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  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
  • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
  • B01J21/066—Zirconium or hafnium; Oxides or hydroxides thereof
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  • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
  • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
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  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/40—Catalysts, in general, characterised by their form or physical properties characterised by dimensions, e.g. grain size
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  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
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  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/03—Precipitation; Co-precipitation
  • B01J37/031—Precipitation
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/03—Precipitation; Co-precipitation
  • B01J37/036—Precipitation; Co-precipitation to form a gel or a cogel
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  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/06—Washing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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  • C01—INORGANIC CHEMISTRY
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  • C01G25/00—Compounds of zirconium
  • C01G25/02—Oxides
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  • C01P2006/14—Pore volume

Definitions

• the invention relates to nanoscale particles and catalytic systems for catalyzing chemical reactions and a process for their synthesis.
• Catalysis involves many reactions, in various technical fields, in particular environmental applications, petrochemistry, or fine chemistry. It consists in modifying the speed of a chemical reaction by bringing the reactants of this reaction into contact with a catalyst, for example platinum, which does not appear in the reaction balance.
• a catalyst for example platinum
• the catalyst is previously deposited on a support, for example in the form of a nanometric powder, the particle size of which is less than 100 nm.
• the particles have rod and needle shapes.
• the particle sol obtained at the end of the hydrothermal processes is only centrifuged and washed with distilled water in a conventional manner, which makes it impossible to obtain a purity of the powder of less than 0.7%. .
• An object of the invention is to provide a powder or a catalytic system which would make it possible to increase the efficiency of the catalysis reactions and a process making it possible to manufacture this powder or catalytic system industrially.
• this object is achieved by means of a process for synthesizing a powder comprising the following successive steps:
• A) preparing a mother liquor comprising: i. an oxide base component or a precursor of said base component and an additional component of formula MC, said additional component being composed of:
• the 100% complement consists of impurities.
• the purity of the powders of particles with a maximum size of less than 250 nm, or even less than 100 nm produced by the hydrothermal route, is limited. Indeed, an impurity content of less than 1% is not considered useful.
• the powders consisting of primary particles having a maximum size of less than 250 nm, preferably less than 100 nm and having an impurity content of less than 0.7%, are particularly suitable as catalysts, or as support for a catalyst in a catalytic system.
• the powders manufactured according to a process according to the invention can thus have a better maintenance over time of the catalytic performances (reaction rate and / or selectivity) than that of the powders according to the prior art.
• the invention also relates to a powder manufactured according to a synthesis method according to the invention.
• Step C) preferably comprises at least one washing operation chosen from
• washing operations should be repeated as many times as necessary until the desired purity is achieved.
• Simple filtration or simple rinsing are not sufficient to obtain an impurity content of less than 0.7% when an additional component of formula MC is introduced into the mother liquor.
• Acid-base neutralization is the preferred washing operation. It preferably comprises a suspension in an aqueous solution having a pH less than or greater than the zero charge point of said base component, depending on whether the impurities to be removed are cationic or anionic, and maintaining said suspension at a temperature below its temperature. boiling point at 1 bar for a period longer than 10 minutes, and filtration.
• the pH is preferably lower than or higher than said zero point of charge of at least 2 pH units, preferably, if possible, still less than or greater than said zero point of charge, of at least 4 pH units.
• the temperature is maintained less than 30 minutes.
• the pH may in particular be adjusted by adding hydrochloric acid and / or nitric acid and / or perchloric acid or by addition of ammonia (NH 4 OH).
• the last operation for removing cationic impurities takes place in an aqueous solution whose pH is adjusted with the aid of an organic acid or a mixture of organic acids and / or the last operation of Removal of anionic impurities takes place in an aqueous solution whose pH is adjusted with the aid of an organic base or a mixture of organic bases.
• step C) comprises at least one rinsing comprising a suspension of the product resulting from the preceding step in a solvent at a temperature below its boiling point at 1 bar for a duration greater than 10 minutes, then a filtration.
• the rinsing is preferably carried out in water having a degree of purity at least equal to that of the osmosis water or in an alcohol of purity greater than 98% by volume.
• the duration of the rinsing is preferably between 10 and 30 minutes.
• the rinsing may in particular be carried out between the washing operations, in particular between two operations to remove cationic or anionic impurities.
• a washing step C) allows the skilled person, possibly multiplying the aforementioned operations, to reach the required level of purity.
• a method according to the invention may also comprise one or more of the following steps:
• a calcination step E) advantageously makes it possible to eliminate the residual moisture and to further improve the purity of the powder by eliminating the organic constituents.
• the powder is calcined for at least 1 hour. More preferably, the calcination temperature exceeds 300 C ⁇ and preferably less than 500 0 C.
• the proportions of the exposed crystal planes are maintained, preferably, in step A), constituting the base and / or the precursor of this base component comprises more than 99.5%, preferably more than 99.8%, more preferably more than 99.9%, of said base component and / or said precursor of this basic component , respectively, as a percentage by weight based on the dry matter.
• the purification is simplified.
• the selection of very pure raw materials to bring a basic constituent and / or a precursor of this basic constituent does not, to date, lead, by the hydrothermal route, to a powder with a low level of impurities according to the invention. invention without a washing step.
• the method according to the invention comprises a washing step.
• the base component and / or the precursor of the base component added to the mother liquor are chosen so that the basic constituent of the powder has, for more than 95%, preferably more than 95%. %, more preferably for more than 99%, more preferably for substantially 100%, a monoclinic structure, in weight percent based on dry matter.
• the base constituent or the precursor of the base component added to the mother liquor may in particular be chosen so that the base component is an oxide among: HfO 2 , ZrO 2 , Eu 2 O 3 , Sm 2 O 3 , MoO 3 , WO 3 , preferably from : HfO 2 , ZrO 2 , MoO 3 , WO 3 , more preferably from ZrO 2 and / or HfO 2 , preferably always so that the base constituent is ZrO 2 zirconia.
• the pH of the mother liquor may be adjusted to be less than 4 if the basic constituent under consideration is selected from HfO 2 , ZrO 2 , Eu 2 O 3 , Sm 2 O 3 , or less than 2, if the constituent of considered base is selected from Hf ⁇ 2, ZrO 2, E ⁇ O 3, Sm 2 O 3, MoO 3 WO 31, or greater than 10.
• the method according to the invention may also comprise one or more of the following optional features:
• the mother liquor may comprise at least 0.5% of the base component of monoclinic structure, in particular zirconia, and / or a precursor of said basic constituent, in percentages by weight based on mother liquor.
• the precursor of the zirconia is a zirconium salt or a partially hydrolyzed zirconium derivative, preferably a zirconium oxyhydroxide.
• the mother liquor comprises a solvent other than water, for example ethanol.
• the content of said other solvent is less than 50% by weight of the liquid phase.
• the source of said base component of monoclinic structure and / or of said precursor of said basic component of monoclinic structure comprises more than 99.5%, preferably more than 99.8%, more preferably more than 99.9%, of said monoclinic structure base component and / or said precursor of said monoclinic structure base component, respectively as a percentage by weight on the basis of the dry matter.
• the purification is simplified.
• the mother liquor is added to at least one soluble agent in an aqueous medium selected from the group of oxoanions, anions of elements from column 17 of the Periodic Table of Elements, OH hydroxide "if the pH of the mother liquor is basic, and mixtures thereof
• the soluble agent in an aqueous medium may be chosen from the group consisting of sulphate (SO 4 2 " ), carbonate (CO 3 2” ), phosphate (PO 4 3 ), fluoride (F “ ), chloride (Cl) 1 perchlorate (CIO 4 “ ), borate (BO 3 3 “ ), nitrate (NO 3 " ), hydroxide ( OH ' ) and mixtures thereof or, if the pH is less than 4 in the group consisting of chloride (Cl “ ), perchlorate (CIO 4 “ ), nitrate (NO 3 " ), and mixtures thereof.
• the content of the agent is greater than 10 -4 mol / l, preferably
• the pH of the mother liquor is adjusted by means of an acid chosen from the group of organic and inorganic acids and their mixtures, or by means of a base chosen from the group of organic bases, inorganic bases and their mixtures .
• the mother liquor is composed of water, agent (s), said basic constituent of monoclinic structure and / or said precursor of said basic constituent, other possible solvents, acid (s), ) or possible baseline (s), any surfactant (s) and any deflocculant (s).
• step B the mother liquor is heated in a closed vessel at a temperature above the boiling point at 1 bar, preferably between 100 ° C. and 300 ° C.
• step B) 1 the rate of rise in temperature is less than 250 ° C / h or less than 200 ° C / h.
• step B) 1 the temperature is preferably maintained at least 1 hour and more preferably, less than 200 hours.
• step B the pressure in the closed vessel, or “reactor”, is greater than or equal to the boiling pressure of the mother liquor.
• the drying temperature is less than 500 D C, preferably less than 200 0 C.
• step D) the drying time is adjusted so that the particle powder has, at the end of this step, a residual moisture of less than 1% by weight.
• the process comprises an additional step subsequent to step C), in which the particles of the powder are doped by means of a dopant chosen from the group consisting of oxoanions, anions of column 17 and cations of the column. 1, and their mixtures.
• the dopant may in particular be chosen from silicates, phosphates, sulphates, chlorides, fluorides, sodium and potassium.
• said additive is composed of: said agent M, and a complement C chosen from the group constituted
• organic radical consists of a group of atoms selected from the group consisting of carbon, hydrogen, oxygen, and nitrogen;
• said additive of formula MC is composed of:
• a complement C chosen from the group consisting of all the positively charged organic molecules whose organic radical consists of a group of atoms selected from the group consisting of carbon, hydrogen and oxygen; , and nitrogen;
• the parameters of the synthesis method according to the invention are preferably adjusted so that
• the primary particles have maximum sizes greater than 10 nm and / or the impurities are such that, in percentages by mass of the dry matter:
• CaO ⁇ 0.1% preferably CaO ⁇ 200 ppm, more preferably CaO ⁇ 100 ppm and / or Na 2 O ⁇ 0.1%, preferably Na 2 O ⁇ 500 ppm, preferably Na 2 O ⁇ 200 ppm, more preferably Na 2 O ⁇ 100 ppm and / or
• SO 4 2 ' ⁇ 0.1%, preferably SO 4 2 " ⁇ 500 ppm, preferably SO 4 2" ⁇ 200 ppm, more preferably SO 4 2 " ⁇ 100 ppm and / or
• Fe 2 O 3 ⁇ 0.1% preferably Fe 2 O 3 ⁇ 200 ppm, preferably Fe 2 O 3 ⁇ 100 ppm, more preferably Fe 2 O 3 ⁇ 50 ppm and / or
• TiO 2 ⁇ 0.1% preferably TiO 2 ⁇ 200 ppm, preferably TiO 2 ⁇ 100 ppm, more preferably TiO 2 ⁇ 50 ppm.
• step A) has the following characteristics:
• the mother liquor then comprises a modifying agent chosen from the group consisting of oxoanions, anions of the elements of column 17 (halides) and their mixtures, preferably from the group consisting of chloride (Cl “ ), perchlorate (CIO 4 " ), nitrate (NO 3 " ) and mixtures thereof.
