Selective Catalytic Reduction Of NO Research Articles

Structure-resolved CFD simulations to guide catalyst packing of selective NO reduction

In this work, monolith and packing structures with different particle shapes (cylinder, sphere, trilobe and Raschig ring) are compared to boost selective catalytic reduction (SCR) of NO reaction. The three-dimension structure-resolved reactor model is established to evaluate the influence of mass transfer and NO reaction performance in different industrial applications. The simulation results show that monolithic catalysts shift from transition regime to reaction-controlled regime, while the cylinder-resolved catalysts shift from diffusion-controlled regime to transition regime as the reaction temperature decreases from 240 to 160 °C for SCR of NO. The monolithic catalyst with excellent mass transfer capacity and the catalyst with cylinder packing structure with high bulk density exhibit highest NO removal efficiency in the coking plant (∼240 °C) and boiler system (∼160 °C), respectively. The catalyst with Raschig ring packing structure exhibits the highest NO removal efficiency in the waste incineration plant (∼200 °C) due to the compromise of reaction–diffusion behavior. A strategy of catalyst structures selection for SCR of NO reaction at different industrial applications based on the reaction–diffusion interaction is proposed, which could shed new light on boosting selective catalytic reduction of NO reaction.

Selective Catalytic Reduction of NOx with NH3 over Cu/SSZ-13: Elucidating Dynamics of Cu Active Sites with In Situ UV–Vis Spectroscopy and DFT Calculations

Selective Catalytic Reduction of NO_<i>x</i> with NH₃ over Cu/SSZ-13: Elucidating Dynamics of Cu Active Sites with In Situ UV–Vis Spectroscopy and DFT Calculations

A comparative study of the thermal and hydrothermal aging effect on Cu-SSZ-13 for the selective catalytic reduction of NO with NH3

In this work, the characterizations of Cu-SSZ-13 after hydrothermal aging (HTA) and thermal aging (TA) at different temperatures (750, 800, and 850 °C) are compared, and the differences between those two serious aged samples are analyzed. With this data, the effect of steam on catalysts deactivation during hydrothermal aging is analyzed. The TA at 750 and 800 °C causes the dealumination and the agglomeration of Cu 2+ ions to CuO, resulting in the activity loss of Cu-SSZ-13. The presence of steam upon HTA at 750 and 800 °C aggravates the catalyst deactivation by increasing the Al detachment and the Cu 2+ agglomeration. The structure and cupric state are almost the same in the Cu-SSZ-13 after TA and HTA at 850 °C, respectively, indicating that the steam has little influence on the deactivation. The formation of CuAl 2 O 4 spinel is the primary reason for the deactivation after both HTA and TA at 850 °C, probably attributed to the strong interaction between Cu 2+ ions and framework Al sites at high temperatures.

Different lead species deactivation on Mn-Ce activated carbon supported catalyst for low-temperature SCR of NO with NH3: Comparison of PbCl2, Pb (NO3)2 and PbSO4

Due to the accumulation of heavy metal compounds produced by the sintering process in steel industry, the catalysts used for low-temperature selective catalytic reduction of NO with NH3 (NH3-SCR) might be seriously deactivated. In this work, the deactivation effect of PbCl2, Pb(NO3)2, and PbSO4 on Mn-Ce activated carbon supported catalyst for low-temperature NH3-SCR of NO was investigated and compared. Poisoned catalysts were provided by impregnating fresh catalysts with Pb(NO3)2, PbSO4 and PbCl2 aqueous solutions, respectively. Deactivation could be observed on the poisoned samples, and the deactivation degree was following PbCl2 > PbSO4 > Pb(NO3)2. The catalytic activities of all samples were tested, and the physicochemical properties of fresh and poisoned catalysts were assessed. PbCl2 caused the most severe deactivation of the catalyst, owing to its poor redox property and surface acidity. Cl- could also react with Mn active sites to form -O-Mn-Cl bonds, resulting in additional acid sites, although these newly generated sites were not reactive in NH3-SCR reaction process. PbSO4 exhibited moderate poisoning effect due to the addition of SO42-, which created new Brønsted acid sites, facilitating the NH3 adsorption and NO reduction. Pb(NO3)2 had the least poisoning impact on the catalyst due to the NO3–, promoting the NH3 activation. The in situ DRIFTS results revealed that NH3-SCR reaction over all samples was governed by Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanism, and did not change due to the lead poisoning. Finally, a possible mechanistic model for different lead salts poisoning over Mn-Ce/AC catalyst was proposed.

