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The low-temperature performance characteristics of a commercial lean NOX trap catalyst were evaluated using infra-red thermography (IRT) before and after a high-temperature aging step. Reaction tests included propylene oxidation, oxygen storage capacity measurements, and simulated cycling conditions for NOX reduction, using H₂ as the reductant during the regeneration step of the cycle. Testing with and without NO in the lean phase showed thermal differences between the reductant used in reducing the stored oxygen and that for nitrate decomposition and reduction. IRT clearly demonstrated where NOX trapping and regeneration were occurring spatially as a function of regeneration conditions, with variables including hydrogen content of the regeneration phase and lean- and rich-phase cycle times.

Typical Lean NOx Trap (LNT) catalyst composition includes precious metal components (Pt, Pd, and/or Rh), responsible for NO oxidation during lean operation and NOx reduction during rich operation. It was found that redox history of commercial LNT catalyst plays a significant role on deciding its NOx conversion under Lean/Rich cyclic condition. Further test had shown that fully formulated LNT catalyst being pre-reduced had shown much better NO reduction activity during the temperature-programmed reduction (TPRx) of NO than the same LNT catalyst being oxidized. The following study with Rh-only and Pt-only catalyst had demonstrated that Rh plays a key role on the large variation of the NO reduction function due to oxidation state change over LNT catalyst.

Selective Catalytic Reduction (SCR) catalysts have been demonstrated as an effective solution for controlling NOx emissions from diesel engines. Typical 2010 Heavy-Duty systems include a DOC along with a catalyzed soot filter (CSF) in addition to the SCR sub-assembly. There is a strong desire to further increase the NOx conversion capability of such systems, to enable additional fuel economy savings by allowing engines to be calibrated to higher engine-out NOx levels. One potential approach is to replace the CSF with a diesel particulate filter coated with SCR catalysts (SCR-DPF) while keeping the flow-through SCR elements downstream, which essentially increases the SCR volume in the after-treatment assembly without affecting the overall packaging. In this work, a system consisting of SCR-DPF was evaluated in comparison to the DOC + CSF components from a commercial 2010 DOC + CSF + SCR system on an engine with the engine EGR on (standard engine-out NOx) and off (high engine-out NOx).

In this work, an alternative method is proposed and validated for quantifying the axial performance of a state-of-the-art Cu zeolite SCR catalyst. Catalyst cores of a standard length, with varying lengths of wash-coated regions were used to axially resolve the functional performance of the SCR catalyst. This proposed method was validated by quantifying the catalyst entrance and exit effects, as well as the effect of non-uniform wash-coat loading densities. This method is less susceptible to some of the complications highlighted in the previous studies, such as flow uniformity between channels, as well as radiative heating effects, since the product gases are sampled across the entire monolith cross-section rather than through a single catalyst channel. The specific catalyst functions quantified include: NO and NH₃ oxidation, NH₃ storage capacity, as well as NOx conversion efficiency.

Mitigation of ammonia slip from SCR system is critical to meeting the evolving NH₃ emission standards, while achieving maximum NOx conversion efficiency. Ammonia slip catalysts (ASC) are expected to balance high activity, required to oxidize ammonia across a broad range of operating conditions, with high selectivity of converting NH₃ to N₂, thus avoiding such undesirable byproducts as NOx or N₂O. In this work, new insights into the behavior of an advanced ammonia slip catalyst have been developed by using accelerated progressive catalyst aging as a tool for catalyst property interrogation. The overall behavior was deconstructed to several underlying functions, and referenced to an active but non-selective NH₃ oxidation function of a diesel oxidation catalyst (DOC) and to the highly selective but minimally active NH₃ oxidation function of an SCR catalyst.

A one-dimensional model of a NOx trap system was developed to describe NOx storage during the lean operation, and NOx release and subsequent reduction during the rich regeneration process. The development of a NOx trap model potentially enables the optimisation of catalyst volume, precious metal loading, substrate type and regeneration strategy for these complex systems. To develop a fundamental description of catalytic activity, experiments were conducted to investigate the key processes involved in isolation (as far as possible), using a Pt/Rh/BaO/Al2O3 model catalyst. A description of the storage capacity as a function of temperature was determined using NOx breakthrough curves and the storage portion of more dynamic lean-rich cycling experiments. NOx breakthrough curves were also used for determination of rate of NOx storage. Kinetics for NOx reduction, as well as CO and HC oxidation, were determined using steady state reactor experiments.

