GB2451863A - Core-shell catalysts and absorbents - Google Patents

Abstract

Active inorganic composites are disclosed which have a core-shell structure which comprises a particulate inorganic core and a shell layer comprising a plurality of inorganic shell particles. The composites may be manufactured by methods utilizing charge reversal to ensure that inorganic particulate material of the shell layer is attracted and bonded to the core particle. The materials find use as catalysts and adsorbents and separation media. The core may be a zeolite and the shell layer may be a zeolite or a mixed metal oxide such as a perovskite.

Description

CORE-SHELL COMPOSITE INORGANIC MATERIALS

INTRODUCTION

100011 The present invention is concerned with composite inorganic materials having a core-shell structure, methods for their preparation and with processes that utilize these materials as catalysts and/or adsorbent materials and/or separation materials. More specifically, this invention is concerned with composite inorganic materials having a core-shell structure derived from two or more particulate inorganic materials, at least one of which is an active material.

BACKGROUND TO THE INVENTION

[00021 Composites of active inorganic materials are known in the art. One group of such materials is composite inorganic catalysts and absorbents derived from, for example, molecular sieve materials and/or metal oxides especially mixed metal oxides.

[00031 Molecular sieves find many uses in physical, physicochemical, and chemical processes; most notably as selective sorbents, effecting separation of components in mixtures, and as catalysts. In these applications the pore structure within the molecular sieve material is normally required to be open; it is then a prerequisite that any structure-directing agent, or template, that has been employed in the manufacture of the molecular sieve be removed, usually by calcination.

Numerous materials are known to act as molecular sieves, among which zeolites form a well-known class.

100041 In International Application WO 94/25151 is described a supported inorganic layer comprising optionally contiguous particles of a crystalline molecular sieve, the mean particle size being within the range of from 20 nm to 1im. This is a membrane.

[0005J In International Application WO 96/0 1683 a membrane structure is described which comprises a planar support, a seed layer and an upper layer.

100061 In International Application WO 97/25 129 a membrane structure is described which comprises a crystalline molecular sieve layer on a planar support and an additional layer of refractory material to occlude voids in the molecular sieve layer.

(00071 In international Application WO 96/0 1686 a membrane structure is described which comprises a substrate, a zeolite or zeolite-like layer, a selectivity enhancing coating in contact with the zeolite layer and optionally a permeable intermediate layer in contact with the substrate.

[00081 In International Application WO 99/2803 I a zeolite catalyst is described which is partially coated with a second zeolite and having controlled surface acidity and which may be used as a catalyst for hydrocarbon conversion processes.

100091 In International Application WO 99/28032 a zeolite catalyst is described which is bound by MFI structure type zeolite and which may be used as an adsorbent or as a catalyst for hydrocarbon conversion processes.

10010) In International Application WO 2000/66263 is described a zeolite bound catalyst containing at least three different zeolites and its use as a catalyst for hydrocarbon conversion processes.

10011) In Published United States Patent Application No. US2002/0179887 is described an inorganic composite comprising perovskite supported on an alumina support. The composite is prepared by the physical mixing of perovskite and alumina followed by sintering.

[00121 In United States Patent No. 6,372,686 is described an inorganic composite comprising perovskite supported on a cordierite or an alumina support. The composite is prepared by washcoating techniques.

10013) In International Application WO 97/33684 there is described a process for the manufacture of molecular sieve films which utilizes colloidal zeolites in combination with charge reversal to deposit a monolayer of colloidal zeolite on a substrate which is then grown into a thin continuous and dense film.

100141 In United States Patent No. 5,705,222 is described a process for preparing nanocomposite particles. The particles have an inner core covered with a polymer layer and an outer layer of shell particle coatings. The nanocomposites are used in the manufacture of ceramic bodies and are derived from nitrides, carbides or metal oxides.

10015] Various techniques have been used in the art to prepare composite catalysts but these techniques have problems and limitations. One particular challenge is to be able to effectively incorporate multiple catalytic and/or adsorbent functionalities in a single composite catalyst. It is particularly difficult to produce core-shell catalyst and adsorbent composite structures without detrimentally affecting the properties of the core component of the composite, whilst at the same time obtaining the desired type and quality of shell component of the composite. It is often found that in attempting to prepare a particular shell material the core material is changed or its properties are detrimentally affected. In some instances it has been found to be impossible to prepare certain shell structures in the presence of certain core materials; the nature of the core material is such that conventional synthesis and manufacturing techniques are unable to provide the desired shell material. A further problem is that in many applications it is envisaged that the ratio of core material to shell material in the final composite will be critical in obtaining optimum performance from the composite. The problem here is that obtaining the desired proportions of core to shell is fraught with difficulty due to the lack of control provided by conventional manufacturing technfques and material limitations.

10016) Therefore, there is a continuing need for new composite inorganic materials and for easily controllable methods for their manufacture that provide catalytic and/or adsorbent materials of good quality and acceptable performance.

SUMMARY OF THE INVENTION

100171 It is an object of the present invention to provide composite inorganic materials having a core-shell structure that are catalytically active and/or have adsorbent and/or separation properties, methods for the manufacture of such composites and their use in adsorption and/or separation and/or hydrocarbon conversion processes.

10018) The preseni invention accordingly provides an active inorganic composite having a core-shell structure, the core comprising particulate inorganic material and the shell layer comprising a plurality of particles of inorganic material, wherein at least one of the materials of the core and/or at least one of the materials of the shell is an active material.

100191 The active inorganic composites of the present invention are active because they comprise at least one active material. The term "active" in relation to the materials used and composites of the present invention and as used herein refers to inorganic materials that are catalytically active and/or have adsorbent and/or separation properties. Thus, the active inorganic composites are characterised by the presence of catalytic and/or adsorbant and/or separation functionality, otherwise termed active functionality, preferably multiple such active functionalities.

[00201 The present invention further provides for a method for the manufacture of an active inorganic composite having a core-shell structure, which method comprises (a) treating (i) a particulate inorganic core precursor A and/or (ii) a plurality of particles of one or more inorganic shell precursor materials B, so as to induce a change in the surface charge of the particles of A and/or B such that the particulate core precursor A has an opposite surface charge from that of the particles of shell precursor materials B and (b) bringing the oppositely charged particles of A and B into contact with each other under conditions such that the particles of inorganic shell precursor material(s) B become bonded to the surface of the particulate inorganic core precursor to form the active inorganic composite having a core-shell structure.

100211 The above is alternatively stated as a method for the manufacture of an active inorganic composite having a core-shell structure, which method comprises (a) treating (I) a particulate inorganic core precursor A, or (ii) a plurality of particles of one or more inorganic 4.

shell precursor materials B, or (iii) a particulate inorganic core precursor A and a plurality of particles of one or more inorganic shell precursor materials B, so as to induce a change in the surface charge of the particle(s) of A and/or B such that the particulate core precursor A has an opposite surface charge from that of the particles of shell precursor materials(s) B and (b) bringing the oppositely charged particles of A and B into contact with each other under conditions such that the particles of inorganic shell precursor material(s) B become bonded to the surface of the particulate inorganic core precursor A to form the active inorganic composite having a core-shell structure.

100221 In a further aspect the present invention provides a conversion process for converting hydrocarbons comprising contacting a hydrocarbon feedstream under hydrocarbon conversion conditions with an active inorganic composite of the invention as defined above or an active inorganic composite manufactured by the method as defined above, to effect conversion of the hydrocarbon feedstream.

10023] In yet another further aspect the present invention provides an adsorption or separation process which comprises contacting a feedstream containing one or more adsorbates under adsorption or separation conditions with an active inorganic composite of the invention as defined above or an active inorganic composite manufactured by the method as defined above, to effect adsorption or separation of one or more of the adsorbates from the feedstream.

(0024] Other features, aspects and advantages of the invention will become better understood with reference to the following description of the invention, the claims, and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

100251 FIGURE 1 is the X-Ray Diffraction (XRD) pattern for a mixed metal oxide (perovskite) precursor material (B) of formula: (Lao6Cao4Feo2Mn0 803) prepared in accordance with Example 5.

