Mixed oxides with improved reducibility

Abstract

Disclosed is a zirconium- and cerium-based mixed oxide composition exhibiting high reducibility, a method for preparing the same, and uses thereof in the field of catalysis.

Description

[0001] This application claims the priority of International Patent Application PCT / CN 2018 / 107177 filed on September 24, 2018, and the content of this patent application is incorporated herein by reference in its entirety for all purposes. In the event of any inconsistency between this application and this PCT application that would affect the clarity of terms or expressions, only this application should be referred to.

[0002] The present invention relates to a zirconium- and cerium-based mixed oxide composition exhibiting high reducibility, to a process for its preparation and to its use in the field of catalysis. [Technical Field]

[0003] "Multifunctional" catalysts are currently used for treating the exhaust gases from internal combustion engines (post-combustion catalysis in motor vehicles). The term "multifunctional" should be understood to mean a catalyst that is capable not only of performing oxidation, in particular the oxidation of carbon monoxide and hydrocarbons present in the exhaust gases, but also of performing reduction, in particular the reduction of nitrogen oxides also present in these gases ("three-way" catalysts). Products based on cerium oxide, zirconium oxide and optionally one or more other rare earth metal oxides now appear to be particularly important and advantageous components included in the compositions of this type of catalyst. For effectiveness, these components must have a high specific surface area, even after having been subjected to a high temperature, for example of at least 1100 °C.

[0004] Another quality required of these catalyst components is reducibility. The term "reducibility" here (and in the remainder of this specification) refers to the ability of the catalyst to be reduced in a reducing atmosphere and to be re-oxidized in an oxidizing atmosphere. In a given temperature range, reducibility is related to the amount of mobile oxygen. Currently, the above-mentioned products have maximum reducibility of the catalyst at a relatively high temperature. Now, there is a need for catalysts having sufficient reducibility in a lower temperature range. Improvements in reducibility are also sought for both individual mixed oxides and catalysts composed of mixed oxides and platinum group metals (or PGM).

[0005] In the current state of the art, it seems that the above-mentioned two characteristics are often difficult to reconcile, namely high reducibility at lower temperatures corresponds to a relatively low specific surface area.

[0006] The object of the present invention is to provide a composition of this type combining a high specific surface area with good reducibility at lower temperatures. [Background Art]

[0007] WO 2013 / 004534 describes a mixed oxide consisting essentially of zirconium and cerium and exhibiting high reducibility. After calcination at 1100 °C for 4 hours, the mixed oxide exhibits at least 8 m 2 / g, more particularly at least 10 m2 The specific surface area of / g. The mixed oxides disclosed in the examples exhibit a specific surface area far lower than 25 m 2 / g.

[0008] US 2009 / 0325793 describes a mixed oxide containing zirconium, cerium, lanthanum, and iron, with an iron content higher than 1.0% (for example, the iron oxide content in the mixed oxide of Example 2: 2.7%). There is also no mention of the specific surface area.

[0009] US 2017072386 describes a mixed oxide containing zirconium, cerium, and iron with a low specific surface area (<2 m 2 / g).

[0010] WO 2007 / 132253 describes a mixed oxide with a low T max These mixed oxides contain tin but do not mention iron. [Description of the Drawings]

[0011] Figure 1 The TPR curves of the following products are disclosed:

[0012] ■ The mixed oxide of Example 1 calcined in air at 1100 °C for 4 hours;

[0013] ■ Catalyst 1 corresponding to the mixed oxide of Example 1 with 0.1% wt Rh aged under the "lean / rich" conditions A1 - A2 disclosed in the examples.

[0014] Figure 2 The TPR curves of the following products are disclosed:

[0015] ■ The mixed oxide of Example 2 calcined in air at 1100 °C for 4 hours;

[0016] ■ Catalyst 2 corresponding to the mixed oxide of Example 2 with 0.1% wt Rh aged under the "lean / rich" conditions A1 - A2. [Detailed Description of the Invention]

[0017] In the present application, the calcination, and in particular the calcination that gives the surface area value thereafter, is calcination in air, unless otherwise mentioned. For the continuity of this specification, it is also specified that, unless otherwise indicated, the limit values are included within the range of the given values.

