Zeolite-containing oxidation catalyst and method of use

Abstract

Oxidation catalyst compositions for treating diesel exhaust include ceria and, optionally, alumina, each having a surface area of at least about 10 m2 / g, and a zeolite, e.g., Beta zeolite. Optionally, platinum may be included in the catalytic material, preferably in amounts which are sufficient to promote some gas-phase oxidation of carbon monoxide (“CO”) and hydrocarbons (“HC”) but which are limited to preclude excessive oxidation of SO2 to SO3. Alternatively, palladium in any desired amount may be included in the catalytic material. The zeolite is optionally doped, e.g., ion-exchanged, with one or more of hydrogen, a platinum group metal or other catalytic metals. The catalyst compositions may be used in a method to treat diesel engine exhaust by contacting the hot exhaust with the catalyst composition to promote the oxidation of gas-phase CO and HC and of the volatile organic fraction component of particulates in the exhaust.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is a continuation-in-part of application Ser. No. 07 / 973,461, filed Nov. 19, 1992.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] This invention relates to a catalyst composition and method for the oxidation of oxidizeable components of diesel engine exhaust, and more specifically to the treatment of such diesel exhaust to reduce the content of particulates and other pollutants discharged to the atmosphere. [0004] 2. Background and Related Art [0005] As is well-known, diesel engine exhaust is a heterogeneous material which contains not only gaseous pollutants such as carbon monoxide (“CO”) and unburned hydrocarbons (“HC”), but also soot particles which comprise both a dry, solid carbonaceous fraction and a soluble organic fraction. The soluble organic fraction is sometimes referred to as a volatile organic fraction (“VOF”), which terminology will be used herein. The VOF may exist in diesel exhaust eit...

AI Technical Summary

Benefits of technology

[0009] Generally, in accordance with the present invention, there is provided a catalyst composition and a method for oxidizing oxidizeable components of diesel engine exhaust in which at least some of a volatile organic fraction of the diesel exhaust is converted to innocuous materials, and in which gaseous HC and CO pollutants may also be similarly converted. The objectives of the invention are attained by an oxidation catalyst comprising a catalytic material comprising a mixture of high surface area ceria, a zeolite and, optionally, a high surface area alumina. The catalytic material optionally may carry a low loading of platinum catalytic metal dispersed thereon or palladium catalytic metal dispersed thereon. Alternatively, or in addition, the zeolite of the catalyst composition may be doped, e.g., ion-exchanged, with a catalytic moiety such as one or more of hydrogen ion, platinum, copper, nickel, cobalt, iron, etc. The method of the invention is attained by flowing a diesel engine exhaust, e.g., the exhaust of a diesel-powered automobile or light truck, into contact under oxidation reaction conditions with a catalyst composition as described above.

Problems solved by technology

One problem faced in the treatment of diesel engine exhaust is presented by the presence of sulfur in diesel fuel.

As is well-known in the art, catalysts used to treat the exhaust of internal combustion engines are less effective during periods of relatively low temperature operation, such as the initial cold-start period of engine operation, because the engine exhaust is not at a temperature sufficiently high for efficient catalytic conversion of noxious components in the exhaust.

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