NO2 Reaction Pathways With NH3 on an Fe-Zeolite SCR Catalyst

2011 ◽  
Author(s):  
Michael A. Smith ◽  
Christopher D. Depcik ◽  
Stefan Klinkert ◽  
John W. Hoard ◽  
Stanislav V. Bohac ◽  
...  
Keyword(s):  
Flow Reactor ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Catalyst System ◽  
Lean Nox Trap ◽  
Scr Catalyst ◽  
Nh3 Scr ◽  
Nox Conversion ◽  
Lean Nox ◽  
System Part

One approach for nitrogen oxides (NOx) emission control of medium duty diesel engines is through the use of a combination Lean NOx Trap and Selective Catalytic Reduction (LNT-SCR) catalyst system. In this system, part of the NOx conversion occurs via an NH3 SCR catalyst that is dependent on the NO2 to NOx ratio of the feed gas with NO2 being a more advantageous oxidizer. One benefit of using this system is the conversion of NO to NO2 over the LNT which increases the NO2:NOx ratio of the feed gas to the SCR catalyst. An experimental study has been performed to investigate the NO2-NH3 reaction for an Fe-based zeolite SCR catalyst using a bench top flow reactor. The increase in NO2 concentration at the inlet of the SCR results in the formation of large quantities of N2O from 200°C to 400°C. Further experiments determined that N2O and NH3 react above 350°C. This has led to a hypothesis that one primary SCR reaction (Slow SCR) can be replaced with two reaction steps featuring NH3, NO2, and N2O. As a result, this paper proposes five NOx reduction reactions as part of a global mechanism, which would account for the observed experimental behavior.

Effect of Butanol on the Performance of DeNOx Aftertreatment Systems of a Diesel Vehicle Under WLTC Driving Conditions

2021 ◽  
Author(s):  
Alejandro Calle-Asensio ◽  
Juan José Hernández ◽  
José Rodríguez-Fernández ◽  
Víctor Domínguez-Pérez
Keyword(s):  
Catalytic Reduction ◽  
Nox Reduction ◽  
Climatic Conditions ◽  
Transport Sector ◽  
Lean Nox Trap ◽  
Diesel Vehicles ◽  
Medium Speed ◽  
Emission Regulations ◽  
Lean Nox ◽  
Light Duty Vehicles

Abstract Advanced biofuels and electrofuels, among which are medium-long chain alcohols, have gained importance in the transport sector with the enforcement of the EU Renewable Energy Directive (2018/2001). In parallel, last European emission regulations have become much more restrictive regarding NOx, so vehicle manufacturers have been forced to incorporate lean NOx trap (LNT) and/or selective catalytic reduction (SCR). Thus, the combination of modern DeNOx devices and the upcoming higher contribution of sustainable biofuels is a new challenge. In this work, two Euro 6 diesel vehicles, one equipped with LNT and the other with ammonia-SCR, have been tested following the Worldwide harmonized Light-duty vehicles Test Cycle (WLTC) at warm (24°C) and cold (−7°C) conditions using conventional diesel fuel and a diesel-butanol (90/10% vol.) blend. While the effect of butanol on the LNT efficiency was not significant, its influence on the SCR performance was notable during the low and medium-speed phases of the driving cycle, mainly under warm climatic conditions. Despite of the lower NOx concentration at the catalyst inlet, the worst efficiency of the SCR with butanol could be attributed to hydrocarbons deposition on the catalyst surface, which inhibits the NOx reduction reactions with ammonia. Moreover, the LNT was not sensitive to the ambient temperature while the SCR performance greatly depended on this parameter.

scholarly journals Numerical Investigation on the Intraphase and Interphase Mass Transfer Limitations for NH3-SCR over Cu-ZSM-5

Processes ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 1966
Author(s):  
Shiyong Yu ◽  
Jichao Zhang
Keyword(s):  
Pressure Drop ◽  
Catalytic Reduction ◽  
Nox Reduction ◽  
Catalytic Performance ◽  
No Oxidation ◽  
Relative Pressure ◽  
Nh3 Scr ◽  
Nox Conversion ◽  
Nh3 Adsorption ◽  
Media Channels

A systematic modeling approach was scrutinized to develop a kinetic model and a novel monolith channel geometry was designed for NH3 selective catalytic reduction (NH3-SCR) over Cu-ZSM-5. The redox characteristic of Cu-based catalysts and the variations of NH3, NOx concentration, and NOx conversion along the axis in porous media channels were studied. The relative pressure drop in different channels, the variations of NH3 and NOx conversion efficiency were analyzed. The model mainly considers NH3 adsorption and desorption, NH3 oxidation, NO oxidation, and NOx reduction. The results showed that the model could accurately predict the NH3-SCR reaction. In addition, it was found that the Cu-based zeolite catalyst had poor low-temperature catalytic performance and good high-temperature activity. Moreover, the catalytic reaction of NH3-SCR was mainly concentrated in the upper part of the reactor. In addition, the hexagonal channel could effectively improve the diffusion rate of gas reactants to the catalyst wall, reduce the pressure drop and improve the catalytic conversion efficiencies of NH3 and NOx.

