Cerium and zirconium based mixed oxides

Abstract

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

Description

[Technical Field]

[0001] This application claims priority from Chinese Patent Application Publication No. 2022 / 111999 filed on August 12, 2022 in international proceedings, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to a mixed oxide of zirconium, cerium, lanthanum, and at least one oxide of a rare earth metal other than cerium and lanthanum, which exhibits high porosity and a high specific surface area, to a method for preparing the same, and to its use in catalytic reactions. [Background technology]

[0003] "Multifunctional" catalysts are currently used for the treatment of exhaust gases from internal combustion engines (automotive reburning catalysis). Multifunctional is understood to mean catalysts that are capable of not only oxidizing, in particular, carbon monoxide and hydrocarbons present in the exhaust gases, but also, in particular, reducing the nitrogen oxides also present in these gases ("three-way" catalysts).

[0004] The catalysts are formed by the interaction of noble metals (e.g., Pd, Pt, Rh) with mixed oxides based on cerium and zirconium, often in admixture with alumina. The mixed oxide must exhibit a suitable porosity. It must therefore exhibit a sufficiently large pore volume and must also contain pores of a size large enough to allow good gas diffusion. The mixed oxide must also exhibit a sufficiently large specific surface area to be usable for catalytic reactions.

[0005] It is known that small pores exhibit the greatest specific surface area. In fact, it is these pores that are most susceptible to sintering. It would therefore be advantageous to develop mixed oxides that offer a good compromise between high pore volume, high surface area, and in which there is a population of small pores that exhibit good heat resistance, even after being maintained at high temperatures. Summary of the Invention [Means for solving the problem]

[0006] The mixed oxide according to the invention as claimed in claim 1 targets such a compromise.

[0007] The present invention relates to mixed oxides of zirconium, cerium, lanthanum, and optionally at least one rare earth metal (REM) other than cerium and lanthanum, in which the weight proportions of these elements, expressed as oxide equivalents, relative to the total weight of the mixed oxide, are as follows: - 8%~47% cerium; - 1%-10% lanthanum; - 0% to 15% of rare earth metals other than cerium and lanthanum; - Remainder as Zirconium and The mixed oxide is - at least 30m after calcination at a temperature of 1100°C for 4 hours 2 / g BET specific surface area; - at least 50m after calcination at 1000°C for 4 hours 2 / g BET specific surface area; - a derivative curve (dV / dlogD) obtained by mercury porosimetry on the mixed oxide after calcination at a temperature of 1100°C for 4 hours, which shows one peak in the range of pores with a diameter of less than or equal to 200 nm, the maximum of which corresponds to a pore diameter, denoted Dp,1100°C / 4h, of 25 to 40 nm, preferably 25 to 38 nm, V and D denoting the pore volume and pore diameter, respectively; - The ratio R{R is included in 0.50~0.60. R=V1 / V2 [In formula: - V1 is the pore volume expressed by pores with diameters in nm between (Dp,1100°C / 4h-15) and (Dp,1100°C / 4h+15); V2 is the pore volume represented by pores with a diameter of 200 nm or less; - V1 and V2 are measured by mercury porosimetry on the mixed oxide after calcination at 1100 °C for 4 h] defined by} and The present invention deals with mixed oxides characterized by exhibiting:

[0008] In another embodiment, the mixed oxide also includes hafnium.

[0009] Therefore, and in a further aspect of the invention, the mixed oxide is characterized in that 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%.

[0010] 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.

[0011] In a still further embodiment, the mixed oxide of the present invention is characterized in that the REM other than cerium and lanthanum is selected from yttrium, neodymium or praseodymium or any combination thereof.

[0012] In a particular embodiment of the invention, the mixed oxide contains only yttrium as the rare earth metal other than cerium and lanthanum.

[0013] In a particular embodiment of the invention, the mixed oxide comprises only two rare earth metals other than cerium and lanthanum, which may be yttrium and neodymium or yttrium and praseodymium.

[0014] In another embodiment, 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.

[0015] In another embodiment, the mixed oxide of the present invention does not contain any rare earth metals other than cerium and lanthanum.

[0016] In a particular embodiment of the invention, the mixed oxide according to one of the claims comprises 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 It essentially consists of:

[0017] In a further embodiment, the mixed oxide of the invention is characterized by a weight proportion of zirconium, expressed as oxide equivalent, comprised between 40 and 91.0%, preferably between 44.0 and 80.0%, more preferably between 44.0 and 76.0%.

[0018] In a still further embodiment, the mixed oxide of the present invention has a density of 0.4 g / cm 3 or more, preferably 0.5 g / cm 3 It has a tap density of at least 1000 ppm.

[0019] In a more particular embodiment, the tap density of the mixed oxide is between 0.5 g / cm and 0.9 g / cm 3 is.

[0020] In a further embodiment, the mixed oxides of the invention are characterized in that the derivative curve (dV / dlogD) obtained by mercury porosimetry on the mixed oxide after calcination at a temperature of 900°C for 4 hours shows one peak in the range of pores with a diameter of less than or equal to 200 nm, the maximum of which corresponds to the pore diameter denoted Dp,900°C / 4h, and 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, and even less than or equal to 11 nm.

[0021] In a further embodiment, the mixed oxides of the invention are characterized by a pore volume (V2) of 0.20 to 0.50 ml / g, in particular of 0.24 to 0.41 ml / g.

[0022] In a still further embodiment, the mixed oxide of the invention provided in the form of a powder has a mean diameter d50 measured by laser diffraction over 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.

[0023] In a more particular embodiment, the mixed oxide of the invention is 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 show two distinct peaks.

[0024] The present invention also provides (a1) an aqueous solution of cerium nitrate and zirconium nitrate is introduced into a stirred vessel containing a basic aqueous solution; (a2) optionally, an aqueous solution of nitrates of rare earth metals (REM) other than cerium and lanthanum is then introduced into the mixture formed in step (a1) and kept stirring; (a2') optionally, heating the mixture obtained at the end of step (a1) or (a2) at a temperature comprised between 50 and 95°C; (a3) an aqueous solution of lanthanum nitrate is then introduced into the mixture formed in step (a2), (a2') or (a1) and kept stirring; (a4) the mixture obtained at the end of step (a3) is heated with stirring; - (a5) a step in which a templating agent is then introduced into the mixture obtained in the preceding step; (a6) optionally, filtering the mixture and washing the precipitate; (a7) the precipitate obtained at the end of step (a6) is calcined at a temperature between 700°C and 1100°C; and (a8) the mixed oxide obtained in step (a7) is optionally ground; The present invention addresses a method for preparing the mixed oxide as described above, comprising:

[0025] In a particular embodiment of the above method, the concentration of the mixed oxides in the aqueous solution after step (a3) is between 30 g / l and 80 g / l, expressed as metal oxides.

[0026] The present invention also relates to mixed oxides obtained by the process described above.

[0027] The present invention further relates to compositions comprising mixed oxides and mixtures with at least one inorganic material.

[0028] In a particular embodiment, the inorganic material of the composition of the present invention is selected from alumina, titanium oxide, cerium oxide, zirconium oxide, silica, spinel, zeolite, silicate, crystalline silicoaluminum phosphate or crystalline aluminum phosphate.

[0029] The present invention is directed to a catalytically active coating layer comprising a mixed oxide as described above or a composition as described above deposited on a surface region of a solid support.

[0030] The present invention is also directed to a catalytic converter for treating automobile exhaust gases, comprising a catalytically active coating layer as described above.

[0031] The use of the mixed oxide or composition as described above in the preparation of a catalytic converter is also encompassed by the present invention as a method for the treatment of exhaust gases from an internal combustion engine, characterized in that a catalytic converter comprising a coating layer of the present invention is used.

[0032] Other features, details and advantages of the invention will become even more fully apparent on reading the description and the accompanying drawings. [Brief explanation of the drawings]

[0033] [Figure 1] 1 shows a porosity profile chart. The vertical axis represents dv / dlogD, the logarithm of the differential penetration in mL / g, and the horizontal axis represents the pore size diameter in nm. FIG. 1 shows the results obtained in Example 1 (solid line) and Comparative Example 1 (dotted line). where Rb is as defined above. DETAILED DESCRIPTION OF THE INVENTION

[0034] definition 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) measured by nitrogen adsorption.

[0035] The term "specific surface area (BET, SBET, SSA or SA)" is understood to mean the BET specific surface area measured by nitrogen adsorption. Specific surface area is well known to those skilled in the art and is measured according to the Brunauer-Emmett-Teller method. The theory of this method was first described in the periodical "The Journal of the American Chemical Society, 60, 309 (1938)." More detailed information on this theory can also be found in Chapter 4 of "Powder surface area and porosity", 2nd edition, ISBN 978-94-015-7955-1. The method of nitrogen adsorption is disclosed in the standard ASTM D 3663-03 (reapproved in 2008). In practice, the specific surface area (BET) can be measured automatically using the Micromeritics Flowsorb II 2300 or Tristar 3000 instruments according to the manufacturer's guidelines. They can also be measured automatically using a Mountech Macsorb Analyzer Model 1-1220 according to the manufacturer's guidelines. Prior to measurement, the sample is degassed, optionally under vacuum, by heating at temperatures up to 300° C. to remove adsorbed volatile species. More specific conditions can be found in the Examples.

