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Reduction of nitrogen oxides in Diesel exhaust gas is a challenging task. This paper reports results from an extensive study using Pt-based catalysts involving synthetic gas activity testing (SCAT), engine bench testing and tests on passenger cars. Preliminary SCAT work highlighted the importance of Pt-dispersion, and both SCAT and bench engine testing yielded comparable NOx conversions under steady state conditions at high HC:NOx ratios. On passenger cars in the European cycle without secondary fuel injection NOx conversion was lower than obtained in the steady state tests. Better conversion was obtained in the FTP cycle, where secondary injection was employed. Higher HC:NOx, ratios and more favourable temperature conditions which were present in the exhaust contributed to this higher conversion.

Enhancements in the thermal stability of three-way catalysts have been achieved by: 1) developing improved methods for the incorporation of ceria into catalyst formulations and 2) identifying a proprietary stabilizer which reduces the rate of ceria sintering at high temperature. Improvements in thermal stability are demonstrated by comparing the FTP and engine dynamometer performance of new formulations with a standard formulation after aging on several high temperature engine dynamometer cycles.

It has long been recognized that the key to achieving stringent emission standards such as ULEV is the control of cold-start hydrocarbons. This paper describes a new approach for achieving excellent cold-start hydrocarbon control. The most important component in the system is a catalyst that is highly active at ambient temperature for the exothermic CO oxidation reaction in an exhaust stream under net lean conditions. This catalyst has positive order kinetics with respect to CO for CO oxidation. Thus, as the concentration of CO in the exhaust is increased, the rate of this reaction is increased, resulting in a faster temperature rise over the catalyst.

A test programme has been conducted to study any potential long term effects of gasoline sulphur on catalyst performance, using a newly developed transient engine-bed ageing cycle. The ageing cycle, which was based on repeated European Extra Urban Drive Cycles, was chosen to ensure that the catalyst experienced a realistically wide range of temperatures and space velocities, together with transients, idle and periods of overrun. Two nominally identical platinum/rhodium catalysts (manufactured from the same batch) with matched lambda sensors, were aged for a period of 80,000 km each, one being aged using a gasoline containing 50 mg/kg (ppm wt) sulphur, the other being aged on the same fuel doped to 450 ppm wt S. The emissions performance of both catalysts was measured after 6,000, 40,000 and 80,000 km ageing, by fitting the catalysts to a test vehicle, and performing emissions tests over the European test cycle at both sulphur levels.

This paper describes the use of advanced three-way catalysts to meet future European and California low emissions legislation. Firstly, it describes the performance of these catalysts tested using the European Stage II test cycle and contrasts their emissions performance over the proposed European Stage III test. The future legislation requires fast catalyst light-off for the low emissions standards to be achieved, therefore the performance of close-coupled catalysts was investigated. The close-coupled catalyst systems gave very low emissions. Space constraints often preclude the use of large volume close-coupled catalysts, and the combination of a small starter catalyst with an underfloor catalyst was tested. This gave performance levels better than the close-coupled configuration. The effect of reducing the underfloor catalyst volume is also described. The work was carried out on a 1.2 litre European Vehicle, the conclusions were verified on a 1.6 litre European vehicle.

A comparison of two different types of NOx reducing catalysts will be worked out. The potential of two De-NOx catalysts using engine out hydrocarbon emissions for NOx conversion will be shown by variation of different engine parameters. An analysis of the hydrocarbon species upstream and downstream catalyst will demonstrate, which components are responsible for the NOx reduction in the exhaust gas of a lean burn engine. By variation of different parameters during adsorbtion and regeneration phases of the adsorber catalyst the efficiency in NOx reduction will be optimized. An assessment of the suitability for lean burn engines will consider the emission reduction efficiency as well as the influence on engine fuel consumption.

Flow-through diesel oxidation catalysts (DOC's) have been shown to be an effective means of reducing emissions from diesel engines. In this work, the further development of diesel oxidation catalysts for the control of emissions from heavy duty engines is illustrated. Laboratory reactor and engine dynamometer data obtained from engine-based accelerated poisoning and aging studies demonstrate that HC, CO and SO2 oxidation by DOC's can be modified by adjusting platinum and vanadium loadings in alumina-based Pt/V catalyst formulations. The performance and durability of this type of catalyst system are demonstrated with several aging cycles on heavy-duty engines. The fresh performance of two catalyst systems was determined on both US Heavy Duty Transient and ECE-R49 Test cycles with a 1991 calibration Perkins Phaser 6.0 L engine. Gas phase emissions were reduced by a similar amount for both catalysts over both cycles (HC: 60-70%, CO: 45-75%).