Rapidly Pulsed Reductants for Diesel NOx Reduction With Lean NOx Traps: Comparison of Alkanes and Alkenes as the Reducing Agent

2016 ◽  
Author(s):  
Amin Reihani ◽  
Brent Patterson ◽  
John Hoard ◽  
Galen B. Fisher ◽  
Joseph R. Theis ◽  
...  
Keyword(s):  
Catalytic Reduction ◽  
Nox Reduction ◽  
Oxygen Storage Capacity ◽  
Pulse Frequency ◽  
Oxygen Storage ◽  
Passenger Cars ◽  
Catalyst Composition ◽  
Nox Conversion ◽  
Lean Nox ◽  
Lean Nox Traps

Lean NOx Traps (LNTs) are often used to reduce NOx on smaller diesel passenger cars where urea-based Selective Catalytic Reduction (SCR) systems may be difficult to package. However, the performance of LNTs at temperatures above 400°C needs to be improved. The use of Rapidly Pulsed Reductants (RPR) is a process in which hydrocarbons are injected in rapid pulses ahead of the LNT in order to improve its performance at higher temperatures and space velocities. This approach was developed by Toyota and was originally called Di-Air (Diesel NOx aftertreatment by Adsorbed Intermediate Reductants) [1]. There is a vast parameter space that needs to be explored in order to maximize the NOx conversion at high temperatures and flow rates while minimizing the fuel penalty associated with the hydrocarbon injections. Four parameters were identified as important for RPR operation: (1) the flow field and reductant mixing uniformity; (2) the pulsing parameters including the pulse frequency, duty cycle, and rich magnitude; (3) the reductant type; and (4) the catalyst composition, including the type and loading of precious metal, the type and loading of NOx storage material, and the amount of oxygen storage capacity (OSC). In this study, RPR performance was assessed between 150°C and 650°C with several reductants including dodecane, propane, ethylene, propylene, H2, and CO. A novel injection and mixer system was designed that allowed for the investigation of previously unexplored areas of high frequency injections up to f = 100Hz. Under RPR conditions, H2, CO, dodecane, and C2H4 provided approximately 80% NOx conversion at 500°C, but at 600°C the conversions were significantly lower, ranging from 40 to 55%. The NOx conversion with C3H8 was low across the entire temperature range, with a maximum conversion of 25% near 300°C and essentially no conversion at 600°C. In contrast, C3H6 provided greater than 90% NOx conversion over a broad range of temperature between 280°C and 630°C. Among the hydrocarbons, this suggested that the high temperature NOx conversion with RPR improves as the reactivity of the hydrocarbon increases.

scholarly journals Deactivation of Cu/SSZ-13 NH3-SCR Catalyst by Exposure to CO, H2, and C3H6

Catalysts ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 929 ◽  
Author(s):  
Auvray ◽  
Mihai ◽  
Lundberg ◽  
Olsson
Keyword(s):  
Flow Reactor ◽  
Catalytic Reduction ◽  
Plug Flow ◽  
Acid Sites ◽  
Drift Spectroscopy ◽  
Scr Catalyst ◽  
Nh3 Scr ◽  
Scr Catalysts ◽  
Nh3 Oxidation ◽  
Diffuse Reflectance Infrared

Lean nitric oxide (NOx)-trap (LNT) and selective catalytic reduction (SCR) are efficient systems for the abatement of NOx. The combination of LNT and SCR catalysts improves overall NOx removal, but there is a risk that the SCR catalyst will be exposed to high temperatures and rich exhaust during the LNTs sulfur regeneration. Therefore, the effect of exposure to various rich conditions and temperatures on the subsequent SCR activity of a Cu-exchanged chabazite catalyst was studied. CO, H2, C3H6, and the combination of CO + H2 were used to simulate rich conditions. Aging was performed at 800 °C, 700 °C, and, in the case of CO, 600 °C, in a plug-flow reactor. Investigation of the nature of Cu sites was performed with NH3-temperature-programed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) of probe molecules (NH3 and NO). The combination of CO and H2 was especially detrimental to SCR activity and to NH3 oxidation. Rich aging with low reductant concentrations resulted in a significantly larger deactivation compared to lean conditions. Aging in CO at 800 °C caused SCR deactivation but promoted high-temperature NH3 oxidation. Rich conditions greatly enhanced the loss of Brønsted and Lewis acid sites at 800 °C, indicating dealumination and Cu migration. However, at 700 °C, mainly Brønsted sites disappeared during aging. DRIFT spectroscopy analysis revealed that CO aging modified the Cu2+/CuOH+ ratio in favor of the monovalent CuOH+ species, as opposed to lean aging. To summarize, we propose that the reason for the increased deactivation observed for mild rich conditions is the transformation of the Cu species from Z2Cu to ZCuOH, possibly in combination with the formation of Cu clusters.