[0036] The porosities indicated are measured by mercury intrusion porosimetry according to standard ASTM D 4284-83 (reapproved 2008) ("Standard method for determining pore volume distribution of catalysts by mercury intrusion porosimetry").

[0037] Within the meaning of the present invention, rare earth metals (REM) are understood to mean the elements of the group consisting of scandium, yttrium and the elements of the periodic table with atomic numbers from 57 to 71, inclusive.

[0038] The rare earth elements, as defined by IUPAC, are a set of 17 chemical elements in the periodic table, specifically the 15 lanthanides, as well as scandium and yttrium. 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).

[0039] Throughout the text of this application, percentages are given as weight of oxide relative to the mixed oxide as a whole, unless otherwise stated.

[0040] Within the meaning of the present invention, cerium oxide is in the form of cerium(IV) oxide (CeO2) and REM oxides are in the form Pr6O 11 With the exception of praseodymium, which is represented by the formula REM2O3, zirconium oxide and hafnium oxide are considered to be in the forms ZrO2 and HfO2.

[0041] For the continuation of this description, it is noted that in any range of values given, the limits are inclusive unless otherwise stated.

[0042] 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.

[0043] Within the meaning of the present invention, tap density is to be understood as the density of a powder sample obtained after mechanical tapping.

[0044] According to the present invention, the pore size is to be understood as the maximum of the pore size distribution in the dV / dlogD curve for pore sizes below 200 nm, unless otherwise defined.

[0045] Detailed Description of the Invention If the disclosure of any patents, patent applications, and publications incorporated herein by reference contradicts the description of this application to the extent that the term may be unclear, the present description shall control.

[0046] mixed oxide The present invention deals with mixed oxides of zirconium, cerium, lanthanum and optionally at least one rare earth metal (REM) other than cerium and lanthanum, in which the weight proportions of these elements, expressed as oxide equivalents, relative to the total weight of the mixed oxide are: 8% to 47% cerium (C); 1% to 10% lanthanum (L); 0% to 15% REMs other than cerium and lanthanum; and the remainder as zirconium (Z).

[0047] The mixed oxides of the present invention are further characterized by a high heat resistance. This resistance is necessary because the coating must withstand high temperatures. In this regard, it must be noted that gasoline engines are mainly operated with a stoichiometric air / fuel mixture, so that the exhaust gases usually exhibit significantly higher temperatures than those associated with lean-burn engines. It is known that the temperatures at which filters for gasoline engines operate are therefore higher than those associated with more conventional diesel particulate filters.

[0048] The mixed oxide of the present invention has a viscosity of at least 30.0 m after calcination at a temperature of 1100° C. for 4 hours. 2 / g, and a BET specific surface area of at least 50.0 m after calcination at a temperature of 1000°C for 4 hours 2 The BET specific surface area in g is further shown.

[0049] The mixed oxide of the present invention is further characterized by the derivative curve (dV / dlogD) obtained by mercury porosimetry after calcination at a temperature of 1100°C for 4 hours, which shows one peak corresponding to the pore diameter, denoted Dp,1100°C / 4h, with a maximum value of 25.0-40.0 nm in the range of pores with diameters of 200 nm or less, where V and D denote the pore volume and pore diameter, respectively.

[0050] The mixed oxide of the present invention has a pore volume of R=V1 / V2, where V1 is the pore volume contributed by pores with a diameter in nm between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15); V2 is the pore volume contributed by pores with a diameter of 200 nm or less; V1 and V2 are measured by mercury porosimetry on the mixed oxide after calcination at 1100°C for 4 h. It is further characterized by a ratio R, defined by:

[0051] Mercury porosimetry is a standard technique used in the field of porous catalysts and consists in the progressive intrusion of mercury into the pores of a porous structure under controlled pressure. Porosity is measured by mercury intrusion according to techniques well known in the art. Porosity can be measured using a Micromeritics Autopore IV 9500 Automatic Mercury Porosimeter according to the manufacturer's guidelines. The porosimeter comprises a powder penetrometer. The method is based on the determination of pore volume as a function of pore size (V = f(d), V meaning pore volume and D meaning pore diameter. From this data it is possible to obtain a curve (C) giving the derivative dV / dlogD.

[0052] The specifics of the measurement methods are given below in the paragraph "Measurement Methods."

[0053] In a particular embodiment of the present invention, the mixed oxide of the present invention has a molecular weight of at least 30.0 m after calcination at a temperature of 1100° C. for 4 hours. 2 / g, at least 32.0m 2 / g, preferably at least 34.0 m 2 / g, and even more preferably at least 36.0 m 2 The BET specific surface area in g is shown.

[0054] In a more particular embodiment of the present invention, the mixed oxide of the present invention has a melting point of 30.0 m after calcination at a temperature of 1100° C. for 4 hours. 2 / g~40.0m 2 / g, preferably 32.0m 2 / g~40.0m 2 / g, preferably 34.0m 2 / g~40.0m 2 / g, and even more preferably 36.0m 2 / g~40.0m 2 The BET specific surface area in g is shown.

[0055] In a particular embodiment of the present invention, the mixed oxide of the present invention has a molecular weight of at least 50.0 m after calcination at a temperature of 1000° C. for 4 hours. 2 / g, at least 55.0m 2 / g, at least 60.0m 2 / g, preferably at least 65.0 m 2 The BET specific surface area in g is shown.

[0056] In a more particular embodiment of the present invention, the mixed oxide of the present invention is 2 / g~70.0m 2 / g, preferably 55.0m 2 / g~70.0m 2 / g, preferably 60.0m 2 / g~70.0m 2 / g, and even more preferably 65.0 m 2 / g~70.0m 2 The BET specific surface area in g is shown.

[0057] In a further embodiment of the present invention, the mixed oxide of the present invention also has a viscosity of 30.0 mPa after calcination at a temperature of 1100°C for 4 hours. 2 / g~40.0m 2 / g, and 50.0 m after calcination at 1000°C for 4 hours. 2 / g~70.0m 2 The BET specific surface area in g is shown.

[0058] In a further embodiment of the present invention, the mixed oxide of the present invention preferably has a melting point of 30.0 m after calcination at a temperature of 1100° C. for 4 hours. 2 / g~40.0m 2 / g, preferably 32.0m 2 / g~40.0m 2 / g, more preferably 34.0m 2 / g~40.0m 2 / g, and even more preferably 36.0 m 2 / g~40.0m 2 / g, and preferably 50.0 m after calcination at a temperature of 1000° C. for 4 hours. 2 / g~70.0m 2 / g, preferably 55.0m 2 / g~70.0m 2 / g, preferably 60.0m 2 / g~70.0m 2 / g, and even more preferably 65.0 m 2 / g~70.0m 2 The BET specific surface area in g is further shown.

[0059] The present invention therefore relates to mixed oxides of zirconium, cerium, lanthanum, and optionally of at least one rare earth metal (REM) other than cerium and lanthanum, in which the weight proportions of these elements, expressed as oxide equivalents, relative to the total weight of the mixed oxide, are as follows: - 8%~47% cerium; - 1%-10% lanthanum; - 0% to 15% of rare earth metals other than cerium and lanthanum; - Remainder as Zirconium and The mixed oxide is After calcination at a temperature of 1100°C for 4 hours, preferably 30.0 m 2 / g~40.0m2 / g, preferably 32.0m 2 / g~40.0m 2 / g, more preferably 34.0m 2 / g~40.0m 2 / g, and even more preferably 36.0m 2 / g~40.0m 2 / g and the BET specific surface area; - after calcination at a temperature of 1000 °C for 4 hours, preferably a BET specific surface area comprised between 50.0 m2 / g and 70.0 m2 / g, preferably between 55.0 m2 / g and 70.0 m2 / g, preferably between 60.0 m2 / g and 70.0 m2 / g, even more preferably between 65.0 m2 / g and 70.0 m2 / g; - a derivative curve (dV / dlogD) obtained by mercury porosimetry on the mixed oxide after calcination at a temperature of 1100°C for 4 hours, which shows one peak corresponding to the pore diameter, denoted Dp,1100°C / 4h, of 25 to 40 nm, preferably 25 to 38 nm, in the range of pores with a diameter of up to 200 nm, V and D denote the pore volume and the pore diameter, respectively; - R is between 0.50 and 0.60, R=V1 / V2 [In formula: - V1 is the pore volume expressed by pores with diameters in nm between (Dp,1100°C / 4h-15) and (Dp,1100°C / 4h+15); V2 is the pore volume represented by pores with a diameter of 200 nm or less; - V1 and V2 are measured by mercury porosimetry on the mixed oxide after calcination at 1100 °C for 4 h] and the ratio R defined by The present invention deals with mixed oxides characterized by exhibiting:

[0060] In a further embodiment of the present invention, the mixed oxide is 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 show two distinct peaks.

[0061] The mixed oxide of the present invention may comprise hafnium, and therefore, in a particular embodiment, the weight proportion of hafnium in the mixed oxide, expressed as oxide equivalents relative to the total weight of the mixed oxide, is not more than 2.5%, indeed even not more than 2.0%.

[0062] In a further embodiment, the mixed oxide of the present invention comprises cerium (Ce), lanthanum (La), REMs other than cerium and lanthanum, zirconium (Zr), and (hafnium) Hf, present in the form of oxides, hydroxides, or oxyhydroxides, or any combination thereof.

[0063] In a preferred embodiment, the mixed oxide of the present invention comprises Ce, La, REM, Zr and Hf present in the form of oxides.

