GB2540240A

GB2540240A - Catalyst particle

Info

Publication number: GB2540240A
Application number: GB1606279.6A
Authority: GB
Inventors: Roy Coupland Duncan
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 2015-04-14
Filing date: 2016-04-12
Publication date: 2017-01-11
Anticipated expiration: 2036-04-12
Also published as: GB201506324D0; WO2016166523A1; GB2540240B

Abstract

A catalyst particle comprises a three-dimensional shaped particle 20 in the form of a cylinder or prism having an axis, one or more side surfaces 22 generally parallel to said axis and first 12 and second 14 end surfaces generally transverse to said axis having at least one axial channel 18 extending through the particle from a first end surface opening 16 in the first end surface to a second end surface opening 20 in the second end surface and at least one transverse channel extending from an opening in a side surface to communicate with said axial channel; characterised in that said first end surface opening of an axial channel is not axially aligned with said second end surface opening of the same axial channel. The catalyst particle may be in the general form of a cylinder having a circular, elliptical parabolic or hyperbolic cross section, or a prism having from 3 to 20 side surfaces wherein said prism has a cross-sectional shape of a regular polygon, and irregular polygon, a spindle shape or a star. The centre of said first end surface opening of an actual channel may be radially offset from the centre of said second end surface opening of the same axial channel by up to 90°.

Description

Catalyst Particle

The invention concerns catalyst particles, reactors containing a bed of such catalyst particles and chemical reactions catalysed by such catalyst particles.

Traditional catalyst pellets and catalyst supports may, by the nature of their manufacture, exhibit two dimensional complexity of design and structure but almost invariably require these geometries to be extended into the third dimension by extrusion or tabletting methods. This third dimension has little potential for geometric complexity as a result. The performance of a catalyst is partly determined by the ability of the catalyst scientist to promote and control the interaction of the gas or liquid stream of reactants with the catalyst itself. This ability is compromised by their limited control over the pellet geometry.

New particle designs, which are made possible using additive layer manufacturing methods, including 3D printing techniques, can provide very high surface area to volume catalysts in combination with control of flow of reactants over and through the catalyst pellets. Control of flow of reactants and products through the catalyst particle improves the opportunity for controlling turbulence and boundary-layer characteristics as a consequence of the reaction distribution through the bed. This is especially effective when combined with enhanced bedpacking which allows control of the thermal distribution in a catalyst bed by modification of flows both vertically and laterally through the bed New catalyst particle shapes allow the advantages of 3D printing methods to contribute to the improvement of the control of chemical reactions in catalyst beds.

According to the invention, we provide a catalyst particle in the form of a three-dimensional shaped particle in the general form of a cylinder or prism having an axis, one or more side surfaces generally parallel to said axis and first and second end surfaces generally transverse to said axis having at least one axial channel extending through the particle from a first end surface opening in the first end surface to a second end surface opening in the second end surface; characterised in that said first end surface opening of an axial channel is not axially aligned with said second end surface opening of the same axial channel.

According to a further aspect of the invention, we provide a catalyst bed comprising a plurality of catalyst particles according to the invention contained within a vessel.

We further provide a method of carrying out a chemical reaction comprising the step of contacting at least one fluid containing at least one starting chemical compound with a catalyst bed according to the invention.

We further provide a method of treating a fluid mixture to selectively remove one or more target components of the mixture by contacting the fluid mixture with a catalyst bed according to the invention.

The catalyst particle may have the general form of a cylinder. A cylinder has a single side surface. The cross-section may be circular, elliptical parabolic, hyperbolic or irregular in shape. At least one of the side or end surfaces of the particle may include grooves, blind channels or indentations. At least one of the side or end surfaces of the particle may include protrusions such as bosses, ridges and lobes, for example. In such a case the cross section may be star-shaped, splined or irregular. The cross section may vary along the axis of the particle. Such variation inevitably occurs due to the presence of the axial and transverse channels. The cross section may, however vary in aspects which are not caused by the presence of the axial and transverse channels.

The catalyst particle may have the general form of a prism. A prism has at least three side surfaces. A catalyst particle in the general form of a prism may have from three to twenty side surfaces. Any of the side surfaces may include grooves, blind channels or indentations. A prism may have a cross-sectional shape of a regular polygon, such as a triangle, a rectangle, pentagon, hexagon, dodecagon etc.; an irregular polygon, a splined shape or a multi-pointed star.

