Cerium-based and zirconium-based mixed oxide

Abstract

The invention relates to a mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth metal (REM) other than cerium and lanthanum, characterized by a BET specific surface, a specific range of pores, and a method for producing such a mixed oxide.

Description

[0001] This application claims priority from international procedure No. CN 2022 / 111999 filed on CE on August 12, 2022, the entire contents of which are incorporated herein by reference for all purposes. Technical Field

[0002] The present invention relates to a mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth metal oxide other than cerium and lanthanum, which exhibits high porosity and high specific surface area, to a process for its preparation and to its use in catalysis.

[0003] Technical issues

[0004] "Multifunctional" catalysts are currently used to treat exhaust gases from internal combustion engines (motor vehicle afterburner catalysis). Multifunctional is understood to mean catalysts which are capable not only of oxidation, in particular of the carbon monoxide and hydrocarbons present in the exhaust gases, but also of reduction, in particular of the nitrogen oxides also present in these gases ("three-way" catalysts).

[0005] The catalyst is produced by the interaction of a noble metal (e.g., Pd, Pt, Rh) with a mixed oxide based on cerium and zirconium, usually as a mixture with aluminum oxide. The mixed oxide must exhibit a suitable porosity. Therefore, it must exhibit a sufficiently large pore volume and also include pores with a sufficiently large size so that the gas may diffuse well. The mixed oxide must also exhibit a sufficiently high specific surface area so that it can be used for catalysis.

[0006] It is known that small-sized pores form the largest specific surface area. In fact, these pores are the most sensitive to sintering. It is therefore advantageous to develop a mixed oxide that exhibits a good compromise between large pore volume, high surface area, even after being kept at high temperatures, and for which there is a population of small-sized pores that exhibits good heat resistance.

[0007] The mixed oxide according to the invention as claimed in claim 1 aims at this compromise. Summary of the invention

[0008] The present invention relates to a mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth metal (REM) other than cerium and lanthanum, the weight ratios of these elements, expressed as oxide equivalents relative to the total weight of the mixed oxide, being as follows:

[0009] - between 8% and 47% cerium;

[0010] - between 1% and 10% lanthanum;

[0011] - between 0% and 15% of rare earth metals other than cerium and lanthanum;

[0012] - the remainder is zirconium,

[0013] Characterized in that the mixed oxide exhibits:

[0014] - After calcination at 1100°C for 4 hours for at least 30 minutes 2 / g BET specific surface area;

[0015] - After calcination at 1000°C for 4 hours, at least 50 minutes 2 / g BET specific surface area;

[0016] the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide, after calcination for 4 hours at a temperature of 1100° C., exhibits, within the range of pores with a diameter less than or equal to 200 nm, a peak whose maximum corresponds to a pore diameter of between 25 and 40 nm, preferably between 25 and 38 nm, denoted Dp,1100° C. / 4h, V and D indicating respectively the pore volume and the pore diameter; and

[0017] - a ratio R comprised between 0.50 and 0.60, R being defined by:

[0018] R=V1 / V2

[0019] in:

[0020] - V1 is the pore volume formed by pores whose diameter in nm is between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15);

[0021] - V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm;

[0022] - V1 and V2 were determined on the mixed oxide by mercury porosimetry after calcination at 1100° C. for 4 h.

[0023] In another aspect, the mixed oxide further comprises hafnium.

[0024] Thus, and in another aspect of the invention, the mixed oxide is characterized in that the weight proportion of hafnium in the mixed oxide, expressed in oxide equivalent relative to the total weight of the mixed oxide, is less than or equal to 2.5%, indeed even less than or equal to 2.0%.

[0025] According to another aspect, the mixed oxide of the invention is characterized in that the elements Ce, La, rare earth metals (REM) other than cerium and lanthanum, Zr and Hf are present in the form of oxides, hydroxides or oxyhydroxides, more particularly in the form of oxides.

[0026] In yet another aspect, the mixed oxide according to the invention is characterized in that the REM other than cerium and lanthanum is chosen from yttrium, neodymium or praseodymium or any combination thereof.

[0027] In a particular aspect of the invention, the mixed oxide comprises only yttrium as rare earth metal besides cerium and lanthanum.

[0028] In a particular aspect of the invention, the mixed oxide comprises only two rare earth metals other than cerium and lanthanum, which rare earth metals may be yttrium and neodymium or yttrium and praseodymium.

[0029] In another aspect, the mixed oxide consists essentially of a mixture of oxides of zirconium, cerium, lanthanum, optionally at least one REM other than cerium and lanthanum, and optionally hafnium.

[0030] In another aspect, the mixed oxide of the present invention does not contain any rare earth metals other than cerium and lanthanum.

[0031] In a specific aspect of the invention, the mixed oxide according to one of the claims consists essentially of the following elements:

[0032] - zirconium, cerium, lanthanum, yttrium and optionally hafnium;

[0033] - zirconium, cerium, lanthanum, yttrium, neodymium and optionally hafnium; or

[0034] - zirconium, cerium, lanthanum, yttrium, praseodymium and optionally hafnium;

[0035] - zirconium, cerium, lanthanum, neodymium, praseodymium and optionally hafnium; or

[0036] - zirconium, cerium, lanthanum and optionally hafnium.

[0037] In another aspect, the mixed oxide of the invention is characterized in that the weight proportion of zirconium, expressed as oxide equivalent, is comprised between 40% and 91.0%, preferably between 44.0% and 80.0%, more preferably between 44.0% and 76.0%.

[0038] In yet another aspect, the mixed oxide of the present invention has a carbon content equal to or greater than 0.4 g / cm 3 , preferably equal to or greater than 0.5 g / cm 3 The tap density.

[0039] In a more specific aspect, the tap density of the mixed oxide is 0.5 g / cm 3 Up to 0.9g / cm 3 .

[0040] In another aspect, the mixed oxide according to the invention is characterized in that, after calcination for 4 hours at a temperature of 900°C, the derivative curve (dV / dlogD) obtained for the mixed oxide by mercury porosimetry exhibits, within the range of pores with a diameter less than or equal to 200 nm, a peak whose maximum corresponds to the pore diameter denoted Dp,900°C / 4h and such that the difference in absolute values ​​(Dp,1100°C / 4h)-(Dp,900°C / 4h) is less than or equal to 15 nm, preferably less than or equal to 12 nm, indeed even less than or equal to 11 nm.

[0041] In another aspect, the mixed oxide of the invention is characterized by a pore volume (V2) of 0.20 to 0.50 ml / g, in particular 0.24 to 0.41 ml / g.

[0042] In yet another aspect, the mixed oxide of the invention provided in powder form has a mean diameter d50 determined by laser diffraction on a volume distribution comprised between 1.0 and 30.0 μm, preferably between 2.0 and 20.0 μm, even more preferably between 3.0 and 10.0 μm.

[0043] In a more specific aspect, the mixed oxide of the invention is characterized in that the derivative curve (dV / dlogD) obtained for the mixed oxide by mercury porosimetry after calcination at a temperature of 900° C. for 4 hours does not exhibit two distinct peaks.

[0044] The present invention also relates to a method for preparing a mixed oxide as described above, comprising the following steps:

[0045] - (a1) introducing an aqueous solution of cerium nitrate and zirconium nitrate into a stirred vessel containing an alkaline aqueous solution;

[0046] (a2) optionally subsequently introducing an aqueous solution of a nitrate of a rare earth metal (REM) other than cerium and lanthanum into the mixture formed in step (a1), while maintaining stirring;

[0047] - (a2') optionally heating the mixture obtained at the end of step (a1) or (a2) at a temperature comprised between 50°C and 95°C;

[0048] - (a3) ​​subsequently introducing an aqueous solution of lanthanum nitrate into the mixture formed in step (a2), (a2') or (a1) and maintaining stirring;

[0049] - (a4) heating the mixture obtained at the end of step (a3) ​​under stirring;

[0050] - (a5) subsequently introducing a templating agent into the mixture obtained in the previous step;

[0051] - (a6) optionally, filtering the mixture and washing the precipitate;

[0052] - (a7) calcining the precipitate obtained at the end of step (a6) at a temperature between 700° C. and 1100° C.; and

[0053] - (a8) optionally grinding the mixed oxide obtained in step (a7).

[0054] In a particular aspect of the above process, the mixed oxide concentration of the aqueous solution after step (a3) ​​is from 30 g / l to 80 g / l, expressed as metal oxides.

[0055] The invention also relates to the mixed oxide obtained by the process described above.

[0056] The invention further relates to a composition comprising the mixed oxide in admixture with at least one mineral material.

[0057] In a particular aspect, the mineral material of the composition of the invention is chosen from alumina, titania, cerium oxide, zirconium oxide, silica, spinel, zeolite, silicate, crystalline silicoaluminophosphate or crystalline aluminum phosphate.

[0058] The invention relates to a catalytically active coating deposited on a surface region of a solid support, the catalytically active coating comprising a mixed oxide as described above or a composition as described above.

[0059] The invention also relates to a catalytic converter for treating exhaust gas from a motor vehicle, the catalytic converter comprising a catalytically active coating as described above.

[0060] The invention also encompasses the use of a mixed oxide or composition as described above in the preparation of a catalytic converter as a method for treating exhaust gas from an internal combustion engine, characterized in that a catalytic converter comprising a coating according to the invention is used.

[0061] Other features, details and advantages of the present invention will become even more fully apparent on reading the description and accompanying drawings.

[0062] picture

[0063] Figure 1 The vertical axis represents dV / dlogD, the logarithm of the differential indentation in mL / g, and the horizontal axis represents the pore size diameter in nm. Figure 1 The results obtained in Example 1 (solid line) and Comparative Example 1 (dashed line) are shown.

[0064] definition

[0065] Within the meaning of the present invention, specific surface area is understood to mean the BET (Brunauer-Emmett-Teller) specific surface area (SBET, SSA or SA) determined by nitrogen adsorption.