[0064] In another embodiment, the mixed oxide of the present invention is characterized in that the REM other than cerium and lanthanum is selected from yttrium, neodymium, praseodymium, or any combination thereof.

[0065] In a particular embodiment of the present invention, the mixed oxide of the present invention contains only yttrium as the REM other than cerium and lanthanum.

[0066] In another particular embodiment of the present invention, the mixed oxide of the present invention comprises cerium, zirconium and only two REMs other than cerium and lanthanum, which may be yttrium and neodymium or yttrium and praseodymium. In a further embodiment, the mixed oxide of the present invention does not comprise any rare REMs other than cerium and lanthanum.

[0067] In a further embodiment, the mixed oxide of the present invention comprises or consists essentially of a mixture of oxides of zirconium, cerium, and lanthanum, and optionally of at least one REM other than cerium and lanthanum, and optionally of hafnium.

[0068] In a still further embodiment, the mixed oxide of the present invention comprises the following elements: - zirconium, cerium, lanthanum, yttrium and optionally hafnium; - zirconium, cerium, lanthanum, yttrium, neodymium and optionally hafnium; - zirconium, cerium, lanthanum, yttrium, praseodymium and optionally hafnium; zirconium, cerium, lanthanum, neodymium, praseodymium and optionally hafnium or zirconium, cerium, lanthanum and optionally hafnium It essentially consists of:

[0069] As far as the proportion of zirconium is concerned, zirconium is present as the remainder of the mixed oxide. The sum of all elements of the mixed oxide of the invention is 100%, and therefore the proportion of zirconium corresponds to the 100% complement of the other elements of the mixed oxide.

[0070] This should be understood to mean that the mixed oxide of the present invention does not contain other elemental oxides than those cited and those that can affect the properties of the mixed oxide of the present invention. The mixed oxide of the present invention may contain elements such as impurities that can arise in particular from the preparation process, for example from the starting materials or reactants used.

[0071] In a particular embodiment 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%.

[0072] In a particular embodiment 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%.

[0073] In a particular embodiment of the present invention, the mixed oxide is characterized in that the weight proportion of rare earth metals other than cerium and lanthanum, expressed as oxide equivalents, may be between 0 and 15.0%, preferably between 1.0 and 15.0%, more preferably between 5.0 and 13.0%.

[0074] In a particular embodiment 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%.

[0075] According to the present invention, the weight proportions of the mixed oxides of zirconium, cerium, lanthanum, optionally hafnium, and optionally at least one REM other than cerium and lanthanum, relative to the total weight of the mixed oxide, are expressed as oxide equivalents as stated.

[0076] The present invention therefore relates to mixed oxides of zirconium, cerium, lanthanum, and optionally of at least one rare earth metal (REM) other than cerium and lanthanum, in which the weight proportions of these elements, expressed as oxide equivalents, relative to the total weight of the mixed oxide, are as follows: - 8% to 47%, preferably 10.0 to 40.0% cerium; - 1% to 10%, preferably 3.5 to 5.0% lanthanum; - 0% to 15%, preferably 1.0 to 15%, more preferably 5.0 to 13.0% of rare earth metals other than cerium and lanthanum; - Remainder as Zirconium and The mixed oxide is a BET specific surface area, after calcination at a temperature of 1100°C for 4 hours, preferably comprised between 30.0 m2 / g and 40.0 m2 / g, preferably between 32.0 m2 / g and 40.0 m2 / g, more preferably between 34.0 m2 / g and 40.0 m2 / g, even more preferably between 36.0 m2 / g and 40.0 m2 / g; - after calcination at a temperature of 1000 °C for 4 hours, preferably a BET specific surface area comprised between 50.0 m2 / g and 70.0 m2 / g, preferably between 55.0 m2 / g and 70.0 m2 / g, preferably between 60.0 m2 / g and 70.0 m2 / g, even more preferably between 65.0 m2 / g and 70.0 m2 / g; - a derivative curve (dV / dlogD) obtained by mercury porosimetry on the mixed oxide after calcination at a temperature of 1100°C for 4 hours, which shows one peak corresponding to the pore diameter, denoted Dp,1100°C / 4h, of 25 to 40 nm, preferably 25 to 38 nm, in the range of pores with a diameter of up to 200 nm, V and D denote the pore volume and the pore diameter, respectively; - R is between 0.50 and 0.60, R=V1 / V2 [In formula: - V1 is the pore volume expressed by pores with diameters in nm between (Dp,1100°C / 4h-15) and (Dp,1100°C / 4h+15); V2 is the pore volume represented by pores with a diameter of 200 nm or less; - V1 and V2 are measured by mercury porosimetry on the mixed oxide after calcination at 1100 °C for 4 h] and the ratio R defined by The present invention deals with mixed oxides characterized by exhibiting:

[0077] In a particular embodiment 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 represented by pores with a diameter of less than or equal to 200 nm.

[0078] The pore volume is measured by mercury porosimetry on the mixed oxide after calcination at 1100° C. for 4 h.

[0079] The mixed oxides of the invention are therefore further characterized by a pore volume V2 of 0.20 to 0.50 ml / g, in particular 0.24 to 0.41 ml / g.

[0080] In a further embodiment, the mixed oxide of the invention is characterized in that the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide after calcination at a temperature of 1100°C for 4 hours corresponds to one peak in the range of pores with diameters of up to 200 nm, the maximum of which corresponds to a pore diameter Dp, 1100°C / 4h, of 25 to 40 nm, preferably 25 to 38 nm, where V and D denote the pore volume and pore diameter, respectively.

[0081] The present invention therefore relates to mixed oxides of zirconium, cerium, lanthanum, and optionally of at least one rare earth metal (REM) other than cerium and lanthanum, in which the weight proportions of these elements, expressed as oxide equivalents, relative to the total weight of the mixed oxide, are as follows: - 8% to 47%, preferably 10.0 to 40.0% cerium; - 1% to 10%, preferably 3.5 to 5.0% lanthanum; - 0% to 15%, preferably 0.1% to 15%, more preferably 5.0% to 13.0% of rare earth metals other than cerium and lanthanum; - Remainder as Zirconium and The mixed oxide is a BET specific surface area, after calcination at a temperature of 1100°C for 4 hours, preferably comprised between 30.0 m2 / g and 40.0 m2 / g, preferably between 32.0 m2 / g and 40.0 m2 / g, more preferably between 34.0 m2 / g and 40.0 m2 / g, even more preferably between 36.0 m2 / g and 40.0 m2 / g; - after calcination at a temperature of 1000 °C for 4 hours, preferably a BET specific surface area comprised between 50.0 m2 / g and 70.0 m2 / g, preferably between 55.0 m2 / g and 70.0 m2 / g, preferably between 60.0 m2 / g and 70.0 m2 / g, even more preferably between 65.0 m2 / g and 70.0 m2 / g; - a derivative curve (dV / dlogD) obtained by mercury porosimetry on the mixed oxide after calcination at a temperature of 1100°C for 4 hours, which shows one peak corresponding to the pore diameter, denoted Dp,1100°C / 4h, of 25 to 40 nm, preferably 25 to 38 nm, in the range of pores with a diameter of up to 200 nm, V and D denote the pore volume and the pore diameter, respectively; - R is between 0.50 and 0.60, R=V1 / V2 [In formula: - V1 is the pore volume expressed by pores with diameters in nm between (Dp,1100°C / 4h-15) and (Dp,1100°C / 4h+15); - V2 is the pore volume represented by pores with a diameter of 200 nm or less] and a ratio R defined by a pore volume V2 of 0.20 to 0.50 ml / g, preferably 0.24 to 0.41 ml / g (where V1 and V2 are measured by mercury porosimetry on the mixed oxide after calcination at 1100°C for 4h) The present invention deals with mixed oxides characterized by exhibiting:

[0082] The mixed oxide of the present invention may also be defined as consisting essentially of mixed oxides of zirconium, of cerium, of lanthanum, and optionally of at least one 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 8% to 47% cerium (C); 1% to 10% lanthanum (L); 0% to 15% rare earth metals other than cerium and lanthanum; the balance as zirconium (Z), and the weight proportions of these elements, expressed as oxide equivalents as stated, relative to the total weight of the mixed oxide, - at least 30m after calcination at a temperature of 1100°C for 4 hours 2 / g, and a BET specific surface area of at least 50 m after calcination at a temperature of 1000°C for 4 hours 2 / g BET specific surface area, - the derivative curve (dV / dlogD) obtained by mercury porosimetry after calcination at a temperature of 1100 ° C for 4 hours, which shows one peak corresponding to the pore diameter, denoted Dp,1100 ° C / 4 h, with a maximum value of 25-40 nm in the range of pores with a diameter of up to 200 nm, and V and D denote the pore volume and pore diameter, respectively; - R is between 0.50 and 0.60, R=V1 / V2 [In formula: - V1 is the pore volume expressed by pores with diameters in nm between (Dp,1100°C / 4h-15) and (Dp,1100°C / 4h+15); V2 is the pore volume represented by pores with a diameter of 200 nm or less; - V1 and V2 are determined by mercury porosimetry on the mixed oxide after calcination at 1100 °C for 4 h] and the ratio R defined by It can be characterized by:

[0083] In another embodiment, the mixed oxide of the present invention can also be defined as consisting essentially of mixed oxides of zirconium, of cerium, of lanthanum, and optionally at least one REM other than cerium and lanthanum, the weight percentages of these elements, expressed as oxide equivalents, relative to the total weight of the mixed oxide being 8% to 47% cerium (C); 1% to 10% lanthanum (L); 0% to 15% rare earth metals other than cerium; 0% to 2.5% hafnium and lanthanum; the balance as zirconium (Z), and the weight percentages of these elements, expressed as oxide equivalents as stated, relative to the total weight of the mixed oxide, - at least 30m after calcination at a temperature of 1100°C for 4 hours 2 / g, and a BET specific surface area of at least 50 m after calcination at a temperature of 1000°C for 4 hours 2 / g BET specific surface area, - the derivative curve (dV / dlogD) obtained by mercury porosimetry after calcination at a temperature of 1100 ° C for 4 hours, which shows one peak corresponding to the pore diameter, denoted Dp,1100 ° C / 4 h, with a maximum value of 25-40 nm in the range of pores with a diameter of up to 200 nm, and where V and D denote the pore volume and pore diameter, respectively; - R is between 0.50 and 0.60, R=V1 / V2 [In formula: - V1 is the pore volume expressed by pores with diameters in nm between (Dp,1100°C / 4h-15) and (Dp,1100°C / 4h+15); V2 is the pore volume represented by pores with a diameter of 200 nm or less; - V1 and V2 are determined by mercury porosimetry on the mixed oxide after calcination at 1100 °C for 4 h] and the ratio R defined by It can be characterized by:

[0084] The expression "consisting essentially of" should be interpreted as follows: "mixed oxide consisting essentially of" means that in addition to the essential elements, other 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 particular mixed oxide.

[0085] In a further embodiment, the mixed oxide of the invention as described immediately above is characterized in that the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide after calcination at a temperature of 1100°C for 4 hours shows one peak in the range of pores with diameters of up to 200 nm, the maximum of which corresponds to a pore diameter Dp, 1100°C / 4h, of 25 to 38 nm, where V and D denote the pore volume and pore diameter, respectively.

[0086] According to the invention, Dp,1000°C / 4h is the pore diameter measured by mercury porosimetry on the mixed oxide after calcination at 1000°C for 4h, and Dp,1100°C / 4h is the pore diameter measured by mercury porosimetry on the mixed oxide after calcination at 1100°C for 4h.

[0087] The mixed oxide of the present invention is therefore a mixed oxide consisting essentially of zirconium, cerium, lanthanum, and optionally at least one rare earth metal (REM) other than cerium and lanthanum, in which the weight proportions of these elements, expressed as oxide equivalents, relative to the total weight of the mixed oxide, are as follows: - 8% to 47%, preferably 10.0 to 40.0% cerium; - 1% to 10%, preferably 3.5 to 5.0% lanthanum; - 0% to 15%, preferably 5.0 to 13.0%, of rare earth metals other than cerium and lanthanum; - Remainder as Zirconium and The mixed oxide is a BET specific surface area, after calcination at a temperature of 1100°C for 4 hours, preferably comprised between 30.0 m2 / g and 40.0 m2 / g, preferably between 32.0 m2 / g and 40.0 m2 / g, more preferably between 34.0 m2 / g and 40.0 m2 / g, even more preferably between 36.0 m2 / g and 40.0 m2 / g; - after calcination at a temperature of 1000 °C for 4 hours, preferably a BET specific surface area comprised between 50.0 m2 / g and 70.0 m2 / g, preferably between 55.0 m2 / g and 70.0 m2 / g, preferably between 60.0 m2 / g and 70.0 m2 / g, even more preferably between 65.0 m2 / g and 70.0 m2 / g; - a derivative curve (dV / dlogD) obtained by mercury porosimetry on the mixed oxide after calcination at a temperature of 1100°C for 4 hours, which shows one peak corresponding to the pore diameter, denoted Dp,1100°C / 4h, of 25 to 40 nm, preferably 25 to 38 nm, in the range of pores with a diameter of up to 200 nm, V and D denote the pore volume and the pore diameter, respectively; - R is between 0.50 and 0.60, R=V1 / V2 [wherein V1 is the pore volume generated by pores with a diameter in nm between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15); and V2 is the pore volume generated by pores with a diameter of 200 nm or less] and a ratio R defined by a pore volume V2 (where V2 is the pore volume represented by pores with a diameter of 200 nm or less) of 0.20 to 0.50 ml / g, in particular 0.24 to 0.41 ml / g (where V1 and V2 are measured by mercury porosimetry of the mixed oxide after calcination at 1100 ° C for 4 hours); It is a mixed oxide characterized by exhibiting the following:

[0088] In a particular embodiment of the invention, the mixed oxide is further characterized in that the derivative curve (dV / dlogD) obtained by mercury porosimetry on the mixed oxide after calcination at a temperature of 900°C for 4 hours shows one peak in the range of pores with a diameter of less than or equal to 200 nm, the maximum of which corresponds to the pore diameter denoted Dp,900°C / 4h, and the difference in absolute values (Dp,1100°C / 4h) - (Dp,900°C / 4h) is less than or equal to 15 nm, even less than or equal to 12 nm, even less than or equal to 11 nm.

[0089] In a particular embodiment of the invention, the mixed oxide is further characterized in that the derivative curve (dV / dlogD) obtained by mercury porosimetry on the mixed oxide after calcination at a temperature of 900°C for 4 hours shows one peak in the range of pores with a diameter of less than or equal to 200 nm, the maximum of which corresponds to the pore diameter denoted Dp,900°C / 4h and the difference in absolute values (Dp,1100°C / 4h) - (Dp,900°C / 4h) is not zero.

[0090] In a still further 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, in which the weight proportions of these elements, expressed as oxide equivalents, relative to the total weight of the mixed oxide, are as follows: - 8% to 47%, preferably 10.0 to 40.0% cerium; - 1% to 10%, preferably 3.5 to 5.0% lanthanum; - 0% to 15%, preferably 5.0 to 13.0%, of rare earth metals other than cerium and lanthanum; - Remainder as Zirconium and Mixed oxides include: a BET specific surface area after calcination at a temperature of 1100°C for 4 hours preferably comprised between 30.0 m2 / g and 40.0 m2 / g, preferably between 32.0 m2 / g and 40.0 m2 / g, more preferably between 34.0 m2 / g and 40.0 m2 / g, even more preferably between 36.0 m2 / g and 40.0 m2 / g; - a BET specific surface area after calcination at a temperature of 1000°C for 4 hours preferably comprised between 50.0 m2 / g and 70.0 m2 / g, preferably between 55.0 m2 / g and 70.0 m2 / g, preferably between 60.0 m2 / g and 70.0 m2 / g, even more preferably between 65.0 m2 / g and 70.0 m2 / g; - a derivative curve (dV / dlogD) obtained by mercury porosimetry on the mixed oxide after calcination at a temperature of 1100°C for 4 hours, which shows one peak corresponding to the pore diameter, denoted Dp,1100°C / 4h, of 25 to 40 nm, preferably 25 to 38 nm, in the range of pores with a diameter of up to 200 nm, V and D denote the pore volume and the pore diameter, respectively; the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide after calcination at a temperature of 900 ° C for 4 hours, in the range of pores with a diameter of less than 200 nm, shows one peak whose maximum corresponds to the pore diameter denoted Dp,900 ° C / 4 h, and the difference in absolute values (Dp,1100 ° C / 4 h) - (Dp,900 ° C / 4 h) is less than 15 nm, even less than 12 nm, even less than 11 nm; - R is between 0.50 and 0.60, R=V1 / V2 where V1 is the pore volume represented by pores with diameters in nm between (Dp,1100°C / 4h-15) and (Dp,1100°C / 4h+15); and V2 is the pore volume represented by pores with diameters of 200 nm or less; and - a pore volume V2 of 0.24 to 0.41 ml / g (where V2 is the pore volume represented by pores with a diameter of 200 nm or less), (where V1 and V2 are measured by mercury porosimetry on the mixed oxide after calcination at 1100 ° C for 4 h); It is a mixed oxide characterized by exhibiting the following:

[0091] The mixed oxide according to the invention is provided in the form of a powder, the median diameter d50 of which, over the volume distribution, measured by laser diffraction, is comprised between 2.5 and 20.0 μm, preferably between 3.0 and 15.0 μm, more preferably between 3.0 and 10.0 μm.

[0092] The mixed oxides according to the invention provided in powder form have a median diameter d10, measured by laser diffraction over a volume distribution, of 0.4 to 2.0 μm, preferably 0.5 to 1.8 μm.

[0093] The mixed oxide according to the invention is provided in the form of a powder and has a median diameter d90, measured by laser diffraction over a volume distribution, of 8.0 to 60.0 μm, preferably 10.0 to 50.0 μm, more preferably 12.0 to 48.0 μm.

[0094] The mixed oxide according to the invention is provided in the form of a powder, the median diameter d99 of which, measured by laser diffraction over the volume distribution, is 20.0 to 120.0 μm, preferably 25.0 to 110.0 μm, more preferably 25.0 to 100.0 μm. d10, d50, d90 and d99 (in μm) have the usual meanings used in statistics. Thus, dn (n = 10, 50, 90 or 99) represents the particle size at which n% of the particles are equal to or smaller than said size. d50 therefore represents the median value. They are measured from the size distribution (by volume) obtained using a laser diffraction particle size analyzer. The conditions for measuring the distribution given in the examples may be applied.

