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A 2005 prototype diesel aftertreatment system consisting of diesel oxidation catalysts (DOC), Cu/zeolite Selective Catalytic Reduction (SCR) catalyst, and Catalyzed Diesel Particulate Filter (CDPF) was aged to an equivalent of 120k mi on an engine dynamometer using an aging cycle that incorporated both city and highway driving modes. The program demonstrated durable reduction in particulate matter (PM) and nitrogen oxides (NOx) emissions to federal Tier 2 levels on a 6000 lbs light-duty truck application. Very low sulfur diesel fuel (∼15 ppm) enabled lower PM emissions, reduced the fuel penalty associated with the emission control system, and improved long-term system durability. A total of 643 filter regenerations occurred during the aging that raised the entire catalyst system to high temperatures on a regular basis. After testing the aged system on a 6000 lbs light-duty diesel truck, a post mortem analysis was completed on core samples taken from the DOC, SCR catalyst, and filter.

The purpose of this work was to examine gasoline particle filters (GPFs) at high mileages. Soot levels for gasoline direct injection (GDI) engines are much lower than diesel engines; however, noncombustible material (ash) can cause increased backpressure, reduced power, and lower fuel economy. In this study, a post mortem was completed of two GPFs, one at 130,000 mi and the other at 150,000 mi, from two production 3.5L turbocharged GDI vehicles. The GPFs were ceramic wall-flow filters containing three-way catalytic washcoat and located downstream of conventional three-way catalysts. The oil consumption was measured to be approaching 23,000 mpqt for one vehicle and 30,000 mpqt for the other. The ash contained Ca, P, Zn, S, Fe, and catalytic washcoat. Approximately 50 wt% of the collected ash was non-lubricant derived. The filter capture efficiency of lubricant-derived ash was about 50% and the non-lubricant metal (mostly Fe) deposition rate was 0.9 to 1.2 g per 10,000 mi.

To meet future particle mass and particle number standards, gasoline vehicles may require particle control, either by way of an exhaust gas filter and/or engine modifications. Soot levels for gasoline engines are much lower than diesel engines; however, non-combustible material (ash) will be collected that can potentially cause increased backpressure, reduced power, and lower fuel economy. The purpose of this work was to examine the ash loading of gasoline particle filters (GPFs) during rapid aging cycles and at real time low mileages, and compare the filter performances to both fresh and very high mileage filters. Current rapid aging cycles for gasoline exhaust systems are designed to degrade the three-way catalyst washcoat both hydrothermally and chemically to represent full useful life catalysts. The ash generated during rapid aging was low in quantity although similar in quality to real time ash. Filters were also examined after a low mileage break-in of approximately 3000 km.

Passenger and light duty diesel vehicles will require up to 90% NOx conversion over the Federal Test Procedure (FTP) to meet future Tier 2 Bin 5 standards. This accomplishment is especially challenging for low exhaust temperature applications that mostly operate in the 200 - 350°C temperature regime. Selective catalytic reduction (SCR) catalysts formulated with Cu/zeolites have shown the potential to deliver this level of performance fresh, but their performance can easily deteriorate over time as a result of high temperature thermal deactivation. These high temperature SCR deactivation modes are unavoidable due to the requirements necessary to actively regenerate diesel particulate filters and purge SCRs from sulfur and hydrocarbon contamination. Careful vehicle temperature control of these events is necessary to prevent unintentional thermal damage but not always possible. As a result, there is a need to develop thermally robust SCR catalysts.

An improved process for determining oven aging times and temperatures for OBD-II threshold catalyst aging has been developed. The new process makes use of a catalyst model along with a kinetic data base in order to project vehicle tailpipe emissions for oven aged catalyst systems. The catalyst oven aging time and temperature required for a given vehicle can be specified such that the actual HC tailpipe emissions are within 15-20% of the desired threshold emission level. It is believed that this process could greatly reduce the need for much of the trial and error iteration which is currently associated with obtaining threshold catalysts for OBD-II calibration purposes.

This paper presents the development of an analytical model that complements laboratory based experiments to provide a tool for Selective Catalyst Reduction (SCR) applications. The model calibration is based on measured data from NOx reduction performance tests as well as ammonia (NH3) adsorption/desorption tests over select SCR catalyst formulations in a laboratory flow reactor. Only base metal/zeolite SCR samples were evaluated. Limited validations are presented that show the model agrees well with vehicle data from Environmental Protection Agency Federal Test Procedure (EPA FTP) emission assessments. The model includes energy and mass balances, several different NH3 reactions with NOx, NH3 adsorption and desorption algorithms, and NH3 oxidation.