[0066] The term "specific surface area (BET, SBET, SSA or SA)" is understood to mean the BET specific surface area determined by nitrogen adsorption. The specific surface area is well known to the skilled person and is measured according to the Bruno-Emmett-Teller method. The theory of the method was originally described in the journal "The Journal of the American Chemical Society [American Chemical Society], 60, 309 (1938)". More detailed information on the theory can also be found in Chapter 4 of "Powder surface area and porosity [powder surface area and porosity]", 2nd edition, ISBN 978-94-015-7955-1. The nitrogen adsorption method is disclosed in the standard ASTM D 3663-03 (reapproved in 2008). In practice, the specific surface area (BET) can be determined automatically with the device Flowsorb II 2300 or the device Tristar 3000 of Micromeritics according to the manufacturer's guidelines (guidelines of the constructor). They can also be determined automatically with a Mountech Macsorb Analyzer model 1-1220 according to the manufacturer's instructions. Prior to the measurement, the sample is optionally degassed under vacuum by heating at a temperature of up to 300° C. to remove adsorbed volatile substances. More specific conditions can be seen in the Examples.

[0067] The indicated porosities are measured by mercury intrusion porosimetry according to standard ASTM D 4284-83 (reapproved in 2008) (“Standard Method for Pore Volume Distribution of Catalysts by Mercury Intrusion Porosimetry”).

[0068] Within the meaning of the present invention, rare earth metals (REM) are understood to mean elements from the group consisting of scandium, yttrium and the elements of the periodic table having an atomic number between 57 and 71 inclusive.

[0069] Rare earth elements as defined by IUPAC are one of a group of seventeen chemical elements (specifically fifteen lanthanide elements plus scandium and yttrium) in the periodic table. The rare earth elements are cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb) and yttrium (Y).

[0070] Throughout the present application, unless otherwise indicated, the proportions are given by weight of the oxide relative to the mixed oxide as a whole.

[0071] Within the meaning of the present invention, cerium oxide is considered to be in the form of cerium dioxide (CeO2), REM oxides are in the form of REM2O3, except that praseodymium is in the form of Pr6O 11 The zirconium oxide and hafnium oxide are in the form of ZrO2 and HfO2.

[0072] For the sake of continuity of the present description it is specified that, unless otherwise stated, the limit values ​​are included in the ranges of these values ​​given.

[0073] As used herein, the singular forms "a," "an," and "the" include both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compound" means one compound or more than one compound.

[0074] Within the meaning of the present invention, tap density is understood to be the density of a powder sample obtained after mechanical tapping.

[0075] According to the invention, pore size is understood, unless defined otherwise, to be the maximum of the pore size distribution in the dV / dlogD curve for pore sizes below 200 nm. DETAILED DESCRIPTION

[0076] Should the disclosure of any patents, patent applications, and publications incorporated herein by reference conflict with the description of the present application to the extent that a term may be unclear, the present description shall take precedence.

[0077] Mixed oxides

[0078] The present invention relates to a mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth metal (REM) other than cerium and lanthanum, the weight proportions of these elements, expressed as oxide equivalents, relative to the total weight of the mixed oxide, being between 8% and 47% of cerium (C); between 1% and 10% of lanthanum (L); between 0% and 15% of REM other than cerium and lanthanum; and the remainder being zirconium (Z).

[0079] The mixed oxides of the invention are furthermore characterized by a high heat resistance. This resistance is necessary because the coating needs to withstand high temperatures. In this respect, it must be borne in mind that gasoline engines are mainly operated with a stoichiometric air / fuel mixture, so that the exhaust gas generally exhibits significantly higher temperatures than a lean-burn engine. Therefore, it is known that gasoline engine filters operate at higher temperatures than more conventional diesel particulate filters.

[0080] The mixed oxides of the present invention further exhibit a strength of at least 30.0 m / s after calcination at a temperature of 1100° C. for 4 hours. 2 / g and a BET specific surface area of ​​at least 50.0 m2 after calcination at 1000°C for 4 hours. 2 / g BET specific surface area.

[0081] The mixed oxide according to the invention is further characterized in that, after calcination at a temperature of 1100° C. for 4 hours, the derivative curve (dV / dlogD) obtained by mercury porosimetry exhibits, within the range of pores with a diameter less than or equal to 200 nm, a peak whose maximum corresponds to a pore diameter between 25.0 and 40.0 nm, denoted Dp,1100° C. / 4h, V and D respectively denoting the pore volume and the pore diameter.

[0082] The mixed oxide of the present invention is further characterized in that it comprises a ratio R between 0.50 and 0.60, which is defined by the following formula: R = V1 / V2, wherein V1 is the pore volume formed by pores whose diameter in nm is between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15); V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm; V1 and V2 are determined for the mixed oxide by mercury porosimetry after calcination at 1100°C for 4 h.

[0083] Mercury porosimetry is a standard technique used in the field of porous catalysts and involves gradually forcing mercury into the pores of a porous structure under controlled pressure. Porosity is measured by mercury intrusion according to well known techniques in the field. Porosity can be determined using a Micromeritics Autopore IV 9500 automatic mercury porosimeter according to the manufacturer's guidelines. Porosimeters include powder penetrometers. The method is based on the determination of the pore volume (V=f(D), V representing the pore volume and D representing the pore diameter) as a function of pore size. From these data, a curve (C) can be obtained giving the derivative dV / dlogD.

[0084] The specificity of this measurement method is given in the following paragraph "Measurement Method".

[0085] In a specific embodiment of the present invention, the mixed oxide of the present invention exhibits at least 30.0 m 2 / g, at least 32.0m 2 / g, preferably at least 34.0m 2 / g, even more preferably at least 36.0m 2 / g BET specific surface area.

[0086] In a more specific aspect of the present invention, the mixed oxide of the present invention exhibits a 2 / g and 40.0m 2 / g, preferably included between 32.0m 2 / g and 40.0m 2 / g, preferably included between 34.0m 2 / g and 40.0m 2 / g, and even more preferably included between 36.0 m 2 / g and 40.0m 2 / g BET specific surface area between.

[0087] In a specific embodiment of the present invention, the mixed oxide of the present invention exhibits at least 50.0 m 2 / g, at least 55.0m 2 / g, at least 60.0m 2 / g, preferably at least 65.0m 2 / g BET specific surface area.

[0088] In a more specific aspect of the present invention, the mixed oxides of the present invention exhibit 2 / g and 70.0m 2 / g, preferably 55.0m 2 / g and 70.0m 2 / g, preferably 60.0m 2 / g and 70.0m 2 / g, even more preferably between 65.0m 2 / g and 70.0m 2 / g BET specific surface area between.

[0089] In another aspect of the present invention, the mixed oxide of the present invention also exhibits a calcination temperature of 1100° C. for 4 hours including 30.0 m 2 / g and 40.0m 2 / g and the BET specific surface area between 50.0 m 2 / g and 70.0m2 / g BET specific surface area between.

[0090] In another aspect of the present invention, the mixed oxide of the present invention further exhibits a temperature of 1100° C. for 4 hours preferably including 30.0 m 2 / g and 40.0m 2 / g, preferably between 32.0m 2 / g and 40.0m 2 / g, more preferably included in 34.0m 2 / g and 40.0m 2 / g, and even more preferably included between 36.0 m 2 / g and 40.0m 2 The BET specific surface area is preferably between 50.0 m / g and 50.0 m / g after calcination at a temperature of 1000°C for 4 hours. 2 / g and 70.0m 2 / g, preferably 55.0m 2 / g and 70.0m 2 / g, preferably 60.0m 2 / g and 70.0m 2 / g, even more preferably between 65.0m 2 / g and 70.0m 2 / g BET specific surface area between.

[0091] The present invention therefore relates to a mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth metal (REM) other than cerium and lanthanum, the weight ratios of these elements, expressed as oxide equivalents relative to the total weight of the mixed oxide, being as follows:

[0092] - between 8% and 47% cerium;

[0093] - between 1% and 10% lanthanum;

[0094] - between 0% and 15% of rare earth metals other than cerium and lanthanum;

[0095] - the remainder is zirconium,

[0096] Characterized in that the mixed oxide exhibits:

[0097] - After calcination at a temperature of 1100°C for 4 hours, preferably including 30.0 m 2 / g and 40.0m 2 / g, preferably between 32.0m 2 / g and 40.0m 2 / g, more preferably included in 34.0m 2 / g and 40.0m2 / g, and even more preferably included between 36.0 m 2 / g and 40.0m 2 / g BET specific surface area;

[0098] - After calcination at a temperature of 1000°C for 4 hours, preferably at 50.0 m 2 / g and 70.0m 2 / g, preferably 55.0m 2 / g and 70.0m 2 / g, preferably 60.0m 2 / g and 70.0m 2 / g, even more preferably between 65.0m 2 / g and 70.0m 2 / g BET specific surface area;

[0099] the derivative curve (dV / dlogD) obtained for the mixed oxide by mercury porosimetry after calcination for 4 hours at a temperature of 1100° C. exhibits a peak whose maximum corresponds to a pore diameter of between 25 and 40 nm, preferably between 25 and 38 nm, denoted Dp,1100° C. / 4h, within the range of pores with a diameter less than or equal to 200 nm, V and D respectively indicating the pore volume and the pore diameter; and

[0100] - The ratio R defined by:

[0101] R=V1 / V2

[0102] in:

[0103] - V1 is the pore volume formed by pores whose diameter in nm is between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15);

[0104] - V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm;

[0105] - V1 and V2 are determined by mercury porosimetry on mixed oxides after calcination at 1100°C for 4 h; and

[0106] Wherein R is comprised between 0.50 and 0.60.

[0107] In another aspect of the invention, the mixed oxide is characterized in that the derivative curve (dV / dlogD) obtained for the mixed oxide by mercury porosimetry after calcination at a temperature of 900° C. for 4 hours does not exhibit two distinct peaks.

[0108] The mixed oxide of the invention may contain hafnium. Thus and in a particular aspect, the weight proportion of hafnium in the mixed oxide, expressed as oxide equivalent relative to the total weight of the mixed oxide, is less than or equal to 2.5%, indeed even less than or equal to 2.0%.

[0109] In another aspect, the mixed oxide of the present invention comprises cerium (Ce), lanthanum (La), REMs other than cerium and lanthanum, zirconium (Zr) and hafnium (Hf) in the form of oxides, hydroxides or oxyhydroxides or any combination thereof.