[0095] According to the present invention, dn is measured by laser diffraction using, inter alia, a Beckman Coulter LS 13320 laser diffraction particle size analyzer (Beckman Coulter, Inc.) using standard procedures predetermined by the instrument software.

[0096] The Fraunhofer mode may be used according to the manufacturer's guidelines (https: / / www.beckmancoulter.com / wsrportal / techdocs?docname=B05577AB.pdf). A relative refractive index of 1.6 is used.

[0097] The measurement may optionally be carried out in water in the presence of a dispersing agent such as sodium hexametaphosphate.

[0098] In a further embodiment, the mixed oxide of the present invention has a density of 0.4 g / cm 3 or more, preferably 0.5 g / cm 3 or more; preferably 0.6 g / cm 3 or more; preferably 0.7 g / cm 3 or more; preferably 0.8 g / cm 3 or more; preferably 0.85 g / cm 3 The mixed oxide is further characterized by a tap density of at least 1000 ppm.

[0099] Tap density according to the present invention can be measured as follows.

[0100] The necessary equipment for the measurement is: - 250mL Class A graduated cylinder with an outer diameter of 40mm and a mass of 192-196g, readable to 2mL (tolerance ±1.0mL). - A settling device capable of producing a nominal 250 taps per minute from a height of 3 mm. The support for the measuring 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). - Laboratory balance capable of weighing to within ±0.1g.

[0101] Approximately 100 g (initial mass) is accurately weighed and poured into a dry graduated cylinder. The graduated cylinder containing the powder sample is then secured onto the cylinder support of the instrument and 1470 taps are performed.

[0102] Read the volume Volume 1 to the nearest 1 mL.

[0103] Perform 1470 taps again and read volume 2 to the nearest 1 mL.

[0104] If the difference between Volume 1 and Volume 2 is less than 2 mL, Volume 2 is the tap volume.

[0105] If the difference between Volume 1 and Volume 2 is more than 2 mL, perform 2940 additional taps. Read volume Volume 3 to the nearest 1 mL.

[0106] - If the difference between Volume 2 and Volume 3 is less than 2 mL, Volume 3 is the tap volume.

[0107] If the difference between Volume 2 and Volume 3 is more than 2 mL, perform 5880 additional taps. Read volume Volume 4 to the nearest 1 mL.

[0108] - If the difference between Volume 3 and Volume 4 is less than 2 mL, Volume 4 is the tap volume.

[0109] If the difference between Volume 3 and Volume 4 is more than 2 mL, n-1 and volume n Repeat the procedure by doubling the number of taps in each step until the difference in volume is less than 2 mL. n is the tap volume.

[0110] The formula for calculating tap density is:

number

[0111] The result is rounded to three decimal places.

[0112] Thus, in a still further 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, in which the weight proportions of these elements, expressed as oxide equivalents, relative to the total weight of the mixed oxide, are as follows: - 8% to 47%, preferably 10.0 to 40.0% cerium; - 1% to 10%, preferably 3.5 to 5.0% lanthanum; - 0% to 15%, preferably 5.0 to 13.0%, of rare earth metals other than cerium and lanthanum; - Remainder as Zirconium and The mixed oxide is a BET specific surface area, after calcination at a temperature of 1100°C for 4 hours, preferably comprised between 30.0 m2 / g and 40.0 m2 / g, preferably between 32.0 m2 / g and 40.0 m2 / g, more preferably between 34.0 m2 / g and 40.0 m2 / g, even more preferably between 36.0 m2 / g and 40.0 m2 / g; - after calcination at a temperature of 1000 °C for 4 hours, preferably a BET specific surface area comprised between 50.0 m2 / g and 70.0 m2 / g, preferably between 55.0 m2 / g and 70.0 m2 / g, preferably between 60.0 m2 / g and 70.0 m2 / g, even more preferably between 65.0 m2 / g and 70.0 m2 / g; - a derivative curve (dV / dlogD) obtained by mercury porosimetry on the mixed oxide after calcination at a temperature of 1100°C for 4 hours, which shows one peak corresponding to the pore diameter, denoted Dp,1100°C / 4h, of 25 to 40 nm, preferably 25 to 38 nm, in the range of pores with a diameter of up to 200 nm, V and D denote the pore volume and the pore diameter, respectively; the derivative curve (dV / dlogD) obtained by mercury porosimetry for the mixed oxide after calcination at a temperature of 900 ° C for 4 hours, in the range of pores with a diameter of less than 200 nm, shows one peak whose maximum corresponds to the pore diameter denoted Dp,900 ° C / 4 h, and the difference in absolute values (Dp,1100 ° C / 4 h) - (Dp,900 ° C / 4 h) is less than 15 nm, even less than 12 nm, even less than 11 nm; - R is between 0.50 and 0.60, R=V1 / V2 [wherein V1 is the pore volume generated by pores with diameters in nm between (Dp, 1100°C / 4h-15) and (Dp, 1100°C / 4h+15); and V2 is the pore volume generated by pores with diameters of 200 nm or less] and a ratio R defined by - a pore volume V2 of 0.24 to 0.41 ml / g (where V2 is the pore volume represented by pores with a diameter of 200 nm or less), (where V1 and V2 are measured by mercury porosimetry on the mixed oxide after calcination at 1100 ° C for 4 h); - 0.4g / cm 3 or more; preferably 0.5 g / cm 3 or more; preferably 0.6 g / cm 3 or more; preferably 0.7 g / cm 3 or more; preferably 0.8 g / cm 3 or more; preferably 0.85 g / cm 3 The mixed oxide is characterized by exhibiting a tap density of the mixed oxide of equal to or greater than 1000 ppm.

[0113] Method for preparing mixed oxides The present invention also relates to a method for preparing a mixed oxide as described above, comprising the following steps: The first step (a1) of the process therefore consists in introducing an aqueous solution of cerium nitrate and zirconium nitrate into a stirred vessel containing an aqueous basic solution. The basic solution may contain an alkali metal or alkaline earth metal hydroxide. Secondary, tertiary, or quaternary amines may also be used. However, amines and aqueous ammonia may be preferred, as they reduce the risk of contamination with alkali metal or alkaline earth metal cations. Urea may also be mentioned.

[0114] The aqueous basic solution may be used in stoichiometric excess for optimum precipitation.

[0115] This combining step is carried out with stirring.

[0116] A second step (a2) of introducing an aqueous solution of nitrates of rare earth metals other than cerium and lanthanum is then introduced into the mixture formed in step (a1) and kept stirring, this step being optional depending on the addition of the aqueous solution of nitrates of rare earth metals (REM).

[0117] In an 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.

[0118] According to a particular embodiment 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.

[0119] 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), and the mixture is kept stirred (step (a3)).

[0120] At the end of step (a3), the resulting mixture is heated with stirring (step (a4)).

[0121] This heating can be carried out at a temperature of at least 100°C, and even more particularly at least 130°C. It can be, for example, between 100°C and 160°C. The heating operation can be carried out by introducing the liquid medium into a closed chamber (a closed reactor of the autoclave type). Under the temperature conditions indicated above and in an aqueous medium, the pressure in the closed reactor can, by way of example, be between an upper limit of 1 bar (105 Pa) and 165 bar (1.65 x 10 7 Pa), preferably 5 bar (5×10 5 Pa) ~ 165 bar (1.65 × 10 7 It can be defined that the heating can be in the range of 100° C. (Pa). Heating can also be carried out in an open reactor for temperatures of about 100° C.

[0122] The heating is carried out under air.

[0123] The heating time can vary within wide limits, for example from 1 to 48 hours, preferably from 2 to 24 hours. Likewise, the temperature increase is carried out at a non-critical rate, so that it is possible to reach a fixed reaction temperature by heating the medium for, for example, 30 minutes to 4 hours; these values are given solely for illustrative purposes.

[0124] The next step (a5) of the method consists in adding a template agent to the mixture.

[0125] The function of the template agent is to control the porosity of the mixed oxide.

[0126] In step (a5), a template agent is added, the template agent comprising a polar chemical group that interacts with the chemical groups at the surface of the mixture. According to the present invention, the template agent can be a combination of template agents. The template agent is removed after the calcination step.

[0127] The template agent can be selected from anionic surfactants, nonionic surfactants, polyethylene glycols and carboxylic acids and their salts, and surfactants of the carboxymethylated fatty alcohol ethoxylate type in any combination thereof.With regard to this additive, reference can be made to the teachings of application WO 98 / 45212, and the surfactants described in this publication can be used.

[0128] Anionic surfactants may include ethoxycarboxylates, ethoxylated fatty acids, sarcosinates, phosphate esters, sulfates such as alcohol sulfates, alcohol ether sulfates and sulfated alkanolamide ethoxylates, or sulfonates such as sulfosuccinates, alkylbenzene sulfonates or alkylnaphthalene sulfonates, or any combination thereof.

[0129] Nonionic surfactants may include 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, polyglyceryl esters and their ethoxylated derivatives, alkylamines, alkylimidazolines, ethoxylated oils, and alkylphenol ethoxylates. In particular, products sold under the Igepal®, Dowanol®, Rhodamox®, and Alkamide® brands may be mentioned, or any combination thereof.