• a modifying agent chosen from the group consisting of oxoanions, anions of the elements of column 17 (halides) and their mixtures, preferably from the group consisting of chloride (Cl “ ), perchlorate (CIO 4 " ), nitrate (NO 3 " ) and mixtures thereof.
• this additive is preferably composed of:
• a complement C chosen from the group consisting of all the positively charged organic molecules whose organic radical consists of a group of atoms selected from the group consisting of carbon, hydrogen and oxygen; , and nitrogen; cations of the elements of columns 1 and 2, preferably the cations of the elements of column 1;
• the concentration of modifying agent in the mother liquor is between 10 -4 mol / l and 10 mol / l.
• step A) shows the following characteristics: - The pH of the mother liquor is greater than 10.
• the mother liquor comprises a modifying agent chosen from the group consisting of oxoanions except borate (BO 3 3 " ), carbonate (CO 3 2" ), nitrate (NO 3 " ), perchlorate (CIO 4 ' ), and mixtures thereof, preferably selected from the group of sulphate (SO 4 2 ' ), phosphate (PO 4 3 " ) and mixtures thereof.
• this additive of formula MC, is preferably composed of:
• organic radical consists of a group of atoms selected from the group consisting of carbon, hydrogen, oxygen, and nitrogen;
• the concentration of modifying agent in the mother liquor is greater than 10 -1 mol / l, with a pH of between 10 and 14.
• step A) has the following characteristics: - The pH of the mother liquor is greater than 10.
• the mother liquor comprises a modifying agent chosen from the group consisting of oxoanions, anions of the elements of column 17 (halides), hydroxide (OH “ ) and their mixtures, preferably chosen from the group consisting of hydroxide (OH “ ), carbonate (CO 3 2 ' ), fluoride (F ' ), chloride (Cl “ ), perchlorate (CIO 4 “ ), borate (BO 3 3” ), nitrate (NO 3 “ ) and mixtures thereof. More preferably, the modifying agent is hydroxide (OH " ).
• this additive is preferably composed of:
• said modifying agent M and a complement C selected from the group consisting of
• the concentration of modifying agent in the mother liquor is less than 10 mol / l if the modifying agent is chosen from the group of borate (BO 3 3 " ), carbonate (CO 3 2" ), nitrate (NO 3 “ ), perchlorate (CIO 4 “ ), hydroxide (OH “ ), anions of column 17 (halides), and mixtures thereof, and preferably the concentration of modifying agent is lower than at 10 "3 mol / l if the modifying agent is selected from the group of oxoanions except borate (BO 3 3” ), carbonate (CO 3 2 “ ), nitrate (NO 3 “ ), perchlorate (CIO 4 “ ), and mixtures thereof.
• the invention also relates to a powder synthesized or likely to have been synthesized according to a synthesis method. according to the invention.
• the particles of such a powder are called "particles according to the invention”.
• the shape of a rod exhibiting, for more than 35%, preferably more than 50%, preferably more than 80%, preferably more than 85% and, preferably, for less than 90%, plans belonging to the family ⁇ 1,1, 1 ⁇ , the primary particles then being called "sticks ⁇ 1,1,1 ⁇ ", and / or - the shape of an exponent plate, for more than 35%, preferably more than
• These primary particles advantageously expose a high percentage of so-called "rare" planes, that is to say of planes other than the most thermodynamically stable plane, and in particular a high percentage of planes of the family ⁇ 1, 1, 0 ⁇ and ⁇ 1, 0,0 ⁇ .
• These crystalline planes are useful for catalyzing or supporting catalysts to expose crystalline planes to which the reaction to be catalyzed is sensitive.
• the primary particles of the powder according to the invention preferably exhibit for at least 90%, preferably at least 95%, preferably for substantially 100%, of the families ⁇ 1, 1.0 ⁇ , ⁇ 1,1, 1 ⁇ and ⁇ 1, 0,0 ⁇ .
• the particles of the powder may be primary particles. They may also occur, at least in part, as secondary particles.
• the maximum particle size of the powder is less than 250 nm, preferably less than 200 nm, preferably less than 150 nm, preferably less than 100 nm, preferably less than 90 nm, preferably less than 80 nm and / or greater than 10 nm, preferably greater than 20 nm.
• the powder according to the invention is in particular intended to serve as catalyst or support for a catalyst to form a catalyst system according to the invention.
• the powder according to the invention can thus itself serve as a catalyst, the particles being uncoated with a catalyst, in particular for catalyzing a reaction sensitive to families of ⁇ 1, 1, 0 ⁇ , ⁇ 1,0,0 ⁇ planes. and ⁇ 1, 1, 0 ⁇ .
• the particles can also be used coated with a catalyst, forming a catalytic system, in particular to catalyze a reaction sensitive to families of ⁇ 1,1, 0 ⁇ and ⁇ 1,1,1 ⁇ planes.
• the invention also relates to a catalyst system comprising a powder of support particles to which crystallites of a catalyst adhere, said powder being in accordance with the invention.
• This catalytic system advantageously makes it possible to exhibit a high percentage of so-called "rare" planes, that is to say of planes other than the most thermodynamically stable plane, and in particular in the case of a catalyst selected from the metals of columns 8, 9 and 10 and of cubic structure, a high percentage of planes of the family ⁇ 1, 0,0 ⁇ .
• Catalyst systems comprising platelet-shaped primary particles predominantly showing ⁇ 1, 0.0 ⁇ family planes are particularly advantageous if the catalyst is selected from the metals of columns 8, 9 and 10 and of cubic structure.
• the primary particles are monocrystalline.
• the catalyst deposited on the surface of the support may be a metal, preferably chosen from the group of metals of columns 8, 9 and 10 of the periodic table of elements, preferably chosen from the group of metals of columns 8, 9; and 10 of the periodic table of elements and having a cubic structure, and mixtures thereof.
• the metal is platinum.
• the catalyst may also be an oxide, preferably chosen from lanthanum oxide and / or transition metal oxides, for example V 2 O 5 or Cr 2 O 3 and / or the oxides of the elements of the columns. and 15, preferably tin (Sn) 1 oxides of lead (Pb) and / or bismuth (Bi).
• the catalyst may also be a carbide, preferably selected from transition metal carbides, such as, for example, molybdenum carbide and / or tungsten carbide.
• the catalyst may also be a sulphide, preferably chosen from transition metal sulphides, preferably molybdenum sulphides and tungsten sulphides, optionally doped with cobalt or nickel (CoMoS for example).
• transition metal sulphides preferably molybdenum sulphides and tungsten sulphides, optionally doped with cobalt or nickel (CoMoS for example).
• CoMoS cobalt or nickel
• the catalyst is a metal selected from the group of metals of columns 8, 9 and 10 of the periodic table and is chosen so that at least 80%, preferably at least 90%, more preferably at least At least 95% by number, more preferably substantially all of the catalyst crystallites have a truncated cuboid or octahedron shaped raft.
• the size of the crystallites is preferably between 1.5 nm and 10 nm, preferably between 3 nm and 10 nm.
• the truncated cubo-octahedron crystallites are formed on the exposed planes ⁇ 1, 1,0 ⁇ and ⁇ 1,1, 1 ⁇ of the support particles, the crystallites in the form of a raft forming on the exposed planes ⁇ 1, 0,0 ⁇ of these particles, in particular when said particles have a monoclinic structure.
• the catalyst is chosen so that at least 80%, preferably at least 90%, more preferably at least 95% by number, more preferably substantially all of the catalyst crystallites of the catalyst system have a shape. which is not a spherical or spherical shape truncated according to the plane of contact with the support.
• the performance of the catalytic system is improved.
• the size of the crystallites of the catalyst is preferably between 1.5 nm and 10 nm, preferably between 3 nm and 10 nm.
• the catalyst represents less than 10%, preferably less than 7%, more preferably less than 5% of the mass of the catalytic system.
• a content of 1% of catalyst is generally suitable.
• Powder containing rods mainly exposing ⁇ 1,1, 0 ⁇ family planes and platelets mainly exposing ⁇ 1, 0,0 ⁇ families are particularly advantageous.
• the invention therefore also relates to a process using a powder according to the invention for catalyzing a chemical reaction.
• a powder according to the invention can be advantageously used to catalyze a reaction sensitive to the structure.
• the invention thus also relates to a process using a powder according to the invention, the primary particles not being coated with catalyst, for catalyzing a reaction chosen from hydrocarbon conversion reactions including selective oxidation reactions, the reactions hydrogenation, dehydrogenation reactions, hydrogenolysis reactions, isomerization reactions, dehydrocyclization reactions, and reforming reactions, or, after at least partial recovery, of said primary particles with a catalyst,
• the catalyst when the catalyst is selected from the group formed by the metals of columns 8, 9 and 10 of the periodic table of the elements and having a cubic structure, and the mixtures thereof, and in particular when the basic component of the particles of support is zirconia, to catalyze a reaction selected from the following group: a. a response where more than 26%, or even more than 35%, or more than 51% of the exposed shots belong to the ⁇ 1, 0,0 ⁇ family and / or more than 35%, or even more than 45%, or even more than 66% or more than 70% of the exposed planes belong to the family ⁇ 1,1,1 ⁇ , in percentages on the basis of the total exposed surface of the catalyst, are sought and / or, b.
• a response where more than 26%, or even more than 35%, or more than 51% of the exposed shots belong to the ⁇ 1, 0,0 ⁇ family and / or more than 35%, or even more than 45%, or even more than 66% or more than 70% of the exposed planes belong to the family ⁇ 1,1,
• reaction selected from hydrocarbon conversion reactions including selective oxidation reactions, hydrogenation reactions, dehydrogenation reactions, hydrogenolysis reactions, isomerization reactions, dehydrocyclization reactions, and reaction reactions.
• reforming c. selective hydrogenation reactions, and particularly selective hydrogenation reactions of molecules containing at least one carbonyl function CO, and reactions of selective hydrogenation of molecules containing at least two double bonds;
• methane formation reactions (“methanation reactions”);
• Fischer-Tropsch synthesis reactions including methanol synthesis reactions, in other words the formation of oxygenated hydrocarbons from carbon monoxide (CO), hydrogen (H 2 ), and / or organic molecules ( biomass for example);
• the base component of the carrier particles is monoclinic, to catalyze a reaction selected from hydrocarbon conversion reactions including selective oxidation reactions, hydrogenation reactions, reaction reactions, dehydrogenation, hydrogenolysis reactions, isomerization reactions, dehydrocyclization reactions, and reforming reactions.
• the powders and catalytic systems according to the invention comprise primary particles whose base constituent is selected from the group formed by zirconia (ZrO 2). 2 ), hafnium oxide (HfO 2 ), a mixture of zirconia and hafnium oxide, molybdenum oxide and tungsten oxide are well suited to catalyze a percentage-sensitive reaction. of exposed crystalline plane (s) of families ⁇ 1, 1, 1 ⁇ and / or ⁇ 1, 0,0 ⁇ .
• the catalytic system according to the invention is also particularly well suited to catalyze a reaction taking place at a temperature below 500X.