[0110] In a preferred aspect, the mixed oxide of the present invention comprises Ce, La, REM, Zr and Hf in the form of oxides.

[0111] In another aspect, the mixed oxide according to the invention is characterized in that the REM other than cerium and lanthanum is selected from yttrium, neodymium, praseodymium, or any combination thereof.

[0112] In a specific aspect of the invention, the mixed oxide according to the invention comprises only yttrium as REM besides cerium and lanthanum.

[0113] In another specific aspect of the invention, the mixed oxide of the invention comprises cerium, zirconium and only two REMs other than cerium and lanthanum, which REMs other than cerium and lanthanum may be yttrium and neodymium or else yttrium and praseodymium. In another aspect, the mixed oxide of the invention does not comprise any REMs other than cerium and lanthanum.

[0114] In another aspect, the mixed oxide of the invention comprises or consists essentially of a mixture of oxides of zirconium, cerium and lanthanum and optionally at least one REM other than cerium and lanthanum and optionally hafnium.

[0115] In yet another aspect, the mixed oxide of the present invention consists essentially of the following elements:

[0116] - zirconium, cerium, lanthanum, yttrium and optionally hafnium;

[0117] - zirconium, cerium, lanthanum, yttrium, neodymium and optionally hafnium;

[0118] - zirconium, cerium, lanthanum, yttrium, praseodymium and optionally hafnium;

[0119] - zirconium, cerium, lanthanum, neodymium, praseodymium and optionally hafnium; or

[0120] - zirconium, cerium, lanthanum and optionally hafnium.

[0121] As far as the proportion of zirconium is concerned, it is present as the remainder in the mixed oxide. The total amount of all elements of the mixed oxide according to the invention is 100%, so that the proportion of zirconium corresponds to a 100% supplement to the other elements of the mixed oxide.

[0122] This is to be understood as meaning that the mixed oxide according to the invention does not contain another element oxide other than those cited and which could have an influence on the characteristics of the mixed oxide according to the invention. The mixed oxide according to the invention may contain elements such as impurities which may arise in particular from its preparation process, for example from the starting materials or starting reactants used.

[0123] In a particular aspect of the invention, the mixed oxide is characterized in that the weight proportion of cerium, expressed as oxide equivalent, may be between 8.0% and 47.0%, preferably between 10.0% and 40.0%.

[0124] In a particular aspect of the invention, the mixed oxide is characterized in that the weight proportion of lanthanum, expressed as oxide equivalent, may be between 1.0% and 10.0%, preferably between 3.5% and 5.0%.

[0125] In a specific aspect of the invention, the mixed oxide is characterized in that the weight proportion of rare earth metals other than cerium and lanthanum, expressed as oxide equivalent, may be between 0% and 15.0%, preferably between 1.0% and 15.0%, more preferably between 5.0% and 13.0%.

[0126] In a particular aspect of the invention, the mixed oxide is characterized in that the weight proportion of zirconium expressed as oxide equivalent may be between 40.0% and 91.0%, preferably between 44.0% and 80.0%, more preferably between 44.0% and 76.0%.

[0127] According to the invention, the weight proportions of the mixed oxide of zirconium, cerium, lanthanum, optionally hafnium and optionally at least one REM other than cerium and lanthanum are expressed in the stated oxide equivalents relative to the total weight of the mixed oxide.

[0128] The present invention therefore relates to a mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth metal (REM) other than cerium and lanthanum, the weight ratios of these elements, expressed as oxide equivalents relative to the total weight of the mixed oxide, being as follows:

[0129] - between 8% and 47%, preferably between 10.0% and 40.0% cerium;

[0130] - between 1% and 10%, preferably between 3.5% and 5.0% lanthanum;

[0131] - between 0% and 15%, preferably between 1.0% and 15%, more preferably between 5.0% and 13.0% of rare earth metals other than cerium and lanthanum;

[0132] - the remainder is zirconium,

[0133] Characterized in that the mixed oxide exhibits:

[0134] - After calcination at a temperature of 1100°C for 4 hours, preferably including 30.0 m 2 / g and 40.0m 2 / g, preferably between 32.0m 2 / g and 40.0m 2 / g, more preferably included in 34.0m 2 / g and 40.0m 2 / g, and even more preferably included between 36.0 m 2 / g and 40.0m 2 / g BET specific surface area;

[0135] - After calcination at a temperature of 1000°C for 4 hours, preferably at 50.0 m 2 / g and 70.0m 2 / g, preferably 55.0m 2 / g and 70.0m 2 / g, preferably 60.0m 2 / g and 70.0m 2 / g, even more preferably between 65.0m 2 / g and 70.0m 2 / g BET specific surface area;

[0136] the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide, after calcination for 4 hours at a temperature of 1100° C., exhibits, within the range of pores with a diameter less than or equal to 200 nm, a peak whose maximum corresponds to a pore diameter of between 25 and 40 nm, preferably between 25 and 38 nm, denoted Dp,1100° C. / 4h, V and D indicating respectively the pore volume and the pore diameter; and

[0137] - The ratio R defined by:

[0138] R=V1 / V2

[0139] in:

[0140] - V1 is the pore volume formed by pores whose diameter in nm is between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15);

[0141] - V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm;

[0142] - V1 and V2 are determined by mercury porosimetry on mixed oxides after calcination at 1100°C for 4 h; and

[0143] Wherein R is comprised between 0.50 and 0.60.

[0144] In a particular aspect of the invention, the mixed oxide is also characterized by its pore volume V2. According to the invention, the pore volume V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm;

[0145] The pore volume is determined for the mixed oxide by mercury porosimetry after calcination at 1100° C. for 4 h.

[0146] The mixed oxides according to the invention are therefore furthermore characterized by a pore volume V2 of 0.20 to 0.50 ml / g, in particular 0.24 to 0.41 ml / g.

[0147] In another aspect, the mixed oxide of the invention is characterized in that, after calcination at a temperature of 1100° C. for 4 hours, the derivative curve (dV / dlogD) obtained for the mixed oxide by mercury porosimetry exhibits a peak in the range of pores with a diameter less than or equal to 200 nm, whose maximum corresponds to a pore diameter Dp,1100° C. / 4h of between 25 and 40 nm, preferably between 25 and 38 nm, V and D representing the pore volume and the pore diameter, respectively.

[0148] The present invention therefore relates to a mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth metal (REM) other than cerium and lanthanum, the weight ratios of these elements, expressed as oxide equivalents relative to the total weight of the mixed oxide, being as follows:

[0149] - between 8% and 47%, preferably between 10.0% and 40.0% cerium;

[0150] - between 1% and 10%, preferably between 3.5% and 5.0% lanthanum;

[0151] - between 0% and 15%, preferably between 1.0% and 15%, more preferably between 5.0% and 13.0% of rare earth metals other than cerium and lanthanum;

[0152] - the remainder is zirconium,

[0153] Characterized in that the mixed oxide exhibits:

[0154] - After calcination at a temperature of 1100°C for 4 hours, preferably including 30.0 m 2 / g and 40.0m 2 / g, preferably between 32.0m 2 / g and 40.0m 2 / g, more preferably included in 34.0m 2 / g and 40.0m2 / g, and even more preferably included between 36.0 m 2 / g and 40.0m 2 / g BET specific surface area;

[0155] - After calcination at a temperature of 1000°C for 4 hours, preferably at 50.0 m 2 / g and 70.0m 2 / g, preferably 55.0m 2 / g and 70.0m 2 / g, preferably 60.0m 2 / g and 70.0m 2 / g, even more preferably between 65.0m 2 / g and 70.0m 2 / g BET specific surface area;

[0156] the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide, after calcination for 4 hours at a temperature of 1100° C., exhibits, within the range of pores with a diameter less than or equal to 200 nm, a peak whose maximum corresponds to a pore diameter of between 25 and 40 nm, preferably between 25 and 38 nm, denoted Dp,1100° C. / 4h, V and D indicating respectively the pore volume and the pore diameter; and

[0157] - The ratio R defined by:

[0158] R=V1 / V2

[0159] in:

[0160] - V1 is the pore volume formed by pores whose diameter in nm is between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15);

[0161] - V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm; and

[0162] where R is between 0.50 and 0.60, and

[0163] A pore volume V2 of 0.20 to 0.50 ml / g, preferably 0.24 to 0.41 ml / g, wherein V1 and V2 are determined by mercury porosimetry for the mixed oxide after calcination at 1100° C. for 4 h.

[0164] The mixed oxide of the present invention may also be defined as consisting essentially of a mixed oxide of zirconium, cerium, lanthanum and optionally at least one REM other than cerium and lanthanum, the weight proportions of these elements, expressed in oxide equivalents, relative to the total weight of the mixed oxide, being between 8% and 47% of cerium (C); between 1% and 10% of lanthanum (L); between 0% and 15% of rare earth metals other than cerium and lanthanum; the remainder being zirconium (Z), the weight proportions of these elements being expressed in the stated oxide equivalents relative to the total weight of the mixed oxide, and characterized in that:

[0165] - After calcination at 1100°C for 4 hours for at least 30 minutes 2 / g and a BET specific surface area of ​​at least 50 m2 after calcination at 1000 °C for 4 hours. 2 / g BET specific surface area,

[0166] - after calcination for 4 hours at a temperature of 1100° C., the derivative curve (dV / dlogD) obtained by mercury porosimetry exhibits, within the range of pores with a diameter less than or equal to 200 nm, a peak whose maximum corresponds to a pore diameter between 25 and 40 nm denoted Dp,1100° C. / 4h, V and D indicating respectively the pore volume and the pore diameter; and

[0167] - The ratio R defined by:

[0168] R=V1 / V2

[0169] in:

[0170] - V1 is the pore volume formed by pores whose diameter in nm is between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15);

[0171] - V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm;

[0172] - V1 and V2 are determined by mercury porosimetry on mixed oxides after calcination at 1100°C for 4 h; and

[0173] Wherein R is comprised between 0.50 and 0.60.

