WO2016135489A1

WO2016135489A1 - Porous hierarchical substrate

Info

Publication number: WO2016135489A1
Application number: PCT/GB2016/050477
Authority: WO
Inventors: Adam Fraser Lee; Christopher Michael Andrew PARLETT; Karen Wilson
Original assignee: Aston University
Priority date: 2015-02-25
Filing date: 2016-02-25
Publication date: 2016-09-01
Also published as: AR103775A1; GB201517749D0; GB201503147D0; GB201715449D0; GB2552911A; TW201714669A

Abstract

The present invention provides a method of producing a substrate comprising a porous network. The method comprises forming a substrate precursor containing an array of template particles; and removing the template particles from the substrate precursor using a solvent at a temperature below room temperature to yield the substrate. The present invention also provides a method of producing a substrate comprising a first porous network and a second porous network, the two porous networks being interconnected. The method comprises: forming a substrate precursor containing an array of first template particles and an array of second template particles; selectively removing the first template particles from the substrate precursor to form the first porous network; and subsequently removing the second template particles from the substrate precursor to form the second porous network.

Description

POROUS HIERARCHICAL SUBSTRATE

Field of the Invention

The present invention relates to a porous substrate, for example, a porous substrate that may be used as a heterogeneous catalyst, a method of making such a porous substrate and uses of such porous substrates.

Background of the Invention

It is known to use a substrate having a network of interconnecting pores as a heterogeneous catalyst for chemical reactions. The porous substrates are formed using sol-gel condensation of the substrate material around an array of template particles and subsequent removal of the template particles. The template particles are typically removed from the substrate by high temperature solvation (e.g. refluxing with solvent at 100 °C) or by calcination. The pores remaining after the removal of the template particles may be treated to provide functional sites which can then act to catalyse a chemical reaction. Use of beads of cross-linked polystyrene as template particles yields a substrate having a network of macropores (with a pore size greater than 50 nm and typically around 200-500nm).

Use of surfactants or tri-block copolymers e.g. poloxamers as templates particles yields a substrate having a network of mesopores (with a pore size between 2-50 nm).

As well as substrates having a uniform range of pore sizes, it is also known to provide substrates having porous networks with different size pore sizes.

Substrates having interconnecting networks of macropores and mesopores are known and the larger macropores are considered to provide easier accessibility for the reactants to access the functionalised mesoporous network. These substrates are formed using two different arrays of template particles e.g. an array of polystyrene beads (to form the macropores) and an array of liquid crystalline surfactant particles (to form the mesopores). The template particles are removed simultaneously by calcination to leave interconnected networks of macropores and mesopores.

It is known to functionalise the macropores and mesopores in a silica substrate using sulphonic acid to yield a macroporous/mesoporous heterogeneous acid catalyst showing effectiveness in transesterification reactions and thus having potential applications in biofuel synthesis (Dhainaut et al, Green Chem., 2010, 12, 296-303).

Macroporous-mesoporous alumina substrates are also known (Dacquin et al, J. Am. Chem. Soc. 2009, 131, 12896-12897). A macroporous-mesoporous silica substrate carrying palladium nanoparticles for the selective oxidation of alcohols to yield commercially important cinnamaldehyde has also been described (Partlett et al., ACS Catal. 2013, 3, 2122-2129).

These known substrates have a single, uniform functionality and therefore can catalyse single step reactions. Multi-step reactions (e.g. cascade reactions) can be catalysed using either a plurality of substrates each having a different functionality, or using a single substrate having dual or multi-functionality. A dual/multi-functionality substrate can be prepared by carrying out more than one functionalization treatment on the pores remaining after the removal of the template particles. The two or more functional sites resulting from the multiple functionalization treatments are uniformly distributed throughout the porous network i.e. the differing functional sites are not spatially segregated within the substrate.

Using multiple uniform functionality substrates hinders chemical processes because all reaction products can access all available functionalities, and hence transformations cannot be selectively directed. With dual/multi-functional substrates, the final desired product yield is often poor because there is little control over the interaction of the starting products and intermediates with the various functional sites.

There remains the need for a single heterogeneous catalyst substrate that can catalyse multi- step reactions and produce an acceptable yield of the desired product

Summary of the Invention In a first aspect, the present invention provides a method of producing a substrate comprising a porous network, said method comprising:

forming a substrate precursor containing an array of template particles; and removing the template particles from the substrate precursor using a solvent at a temperature below room temperature to yield the substrate. The first aspect of the present invention allows removal of template particles at sub-ambient temperatures unlike the known methods which require high temperature solvation or calcination. Such a method presents possibilities for the selective removal of template particles in situations where multiple arrays of differing template particles are provided as described in the second aspect of the present invention discussed below. The high temperature methods of template particle removal previously used are aggressive and do not allow for selective template removal.

Optional features of the invention will now be set out. These are applicable singly or in any combination with any aspect of the invention.

The temperature of the solvent used to remove the template particles may be at or below 0°C (e.g. at or below -5°C or -7°C).

In some embodiments, the template particle is formed of a polymer. The polymer may be an un-cross-linked polymer such as an un-cross-linked hydrophobic polymer or may be cross- linked. The template particle may be formed of polystyrene (PS), polylactic acid (PLA) or poly(methyl methacrylate) (PMMA) which may either be un-cross-linked or cross-linked.

The polystyrene beads used as template particles in known methods are typically cross-linked and require meticulous preparation. In contrast, un-cross-linked polymers e.g. un-cross-linked polystyrene can be used in the present invention and the preparation of this does not need to be so accurately controlled.

The solvent used to remove the polystyrene template particles may be an aromatic solvent e.g. benzene, xylene, mesitylene or toluene. Toluene is preferred for cost and toxicity reasons. The solvent used to remove the PLA template particles may be an organic solvent such as tetrahydrofuran (THF), a chlorinated organic solvent or acetonitrile. The solvent used to remove the PMMA template particles may be an organic solvent such as methyl isobutyl ketone, methyl acetate or THF, or a binary solvent mixture such as acetonitrile/alcohol (e.g. methanol, ethanol or propanol).

The substrate and substrate precursor may be formed of alumina, silica, a metal oxide such as zirconia, titania or ceria or mixed metal oxides. Known methods can be used to form the substrate precursor. For example, the template particle array may be pre-formed and the substrate material formed around the template particle array using sol-gel synthesis or co- precipitation.

