High deNOx Performance Research Articles

Development of a model based strategy for catalyst screening to control NOx and N2O emissions in NH3-SCR process towards Eu7 readiness

Transient kinetic models were used to compare different commercial NH3-SCR catalytic monoliths under World Harmonized Transient Cycle (WHTC) conditions for NOx abatement performance, N2O formation and NH3 slip. Towards this goal, kinetic models for four Cu-zeolite, two Vanadia and one Fe-zeolite formulation were developed using experimental data of NH3 adsorption, desorption, NH3 oxidation, NO oxidation, Standard SCR and Fast SCR reactions. Models were in very good agreement with experimental data. Cu and Fe-zeolite formulations showed high deNOx activity with cycle efficiencies > 90% and > 95% respectively, for cold and warm WHTC runs, whereas Vanadia formulations outshined with negligible N2O formation. Simulations were performed to assess the variation of tailpipe NOx as a function of reactor volume. A plateau in deNOx performance was observed for all formulations as a function of the reactor volume which was around 30 and 50 L for cold and warm WTHC runs, respectively. This was found to be due to the decreasing temperature and fractional coverage of adsorbed NH3 along the axial distance of the reactors. Models were also used to develop hybrid reactor in series designs. Successive SCR reactors consisting of different formulations were simulated. The most successful design in terms of high deNOx performance and low N2O formation was with a reactor using a Vanadia catalyst followed by a reactor with Cu-zeolite catalyst. This resulted in a very similar deNOx performance but with a significantly lower N2O emissions as compared to a reactor with the same total volume consisting of Cu-zeolite.

MnCe/GAC-CNTs catalyst with high activity, SO2 and H2O tolerance for low-temperature NH3-SCR

SO2 and H2O tolerance is a crucial issue for low-temperature selective catalytic reduction of NO with NH3 (NH3-SCR) in practical application. In the present work, MnCe/GAC-CNTs catalysts were prepared and showed high activity, SO2 and H2O tolerance for low-temperature NH3-SCR. The catalysts were characterized by SBET, XPS, XRD, NH3−TPD, and DRIFTs. MnCe/GAC-CNTs exhibited higher catalytic activity and H2O + SO2 tolerance than CeO2/GAC-CNTs due to electron transfer between Ce and Mn species (Ce4+ + Mn3+ ↔ Ce3+ + Mn4+) accompanied with higher proportion Ce3+, and the improvement of surface acidity concentration and strength. Besides, Mn addition inhibited the oxygen inhibitory effect, enhanced the adsorption of NO, and increased the proportion diameter, which were beneficial to SO2/H2O resistance. Furthermore, the presence of Mn suppressed the formation of hydroxyl group, inhibited the adsorption of SO2, ultimately limited electron transfer between SO2 and Ce4+, which led to high SO2 tolerance of the MnCe/GAC–CNTs catalyst. Therefore, MnCe/GAC-CNTs catalyst with high deNOx performance and SO2/H2O tolerance, showed the potential of practical low-temperature deNOx application.

H2-SCR 촉매의 NOx와 CO 저감 성능에 관한 ZrO2와 La의 영향

This study is to improve the reduction performance of NOx and CO harmful gases and to investigate effect of ZrO₂ and La on the NOx and CO reduction performance of H₂-SCR catalyst. A model gas reactor was used, and catalyst temperature was tested in a steady state. The 0.5Pt-2CeO₂-2ZrO₂/TiO₂ catalyst had high de-NOx performance and showed a wide window distribution in the temperature range from 125℃ to 255℃. When an appropriate amount of ZrO₂ was supported, the de-NOx performance was improved by preventing oxidation at medium temperature of the reducing agent, H₂. It became active from the catalyst with a small amount of La supported, and the de-NOx performance was improved in the temperature range from 175℃ to 200℃. In the H₂-SCR catalyst to which the additive catalysts (ZrO₂, La) were added, the reaction rate was lowered, and the temperature of the gas discharged from the internal combustion engine must be considered. Since a large amount of coating may lower the catalyst dispersion of noble metals pt, the optimal coating amount should be studied in consideration of catalyst cost and performance.

