HK1101385B - Method for making metal oxides - Google Patents

Description

Method for producing metal oxide

Technical Field

The present invention relates generally to complex oxide materials. Complex oxides are oxides comprising two or more different metal elements. They are suitable for a variety of uses, including as catalysts and a wide range of electronic materials. In a preferred embodiment, the present invention relates to a method for manufacturing porous complex oxides with improved high temperature stability. In another aspect, the invention also relates to a method of making a porous non-refractory oxide.

Background

In general, the crystal structure ratio of oxides containing several different metal elements such as Al₂O₃And SiO₂Is complex. In addition, achieving phase purity (i.e., the presence of the desired crystalline phase and the absence of the undesired phase) in these complex compounds is generally very difficult. This is because these complex crystal structures are very sensitive to changes in chemical composition.

Thus, in order to achieve uniform, consistent properties critical to many applications, uniform dispersion of the elements must be ensured, which results in complex oxides of the desired purity. One difficulty that arises in achieving this uniform distribution of elements is the different ways in which the elements can behave during processing.

For example, the precipitation and reaction rates can vary greatly for various elements, leading to segregation in processes such as co-precipitation and sol-gel processing. Different elements may also respond very differently to temperature and atmosphere. For example, many metal elements used to form complex oxides have relatively low melting points. If an atmosphere with sufficient reducibility is present during the heat treatment, these elements will be present in the form of metals rather than oxides and will melt. Such melting can lead to severe segregation, substantial formation of impurity phases, and loss of surface area.

Despite these difficulties, there are various methods known in the art for fabricating complex oxides.

These methods include:

shake and bake "

Coprecipitation

Thermal evaporation and sputtering techniques

Polymer compounding (complex) technique

Sol gel

The "shake-bake" method is the roughest and simplest. An example is illustrated in us patent 5932146. Different oxide powders, each containing one or more desired elements, are simply mixed together, milled and then fired at high temperature so that the different elements can be uniformly mixed by diffusion. The problem with this method is that the raw material is very heterogeneous; very high sintering temperatures are therefore required to achieve uniformity. Intermediate grinding is also often required. High sintering temperatures greatly reduce the surface area, and long sintering times, high temperatures and intermediate grinding lead to very high processing costs. Some desired phases and phase purities may not even be obtained using this method.

The co-precipitation method can provide a more uniform precursor for relatively simple metal oxides. In Applied Catalysis A: examples are described in General, 235, pages 79 to 92, 2002(Zhang-Steenwinkel, Beckers and Bliek) and J.of Power Sources, 86, pages 395 to 400, 2000(Morie, Sammes and Tompsett). These methods have the disadvantage of being very difficult due to the various elements. Different elements all precipitate at different rates, so for some materials, non-uniformity is a major problem and still require a fairly high sintering temperature. For example, the Zhang-Steenwinkel et al process requires temperatures in excess of 800 ℃ to form a suitable crystalline phase, and the Morie et al process requires 1000 ℃. In addition, the precipitating agents necessary to achieve proper precipitation and chemical homogeneity are often expensive.

Most thermal evaporation and spray techniques are more involved in the production of oxide films or coatings. These techniques include techniques such as gas condensation processing, chemical vapor condensation, plasma spraying, and spray pyrolysis (spray pyrolysis). The most important of these techniques for batch processing is spray pyrolysis (Messing et al, 1994).

Spray pyrolysis is a process for producing powders of metals or oxides by thermal decomposition of metal salts or organometallic solutions. These solutions are first converted into aerosols by passing through an atomizing nozzle (atomizing nozzle) or an ultrasonic transducer. The aerosol is then sputtered into a heated zone or surface that is sufficiently hot to cause evaporation of the solvent and subsequent precipitation of the metal or oxide.

Generally, changing the aerosol decomposition parameters by changing the reaction temperature and carrier gas composition is a fundamental operating variable in spray pyrolysis processes. In addition, the solubility properties of the addition, such as precursor composition, concentration or co-solvent, may be critical to achieving the desired product composition and morphology. Limitations of spray pyrolysis processes include difficulty in controlling phase ratios, low productivity, and formation of low density hollow particles.

For relatively simple oxides, the polymer compounding process can also provide a fairly uniform distribution of elements. An example for La-based perovskites is described in Key Engineering Materials, 206-. The main problem with these processes is that the polymers used are prone to exothermic combustion. This can make handling difficult. In addition, with the multi-element compound, some elements cannot be coordinated with the polymer, and thus a uniform element distribution cannot be obtained.

Sol gel processes generally require careful control of processing conditions to form a uniform precursor. Examples of sol-Gel processes for La-Ca-Mn perovskites are described in J.Sol-Gel Science and Technology 25, pp.147-157, 2002(Mathur and Shen) and Chemistry of Materials 14, pp.1981-88, 2002(Pohl and Westin). Sol-gels can become extremely difficult as the complexity of the compounds increases, and some elements are not suitable at all for sol-gel processes. Sol gels are generally difficult to scale up and the raw materials required can be quite expensive.

Us patent No.6752979 in the name of the applicant describes a method of producing complex metal oxides with a uniform distribution of elements. This method has proven suitable for a wide variety of complex oxides. The method provides phase pure oxide with large surface area by using low processing temperature.

In addition to correcting for the oxide crystal structure and the uniform distribution of elements, in many applications, the porosity present between sintered grains of oxide is important for performance. For applications requiring good fluid (gas or liquid) migration, larger, interconnected pores (> about 1 μm) are generally desirable. For example, it is known to provide solid oxide fuel cell electrodes with macropores in the oxide (e.g., U.S. patent nos. 4883497 and 6017647). Most of these methods use various pore formers, i.e., materials in the ceramic material that can be dissolved or burned off. Pore formers are typically larger than 1 μm to enable the formation of pores of this size. Pores of this size are too large to increase the surface area of the material significantly.

Materials with a large number of small pores (< about 7nm) generally exhibit high surface areas. High surface areas are useful for applications such as catalysts that take advantage of surface properties. Small pores and high surface area can be obtained if the structure is made up of a large number of very small particles loosely packed together. Various organic pore formers may also be used to form very small pores. Smaller pores generally cannot withstand higher temperatures and therefore generally result in low high temperature stability.

Pores in the "intermediate" size range (about 7nm to about 250nm) are also useful for enhancing fluid flow, and are small enough to make a significant contribution to surface area. They have been found to improve the high temperature stability of some simple metal oxides. Us patent 6139814 describes a method for manufacturing Ce-based oxide having improved high temperature stability. While the reason for thermal stability is not certain, the patent speculates that stability is due, at least in part, to the presence of average pore sizes in the "mesoscale" range (examples show average pore sizes of about 9 nm). The method of' 814 involves absorbing a liquid solution of metal ions into the pores of a constructed fibrous material, such as filter paper. The liquid is dried and the material is fired to remove the cellulose. Thus, solids are formed in the pores of the cellulose, and the pores of the cellulose shape the solids. However, this approach has several disadvantages. Very high organic: the metal oxide ratio (up to > 100: 1), which, together with the relatively high cost of suitable cellulosic materials, results in expensive processing costs. Absorbing liquids into solids such as paper is also an awkward process that scales up. Finally, simply drying a solution of metal ions to form a solid is also undesirable for creating a uniform distribution of different elements needed for more complex materials.