In some embodiments, the method further comprises forming functional sites on the surface of the substrate within the porous network. The functional sites may be formed by chemisorption (covalent, ionic, hydrogen), electrostatic physisorption or ligand exchange using various chemical species. For example, chemisorption or electrostatic physisorption of metal-containing nanoparticles, covalent/ionic/hydrogen bonding of organic acid/base species, covalent bonding of aliphatic or aromatic hydrocarbons, organic ligand species and ligand exchange to form a metal complex or adlayer deposition of an oxide such as alumina, ceria or zirconia via gas, vapour or liquid phase deposition of a precursor (e.g. an alkoxy, halide or hydroxide precursor) may be used to functionalise the surface within the porous network.

Once functionalised, the substrate can be used as a heterogeneous catalyst for a wide variety of chemical reactions. In a second aspect, the present invention provides a method of producing a substrate comprising a first porous network and a second porous network, the two porous networks being interconnected, said method comprising:

forming a substrate precursor containing an array of first template particles and an array of second template particles;

selectively removing the first template particles from the substrate precursor to form the first porous network; and

subsequently removing the second template particles from the substrate precursor to form the second porous network.

By selectively removing the first template particles, it becomes possible to selectively functionalise the pores in the first network without affecting the pores in the second porous network. This presents options for a catalyst architecture not previously known.

In some embodiments, the first and second template particles have differing chemical and/or physical properties.

For example, in some embodiments, the first and second template particles may have differing sizes. For example, the first template particles may be larger than the second template particles, e.g. such that the first porous network comprises macropores and the second porous network comprises mesopores.

The macropores preferably have a size of 50ηηι-10μΓΤΐ as determined by mercury porosimetry or electron microscopy. The mesopores preferably have a size of 2-50 nm and more preferably, 2.5-14 nm as determined by nitrogen physisorption and application of the BJH method to analysis of the corresponding isotherms.

In some embodiments, the first and second template particles have differing thermostability. In some embodiments, the first and second template particles have differing polarity. In some embodiments, the first and second template particles have differing photochemistry. These chemical/physical differences can be used to facilitate selective removal of the first template particles.

In some embodiments, the invention comprises using a solvent at a temperature below room temperature (e.g. at or below 0°C) to selectively remove the first template particles. The temperature of the solvent used to remove the first template particles may be at or below -5°C (e.g. at or below -7°C).

In some embodiments, the first template particle is formed of a polymer. The polymer may be an un-cross-linked polymer such as an un-cross-linked hydrophobic polymer or may be cross- linked. The template particle may be formed of polystyrene (PS), polylactic acid (PLA) or poly(methyl methacrylate) (PMMA) which may be either un-cross-linked or cross-linked. The solvent used to remove the polystyrene template particles may be an aromatic solvent e.g. benzene, xylene, mesitylene or toluene. Toluene is preferred for cost and toxicity reasons. The solvent used to remove the PLA template particles may be an organic solvent such as tetrahydrofuran (THF), a chlorinated organic solvent or acetonitrile. The solvent used to remove the PMMA template particles may be an organic solvent such as methyl isobutyl ketone, methyl acetate or THF, or a binary solvent mixture such as acetonitrile/alcohol (e.g. methanol, ethanol or propanol).

In some embodiments, the second template particles are formed of a surfactant. The surfactant may be a non-ionic surfactant or may be a cationic surfactant such as cetyltrimethylammonium bromide (CTAB) or its derivatives (with differing length alkyl groups and/or differing counter ions). In some embodiments, the second template particles are formed of a non-ionic block copolymer such as a poloxamer (e.g. Pluronic P123). In some embodiments, the second template particles are formed of a carboxylic acid.

In some embodiments, the method comprises subsequently removing the second template particles using thermal processing (e.g. furnace or microwave irradiation), chemical extraction (optionally under thermal, microwave or ultrasonic conditions), chemical decomposition (e.g. using concentrated inorganic acid such as concentrated sulphuric acid) or UV/visible irradiation.

In some embodiments, the method comprises subsequently removing the second template particles by solvation using a solvent at its reflux temperature e.g. at a temperature above room temperature (e.g. at or above 50°C or at or above 70°C). The solvent may be a polar solvent such as an alcohol, e.g. a C1-C6 alcohol, namely methanol, ethanol, i-propanol, butanol, pentanol or hexanol. A non-polar solvent such as toluene or xylene or a supercritical fluid such as carbon dioxide or water could also be used.

In some embodiments, the method comprises forming first functional sites on the surface of the substrate within the first porous network and/or forming second functional sites on the surface of the substrate within the second porous network.

The surfaces within the first and/or second porous network may be functionalised by physisorption or chemisorption (covalent, ionic, hydrogen bonding) or ligand exchange at the surface hydroxyl groups within the first/second porous network. For example, chemisorption or electrostatic physisorption of metal-containing nanoparticles, covalent/ionic/hydrogen bonding of organic acid/base species, covalent bonding of aliphatic or aromatic hydrocarbons, organic ligand species and ligand exchange to form a metal complex or adiayer deposition of an oxide such as alumina, ceria or zirconia via gas, vapour or liquid phase deposition of a precursor (e.g. an alkoxy, halide or hydroxide precursor) may be used to functionalise the surfaces within the porous networks. In preferred embodiments, the surfaces within the first porous network are functionalised by covalent bonding.

The first and/or second functional sites may comprise a catalytic metal (e.g. platinum (Pt) or palladium (Pd)), a fluorescent marker, an acidic group, a basic group, a hydrophilic group or a hydrophobic group. Where the pores in the first and/or second porous network are macropores, the first/second functional site may comprise an enzyme or dye. In preferred embodiments, the first and second functional sites differ from one another and the first and second functional sites differ in functionality from one another.

In some embodiments, the method comprises forming first functional sites on the surface of the first porous network before subsequently removing the second template particles from the substrate precursor. In this way, the first porous network will be functionalised whilst the second porous network remains unaffected.

In these embodiments, the first functional sites are preferably covalently linked and, preferably, only decompose at elevated temperature (e.g. above ~250°C). Therefore they remain unaffected during the second template removal. In some embodiments, the method comprises forming second functional sites on the surface of the second porous network after subsequently removing the second template particles from the substrate precursor.

Accordingly, some embodiments provide a method of producing a substrate comprising a first porous network having first functional sites and a second porous network having second functional sites, the two porous networks being interconnected, said method comprising: forming a substrate precursor containing an array of first template particles and an array of second template particles;

selectively removing the first template particles from the substrate precursor to form the first porous network;

forming the first functional sites on the surface of the first porous network;

subsequently removing the second template particles from the substrate precursor to form the second porous network; and

forming the second functional sites on the surface of the second porous network.

In some embodiments, the first functional sites are selected to block subsequent functionalisation of the pores of the first porous network by the reagent used to form the second functional sites.

