WO2001000323A1

WO2001000323A1 - Process for coating metal fibrous material

Info

Publication number: WO2001000323A1
Application number: PCT/US2000/016548
Authority: WO
Inventors: Nelleke Van Der Puil; Joakim Carlberg; Rudolf A. Overbeek; Yun-Feng Chang; Lawrence L. Murrell
Original assignee: Abb Lummus Global, Inc.
Priority date: 1999-06-29
Filing date: 2000-06-15
Publication date: 2001-01-04
Also published as: AU5616900A

Abstract

A product comprised of a three dimensional network comprised of metal fibrous material is coated with a particulate coating by use of a coating bath including dispersed particles, wherein the bath has a viscosity of less than 175 centistokes and a surface tension of no greater than 300 dynes/cm. In one embodiment, the particles are a catalyst or a catalyst precursor or a catalyst support to thereby provide a catalyst structure in which catalyst may be supported as a coating in the interior and on the exterior of a three-dimensional network of material having a high void volume.

Description

PROCESS FOR COATING METAL FIBROUS MATERIAL

This application claims pπoπty based on and is a contmuation-in-part of provisional application Seπal No 60/141.554, filed June 29, 1999

The invention relates to coated products and the production thereof In a particular aspect, the present invention relates to the production of a coated three- dimensional network of mateπal in which mteπor and exteπor portions of the mateπal are coated The mvention further relates to the production of a coated catalyst structure wherein the structure is formed from a plurality of layers of fibers (in particular metal fibers) that are coated with a particulate coating that includes a catalyst

United States Application Seπal No 09/156,023 filed on September 17, 1998, discloses a process for coating a three-dimensional network of mateπal by use of an electrophoretic coating procedure

Applicant has found that it is possible to coat such three-dimensional mateπals effectively without the use of an electric current by controlling the coating bath conditions

In accordance with one aspect of the present invention, there is provided a process for depositing particles, as a coating, on a porous product or support compπsed of a three dimensional network of matenal compπsing metal fibers, with the particles being applied to such a product or support by contacting the product with a liquid coating composition (preferably in the form of a coating bath) that includes finely divided particles dispersed in a liquid under conditions such that the coating composition enters or wicks into the inteπor of the three-dimensional network of material and forms a porous coating on both interior and exterior portions of the material.

In a preferred embodiment, the liquid coating composition has a kinematic viscosity of no greater than 175 centistokes and a surface tension of no greater than 300 dynes/cm.

More particularly, the porous three-dimensional network of material is a meshlike material comprised of a plurality of layers of fiber or wires and, therefore, differ from a woven wire or mesh. In a preferred embodiment, the fibers or wires in the various layers are randomly oriented.

One or more metals may be used in producing a metal mesh. Alternatively, the mesh fibers may be formed from or include materials other than metals alone or materials other than metals in combination with metals (e *., metals in combination with ceramics or carbon).

In a preferred embodiment wherein the mesh-like structure is comprised of a plurality of layers of fibers to form the three-dimensional network of materials, the thickness of such support is at least five microns, and generally does not exceed ten millimeters. In accordance with a preferred embodiment, the thickness of the network is at least 50 microns and more preferably at least 100 microns and generally does not exceed 2 millimeters.

In general, the thickness or diameter of the fibers which form the plurality of layers of fibers is less than about 500 microns, preferably less than about 150 microns and more preferably less than about 30 microns. In a preferred embodiment, the thickness or diameter of the fibers is from about 8 to about 25 microns.

The three-dimensional mesh-like structure may be produced as described in U.S. Patent Number 5,304,330; 5,080,962; 5,102,745; or 5,096,663. It is to be understood, however, that such mesh-like structure may be formed by procedures other than as described in the aforementioned patents.

The mesh-like structure that is employed in the present invention (without supported catalyst on the mesh) has a void volume which is at least 45%, and is preferably at least 55% and is more preferably at least 65% and still more preferably is at least about 85% (for example, at least 90%). In general, the void volume does not exceed about 98%. The term "void volume" as used herein is determined by dividing the volume of the structure which is open by the total volume of the structure (openings and mesh material) and multiplying by 100. In general, the average void opening is at least 10 microns and preferably at least 20 microns.