The catalyst particle has first and second end surfaces which are generally transverse to the axis of the catalyst particle. One or both of the end surfaces may be planar. One or both of the end surfaces may be convex, concave or may be undulating in a regular or irregular manner. The end surfaces may be normal to the axis of the particle or may be angled relative to the side surface(s) at more or less than 90 degrees. Where the end surface is not planar the angle of the surface relative to the side surface may be taken to be the angle of a plane passing through two points which are each located at an edge where a side surface meets the end surface. The two points are usually on opposed portions of the side surface(s) of the particle.

The catalyst particle comprises at least one axial channel extending through the particle from a first end surface opening in the first end surface to a second end surface opening in the second end surface, thereby forming a channel through which a material may enter the particle at one end surface, pass through the particle and exit the particle at the other end surface. The term "axial channel" is not intended to mean that the channels are necessarily parallel with the axis of the particle. In preferred embodiments the channels are not parallel with the axis of the particle. By axial channel we mean a channel that extends from one end surface of the particle to the other end surface of the particle.

The catalyst particle may comprise from 1 to 20 axial channels usually from 2 to about 10 axial channels. The catalyst particle may comprise from 2 to 100 axial channels per cm2 of cross-section. The channels may be straight or curved. They may provide a tortuous path through the particle between the end openings. The channel may have a cross-section which is of any shape, although generally circular, elliptical or polygonal shapes such as square/rectangular channels may be usual. The channel may include ribs, flutes or vanes on its internal surface. The channel may have a cross-section which varies along the length of the channel. The internal surface of the channel may be shaped to promote mixing of a fluid as it passes through the channel, for example by providing a threaded or helical channel. The axial channels may or may not have parallel walls. An axial channel may be wider at an end or towards the centre of the channel. Therefore a channel may include a narrow portion adjacent either of the end openings or between the end openings. . A channel having a relatively narrow portion between two wider openings may be described as “waisted”. The end openings of the axial channels may be the same or different from those of each other axial channel. The end openings may differ in shape or in size. The first and second end openings of a single channel may be different from each other. The end openings may differ in shape or in size. Thus an axial channel may have a first end opening which is larger or smaller than the second end opening. An axial channel may form or join with a cavity within the particle. At least two axial channels may join to form a cavity within the particle.

Catalyst particles having holes or channels passing through them from one end to the other are not novel and are commonly found in the chemical process industries. The catalyst particle of the invention is distinguished from such known particles by the fact that the first end surface opening of an axial channel is not axially aligned with the second end surface opening of the same axial channel. In other words, the openings of the channel are offset from each other. When the particle is cylindrical, so that the end surfaces can be said to have a radius, the centre of the first end surface opening of an axial channel is radially offset from the centre of said second end surface opening of the same axial channel. The amount of radial offset depends on the number of openings and their size, relative to the area of the end surface within which they are formed. For a catalyst particle having four axial channels in which the diameter of the end openings is less than about 40% of the diameter of the end surface, the first and second end openings may be radially offset by up to 90 degrees. Normally the first and second end openings may be radially offset by at least 10 degrees. Typically the offset may be from 15 to 70 degrees.

The catalyst particle may comprise at least one transverse channel extending from an opening in a side surface to communicate with said axial channel. The catalyst particle may comprise from 0 to 10 transverse channels. The catalyst particle may comprise from 1 to 100 transverse channels per cm2 of cross-section. The transverse channels may be straight, angled or curved. They may provide a tortuous path through the particle between the side surface opening and an axial channel. The transverse channel may have a cross-section which is of any shape, although generally circular, elliptical or polygonal shapes such as square/rectangular channels or triangular channels may be usual. The openings in the side surface of the catalyst particle may be located at any position between the two ends of the particle. When there is more than one transverse channel, their openings may be at, or centred on, respective locations which are at the same distance from one end of the particle, or at different distances. The number of transverse channels and their location is selected so that sufficient of the side surface is preserved to retain sufficient strength in the particle to enable it to be handled and used without significant risk of breakage. For example, if more than one of the transverse channels are located around the same circumference of the particle at the same distance from each end of the particle, then it is desirable that their area preserves at least 50% of the circumference as solid material.