Stricter emission standards in the near future require not only a high conversion efficiency of the toxic air pollutants but also a substantial reduction of the greenhouse gases from automotive exhaust. Advanced engines with improved fuel efficiency can reduce the greenhouse gas emissions; their exhaust temperature is, however, also low. This consequently poses significant challenges to the emission control system demanding the catalysts to function at low temperatures both during the cold start period and under the normal engine operation conditions. In this paper, we will introduce a gasoline Cold Start Concept (gCSC™) technology developed for advanced stoichiometric-burn gasoline engines to meet future stringent emission regulations. To improve the low temperature performance of three-way catalysts, a novel Al2O3/CeO2/ZrO2 mixed oxide was developed.

Catalytic emission control systems are installed on nearly all automobiles and heavy-duty trucks produced today to reduce exhaust emissions for the vehicles to meet government regulations. Current systems can achieve very high efficiencies in reducing tailpipe emissions once the catalytic components reach their operating temperatures. They are, however, relatively ineffective at temperatures below their operating temperature windows, especially during the cold start period of the vehicles. With the increasingly stringent government regulations, reducing the emissions during the cold start period before the catalytic components reach their operating temperatures is becoming a major challenge. For cold start HC control, HC traps based on zeolites have been investigated and commercialized for certain applications. For cold start NOx control, especially in lean burn engine exhaust, NOx storage and release catalysts have been evaluated.

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.

NOx adsorber catalyst technology has been successfully applied on diesel vehicles to enable them to satisfy stringent NOx emission regulations. One limitation of this technology is the requirement to regularly desulfate the adsorber to maintain high NOx conversion efficiency. In addition to adding significant engine and calibration complexity, these high temperature desulfation events accelerate the thermal degradation of the exhaust system components. Minimization of the severity and the frequency of the desulfation events is highly desirable. Laboratory studies to understand desulfation processes and to identify improved NOx Adsorber washcoat compositions are described. These studies led to a new generation of NOx adsorber catalysts with reduced desulfation temperatures, faster desulfation rates and enhanced low-temperature activity. The new generation of catalysts also enabled the potential for PGM thrifting, especially for applications with low engine- out NOx emissions.

A novel laboratory methodology has been developed and applied to evaluate performance of NOx Adsorber catalysts, based on the detailed analysis of micro-core samples obtained from various locations in a full-size catalyst. The technique includes a protocol for evaluating various aspects of NOx performance, as well as direct measurements of the amount of sulfur on the catalyst. This method was used to determine the NOx performance and distribution of sulfur loading on several engine aged catalysts. It showed the ability to differentiate poor NOx performance due to insufficient desulfation from that due to thermal degradation. This method further quantifies different forms of sulfur that are present on the catalyst. These forms of sulfur are distinguished by the temperature at which they are removed. In addition, the aspects of sulfur behavior that are important to this technique are discussed.

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.

Selective catalytic reduction (SCR) of NOx by NH3 is under intensive development as a technology to enable diesel engines to meet stringent NOx emission regulations. Cu/zeolite SCR catalysts are leading candidates because of their ability to catalyze NOx reduction at the low temperatures encountered on many diesel vehicles. However, both engine evaluation and laboratory studies indicated that commonly available Cu/zeolite SCR catalysts did not have sufficient thermal stability to maintain performance during the full useful life of a vehicle (with steady-state NOx conversion decreasing ~ 10% over 64 hours of hydrothermal aging at 670 °C). Characterization of aged Cu/zeolite catalysts revealed that the loss of zeolite acidity was the main deactivation mechanism; while the zeolite support maintained its framework structure and surface area after aging. Improvement of the hydrothermal stability of the acid sites resulted in a new generation of SCR catalysts.

Emission control systems combining NOx Adsorber catalysts with Selective Catalytic Reduction catalysts (NAC + SCR) offer potential performance advantages for NOx control under lean conditions compared to systems consisting of only one of these technologies. The combined systems, however, also present new catalyst design challenges. In contrast to NAC-only systems, formation of NH₃ over the NAC component under NOx regeneration conditions is a desirable feature in the combined (NAC + SCR) system. The SCR component in the combined system needs to be as thermally durable as the stand-alone SCR technology and also has to withstand repeated high-temperature lean/rich transients encountered during periodic desulfation of the upstream NAC component. In this study, advanced NAC and SCR components were developed specifically for the combination system. The advanced NAC component exhibited a wider operating temperature window and higher NH₃ generation activity at reduced PGM loading.