• the maximum size of the primary support particles can advantageously be maintained less than 250 nm, preferably less than 100 nm, and the size of the catalyst crystallites carried by the support can be kept below 10 nm.
• the crystallites can, throughout the reaction, expose other crystalline planes than those of the family of thermodynamically thermodynamically stable crystalline planes.
• the family of thermodynamically most stable planes in temperature is the family ⁇ 1, 1, 1 ⁇ .
• a “catalytic system” is an assembly consisting of a support, in the form of powder, and a catalyst fixed on said support.
• Crystallite to refer to a catalyst crystal that has grown on a support and the term “particle” to refer to a carrier powder. Structurally, however, a support primary particle may be a crystal. For convenience, the term “crystal” is used to designate indifferently a primary support particle or a crystallite.
• a basic constituent of a particle is said to have a "monoclinic structure" when at least 90% of its volume is of monoclinic structure.
• a particle is said to have a "smooth contour" when, in an observation plane, it is possible to visualize, at a scale of about 10 nm / cm, a top view of the particle, the line of sight being thus substantially depending on the length of the particle, the edges defining the contour of the particle have no or few steps (recesses) and / or corners (asperities).
• a smooth outline may also be characterized by a proportion of exposed planes belonging to families other than the families ⁇ 1, 1, 1 ⁇ , ⁇ 1, 1, 0 ⁇ and ⁇ 1, 0,0 ⁇ less than 10% of the total area of the exposed planes. Preferably, according to the invention, this proportion is less than 5%, preferably substantially zero.
• a "powder” is a set of particles. These particles can be
• Primary that is to say, not associated with other particles
• secondary that is to say constituted by agglomerates or aggregates of primary particles
• the association of the primary particles results from a low intensity bond, for example by charge effects or by polarity.
• the association between the primary particles is stronger than in the case of an association in the form of agglomerates.
• the primary particles can be chemically bonded to one another. Breakage of agglomerates into smaller agglomerates or primary particles is therefore easier than breakage of aggregates into smaller aggregates or primary particles.
• support means a support in the form of a powder.
• the "base constituent" of a carrier particle is the major constituent, preferably greater than 90%, preferably more than 99%, by weight of this particle.
• the carrier particles of the invention consist of a base component and impurities.
• a “modifying agent” is a constituent of the mother liquor, soluble in an aqueous medium and having a chemical interaction with the oxide of the solid element forming the basic constituent, or the precursor of this oxide present in the mother liquor which is sufficiently strong. so that its presence or absence in the mother liquor can (particularly as a function of its quantity and the pH of the mother liquor) influence the morphology of the particles obtained at the end of the hydrothermal treatment.
• the "modifying" nature of an agent thus depends on the nature, or even the crystallographic structure, of the oxide of the solid element or of the precursor of this oxide, of the concentration of the agent in the mother liquor and of the pH of the latter.
• the agents selected from the group of oxoanions, anions of the elements of column 17 of the periodic table of the elements, OH ' hydroxide, and mixtures thereof are "modifiers" only if the oxide of the solid element or the precursor of this oxide are of monoclinic structure and in the concentration and pH ranges described below.
• the “maximum size” of a primary particle of a powder is defined by its largest dimension measured in an observation plane generally produced by electron microscopy.
• the “maximum size of a set (or powder) of primary particles” corresponds to the “maximum size” of the particle of this set having the greatest maximum size.
• the "size" of catalyst crystallites deposited on the surface of the support particles is defined by their average surface area. It can be determined from the dispersion value of this catalyst, measured in particular by hydrogen chemisorption, when the catalyst belongs to the group of metals of cubic structure of columns 8, 9 and 10 or by measurement from observations of electron microscopy, especially when the catalyst belongs to the group of carbides, sulphides and oxides identified as catalysts, described in more detail below.
• the percentiles or "percentiles" 50 (D 50 ), and 90 (D 90 ) are the particle sizes of a powder corresponding to the percentages by weight, 50% and 90% respectively, on the cumulative particle size distribution curve. particles of the powder, the particle sizes being ranked in ascending order. For example, 90% by weight of the particles of the powder have a size less than D 90 and 10% of the particles by mass have a size greater than D 90 . Percentiles can be determined using a particle size distribution using a sedigraph. D 50 corresponds to the "median size" of a set of particles, that is to say the size dividing the particles of this set into first and second populations equal in mass, these first and second populations comprising only particles having a size greater or smaller respectively than the median size.
• particle size of a powder conventionally means the size of particles determined by a sedigraphic analysis carried out to characterize a particle size distribution.
• the sedigraphy may for example be carried out using a sedigraph Sedigraph 5100 from the company Micromeritics ® .
• a set of planes with a particular atomic arrangement ie a specific arrangement of specific atoms, is conventionally called a "family of crystalline planes" or "crystalline form”, denoted ⁇ h, k, l ⁇ . This definition therefore excludes atomic arrangements extending along a curved surface.
• the plane of the family ⁇ h, k, l ⁇ characterized by a particular orientation defined by its Miller indices (h, k), is called a "crystalline plane", conventionally designated by its Miller indices (h, k, l). l).
• the family of crystalline planes ⁇ h, k, l ⁇ thus includes all the planes
• the family of crystal planes ⁇ 1, 0,0 ⁇ is the set of crystal planes (1, 0,0), (0,1, 0), (0,0,1), (-1, 0.0), (0 -1, 0) and (0.0, -1).
• An "exposed crystalline plane" of a crystal is a crystalline plane in contact with the outside, unlike a plane attached to a support for example. Only primary particles are considered when reference is made to an exposed crystalline plane of a particle. When reference is made to carrier particles in a catalytic system, the exposed planes are considered to include the at least partially covered planes of catalyst. In other words, to evaluate the percentages of crystalline planes exposed by particles, the presence of the catalyst on the surface of these particles is not taken into consideration.
• a family of crystalline planes exposed ⁇ h, k, l ⁇ is the set of exposed crystalline planes of said family.
• the family of crystalline planes exposed ⁇ 1, 0,0 ⁇ is the set of exposed crystalline planes, and only these, among the crystalline planes (1, 0,0), (0,1, 0), (0,0,1), (-1, 0,0), (0, -1, 0) and (0,0, -1).
• An exposed crystalline plane is said to be “favorable” when its contact with reactants promotes a chemical reaction.
• a family of plans is called “favorable” when it includes at least one favorable crystalline plane.
• a family of shots is said to be "most favorable" when it has the most favorable crystalline plane.
• the "axis of growth" is the main direction of the growth of a crystal.
• the growth axis is not necessarily related to the exposed planes of the crystal.
• a primary particle has a "stick" shape when it meets the following three conditions:
• the cross section is substantially constant over the entire length of the rod, substantially polygonal and has at least 4 sides.
• the cross section of a rod primary particle according to the invention preferably has less than 8 sides.
• the primary rod-shaped particles are such that 1.5 ⁇ L / W ⁇ 5, preferably 2 ⁇ UW ⁇ 4.
• Figure 1 shows a diagram of a primary particle in the form of a rod.
• a primary particle has a "wafer" shape when it meets the following three conditions:
• the cross section is substantially constant over the entire length of the wafer, is substantially polygonal and has at least 4 sides.
• the cross section of a wafer particle according to the invention preferably has less than 8 sides.
• the platelet-shaped primary particles are such that 6 ⁇ L ⁇ / 1 ⁇ 8 and 2 ⁇ L ⁇ / V2 ⁇ 4.
• Figure 2 shows the schematic of a primary particle in the form of a wafer.
• a raft corresponds to a flat cross-sectional shape of substantially constant general shape over its entire thickness (for example always octahedral whatever the cross sectional plane considered). Specifically, a crystallite has a "raft" form when it meets the following four conditions:
• the cross-section of the raft-shaped crystallite is substantially polygonal and has at least 4 sides. Preferably, it comprises less than 8 sides.
• the raft-shaped crystallites are such that 4 ⁇ W / E ⁇ 6.
• Figure 7 shows a schematic of a crystallite in the form of a raft.
• a cubo-octahedron is an isotropic form, that is to say having no preferred growth axis, and faceted, the number of faces being greater than 14 and preferably less than 26.
• a truncated cubo-octahedron is a cubo-octahedron which is not whole, but cut along a contact plane with a support.
• Figures 6a and 6b show photographic snapshots and diagrams of a crystallite in the form of a truncated cubo-octahedron, in top and side views, respectively.
• Oxoanion is an oxide containing anion, of the form QO x ⁇ " , Q being a metal (for example silicon) or a non-metal (for example carbon, phosphorus, sulfur), n being an integer greater than or equal to 1 and x being equal to (n + w) / 2 , with w the valence of the metal or non-metal considered.
• Q being a metal (for example silicon) or a non-metal (for example carbon, phosphorus, sulfur)
• n being an integer greater than or equal to 1
• x being equal to (n + w) / 2 , with w the valence of the metal or non-metal considered.
• impurities is meant the inevitable constituents introduced involuntarily and necessarily with the raw materials or resulting from reactions with these constituents. Impurities are not necessary constituents, but only tolerated.
• the compounds forming part of the group of oxides, nitrides, oxynitrides, carbides, oxycarbides, carbonitrides and metallic species of sodium and other alkalis, iron, vanadium and chromium are impurities if their presence is not desired.
• Hafnium oxide is not considered an impurity when the desired product is zirconia or a product based on zirconia and hafnium oxide.
• the impurities may be incorporated into the primary particles of the powder according to the invention or may constitute independent particles. In the present description, these two types of impurities are not distinguished.
• a "dopant" is a component added voluntarily in order to become a constituent of the final product.
• a “hydrothermal” process is a well known method of heating an aqueous solution, in a closed vessel, at a temperature above the boiling point at atmospheric pressure and at a pressure equal to or greater than the pressure. minimum necessary to avoid boiling of the aqueous solution.
• the term "sol” conventionally refers to a dispersion or suspension of colloidal particles in a liquid phase (for example in an aqueous medium). Particles in a soil are usually little or not agglomerated.
• the "zero point of load”, PCN is defined as follows.
• the surface charge of an oxide in suspension, ⁇ results from acid-base equilibria. It therefore depends on the pH and the ionic strength of the solution, ⁇ can be positive, negative or zero depending on the conditions of the medium.
• the zero point of charge defines the pH of the medium for which the load ⁇ is canceled.
• pH ⁇ PCN the charge ⁇ is positive.
• PCN pH> PCN
• the value of the NCP is directly related to the nature of the oxide.
• the hourly volume velocity of a gas is defined as the volume of gas passing per unit volume of the reactor and per unit of time. It is expressed in h "1 .
• a reaction is said to be "structurally sensitive" when it is modified not only by the nature of the catalyst and the amount of catalyst surface accessible to the reagents, but also by the morphology and exposed crystal planes of the catalyst. . Unless mentioned otherwise, the percentages used to characterize the proportion of exposed planes always refer to percentages relative to the total area of the exposed planes expressed in m 2 .