The particles that are to be coated onto and into the mesh-like structure include particles that have an average particle size of at least 0.5 micron, for example, at least 1.0 micron. In general, the average particle size does not exceed 20 microns. Alternatively, the coating bath may exclusively contain particles of a size smaller than 0.5 μm.

The coating bath may preferably also include particles of a smaller particle size (average particle size of less than 150 nm). which are to be coated onto and into the mesh-like structure in conjunction with the larger particles (particles having an average particle size of at least 0.5 micron).

A coating of larger particles (particles of an average particle size of greater than 0.5 micron) may be applied more effectively if the coating bath employed in such coating process includes particles having an average particle size of less than 150 nanometers in addition to the larger particles.

Although applicant does not intend to be bound by any theoretical reasoning, it is believed that the smaller particles function to bind more effectively the larger particles to each other and/or to the support or product that is being coated. In effect, the smaller particles function as a "glue" to improve the adherence of the larger particles to each other and/or to the coated product or support. At the same time, the smaller particles can change the physical characteristics of the coating bath, in particular the viscosity and surface tension.

In a particularly preferred embodiment, the larger particles that are to be coated onto the product or support are either a catalyst support, catalyst precursor, a catalyst, or a catalyst or catalyst precursor on a paniculate support.

The smaller particles may be the same material as the larger particles or may be a different material.

In many cases, it is desirable to produce a catalyst system in which a catalyst in particle form (the particle form of the catalyst coated on the mesh-like structure may be a particulate catalyst support coated or impregnated with a catalyst) is present as a coating in which the particulate catalyst, when supported on the mesh-like structure, has an average particle size greater than 0.5 micron. In such cases, in a process for coating particles of a catalyst or catalyst precursor or catalyst support (with or without a catalyst or catalyst precursor) onto a mesh-like structure which catalyst, catalyst precursor or support has an average particle size greater than 0.5 micron, it is desirable that the coating bath that contains such larger particles also includes smaller particles (in the form of a sol or colloid) in an amount that provides for a coating of the larger particles onto the mesh-like structure such that the coating of the larger particles effectively adheres to the structure. The smaller particles may be comprised of the same material as the larger particles or may be a different material or materials or may include the material of the larger particle plus a different material. As hereinabove indicated, it is believed that the smaller particles function as a "glue" that improves adherence of the larger particles to each other and/or the non-particulate support. It is also within the spirit and scope of the invention to use only smaller particles in the coating composition, e.g., an average particle size of less than 150 nanometers.

As hereinabove indicated the average particle size of the smaller particles is generally less than 150 nanometers. In general, the average particle size is at least 2 nanometers. For example, in one embodiment, the average particle size is from 20-40 nanometers.

The larger particles that are to be coated onto the non-particulate support generally have an average particle size of at least 0.5 micron for example, at least 1.0 micron. In general, the average particle size does not exceed 20 microns.

In the coating bath, the relative amounts of the larger and smaller particles are selected to achieve in the final coating the desired amount of larger particles and an amount of smaller particles that provides for effective adherence of the coating containing the larger particles to the mesh-like structure. In general, based on the total amount of the larger and smaller particles, the amount of smaller particles used in the coating bath is from .01 % to 40% by weight.

In a preferred embodiment, the three-dimensional mesh-like material is oxidized before coating; e.g., heating in air at a temperature of from 300°C up to 700°C.

In some cases, if the mesh-like material is contaminated with organic material, the mesh-like material is cleaned prior to oxidation; for example, by washing with an organic solvent such as acetone.

The coating bath is preferably an aqueous coating bath in which the particles are dispersed. As hereinabove indicated, the kinematic viscosity of the coating bath is preferably less than 175 centistokes and the surface tension thereof is less than 300 dynes/cm.

In a preferred embodiment of the invention, the mesh-like structure that is coated includes metal wires or fibers and the metal wires or fibers that are coated are selected or treated in a manner such that the surface tension thereof is higher than 50 dynes/cm, as determined by the method described in "Advances in Chemistry, 43, Contact Angle. Wettability and Adhesion, American Chemical Society, 1964."