For example, the first functional sites may occupy all available surface hydroxyl groups within the first porous network rendering it unsusceptible to further functionalisation, inaccessible, or the first functional sites may be selected to repel the reagent used to form the second functional sites. For example, the first functional site may comprise a hydrophobic functionality which forms strong covalent bonds with the hydroxyl groups on the surface of the first porous network and which also repels an aqueous reagent e.g. an aqueous metal (e.g. Pt) salt solution which is subsequently used to form catalytic metal (e.g. Pt) particles in the second porous network. The hydrophobic functionality at the first functional site may comprise alkyl chains such as alkyl chains containing 6 or more carbon atoms e.g. octyl chains or aromatic groups such as phenyl. In these embodiments, the method may comprise forming the first functional sites on the surface of the first porous network by hydrolysis of alkylsilane precursors

Catalytic platinum sites can be introduced using an aqueous platinum salt solution such as aqueous h PtCk Chemical or photochemical reduction may be carried out to induce metal nanoparticle formation at the second functional sites, where reduction may be conducted at a low temperature (e.g. 25-100 °C).

In other embodiments, the step of forming the first functional sites comprises introducing a hydrophilic species (e.g. a bulky polyalcohol or alcohol/carboxylic acid functionalised organosilane species). In these embodiments, the step of forming the second functional sites comprises introducing a hydrophobic species (e.g. a capped metal (e.g. Pt) nanoparticle). The hydrophilic groups at the first functional site will repel the Pt nanoparticles exclusively into the second porous network. A further hydrophilic species (e.g. aqueous metal (e.g. Pd) salt solution) can be introduced to selectively enter the macropores (being too large to enter the mesopores and repelled from the mesopores by the hydrophobic Pt nanoparticles). In some embodiments, where the pores of the first porous network and second porous network differ in size, the functional sites may be selected such that they are too large to form in the smaller pores. For example, the first functional sites may comprise bulky hydrophobic or hydrophilic groups having a size too large to enter mesopores (e.g. in the second porous network) but which are able to enter macropores (e.g. in the first porous network.) The first functional sites may further comprise a catalytic metal and may be formed from pre-formed metal containing particles e.g. Pd-containing nanoparticles which are too large to enter the mesopores.

A particularly preferred embodiment provides a method of producing a substrate comprising a first porous network having catalytic palladium sites and a second porous network having catalytic platinum sites, the first porous network comprising macropores and the second porous network comprising mesopores, the two porous networks being interconnected, said method comprising: forming a substrate precursor containing an array of first template particles and an array of second template particles;

selectively removing the first template particles from the substrate precursor to form the first porous network comprising macropores;

forming hydrophobic functional sites on the surface of the first porous network;

subsequently removing the second template particles from the substrate precursor to form the second porous network comprising mesopores; and

introducing catalytic platinum sites on the surface of the second porous network using an aqueous platinum salt solution; and

introducing catalytic palladium sites in the first porous network.

The catalytic palladium sites can be introduced using preformed Pd nanoparticles. This allows their size to be controlled so that they are larger than the mesopore dimensions and thus cannot physically fit into them. Suitable preformed nanoparticles are oleylamine capped Pd nanoparticles which may have a dimension of 5-50nm. The capping agent imparts a hydrophobic character to the nanoparticles. Unstabilized Pd nanoparticles may also be used.

The catalytic platinum sites can be introduced using an aqueous platinum salt solution such as aqueous hkPtCk Metal reduction at low temperature (e.g. 25-100°C) may be carried out to induce metal nanoparticle formation.

A further preferred embodiment provides a method of producing a substrate comprising a first porous network having catalytic palladium sites and a second porous network having catalytic platinum sites, the first porous network comprising macropores and the second porous network comprising mesopores, the two porous networks being interconnected, said method comprising:

forming hydrophilic functional sites on the surface of the first porous network;

subsequently removing the second template particles from the substrate precursor to form the second porous network comprising mesopores;

introducing catalytic platinum sites on the surface of the second porous network using a hydrophobic platinum nanoparticle; and introducing catalytic palladium sites using an aqueous palladium salt solution in the first porous network.

The hydrophilic functional sites in the first porous network may be introduced using a bulky polyalcohol or alcohol/carboxylic acid functionalised organosilane species. In these embodiments, the step of forming the second functional sites comprises introducing a hydrophobic capped Pt nanoparticle. The hydrophilic groups at the first functional site will repel the Pt nanoparticles exclusively into the second porous network. An aqueous Pd salt solution is then introduced to selectively enter the macropores (being too large to enter the mesopores and repelled from the mesopores by the hydrophobic Pt nanoparticles). In other preferred embodiments the first functional sites comprise an enzyme and the second functional sites comprise a catalytic metal (e.g. Pt/Pd), an acidic group or a basic group.

In other preferred embodiments, the first functional sites comprise a first fluorescent marker and the second functional sites comprise a second fluorescent marker.

In other preferred embodiments, the first functional sites comprise an acidic or basic functionality and the second functional sites comprise a catalytic metal.

In other preferred embodiments, the first functional sites comprise a catalytic metal and the second functional sites comprise an acidic or basic functionality.

In other preferred embodiments, the first functional sites comprise an acidic functionality and the second functional sites comprise a basic functionality. In other preferred embodiments, the first functional sites comprise a basic functionality and the second functional sites comprise an acidic functionality.

The acidic functionality may be a Br0nsted acid functionality which may be introduced by using a thiolated organosilane precursor which can be subsequently oxidised to sulphonic acid.

The acidic functionality may be a Lewis acid functionality which may be introduced by using a metal alkoxide precursor which can be subsequently oxidised to a metal oxide (e.g. ZrC>2 or Ti0₂). The acidic functionality may be a carboxylic acid functionality which may be introduced by using an organosilane with carboxylic acid groups or an organosilane precursor with nitrile groups that can be converted into carboxylic acid groups via acid or base hydrolysis.

The basic functionality may be an amine functionality which may be introduced by using an organosilane with amine functional groups, or an organosilane precursor with nitrile groups that can be converted into amine groups via reduction e.g. with UAIH4.

Enzyme functionality may be introduced by using an organosilane having carboxylic or amine functional groups and then hydrogen bonding or covalent bonding of amine or carboxylate functions within the enzyme to the organosilane carboxylate or amine functional groups. In some embodiments, the substrate and substrate precursor is formed of alumina, silica, a metal oxide such as zirconia, titania or ceria or mixed metal oxides. Known methods can be used to form the substrate precursor. For example, the template particle arrays may be preformed and the substrate material formed around the template particle array using sol-gel synthesis. In a third aspect, the present invention provides a method of producing a substrate comprising a first porous network having first functional sites and a second porous network having second functional sites, the first porous network comprising macropores and the second porous network comprising mesopores, the two porous networks being interconnected, said method comprising:

removing the first template particles and second template particles from the substrate precursor to form the first porous network comprising macropores and the second porous network comprising mesopores;

forming the first functional sites on the surface of the first porous network; and subsequently forming the second functional sites on the surface of the second porous network.

