Diesel carbon monoxide oxidation

Since 1975 catalysts have been fitted to vehicles to control emissions, initially of hydrocarbons and carbon monoxide (oxidation catalysts), and latterly also of oxides of nitrogen (three way catalysts). This contribution will demonstrate the ability of precious metal based catalysts not only to control carbon monoxide, hydrocarbons and nitrogen oxides but also the polynuclear aromatic fraction from both gasoline and diesel fuelled vehicles. The data will include that from both fresh and aged catalyst systems and also those exposed to leaded gasoline. 

Diesel Unbumed Hydrocarbon and Carbon Monoxide Oxidation... 

With the proliferation of diesel equipment in mining, emissions are a concern. Some of the previously mentioned gases (e.g., carbon monoxide, oxides of nitrogen, and sulfur dioxide) are generated by diesel equipment, but diesel particulate matter (DPM) is also generated, which is classified as a carcinogen primarily because of the polycyclic aromatic hydrocarbons it contains (Anon. 1988 Lowndes and Moloney 1996). The control of diesel emissions will also be discussed later. 

As an alternate to LNG, natural gas can be chemically converted to methanol, chemical feedstocks (such as ethylene), gasoline, or diesel fuel. Most processes start with the conversion of methane to synthesis gas, a mixture of carbon monoxide and hydrogen. This can be done partial oxidation, an exothermic reaction ... 

The reactions that occur to auto-exhaust emissions when exposed to plasma include oxidation of HCs, carbon monoxide, and partially diesel PM also. Nitric oxide (NO) can be oxidized by plasma to N02. Plasma alone, due to its oxidizing character, is not a viable NO control method. However, combinations of plasma with catalysts, referred to as plasma-assisted catalysts or simply plasma catalysts , have been suggested for NO reduction. The plasma is believed to show potential to improve catalyst selectivity and removal efficiency. Current state-of-the-art plasma catalysts have efficiencies comparable to those of active DeNO systems, removing about 50% of NO at a fuel economy penalty of less than 5% [85],... 

Compliance with the EuroIII standards (2000) forced the fitting of Diesel oxidation catalysts (DOC) in the exhaust line [for the after-treatment of unburnt hydrocarbons (HC) and carbon monoxide (CO)]. Additionally, the exhaust gas recirculation (EGR) was adapted to reduce the engine-out emissions of nitrogen oxides (NOx). 

Daimler-Benz has accumulated data on NECAR III emissions with a dynamometer programmed for a mix of urban and suburban driving. The results were promising since there were zero emissions for nitrogen oxide and carbon monoxide, and extremely low hydrocarbon emissions of only. 0005 per gram per mile. NECAR III did produce significant quantities of carbon dioxide similar to the emissions of a direct-injection diesel engine where the fuel is injected directly into the combustion chamber. Direct-injection produces less combustion residue and unburned fuel. 

Sulfur oxides, nitrogen oxides, hydrogen sulfide, and carbon dioxide are commonly produced during refining operations or during use of the refined products. For example, the most common toxic gases present in diesel exhaust include carbon monoxide, sulfur dioxide, nitric oxide, and nitrogen dioxide. 

Diesel emissions contain low concentrations of carbon monoxide and hydrocarbons. The major problem with diesel emissions are nitric oxides and particles as these are the most difficnlt to rednce. 

Because of the low-sulfur, -nitrogen, and -aromatic content of Fischer-Tropsch fuels, there is renewed interest in these products. In two recent studies, Fischer-Tropsch diesel was evaluated and compared to an ultra-low sulfur California diesel and to a 49 cetane number, low-sulfur diesel. In the two studies, carbon monoxide, nitrogen oxide, hydrocarbon, particulate, and carbon dioxide emissions were reduced in vehicles fuels by Fischer-Tropsch diesel. The fuel economy, however, was also reduced. The low aromatic content and high concentration of waxlike hydrocarbons in Fischer-Tropsch diesel can lead to the need for special handling and treatment of the fuel to prevent gelling when used in cold-temperature conditions. 