scholarly journals Lean and rich aging of a Cu/SSZ-13 catalyst for combined lean NOx trap (LNT) and selective catalytic reduction (SCR) concept

2019 ◽  
Vol 9 (9) ◽  
pp. 2152-2162 ◽  
Author(s):  
Xavier Auvray ◽  
Ann Grant ◽  
Björn Lundberg ◽  
Louise Olsson
Keyword(s):  
Selective Catalytic Reduction ◽  
Catalytic Reduction ◽  
Lean Nox Trap ◽  
Nox Trap ◽  
Scr Catalyst ◽  
Lean Nox

In the combined lean NOx trap (LNT) and selective catalytic reduction (SCR) concept, the SCR catalyst can be exposed to rich conditions during deSOx of the LNT.

scholarly journals Combination of LNT and SCR for NOx reduction in passenger car applications

2014 ◽  
Vol 157 (2) ◽  
pp. 60-67
Author(s):  
Teuvo MAUNULA
Keyword(s):  
Catalytic Reduction ◽  
Nox Reduction ◽  
Main Reaction ◽  
Maximum Temperature ◽  
Lean Nox Trap ◽  
Particulate Emissions ◽  
Passenger Cars ◽  
Experimental Conditions ◽  
Scr Catalyst ◽  
Scr Catalysts

The removal of NOx and particulate emissions in light-duty diesel vehicles will require the use of aftertreatment methods like Diesel Particulate Filters (DPF) and Selective Catalytic Reduction (SCR) with urea and Lean NOx Trap (LNT) (Euro 6 and beyond). A new concept is the combination of LNT + SCR, which enables on-board synthesis of ammonia (NH3), which reacts with NOx on the SCR catalyst. The main application for this kind system will be lighter passenger cars, where LNTs may be used instead of full urea-SCR system. That particular combinatory system was investigated by developing platinum (Pt) and rhodium (Rh) containing LNTs and SCR catalysts in this study. In the use conditions, the maximum temperature may reach temperatures up to 800 °C and NOx reduction reactions should proceed without NO2 assistance in the SCR position after LNT and DPF. PtRh/LNT with the total loadings of 85 g/cft (2.8 g/L) and higher resulted in a high NOx efficiency above 80–90% with a broad operation window in the laboratory simulations. In the experimental conditions, a higher NH3 concentration after LNT was essential to simulate well the operation of SCR catalysts. The developed Cu-SCR catalyst showed a high hydrothermal durability up to the ageing temperature of 800 °C and a wide operation window without the NO2 assistance (NO only in feed). Fe-SCR and V-SCR catalysts were more dependent on NO2. A studied concept had an air injection after LNT to keep SCR condition always in lean side, where the SCR reaction was promoted by oxygen resulting in high reduction selectivity to nitrogen (N2) without NH3 emissions. The simulations in reaction conditions and system design resulted in the proposals for the optimal design and main reaction mechanism in DOC + DPF + LNT + SCR systems.

scholarly journals Hybrid Technology for DeNOxing by LNT-SCR System for Efficient Diesel Emission Control: Influence of Operation Parameters in H2O + CO2 Atmosphere

Catalysts ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 228
Author(s):  
Marina Cortés-Reyes ◽  
Concepción Herrera ◽  
María Ángeles Larrubia ◽  
Luis J. Alemany
Keyword(s):  
Catalytic Reduction ◽  
Scale Up ◽  
Lean Nox Trap ◽  
Scr Catalyst ◽  
Temperature Range ◽  
Small Pore ◽  
Lean Nox ◽  
Operation Parameters ◽  
The Rich ◽  
Scr System

The behavior and operation parameters were analyzed for the hybrid LNT-SCR (Lean NOx-Trap–Selective Catalytic Reduction) system with advanced catalyst formulations. Pt-Ba-K/Al2O3 was used as an NSR (NOx Storage and Reduction) or LNT catalyst effective in NOx and soot simultaneous removal whereas Cu-SAPO-34 with 2 wt.% of copper inside the structure was the small pore zeolite employed as the SCR catalyst. Under alternating and cyclic wet conditions, feeding volumetric concentrations of 1000 ppm of NO, 3% of O2, 1.5% of water, 0.3% of CO2, and H2 as a reductant, the NOx-conversion values were above 95% and a complete mineralization to nitrogen was registered using θ ≤ 3 (20 s of regeneration) and a hydrogen content between 10,000 and 2000 ppm in the whole temperature range tested. An excess of hydrogen fed (above 1% v/v) during the rich phase is unnecessary. In addition, in the low temperature range below 250 °C, the effect is more noticeable due to the further ammonia production and its possible slip. These results open the way to the scale up of the coupled catalytic technologies for its use in real conditions while controlling the influence of the operation map.

