Three-way-conversion

Catalytic Unit. The catalytic unit consists of an activated coating layer spread uniformly on a monolithic substrate. The catalyst predominantly used in the United States and Canada is known as the three-way conversion (TWC) catalyst, because it destroys aU three types of regulated poUutants HC, CO, and NO. Between 1975 and the early 1980s, an oxidation catalyst was used. Its use declined with the development of the TWC catalyst. The TWC catalytic efficiency is shown in Figure 5. At temperatures of >300° C a TWC destroys HC, CO, and NO effectively when the air/fuel mixture is close to... 

J. J. Mooney, C. E. Thompson, and J. C. Dettiing, Three-Way Conversion Catalysts—Tart of the New Emission Control System, SAE 770365, Society of Automotive Engineers, Warrendale, Pa., 1977. 

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. 

Falk, C. B. Mooney, J. J. "Three-Way Conversion Catalysts Effect of Closed-Loop Feed-Back Control and Other Parameters on Catalyst Efficiency" SAE Paper No. 800462, 1980. 

Three-way catalytic converter chemical reactions and surface chemistry, 10 46-50 design of, 10 39-46 surface chemistry and reaction mechanisms, 10 49-50 Three-way control valves, 20 686 Three-way conversion (TWC) catalysts, 10 38, 40... 

The second contribution comes from a major catalyst manufacturer and illustrates how insight in the reaction paths involved in three-way conversion leads to a fundamental, i.e. based on first principles, model. The emphasis in this contribution is on the chemistry rather than on the reactor model, i.e. on the description of the physical phenomena occurring in the monolith reactor. In this sense, this contribution is the bridge from the first to the third contribution. 

Over AU/AI2O3 the reaction between carbon monoxide and nitric oxide is severely inhibited by oxygen, and this unfortunately militates against the promise of its use for three-way conversion at low temperature. Nevertheless the effectiveness of a gold-containing catalyst developed at the Anglo-American Research Laboratories in South Africa has been demonstrated (Figure 11.3).42 It consisted of 1% Au/CoOx in admixture with... 

Three-Way Conversion (TWC) Catalyst. The dual-bed method requires net fuel-rich operation of the engine and therefore lower fuel economy. Interest has heightened recently in a technique to control all three pollutants—carbon monoxide, hydrocarbon, and nitrogen oxides— by maintaining the air/fuel (A/F) at near-stoichiometric ratios and by converting all pollutants over a single catalyst. A sensor is used to control the partial pressure of oxygen in the exhaust stream by feedback to a carburetion or fuel injection system (13). The increased cost of the sensor-carburetor system will be compensated for by better fuel economy,... 

Three-Way Conversion (TWC) Catalyst. TWC-1 was evaluated on the same test unit with the catalyst inlet temperature raised to 650°C. The conversion of all three pollutants over a virgin catalyst is shown in Figure 11. The conversions of carbon monoxide and hydrocarbon at nominal A/F ratios much less than stoichiometric must be attributable mostly to steam reforming since the oxygen available was not sufficient to account for the observed conversion levels. This activity was lost... 

Engine and vehicle evaluation results indicate that SMART Pd technology achieves performances equivalent in three-way conversion, and superior in ammonia and hydrogen sulfide formation, to those of Pt/Rh catalysts. FTP testing on a 1993 vehicle suggests that LEV NMOG and ULEV CO and NOx are possibilities with SMART Pd technology. 

COLD START HYDROCARBON EMISSIONS CONTROL VIA ADMIXING THREE WAY CONVERSION CATALYSTS WITH HEAT EXCHANGE AND HYDROCARBON ADSORPTION... 

P. Oser, Catalyst Systems with andEmphasis on Three-Way Conversion and Novel Concepts, SAE 790306, Society of Automotive Engineets, Warrendale, Pa., 1979. 

In a bold defense of the Families of Love in 1580, called an Apology for the Service of Love, the Family describes how death is life. They assert that sin is repairable in life. The Apology is set as a three-way conversation in which the Exile, a Familist, seeks to convince two curious individuals that the Family of Love was neither heretical nor ... 

This chapter will begin with the three-way-conversion (TWC) catalyst, which simultaneously converts CO, hydrocarbons and nitrogen oxides. TWC catalysts are currently used on all gasoline-powered passenger cars made in the US, as well as in many other world markets. The three milestones cited will be ceria, ceria-zirconia and close-coupled palladium. The first two of these bear on the central theme of gas-composition control, without which three-way conversion cannot be realized. The third milestone allowed the catalyst to become active at a much earlier point in the test cycle, leading to a major reduction in the amount of hydrocarbon emissions. 

The two major advances cited thus far have involved problems that were solved by the introduction of new materials. First, the fast oxidation-reduction properties of ceria (combined with sophisticated electronic A/F control) made three-way conversion a viable concept. Second, the replacement of ceria with ceria-zirconia vastly improved the ability of the oxygen storage function to survive exposure to high temperature. 

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