In coating a mesh-like structure that includes metal fibers, the liquid coating composition preferably has a surface tension from about 50 to 300 dynes/cm. and more preferably from about 50 to 150 dynes/cm, as measured by the capillary tube method, as described in T.C. Patton. "Paint Flow and Pigment Dispersion", 2^nd Ed., Wiley- Interscience, 1979, p. 223. At the same time, the liquid coating composition has a kinematic viscosity of no greater than 175 centistokes, as measured by a capillary viscometer and described in P.C. Hiemenz. "Principles of colloid and Surface Chemistry", 2^nd Ed., Marcel Dekker Inc., 1986, p. 182.

In such an embodiment, the surface tension of the metal being coated is coordinated with the viscosity and surface tension of the liquid coating composition such that the liquid coating composition is drawn into the interior of the structure to produce a particulate coating on the mesh-like structure. The metal to be coated preferably has a surface tension which is greater than 50 dynes/cm and preferably is higher than the surface tension of the liquid coating composition to obtain spontaneous wetting and penetration of the liquid into the interior of the mesh.

In the case where the metal of the structure that is to be coated does not have the desired surface tension, the structure may be heat-treated to produce the desired surface tension.

The liquid coating composition can be prepared without any binders or adhesives for causing adherence of the particulate coating to the structure.

The surface of the structure to be coated may also be chemically or physically modified to increase the attraction between the surface and the particles that form the coating; ^, heat treatment or chemical modification of the surface.

The solids content of the coating bath is generally at least 5%. preferably at least 10%) and more preferably at least 20%, all by weight. In general, the solids content does not exceed 60%, preferably does not exceed 50% and more preferably does not exceed 40%. all by weight.

The bath may also contain additions such as surfactants, dispersants etc. In general, the weight ratio of additives to particles in the coating bath is from 0.0001 to 0.4 and more preferably from 0.001 to 0.1.

The mesh-like material is preferably coated by dipping the mesh-like material into a coating bath one or more times while drying or calcining in between dippings. The bath may also contain organic solvents and may even be non-aqueous. The temperature of the bath is preferably at room temperature, but has to be sufficiently below the boiling point of the liquid in the bath.

After coating, the mesh-like material that includes a porous coating comprised of a plurality of particles is dried, preferably with the material in a vertical position. The drying is preferably accomplished by contact with a flowing gas (such as air) at a temperature of from 20° to 150°C more preferably from 100°C to 150°C. After drying, the coated mesh-like material is preferably calcined, for example, at a temperature of from 250°C to 800°C, preferably 300°C to 500°C. In a preferred embodiment, the temperature and air flow are coordinated in order to produce a drying rate that does not adversely affect the catalyst coating, e *., cracking, blocking of pores, etc. In many cases, a slower rate of drying is preferred.

The thickness of the formed coating may vary. In general, the thickness is at least 1 micron and in general no greater than 100 microns.

The particles that are to be coated onto the support may be comprised of a single material or multiple materials (two, three or more different materials).

The interior portion of the product that is coated in accordance with the invention has a porosity which is sufficient to allow the particles which comprise the coating to penetrate or migrate into the three dimensional network. Thus, the pore size of the three dimensional material and the particle size of the particles comprising the coating, in effect, determine the amount and uniformity of the coating that can be deposited in the interior of the network of material and/or the coating thickness in the network. The larger the pore sizes the greater the thickness of the coating which can be uniformly coated in accordance with the invention.

The product or support which is coated may have different pore sizes over the thickness thereof, and within the scope of the invention, it is contemplated that the three dimensional product which is coated will have a uniform porosity throughout or that its porosity will vary and that such product may be a laminated and/or comprised of the same or different materials and/or may have multi-layers.

The particulate material which is used as the coating may be comprised of a single material or a mixture of materials and when a mixture is used, the particles may be a composite comprised of smaller particles (a sol) which adheres to larger particles.

In a preferred embodiment, the particles which are applied to the three dimensional network of porous material may be catalyst particles or a catalyst support and/or a catalyst support containing active catalyst or precursor and/or a catalyst precursor. In such an embodiment, the particles preferably form a uniform coating over a defined thickness of the interior of the three dimensional network of material, with such three-dimensional network of material being porous (having a void volume), and with the coating of particles on such material also being porous. In this manner, it is possible to provide an overall catalyst structure in which there is a high void volume and wherein catalyst is uniformly distributed through a defined thickness of the interior of the three dimensional network.