In some embodiments, the step of forming the first functional sites comprises introducing a first functional species that is too large to enter the mesopores. For example, preformed catalytic metal (e.g. Pd) nanoparticles, an enzyme or dye or a bulky hydrophilic species e.g. a polyalcohol or alcohol/carboxylic acid functionalised organosilane species or a bulky hydrophobic group such as alkyl chains containing 6 or more carbon atoms e.g. octyl chains or aromatic groups such as phenyl having a size larger than the size of the mesopores can be used.

For example, the first functional sites may occupy all available surface hydroxyl groups within the first porous network rendering it unsusceptible to further functionalisation, inaccessible, or the first functional sites may be selected to repel the reagent used to form the second functional sites. In some embodiments, the step of forming the first functional sites comprises introducing a hydrophobic species that is too large to enter the mesopores. In these embodiments, the step of forming the second functional sites comprises introducing a hydrophilic species (e.g. an aqueous metal (Pt) salt solution).

The hydrophobic species can bind to the surface hydroxyl groups in the first porous network. By binding to the surface hydroxyl groups, the hydrophobic species blocks the formation of any second functional sites within the first porous network. The hydrophobic functionality at the first functional site may comprise alkyl chains such as alkyl chains containing 6 or more carbon atoms e.g. octyl chains or aromatic groups such as phenyl. In these embodiments, the method may comprise forming the first functional sites on the surface of the first porous network by hydrolysis of organosilane precursors The step of forming the second functional sites comprises introducing an aqueous metal (e.g. Pt) salt solution into the second porous network. The hydrophobic groups at the first functional site will repel the aqueous solution and the metal salt exclusively into the second porous network. Catalytic platinum sites can be introduced using an aqueous platinum salt solution such as aqueous hkPtCk Metal reduction at low temperature (e.g. 25-100°C) is carried out to induce metal nanoparticle formation at the second functional sites.

Catalytic metal sites can then be introduced into the first porous network using pre-formed Pd nanoparticles which are too large to enter the mesopores.

In other embodiments, the step of forming the first functional sites comprises introducing a hydrophilic species (e.g. a bulky polyalcohol or alcohol/carboxylic acid functionalised organosilane species) that is too large to enter the mesopores. In these embodiments, the step of forming the second functional sites comprises introducing a hydrophobic species (e.g. a capped metal (e.g. Pt) nanoparticle). The hydrophilic groups at the first functional site will repel the Pt nanoparticles exclusively into the second porous network. A further hydrophilic species (e.g. aqueous metal (e.g. Pd) salt solution) can be introduced to selectively enter the macropores (being too large to enter the mesopores and repelled from the mesopores by the hydrophobic Pt nanoparticles).

In other preferred embodiments the first functional sites comprise an enzyme and the second functional sites comprise a catalytic metal (e.g. Pt/Pd), an acidic group or a basic group. In other preferred embodiments, the first functional sites comprise a first fluorescent marker and the second functional sites comprise a second fluorescent marker.

In other preferred embodiments, the first functional sites comprise an acidic functionality and the second functional sites comprise a basic functionality.

In other preferred embodiments, the first functional sites comprise a basic functionality and the second functional sites comprise an acidic functionality. The acidic functionality may be a Br0nsted acid functionality which may be introduced by using a thiolated organosilane precursor which can be subsequently oxidised to sulphonic acid.

The acidic functionality may be a Lewis acid functionality which may be introduced by using a metal alkoxide precursor which can be subsequently oxidised to a metal oxide (e.g. ZrC>2 or Ti0₂).

The acidic functionality may be a carboxylic acid functionality which may be introduced by using an organosilane with carboxylic acid groups or an organosilane precursor with nitrile groups that can be converted into carboxylic acid groups via acid or base hydrolysis.

Enzyme functionality may be introduced by using an organosilane having carboxylic or amine functional groups and then hydrogen bonding or covalent bonding of amine or carboxylate functions within the enzyme to the organosilane carboxylate or amine functional groups. In some embodiments, the substrate and substrate precursor is formed of alumina, silica, a metal oxide such as zirconia, titania or ceria or mixed metal oxides. Known methods can be used to form the substrate precursor. For example, the template particle arrays may be preformed and the substrate material formed around the template particle array using sol-gel synthesis. In a fourth aspect, the present invention provides a substrate comprising a first porous network having first functional sites and a second porous network having second functional sites, wherein the first and second functional sites are spatially separated/segregated and functionally/chemically different.

In preferred embodiments, the pores in the first porous network are larger than the pores in the second porous network. For example, the first porous network may comprise macropores and the second porous network may comprise mesopores.

In some embodiments, the first functional sites comprise a catalytic metal (e.g. Pt/Pd), an enzyme, a dye, a fluorescent marker, an acidic group, a basic group, a hydrophilic group or a hydrophobic group. In some embodiments, the second functional sites comprise a catalytic metal (Pt/Pd), a fluorescent marker, an acidic group, a basic group, a hydrophilic group or a hydrophobic group.

In some embodiments, the first functional sites comprise an enzyme and the second functional sites comprise a catalytic metal (Pt/Pd), an acidic group or a basic group. Such a substrate can be used to as a bio-chem catalyst to catalyse a multi-step reaction.

In some embodiments, the first functional sites comprise a first fluorescent marker and the second functional sites comprise a second fluorescent marker. Such a substrate could be used as a sensing device (e.g. protein sensing device) able to discriminate between the presence of multiple analytes on the basis of their size, for example enzymes such as myloperoxidase (<5 nm) and C-reactive protein (> 5 nm) in clinical applications.

In some embodiments, the first functional sites comprise an acidic functionality and the second functional sites comprise a catalytic metal. Such a substrate can be used as a catalyst for the conversion of glucose to sorbitol. In some embodiments, the first functional sites comprise Pd and the second functional sites comprise Pt. Such a substrate can be used as a catalyst for selective oxidation of alcohols to acids e.g. cinnamyl alcohol to cinnamic acid (via cinnamaldehyde).

Cinnamic acid is an important flavorant and essential oil. Pd is highly selective for catalyzing cinnamyl alcohol oxidation to cinnamaldehyde but promotes decarbonylation of the resultant aldehyde product. In contrast, Pt favours undesired hydrogenation of cinnamyl alcohol (via reactively-formed surface hydrogen) to 3-phenylpropionaldehyde, but is highly selective towards cinnamaldehyde oxidation to the desirable cinnamic acid product.