• FIG. 1 represents a diagram of a primary particle in the form of a stick
• FIG. 2 represents a diagram of a primary particle in the form of a wafer
• FIGS. 3a and 3b represent photographs of a stick in plan view and in side view, respectively, FIG. 3a. being particularly representative of a rod having a smooth contour
• FIGS. 4a and 4b show photographic snapshots of a set of platelets and a wafer, respectively, predominantly exposing the planes of the family ⁇ 1, 0,0 ⁇ ;
• FIGS. 5a and 5b are photographic snapshots of rods predominantly showing the family ⁇ 1, 1, 1 ⁇ .
• FIGS. 6a and 6b show photographic snapshots and diagrams of a crystallite in the form of a truncated cubo-octahedron, in top and side views, respectively;
• FIG. 7 represents a diagram of a crystallite in the form of a raft.
• step A a stock solution or an aqueous mother suspension, hereinafter called “mother liquor”, containing the oxide of the solid element to be manufactured or a precursor of this oxide is prepared.
• This solution is determined according to the parameters of step B) in order to obtain the desired primary particles.
• the mother liquor typically contains a solid content (oxide of the element or precursor of this oxide) of between 0.5 and 40% by weight.
• the synthesis method may in particular be used to manufacture a monoclinic oxide, in particular chosen from: HfO 2 , ZrO 2 , Eu 2 O 3 , Sm 2 O 3 , MoO 3 ,
• the monoclinic oxide is selected from HfO 2 , ZrO 2 , MoO 3 , WO 3 , preferably from ZrO 2 and HfO 2 and mixtures thereof.
• the monoclinic oxide is ZrO 2 zirconia.
• the mother liquor may contain the monoclinic oxide (s) to be manufactured. It may also contain a precursor of these oxides.
• the liquid phase of the mother liquor may be water.
• other water-miscible solvents for example ethanol, may be included in the liquid phase.
• the content of other solvents is less than 50% by weight of the liquid phase.
• the aqueous mother liquor further comprises at least one additional constituent of formula MC, said additional constituent being composed of:
• an agent M selected from the group of oxoanions, anions of the elements of column 17 of the periodic table of the elements, OH ' hydroxide , and mixtures thereof, and
• the pH of the mother liquor can be adjusted by adding organic and inorganic acids and / or bases.
• the agent is a modifying agent
• the pH of the mother liquor, the nature and the amount of the modifying agent influence the morphology as well as the nature and the proportion of the exposed planes of the finally obtained elementary particles.
• step B) the mother liquor is heated in a closed vessel at a temperature above the boiling temperature at 1 bar, preferably between 100 C C and 300 0 C and at a pressure equal or higher than the boiling pressure of the mother liquor.
• this method makes it possible to obtain directly the primary particles of the oxide of the element under consideration.
• the hydrothermal treatment can be carried out in a batch reactor, called in batch, or in a continuous reactor. Residence times are generally shorter and generally higher temperatures in a continuous reactor compared to those in a batch reactor.
• the reactor is heated to the desired temperature, then the temperature is maintained at least 1 hour and preferably less than 200 hours.
• the holding time of the temperature may vary depending on the reactor temperature and the concentrations in the mother liquor. It can be determined by routine tests.
• the choice of the temperature / hold time pair also influences the size of the primary particles. This pair is therefore chosen so as to obtain a maximum primary particle size of less than 250 nm, preferably less than 100 nm.
• the pressure in the reactor is greater than or equal to the boiling pressure of the mother liquor. It can be autogenous, that is to say, correspond to the vapor pressure of the water at the reactor temperature, hydraulic, or can result from the addition of an inert gas such as nitrogen. The pressure is chosen so that the final product obtained is in the desired crystalline phase.
• the reactor is then cooled to a temperature below the boiling point at 1 bar.
• the soil obtained is isolated. It contains a liquid fraction and "crude" particles that have a high content of impurities. The inventors have discovered that these impurities adversely affect the efficiency of the particles whether they are used as a catalyst support or as a catalyst.
• Steps A) and B) are known for hydrothermally producing raw particles.
• the solid phase of the sol consisting of raw particles is purified, during step C), so that its content of impurities is less than 0.7%, preferably less than 0.5%, of preferably less than 0.3%, more preferably less than 0.1%, in percentages by mass of dry matter.
• the purification of the raw particles from the soil preferably comprises the following steps C1 to C3:
• Step C1 optional, consists in decreasing the amount of the liquid phase and / or purifying said liquid phase of the soil.
• the term "decrease in the amount of the liquid phase of the soil” any operation for removing a part or all of the liquid phase of said soil.
• Step C1 does not achieve with the usual procedures the purity levels desired in the final powder. It is therefore preferable to apply a C2 step and / or an additional purification step C3.
• Step C2 consists of the removal of cationic impurities.
• cationic impurity means a molecule containing elements other than carbon (C), hydrogen (H), oxygen (O) and positively charged nitrogen (N) 1 contained in the liquid phase of the soil and / or fixed on the raw particles from the soil.
• the liquid phase of the soil and the raw particles of the soil may not contain cationic impurities, for example in the case of the use of hydrochloric acid (HCI). Step C2 is then useless.
• HCI hydrochloric acid
• the product resulting from the preceding process step (step B) or step C1) is suspended in an aqueous solution having a pH below the zero point of charge (PCN) of the oxide of the final element under consideration.
• this pH is less than 2 pH units to said PCN, more preferably less than 4 pH units to said PCN.
• the PCN values of the principal oxides can be consulted, for example, on pages 255 to 308 of the book "From the Solution to Oxide", J-P. Jolivet, CNRS Editions, Paris (1994).
• the pH of the suspension is regulated by addition of organic and / or inorganic acid. Of the acids, nitric acid and / or perchloric acid are preferred.
• This suspension is maintained, preferably with stirring, at a temperature below its boiling point at 1 bar, preferably at room temperature, for a period preferably of greater than 10 minutes and preferably less than 30 minutes.
• This suspension is then filtered by any means known to those skilled in the art.
• step C2 It is possible to repeat step C2 several times if the desired cationic purity required.
• Step C3 consists of the removal of anionic impurities.
• An "anionic impurity” is a molecule containing elements other than carbon (C), hydrogen (H), oxygen (O) and nitrogen (N), negatively charged and contained in the liquid phase of the soil and / or attached to the particles. rough soil.
• the liquid phase of the soil and the raw particles of the soil may not contain anionic impurities, for example in the case of the use of ammonia (NH 4 OH). Step C3 is then useless.
• the product resulting from the preceding process step (B) or C1 or C2) is suspended in an aqueous solution having a pH greater than the zero point of charge of the oxide of the final element under consideration.
• this pH is greater than 2 pH units to said PCN, more preferably greater than 4 pH units to said PCN 1 if the PCN is less than 10.
• the pH of the suspension is regulated by adding an organic and / or inorganic base.
• an organic and / or inorganic base it is preferred to use ammonia NH 4 OH.
• This suspension is maintained, preferably with stirring, at a temperature below its boiling point at 1 bar, preferably at room temperature, for a period preferably of greater than 10 minutes and preferably less than 30 minutes.
• This suspension is then filtered by any means known to those skilled in the art.
• step C3 It is possible to repeat step C3 several times if the purity required anionic species requires.
• an optional C4 rinse in a solvent preferably in water having a degree of purity at least equal to that of the osmosis water or in an alcohol of purity greater than 98 % by volume, preferably greater than 99% by volume, can be achieved.
• This operation consists of suspending the product from the preceding step in this solvent, preferably with stirring, at a temperature below its boiling point at 1 bar, preferably at room temperature, for a period of preferably greater than 10 minutes and preferably less than 30 minutes.
• This suspension is then filtered by any means known to those skilled in the art.
• the product obtained consists of moist purified particles.
• step D) 1 after purification the liquid fraction is removed by drying.
• a purified particle powder is thus obtained according to the invention. Any method well known to those skilled in the art can be used.
• the drying temperature is generally less than 500 ° C., preferably less than 200 ° C.
• the drying time is adjusted so that the powder of purified particles has, at the end of this step, a residual moisture less than 100 ° C. 1% by mass.
• the powder is calcined, preferably for at least one hour.
• the calcination temperature is preferably greater than 300 ° C. and preferably less than 500 ° C. in order to avoid the transformation of the exposed planes towards the thermodynamically most stable plane.
• This step E) makes it possible to eliminate the residual moisture and any organic species present in the powder of purified particles obtained at the end of step D).
• a final deagglomeration step may also be added after step E) or step D), in order to emit any agglomerates in the final powder.
• step A) The synthesis method according to the invention described above (steps A) to E)) is advantageously used to produce a powder of primary particles according to the invention.
• the process then has the following particularities: Step A)
• step A a stock solution or an aqueous mother suspension, hereinafter called “mother liquor”, containing zirconia or a precursor of zirconia is prepared. This solution is determined according to the parameters of step B) in order to obtain the desired primary particles.
• the mother liquor contains at least 0.5% zirconia or an equivalent amount of precursor, in percentages by weight based on the mother liquor.
• the precursor of the zirconia may be a zirconium salt or a partially hydrolyzed zirconium derivative.
• this precursor is a zirconium oxyhydroxide, also called “hydrated zirconia” or “zirconium hydroxide", without being limited thereto.
• This compound can be obtained by precipitation of zirconium salts in basic or neutral medium.
• Suitable zirconium oxyhydroxide powders are commercially available, for example, from the company SEPR Saint Gobain ZirPro (France) under the trade designation ZHO. These powders have a median diameter of 20 microns.
• the liquid phase of the mother liquor may be water. However, other water-miscible solvents, for example ethanol, may be included in the liquid phase. Preferably, the solvent content is less than 50% by weight of the liquid phase.
• the aqueous mother liquor may comprise a modifying agent.
• the agent may be added as an additive or provided by the precursor of the zirconia.
• the aqueous soluble agent may be selected from the group of oxoanions, anions of the elements of column 17 (halides) and hydroxide (OH “ ) and mixtures thereof, preferably from the group consisting of sulfate ( SO 4 2 ' ), carbonate (CO 3 2 “ ), phosphate (PO 4 3” ), fluoride (F “ ), chloride (Cl “ ), perchlorate (ClO 4 " ), nitrate (NO 3 “ ), borate (BO 3 3” ), hydroxide (OH “ ) and mixtures thereof.
• the agent can be corrosive and therefore requires suitable equipment.
• mother liquor pHs of between 4 and 10 do not make it possible to obtain primary particles in platelet or rod form according to the invention, whatever the preparation conditions used.
• the pH of the mother liquor can be adjusted by adding organic and inorganic acids and / or bases.
• the pH of the mother liquor is made acidic and less than 4.
• the modifying agents used are then preferably selected from the group consisting of oxoanions, anions of the elements of column 17 (halides) and their mixtures, preferably from the group consisting of chloride (Cl “ ), perchlorate (CIO 4 “ ) and nitrate (NO 3 " ) and their mixtures
• this additive is preferably composed of:
• a complement C chosen from the group constituted of all the positively charged organic molecules whose organic radical consists of a group of atoms selected from the group consisting of carbon, hydrogen, oxygen, and nitrogen; cations of the elements of columns 1 and 2, preferably the cations of the elements of column 1;
• the proportion of exposed crystalline planes belonging to the family ⁇ 1, 1, 1 ⁇ is regulated by the pH and by the amount of modifying agent. For maximum sizes greater than 10 nm, the proportions of the exposed crystalline planes do not advantageously depend on the maximum size of the primary particles.
