The Impact of Ammonium Nitrate Species on Low Temperature NOx Conversion Over Cu/CHA SCR Catalyst

A selective catalytic reduction (SCR)-coated particulate filter was evaluated by means of dynamic tests performed using NH 3 , NO 2 , O 2 and H 2 O. The reactions were examined both prior to and after soot removal in order to study the effect of soot on ammonium nitrate formation and decomposition, ammonia storage and NO 2 SCR. A slightly larger ammonia storage capacity was observed when soot was present in the sample, which indicated that small amounts of ammonia can adsorb on the soot. Feeding of NO 2 and NH 3 in the presence of O 2 and H 2 O at low temperature (150, 175 and 200°C) leads to a large formation of ammonium nitrate species and during the subsequent temperature ramp using H 2 O and argon, a production of nitrous oxides was observed. The N 2 O formation is often related to ammonium nitrate decomposition, and our results showed that the N 2 O formation was clearly decreased by the presence of soot. We therefore propose that in the presence of soot, there are fewer ammonium nitrate species on the surface due to the interactions with the soot. Indeed, we do observe CO 2 production during the reaction conditions also at 150°C, which shows that there is a reaction with these species and soot. In addition, the conversion of NO x due to NO 2 SCR was significantly enhanced in the presence of soot; we attribute this to the smaller amount of ammonium nitrate species present in the experiments where soot is available since it is well known that ammonium nitrate formation is a major problem at low temperature due to the blocking of the catalytic sites. Further, a scanning electron microscopy analysis of the soot particles shows that they are about 30–40 nm and are therefore too large to enter the pores of the zeolites. There are likely Cu x O y or other copper species available on the outside of the zeolite crystallites, which could have been enhanced due to the hydrothermal treatment at 850°C of the SCR-coated filter prior to the soot loading. We therefore propose that soot is interacting with the ammonium nitrate species on the Cu x O y or other copper species on the surface of the zeolite particles, which reduces the ammonium nitrate blocking of the catalyst and thereby results in higher NO 2 SCR activity.

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Effects of equal channel angular pressing and heat treatments on the microstructures and mechanical properties of selective laser melted and cast AlSi10Mg alloys

Archives of Civil and Mechanical Engineering ◽

10.1007/s43452-021-00246-y ◽

2021 ◽

Vol 21 (3) ◽

Author(s):

Przemysław Snopiński ◽

Mariusz Król ◽

Marek Pagáč ◽

Jana Petrů ◽

Jiří Hajnyš ◽

...

Keyword(s):

Mechanical Properties ◽

Low Temperature ◽

Equal Channel Angular Pressing ◽

Heat Treatments ◽

Electron Backscattered Diffraction ◽

Angular Pressing ◽

Low Temperature Annealing ◽

Transmission Electron ◽

Before And After ◽

The Impact

AbstractThis study investigated the impact of the equal channel angular pressing (ECAP) combined with heat treatments on the microstructure and mechanical properties of AlSi10Mg alloys fabricated via selective laser melting (SLM) and gravity casting. Special attention was directed towards determining the effect of post-fabrication heat treatments on the microstructural evolution of AlSi10Mg alloy fabricated using two different routes. Three initial alloy conditions were considered prior to ECAP deformation: (1) as-cast in solution treated (T4) condition, (2) SLM in T4 condition, (3) SLM subjected to low-temperature annealing. Light microscopy, transmission electron microscopy, X-ray diffraction line broadening analysis, and electron backscattered diffraction analysis were used to characterize the microstructures before and after ECAP. The results indicated that SLM followed by low-temperature annealing led to superior mechanical properties, relative to the two other conditions. Microscopic analyses revealed that the partial-cellular structure contributed to strong work hardening. This behavior enhanced the material’s strength because of the enhanced accumulation of geometrically necessary dislocations during ECAP deformation.

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TWC-SCR Aftertreatment System Evaluation for a Lean Burn Gasoline Engine Operating in HCCI, SACI, and SI Combustion Modes

ASME 2016 Internal Combustion Engine Fall Technical Conference ◽

10.1115/icef2016-9441 ◽

2016 ◽

Cited By ~ 1

Author(s):

Jordan Easter ◽

Stanislav V. Bohac

Keyword(s):