When biodiesel is blended with diesel fuel, the emissions results change somewhat. A significant decrease in hydrocarbon and carbon monoxide emissions is typical, no change or a small increase in oxides of nitrogen emissions, and significant reduction in particulate emissions. Emissions of toxins would also decrease according to the percentage substitution of diesel fuel. 

Under diesel conditions, carbon monoxide and hydrocarbon oxidation is favoured. Under the highly oxidising conditions encountered in the diesel gas stream, reduction of nitric oxide is not expected. A nitric oxide conversion window is observed at temperatures between 493 and 623 with a T50 value of 523 K. However, large NO absorption bands are observed at temperatures above and below the conversion window.28... 

Other pollutants in Diesel exhaust, besides carbon monoxide, are primarily aldehydes (OCHR), sulfur dioxide (SO2), nitrous oxides (NOx, max. 0.1%), and hydrocarbons (C xHy). The smell or stench for which Diesel engines are notorious is caused by trace amounts of certain hydrocarbons and aldehydes which the most modem analytical instruments can barely identify, let alone measure. The sensitivity of the human nose to these compounds is, however, extremely high and out of all proportion to the actual quantities present. Some of the hydrocarbons are considered carcinogenic and thus represent a potential long-term hazard, but they are irrelevant to our study. 

The focus for the reduction of harmful diesel emissions is mainly on particulate matter (PM) and NO,. Both components are harmful to health and environment and are present in relatively large quantities. The other regulated harmful emissions, hydrocarbons and carbon monoxide, can be removed with relatively simple measures, such as flow-through monoliths with an oxidation catalyst. Some of the techniques used for removal of particulate matter and/or NO,... 

Hydrocarbon, carbon monoxide, and particulate matter are all reduced in both direct and indirect inject diesel engines fueled with biodiesel when compared with diesel, whereas nitrogen oxide emissions are increased (30-33). 

Figure 6 Effect of platinum content (g ft ) in diesel oxidation catalysts on tailpipe emissions in the ECE R49 test carbon monoxide (a), hydrocarbon (b), soluble organic fraction (c), sulfur trioxide (d), and particulates (e). The fuel sulfur content was 500 ppm.

As discussed in Chapter 7, polluted air varies in composition from locale to locale and with the time of day and meteorological conditions in a given locale. Polluted urban air contains oxides of sulfur and nitrogen, carbon monoxide, ozone, uncombusted and partially combusted hydrocarbons from gasoline and diesel vehicles, and particulate matter. PM 2.5 particulates, the standard for evaluating pollution related to cardiovascular disease, are composed of combustion products, airborne soil, sulfates, nitrates, and heavy metals as listed in Table 29.4.141-45 ... 

Prior to 1995, around 85 million people (one-third U.S. population) lived in urban areas. The air quality of these areas violated federal public health standards, largely because of automotive pollutants. Gasoline and diesel-fueled cars, trucks, and buses produced half of all air pollution in the United States. This air pollution includes 66% of airborne carbon monoxide, 31%i of smog-forming hydrocarbons, and 43%i of lungdamaging nitrogen oxide. 

Enabling of exhaust aftertreatment systems to be used on gasoline and diesel engines that will significantly reduce emissions of nitrogen oxides, carbon monoxide, hydrocarbons, and particulates. 

Since about 1991, diesel oxidation catalysts have been generally applied to passenger cars in the European Union and to some medium and heavy duty trucks in the USA. Their principle of operation is shown in Fig. 101. The amount of carbon monoxide, hydrocarbons and aldehydes is reduced by oxidation of these components to carbon dioxide and water. The mass of particulate matter emitted is reduced by the oxidation of the liquid hydrocarbons, which are adsorbed on the particulates. These liquid hydrocarbons originate both from the fuel and the lubricating oil, and are commonly denoted as the soluble organic fraction (SOF). The adsorbed polynuclear aromatic hydrocarbons are also removed by oxidation. 

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