• the amount of exposed crystal planes of the ⁇ 1, 1, 1 ⁇ family decreases as the pH increases.
• the concentration of modifying agent in the mother liquor is between 10 4 mol / l and 10 mol / l. This concentration modifies the proportions of the different families of exposed crystalline planes. Routine tests allow the concentration to be adjusted according to the desired proportions.
• the pH of the mother liquor is made basic and superior e 10.
• the modifying agents used are then selected from the group of oxoanions except borate (BO 3 3 " ), carbonate (CO 3 2” ), nitrate (NO 3 “ ), perchlorate (CIO 4 “ ), and mixtures thereof. ; preferably selected from the group of sulphate (SO 4 2 “ ), phosphate (PO 4 3” ) and mixtures thereof.
• this additive is composed of:
• a complement C chosen from the group constituted of all the positively charged organic molecules whose organic radical consists of a group of atoms selected from the group consisting of carbon, hydrogen, oxygen, and nitrogen; - cations of the elements of column 1;
• the proportion of exposed crystal planes of the ⁇ 1, 1, 0 ⁇ family is regulated by the pH and the amount of modifying agent. For maximum sizes greater than 10 nm, the relative proportions of the different crystalline planes exposed do not depend on the size of the primary particles.
• the proportion of exposed crystal planes belonging to the family ⁇ 1, 1, 0 ⁇ increases if the concentration of modifying agent increases.
• the concentration of modifying agent is greater than 10 -1 mol / l, preferably with a pH of between 10 and 14.
• the concentration of modifying agent can be however, lower if the pH increases: A concentration of 0.01 mol / l is thus suitable for a pH of 13. If the amount of modifying agent is not sufficient, platelets according to the invention will be obtained.
• the domains of rods exposing ⁇ 1, 1,0 ⁇ family planes and platelets with ⁇ 1, 0,0 ⁇ family planes are indeed continuous. In other words, for a given pH, there is a limit value below which platelets will be obtained and above which rods will be obtained.
• the pH of the mother liquor is made basic and superior to
• the modifying agents used are chosen from the group consisting of the oxoanions, the anions of the elements of the column 17 (halides), the hydroxide (OH “ ) and their mixtures, preferably chosen from the group consisting of hydroxide (OH ) 1 carbonate (CO 3 2 " ), fluoride (F “ ), chloride (Cl “ ), perchlorate (CIO 4 “ ), borate (BO 3 3 “ ), nitrate (NO 3 ' ) and of their mixtures. More preferably, the modifying agent is hydroxide (OH " ). In the case where the modifying agent is introduced in the form of an additive of formula MC, this additive is composed of:
• a complement C chosen from the group consisting of all the positively charged organic molecules whose organic radical consists of a group of atoms selected from the group consisting of carbon, hydrogen and oxygen; , and nitrogen;
• the proportion of the exposed crystalline planes belonging to the ⁇ 1, 0,0 ⁇ family is regulated by the pH and by the amount of modifying agent. For sizes greater than 10 nm, the relative proportions of the different crystalline planes exposed do not depend on the size of the primary particles.
• the proportion of the exposed crystalline planes belonging to the family ⁇ 1, 0,0 ⁇ , or even the morphology of the particles varies with the amount of modifying agent. In particular, this proportion decreases if the concentration of modifying agent increases.To obtain a particle powder which is substantially exclusively in the form of said platelets, the concentration of the abovementioned modifying agents must always be less than 10 -3 mol / l.
• the concentration of modifying agent does not affect the proportion of crystalline planes exhibits belonging to the family ⁇ 1, 0,0 ⁇ .
• the concentration of modifying agent is less than 10 mol / l.
• Step B) the mother liquor is heated in a closed vessel at a temperature above the boiling point to 1 bar, preferably between 100 0 C and 300 0 C.
• the morphology, the nature and proportions of the exposed crystalline planes of the primary particles do not depend on the temperature of the hydrothermal treatment, but these temperature values allow a short treatment time (to obtain the desired size and morphology), which allows a the industrial scale of the invention.
• the reactor is heated to the desired temperature, then the temperature is maintained at least 1 hour and preferably less than 200 hours.
• the choice of the temperature / hold time pair also influences the size of the primary particles. This pair is therefore chosen so as to obtain a maximum primary particle size of less than 250 nm, preferably less than 100 nm.
• the pressure in the reactor is equal to or greater than the boiling pressure of the mother liquor.
• This pressure may be autogenous, that is to say, correspond to the steam pressure of the water at the reactor temperature, hydraulic, or may result from the addition of an inert gas such as nitrogen.
• the pressure is determined so that the final product obtained is in the desired crystalline phase.
• the final product is then in monoclinic form.
• the hydrothermal treatment can be carried out in a "batch" reactor or in a continuous reactor. The residence times are generally shorter and the temperatures are generally higher in a continuous reactor than in a batch reactor.
• the resulting soil is then isolated. It contains a liquid fraction and "crude" particles of monoclinic zirconia which have a high content of impurities. The inventors have discovered that these impurities adversely affect the efficiency of the particles whether they are used as a catalyst support or as a catalyst.
• the primary particles have a smooth outline, even when their size is greater than 50 nm.
• the selectivity of the catalysis is improved.
• the rate of rise in temperature of the reactor used for the hydrothermal treatment is less than 250 ° C., preferably less than 200 ° C. per hour.
• the solid phase of the sol consisting of crude particles of monoclinic zirconia is purified, during step C), so that its impurity content is less than 0.7%, preferably less than 0.5. %, preferably less than 0.3%, more preferably less than 0.1%, in percentages by weight of the dry matter.
• the known purification methods can be used in step C).
• the purification of the raw particles of the sol preferably comprises one or more of the following steps C1 to C3: Step C1, optional, consists in reducing the quantity of the liquid phase and / or purifying said liquid phase of the soil.
• the term "decrease in the amount of the liquid phase of the soil” any operation for removing a part or all of the liquid phase of said soil.
• These methods are well known to those skilled in the art and may include - filtration, with or without prior resuspension of the soil, dialysis, with or without resuspension of the soil, - purification with resins ion exchangers, with or without re-suspending the soil, rinsing, and the combinations of these techniques.
• purification of the liquid phase of the soil means any operation that makes it possible to reduce the concentration of ionic species in the liquid solution of the soil. These methods are well known to those skilled in the art and may include dialysis, purification methods using ion exchange resins or dilution rinsing.
• Step C2 consists of the removal of cationic impurities.
• cationic impurity means a molecule containing elements other than carbon (C), hydrogen (H) 1 oxygen (O) and positively charged nitrogen (N) 1 contained in the liquid phase of the soil and / or fixed on the raw particles from the soil.
• the product resulting from the preceding process step (B) or C1) is suspended in an aqueous solution having a pH of less than 7, more preferably less than 5.
• the pH of the suspension is regulated by addition of organic and / or inorganic acid.
• organic and / or inorganic acid include organic and / or inorganic acid.
• nitric acid, perchloric acid and / or hydrochloric acid (HCl) are preferred.
• This suspension is maintained, preferably with stirring, at a temperature below its boiling point at 1 bar, preferably at room temperature, for a period greater than 10 minutes, and preferably less than 30 minutes.
• This suspension is then filtered by any means known to those skilled in the art. It is possible to repeat step C2 several times if the desired cationic species purity requires it. The number of steps C2 can be determined by routine tests.
• step C2 is not repeated, a single step C2 being sufficient for zirconia.
• Step C3 consists of the removal of anionic impurities.
• An "anionic impurity” is a molecule containing elements other than carbon (C), hydrogen (H), oxygen (O) and nitrogen (N), charged negatively and contained in the liquid phase of the soil and / or fixed on the raw particles of the soil.
• the product resulting from the preceding process step (B) or C1 or C2) is suspended in an aqueous solution having a pH greater than 11.
• the pH of the suspension is adjusted by adding an organic base and / or or inorganic.
• bases it is preferred to use ammonia NH 4 OH.
• This suspension is maintained, preferably with stirring, at a temperature below its boiling point at 1 bar, preferably at room temperature, for a period of preferably greater than 10 minutes and preferably less than 30 minutes.
• This suspension is then filtered by any means known to those skilled in the art.
• step C3 It is possible to repeat step C3 several times, if the purity required anionic species requires it.
• the number of C3 steps can be determined by routine tests.
• step C3 is not repeated, a single step C3 being sufficient for zirconia.
• an acid-base neutralization comprises an operation of removal of cationic impurities and / or removal operation of anionic impurities.
• the last operation for removing cationic impurities is carried out in an aqueous solution whose pH is adjusted with the aid of an organic acid or a mixture of organic acids and / or the last operation for removing anionic impurities is carried out in an aqueous solution whose pH is adjusted using an organic base or a mixture of organic bases.
• an optional C4 rinse in a solvent preferably a water having a degree of purity at least equal to that of osmosis water or an alcohol of purity greater than 98% by volume, preferably greater than 99% by volume
• a solvent preferably a water having a degree of purity at least equal to that of osmosis water or an alcohol of purity greater than 98% by volume, preferably greater than 99% by volume
• This operation consists of the suspension of the product from the preceding step in this solvent, preferably with stirring, at a temperature below its boiling point at 1 bar, preferably at room temperature, for a period greater than 10 minutes, preferably less than 30 minutes.
• This suspension is then filtered by any means known to those skilled in the art.
• the purified product obtained is substantially composed of monoclinic zirconia particles.
• the purification is sufficient so that the powder obtained after step D) is constituted for more than 99.3%, preferably for more than 99.5%, preferably for more than 99.7%. %, more preferably for more than 99.9% of zirconia, the 100% complement consisting of impurities, in percentages by mass on the basis of the dry matter.
• Step D) In step D), after purification, the liquid fraction is removed by drying.
• a purified particle powder is thus obtained according to the invention. Any method well known to those skilled in the art can be used.
• the drying temperature is generally less than 500 ° C., preferably less than 200 ° C.
• the drying time is adjusted so that the powder of purified particles has, at the end of this step, a residual moisture of less than 1%. in mass.
• the zirconia powder is preferably calcined for at least one hour.
• the calcination temperature is preferably greater than 300 ° C. and preferably less than 500 ° C.
• This step makes it possible to eliminate the residual moisture present in the powder obtained at the end of step D), as well as any organic species remaining in said powder, without modifying the morphology and the nature of the particles, or the proportions of exposed crystalline planes.
• the pore volume of the agglomerates of the primary particles of the zirconia powder obtained is generally between 0.1 and 0.2 cm 3 per gram of said powder.
• a disagglomeration step F) can be carried out in order to emulsify the agglomerates of this powder.
• the primary particles have a maximum size of less than 250 nm, preferably less than 200 nm, preferably less than 150 nm, preferably less than 100 nm, preferably less than 90 nm, preferably less than 80 nm and greater than 10 nm. nm, preferably greater than 20 nm.
