WO2006027593A2

WO2006027593A2 - Gelcasting of a ceramic catalyst carrier

Info

Publication number: WO2006027593A2
Application number: PCT/GB2005/003472
Authority: WO
Inventors: Rodney Martin Sambrook
Original assignee: Dytech Corporation Limited
Priority date: 2004-09-10
Filing date: 2005-09-08
Publication date: 2006-03-16
Also published as: GB0420156D0; WO2006027593A3; GB2417921A

Abstract

A method of fabricating a catalyst carrier, comprises forming a slurry of ceramic particles in a liquid carrier, the liquid carrier comprising a binder species, applying the dispersion to a non-sacrificial mould surface having formations provided therein or thereon, causing the binder species to set to provide a green form, removing the green form from the mould surface, drying and firing the green form, wherein the setting of the binder species to provide a green form which is removeable from the mould surface, preferably, takes less than 120 minutes. Catalyst carriers and tape casting apparatus for making the same are also disclosed.

Description

CATALYSIS

This invention relates to catalysis, particularly, but not exclusively, to catalyst carriers and to catalyst carriers carrying catalyst.

Catalyst carriers used in highly exothermic or endothermic reactions must be made from materials with excellent thermal stability and high mechanical strength. Of necessity, this usually means carriers with relatively low surface area and high bulk volume. Because of the high volume to surface area ratio, the catalyst efficiency and activity is lowered and the pressure-drop across the carrier high.

Various products have sought to enhance geometric surface area, reduce pressure drop and bulk volume by the use of a multiplicity of holes and/or surface corrugations to achieve the required properties.

US 6670305 discloses a tape casting method for making a monolithic catalyst with micro-scale flow channels for auto-thermal reforming of hydrocarbon fuels. Catalyst layers and fugitive layers of polymeric nature (later to be burnt-off) are tape cast repeatedly onto a substrate layer, to form a multi-layer green form. After each casting the layers are allowed to dry. The fugitive layer has a thickness of between 1 and 150μm, and the catalyst layer a thickness of between 1 and 200μm. Once the green form is dried, the free¬ standing catalyst is peeled from the substrate, cut into strips and rolled or folded into bulk shapes before firing to ensure fugitive layer burnout and final sintering. US 4025462 discloses forming a slurry of ceramic particles, plastic supporting matrix, plasticizer, organic solvent and a deflocculant and ball milling the slurry. The milled slurry is then cast to form a film and the solvent removed to provide a self-supporting green ceramic tape. The tape is then moulded to form a corrugated first member and a flat second member and these are then stacked in alternating layers of tape cast first and second members. The corrugated sheets therefore created the flow channels to form a ceramic cellular structure.

In US 4130452 a sacrificial sheet (for example made of wax or polymers) is perforated with holes or patterns and is placed on top of another sacrificial sheet of the same composition. Catalyst slurry is then tape cast onto this arrangement. The green tape is then cut into strips and rolled or stacked to form the catalyst shapes before burnout of the sacrificial sheets and binders and final sintering. The binders used are thermosetting resins and harden, at room temperature, in about ten days.

It is an object of the present invention to produce catalyst carriers with high geometric surface areas. It is a further, non-exclusive, object of the invention to provide catalyst carriers with high, and/or pre-defined, amounts of micro and macro porosity. It is an non-exclusive advantage of the invention that the catalyst carriers can be formed quickly and easily. In this specification, the term catalyst carrier may relate to a carrier comprising a catalytic species {i.e. is provided in situ) or which carries a catalytic species (e.g. the catalyst is coated, impregnated, deposited onto the external and/or internal surface and/or within the pore structure of the carrier walls and/or within the voids of the carrier subsequent to formation of the carrier). In either case, both of which situations are intended to fall within the scope of the invention, the finished catalyst carrier is, to all intents and purposes, a catalyst.

Accordingly, a first aspect of the invention provides a method of fabricating a catalyst carrier, the method comprising forming a slurry of ceramic particles in a liquid carrier, the carrier comprising a binder species, applying the dispersion to a mould surface having formations provided therein or thereon, causing the binder species to set to provide a green form, drying and firing the green form, wherein the setting of the binder species to provide a green form which is removeable from the mould surface takes less than 120 minutes.