The use of urea-based selective catalytic reduction (SCR) is a promising method for achieving U.S. Tier 2 diesel emission standards for NOx. To meet the Tier 2 standards for Particulate Matter (PM), a catalyzed diesel particulate filter (CDPF) will likely be present and any ammonia (NH3) that is not consumed over an SCR catalyst would pass over the CDPF to make nitrous oxide (N2O) emissions and/or oxides of nitrogen (NOx), or exit the exhaust system as NH3. N2O is undesirable due to its high greenhouse gas potential, while NOx production from the slipped NH3 would reduce overall system NOx conversion efficiency. This paper reviews certain conditions where NH3 slip past an SCR system may be a concern, looks at what would happen to this slipped NH3 over a CDPF, and evaluates the performance of various supplier NH3 slip catalysts under varied space velocities, temperatures and concentrations of NH3 and NOx.

Urea-based Selective Catalytic Reduction (SCR) has the potential to meet U.S. Diesel Tier 2 Bin 5 emission standards for NOx in 2010. The operating and driving conditions of light-duty and heavy-duty vehicles make it necessary to customize catalyst features to the application. This paper reviews the selection of SCR catalyst technology for the U.S. and the appropriate aging and poisoning protocols for current supplier SCR catalysts. Generally, light-duty applications require SCR catalysts to function well at low temperature whereas heavy-duty applications require functionality at high temperature and high space velocity. One main durability requirement of SCR formulations involves withstanding the high temperature process of regenerating particulate filters from accumulated soot. Unrefined engine exhaust temperature control coupled with the inexact temperature measurement may also expose SCR catalysts to additional over-temperature conditions.

Urea selective catalytic reduction (SCR) catalysts have the capability to deliver the high NOx conversion efficiencies required for future emission standards. However, the potential for the occasional over-temperature can lead to the irreversible deactivation of the SCR catalyst. On-board diagnostics (OBD) compliance requires monitoring of the SCR function to make sure it is operating properly. Initially, SCR catalyst performance metrics such as NOx conversion, NH3 oxidation, NH3 storage capacity, and BET surface area are within normal limits. However, these features degrade with high temperature aging. In this work, a laboratory flow reactor was utilized to determine the impact on these performance metrics as a function of aging condition. Upon the completion of a full time-at-temperature durability study, four performance criteria were established to help determine a likely SCR failure.

An advanced diesel aftertreatment system utilizing Selective Catalytic Reduction (SCR) with urea for lean nitrogen oxides (NOx) control was tested on a 2.7L V6 Land Rover vehicle to demonstrate the capability of achieving Tier 2 Bin 5 and lower emission standards for light-duty trucks. SCR washcoat was applied to a diesel particulate filter (DPF) to perform NOx and particulate reduction simultaneously. Advanced SCR systems employed both traditional SCR catalysts and SCR-coated filters (SCRF) to improve the NOx reduction efficiency. The engine-out NOx level was adjusted by modifying the EGR (Exhaust Gas Recirculation) calibration. Cold start NOx performance was improved by SCR warm-up strategy and urea over injection. This study showed the advanced SCR system could tolerate higher NH₃ storage in the SCR catalyst, resulting in overall higher NOx conversion on the FTP-75 test cycle.

Ford Motor Company is participating in the Department of Energy's (DOE) Ultra-Clean Transportation Fuels Program with the goal to explore the development of innovative emission control systems for advanced compression-ignition direct-injection (CIDI) transportation engines. CIDI (or diesel) engines have the advantages of a potential 40% fuel economy improvement and 20% less CO2 emissions than current gasoline counterparts. To support this goal, Ford plans to demonstrate an exhaust emission control system that provides high efficiency particulate matter (PM) and NOx reduction. Very low sulfur diesel fuel will be used to enable low PM emissions, reduce the fuel economy penalty associated with the emission control system, and increase the long-term durability of the system. The end result will allow vehicles with CIDI engines to be Tier II emissions certified at a minimum cost to the consumer.

U.S. federal vehicle emission standards effective in 2007 require tight control of NOx and hydrocarbon emissions. For light-duty vehicles, the current standard of Tier 2 Bin 5 is about 0.07 g/mi NOx and 0.09 g/mi NMOG (non-methane organic gases) at 120,000 mi. However, the proposed future standard is 0.03 g/mi for NMOG + NOx (~SULEV30) at 150,000 mi. There is a significant improvement needed in catalyst system efficiencies for diesel vehicles to achieve the future standard, mainly during cold start. In this study, a less than 6000 lbs diesel truck equipped with an advanced urea Selective Catalytic Reduction (SCR) system was used to pursue lower tailpipe emissions with an emphasis on vehicle calibration and catalyst package. The calibration was tuned by optimizing exhaust gas recirculation (EGR) fuel injection and cold start strategy to generate desirable engine-out emissions balanced with reasonable temperatures.