[0174] On the other hand, the mixed oxide of the present invention can also be defined as consisting essentially of a mixed oxide of zirconium, cerium, lanthanum and optionally at least one REM other than cerium and lanthanum, the weight proportions of these elements, expressed in oxide equivalents, relative to the total weight of the mixed oxide, being between 8% and 47% of cerium (C); between 1% and 10% of lanthanum (L); between 0% and 15% of rare earth metals other than cerium and lanthanum; between 0% and 2.5% of hafnium; the remainder being zirconium (Z), the weight proportions of these elements, expressed in the stated oxide equivalents relative to the total weight of the mixed oxide, and characterized in that:

[0175] - After calcination at 1100°C for 4 hours for at least 30 minutes 2 / g and a BET specific surface area of ​​at least 50 m2 after calcination at 1000 °C for 4 hours. 2 / g BET specific surface area,

[0176] - after calcination for 4 hours at a temperature of 1100° C., the derivative curve (dV / dlogD) obtained by mercury porosimetry exhibits, within the range of pores with a diameter less than or equal to 200 nm, a peak whose maximum corresponds to a pore diameter between 25 and 40 nm denoted Dp,1100° C. / 4h, V and D indicating respectively the pore volume and the pore diameter; and

[0177] - The ratio R defined by:

[0178] R=V1 / V2

[0179] in:

[0180] - V1 is the pore volume formed by pores whose diameter in nm is between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15);

[0181] - V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm;

[0182] - V1 and V2 are determined by mercury porosimetry on mixed oxides after calcination at 1100°C for 4 h; and

[0183] Wherein R is comprised between 0.50 and 0.60.

[0184] The expression "consisting essentially of" should be interpreted as follows: "Mixed oxide consisting essentially of" means that other elements besides the mandatory elements may be present, provided that the essential characteristics of the claimed composition are not substantially affected by the presence of said other elements. All technical features and embodiments disclosed previously also apply to this specific mixed oxide.

[0185] In another aspect, the mixed oxide of the invention as just described is characterized in that, after calcination at a temperature of 1100° C. for 4 hours, the derivative curve (dV / dlogD) obtained for the mixed oxide by mercury porosimetry exhibits a peak within the range of pores with a diameter less than or equal to 200 nm, whose maximum corresponds to a pore diameter Dp,1100° C. / 4h between 25 and 38 nm, V and D representing the pore volume and the pore diameter, respectively.

[0186] According to the present invention, Dp,1000°C / 4h is the pore diameter determined by mercury porosimetry for the mixed oxide after calcination at 1000°C for 4h, and Dp,1100°C / 4h is the pore diameter determined by mercury porosimetry for the mixed oxide after calcination at 1100°C for 4h.

[0187] Thus, the mixed oxide of the invention is a mixed oxide consisting essentially of zirconium, cerium, lanthanum and optionally at least one rare earth metal (REM) other than cerium and lanthanum, the weight proportions of these elements, expressed as oxide equivalents relative to the total weight of the mixed oxide, being as follows:

[0188] - between 8% and 47%, preferably between 10.0% and 40.0% cerium;

[0189] - between 1% and 10%, preferably between 3.5% and 5.0% lanthanum;

[0190] - between 0% and 15%, preferably between 5.0% and 13.0% of rare earth metals other than cerium and lanthanum;

[0191] - the remainder is zirconium,

[0192] Characterized in that the mixed oxide exhibits:

[0193] - After calcination at a temperature of 1100°C for 4 hours, preferably including 30.0 m 2 / g and 40.0m 2 / g, preferably between 32.0m 2 / g and 40.0m 2 / g, more preferably included in 34.0m 2 / g and 40.0m 2 / g, and even more preferably included between 36.0 m 2 / g and 40.0m 2 / g BET specific surface area;

[0194] - After calcination at a temperature of 1000°C for 4 hours, preferably at 50.0 m 2 / g and 70.0m 2 / g, preferably 55.0m2 / g and 70.0m 2 / g, preferably 60.0m 2 / g and 70.0m 2 / g, even more preferably between 65.0m 2 / g and 70.0m 2 / g BET specific surface area;

[0195] the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide, after calcination for 4 hours at a temperature of 1100° C., exhibits, within the range of pores with a diameter less than or equal to 200 nm, a peak whose maximum corresponds to a pore diameter of between 25 and 40 nm, preferably between 25 and 38 nm, denoted Dp,1100° C. / 4h, V and D indicating respectively the pore volume and the pore diameter; and

[0196] - The ratio R defined by:

[0197] R=V1 / V2

[0198] wherein V1 is the pore volume formed by pores whose diameter in nm is between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15); V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm; and wherein R is comprised between 0.50 and 0.60, and

[0199] a pore volume V2 of 0.20 to 0.50 ml / g, in particular 0.24 to 0.41 ml / g, wherein V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm,

[0200] Therein, V1 and V2 were determined for the mixed oxides by mercury porosimetry after calcination at 1100° C. for 4 hours.

[0201] In a specific aspect of the invention, the mixed oxide is further characterized in that, after calcination for 4 hours at a temperature of 900°C, the derivative curve (dV / dlogD) obtained for the mixed oxide by mercury porosimetry exhibits, within the range of pores less than or equal to 200 nm in diameter, a peak whose maximum corresponds to the pore diameter denoted Dp,900°C / 4h, and such that the difference in absolute values ​​(Dp,1100°C / 4h)-(Dp,900°C / 4h) is less than or equal to 15 nm, indeed even less than or equal to 12 nm, indeed even less than or equal to 11 nm.

[0202] In a specific aspect of the invention, the mixed oxide is further characterized in that, after calcination at a temperature of 900°C for 4 hours, the derivative curve (dV / dlogD) obtained for the mixed oxide by mercury porosimetry exhibits, within the range of pores less than or equal to 200 nm in diameter, a peak whose maximum corresponds to the pore diameter denoted Dp,900°C / 4h and such that the difference in absolute values ​​(Dp,1100°C / 4h)-(Dp,900°C / 4h) is not zero.

[0203] In yet another aspect of the invention, the mixed oxide of the invention is a mixed oxide of zirconium, cerium, lanthanum and optionally at least one REM other than cerium and lanthanum, the weight ratios of these elements expressed as oxide equivalents relative to the total weight of the mixed oxide being as follows:

[0204] - between 8% and 47%, preferably between 10.0% and 40.0% cerium;

[0205] - between 1% and 10%, preferably between 3.5% and 5.0% lanthanum;

[0206] - between 0% and 15%, preferably between 5.0% and 13.0% of rare earth metals other than cerium and lanthanum;

[0207] - the remainder is zirconium,

[0208] Characterized in that the mixed oxide exhibits:

[0209] - After calcination at a temperature of 1100°C for 4 hours, preferably including 30.0 m 2 / g and 40.0m 2 / g, preferably between 32.0m 2 / g and 40.0m 2 / g, more preferably included in 34.0m 2 / g and 40.0m 2 / g, and even more preferably included between 36.0 m 2 / g and 40.0m 2 / g BET specific surface area;

[0210] - After calcination at a temperature of 1000°C for 4 hours, preferably at 50.0 m 2 / g and 70.0m 2 / g, preferably 55.0m 2 / g and 70.0m 2 / g, preferably 60.0m 2 / g and 70.0m 2 / g, even more preferably between 65.0m 2 / g and 70.0m2 / g BET specific surface area;

[0211] - after calcination for 4 hours at a temperature of 1100° C., the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide exhibits, within the range of pores with a diameter less than or equal to 200 nm, a peak whose maximum corresponds to a pore diameter of between 25 and 40 nm, preferably between 25 and 38 nm, denoted Dp,1100° C. / 4h, V and D respectively indicating the pore volume and the pore diameter;

[0212] - after calcination for 4 hours at a temperature of 900° C., the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide exhibits, within the range of pores less than or equal to 200 nm in diameter, a peak whose maximum corresponds to the pore diameter denoted Dp,900° C. / 4 h and such that the absolute value of the difference (Dp,1100° C. / 4 h)-(Dp,900° C. / 4 h) is less than or equal to 15 nm, indeed even less than or equal to 12 nm, indeed even less than or equal to 11 nm;

[0213] - The ratio R defined by:

[0214] R=V1 / V2

[0215] wherein V1 is the pore volume formed by pores whose diameter in nm is between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15); V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm; wherein R is comprised between 0.50 and 0.60, and

[0216] - a pore volume V2 of 0.24 to 0.41 ml / g, wherein V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm,

[0217] Therein, V1 and V2 were determined for the mixed oxides by mercury porosimetry after calcination at 1100° C. for 4 hours.

[0218] The mixed oxide according to the invention is provided in the form of a powder with a median diameter d50 determined by laser diffraction on a volume distribution comprised between 2.5 and 20.0 μm, preferably between 3.0 and 15.0 μm and more preferably between 3.0 and 10.0 μm.

[0219] The mixed oxide according to the invention is provided in the form of a powder having a median diameter d10 determined by laser diffraction on a volume distribution of between 0.4 and 2.0 μm, preferably from 0.5 to 1.8 μm.

[0220] The mixed oxide according to the invention is provided in the form of a powder having a median diameter d90 determined on a volume distribution by laser diffraction of between 8.0 and 60.0 μm, preferably from 10.0 to 50.0 μm and more preferably from 12.0 to 48.0 μm.

[0221] The mixed oxide according to the invention is provided in the form of a powder with a median diameter d99 determined on a volume distribution by laser diffraction of between 20.0 and 120.0 μm, preferably from 25.0 to 110.0 μm and more preferably from 25.0 to 100.0 μm.

[0222] D10, D50, D90 and D99 (in μm) have the usual meaning used in statistics. Thus, dn (n=10, 50, 90 or 99) represents the following particle size, so that n% of the particles are less than or equal to the particle size. D50 therefore represents the median. These parameters are determined based on the particle size distribution (by volume) obtained with a laser diffraction particle size analyzer. The distribution measurement conditions given in the examples can be applied.

[0223] According to the present invention, dn is determined by laser diffraction, in particular with a Beckman Coulter LS13320 laser diffraction particle size analyzer (Beckman Coulter, Inc.) using a standard procedure predetermined by the instrument software.

[0224] The Fraunhofer mode ( https: / / www.beckmancoulter.com / wsrportal / techdocs?docname=B05577AB.pdf ). A relative refractive index of 1.6 was used.