A second aspect of the invention provides a method of fabricating a catalyst carrier, the method comprising forming a slurry of ceramic particles in a liquid carrier, the liquid carrier comprising a binder species, applying the dispersion to a non-sacrificial mould surface having formations provided therein or thereon, causing the binder species to set to provide a green form, removing the green form from the mould surface, drying and firing the green form, wherein the setting of the binder species to provide a green form which is removeable from the mould surface, preferably, takes less than 120 minutes. In this specification, the term 'non-sacrificial mould surface' is intended to mean a mould surface which may be used again subsequent to the removal of the green form therefrom. That is to say that it is also unnecessary to destroy the mould surface to remove the green form therefrom.

The ceramic particles may be or may comprise a catalytic species.

The binder species is preferably a polymerisable monomeric species which may be a bi-functional monomeric species or a poly-functional monomeric species. If the polymeric species is bi-functional, the liquid carrier may also comprise a poly-functional monomeric species, and vice versa.

In this specification, the terms 'bi-functional monomer' and 'bi-functional monomeric species' are intended to relate to monomers which give two and only two linkages to other monomers to form, say, linear polymers. The terms 'poly- functional monomer' and 'poly-functional monomeric species' are intended to relate to monomers which give more than two linkages and are therefore usually able to cross-link to other monomers to form a three-dimensional network.

Suitable polymers are alkenes, acrylates, methacrylates, esters, anhydrides, acrylamides, or other polymerisable substances such as agarose, cellulose and so on. The polymerisable monomeric species may comprise homopolymer units or copolymers (including ter and higher polymers). A pre-mix of the polymerisable monomer(s) may be provided to which a species to cause polymerization may be added. Other binder species which may be used in addition or alternatively include polyvinyl alcohols (PVAs), alginates, starches and so on.

The slurry, and hence the green for, is preferably free from thermosetting resins.

The ceramic particles may comprise one or more of alumina, silica, hydroxyapatite, zirconia, silicon carbide, tin oxide, kyanite, cordierite, mullite, spinel, perovskites, titanium dioxide, zinc oxide, nickel aluminate, aluminium titanate, rare earth metal silicates, rare earth oxides, spinels and the like.

The dispersion may comprise 'active' catalytic species and/or the precursors thereof, for example one or more of molecular sieve, nickel oxide, iron oxide, manganese oxide, chromium oxide and other catalyst materials.

The particle size and size distribution should be chosen to meet the requirements of catalyst efficiency, sintered body strength, rheological property of the slurry and so on. The usual particle size range is between 100nm to 100μm, preferably between 300nm to 30μm.

The slurry may also comprise one or more of solvents, dispersants, pore formers, plasticizers, viscosity modifiers and catalyst activity enhancers.

To uniformly suspend the catalyst particles in the slurry one or more dispersants may be added to introduce steric and/or electrostatic stabilisation. Acrylic acid based polymers of specific molecular size range are most widely used dispersants although other phosphate based, non-ionic dispersants are also suitable for the present invention. The selection of dispersants is still mainly based on experience and trial and error rather than scientific guidelines. Care must be taken to avoid or suppress chemical reactions between the monomers and dispersants or between the catalyst particles and dispersants.

Plasticizers may also be added if the process requires dry green form deformation.

A suitable amount of plasticizer in the green form will make the dry green form flexible at room temperature. Preferred plasticizers are those which are water soluble, environmentally friendly such as glycerol and polyethyleneglycol of various molecular sizes.

Viscosity modifiers may also be added to adjust the slurry viscosity to reduce the tendency of catalyst particle sedimentation or segregation, to reduce large air bubble entrapment, and to improve the casting conditions.

Sacrificial pore formers may also be added into the slurry if porosity is required within the catalyst body. There are many suitable pore formers widely used in the industry and the suitable one for this work include olive stone and almond shell powder of specific particle size and polymeric particles such as polyruric spheres. Pore formers should be carefully chosen so that after burnoff they do not leave residuals detrimental to the catalyst, that they burnoff well below the sintering temperature, that they do not deform (such as swelling) during slurry preparation and casting. Porosity in the body may be provided by introducing air or another gas, for example by mechanical agitation, blowing or in situ gas generation into the slurry prior to casting. Porosity in the body may also be introduced by emulsifying the slurry with low boiling point blowing agents such as cyclopentane and cyclohexane. The blowing agent expands and evaporates, for example during and after the exothermic polymerization, and forms pores in the cast body.