10026] FIGURE 2 is the Scanning Electron Micrograph (SEM) for the material of Figure 1.

100271 FIGURE 3 shows the SEM of a ZSM-5 core crystal that has been treated with perovskite particles without removal of excess cationic polymer, as prepared in accordance with

Example 6.

10028] FIGURE 4 shows the SEM for an active inorganic composite according to the invention having a shell of perovskite particles on a ZSM-5 core crystal, prepared in accordance

with Example 7.

10029] FIGURE 5 shows the XRD pattern for the material of Figure 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[00301 In the active inorganic composites of the present invention the core comprises a particulate inorganic material, and it is envisaged in one embodiment that the core may comprise an active material imparting the desired activity to the composite. The core material may comprise a single material or a mixture of different materials. The particulate core may be a single particle or alternatively an agglomerated particle comprising a plurality of smaller particles. The particles of such plurality of smaller particles may be of the same material or may be two or more particles of different materials. In this embodiment one or more or all of the particles making up the agglomerated particle may be an active material. Hereinafter the particulate core, whether comprising a single particle or an agglomeration of particles, may simply be referred to as a "core" or "particle" for convenience.

[0031] In a further aspect of the present invention it is envisaged that the shell layer of the active inorganic composite may comprise one or more active materials that impart the desired activity to the composite. It is envisaged that the shell layer may comprise particles that are substantially identical to each other in terms of their chemical composition and/or properties and/or size and/or structure and/or shape. Alternatively, the particles making up the shell layer may be two or more materials that differ from each other in some way, such as composition and/or properties and/or size and/or structure and/or shape; it is preferred however that at least one of these particles is an active material and more preferably that all of the particles are active materials. When the shell layer comprises a plurality of different particulate materials it is envisaged that substantially all of the materials may be active materials. It is also envisaged that when there are two or more different particulate materials in the shell layer they may be materials having differing activity, meaning different types and/or magnitudes of activity.

[0032] The core and shell may comprise particles of the same material type e.g. they may both be molecular sieve materials such as materials with catalytic activity and/or adsorption and/or separation properties. The core and shell may comprise particles of the same material.

[0033] The active inorganic composite of the present invention may have an inorganic core which is active and an inorganic shell which is inactive, or an inorganic core which is inactive and an inorganic shell which is active, or it may be a composite in which both the core and shell are active material.

100341 The shell of the active inorganic composite may comprise a single layer of inorganic particles and the layer may be contiguous, meaning that each particle of the shell is in contact with at least one other shell particle. Preferably each shell particle is in contact with at least two, more preferably several, other shell particles. This arrangement results in a film like layer of shell material encapsulating the particulate core (particle or particles). The particles of the shell may be in the form of a monolayer. The term monolayer in the context of the present invention is taken to mean a layer comprising particles which are substantially in the same plane as adjacent particles deposited on a substrate, ie the particulate core, It will be understood that the monolayer will be disposed on the plane (which normally will not be flat) defined by the surface of the particulate core. The particles and other materials if present may be close packed to provide a classical monolayer. Alternatively the particles (and other materials if present) need not be close packed and therefore are present as a sub-monolayer.

100351 The present invention is particularly suitable for the production of thin shell layers. The shell layer may for example have a maximum thickness of 2000 nm preferably of 1000 nm, more preferably of 500 nm and most preferably of 250 nm. The minimum thickness of the shell will depend on the diameter of the shell particles but may be, for example 10 nm, which thickness is therefore the preferred lower end of the shell thickness ranges where the upper end of those ranges are the maximum values given above. Preferably the shell thickness and/or the average shell thickness is in the range of from 10 to 2000 nm, more preferably 25 to 1000 nm and most preferably 50 to 500 nm.

10036] The active inorganic composite may have a larger specific surface area than that of the core particle even though the shell component of the composite is thin and the overall particle dimensions of the composite particle are not significantly different from those of the core particle. The increase in specific surface area is due to the larger specific surface area presented by the shell layer due to the shape of the particles making up the shell layer and/or the physical form of the layer and/or to the pore structure (if any) of the material employed for the shell particles. The active inorganic composite may for example have a specific surface area that is increased, depending on the nature of the material selected for the shell particles, by 5% or greater compared to the specific surface area of the core particle; preferably it is increased by 10% or greater, more preferably increased by 20% or greater, more preferably increased by 30% or greater and most preferably increased by 50% or greater. The measurement of specific surface area may be by any convenient method, such as BET t00371 In the active inorganic composite of the present invention the particulate core is of larger dimensions than the particles that make up the shell layer The particulate core (whether a single particle or an agglomerate of two or more particles) may be considered to have a particle size' that is the largest dimension of the particle or agglomerate. The "average particle size" of a plurality of core particles and/or agglomerates that are employed in manufacturing the active inorganic composites may be determined by measuring the largest dimension of a representative number (for example, 30) of representative core particles or agglomerates eg by means of scanning electron microscopy. The average particle size can then be calculated by normal mathematical means, that is summing the largest dimension of"n" (say, 30) representative particles and dividing the sum by "n". It is preferred that the particulate core of the active inorganic composite has an average particle size of 100 nm or greater, more preferably 500 nm or greater, even more preferably 600 nm or greater and most preferably 1000 nm or greater.

Preferably the particulate core has an average particle size of 100 to 5000 nm, more preferably to 3000 nm, even more preferably 400 to 2000 nm and most preferably 500 to 1000 nm. It is preferred that the shell particles have an average particle size of 1000 nm, more preferably 500 nm, even more preferably 300 nm such as 200 nm and most preferably < 100 nm.

Ideally the shell particles have an average particle size within the range of from I to 300 nm, more preferably within the range of from 2 to 200 nm, even more preferably within the range of from 5 to 150 nm and most preferably within the range of 10 to 100 nm.

100381 The particulate core and the particles of the shell may be of any inorganic material with the proviso that the core and/or the shell comprises at least one active inorganic material as hereinbefore defined.

10039] One preferred class of active materials for use in the active inorganic composites of the present invention are molecular sieves. Molecular sieves can be classified in various categories, for example according to their chemical composition and their structural properties. A group of molecular sieves of commercial interest is the group comprising the zeolites, which are defined as crystalline aluminium silicates. Another category of interest is that of the metal silicates, structurally analogous to zeolites, but for the fact that they do not contain aluminium (or only very small amounts thereof). Suitable molecular sieves for use in the present invention therefore include silicates, alumi nosil icates, aluminophosphates, sil icoalum inophosphates, metalloalum inophosphates and metal loaluminophosphosi I icates. An excellent review of molecular sieves is given in "Molecular Sieves -Principles of Synthesis and Identification" (R.

Szostak, Van Reinhold, New York, 1989).

100401 Apart from their chemical composition molecular sieves are also classified according to their structure type. Representative examples are molecular sieves/zeolites of the structure types AFI, AEL, BEA, CHA, EUO, FAU, FER, KFI, LTA, LTL, MAZ, MOR, MEL, MiT, MTW, OFF, TON, MWW and, especially, MFI; as well as other microporous materials for which no structure type code has been assigned such as intergrown materials like ZSM-48 or precursor materials such as members of the MCM-22 family. Some of these materials whilst not being true zeolites as such are frequently referred to in the literature as such. Examples of molecular sieves that are of major interest for the present invention include those of structure type LTL, MFI, FAU, MOR, particularly the materials ZSM-5, ZSM-12, ZSM-23, ZSM-48 and materials of the MCM-22 family.

(00411 The term "MCM-22 family material" (or "material of the MCM-22 family" or "molecular sieve of the MCM-22 family" or "MCM-22 family zeolite"), as used herein, includes one or more of: * molecular sieves made from a common first degree crystalline building block unit cell, which unit cell has the MWW framework topology. (A unit cell is a spatial arrangement of atoms which if tiled in three-dimensional space describes the crystal structure. Such crystal structures are discussed in the "Atlas of Zeolite Framework Types", Fifth edition, 2001, the entire content of which is incorporated as reference); * molecular sieves made from a common second degree building block, being a 2-dimensional tiling of such MWW framework topology unit cells, forming a monolayer of one unit cell thickness, preferably one c-unit cell thickness; * molecular sieves made from common second degree building blocks, being layers of one or more than one unit cell thickness, wherein the layer of more than one unit cell thickness is made from stacking, packing, or binding at least two monolayers of one unit cell thickness. The stacking of such second degree building blocks can be in a regular fashion, an irregular fashion, a random fashion, or any combination thereof; and * molecular sieves made by any regular or random 2-dimensional or 3-dimensional combination of unit cells having the MWW framework topology.

