Applications catalytic converters

F. W. Kaiser and co-workers, Optim tion of an Electrically-Heated Catalytic Converter System—Calculations and Application, SAE 930384, Society of Automotive Engineers, Warrendale, Pa., 1993. 

In summaiy, diesel fuel with veiy low to no sulfur content is now possible with chemical and technological advances. Along with catalytic converters, electronic fuel systems, and sensors, the diesel engine for the new millennium will he capable of complying with ever more stringent EPA exliaust emissions. The diesel engine will continue to sei"ve as the main global workliorse for all of the many thousands of different applications of its power cycle. 

Microporous catalysts are heterogeneous catalysts used in catalytic converters and for many other specialized applications, because of their very large surface areas and reaction specificity. Zeolites, for example, are microporous aluminosilicates (see Section 14.19) with three-dimensional structures riddled with hexagonal channels connected by tunnels (Fig. 13.38). The enclosed nature of the active sites in zeolites gives them a special advantage over other heterogeneous catalysts, because an intermediate can be held in place inside the channels until the products form. Moreover, the channels allow products to grow only to a particular size. 

There is a general trend toward structured packings and monoliths, particularly in demanding applications such as automotive catalytic converters. In principle, the steady-state performance of such reactors can be modeled using Equations (9.1) and (9.3). However, the parameter estimates in Figures 9.1 and 9.2 and Equations (9.6)-(9.7) were developed for random packings, and even the boundary condition of Equation (9.4) may be inappropriate for monoliths or structured packings. Also, at least for automotive catalytic converters. 

Emission control from heavy duty diesel engines in vehicles and stationary sources involves the use of ammonium to selectively reduce N O, from the exhaust gas. This NO removal system is called selective catalytic reduction by ammonium (NH3-SGR) and it is additionally used for the catalytic oxidation of GO and HGs.The ammonia primarily reacts in the SGR catalytic converter with NO2 to form nitrogen and water. Excess ammonia is converted to nitrogen and water on reaction with residual oxygen. As ammonia is a toxic substance, the actual reducing agent used in motor vehicle applications is urea. Urea is manufactured commercially and is both ground water compatible and chemically stable under ambient conditions [46]. 

In this paper, we first briefly describe both the single-channel 1-D model and the more comprehensive 3-D model, with particular emphasis on the comparison of the features included and their capabilities/limitations. We then discuss some examples of model applications to illustrate how the monolith models can be used to provide guidance in emission control system design and implementation. This will be followed by brief discussion of future research needs and directions in catalytic converter modeling, including the development of elementary reaction step-based kinetic models. 

The necessity of having a post catalyst layer which can eliminate slipping ammonia (in addition, since CO and HC also must be eliminated, current catalytic SCR-urea systems applied to diesel engine emissions are composed typically of five catalytic layers, making the size of the catalytic converter quite large and therefore applicable essentially only to heavy-duty trucks and buses). 

Schar, C.M., Onder, C.H. and Geering, H.P. (2006) Control of an SCR Catalytic Converter System for a Mobile Heavy-Duty Application, IEEE Trans. Contr. Sys. Technol., 14, 641. 

This asymmetric catalytic reaction has found wide application in converting functionalized ketones to the corresponding secondary alcohols with high ee. A general illustration is given in Scheme 6-32. Five- to seven-membered chelate complexes, formed by the interaction of the Ru atom with carbonyl oxygen and a heteroatom X, Y, or Z may be the key intermediates that cause the high enantioselectivity in the reaction.67... 

Innovation drivers An important impulse was the classification of ceramic fibres as carcinogenic category K2 (Directive 97/69/EC), which has been applicable since January 1998. Since July 2001 there has been a ban on the marketing of ceramic fibres for the general public . An impending ban also for the industrial sector caused alarm in the automotive industry. A scientific study by Wuppertal University" also directed attention on the subject of ceramic fibres in catalytic converter recycling . 

Platinum is a relatively rare earth metal usually found with related metals osmium and iridium. While it has a number of industrial applications, its common consumer application is in catalytic converters. This application has actually increased platinum concentrations in roadside dust. The ability of platinum and its derivatives to kill cells or inhibit cell division was discovered in 1965. Platinum-based drugs, such as cisplatin, are used to treat ovarian and testicular cancer, and cancers of the head and neck, as well as others. Unfortunately, the toxic side effects of these agents often limit their usefulness. 

Platinum also is used extensively as a catalyst in hydrogenation, dehydrogenation, oxidation, isomerization, carbonylation, and hydrocracking. Also, it is used in organic synthesis and petroleum refining. Like palladium, platinum also exhibits remarkable abdity to absorb hydrogen. An important application of platinum is in the catalytic oxidation of ammonia in Ostwald s process in the manufacture of nitric acid. Platinum is installed in the catalytic converters in automobile engines for pollution control. 