In some embodiments of the invention the internal voids of the catalyst carrier may be filled with a foam material either catalytic or non-catalytic in nature either homogeneously or in zones to create differing reaction zones and/or control mass and heat transfer in local areas.

Other catalyst activity enhancers may also be added to improve the catalyst efficiency. These enhancers include those materials promoting the catalyst selectivity, avoiding the active catalyst particles forming agglomerate, and spacing the active catalyst particles more evenly in the catalyst body.

The catalyst slurry preparation generally includes the mixing of all the ingredients together or in preferred sequence with the monomers and solvents. The prepared slurry will usually have a consistency of easy flowing or pouring, slow or no particles settling and segregation before and during casting, and uniform composition distribution throughout the slurry body.

The method may comprise the preliminary step of designing and preparing the mould surface and preparing a mould surface according to the design. Preferably, the mould surface will have intrinsic 'mould-releasing' characteristics. For example, the mould surface may be fabricated from a material comprising self- lubricating polymeric species, for example oil-filed Nylon 6 or MoS₂-filled Nylon 6 (for example, those supplied by Bay Plastics Limited of North Shields, United Kingdom under the registered trademarks Nyloil and Nylatron respectively). Alternatively, the mould surface may be formed from metal, wood or other polymeric species.

The mould may be formed as a discrete (i.e. stand-alone) mould member or may be formed as a continuous belt-type mould member.

The mould, or at least the mould surface, will preferably be fabricated from a readily machinable material (the materials disclosed above satisfying the requirement) so that the mould surface can be provided with, for example, one or more of a series of shaped holes in say staggered or linear fashion, channels in linear, curved, zig-zagged, swirled or other shapes, notched diamond-shaped channels and so on or a combination thereof, which, in the finished catalyst carrier, will allow for interconnectivity for fluid flow whilst also providing a degree of control over direction of flow. The mould surface may also be provided with formations or projections thereon corresponding to the above- identified holes or channels. In either case the projections, ridges, holes, channels efc. may or may not be of the same dimensions within the catalyst carrier. Furthermore the nature of these patterns may be zoned within the catalyst carrier to provide fine control over heat and mass transfer. The mould surface will preferably have a smooth, preferably substantially planar, finish to facilitate removal of the green form therefrom.

In preferred embodiments the slurry is cast directly on to the mould surface. A further and/or more specific aspect of the invention provides a method of fabricating a catalyst carrier, the method comprising forming a mould surface having a desired arrangement of formations therein or thereon, forming a slurry of ceramic particles in a liquid carrier, the carrier comprising a polymerisable monomeric species, applying the dispersion to the mould surface, causing the monomeric species to polymerise to provide a green form, removing the green form from the mould surface, preferably within 120 minutes of commencement of the polymerization of the monomeric species, drying and firing the green form.

The green form may be achieved in less than 60 minutes, preferably less than 30 minutes and most preferably less than 15 minutes.

The method or methods may comprise the subsequent step of cutting the green form into sheets which may be stacked above one another or rolled into a cylinder to provide the catalyst carrier. It will be appreciated that the fired ceramic article will have formations along its length corresponding to a 'positive' or 'negative' of the formations formed in or on the mould surface respectively.

The body and/or walls of the catalyst carriers typically have a porosity of from 5 to 90%. They may typically have a thickness of from 0.3 to 3 mm with spacings between the walls of from 0.1 to 2.5 mm i.e. the longest projections will have a length between 0.1 and 2.5 mm.

A further aspect of the invention provides tape casting apparatus for providing a catalyst carrier, the apparatus comprising slurry mixing means and slurry delivery means to deliver slurry from said slurry mixing means to a mould surface, a doctor blade to spread slurry delivered from said slurry delivery means onto a mould surface and in-line mixing means located upstream of the doctor blade in said slurry delivery means, said in¬ line mixing means being arranged to mix a initiator and/or polymerization catalyst into slurry delivered through said slurry delivery means, the initiator and/or polymerization catalyst polymerizing a monomeric polymerisable species provided in the slurry delivered through said slurry delivery means.

A yet further aspect of the invention provides a method of casting a ceramic slurry on to a mould, the method comprising mixing ceramic particles and a binder species, for example a monomeric polymerisable species, to provide a slurry; delivering the slurry to a mould surface and spreading the slurry onto the mould surface using a doctor blade; and comprising mixing an initiator and/or polyermization catalyst into and with the slurry at a point upstream of the doctor blade to commence setting of the binder species, for example polymerization of the polymerisable monomeric species.