Highly reactive methyl group drives selective catalytic reduction of NOx by methanol on bismuth oxide nanoparticle implanted FER zeolite

Selective catalytic reduction by methanol (Methanol-SCR) is a promising technology for the deNOx treatment of the exhaust with high concentration of sulfur. Herein, nano-bismuth oxide implanted FER zeolites (Bi-FER) have been successfully synthesized as Methanol-SCR catalysts, on which the optimum reaction temperature shows a big shift from 450 down to 300 °C comparing with state of the art. The catalytic active species of Bi-FER catalyst have been investigated by multi-characterization methods combined by theoretical simulation. Methyl groups generated on Brønsted acid sites neighboring with nano-bismuth oxide were demonstrated to exhibit extraordinary reactivity towards NOx, resulting in a high deNOx performance at low temperature. A strategy by the activation of methanol to produce reactive methyl groups was put forward for the development of Methanol-SCR catalysts.

MnOx-pillared rectorite prepared by in situ deposition as efficient catalysts for low-temperature NH3-SCR: The influences of manganese (II) precursors

MnOx pillared rectorite (REC) catalysts (10 wt% based upon Mn element and the mass of clay) were prepared by in situ deposition using different manganese (II) precursors, e.g., Mn(NO3)2, Mn(Ac)2, MnSO4 and MnCl2 to react with KMnO4, respectively. Unsupported MnOx was also prepared through reaction between Mn(Ac)2 and KMnO4 solution. The samples were characterized by XRD, SEM, low-temperature N2 adsorption, HRTEM, H2-TPR, NH3-TPD, TPSR and XPS. And the deNOx performances for low-temperature NH3-SCR were evaluated. The results showed that the unsupported amorphous MnOx had much higher deNOx performance than different MnO2 phases. For the MnOx pillared REC catalysts, deNOx performances decreased in the order of Mn10/REC-Ac- > Mn10/REC-Cl- > Mn10/REC-SO42- > Mn10/REC-NO3-. The Mn10/REC-AC- MnOx-Ac-/REC showed the best redox properties, richest weak acid sites and best dispersion of MnOx and content of Mn4+, which contributed to its high activity. Moreover, even under working conditions with GHSV up to 105,000 h−1, high deNOx performance and good stability was also observed for Mn10/REC-Ac- catalyst.

One-pot synthesis of Cu–Ce co-doped SAPO-5/34 hybrid crystal structure catalysts for NH3-SCR reaction with SO2 resistance

SAPO-34, SAPO-5/34 based catalysts doped with Cu, Ce as active components were synthesized via a one-pot hydrothermal method by using different amounts of additive (α-cellulose), and their catalytic activities were measured for selective catalytic reduction (SCR) of NO with NH3. The synthesized Cu–Ce co-doped products switch from cubic SAPO-34, to flower-like aggregated SAPO-5/34, hybrid crystal SAPO-5/34, and finally to spherical aggregated SAPO-34 with the increase of α-cellulose amount. The Cu–Ce co-doped SAPO-5/34 hybrid crystal structure catalysts with 0.75 mol ratios of C/P (Cu–Ce/SP-0.75) exhibit excellent NH3-SCR activity with higher than 90% NOx conversion in the temperature range of 180–450 °C, at WHSV of 20000 mL/(g·h). Furthermore, the catalyst displays outstanding sulfur resistance and NOx conversion maintains above 90% at 200–450 °C after adding 100 ppm of SO2. The characteristic results suggest that the high deNOx performance of Cu–Ce/SP-0.75 is due to the enhanced accessibility, abundant activity species, excellent redox property and high adsorptive and activated capacity for NH3.