[0225] The measurement may optionally be carried out in water in the presence of a dispersant such as sodium hexametaphosphate.

[0226] In another aspect, the mixed oxide of the present invention is further characterized in that the tap density of the mixed oxide is equal to or greater than 0.4 g / cm 3 ; preferably equal to or greater than 0.5g / cm 3 ; preferably equal to or greater than 0.6g / cm 3 ; preferably equal to or greater than 0.7g / cm 3 ; preferably equal to or greater than 0.8g / cm 3 ; preferably equal to or greater than 0.85g / cm 3 .

[0227] The tap density according to the present invention can be measured as follows.

[0228] The equipment required for the measurements is:

[0229] - A 250 mL Class A graduated cylinder readable to 2 mL (tolerance ±1.0 mL), with an outer diameter of 40 mm and a mass between 192 and 196 g.

[0230] - Sedimentation device capable of nominally 250 taps from a height of 3 mm in 1 min. The support of the graduated cylinder has a mass of 450 g. The PT-TD300 model from Pharma Test is capable of measuring the tap density ( https: / / www.pharma-test.de / wp-content / uploads / 2017 / 08 / ptag-49-30000-pt-td300-e.pdf )

[0231] -Laboratory balance capable of weighing to ±0.1g.

[0232] About 100 g (initial mass) was accurately weighed and poured into a dry graduated cylinder. The graduated cylinder containing the powder sample was then fixed on the cylinder support of the apparatus and tapped 1470 times.

[0233] Read Volume 1 to the nearest 1 mL.

[0234] Tap 1470 times again and read Volume 2 to the nearest 1 mL.

[0235] If the difference between Volume 1 and Volume 2 is less than 2 mL, Volume 2 is the tapped volume.

[0236] If the difference between Volume 1 and Volume 2 is greater than 2 mL, perform an additional 2940 taps. Read Volume 3 to the nearest 1 mL.

[0237] - If the difference between Volume 2 and Volume 3 is less than 2 mL, then Volume 3 is the tapped volume.

[0238] If the difference between Volume 2 and Volume 3 is greater than 2 mL, perform an additional 5880 taps. Read Volume 4 to the nearest 1 mL.

[0239] - If the difference between volume 3 and volume 4 is less than 2 mL, then volume 4 is the tapped volume

[0240] If the difference between volume 3 and volume 4 is greater than 2 mL, repeat the procedure by doubling the number of taps in each step until the volume n-1 With volume n The difference between the volumes is less than 2 mL. n is the tapped volume.

[0241] The formula used to calculate the tap density is:

[0242]

[0243] Round the result to the nearest hundredth.

[0244] Thus, in yet another aspect of the invention, the mixed oxide of the invention is a mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth metal (REM) other than cerium and lanthanum, the weight ratios of these elements, expressed as oxide equivalents relative to the total weight of the mixed oxide, being as follows:

[0245] - between 8% and 47%, preferably between 10.0% and 40.0% cerium;

[0246] - between 1% and 10%, preferably between 3.5% and 5.0% lanthanum;

[0247] - between 0% and 15%, preferably between 5.0% and 13.0% of rare earth metals other than cerium and lanthanum;

[0248] - the remainder is zirconium,

[0249] Characterized in that the mixed oxide exhibits:

[0250] - After calcination at a temperature of 1100°C for 4 hours, preferably including 30.0 m 2 / g and 40.0m 2 / g, preferably between 32.0m 2 / g and 40.0m 2 / g, more preferably included in 34.0m 2 / g and 40.0m 2 / g, and even more preferably included between 36.0 m 2 / g and 40.0m 2 / g BET specific surface area;

[0251] - After calcination at a temperature of 1000°C for 4 hours, preferably at 50.0 m 2 / g and 70.0m 2 / g, preferably 55.0m 2 / g and 70.0m 2 / g, preferably 60.0m 2 / g and 70.0m 2 / g, even more preferably between 65.0m 2 / g and 70.0m 2 / g BET specific surface area;

[0252] - after calcination for 4 hours at a temperature of 1100° C., the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide exhibits, within the range of pores with a diameter less than or equal to 200 nm, a peak whose maximum corresponds to a pore diameter of between 25 and 40 nm, preferably between 25 and 38 nm, denoted Dp,1100° C. / 4h, V and D respectively indicating the pore volume and the pore diameter;

[0253] - after calcination for 4 hours at a temperature of 900° C., the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide exhibits, within the range of pores less than or equal to 200 nm in diameter, a peak whose maximum corresponds to the pore diameter denoted Dp,900° C. / 4 h and such that the difference in absolute values ​​(Dp,1100° C. / 4 h)-(Dp,900° C. / 4 h) is less than or equal to 15 nm, indeed even less than or equal to 12 nm, indeed even less than or equal to 11 nm; and

[0254] - The ratio R defined by:

[0255] R=V1 / V2

[0256] wherein V1 is the pore volume formed by pores whose diameters in nm are between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15); V2 is the pore volume formed by pores whose diameters are less than or equal to 200 nm; and

[0257] where R is between 0.50 and 0.60, and

[0258] - a pore volume V2 of 0.24 to 0.41 ml / g, wherein V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm,

[0259] wherein V1 and V2 are determined by mercury porosimetry on the mixed oxide after calcination at 1100° C. for 4 h; and

[0260] - the tap density of the mixed oxide is equal to or greater than 0.4 g / cm 3 ; preferably equal to or greater than 0.5g / cm 3 ; preferably equal to or greater than 0.6g / cm 3 ; preferably equal to or greater than 0.7g / cm 3 ; preferably equal to or greater than 0.8g / cm 3 ; preferably equal to or greater than 0.85g / cm 3 .

[0261] Process for preparing mixed oxides

[0262] The present invention also relates to a method for preparing a mixed oxide as described above, comprising the following steps:

[0263] Therefore, the first step (a1) of the method comprises introducing an aqueous solution of cerium nitrate and zirconium nitrate into a stirred vessel containing an alkaline aqueous solution. The alkaline solution may contain an alkali metal or alkaline earth metal hydroxide. Secondary amines, tertiary amines or quaternary amines may also be used. However, amines and ammonia water may be preferred because they reduce the risk of contamination by alkali metal or alkaline earth metal cations. Urea may also be mentioned.

[0264] The alkaline aqueous solution may be used in a stoichiometric excess in order to ensure optimal precipitation.

[0265] This mixing is carried out under stirring.

[0266] In a second step (a2), an aqueous solution of nitrates of rare earth metals other than cerium and lanthanum is then introduced into the mixture formed in step (a1), maintaining stirring. This step optionally depends on the addition of an aqueous solution of nitrates of rare earth metals (REM).

[0267] In optional step (a2'), the mixture obtained at the end of step (a1 ) or (a2) is heated at a temperature comprised between 50 and 95°C.

[0268] According to a particular aspect of the invention, the concentration of the mixture at the end of (a1), (a2) or (a2') is between 30 and 100 g / l, expressed as metal oxide.

[0269] At the end of step (a1), (a2) or (a2′), an aqueous solution of lanthanum nitrate is then introduced into the mixture formed in step (a2), (a2′) or (a1), the mixture being kept stirred (step (a3)).

[0270] At the end of step (a3), the mixture obtained is heated with stirring (step (a4)).

[0271] This heating can be carried out at a temperature of at least 100° C. and even more particularly at least 130° C. For example, the temperature can be between 100° C. and 160° C. This heating operation can be carried out by introducing the liquid medium into a closed chamber (closed reactor of the autoclave type). Under the temperature conditions given above, and in an aqueous medium, it can therefore be indicated by way of illustration that the upper limit of the pressure variation in the closed reactor can be between 1 bar (10 5 Pa) and 165 bar (1.65×10 7 Pa), preferably 5 bar (5×10 5 Pa) and 165 bar (1.65×10 7The heating can also be carried out in an open reactor at a temperature of about 100°C.

[0272] The heating is carried out in air.

[0273] The heating time can vary within wide limits, for example between 1 and 48 hours, preferably between 2 and 24 hours. Likewise, the increase in temperature is carried out at a non-essential rate, and it is therefore possible to reach a fixed reaction temperature by heating the medium for, for example, between 30 minutes and 4 hours, these values ​​being given purely indicatively.

[0274] The next step (a5) of the process involves adding a templating agent to the mixture.

[0275] The function of the template is to control the porosity of the mixed oxide.

[0276] In step (a5) a template is added, the template comprising polar chemical groups that interact with chemical groups at the surface of the mixture. According to the invention, the template may be a combination of templates. The template is removed after the calcination step.

[0277] The template can be selected from anionic surfactants, nonionic surfactants, polyethylene glycol and carboxylic acid and its salt, and carboxymethylated fatty alcohol ethoxylate type surfactants or any combination thereof. Regarding this additive, reference can be made to the teaching of application WO 98 / 45212, and the surfactants described in this document can be used.

[0278] As anionic surfactants, mention may be made of ethoxy carboxylates, ethoxylated fatty acids, sarcosinates, phosphates, sulfates, such as alcohol sulfates, alcohol ether sulfates and sulfated alkanolamide ethoxylates, or sulfonates, such as sulfosuccinates, alkylbenzenesulfonates or alkylnaphthalenesulfonates, or any combination thereof.

[0279] As nonionic surfactants, mention may be made of acetylenic surfactants, alcohol ethoxylates, alkanolamides, amine oxides, ethoxylated alkanolamides, long-chain ethoxylated amines, ethylene oxide / propylene oxide copolymers, sorbitan derivatives, ethylene glycol, propylene glycol, glycerol, polyglycerol esters and ethoxylated derivatives thereof, alkylamines, alkylimidazolines, ethoxylated oils and alkylphenol ethoxylates. Mention may be made in particular of the compounds sold under the trademark and products sold or any combination thereof.

[0280] As for carboxylic acids, in particular aliphatic monocarboxylic acids or dicarboxylic acids may be used and among these, more particularly saturated acids may be used. Thus, in particular formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid or palmitic acid or any combination thereof may be mentioned. As dicarboxylic acids, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid may be mentioned. Fatty acids may also be used, and more particularly saturated fatty acids or any combination thereof may be used. They may in particular be of the formula CH3-(CH2) m A saturated linear acid of -COOH, m being an integer between 6 and 20, more particularly between 9 and 15. It is also possible to use the salts of all the acids mentioned, in particular the ammonium salts. By way of example, mention may be made more particularly of lauric acid and ammonium laurate.

