Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/02—Inorganic material
  • B01D71/024—Oxides
  • B01D71/0271—Perovskites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
  • B01D53/228—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion characterised by specific membranes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/32—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by electrical effects other than those provided for in group B01D61/00
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • 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
  • B01J35/58—Fabrics or filaments
  • B01J35/59—Membranes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • 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
  • B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
  • B01J37/0018—Addition of a binding agent or of material, later completely removed among others as result of heat treatment, leaching or washing,(e.g. forming of pores; protective layer, desintegrating by heat)
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
  • C01B13/02—Preparation of oxygen
  • C01B13/0229—Purification or separation processes
  • C01B13/0248—Physical processing only
  • C01B13/0251—Physical processing only by making use of membranes
  • C01B13/0255—Physical processing only by making use of membranes characterised by the type of membrane
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen; Reversible storage of hydrogen
  • C01B3/02—Production of hydrogen; Production of gaseous mixtures containing hydrogen
  • C01B3/32—Production of hydrogen; Production of gaseous mixtures containing hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide or air
  • C01B3/34—Production of hydrogen; Production of gaseous mixtures containing hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide or air by reaction of hydrocarbons with gasifying agents
  • C01B3/36—Production of hydrogen; Production of gaseous mixtures containing hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide or air by reaction of hydrocarbons with gasifying agents using oxygen; using mixtures containing oxygen as gasifying agents
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/26—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on ferrites
  • C04B35/2641—Compositions containing one or more ferrites of the group comprising rare earth metals and one or more ferrites of the group comprising alkali metals, alkaline earth metals or lead
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2325/00—Details relating to properties of membranes
  • B01D2325/26—Electrical properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2210/00—Purification or separation of specific gases
  • C01B2210/0043—Impurity removed
  • C01B2210/0046—Nitrogen
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
  • Y02C20/00—Capture or disposal of greenhouse gases
  • Y02C20/20—Capture or disposal of greenhouse gases of methane

Definitions

• Perovskite material process for preparation and use in a membrane catalytic reactor
• the present invention relates to a mixed conductive material (electronic and anionic O 2 " ) of perovskite structure, its preparation process and its use in a membrane catalytic reactor for carrying out the operation of reforming methane or natural gas into synthesis (H 2 / CO mixture).
• the catalytic membrane reactors (Catalytic Membrane Reactor in English, hereinafter referred to as: CMR) produced from such ceramic materials, allow the separation of oxygen from the air, the diffusion of this oxygen in ionic form through the ceramic material and the chemical reaction of the latter with natural gas (mainly methane) on catalytic sites (particles of Ni or noble metals) deposited on the membrane.
• Perovskite is a mineral with the formula CaTiO 3 having a specific crystal structure which can be demonstrated by X-ray diffraction (XRD).
• XRD X-ray diffraction
• the elementary mesh of this compound is a cube, the vertices of which are occupied by the Ca 2+ cations, the center of the cube by the Ti 4+ cation and the center of the faces by the oxygen O 2 " anions.
• the oxides of the family of perovskites are represented by the general formula ABO 3 in which A and B are metal cations whose sum of charges is equal to +6.
• A is in principle an element of the group of lanthanides and B is a transition metal.
• Perovskite is called all the compounds of formula ABO, where A and B may be the above-mentioned chemical elements or mixtures of these elements with other cations, and having the crystal structure described above.
• the partial substitution of the elements A and B by elements A 'and B' to form a perovskite compound of type A 1-X A ' X B 1-y B' y O causes numerous modifications within the material which can prove to be particularly interesting for intended application.