Embodiments of the present invention having Pd as the first functional sites and Pt as the second functional sites provide a catalyst design that ensures that cinnamyl alcohol is oxidized over Pd prior to encountering Pt sites, while permitting the reactively-formed cinnamaldehyde able to subsequently access Pt sites for the selective production of cinnamic acid in the second oxidation step. Such a goal is achievable through the spatial control over the location of Pd and Pt within the substrate. In some embodiments, the first functional sites comprise an acidic functionality and the second functional sites comprise a basic functionality. Such a substrate can be used as a catalyst for conversion of cellulose to hydroxymethylfurfural (HMF) or conversion of bio-oil to biodiesel, preventing subsequent poisoning of base sites required to catalyse oil component via transesterification.

In some embodiments, the substrate is formed of alumina, silica, a metal oxide such as zirconia, titania or ceria or mixed metal oxides.

Brief Description of the Drawings

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

Figures 1 A and 1 B show transmission electron microscopy images of the substrate precursor before (Figure 1A) and after (Figure 1 B) toluene extraction;

Figure 2 shows stacked nitrogen porosimetry isotherms of the substrate prior to extraction and after consecutive extractions of the first template particles; Figure 3 shows surface area as a function of number of toluene extractions;

Figure 4 shows the results of thermogravimetric analysis;

Figure 5 shows the nitrogen porosimetry isotherm of the substrate after octyl functionalisation;

Figure 6 shows the nitrogen porosimetry isotherm of the substrate after extraction of the second template particles (P123) and mesopores size analysis; Figure 7 shows thermogravimetric analysis of the substrate prior to P123 template particle extraction (C8 functionalised) and after extraction of P123 template particles;

Figures 8A and 8B show the water contact angle analysis of the octyl functionalised substrate post P123 template particle extraction (Fig 8A) and of a comparable material (Fig 8B) that has not been octyl functionalised; Figures 9A and 9B show high resolution scanning transmission electron microscopy images, showing Pt nanoparticles within the mesopores of the substrate;

Figure 10 shows the particle size distribution for Pt nanoparticles; Figures 1 1A and 1 1 B show high resolution scanning transmission electron microscopy images of the substrate after introduction of Pd nanoparticles;

Figure 12 shows the particle size distribution for Pt nanoparticles and Pd nanoparticles in the bimetallic substrate; Figure 13 shows energy dispersive x-ray spectroscopy of areas of mesoporosity and macroporosity;

Figures 14A and 14B show cinnamyl alcohol conversions for the bimetallic substrate; and

Figure 15 shows a comparison of cinnamyl alcohol conversion and cinnamaldehyde and cinnamic acid production for the bimetallic substrate with conventional substrates. Experimental

A substrate precursor comprising an array of first template particles comprising un-cross- linked polystyrene beads template particles and an array of second template particles comprising Pluronic P123 was formed.

The substrate precursor was synthesised via the methodology reported by Sen at al, Chemistry of Materials, 2004, 16, 2044-2054.

Styrene (105 cm³) was washed five times with sodium hydroxide solution (0.1 M, 1 : 1 vol/vol) followed by five washings with distilled water (1 : 1 vol/vol) to remove polymerisation inhibitors. The washed organic phase was added to nitrogen degassed water (850 cm³) at 80°C followed by dropwise addition of aqueous potassium persulfate solution (0.24M, 50 cm³) with 300 rpm agitation. The reaction proceeded for 22 h, after which the solution had turned white due to the formation of polystyrene nanospheres. Solid product was recovered and colloidal crystal arrangement induced by centrifugation (8000 rpm, 1 h). The resulting highly ordered polystyrene colloidal nanosphere crystalline matrix was finally ground to a fine powder for use as the first template particles. Pluronic P123 (2 g) was sonicated with hydrochloric acid acidified water (pH 2, 2 g) at 40°C to a homogeneous gel.

6g of the un-cross-linked polystyrene particles was added mixing at 100 rpm was carried out to a homogenise the gel over the course of two minutes. The gel was then dried at 40 °C under vacuum at 100 mbar to a solid powder. After 2 hours, the solid was exposed to the atmosphere at room temperature for 24 hours.

The first template particles were removed by placing 10g of substrate precursor in 100ml of toluene at -8°C for 1 minute under high speed agitation at speeds above 600 rpm. The solid was recovered by vacuum filtration and washed with cold toluene. The extraction was subsequently repeated four times to fully extract the polystyrene template particles.

Figures 1A and 1 B show transmission electron microscopy images of the substrate precursor before (Figure 1A) and after (Figure 1 B) toluene extraction. It can be seen that a first porous network comprising macropores having an average size of 400 nm was generated. The Pluronic 123 template particles remained intact within the substrate precursor. This was confirmed by nitrogen porosimetry, thermogravimetric analysis (TGA) and gel permeation chromatography (GPC).

Nitrogen porosimetry was undertaken on a Quantachrome Autosorb IQTPX porosimeter with analysis using ASiQwin v3.01 software. Samples were degassed at 150°C for 12 h prior to recording ISh adsorption/desorption isotherms. BET surface areas were calculated over the relative pressure range 0.02-0.2. Mesopore properties were calculated applying the BJH method to the desorption isotherm for relative pressures >0.35, and fitting of isotherms to the relevant DFT kernel within the software package.Thermogravimetric analysis (TGA) was conducted using a Stanton Redcroft STA 780 thermal analyser at 10°Cmin-¹ under flowing N₂/0₂ (80:20 v/v 20 cm³min-¹).

Figure 2 shows stacked nitrogen porosimetry isotherms of the substrate prior to extraction and after consecutive extractions of the first template particles showing generation of macroporosity (sharp increase in volume at high relative pressure -0.95) and absence of mesoporosity (no increase in volume over the relative pressure range of 0.3-0.9) i.e. no extraction of second template particles (Pluronic P123).

Figure 3 shows surface area as a function of number of extractions showing an increasing surface area with extraction up to a maximum after four extractions, due to removal of the first template particles from the macropores, and a subsequent plateau due to complete extraction of the first template particles with no subsequent extraction of the second template particles. Figure 4 shows the results of thermogravimetric analysis showing the levels of the first and second template particles remaining in the material after consecutive extractions of the first template particles. Extraction of the first template particles increased up to four extractions with levels of the second template particles unaffected.

Next the macropores in the first porous network were functionalised with octyl groups at the first functional sites by either refluxing an organosilane precursor in heptane solvent overnight, or room temperature wet impregnation with the organosilane precursor. In one embodiment, 2g of the substrate precursor was stirred in 6cm³ of triethoxy(octyl)silane for 3 minutes and recovered by vacuum filtration before drying overnight at room temperature.