Alkali and alkaline earth metal impurities found in diesel fuels are potential poisons for diesel exhaust catalysts. Using an accelerated aging procedure, a set of production exhaust systems from a 2011 Ford F250 equipped with a 6.7L diesel engine have been aged to an equivalent of 150,000 miles of thermal aging and metal exposure. These exhaust systems included a diesel oxidation catalyst (DOC), selective catalytic reduction (SCR) catalyst, and diesel particulate filter (DPF). Four separate exhaust systems were aged, each with a different fuel: ULSD containing no measureable metals, B20 containing sodium, B20 containing potassium and B20 containing calcium. Metals levels were selected to simulate the maximum allowable levels in B100 according to the ASTM D6751 standard. Analysis of the aged catalysts included Federal Test Procedure emissions testing with the systems installed on a Ford F250 pickup, bench flow reactor testing of catalyst cores, and electron probe microanalysis (EPMA).

A novel method of desulfating lean NOx traps has been developed. Rapid, large amplitude modulation of the air to fuel ratio creates an exotherm of approximately 300°C in the LNT. AFR modulation results in oxidant and reductant breakthough in a three-way catalyst mounted upstream of the LNT. During lean modulation, oxygen is stored in the LNT. During rich modulation, the reductant reacts catalytically with the stored oxygen in the LNT, generating a substantial exotherm. Rich and lean AFR events are selected commensurate with the number of cylinders in the engine, resulting in each cylinder having exactly the same AFR history. This permits a deterministic programming of spark advance and precise coordination of spark advance with the transient fueling effect. The spark advance is retarded for the rich events and increases stepwise for groups of lean events. This strategy results in minimal disturbances in the engine imep.

Diesel aftertreatment systems configured with a diesel oxidation catalyst (DOC) upstream of an urea selective catalytic reduction (SCR) catalyst run the risk of precious metal contamination. During active diesel particulate filter (DPF) regeneration events, the DOC bed temperature can reach up to 850°C. Under these conditions, precious metal (especially Pt) can be volatized and then deposited on a downstream SCR catalyst. In this paper, the impact of ultra-low contamination of platinum group metals (PGM) on the SCR catalyst was studied. A method based on precious metal volatilization of a Pt-rich DOC at 850°C and under lean gas conditions was employed to contaminate downstream FeSCR and CuSCR formulations. The contamination resulted in poor NOx conversion (via NOx remake) and excessive N2O formation. The precious metal volatilization method was employed to screen various Pt/Pd based DOCs to avoid contamination of the downstream FeSCR.

It is anticipated that future gasoline engines will have improved mechanical efficiency and consequently lower exhaust temperatures at low load conditions, although the exhaust temperatures at high load conditions are expected to remain the same or even increase due to the increasing use of downsized turbocharged engines. In 2014, a collaborative project was initiated at Ford Motor Company, Oak Ridge National Lab, and the University of Michigan to develop three-way catalysts with improved performance at low temperatures while maintaining the durability of current TWCs. This project is funded by the U.S. Department of Energy and is intended to show progress toward the USDRIVE target of 90% conversion of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) at 150 °C after high mileage aging. The testing protocols specified by the USDRIVE ACEC team for stoichiometric S-GDI engines were utilized during the evaluation of experimental catalysts at all three facilities.

This paper, written in collaboration with Ford, evaluates the effectiveness of higher cell density combined with higher porosity, lower thermal mass substrates for emission control capability on a customized, RDE (Real Driving Emissions)-type of test cycle run on a chassis dynamometer using a gasoline passenger car fitted with a three-way catalyst (TWC) system. Cold-start emissions contribute most of the emissions control challenge, especially in the case of a very rigorous cold-start. The majority of tailpipe emissions occur during the first 30 seconds of the drive cycle. For the early engine startup phase, higher porosity substrates are developed as one part of the solution. In addition, further emission improvement is expected by increasing the specific surface area (GSA) of the substrate. This test was designed specifically to stress the cold start performance of the catalyst by using a short, 5 second idle time preceding an aggressive, high exhaust mass flowrate drive cycle.