Selective catalytic reduction of NO x with NH3 assisted by non-thermal plasma over CeMnZrO x @TiO2 core–shell catalyst

The presented work reports the selective catalytic reduction (SCR) of NO x assisted by dielectric barrier discharge plasma via simulating marine diesel engine exhaust, and the experimental results demonstrate that the low-temperature activity of NH3-SCR assisted by non-thermal plasma is enhanced significantly, particularly in the presence of a C3H6 additive. Simultaneously, CeMnZrO x @TiO2 exhibits strong tolerance to SO2 poisoning and superior catalytic stability. It is worthwhile to explore a new approach to remove NO x from marine diesel engine exhaust, which is of vital significance for both academic research and practical applications.

Insight into the effects of Cu2+ ions and CuO species in Cu-SSZ-13 catalysts for selective catalytic reduction of NO by NH3

Different Cu precursors were adopted to adjust the isolated Cu2+ ions and CuO species in the Cu-SSZ-13 catalysts. The Cu2+ ions were mainly located at eight-member rings in the catalysts with the Cu precursors of Cu(NO3)2 (Fresh-I) and CuSO4 (Fresh-II), while that located at six-member rings in the catalysts with the Cu precursors of CuCl2 (Fresh-III) and Cu(CH3COO)2 (Fresh-IV). All catalysts showed>90% of NO conversion and 100% of N2 selectivity at 200–680 °C. Fresh-I and Fresh-II catalysts showed an unexpected increase of the high-temperature activity after hydrothermal treatment. The characterizations revealed that the hydrothermal treatment promoted the production of CuO species, which accelerated the adsorption of NOx species to enhance the high-temperature SCR activity. Moreover, the SCR reaction pathway changed from Langmuir-Hinshelwood to Eley-Rideal mechanisms for the Fresh-II catalyst after the hydrothermal treatment, which was verified by in situ DRIFTS.

Green synthesis of ZSM-5 zeolite for selective catalytic reduction of NO via template-free method from tailing residue

The task of circular economy in mining industry is to develop and utilize a large number of tailing residue that has been shelved for a long time. An economical and sustainable utilization strategy of potassium feldspar tailing residue is reported. The ZSM-5 zeolite catalysts using tailing residue as raw materials by a template-free hydrothermal method are synthesized for selective catalytic reduction (SCR), abandoning the high pollution and energy consumption method of zeolite synthesis from fine chemicals. The effects of feed NaOH and Al2(SO4)3·18H2O on tailing residue and zeolite products are systematically studied, which proved that the silicon and aluminum elements in the tailing residue can be efficiently utilized. The results of scaling up experiment and experiment without additional aluminum confirm the feasibility and repeatability of tailing residue utilization. The synthesized ZSM-5 was used to prepare the Ce-Fe-ZSM-5 catalyst for NO reduction to N2 and showed excellent activity, with the NOx conversion remaining above 80% at the range of 300 °C~500 °C. The synergistic effect of Ce and Fe ions promoted the formation of more chemisorbed oxygen and accelerated the reaction rate of NO and NH3 adsorbed on the catalyst surface, resulting in a significant increase in the low-temperature activity of 1%Ce-Fe-ZSM-5. In this study, zeolite catalysts with excellent catalytic effect from tailing residue that can be used in petrochemical fields are successfully synthesized. The route is economic, environmental, and recyclable, which provides an opportunity for comprehensive development and application of tailing residue.

SO2 Poisoning of Cu-CHA deNO x Catalyst: The Most Vulnerable Cu Species Identified by X-ray Absorption Spectroscopy.