• the impurity content of the powder according to the invention is preferably less than 0.7%, preferably less than 0.5%, preferably less than 0.3%, more preferably less than 0.1%, percentages by mass of dry matter.
• the impurities are preferably such that, in percentages by mass of dry matter:
• Al 2 O 3 ⁇ 0.1% preferably Al 2 O 3 ⁇ 200 ppm, more preferably Al 2 O 3 ⁇ 100 ppm and / or - MgO ⁇ 0.1%, preferably MgO ⁇ 200 ppm, preference
• MgO ⁇ 100 ppm more preferably MgO ⁇ 50 ppm and / or
• CaO ⁇ 0.1% preferably CaO ⁇ 200 ppm, more preferably CaO ⁇ 100 ppm and / or
• Fe 2 O 3 ⁇ 0.1% preferably Fe 2 O 3 ⁇ 200 ppm, preferably Fe 2 O 3 ⁇ 100 ppm, more preferably Fe 2 O 3 ⁇ 50 ppm and / or TiO 2 ⁇ 0.1%, preferably TiO 2 ⁇ 200 ppm, preferably TiO 2 ⁇ 100 ppm, more preferably TiO 2 ⁇ 50 ppm.
• Each primary particle is constituted, excluding impurities, of a crystal having, for more than 95%, preferably for more than 97%, more preferably for more than 99% of its mass, more preferably for substantially 100%, a monoclinic structure.
• the complement of zirconia in monoclinic form is stabilized zirconia in quadratic or cubic form.
• the powder has the following characteristics: - Specific area of the particles, calculated by the BET method, greater than
• more than 95% by number of the primary particles of the powder have a shape different from a spherical or spherical truncated shape. More specifically, at least 90%, preferably at least 95%, more preferably at least 99% by number of dry matter, more preferably substantially all the particles of the powder have a wafer and / or rod form. In general, on a powder directly obtained at the end of step D), these percentages relate to only one of these two forms. A mixture of different powders is however possible to change the respective percentages of platelets and rods. Surprisingly, the inventors have discovered that such platelet and / or rod zirconia particles exhibit families of rare ⁇ 1, 1.0 ⁇ and ⁇ 1,0,0 ⁇ crystal planes. In addition, they have also found that such particles allow the development of crystallites of metal of cubic structure columns 8, 9 and 10, and in particular platinum, which expose the families of planes ⁇ 1, 1, 1 ⁇ and ⁇ 1, 0,0 ⁇ .
• the invention extends in particular to primary particles of hafnium oxide (HfO 2 ).
• the invention extends to primary particles consisting, excluding impurities, of zirconia and hafnium oxide, the proportion of hafnium oxide may be between 0 and 100%.
• the invention extends to the use of other powders than a zirconia single crystal powder (ZrO 2 ), in particular to a molybdenum oxide powder (MoO 3 ) and / or a powder of tungsten oxide (WO 3 ) which can also be obtained hydrothermally. These powders are monoclinic, nanometric, and monocrystalline. The morphologies and crystal planes of the primary particles of molybdenum oxide and tungsten oxide are identical to those of the zirconia according to the invention.
• the primary particles of hafnium oxide, hafnium oxide and zirconia, molybdenum oxide, tungsten oxide can be prepared in a manner similar to the synthesis method described above for the particles of zirconia.
• the dopant is selected from the group consisting of oxoanions, column 17 anions (halides), column 1 (alkaline) cations, and mixtures thereof. More preferably, the oxoanions are chosen from silicates, phosphates and sulphates, the halohydrides are selected from chlorides and fluorides, and the alkalis are selected from sodium and potassium.
• the invention thus relates to a mixture, hereinafter referred to as "particulate mixture", consisting of a powder according to the invention, the particles of which are associated with a dopant.
• the dopant can be located on the surface of the particles and completely or partially cover this surface. All particles of a particulate mixture according to the invention do not necessarily contain dopant.
• the molar quantity of dopant is determined so as to represent less than 40%, preferably less than 20%, preferably less than 10%, preferably less than 5%, or even less than 3% of the mass of the mixture. particulate.
• the dopant can be combined with the powder according to the invention by any method known to those skilled in the art, for example by an impregnation process.
• the invention thus relates to a process for producing a particulate mixture according to the invention, in which a dopant, in particular a suspension of a dopant, is mixed with a powder according to the invention.
• the invention also relates to a porous body comprising particles according to the invention, and in particular the following three embodiments:
• the invention relates to a porous body (1) obtained by consolidation heat treatment of a green body obtained by shaping a powder according to the invention.
• the invention also relates to such a green body which can itself be a porous body.
• this porous body has a porosity greater than 30% and / or less than 90%.
• the invention relates to a porous body (2) whose surface of accessible pores, or "open ", Carries particles according to the invention.
• All accessible pores of a porous body (2) may be concerned, or only a part of them, in particular the only pores of a superficial layer of the porous body, the superficial layer extending for example to a lower depth at 10% of the thickness of said porous body, or the only pores located in the core of the porous body, for example at a distance from the outer surface of the porous body of at least 50% of the thickness of said porous body.
• the proportion of pores carrying particles according to the invention may be homogeneous through the porous body, but may also vary depending on the distance from the outer surface of the porous body.
• the material of said porous body is not obtained from a powder or a particulate mixture according to the invention.
• said porous body comprises more than 50%, preferably more than 80% by weight of alumina.
• said porous body has a porosity greater than 30% and / or less than 90%.
• the invention relates to a porous body (3) made of a material in which particles according to the invention are intimately mixed with particles which do not conform to the invention, by example of alumina particles.
• said porous body comprises more than 50%, preferably more than 80% by weight of alumina.
• the porous body has a porosity greater than 30% and / or less than 90%
• the invention proposes a method of manufacturing a porous body comprising the following successive steps:
• step (e) optionally, depositing a catalyst on the outer surface of said porous body and / or on the surface of accessible pores.
• the liquid may in particular comprise an aqueous solution, and in particular water.
• the binder makes it possible in particular to facilitate the extrusion and / or to increase the mechanical properties in green and after consolidation of the porous body and / or to improve the textural properties thereof (specific surface, porosity).
• the green body can be formed by extrusion, pressing, injection, atomization, agglomeration in mold, coagulation into drops.
• the green body may in particular be produced by extrusion, in particular in the form of a granule or "pellet".
• this granule has a diameter of between 4 and 4.5 mm, for example of 4.2 mm, and a length of between 3 and 10 mm.
• the method can then be used to simultaneously manufacture a plurality of green bodies, and then porous bodies (1) or (3).
• the thermal consolidation treatment may be effected by heat treatment at a temperature below 600 0 C, preferably below 550 0 C 1 or even less than 500 0 C, for example for at least two hours .
• the consolidation temperature is greater than 450 ° C.
• the dopant is selected from the group consisting of oxoanions, anions of column 17, cations of column 1, and mixtures thereof.
• the dopant may in particular be chosen from silicates, phosphates, sulphates, chlorides, fluorides, sodium and potassium.
• the catalyst may in particular be chosen from the group formed by the metals of columns 8, 9 and 10 of the periodic table of the elements and having a cubic structure, the mixtures thereof, the lanthanum oxide, transition metal oxides, column 14 and 15 oxide elements, transition metal carbides, and transition metal sulfides.
• a porous body (2) To manufacture a porous body (2), conventional methods of manufacturing a porous ceramic body can be implemented. This porous body can then be impregnated from a suspension of a powder according to the invention. The suspension can thus penetrate into the porous body and reach accessible pores within the porous body. Particles according to the invention can thus be deposited on the outer surface of the porous body and / or on the surface of all accessible pores of the porous body. The particles according to the invention may advantageously be used in the context of a catalytic system.
• the support is impregnated with a solution, aqueous or not, containing a precursor of the catalyst.
• the impregnated support then undergoes a maturation step allowing the impregnation solution to penetrate by capillarity into the pores of the support.
• the duration of this step is generally greater than 5 hours.
• the impregnated support is then dried by any drying means known to those skilled in the art, such as for example by steaming, under vacuum or not.
• the drying temperature is generally less than 500 0 C 1 the drying time being adjusted so that the impregnated support has, at the end of this stage, a residual humidity lower than 1% by mass.
• the impregnated and dried support is then subjected to an optional calcination step, generally at a temperature above 300 0 C and less than 500 c C, and generally for a period of greater than one hour bearing.
• the calcination step makes it possible to eliminate any binders contained in the support and originating from the impregnating solution.
• the drying step and the calcination step are carried out in a single operation.
• the impregnated support dried and optionally calcined then undergoes an optional activation operation, known to those skilled in the art.
• This step is carried out under a controlled atmosphere, adjusted to the selected catalyst (for example under a sulfurizing mixture for a sulfide-based catalyst), generally at a temperature of between 100 ° C. and 500 ° C., for a duration of plateau greater than 1 hour.
• the support can be qualified as a "catalytic system”.
• this activation step can be carried out directly in the catalytic reactor.
• An additional optional step of passivation can be performed after activation, in particular to facilitate the transport of the catalytic system. Generally, this step is carried out under a gas sweep in an oxidizing medium, at temperatures below 100 ° C. A reactivation step must then be carried out in the reactor.
• the amount of catalyst deposited on the support particles is preferably limited so as to avoid excessive crystallite growth.
• a Excess catalyst can indeed lead to a change in the nature and quantity of the planes exposed by the crystallites.
• the catalyst represents less than 10%, preferably less than 7%, preferably still less than 5% of the mass of the catalyst system.
• a content of 1% of catalyst is generally suitable.
• the process is determined so that the size of the catalyst crystallites is greater than 1.5 nm.
• the inventors have in fact discovered that a size greater than 1.5 nm makes it possible to prevent the crystallites from taking a spherical or spherical shape truncated by a plane of contact with the support particle, in particular when the catalyst is a metal of cubic structure of columns 8, 9 and 10 of the periodic table of elements, and in particular platinum.
• a manufacturing method comprising the following steps:
• step II impregnating a support powder according to the invention by means of the solution prepared in step I); III) Maturation to allow the impregnating solution to penetrate by capillarity into the pores of the support;
• step Vl activation in the reactor preferably under the same conditions as those of step Vl).
• step I in the case of platinum as catalyst, a solution of platinum precursor, such as platinum tetramine nitrate Pt (NH 3 ) 4 (NO 3 ) 2 (for example manufactured by Sigma) can be prepared. Aldrich).
• platinum precursor such as platinum tetramine nitrate Pt (NH 3 ) 4 (NO 3 ) 2 (for example manufactured by Sigma)
• the impregnation can be carried out, according to a conventional procedure, without excess solution.
• the maturation preferably lasts at least 5 hours and more preferably lasts about 8 hours. It is carried out at a temperature below 10O 0 C 1 more preferably at room temperature.
• step IV the drying is preferably carried out in an oven at 110 ° C. for at least 12 hours, so that the residual moisture content of the support is less than 1% by weight.
• the calcination is preferably carried out under air and, more preferably, for at least one hour, preferably for about 2 hours, and preferably at a temperature of between 300 ° C. and 500 ° C.
