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Commercial three way catalysts (TWC) are designed to eliminate HC, CO and NOx pollutants emitted from gasoline powered internal combustion engines. TWC have been optimized over many years to meet ever more stringent emission regulations. It has long been speculated that surface electrical conductivity may be a key parameter in controlling catalytic activity, however until now it has not been possible to reliably measure this physical parameter on a catalytic surface. In this study, the surface electrical conductivity of catalyst powders, such as Rh/ CeO1-x-ZrxO2, Rh/ZrO2 and Rh/Al2O3, were measured by EUPS (Extreme Ultraviolet excited Photoelectron Spectroscopy). Then the measured electrical conductivity was compared with catalyst performance from CO-NO and water gas shift reactions which are important for controlling automobile exhaust emissions from gasoline vehicles.

Battery models are being developed as a component of the powertrain systems of hybrid electric vehicles (HEVs) to predict the state of charge (SOC) accurately. Electrically heated catalysts (EHCs) can be employed in the powertrains of HEVs to reach the catalyst light off temperature in advance. However, EHCs draw power from the battery pack and hence sufficient energy needs to be stored to power auxiliary components. In series HEVs, the engine is primarily used to charge the battery pack. Therefore, it is important to develop a control strategy that triggers engine start/stop conditions and reduces the frequency of engine operation to minimize the equivalent fuel consumption. In this study, a battery pack model was constructed in MATLAB-Simulink to investigate the SOC variation of a high-power lithium ion battery during extreme engine cold start conditions (-7°C) with/without application of an EHC.

For diesel emission control systems containing a Diesel Oxidation Catalyst (DOC) and a Catalyzed Soot Filter (CSF) the DOC is used to oxidize the additional fuel injected into the cylinder and/or the exhaust pipe for the purpose of increasing the CSF inlet temperature during the soot regeneration. Hydrocarbon (HC) oxidation performance of the DOC is affected by HC species as well as a catalyst design, i.e., precious metal species, support materials and additives. How engine-out HC species vary as a function of fuel supply conditions is not well understood. In addition, the relationship between catalyst design and oxidation activity of different hydrocarbon species requires further study. In this study, diesel fuel was supplied by in-cylinder, post injection and exhaust HC species were measured by a gas chromatograph-mass spectrometry (GC-MS) and a gas analyzer. The post injection timing was set to either 73°, 88° or 98° ATDC(after top dead center).

This paper describes the development of an integrated simulation model for evaluating the effects of electrically heating the three-way catalyst (TWC) in a series hybrid electric vehicle (s-HEV) on fuel economy and exhaust gas purification performance. Engine and TWC models were developed in GT-Power to predict exhaust emissions during transient operation. These models were validated against data from vehicle tests using a chassis dynamometer and integrated into an s-HEV model built in MATLAB/Simulink. The s-HEV model accurately reproduced the performance characteristics of the vehicle’s engine, motor, generator, and battery during WLTC mode operation. It can thus be used to predict the fuel consumption, emissions, and performance of individual powertrain components. The engine combustion characteristics were reproduced with reasonable accuracy for the first 50 combustion cycles, representing the cold-start condition of the driving mode.

Palladium catalysts are known to show higher methane oxidation performance than platinum and/or rhodium catalysts. In this paper, the higher oxidative dehydrogenation activity on palladium is proposed as a reason for the superior methane oxidation. When other oxidation reactions are considered, higher affinity of palladium to oxygen has also been suggested[1]. In this study, oxygen chemical potential on platinum and palladium catalyst surfaces under oxidation conditions was measured using a specially designed electrochemical sensor. The oxygen chemical potential was calculated from the sensor potential by the Nernst equation. As a result, oxygen potential on palladium during the methane oxidation reaction was found to be much higher than that of platinum, correlating with affinity to oxygen and higher methane oxidation performance. The rate of oxygen adsorption and desorption on platinum and palladium was evaluated in an engine experiment using a dual lambda-sensor procedure.

Precious metal catalysts, such as Pt/Al2O3, are the primary active ingredient in diesel oxidation catalysts (DOC) used to control CO, HC and SOF emissions. Sintering of precious metal is one of the main deterioration factors of catalytic performance. In hot applications sintering of the alumina support material has also been suggested to accelerate precious metal sintering. Investigation of sintering rates may allow estimation of the catalyst life and provide information important for catalyst durability improvement. In this study, Pt/Al2O3 was used as a model catalyst and a sintering model for thermal aging was constructed. Pt sintering could be expressed by a differential equation which includes both Pt and support material sintering, but better fit to experimental data resulted from inclusion of a factor that includes an Al2O3 phase change.

Three way catalysts (TWC) contain Oxygen Storage Component (OSC) materials to enhance HC, CO oxidation and NOx reduction performance under standard operating conditions where there is rapid perturbation of the air-to-fuel ratio (A/F). The OSC function is required to storage and to release oxygen, however the optimum storage capacity and release rate to maximize HC, CO and NOx conversion varies as a function of engine operating conditions, such as A/F perturbation frequency, amplitude and temperature. At the same time, it is necessary for the vehicle on board diagnostics (OBD) systems to monitor that the catalyst OSC is functioning correctly. Detailed understanding of how OSC characteristics can simultaneously match gas performance and OBD functionality are not well known. In this study, modeling of the OSC function was attempted by considering chemical functions to be analogous to that in an equivalent electrical circuit, having components of resistance and capacitance.