A-site defects in LaSrMnO3 perovskite-based catalyst promoting NOx storage and reduction for lean-burn exhausts

Herein, we report the high De-NOx performance of the A-site defective perovskite-based Pd/La0.5Sr0.3MnO3 catalyst. The formation of the defective perovskite structure can be proved by both the increased Mn4+/Mn3+ ratio and serious lattice contraction due to cationic nonstoichiometry. It promotes the Sr doping into perovskite lattice and reduces the formation of the SrCO3 phase. Our results demonstrate that below 300 °C the A-site defective perovskite can be more efficiently regenerated than the SrCO3 phase as NOx storage sites due to the latter's stronger basicity, and also exhibits the higher NO oxidation ability than the A-site stoichiometric and excessive catalysts. Both factors promote the low-temperature De-NOx activity of the Pd/La0.5Sr0.3MnO3 catalyst through improving its NOx trapping efficiency. Nevertheless, above 300 °C, the NOx reduction becomes the determinant of the De-NOx activity of the perovskite-based catalysts. A-site defects can weaken the interactions between perovskite and Pd, inducing activation of Pd sites by in-situ transformation from PdO to metallic Pd in the alternative lean-burn/fuel-rich atmospheric alternations, which boosts the De-NOx activity of the Pd/La0.5Sr0.3MnO3 catalyst. The Pd/La0.5Sr0.3MnO3 catalyst exhibits the high sulfur tolerance as well. These findings provide insight into optimizing the structural properties and catalytic activities of the perovskite-based catalysts via tuning formulation, and have potential to be applied for various related catalyst systems.

Selective catalytic reduction of NO by NH3 over CuO–CeO2 in the presence of SO2

The reaction between NO2 and NH3/NH4+ induced the formation of NHX<3 species with high oxidability; NHX<3 promoted the surface sulfate decomposition; high de-NOX performance was achieved in the presence of SO2 at low temperature.

Enhanced low-temperature NH3-SCR activity of a V2O5/TiO2 composite prepared via chemical vapor condensation and impregnation method

A novel V2O5/TiO2 composite material was synthesized by chemical vapor condensation (CVC) method. It exhibited nearly 100% NH3-SCR activity at 250°C. Characterization results show that the V2O5/TiO2 material prepared by CVC had a higher specific surface area compared to that of V2O5 supported on TiO2 (P25) and its commercially available equivalent material. In particular, V2O5/TiO2 material prepared by CVC had well-balanced V4+/V5+ ratio, resulting in high deNOx performance.

Combination of Photocatalysis and HC/SCR for Improved Activity and Durability of DeNOx Catalysts

A photocatalytic HC/SCR system has been developed and its high deNOx performance (54.0-98.6% NOx conversion) at low temperatures (150-250 °C) demonstrated by using a representative diesel fuel hydrocarbon (dodecane) as the reductant over a hybrid SCR system of a photocatalytic reactor (PCR) and a dual-bed HC/SCR reactor. The PCR generates highly active oxidants such as O3 and NO2 from O2 and NO in the feed stream, followed by the subsequent formation of highly efficient reductants such as oxygenated hydrocarbon (OHC), NH3, and organo-nitrogen compounds. These reductants are the key components for enhancing the low temperature deNOx performance of the dual-bed HC/SCR system containing Ag/Al2O3 and CuCoY in the front and rear bed of the reactor, respectively. The OHCs are particularly effective for both NOx reduction and NH3 formation over the Ag/Al2O3 catalyst, while NH3 and organo-nitrogen compounds are effective for NOx reduction over the CuCoY catalyst. The hybrid HC/SCR system assisted by photocatalysis has shown an overall deNOx performance comparable to that of the NH3/SCR, demonstrating its potential as a promising alternative to the current urea/SCR and LNT technologies. Superior durability of HC/SCR catalysts against coking by HCs has also been demonstrated by a PCR-assisted regeneration scheme for deactivating catalysts.