The edges of the catalyst particle may be sharply angled. Edges of the catalyst particle may be rounded or chamfered. Rounded or chamfered edges are less susceptible to damage through handling of the catalyst particles. Rounded edges also provide a benefit in avoiding concentration of stress in the particle which could lead to particle breakage.

The catalyst particle may itself be catalytically active or it may be a catalyst support which is suitable for supporting a catalytically active material. The catalyst particle may comprise a catalytically active composition. By catalytically active composition we mean a composition which has catalytic properties for at least one chemical reaction. The catalyst particle may be formed entirely of one or more than one catalytically active composition. Alternatively the catalyst particle may be formed partially of at least one catalytically active composition, for example a catalytically active composition may be present at one or more surfaces of the catalyst particle. The catalytically active material may be present over the whole or only portions of the surfaces of the particle. Different catalytically active materials may be present at different surfaces of the particle. For example a catalytically active material may be present at the surfaces of one or more axial or transverse channels whilst either no catalytically active material is present at other surfaces of the particle or a different catalytically active material may be present at other surfaces of the particle. A catalytically active material may be present beneath a surface of the particle e.g. the catalytically active material is distributed in the form of an egg-shell. The catalytically active material may be present throughout or substantially throughout the catalyst particle. It is known in the design of catalysts to design catalyst particles having a catalytic material located at a particular depth beneath the surface of the particle in order to avoid loss of activity through abrasion of the catalyst surface during use.

Regardless of how the catalytically active material is present, different catalytic materials (e.g. 2, 3, 4 or 5) may be present. Moreover, one or more catalytically active materials, which may be the same or different, may be present over the whole or portions of the surfaces of the particle and one or more catalytically active materials, which may be the same or different, may be present beneath the surface of the particle and/or throughout or substantially throughout the catalyst particle.

When the catalyst particle is a catalyst support which is suitable for supporting a catalytically active material, it may be loaded with catalytically active material by methods known in the catalyst manufacturing industry, including metal vapour deposition, coating, impregnation, precipitation of a catalytically active composition, wash coating, pan coating and slurry dipping (dip coating). Suitable compounds for impregnation, precipitation and pan coating include soluble metal compounds such as metal nitrates, halides, carboxylates, sulphates etc. Suitable compounds for slurry dipping include insoluble metal compounds such as metals or metal oxides.

The catalyst particle in the form of a catalyst support may be formed from a variety of materials which are known for use as catalyst supports. Typical materials include metal oxides and ceramics such as alumina, silica, zirconia, titania, magnesia, silicon nitride, silicon carbide, carbon and mixtures thereof. A conventional ceramic catalyst support may also be used. The catalyst support powder may also comprise one or more transition metal compounds, including lanthanide metal compounds and actinide metal compounds, selected from metal oxides, metal hydroxides, metal carbonates, metal hydroxycarbonates or mixture thereof. The transition metal compound may comprise a single or mixed metal oxide or a composition comprising two or more transition metal oxides. Preferably, the catalyst support powder comprises an alumina, metal-aluminate, silica, alumino-silicate, titania, zirconia, magnesia, zinc oxide, or a mixture thereof.

Although the term “catalyst particle” has been used throughout this specification, we include catalytically inert particles in the term “catalyst particle”. Therefore catalyst particles according to the invention may not be used to catalyse a chemical reaction. As is known in the chemical industry, catalytically inert particles may be used to manage fluid flow, heat transfer, catalytic activity etc. by providing layers of such inert particles within a catalyst bed, mixing inert particles with catalytically active particles within a catalyst bed or by providing separate beds of inert particles. Catalyst particles according to the invention may be catalytically inert, i.e. they may not include a catalytically active component.

The catalytically active composition, when present, may comprise at least one metal or metal compound selected from the group consisting of Na, K, Mg, Ca, Ba, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, La, Hf, W, Re, Ir, Pt, Au, Pb, or Ce.

The metal of metal compound may preferably comprise a precious metal, e.g. comprising one or more of Pt, Pd, Ir, Ru, Re, optionally mixed with one or more transition metals. The metal or metal compound may preferably comprise one or more transition metal compounds, including lanthanide metal compounds and actinide metal compounds. The transition metal compounds may be a metal oxide, metal hydroxide, metal carbonate, metal hydroxycarbonate or mixture thereof. Transition metal oxides may comprise a single or mixed metal oxide such as a spinel or perovskite, or a composition comprising two or more transition metal oxides.