The implementations of the Tier 2 and LEVII emission levels require fast catalyst light-off and fast closed loop control through high-speed engine management. The paper describes the development of innovative catalyst designs. During the development thermal and mechanical boundary conditions were collected and component tests conducted on test rigs to identify the emission and durability performance. The products were evaluated on a Super Imposed Test Setup (SIT) where thermal and mechanical loads are applied to the test piece simultanously and results are compared to accelerated vehicle power train endurance runs. The newly developed light-off catalyst with Perforated Foil Technology (PE) showed superior emission light-off characteristic and robustness.

This paper describes the development of new high performance three-way catalyst (TWC) formulations with improved activity and enhanced thermal stability. These new TWC formulations enable the converter to be fitted closer to the engine and allow this future legislation to be met with catalysts using PGM levels significantly lower than those currently being employed. The performance benefits of these advanced platinum- and palladium-based catalysts are demonstrated on a number of different vehicles after bench-engine ageing.

A test method, based on parallel sample testing with exhaust fuel injection and certain test procedures, has been developed for diesel lean-NOx catalyst evaluation purposes. The results of the verification tests show uniform distribution of both the exhaust gas and the injected fuel, and a high degree of fuel evaporation. Test procedures are discussed from several points of view. The test method offers a precise and efficient way of testing lean-NOx catalysts on heavy duty diesel engines.

The emissions performance of catalytic converters under different conditions of flow distribution was investigated. Computational Fluid Dynamics methods were utilised to model the maldistribution effects of different inlet cones. The effects of maldistribution on ageing, light-off and conversion were investigated using steady state tests on an engine bench. Emission testing was also conducted on a vehicle throughout ECE and EUDC test cycles. Maldistribution was found to have a significant effect on the efficiency of the catalyst during the early stages of the ECE cycle for both fresh and aged catalysts. The effects were less significant over later stages of the ECE cycle and throughout the EUDC except NOx where maldistribution did have an effect on the conversion at higher flow rates during the later stages of the test.

One possibility to improve the fuel economy of SI-engines is to run the engine with a lean air-fuel-ratio (AFR). Hydrocarbon and carbon monoxide after-treatment has been proven under lean operation, but NOx-control remains a challenge to catalyst and car manufacturers. One strategy that is being considered is to run the engine lean with occasional operation at stoichiometry. This would be in conjunction with a three-way-catalyst (TWC) to achieve stoichiometric conversion of the three main pollutants in the normal way and a NOx trap. The NOx trap stores NOx under lean operation to be released and reduced under rich conditions. The trap also functions as a TWC and has good HC and CO conversion at both lean and stoichiometric AFR's. Under lean conditions NO is oxidised to NO2 on Pt which is then adsorbed on an oxide surface. Typical adsorbent materials include oxides of potassium, calcium, zirconium, strontium, lanthanum, cerium and barium.

The influence of catalyst volume, cell density and precious metal loading on the catalyst efficiency were investigated to design a low cost catalyst system. In a first experiment the specific loading was kept constant for a 500cpsi and a 900cpsi substrate. In a second experiment the palladium loading was reduced on the 900cpsi substrate and the same PM loading was applied to a 1200cpsi substrate with lower volume. Finally the loading was further reduced for the 1200cpsi substrate. The following parameters were studied after aging: Catalyst performance of standard cell density compared to high cell density technology Light-off performance and catalyst efficiency as a function of Palladium loading and substrate cell density Catalyst efficiency as a function of AFR biasing The performance of the aged catalysts was investigated in a lambda sweep test and in light-off tests at an engine bench.

Recently, significantly more demanding emissions standards for the Mercosur region were proposed, and the intention is that these will be introduced in 2004 and 2008. This paper describes the development of new high performance three-way catalyst formulations for conventional gasoline/gasohol fueled engines that enables them to meet these stringent standards without increasing the content of platinum group metals above the levels currently employed. The performance benefits of these advanced platinum and palladium-based catalysts are demonstrated on both engine bench and vehicles.