Preferably the mould is a shaped mould surface, for example one comprising an array of formations thereon or therein, arranged to provide a cast ceramic article having corresponding formations in or on a surface thereof.

In order that the invention may be more fully understood, it will now be described with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a part of a first embodiment of catalyst carrier made by the method of the invention; Figure 1 A is a perspective view of the part of the carrier of Figure 1 ;

Figure 2 is a plan view of a part of a second embodiment of catalyst carrier made by the method of the invention;

Figure 2A is a perspective view of the part of the carrier of Figure 2;

Figure 3 is a perspective view of a mould surface used in the method of the invention;

Figure 4 is a schematic representation of a tape-casting apparatus useful in the method of the invention;

Figure 5 is a perspective view of the carrier of Figure 1 and 1 A, configured for use; and

Figure 6 is a perspective view of a stack of the carriers of Figures 2 and 2A, configured for use.

Referring to Figure 1 and 1A, there is shown a catalyst carrier 1 comprising a ceramic body 2 from which a plurality of integral cylindrical projections 3 extend.

In Figures 2 and 2A there is shown a catalyst carrier 11 comprising a ceramic body 12 having an integral saw-tooth formation 13 on, or as, an upper surface.

The bodies 2, 12 of the carriers 1 , 11 may be dense or may have a defined priority

(e.g. 5-90%). The projections may have a thickness of from 0.3 to 3mm and may be spaced apart by 0.1 to 2.5mm. The length of the projections may be from 0.1 to 2.5mm. Figure 3 shows a part of a non-sacrificial mould 20 used to fabricate a catalyst carrier 1. The mould 20 has an array of cylindrical indentations 21 formed in a mould surface 22 and is provided with a peripheral wall 23 which bounds and defines the edge of the mould surface 22 (only one wall 23 being shown for the sake of clarity). The mould surface 22 of the mould 20 is delimited at points along its length by transverse walls 24.

The mould 20 may be fabricated from oil-filled Nylon 6 or MoS₂-filled Nylon 6, both of which may be supplied by Bay Polymers of North Shields, United Kingdom, under the registered trademarks Nyloil and Nylatron respectively. The material is machined to provide the desired configuration and shape of mould surface 22.

To form a catalyst carrier 1 , 11 a modified tape-casting apparatus may be used, as shown in Figure 4. A slurry or dispersion of a ceramic material in a medium is provided in a slurry mixing system 51 and a slurry delivery system 52. The medium also comprises a polymerisable monomeric species and may comprise a catalyst material to provide the catalytic action for the carrier. An in-line mixer 53 mixes an initiator and polymerization catalyst into the slurry 54 as it passes through or along the slurry delivery system 52.

The in-line mixer 53 is provided immediately upstream of a doctor blade 55 which spreads the dispersion 54, with added initiator and polymerization catalyst, onto a mould

20. The mould 20 is formed as a continuous belt-type mould and the doctor blade 55 continuously applies the dispersion directly to the mould surface 22 as it passes the blade.

In situ polymerization of the monomeric species occurs within minutes to provide a green form 56 which may be removed from the mould surface 22. Because the mould 20 has peripheral walls 23 and transverse walls 24, the green form ceramic catalyst carrier is provided in usable lengths.

The green form is then shaped to the required shape, two of which are shown in Figures 5 and 6. In the former, the green form 30 is formed into a roll 31 and, in the latter, the green form 40 is stacked with other green forms to provide a stack of sheets 41. The stack may allow co-current, counter-current or cross-flow configurations. In any case, it will be appreciated that the form of the upper surface of the mould ensures that there are gaps, and hence flow channels, between adjacent surfaces.

The shaped green forms 30, 40 are then dried at either room temperature or at elevated temperatures followed by binder burnout (at, say, 200 to 700 ⁰C) followed by sintering (at, say, 500 to 1600 ⁰C).

If required, pore formers such as olivestone, almond shell powder, polymeric thermoplastics spheres and so on may be provided in the dispersion to provide corresponding macroporous voids in the sintered material. The main requirement is that the pore-formers do not affect or react with any catalyst which is provided in the dispersion or leave any residues which would or could likewise affect the catalyst.

Fabrication of a catalyst carrier has been carried out according to the following Examples: Example 1

A mould was prepared by drilling 5mm diameter holes about 5mm deep into a thermoplastic part. The holes are arranged as shown in Figure 3.

