Automotive exhaust catalysts

ALUMDJUMCOMPOUNDS - ALUMINIUMOXIDE(ALUMINA) - ACTIVATED] (Vol 2) -in automotive exhaust catalyst [EXHAUST CONTROL, AUTOMOTIVE] (Vol 9)... 

Automotive Emission Control Catalysts. Air pollution (qv) problems caused by automotive exhaust emissions have been met in part by automotive emission control catalysts (autocatalysts) containing PGMs. In the United States, all new cars have been requited to have autocatalyst systems since 1975. In 1995, systems were available for control of emissions from both petrol and diesel vehicles (see Exhaust control, automotive). 

Cordierite [12182-53-5] Mg Al Si O g, is a ceramic made from talc (25%), kaolin (65%), and Al O (10%). It has the lowest thermal expansion coefficient of any commercial ceramic and thus tremendous thermal shock resistance. It has traditionally been used for kiln furniture and mote recently for automotive exhaust catalyst substrates. In the latter, the cordierite taw materials ate mixed as a wet paste, extmded into the honeycomb shape, then dried and fired. The finished part is coated with transition-metal catalysts in a separate process. 

G. B. Fisher and co-workers. The Kole of Ceria in Automotive Exhaust Catalysis and OBD-II Catalyst Monitoring, SAE 931034, Society of Automotive Engineers, Warrendale, Pa., 1993. 

Nonselective catalytic reduction systems are often referred to as three-way conversions. These systems reduce NO, unbumed hydrocarbon, and CO simultaneously. In the presence of the catalyst, the NO are reduced by the CO resulting in N2 and CO2 (37). A mixture of platinum and rhodium has been generally used to promote this reaction (37). It has also been reported that a catalyst using palladium has been used in this appHcation (1). The catalyst operation temperature limits are 350 to 800°C, and 425 to 650°C are the most desirable. Temperatures above 800°C result in catalyst sintering (37). Automotive exhaust control systems are generally NSCR systems, often shortened to NCR. 

Serious research in catalytic reduction of automotive exhaust was begun in 1949 by Eugene Houdry, who developed mufflers for fork lift trucks used in confined spaces such as mines and warehouses (18). One of the supports used was the monolith—porcelain rods covered with films of alumina, on which platinum was deposited. California enacted laws in 1959 and 1960 on air quality and motor vehicle emission standards, which would be operative when at least two devices were developed that could meet the requirements. This gave the impetus for a greater effort in automotive catalysis research (19). Catalyst developments and fleet tests involved the partnership of catalyst manufacturers and muffler manufacturers. Three of these teams were certified by the California Motor Vehicle Pollution Control Board in 1964-65 American Cyanamid and Walker, W. R. Grace and Norris-Thermador, and Universal Oil Products and Arvin. At the same time, Detroit announced that engine modifications by lean carburation and secondary air injection enabled them to meet the California standard without the use of catalysts. This then delayed the use of catalysts in automobiles. 

Evaluation of Catalysts As Automotive Exhaust Treatment Devices," Report of the Catalyst Panel to the Committee on Motor Vehicle Emissions, National Academy of Sciences, Washington, D.C., 1973. 

The effect of alkali addition on the adsorption of NO on metal surfaces is of great importance due to the need of development of efficient catalysts for NO reduction in stationary and automotive exhaust systems. Similar to CO, NO always behaves as an electron acceptor in presence of alkalis. 

I.V. Yentekakis, C.A. Pliangos, V.G. Papadakis, X.E. Verykios, and C.G. Vayenas, Support and NEMCA-induced Promotional Effects on the Activity of Automotive Exhaust Catalysts in A. Frennet and Journal-M. Bastin (eds.) Catalysis and Automotive Pollution Control HI, Stud. Surf. Sci. Catal. 96, 375-385 (1995). 

C. Pliangos, I.V. Yentekakis, V.G. Papadakis, C.G. Vayenas, and X.E. Verykios, Support-induced promotional effects on the activity of automotive exhaust catalysts 1. The case of oxidation of light hydrocarbons, Appl. Catal. B 14, 161-173 (1997). 

Ask the average person in the street what a catalyst is, and he or she will probably tell you that a catalyst is what one has under the car to clean up the exhaust. Indeed, the automotive exhaust converter represents a very successful application of catalysis it does a great job in removing most of the pollutants from the exhaust leaving the engines of cars. However, catalysis has a much wider scope of application than abating pollution. 

CO oxidation, an important step in automotive exhaust catalysis, is relatively simple and has been the subject of numerous fundamental studies. The reaction is catalyzed by noble metals such as platinum, palladium, rhodium, iridium, and even by gold, provided the gold particles are very small. We will assume that the oxidation on such catalysts proceeds through a mechanism in which adsorbed CO, O and CO2 are equilibrated with the gas phase, i.e. that we can use the quasi-equilibrium approximation. 

