation of these catalysts is the low denitrification (DeNOx) efficiency of flue gas at temperatures below 200 °C. In this study, the effect of Fe doping on the low-temperature SCR activity of V/W/TiO2 catalysts was investigated. The addition of 0.5 wt% Fe to V/W/TiO2 catalysts resulted in excellent DeNOx efficiency (84%) at 180 °C. The presence of Fe as a structural and electronic promoter in the V/W/TiO2 catalyst increased the dispersion of W5+, Fe3+, and non-stoichiometric V4+ species and improved the redox properties of the catalyst. In addition, the DeNOx efficiency of low-temperature NH3-SCR was greatly affected by the adsorption capacity of the NH3-Lewis acid sites and the reoxidation ability of the V/W-0.5Fe/TiO2 catalyst.

Simultaneous removal of NO and CO over Ni-Ce bifunctional catalyst supported by modified activated coke at oxygen-rich condition

The modified activated coke (AC-N) supported Ni-Ce transition metal catalyst prepared by incipient-wetness impregnation method can simultaneously catalyze the ammonia selective catalytic reduction (NH3-SCR) reaction and CO oxidation reaction, realizing the removal of NO and CO under low temperature and oxygen-rich conditions. The Ni-Ce/AC-N catalyst can achieve high-efficiency conversion of NO and CO at 175–250 °C, and the conversion rates of NO and CO are both above 95% in this temperature range. After modified by nitric acid, the active coke support has a stronger interaction with metal components, which is conducive to better dispersion of the active components on the catalyst surface, and improves the specific surface area and redox capacity of the catalyst. The synergistic effect between Ni and Ce results in more Ni2+ and Ce3+ species on the catalyst surface, which is beneficial to the improvement of catalytic activity.

Rate Controlling in Low-Temperature Standard NH3-SCR: Implications from Operando EPR Spectroscopy and Reaction Kinetics.

A series of seven Cu/SSZ-13 catalysts with Si/Al = 6.7 are used to elucidate key rate-controlling factors during low-temperature standard ammonia-selective catalytic reduction (NH3-SCR), via a combination of SCR kinetics and operando electron paramagnetic resonance (EPR) spectroscopy. Strong Cu-loading-dependent kinetics, with Cu atomic efficiency increasing nearly by an order of magnitude, is found when per chabazite cage occupancy for Cu ion increases from ∼0.04 to ∼0.3. This is due mainly to the release of intercage Cu transfer constraints that facilitates the redox chemistry, as evidenced from detailed Arrhenius analysis. Operando EPR spectroscopy studies reveal strong connectivity between Cu-ion dynamics and SCR kinetics, based on which it is concluded that under low-temperature steady-state SCR, kinetically most relevant Cu species are those with the highest intercage mobility. Transient binuclear Cu species are mechanistically relevant species, but their splitting and cohabitation are indispensable for low-temperature kinetics.

New insight on N2O formation over MnOx/TiO2 catalysts for selective catalytic reduction of NOx with NH3

High N2O selectivity of MnOx-TiO2 catalyst hinders its development in ammonia selective catalytic reduction (NH3-SCR) of NOx. Herein, a series of MnOx-TiO2 catalyst with different Mn/Ti ratio were prepared by wet-impregnation method to study the N2O formation during ammonia selective catalytic reduction (NH3-SCR) of NOx from the perspective of catalyst. It is found that MnOx and TiO2 species are the mainly redox and acid sites for the NH3-SCR denitration reaction over MnOx-TiO2 catalyst, respectively. As the Mn/Ti ratio increases, MnOx species layer expanded on TiO2 support, leading to increase of redox sites but decrease of surface acid sites. These changes contribute to the occurrence of the no-selective oxidation of NH3 on MnOx species and the over-activation of NH3 at Mn-Ti interface, resulting in the formation of N2O via the route of 2NH3 + 2O2 → N2O + 3H2O and 4NO + 4NH3 + 3O2 → 4N2O + 6H2O, respectively. Through this work, it can be speculated that both improving MnOx dispersion and increasing surface acidity of catalyst are feasible strategy for suppressing the N2O formation on MnOx-TiO2.