Figure 5 shows the nitrogen porosimetry isotherm of the substrate after octyl functionalisation which is comparable to that obtained prior to octyl functionalisation with no degree of mesoporosity from P123 template particle removal showing that P123 template particles remained within the substrate during the functionalisation of the first porous network. A surface area of 19 m³ g^_ concurs with the parent material.

Next, the P123 template particles were removed by refluxing 2g of the substrate template overnight (18 hours) with methanol (400cm³). Figure 6 shows the nitrogen porosimetry isotherm of the substrate after extraction of the second template particles (P123) and shows increased volume of nitrogen absorbed due to increased surface area (up to 300 m²g^_ ) which results from mesopore evacuation, via P123 removal, which is evident from the type IV isotherm shape. Mesopore size analysis, using the BJH methodology (insert), reveals average mesopore diameter of 3.5 nm. Figure 7 shows thermogravimetric analysis of the substrate prior to P123 template particle extraction (C8 functionalised) and after extraction of P123 template particles. The mass loss for material prior to extraction, at ~190°C is due to combustion of P123 with this feature absent in the extracted material, confirming removal of the P123 template particles.

Figures 8A and 8B show the water contact angle analysis of the octyl functionalised substrate post P123 template particle extraction (Fig 8A) and of a comparable material (Fig 8B) that has not been octyl functionalised and where the first and second template particles have be extracted under identical conditions.

Contact angle measurements were carried out on a Kruss DSA100 drop shape analyser, fitted with a digital camera for continuous data collection. Water drop shapes were analysed 10 seconds after deposition via DSA3 software. The high contact angle of the water droplet of 137° for the octyl functionalised material is indicative of a hydrophobic material, in contrast the unfunctionalised material which instantaneously adsorbs the water droplet into the substrate which is indicative of a substrate that exhibits no hydrophobicity. Next the substrate (06. g) was stirred with 1wt% aqueous h PtCle (3cm³, 0.01575g Pt, salt) in the dark. The platinum nanoparticles were driven selectively into the mesopores since the hydrophobic groups in the macropores repelled the aqueous solution. A dry porwder was obtained by gentle heating of the slurry at 50oC for 10 hours followed by low temperature (100 °C) metal reduction under H2 (10 cm³min-¹) for one hour to leave Pt particles having an average diameter of 2.2 nm within the mesopores. A Pt loading of 0.73 wt% was observed.

Figures 9A and 9B show high resolution scanning transmission electron microscopy images, In the dark field (Fig 9A) Pt nanoparticles appears as bright spots and in the bright field (Fig 9B) Pt nanoparticles appear as black sports showing Pt nanoparticles within the mesopores of the substrate. High resolution scanning transmission electron microscopy (S)TEM images were recorded on either a FEI Tecnai F20 FEG TEM operating at 200 kV equipped with an Oxford Instruments X-Max SDD EDX detector (1 Onm diameter spot-size) or a JEOL 21 OOF FEG STEM operating at 200keV and equipped with a spherical aberration probe corrector (CEOS GmbH) and a Bruker XFIash 5030 EDX. Figure 10 shows the particle size distribution for Pt nanoparticles highlighting that ~ 98 % particles are smaller than the average mesopore size and are thus able to fit within the second pore network of the substrate.

Near monodisperse palladium nanoparticles of 5.6 ±0.8 nm diameter were prepared adapting the protocol of Mazumder and Sun (J. Am. Chem. Soc. 131 , 4588-4589 (2009)) to employ a readily available borane complex, and extending the duration of particle aging at 90 °C in order to obtain larger nanoparticles. Synthesis was carried out using standard Schlenk techniques under an argon atmosphere. After evacuation of Pd(acac)2 (73 mg, Alfa Aesar) in a 3-neck round bottom flask and backfilling with Argon (repeated three times), oleylamine (15 cm3, Acros 26 Organics, 80-90 %) was added and the flask heated to 60 °C while stirring. Addition of borane triethylamine (0.52 cm3, Aldrich, 97 %) turned the solution from pale yellow to pale brown and was immediately followed by heating to 90 °C within 15 minutes, during which time the solution turned black indicating colloidal nanoparticle formation. Heating was continued at 90 °C for 90 minutes before cooling to room temperature. Ethanol (Fisher Scientific, HPLC grade, ca. 30 cm³) was added to this suspension, precipitating the nanoparticles, which were then extracted by centrifugation (8000 rpm, 20 minutes, 50cm³ plastic centrifuge tube, prewashed with ethanol). The resulting solid was re-dispersed in hexane (ca. 4cm³, Fisher Scientific, reagent grade), and the volume of hexane evaporated to around 2 cm³ under flowing argon before precipitation by the addition of the minimum quantity of ethanol and separation by centrifugation (6000 rpm, 10 minutes). Washing in ca. 2cm³ hexane and precipitation with ethanol, followed by centrifugation was repeated a further two times to remove any excess oleylamine and other residual synthetic agents. The solid was finally re-dispersed and stored in hexane (30cm³) until further use.

The Pd content of this nanoparticle solution was determined by ICP-OES to be 11.0 ±0.12 mg (in 30cm³), indicating around 43 % of the initial Pd is present in the nanoparticles after purification.

The as-prepared nanoparticles were characterised by TEM by casting one droplet of nanoparticle solution onto a holey carbon coated copper grid (Agar Scientific) and evaporation to dryness. TEM imaging was performed using a JEOL 2100F FEG TEM with a Schottky field emission source, equipped with an Oxford INCAx-sight Si(Li) detector for energy dispersive spectroscopy. The accelerating voltage was 200 kV. The particle size distribution was obtained from imaging 6 different areas of the grid and measuring the diameter over 800 individual nanoparticles. No variation in particle size was apparent in different regions of the grid.

Next, the substrate (0.3g) was treated with 6.5cm³ of a 1 wt% heptane solution of the preformed oleylamine capped palladium nanoparticles.

The size of the pre-formed nanoparticles was larger than the average mesopore size.

The resulting solid was stirred in solution for 1 hours before solvent evaporation at room temperature to leave a dry powder.

Tests showed that catalytic Pd sites were contained within the macropores and catalytic Pt sites were contained within the mesopores. Figures 1 1A and 1 1 B show high resolution scanning transmission electron microscopy images of the substrate after introduction of Pd nanoparticles. In the bright field (Fig 11 A) and dark field (Fig 1 1 B) larger Pd nanoparticlesare shown within the macropores of the substrate. The presence of Pt within the mesopores is also viable, as these are deposited prior to Pd deposition. Using dark field configurations it is possible to distinguish between Pd and Pt due to the atomic number contrast nature of the technique which results in Pt appear brighter than Pd, (highlighted in Fig 11 B).