[00421 Molecular sieves of the MCM-22 family include those molecular sieves having an X-ray diffraction pattern including d-spacing maxima at 12.4�0.25, 6.9�0.15, 3.57�0.07 and 3.42�0.07 Angstrom. The X- ray diffraction data used to characterize the material are obtained by standard techniques such as using the K-alpha doublet of copper as incident radiation and a diffractometer equipped with a scintillation counter and associated computer as the collection system. The MCM-22 family materials are further discussed in W.J. Roth, Stud. Surf. Sc. Cat.

158, 19-26 (2005).

100431 Materials of the MCM-22 family include MCM-22 (described in U.S. Patent No. 4,954,325), PSH-3 (described in U.S. Patent No. 4,439,409), SSZ-25 (described in U.S. Patent No. 4,826,667), ERB-l (described in European Patent No. 0293032), ITQ-1 (described in U.S. Patent No 6,077,498), ITQ-2 (described in International Patent Publication No. W097/17290), MCM-36 (described in U.S. Patent No. 5,250,277), MCM-49 (described in U.S. Patent No. 5,236,575), MCM-56 (described in U.S. Patent No. 5,362,697), UZM-8 (described in U.S. Patent No. 6,756,030), and mixtures thereof. Molecular sieves of the MCM-22 family are useful as the alkylation catalysts. Particular members of the MCM-22 family that may be used in alkylation reactions include MCM-49, MCM-56 and isotypes of MCM- 49 and MCM-56, such as ITQ-2.

[0044J The morphology of the active material employed as particulate core and/or as the shell particles in the composites of the invention may be varied. For example the particles of core or shell may be substantially spherical or of layered or pillared structure as discussed in Roth (idem).

100451 The preferred molecular sieve that may be employed as core and/or shell will depend on the chosen application of the composite. This may be, for example, separation e.g. by adsorption or catalytic applications, or combined reaction and separation. The molecular sieve selected will also depend on the size of the molecules being treated. There are many known ways to tailor the properties of the molecular sieves, for example, structure type, chemical composition, ion-exchange, and activation procedures.

[0046J Further classes of active materials that may be used in the present invention are the active metal oxides and especially the active mixed metal oxides. These are described in, for example, Rodriguez, Catalysis Today 85, 177-192 (2003). Mixed-metal oxides play a very important role in many areas of chemistry, physics, materials science, and geochemistry. In technological applications, they are used in the fabrication of microelectronic circuits, piezoelectric devices and as catalysts. For example, mixed metal oxides are active catalysts for the selective hydrogenation and isomerization of olefins, the water-gas shift reaction, dehydrogenation of alcohols, the oxidation of CO and alkanes, NO reduction, S02 destruction, photolysis of water, etc. In principle, several phenomena can contribute to the superior performance of these complex systems, so scientific criteria are applied in choosing the "right" combination of elements when designing a mixed-metal oxide catalyst. With respect to single-metal oxides, the chemical behavior of mixed-metal oxides may be different as a consequence of several factors. In some situations, the cations in a mixed-metal oxide can work in a cooperative way catalyzing different steps of a chemical process. Furthermore, the combination of two metals in an oxide matrix can produce materials with structural or electronic properties that can lead to superior catalytic activity or selectivity. At a structural level, a dopant can introduce stress into the lattice of an oxide host, inducing in this way the formation of defects that have a high chemical activity. On the other hand, the lattice of the oxide host can impose on the dopant element non-typical coordination modes with a subsequent perturbation in the dopant chemical -10-properties. Finally, metal/metal or metal/oxygen/metal interactions in mixed-metal oxides can give electronic states not seen in single-metal oxides.

[0047] The nature of the mixed metal oxide is preferably designed in dependence on the type of application envisaged for the active inorganic composite of the invention. Thus, from a knowledge of the catalytic function required for the target application, the "right" combination of elements is selected in order to make a mixed metal oxide having suitable catalytic performance for the application. Guidelines for such design of mix metal oxides have been described in the literature. Examples of such publications, each incorporated herein by reference, include; I.E Wachs et al., Catalysis Today, 78, 13-24 (2003); I.E Wachs et al., Catalysis Today, 100, 79-94 (2005); E. Bordes et al., Catalysis Today, 61, 197-20 I (2000); and E. Bordes et al., Phys. Chem.Chem. Phys., 1, 5735-5744 (1999).

[0048] For some applications, the metal oxides/mixed metal oxides may for example comprise one or more metals selected from La, Ca, Fe and Mn. The mixed metal oxides may have for example a perovskite structure.

[0049] It is preferred that the shell layer is derived from particles that are colloidal in nature.

When the shell particles are molecular sieve it is preferred that they are nanocrystals and are molecular sieve nanocrystals with a size of less than 200 nm, preferably 120 nm, the crystal structure of which can be identified by X-ray diffraction. There are various methods described in the art for the preparation of colloidal particles. International Application WO 94/05597, the teaching of which is hereby incorporated by reference, describes a method whereby it is possible to synthesize colloidal suspensions of discrete molecular sieve particles. Such particles are suitable for use in the preparation of shell structures according to the present invention.

Molecular sieves such as zeolites or crystalline microporous metal silicates are generally synthesized by hydrothermal treatment of a silicate solution with a well-defined composition.

This composition, as well as the synthesis parameters such as temperature, time and pressure, determine the type of product and the crystal shape obtained. These materials may also be prepared in accordance with the method set forth in WO 93/08 125, the teaching of which is hereby incorporated by reference. In that method, a synthesis mixture is prepared by boiling an aqueous solution of a silica source and optionally an organic structure directing agent, under conditons sufficient to cause substantially complete dissolution of the silica source. The organic structure directing agent, if used, is advantageously introduced into the synthesis mixture in the form of a base, specifically in the form of a hydroxide, or in the form of a salt, e.g., a halide,

-II -

especially a bromide. Mixtures of a base and a salt thereof may be used, if desired or required, to adjust the pH of the mixture.

100501 The colloidal particles are capable of forming a stable dispersion and produce particularly suitable shell layers for the active inorganic composites of the present invention Representative examples of molecular sieves (zeolites) which can be used to prepare the shell layer, for example from colloidal particles include but are not limited to those of structure types AFI, AEL, BEA, CHA, EUO, FAU (includes zeolite X and zeolite Y), FER, KFI, LTA, LTL, MAZ, MOR, MEL, Mm, MIT, MTW, MWW, OFF, TON, zeolite beta, ZSM-48 and especially MFI zeolites. Other suitable molecular sieve particles may be prepared by the methods described in PCT/EP96/03096, PCT/EP96/03097, and PCT/EP96/03098, the disclosures of which are all hereby incorporated by reference.

100511 Ihe core and/or shell of the active inorganic composite may each comprise a mixture of more than one material, and the additional materials may or may not be inorganic materials and/or may not be active inorganic materials. It is preferred that both the core and the shell comprise at least one active inorganic material. It is preferred that the core comprises a single inorganic active material. It is also preferred that the shell comprises a single inorganic active material that may or may not be the same material as the core. The core and the shell may, and for many uses advantageously do, consist essentially of inorganic active material e.g. molecular sieve or mixed metal oxide catalysts and/or adsorbents, or they may be a composite of the inorganic active material and intercalating materials which may be organic or inorganic. The intercalating materials may be the same in both the core and the shell. For the shell the intercalating materials may be applied simultaneously with or after deposition of the active inorganic material. The intercalating material is advantageously present in a sufficiently low proportion of the total material of the shell such that the active inorganic particles remain contiguous. Suitable materials for the core and for the shell include, for example, silica and/or metal oxide; metal particles; metal particles with metal oxides and/or silica. The shell layer may be formed, for example from a solution containing nanocrystalline or colloidal active inorganic particles or a mixture of metal oxide and nanocrystalline or colloidal active inorganic particles or a mixture of nanocrystalline or colloidal active inorganic particles and colloidal metal.