In many cases supports are shaped into simple cylinders (1-5 mm in diameter and 10-20 mm in length) in an extrusion process. The support powder is mixed with binders and water to form a paste that is forced through small holes of the desired size and shape. The paste should be sufficiently stiff such that the ribbon of extmded material maintains its shape during drying and shrinking. When dried, the material is cut or broken into pieces of the desired length. Extrusion is also applied to make ceramic monoliths such as those used in automotive exhaust catalysts and in DeNOx reactors. 

Nowadays, based on the amount of processed material, hydrotreating is the largest process in heterogeneous catalysis. On the basis of catalysts sold per year, hydro-treating ranks third after automotive exhaust and fluid catalytic cracking [R. Prins, V.H.J. de Beer and G.A. Somorjai, Catal. Rev.-Sci. Eng. 31 (1989) 1]. 

Sulfur in cmde oil is mainly present in organic compounds such as mercaptans (R-SH), sulfides (R-S-R ) and disulfides (R-S-S-R ), which are all relatively easy to desulfurize, and thiophene and its derivatives (Fig. 9.2). The latter require more severe conditions for desulfurization, particularly the substituted dibenzothiophenes, such as that shown in Fig. 9.2. Sulfur cannot be tolerated because it produces sulfuric add upon combustion, and it also poisons reforming catalysts in the refinery and automotive exhaust converters (particularly those for diesel-fueled cars). Moreover, sulfur compounds in fuels cause corrosion and have an unpleasant smell. 

Figure 10.5. Monolith, washcoat and noble metal particles in an automotive exhaust catalyst.

One of the most straightforward methods to reduce carbon dioxide emissions is to enhance the fuel efficiency of engines. The three-way catalyst, although very successful at cleaning up automotive exhaust, dictates that engines operate at air-to-fuel ratios of around 14.7 1. Unfortunately, this is not the optimum ratio with respect to fuel efficiency, which is substantially higher under lean-burn conditions at A/F ratios of about 20 1, where the exhaust becomes rich in oxygen and NOx reduction is extremely difficult (Fig. 10.1). 

As with the automotive exhaust converter, the SCR catalyst is designed to handle large flows of gas (e.g. 300 N s for a 300 MW power plant) without causing a significant pressure drop. Figure 10.12 shows a reactor arrangement with about 250 m of catalyst in monolithic form, sufficient for a 300 MW power plant. 

Why is the automotive exhaust catalyst called a three-way catalyst ... 

Why does an automotive exhaust catalyst have a control system to regulate the composition of the air-fuel mixture How is this control performed ... 

Rokosz, M.J., Chen, A.E., Lowe-Ma, C.K. et al. (2001) Characterization of phosphorus-poisoned automotive exhaust catalysts, Appl. Catal. B Environ., 33, 205. 

Matsumoto, S. (2000) Catalytic Reduction of Nitrogen Oxides in Automotive Exhaust Containing Excess Oxygen by NOx Storage-Reduction Catalyst, Cat. Tech., 4, 102. 

Potentialities of silver-based catalysts in automotive exhaust systems... 

Cerium oxides are outstanding oxide materials for catalytic purposes, and they are used in many catalytic applications, for example, for the oxidation of CO, the removal of SOx from fluid catalytic cracking flue gases, the water gas shift reaction, or in the oxidative coupling reaction of methane [155, 156]. Ceria is also widely used as an active component in the three-way catalyst for automotive exhaust pollution control,... 

New reactor technologies are currently under development, and these include meso- and micro-structured reactors or the use of membranes. Among meso-structured reactors, monolithic catalysts play a pre-eminent role in environmental applications, initially in the cleaning of automotive exhaust gases. Beside this gas-solid application, other meso-structures such as membranes [57, 58], corrugated plate or other arranged catalysts and, of course, monoliths can be used as multiphase reactors [59, 60]. These reactors also offer a real potential for process intensification, which has already been demonstrated in commercial applications such as the production of hydrogen peroxide. 

The structure of supported rhodium catalysts has been the subject of intensive research during the last decade. Rhodium is the component of the automotive exhaust catalyst (the three-way catalyst) responsible for the reduction of NO by CO [1], In addition, it exhibits a number of fundamentally interesting phenomena, such as strong metal-support interaction after high temperature treatment in hydrogen [21, and particle disintegration under carbon monoxide [3]. In this section we illustrate how techniques such as XPS, STMS, EXAFS, TEM and infrared spectroscopy have led to a fairly detailed understanding of supported rhodium catalysts. 

Automotive exhaust catalysts, activated alumina applications, 2 399 Automotive fuels, toluene in, 25 179-180 Automotive gear oils, 15 236-237 Automotive industry... 

Cordarone, molecular formula and structure, 5 95t Cordierite, automotive exhaust catalyst support, 2 399... 

Ciambelli, P Corbo, P Migliardini, F. Potentialities and limitations of lean de-NOx catalysts in reducing automotive exhaust emissions, Catal. Today, 2000, Volume 59, Issues 3-4. 279-286... 

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