[0018] The present invention relates to a mixed oxide of zirconium, cerium, lanthanum, iron, and optionally at least one rare earth element (RE) other than cerium and other than lanthanum, having the following composition:

[0019] ■ Cerium between 18.0 wt% and 45.0 wt%;

[0020] ■ Lanthanum between 1.0 wt% and 15.0 wt% by weight;

[0021] ■ One or more rare earth elements (RE) other than cerium and lanthanum up to 15.0 wt%;

[0022] ■ Iron between 0.05 wt% and 0.25 wt%, more particularly between 0.05 wt% and 0.20 wt%, even more particularly between 0.05 wt% and 0.15 wt%;

[0023] ■ The balance being zirconium;

[0024] Exhibits the following properties after calcination in air at 1100 °C for 4 hours:

[0025] ■ At least 25 m 2 / g, more particularly at least 26 m 2 / g, more particularly at least 28 m 2 / g, even more particularly at least 30 m 2 / g of BET specific surface area;

[0026] ■ A maximum reduction temperature (T max ) of at most 530 °C, more particularly at most 500 °C.

[0027] The elements mentioned above are usually present as oxides in the mixed oxide. However, they can also be present partially in the form of hydroxides or hydroxyoxides.

[0028] The mixed oxide of the present invention can also contain the element hafnium. Indeed, this element is usually present in combination with zirconium in ores occurring in nature. The relative proportion of hafnium with respect to zirconium depends on the ore from which zirconium is extracted. In some ores, the relative proportion of Zr / Hf by weight can be about 50 / 1. Thus, baddeleyite contains approximately 98 wt% of ZrO2 and 2 wt% of HfO2. Like zirconium, hafnium is usually present as an oxide. However, it is not excluded that hafnium is also present partially in the form of hydroxides or hydroxyoxides. The proportion of hafnium is less than or equal to 2.5 wt%, even less than or equal to 2.0 wt%.

[0029] As is the case in the field of mixed oxides, the proportions of the elements are given by weight of the oxides with respect to the total of the mixed oxide. For the calculation of these proportions, the following oxides are considered: CeO2, Fe2O3, ZrO2, HfO2, La2O3, RE2O3 (excluding Pr for which Pr6O 11)All RE other than those specified. Thus, for example, a cerium proportion of 20.0 wt% means that the proportion by weight of CeO2 in the mixed oxide is 20.0%. The proportion of an element is determined by common analytical methods such as X-ray fluorescence or by inductively coupled plasma mass spectrometry. It is also noted that the limiting values are included within the range of the given values unless otherwise mentioned.

[0030] The mixed oxide of the present invention contains the above-mentioned elements in the above-mentioned proportions, but it may additionally contain other elements, such as impurities. These impurities may originate from the raw materials or starting materials used in the method for preparing the mixed oxide. The total proportion of these impurities may generally be less than 0.2 wt% relative to the mixed oxide.

[0031] First, the mixed oxide according to the present invention is characterized by the nature and proportion of its components. The proportion of cerium in the mixed oxide is between 18.0 wt% and 45.0 wt%, more particularly between 18.0 wt% and 42.0 wt%. The proportion of cerium can be between 18.0 wt% and 22.0 wt% or between 28.0 wt% and 32.0 wt% or between 38.0 wt% and 42.0 wt%.

[0032] The proportion of lanthanum in the mixed oxide is between 1.0 wt% and 15.0 wt%, more particularly between 3.0 wt% and 12.0 wt%. This proportion can be between 3.0 wt% and 7.0 wt%. This proportion can also be between 1.0 wt% and 7.0 wt%, more particularly between 1.0 wt% and 5.0 wt%.

[0033] The proportion of iron in the mixed oxide is between 0.05 wt% and 0.25 wt%, more particularly between 0.05 wt% and 0.20 wt%, even more particularly between 0.05 wt% and 0.15 wt%. The proportion of iron can also be between 0.10 wt% and 0.20 wt%, more particularly between 0.10 wt% and 0.15 wt%. According to the examples, the proportion of iron is strictly higher than 0.10 wt% (>0.10 wt%). Due to the proportion of iron oxide and the process used, the iron oxide is well distributed in the mixed oxide. Moreover, XRD does not show any peaks caused by iron oxide.

[0034] The mixed oxide may also contain at least one rare earth element other than cerium and other than lanthanum. The one or more rare earth elements may preferably be selected from the group consisting of Nd, Y, and Pr. More particularly, Y and Pr are preferred.

[0035] The total proportion of one or more rare earth elements other than cerium and other than lanthanum in the mixed oxide is up to 15.0 wt%. According to the examples, this total proportion can be up to 10.0 wt%, more particularly up to 7.0 wt%.