Preferably, nanocrystalline or colloidal active inorganic materials or a mixture of nanocrystalline or colloidal active inorganic material and metal oxide are used to form the shell layer. The metal oxides from which the shell layer may be prepared may be, for example, colloidal metal oxides or polymeric metal oxides prepared from sol-gel processing. In this aspect of the present invention the metal oxides which may be used herein are preferably selected from the group consisting of colloidal alumina, colloidal silica, colloidal zirconia, colloidal titania and polymeric metal oxides prepared from sol-gel processing and mixtures thereof. The colloidal metals which can be used include copper, platinum and silver.

100521 The method of the present invention requires that either the surface of the core particles are treated or the surfaces of the shell particles are treated or both the core and shell particles are treated so as to induce a reversal of the surface charge of one or both of the particle groups. It is preferred that when the core is treated its surface charge is reversed from negative to positive.

Charge reversal may be achieved by pH control or other chemical and/or non-chemical methods.

In a preferred embodiment the surface charge reversal of the core and/or shell particles is achieved by chemical treatment. Preferably this is achieved through the use of one or more polymers and most preferably the polymer or polymers used are cationic polymers. In a preferred embodiment the treated particle or particles are washed after treatment so as to remove excess chemical treatment agent.

100531 When molecular sieve materials are used as the core particle it should be remembered that the majority of the molecular sieves of interest in the present invention are metal silicates and these may be characterized as having a negative charge in neutral or alkaline aqueous suspensions. The magnitude of the surface charge is generally at its highest in the pH range 8-12 and hence this pH range is suitable for adsorbing (bonding) shell particles onto these core particles.

[0054j In addition certain types of molecular sieves are typically prepared in the presence of tetraalkyl ammonium ions in stoichiometric excess. In such cases, the adsorption (bonding) of shell particles is promoted if the excess tetraalkyl ammonium ions in these particles are replaced by, for instance, ammonium ions. This may be achieved by allowing the shell particle suspension to pass through a column packed with an organic ion exchange resin in the ammonium form, or by adding ion exchange resin in such form to a particle-containing suspension and, after complete ion exchange, separating the ion exchange resin from the suspension through for example filtration or centriluigation.

100551 The charge reversal may be achieved by treating the particles with a cationic polymer, preferably in the form of a solution containing for example 0.1 to 4 weight % cationic polymer.

The pH value for the charge reversal is selected after considering both the particle and the polymer chemistry. However, cationic polymers may be used within a wide p1-I range. The repeat unit in such polymers can be for example quaternary amines with hydroxyl groups in the main chain. An example of such a polymer is Berocell 6100, a water soluble polymer with a repeat -13-unit [CH2CH(OH)CH2N(CH3)2]+ and a molecular weight of about 50,000 g/mol, marketed by Akzo Nobel AB, Sweden. Other cationic polymers are well known in the art.

(0056] For certain particles it may be advantageous, in order to impart to them satisfactory surface properties, to submit them to one or more pre-treatment steps, aimed at cleaning their surface or modifying their surface chemistry. In such cases, it is advantageous to treat the particles in one or more alkaline, acid or oxidizing cleaning steps, or combinations of such steps.

Another way of enhancing shell layer deposition is to carry out the adsorption (bonding to the particulate core) in two or more steps, as the case may be, with an intermediate charge reversal.

In some cases coupling agents may be used in the particle that is not subjected to surface charge reversal, for instance of the silane type. These may be used according to known techniques. Such coupling agents are characterized by the fact that they consist of two functional groups, one of them having affinity for one particle surface e.g. core particle surface and the second one binding to the other particle surface e.g. of the shell particles. For bonding molecular sieve e.g. zeolite or metal silicate particles to particle surfaces that are highly metallic in nature, silane containing a thiol group is often suitable. Coupling agents are made by for example Dow Corning and Union Carbide and they are generally used for incorporating inorganic fillers and reinforcing agents into organic polymers. The coupling agent may be deposited on the particle and then hydrolyzed to provide the required surface charge or it may have inherent functionality which provides the required charge. Suitable coupling agents are chemicals which are well known in the art.

Examples are those supplied by OSi specialties as "Silquest Silanes" and as indicated in their 1994 brochure for these products. The coupling agent may be utilized in conjunction with the cationic polymers as indicated above to provide the required surface charge. Thus the charge reversal or control may be achieved by: utilization of the appropriate pH of the solution into which the substrate is immersed and which contains the particles to induce opposite charges on particle surfaces; deposition of a cationic polymer which imparts appropriate charge reversal; or utilization of a coupling agent with or without hydrolysis andl or with a suitable cationic polymer.

100571 The shell deposition process may be repeated a number of times in order to ensure the complete formation of a true shell layer e.g. a monolayer or to achieve the desired density of coverage of the core particle substrate surface with a sub-monolayer.

100581 For certain types of molecular sieves, a final calcination step is desirable and often necessary to burn off the organic molecules in the pore structure, thus providing an internal pore structure available for adsorption, separation, catalysis or ion exchange. It is preferred that the -14 -active inorganic composites prepared according to the present invention are calcined. For example, this may comprise a treatment in air at a temperature exceeding 400 °C.

[0059) In a further embodiment, after formation of the shell via deposition of particles, the resultant product may not be an active inorganic composite because the materials used as the core or as the shell layer may not be active inorganic materials. In this situation a further process step is required to convert one or more of the materials of the core and/or shell from inactive inorganic materials or precursors into the desired active inorganic material or materials. For example the shell may comprise silica, which may be converted to molecular sieve e.g. a zeolite under appropriate conditions e.g. hydrothermal synthesis conditions and with use of an appropriate synthesis solution. After hydrothermal treatment the shell is converted from inactive material into active material to produce an active inorganic composite according to the present invention, it may be that all of the material of the shell layer is converted to active material or only those portions with the requisite precursor properties for conversion to an active material e.g. zeolite.

[00601 The active inorganic composites of the present invention may be used in the form of an extrudate with binder, in which the active inorganic composites are dispersed within the binder.

The active inorganic composites are typically bound by forming a composite aggregate such as a pill, sphere, or extrudate. The extrudate is usually formed by extruding the active inorganic composites in the presence of a binder and drying and calcining the resulting extrudate. The binder materials used are resistant to the temperatures and other conditions, e.g., mechanical attrition, which occur in various chemical or petrochemical processes such as hydrocarbon conversion processes. Examples of binder materials include amorphous materials such as alumina, silica, titania, silica-alumina, silica-zirconia and various types of clays.

[00611 In a preferred embodiment of the active inorganic composite of the invention, an additional inorganic material is formed on the shell layer. This may be deposited on or grown from the shell layer. For example it may be grown from the shell layer via crystallization and most preferably crystallization under hydrothermal conditions from a synthesis solution for a molecular sieve.

[0062) The inorganic material deposited on or grown from the shell layer of the active inorganic composite may form a complete Continuous layer over the surface of the shell layer or may be present as a discontinuous layer having discrete regions of material. The morphology of this third layer may be selected by adjusting the ratio of active material e.g. colloidal material and intercalating material such as metal oxide present in the shell layer. The active inorganic material especially when present as colloidal particles may act as nucleation sites for the growth of the third inorganic layer and the density of these sites in the shell layer may be controlled. The nucleation density can be controlled by the relative proportions of active inorganic particles and metal oxides (with the density decreasing as the amount of the metal oxide utilized increases) as well as the size of the active inorganic particles in the shell layer.

[0063J Catalytically active sites may be incorporated in the molecular sieve that may be used as component(s) of the active inorganic composite e.g., by selecting as the molecular sieve a zeolite with a finite Si02:Al203 ratio, preferably lower than 300. The strength of these sites may also be tailored by ion-exchange. The composite may also be steamed, or treated in other manners known per se, to adjust properties.

