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Unique silver/alumina (Ag-Al₂O₃) catalysts developed using high-throughput discovery techniques in collaboration with BASF Corporation were investigated at General Motors Corporation under simulated lean-burn engine exhaust feed conditions for the selective catalytic reduction of NOx using hydrocarbons (HC-SCR). Hydrocarbon mixtures were used as the reductant to model the multi-component nature of diesel fuel and gasoline. Previous work has shown promising HC-SCR results in both laboratory reactor and engine dynamometer testing. This report investigates several aspects of HC-SCR catalyst durability, including thermal durability, sulfur tolerance, and hydrocarbon deactivation.

A unique catalyst developed using high-throughput discovery techniques in collaboration with BASF Corporation and Accelrys, Inc. was investigated at General Motors under simulated diesel engine exhaust feed conditions for the selective catalytic reduction of NOx. A hydrocarbon mixture was used as the reductant to model the multi-component nature of diesel fuel and the catalyst was evaluated over a wide range of temperatures (150 - 550°C) relevant to light-duty diesel exhaust. This report investigates the effects of NOx (as NO or NO2), hydrocarbon concentration level (HC:NOx ratio), oxygen concentration, NO concentration, catalyst space velocity, catalyst temperature, and the co-presence of hydrogen on steady-state NOx reduction activity. Using these results, a control strategy was developed to maximize NOx conversion over the wide-ranging exhaust conditions likely to be encountered in light-duty diesel applications.

The effects of varying nozzle spray angle and rail pressure on emissions and thermal efficiency each were explored using a 103-mm bore direct-injection single-cylinder diesel engine. Spray angles from 120° to 158° significantly changed the spray targeting within the 16:1 compression ratio reentrant-shaped piston bowl. At one part load operating condition injection timing was varied over a range of 15° to 30° btc to investigate pre-mixed compression ignition (PCI) combustion with 800 bar rail pressure while varying EGR to maintain a constant low NOx emission index of 0.4 g/kg. The observed trends are explained by the combined effects of spray angle and injection timing and, in particular, the calculated amount of liquid spray that misses the piston bowl is directly linked to the measured increases in HC, CO, and smoke emissions and a reduction in thermal efficiency.

The two most common NOx reducing technologies, in an oxygen abundant exhaust stream, are urea selective catalytic reduction urea-SCR and lean NOx trap (LNT) catalysts. Each technology has advantages and disadvantages. Another selective catalytic reduction (SCR) catalyst that uses hydrocarbons (HC-SCR), specifically diesel fuel, as the reductant to reduce NOx emissions was investigated. This catalyst is a result of a high throughput discovery project and conducted in cooperation with BASF, Accelrys and funded by the Department of Energy (DOE.) Several full size 5.0L monolith catalysts were made and evaluated using a V6 turbo charged diesel engine connected to a dynamometer running light-duty transient test cycles. The NOx efficiency on the HWYFET and US06 tests were measured to be 92% and 76% respectively. The FTP was 60% on a weighted basis.

At the current state of diesel engine technology, all diesel engines require some sort of NOx control device to comply with Tier II Bin 5 light-duty or 2010 heavy-duty NOx emission standards. Selective Catalytic Reduction of NOx with hydrocarbons (HC-SCR) to reduce NOx from diesel exhaust emissions is an attractive technology for lean NOx control, especially when diesel fuel is used as the reductant. However, it has been reported that when diesel fuel is used as the reductant catalyst deactivation occurred. Even though this kind of deactivation is reversible at high enough temperatures, it is a deficiency that needs to be overcome for the successful implementation of the technology. We studied the HC-SCR catalyst deactivation using diesel fuel as the reductant. The variables investigated included catalyst temperature, HC:NOx ratio, NOx concentration, and space velocity. The results showed that one single parameter can be used to measure the catalyst deactivation: the HC-SCR activity.

To comply with Tier II Bin 5 light-duty or 2010 heavy-duty NOx emission standards, all diesel engines require some sort of NOx control device. Selective Catalytic Reduction of NOx with hydrocarbons (HC-SCR) to reduce NOx from diesel exhaust emissions is an attractive technology for lean NOx control, especially when diesel fuel is used as the reductant. However, it has been reported that when diesel fuel is used as the reductant catalyst deactivation occurred (1). In a companion paper, we demonstrated that the HC-deactivation is caused by the mismatch of the adsorption and desorption processes of either the reactants or the products of a normal SCR reaction (2). In this paper, we probe the nature of the catalyst deactivation with various reductants. Both hydrocarbons and oxygenates were used as the reductants. The deactivation or the mismatch in adsorption and desorption rates is molecular size or chain length dependent.

A unique silver/alumina selective catalytic reduction (SCR) catalyst which used hydrocarbons (HC-SCR) to reduce NOx emissions was investigated. Diesel fuel or ethanol were used as the reductants to evaluate catalyst performance. Several full size 5.0L monolith 2.0 and 3.0 wt.% Ag2O-Al2O3 catalysts were created. Testing was conducted using a 6.6L Duramax turbocharged heavy duty diesel engine. Dynamometer testing on the heavy duty FTP and SET 13 transient test cycles was conducted. The NOx conversion efficiency was evaluated as a function of catalyst volume, inlet cone angle, hydrocarbon to NOx ratio (HC:NOx), and space velocity. Oxygen effects on the NOx reaction and the HC slip past the HC-SCR catalyst were also determined. An FTIR was used to evaluate unregulated emissions. Testing on the heavy duty FTP and SET 13 test cycles, with diesel fuel as the reductant, resulted in a 60% and 65% NOx conversion reduction respectively.

The steady-state reduction of NOx at temperatures between 150-300°C has been investigated under simulated lean-burn conditions using a two-stage transient flow reactor system consisting of non-thermal plasma in combination with a sodium Y zeolite catalyst. Reactivity comparisons were made with and without plasma operation in order to identify the plasma-generated hydrocarbon species necessary for the selective catalytic reduction (SCR) of NOx. With propene as the hydrocarbon in the feed, NO is completely oxidized to NO2 in the plasma and the formation of oxidized carbon-containing species include formaldehyde, acetaldehyde, carbon monoxide, carbon dioxide, and methanol. Fourier transform infrared (FTIR) measurements indicate a close carbon balance between plasma inlet and outlet gas feed concentrations, signifying the major species have been identified.