A method for preparing silica having pores in the size range of about 10nm is described in J.Port Materials 7, page 435-441, 2000(Ermakova et al). Various carbon substrates were impregnated with silica gel, dried and then burned off. Increased pore size is obtained by using this method. When catalytically acting filamentous carbon is used as carbon source, an increased thermal stability is obtained. The thermal stability of the pores produced by the other, more spherical carbon particles was not tested. Unfortunately, the sol-gel process used is not ideal for forming many perovskite materials, particularly on a commercial scale. Also, injecting solids is an unwieldy process for scaling up. Another problem is that the ratio of carbon material to oxide is quite high (up to 30). This increases the cost of manufacturing, lowers productivity, and exacerbates the problem with respect to impurity elements in carbon.

Us patent 4624773 describes a process for the catalytic cracking of a hydrocarbon feedstock. Part of the process is the production of an alumino-silicate material with pores preferably ranging from 100 to 600nm to improve the flowability of the gas into the catalyst. The method comprises the following steps: a gel of alumina and silica is produced, and reticulated carbon particles having a length of about 50 to 3000nm are mixed in. After the formation of the alumino-silicate solid, the carbon particles are burned off to form pores of the desired size range. The process requires that the smaller pores in the high surface area alumino-silicate zeolite structure be provided unaffected by the burn-out process.

The gelling techniques used in the process for forming the alumino-silicate solids are not suitable for more complex materials requiring higher chemical homogeneity, particularly on a commercial scale. Also, the pores created to maximize gas flow are larger than necessary to create a thermally stable surface area. Finally, carbon is a strong reductant and is widely used in mineral processing to reduce oxides to metals. This is not the case, however, for the oxides of aluminum and silicon, since these oxides are quite stable and difficult to reduce, but many other metal oxides, including the metals typically used in complex oxides, are more likely to be reduced by carbon. The reducibility of the different elements is generally shown in the Ellingham diagram. Oxides such as Al that tend towards the bottom of the figure are difficult to reduce, while at the top they are much easier to reduce. Metals such as iron, nickel, cobalt, manganese, chromium and potassium are much easier to reduce than Al. The Ellingham diagram also shows the effect of reducing carbon, particularly carbon monoxide in the heat treatment atmosphere.

In the treatment of complex oxides, particularly in thermal treatment, the presence of metals may present serious difficulties due to segregation and/or the inability to form the required oxide phases with other elements. Thus, it is unclear whether intimate mixing of the intermediate-sized carbon particles and the oxide precursor will allow proper development of the desired phase. Also, the presence of metals or other reduced oxide forms can greatly increase the degree of sintering, resulting in severe loss of surface area and poor thermal stability.

An example of the problems associated with the addition of carbon-based Materials to oxide precursors is outlined in J.of Materials Science 35(2000), pages 565639-5639, which describes the formation of La by using burnt-off cellulose_0.8Sr_0.2CoO₃A method of making a material. It was found that if carbon dioxide is not removed fast enough, carbonates will form in the matrix and thus higher calcination temperatures are required to obtain phase purity.

GB2093816, formulated by Asia Oil Company Ltd and Mitsubishi Chemical industries Ltd, describes a process for manufacturing a porous refractory inorganic oxide product. GB2093816 provides a porous refractory inorganic oxide product having a pore distribution with a distinct peak at a diameter of 10nm to 100nm and a pore volume (porosity) of 0.11cc/g or more at a radius of 10nm to 50nm obtained by: shaping a mixture of carbon black and a refractory inorganic oxide and/or a precursor of a refractory inorganic oxide; drying the product; it is fired in an oxygen-containing gas stream while burning off the carbon black.

It is clear that GB2093816 is limited to the manufacture of refractory inorganic oxide products. Typical refractory inorganic oxides used in GB2093816 comprise inorganic oxides such as alumina, silica, titania, zirconia, thoria, boria, zeolites and clays. The practical examples given in GB2093816 only show the formation of refractory inorganic oxides with the addition of alumina, silica, titania, silica alumina (silica alumina), boron oxide, zeolites, kaolin and sepiolite.

With the exception of example 10, which uses titanium tetrachloride as a precursor for the precipitation reaction to form titanium oxide, the examples given in GB2093816 all use solid particulate starting materials to obtain a mixed oxide product. The product of example 10 is titanium oxide, not a mixed oxide.

GB2093816 uses carbon black having an average diameter of 15 to 300 nm. GB2093816 also states that the final firing temperature in the step of burning off the carbon black is about 500 ℃ or more, [ however, the upper limit is not critical as long as the porous refractory inorganic oxide product is not deactivated by the support or catalyst.

The process conditions and starting materials used in GB2093816 may require relatively high process temperatures to obtain complex oxide matrices comprising a mixture of metals. These process conditions are clearly disclosed in GB2093816, confirming that no complex metal oxide phases are formed. The inventors of the present invention therefore believe that, in fact, the so-called mixed inorganic oxides formed in GB2093816 consist of a mixture of separate grains or particles of feed material, such that each grain or particle contains only one of the feed materials therein. Thus, GB2093816 does not produce complex metal oxide phases comprising two or more different metals from different precursor components forming the particles.

Review of the prior art shows that there is a lack of a reliable and commercially viable method of making complex metal oxide materials with pores ranging in size from about 7nm to 250 nm.

There is also a strong need for complex oxide materials with improved thermal stability and methods of making such materials.

Disclosure of Invention

In a first aspect, the present invention provides a method of manufacturing a porous complex oxide, the method comprising providing a mixture of:

a) precursor elements suitable for producing complex oxides; or

b) One or more precursor elements and one or more metal oxide particles suitable for producing complex oxide particles; and

c) selecting a particulate carbonaceous pore former material for providing a pore size in the range of about 7nm to 250nm,

and, treating the mixture to

(i) Forming a porous complex oxide in which two or more of the precursor elements from the above (a) or one or more of the precursor elements from the above (b) and one or more of the metals in the metal oxide particles are introduced into a phase of the complex metal oxide, and the complex metal oxide has a crystal grain size of about 1nm to 150 nm; and

(ii) the pore-forming material is removed under conditions that substantially preserve the porous structure and composition of the complex oxide.

Unlike the process described in GB2093816, which results in the formation of a metal oxide phase that simply reflects (mirror) the phase of the metal oxide particles used as the feedstock particles in the process, or alternatively, produces a metal oxide phase from a precursor element that contains only a single refractory metal, the process of the present invention produces a complex metal oxide that includes the incorporation in the metal oxide phase of a complex metal oxide phase of two or more metals (in some embodiments, more than two metals) from the precursor or from the precursor and the metal oxide particles used as the feedstock. It is understood that the metal oxide phase comprises a matrix of metal oxide phases that contains an oxide structure incorporating two or more metals. Suitably, the two or more metals are uniformly distributed throughout the complex metal oxide phase.

Suitably, a single phase complex metal oxide is formed. However, the present invention also encompasses the formation of one or more phases of complex metal oxide phases and other metal oxides, or the formation of two or more complex metal oxide phases, with or without any other metal oxide phases. More suitably, each complex metal oxide phase formed is a phase pure phase (phase pure phase), i.e. the phase comprises only the desired crystalline phase and not the undesired crystalline phase.

The complex metal oxide may comprise two or more metals, such as two or more metals selected from the group consisting of the metals having atomic numbers 3, 4, 11, 12, 19-32, 37-51, 55-84, and 87-103. In one embodiment, the two or more metals in the complex metal oxide may comprise at least one non-refractory metal, such as at least one metal selected from the group consisting of the metals having atomic numbers 3, 4, 11, 19-21, 23-32, 37-39, 41-51, 55-84, and 87-103. In this embodiment, the metal oxide may contain other metals such as Ti, Al, Zr, and Mg in addition to the non-refractory metals specified above.