[00641 The active material composites of the present invention, particularly but not exclusively those in the form of pills, spheres or extrudates with binder, find particular application in hydrocarbon conversion processes and adsorption or separation processes. Examples of preferred processes include hydrocarbon conversion process where reduced non-selective acidity is important for reaction selectivity andlor the maintenance of catalyst activity, such as alkylation, dealkylation, disproportionation, and transalkylation reactions. The conversion of hydrocarbon feeds can take place in any convenient mode, for example, in fluidized bed, moving bed, or fixed bed reactors depending on the types of process desired. Examples of hydrocarbon conversion processes include, as non-limiting examples, the following: [0065J (A) The catalytic cracking of a naphtha feed to produce light olefins. Typical reaction conditions include temperatures of from about 500°C to about 750°C, pressures of subatmospheric or atmospheric, generally ranging upto about 1.01 MPa (10 atmospheres) gauge and residence time (volume of the catalyst feed rate) from about 10 milliseconds to about 10 seconds.

100661 (B) The catalytic cracking of high molecular weight hydrocarbons to lower molecular weight hydrocarbons. Typical reaction conditions for catalytic cracking include temperatures of from about 400°C to about 700°C, pressures of from about 10.1 kPa (0.1 atmosphere) to about 3.04 MPa (30 atmospheres), and weight hourly space velocities of from about 0.1 to about 100 hf'.

[00671 (C) The transalkylation of aromatic hydrocarbons in the presence of polyalkylaromatic hydrocarbons. Typical reaction conditions include a temperature of from about 200°C to about 500°C, a pressure of from about atmospheric to about 20.3 MPa (200 atmospheres), a weight hourly space velocity of from about 1 to about IOOhf' and an aromatic hydrocarbon/polyalkylaromatic hydrocarbon mole ratio of from about 0.5/1 to about 16/1. -16-

100681 (D) The isomerization of aromatic (e. g., xylene) feedstock components. Typical reaction conditions for such include a temperature of from about 230°C to about 510°C, a pressure of from about 51 kPa (0.5 atmospheres) to about 5.1 MPa (50 atmospheres), a weight hourly space velocity of from about 0.1 to about 200 hr1 and a hydrogen / hydrocarbon mole ratio of from about 0 to about tOO.

100691 (E) The dewaxing of hydrocarbons by selectively removing straight chain paraftins The reaction conditions are dependent in large measure on the feed used and upon the desired pour point. Typical reaction conditions include a temperature between about 200°C and 450°C, a pressure up to 20.7 MPag (3,000 psig) and a liquid hourly space velocity from 0.1 to 20.

f0070J (F) The alkylation of aromatic hydrocarbons, e. g., benzene and alkylbenzenes, in the presence of an alkylating agent, e. g., olefins, formaldehyde, alkyl halides and alcohols having I to about 20 carbon atoms. Typical reaction conditions include a temperature of from about 100°C to about 500°C, a pressure of from about atmospheric to about 20.3 MPa (200 atmospheres), a weight hourly space velocity of from about lhr' to about100hr and an aromatic hydrocarbon/alkylating agent mole ratio of from about I/Ito about 20/1.

[0071) (0) The alkylation of aromatic hydrocarbons, e. g., benzene, with long chain olefins, e.

g, C14 olefin. Typical reaction conditions include a temperature of from about 50°C to about 200°C, a pressure of from about atmospheric to about 20.3 MPa (200 atmospheres), a weight hourly space velocity of from about 2hr' to about 2000h(' and an aromatic hydrocarbon/olefin mole ratio of &om about I/I to about 20/I. The resulting products from the reaction are long chain alkyl aromatics which when subsequently sulfonated have particular application as synthetic detergents.

[0072) (H) The alkylation of aromatic hydrocarbons with light olefins to provide short chain alkyl aromatic compounds, e. g., the alkylation of benzene with propylene to provide cumene or with butene to provide sec. butylbenzene. Typical reaction conditions include a temperature of from about 10°C to about 200°C, a pressure of from about 101 kPa to 3.04 MPa(l to 30 atmospheres), and an aromatic hydrocarbon weight hourly space velocity (WHSV) of from lhr1 to about 50hr.

[0073) (1) The hydrocracking of heavy petroleum feedstocks, cyclic stocks, and other hydrocrack charge stocks. The catalyst will contain an effective amount of at least one hydrogenation component of the type employed in hydrocracking catalysts.

100741 (J) The alkylation ofa reformate containing substantial quantities of benzene and toluene with fuel gas containing short chain ulefins (e. g., ethylene and propylene) to produce mono-and dialkylates. Preferred reaction conditions include temperatures from about 100°C to about 250°C, a pressure of from about 690 kPag to 5.52 MPag (100 to 800 psig), a WHSV-olefin from about 0.4hr1 to about 0.8hr', a WHSV-reformate of from about 1 hr1 to about 2hr1 and, optionally, a gas recycle from about 1.5 to 2.5 vollvol fuel gas feed.

100751 (K) The alkylation of aromatic hydrocarbons, e. g., benzene, toluene, xylene, and naphthalene, with long chain olefins, e. g. C14 olefin, to produce alkylated aromatic lube base stocks. Typical reaction conditions include temperatures from about 160°C to about 260°C and pressures from about 2.41 kPag to 3.10 MPag (350 to 450 psig).

100761 (L) The alkylation of phenols with olefins or equivalent alcohols to provide long chain alkyl phenols. Typical reaction conditions include temperatures from about 100°C to about 250°C, pressures from about 6.9 kPag to 2.07 MPag (Ito 300 psig) and total WHSV of from about 2hr1 to about 10hr.

10077] (M) The conversion of light paraffins to olefins and/or aromatics. Typical reaction conditions include temperatures from about 425°C to about 760°C and pressures from about 69 kPag to 13.79 MPag (10 to 2000 psig). Processes for preparing aromatic compounds from light paraffins are described in United States Patent 5,258,563, which is hereby incorporated by reference.

[0078) (N) The conversion of light olefins to gasoline, distillate and lube range hydrocarbons.

Typical reaction conditions include temperatures of from about 175°C to about 375°C and a pressure of from about 690 kPag to 13.79 MPag (100 to 2000 psig).

100791 (0) Two-stage hydrocracking for upgrading hydrocarbon streams having initial boiling points above about 200°C to premium distillate and gasoline boiling range products or as feed to further fuels or chemicals. In a first stage, the composites of the invention are used as catalysts comprising one or more catalytically active substances, eg a Group VIII metal, and the effluent from the first stage is reacted in a second stage using a second zeolite catalyst, for example, zeolite Beta, comprising one or more catalytically active substances, e. g., a Group VIII metal.

Typical reaction conditions include temperatures from about 315°C to about 455°C, a pressure from about 2.76 to 17.24 MPag (400 to 2500 psig), hydrogen circulation of from about 178 to 1780 m3/m3(1000 to 10,000 SCF/bbl) and a liquid hourly space velocity (LHSV) of from about 0.1 to 10.

100801 (P) A combination hydrocracking/dewaxing process in the presence of the zeolite bound zeolite catalyst comprising a hydrogenation metal and a zeolite such as zeolite Beta. Typical reaction conditions include temperatures from about 3 50°C to about 400°C, pressures from about 9.6 to 10.7 MPag (1400 to 1500 psig), LHSVs from about 0.4 to about 0.6 and a hydrogen circulation from about 534 to 890 m3/m3 (3000 to 5000 SCF/bbl).

f0081] (Q) The reaction of alcohols with olefins to produce mixed ethers, c. g., the reaction of methanol with isobutene and/or isopentene to provide methyl-t-butyl ether (MTBE) and/ort-amyl methyl ether (TAME). Typical conversion conditions include temperatures from about 20°C to about 200°C, pressures from 203 kPa to 20.3 MPa (2 to 200 atm), WHSV (gram olefin per hour gram-zeolite) from about 0.1 hr' to about 200hr' and an alcohol to olefin molar feed ratio from about 0.1/Ito about 5/1.

