The trapping and regeneration behaviors of a diesel particulate filter (DPF), including particle size, are examined via engine dynamometer testing. The exhaust system consists of two active lean NO x (ALN) catalysts in series followed by a catalyzed DPF. Forced regenerations are accomplished by injecting diesel fuel into the exhaust in front of the ALN catalysts to generate an exotherm sufficient to induce soot oxidation. Results are reported for two diesel fuels, one with 340 ppm sulfur, and the other with 4 ppm sulfur, and as a function of DPF regeneration temperature. The results show the DPF to be very effective at removing particulate matter, >99% efficiency. The <1% of particles that escape trapping exhibit a size distribution very similar to engine out soot. During regeneration, particle emissions remain well below engine out levels for the low sulfur fuel, but exhibit a temporary nucleation mode of about ten times the engine out level for the high sulfur fuel. The regeneration rate increases exponentially with temperature, and the fastest regenerations suffer the lowest fuel economy penalty.

10.4271/2003-01-0047

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Citations (36)

Diesel Aftertreatment Modeling: A Systems Approach to NO_x Control

Industrial & Engineering Chemistry Research (2007)

Santhoji Katare Joseph E. Patterson Paul M. Laing

Stringent North American emission regulations present several challenges for lean-burn diesel vehicles that offer significant fuel economy advantages over gasoline vehicles. This article presents a useful systems approach to developing robust models and combining them to analyze diesel aftertreatment (AT) technologies: (1) the diesel oxidation catalyst (DOC) that oxidizes carbon monoxide (CO), unburned hydrocarbons (HCs), and nitric oxide (NO), and stores HCs and (2) the urea-based selective catalytic reduction (SCR) catalyst that hydrolyzes aqueous urea to ammonia (NH3), which, in turn, reduces nitrogen oxides (NOx). The DOC and SCR models integrate information from multiple sourcesdetailed thermal balances, laboratory performance data, phenomenological descriptions of adsorption and desorption in the catalyst, and experience-based correlationsusing optimization and statistical tools. The DOC model predicts cumulative HC and CO tailpipe vehicle emissions as well as DOC NOx outlet composition (NO vs NO2). The SCR model uses the exotherm and NO2 information from the DOC model to predict NOx conversion and NH3 slip. System-level analyses that have resulted in important insights are highlighted using case studies, including (1) extrapolation of the downstream injection exotherm vehicle data for a fresh DOC to an aged DOC; (2) analysis of the effects of NO2 produced in the DOC, SCR aging conditions, and NH3 storage capacity on the NOx reduction performance of the SCR on a 6000-lb light-duty truck, and (3) development of urea injection strategies based on a tradeoff between NOx reduction and NH3 slip.

Selective catalytic reduction

Nitrogen oxides

10.1021/ie0612515

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Citations (45)

Rhodium Catalyst Structural Changes during, and Their Impacts on the Kinetics of, CO Oxidation

JACS Au (2023)

Silvia Mariño Lai Wei Marina Cortés‐Reyes Yisun Cheng Paul M. Laing

Catalysts can undergo structural changes during the reaction, affecting the number and/or the shape of active sites. For example, Rh can undergo interconversion between nanoparticles and single atoms when CO is present in the reaction mixture. Therefore, calculating a turnover frequency in such cases can be challenging as the number of active sites can change depending on the reaction conditions. Here, we use CO oxidation kinetics to track Rh structural changes occurring during the reaction. The apparent activation energy, considering the nanoparticles as the active sites, was constant in different temperature regimes. However, in a stoichiometric excess of O2, there were observed changes in the pre-exponential factor, which we link to changes in the number of active Rh sites. An excess of O2 enhanced CO-induced Rh nanoparticle disintegration into single atoms, affecting catalyst activity. The temperature at which these structural changes occur depend on Rh particle size, with small particle sizes disintegrating at higher temperature, relative to the temperature required to break apart bigger particles. Rh structural changes were also observed during in situ infrared spectroscopic studies. Combining CO oxidation kinetics and spectroscopic studies allowed us to calculate the turnover frequency before and after nanoparticle redispersion into single atoms.

Particle (ecology)

Stoichiometry

Reaction rate

10.1021/jacsau.2c00595

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Citations (8)

Laboratory Studies and Mathematical Modeling of Urea SCR Catalyst Performance

SAE technical papers on CD-ROM/SAE technical paper series (2007)

Jeong Y. Kim Giovanni Cavataio Joseph E. Patterson Paul M. Laing Christine Lambert

10.4271/2007-01-1573

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Citations (27)