It has been unexpectedly found that the porous complex oxides so formed exhibit improved high temperature stability and greatly increased pore volume or surface area, such as in the temperature range of about 750 ℃ to 1000 ℃. The complex oxide also suitably exhibits a substantially homogeneous composition in each phase. Applicants have unexpectedly found that the complex oxides formed having the above ranges of grain sizes and the above ranges of pore sizes have a high initial surface area combined with improved surface area thermal stability.

Applicants have found that if the grain size of the complex oxide is greater than 150nm, the material will not have sufficient surface area. Similarly, if the pore size is greater than about 250nm, sufficient surface area may not be obtained after aging at high temperatures. High surface areas can be obtained if the pore size is less than about 10nm, however, the pores and thus the surface area are not thermally stable at high temperatures.

Unlike GB2093816, the process of the present invention can be used to form non-refractory complex metal oxide phases. The inventors have surprisingly found that the process of the present invention need not be limited to the manufacture of refractory oxides that are difficult to reduce. In contrast, all examples of GB2093816 produce oxide phases of alumina, silica, titania, silica-alumina, boria, zeolite, kaolin or sepiolite. All of these metal oxides are extremely inert and very difficult to reduce with carbon.

In this aspect of the invention, the complex oxide so formed may be of any suitable type. The complex metal oxide phase may be a perovskite. The crystal structure is of the chemical formula CaTiO₃The crystal structure of the mineral "perovskite". There are a large number of different compounds having perovskite crystal structures, including SrTiO₃、YBa₂Cu₃O_xSemiconductors, and many La-based perovskites suitable for use as catalysts and as electrodes in solid oxide fuel cells. La-based perovskites including LaMnO₃、LaCoO₃、LaFeO₃And LaGaO₃。

Different elements may be substituted into the oxide lattice to achieve desired physical properties. For example, for perovskites, the substitution may be at the A site (e.g., at LaMnO)₃In which Sr replaces La) and/or the B position (e.g. in LaMnO)₃In which Mn is replaced with Ni). Substitutions of various elements may be made in either or both positions to further adapt the physical properties to a particular application. Perovskite compositions (Ln) are described, for example, in U.S. Pat. No. 5932146 for use as solid oxide fuel cell electrodes_0.2La_0.4Nd_0.2Ca_0.2)(Mn_0.9Mg_0.1)O₃Wherein Ln is substantially La_0.598Nd_0.184Pr_0.81Ce_0.131Ca_0.002Sr_0.004。

There are many other examples of complex oxides developed for a wide range of applications, and the present invention is equally applicable to them.

The precursor elements useful in the mixtures of the invention may be of any suitable type, depending on the complex oxide to be formed. Any suitable metal and source of metal cations may be used. Mixtures of metals with metal compounds including one or more of oxides, acetates, carbonates, nitrates, and the like may be used.

The mixture of precursor elements or complex oxides and pore-forming material may be of any suitable type. The mixture may be a solid phase mixture, or formed as a solution or dispersion, or the like.

In one embodiment, as described below, the precursor elements and pore-forming material may be mixed to form a solid phase mixture, followed by appropriate thermal treatment to form the complex oxide.

In another embodiment, complex oxide particles can be formed from appropriate precursor elements and a pore-forming material is mixed with the complex oxide particles to form a mixture.

The mixture may alternatively be provided in the form of a solution or dispersion. For example, a solid phase mixture can be first formed and then dispersed or dissolved in a suitable solvent.

In another embodiment, the precursor element mixture may be first formed in a solution and the pore-forming material may be subsequently added to the solution. Alternatively, the precursor elements and at least a portion of the pore-forming material may be mixed to form a mixture of the solid phase mixture and dissolved in a suitable solvent.

Most suitably, the precursor elements form part of a solution that is mixed with the pore-forming material and the metal oxide particles (if used).

In the case of forming a dispersion or solution, any suitable solvent may be used. Although inorganic and organic solvents such as acids (e.g., hydrochloric or nitric acid), ammonia, alcohols, ethers, and ketones can be used, water is the preferred solvent.

The mixture may preferably comprise a surfactant. The surfactant may be of any suitable type. Surfactants of the type described in international patent application publication No. WO 02/42201 to the applicant, the entire contents of which are incorporated herein by reference, have been found to be suitable.

Some examples include: brij C₁₆H₃₃(OCH₂CH₂)₂OH, designated as C₁₆EO₂，(Aldrich)；Brij 30，C₁₂EO₄，(Aldrich)；Brij 56，C₁₆EO₁₀，(Aldrich)；Brij 58，C₁₆EO₂₀，(Aldrich)；Brij 76，C₁₈EO₁₀，(Aldrich)；Brij78，C₁₆EO₂₀，(Aldrich)；Brij 97，C₁₈H₃₅EO₁₀，(Aldrich)；Brij 35，C₁₂EO₂₃，(Aldrich)；Triton X-100，CH₃C(CH₃)₂CH₂C(CH₃)₂C₆H₄(OCH₂CH₂)_xOH，x＝10(av)，(Aldrich)；TritonX-114，CH₃C(CH₃)₂CH₂C(CH₃)₂C₆H₄(OCH₂CH₂)₅Oh (aldrich); tween 20, poly (ethylene oxide) (20) sorbate monokayrate (Aldrich); tween 40, poly (ethylene oxide) (20) sorbitan monopalmitate (Aldrich); tween 60, poly (ethylene oxide) (20) sorbitan monostearate (Aldrich); tween, poly (ethylene oxide) (20) sorbitan monooleate (Aldrich); and Span 40, sorbitan monopalmitate (Aldrich), Terital TMN 6, CH₃CH(CH₃)CH(CH₃)CH₂CH₂CH(CH₃)(OCH₂CH₂)₆OH(Fulka)；TergitalTMN 10，CH₃CH(CH₃)CH(CH₃)CH₂CH₂CH(CH₃)(OCH₂CH₂)₁₀Oh (fulka); block copolymers having poly (oxyethylene) -poly (oxypropylene) -poly (oxyethylene) (EO-PO-EO) sequences centred on two primary hydroxyl-terminated (hydrophobic) poly (propylene glycol) cores; pluronic L121 (C)_Mav＝4400)，EO₅PO₇₀EO₅(BASF)；Pluronic L64(_Mav＝2900)，EP₁₃PO₃₀EO₁₃(BASF)；Pluronic P65(_Mav＝3400)，EP₂₀PO₃₀EO₂₀(BASF)；Pluronic P85(_Mav＝4600)，EO₂₆PO₃₉EO₂₆(BASF)；PluronicP103(_Mav＝4950)，EO₁₇PO₅₆EO₁₇(BASF)；Pluronic P123(_Mav＝5800)，EO₂₀PO₇₀EO₂₀(Aldrich)；Pluronic F68(_Mav＝8400)，EO₈₀PO₃₀EO₈₀(BASF)；Pluronic F127(_Mav＝12600)，EO₁₀₆PO₇₀EO₁₀₆(BASF)；Pluronic F88(_Mav＝11400)，EO₁₀₀PO₃₉EO₁₀₀(BASF)；Pluronic 25R4(_Mav＝3600)，PO₁₉EO₃₃PO₁₉(BASF); having four EO's attached to an ethylenediamine core and capped with a secondary hydroxyl group_n-PO_mChain (or, conversely, four POs_n-EO_mChain) of star-shaped diblock copolymers; tetronic 908(_Mav＝25000)，(EO₁₁₃PO₂₂)₂NCH₂CH₂N(PO₁₁₃EO₂₂)₂(BASF)；Tetronic 901(_Mav＝4700)，(EO₃PO₁₈)₂NCH₂CH₂N(PO₁₈EO₃)₂(BASF); and Tetronic 90R4 (C: (C))_Mav＝7240)，(PO₁₉BO₁₆)₂NCH₂CH₂N(EO₁₆PO₁₉)₂(BASF)。

The surfactant is a nonionic surfactant. Other surfactants that may be used include:

anionic surfactant:

alcohol ethoxy carboxylate (Alcohol Ethoxycarbonyl) (R- (O-CH2-CH2) x-O-CH2-CH2-OH) (NEODOX AEC)

Alkyl ethoxy carboxylic acid (R- (O-CH2-CH2) x-O-CH2-CO2H) (EMPICOL C)

Sodium dodecyl sulfate CH₃(CH₂)₁₁OSO₃NA

There are several manufacturers. Sigma is an example.