The catalytically active composition may further comprise one or more powdered inert materials such as alumina, silica, silicon nitride, silicon carbide, carbon and mixtures thereof. Ceramics such as cordierite may also be present. The catalytically active composition may comprise a zeolite.

Where the catalyst particle comprises one or more reducible metal compounds, it may be subjected to a reduction step to convert the metal compounds to the corresponding metals. This may be performed directly on the catalyst particle without a prior heating step, or may be performed after a heating step, to convert reducible metal oxides to the corresponding metals. The reduction may be achieved by exposing the catalyst particle to a hydrogen-containing gas stream at a temperature in the range 150 to 800°, preferably 150 to 600°C.

Catalysts comprising reduced metals may be pyrophoric and so it is desirable that the reduced metal in the catalyst particle is passivated by controlled exposure of the catalyst particle to an oxygen-containing gas stream to form a passivating layer on the reduced metal.

The catalyst particle according to the invention may have various dimensions. The length of the catalyst particle may be within the range from 0.5mm to 100mm. Typical particles may have a length in the range from 3-15 mm. The diameter or maximum width of the catalyst particle may be within the range from 0.5mm to 100mm. Typical particles may have a diameter or width in the range from 3-15 mm. A catalyst particle according to the invention includes a monolith suitable for automotive or stationary emission control devices. The monolith may comprise a honeycomb structure. The diameter or maximum width of the monolithic catalyst particle may be in the range from 10-1000 mm, such as 25-100 mm. The length of the monoliths may be in the range of 1-100 mm, such as 5-80 mm, for example 10-75 mm, e.g. 15-70 mm. Each monolith may be stacked on another monolith to create longer catalytic pathways.

The catalyst may be formed by any known manufacturing method. The complexity of the catalyst particle according to the invention makes manufacture by additive layer manufacturing (ALM) methods (also known as 3D printing) particularly advantageous.

Suitable methods of additive layer manufacturing are discussed in WO2012/032325. A suitable method comprises the steps of (a) forming a layer of a powdered catalyst or catalyst support material, (b) binding or fusing the powder in said layer according to a predetermined pattern, and (c) repeating (a) and (b) layer upon layer to form a catalyst particle. ALM processes are enabled by conventional 3D design computer packages that allow design of the catalyst particle as a so-called, “STL file”, which is a simple mesh depiction of the 3D shape. The STL file is dissected using the design software into multiple two-dimensional layers, which are the basis for the fabrication process. The fabrication equipment, reading the two-dimensional pattern, then sequentially deposits layer upon layer of powder material corresponding to the 2D slices. In order that the catalyst particle has structural integrity, the powder material is bound or fused together as the layers are deposited. The process of layer deposition and binding or fusion is repeated until a robust catalyst particle is generated. The un-bound or un-fused powder is readily separated from the catalyst particle, e.g. by gravity, or blowing. A number of ALM binding and fusion fabrication techniques are available, notably 3D printing and laser sintering techniques. Any of the techniques may however be used.

In laser sintering, the process comprises three steps in which a thin layer of powder material is initially applied to a base plate using a blade, roller or moving hopper. The thickness of the layer is controlled. Laser radiation is applied in two dimensions to fuse the layer. The laser position is controlled, e.g. using galvanometer mirrors, according to the desired pattern. After the layer is fused, the plate on which the layer rests is moved downwards by the thickness of one layer and a fresh layer of powders screened over the fused later. The procedure is repeated thus producing the catalyst particle in three dimensions. After the shape is formed, the un-fused powder is separated from the catalyst particle simply by gravity or by blowing it away.

Direct laser sintering performs the process at elevated temperature using a solid state fibre laser. Such a system is commercially available from Phenix Systems, for example as described in WO 2005002764.

An alternative approach is to use a powder material with a polymeric coating or a composition comprising a powder material and a polymeric binder. In this case, the laser acts to melt the binder. This technique has the advantage that the laser power may be considerably lower than the fusion method laser. Polymeric coating technology is available commercially from EOS GmbH. A further alternative, known as stereolithography, uses the powder as a dispersion in a monomer, which acts as a binder when it is “cured” in layers by photopolymerisation using a UV laser. The power material may be up to about 60% by volume in the monomer. Suitable equipment for performing this process is available commercially from the Cerampilot.

