This invention is directed to monolithic ceramic catalyst supports and particularly to honeycomb supports which contain a discrete high surface phase incorporated within the ceramic matrix
The conventional ceramic monolithic catalyst consists of a ceramic support with a coating of high surface material upon which the catalyst is actually deposited. In particular, the ceramic support is normally prepared by first sintering a mold of clay or other ceramic material at a high temperature to impart density and strength. This procedure normally results in the ceramic's having a very small surface area, and consequently the ceramic must be coated with another material having a higher surface area, as well as specific chemical characteristics, on which to actually deposit the catalyst. This procedure of depositing a high surface area "wash coat" on the low surface area ceramic wall is disclosed, for example, in U.S. Pat. Nos. 2,742,437 and 3,824,196.
Catalyst supports of this kind suffer from several disadvantages. In service, the supports are exposed to a flow of gases which often contain dusts or particulate matter, which can cause the high surface area coating to flake off the underlying ceramic support. This phenomenon can also occur where the support is exposed to thermal cycling because the wash coat and the underlying ceramic material often have different thermal expansion coefficients. Furthermore, catalysts deposited on the high surface area wash coat are susceptible to poisoning, such as by lead or phosphorous in service in automobile converters, and therefore must be periodically regenerated or replaced. It is therefore an object of the present invention to provide a monolithic support having a high surface area which is not easily abraded and which supports catalysts in a manner that resists poisoning. It is a further object of the invention to provide a monolithic support which has good mechanical properties while retaining the porosity and high surface area necessary for proper catalytic functioning. These and other objects are met by the invention to be described.
USPTO Backgrounds
USPTO Backgrounds