Cationic surfactant:

chloride of sixteen kindsAlkyl trimethyl ammonium chloride (Cetyltrimethyl ammonium chloride) CH₃(CH₂)₁₅N(CH₃)₃Cl Aldrich

Hexadecyltrimethylammonium bromide (Cetyltrimethylammoniumbromide) CH₃(CH₂)₁₅N(CH₃)₃BT Aldrich

Cetylpyridinium chloride (Cetylpyridinium chloride) C₂₁H₃₅NCl Sigma

This list should not be considered exhaustive.

The pore-forming particles may be of any suitable type. The particles should be of a suitable size to produce a pore size in the "mid-range" (e.g., pore diameters of about 7nm to 250nm, preferably 10nm to 150 nm). Pore-forming particles of about 7nm to 300nm, preferably about 10nm to 150nm, more preferably about 10nm to 100nm, may be used. Carbon particles are preferred, and carbon black particles are more preferred.

The carbonaceous particles used as pore formers in the methods of the present invention are believed to promote the formation of pores of a desired size range by providing a region that prevents the residence of one or more precursors and metal oxide particles when forming the complex metal oxide phase and subsequently removing the pore-forming particles. Therefore, nano-sized pore-forming particles are required. This method should be distinguished from other methods that use a porous carbonaceous matrix (such as filter paper or activated carbon) to absorb the liquid phase precursor mixture and subsequently remove the matrix. The size of the matrix used in these methods is typically several orders of magnitude larger than the pore-forming particles used in the present invention. These existing methods are difficult to scale beyond the laboratory scale.

In a particularly preferred embodiment of the present invention, carbon black is used as the pore-forming particles.

The pore-forming particles are preferably removed by heat treatment.

The components required to form the complex oxide should be uniformly dispersed to form a mixture of precursor elements. The elements may be mixed by any suitable method known in the art. The pore-forming particles should also be dispersed into the mixture by using a method well known in the art, including a high-speed shearing apparatus, an ultrasonic device, a roll crusher, a ball mill, a sand mill, and the like. Applicants have found that better dispersion of the carbon-containing pore-forming particles in this stage results in more carbon-containing pore-forming particles being intimately mixed with the precursor and thus more pores being in the desired size range. In another preferred embodiment, air is removed from the carbonaceous pore-forming particles by vacuum prior to mixing with the liquid. The liquid is then mixed with the carbon by using a dispersion method. This results in better dispersion of the carbon particles in solution, more intimate mixing of the carbon particles in the precursor, and more porosity in the preferred size range.

The pore-forming particles may be wholly or partially contained in the mixture prior to dispersion.

The treatment of the mixture to form the complex oxide may be any suitable type of treatment that provides a complex oxide having a substantially uniform composition.

In one embodiment, the formation of the porous complex oxide may thus comprise two basic steps:

1. resulting in particles comprised of a complex oxide or a mixture of complex oxide precursor elements and carbon particles.

2. The particles from step (1) are heat treated to form the desired oxide phase from the precursor, if one is used, and to substantially remove (e.g., burn off) the carbon particles to create pores.

Steps (1) and (2) may occur sequentially or simultaneously.

In step 1, the elements in the oxide precursor should be uniformly dispersed. If they are not uniformly dispersed, very high temperatures are required to uniformly disperse the elements and form the correct phase, which may reduce the number and size of the pores, or eliminate them altogether. If the elements are not substantially uniform, the desired phase and/or phase purity and grains in the proper size range will not be obtained.

At least some of the carbon particles should preferably be intimately mixed with the oxide or oxide precursor. If no carbon particles are intimately mixed with the oxide or oxide precursor, but rather the carbon particles are present only as large agglomerates in which the oxide or oxide precursor is not present, then pores of the correct size will not be formed. The size of the carbon particles and the volume of these particles can be selected to accommodate the desired pore size and pore volume.

Any method suitable for producing an oxide or oxide precursor having a substantially uniform distribution of elements can be used in the method of the present invention if carbon particles of the appropriate size can be added to the method such that at least some of the carbon particles are intimately mixed with the precursor and the method can produce an oxide having the appropriate grain size.

Thus, in a preferred embodiment of the invention, the method further comprises the preliminary steps of: providing a solution comprising a complex oxide precursor element of a metal cation, a source of carbon particles and a non-ionic, cationic or anionic surfactant; mixing the solution, surfactant and carbon particles so as to form surfactant micelles, and the mixture forming a substantially homogeneous dispersion; and heating the mixture to form the complex metal oxide under conditions to substantially remove the carbon particles.

In another preferred embodiment, the oxide precursor may be prepared according to the method described in U.S. patent No.6752979, issued to the applicant, the entire disclosure of which is incorporated herein by reference. The method comprises the following steps:

a) preparing a solution comprising one or more metal cations;

b) mixing the solution from step (a) with a surfactant under conditions such that surfactant micelles form within the solution to thereby form a micellar liquid; and

c) heating the micellar liquid from step b) above to form the metal oxide, the heating step occurring at a temperature and for a time to remove the surfactant and thereby form metal oxide particles having a disordered pore structure,

in a preferred embodiment of the invention, carbon black particles are added to the solution from a) or the mixture from b), and the heat treatment also substantially removes (burns off) the carbon black particles. Preferably, the carbon particles are added to the solution of step a) before mixing.

In another preferred embodiment, the carbon particles are mixed with the cationic solution in step a) or the mixture from step b) or both by the method as described above. The carbon black particles are preferably dispersed into the initial solution and/or solution-surfactant mixture by high shear, sonication, evacuation of the particles prior to addition to the liquid (cavitation), or combinations thereof.

In another preferred embodiment, a mixture of complex oxide and carbon particles may be provided by mixing carbon particles with complex oxide particles having a size range that is similar to or smaller than a target grain size.

Alternatively, or in addition, the complex oxide may be formed by using methods well known in the art. The complex oxides can be produced by using polymer compounding, co-precipitation or sol-gel methods, thermal evaporation, hydrothermal methods or any other suitable method or combination thereof. Examples of such methods are given in U.S. patent no 6139816(Liu et al), U.S. patent no 5879715(Higgens et al), U.S. patent no 5770172(Linehan et al), U.S. patent no 5698483(Ong et al), U.S. patent no 6328947(Monden et al), U.S. patent no 5778950(Imamura et al), and U.S. patent application publication no 2005/0008777(McCleskey et al). The above-mentioned patents and patent applications are hereby incorporated by cross-reference in their entirety for disclosure. The method of the first aspect of the invention is particularly applicable to a method of making metal oxides in which a solution comprising one or more precursors is mixed with a surfactant or polymer and subsequently treated, typically by heating, to form a complex metal oxide.