DeNOx Performance and Reaction Mechanism of the Di-Air System

The detailed reaction mechanism of Di-Air, which showed the unprecedented high deNOx performance at high temperature conditions, was studied in this work. Since the Di-Air phenomenon occurs with continuous short pulse injections of hydrocarbons over NSR (NOx storage and reduction) catalyst, this study focused on the specific function of HC as an effective reductant for NOx reduction reaction. As a first step, the deNOx performance was compared with three different reductant gases including CO, H2 and C3H6 in a modified synthetic gas bench equipped with a gas injector which enables continuous small amount of injections. At inlet gas temperature of 450 °C C3H6 showed the best deNOx performance whereas H2 was the best at 150 °C. Moreover the result of temperature programmed desorption showed that intermediate species represented by –NCO (isocyanates) produced from C3H6 was thermally more stable than that produced from CO. These results confirmed that the injected HC reacts with adsorbed NOx on NSR catalyst generating thermally stable intermediates, which could contribute the high deNOx performance at high temperature conditions.

DeNOx performance of Ag/Al2O3 catalyst using simulated diesel fuel–ethanol mixture as reductant

The NOx reduction activity of Ag/Al2O3 catalyst has been investigated systematically, using a mixture of simulated diesel fuel (SD) and ethanol (E) as the reductant with special interest in the low temperature deNOx performance below 350°C. The Ag loading and catalyst operating conditions such as C1/NOx and ethanol/simulated diesel fuel (E/SD) ratios have been optimized in order to achieve the maximum deNOx performance of the Ag/Al2O3 catalyst. Ammonia has been identified as the most abundant reaction intermediate over the Ag/Al2O3 catalyst under the optimized operating conditions. To further enhance the deNOx performance by utilizing the NH3 formed over the Ag/Al2O3 catalyst, a dual-bed reactor system has been employed with CuZSM5 catalyst in the rear bed consecutively following the front bed containing the Ag/Al2O3. The NOx-to-N2 conversion in this dual-bed system increased up to 85% from 275 to 450°C, mainly due to the NH3 oxidation to N2 by the CuZSM5 in the rear bed. Physicochemical characterization of the Ag/Al2O3 catalysts by UV–vis, TEM and EELS has indicated that both ionic and metallic Ag formed on the catalyst surface play important roles for the high deNOx performance of the present catalytic system; the ionic Ag including Ag+ and Agδ+ is the active reaction site for the reduction of NOx to N2, while the metallic Ag is responsible for the partial oxidation of hydrocarbons (HCs) which promotes the initiation of the HC/SCR process in the low temperature range. The optimum ionic/metallic (I/M) ratio of Ag species on Al2O3 support surface appears to be in the range of 1.4–1.7, depending upon the catalyst temperature range of interest.

DeNOx performance of Ag/Al2O3 catalyst by n-dodecane: Effect of calcination temperature

The effect of the calcination temperature of Ag/Al2O3 catalyst on NO removal activity by n-dodecane as a diesel simulant has been examined with respect to the Ag loading and C1/NO feed ratio under a feed gas condition containing both excess H2O and oxygen. The higher the catalyst calcination temperature and Ag loading, the higher deNOx activity that has been achieved in the reaction temperature range lower than 300°C. 56% of the NO conversion to N2 has been attained over Ag(2)-800 catalyst at 300°C when the C1/NO feed ratio to the reactor is 6. The amount of the metallic Ag formed on the catalyst surface responsible for the high deNOx performance in the temperature region lower than 300°C increases upon the increase of the catalyst calcination temperature from 550 to 800°C and of the Ag loading from 1 to 3wt.%, as determined by UV–vis and XPS. The –NCO species formed on the catalyst surface with acetate, formate and carbonate compounds produced from the partial oxidation of n-dodecane is a critical reaction intermediate for the present reaction system, as identified by in situ IR study. The formation of the –NCO species on the catalyst surface becomes apparent, particularly at 300°C as the catalyst calcination temperature increases.