[0130] As for the carboxylic acid, in particular, aliphatic monocarboxylic acids or dicarboxylic acids may be used, among which, 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, 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, more particularly, saturated fatty acids, or any combination thereof may also be used. They are particularly those of the formula CH3(CH2)). m It may be a saturated linear acid of -COOH (m is an integer from 6 to 20, more particularly from 9 to 15). Salts of all the acids mentioned may also be used, in particular the ammonium salts. By way of example, mention may more particularly be made of lauric acid and ammonium laurate.

[0131] Finally, surfactants selected from the carboxymethylated fatty alcohol ethoxylate type can be used. 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 chain end. These products have the formula: R1-O-(CR2R3-CR4R5-O) n-CH2-COOH, where R1 represents a saturated or unsaturated carbon chain, the length of which is generally at most 22 carbon atoms, preferably at least 12 carbon atoms; R2, R3, R4 and R5 may be identical and represent hydrogen, or R2 may represent a CH3 group and R3, R4 and R5 represent hydrogen; and n is a non-zero integer which may be less than or equal to 50, more particularly ranging from 5 to 15 (these values are inclusive). It should be noted that the surfactant may consist of a mixture of products of the above formula, where R1 may be saturated or unsaturated, respectively, or a mixture of products containing both CH2-CH2-O- and -C(CH2)-CH2-O- groups.

[0132] The template agent may be added directly to the mixture resulting from step (a4). In this case, it is preferably added to the mixture, the temperature of which is at most 60° C.

[0133] The amount of template agent used, expressed as a percentage by weight of template agent relative to the mixed oxide, is generally between 5% and 100%, more particularly between 15% and 60%.

[0134] At the end of step (a5), the mixture is optionally filtered and the precipitate is washed (a6). In a preferred embodiment, the precipitate is washed with water.

[0135] In step (a7) of the process of the present invention, the recovered precipitate is then calcined. This calcination allows the crystallinity of the product formed to develop, and it can also be adjusted and / or selected depending on the subsequent operating temperature intended for the composition according to the present invention, taking into account the fact that the specific surface area of the product decreases as the calcination temperature used increases. Such calcination is generally carried out under air, although calcinations carried out, for example, under inert gas or under controlled atmospheres (oxidizing or reducing) are not very definitely excluded.

[0136] Unless otherwise specified, calcinations are carried out under air.

[0137] In practice, the calcination temperature is generally limited to a range of values between 700°C and 1100°C, more particularly between 900°C and 1100°C, and even more particularly between 1000°C and 1100°C.

[0138] The duration of the calcination is not critical and depends on the temperature. Purely by way of example, it can be at least 2 hours, more particularly from 2 hours to 6 hours, even more particularly from 2 to 4 hours.

[0139] Finally, but optionally, the mixed oxide obtained in step (a7) may be ground (a8).

[0140] In a particular aspect, the present invention deals with mixed oxides obtainable by the methods described above.

[0141] In another particular aspect, the present invention provides a method for producing a pharmaceutical composition comprising the steps of: (a1) an aqueous solution of cerium nitrate and of zirconium nitrate is introduced into a stirred vessel containing an aqueous basic solution; - (a2) optionally, an aqueous solution of a nitrate of a rare earth metal (other than cerium or lanthanum) is then introduced into the mixture formed in step (a1) and kept stirring; (a2') optionally, the mixture obtained at the end of step (a1) or (a2) is heated at a temperature comprised between 50 and 95°C; - (a3) an aqueous solution of lanthanum nitrate is then introduced into the mixture formed in step (a2), (a2') or (a1) and kept stirring. (a4) the mixture obtained at the end of step (a3) is heated with stirring; - (a5) a step in which a templating agent is then introduced into the mixture obtained in the preceding step; - (a6) optionally, filtering the mixture and washing the precipitate; (a7) the precipitate obtained at the end of step (a6) is calcined at a temperature between 700°C and 1100°C; - (a8) the mixed oxide obtained in step (a7) is optionally ground. 1. A method for preparing a mixed oxide comprising: The mixed oxide is a mixed oxide of zirconium, cerium, lanthanum and optionally at least one REM other than cerium and lanthanum, in which the weight proportions of these elements, expressed as oxide equivalents, relative to the total weight of the mixed oxide, are as follows: - 8%~47% cerium; - 1%-10% lanthanum; - 0% to 15% of rare earth metals other than cerium and lanthanum; - 0% to 2.5% hafnium; - Remainder as Zirconium This relates to a method.

[0142] Compositions containing mixed oxides The present invention also relates to a composition comprising a mixed oxide as described above or obtained by a process as described above and in admixture with at least one inorganic substance.

[0143] According to a particular embodiment, the composition comprises at least one inorganic material selected from alumina, titanium oxide, cerium oxide, zirconium oxide, silica, spinel, zeolite, silicate, crystalline silicoaluminophosphate or crystalline aluminophosphate, or any combination thereof.

[0144] catalytically active coating layer The present invention also relates to a catalytically active coating layer deposited on the surface area of a solid support, prepared from the mixed oxide obtained by this method or from a composition as described above.

[0145] In a further embodiment, a catalytic converter is for treating automobile exhaust gases and includes a coating layer as described above.

[0146] Use of mixed oxides The mixed oxide of the present invention can be used in the field of exhaust gas treatment.The mixed oxide of the present invention can be used to reduce the amount of pollutants present in the exhaust gas emitted by the internal combustion engine of a vehicle.

[0147] The mixed oxides can be used in the preparation of catalytic converters used to treat exhaust gases emitted by internal combustion engines of vehicles. The catalytic converter comprises at least one catalytically active layer prepared by depositing a catalyst composition on a solid support. The function of the layer is to chemically convert some pollutants in the exhaust gases into products that are less harmful to the environment. The solid support can be a monolith made of ceramic, such as cordierite, silicon carbide, alumina titanate, or mullite, or a metal, such as Fecralloy. The support is usually made of cordierite, which exhibits a large specific surface area and low pressure loss. The monolith is often honeycomb-shaped.

[0148] The catalyst composition comprises (i) at least one inorganic material, such as alumina; (ii) one or more platinum group metals; and (iii) at least one mixed oxide of the present invention Includes:

[0149] The mixed oxides can be used to prepare catalytic wall-flow monoliths. Catalytic wall-flow monoliths include 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. They function by forcing the flow of exhaust gas (including particulate matter) through a wall formed by the porous support. Porosity helps retain the particulate matter. The monolith preferably has a first face and a second face defining a longitudinal direction therebetween. In use, one of the first and second faces is an inlet face for the exhaust gas, and the other is an outlet face for the treated exhaust gas. As is conventional for wall-flow monoliths, it has first and second pluralities of channels extending longitudinally. The first plurality of channels is open on the first face and closed on the second face. The second plurality of channels is open on the second face and closed on the first face. The channels are preferably parallel to one another to provide a consistent wall thickness between the channels. As a result, gas entering one of the channels cannot exit the monolith without diffusing through the channel walls into the other channels, which are closed with the introduction of a sealant material into the open ends of the channels.

[0150] Preferably, the number of channels in the first plurality is equal to the number of channels in the second plurality, with each plurality being uniformly distributed throughout the monolith. Preferably, in a plane perpendicular to the longitudinal direction, the wall-flow monolith has 100 to 500 channels per square inch (cpsi), preferably 200 to 400 cpsi. For example, on the first face, the density of the open first channels and closed second channels is 200 to 400 channels per square inch. The channels can have cross-sections that are rectangular, square, circular, oval, triangular, hexagonal, or other polygonal shapes.

[0151] To facilitate the passage of the exhaust gas to be treated through the channel walls, the monolith is formed from a porous substrate. The substrate also serves as a support for holding the catalyst composition. Suitable materials for forming the porous substrate include ceramic-grade materials such as cordierite, silicon carbide, silicon nitride, zirconia oxide, mullite, spodumene, alumina-silica-magnesia, or zirconium silicate, or porous refractory metals. Wall-flow substrates can also be formed from ceramic fiber composites. Preferred wall-flow substrates are formed from cordierite and silicon carbide. Such materials can withstand the environments, especially the high temperatures, encountered in treating exhaust gas streams and can be made sufficiently porous. Such materials and their use in the manufacture of porous monolith substrates are well known in the art.

[0152] The catalyst composition is applied to the porous substrate in the form of a layer. Traditionally, the loading of the layer should not be too high to avoid back pressure. Loadings are typically 1.0 g / in. 3 ~0.1g / inch 3 , preferably 0.7 g / inch 3 ~0.25g / inch 3 , and most preferably 0.6g / inch to 0.5g / inch 3 It could be.

[0153] The catalyst composition comprises alumina, preferably gamma-alumina. The alumina may also comprise lanthanum, praseodymium, or a combination of the two. The alumina is preferably lanthanum-stabilized alumina. Alumina is an advantageous carrier material because it exhibits a high surface area and is a refractory metal oxide. This translates to good thermal performance required for the high temperature conditions encountered. The catalyst composition also comprises one or more platinum group metals (PGMs). The PGMs are selected from the group consisting of Pt, Pd, Rh, Re, and Ir. The PGMs serve to catalyze the reactions required to treat exhaust gases and the combustion of soot particles. Preferably, the PGMs are Pt, Pd, and Rh; Pd and Rh; or Pd only; or Rh only.

[0154] Methods that can be used for the preparation of catalytic wall-flow monoliths are disclosed in WO 2017 / 109514, the contents of which are incorporated by reference in their entirety. More specifically, the method disclosed in Example 3 of WO 2017 / 109514 can be used.