[0036] According to another example, the total proportion of one or more rare earth elements other than cerium and other than lanthanum in the mixed oxide can be at least 10.0 wt%, particularly at least 12.0 wt%. This example is particularly applicable when the proportion of iron is higher than 0.15 wt%, or even higher than 0.20 wt%. According to this other example, the mixed oxide contains at least 10.0 wt%, more particularly at least 12.0 wt% of yttrium.

[0037] Zirconia constitutes the remainder of the composition. The proportion by weight of zirconium is the remainder of 100% of the other elements of the mixed oxide. The proportion of zirconium in the mixed oxide is at least 45.0 wt%, more particularly at least 49.0 wt%, even more particularly at least 50.0 wt%, even more particularly at least 54.0 wt% or at least 55.0 wt%. This proportion can be up to 77.0 wt% or up to 70.0 wt%.

[0038] A specific composition C1 according to the invention corresponds to the following composition:

[0039] ■ Cerium between 18.0 wt% and 22.0 wt%;

[0040] ■ Lanthanum between 3.0 wt% and 7.0 wt%;

[0041] ■ Yttrium between 3.0 wt% and 7.0 wt%;

[0042] ■ Iron between 0.05 wt% and 0.25 wt% by weight, more particularly between 0.05 wt% and 0.20 wt% by weight, even more particularly between 0.05 wt% and 0.15 wt% by weight;

[0043] ■ The remainder is zirconium.

[0044] For composition C1, the proportion of zirconium can be between 64.0 wt% and 76.0 wt% by weight.

[0045] Another specific composition C2 according to the invention corresponds to the following composition:

[0046] ■ Cerium between 28.0 wt% and 32.0 wt%;

[0047] ■ Lanthanum between 3.0 wt% and 7.0 wt%;

[0048] ■ Yttrium between 3.0 wt% and 7.0 wt%;

[0049] ■ Iron between 0.05 wt% and 0.25 wt%, more particularly between 0.05 wt% and 0.20 wt%, even more particularly between 0.05 wt% and 0.15 wt%;

[0050] ■ The balance being zirconium.

[0051] For composition C2, the proportion of zirconium can be between 54.0 wt% and 66.0 wt% by weight.

[0052] Another specific composition C3 according to the invention corresponds to the following composition:

[0053] ■ Cerium between 38.0 wt% and 42.0 wt%;

[0054] ■ Lanthanum between 3.0 wt% and 6.0 wt%;

[0055] ■ Yttrium between 3.0 wt% and 6.0 wt%;

[0056] ■ Iron between 0.05 wt% and 0.25 wt%, more particularly between 0.05 wt% and 0.20 wt%, even more particularly between 0.05 wt% and 0.15 wt%;

[0057] ■ The balance being zirconium.

[0058] For composition C3, the proportion of zirconium can be between 46.0 wt% and 56.0 wt% by weight. According to the examples, for composition C3, the proportion of zirconium can be between 46.0 wt% and 56.0 wt% by weight, this latter value being excluded.

[0059] For these three specific compositions C1 - C3, all the remaining proportions are the same, and the lanthanum content can also be between 1.0 wt% and 7.0 wt%, more particularly between 1.0 wt% and 5.0 wt%.

[0060] The mixed oxide of the invention is also characterized by a high specific surface area. The term "specific surface area (BET)" should be understood to mean the BET specific surface area determined by nitrogen adsorption (BET: Brunauer - Emmett - Teller). This technique is well known to the person skilled in the art (see, for example, JACS 1938, 60 , 309). The specific surface area can be obtained according to standard ASTM D3663 - 03 (reapproved in 2015). The specific surface area can be determined by the method disclosed in the examples.

[0061] The BET specific surface area of the mixed oxide can be at least 70 m2 / g, and more particularly at least 75 m 2 / g.

[0062] After calcination in air at 1100 °C for 4 hours, the BET specific surface area of the mixed oxide is at least 25 m 2 / g, and more particularly at least 26 m 2 / g, and more particularly at least 28 m 2 / g, and even more particularly at least 30 m 2 / g. This specific surface area can be up to 40 m 2 / g, and more particularly up to 35 m 2 / g, and even more particularly up to 31 m 2 / g. This specific surface area can be included between 25 and 40 m 2 / g, and more particularly between 26 and 40 m 2 / g, and more particularly between 28 and 40 m 2 / g, and even more particularly between 30 and 40 m 2 / g. This specific surface area can also be included between 25 and 31 m 2 / g.