In these methods, but particularly the latter, the catalyst particle may be subjected to a subsequent heat treatment, which may be carried out to burn out and remove any polymeric binder and/or alter the physiochemical properties of the catalyst particle, such as its strength.

As an alternative to laser sintering or stereolithography, the ALM method may be based on printing of a binder onto the powdered material with or without subsequent heating. Generally this method uses a multiple array ink-jet printing head to spray a layer of a liquid binder on the powder layer to hold the particles together. The support plate moves down in the same manner as previously and again the procedure is repeated building up the catalyst particle as before. The layers in this case may be in the range 0.02 to 5.0 mm thick. Subsequent heat treatment is commonly applied to remove the binder. Suitable equipment for performing this process is available commercially from the Z-Corporation in the USA, which has been acquired by 3D Systems.

The additive layer manufacturing method preferably comprises a 3D printing or a laser sintering technique. Thus in one embodiment, the powder in each layer is fused by a laser. In another embodiment, the powder in each layer is bound together with a binder, which may be an inorganic binder such as a calcium aluminate cement or an organic binder, such as a phenolic polymer cellulose, gum or polysaccharide binder. A burnout additive may be included in the catalyst powder or binder to control the porosity of the resulting catalyst particle.

Howsoever the catalyst particle is formed it may be desirable to subject it to a subsequent heating step, which may be performed to burn out organic materials such as binders or poremodifying materials, and/or modify the physiochemical properties, e.g. convert non-oxidic metal compounds into the corresponding metal oxides and/or fuse the powdered material. The heating step may be performed at a maximum temperature in the range 300 to 1700°C, preferably 500 to 1200°C.

The catalyst particles, which may comprise a catalytically active material, may be used in the form of a bed of particles within a reactor. The ability to produce geometric shapes that may not be possible with traditional production methods allows better control over bed packing and/or the resultant pressure drop. This ability to control pressure drop can contribute to reactor efficiency. 3D printing allows the design of internal fluid flow paths which control thermal flow. As many catalytic processes are limited by temperature effects, the ability to control convective thermal transfer within the system may allow increased conversion efficiency and/or selectivity. Reactor design may also be constrained by thermal considerations i.e. getting heat in or out of the system effectively. Thus, 3D printing may offer more freedom in reactor design by controlling thermal flow.

The catalyst particles according to the invention may also offer an increased active surface area to volume ratio allowing reactions to be more efficient in a smaller catalyst bed. This may allow smaller catalyst beds to be designed, while may maintain the performance of traditional beds, thus reducing capital costs.

According to the invention, we therefore further provide a chemical reaction vessel containing a catalyst bed comprising a plurality of catalyst particles according to the invention. The reaction vessel has at least one opening for allowing chemical compounds to pass into and out of the vessel. The reaction vessel may be an axial flow or a radial flow reactor. A particle bed (catalyst bed) may be formed from different particles of the invention. Alternatively all of the particles forming a catalyst bed may be essentially identical (differing only within manufacturing tolerances). The size, shape and internal void space may vary between particles in the same catalyst bed. The nature or concentration of a catalytically active material may vary between particles in the same catalyst bed. Different catalyst particles may be mixed together to form an essentially homogeneous mixture of particles forming the bed. Alternatively a catalyst bed may be formed of distinct volumes within which the catalyst particles are similar but differ from the catalyst particles within a different volume of the bed. For example, a catalyst bed may be formed of layers comprising catalyst particles of the present invention in which the characteristics of size, shape, internal voidage, and/or catalytically active material differ between layers. The boundary between any two layers may be sharp or graduated. The boundary may be facilitated by a physical structure such as a support, e.g. in the form of a screen. Use of catalyst particles having a smaller voidage (intraparticle and/or inter-particle) may provide a method of controlling flow within the bed so that reaction rate may be controlled across the bed. Control of reaction rate in this way may be used to control the temperature profile within a catalyst bed.