• the subject of the invention is a mixed electronic conductive material and O 2 " anions of crystalline structure of the perovskite type, characterized in that it consists essentially of a compound of formula (I ): A -xu) A ⁇ » A « B -syv) B ⁇ B * B- O 3- ⁇ (I), formula (I) in which: a, a-1, a ", b, (b + l), (b + ⁇ ) and b “are whole numbers representing the respective valences of the atoms A, A ', A", B, B' and B "; a, a", b, b “, ⁇ , x , y, s, u, v and ⁇ are such that the electrical neutrality of the crystal lattice is preserved, a> l, a ", b and b" are greater than zero;
• A represents an atom chosen from scandium, yttrium or from the families of lanthanides, or actinides, or alkaline earth metals
• a 'different from A represents an atom chosen from scandium, yttrium or from the families of lanthanides, actinides or alkaline earth metals
• a "different from A and A ' represents an atom chosen from aluminum (Al), gallium (Ga), indium (In), thallium (Tl) or in the family of alkaline earth metals
• B represents an atom chosen from transition metals able to exist under several possible valences
• B 'different from B represents an atom chosen from transition metals, aluminum (Al), indium (In), gallium (Ga), germanium (Ge), antimony (Sb), bismuth (Bi), tin (Sn), lead (Pb) or titanium (Ti);
• B "different from B and B ', represents an atom chosen from transition metals, metals of the alkaline earth family, aluminum (Al), indium (In), gallium (Ga), germanium ( Ge), antimony (Sb), bismuth (Bi), tin (Sn) lead (Pb) or titanium
• T By family of alkaline earth metals is meant for A, A 'or B ", an atom essentially chosen from magnesium (Mg), calcium (Ca), strontium (Sr) or barium (Ba).
• lanthanides is designated for A, an atom chosen essentially from lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), Tyrterbium (Yb) and lutetium (Lu).
• La lanthanum
• Ce cerium
• Pr praseodymium
• Nd neodymium
• Sm samarium
• Eu europium
• Gd gadolinium
• Tb terbium
• Dy dysprosium
• B transition able to exist under several possible valences
• the metals having at least two adjacent possible degrees of oxidation, and more particularly an atom chosen among titanium (Ti), vanadium (V), chromium (Cr ), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), molybdenum (Mo) ruthenium (Ru), rhodium (Rh), tantalum (Ta), tungsten (W), rhenium (R e), osmium (Os), iridium (Ir) or platinum (Pt).
• transition metals denotes, for B ′ or B ′′, an atom chosen essentially from titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), zirconium (Zr), niobium (Nb), molybdenum (Mo) ruthenium (Ru), rhodium (Rh) , palladium (Pd), silver (Ag), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium ( Ir), platinum (Pt) or gold (Au).
• the invention relates to a material as defined above, for which in the formula (I), ⁇ is equal to an optimum value ⁇ op. , which allows it to provide optimum ionic conductivity for sufficient stability under the conditions of pressure and operating temperature as a mixed ionic and electronic conductor.
• ⁇ is equal to an optimum value ⁇ op.
• the invention relates to a material as defined above, for which, in formula (I), a and b are equal to 3.
• the invention relates to a material as defined above, for which, in formula (I), u is equal to zero.
• the invention relates to a material as defined above, for which in the formula (I), u is different from zero. According to a fifth particular aspect, the invention relates to a material as defined above, for which, in formula (I), the sum (y + v) is equal to zero. According to a sixth particular aspect, the invention relates to a material as defined above, for which, in formula (I), the sum (y + v) is different from zero.
• the invention relates to a material as defined above, for which, in formula (I), A is chosen from La, Ce, Y, Gd, Mg, Ca, Sr or Ba and more particularly for object a material of formula (la): La -XU) O 3- ⁇ (la), corresponding to formula (I), in which a and b are equal to 3 and A represents a lanthanum atom.
• the invention relates to a material as defined above, for which in formula (I), A 'is chosen from La, Ce, Y, Gd, Mg, Ca, Sr or Ba and more particularly for object, a material of formula (Ib): A ⁇ V xu) Sr TM O 3- ⁇ (Ib), corresponding to formula (I), in which a and b are equal to 3 and A 'represents a strontium atom.
• the invention relates to a material as defined above, for which in the formula (I), B is chosen from Fe, Cr, Mn, Co, Ni or Ti.
• the invention relates to a material as defined above, for which in the formula (I), B 'is chosen from Co, Ni, Ti, Mn, Cr, Mo, Zr, V or Ga
• the invention relates to a material as defined above, for which in formula (I), A "is . selected from Ba, Ca, Al or Ga As an example of material there is one for which the formula (I) is either: the XU) S. Al ⁇ u Fe -SV) Fe TM Ti v O 3- ⁇ , La -XU) Sr TM Al TM Fe -sv) Fe TM Ga v O 3- ⁇ , L a ⁇ . x) ⁇ f. s . v) ⁇ i ⁇ s F Qv o 2 .