• the rise ramp is preferably less than 10 ° C / min, more preferably about 2 ° C / min.
• the calcination is carried out under gas flushing.
• the catalyst is preferably activated by reduction under hydrogen (H 2 ), more preferably for at least 1 hour, preferably for about 6 hours, and more preferably at a temperature of between 100 ° C. and 500 ° C.
• the rise ramp is preferably less than 10 ° C / min, more preferably about 2 ° C / min.
• the activation is carried out under hydrogen scavenging.
• the activation temperature is preferably between 300 and 500 ° C.
• the catalyst is passive while flushing with inert gases containing a few ppm of oxygen, preferably under nitrogen containing a few ppm of O 2 , preferably at a temperature below 100 ° C., more preferably at room temperature and more preferably for about 1 hour.
• a catalytic system according to the invention is obtained.
• This method of preparation is not the only method that can be implemented to prepare a catalyst system according to the invention.
• a catalyst deposition by Chemical Vapor Deposition (CVD) may very well be suitable.
• a selective impregnation consists of "masking" certain planes of the support particles so that they are no longer accessible to the catalyst during the deposition of the latter. It is thus possible to keep exposed only the planes of support particles allowing the growth of crystallites exposing favorable planes or families of planes favorable to the reaction to be catalyzed.
• the effectiveness of the catalyst is thus optimized. At the same amounts of catalyst, the performance of the catalyst system is improved, with a larger percentage of the catalyst surface exposing useful planes. Conversely, with identical catalytic performances, the quantity of catalyst consumed is reduced.
• the catalyst deposited on the surface of the support may be a metal, preferably chosen from the group of metals of columns 8, 9 and 10 of the periodic table of elements, preferably chosen from the group of metals of columns 8, 9 and 10 of the periodic table of elements and having a cubic structure, and mixtures thereof.
• the metal is platinum.
• the catalyst may also be an oxide, preferably chosen from lanthanum oxide and / or transition metal oxides, for example V 2 O 5 or Cr 2 O 3 and / or the oxides of the elements of the columns 14 and 15, preferably the oxides of tin (Sn), lead (Pb) and / or bismuth (Bi).
• oxides of tin (Sn), lead (Pb) and / or bismuth (Bi) preferably the oxides of tin (Sn), lead (Pb) and / or bismuth (Bi).
• the catalyst may also be a carbide, preferably selected from transition metal carbides, such as, for example, molybdenum carbide and / or tungsten carbide.
• the catalyst may also be a sulphide, preferably selected from transition metal sulphides, preferably molybdenum sulphides and tungsten sulphides, optionally doped with cobalt or nickel (CoMoS for example).
• the catalyst is selected so that at least 80%, preferably at least 90%, more preferably at least 95% by number, more preferably substantially all of the catalyst crystallites of the catalyst system have a shape which is not a spherical or spherical shape truncated according to the contact plane with the support.
• the performance of the catalytic system is improved.
• the size of the crystallites of the catalyst is preferably between 1.5 nm and 10 nm, preferably between 3 nm and 10 nm.
• the catalyst is less than 10%, preferably less than 7%, more preferably less than 5% of the mass of the catalyst system.
• a content of 1% of catalyst is generally suitable.
• the catalyst is a metal selected from the group of metals of columns 8, 9 and 10 of the periodic table and is chosen so that at least 80%, preferably at least 90%, more preferably at least 95% by number, more preferably substantially all of the catalyst crystallites have a truncated cuboid or octahedron shaped raft.
• the size of the crystallites is preferably between 1.5 nm and 10 nm, preferably between 3 nm and 10 nm.
• the truncated cubo-octahedral crystallites are formed on the exposed planes ⁇ 1, 1,0 ⁇ and ⁇ 1,1,1 ⁇ of the support particles, the crystallites in form of raft forming on the exposed planes ⁇ 1, 0,0 ⁇ of these particles, in particular when said particles have a monoclinic structure.
• the morphology of the crystals can be determined from observations made in High Resolution Transmission Electron Microscopy (METHR) after ultrasonic dispersion of the samples.
• METHR High Resolution Transmission Electron Microscopy
• the determination of the morphology of the primary particles and crystallites, the determination of the exposed crystalline planes and the quantification of the proportion of these planes are carried out as follows:
• Each image being considered as a view in a precise direction it is then possible, after determining the morphology of a crystallite or a particle, to select the images showing at least one face exposed perpendicularly to the observation plane.
• This exposed face is in the form of an edge in said cliche.
• the corresponding exposed crystalline plane can then be determined.
• This procedure is used for all exposed faces of the crystallite or particle to determine all of its exposed crystalline planes.
• the proportion of the exposed crystalline planes of the family ⁇ h, k, l ⁇ is equal to the sum of all the exposed surfaces of the crystalline planes of the family ⁇ h, k, l ⁇ divided by the total sum of the exposed surfaces.
• CC chloride ions The determination of the CC chloride ions is carried out after pyrohydrolysis by ion chromatography.
• the carbon and sulfur contents (converted to sulphate content SO 4 2 " ) are measured on a Sulfur Carbon analyzer, model C 1 S-MAT 5500 (marketed by Str ⁇ hleim Inst).
• the textural properties are determined by physical adsorption / desorption of N 2 at -196 ° C.
• the samples are first desorbed under vacuum at 400 ° C. for 2 hours for the calcined supports and at 100 ° C. for 10 hours for the non-calcined carriers .
• the specific area is calculated by the BET method (Brunauer Emmet Teller) as described in Journal of American Chemical Society 60 (1938) pages 309-316.
• the pore volume V P is determined with the method BJH [described by EP. Barrett, LG Joyner, PH Halenda, J. Am. Chem. Soc. 73 (1951) 373] applied to the desorption branch of the isotherm.
• the unpacked density is determined by the following method: in a graduated cylinder of 250 cm 3 having a mass Mo (in g), is poured, using a funnel, a volume of powder of between 240 and 250 cm 3 . The volume is then read on the test tube
• the unpacked density, in g / cm 3 is determined according to the following relationship:
• Unpacked density (MI-Mo) / Vo.
• the X-ray powder diffraction patterns are obtained on a BRUKER D5005 diffractometer, using copper Ka radiation (1.54060 A).
• the intensity data are recorded over a 2 ⁇ interval of 3-80 ° with a step of 0.02 ° and a counting time of 1s per step.
• the crystalline phases are identified by comparison with the standard JCPDS files.
• the crystal structure can be confirmed by other well known methods such as Raman spectroscopy or, locally at the level of a primary particle, by transmission electron microscopy.
• the dispersion of this type of catalyst is determined by hydrogen chemisorption.
• the chemisorption measurements were performed on an ASAP 2010 device (marketed by Micromeritics).
• the amount of chemisorbed hydrogen (HCirr) is determined from the extrapolation at zero pressure of the linear branch of the total and reversible adsorption isotherms as described in [G. Bergeret, P. Gallezot, Handbook of Hetrogenic Catalysis, G. Ertl, H. Knozinger, J. Weitkamp Eds., Wiley-VCH, Weinheim, Vol. 2 (1997)].
• the dispersion is given by the relation:
• HCirr being the number of moles of chemisorbed H 2 and n toX the total number of catalyst atoms belonging to the group of metals of cubic structure of columns 8, 9 and 10.
• the size of a catalyst crystallite is defined as the average surface area of the catalyst crystallite. It can be measured on the basis of observations made by electron microscopy, in particular for the catalysts belonging to the group of carbides, sulphides or oxides, and / or by measuring the dispersion of said catalyst on the surface of the support (method used, for example, for catalysts forming part of the group of metals of cubic structure of columns 8, 9 and 10).
• the determination of the average surface dimension from electron microscopy observations is as follows: The sample to be observed is scattered under ultrasound in ethanol. The suspension is then deposited on a carbon-coated copper grid. A large number of high-resolution crystallite images are made, generally more than 50. From these images, if n, is the number of crystallites having a maximum dimension in the observation plane di, the average surface dimension ds is defined by the following formula:
• D being the catalyst dispersion "Ca" at the surface of the support (expressed in%), pc at the catalyst density (in g / m 3 ), Ca Ca the area occupied by a catalyst atom Ca (in m 2 ) , M Ca the molar mass of the catalyst Ca (in g / mol) and Na the Avogadro number.
• the inventors have verified that the hypothesis of the cubic form is realistic within the framework of the morphologies described in the present description, namely the raft and truncated cubo-octahedron shapes, by verifying that the average surface dimension of a sample of Metallic crystallites of cubic structure of columns 8, 9 or 10 is identical for the two methods described above.
• V m ⁇ 0 F with the molar flow rate of reactant to the reactor inlet (molr e ac t i f -s "1 ); ⁇ , the degree of conversion, less than 20% in the context of the catalytic reactions used for the examples and m the mass of the catalytic system (g) - and D denotes the dispersion of the catalyst determined by hydrogen chemisorption, expressed in% .
• the molar flow rate of the reagent at the reactor inlet, F 0 is calculated according to the following equation:
• G t o ta i denoting the total flow rate of the reagent under normal conditions of temperature and pressure in cm 3 .s ⁇ 1 ; P r the partial pressure in reagent in Pa and P, ota ⁇ the total pressure in Pa.
• the porosity of a porous body is defined as the following ratio:
• the absolute density, expressed in g / cm 3 is determined using a ACCUPYC 1330 helium pycnometer sold by the company MICROMERITICS, the apparent density, expressed in g / cm 3 , is measured on a test device. type GEOPYC 1360 marketed by the company MICROMERITICS.
• the main physico-chemical properties of the powder thus obtained are given in Table 1.
• This powder has a specific surface area after calcination at 550 ° C. of 80 m 2 / g and has more than 99% of monoclinic phase as shown by its diffractogram. in X-rays.
• the primary particles are in a quasi-spherical form.
• the powder exposes 30% of family plans ⁇ 1, 1, 1 ⁇ , 10% of family plans ⁇ 1, 1, 0 ⁇ , 10% of family plans ⁇ 1, 0,0 ⁇ and 50% other family plans with Miller indices greater than 1.
• the rest of the sol is then resuspended and the pH is adjusted to 8 by addition of 0.1 N hydrochloric acid.
• the suspension is then filtered and then washed with 200 ml of deionized water on a Buchner type filter.
• the cake thus obtained is then resuspended in 500 ml of deionized water and the pH is adjusted to 5 by addition of 0.1 N hydrochloric acid.
• the suspension is then filtered and then washed with 200 ml of deionized water. on a Buchner type filter.
• the cake obtained is resuspended in 500 ml of deionized water and the pH is adjusted to 11 by adding ammonia (NH 4 OH) to 1 N.
• the suspension is then filtered and then washed twice with 200 ml of water. permutated water on a Buchner type filter.
• the resulting cake is then dried in an oven for at least 12 hours at 11O 0 C then 1 delumped the agate mortar.
• the powder obtained is calcined in air for 2 hours at a temperature ramp of 2 ° C./min; air flow rate of 100 ml / min, ie an hourly volume velocity WH of 300 h -1 at 400 ° C.
• the main physicochemical properties of the powder thus obtained are given in Table 1.