The catalyst particles within a catalyst bed may be in an aligned form. In this instance, the catalyst bed may have a long-range order where the catalyst particles pack together over the whole or substantially the whole of the catalyst bed i.e. the geometric arrangement of the catalyst particles pack together such that repeating units of the catalyst particles are formed. The repeating units can be, for example, a packed plane or lattice of catalyst particles where the repeating unit in one part of the reactor is the same or substantially the same as the repeating unit in another part. The catalyst particles may self-assemble into an aligned catalyst bed on being deposited into the reactor. Re-assembly may be facilitated by incorporation of fracture planes or points for the purpose of controlled breakage during installation or service. The catalyst particles within a catalyst bed may be in an unaligned form. The catalyst particles therefore may be randomly arranged or may have a short-range order. In the latter instance, while there may be areas within the catalyst bed where the catalyst particles pack together in an ordered fashion, there is no or substantially no order over the whole or substantially the whole of the catalyst bed.

The catalyst particles within a catalyst bed may have an ordered orientation as they pack in an aligned or unaligned form in the bed. For example, the particles may pack together randomly but have a better than random probability of a certain orientation. The present invention envisages the advantage of the orientation of the particles by placing internal channels such that a greater proportion of the bed may follow a long-range ordered orientation. A method of carrying out a chemical reaction, according to the invention, comprises the step of contacting one or more starting chemical compounds with a catalyst bed comprising a plurality of catalyst particles according to the invention to form at least one product chemical compound. The contacting step normally takes place within a reaction vessel. The chemical reaction may include a sorption process for the removal of materials such as sulphur compounds or heavy metals, for example, from process streams for purification.

The chemical reaction may comprise any of a large number of known chemical transformations, including hydrogenation, oxidation, hydrodesulphurisation, steam reforming including pre-reforming, catalytic steam reforming, autothermal reforming and secondary reforming and reforming processes used for the direct reduction of iron, catalytic partial oxidation, a water-gas shift including isothermal-shift, sour shift, low-temperature shift, intermediate temperature shift, medium temperature shift and high temperature shift reactions, a methanation, a hydrocarbon synthesis by the Fischer-Tropsch reaction, methanol synthesis, ammonia synthesis, ammonia oxidation and nitrous oxide decomposition reactions, or selective oxidation or reduction reactions of internal combustion engine or power station exhaust gases.

The sorption process may comprise a method of treating a fluid mixture to selectively remove one or more target components of said mixture comprising contacting said fluid with a packed bed comprising a plurality of catalyst particles according to the invention such that at least a portion of said target components are transferred from said fluid mixture to said catalyst particles. The target components comprise sulphur, a compound of sulphur, a metal, a metal compound ora carbonaceous particulate material, for example. The sorption process may be a sorption selected from the recovery of sulphur compounds or heavy metals such as mercury and arsenic from contaminated gaseous or liquid fluid streams, or particulate matter such as carbonaceous particles, e.g. soot, from the exhaust gases of internal combustion engines and power stations. Although the term “catalyst particle” has been used throughout this specification, we include sorbent particles in the term “catalyst particle”. Therefore catalyst particles according to the invention may not be used to catalyse a chemical reaction. Catalyst particles according to the invention may not include a catalytically active component.

The invention will be further described, by way of example only, with reference to the accompanying drawings, which are:

Figure 1 A: a schematic perspective view of a first embodiment of catalyst particle according to the invention.

Figure 1 B: a plan view of the first end surface of the catalyst particle shown in Figure 1A.

Figure 1 C: a plan view of the second end surface of the catalyst particle shown in Figure 1A.

Figure 1 D: a schematic view of first and second end surfaces of the catalyst particle shown in Figure 1A.

Figure 2: a schematic view of a second embodiment of the invention.

Figure 3A: a schematic view of a section through a third embodiment of the invention; and Figure 3 B: showing three cross sections through the particle shown in Figure 3A.

Figure 4: Test data from Example 1.

Figure 5: a photograph of the particles shown in Figure 3.

Figure 6: Test data from Example 2.