[0155] Exhaust gas treatment method The present invention also relates to a method for treating exhaust gases from an internal combustion engine, characterized in that it uses a catalytic converter comprising a coating layer as described above.

[0156] The examples herein below are intended to illustrate, but not limit, the present invention.

[0157] Measurement method according to the present invention Pore volume and pore diameter measurements The given pore volume and pore diameter are measured by mercury (Hg) porosimetry using a Micromeritics Autopore IV 9500 porosimeter and calculated by the Washburn relationship with theta contact angle equal to 130° and gamma surface tension equal to 485 dynes / cm; each sample is prepared as follows: each sample is pre-dried in an oven at 200°C for 2 hours.

[0158] The following parameters may be used: penetrometer used: 3.2 ml; capillary volume: 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 mmHg is applied to the sample for 5 minutes.

[0159] The equilibration times are as follows: low pressure (1.3-30 psi) range: 20 seconds - high pressure (30-60,000 psi) range: 30 seconds. Prior to measurement, the samples are degassed in an oven at 100°C for a minimum of 15 minutes.

[0160] Specific surface area measurement BET specific surface area is measured automatically on a Mountech Macsorb analyzer model I-1220. Prior to any measurement, the sample is carefully degassed to desorb volatile adsorbed species. To do so, the sample can be heated in the instrument's cell under vacuum at 210°C for 30 minutes.

[0161] The BET measurements are carried out at one point with a relative pressure P / P0 of 0.3.

[0162] The porosities indicated are measured by mercury intrusion porosimetry according to standard ASTM D 4284-83 (reapproved 2008) ("Standard method for determining pore volume distribution of catalysts by mercury intrusion porosimetry").

[0163] A Micromeritics Autopore IV 9500 instrument equipped with a powder penetrometer can be used by following the manufacturer's recommended instructions.

[0164] 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) can exhibit one or more peaks, each located at a diameter denoted Dp. Pores considered characteristic for the present invention are those exhibiting a diameter of less than or equal to 200 nm.

[0165] For the mercury porosimetry technique, a Micromeritics Autopore IV 9500 machine equipped with a powder penetrometer may be used according to the instructions recommended by the manufacturer. The standard ASTM D 4284-83 (reapproved 2008) procedure may be followed. [Example]

[0166] Example 1: Composition CeO2 40% - ZrO2 50% - La2O 35% - Y2O 35% This example describes the preparation of compositions of cerium, zirconium, lanthanum, and yttrium in respective weight percentages of the oxides of 40%, 50%, 5%, and 5%.

[0167] 48.55 liters of deionized water and 11.36 liters of cerium nitrate solution ([Ce 3+ A solution is prepared by mixing 23.81 liters of zirconium oxynitrate solution ([ZrO2] = 277 g / L, density = 1.442 kg / L) with 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 is stirred for 30 minutes.

[0168] A settling tank equipped with a four-blade impeller is charged with 68.17 liters of aqueous ammonia solution ([NH3] = 15.1 wt% and density = 0.941 kg / L) and 41.83 L of deionized water.

[0169] The solution containing cerium and zirconium prepared above is then introduced into the precipitation tank in 60 minutes. The stirring speed during precipitation is 220 rpm.

[0170] 3.09 liters of yttrium nitrate solution ([Y 3+ ]=1.89 mol / L, density=1.411 kg / L) is then added to the precipitation tank at the same flow rate as the solution containing cerium and zirconium.

[0171] The temperature of the mixture is then raised to 60°C.

[0172] 2.24 liters of lanthanum nitrate solution ([La 3+ ]=1.81 mol / L, density=1.473 kg / L) is then added to the precipitation tank at the same flow rate as the solution containing cerium and zirconium.

[0173] The mixture is then aged under stirring in an autoclave at 150° C. for 2 hours.

[0174] The temperature is then reduced to about 60°C and 4.356 kg of lauric acid are introduced under stirring. The mixture is maintained under stirring for 1 hour.

[0175] The mixture is then filtered and the cake is washed with 60 liters of deionized water.

[0176] The solid obtained is calcined at 850° C. for 3 hours.

[0177] [Table 1]

[0178] Example 2 - Composition CeO2 10% - ZrO2 72% - La2O 35% - Y2O 38% - Nd2O 35% This example describes the preparation of compositions of cerium, zirconium, lanthanum, yttrium, and neodymium in respective weight percentages of oxide of 10%, 72%, 5%, 8%, and 5%.

[0179] 62.21 liters of deionized water and 2.6 liters of cerium nitrate solution ([Ce 3+ A solution is prepared by mixing 31.38 liters of zirconium oxynitrate solution ([ZrO2] = 277 g / L, density = 1.442 kg / L) with 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 is stirred for 30 minutes.

[0180] A settling tank equipped with a four-blade impeller is charged with 73.89 liters of aqueous ammonia solution ([NH3] = 15.1 wt% and density = 0.941 kg / L) and 47.11 liters of deionized water.

[0181] The solution containing cerium and zirconium prepared above is then introduced into the precipitation tank for 60 minutes.

[0182] 4.54 liters of yttrium nitrate solution ([Y 3+ ]=1.89 mol / L, density=1.411 kg / L) and 2.03 L of neodymium nitrate solution ([Nd 3+ ]=1.77 mol / L, density=1.474 kg / L) is mixed with cerium and zirconium. This solution is then added to the precipitation tank at the same flow rate as the solution containing cerium and zirconium.

[0183] The temperature of the mixture is then raised to 60°C.

[0184] 2.05 liters of lanthanum nitrate solution ([La3+]=1.81 mol / L, density=1.473 kg / L) is then added to the precipitation tank at the same flow rate as the solution containing cerium and zirconium.

[0185] The mixture is then aged under stirring in an autoclave at 150° C. for 2 hours.

[0186] The temperature is then reduced to approximately 60°C and 3.993 kg of lauric acid are introduced under stirring. The mixture is maintained under stirring for 1 hour.

[0187] The mixture is then filtered and the cake is washed with 60 liters of deionized water.

[0188] The solid obtained is calcined at 1020° C. for 2 hours.

[0189] [Table 2]

[0190] Example 3 - Composition CeO2 24% - ZrO2 60% - La2O3 3.5% - Y2O3 12.5% This example describes the preparation of compositions of cerium, zirconium, lanthanum and yttrium in respective weight percentages of oxide of 24%, 60%, 3.5%, 12.5%.

[0191] 61.81 liters of deionized water and 6.25 liters of cerium nitrate solution ([Ce 3+ A solution is prepared by mixing 26.15 liters of zirconium oxynitrate solution ([ZrO2] = 277 g / L, density = 1.442 kg / L) with 11.48 liters of concentrated nitric acid solution ([HNO3] = 67 wt%, density = 1.399 kg / L) and 5.79 liters of aqueous hydrogen peroxide solution ([H2O2] = 35 wt%, density = 1.135 kg / L). After this addition, the solution is stirred for 30 minutes.

[0192] A settling tank equipped with a four-blade impeller is charged with 68.81 liters of aqueous ammonia solution ([NH3] = 15.1 wt% and density = 0.941 kg / L) and 52.19 liters of deionized water.

[0193] The solution containing cerium and zirconium prepared above is then introduced into the precipitation tank for 60 minutes.

[0194] 7.09 liters of yttrium nitrate solution ([Y 3+ ]=1.89 mol / L, density=1.411 kg / L) is then added to the precipitation tank at the same flow rate as the solution containing cerium and zirconium.

[0195] The temperature of the mixture is then raised to 60°C.

[0196] 1.44 liters of lanthanum nitrate solution ([La 3+]=1.81 mol / L, density=1.473 kg / L) is then added to the precipitation tank at the same flow rate as the solution containing cerium and zirconium.

[0197] The mixture is then aged under stirring in an autoclave at 150° C. for 2 hours.

[0198] The temperature is then reduced to about 60°C and 3.993 kg of lauric acid are introduced under stirring. The mixture is maintained under stirring for 1 hour.

[0199] The mixture is then filtered and the cake is washed with 60 liters of deionized water.

[0200] The solid obtained is calcined at 850° C. for 3 hours.

[0201] [Table 3]

[0202] Comparative Example 1 - Composition CeO240%-ZrO250%-La2O35%-Y2O35% This example describes the preparation of compositions of cerium, zirconium, lanthanum, and yttrium in respective weight percentages of the oxides of 40%, 50%, 5%, and 5%.

[0203] 63.4 liters of deionized water and 11.36 liters of cerium nitrate solution ([Ce 3+ A solution is prepared by mixing 23.77 liters of zirconium oxynitrate solution ([ZrO2] = 277 g / L, density = 1.442 kg / L) with 2.88 liters of concentrated nitric acid solution ([HNO3] = 67 wt%, density = 1.399 kg / L). Then, 3.09 liters of yttrium nitrate solution ([Y 3+ = 1.89 mol / L, density = 1.411 kg / L) and 2.24 L of 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) is added. After this addition, the solution is stirred for 30 minutes.

[0204] A settling tank equipped with a four-blade impeller is charged with 48.48 liters of aqueous ammonia solution ([NH3] = 15.1 wt% and density = 0.941 kg / L) and 61.52 liters of deionized water.

[0205] The solution containing cerium, zirconium, yttrium and lanthanum prepared above is then introduced into the precipitation tank for 60 minutes.