High deNOx performance of Mn/TiO 2 catalyst by NH 3

The deNOx performance of the s-Mn/TiO 2 catalyst prepared by sol–gel method has been significantly enhanced, particularly in the low temperature region. Mn is basically incorporated into the matrix of Ti and becomes a structural component of s-MnO 2/TiO 2 mixed oxide, whereas by impregnation method it simply exists on the surface of i-Mn/TiO 2. The well-dispersed Mn over s-Mn/TiO 2 catalyst is the primary cause for the high deNOx performance compared to that over i-Mn/TiO 2. The addition of Fe onto the Mn/TiO 2 catalyst improves the NOx removal activity by NH 3 in a wide operating temperature window, including the low temperature region less than 250 °C, regardless of the catalyst preparation methods. Including NO 2 (NO 2/NO = 1) in the feed gas stream further enhances the low temperature deNOx activity of Mn/Fe/TiO 2 catalyst.

Passive NOx Reduction with CO Using Pd/TiO2/Al2O3 + WGSR Catalysts Under Simulated Post-Euro IV Diesel Exhaust Conditions

This study deals with diesel DeNOx catalysis by physically mixed Pd/TiO2/Al2O3 and water–gas-shift-reaction (WGSR) catalysts under CO-rich conditions at a CO/NOx ratio of 16. In the post-Euro IV era, many diesel engines are expected to produce CO-rich exhaust emissions due to the trend toward emission regulation and limitations in related technologies. Under these circumstances, the passive DeNOx strategy utilizing CO as a single reductant can be considered appropriate. The Pd/TiO2/Al2O3 catalyst is well known for its high DeNOx performance when CO and H2 are available as NOx reductants. However, when CO is used as a single reductant, the catalyst shows poor DeNOx activity, even if the CO concentration is exceptionally high (CO/NOx = 16). In this study, the DeNOx activity of Pd/TiO2/Al2O3 was noticeably improved by physically mixing it with a proper WGSR catalyst (Cu/ZnO/Al2O3), which is capable of producing H2 and feeding it to Pd/TiO2/Al2O3 successfully even in the presence of O2. The NOx conversion exceeded 70% at 400–450 °C using a Pd/TiO2/Al2O3 + Cu/ZnO/Al2O3 catalyst mixture at a weight ratio of 33:67. The reaction gas consisted of 500 ppm NO, 8000 ppm CO, 8 vol.% O2, 5 vol.% CO2 and 10 vol.% H2O and w/f was 0.1 g s/cm3.

Numerical simulation of de-NOx performance by repetitive pulsed discharge when added with hydrocarbons such as ethylene

Emission regulations are gradually being tightened recently to prevent further air pollution. Cost-effective and efficient technologies must be developed to process the NOx generated in the combustion of fossil fuels. One of the candidate technologies to process NOx is the denitrification of flue gas by pulsed corona discharge, which has been demonstrated experimentally to show high de-NOx performance. However, the optimization of operation conditions and the appropriate understanding of the de-NOx process still remain to be clarified. Therefore, following our previous study on ammonia injection, we have simulated in the present study the de-NOx process to which hydrocarbons such as ethylene have been added to provide guidelines on its proper operation conditions and its main reaction paths to remove NOx. The simulated results show that the removal efficiency in a case of ethylene addition becomes lower than for ammonia addition, but the de-NOx energy consumption rate becomes lower than for ammonia injection. However, with ethylene injection the production of the pollutant, formaldehyde, limits the allowable amount of injected ethylene. The de-NOx performance is better with propylene than ethylene injection because propylene reacts with the OH radical more than ethylene to oxide NOx. However, formaldehyde is also produced in the case of propylene injection, limiting the allowable amount of injected propylene. The de-NOx performance is also assessed in a case where HNO2 is considered as NxOy.