Cu-exchanged chabazite zeolites (Cu-CHA) are effective catalysts for the NH3-assisted selective catalytic reduction of NO (NH3-SCR) for the abatement of NOx emission from diesel vehicles. However, the presence of a small amount of SO2 in diesel exhaust gases leads to a severe reduction in the low-temperature activity of these catalysts. To shed light on the nature of such deactivation, we characterized a Cu-CHA catalyst under well-defined exposures to SO2 using in situ X-ray absorption spectroscopy. By varying the pretreatment procedure prior to the SO2 exposure, we have selectively prepared CuI and CuII species with different ligations, which are relevant for the NH3-SCR reaction. The highest reactivity toward SO2 was observed for CuII species coordinated to both NH3 and extraframework oxygen, in particular for [CuII2(NH3)4O2]2+ complexes. Cu species without either ammonia or extraframework oxygen ligands were much less reactive, and the associated SO2 uptake was significantly lower. These results explain why SO2 mostly affects the low-temperature activity of Cu-CHA catalysts, since the dimeric complex [CuII2(NH3)4O2]2+ is a crucial intermediate in the low-temperature NH3-SCR catalytic cycle.

Co-doped MnCeOx/ZrO2 catalysts for low temperature selective catalytic reduction of NO

Co-doped MnCeOx/ZrO2 catalysts for low temperature selective catalytic reduction of NO

Three-dimensionally ordered macroporous Ce-W-Nb oxide catalysts for selective catalytic reduction of NO with NH3

• Ce-W catalyst is optimized by combining Nb-modification and structural manipulation. • 3DOM structure provides abundant diffusion channels for catalytic reactions. • 3DOM structure ensures the high dispersion of active components. • Synergistic effect among the species of Ce, Nb and W promotes the increase of O α . • Active NH 3 and NO x species are increased over 3DOM Ce-W-Nb catalysts. A string of 3DOM Ce-W-Nb ternary catalysts for NH 3 -SCR were prepared by a colloidal template method. The 3DOM Ce-W-Nb 0.15 catalyst had the best SCR activity and yielded more than 90% NO conversion at 275 ∼ 450 °C in the high GHSV of 120,000 h −1 . In addition, it exhibited good tolerance to H 2 O and SO 2 . The addition of Nb increased the number of active sites and made them dispersed more evenly, optimized the pore structure to a certain extent, and increased the specific surface area. The interaction among Ce, W, and Nb species promoted the increase of chemisorbed oxygen and enhanced the redox properties, thus contributing to the satisfactory SCR activity at low temperatures. In addition, the synergistic effect between Nb and W provided sufficient Lewis acid sites for the 3DOM Ce-W-Nb x catalyst, which was conducive to the good SCR performance at high temperatures. The NH 3 -SCR reaction on 3DOM Ce-W-Nb x catalysts followed both Eley-Rideal and Langmuir-Hinshelwood mechanisms. The doping of Nb was beneficial to boost the adsorption of NH 3 and improved the reactivities of NH 3 adsorbed species while facilitating the generation of active NO x species. These accelerated the reaction rate and optimized the reaction path.

Boosting low-temperature selective catalytic reduction of NO with NH3 of V2O5/TiO2 catalyst via B-doping

A series of B-doped V2O5/TiO2 catalysts has been prepared the by sol-gel and impregnation methods to investigate the influence of B-doping on the selective catalytic reduction (SCR) of NOx with NH3. X-ray diffraction, Brunauer-Emmett-Teller specific surface area, scanning electron microscope, X-ray photoelectron spectroscopy, temperature-programmed reduction of H2 and temperature-programmed desorption of NH3 technology were used to study the effect of the B-doping on the structure and NH3-SCR activity of V2O5/TiO2 catalysts. The experimental results demonstrated that the introduction of B not only improved the low-temperature SCR activity of the catalysts, but also broadened the activity temperature window. The best SCR activity in the entire test temperature range is obtained for VTiB2.0 with 2.0% doping amount of B and the NOx conversion rate is up to 94.3% at 210 °C. The crystal phase, specific surface area, valence state reducibility and surface acidity of the active components for the as-prepared catalysts are significantly affected by the B-doping, resulting in an improved NH3-SCR performance. These results suggest that the V2O5/TiO2 catalysts with an appropriate B content afford good candidates for SCR in the low temperature window.