• the invention also relates to a process for the preparation of a mixed electronic conductive material and of O 2 " anions of crystal structure of the perovskite type.
• pO 2 partial pressure of oxygen
• A is more particularly chosen from La, Ce, Y, Gd, Mg, Ca, Sr or Ba and, in this case, the material prepared by the process as defined above is preferably a material of formula (a): La (1-XU) A ' x A " u B (1-yv) B' y B" v O 3- ⁇ (a), corresponding to formula (F), in which A represents a lanthanum atom.
• a ' is more particularly chosen from La, Ce, Y, Gd, Mg, Ca, Sr or Ba and, in this case, the material prepared by the process as defined above is preferably a material of formula (I'b): A (1-xU) Sr x A " u B ( 1-yV ) B ' y B" v O 3- ⁇ (I'b), corresponding to formula (I 1 ), in which a and b are equal to 3 and A 'represents a strontium atom.
• the powders of high purity precursors are previously washed and / or dried and / or heated to 600 ° C. to extract the volatile compounds and the adsorbed water. They are then weighed and mixed in the appropriate proportions to obtain the desired mixture.
• Step (a) generally consists of a calcination which takes place at a temperature generally between 800 ° C. and 1,500 ° C., preferably between 900 and 1,200 ° C. , for 5h to 15h in air or in a controlled atmosphere. a DRX analysis then makes it possible to check the reaction state of the powders. If necessary, the powder is again ground, then calcined according to the same protocol until the reaction of the precursors is complete and results in the desired perovskite phase.
• the powder has a majority perovskite phase and possibly a small amount of secondary phases (reactivity between part of the precursors resulting in suboxides) varying between 0 and 10% by volume.
• the nature and the fraction of these phases can vary according to the temperatures reached, the homogeneity of the mixture or the type of atmosphere used.
• the powder formed can be ground to adapt the size, shape and specific surface of the grains to the shaping protocol used. The granulometry of the powder is controlled by a granulometer or by SEM or by any other specific device.
• the shaping step (b) can consist of: - an extrusion, for example in the form of tubes or plates or cellular structures - a co-extrusion, for example of porous tubes or plates (ses) and a dense membrane - by pressing, for example in the form of a tube or discs or cylinders or plates - in a strip casting, for example in the form of plates which can subsequently be cut.
• These processes generally require the addition of organic materials such as binders and plasticizers which confer the flow properties adapted to the process and mechanical properties favorable for handling in raw form, that is to say before sintering, of the object.
• the elimination of organic elements requires a heat treatment step prior to sintering.
• This step (c), called debinding, is carried out in an oven in air or in a controlled atmosphere, with a suitable thermal cycle, generally by pyrolysis with slow heating kinetics up to a level of between 200 and 700 ° C., preferably between 300 ° C and 500 ° C.
• the relative density of the membranes must be at least 55% to facilitate the densification of the object during sintering.
• Step (d) of sintering is carried out between 800 and 1500 ° C, preferably between 1000 ° C and 1400 ° C for 2 to 3 hours, under a controlled atmosphere (pO 2 ) and on a support having little or no of interaction with the material.
• the powder obtained in step (a) is shaped by strip casting (step b).
• suitable organic compounds as a binder for example a methacrylate resin, PVB
• dispersants for example a phosphoric ester
• plasticizer for example dibutyl phthalate
• step (c) is carried out by controlling the partial oxygen pressure (pO 2 ) of the gaseous atmosphere surrounding the material to be debonded.
• step (d) is carried out under a gaseous atmosphere comprising a partial pressure of oxygen controlled between 10 "7 Pa to 10 5 Pa, preferably close to 0.1 Pa and in in this case step (a) is preferably carried out in air.
• the invention relates to a material of formula (F), as defined above, and more particularly a material of formula (a), (I'b), (Fc) or
• ⁇ is a function of the partial pressure of oxygen in the gaseous atmospheres in which steps (a), (d) and possibly step (c) of the process as defined above take place above.