Conversion Efficiency ◽

Gasoline Engine ◽

Fuel Efficiency ◽

Compression Ignition ◽

Scr Catalyst ◽

Advanced Combustion ◽

Nox Conversion ◽

Combustion Modes ◽

Scr System ◽

Nox Conversion Efficiency

Low temperature and dilute Homogenous Charge Compression Ignition (HCCI) and Spark Assisted Compression Ignition (SACI) can improve fuel economy and reduce engine-out NOx emissions to very low values, often less than 30 ppm. However, these combustion modes are unable to achieve stringent future regulations such as SULEV 30 without the use of lean aftertreatment. Though active selective catalytic reduction (SCR) with urea injection and lean NOx traps (LNT) have been investigated as options for lean gasoline engines, a passive TWC-SCR system is investigated in this work because it avoids the urea storage and dosing hardware of a urea SCR system, and the high precious metal cost of an LNT. The TWC-SCR concept uses periodic rich operation to produce NH3 over a TWC to be stored on an SCR catalyst for subsequent NOx conversion during lean operation. In this work a laboratory study was performed with a modified 2.0 L gasoline engine that was cycled between lean HCCI and rich SACI operation, or between lean and rich SI (spark ignited) combustion, to evaluate NOx conversion and reduced fuel consumption. Different lambda values during rich operation and different times held in rich operation were investigated. Results are compared to a baseline case in which the engine is always operated at stoichiometric conditions. SCR system simulations are also presented that compare system performance for different levels of stored NH3. With the configuration used in this study, lean/rich HCCI/SACI operation showed a maximum NOx conversion efficiency of 10%, while lean/rich SI operation showed a maximum NOx conversion efficiency of 60%. However, if the low conversion efficiency of lean/rich HCCI/SACI operation could be improved through higher brick temperatures or additional SCR bricks, simulation results indicate TWC-SCR aftertreatment has the potential to provide near-zero SCR-out NOx concentration and increased system fuel efficiency. In these simulations, fuel efficiency improvement relative to stoichiometric SI were 7 to15% for lean/rich HCCI/SACI with zero tailpipe NOx and −1 to 5% for lean/rich SI with zero tailpipe NOx emissions. Although previous work indicated increased time for NH3 to start forming over the TWC during rich operation, less NH3 production over the TWC per fuel amount, and increased NH3 slip over the SCR catalyst for advanced combustion systems, if NOx conversion efficiency could be enhanced, improvements in fuel economy and low engine-out NOx from advanced combustion modes would more than make up for these disadvantages.

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Study on the Dyeing Behavior of Wool Fiber Treated with Nano-SiO2/Ag Antibacterial Agent

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.332-334.27 ◽

2011 ◽

Vol 332-334 ◽

pp. 27-30 ◽

Cited By ~ 2

Author(s):

Mei Niu ◽

Zi Lu Wu ◽

Jin Ming Dai ◽

Wen Sheng Hou ◽

Sheng Shi ◽

...

Keyword(s):

Low Temperature ◽

Antibacterial Agent ◽

Important Influence ◽

Wool Fiber ◽

Experimental Results ◽

Ultrasonic Frequency ◽

Acid Dyes ◽

Nano Sio2 ◽

Dyeing Process ◽

The Impact

Wool fiber was firstly pretreated by nano-SiO2/Ag antibacterial agent, and then dyed with an acid dyes at low temperature by ultrasonic dyeing. Many factors had an important influence on the dye ability and the antibacterial behavior during the dyeing process of antibacterial wool fiber. The experimental results indicate that the dye-takeup rates of antibacterial wool fiber were enhanced with the increase of the concentration of nano-SiO2/Ag, the dyeing temperature, the dyeing time and the ultrasonic frequency (less than 60Hz). However, the antibacterial ratios of wool fiber were declined in the impact of these factors other than the concentration of antibacterial agent.

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Low Temperature Pre-Epi Treatment: Critical Parameters to Control Interface Contamination

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.145-146.177 ◽

2009 ◽

Vol 145-146 ◽

pp. 177-180 ◽

Cited By ~ 16

Author(s):

Roger Loo ◽

Andriy Hikavyy ◽

Frederik E. Leys ◽

Masayuki Wada ◽

Kenichi Sano ◽

...

Keyword(s):

Low Temperature ◽

Sige Layer ◽

Ex Situ ◽

Critical Parameters ◽

Process Equipment ◽

Successful Implementation ◽

Lifetime Measurements ◽

Deposition Processes ◽

Cleaning Methods ◽

The Impact

Several device concepts have been further evaluated after the successful implementation of epitaxial Si, SiGe and/or Si:C layers. Most of the next device generations will put limitations on the thermal budget of the deposition processes without making concessions on the epitaxial layer quality. In this work we address the impact of ex-situ wet chemical cleans and in-situ pre-epi bake steps, which are required to obtain oxide free Si surfaces for epitaxial growth. The combination of defect measurements, Secondary Ion Mass Spectroscopy, photoluminescence, lifetime measurements, and electrical diode characterization gives a very complete overview of the performance of low-temperature pre-epi cleaning methods. Contamination at the epi/substrate interface cannot be avoided if the pre-epi bake temperature is too low. This interface contamination is traceable by the photoluminescence and lifetime measurements. It may affect device characteristics by enhanced leakage currents and eventually by yield issues due to SiGe layer relaxation or other defect generation. A comparison of state of the art 200 mm and 300 mm process equipment indicates that for the same thermal budgets the lowest contamination levels are obtained for the 300 mm equipments.

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