Figure 1 A- D show views of a catalytic particle according to one embodiment of the invention. The particle 10 is generally cylindrical and has a circular cross section, a side surface 22 and first and second end surfaces 12 and 14, which are planar in this embodiment. Four channels 18 (only one channel is shown on the drawing for clarity purposes) extend through the particle from the first end surface to the second end surface, each communicating with a respective opening 16 in the first end surface and a respective opening 20 at the second end surface. The direction of the channel is not parallel to the axis of the cylinder 10, with the result that the openings 16 and 20 are not in alignment with each other. Figure 1D shows the plan views of end surfaces 12 and 14 superimposed on one another, which shows the offset of holes 20 from holes 16, which in this case is a radial offset of about 23 degrees.

Figure 2 shows a schematic view of a second embodiment of the invention. The particle 30 is similar to the particle 10, having axial channels with offset openings on the top and bottom end surfaces. In this embodiment there are also transverse channels 32 which extend from an opening in the side wall through the particle.

Figure 3A shows a perspective view of a section through a third embodiment of a catalyst particle according to the invention. The catalyst particle 40 is generally cylindrical having a side surface 42 formed by side wall 44 and two circular end surfaces formed by end walls 50 (only one of which is shown in Fig 3A). Openings 56 in the end wall form axial channels. As shown in Fig 3B, openings 56A in the first end wall 50A are not in axial alignment with openings 56B in end wall 50B. A cavity 52 is present in the particle, bounded by side wall 44, end walls 50 and a central structure 46 which is joined to the top and bottom end walls. Four transverse channels 48, having a generally square section in this embodiment, extend from the side surface 42 through wall 44 to the cavity 52. Figure 3B shows three cross sections through the particle shown in Figure 3A. The upper and lower sections depicted are transverse sections through the end walls 50A and 50B and the middle section is through a portion of the particle including the transverse channels 48.

Examples

Example 1 A catalyst comprising particles having the shape depicted in Figure 3, having a length of 5.4mm and a diameter of 6.0mm were manufactured. The four axial channels were 1,3mm in diameter at the surface and the transverse channels were 1.2 x 1.3mm. The particles was formed from alumina and manufactured using an additive layer manufacturing method using a 3D printer. The particles were coated with a slurry containing a solid commercial oxidation catalyst formulation at 40% solids concentration. The coating method used was by adding the formed catalyst particles to a beaker of the slurry, mixing, filtering off the excess slurry and then drying the coated particles at 110°C for 22 hours. The particles were then sieved and weighed. A catalyst was tested to perform oxidation of ammonia. In these tests a reactor basket of 40 mm internal diameter was charged with approximately 40g of catalyst. The catalyst comprised pellets of the shape shown in Figure 3 formed from a catalyst support material which was then coated with a slurry of a particulate commercial base metal catalyst composition. The catalyst pellets had a length of 5.4 mm and a diameter of 6mm. The axial channel openings had a diameter 1,3mm and the transverse channel openings 1.2 x 1.3 mm. A woven stainless steel gauze was clamped into the lower basket flange to support the catalyst. The catalyst bed was 54 mm deep and 40 mm in diameter. The catalysts were tested over 3 days under the following process conditions: 10 Nm3h"1 air, 10 % vol NH3, 200°C preheat and 4 bara. The evolved gases were analysed and the conversion efficiency (for NH3 to NO, expressed as a percentage) and amount of N20 by-product in the product gas stream recorded. The results are shown in Figure 4.

Example 2 A catalyst comprising particles having the shape depicted in Figure 3, having a length of 5.4mm and a diameter of 6.0mm were manufactured. The four axial channels were 1,3mm in diameter at the surface and the transverse channels were 1.2 x 1,3mm. The particles was formed from alumina and manufactured using an additive layer manufacturing method using a 3D printer. A metal cylinder with an inner diameter of 48mm and a fine wire mesh with 3.3mm apertures were manufactures. This was loaded with the catalyst particles and subjected to back pressure measurements. Pressure measurements were taken at flow rates of air at 50m3/h and 80m3/h. The results comparing the bare (unloaded) cylinder to the particle loaded cylinder are shown in Figure 6.

Claims

1. A catalyst particle in the form of a three-dimensional shaped particle in the general form of a cylinder or prism having an axis, one or more side surfaces generally parallel to said axis and first and second end surfaces generally transverse to said axis having at least one axial channel extending through the particle from a first end surface opening in the first end surface to a second end surface opening in the second end surface and at least one transverse channel extending from an opening in a side surface to communicate with said axial channel; characterised in that said first end surface opening of an axial channel is not axially aligned with said second end surface opening of the same axial channel.