The heat treatment step in the process of the invention may be carried out by using any suitable apparatus known in the art, for example, a tube, belt or muffle furnace, a fluidized bed furnace, a multiple hearth furnace, a rotary calciner, a heated substrate, a thermal spray calciner, a spray calciner, etc.

If the oxide or oxide precursor comprises individual particles that are not connected, the heat treatment should be such that some connections are formed between the particles before the carbon burns out. If such a network is not formed before the carbon burns out, the pores will collapse.

The heat treatment then removes ("burns out") the carbon to create pores and converts the oxide precursor into the desired oxide crystal structure.

The heating step results in the formation of a pore structure of the metal oxide and the particles. Unlike prior art processes for producing complex metal oxides, the method of the present invention only moderately requires relatively low application temperatures. In fact, in experimental work carried out to date, application temperatures below about 350 ℃ have been found to be suitable. The maximum application temperature reached in step (c) is preferably no more than about 750 deg.C, more preferably no more than about 650 deg.C, and most preferably about 300-350 deg.C.

The heating step may comprise rapid heating to a maximum desired temperature, or may comprise a more precisely controlled heat treatment mechanism.

Thus, in another preferred embodiment of the present invention, the heat treatment step comprises the steps of:

the dispersion is subjected to a heat treatment profile over a predetermined time to reach the desired maximum temperature.

For example, the heating step may be carried out in a controlled atmosphere. The heating step may comprise heating to a drying temperature (typically below the boiling temperature of the mixture) to dry the mixture, then slowly raising the temperature to the maximum application temperature, or then sequentially increasing to an intermediate temperature before finally reaching the maximum application temperature. The duration of the heating step may vary widely such that the preferred time in step (c) is from 15 minutes to 24 hours, more preferably from 15 minutes to 2 hours, most preferably from 15 minutes to 1 hour.

The heat treatment profile may range from about 100 deg.C to 750 deg.C, preferably from about 100 deg.C to 650 deg.C, and more preferably from about 100 deg.C to 300 deg.C. It will be appreciated that the selected heat treatment profile will depend on the specific composition of the complex oxide being treated.

The heat treatment step is preferably carried out under oxygen-enriched conditions. This may be achieved by providing a suitable air flow within the hot environment.

In a preferred embodiment, the heat treatment should promote the penetration of oxygen into the particles during the carbon burn-off phase. Preferred apparatus comprises a fluidized bed furnace or the like. Smaller oxide or oxide precursor/carbon particle sizes also promote oxygen permeation. Applicants have found that better permeation of oxygen can lead to better thermal stability. Without being bound to any particular theory, applicants believe that better oxygen permeation results in more complete removal of carbon at lower temperatures and thus maintains a more oxidizing atmosphere. Less oxygen results in carbon retention at higher temperatures and capture of reducing gases such as carbon monoxide, resulting in a very reducing environment. This can result in some metal formation and retention of the metal to very high temperatures, which can lead to sintering and loss of surface area. Oxygen permeation may be facilitated by moving the oxide relative to an oxygen-containing atmosphere to thereby reduce the thickness of the boundary layer around the oxide and thereby increase the diffusion rate of oxygen into the oxide. It is suitable to treat the oxides in a fluidized bed furnace or in a furnace in which an oxygen-containing atmosphere is passed.

Also, a heat treatment that allows burning off of carbon at a relatively low temperature, for example, at a temperature of about 100 to 750 ℃, preferably about 100 to 650 ℃, and more preferably about 100 to 300 ℃ is preferred. Burning off at sufficiently high temperatures can lead to uncontrolled exothermic burnout of the carbon, which severely reduces the surface area. Also, applicants believe that the retention of carbon to higher temperatures reduces high temperature stability by the mechanism described above.

To avoid deviating from the desired temperature profile of the burn-up step, precise control of the burn-up step should be maintained. For example, accurate monitoring of the temperature during burn-up may be used. If an undesirable increase in temperature is observed (indicating excessive energy production due to an increase in the exothermic combustion rate of carbon), the atmosphere supplied to the furnace can be controlled by reducing the partial pressure of oxygen. One way to achieve this result is to inject additional nitrogen or other inert or non-reactive gas. This not only reduces the partial pressure of oxygen, but also serves to cool the furnace. Since it is also desirable to maintain an oxidizing atmosphere during the burn-off of the carbon containing pore formers, this method of controlling the temperature should be used only when a rapid response to temperature excursions is required or excursions occur significantly and the oxidation of the carbon must be rapidly reduced or stopped (e.g., for safety reasons). Alternatively, additional cooling may be provided. Satisfactory results can also be obtained by not closely monitoring the temperature during burn-up, but by keeping the temperature during burn-up below a specified maximum temperature. The maximum temperature specified may vary greatly depending on the particular complex metal oxide being formed. As another alternative, the method of the present invention may be operated under specified operating conditions (such as oxygen flow rate and furnace cooling) and maintained quality control protocols that reject any off-grade product. The presence of defective products can be determined by testing of the product or by monitoring techniques that monitor one or more operating parameters and reject any product formed when one or more parameters deviate from a specified range of values. For example, a simple thermocouple may be used to monitor the maximum temperature reached during the process and the product may be rejected if the maximum temperature exceeds a specified maximum or if visual inspection indicates that the mix or product is red hot during processing.

In a second aspect of the present invention, there is provided a porous complex oxide material, wherein the complex oxide material exhibits high temperature stability and comprises an oxide component represented by the following general formula:

A_1-xB_xMO₃

here, the first and second liquid crystal display panels are,

a is a mixture of lanthanides;

b is a divalent or monovalent cation;

m is an element or a mixture of elements selected from the group consisting of 22 to 32 atomic numbers, 40 to 51 atomic numbers, and 73 to 83 atomic numbers; and

x is a number in the range 0.1. ltoreq. x.ltoreq.0.5.

The complex oxide material is preferably made by the method of the first aspect of the invention.

The complex oxide material may be a suitable phase (e.g., single phase or multi-phase) having an initial surface area of greater than about 15m²A/g, preferably greater than about 20m²Per g, more preferably greater than about 30m²(ii) a surface area of greater than about 5m after aging for 2 hours at a temperature of 1000 ℃ in air²Per g, more preferably greater than about 10m²/g, most preferably greater than about 15m²/g。

The complex oxide material may exhibit a substantially uniform composition.

The complex oxide material may comprise a perovskite material.

The complex oxide material may generally exhibit an average grain size of about 2 to 150nm, preferably about 2 to 100nm, and have a pore size range of about 7 to 250nm, preferably about 10 to 150 nm. However, the average grain and pore size of the complex oxide material may vary depending on the particular complex oxide selected.

For example, for CeZrO₂Complex oxide materials of the type (I), the average grain size may preferably fall at the lower end of this range, for example, in the range of about 2 to 50nm, more preferably about 2 to 10nm, and the pores are in the range of about 7 to 50nm, more preferably about 7 to 30 nm.

The complex oxide material of lanthanum manganate type may exhibit an average grain size of about 2 to 100nm, more preferably about 2 to 30nm, and pores in the range of about 15 to 200nm, more preferably about 15 to 150 nm.