[0206] The temperature of the mixture is then increased to 95°C.

[0207] The mixture is then aged under stirring in an autoclave at 120° C. for 2 hours.

[0208] The temperature is then reduced to about 60°C and 4.356 kg of lauric acid are introduced under stirring. The mixture is maintained under stirring for 1 hour.

[0209] The mixture is then filtered and the cake is washed with 60 liters of deionized water.

[0210] The solid obtained is calcined at 850° C. for 3 hours.

[0211] [Table 4]

[0212] Comparative Example 2 - Composition CeO240%-ZrO250%-La2O35%-Y2O35% This example describes the preparation of compositions of cerium, zirconium, lanthanum, and yttrium at respective weight percentages of the oxides of 40%, 50%, 5%, and 5% according to the method described in WO 2017 / 187085.

[0213] A solution of cerium nitrate and zirconium nitrate is prepared by introducing 95.43 liters of water, 11.3 liters of an aqueous zirconium nitrate solution ([ZrO2] = 266 g / l; density = 1.408 kg / l) and also 5.8 liters of an aqueous cerium nitrate solution ([CeO2] = 259 g / l; density = 1.439 kg / l) into a vessel. An aqueous solution of lanthanum nitrate and yttrium nitrate is also prepared by introducing 10.77 liters of water, 0.53 liters of a lanthanum nitrate solution ([La2O3] = 472.5 g / l; density = 1.711 kg / l) and 1.2 liters of an yttrium nitrate solution ([Y2O3] = 208.5 g / l; density = 1.391 kg / l) into another vessel.

[0214] The ammonia solution (12 liters at 12 mol / l) is introduced with stirring into a reactor of approximately 250 liters equipped with a stirrer with pitched blades, and the solution is then made up with distilled water to obtain a basic aqueous solution with a total volume of 125 liters, which makes it possible to provide a 40% molar stoichiometric excess of ammonia relative to the cations present in the two solutions described above.

[0215] The two solutions prepared above are kept under continuous stirring. The cerium nitrate and zirconium nitrate solutions are introduced into the stirred reactor containing the ammonia solution, the stirring of which is adjusted to a speed of 200 rpm (80 Hz), over a period of 45 minutes. The lanthanum nitrate and yttrium nitrate solutions are then introduced into the stirred reactor, the stirring of which is now adjusted to 25 rpm (10 Hz), over a period of 15 minutes. A mixture is obtained.

[0216] The mixture is poured into a stainless steel autoclave equipped with a stirrer. The mixture is heated at 150°C with stirring for 2 hours. It is then allowed to cool to a temperature below 60°C and 1.65 kg of lauric acid is added to the mixture. The mixture is kept stirring for 1 hour.

[0217] The mixture is then filtered, and the precipitate is then washed with an aqueous ammonia solution with a pH of 9.5 in a volume equal to the volume of the filtered mother liquor (washing is carried out with 250 liters of aqueous ammonia). The resulting solid product is then calcined at 950°C for 3 hours under air to recover approximately 5 kg of mixed oxide. The resulting solid is calcined at 825°C for 3 hours.

[0218] [Table 5]

Claims

1. Mixed oxides of zirconium, cerium, lanthanum, and optionally at least one rare earth metal (REM) other than cerium and lanthanum, in which the weight proportions of these elements, expressed as oxide equivalents, relative to the total weight of said mixed oxide, are as follows: - 8% to 47% cerium; - 1% to 10% lanthanum; - 0% to 15% of rare earth metals other than cerium and lanthanum; - remainder as zirconium and The mixed oxide is - at least 30 m after calcination at a temperature of 1100 ° C for 4 hours ２ / g BET specific surface area; - at least 50 m after calcination at a temperature of 1000 ° C for 4 hours ２ / g BET specific surface area; - a derivative curve (dV / dlogD) obtained by mercury porosimetry on said mixed oxide after calcination at a temperature of 1100°C for 4 hours, which shows, in the range of pores with a diameter of up to 200 nm, one peak with a maximum value corresponding to a pore diameter, denoted Dp,1100°C / 4h, of 25 to 40 nm, preferably 25 to 38 nm, V and D denote the pore volume and the pore diameter, respectively; - R is comprised between 0.50 and 0.60, R = V1 / V2 [In the formula: V1 is the pore volume expressed by pores with diameters in nm between (Dp,1100°C / 4h-15) and (Dp,1100°C / 4h+15); V2 is the pore volume represented by pores with a diameter of 200 nm or less; V1 and V2 are measured by mercury porosimetry on the mixed oxide after calcination at 1100°C for 4h. and a ratio R defined by 10. A mixed oxide, characterized in that:

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

3. 3. A mixed oxide according to claim 2, characterized in that the weight proportion of hafnium in the mixed oxide, expressed as oxide equivalent with respect 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. 4. Mixed oxide according to claim 1, characterized in that the elements Ce, La, 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.

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

6. 6. A mixed oxide according to claim 1, which contains only yttrium as REM other than cerium and lanthanum.

7. A mixed oxide according to any one of claims 1 to 5, containing only two REM other than cerium and lanthanum, which may be yttrium and neodymium or yttrium and praseodymium.

8. 8. A mixed oxide according to any one of claims 1 to 7, comprising a mixture of oxides of zirconium, of cerium, of lanthanum, optionally of at least one REM other than cerium and lanthanum, and optionally of hafnium.

9. 5. A mixed oxide according to claim 1, which does not contain any rare earth metals other than cerium and lanthanum.

10. 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 9. The mixed oxide according to claim 1, consisting essentially of

11. Mixed oxide according to any one of the preceding claims, characterized in that the weight proportion of zirconium, expressed as oxide equivalent, can be between 40.0% and 91.0%, preferably between 44.0 and 80.0%, more preferably between 44.0 and 76.0%.

12. The tap density of the mixed oxide is 0.4 g / cm ３ or more, preferably 0.5 g / cm ３ The mixed oxide according to any one of claims 1 to 11, characterized in that

13. The tap density of the mixed oxide is 0.5 g / cm ３ ~0.9 g / cm ３ 13. The mixed oxide according to claim 12, wherein

14. 14. The mixed oxide according to claim 1, characterized in that the derivative curve (dV / dlogD) obtained by mercury porosimetry for said mixed oxide after calcination at a temperature of 900°C for 4 hours shows one peak in the range of pores with a diameter of 200 nm or less, the maximum of which corresponds to the pore diameter denoted Dp,900°C / 4h, and the difference in absolute values (Dp,1100°C / 4h) - (Dp,900°C / 4h) is 15 nm or less, preferably 12 nm or less, or even 11 nm or less.

15. 15. The mixed oxide according to claim 1, characterized by a pore volume V2 of 0.20 to 0.50 ml / g, in particular 0.24 to 0.41 ml / g.

16. 16. The mixed oxide according to any one of the preceding claims, which is provided in the form of a powder and whose average diameter d50, measured by laser diffraction over the volume distribution, is 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. 17. The mixed oxide according to any one of claims 1 to 16, characterized in that the derivative curve (dV / dlogD), obtained by mercury porosimetry for said mixed oxide after calcination at a temperature of 900°C for 4 hours, does not show two distinct peaks.

18. Next steps: (a1) an aqueous solution of cerium nitrate and of zirconium nitrate is introduced into a stirred vessel containing an aqueous basic solution; (a2) optionally, an aqueous solution of nitrates of rare earth metals other than cerium and lanthanum is then introduced into the mixture formed in step (a1) and kept stirred; (a2') optionally, the mixture obtained at the end of step (a1) or (a2) is heated at a temperature comprised between 50 and 95°C; (a3) an aqueous solution of lanthanum nitrate is then introduced into the mixture formed in step (a2'), (a2) or (a1) and kept stirring; (a4) the mixture obtained at the end of step (a3) is heated with stirring; (a5) a step in which a templating agent is then introduced into the mixture obtained in the preceding step; (a6) optionally, filtering the mixture and washing the precipitate; (a7) the precipitate obtained at the end of step (a6) is calcined at a temperature between 700°C and 1100°C; (a8) the mixed oxide obtained in step (a7) is optionally ground; A process for preparing the mixed oxide according to any one of claims 1 to 17, comprising:

19. 19. The method of claim 18, wherein the concentration of mixed oxides in the aqueous solution after step (a3) is between 30 g / l and 80 g / l, expressed as metal oxides.

20. 20. A mixed oxide obtainable by the method according to claim 18 or 19.

21. A composition comprising a mixed oxide according to any one of claims 1 to 17 or according to claim 20 in admixture with at least one inorganic substance.

22. 22. The composition of claim 21, wherein the inorganic material is selected from alumina, titanium oxide, cerium oxide, zirconium oxide, silica, spinel, zeolite, silicate, crystalline silicoaluminum phosphate, or crystalline aluminum phosphate.

23. A catalytically active coating layer deposited on the surface of a solid support, comprising a mixed oxide according to any one of claims 1 to 17 or according to claim 20 or a composition according to claim 21 or 22.

24. 24. A catalytic converter for treating automotive exhaust gases comprising a catalytically active coating layer according to claim 23.

25. Use of a mixed oxide according to any one of claims 1 to 17 or according to claim 20 or of a composition according to claim 21 or 22 in the preparation of a catalytic converter.

26. A method for treating exhaust gases from an internal combustion engine, characterized in that a catalytic converter comprising the coating layer according to claim 24 is used.

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