Catalyst structure with catalyst support particles forged into substrate surface and method of manufacture

A catalyst structure is formed by forging catalyst support particles from a slurry into the surface of a metal substrate such that the particles protrude from the surface and are permanently fixed into the surface. The forging is accomplished by engaging rollers with the surface as it passes through the slurry to press the particles into the surface. The rollers may be brush rollers, fabric rollers or solid rollers. The particles may be any particles which are capable of having a catalyst deposited thereon and which are hard enough to forge into the metal substrate. The catalyst material is then deposited onto the catalyst support particles.

BACKGROUND OF THE INVENTION

The present invention relates to a catalyst structure comprising a substrate having protruding catalyst support particles permanently fixed into the surface of the substrate with a catalyst deposited thereon and to the method of manufacture.

Catalyst structures have been disclosed in the prior art which involve the placement of catalyst materials onto the surface of a substrate. At least one of the uses for these prior art catalytic structures is for the conversion of atmospheric ozone to molecular oxygen as well as the conversion of other airborne pollutants such as carbon monoxide and unburned hydrocarbons into harmless compounds such as carbon dioxide and water vapor. One particular use has been for the construction of automotive heat exchangers such as radiators and air conditioning condensers.

U.S. Pat. No. 4,206,083 discloses the co-precipitation of platinum, palladium and manganese oxide on a ceramic support forming a catalyst for the decomposition of ozone in air. The ceramic support is impregnated with a solution containing the precursors of the desired catalyst. The impregnated support is then dried and heated to produce platinum and palladium metal and manganese oxide.

In U.S. Pat. No. 4,343,776, an ozone abatement catalyst is described having a carrier or support of a porous refractory skeletal structure or metal monoliths of aluminum or other materials preferably having a plurality of flow-through channels. A platinum group metal and a non-precious Group VIII metal oxide or aluminate, such as an oxide or aluminate of iron, cobalt and nickel, are applied to the external surface of the carrier or support with the metal oxide or aluminate being applied with an alumina slip preferably prior to the application of the platinum group metal.

U.S. Pat. No. 5,187,137 likewise discloses an ozone decomposing catalyst comprising a manganese oxide together with palladium or palladium oxide formed as a thin film on a support. The support may be formed from various metal oxides or it may be a metal support. The catalyst is applied to the support as a thin film preferably with an alumina sol as a binder.

Another catalyst composition which is described as being adapted for ozone abatement is disclosed in U.S. Pat. No. 5,422,331. This catalytic material comprises a substrate, which may be aluminum, with an undercoat layer containing a mixture of fine particulate refractory metal oxide and a sol such as a silica sol providing good adherence to the substrate. An overlayer also contains a refractory metal oxide on which is dispersed a catalytic metal component, such as palladium and manganese components, which is then calcined.

U.S. Pat. No. 5,997,831 specifically discloses a method of treating the atmosphere to convert pollutants such as ozone, hydrocarbons and carbon monoxide to harmless compounds involving contacting the atmosphere with a heat exchanger which has an outer surface coated in selected areas with a catalytic layer. The catalyst may be manganese oxide and/or precious metals applied by dipping or spraying and the catalytic layer is coated with a porous protective coating such as a polymer.

Another catalyst structure is disclosed in the copending U.S. patent application Ser. No. 09/590,736 filed Jun. 8, 2000 by the inventors of the present application in which catalyst particles are dispersed over and forged into the surface of a metal substrate member with the catalyst particles protruding from and fixed to the substrate.

SUMMARY OF THE INVENTION

The present invention relates to a method of forming a catalytic structure particularly suited to the treatment of the atmosphere to remove atmospheric pollutants. The invention relates specifically to the formation of catalysts for the decomposition of ozone to form molecular oxygen but is also applicable to catalyst materials for a range of other reactions including, for example, the decomposition of hydrocarbons and the oxidation of carbon monoxide. An object of the invention is to provide an improved method of forming a metal substrate having a surface with particles dispersed over and fixed to the surface which protrude from the surface and which comprise a support and a catalytic material.