Oxidation of NO to NO₂ over a Diesel Oxidation Catalyst (DOC) plays an important role in different types of aftertreatment systems, by enhancing NOx storage on adsorber catalysts, improving the NOx reduction efficiency of SCR catalysts, and enabling the passive regeneration of Diesel Particulate Filters (DPF). The presence of hydrocarbon (HC) species in the exhaust is known to affect the NO oxidation performance over a DOC; however, specific details of this effect, including its underlying mechanism, remain poorly understood. Two major pathways are commonly considered to be responsible for the overall effect: NO oxidation inhibition, due to the presence of HC, and the consumption of the NO₂ produced by reaction with hydrocarbons. In this work we have attempted to decouple these two pathways, by adjusting the catalyst inlet concentrations of NO and NO₂ to the thermodynamic equilibrium levels and measuring the composition changes over the catalyst in the presence of HC species.

Since early 2010, most new medium- and heavy-duty diesel vehicles in the US rely on urea-based Selective Catalytic Reduction (SCR) technology for meeting the most stringent regulations on nitrogen oxides (NOx) emissions in the world today. Catalyst technologies of choice include Copper (Cu)- and Iron (Fe)-based SCR. In this work, the performances of Fe-SCR and Cu-SCR were investigated in the most commonly used DOC + CSF + SCR system configuration. Cu-SCR offered advantages over Fe-SCR in terms of low temperature conversion, NO₂:NOx ratio tolerance and NH₃ slip, while Fe-SCR demonstrated superior performance under optimized NO₂:NOx ratio and at higher temperatures. The Cu-SCR catalyst displayed less tolerance to sulfur (S) exposure. Reactor testing has shown that Cu-SCR catalysts deactivate at low temperature when poisoned by sulfur.

The modern Diesel engine is one of the most versatile power sources available for mobile applications. The high fuel economy and power of the Diesel engine has long made it the choice for heavy-duty applications worldwide. Over the coming years, global emissions legislation applied to heavy-duty Diesel (HDD) engines will become more and more stringent, necessitating the use of advanced emissions control technologies. In particular, the coming exhaust gas emissions legislation focuses on particulate matter (PM) emissions and emissions of nitrogen oxides (NOx). A filtration device can control PM emissions, and a possible technology for the abatement of NOx emissions involves NOx absorber catalysts. This paper describes investigations into the activity and system behaviour of a prototype HDD exhaust system based on NOx absorber technology. The system consists of a “single leg” containing NOx absorber catalyst that is bypassed during rich regeneration of the NOx absorbers.

The phase-in of US EPA Tier 3 and California LEV III emission standards require further reduction of tailpipe criteria pollutants from automobiles. At the same time, the mandate for reducing Green House Gas (GHG) emissions continuously lowers the exhaust temperature. Both regulations pose significant challenges to emission control catalyst technologies, especially for cold start emissions. The recently developed diesel cold start concept technology (dCSC™) shows promising results. It stores NOx and HC during the cold start period until the downstream catalytic components reach their operating temperatures, when the stored NOx/HC are subsequently released and converted. The technology also has oxidation functions built in and acts as a diesel oxidation catalyst under normal operating conditions. In a US DOE funded project, the diesel cold start concept technology enabled a high fuel efficiency vehicle to achieve emissions targets well below the SULEV30 emission standards.

The effects of propylene (C₃H₆) and dodecane (n-C₁₂H₂₆) exposure on the NH₃-based selective catalytic reduction (SCR) performance of two Cu-exchanged zeolite catalysts were investigated. The first sample was a model Cu/beta zeolite sample and the second a state-of-the-art Cu/zeolite sample, with the zeolite material characterized by relatively small pores. Overall, the state-of-the-art sample performed better than the model sample, in terms of hydrocarbon inhibition (which was reduced) and N₂O formation (less formed). The state-of-the-art sample was completely unaffected by dodecane at temperatures lower than 300°C, and only slightly inhibited (less than 5% conversion loss), for standard SCR, by C₃H₆. There was no evidence of coke formation on this catalyst with C₃H₆ exposure. The model sample was more significantly affected by hydrocarbon exposure. With C₃H₆, inhibition is associated with its partial oxidation intermediates adsorbed on the catalyst surface.