Effect of Cu loading content on the catalytic performance of Cu-USY catalysts for selective catalytic reduction of NO with NH3

Series of Cu-USY zeolite catalyst with different Cu loading content were synthesized through simple impregnation method. The obtained catalysts were subjected to selective catalytic reduction of NOx with NH3 (NH3-SCR) performance evaluation, structural/chemical characterizations such as X-ray diffraction (XRD), N2 adsorption/desorption, H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD) as well as detailed in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments including CO adsorption, NH3 adsorption and NO+O2 in situ reactions. Results show that Cu-USY with proper Cu loading (in this work 5Cu-USY with 5 wt.% Cu) could be promising candidates with highly efficient NH3-SCR catalytic performance, relatively low byproduct formation and excellent hydrothermal stability, although its SO2 poisoning tolerability needs alleviation. Further characterizations reveal that such catalytic advantages can be attributed to both active cu species and surface acid centers evolution modulated by Cu loading. On one hand, Cu species in the super cages of zeolites increases with higher Cu content and being more conducive for NH3-SCR reactivity. On the other hand, higher Cu loading leads to depletion of Brønsted acid centers and simultaneous formation of abundant Lewis acid centers, which facilitates NH4NO3 reduction via NH3 adsorbed on Lewis acid centers, thus improving SCR reactivity. However, Cu over-introduction leads to formation of surface highly dispersed CuOx, causing unfavorable NH3 oxidation and inferior N2 selectivity.

Fabrication of wide temperature FexCe1-xVO4 modified TiO2-graphene catalyst with excellent NH3-SCR performance and strong SO2/H2O tolerance.

Selective catalytic reduction of NO with NH3 (NH3-SCR) is one of the most common technique for elimination of NOx. The promotional effect of Fe additive on the NH3-SCR activity of the CeVO4/TiO2-graphene (GE) is systematically studied. The results exhibited that the low-temperature NOx conversion could be enhanced dramatically via the addition of Fe and Fe0.5Ce0.5VO4/TiO2-GE displayed the highest conversion of NOx in the wide temperature window (200-400°C). It is because that Fe3+ + Ce3+ ↔ Fe2+ + Ce4+ facilitated the oxidization of NO to NO2 at low temperature and led to the "Fast SCR," thereby raising the SCR performance. What is more, the introduction of Fe enhanced redox ability, the surface relative percentage of Ce3+, V5+ and the chemical adsorbed oxygen. Furthermore, the high surface concentration of Ce3+ species can produce more active oxygen and leads to the "Fast SCR" reaction. In addition, the Fe0.5Ce0.5VO4/TiO2-GE catalyst showed excellent H2O/SO2 tolerance, which may be due to the decomposition of ammonium bisulphite under high temperature and the hydrophobicity of graphene. What is more, it displayed outstanding the stability. This work would provide theoretical reference for the practical application of NOx abatement via NH3-SCR.

Effect of reduction on NO + CO reaction performance of CuO-Co3O4 symbiotic oxide porous nanosheet and DFT calculation

As an ideal substitute for the precious metals in the selective catalytic reduction of NO by CO, transition metal oxides perform very well. Thus, a series of CuO - Co3O4 symbiotic oxide porous nanosheet catalysts are prepared with a CTAB-assisted hydrothermal method. Cu5 with the ratio of Cu and Co is 5 : 10, has the best activity on the premise of maintaining the nanosheet structure. Reduction pretreatment of Cu5 with H2 is carried out, and the surface will be rapidly oxidized in air. In this period, Cu, CuO and Co3O4 were produced and coexisted on surface. Cu5-re-163 exhibits greatly higher N2 selectivity but a little inferior NO conversion. Further DFT calculation and characterizations proved that [N] free radicals exist during the reaction. The reaction on Cu5 and Cu-re-163 follow L-H and E-R mechanism respectively. [N] radicals on the latter are much easier to desorb, so that they are easy to combine with each other to form N2 rather than with NO to generate N2O, as the reason why Cu5-re-163 has better selectivity.