10082] (R) The disproportionation of aromatics, e. g., the disproportionation of toluene, to make benzene and paraxylene. Typical reaction conditions include a temperature of from about 200°C to about 760°C, a pressure of from about atmospheric to about 6.08 MPa (60 atmosphere), and a WI-ISV of from about 0.lhr' to about 30hf'.

100831 (S) The conversion of naphtha (eg. C6-C10) and similar mixtures to highly aromatic mixtures. Thus, normal and slightly branched chained hydrocarbons, preferably having a boiling range above about 40°C, and less than about 200°C, can be converted to products having a substantial higher octane aroniatics content by contacting the hydrocarbon feed with the composites of the present invention at a temperature in the range of from about 400°C to 600°C, preferably 480°C to 550°C at pressures ranging from atmospheric to 4 MPa (40 bar), and liquid hourly space velocities (LHSV) ranging from 0.1 to 15.

[00841 (T) Selectively separating hydrocarbons by adsorption of the hydrocarbons. Examples of hydrocarbon separation include xylene isomer separation and separating olefins from a feed stream containing olefins and parafTins.

[0085] (U) The conversion of oxygenates, e. g. alcohols, such as methanol, or ethers, such as dimethylether, or mixtures thereof to hydrocarbons including olefins and aromatics with reaction conditions including a temperature of from about 275°C to about 600°C, a pressure of from about 51 kPa to 5.1 MPa (0.5 atmosphere to 50 atmospheres) and a liquid hourly space velocity of from about 0,1 to about 100.

100861 (V) The oligomerization of straight and branched chain olefins having from about 2 to about 5 carbon atoms. The oligomers which are the products of the process are medium to heavy olefins which are useful for both fuels, i.e. gasoline or a gasoline blending stock, and chemicals.

The oligomerization process is generally carried out by contacting the olefin feedstock in a gaseous phase state with a catalyst at a temperature in the range of from about 250°C to about 800°C, a LHSV of from about 0.2 to about 50 and a hydrocarbon partial pressure of from about 10.1 kPa to 5.1 MPa (0.1 to 50 atmospheres). Temperatures below about 250°C may be used to oligomerize the feedstock when the feedstock is in the liquid phase when contacting the zeolite -19-catalyst. Thus, when the olefin feedstock contacts the catalyst in the liquid phase, temperatures of from about 10°C to about 250°C may be used.

[00871 (W) The conversion of C2 unsaturated hydrocarbons (ethylene and/or acetylene) to aliphatic C6.12 aldehydes and converting said aldehydes to the corresponding C2 alcohols, acids, or esters. In general, the catalytic conversion conditions include a temperature of from about 100°C to about 760°C, a pressure of from about 10.1 kPa to 20.3 MPa (0.1 to 200 atmospheres) and a weight hourly space velocity of from about 0.08hr' to about 2,000h('.

[00881 Processes that find particular application using the active inorganic composite catalysts of the present invention are those where two or more reactions are taking place within the composite catalyst. Each of the active materials of this catalyst would be separately tailored to promote or inhibit different reactions. A process using such a catalyst benefits not only from greater apparent catalyst activity, greater catalyst accessibility, and reduced non-selective surface acidity possible with such catalysts, but also from the possibility to obtain tailored catalyst systems.

[0089J The present invention is further described by way of the following examples. These examples are intended to illustrate or be representative of the invention and are not in any way intended to limit its scope.

EXAMPLE 1

100901 Preparation of an active inorganic composite of LTL zeolite core and MFI zeolite shell layer.

(00911 LTL zeolite crystals were prepared from two solutions having the following compositions: 100921 Solution A comprised 178.13 g of KOH [87.5%], 40.87 g Al(OH)3 [99.3%] and 301.63 g of water.

100931 Solution B comprised 0.2052 g of Mg(N03)2.6H20 in 130.0 g of water.

100941 The synthesis was carried out by mixing 784.17 g of Ludox HS4O (a colloidal silica sol which is supplied byW.R. Grace Davision comprising 4Owt% Si02 and 60% H20) with 442.00 g of water. Solution B was added to this mixture and mixed. 43.20 g of water was used to rinse the solution B container. This water was added to the mixture. The mixture was stirred for another 5 minutes. To this mixture was added solution A using 78.04 g of rinse water. The resulting mixture was stirred for 2 minutes before it was transferred to a 2 liter stainless steel autoclave.

The autoclave was heated to 170 C over a period of 9 hours and 40 minutes and was kept at this temperature for 96 hours. After cooling the crystals were separated from the mother liquor and washed with water.

[0095] MFI zeolite (molar composition: 10SiO2/0.54Na2O/3.O3TPAOHJI5OH2O) was prepared as follows: 1587.71g oftetrapropylammonium hydroxide [TPAOH] (20% in water, Fluka brand, as supplied by Sigma-Aldrich Corporation) was poured in a glass beaker. Then, 22.47 12g NaOH (98.7%, as supplied by Mallinckrodt Baker, Inc.) was added and stirred until it was completely dissolved, To the solution was added 352.OOg silicic acid (89.80%, as supplied by Mallinckrodt Baker, Inc.) and the resulting mixture was heated to boiling while stirring. The mixture was allowed to boil until the silicic acid was completely dissolved. Thereafter the solution was allowed to cool down and water was added to compensate for water loss during boiling. The resulting synthesis mixture was poured into a polypropylene bottle and heated during boiling under reflux for 29 days at 50°C in an oil bath. After the synthesis, the material was washed using a high speed centrifuge until the pH of the wash water was below 10.

[00961 1.04 g of LTL zeolite crystals prepared as described above were weighed on a Whatman 42 filter paper, which was then formed into a cone. These LTL zeolite crystals were treated with 12.07 g of cationic polymer solution (Redifloc 4150, 0.4 wt% and pH 8) by pouring the cationic polymer solution into the filter paper cone and allowing the liquor to pass over the LTL zeolite crystals and through the filter paper. The treated LTL zeolite crystals were washed three times with separate 15 g aliquots of 0.IN NH4OH to remove excess cationic polymer.

[0097J The washed LTL zeolite cr ystals were treated with 10.0 g of a colloidal suspension of the MFI zeolite colloidal crystals that had been prepared as described above, by pouring the colloidal suspension into the filter paper and allowing it to pass over the washed LTL zeolite crystals and through the filter paper. The resultant powder was washed three times with 15 g of O.IN NH4OH and the washed powder was dried on the filter paper overnight at 120°C.

[0098J The resultant product was an active inorganic composite comprising a core of LTL zeolite with a thin shell layer of MFI zeolite particles.

EXAMPLE 2

f0099j Preparation of an active inorganic composite of FAU zeolite core and silicalite-1 shell layer.

[01001 FAU zeolite crystals were prepared according to a standard procedure described in the section "High -silica Faujasite EMC- 1" in "Verified Synthesis of Zeolite Materials" published on behalf of the International Zeolite Association, H. Robson Ed., Second Edition page 159, Elsevier 2001.

101011 1.00 g of the FAU zeolite crystals) were soaked in a cationic polymer solution (Redifloc 4150, 0.4 wt% and pH 8) with stirring for 5 minutes. The solution with FAU zeolite crystals was then centrifuged for 15 minutes at 3500 rpm in a bench top centrifuge (Heraeus Laboflige 400). After centrifugation the slightly hazy liquor was decanted and the powder was washed 3 times with centriftigation (15 mins 3500 rpm) with 0.IN NH4OH. The washed, polymer-treated FAU crystals were soaked in 10.00 g of a colloidal suspension of silicalite-l colloidal particles (1 wt% and average particle size about 50 am as measured by scanning electron microscopy) for 15 minutes. The suspension containing the FAU crystals was then centrifuged for 15 minutes at 3500 rpm, and the powder that resulted after decanting of the liquor was washed 3 times with centriftigation (IS mins @3500 rpm) with 0.IN NH4OH.

[0102] The resultant product was an active inorganic composite comprising a core of FAU zeolite with u thin shell layer of silicalite-i particles having an average particle size of about 50 nm, as measured by scanning electron microscopy.