[0063] After calcination in air at 1000 °C for 4 hours, the mixed oxide of the present invention can also exhibit a BET specific surface area of at least 50 m 2 / g, and more particularly at least 55 m 2 / g, and even more particularly at least 60 m 2 / g. This specific surface area can be included between 50 and 70 m 2 / g, and more particularly between 55 and 65 m 2 / g. This specific surface area can be included between 60 and

[0064] The mixed oxides of the present invention are further characterized by an improved reducibility. The method used to characterize the reducibility is temperature-programmed reduction (TPR). This technique for characterizing inorganic oxides is well known to those skilled in the art: see, for example, the chapter "Thermal Methods" by Adrien Mekki-Berrada and Aline Auroux in Characterization of Solid Materials and Heterogeneous Catalysts, Volume 1, Wiley, isbn978-3-527-32687-7; or "Temperature Programmed Reduction and Sulphiding" by F. Kapteijn, J. A. Moulijn, A. Tafaoui in "An Integrated Approach to Homogeneous, Heterogeneous and Industrial Catalysis", Elsevier, 1993, isbn978-0-080-88698-5.

[0065] T max with V H2 is determined by TPR. The determination of T max with V H2 is carried out by measuring the hydrogen consumption of the mixed oxide as a function of temperature (hydrogen consumption vs. T) when the mixed oxide is heated. The hydrogen consumption is measured with a thermal conductivity detector (TCD) when the mixed oxide is heated from 50 °C to 900 °C at a ramp rate of 10 °C / min in a reducing atmosphere composed of Ar (90.0 vol%) and H2 (10.0 vol%). T max is defined as the temperature at which the TCD signal intensity is maximum on the TPR curve.

[0066] Examples of TPR curves are given in Figure 1 and Figure 2 The obtained TPR curves give the TCD signal intensity (y-axis) as a function of the sample temperature (x-axis). In this regard, the original signal of the TCD is negative, so usually the opposite of the original signal is plotted, such that the TPR curve contains at least one peak with a maximum. T max corresponds to the temperature at which hydrogen absorption is maximum (the peak on the TPR curve).

[0067] T max with VH2 The measurement can be carried out using a Micromeritics Autochem 2920 machine.

[0068] After calcination in air at 1100 °C for 4 hours, the mixed oxide exhibits a maximum reduction temperature (T max ) of at most 530 °C, more particularly at most 500 °C. Generally, T max is at least 400 °C, more particularly at least 460 °C, even more particularly at least 490 °C. T max can be included between 460 °C and 530 °C, more particularly between 460 °C and 500 °C, even more particularly between 490 °C and 530 °C. T max can be included between 490 °C and 500 °C. Generally, the mixed oxide of the present invention exhibits a single peak in the range of 50 °C - 550 °C.

[0069] This method also enables the determination of the total hydrogen consumption (or hydrogen uptake) between 200 °C and 800 °C (denoted as V H2 ). V H2 is calculated from the disappearance surface area of the hydrogen signal relative to the baseline. After calcination in air at 1100 °C for 4 hours, the mixed oxide of the present invention can exhibit a total hydrogen consumption of at least 17.0 mL hydrogen per gram of mixed oxide. V H2 can range from 17.0 to 25.0 mL / g. This volume is expressed under normal conditions (20 °C; 1 bar).

[0070] The mixed oxide of the present invention can also be characterized in that after calcination in air at 1000 °C for 4 hours, the total pore volume (TPV) is between 0.20 and 0.40 mL / g, preferably between 0.30 and 0.40 mL / g. This total pore volume is measured by conventional N2 porosimetry. The measurement of TPV can be carried out using a Tristar II 3020 machine. This fully automated machine enables high-quality porosity measurements of solid materials by using N2 adsorption technology.

[0071] The mixed oxide of the present invention can also be characterized by a cubic or tetragonal crystal structure, preferably exhibiting a unique phase. The crystal structure is measured by conventional X-ray diffraction techniques.

[0072] The mixed oxide of the present invention can be prepared by the method disclosed below, which involves chlorides of Zr and Ce, NaOH as the base for precipitation, and the addition of sulfate anions. By this method, a mixed oxide can be obtained that contains low amounts of SO4 2- , Na + and Cl -。The amount of Na in the mixed oxide can be less than 150 ppm, more particularly less than 100 ppm. This amount can be comprised between 10 ppm and 150 ppm, more particularly between 20 ppm and 150 ppm, even more particularly between 20 ppm and 100 ppm.

[0073] The amount of Cl in the mixed oxide can be less than 100 ppm, more particularly less than 50 ppm. This amount can be comprised between 1 ppm and 100 ppm, more particularly between 1 ppm and 50 ppm, even more particularly between 5 ppm and 50 ppm.