In the case where the particles are in the form of a catalyst precursor, the product, after the deposit of the particles, is treated to convert the catalyst precursor to an active catalyst. In the case where the particles which are deposited in the three dimensional network of material is a catalyst support, active catalyst or catalyst precursor may then be applied to such support, e *., by spraying, dipping, or impregnation.

Catalytically active material or precursors can be many-fold. For example, as representative but non limiting examples the catalytically active material may comprise one or more of Group VIB, VIIB, VIII catalytically active metals, metal oxide or sulfides and mixtures thereof and optionally including activators such as phosphorous, halogen or boron or such Group VIB, VIIB, VIII catalytically active metals, metal oxides or metal sulfides or metal nitrides and optionally including activators such as phosphorus, halogen or boron and mixtures thereof deposited on a refractory metal oxide base such as alumina, silica, silica/alumina, titania, zirconia. etc. and mixtures thereof, and alumino-silicate such as natural or synthetic zeolites such as zeolite X, zeolite Y, zeolite beta, ZSM-5, offretite, mordenite, eronite, etc. and mixtures thereof. Oxides like alumina, zeolites, zirconia, silica, titania-phases, vanadia-phases, transition- aluminas, zinc-oxide phases, can be deposited directly from suspensions e ^, as nano- or micrometer particles or from sols of said compounds or from mixtures of both. Coated particles may include carbon supports, such as carbon black, oxidized carbon supports, carbon molecular sieves, etc.. that are porous or non-porous.

In general, the particles that are applied to the three dimensional material (catalyst, catalyst support, catalyst precursor) are inorganic particles.

In using a coating bath, the coating bath in some cases may include additives. These additives change the physical characteristics of the coating bath, in particular the viscosity and surface tension such that during dipping penetration of the mesh takes place and a coating can be obtained with a homogeneous distribution on the interior and exterior of the mesh. Sols not only change the physical properties of the coating bath, but also act as binders. For example, to get a gamma-alumina coating with a very strong attachment between the oxide and the metal wire, alumina powder is suspended in an aqueous system and alumina sol is added to obtain, for example, a concentration between 1 and 30 wt.% alumina in such aqueous system. After the deposition, the article is dried and calcined. The dried and calcined sol is a good binder for alumina.

As representative stabilizing agents there may be mentioned: a polymer like polyacrylic acid, acrylamines, organic quaternary ammonium compounds, or other special mixes which are selected based on the particles. Alternatively an organic solvent can be used for the same purpose. Examples of such solvents are alcohols or liquid paraffins. Control of the pH of the slurry, for example, by addition of ITNO, is another method of changing the viscosity and surface tension of the coating slurry.

In preparing a catalyst in accordance with the invention, the catalyst may be applied to the support in a variety of ways.

In one embodiment, a particulate catalyst support may be applied to the support by coating in accordance with the invention, followed by application of a catalyst solution to the coated product; e.g., by spraying, impregnation or dipping.

In another embodiment, unsupported catalyst particles may be applied to a support in accordance with the invention.

In a further embodiment, a particulate catalyst support having catalyst or catalyst precursor applied thereto is coated onto the support in accordance with the invention. In any of the above procedures, the coating may be accomplished with or without slurry modifying agents in the coating mix.

In a further embodiment, a binder may be applied to the three-dimensional network prior or subsequent to coating with a particulate material, with such binder preferably being applied by coating in accordance with the invention.

In yet a further embodiment, multiple coatings may be applied to the same product in multiple coating steps, which coatings may be the same or different from each other.

These and other embodiments should be apparent to those skilled in the art from the teachings herein.

After the deposition of the coating, the article that has been coated is dried. Subsequently a second heating step is performed to achieve a proper bonding of the coating onto the surface and to make the coating itself more stable against abrasion and other influences. Also during the heating step organic agents, anions from the inorganic acids and solvents from the coating bath are removed. The specific heating cycles and conditions are dependent on the coating. When sols are used, the heating cycle allows the formation of the appropriate crystallographic phase. An alumina-sol, for example, can be dried at 1 10°C and treated afterwards at 550°C in an inert or oxygen-containing atmosphere to form a transitional-alumina.