[0281] Finally, it is possible to use surfactants chosen from those of the carboxymethylated fatty alcohol ethoxylate type. Products of the carboxymethylated fatty alcohol ethoxylate type are understood to mean products consisting of ethoxylated or propoxylated fatty alcohols containing a CH2-COOH group at the end of the chain. These products may correspond to the following formula: R1-O-(CR2R3-CR4R5-O) n -CH2-COOH, wherein R1 represents a saturated or unsaturated carbon chain, the length of which is generally up to 22 carbon atoms, preferably at least 12 carbon atoms; R2, R3, R4 and R5 may be identical and represent hydrogen or else R2 may represent a CH3 group and R3, R4 and R5 represent hydrogen; and n is a non-zero integer which may range up to 50 and more particularly between 5 and 15 (these values ​​are included). It should be noted that the surfactant may be composed of a mixture of products having the above formula (wherein R1 may be saturated or unsaturated, respectively) or products which additionally contain both CH2-CH2-O- and -C(CH2)-CH2-O- groups.

[0282] The templating agent may be added directly to the mixture resulting from step (a4). In this case, it is preferably added to the mixture at a temperature of at most 60°C.

[0283] The amount of template used, expressed as a percentage by weight of template relative to the mixed oxide, is generally between 5% and 100%, more particularly between 15% and 60%.

[0284] At the end of step (a5), the mixture is optionally filtered and the precipitate is washed (a6). In a preferred aspect, the precipitate is washed with water.

[0285] In step (a7) of the process of the invention, the recovered precipitate is subsequently calcined. This calcination makes it possible to develop the crystallinity of the product formed and it can also be adjusted and / or selected as a function of the subsequent working temperature intended for the composition according to the invention, this being done taking into account the fact that the specific surface area of ​​the product decreases with an increase in the calcination temperature used. This calcination is generally carried out in air, but calcinations in an inert gas or a controlled atmosphere (oxidizing or reducing), for example, are obviously not excluded.

[0286] Unless otherwise stated, calcinations were carried out in air.

[0287] In practice, the calcination temperature is generally limited to a range of values ​​between 700 and 1100°C and more particularly between 900 and 1100°C, even more particularly between 1000 and 1100°C.

[0288] The duration of calcination is not critical and depends on the temperature. In a completely indicated manner, it may be at least 2 hours and more particularly between 2 and 6 hours, even more particularly between 2 and 4 hours.

[0289] Finally, but alternatively, the mixed oxide (a8) obtained in step (a7) can be ground.

[0290] In a particular aspect, the invention relates to a mixed oxide obtainable by the process described above.

[0291] In another specific aspect, the present invention also relates to a method for preparing a mixed oxide, the method comprising the following steps:

[0292] - (a1) introducing an aqueous solution of cerium nitrate and zirconium nitrate into a stirred vessel containing an alkaline aqueous solution;

[0293] (a2) optionally subsequently introducing an aqueous solution of a nitrate of a rare earth metal (other than cerium or lanthanum) into the mixture formed in step (a1), while maintaining stirring;

[0294] - (a2') optionally heating the mixture obtained at the end of step (a1) or (a2) at a temperature comprised between 50°C and 95°C;

[0295] - (a3) ​​subsequently introducing an aqueous solution of lanthanum nitrate into the mixture formed in step (a2), (a2') or (a1) and maintaining stirring;

[0296] - (a4) heating the mixture obtained at the end of step (a3) ​​under stirring;

[0297] - (a5) subsequently introducing a templating agent into the mixture obtained in the previous step;

[0298] - (a6) optionally, filtering the mixture and washing the precipitate;

[0299] - (a7) calcining the precipitate obtained at the end of step (a6) at a temperature between 700° C. and 1100° C.;

[0300] - (a8) optionally grinding the mixed oxide obtained in step (a7);

[0301] Wherein the mixed oxide is a mixed oxide of zirconium, cerium, lanthanum and optionally at least one REM other than cerium and lanthanum, the weight ratios of these elements expressed as oxide equivalents relative to the total weight of the mixed oxide are as follows:

[0302] - between 8% and 47% cerium;

[0303] - between 1% and 10% lanthanum;

[0304] - between 0% and 15% of rare earth metals other than cerium and lanthanum;

[0305] - between 0% and 2.5% hafnium;

[0306] - The remainder is zirconium.

[0307] Compositions comprising mixed oxides

[0308] The invention also relates to a composition comprising the mixed oxide as described above or obtained by a process as described above in admixture with at least one mineral material.

[0309] According to a particular aspect, the composition comprises at least one mineral material chosen from alumina, titania, cerium oxide, zirconium oxide, silica, spinel, zeolite, silicate, crystalline silicoaluminophosphate or crystalline aluminum phosphate or any combination thereof.

[0310] Catalytically active coating

[0311] The invention also relates to a catalytically active coating deposited on the surface region of a solid support, prepared from the mixed oxide, obtained by the process or from a composition as described above.

[0312] In another aspect, the catalytic converter is for treating motor vehicle exhaust and comprises a coating as described above.

[0313] Uses of mixed oxides

[0314] The mixed oxide of the invention can be used in the field of exhaust gas treatment.The mixed oxide of the invention can be used to reduce the amount of pollutants present in the exhaust gas released by the internal combustion engine of a vehicle.

[0315] The mixed oxide can be used to prepare a catalytic converter, which is used to treat the exhaust gas released by the internal combustion engine of a vehicle. The catalytic converter includes at least one catalytically active layer prepared by depositing a catalytic composition on a solid support. The effect of this layer is to chemically convert some pollutants of the exhaust gas into products that are less harmful to the environment. The solid support can be a monolith made of ceramic (such as cordierite), silicon carbide, aluminum titanate or mullite, or metal (such as Fecralloy). The support is usually made of cordierite, showing a large specific surface area and a low pressure drop. The monolith is usually honeycomb-type.

[0316] The catalytic composition comprises:

[0317] (i) at least one mineral material, such as alumina;

[0318] (ii) one or more platinum group metals; and

[0319] (iii) at least one mixed oxide according to the invention.

[0320] The mixed oxide can be used to prepare a catalytic wall-flow monolith. The catalytic wall-flow monolith includes a porous support and a catalytic composition on the surface of the support. Wall-flow monoliths are well known in the art for use as particulate filters. These particulate filters work by passing an exhaust gas flow (including particulate matter) through a wall formed by a porous support. Porosity helps retain particulate matter. The monolith preferably has a first face and a second face defining a longitudinal direction between them. In use, one of the first face and the second face will be the inlet face of the exhaust gas, and the other face will be the outlet face of the treated exhaust gas. As is conventional for wall-flow monoliths, it has a first and a second plurality of channels extending in a longitudinal direction. The first plurality of channels opens at the first face and closes at the second face. The second plurality of channels opens at the second face and closes at the first face. The channels are preferably parallel to each other to provide a constant wall thickness between the channels. As a result, a gas entering one of the plurality of channels cannot leave the monolith without diffusing through the channel wall into the other plurality of channels. The channel is closed by introducing a sealant material into the open end of the channel.

[0321] Preferably, the number of channels in the first plurality of channels is equal to the number of channels in the second plurality of channels, and each plurality of channels is evenly distributed throughout the monolith. Preferably, the wall flow monolith has 100 to 500 channels / square inch (cpsi), preferably 200 to 400 cpsi, in a plane perpendicular to the longitudinal direction. For example, on the first face, the density of the first channels opened and the second channels closed is 200 to 400 channels / square inch. The channels may have a cross-section of a rectangular, square, circular, elliptical, triangular, hexagonal, or other polygonal shape.

[0322] In order to facilitate the passage of the exhaust gas to be treated through the channel wall, the monolith is formed by a porous substrate. The substrate also serves as a support for the catalytic composition. Suitable materials for forming the porous substrate include ceramic-like materials (such as cordierite), silicon carbide, silicon nitride, zirconium oxide, mullite, spodumene, alumina-silicon dioxide-magnesium oxide or zirconium silicate, or porous refractory metals. The wall-flow substrate can also be formed by a ceramic fiber composite material. A preferred wall-flow substrate is formed by cordierite and silicon carbide. Such materials can withstand the environment encountered in the treatment of exhaust gas flow, especially high temperatures, and can be made sufficiently porous. Such materials and their use in the manufacture of porous monolithic substrates are well known in the art.

[0323] The catalytic composition is applied in the form of a layer on a porous substrate. Traditionally, the loading of the layer should not be too high to avoid back pressure. The loading can be between 1.0 g / in 3 Up to 0.1g / in 3 Between, preferably 0.7g / in 3 Up to 0.25g / in 3 , and most preferably 0.6 g / in 3 Up to 0.5g / in 3 .

[0324] The catalytic composition comprises alumina, preferably γ-alumina. The alumina may also contain lanthanum, praseodymium or a combination of the two. The alumina is preferably lanthanum-stabilized alumina. Alumina is an advantageous support material because it exhibits a high surface area and is a refractory metal oxide. This results in a good heat capacity required for the high temperature conditions encountered. The catalytic composition also comprises one or more platinum group metals (PGM). The PGM is selected from the group consisting of Pt, Pd, Rh, Re, Ir. The PGM is used to catalyze the reactions required for the treatment of exhaust gas and the combustion of soot particles. Preferably, the PGM is Pt, Pd and Rh; Pd and Rh; or only Pd; or only Rh.

[0325] A method that can be used to prepare a catalytic wall flow monolith is disclosed in WO 2017 / 109514, the contents of which are fully incorporated by reference. More particularly, the method disclosed in Example 3 of WO 2017 / 109514 can be used.

[0326] Method for treating exhaust gas

[0327] The invention also relates to a method for treating exhaust gas from an internal combustion engine, characterized in that a catalytic converter comprising a coating as described above is used.

[0328] The examples which follow are intended to illustrate rather than limit the invention.

