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Future LEV-III tailpipe (TP) emission regulations pose an enormous challenge forcing the fleet average of light-duty vehicles produced in the 2025 model year to perform at the super ultralow emission vehicle (SULEV-30) certification levels (versus less than 20% produced today). To achieve SULEV-30, regulated TP emissions of non-methane organic gas (NMOG) hydrocarbons (HCs) and oxygenates plus oxides of nitrogen (NOx) must be below a combined 30 mg/mi (18.6 mg/km) standard as measured on the federal emissions certification cycle (FTP-75). However, when flex-fuel vehicles use E85 fuel instead of gasoline, NMOG emissions at cold start are nearly doubled, before the catalytic converter is active. Passive HC traps (HCTs) are a potential solution to reduce TP NMOG emissions. The conventional HCT design was modified by changing the zeolite chemistry so as to improve HC retention coupled with more efficient combustion during the desorption phase.

In the development of HC traps (HCT) for reducing vehicle cold start hydrocarbon (HC)/nitrogen oxide (NOx) emissions, zeolite-based adsorbent materials were studied as key components for the capture and release of the main gasoline-type HC/NOx species in the vehicle exhaust gas. Typical zeolite materials capture and release certain HC and NOx species at low temperatures (<200°C), which is lower than the light-off temperature of a typical three-way catalyst (TWC) (≥250°C). Therefore, a zeolite alone is not effective in enhancing cold start HC/NOx emission control. We have found that a small amount of Pd (<0.5 wt%) dispersed in the zeolite (i.e., BEA) can significantly increase the conversion efficiency of certain HC/NOx species by increasing their release temperature. Pd was also found to modify the adsorption process from pure physisorption to chemisorption and may have played a role in the transformation of the adsorbed HCs to higher molecular weight species.

Passive in-line catalyzed hydrocarbon (HC) traps have been used by some manufacturers in the automotive industry to reduce regulated tailpipe (TP) emissions of non-methane organic gas (NMOG) during engine cold-start conditions. However, most NMOG molecules produced during gasoline combustion are only weakly adsorbed via physisorption onto the zeolites typically used in a HC trap. As a consequence, NMOG desorption occurs at low temperatures resulting in the use of very high platinum group metal (PGM) loadings in an effort to combust NMOG before it escapes from a HC trap. In the current study, a 2.0 L direct-injection (DI) Ford Focus running on gasoline fuel was evaluated with full useful life aftertreatment where the underbody converter was either a three-way catalyst (TWC) or a HC trap. A new HC trap technology developed by Ford and Umicore demonstrated reduced TP NMOG emissions of 50% over the TWC-only system without any increase in oxides of oxygen (NOx) emissions.

In-line hydrocarbon (HC) traps are not widely used to reduce HC emissions due to their limited durability, high platinum group metal (PGM) concentrations, complicated processing, and insufficient hydrocarbon (HC) retention temperatures required for efficient conversion by the three-way catalyst component. New trapping materials and system architectures were developed utilizing an engine dynamometer test equipped with dual Fourier Transform Infrared (FTIR) spectrometers for tracking the adsorption and desorption of various HC species during the light-off period. Parallel laboratory reactor studies were conducted which show that the new HC trap formulations extend the traditional adsorption processes (i.e., based on physic-sorption and/or adsorption at acid sites) to chemical reaction mechanisms resulting in oligomerized, dehydro-cyclization, and partial coke formation.

Ethanol has been gaining attention as a partial substitute in North American pump gasoline in amounts up to 85% ethanol and 15% gasoline, or what is commonly known as “E85”. The problems with E85 fuel for cold start emissions relative to gasoline fuel are the lower energy density and vapor pressure for combustion. Each contributes to excess E85 fuel injected during cold start for comparable combustion quality and drivability to gasoline. The excess emissions occur before the first three-way catalyst (TWC) converter is warmed-up and active for engine-out exhaust conversion. The treatment of non-methane organic gas (NMOG) emissions from the combustion of E85 and gasoline was evaluated using several different zeolite based hydrocarbon (HC) traps coated with different precious metal loadings and ratios. These catalyzed HC traps were evaluated in a flow reactor and also on a gasoline Partial Zero Emissions Vehicle (PZEV) with experimental flexible fuel capability.

The performance of zeolite based, catalyzed hydrocarbon (HC) traps were evaluated with different inlet HC species and warm up profiles. Five different settings of cold–start spark timing were used each on separate FTP75 vehicle emission tests with constant neutral engine idle speed and fueling schedule. A test vehicle aftertreatment system that consisted of two converter assemblies, close-coupled and underbody, was modified by exchanging the bricks in the latter assembly with HC traps. With increasing spark retard from 9° BTDC to −17° BTDC, exhaust temperature increased, engine–out non–methane hydrocarbon (NMHC) emissions decreased, the concentration of large chain (C6+) HC species decreased and the small chain (C2–3) HC species increased. Lab flow reactor experiments showed that HC traps do not effectively manage small chain HC species with efficient adsorption or retention to conversion.

The effects of PGM zoning and washcoat staging have been investigated as a means to lower the cost and simultaneously improve the performance of a lean NOx trap system. It is shown that reverse PGM zoning can be used to reduce the cost of the LNT while essentially maintaining the NOx performance of a similarly-sized trap with a uniformly high PGM loading. In addition, the effective temperature window of the trap can be expanded by staging different NOx trap formulations that are optimized for different temperature ranges. Alternatively, LNT washcoat staging can be used to improve the hydrocarbon conversion of the trap while maintaining good NOx performance. Laboratory data and vehicle data are presented for several NOx trap system combinations that demonstrate the improved performance that can be obtained from a combination of reverse PGM zoning and washcoat staging.

The majority of unburned hydrocarbon emissions from vehicles occur during cold start operation of the vehicle before the catalyst system has heated to the point where it has reached high operating efficiency. One promising technology to reduce cold start hydrocarbon emissions is the catalyzed hydrocarbon trap. This paper presents the results of a vehicle, laboratory, and modeling study of the performance of this relatively new type of catalyst. A procedure to evaluate trap performance in the laboratory is presented that correlates well with trap performance on a vehicle. Additionally, a mathematical model of the catalyzed hydrocarbon trap is presented. This model utilizes laboratory determined parameters to calibrate the model for specific catalyzed hydrocarbon trap formulations to simulate the performance of that formulation on a vehicle. Data is presented that shows the model agrees well with vehicle data during the bag 1 portion of the Federal Test Procedure.

Catalyzed hydrocarbon traps have shown promise in reducing cold-start tailpipe hydrocarbon emissions from gasoline powered vehicles. In this paper, we report the use of catalyzed hydrocarbon trap technology to reduce the non-methane hydrocarbon emissions from a flex-fuel vehicle that can operate on fuel mixtures ranging from pure gasoline to 85% ethanol/15% gasoline. We have found that hydrocarbon traps show a substantially greater reduction in hydrocarbon emissions when used with ethanol fuel than with gasoline. We present laboratory and vehicle test results that show that tailpipe non-methane hydrocarbon emissions from a flex-fuel vehicle can be reduced by 43% when using 85% ethanol/15% gasoline fuel and 16% when using gasoline fuel from a baseline exhaust system using a three-way catalyst. These results were obtained using a catalyzed hydrocarbon trap specifically formulated for use with ethanol fuel.