More preferably, the complex oxide material may exhibit a substantially dispersed range of pore sizes.

In a third aspect, the present invention provides a method for producing a porous non-refractory metal oxide, the method comprising providing a mixture of:

a) one or more precursor elements suitable for producing a non-refractory metal oxide, particles of a non-refractory oxide, oxide particles that are precursors of a non-refractory oxide, or mixtures of two or more thereof; and

b) selecting a particulate carbonaceous pore former material for providing a pore size in the range of about 7nm to 250nm,

and, treating the mixture to

(i) Forming a porous non-refractory metal oxide, and the non-refractory metal oxide has a grain size of about 1nm to 150 nm; and

(ii) the pore-forming material is removed under conditions such that the porous structure and composition of the non-refractory metal oxide is substantially retained.

Suitably, in step (i) above, one or more of the precursor elements from (a) above are added to the phase of the non-refractory metal oxide.

The one or more precursor elements may include one or more metal compounds comprising one or more metals selected from the group consisting of the metals having atomic numbers 3, 4, 11, 19-21, 23-32, 37-39, 41-51, 55-84, and 87-103. The one or more metal compounds may be oxides, acetates, carbonates, nitrates and the like.

Unlike the first aspect of the invention, the method of the third aspect of the invention comprises forming a porous metal oxide having a defined grain size and pore size of only one metal (i.e. not a complex oxide) in the oxide phase. However, the third aspect of the present invention is limited to the formation of non-refractory metal oxides. The formation of such non-refractory metal oxides in this manner is a very surprising result since the presence of the carbonaceous pore-forming particles is believed to potentially result in the reduction of the non-refractory metal oxide during the step of removing the pore-forming particles, which of course destroys or substantially impairs the metal oxide phase. However, the inventors of the present invention have found that the method of the third aspect of the present invention can in fact form such non-refractory metal oxides.

In one embodiment, the method of the third aspect of the invention provides the precursor element as a solution or dispersion. For example, a solid phase mixture may be formed first and then dispersed or dissolved in a suitable solvent.

In one embodiment, the precursor elements and pore-forming material may be mixed to form a solid phase mixture, followed by formation of the oxide by appropriate thermal treatment, as described below.

In another embodiment, oxide particles may be formed from appropriate precursor elements, and pore-forming materials are mixed with the oxide particles to form a mixture.

The mixture may optionally be provided as a solution or suspension. For example, a solid phase mixture may be formed first and then dispersed or dissolved in a suitable solvent.

In another embodiment, the precursor elements may be formed first in solution, followed by the addition of the pore-forming material to the solution. Alternatively, the precursor elements and at least a portion of the pore-forming material can be mixed to form a solid phase mixture, and the mixture dissolved in a suitable solvent.

In the case of forming a dispersion or solution, any suitable solvent may be used. Although inorganic and organic solvents such as acids (e.g., hydrochloric or nitric acid), ammonia, alcohols, ethers, and ketones can be used, water is the preferred solvent.

The method of the third aspect of the invention is particularly applicable to a method of making a metal oxide in which a solution comprising one or more precursors is mixed with a surfactant or polymer and then heated, typically by heating, to form the metal oxide.

Further features of embodiments of the third aspect of the invention are as described with reference to the various embodiments of the invention and need not be re-described for convenience and brevity.

The method of the third aspect of the invention has been used to produce copper oxide having a large specific surface area. Other oxides, whether complex oxides or oxides comprising a single metal species, have also been made by the process of the second aspect of the invention.

The methods of the first and third aspects of the invention are particularly suitable for making metal oxide powders.

Drawings

Figure 1 shows the pore size distribution of the materials prepared in examples 1 and 2 after heat treatment to 650 ℃.

FIG. 2 shows the surface areas and La obtained after heat treatment at 650 ℃ and 800 ℃ for examples 18 to 22₂O₃The relationship between the contents.

FIG. 3 shows the pore volumes and La obtained after heat treatment at 650 ℃ for examples 18 to 22₂O₃The relationship between the contents.

FIGS. 4a and 4b show the XRD patterns of Ce0.45Zr0.45La0.10x heat-treated to 450 ℃ prepared a) without carbon (example 28) and b) with carbon (example 29).

FIGS. 5a and 5b show XRD patterns of Ce0.45Zr0.45La0.10x heat-treated to 800 ℃ prepared a) without carbon (example 28) and b) with carbon (example 29).

Detailed Description

Example 1

La was prepared according to the following method_0.8Sr_0.2Ni_0.04Pd_0.06Mn_0.9O₃. By mixing 149 g of La (NO)₃)₃·6H₂O, 18.2 g Sr (NO)₃)₂6.86 g Pd (NO)₃)₂·xH₂O, 2.04 g NiCO₃And 138.3 g Mn (NO) in 233g/L Mn in an aqueous solution₃)₂Dissolved in a mixture of 135 g of water and 12 g of HNO₃(70%) to make a solution. 119 grams of this solution was mixed with 72 grams of Brij 30 surfactant. The mixture was slowly heated to 300 ℃. The dried product was then heat treated in a tube furnace with air flow at temperatures of 300 deg.C, 350 deg.C, 400 deg.C, 450 deg.C, 500 deg.C, 600 deg.C and 650 deg.C for 0.5 hours.

XRD showed the material to be a single phase perovskite. The surface area obtained after this heat treatment was 17.8m²(ii) in terms of/g. Figure 1 shows the pore size distribution. TEM showed an average grain size of about 50 nm. After heat treatment at 1000 ℃ for 2 hours, the surface area was 6.9m²/g。

Example 2

Except that 16.15 grams of carbon black (Cabot Monarch 1300, average primary particle size 13nm, DBP oil absorption 100cc/g, nitrogen surface area 560 m) was stirred with a magnetic stirrer prior to mixing with the surfactant²(g) La was prepared in the same manner as in example 1 except that it was mixed with the solution_0.8Sr_0.2Ni_0.04Pd_0.06Mn_0.9O₃. The solution/carbon black mixture was dispersed by a high speed shearer (shearer), then mixed with the surfactant, and then dispersed again. The same heat treatment as in example 1 was applied.

XRD showed the material to be a single phase perovskite. The surface area obtained after the heat treatment was 24.7m²(ii) in terms of/g. Figure 1 shows the pore size distribution. TEM watchThe mean grain size is about 50 nm. After heat treatment at 1000 ℃ for 2 hours, the surface area was 10.04m²/g。

It should be noted that the addition of carbon black provides significantly larger pores and the material is more stable at high temperatures.

Example 3

La was prepared in the same manner as in example 2, except that the heat treatment comprised directly placing the material heated to 300 ℃ at a temperature of 1000 ℃_0.8Sr_0.2Ni_0.04Pd_0.06Mn_0.9O₃. After heat treatment at 1000 ℃ for 2 hours, the surface area was 1.9m²/g。

This example shows that the addition of carbon black to the perovskite is not sufficient by itself to provide high temperature stability. The heat treatment conditions used in this example resulted in a disruption of the surface area of the material. It is assumed that the large temperature step changes used in this embodiment result in uncontrolled burning of carbon from the oxide, which results in localized areas of very high temperature. This is assumed to result in sintering and reduction of the metal oxide. In other words, the composition and pore structure of the metal oxide is not maintained during the carbon burn-off process.

Example 4

La was prepared in the same manner as in example 3, except that there was no gas flow in the tube furnace_0.8Sr_0.2Ni_0.04Pd_0.06Mn_0.9O₃. The rest of the procedure was the same.