Figure 12 shows the particle size distribution for Pt nanoparticles and Pd nanoparticles in the bimetallic substrate, compared to equivalent monometallic materials. These show that size is unaffected by the presence of both metals, with the average size of the Pt particles being smaller than the average diameter of the second pore structure whereas the size of the Pd nanoparticles is larger than the second pore structure.

Figure 13 shows energy dispersive x-ray spectroscopy of areas of mesoporosity and macroporosity further showing the precise location of the Pd and Pt nanoparticles. Areas of secondary porosity (mesoporosity), where silicon (Si) and oxygen (O) are strongest also show presence of discrete Pt sites and absence of Pd, whereas first porosity (macropore) regions show reduced silica and oxygen levels, due to large emptiness, and show levels of Pd and the absence of Pt.

The dual-functionalised substrate was used as a catalyst in the selective oxidation of cinnamyl alcohol to cinnamic acid at 150 °C with 5 bar O2.

The catalytic selective oxidations were performed in a 100 cm³ Buchi miniclave stirred batch reactor on a 75 cm³ scale at 150 °C. 12.5 mg of catalyst was added to reaction mixtures containing 4.2 mmol cinnamyl alcohol (0.562 g), an internal standard (mesitylene, 0.1 cm³), and toluene solvent (75 cm³) at 150°C under 5 bar oxygen and stirring. Reactions were periodically sampled for off-line gas chromatography analysis via a Varian 3800GC with 8400 autosampler fitted with a CP-SN5 CB column (15m x 0.25mm x 0.25μηι). Conversion, selectivity and yields were calculated via calibration to reference compounds and quoted ±2 %. Turnover Frequencies for cinnamyl alcohol conversion are quoted relative to the surface density of PdO sites (determined by XPS), and for cinnamic acid production relative to the surface density of PtC>2 sites (determined by XPS), being the respective active sites for selective oxidation over Pd nanoparticles and Pt nanoparticles. Results showed that the conversion rates were comparable to monometallic Pd or Pt catalysts prepared on the identical substrate, but that the yield of cinnamic acid was an order of magnitude higher than achievable with either single metal catalyst.

The Pd catalytic sites will catalyse the conversion to the aldehyde - the alcohol will achieve good exposure to the Pd catalyst as a result of the large pore size in the first porous network. The Pt catalyst site will then catalyse oxygen insertion into the C-H of the aldehyde forming the acid.

Figures 14A and 14B show cinnamyl alcohol conversions for the bimetallic substrate are comparable to both monometallic substrates, Pd in macropores or Pt in mesopores (Figure 14A). The true benefit of the bimetallic system is apparent when cinnamic acid yield (Figure 14B), the desired product from consecutive oxidations, is evaluated with a 10 fold increase in productive for the bimetallic substrate over either of the monometallic substrates.

Figure 15 also shows a comparison of cinnamyl alcohol conversion and cinnamaldehyde and cinnamic acid production for the inventive bimetallic substrate (with spatially segregated Pd/Pt sites) with conventional monometallic catalysts, their combination as a physical mixture and conventional bimetallic substrates (with co-localised, un-segregated Pd/Pt sites).

The conventional substrates proved ineffective, with either low rates of alcohol oxidation, poor selectivity to the cinnamaldehyde intermediate and/or very poor acid production, demonstrating the inability of Pd or Pt to either individually catalyze the multi-step, cascade reaction, or to communicate effectively when isolated in discrete catalyst support particles.

In contrast, the spatial compartmentalization of Pd and Pt within separate but interconnected pore networks, mere nanometres apart, permits control over the reaction sequence enabling oxidation of cinnamyl alcohol entering the macropores to cinnamaldehyde over Pd, and subsequent aldehyde diffusion into the mesopores and oxidation to cinnamic acid over Pt, conferring an order of magnitude enhancement in cinnamic acid yield.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

All references referred to above are hereby incorporated by reference.

Claims

I . A method of producing a substrate comprising a first porous network and a second porous network, the two porous networks being interconnected, said method comprising: forming a substrate precursor containing an array of first template particles and an array of second template particles;

2. A method according to claim 1 wherein the first and second template particles have differing chemical and/or physical properties.

3. A method according to claim 2 wherein the first template particles are larger than the second template particles such that the first porous network comprises macropores and the second porous network comprises mesopores.

4. A method according to claim 2 or 3 wherein the first and second template particles have differing thermostability and/or differing polarity and/or differing photochemistry.

5. A method according to any one of the preceding claims comprising using a solvent at a temperature below room temperature to selectively remove the first template particles.

6. A method according to claim 5 wherein the temperature of the solvent used to remove the first template particles is at or below 0°C.

7. A method according to claim 5 or 6 wherein the temperature of the solvent used to remove the first template particles is at or below -5°C.

8. A method according to claim 7 wherein the solvent is an aromatic solvent.

9. A method according to claim 8 wherein the solvent is benzene, xylene, mesitylene or toluene.

10. A method according to any one of the preceding claims wherein the first template particle is formed of a polymer.

I I . A method according to claim 10 wherein the polymer is an un-cross-linked polymer.

12. A method according to claim 10 or 1 1 wherein the polymer is polystyrene (PS), polylactic acid (PLA) or poly(methyl methacrylate) (PMMA).

13. A method according to any one of the preceding claims wherein the second template particles are formed of a surfactant, a non-ionic block copolymer or a carboxylic acid.

14. A method according to any one of the preceding claims comprising subsequently removing the second template particles using thermal processing, chemical extraction, chemical decomposition or UV/visible irradiation.

15. A method according to claim 14 comprising subsequently removing the second template particles by solvation using a polar solvent at a temperature above room temperature.

16. A method according to claim 15 wherein the polar solvent is methanol, ethanol or iso- propanol.

17. A method according to any one of the preceding claims comprising forming first functional sites on the surface of the substrate within the first porous network and/or forming second functional sites on the surface of the substrate within the second porous network.

18. A method according to claim 17 wherein the surfaces within the first porous network are functionalised by covalent bonding.

19. A method according to claim 17 or 18 wherein the first and/or second functional sites comprise a catalytic metal, a fluorescent marker, an acidic group, a basic group, a hydrophilic group or a hydrophobic group, an enzyme or a dye.

20. A method according to any one of claims 17 to 19 wherein the first and second functional sites differ in functionality from one another.

21. A method according to any one of claims 17 to 20 comprising forming the first functional sites on the surface of the first porous network before subsequently removing the second template particles from the substrate precursor.