[0074] The amount of SO4 2- in the mixed oxide can be less than 200 ppm, more particularly less than 150 ppm, even more particularly less than 100 ppm. This amount can be comprised between 5 ppm and 200 ppm, more particularly between 5 ppm and 150 ppm, even more particularly between 5 ppm and 100 ppm. The amounts of Na, Cl and sulfate are given in ppm by weight and relative to the whole of the mixed oxide.

[0075] The present invention more particularly relates to a mixed oxide consisting of or essentially consisting of a combination of oxides of zirconium, cerium, lanthanum, iron, optionally at least one rare earth element other than cerium and lanthanum, and optionally hafnium, said mixed oxide having the following composition:

[0076] ■ Cerium between 18.0 wt% and 45.0 wt%;

[0077] ■ Lanthanum between 1.0 wt% and 15.0 wt%;

[0078] ■ One or more rare earth elements (RE) other than cerium and lanthanum up to 15.0 wt%;

[0079] ■ Iron between 0.05 wt% and 0.25 wt%, more particularly between 0.05 wt% and 0.20 wt%, even more particularly between 0.05 wt% and 0.15 wt%;

[0080] ■ Hafnium between 0 and 2.5 wt%, more particularly between 0 and 2.0 wt%;

[0081] ■ The remainder being zirconium;

[0082] Exhibits the following properties after calcination in air at 1100 °C for 4 hours:

[0083] ■ At least 25 m 2 / g, more particularly at least 26 m 2 / g, more particularly at least 28 m 2 / g, and even more particularly at least 30 m 2 / g BET specific surface area;

[0084] ■ A maximum reduction temperature (T max ) of at most 530 °C, more particularly at most 500 °C.

[0085] The expression "consisting essentially of" shall be interpreted as allowing the presence of other elements in addition to the mandatory elements, provided that the essential characteristics of the claimed composition are not substantially affected by the presence of said other elements. All previously disclosed technical features and embodiments also apply to the mixed oxide thus disclosed, particularly to the compositions C1, C2 and C3 disclosed above.

[0086] Regarding the use of the mixed oxide according to the invention, this belongs to the field of catalytic control of motor vehicle pollution. The mixed oxide according to the invention can be used to prepare a catalytic converter, which serves to treat the exhaust gases of motor vehicles. The catalytic converter includes a catalytically active coating prepared from the mixed oxide and deposited on a solid support. The function of this coating is to convert certain pollutants in the exhaust gases, particularly carbon monoxide, unburned hydrocarbons and nitrogen oxides, into products less harmful to the environment by means of chemical reactions.

[0087] The chemical reactions involved can be the following chemical reactions:

[0088] 2CO + O2 → 2CO2

[0089] 2NO + 2CO → N2 + 2CO2

[0090] 4C x H y +(4x + y)O2 → 4x CO2 + 2y H2O

[0091] The solid support can be a metal monolith, such as an Fe-Cr alloy, or made of ceramic. The ceramic can be cordierite, silicon carbide, aluminum titanate or mullite. Commonly used solid supports consist of monoliths that are usually cylindrical and contain a large number of small parallel channels with porous walls. This type of support is usually made of cordierite and exhibits a compromise between high specific surface and limited pressure drop.

[0092] A coating commonly referred to as a "washcoat" is deposited on the surface of a solid support. The coating is formed from a composition comprising a mixed oxide mixed with at least one mineral material. The mineral material is selected from the group consisting of: alumina, titanium oxide, cerium oxide, zirconium oxide, silica, spinel, zeolite, silicate, crystalline silicoaluminophosphate, and crystalline aluminum phosphate. The composition may also contain other additives specific to each formulator: H2S scavengers, organic or inorganic modifiers having a promoting effect on coating, colloidal alumina, etc. Thus, the coating contains such a composition. Alumina is a commonly used mineral material, and it is possible that this alumina is optionally doped with, for example, alkaline earth metals such as barium. The coating also contains at least one dispersed PGM, which is more particularly selected from the group consisting of Pt, Rh, or Pd. The amount of PGM is generally between 1 and 400 g, with respect to the amount of the monolith, expressed in ft 3 The noble metal has catalytic activity.