[0329] The measurement method according to the present invention:

[0330] Measurement of pore volume and pore diameter

[0331] The pore volumes and pore diameters given were measured by mercury (Hg) porosimetry using a Micromeritics Autopore IV 9500 porosimeter and calculated via the Washburn relationship with a theta contact angle equal to 130° and a gamma surface tension equal to 485 dynes / cm; the preparation of each sample was carried out as follows: each sample was predried in an oven at 200°C for 2 hours.

[0332] The following parameters may be used: penetrometer used: 3.2 ml; volume of capillary: 0.412 ml; maximum pressure ("head pressure"): 4.68 psi; contact angle: 130°; surface tension of mercury: 485 dynes / cm; density of mercury: 13.5335 g / ml. At the start of the measurement, a vacuum of 50 mm Hg is applied to the sample for 5 min.

[0333] The equilibration times were as follows: low pressure range (1.3-30 psi): 20 s - high pressure range (30-60000 psi): 30 s. Prior to measurement, the samples were degassed in an oven at 100° C. for a minimum of 15 min.

[0334] Measurement of specific surface area

[0335] The BET specific surface area is determined automatically on a Macsorb analyzer model I-1220 from the company Moteng. Before any measurement, the sample is carefully degassed to desorb volatile adsorbed substances. For this purpose, the sample can be heated in a small chamber of the device in a vacuum at 210° C. for 30 min.

[0336] The BET measurement was performed at 1 point at a relative pressure P / P0 of 0.3.

[0337] The indicated porosities are measured by mercury intrusion porosimetry according to standard ASTM D 4284-83 (reapproved in 2008) (“Standard Method for Pore Volume Distribution of Catalysts by Mercury Intrusion Porosimetry”).

[0338] A Micromeritics Autopore IV 9500 apparatus equipped with a powder penetrometer can be used by following the manufacturer's recommended instructions.

[0339] Mercury intrusion porosimetry makes it possible to obtain the pore volume (V) as a function of the pore diameter (D). From these data, it is possible to obtain a curve (C) representing the derivative of the function V as a function of log D (dV / dlogD). The derivative curve (C) may exhibit one or more peaks, each located at a diameter represented by Dp. The pores considered to be characteristic of the invention are those exhibiting a diameter less than or equal to 200 nm.

[0340] For the mercury porosimetry technique, a Micromeritrics Autopore IV 9500 machine equipped with a powder penetrometer may be used according to the manufacturer's recommended instructions. The procedure of standard ASTM D 4284-83 (reapproved in 2008) may be followed.

[0341] Examples

[0342] Example 1: Composition CeO2 40% - ZrO2 50% - La2O3 5% - Y2O3 5%

[0343] This example describes the preparation of a composition of cerium, zirconium, lanthanum and yttrium in weight proportions corresponding to the oxides of 40%, 50%, 5% and 5%.

[0344] By mixing 48.55 liters of deionized water, 11.36 liters of cerium nitrate solution ([Ce 3+ A solution was prepared by mixing 10.44 liters of concentrated nitric acid solution ([HNO3] = 67 wt%, density = 1.399 kg / L) and 10.50 liters of aqueous hydrogen peroxide solution ([H2O2] = 35 wt%, density = 1.135 kg / L). After this addition, the solution was stirred for 30 minutes.

[0345] In a precipitation tank equipped with a 4-blade impeller, 68.17 liters of aqueous ammonia solution ([NH3] = 15.1 wt% and density = 0.941 kg / L) and 41.83 liters of deionized water were charged.

[0346] The solution containing cerium and zirconium prepared above was then introduced into the precipitation tank over 60 minutes. The stirring speed during precipitation was 220 rpm.

[0347] Then 3.09 liters of yttrium nitrate solution ([Y 3+ ]=1.89 mol / L, density=1.411 kg / L) is added to the precipitation tank at the same flow rate as the solution containing cerium and zirconium.

[0348] The temperature of the mixture was then raised to 60°C.

[0349] Then 2.24 liters of lanthanum nitrate solution ([La 3+ ]=1.81 mol / L, density=1.473 kg / L) is added to the precipitation tank at the same flow rate as the solution containing cerium and zirconium.

[0350] The mixture was then aged in an autoclave at 150° C. for 2 hours with stirring.

[0351] Then, the temperature was lowered to about 60° C. and 4.356 kg of lauric acid were introduced under stirring. The mixture was kept under stirring for 1 hour.

[0352] The mixture was then filtered and the filter cake was washed with 60 liters of deionized water.

[0353] The obtained solid was calcined at 850°C for 3 hours.

[0354]

[0355] Example 2 - Composition CeO2 10% - ZrO2 72% - La2O3 5% - Y2O3 8% - Nd2O3 5%

[0356] This example describes the preparation of a composition of cerium, zirconium, lanthanum, yttrium and neodymium in corresponding weight proportions of the oxides of 10%, 72%, 5%, 8% and 5%.

[0357] By mixing 62.21 liters of deionized water, 2.6 liters of cerium nitrate solution ([Ce 3+ A solution was prepared by adding 13.78 liters of concentrated nitric acid solution ([HNO3] = 67 wt%, density = 1.399 kg / L) and 2.41 liters of aqueous hydrogen peroxide solution ([H2O2] = 35 wt%, density = 1.135 kg / L). After this addition, the solution was stirred for 30 minutes.

[0358] In a precipitation tank equipped with a 4-blade impeller, 73.89 liters of aqueous ammonia solution ([NH3] = 15.1 wt% and density = 0.941 kg / L) and 47.11 liters of deionized water were charged.

[0359] The solution containing cerium and zirconium prepared above was then introduced into a precipitation tank over 60 minutes.

[0360] By mixing 4.54 L of yttrium nitrate solution ([Y 3+ ]=1.89mol / L,density=1.411kg / L) and 2.03L neodymium nitrate solution ([Nd 3+]=1.77mol / L, density=1.474kg / L) to prepare a solution. This solution is then added to the precipitation tank at the same flow rate as the solution containing cerium and zirconium.

[0361] The temperature of the mixture was then raised to 60°C.

[0362] Then 2.05 liters of lanthanum nitrate solution ([La 3+ ]=1.81 mol / L, density=1.473 kg / L) is added to the precipitation tank at the same flow rate as the solution containing cerium and zirconium.

[0363] The mixture was then aged in an autoclave at 150° C. for 2 hours with stirring.

[0364] Then, the temperature was lowered to about 60° C. and 3.993 kg of lauric acid were introduced under stirring. The mixture was kept under stirring for 1 hour.

[0365] The mixture was then filtered and the filter cake was washed with 60 liters of deionized water.

[0366] The obtained solid was calcined at 1020°C for 2 hours.

[0367]

[0368] Example 3 - Composition CeO2 24% - ZrO2 60% - La2O3 3.5% - Y2O3 12.5%

[0369] This example describes the preparation of a composition of cerium, zirconium, lanthanum and yttrium in weight proportions corresponding to the oxides of 24%, 60%, 3.5% and 12.5%.

[0370] By mixing 61.81 liters of deionized water, 6.25 liters of cerium nitrate solution ([Ce 3+ ]=2.7mol / L, density=1.707kg / L) and 26.15 liters of zirconium oxynitrate solution ([ZrO2]=277g / L, density=1.442kg / L) to prepare a solution. To this solution, 11.48 liters of concentrated nitric acid solution ([HNO3]=67wt%, density=1.399kg / L) and 5.79 liters of aqueous hydrogen peroxide solution ([H2O2]=35wt%, density=1.135kg / L) were added. After this addition, the solution was stirred for 30 minutes.

[0371] In a precipitation tank equipped with a 4-blade impeller, 68.81 liters of aqueous ammonia solution ([NH3] = 15.1 wt% and density = 0.941 kg / L) and 52.19 liters of deionized water were charged.

[0372] The solution containing cerium and zirconium prepared above was then introduced into a precipitation tank over 60 minutes.

[0373] Then 7.09 liters of yttrium nitrate solution ([Y 3+ ]=1.89 mol / L, density=1.411 kg / L) is added to the precipitation tank at the same flow rate as the solution containing cerium and zirconium.

[0374] The temperature of the mixture was then raised to 60°C.

[0375] Then 1.44 liters of lanthanum nitrate solution ([La 3+ ]=1.81 mol / L, density=1.473 kg / L) is added to the precipitation tank at the same flow rate as the solution containing cerium and zirconium.

[0376] The mixture was then aged in an autoclave at 150° C. for 2 hours with stirring.

[0377] Then, the temperature was lowered to about 60° C. and 3.993 kg of lauric acid were introduced under stirring. The mixture was kept under stirring for 1 hour.

[0378] The mixture was then filtered and the filter cake was washed with 60 liters of deionized water.

[0379] The obtained solid was calcined at 850°C for 3 hours.

[0380]

[0381] Comparative Example 1 - Composition CeO2 40% - ZrO2 50% - La2O3 5% - Y2O3 5%

[0382] This example describes the preparation of a composition of cerium, zirconium, lanthanum and yttrium in weight proportions corresponding to the oxides of 40%, 50%, 5% and 5%.

[0383] By mixing 63.4 liters of deionized water, 11.36 liters of cerium nitrate solution ([Ce 3+ ]=2.7mol / L, density=1.707kg / L) and 23.77 liters of zirconium oxynitrate solution ([ZrO2]=277g / L, density=1.442kg / L) to prepare a solution. To this solution, 2.88 liters of concentrated nitric acid solution ([HNO3]=67wt%, density=1.399kg / L) were added. Then, 3.09 liters of yttrium nitrate solution ([Y 3+ ]=1.89mol / L, density=1.411kg / L) and 2.24L lanthanum nitrate solution ([La 3+ ]=1.81 mol / L, density=1.473 kg / L). Finally, 3.29 liters of aqueous hydrogen peroxide solution ([H2O2]=35 wt%, density=1.135 kg / L) were added. After this addition, the solution was stirred for 30 minutes.

[0384] In a precipitation tank equipped with a 4-blade impeller, 48.48 liters of aqueous ammonia solution ([NH3] = 15.1 wt% and density = 0.941 kg / L) and 61.52 liters of deionized water were charged.

[0385] The solution containing cerium, zirconium, yttrium and lanthanum prepared above was then introduced into a precipitation tank over a period of 60 minutes.