Thus, in accordance with the present invention, it is possible to apply a uniform coating to essentially all of the material for a defined thickness of the interior portion of the porous three-dimensional network. For example, if such three-dimensional network is comprised of fibers or wires or mixtures thereof, each of the fibers or wires in the defined thickness can be coated with such particles in a uniform manner.

Although, in a preferred embodiment, essentially the entire thickness of the material is coated with the particles, it is within the spirit and scope of the invention to coat less than the entire thickness with such particles. It is also possible within the spirit and scope of the present invention to have various coating thickness within the three dimensional structure.

The invention further relates to a catalytic reactor wherein the reactor contains at least one fixed bed of catalyst comprised of a coated, porous, three-dimensional product in accordance with the present invention.

The coating of the porous, three-dimensional product includes an appropriate catalyst. All or a portion of the coating is applied to the product or support by a procedure as hereinabove described wherein the coating which is applied is comprised of catalyst alone, or combination of catalyst and support or support and in the case where only the catalyst support is applied by coating, the catalyst is subsequently applied by another procedure, e.g. spray-coating or dipping or impregnation.

The reactor contains at least one catalyst bed, and such catalyst bed may be formed from one or more layers of coated product in accordance with the invention. In most cases, the catalyst bed is comprised of multi-layers of such coated product.

The coated product, in accordance with the present invention, may be formed into a wide variety of shapes and, therefore, may be employed as a packing element for a catalytic reactor. Thus, for example, the mesh may be fabricated into corrugated packing elements, wherein each corrugated packing element which forms the fixed catalyst bed is formed of the coated product. The catalyst bed can be formed from a plurality of such corrugated elements, and the elements may be arranged in a wide variety of shapes and forms.

In accordance with another aspect of the present invention, there is provided a catalyst structure that is comprised of a plurality of layers of fibers (the layers form a three dimensional network of material), with the fibers being randomly oriented in said layers, with the fibers being coated with a porous particulate coating wherein the particulate coating is applied to the fibers in a particulate form.

Thus, in producing the catalyst structure the particulate coating comprising the catalyst or a catalyst precursor or a catalyst support (the catalyst support may or may not include a catalyst or catalyst precursor) is applied to the fibers during the coating process in the form of particles.

In accordance with an aspect of the present invention, there is provided a process (and resulting product) for producing a catalytic structure that is comprised of a support structure that is coated with a particulate coating comprising a catalyst. The support structure is a porous mesh like structure comprised of multiple layers of randomly oriented fibers wherein the fibers in the interior of the mesh like structure and the fibers on the exterior portion of the mesh-like structure are coated with the particulate coating. In accordance with the present invention the particles of the particulate coating are in the form of particles when being applied to the fibers.

The use of a catalyst coated packing in a reactor, in particular a fixed bed reactor in accordance with the invention can provide one or more of the following improvements: low by-product formation (improved selectivity); higher volumetric activity per unit of reactor volume; enhanced catalyst life, minimization or elimination of back-mixing; lower pressure drop; improved mixing of reactants and/or products as liquids and/or gases; higher geometric surface area to volume ratio of the catalyst; improved mass and heat transfer; etc.

The catalytic reactor may be employed for a wide variety of chemical reactions. As representative examples of such chemical reactions, there may be mentioned hydrogenation reactions, oxidations, dehydrogenation reactions, catalytic or steam reforming, alkylation reactions, hydrotreating, condensation reactions, hydrocracking, etherification reactions, isomerization reactions, selective catalytic reductions, catalytic removal of volatile organic compounds, etc.

The invention will be further described with respect to the following examples: however, the scope of the invention is not to be limited thereby:

Example Example 1

A 5 cm x 1 cm strip of a 0.7 mm thick stainless steel fiber sheet with a fiber diameter of 12 μm and a porosity of 90% was washed with acetone. Next, the sample was calcined in air at 300°C for 1 hour.

A slurry was made by mixing 20 g of catalyst powder and 80 g of water. The catalyst powder had a mean particle size of 3.157 μm and no particles smaller than 0.2 μm. No additives were used. The kinematic viscosity of the slurry as determined by the capillary viscometer was 194 centistokes. The surface tension as determined by the capillary tube method was 169 dynes/cm. The mesh sample was dried in a ventilated furnace at 120°C for 15 minutes.

From light microscopy it was concluded that the coating was deposited mainly on the exterior surface of the strip.