[0093] One method of dispersing PGM and preparing the catalyst involves mixing an aqueous solution of a salt of PGM with an aqueous suspension of a mixed oxide or a mineral material or a mixture formed from a mixed oxide and a mineral material; drying the mixture to remove some or all of the water, and calcining the solid in air. For example, the salt may be a chloride or nitrate of a noble metal (e.g., Rh nitrate as in the examples). Water is removed from the suspension in order to immobilize the noble metal, the solid is dried and calcined in air at a temperature generally between 300 °C and 800 °C. An example of the preparation of the catalyst can be found in Example 1 of US 7,374,729. III The coating is obtained by applying the suspension to the solid support. Thus, the coating exhibits catalytic activity and can act as a pollution control catalyst. The pollution control catalyst can be used to treat the exhaust gas from an internal combustion engine. Finally, the catalytic system of the present invention and the mixed oxide can be used as a NO

[0094] scavenger or even to promote the reduction of NO x in an oxidative environment. x For this reason, the present invention also relates to a method for treating the exhaust gas from an internal combustion engine, characterized in that it uses a catalytic converter comprising a coating as described above.

[0095] A particular advantage of the mixed oxide of the present invention is that the PGM on the catalyst is well-dispersed and uniformly distributed.

[0096] The mixed oxide of the present invention can be prepared by the following method comprising the following steps:

[0097] Method for preparing the mixed oxide of the present invention

[0098] The mixed oxide of the present invention can be prepared by the following method comprising the following steps:

[0099] (a1) An aqueous solution containing sulfate anions (SO4 2- ) , zirconium chloride salt and cerium(III) chloride is introduced into a stirred tank containing an aqueous alkaline solution of sodium hydroxide to form a precipitate;

[0100] (b1) Then, an aqueous solution of iron(III) chloride and optionally a salt of at least one rare earth element (RE) other than cerium and lanthanum is introduced into the stirred tank;

[0101] (c1) The precipitate obtained at the end of step (b1) is separated from the liquid medium and repulped in water to reduce the amount of SO4 2- 、Na + and Cl - ;

[0102] (d1) The precipitate obtained at the end of step (c1) is heated in an aqueous medium;

[0103] (e1) A lanthanum salt is added to the suspension of the precipitate;

[0104] (f1) An organic texturizing agent is added to the mixture obtained at the end of step (e1);

[0105] (g1) The solid material obtained at the end of step (e1) is separated from the liquid medium and calcined in air.

[0106] In step (a1), an aqueous solution containing sulfate anions (SO4 2- ) , zirconium chloride salt and cerium(III) chloride (designated as CZR solution for simplicity) is introduced into a tank containing an aqueous alkaline solution of sodium hydroxide to form a precipitate. The zirconium chloride salt can be ZrOCl2.

[0107] The CZR solution contains between 0.5 and 2.0 moles of sulfate anions (SO4 2- ) per mole of zirconium and cerium elements. This molar ratio of SO4 2- / (Zr + Ce) is preferably in the range of 0.7 - 1.5. The sulfate anions are conveniently provided by adding sulfuric acid.

[0108] The CZR solution can be pre - degassed using an inert gas. This can be carried out by circulating the inert gas above the aqueous solution or by injecting the inert gas into the CZR solution to saturate the CZR solution with the inert gas. The "inert gas" is a gas that does not react with the reactants under the conditions used in the process. The inert gas can be, for example, an oxygen - free atmosphere such as nitrogen or argon. The injection can include bubbling the inert gas into the CZR solution.

[0109] The amount of NaOH in the alkaline solution is such that the pH of the alkaline solution is not lower than 7, and preferably the amount is such that the pH is between 7.0 and 11.0. The amount of NaOH generally causes the alkaline compound to be in molar excess relative to Zr, Ce, and RE. An aqueous solution of about 10% wt NaOH can be conveniently used.

[0110] The reaction in step (a1) is preferably carried out under an inert atmosphere, notably in a closed reactor or in a semi-closed reactor. The contact is generally carried out in a stirred tank reactor. Step (a1) can be carried out at a temperature between 5 °C and 50 °C.

[0111] In step (b1), an aqueous solution of ferric chloride and optionally a salt of at least one rare earth element (RE) other than cerium and lanthanum is introduced into the tank. The salt of RE can be, for example, a nitrate or a chloride, such as praseodymium nitrate, neodymium nitrate, yttrium(III) chloride (YCl3) or yttrium nitrate (Y(NO3)3). The aqueous solution can also contain salts of one or several rare earth elements.

[0112] In step (c1), the precipitate obtained at the end of step (b1) is separated from the liquid medium and repulped in water to reduce the amount of SO4 2- 、Na + and Cl - The separation can be carried out, for example, by centrifugation or by decantation using a Nutsche filter. The precipitate can be optionally washed with water. The washing is used to reduce the amount of SO4 2- 、Na + and Cl - ions in the solid precipitate and thus in the final mixed oxide. Additionally, the precipitate can be optionally dried, notably at a temperature between 40 °C and 80 °C.