XRD showed the material to be a perovskite phase. The full width at half maximum (FWHM) of the peak was similar to the FWHM of the peak in examples 1 and 2, indicating that the grain size was similar (i.e., about 50 nm). The surface area obtained after this heat treatment was 22.1m²(ii) in terms of/g. After heat treatment at 1000 ℃ for 2 hours, the surface area was 9.1m²/g。

The results were compared with those of example 2 (10.2 m)²Comparison of/g) shows the beneficial effect of increasing oxygen during heat treatment. The inventors believe thatLess oxygen provides reducing conditions in the furnace which can lead to the formation of metal in the material. This can cause sintering and a reduction in surface area and porosity.

Examples 5 to 8

La was prepared in a similar manner to example 2 using different amounts of carbon black (Raven 850)_0.8Sr_0.2Ni_0.04Pd_0.06Mn_0.9O₃。

XRD showed the material to be a perovskite phase and the peak FWHM was similar to examples 1 and 2.

The surface area, pore volume and pore size distribution are shown in table 1 and clearly depend on the amount of carbon black used.

TABLE 1

Examples	Amount of carbon Black (g)	Surface area (m) at 650 ℃/g)	Pore volume (cc.g) of 2 to 200nm diameter	Pore volume (cc.g) of 10 to 200nm diameter	Pore volume (cc.g) of 50 to 200nm diameter
						5	8	37	0.22	0.2	0.1
6	16	44	0.33	0.31	0.18
						7	32	44	0.34	0.32	0.22
8	48	51	0.41	0.39	0.25

Examples 9 to 11 La Using different carbon blacks_0.8Sr_0.2Ni_0.04Pd_0.06Mn_0.9O₃Examples

Shows the use of different types of carbon black pore formers for the formation of a pore from a complex oxide La_0.8Sr_0.2Ni_0.04Pd_0.06Mn_0.9O₃Examples of the effects of the surface area and pore structure obtained.

The oxide was formed by using the method described in example 2, except that different types of carbon black were used.

XRD showed that all compounds were perovskite structures with peak FWHM similar to examples 1 and 2, indicating a grain size of about 50 nm. The results of the surface area and pore structure obtained are shown in table 2.

TABLE 2

Examples 12 to 13

In examples 12 to 13, La was prepared in the same manner as in examples 1 and 2 (without carbon and with carbon), respectively, except that polyethylene glycol (molecular weight 4000) was used in place of the surfactant_0.8Sr_0.2Ni_0.04Pd_0.06Mn_0.9O₃. XRD showed a perovskite phase, and a small amount of impurity peak example 12. The surface area and pore volume are shown in table 3. It is clear that the addition of carbon increases the number of larger pores.

TABLE 3

Examples 14 to 15

Preparation of La by coprecipitation technique_0.8Sr_0.2Ni_0.04Pd_0.06Mn_0.9O₃Examples 14 and 15 were made with carbon (17.8g of Monarch 1300) or without carbon. A solution was prepared in the same manner as in example 1. Another solution was prepared by dissolving 55g of ammonium oxalate in 960 g of water. These solutions were combined by slowly adding each solution to a stirred vessel to produce a precipitate. The precipitate was washed, filtered and dried at-100 ℃ and then washed withThe heat treatment was carried out in the same manner as in example 1.

XRD showed a perovskite phase and some separate peaks. The surface area and pore volume are shown in table 4.

It is clear that the effect of carbon on the pore distribution is much less than that observed in the examples using surfactants and polyethylene glycol. Without being bound to any particular theory, the inventors believe that the large liquid volumes often required for co-precipitation result in very dispersed precipitate particles and carbon particles. This can make it difficult to disperse the carbon particles sufficiently between the precipitates to create the desired porosity.

TABLE 4

Examples 16 to 21 Ce using different types of carbon blacks_0.54Zr_0.37La_0.03Pr_0.06O_xExamples

These examples show the use of different types of carbon black pore formers for the formation of a pore from a complex oxide Ce_0.54Zr_0.37La_0.03Pr_0.06O_xThe surface area and pore structure obtained.

The component Ce is prepared by dissolving appropriate amounts of cerium nitrate, zirconium carbonate, lanthanum nitrate and praseodymium nitrate in a water/nitric acid solution_0.54Zr_0.37La_0.03Pr_0.06O_xAn oxide of (a). 33 grams of carbon black was dispersed into the solution using a high speed shear, 70 grams of Erunon LA4 surfactant was added and the mixture was redispersed. The mixture was slowly heated to 300 ℃. The dried product was then heat treated in a tube furnace with air flow at temperatures of 300 deg.C, 350 deg.C, 400 deg.C, 450 deg.C, 500 deg.C, 600 deg.C and 650 deg.C for 0.5 hour.

XRD showed the sample to be a single phase and TEM showed the average grain size of the materials prepared in these examples after heating to 650 ℃ to be 5-10 nm. Other examples exhibit similar FWHM XRD peaks, indicating similar grain sizes.

The surface area and pore volume of the samples using the different carbon blacks are shown in table 5 below along with the particle size and oil absorption values of the carbon blacks. The surface area obtained after heat treatment at a temperature of 1000 c for 2 hours is also shown in the figure.

TABLE 5

It is clear that the pore structure and surface area can be varied by using carbon blacks with different morphological characteristics.

Examples 22 to 26 having an excessive La content

La was prepared in a similar manner to the previous examples_0.8Sr_0.2Mn_0.9Ni_0.04Pd_0.06O₃+La₂O₃A material. La₂O₃The amount of (C) varies between 2.5 wt% and 20 wt%. XRD showed perovskite phase plus excess La due to addition₂O₃Increased amount of La₂O₃And (4) phase(s). FIGS. 2 and 3 show the surface areas and La obtained after heat treatment at 650 ℃ and 800 DEG C₂O₃The relationship between the contents.

This example shows that the pore structure of the oxide composition can be altered by adding varying amounts of the second phase.

Example 27 excess CeO₂(7b)

La was prepared in a similar manner to example 1_0.8Sr_0.3Ni_0.04Pd_0.06Mn_0.9O₃+10 wt% of CeO₂. The components are specifically selected to provide a perovskite phase and independentCeO₂Phase (excess CeO)₂In an amount that cannot be added to the perovskite phase). XRD showed the material to be a perovskite phase and CeO₂. The surface area obtained was 28.9m²And a pore volume of 0.26cc/g at 3nm to 200nm, about 0.25cc/g at 10nm to 200nm, and about 0.175cc/g at 50nm to 200 nm. After a heat treatment at 1000 ℃ for 2 hours, the surface area was 11.7m²/g。

Examples 28 and 29 Ce prepared by hydrothermal method_0.45Zr_0.45La_0.1O_x

Preparation of Ce by using a hydrothermal method analogous to known methods used for analogous compounds_0.45Zr_0.45La_0.1O_x。

49.3 grams of cerium (IV) ammonium nitrate, 27.4 grams of zirconium carbonate, and 8.66 grams of lanthanum nitrate were dissolved in a solution containing 940 grams of water and 63 grams of nitric acid (70%). The mixture was heated at a temperature of about 95 ℃ for about 24 hours, thereby causing a precipitate to form. Finally 150ml of ammonia solution (%) were added and the precipitate was washed, separated by filtration and dried at a temperature of about 100 ℃. Then, heat treatment is performed. The temperature is raised from 150 ℃, and the temperature is preserved for 0.5 hour at 150 ℃, 200 ℃, 250 ℃, 300 ℃, 350 ℃, 400 ℃ and 450 ℃ in sequence. The surface area after the heat treatment was 145m²(ii) in terms of/g. The pore volume is shown in table 6, and XRD is shown in fig. 4.