Promoting NH3-SCR denitration via CO oxidation over CuO promoted V2O5-WO3/TiO2 catalysts under oxygen-rich conditions

Ammonia selective catalytic reduction (NH3-SCR) technique for nitrogen oxide (NOx) elimination of low temperature flue gas (<200 °C) requires huge energy consumption and operation costs. In this work, a CuO modified V2O5-WO3/TiO2 (Cu/VWTi) catalyst are constructed to achieve the aim of enhancing the temperature of flue gas via using the heat released by CO oxidation, thereby promoting the NH3-SCR of NOx reaction. Benefiting from the synergistic effect between CuO and VWTi in the adsorption and activation of reactants, Cu/VWTi catalyst shows high NOx (>90%) and CO (>90%) removal efficiency at the temperature range of 225–270 °C and a GHSV of 40,000 h−1. Moreover, it is found that the completely oxidation of 2000 ppm CO can increase the flue gas temperature by about 20 °C. Therefore, developing catalyst that can achieve simultaneously NH3-SCR of NOx and CO oxidation is a feasible method to deduce the energy consumption and operation costs of NH3-SCR of NOx system in low temperature flue gas. Finally, the reaction process and SO2 deactivation effect over Cu/VWTi catalyst was studied via in-situ DRIFT. This work might provide some guidance for the design of catalysts to eliminate multiple pollutants.

New CHA-Type aluminoborosilicates as efficient catalysts for MTO and NH3-SCR of NOx reactions

The small-pore CHA-type zeolites have received intensive attentions due to their outstanding performance in both of the methanol-to-olefin (MTO) process and ammonia selective catalytic reduction of nitrogen oxides (NH3-SCR of NOx) reactions. However, the costly synthesis of CHA-type aluminosilicate is a great issue for the practical application. In this study, a novel and cheap organic structure-directing agent of N,N,N-trimethylisobutylammonium hydroxide was developed and used to synthesize CHA-type zeolites (name as ECNU-25) with boric acid as the supporting agent. The Si/Al ratio in the synthetic gel could be tailored in a wide range of 50 - ∞. [Al,B]-ECNU-25 zeolite thus synthesized served as an effective catalyst for the MTO reaction. After Cu2+-exchange, the Cu-[Al,B]-ECNU-25 was also highly active in the NH3-SCR of NOx.

Inhibition effect of naphthalene on V2O5-WO3/TiO2 catalysts for low-temperature NH3-SCR of NOx

Coal tar in the glass furnace flue gas can poison the V2O5-WO3/TiO2 (VWTi) catalyst used for ammonia selective catalytic reduction (NH3-SCR) of NOx. Herein, naphthalene (Nap), as one of the main components of coal tar, was selected to investigate the poisoning effect of coal tar on VWTi catalyst in the range of 200–280 ℃. The experimental results showed that the activity of VWTi catalyst decreased sharply with the introduction of Nap vapor, and the NOx conversion was less than 20% after the introduction of 1 h at the temperature range of 200–280 ℃. The poison processing and mechanism were systematically investigated. It was found that the Nap preferentially consumes active oxygens on the catalyst to form phthalic anhydride (PA) with a higher boiling point, which covers the active sites and leads to the deactivation of VWTi catalyst. Temperature affects the accumulation of deposits and the conversion rate of Nap, thus poisoning effect of Nap on VWTi is temperature-sensitive. The deposited Nap can be removed at high temperatures. Therefore, the inactivated catalysts can be regenerated by high temperature treatment.

A Bifunctional Multishell Catalyst with a Wide Operating Temperature Window for NOx Abatement by Ammonia-Selective Catalytic Reduction

A Bifunctional Multishell Catalyst with a Wide Operating Temperature Window for NO_<i>x</i> Abatement by Ammonia-Selective Catalytic Reduction

The promotional role of Nd on the catalytic activity and hydrothermal stability of Cu-SAPO-18 catalyst for NH3-SCR reaction

The Cu-SAPO-18 was prepared by the one-pot method and modified through hydrothermal post-treatment, metal-doped Nd(x)/Cu-SAPO-18 (x = 0.4, 0.8, 1.2, 1.6) catalysts were obtained. The catalytic performance of fresh and aged Nd(x)/Cu-SAPO-18 was evaluated by ammonia selective catalytic reduction (NH3-SCR) reaction. The NOx conversion rate of Nd (1.2)/Cu-SAPO-18 was highest. More than 94.5% NOx conversion was maintained over the aged Nd(x)/Cu-SAPO-18 during 250–450°C, which was almost 10% higher than the conversion of aged Cu-SAPO-18. Various techniques including XRD, XRF, BET, SEM, 27Al MAS NMR, XPS, UV-vis, NH3-TPD, H2-TPR, were applied to explore the effect of Nd content on the physiochemistry property of Cu-SAPO-18. The addition of Nd effectively maintained the relatively large specific surface area and uniform pore size distribution. Moreover, the dealumination progress of Cu-SAPO-18 was mitigated and the aggregation of copper species during hydrothermal aging process was restrained. Thus, Nd(x)/Cu-SAPO-18 owed less CuOx and more amount of isolated Cu2+ ions, which stabilized catalyst structure by entering the double 6-membered ring (D6R). Meanwhile, the incorporation of Nd enhanced the redox property and stabilised surface acid sites of Cu-SAPO-18, which were responsible for facilitating the adsorption and activation of reactants.