Difference of engine combustion characteristics, species and amount of exhaust gas and PM (particulate matter consisted of SOF and Soot and Ash), and especially PM oxidation characteristics were studied when diesel fuel or bio-fuel, here PME (palm oil methyl ester) as an example, was used as a fuel. The fueling rate was adjusted to obtain the same torque for both fuels and engine was operated under several range of EGR (Exhaust Gas Recirculation) ratio. Under such conditions, PME showed shorter ignition delay time and lower R.H.R (rate of heat release) under 0-40% EGR ratio. With respect to engine exhaust gas species, CO, NO, THC and HCHO, CH3CHO concentration was almost the same when the EGR ratio is higher than 35% (Intake-Air/Fuel: A/F=20). However, PME also showed lower exhaust gas emission when the EGR ratio is higher than 30%.

To predict how DOC performance deteriorates with a lifetime of use, it is important to understand the mechanisms of catalyst aging. In off-road applications, due to the continuous high load usage and relatively high oil consumption rate, poisoning of the Diesel Oxidation Catalyst (DOC) with Phosphorus may become an important durability issue. In this study, 3D modeling has been performed to study the P poisoning mechanism and 1D modeling has been performed to investigate P poisoning parameters that effect DOC performance deterioration. From postmortem analysis on engine aged DOCs there is a general trend that P deposits tend to collect at the outermost catalyst surface. Two types of 3D modeling were performed in this study to understand how P migrates into the bulk of the catalyst. In one case, P migrates into catalyst layer by gas phase diffusion and in the other case P first adsorbs on the catalyst surface and then migrates by solid diffusion into the bulk.

Pre-filter diesel oxidation catalyst (DOC) development for a DOC-CSF system has been conducted. The pre-filter DOC is required to efficiently oxidize fuel and generate heat to regenerate accumulated soot within the catalyzed soot filter (CSF). Therefore, high thermal durability is required. In addition, good transient hydrocarbon (HC) activity is required for the DOC to reduce tailpipe HC emissions. The required performance is dependent on the OEM's system control strategy. A DOC catalyst designed to have well dispersed Pt showed high fuel combustion performance. Such high Pt dispersion was obtained by using high specific surface area Al2O3. Zeolite included into the catalyst formulation showed higher transient HC performance compared to a catalyst without zeolite. The effective catalyst layer depth with respect to transient HC activity was studied by computer simulation.

Sulfate generation by diesel oxidation catalysts (DOC) is still a problem although sulfur concentration in the diesel fuel will be reduced in future. Two approaches were attempted to reduce the sulfate generation without inhibiting the HC and CO oxidation performance. One was to use an optimized support material that adsorbs less SO2 and has sufficient specific surface area for HC/CO oxidation. Another approach was to apply a layer on the catalyst, which prevents SO2 adsorption. Sulfate generation was successfully reduced while maintaining high HC/CO oxidation performance.

Ag/Al2O3 was studied as a HC-SCR (Hydrocarbon - Selective Catalytic Reduction) catalyst for diesel application[1, 2 and 3]. Performance required of (or from) this catalyst is high NOx conversion with high thermal durability and sulfur resistance. Also low HC slip is desired. The Ag/Al2O3 system was improved by addition of additives. In the diesel 13-mode (Japan) evaluation, improved Ag/Al2O3 catalyst showed higher de-NOx activity (>50%) compared to the original when fresh. Improved Al2O3 catalyst showed smaller hysteresis of de-NOx activity between ramping up and down the temperature and smaller amount of HC slip. To study the improvement effect, interactions between the HC and catalyst were investigated by TG/DTA-MS (define) and FT-IR (define). TG/DTA measurement results showed that HC/O2 reaction was restrained in the improved catalyst. These results suggest that there was sufficient of HC for NOx reduction on the improved catalyst.

Soot (here, total particulate matter; TPM) accumulation in a diesel particulate filter (DPF) was characterized for two different engine conditions (high speed / high load and low speed / low load). Soot weight distribution within the filter was different in two engine conditions the accumulated PM layer was thicker when the engine conditions were low speed / low load even though the accumulated soot amounts were almost equivalent. Flow field conditions in a DPF were calculated and soot accumulation conditions were assumed from the solution. In the axial direction (with gas flow) uniform soot accumulation was suggested. However, in the radial direction (from center to side), non-uniform accumulation was suggested from the flow field solution and this result was experimentally confirmed. Temperature distribution in the DPF during uncontrolled soot regeneration was also calculated. The simulation suggested that the highest temperature would be observed in the back middle area of DPF.