2. A catalyst particle according to claim 1, in the general form of a cylinder having a circular, elliptical parabolic or hyperbolic cross-section.

3. A catalyst particle according to claim 1, in the general form of a prism having from three to twenty side surfaces and wherein said prism has a cross-sectional shape of a regular polygon, an irregular polygon, a splined shape or a star.

4. A catalyst particle according to any one of the preceding claims wherein one or both of said end surfaces is planar.

5. A catalyst particle according to any one of the preceding claims wherein one or both of said end surfaces is convex or concave.

6. A catalyst particle according to any one of the preceding claims wherein one or both of said end surfaces is undulating.

7. A catalyst particle according to any one of the preceding claims wherein one or both of said end surfaces is not normal to the axis of the particle.

8. A catalyst particle according to any one of the preceding claims wherein one or both of said end surfaces is normal to the axis of the particle.

9. A catalyst particle according to any one of the preceding claims comprising from 2 to 20 axial channels.

10. A catalyst particle according to any one of claims 1 to 8 comprising from 2 to 100 axial channels per cm2 of cross-section.

11. A catalyst particle according to any one of the preceding claims, wherein the centre of said first end surface opening of an axial channel is radially offset from the centre of said second end surface opening of the same axial channel by up to 90 degrees.

12. A catalyst particle according to any one of the preceding claims, wherein the centre of said first end surface opening of an axial channel is radially offset from the centre of said second end surface opening of the same axial channel by at least 10 degrees.

13. A catalyst particle according to any one of the preceding claims comprising from 1 to 20 transverse channels.

14. A catalyst particle according to any one of claims 1 to 12 comprising from 1 to 100 transverse channels per cm2 of cross-section.

15. A catalyst particle according to any one of the preceding claims comprising a catalytically active composition having catalytic properties for at least one chemical reaction.

16. A catalyst particle according to claim 15, wherein said catalytically active composition comprises at least one metal or metal compound selected from Na, K, Mg, Ca, Ba, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Sn, Sb, La, Hf, W, Re, Ir, Pt, Au, Pb, or Ce and compounds thereof.

17. A catalyst particle according to claim 15 or claim 16, wherein the catalytically active composition is distributed on the surface of the catalyst particle and/or beneath the surface of the catalyst particle.

18. A catalyst particle according to any one of claims 15 to 17, wherein the catalytically active composition is distributed throughout or substantially throughout the catalyst particle.

19. A chemical reaction vessel containing a catalyst bed comprising a plurality of catalyst particles according to any one of claims 1 to 18.

20. A method of carrying out a chemical reaction comprising the step of contacting at least one starting chemical compound with a catalyst bed comprising a plurality of catalyst particles according to the invention to form at least one product chemical compound.

21. A method according to claim 2020, wherein said chemical reaction comprises a reaction comprising hydrogenation, dehydrogenation, oxidation, hydrodesulphurisation, steam reforming including pre-reforming, catalytic steam reforming, autothermal reforming, secondary reforming, reforming processes used for the direct reduction of iron, catalytic partial oxidation; a water-gas shift including isothermal-shift, sour shift, low-temperature shift, intermediate temperature shift, medium temperature shift and high temperature shift reactions; a methanation, a hydrocarbon synthesis by the Fischer-Tropsch reaction, methanol synthesis, ammonia synthesis, ammonia oxidation, nitrous oxide decomposition, selective oxidation or reduction reactions of internal combustion engine or power station exhaust gases.

22. A method of treating a fluid mixture to selectively remove one or more target components of said mixture comprising contacting said fluid with a packed bed comprising a plurality of catalyst particles according to any one of claims 1 to 18 such that at least a portion of said target components are transferred from said fluid mixture to said catalyst particles.

23. A method according to claim 22, wherein said target components comprise a material selected from the group consisting of sulphur, a compound of sulphur, a metal, a metal compound and a carbonaceous particulate material.

24. A method according to claim 20 or claim 21, wherein said one or more starting chemical compound is selected from the classes of chemical compounds consisting of hydrocarbons, nitrogen oxides, substituted hydrocarbons, alcohols, amines, ethers, aromatic hydrocarbons and substituted aromatic hydrocarbons.