A slurry of the following composition was prepared by thorough mixing (parts in weight) • fine alumina powder (average particle size 0.5μm) 75;

• 30% aqueous solution of ammonium acrylic acid salt (bi-functional monomer) and up to 1% methylenebisacrylamide (poly-functional monomer) 20;

• water 10;

• ammonium acrylate dispersant 2.5. For a 30ml slurry batch 1mJ! of 25% ammonium persulphate solution (initiator) and 50μl of N, N, N', N'-tetramethylethylenediamine (catalyst) are mixed into the slurry and cast onto the mould surface to a height of about 1-2 mm. The slurry gels within about 1 minute and the gelled green form is peeled off of the mould and rolled into a cylinder shape, as shown in Figure 5. It is then dried and fired to 152O⁰C for 2 hours. The shape formed in this way is very strong and has a dense body (micro density >90%).

Example 2

A slurry was prepared as per Example 1 , with the exception that 10 parts of olivestone powder (-100 mesh) was added to the slurry as a pore former. The rolled cylinders were fired to 135O⁰C for 2 hours. The measured pore volume of the micro-pores is 0.2 ml/g, equivalent to a 45% micro- porosity.

Example 3

A slurry was prepared as per Example 1 , with the exception that instead of 75 parts of the disclosed fine alumina powder, only 70 was added. A further 5 parts of coarser alumina (average particle size 6μm) was added as well as 13 parts of olivestone powder (-100 mesh). The rolled cylinders were fired to 132O⁰C for 2 hours. The measured micro- porosity is 0.25 ml/g, equivalent to a 50% micro-porosity. Example 4

A slurry was prepared as per Example 3 but instead of 13 parts of (-100 mesh) olivestone 8 parts of olivestone (-100 mesh) and 10 parts of olivestone (-100, +125 mesh) are added to form a bi-modal pore structure. Two sets of rolled cylinders were made with the slurry and were fired to 132O⁰C and 135O⁰C respectively. The measured micro-pore volumes were 0.36 and 0.30 ml/g respectively, equivalent to 58% and 54% micro-porosity.

Example 5

Tapes of the various compositions as given in Examples 1 to 4 were cast onto a corrugated surface with the grooves of 1.5mm wide and 1.5mm deep as shown in Figure

2 and 2A. To improve the room temperature flexibility of the green forms after drying, up to 10 parts glycerol (plasticizer) was added. The cast tapes were then rolled into cylinders or cut into squares and fired to 135O⁰C. With the addition of plasticizer it is possible to reshape the green form after room temperature drying. This is particularly useful if flat sheets are to be fabricated.

The so-formed catalyst carriers were found to be suitable as catalyst carriers in steam reforming, autothermal reforming, partial oxidation, or in other fixed bed reactors involving endothermic or exothermic reactions.

The carriers may be used in heat exchangers, filters, catalytic filters and so on, as will be appreciated by the skilled man.

The catalyst carriers were found to show much increased surface area and a lower pressure drop than other catalyst carriers known in the art. Specific geometric areas and measured pressure drops of the catalyst carriers made according to Example 1 are compared with various catalyst carriers in Table 1. Table 1

Unit surface Specific surface

No. Shape Dimension, mm area/ cm² No. per litre cmV Pressure drop/μbar

1 Sphere 16 8.04 326 2625 20

2 Fluted ring 16x16x7 15.89 187 2964 15

3 Cylinder, 50% 16x16 12.06 187 2250 17

4 Cylinders, 20% 16x16 12.06 187 2250 19

5 Ex 1 diff formations 16x16x1 98.56 187 18382 20

6 Ex 1 16x16x1 37.70 187 7031 11

1. Ceramic dense spheres with smooth surface, diameter 16mm;

2. Extruded fluted rings with 16mm outer diameter and 7mm central hole, 6 flutes;

3. Gelcast ceramic cylinders of 50% theoretical density, 16mm diameter and 16mm length;

4. Foamed ceramic cylinders with smooth skin, foam density 20%, 16mm diameter and 16mm length;

5. Catalyst carriers made in the same manner as Example 1 but with different mould formations. On one surface there are random channels of 0.3mm width and depth. Green form thickness about 1mm, carrier size 16mm diameter and 16mm length;

6. Carrier size 16mm diameter and 16mm length.

Comparing with the spheres of the same diameter the specific geometric surface area of the catalyst carriers given in Example 1 is almost 3 times as high and the sample with finer formations (No.5 in Table 1) has a specific area of 7 times as that of the equivalent spheres. The pressure drop in the case of Example 1 is only about half of that of the spheres.