Comparative example 29

Ce was prepared in the same manner as in example 28, except that 32 g of Raven 850 carbon black was added to the solution and dispersed with a high speed shearer_0.45Zr_0.45La_0.1O_x. Hydrothermal heating and heat treatment were then carried out in the same manner. The surface area of the sample was about 100m²(ii) in terms of/g. The pore volume is shown in table 6, and XRD is shown in fig. 4. Compared to example 28, it can be seen that the addition of carbon increases the volume of macropores. XRD, however, shows that the addition of carbon results in the formation of oxides with slightly separated ceria-rich and zirconia-rich phases. This is confirmed by the double peak, the separated peak towards CeO₂And ZrO₂The peak position shifts. Thus, carbon has affected the hydrothermal precipitation process, resulting in significant separation of different elemental species and increased pore volume. This effect is more clearly shown in fig. 5, which fig. 5 shows XRD of two exemplary compounds with an additional heat treatment applied at 800 ℃ for 0.5 h.

TABLE 6

Examples 30 to 32CuO

CuO was prepared by using a method similar to the previous example. Example 30 was slowly heat treated to 350 ℃ with incubation at 150 ℃, 200 ℃, 250 ℃, 300 ℃ and 350 ℃ for 0.5 hour. Example 31 was also heat treated in a similar manner but it was observed that the sample was severely overheated during the heat treatment, thereby reddening (red glow) in the region indicating that the sample experienced temperatures well above 350 ℃. Example 32 was subjected to a slower heat treatment with the additional step of holding at 225 ℃ for 1 hour. This heat treatment was found to produce materials with more consistent properties, and no high temperature excursions were observed.

XRD of all materials showed only CuO phase. The surface area and pore volume obtained are listed in table 7.

TABLE 7

Surprisingly, these examples show that heat-sensitive materials can be produced by using the method of the invention with appropriate heat treatment.

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the present invention.

It will be further understood that the term "comprises" (or grammatical variants thereof), as used in this specification, is equivalent to "includes" and should not be taken as excluding the presence of other elements or features.

Claims (25)

1. A method for manufacturing a porous complex oxide, the method comprising the steps of: providing a mixture of:

a) precursor elements suitable for producing complex oxides; or

b) One or more precursor elements and one or more metal oxide particles suitable for producing particles of complex oxides; and

c) a particulate carbonaceous pore-forming material selected to provide a pore size in the range of from 7nm to 250nm,

wherein at least one of the precursor elements is present in the form of a solution,

and, treating the mixture to

(i) Forming a porous complex oxide in which two or more of the precursor elements from the above (a) or one or more of the precursor elements from the above (b) and one or more of the metals in the metal oxide particles are added to a phase of the complex metal oxide, and the complex metal oxide has a crystal grain size of 1nm to 150 nm; and

(ii) the pore-forming material is removed under conditions such that the porous structure and composition of the complex oxide is substantially retained.

2. The method of claim 1, wherein the pore-forming material has a particle size in the range of 7nm to 300 nm.

3. The method of claim 1, wherein the mixture further comprises a surfactant or a polymer.

4. The method of claim 1, wherein a single phase complex metal oxide is formed.

5. The method of claim 1, wherein a phase of the complex metal oxide and one or more phases of the other metal oxides are formed.

6. The method of claim 1, wherein two or more complex metal oxide phases are formed with or without any other metal oxide phases.

7. The method of claim 1, wherein each complex metal oxide phase formed is a phase pure phase.

8. The method of claim 1, wherein the pore-forming material has a particle size of 10nm to 150 nm.

9. The method of claim 1, wherein the pore-forming material has a particle size of 10nm to 100 nm.

10. The method of claim 1, wherein the pore-forming material is particles of carbon black.

11. The method of claim 1, wherein the components for forming the complex oxide are uniformly dispersed to form a mixture of precursor elements.

12. The method of claim 11, wherein the pore-forming particles are dispersed in the mixture by a method selected from the group consisting of high shear, ultrasonic mixing, rolling, ball milling, or sand milling.

13. The method of claim 1, wherein prior to forming the mixture, air is removed from the carbon-containing pore-forming material by vacuum.

14. A method as claimed in claim 1, characterized in that the method comprises the following steps: providing a solution of a complex oxide precursor element comprising a metal cation, a source of carbon particles and a non-ionic, cationic or anionic surfactant, mixing the solution, surfactant and carbon particles to form a mixture such that surfactant micelles are formed and the mixture forms a substantially homogeneous dispersion, heating the mixture to form the complex metal oxide under conditions to substantially remove the carbon particles.

15. The method of claim 14, wherein the method comprises the steps of:

a) preparing a solution comprising one or more metal cations;

b) mixing the solution from step (a) with a surfactant under conditions such that surfactant micelles form within the solution to thereby form a micellar liquid; and

c) heating the micellar liquid from step b) above to form a metal oxide, the heating step being carried out at a temperature and for a time to remove the surfactant and thereby form metal oxide particles having a disordered pore structure,

wherein carbon black particles are added to the solution from a) or the mixture from b), and the heating step also substantially removes the carbon black particles.

16. The method of claim 15, wherein carbon black particles are added to the solution of step a) prior to mixing.

17. The method of claim 1, wherein the step of treating the mixture to form complex metal oxides and remove carbonaceous particles comprises heating the mixture to a temperature of from 100 ℃ to 750 ℃.

18. The method of claim 17, wherein the temperature falls within the range of 100 ℃ to 650 ℃.

19. The method of claim 17, wherein the temperature falls within the range of 100 ℃ to 300 ℃.

20. The method of claim 1, wherein the treatment applied to the mixture is a thermal treatment, and wherein one or more of the temperature, cooling rate, or oxygen partial pressure is controlled during the thermal treatment step to minimize or avoid reduction of the complex metal oxide during removal of the carbonaceous particles.

21. The method of claim 20, wherein the temperature is controlled such that a specified maximum temperature is not exceeded during the removal of the carbonaceous particles.

22. The method of claim 1, wherein the complex metal oxide comprises two or more metals having atomic numbers of 3, 4, 11, 12, 19-32, 37-51, 55-84, and 87-103.

23. A method of making a porous metal oxide, the method comprising providing a mixture of:

a) one or more precursor elements suitable for producing a non-refractory metal oxide, at least one of the one or more precursor elements being in solution; and

b) selecting a particulate carbonaceous pore-forming material for providing a pore size in the range of from 7nm to 250nm,

c) a surfactant or a polymer, and a surfactant or a polymer,

and, treating the mixture to

(i) Forming a porous metal oxide, wherein the non-refractory metal oxide has a grain size in the range of 1nm to 150 nm; and

(ii) the pore-forming material is removed under conditions that substantially preserve the porous structure and composition of the metal oxide.

24. The method of claim 23, comprising the steps of:

preparing a solution comprising one or more metal cations;

mixing the solution with a surfactant under conditions such that surfactant micelles form within the solution to thereby form a micellar liquid; and

heating the micellar liquid to form a metal oxide, the heating step being carried out at a temperature and for a time to remove the surfactant and thereby form metal oxide particles,

wherein carbon black particles are added to the solution and the heating step also substantially removes the carbon black particles.

25. The method of claim 23, wherein the pore-forming material has a particle size in the range of 7nm to 300 nm.