Example 2

A slurry was made by mixing 20 g of the same catalyst powder as in Example 1 and 80 g of water. However, in this slurry, the average particle size was 0.97 μm and about 10% of the particles were smaller than 0.1 μm. As a result, the kinematic viscosity of the slurry dropped to 1.3 centistokes and the surface tension was 128 dynes/cm. A 5 x 1 cm strip of the same support material as in example 1 that had been treated according to the procedure in example 1, was immersed and dried in a ventilated furnace at 120°C for 15 minutes. From light microscopy it was concluded that the coating was well dispersed over the interior and exterior surface of the strip. Example 3

A highly porous stainless steel fiber paper sample weighing 3.4034 g was coated with a slurry containing 5 wt. % solids of a 2 wt. % Pd catalyst on alumina by dipping in the free flowing slurry having a kinematic viscosity in the order of 1 centistoke and removing excess slurry by blotting on a paper towel. After drying the sample in air for 5 minutes and at 120°C for 0.75 hours the sheet plus dry catalyst weighed 3.6123 g or 5.78 weight percent. This sample was calcined at 350°C for 1 hour at a ramp rate of 30 degrees per minute from ambient temperature. Propylene then was hydrogenated to propane in the presence of the supported catalyst at 50°C and 400 psi. The propylene conversion was 56%> at a space velocity of 62.5 min^"1. Example 4

A highly porous stainless steel fiber paper sample weighing 4.0070 g was coated with a slurry containing 10 wt. % solids of a 2 wt. % Pd catalyst on alumina by dipping in the free flowing slurry having a kinematic viscosity in the order of 1 centistoke. and removing excess slurry by blotting on a paper towel. After drying the sample in air for 5 minutes and at 120°C for 0.75 hours, this sample was then coated a second time in a slurry containing 5 wt. % solids of a 2 wt. % Pd catalyst on alumina by dipping in the free flowing slurry having a kinematic viscosity in the order of 1 centistoke, and removing excess slurry by blotting on a paper towel. After drying the sample in air for 5 minutes and at 120°C for 0.75 hours, the sample was calcined at 350°C for 1 hour at a ramp rate of 30 degrees per minute from ambient temperature. The sheet plus dry catalyst weighed 4.7500 g or 15.6 weight percent. Propylene then was hydrogenated to propane in the presence of the supported catalyst at 50°C and 400 psi. The propylene conversion was 45 % at a space velocity of 70.9 min '. Example 5

A highly porous stainless steel fiber paper sample weighing 4.0182 g was coated with a slurry containing 10 wt. % solids of a 2 wt. % Pd catalyst on alumina by dipping in the free flowing slurry having a kinematic viscosity of in the order of 1 centistoke, and removing excess slurry by blotting on a paper towel. After drying the sample in air for 5 minutes and at 120°C for 0.75 hours and calcining the sheet 350°C for 1 hour at a ramp rate of 30 degrees per minute from ambient temperature. Propylene then was hydrogenated to propane in the presence of the supported catalyst at 50°C and 400 psi. The propylene conversion was 46% at a space velocity of 60.2 min^"'. Example 6

A 20 wt. % solids slurry of a V_:O₅ WO₁/TiO₂ catalytic material was prepared by ball milling to <1 micron size. To 88.47g of this slurry, 0.37g of nitric acid stabilized zirconia sol was added. Additionally, 0.89g of ammonium sulfate was also added to this slurry. The slurry had an estimated kinematic viscosity in the order of from 3 to 5 centistokes. The pH of this slurry was found to be 7.81. Ammonium hydroxide was added to this slurry to increase the pH to 8.44.

Sheets fabricated from stainless steel metal fibers were coated using this slurry.

The sheets were then dried at 120°C for 1 hour and subsequently calcined at 350° for 4 hours. The uptake of catalytic material on the metal fiber sheets was found to be 24%.