The pressure drop data given in Table 1 were measured in a 64mm diameter 140mm length miniature reactor with nitrogen as the flow medium. Flow rate was fixed at 30i.min^"1. The green form tapes formed using the tape casting apparatus may be combined with other catalyst tapes made using the apparatus (or otherwise) to provide a dual (or multi) purpose catalyst carrier. For example, tapes of different compositions may be rolled or stacked together to provide a catalyst carrier having a combined physical and/or catalytic properties of the tapes.

The mould need not be of a continuous belt-type mould and may be any suitable mould surface. The form and pattern of the formations therein or thereon may be any chosen for a particular task, for example the indentations may be shaped to provide a carrier having hemispherical projections, elongate, curved or other shaped projections.

If the carrier is formed from a non catalytic ceramic material (i.e. a ceramic material having no or little catalytic activity) a catalytic material may be coated, impregnated and/or deposited over some or all of the shaped surface of the carrier either prior to or after binder burnout and final sintering.

In non-catalytic applications the invention can offer the possibility of ceramic microchannel heat exchangers or chemical reactors for high and low temperature applications for liquid and gaseous feeds or a combination of both. Other applications include absorption of gases in liquids in co-current and counter current flow systems.

In some embodiments the polymersible monover may be pre-mixed with an initiator and the pre-mix solution added to the ceramic material.

Claims

1. A method of fabricating a catalyst carrier, the method comprising forming a slurry of ceramic particles in a liquid carrier, the carrier comprising a binder species, applying the slurry to a mould surface having formations provided therein or thereon, causing the binder species to set to provide a green form, drying and firing the green form, wherein the setting of the binder species to provide a green form which is removeable from the mould surface takes less than 120 minutes.

2. A method of fabricating a catalyst carrier, the method comprising forming a slurry of ceramic particles in a liquid carrier, the liquid carrier comprising a binder species, applying the slurry to a non-sacrificial mould surface having formations provided therein or thereon, causing the binder species to set to provide a green form, removing the green form from the mould surface, drying and firing the green form.

3. A method according to Claim 2, wherein the setting of the binder species to provide a green form which is removeable from the mould surface, takes less than 120 minutes.

4. A method according to any of Claims 1 to 3, wherein the ceramic particles are or comprise a catalytic species.

5. A method according to any preceding Claims, wherein the binder species is a polymerisable monomeric species.

6. A method according to Claim 5, wherein the monomeric species is a bi-functional monomeric species or a poly-functional monomeric species.

7. A method according to Claim 6, wherein if the polymeric species is bi-functional, the liquid carrier also comprises a poly-functional monomeric species, and vice versa.

8. A method according to any of preceding Claims, wherein the binder comprises one or more of polymers such as alkenes, acrylates, methacrylates, esters, anhydrides, acrylamides, agarose, cellulose, polyvinyl alcohols (PVAs), alginates, starches.

9. A method according to any preceding Claim, wherein the ceramic particles comprise one or more of alumina, silica, hydroxyapatite, zirconia, silicon carbide, tin oxide, kyanite, cordierite, mullite, spinel, perovskites, titanium dioxide, zinc oxide, nickel aluminate, aluminium titanate, rare earth metal silicates, rare earth oxides, spinels and the like.

10. A method according to any preceding Claim, comprising adding active catalytic species and/or the precursors thereof, to the slurry.

11. A method according to Claim 10, wherein the active catalytic species comprises one or more of molecular sieve, nickel oxide, iron oxide, manganese oxide, chromium oxide and other catalyst materials.

12. A method according to any preceding Claim, comprising adding one or more of solvents, dispersants, pore formers, plasticizers, viscosity modifiers and catalyst activity enhancers to the slurry.

13. A method according to any preceding Claim, comprising adding one or more dispersants to the slurry to introduce steric and/or electrostatic stabilisation.

14. A method according to any preceding Claim, comprising adding plasticizers to the slurry.

15. A method according to any preceding Claim, comprising adding viscosity modifiers to the slurry to adjust the viscosity thereof.