Rapidly Pulsed Reductants for Diesel NOx Reduction With Lean NOx Traps: Comparison of Alkanes and Alkenes as the Reducing Agent

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Amin Reihani ◽  
Brent Patterson ◽  
John Hoard ◽  
Galen B. Fisher ◽  
Joseph R. Theis ◽  
...  
Keyword(s):  
Catalytic Reduction ◽  
Nox Reduction ◽  
Oxygen Storage Capacity ◽  
Oxygen Storage ◽  
Passenger Cars ◽  
Catalyst Composition ◽  
Nox Conversion ◽  
Lean Nox ◽  
Adsorbed Intermediate ◽  
Lean Nox Traps

Lean NOx traps (LNTs) are often used to reduce NOx on smaller diesel passenger cars where urea-based selective catalytic reduction (SCR) systems may be difficult to package. However, the performance of LNTs at temperatures above 400 °C needs to be improved. Rapidly pulsed reductants (RPR) is a process in which hydrocarbons are injected in rapid pulses ahead of the LNT in order to improve its performance at higher temperatures and space velocities. This approach was developed by Toyota and was originally called Di-Air (diesel NOx aftertreatment by adsorbed intermediate reductants) (Bisaiji et al., 2011, “Development of Di-Air—A New Diesel deNOx System by Adsorbed Intermediate Reductants,” SAE Int. J. Fuels Lubr., 5(1), pp. 380–388). Four important parameters were identified to maximize NOx conversion while minimizing fuel penalty associated with hydrocarbon injections in RPR operation: (1) flow field and reductant mixing uniformity, (2) pulsing parameters including the pulse frequency, duty cycle, and magnitude, (3) reductant type, and (4) catalyst composition, including the type and loading of precious metal and NOx storage material, and the amount of oxygen storage capacity (OSC). In this study, RPR performance was assessed between 150 °C and 650 °C with several reductants including dodecane, propane, ethylene, propylene, H2, and CO. Under RPR conditions, H2, CO, C12H26, and C2H4 provided approximately 80% NOx conversion at 500 °C; however, at 600 °C the conversions were significantly lower. The NOx conversion with C3H8 was low across the entire temperature range. In contrast, C3H6 provided greater than 90% NOx conversion over a broad range of 280–630 °C. This suggested that the high-temperature NOx conversion with RPR improves as the reactivity of the hydrocarbon increases.

scholarly journals The Effect of Tourmaline on SCR Denitrification Activity of MnOx/TiO2 at Low Temperature

Catalysts ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1020
Author(s):  
Yizhe Helian ◽  
Suping Cui ◽  
Xiaoyu Ma
Keyword(s):  
Low Temperature ◽  
Catalytic Reduction ◽  
Catalytic Performance ◽  
Scr Catalyst ◽  
Highly Efficient ◽  
Nh3 Scr ◽  
Catalytic Material ◽  
Acidic Sites ◽  
Denitrification Activity ◽  
The Stability

Selective catalytic reduction (SCR) technology is the most widely used flue gas denitration technology at present. The stability of a catalyst is the main factor limiting the development of this technology. In this study, an environmentally friendly and highly efficient NH3-SCR catalyst was prepared by coprecipitation method from acidolysis residue of industrial waste and tourmaline. We found that the addition of tourmaline has an important impact on the denitration activity of the catalytic material. The NOx conversion exceeded 97% at 200 °C with the dosage of 10% tourmaline, which is about 7% higher than that without doping. The improvement of catalytic performance was mostly attributed to the permanent electrodes of tourmaline, which effectively promotes the dispersion of MnOx/TiO2 catalytic materials, increases the number of acidic sites and changes the valence distribution of manganese ions in products, which speeds up the diffusion of protons and ions, resulting in the acceleration of redox reaction. These as-developed tourmaline-modified MnOx/TiO2 materials have been demonstrated to be promising as a new type of highly efficient low-temperature NH3-SCR catalyst.

Sign in / Sign up

Export Citation Format

Share Document