EXAMPLE 3

[0103] Preparation of an active inorganic composite of ZSM-48 zeolite core and silicalite-l shell layer.

-22 - [0104J ZSM-48 zeolite crystals were prepared by the following method.

[01051 A solution was prepared by combining 0.71 g of A12(S04)3.18H20, 5.75 g of NaOH [98.7%], and 34.91 g of 1,6 diaminohexane in 428.78 g of water. This solution was added to 148.14 g of Ludox AS4O (4Owt % silica in water, W.R. Grace Division) and mixed for 5 minutes. 163.29 g of water was used to rinse the container used for starting solution and this water was added to the mixture. To this homogeneous mixture were added 3.028 g of a 0.25 wt% slurry of colloidal zeolite Beta seeds prepared according to EP-A-609304. The resulting mixture was mixed for another 5 minutes before being transferred to a I liter stainless steel autoclave.

The autoclave was heated over a period of 2 hrs to 150 C and was kept at this temperature for 40 hrs. After cooling the crystals were separated from the mother liquor and washed with water [0106J 2.00 g of the ZSM-48 zeolite crystals prepared as described above were dispersed in a cationic polymer solution (100 ml, 5 wt% Redifloc 4150 and pH 8) with ultra-sonication. The solution with ZSM-48 zeolite crystals was then centrifuged for IS minutes at 3500 rpm in a bench top centrifuge (Heraeus Laboftige 400). After centriftigation the clear supernatant was decanted and the powder was redispersed in 125 ml of 0.IN NH4OH in an ultrasonic bath for 10 minutes. This redispersed powder was centrifuged for 15 minutes at 3500 rpm and the clear supernatant was decanted. The redispersion and centrifugation was repeated a further two times.

ml of a colloidal suspension of silicalite-1 colloidal particles (7.24 wt% and an average particle size about 50 nm as measured by scanning electron microscopy) was added to the powder and mixed for 15 minutes. This suspension was then centrifuged for 15 minutes at 3500 rpm after which the supernatant was still milk white suggesting that excess colloidal seeds had been present in this treatment stage. The supematant was decanted and the powder was redispersed in 125 ml of 0.lN NH4OH stirred using a magnetic stirrer for 10 minutes, followed by centrifugation for 15 minutes at 3500 rpm after which the supernatant (still hazy) was decanted. These redispersion and centrifugation steps were repeated a further 4 times until the final wash water was clear. The resultant washed powder was dried in an oven at 120°C.

[01071 The resultant product was an active inorganic composite comprising a core of ZSM-48 zeolite with a thin shell layer of silicalite-I particles having an average particle size of about 50 nm, as measured by scanning electron microscopy.

EXAMPLE 4

[0108] Preparation of an active inorganic composite of ZSM-23 zeolite core and silicalite-l shell layer.

-23 - (01091 29.83 g of ZSM-23 zeolite crystals were dispersed in a cationic polymer solution (250 14g, S wt% Redifloc 4150 and p1-I 8) for 10 minutes. The ZSM-23 zeolite comprised agglomerates of near-spherical morphology and approximately 5000 am (5tm) diameter. A typical method for preparation of ZSM-23 is given in IJS-A-4076842. The solution containing ZSM-23 zeolite crystals was then centrifuged for 15 minutes at 3500 rpm in a bench top centrifuge (Heraeus Cryofuge Classic). After centrifugation the supernatant was decanted and the powder was redispersed in 250 ml of 0.IN NH4OH with stirring for 10 minutes. This redispersed powder was centrifuged for 15 minutes at 3500 rpm and the clear supernatant was decanted. The redispersion and centriftugation was repeated a further two times. The powder was then dispersed in 100 ml of a colloidal suspension of silicalite-l colloidal particles (32.8 wt% of unwashed silicalite-1 seeds in the slurry) for 10 minutes. This suspension was then centrifuged for 15 minutes at 3500 rpm after which the supernatant was still milk white and was decanted. The powder was washed three times using redispersion in 250 ml of 0. IN NH4OH with stirring for 10 minutes followed by centrifugation for 15 minutes at 3500 rpm, with decantation of the supernatant between washing cycles. The resultant powder was dried overnight in an oven at 120°C.

(01101 The resultant product was an active inorganic composite comprising a core of ZSM-23 zeolite with a thin shell layer of silicalite-1 particles having an average particle size of about 50 nm as measured by scanning electron microscopy.

EXAMPLE 5

[0111] This Example describes the synthesis of a mixed metal oxide (perovskite) precursor of formula: (Lao6Cao4Feo2Mno8O3). Its use in the preparation of an active inorganic composite with ZSM-5 is described in Example 6 (comparison) and Example 7.

101121 The perovskite precursor was generally prepared by mixing sufficient quantities of water soluble metal ions in basic aqueous solution containing quaternary ammonium salts and Na2CO3 After precipitation and washing the precursor was calcined for 6 hours at 800°C to effect crystallization.

(01131 The following stock solutions were prepared.

lMFe(N03)3.9H20 40.4g/IOOmI IM La(N03)3.6H20 43.3 g/l00 ml IM Ca(N03)2.4H20 23.62 g/l00 ml IM Mn(N03)2.6H20 40.4 g/lOO ml -24 - [01141 The following solutions were prepared.

Solution A (Prepared in glass separation funnel).

6.15 g IMFe(N03)3.9H20 l.77g Fe(N03)3.9H20 0.24g Fe 18.01 g I M La(N03)3.6H20 = 5.44 g La(N03)3.6H20 = 1.75 g La 25.90gH2O Solution B (Prepared in glass separation funnel).

11.228 IM Ca(N03)3.9H20 = 2.14 g Ca(N03)3.9H20 0.36 g Ca 22.82 g IM Mn(N03)3.6H20 = 5.09 g Mn(N03)3.6H20 = 0.97 g Mn 15.95gH20 Solution C (Prepared in a IL plastic bottle).

15.00 g NaHCO3 500.00 g H20 45.O3gTEAOH35% 101151 Solution C was stirred vigorously using a magnetic stirrer. Solutions A and B were added dropwise to solution C over a period of 10 minutes followed by 1 hour of continuous stirring.

[01161 The resulting mixture was transferred to a 1 L centrifuge bottle. The mixture was centrifuged for 10 mins � 4000 rpm and the clear top liquor was decanted. The remaining material was redispersed in 750 ml H20 and placed in an ultrasonic bath for 15 mins. The mixture was centrifuged for 10 mins 4000 rpm and the clear top liquor was decanted. The remaining material was redispersed in 250 ml isopropanol and placed in an ultrasonic bath for 15 mins. The mixture was centrifuged for 10 mins 4000 rpm and the clear top liquor was decanted. The remaining material was redispersed for a final time in 250 ml isopropanol and placed in an ultrasonic bath for 15 mins. The mixture was centrifuged for 10 mins 4000 rpm and the clear top liquor was decanted. The remaining material was dried for 12 hours at 120°C and calcined at 800°C for 6 hours.

[0117J The material was analyzed using X-ray diffraction and scanning electron microscopy.

The material was determined to be a microcrystalline perovskite mixed metal oxide with minor impurities of a second (unidentified) perovskite phase. The primary perovskite particles displayed a particle size of 100-200 nm. According to laser diffraction a bimodal particle size distribution is present in this sample stemming from the agglomeration of the primary perovskite particles. The sample was found to have a surface area of 12.5 m2/g by nitrogen physisorption.

The XRL) pattern for this sample is shown in Figure 1 and the SEM is shown in Figure 2.

101181 An ultrasound technique was used in an attempt to disperse the perovskite particles in water. However, the surface charge (zetapotential) of the perovskite particles was found to be a low positive value favoring agglomeration. The perovskite particles could be dispersed in water, however, with the aid of a cationic polymer and the use of ultrasound. The polymer employed was a quatemary amine polymer, Bewoten C4l0, supplied by Akzo Nobel. This was mixed with water to form a 0.2 wt% solution, which was brought to a pH value of 8 with 0.1 NFI4OH. 25 ml of the resulting solution were added to 0.3g of the perovskite mixed metal oxide particles prepared as described above, to form a 1.2 wt% dispersion. The addition of the cationic polymer increased the surface charge of the perovskite particles giving strongly positive values for surface charge. Dispersion results showed that deagglomeration of the perovskite particles was achieved with addition of the cationic polymer. The increase of the surface charge on adhesion of the positively charged polymer onto the perovskite surface led to increased interparticle repulsion and stabilization of the dispersion.