16. A method according to any preceding Claim, comprising adding sacrificial pore formers to the slurry.

17. A method according to any preceding Claims, comprising introducing air or another gas, for example by mechanical agitation, blowing or in situ gas generation into the slurry prior to casting.

18. A method according to any preceding Claim, comprising filling at least some of any internal voids of the catalyst carrier with a foam material which is either catalytic or non-catalytic in nature.

19. A method according to Claim 18, comprising filling any internal voids either homogeneously or in zones to create differing reaction zones and/or control mass and heat transfer in local areas.

20. A method according to any preceding Claim, comprising adding catalyst activity enhancers to the slurry to improve the catalyst efficiency.

21. A method according to any preceding Claim, comprising the preliminary step of designing and preparing the mould surface and preparing a mould surface according to the design.

22. A method according to Claim 21 , comprising forming the mould surface with intrinsic 'mould-releasing' characteristics.

23. A method according to Claim 21 or 22, comprising forming the mould as a discrete mould member or as a continuous belt-type mould member.

24. A method according to any of Claims 21 to 23, comprising forming the mould surface with one or more of a series of shaped holes in staggered or linear fashion, channels in linear, curved, zig-zagged, swirled or other shapes, notched diamond-shaped channels and so on or a combination thereof.

25. A method according to any of Claims 21 to 24, comprising forming the mould surface with formations or projections thereon

26. A method according to any of Claims 21 to 25, comprising forming the mould surface with different zones of projections and/or patterns to provide fine control over heat and mass transfer within a so-formed catalyst carrier.

27. A method according to any of Claims 21 to 26, comprising forming the mould surface with a smooth, preferably substantially planar, finish to facilitate removal of the green form therefrom.

28. A method according to any preceding Claim, comprising casting the slurry directly on to the mould surface.

29. A method of fabricating a catalyst carrier, the method comprising forming a mould surface having a desired arrangement of formations therein or thereon, forming a slurry of ceramic particles in a liquid carrier, the carrier comprising a polymerisable monomeric species, applying the dispersion to the mould surface, causing the monomeric species to polymerise to provide a green form, removing the green form from the mould surface within 120 minutes of commencement of the polymerization of the monomeric species, drying and firing the green form.

30. A method according to any preceding Claim, wherein the green form is achieved in less than 60 minutes, preferably less than 30 minutes and most preferably less than 15 minutes.

31. A method according to any preceding Claim, comprising the subsequent step of cutting the green form into sheets which are stackable above one another or rolled into a cylinder to provide the catalyst carrier.

32. A catalyst carrier (1 ; 11) formed by the method of any of Claims 1 to 31.

33. A catalyst carrier (1 ; 11) according to Claim 32, wherein the catalyst carriers (1 ; 11 ) have a porosity of from 5 to 90%.

34. A catalyst carrier (1 ; 11 ) according to Claims 32 or 33 having projections (3;13) upstanding from a body portion (2; 12).

35. A catalyst carrier (1 ; 11 ) according to Claim 32 or 33, wherein the projections of the carrier have a thickness of from 0.3 to 3 mm with spacings between the projections (3; 13) of from 0.1 to 2.5 mm.

36. A tape casting apparatus for providing a catalyst carrier, the apparatus comprising slurry mixing means (51) and slurry delivery means (52) to deliver slurry from said slurry mixing means (51) to a mould surface (20), a doctor blade (55) to spread slurry delivered from said slurry delivery means (52) onto a mould surface (20) and in-line mixing means (53) located upstream of the doctor blade (55) in said slurry delivery means (52), said in-line mixing means (53) being arranged to mix a initiator and/or polymerization catalyst into slurry delivered through said slurry delivery means (52), the initiator and/or polymerization catalyst polymerizing a monomeric polymerisable species provided in the slurry delivered through said slurry delivery means (52).

37. A method of casting a ceramic slurry on to a mould, the method comprising mixing ceramic particles and a binder species, for example a monomeric polymerisable species, to provide a slurry; delivering the slurry to a mould surface and spreading the slurry onto the mould surface using a doctor blade; and comprising mixing an initiator and/or polyermization catalyst into and with the slurry at a point upstream of the doctor blade to commence setting of the binder species, for example polymerization of the polymerisable monomeric species.

38. Apparatus according to Claim 36, wherein the mould surface (20) comprises a shaped mould surface, for example one comprising an array of formations thereon or therein, arranged to provide a cast ceramic article having corresponding formations in or on a surface thereof.