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Journal Article

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

2017-03-28
2017-01-0953
Cu/CHA catalysts have been widely used in the industry, due to their desirable performance characteristics including the unmatched hydrothermal stability. While broadly recognized for their outstanding activity at or above 200°C, these catalysts may not show desired levels of NOx conversion at lower temperatures. To achieve high NOx conversions it is desirable to have NO2/NOx close to 0.5 for fast SCR. However even under such optimal gas feed conditions, sustained use of Cu/CHA below 200°C leads to ammonium nitrate formation and accumulation, resulting in the inhibition of NOx conversion. In this contribution, the formation and decomposition of NH4NO3 on a commercial Cu/CHA catalyst have been investigated systematically. First, the impact of NH4NO3 self-inhibition on SCR activity as a function of temperature and NO2/NOx ratios was investigated through reactor testing.
Technical Paper

The Effects of Thermal Degradation on the Performance of a NOX Storage/Reduction Catalyst

2009-04-20
2009-01-0631
The performance characteristics of a commercial lean-NOX trap catalyst were evaluated between 200 and 500°C, using H2, CO, and a mixture of both H2 and CO as reductants before and after different high-temperature aging steps, from 600 to 750°C. Tests included NOX reduction efficiency during cycling, NOX storage capacity (NSC), oxygen storage capacity (OSC), and water-gas-shift (WGS) and NO oxidation reaction extents. The WGS reaction extent at 200 and 300°C was negatively affected by thermal degradation, but at 400 and 500°C no significant change was observed. Changes in the extent of NO oxidation did not show a consistent trend as a function of thermal degradation. The total NSC was tested at 200, 350 and 500°C. Little change was observed at 500°C with thermal degradation but a steady decrease was observed at 350°C as the thermal degradation temperature was increased.
Technical Paper

Sustained Low Temperature NOx Reduction

2018-04-03
2018-01-0341
Sustained NOx reduction at low temperatures, especially in the 150-200 °C range, shares some similarities with the more commonly discussed cold-start challenge, however, poses a number of additional and distinct technical problems. In this project, we set a bold target of achieving and maintaining 90% NOx conversion at the SCR catalyst inlet temperature of 150 °C. This project is intended to push the boundaries of the existing technologies, while staying within the realm of realistic future practical implementation. In order to meet the resulting challenges at the levels of catalyst fundamentals, system components, and system integration, Cummins has partnered with the DOE, Johnson Matthey, and Pacific Northwest National Lab and initiated the Sustained Low-Temperature NOx Reduction program at the beginning of 2015 and completed in 2017.
Journal Article

Reformate Exhaust Gas Recirculation (REGR) Effect on Particulate Matter (PM), Soot Oxidation and Three Way Catalyst (TWC) Performance in Gasoline Direct Injection (GDI) Engines

2015-09-01
2015-01-2019
Gasoline direct injection (GDI) engines have become very attractive in transportation due to several benefits over preceding engine technologies. However, GDI engines are associated with higher levels of particulate matter (PM) emissions, which is a major concern for human health. The aim of this work is to broaden the understanding of the effect of hydrogen combustion and the influence of the three way catalytic converter (TWC) on PM emission characteristics. The presence of hydrogen in GDI engines has been reported to reduce fuel consumption and improve the combustion process, making it possible to induce higher rates of EGR. A prototype exhaust fuel reformer build for on-board vehicle hydrogen-rich gas (reformate) production has been integrated within the engine operation and studied in this work.
Technical Paper

Development of a Kinetic Model to Evaluate Water Storage on Commercial Cu-Zeolite SCR Catalysts during Cold Start

2017-03-28
2017-01-0968
Commercial Cu-Zeolite SCR catalyst can store and subsequently release significant amount of H2O. The process is accompanied by large heat effects. It is critical to model this phenomenon to design aftertreatment systems and to provide robust tuning strategies to meet cold start emissions and low temperature operation. The complex reaction mechanism of water adsorption and desorption over a Cu-exchanged SAPO-34 catalyst at low temperature was studied through steady state and transient experiments. Steady state isotherms were generated using a gravimetric method and then utilized to predict water storage interactions with respect to feed concentration and catalyst temperature. Transient temperature programmed desorption (TPD) experiments provided the kinetic information required to develop a global kinetic model from the experimental data. The model captures fundamental characteristics of water adsorption and desorption accompanied by the heat effects.
Technical Paper

Advanced Catalyst Solutions for Hydrocarbon Emissions Control During Rich Operation of Lean NOx Trap Systems

2009-04-20
2009-01-0282
The operation of NOx Adsorber catalysts (NAC), also often referred to as Lean NOx Trap catalysts or NOx Storage-reduction catalysts, entails frequent periodic NOx regeneration events. These are accomplished by creating a net reducing, fuel-rich environment in the exhaust. The reduction of hydrocarbon emissions which occur during such fuel-rich events is challenging, due to the oxygen-deficient environment. In order to overcome this limitation, two possibilities exist: (i) oxygen can be stored during lean phase, to be used for hydrocarbon slip oxidation in the subsequent rich phase, or (ii) unreacted hydrocarbons can be trapped during the rich phase and oxidized during the following lean phase. In this work, two groups of catalytic solutions were developed and evaluated for hydrocarbon emission control based on these approaches: an Oxygen Storage Compound (OSC) based catalyst and zeolite-based hydrocarbon trap catalyst.
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