The catalyst thus prepared was tested for its NO reduction capability, wherein NO was reacted with ammonia to form nitrogen and water in the presence of the catalyst. A NO conversion of 91% was observed at a temperature of 350°C and a space velocity of

25000 h^"'. The conditions of the testing are listed below:

NO Concentration: 410 ppm

NH^ Concentration: 390 ppm

Oxygen Concentration: 5%

CO₂ Concentration: 13%

H₂O Concentration: 8%

Example 7

A 20 wt. % solids slurry of a V₂O₅ WO,/TiO₂ catalytic material was prepared by ball milling to<l micron size. The slurry was diluted by adding distilled water and the soids content was reduced to 11%. To 624.9g of this slurry, 1.3g of nitric acid stabilized zirconia sol was added. Additionally, 6.25g of ammonium sulfate was also added to this slurry. The slurry had an estimated kinematic viscosity in the order of 3 to 5 centistokes. The pH of this slurry was found to be 7.8. Ammonium hydroxide was added to this slurry to increase the pH to 8.3.

A 3" x 3" x 3" structure fabricated from corrugated metal fibers sheets was coated using this slurry. The structure was then dried at 120°C for 1 h. The structure was coated a second time and dried at 120°C for 1 h. This was followed by the calcination of the structure at 350°C for 4 h. The uptake of catalytic material on the metal fiber sheets was found to be 18.7%. The catalyst thus prepared was tested for its

NO reduction capability, wherein NO was reacted with ammonia to form nitrogen and water in the presence of the catalyst. A NO conversion of 87% was observed at a temperature of 350°C and a space velocity of 25000 h'^". The conditions of the testing are listed below:

NO Concentration : 410 ppm

NH-, Concentration: 390 ppm

Oxygen Concentration: 5%

CO₂ Concentration : 13 %

H₂O Concentration: 8%

Example 8

A 20 wt. % solids slurry of a V₂O₅ WO-,/TiO₂ catalytic material was prepared by ball milling to <1 micron size. The slurry was diluted by adding distilled water and the solids content was reduced to 1 1%. To 624.9g of this slurry, 1.3g of nitric acid stabilized zirconia sol was added. Additionally, 6.25g of ammonium sulfate was also added to this slurry. The slurry had an estimated kinematic viscosity in the order of from 3 to 5 centistokes . The pH of this slurry was found to be 7.8. Ammonium hydroxide was added to this slurry to increase the pH to 8.3.

A 3" x 3" x 3" structure fabricated from corrugated metal fibers sheets was coated using this slurry. The structure was then dried at 120°C for lh. The structure was coated thrice with intermittent drying at 120°C for 1 h. This was followed by the calcination of the structure at 350°C for 4h. The uptake of catalytic material on the metal fiber sheets was found to be 23.7%. The catalyst thus prepared was tested for its

NO reduction capability, wherein NO was reacted with ammonia to form nitrogen and water in the presence of the catalyst. A NO conversion of 88% was observed at a temperature of 350°C and a space velocity of 25000 h^"'. The conditions of the testing are listed below:

NO Concentration: 410 ppm

NH-, Concentration: 390 ppm

Oxygen Concentration: 5%

CO₂ Concentration: 13%

H₂O Concentration: 8%

Numerous modifications and variations of the present invention are possible in light of the above teachings and therefore, within the scope of the impended claims, the invention maybe practiced otherwise than as particularly described.

Claims

WHAT IS CLAIMED IS:

1. A process for applying a coating to a product comprising a porous three dimensional network of material, which process comprises: coating a porous product comprised of a plurality of layers of fibers formed into a three-dimensional network of material comprising metal fibers by contact with a coating bath comprising a plurality of particles dispersed in a liquid, said coating bath having a kinematic viscosity of no greater than 175 centistokes and a surface tension of no greater than 300 dynes/cm to coat at least a portion of the interior and exterior surface of the product.

2. The process of Claim 1 wherein the particles comprise a member selected from the group consisting of an unsupported catalyst, a catalyst support, a supported catalyst, an unsupported catalyst precursor and a supported catalyst precursor.

3. The process of Claim 1 wherein the coating is applied to the interior and penetrates into the interior of the product to a depth of at least 5 microns.

4. The process of Claim 3 wherein the fibers have a thickness of less than 500 microns.

5. The process of Claim 3 wherein the particles have an average particle size of less than 100 microns.

6. The process of Claim 3 wherein the product which is coated has an average void opening of at least 10 microns.

7. The process of Claim 1 wherein the thickness or diameter of the fibers is from about 8 to about 25 microns.

8. The process of Claim 7 wherein the porous product prior to coating has a void volume of about 90% to 98%.