The invention involves forming a catalytic structure having catalyst support particles dispersed over and forged into the surface of a substrate member whereby the particles are protruding from and permanently fixed to the substrate. The substrate is a metal sheet or body, preferably aluminum or copper. A slurry containing catalyst support particles which are capable of being forged into the surface of the substrate is applied to the surface of the substrate and the particles are pressed against the surface of the substrate to fixedly forge the particles into the surface. The substrate is preferably in web form and the slurry is continuously applied. Pressing the particles against the surface is preferably accomplished with a rotating brush, a fabric or so-called molleton roller or solid rollers such as a solid metal roller or hard rubber roller. The catalyst support particles may comprise any particulate material which is capable of absorbing and supporting the catalyst material and which is capable of being forged into the substrate surface. The catalyst material is then applied to the forged catalyst support particles.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention begins with a substrate member which is formed of a metal capable of having catalyst support particles forged into the surface. In the preferred form, the substrate is a web of the substrate material which is continuously treated in accordance with the invention to be described and which may then be cut into desired catalytic structural shapes. However, the substrate may also be individual sheets or shaped members. The preferred substrate material is aluminum or copper but other metallic substrates can be used.

The particles for use in the present invention comprise any particulate material which is capable of absorbing and supporting a catalyst material and which is capable of being forged into the surface of the substrate. That is, the particulate catalytic support material must be hard enough to be pressed and forged into the substrate surface. The preferred support particles are oxide particles because they are hard enough to forge and they are particularly effective catalyst supports. Examples of particulate support materials include the natural and synthetic zeolites and the following minerals:

In the present invention, the catalyst support particles are forged into the surface of the substrate from a slurry. By this forging action, the particles actually penetrate into the surface whereby they are firmly captured by the forged substrate material but still substantially exposed at the surface. Although an aqueous slurry is preferred, the slurry could be formed from any desired liquid.

The forging of the support particles into the substrate in the present invention takes place by applying the slurry to the substrate and pressing the particles in the slurry against the substrate with a force sufficient to forge the particles partially into the substrate such that the particles protrude from the surface and such that the particles are permanently fixed into the substrate. The preferred method is to continuously treat a web of the substrate material although the invention is equally applicable to the treatment of individual sheets of substrate or to specific objects formed of the substrate material such as fan or propeller blades. As the slurry is applied to the surface of the substrate material, the substrate is engaged by one or usually a series of rotating pressure cylinders or rolls which force the particles into the substrate. However, an excessive number of rolls or an excessive number of passes through the rolls will result in the particles being fully forged into the substrate whereby they no longer protrude from the surface resulting in a reduction of the exposure of the particles and in the ultimate catalytic efficiency. The pressure cylinders or rolls are preferably brush rolls, of the same type as used for the brush graining of plates, or molleton rolls which are fabric rolls such as used for polishing. However, solid rolls can also be used such as metal rolls or hard rubber rolls.

Several factors impact on the selection of the specific operating conditions for the forging process. The hardness and cutting nature of the catalytic support particles being forged and the hardness of the metal or alloy being used as the substrate are significant factors. Each catalytic reaction for which a catalytic support structure is being prepared will have an optimum size and distribution condition for the catalyst that will yield an optimum catalytic efficiency. Thus the selection of variables such as the particle size, concentration of particles in the slurry, roller pressure and the rotation rate of the roller will vary with each specific application.

The next step in the formation of the catalyst structure is the application of the active catalyst material to the catalyst support particles. Merely as examples, active catalyst materials such as platinum, palladium and rhodium or catalytic oxides such as manganese oxide may be deposited on the catalyst support particles or combinations thereof. Any of the conventional catalyst deposition techniques may be employed such as precipitation, adsorption, ion exchange and impregnation. For a description of deposition techniques, reference is made to the book, Principles of Catalyst Development, previously referred to and specifically to pages 108 to 120.

The present invention produces a catalyst structure having a metal substrate with catalyst containing particles dispersed over at least one of the surfaces of the substrate and with these catalyst containing particles being forged into the surface whereby they are fixed in place. This permits the structure to be handled, cut, shaped and fabricated into products such as heat exchanger parts without destroying the catalytic surface such as by spalling of a coating. The particles on the surface also increase the surface area and create turbulence which results in the beneficial mixing of the air or other fluid flowing over the surface to increase the contact between the reactants and the catalyst.