22. A method according to any one of claims 17 to 21 comprising forming second functional sites on the surface of the second porous network after subsequently removing the second template particles from the substrate precursor.

23. A method according to any one of claims 17 to 22 wherein the first functional sites are selected to block subsequent functionalisation of the pores of the first porous network with second functional sites.

24. A method according to any one of claims 17 to 23 wherein the first functional sites have a hydrophobic or hydrophilic functionality.

25. A method according to claim 24 wherein the first functional sites the first functional sites have a hydrophobic functionality and comprise alkyl groups or aromatic groups.

26. A method according to any one of claims 17 to 25 wherein the first functional sites have a hydrophobic functionality and forming second functional sites on the surface of the substrate within the second porous network comprises introducing an aqueous solution of a metal salt.

27. A method according to any one of claims 17 to 24 wherein the first functional sites have a hydrophilic functionality and comprise alcohol groups or alcohol/carboxylic acid functionalised organosilane species.

28. A method according to claim 27 wherein forming second functional sites on the surface of the substrate within the second porous network comprises introducing a hydrophobic metal nanoparticle.

29. A method according to any one of the preceding claims for producing the substrate comprising the first porous network having first functional sites and the second porous network having second functional sites, the two porous networks being interconnected, said method comprising:

forming the substrate precursor containing the array of first template particles and the array of second template particles;

forming the first functional sites on the surface of the first porous network; subsequently removing the second template particles from the substrate precursor to form the second porous network; and

30. A method according to any one of claims 1 to 26 for producing the substrate comprising the first porous network having catalytic palladium sites and the second porous network having catalytic platinum sites, the first porous network comprising macropores and the second porous network comprising mesopores, the two porous networks being interconnected, said method comprising:

subsequently introducing catalytic palladium sites in the first porous network.

31. A method according to claim 30 wherein the catalytic palladium sites are introduced using preformed palladium nanoparticles.

32. A method according to any one of claims 1 to 24 for producing a substrate comprising a first porous network having catalytic palladium sites and a second porous network having catalytic platinum sites, the first porous network comprising macropores and the second porous network comprising mesopores, the two porous networks being interconnected, said method comprising:

subsequently removing the second template particles from the substrate precursor to form the second porous network comprising mesopores; and introducing catalytic platinum sites on the surface of the second porous network using a hydrophobic platinum nanoparticle; and

introducing catalytic palladium sites using an aqueous palladium salt solution in the first porous network.

33. A method of producing a substrate comprising a porous network, said method comprising:

forming a substrate precursor containing an array of template particles; and removing the template particles from the substrate precursor using a solvent at a temperature below room temperature to yield the substrate.

34. A method according to claim 33 wherein the temperature of the solvent used to remove the template particles is at or below 0°C.

35. A method according to claim 33 or 34 wherein the temperature of the solvent used to remove the template particles is at or below -5°C.

36. A method according to claim 35 wherein the solvent is an aromatic solvent.

37. A method according to claim 36 wherein the solvent is benzene, xylene, mesitylene or toluene.

38. A method according to any one of claims 33 to 37 wherein the template particle is formed of a polymer.

39. A method according to claim 38 wherein the polymer is an un-cross-linked polymer.

40. A method according to claim 38 or 39 wherein the polymer is polystyrene (PS), polylactic acid (PLA) or poly(methyl methacrylate) (PMMA).

41. A method according to any one of claims 33 to 40 further comprising forming functional sites on the surface of the substrate within the porous network.

42. A method of producing a substrate comprising a first porous network having first functional sites and a second porous network having second functional sites, the first porous network comprising macropores and the second porous network comprising mesopores, the two porous networks being interconnected, said method comprising: forming a substrate precursor containing an array of first template particles and an array of second template particles;

43. A method according to claim 42 wherein the step of forming the first functional sites comprises introducing a first functional species that is too large to enter the mesopores.

44. A method according to claim 43 wherein the first functional species is a catalytic metal, an enzyme, a dye, a hydrophobic species or a hydrophilic species.

45. A method according to any one of claims 42 to 44 wherein the step of forming the first functional site comprises introducing a hydrophobic species that is too large to fit into the mesopores and the step of forming the second functional sites comprises introducing an aqueous metal salt solution into the second porous network.

46 A method according to claim 45 further comprising introducing a metal nanoparticle that is too large to fit into the mesopores.

47. A method according to any one of claims 42 to 44 wherein the step of forming the first functional site comprises introducing a hydrophilic species that is too large to fit into the mesopores and the step of forming the second functional sites comprises introducing an hydrophobic metal nanoparticle into the second porous network.

48. A method according to claim 47 further comprising introducing an aqueous metal salt solution into the hydrophilic macropores.

49. A substrate comprising a first porous network having first functional sites and a second porous network having second functional sites, wherein the first and second functional sites are spatially separated/segregated and functionally and/or chemically different.

50. A substrate according to claim 49 wherein the pores in the first porous network are larger than the pores in the second porous network.

51. A substrate according to claim 50 wherein the first porous network comprises macropores and the second porous network comprise mesopores.

52. A substrate according to any one of claims 49 to 51 wherein the first functional sites comprise a catalytic metal, an enzyme, a dye, a fluorescent marker, an acidic group, a basic group, a hydrophobic group or a hydrophilic group.

53. A substrate according to any one of claims 49 to 52 wherein the second functional sites comprise a catalytic metal, a fluorescent marker, an acidic group, a basic group, a hydrophobic group or a hydrophilic group.

54. A substrate according to any one of claims 49 to 53 wherein the first functional sites comprise an enzyme and the second functional sites comprise a catalytic metal, an acidic group or a basic group.

55. A substrate according to any one of claims 49 to 54 wherein the first functional sites comprise a first fluorescent marker and the second functional sites comprise a second fluorescent marker.

56. A substrate according to any one of claims 49 to 55 wherein the first functional sites comprise an acidic functionality and the second functional sites comprise a catalytic metal.

57. A substrate according to any one of claims 49 to 51 wherein the first functional sites comprise catalytic Pd nanoparticles and the second functional sites comprise catalytic Pt nanoparticles.

58. Use of a substrate according to any one of claims 49 to 57 as a catalyst or as a sensing device.

59. Use of a substrate according to claim 58 for the selective aerobic oxidation of an alcohol to an acid.

60. Use according to claim 59 for the selective oxidation of cinnamyl alcohol to cinnamic acid.

61. A method substantially as any one embodiment herein described with reference to the accompanying figures.

62. A substrate substantially as any one embodiment herein described with reference to the accompanying figures.

63. Use of a substrate substantially as any one embodiment herein described with reference to the accompanying figures.