A strategy for constructing highly efficient Co3O4-C@SiO2 nanofibers catalytic membrane for NH3-SCR of NO and dust filtration

The strategy of constructing catalytic membrane has a significant influence on its structure and performance. In this work, Co3O4-Cx@SiO2 nanofiber membranes (NFMs) were fabricated by an in-situ growth–pyrolysis–oxidation strategy. The Co3O4-Cx catalyst derived from ZIF-67 was wrapped around nanofibers, which helps to maintain a stable membrane structure, then suppressing the reduction of gas permeability. Among the Co3O4-Cx catalyst, the carbon skeleton can prevent the agglomeration of Co3O4 nanoparticles, obtaining an ultra-fine Co3O4 nanoparticles with high dispersibility, redox property and surface area. The obtained Co3O4-C300@SiO2 NFM exhibits outstanding ammonia selective catalytic reduction (NH3-SCR) denitrification activity (T90 = 225 °C at a GHSV of 77,000 h−1). The effect of catalyst loading on PM2.5 filtration performance of SiO2 NFM was also tested. Co3O4-C300@SiO2 NFM has higher filtration efficiency (99.99%) than SiO2 NFM at a lower pressure drop of 58 Pa, which suggests that catalyst loading via our method can improve the filtration performance of SiO2 NFM. This work might provide a universal strategy for the design and preparation of highly efficient catalytic membrane.

LITERATURE STUDY OF THE EFFECT ON DOPING COMPONENT ON THE CE-TI OXIDE CATALYST FOR FLUE GAS DENITRATION WITH NH3-SCR

The Ce-Ti oxide catalyst is viewed as an innovation for the reduction of nitrogen oxide (NO x ) and owns outstanding activity in ammonia-selective catalytic reduction (NH 3 -SCR) that became the most used denitration reaction in industry. In the flue gas, there will be many substances that inhibit the catalytic activity. Therefore, adding some components to the Ce-Ti oxide catalyst can be a solution. The aim of this literature study is to analyze the effect of doping components (Fe, Zr, Cu, K) on Ce-Ti oxide catalyst in the NH 3 -SCR reaction. Several theories and data methods were collected by comparing data based on catalytic activity and characterization of the catalysts. The activity of the catalyst was obtained by calculating the NO x conversion. The characterization of the catalysts was detected by BET, H 2 -TPR, NH 3 -TPD, and XPS. The analysis based on the literature study exhibited a catalyst with the best activities, structures, and properties required to successfully reduce NO x . The results indicate that the effect on doping components of Fe, Zr, and Cu can enhance the characteristics and protect the reduction ability, whilst the doping of K decreases surface acidity and reducibility on Ce-Ti oxide catalyst.

Mechanistic study of Ce–La–Fe/γ-Al2O3 catalyst for selective catalytic reduction of NO with NH3

A number of Ce–La–Fe/γ-Al2O3 catalysts were prepared by impregnation and microwave hydrothermal heating based on the ratio of Ce, La, and Fe in natural bastnäsite to examine the synergistic relationship between Ce, La, and Fe in natural bastnäsite and its effects on ammonia selective catalytic reduction (NH3-SCR). The results demonstrated that an increase in Fe species is beneficial to the denitration performance of catalysts with a Ce:La:Fe mole ratio of 1:0.6:0.12, thus providing high NO conversion (>95%) at 350 °C. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy results confirmed the formation of a solid solution between Ce, La, and Fe in the catalysts. The BET isotherms and NH3-TPD demonstrated that the addition of Fe increased the surface area and strengthened the surface acidity of Lewis acid sites. XPS and in situ DRIFTS indicated that electron transfer occurred between Fe3+/Fe2+ and Ce4+/Ce3+ redox cycles in the catalyst, thereby improving the adsorption and activation ability of NO and NH3. NO species were adsorbed on the catalysts in the form of monodentate nitrate, and then monodentate nitrate was oxidized to bidentate nitrate. The SCR reaction route was the coexistence of Eley–Rideal and Langmuir–Hinshelwood mechanisms.

Amorphous Feox–Mn0.1oy Catalyst with Rich Oxygen Vacancies for Ammonia Selective Catalytic Reduction of Nitrogen Oxide at Low Temperatures

Amorphous Feox–Mn0.1oy Catalyst with Rich Oxygen Vacancies for Ammonia Selective Catalytic Reduction of Nitrogen Oxide at Low Temperatures