• the invention finally relates to the use of the material as defined above, as a mixed conductive material (electronic and ionic conductor) of a catalytic membrane reactor, intended to be used for synthesizing synthesis gas by oxidation of methane or natural gas.
• Figure 1 is a schematic representation of the anionic and electronic diffusion through the membrane catalytic reactor in operation. The following description illustrates the invention without however limiting it.
• This grinding by attrition leads to a homogeneous mixture of the grains of powder of smaller diameter having a relatively spherical shape and having a monomodal granular distribution.
• the average diameter of the grains is between 0.3 ⁇ m and 2 ⁇ m.
• the contents of the jar are sieved using a 200 ⁇ m grid to separate the powder and the beads.
• the sieve is dried and stored before being calcined.
• the powder mixture obtained is calcined on an alumina refractory in an oven.
• the partial pressure of oxygen in the atmosphere is imposed by the circulation in the furnace of a suitable gas or mixture of gases. It is controlled so as to remain in the interval [10-7 Pa to 10 5 Pa].
• the oven is swept by the gas mixture before performing the temperature rise ramp, to establish the desired partial pressure of oxygen, which is controlled by an oxygen sensor or a chromatograph placed at the outlet of the oven.
• the gas mixture is composed of 0 to 100% oxygen, the balance being another type of gas, preferably argon or nitrogen or carbon dioxide.
• the temperature is then increased to a level between 900 ° C and 1200 ° C and for 5h to 15h.
• the rate of temperature rise is typically between 5 ° C / min and 15 ° C / min, the rate of descent is governed by the natural cooling of the oven.
• a DRX analysis then makes it possible to check the reaction state of the powders.
• the powder is optionally ground and / or calcined again according to the same protocol until the reaction of the precursors is complete and results in the desired perovskite phase.
• the perovskite powder obtained is shaped according to the conventional methods used for ceramic materials. Such processes systematically call for additions of organics which must be extracted by pyrolysis (step c: debinding) before the actual sintering step at high temperature (step d).
• step d The resulting ceramic part is introduced into the furnace, the partial oxygen pressure of which is regulated as in the preceding calcination step.
• the temperature is increased slowly, approximately 0.1 ° C / min to 2 ° C / min until a first level between 300 ° C and 500 ° C (step c debinding).
• the landing time varies between 0 and 5 hours depending on the additions used and the volume of the room. This operation takes place in a controlled or uncontrolled atmosphere.
• the oxygen content is between 10 ⁇ 7 Pa and 10 5 Pa, preferably less than or equal to 0.1 Pa.
• the temperatures for which the fluxes are measured vary between 500 and 1000 ° C.
• the oxidizing and reducing gases used in this example are air and argon respectively.
• the measurements are carried out over several hours of operation.
• the oxygen contents contained in the argon downstream of the thermal enclosure are measured using an oxygen probe and / or a gas chromatograph (GC).
• Table 1 highlights the influence of the synthesis protocol on a material described in the Figure 5 shows the stability of the oxygen permeation flow over more than 100 hr of operation for an air / argon mixture at 1000 ° C. and atmospheric pressure on either side.
• XRD XRD analyzes on bulk or powder samples take place at different stages of the synthesis protocol (after calcination, after sintering or in post mortem) and allow the nature of the material to be verified (phase, system crystalline) and its evolution according to the protocol.
• thermogravimetric analysis The evaluation of the sub-stoichiometry of the material, that is to say the value of ⁇ in the formulation described in this invention, according to the synthesis protocol used is made by measuring loss or gain in mass as a function of temperature and partial pressure of oxygen.
• the powders must be dried beforehand, so that the variation in mass is only attributable to an exchange of oxygen with the atmosphere.
• the powder or sintered material reduced to powder and dried is placed in an alumina crucible in the compartment provided for this purpose of the thermobalance.
• the thermal program and the partial oxygen pressure of the medium are adjusted in accordance with those of the calcination or sintering protocol for the material.
• the mass variation signal recorded as a function of temperature for a fixed partial pressure of oxygen makes it possible to deduce the sub-stoichiometry of the oxygen material.