[0113] In step (d1), the precipitate obtained at the end of step (c1) is heated in an aqueous medium. This heat treatment consists of heating the medium and maintaining it at a temperature generally comprised between 60 °C and 200 °C, and more particularly between 95 °C and 150 °C. The duration of this treatment can be between 1 hour and 4 hours. Examples of heat treatments are disclosed in the examples, by which the suspension is aged for 1 hour at 97 °C. This treatment can also be carried out in an inert atmosphere, the description of which for step (a) applies here equally. Similarly, the treatment can be carried out in a stirred reactor. After the heat treatment, the solid material can be washed with water. This washing can be carried out in various ways with or without solid / liquid separation. It can thus be carried out by separating the solid particles from the liquid phase, for example by frontal filtration, sedimentation or centrifugation. The resulting solid is then resuspended in the aqueous phase. The method can also be carried out by tangential filtration. If necessary, this washing can be optionally repeated, for example until a given conductivity of the suspension is obtained, whereby this conductivity measures the amount of impurities present in this suspension.

[0114] In step (e1), a lanthanum salt, notably in liquid or solid form, can be added to the mixture obtained at the end of step (d1). Lanthanum nitrate can be conveniently used.

[0115] In step (f1), an organic structuring agent is added to the mixture obtained at the end of step (e1). An organic structuring agent means an organic compound capable of controlling the porous structure, notably the mesoporous structure, of the mixed oxide, such as a surfactant. The term "mesoporous structure" refers to an inorganic structure containing pores having a diameter comprised between 2 and 50 nm, described by the term "mesopores". The organic structuring agent can be added in the form of a solution or a suspension. The amount of the organic structuring agent, expressed as a weight percentage of the additive relative to the weight of the mixed oxide obtained after the calcination step (g1), is generally between 5 and 100 wt% and more particularly between 15 and 60 wt%.

[0116] The organic texture agent is preferably selected from the group consisting of: anionic surfactants, nonionic surfactants, polyethylene glycol, carboxylic acids and their salts, and surfactants of the carboxymethylated fatty alcohol ethoxylate type. Regarding such an additive, reference may be made to the teachings of application WO-98 / 45212, and the surfactants described in this document may be used. As anionic surfactants, mention may be made of ethoxycarboxylates, ethoxylated fatty acids, sarcosinates, phosphate esters, sulfates such as alcohol sulfates, alcohol ether sulfates, and sulfated alkanolamide ethoxylates, and sulfonates such as sulfosuccinates, and alkylbenzene or alkylnaphthalene sulfonates. As nonionic surfactants, mention may be made of acetylenic surfactants, alcohol ethoxylates, alkanolamides, amine oxides, ethoxylated alkanolamides, long-chain ethoxylated amines, copolymers of ethylene oxide / propylene oxide, sorbitan derivatives, ethylene glycol, propylene glycol, glycerol, polyglycerol esters and their ethoxylated derivatives, alkylamines, alkylimidazolines, ethoxylated oils, and alkylphenol ethoxylates. In particular, mention may be made of the products sold under the trademarks and Regarding carboxylic acids, aliphatic monocarboxylic acids or dicarboxylic acids may be specifically used, and among these, saturated acids are more particularly used. Fatty acids may also be used and more particularly saturated fatty acids. Thus, mention may be made in particular of formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, and palmitic acid. As dicarboxylic acids, mention may be made of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid.

[0117] Salts of carboxylic acids may also be used, particularly ammonium salts. By way of example, mention may be made more particularly of lauric acid and ammonium laurate.

[0118] Finally, surfactants selected from those of the carboxymethylated fatty alcohol ethoxylate type may also be used. The expression "products of the carboxymethylated fatty alcohol ethoxylate type" is intended to mean products consisting of ethoxylated or propoxylated fatty alcohols containing a CH2-COOH group at the end of the chain.

[0119] These products may correspond to the following formula:

[0120] R1-O-(CR2R3-CR4R5-O) n -CH2-COOH

[0121] Wherein R1 represents a saturated or unsaturated carbon-based chain, typically having a length of up to 22 carbon atoms, preferably at least 12 carbon atoms; R2, R3, R4, and R5 can be the same and can represent hydrogen or alternatively R2 can represent an alkyl group such as a CH3 group and R3, R4, and R5 represent hydrogen; n is a non-zero integer that can be up to 50 and more particularly between 5 and 15 (these values included). It will be noted that the surfactant can consist of products having the above formula (wherein R1 can be saturated or unsaturated respectively) or alternatively, a mixture of products containing both -CH2-CH2-O- and -C(CH3)-CH2-O- groups.