Future US emissions limits are likely to mean a sophisticated nitrogen oxide (NOx) reduction technique is required for all vehicles with a diesel engine, which is likely to be either NOx trap or selective catalytic reduction (SCR) technology. To investigate the potential of SCR for NOx reduction on a light duty vehicle, a current model vehicle (EUII M1 calibration), of inertia weight 1810 kg, was equipped with an urea-based SCR injection system and non-vanadium, non-zeolitic SCR catalysts. To deal with carbon monoxide (CO), hydrocarbon (HC) and volatile organic fraction (VOF), a diesel oxidation catalyst was also incorporated into the system for most tests. Investigations into the effect of placing the oxidation catalyst at different positions in the system, changing the volume of the SCR catalysts, increasing system temperature through road load changes, varying the SCR catalyst composition, and changing the urea injection calibration are discussed.

When performing catalyst modeling and parameter tuning it is desirable that the experimental data contain both transient and stationary points and can be generated over a short period of time. Here a method of creating such concentration transients for a full scale engine rig system is presented. The paper describes a valuable approach for changing the composition of engine exhaust gas going to a DOC (or potentially any other device) by conditioning the exhaust gas with an additional upstream DOC and/or SCR. By controlling the urea injection and the DOC bypass a wide range of exhaust compositions, not possible by only controlling the engine, could be achieved. This will improve the possibilities for parameter estimation for the modeling of the DOC.

In the USA, hydrogen sulfide emissions from three-way catalytic converter-equipped automobiles are effectively suppressed by the addition of nickel to catalyst formulations. This approach is generally not utilized in catalyst formulations for Europe because of European concern about the health, safety and environmental issues surrounding the use of nickel. A modified form of iron oxide has been identified which suppresses hydrogen sulfide emissions from three-way catalysts. This suppression has been achieved without affecting the fresh or aged performance of the catalyst, a problem often encountered with other materials. The performance and durability of catalyst formulations incorporating the new material are demonstrated with a variety of aging and evaluation protocols.

The effect of changing catalyst precious metal ratios and loadings on close coupled catalytic converter efficiencies has been studied. The three precious metals were platinum, palladium and rhodium. The specific matrix used for the development of response surface models is a central composite design and provides the capability of visually optimising the precious metal loadings. Catalysts were evaluated using perturbed scans. lightoff curves from the dynamometer aged, and vehicle emission tests. These scans show percent conversion efficiencies of the three legislated gases; HC, CO and NOx, over a range of Air Fuel Ratios (λ). Whilst lean and rich lightoff curves provide indications of conversion efficiencies at varying temperatures. Prior to testing the catalysts were aged, using an accelerated dynamometer ageing process, to 80K simulated kilometres. The catalysts were then fitted to a vehicle and chassis roll emission tests conducted.

The objective of this effort was to develop an understanding of how different converter substrate cell structures impact tailpipe emissions and pressure drop from a total systems perspective. The cell structures studied were the following: The catalyst technologies utilized were a new technology palladium only catalyst in combination with a palladium/rhodium catalyst. A 4.0-liter, 1997 Jeep Cherokee with a modified calibration was chosen as the test platform for performing the FTP test. The experimental design focused on quantifying emissions performance as a function of converter volume for the different cell structures. The results from this study demonstrate that the 93 square cell/cm2 structure has superior performance versus the 62 square cell/cm2 structure and the 46 triangle cell/cm2 structure when the converter volumes were relatively small. However, as converter volume increases the emissions differences diminish.

Selective NOx recirculation (SNR), involving adsorption, selective external recirculation and decomposition of the NOx by the combustion process, is itself a promising technique to abate NOx emissions. Three types of materials containing Ba: barium aluminate, barium tin perovskite and barium Y-zeolites have been developed to adsorb NOx under lean-burn or Diesel conditions, with or without the presence of S02. All these materials adsorb NO2 selectively (lean-burn conditions), and store it as nitrate/nitrite species. The desorption takes place by decomposition of these species at higher temperatures. Nitrate formation implies also sulfate formation in the presence of SO2 and SO3, while the NO2/SO2 competition governs the poisoning of such catalysts.