A methodology for structure dependent global kinetic models: Application to the selective catalytic reduction of NO by hydrocarbons

Global kinetic models capable of capturing experimentally observed features of catalytic reactions are vital in design and optimization studies. In this work, a detailed analysis of the selective catalytic reduction of NO and NO2, particularly in automotive exhaust control is undertaken. The prominent metal based catalysts for this reaction range from Pt, Au & Rh to cheaper options including Cu, Ag & Co supported on Al2O3, SiO2, and occasionally, zeolites. Here, we focus on Ag & Co supported on Al2O3 catalysts, and propose a computationally tractable kinetic model capable of capturing the observed SCR features across a range of catalyst synthesis and reactor operating conditions. In particular, the effects of metal loading on catalyst performance are closely examined. In SCR, an important aspect is the catalytic activity at higher inlet O2 concentrations. The global kinetic model proposed here is shown to predict the trends with respect to reactor temperature and inlet feed compositions (including O2), well, for both catalysts.

Effect of K-Modified Blue Coke-Based Activated Carbon on Low Temperature Catalytic Performance of Supported Mn-Ce/Activated Carbon.

To clarify the K modified effects over activated carbon (AC) supported Mn–Ce oxide catalysts, several Mn–Ce/AC and xK–Mn–Ce/AC mixed oxide catalysts prepared via an impregnation method supported on AC were investigated for low-temperature selective catalytic reduction (SCR) of NO with NH3 in the simulated sintering flue gas. The Mn–Ce/AC catalyst with a K loading of 8% showed the highest catalytic activity, corresponding to 92.1% NO conversion and 92.5% N2 selectivity at 225 °C with a space velocity of 12,000 h–1. Furthermore, the 0.08K–Mn–Ce/AC catalyst exhibited better resistance to SO2 and H2O than Mn–Ce/AC, which could convert 72.3% and 74.1% of NO at the presence of 5% SO2 and H2O, respectively. After K modification, the relative ratios of Mn4+/Mnn+ as well as Ce3+/Cen+ and surface adsorbed oxygen increased. Additionally, the reduction performance of the catalyst was improved obviously, and both acid strength and quantity of acid sites increased significantly after the K species were introduced in Mn–Ce/AC. Especially, the NO adsorption capacity of the catalyst was enhanced, which remarkably promoted the denitration efficiency and SO2 resistance. The SCR of NO with NH3 on K–Mn–Ce/AC catalysts followed the L-H mechanism.

MnFe@CeOx Core–Shell Nanocages for the Selective Catalytic Reduction of NO with NH3 at Low Temperature

MnFe@CeO_<i>x</i> Core–Shell Nanocages for the Selective Catalytic Reduction of NO with NH₃ at Low Temperature

Micro-/mesoporous copper-containing zeolite Y applied in NH3-SCR, DeNO

Zeolite Y was prepared by a dense-gel method and subsequently modified either by treatment with diethylamine (DEA), sodium hydroxide (NaOH) or disodium ethylenediaminetetraacetate (Na 2 H 2 EDTA), or by sequential treatment (H 4 EDTA-NaOH or H 4 EDTA-NaOH-Na 2 H 2 EDTA). Individual treatment did not succeed in introducing mesoporosity in the parent zeolite Y, while the sequential treatment lead to formation of mesopores. After introduction of Cu 2+ ions, the obtained materials were studied as catalysts for the selective catalytic reduction of NO x by NH 3 (NH 3 -SCR, DeNO x ). The catalytic investigations reveal a similar NO conversion for all Cu-containing catalysts up to 450 °C, independent of the introduced mesoporosity. Insights into the dynamics of NH 3 -SCR intermediates through rapid scan FT-IR show that for Cu–Y, the rate-determining step is the formation of the mixed [Cu(O − )(NH 3 ) n -1 (NO)] 2+ complexes, which initiate the NH 3 -SCR reaction. • Formation of mesopores in zeolite Y by sequential treatment. • NO conversion for Cu–Y independent of the introduced mesoporosity. • Formation of the mixed [Cu(O − )(NH 3 ) n -1 (NO)] 2+ complexes, initiating NH 3 -SCR.

Cerium modified copper-based mordenite zeolite catalyst for high-temperature selective catalytic reduction NO with NH3 of gas turbines

Cerium modified copper-based mordenite zeolite catalyst for high-temperature selective catalytic reduction NO with NH3 of gas turbines

Enhancing the Selective Catalytic Reduction of NOx at Low Temperature by Pretreatment of Hydrocarbons in a Gliding Arc Plasma

Enhancing the Selective Catalytic Reduction of NO_<i>x</i> at Low Temperature by Pretreatment of Hydrocarbons in a Gliding Arc Plasma