EXAMPLE 6 (Comparison) 10119] The perovskite particles of Example 5 dispersed in water with cationic polymer were used in an attempt to prepare an active inorganic composite with a ZSM-5 core.

[01201 The materials used in this Example were large crystal ZSM-5 prepared using a standard recipe (ZSM-5 particles of about 2000 nm) and the aqueous dispersion of perovskite particles treated with cationic polymer, prepared as described in Example 5. The large crystal ZSM-5 particles were added to the dispersion and then the solids were recovered by centrifugation. The isolated material was evaluated using a scanning electron microscope and the SEM is shown in Figure 3. This figure shows that the material consists of a physical mixture of perovskite agglomerates and ZSM-5 zeolite crystals. The particles are not bound to each other in core-shell confIguration as required for composites according to the invention. It is believed that the perovskite particle dispersion had an excess of cationic polymer present which also affected the surface properties of the ZSM-5 crystals making ii impossible for the perovskite particles to adhere (bond) to the surface of the ZSM-5 particles.

EXAMPLE 7

10121) The perovskite particles of Example 5 dispersed in water with cationic polymer were used to prepare an active inorganic composite with a ZSM-5 core.

-26 - 101221 A sample of the aqueous dispersion of cationic polymer-treated perovskite particles that had been prepared as described in Example 5 was used as one of the starting materials. However, in contrast to Example 6, the dispersion was first centrifuged and the thus-separated perovskite particles were washed with NH4OH solution to remove excess polymer. The washed particles were then red ispersed in water and the resulting dispersion was used to treat a sample of the same ZSM-5 crystals as had been used in Example 6. The procedure of Example 6 was repeated and the resulting ZSM-5/perovskite agglomerates were removed by centrifugation and calcined in order to remove the polymer and strengthen the zeolite/perovskite bonding. The isolated material was evaluated using a scanning electron microscope and the SEM is shown in Figure 4. The XRD analysis of the material is shown in Figure 5. The SEM shows that the product has an even shell layer of small perovskite particles adhered to the surface of the ZSM-5 core crystal. The XRD pattern shows a mixture of perovskite and MFI with approximately 30% of the material being perovskite.

101231 While the present invention has been described and illustrated by reference to particular embodiments, those of ordinary skill in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. For this reason, then, reference should be made solely to the appended claims for purposes of determining the true scope of the present invention.

Claims (37)

-27 - CLAIMS

1. An active inorganic composite having a core-shell structure, the core comprising particulate inorganic material and the shell layer comprising a plurality of particles of inorganic material, wherein at least one of the materials of the core and/or at least one of the materials of the shell is an active material.

2. The composite as claimed in claim I wherein the core comprises an active material and the shell comprises material which is not active.

3. The composite as claimed in claim 2 wherein none of the shell material(s) is an active material.

4. The composite as claimed in claim I wherein the core is not an active material and the shell comprises active material.

5. The composite as claimed in claim I wherein both the core and shell comprise active material.

6. The composite as claimed in claim I wherein the core comprises molecular sieve.

7. The composite as claimed in claim I wherein the shell comprises molecular sieve.

8. The composite as claimed in claim I wherein the shell comprises one or more metal oxides.

9. The composite as claimed in claim 8 wherein the shell comprises one or more mixed metal oxides.

10. The composite as claimed in claim 8 or 9 wherein the metal oxide or mixed metal oxide comprises one or more of the oxides of Fe, Ca, Mn and La.

II. The composite as claimed in claim 9 or claim 10 wherein the mixed metal oxide comprises one or more mixed metal oxides of perovskite structure.

12. The composite as claimed in claim 6 or claim 7 wherein the molecular sieve is a zeolite.

13. The composite as claimed in claim 12 wherein the zeolite is one or more of ZSM-5, ZSM-23, ZSM-48, FAU zeolite, LTL zeolite, silicalite-1 and members of the MCM-22 family.

14. The composite as claimed in any one the preceding claims wherein the shell layer comprises colloidal particles.

15. The composite as claimed in any one of the preceding claims wherein the shell layer has a thickness in the range of from 10 to 2000 nm.

16. The composite as claimed in any one of the preceding claimswherein the core has an average particle size in the range of from 100 to 5000 nm * 28 -

17 The composite as claimed in any one of the preceding claims wherein the shell particles have an average particle size in the range of from Ito 300 nm

18 The composite as claimed in claim 17 wherein the shell particles have an average particle size in the range of from 5 to 150 nm.

19. A method for the manufacture of an active inorganic composite having a core-shell structure, which method comprises (a) treating (i) a particulate inorganic core precursor A and/or (ii) a plurality of particles of one or more inorganic shell precursor materials B, so as to induce a change in the surface charge of the particle(s) of A and/or B such that the particulate core precursor A has an opposite surface charge from that of the particles of shell precursor material(s) B and (b) bringing the oppositely charged particles of A and B into contact with each other under conditions such that the particles of inorganic shell precursor material(s) B become bonded to the surface of the particulate inorganic core precursor A to form the active inorganic composite having a core-shell structure.

20. The method as claimed in claim 19 wherein the particulate core precursor A is an active material and the shell precursor material B comprises material which is not active.

21. The method as claimed in claim 19 wherein the particulate core precursor A is not an active material and the shell precursor material B comprises active material.

22. The method as claimed in claim 19 wherein both the particulate core precursor A and shell precursor material B comprise active material.

23. The method as claimed in claim 19 wherein the particulate core precursor A comprises molecular sieve.

24. The method as claimed in claim 19 wherein the shell precursor material B comprises molecular sieve.

25. The method as claimed in claim 19 wherein the shell precursor material B comprises one or more metal oxides.

26. The method as claimed in claim 19 wherein the shell precursor material B comprises one or more mixed metal oxides.

27. The method as claimed in claim 25 or 26 wherein the metal oxides or mixed metal oxides comprise one or more of the oxides of Fe, Ca, Mn and La.

28. The method as claimed in claim 26 or 27 wherein the mixed metal oxides comprise one or more mixed metal oxides of perovskite structure.

29. The method as claimed in claim 23 or 24 wherein the molecular sieve is a zeolite.

30. The method as claimed in claim 29 wherein the zeolite is one or more of ZSM-5, ZSM- 23, ZSM-48, FAU zeolite, LTL zeolite, silicalite-l and members of the MCM-22 family.

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31. The method as claimed in any one of claims 19 to 30 wherein the particles of inorganic shell precursor material(s) B comprise colloidal particles.

32 The method as claimed in claim 3 I wherein the particles have an average particle size of 500 nm or less.

33. The method as claimed in any one of claims 19 to 32 wherein the treatment to induce the change in surface charge is achieved by contact of the core particle or the shell particles with a solution comprising a cationic polymer.

34. The method as claimed in claim 33 wherein excess cationic polymer is washed from the particle(s) before bringing the particles into contact.

35. A catalyst or an adsorbent comprising an active inorganic composite according to any one of claims I to 18 or as prepared by the method of any one of claims 19 to 34 and inorganic binder.

36. A conversion process for converting hydrocarbons comprising contacting a hydrocarbon feedstream under hydrocarbon conversion conditions with an active inorganic composite according to any one of claims ito 18 or as prepared by the method of any one of claims 19 to 34 or a catalyst according to claim 35 to effect conversion of the hydrocarbon feed stream.

37. An adsorption or separation process which comprises contacting a feedstream containing one or more adsorbates under adsorption or separation conditions with an active inorganic composite according to any one of claims ito 18 or as prepared by the method of any one of claims 19 to 34 to effect adsorption or separation of one or more of the adsorbates from the feedstream.