[0386] The temperature of the mixture was then raised to 95°C.

[0387] The mixture was then aged in an autoclave at 120° C. for 2 hours with stirring.

[0388] Then, the temperature was lowered to about 60° C. and 4.356 kg of lauric acid were introduced under stirring. The mixture was kept under stirring for 1 hour.

[0389] The mixture was then filtered and the filter cake was washed with 60 liters of deionized water.

[0390] The obtained solid was calcined at 850°C for 3 hours.

[0391]

[0392] Comparative Example 2 - Composition CeO2 40% - ZrO2 50% - La2O3 5% - Y2O3 5%

[0393] This example describes the preparation of a composition of cerium, zirconium, lanthanum and yttrium in a weight ratio of 40%, 50%, 5% and 5% oxides according to the method described in WO 2017 / 187085.

[0394] The cerium nitrate and zirconium nitrate solutions were prepared by mixing 95.43 liters of water, 11.3 liters of zirconium nitrate aqueous solution ([ZrO2] ＝266 g / l; density = 1.408 kg / l) and also 5.8 liters of aqueous cerium nitrate solution ([CeO2] = 259 g / l; density = 1.439 kg / l) were introduced into a container. An aqueous solution of lanthanum nitrate and yttrium nitrate was also prepared by introducing 10.77 liters of water, 0.53 liters of lanthanum nitrate solution ([La2O3] = 472.5 g / l; density = 1.711 kg / l) and 1.2 liters of yttrium nitrate solution ([Y2O3] = 208.5 g / l; density = 1.391 kg / l) into another container.

[0395] The ammonia solution (12 l at 12 mol / l) was introduced under stirring into a reactor of about 250 l equipped with a stirrer with inclined blades, and the solution was subsequently made up with distilled water to obtain an alkaline aqueous solution with a total volume of 125 l. This made it possible to provide a stoichiometric excess of ammonia of 40 mol % relative to the cations present in the two solutions mentioned above.

[0396] The two solutions prepared above were kept under continuous stirring. The solutions of cerium nitrate and zirconium nitrate were introduced into a stirred reactor containing ammonia solution within 45 min, and the stirring was adjusted to a rate of 200 rpm (80 Hz). Then, within 15 min, the solutions of lanthanum nitrate and yttrium nitrate were introduced into a stirred reactor, and the stirring was adjusted to 25 rpm (10 Hz). A mixture was obtained.

[0397] The mixture was poured into a stainless steel autoclave equipped with a stirrer. The mixture was heated at 150°C for 2 h under stirring. It was then cooled to a temperature below 60°C and 1.65 kg of lauric acid was added to the mixture. The mixture was kept stirring for 1 h.

[0398] The mixture was then filtered and the precipitate was then washed with an aqueous ammonia solution of pH = 9.5, the ratio of which was one time the volume of the filtered mother liquor (washed with 250 liters of aqueous ammonia solution). The solid product obtained was then calcined at 950° C. for 3 h in air to recover about 5 kg of mixed oxides. The solid obtained was calcined at 825° C. for 3 hours.

[0399]

Claims

1. A mixed oxide of zirconium, cerium, lanthanum and optionally at least one rare earth metal (REM) other than cerium and lanthanum, the weight ratios of these elements, expressed as oxide equivalents relative to the total weight of the mixed oxide, being as follows: - between 8% and 47% cerium; - between 1% and 10% lanthanum; - between 0% and 15% of the rare earth metals other than cerium and lanthanum; - the remainder is zirconium, It is characterized in that The mixed oxide exhibits: - After calcination at 1100°C for 4 hours, at least 30 minutes 2 / g BET specific surface area; - After calcination at 1000°C for 4 hours, at least 50m 2 / g BET specific surface area; the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide, after calcination for 4 hours at a temperature of 1100° C., exhibits, within the range of pores with a diameter less than or equal to 200 nm, a peak whose maximum corresponds to a pore diameter of between 25 and 40 nm, preferably between 25 and 38 nm, denoted Dp,1100° C. / 4h, V and D indicating respectively the pore volume and the pore diameter; and - The ratio R defined by: R=V1 / V2 in: - V1 is the pore volume formed by pores whose diameter in nm is between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15); - V2 is the pore volume formed by pores whose diameter is less than or equal to 200 nm; - V1 and V2 are determined by mercury porosimetry on the mixed oxide after calcination at 1100° C. for 4 h; and Wherein R is comprised between 0.50 and 0.

60.

2. The mixed oxide according to claim 1, characterized in that The mixed oxide also contains hafnium.

3. The mixed oxide according to claim 2, characterized in that The weight proportion of hafnium in the mixed oxide, expressed in oxide equivalent relative to the total weight of the mixed oxide, is less than or equal to 2.5%, indeed even less than or equal to 2.0%.

4. The mixed oxide according to any one of claims 1 to 3, characterized in that The elements Ce, La, REMs other than cerium and lanthanum, Zr and Hf are present in the form of oxides, hydroxides or oxyhydroxides, more particularly in the form of oxides.

5. The mixed oxide according to any one of claims 1 to 4, characterized in that The REM other than cerium and lanthanum is selected from yttrium, neodymium or praseodymium or any combination thereof.

6. The mixed oxide as claimed in claim 1, which comprises only yttrium as REM besides cerium and lanthanum.

7. The mixed oxide as claimed in claim 1, comprising only two REMs other than cerium and lanthanum, which REMs may be yttrium and neodymium or yttrium and praseodymium.

8. The mixed oxide as claimed in claim 1, comprising a mixture of oxides of zirconium, cerium, lanthanum, optionally at least one REM other than cerium and lanthanum, and optionally hafnium.

9. The mixed oxide as claimed in claim 1, which does not contain any rare earth metals other than cerium and lanthanum.

10. The mixed oxide according to any one of claims 1 to 8, which consists essentially of the following elements: - zirconium, cerium, lanthanum, yttrium and optionally hafnium; - zirconium, cerium, lanthanum, yttrium, neodymium and optionally hafnium; or - zirconium, cerium, lanthanum, yttrium, praseodymium and optionally hafnium; - zirconium, cerium, lanthanum, neodymium, praseodymium and optionally hafnium; or - Zirconium, cerium, lanthanum and optionally hafnium.

11. The mixed oxide according to claim 1, characterized in that The weight proportion of zirconium expressed as oxide equivalent may be between 40.0% and 91.0%, preferably between 44.0% and 80.0%, more preferably between 44.0% and 76.0%.

12. The mixed oxide according to any one of the preceding claims, characterized in that The tap density of the mixed oxide is equal to or greater than 0.4 g / cm 3 , preferably equal to or greater than 0.5 g / cm 3 .

13. The mixed oxide according to claim 12, characterized in that The tap density of the mixed oxide is 0.5 g / cm 3 Up to 0.9g / cm 3 .

14. The mixed oxide according to claim 1, characterized in that After calcination for 4 hours at a temperature of 900°C, the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide exhibits, within the range of pores less than or equal to 200 nm in diameter, a peak whose maximum corresponds to the pore diameter denoted Dp,900°C / 4h and such that the difference in absolute value (Dp,1100°C / 4h)-(Dp,900°C / 4h) is less than or equal to 15 nm, preferably less than or equal to 12 nm, indeed even less than or equal to 11 nm.

15. The mixed oxide according to any one of the preceding claims, characterized in that A pore volume V2 of 0.20 to 0.50 ml / g, in particular 0.24 to 0.41 ml / g.

16. The mixed oxide as claimed in any one of the preceding claims, provided in the form of a powder, having a mean diameter d50 determined by laser diffraction on a volume distribution comprised between 1.0 and 30.0 μm, preferably between 2.0 and 20.0 μm, even more preferably between 3.0 and 10.0 μm.

17. The mixed oxide according to any one of the preceding claims, characterized in that The derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide after calcination at a temperature of 900° C. for 4 hours does not exhibit two distinct peaks.

18. A method for preparing a mixed oxide as claimed in any one of claims 1 to 17, comprising the following steps: - (a1) introducing an aqueous solution of cerium nitrate and zirconium nitrate into a stirred vessel containing an alkaline aqueous solution; (a2) optionally subsequently introducing an aqueous solution of a nitrate of a rare earth metal other than cerium and lanthanum into the mixture formed in step (a1), while maintaining stirring; - (a2') optionally heating the mixture obtained at the end of step (a1) or (a2) at a temperature comprised between 50°C and 95°C; - (a3) ​​subsequently introducing an aqueous solution of lanthanum nitrate into the mixture formed in step (a2'), (a2) or (a1) and maintaining stirring; - (a4) heating the mixture obtained at the end of step (a3) ​​under stirring; - (a5) subsequently introducing a templating agent into the mixture obtained in the previous step; - (a6) optionally, filtering the mixture and washing the precipitate; - (a7) calcining the precipitate obtained at the end of step (a6) at a temperature between 700° C. and 1100° C.; and - (a8) optionally grinding the mixed oxide obtained in step (a7).

19. The process of claim 18, wherein after step (a3) ​​the aqueous solution has a mixed oxide concentration expressed as metal oxides of 30 g / l to 80 g / l.

20. A mixed oxide obtainable by the process as claimed in claim 18 or 19.

21. A composition comprising a mixture of a mixed oxide as claimed in any one of claims 1 to 17 or as claimed in claim 20 and at least one mineral material.

22. The composition of claim 21, wherein the mineral material is selected from alumina, titania, cerium oxide, zirconium oxide, silicon dioxide, spinel, zeolite, silicate, crystalline silicoaluminophosphate or crystalline aluminum phosphate.

23. A catalytically active coating deposited on a surface region of a solid support, comprising a mixed oxide as claimed in one of claims 1 to 17 or as claimed in claim 20 or a composition as claimed in claim 21 or 22.

24. A catalytic converter for treating exhaust gas from a motor vehicle, comprising a catalytically active coating as claimed in claim 23.

25. Use of a mixed oxide as claimed in any one of claims 1 to 17 or as claimed in claim 20 or a composition as claimed in claim 21 or 22 for the production of a catalytic converter.

26. A method for treating exhaust gas from an internal combustion engine, characterized in that Use of a catalytic converter comprising a coating as claimed in claim 24.

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