While SuperLig technology is stiU being developed for use in radionnchde applications, it is commercially available for applications involving the removal of rhodinm from antomobile catalytic converters, the recovery of bismnth and antimony from copper-refinery streams, and for the extraction of other metals from water. 

RCF is sold in a variety of forms, such as loose fiber, blanket, boards, modules, doth, cements, putties, paper, coatings, felt, vacuum-formed shapes, rope, braid, tape, and textiles. The products are principally used for industrial applications as insulation in furnaces, heaters, kiln linings, furnace doors, metal launders, tank car insulation, and other uses up to 1400°C. RCF-consuming industries indude ferrous and nonferrous metals, petrochemical, ceramic, glass, chemical, fertilizer, transportation, construction, and power generation/incineration. Some newer uses include commercial fire protection and applications in aerospace, eg, heat shields and automotive, eg, catalytic converters, metal reinforcement, heat shields, brake pads, and airbags. 

In fact, most of us benefit from the use of catalysis. Automotive catalytic converters have represented the most massive application of environmental catalysis and one of the most challenging and successful cases in catalysis, generally. Automobile catalysts deseive a few more comments. The engine exhaust emission is a complex mixture, whose composition and flow rate change continuously depending on a variety of factors such as driving conditions, acceleration, and speed. Despite the variability of the conditions, three-way catalysts have achieved the reduction of exhaust carbon monoxide, hydrocarbons, and... 

The need for controlling the exhaust emissions from automotive vehicles has been recognized since 1975. The most effective and tested method proved to be the installation of diree-way catalysts at the exhaust emission system of cars. The development and the improvement M of such catalysts was and will be a complicated effort, since a cat-alyst placed in a vehicle should simultaneously accelerate oxida-tion and reduction reactions, under continuously changing conditions of temperature and space velocity, in contrast to industrial applications where catalysts operate under fixed and MjM controlled conditions. Generally, the catalytic converter of a vehicle has to satisfy the following requirements ... 

Monolithic catalysts have found a wide range of applications in the removal of pollutants from air, especially in the automotive industry. Specifically, the demand for large surface to small volume, high conversions achieved for low retention times, and low pressure drop led to the development of monolithic supports. More information on automotive catalytic converters has been given in Chapter 1. Usually, a thin layer of alumina is deposited onto a monolith for keeping the precious metal used for air pollutants abatement dispersed. The oxidations that take place are highly exothermic and the reaction rates achieved are in turn high. Hence, the reactants diffuse only a small distance... 

An important requirement of kinetic studies for automotive aftertreatment devices is the capability of performing dynamic reactive experiments. Steady-state tests provide useful information for identification of reaction pathway and stoichiometry, but cannot capture the real operating behavior of catalytic converters for vehicles, which is transient in nature. Indeed, this is so not only because of the continuously changing conditions (temperature, composition, flow rate) of the engine exhausts as extensively addressed in the following sections, the principles of NSRC and SCR applications largely rely on the storage/reaction/release dynamics of NOx and of NH3, respectively. 

Another important application of heterogeneous catalysts is in automobile catalytic converters. Despite much work on engine design and fuel composition, automotive exhaust emissions contain air pollutants such as unburned hydrocarbons (CxHy), carbon monoxide, and nitric oxide. Carbon monoxide results from incomplete combustion of hydrocarbon fuels, and nitric oxide is produced when atmospheric nitrogen and oxygen combine at the high temperatures present in an... 

ICP-MS is useful for analysis of catalysts from two perspectives The composition of the catalysts must be carefully controlled, particularly because the active elements are often expensive. The catalysts are often finely distributed in a substrate material so their concentration in the bulk material may be quite low. Second, catalysts, particularly those used in automotive catalytic converters, can be a significant source of platinum group elements in the environment. Re and Pt have been measured in catalysts by ICP-MS [193], Procedures for the analysis of used catalytic converter materials by ICP-MS have been reported [355]. Accurate measurements are essential for many of these applications so isotope dilution-based concentration calibration is commonly used. 

Aluminas are used in various catalytic applications, a-, y-, and -aluminas are all used as support materials, the first one in applications where low surface areas are desired, as in partial oxidation reactions. The latter two, and especially y-alumina, in applications where high surface areas and high thermal and mechanical stability are required. One of the most prominent applications of y-alumina as support is the catalytic converter for pollution control, where an alumina washcoat covers a monolithic support. The washcoat is impregnated with the catalytically active noble metals. Another major application area of high-surface aluminas as support is in the petrochemical industry in hydrotreating plants. Alumina-supported catalysts with Co, Ni, and/or Mo are used for this purpose. Also, all noble metals are available as supported catalysts based on aluminas. Such catalysts are used for hydrogenation reactions or sometimes oxidation reactions. If high... 

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