Three Way Catalysts (TWC) contain oxygen storage components (OSC) to enhance HC, CO oxidation and NOx reduction performance under standard operating conditions where there is rapid perturbation of the air-to-fuel ratio (A/F). The OSC function is required to storage and to release oxygen, however the optimum storage capacity and release rate to maximize HC, CO and NOx conversion varies as a function of engine operating conditions, such as A/F perturbation frequency, amplitude and temperature. At the same time it is necessary for the vehicle on board diagnostics (OBD) systems to monitor that the catalyst OSC is functioning correctly. Detailed understanding of how OSC characteristics can simultaneously match gas performance and OBD functionality are not well known. In this study, several TWC catalysts were prepared with different types of OSC materials such that oxygen storage capacity and activation energy for oxygen release could be varied over a wide range.

Diesel exhaust emission control systems often contain DOC (Diesel Oxidation Catalyst) + CSF (Catalyzed Soot Filter) components. In this system PM (particulate matter) is filtered and accumulated in the CSF and such filtered PM is periodically combusted by supplying heat to the CSF. The heat to CSF is generated within the DOC by an exothermic reaction with extra fuel supplied to the DOC. Here the exothermic performance of DOC depends on not only the active catalytic site (such as Pt and/or Pd) but also on the characteristics of the porous material supporting the precious metals. Various properties of Al2O3, i.e. pore diameter, pore volume, BET surface area, acidity, basicity and the Ea (activation energy) of fuel combustion, used in DOCs and PGM particle size of each DOC were measured. The fuel combustion performance of each DOC was evaluated by diesel engine bench.

Modern diesel emission control systems often use Urea Selective Catalytic Reduction (Urea-SCR) for NOx control. One of the most active SCR catalysts is based on Cu-zeolite, specifically Cu-Chabazite (Cu-CHA), also known as Cu-SSZ-13. The Cu-SCR catalyst exhibits high NOx control performance and has a high thermal durability. However, its catalytic performance deteriorates upon long-term exposure to sulfur. This work describes our efforts to investigate the detailed mechanism of poisoning of the catalyst by sulfur, the optimum conditions required for de-sulfation, and the recovery of catalytic activity. Density functional theory (DFT) calculations were performed to locate the sulfur adsorption site within the Cu-zeolite structure. Analytical characterization of the sulfur-poisoned catalyst was performed using Extreme Ultraviolet Photoelectron Spectroscopy (EUPS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS).

To meet the severe PM (Particulate Matter) emission regulation for diesel vehicles, use of a DOC (Diesel Oxidation Catalyst) + CSF (Catalyzed Soot Filter) emission control system has recently been started in Japan. The CSF is used for diesel exhaust soot filtering, and the accumulated soot is periodically combusted to regenerate the CSF. The heat required for the soot regeneration is supplied from the DOC pre-cat under a specific regeneration mode. Additional fuel is supplied to the DOC by post injection and/or fuel dosing into the exhaust pipe upstream of DOC. The resulting exotherm provides the heat for soot combustion on the CSF. Uniform and controlled soot combustion in the CSF is necessary to maintain system durability during the vehicle's life. There are concerns that non-uniform fuel supply to the DOC front face may lead to non-uniform soot combustion in the CSF.

The reduction of NOx in exhaust gas has been a major challenge in diesel engine development. For the NOx reduction issues, a new Lean NOx Catalyst (LNC) aftertreatment system has been developed by Honda. A feature of the LNC system is the method that is used to reduce NOx through an NH₃-Selective Catalytic Reduction (NH₃-SCR). In an LNC system NOx is adsorbed at lean conditions, then converted to NH₃ at rich conditions and subsequently reduced in the next lean phase. In recent years, as the efficiency of the diesel engine has improved, the exhaust gas temperatures have been reduced gradually. Therefore, the aftertreatment system needs to be able to purify NOx at lower temperatures. The development of a new LNC which has a high activity at low temperature has been carried out. For the improvement of the LNC three material improvements were developed. The first of these was the development of a NOx adsorbent which is matching the targeted exhaust gas temperatures.

Combustion behavior of the SOF (Soluble organic fraction) fraction of diesel particulate by flow-thru type diesel oxidation catalysts (DOC) was studied. A two brick DOC system with an air gap showed higher SOF performance than a single brick DOC of the same total volume. Collision frequency of the TPM (total particulate matter) to the catalyst layer was studied by calculation of the turbulence energy in the gas flow channel. No large difference in collision frequency was observed between one brick and two bricks. The front face effect was calculated from the geometric surface and it was confirmed that such an effect was small in the two brick DOC case. The SOF performance advantage for the two brick DOC system separated by an air gap was due to a thermo-mass effect created by reducing the DOC volume.

The transient HC performance of diesel oxidation catalysts is known to be greatly improved by addition of Zeolite material. The authors already reported how to estimate the effective washcoat thickness in our previous study [1]. To understand in more detail the effective catalyst layer thickness, a precise gas diffusion model and parameters of HC adsorption and desorption rate were determined in this study. The random pore model was used for a gas diffusion calculation to simulate the macro porosity of the catalyst layer and micro porosity of the Zeolite material. HC adsorption capacity as a function of temperature and HC concentration was measured by Temperature Programmed Desorption (TPD). HC desorption rate was evaluated by changing the TPD ramping rate. HC reaction rate was evaluated by using a model gas reactor. Calculated catalyst performance correlated to the experimental results, thus validating the model.