• FIG. 4 is a schematic sectional view of the reactor used.
• the membranes (1) have a diameter of around 25 mm and a thickness which can vary between 0.1 and 2 mm. They are positioned individually on the top of an alumina tube (2) placed in a thermal enclosure (3).
• the dense alumina tube contains a controlled atmosphere (4) which will play a reducing role in operation (neutral or reducing gas).
• the face of the opposite membrane is swept by an oxidizing atmosphere (5) (variable air or pO 2 ).
• the tightness between the two atmospheres is guaranteed at high temperature by the presence of a tight seal (6) between the alumina tube and the membrane.
• the oxygen sub-stoichiometry is ensured by a preparation stage, whether it is synthesis (or calcination, stage a) and / or sintering (stage d) (the latter including the cycle debinding, step c)), at high temperature (> 900 ° C) under a controlled atmosphere having a low partial pressure of controlled oxygen.
• the thermal enclosure can therefore be swept by a neutral gas (eg N or Ar) or a reducing gas (eg H 2 / N 2 or H 2 / He) or be placed under dynamic vacuum.
• a neutral gas eg N or Ar
• a reducing gas eg H 2 / N 2 or H 2 / He
• the mixture of precursors can be calcined in air or in neutral gas then sintered in neutral gas (controlled pO 2 ⁇ 0.2).
• the evolution of the oxygen network content can be followed by X-ray diffraction (DRX) or by thermogravimetry (ATG). Indeed, the appearance of vacancies in the crystal lattice of the material modifies its structure and / or its crystalline parameters.
• DRX X-ray diffraction
• ATG thermogravimetry
• the material synthesized in air or under argon does not have the same crystalline system. Indeed, we note that all the peaks are fine during a synthesis under argon while certain peaks are split (they have a shoulder) during a synthesis in air. The synthesis of this material under argon thus leads to a cubic symmetry while the synthesis in air leads to a rhombohedral symmetry. We know that the repulsion between cations is greater in a sub-stoichiometric material, which has the effect of increasing the volume of the mesh.
• the synthesis protocol under a controlled pO 2 atmosphere also offers another advantage, that of greatly reducing the presence of secondary phases in the sintered membrane. Indeed, the synthesis of a powder from precursors rarely leads to the formation of a single phase. These secondary phases can indirectly decrease the performance of the material since their presence modifies the formulation of the main phase by depleting it in certain elements. However, as it is difficult to predict in advance that it will be exactly the proportion and the nature of the secondary phases, the formulation of the final material cannot be guaranteed from an adjustment of the initial quantities of precursors.
• the secondary phases included in our air-sintered materials are compounds of type ABO 3 , AB 2 O 4 , A BO 4 or mixed compounds AA ⁇ O 3 , ABB'O 3 or
• FIG. 3 illustrates the influence of the preparation protocol ( synthesis and sintering) on the nature of the phases present in the material. It highlights in particular the interest of sintering the material under low partial pressures of oxygen to favor the presence of a sub-stoichiometric phase and reduce that of the inclusions which deplete the material in certain elements at the expense of the conduction properties.
• the present invention highlights the influence of the preparation protocol on its performance, in particular by the synthesis stage (stage a) and / or sintering stage (stage d) under low partial pressures of oxygen (vacuum, neutral gases or reducers).
• FIG. 6 illustrates the diffusion of oxygen in such a membrane catalytic reactor. It is therefore understood that the material must have oxygen vacancies within it to be used for a CMR application.
• This search for a sub-stoichiometry of the material begins with its initial formulation, in particular by doping the material with an element capable of creating gaps. Then in a second step, the sub stoichiometry is obtained by the preparation protocol.
• strontium which acts as a doping element on lanthanum.
• Sr 2+ has an ion radius close to La 3+ , so that it is integrated into the perovskite network.
• its charge is different since it has an electron additional.
• the substitution of lanthanum by strontium therefore causes an electronic overload which is immediately compensated by the crystal to maintain its neutrality. According to a first mechanism, this compensation is ensured by the departure of oxygen which creates positively charged vacancies so that the positive charges cancel the negative charges.

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