• the powder obtained exhibits more 99% of monoclinic phase as shown by its X-ray diffractogram.
• the morphology of the powder is given in Table 2.
• the primary particles are in the form of platelets exposing up to 50% of the planes of the family ⁇ 1
• the other planes exposed by these particles are the family plans ⁇ 1, 1, 0 ⁇ up to 35%, the family plans ⁇ 1, 1, 1 ⁇ up to 10% and family plans with Miller indices greater than 1 at 5%.
• the rest of the soil is filtered and then washed twice with 200 ml of deionized water on a Buchner type filter.
• the cake thus obtained is then resuspended in 500 ml of deionized water and the pH is adjusted to 5 by addition of 0.1 N hydrochloric acid.
• the suspension is then filtered and then washed with 200 ml of deionized water. on a Buchner type filter.
• the cake obtained is resuspended in 500 ml of deionized water and the pH is adjusted to 11 by adding ammonia to 1 N.
• the suspension is then filtered and then washed twice with 200 ml of deionized water on a filter. Buchner type.
• the cake obtained is then dried in an oven for at least 12 h at 110 ° C. and then spotted with agate mortar.
• the powder obtained was calcined in air for 2 hours (ramp 2 ° C / min, air flow rate of 100 ml / min, an hourly space velocity HSV of 300 h "1) 400 0 C.
• Main The physico-chemical properties of the powder thus obtained are given in Table 1.
• the powder obtained has more than 99% of monoclinic phase, as shown by its X-ray diffractogram.
• the morphology of the powder is given in Table 2.
• primary particles are in the form of rods exposing up to 75% of the family ⁇ 1, 1, 0 ⁇ .
• the other planes exposed by these particles are the ⁇ 1, 0,0 ⁇ family height planes.
• the rest of the soil is filtered and then washed twice with 200 ml of deionized water on a Buchner type filter.
• the cake thus obtained is then resuspended in 500 ml of deionized water and the pH is adjusted to 5 by addition of 0.1 N hydrochloric acid.
• the suspension is then filtered and then washed with 200 ml of deionized water. on a Buchner type filter.
• the cake obtained is resuspended in 500 ml of deionized water and the pH is adjusted to 11 by adding ammonia to 1 N.
• the suspension is then filtered and then washed twice with 200 ml of deionized water on a filter. Buchner type.
• the cake obtained is then dried in an oven for at least 12 hours at 110 0 C, then spotted with agate mortar.
• the powder obtained was calcined in air for 2 hours (ramp 2 ° C / min, air flow rate of 100 ml / min, an hourly space velocity HSV of 300 h -1) at 400 0 C.
• Main The physico-chemical properties of the powder thus obtained are given in Table 1.
• the powder obtained is present in more than 99% of monoclinic phase as shown by its X-ray diffractogram.
• the morphology of the powder is given in Table 2.
• Primary particles are in the form of rods exposing up to 60% of the ⁇ 1, 1.0 ⁇ family planes. The other planes exposed by these particles are family plans ⁇ 1, 0,0 ⁇ at 25%, family plans ⁇ 1,, 1, 1 ⁇ at 10% and family plans with Miller indices greater than 1 at 5%.
• Teflon® PTFE which is then sealed in a stainless steel autoclave, then placed in an oven regulated at 200 ° C. One hour is necessary to reach into the bomb at set temperature. The mother liquor is maintained at 200 ° C. for 100 hours and then cooled to room temperature. At this moment, the bomb is removed from the stainless steel autoclave. This procedure generates a self consisting of a solid phase and a liquid supernatant. Some of the liquid is siphoned off.
• the pH of the sol is then adjusted to 8 by addition of ammonia to 1 N.
• the suspension is then filtered and then washed twice with 200 ml of deionized water on a Buchner type filter.
• the cake obtained is resuspended in 500 ml of deionized water and the pH is adjusted to 11 by adding ammonia to 1 N.
• the suspension is then filtered and then washed twice with 200 ml of deionized water on a filter. Buchner type.
• the cake obtained is then dried in an oven for at least 12 hours at
• the main physico-chemical properties of the powder thus obtained are given in Table 1.
• the powder obtained has more than 99% of monoclinic phase as shown by its X-ray diffractogram.
• the morphology of the powder is given in Table 2.
• the primary particles are in the form of rods exposing up to 65% of the pians of the ⁇ 1, 1, 1 ⁇ family.
• the other planes exposed by these particles are family plans ⁇ 1, 1, 0 ⁇ at 10%, family plans ⁇ 1,0,0 ⁇ at 20% and family plans with Miller indices greater than 1 at 5%.
• Example 6 (Sticks ⁇ 1,1,0 ⁇ having a level of impurities higher than that of Example 3)
• the rest of the soil is filtered on a Buchner type filter.
• the cake thus obtained is then resuspended in 500 ml of deionized water and the pH is adjusted to 5 by addition of 0.1 N hydrochloric acid.
• the suspension is then filtered on a Buchner type filter and then washed with 200 ml of permutated water on a Buchner type filter.
• the suspension is then filtered and then washed twice with 200 ml of deionized water on a Buchner type filter.
• Example 6 in accordance with the invention.
• the impurity content has however, it was maintained at a level higher than that of Examples 1 to 5 in order to evaluate the effect of the impurities, as described below.
• the cake obtained is then dried in an oven for at least 12 h at 110 0 C and then spotted with agate mortar.
• the powder obtained was calcined in air for 2 hours (heating ramp of 2 ° C / min, air flow rate of 100 ml / min or an hourly space velocity HSV of 300 h -1)) to 400 0 C.
• the main physico-chemical properties of the powder thus obtained are given in Table 1.
• the level of anionic impurities such as CI " and SO 4 2" is greater than the level of these same impurities in Example 3 having undergone a step full wash.
• the powder obtained has more than 99% monoclinic phase.
• the morphology of the powder is given in Table 2.
• the primary particles are in the form of rods exposing up to 75% the planes of the ⁇ 1, 1, 0 ⁇ family.
• the other planes exposed by these particles are the family plans ⁇ 1, 0,0 ⁇ at 5%, the family plans ⁇ 1,1, 1 ⁇ at 15% and families of plans with Miller indices greater than 1 at 5%.
• This filtration-washing operation does not make it possible to reach high levels of purity ( ⁇ 0.7%), as in the powders of the invention.
• the cake obtained is then dried in an oven for at least 12 h at 110 0 C and then spotted with agate mortar.
• the powder obtained was calcined in air for 2 hours (heating ramp of 2 ° C / min, air flow rate of 100 ml / min or an hourly space velocity HSV of 300 h -1)) to 400 0 C.
• the main physico-chemical properties of the powder thus obtained are given in Table 1.
• the level of ionic impurities such as Na + (expressed as Na 2 O) and SO 4 2 " is greater than the level of these same impurities.
• Example 3 The powder obtained has more than 99% monoclinic phase
• the morphology of the powder is given in Table 2.
• the primary particles are in the form of rods 75% exposing the planes of the family ⁇ 1, 1, 0 ⁇
• the other planes exposed by these particles are the family plans ⁇ 1,0,0 ⁇ at the height of 5%, the family plans ⁇ 1, 1, 1 ⁇ at the level of 15% and plan families with Miller indices greater than 1 at 5%.
• Example 1 shows that impurity contents of less than 0.7% are possible, without thorough washing, hydrothermally, when the mother liquor does not contain an agent chosen from the group of oxoanions, anions from column 17, hydroxide OH and mixtures thereof.
• the powders of Examples 1, 2, 3, 5 and 6 were used in the manufacture of catalytic systems using platinum as catalyst and having a platinum mass content of about 1%.
• the crystallite size was greater than 1.5 nm and less than 10 nm.
• Catalytic tests were carried out on a hydrogenation reaction of ortho-xylene (1, 2-dimethylbenzene) in a fixed-bed opened pyrex reactor operating at low conversion and at atmospheric pressure.
• the following procedure 20 mg of the catalyst system (in this case the zirconia powder of Examples 1, 2, 3, 5, 6, coated with platinum) and 50 mg of ground quartz (80-125 ⁇ m) are placed in the reactor and activated at 300 ° C. (temperature ramp 4 ° C./min) under H 2 (flow rate of 27 cm 3 / min, ie an hourly volume velocity WH of 80 h -1 ).
• the temperature is then set at 200 ° C. and the hydrogen-orthoxylene reaction mixture is introduced into the reactor.
• the ortho-xylene partial pressure is 4 kPa (condenser temperature 50 c C).
• the activity of the catalytic system stabilizes after 2 hours.
• the reaction temperature is then set at 100 ° C.
• the performance of the catalytic system tested is measured 200 minutes after the introduction of the reagents.
• the catalytic performances are not significantly improved by the morphology of the support particles.
• the catalytic properties were then studied on a selective hydrogenation reaction of crotonaldehyde (2-butenal) crotyllic alcohol, CrOH.
• the hydrogenation reaction of crotonaldehyde is studied in the vapor phase at atmospheric pressure at 100 ° C. in a fixed-bed open microreactor. Hydrogen is bubbled into the liquid crotonaldehyde contained in a saturator at room temperature.
• the reaction mixture then passes through a condenser maintained at 0 ° C. in a thermostatic bath, thereby fixing the crotonaldehyde partial pressure at 1.1 ⁇ 10 3 Pa.
• 50 mg of the catalytic test system manufactured as described above are placed in a reactor and diluted in 50 mg of crushed quartz.
• the catalyst is then activated at 300 ° C. under H 2 for 6 hours.
• thermocouple located in a thermowell at the level of the catalytic bed
• the composition of the mixture leaving the reactor is analyzed every 20 minutes by gas chromatography (HP 4890). is equipped with a flame ionization detector (FID) on a CP-SIL 5CB column
• Example 9 thus makes it possible to considerably improve the catalytic properties with a double intrinsic velocity V and selectivity, S Cf0H 55% greater than those of the reference powder.
• the support powder of Example 2 differs from that of Example 1 by the morphology of the primary particles.
• a comparison of these examples shows that the anisotropic morphology gives better results.
• a comparison of the catalytic systems 9, 10 and 12 shows that not all the anisotropic morphologies are suitable for a reaction sensitive to the determined structure.
• the catalyst system 10 obtained from the rod-shaped carrier powder of Example 3 thus exhibits few planes to which the reaction would be sensitive, the catalytic performance being similar to that of Example 8.
• a comparison of Examples 9 and 5 10 shows that among the anisotropic morphologies tested, the platelet morphology is the only one that is effective.
• the inventors have also found that this difference in efficiency results from the crystalline planes exposed by the primary particles of the support.
• the inventors have thus discovered that it is advantageous to choose particles exhibiting particular crystalline planes.
• Example 10 demonstrates the benefit of the advanced wash purification step.
• the intrinsic speed is in fact improved by 56% and the selectivity with respect to the crotyllic alcohol is improved by 75%.
• the invention provides particles which, directly or in catalytic systems, allow, thanks to a enhanced purification, improve the efficiency of catalysis of structure-sensitive reactions.
• a powder according to the invention could be used, for example, as a mineral filler, as an abrasive or in the field of filtration.

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