[0122] In step (f1), the solid material obtained at the end of step (e1) is separated from the liquid medium and calcined in air. The separation can be carried out as for step (b1). The solid material can optionally be washed with an aqueous solution, preferably water at an alkaline pH (such as an aqueous solution of ammonia). Additionally, the precipitate can optionally be dried to a suitable extent. The temperature can be between 500 °C and 1200 °C. The choice of temperature can be made as desired, depending on the required values of specific surface area and bulk density. The duration of calcination can be appropriately determined according to the temperature and is preferably between 1 and 20 hours. Calcination can preferably be carried out at a temperature between 750 °C and 900 °C.

[0123] The mixed oxides of the present invention can more particularly be prepared by adapting the formulations provided in Examples 2 and 3 to the nature and amount of the reactants. The present invention also relates to a mixed oxide obtainable by the method disclosed above.

[0124] [Examples]

[0125] Specific surface area (BET)

[0126] The specific surface area is automatically determined on a Flowsorb II 2300. Before any measurement, the sample is carefully degassed to desorb adsorbed substances. For this purpose, the sample can be heated in an oven at 200 °C for 2 hours and then at 300 °C for 15 minutes in the cell of the apparatus.

[0127] N2 porosity determination method

[0128] TPV is determined by N2 porosimetry. Following the manufacturer's recommendations, a Micromeritics Tristar II 3020 apparatus is used. The BJH method with Harkins and Jura isotherms is used.

[0129] TPR

[0130] The reducibility of the mixed oxide or catalyst was determined by measuring the hydrogen consumption. The hydrogen consumption was measured with a thermal conductivity detector (TCD) while the sample was heated from 50 °C to 900 °C at a ramp of 10 °C / min in a reducing atmosphere consisting of Ar (90.0 vol%) and H2 (10.0 vol%). The measurement was carried out using a Micromeritics Autochem 2920 machine. The hydrogen uptake (V H2 ) was calculated from the disappearance area of the hydrogen signal (from the TCD) relative to the baseline. V H2 was determined at temperatures between 200 °C and 800 °C. The baseline for TPR corresponded to the line of the equation y = y0, where y0 is the signal intensity at 50 °C.

[0131] Preparation of the catalyst containing Rh (rhodium content: 0.1 wt%)

[0132] The catalyst was prepared by a method comprising the following steps: wet impregnating the mixed oxide with an aqueous solution of rhodium nitrate; drying to remove part or all of the water and calcining in air at 500 °C for 4 h. Catalysts 1 and 2 corresponded to the impregnation of the mixed oxides of Example 1 (comparative, without iron) and 2 (present invention), respectively.

[0133] Then, the catalyst was aged for 6 h at 1000 °C in the following atmosphere, which was alternately:

[0134] - Atmosphere A1 consisting of 2.7 vol% O2 / 10.0 vol% H2O / balance N2, and applied for 90 s; then

[0135] - Atmosphere A2 consisting of 2.7 vol% CO / 10.0 vol% H2O / balance N2, and applied again for 90 s;

[0136] - The cycle of alternating atmospheres A1 - A2 was repeated for the entire 6 h of aging.

[0137] Comparative Example 1: Mixed oxide prepared by a method not involving FeCl3

[0138] This example aimed to prepare a composition based on cerium, zirconium, lanthanum, and yttrium, having the following corresponding oxide ratios: 40 wt%, 50 wt%, 5 wt%, 5 wt%. The preparation was carried out in a reactor of approximately 300 liters equipped with a stirrer with inclined blades.

[0139] First, an aqueous solution was prepared by mixing 42.8 L of deionized water (DIW) and 16.71 L of an aqueous CeCl3 solution ([Ce] = 1.53 mol / L, d 1.33), and 15.43 kg of an aqueous ZrOCl2 solution (36.2 wt% ZrO2) was added thereto. 37.25 L of an aqueous H2SO4 solution (8.77 wt%; density 1.05) was added to this solution.

[0140] After adding sulfuric acid, the solution was continuously mixed for 2 hours. Precipitation was initiated by transferring the obtained aqueous solution to a precipitation tank pre-filled with 100 L of an aqueous NaOH solution (10.8% wt; density 1.099) within 50 minutes. During precipitation, the stirring speed was 220 rpm.

[0141] An aqueous yttrium chloride solution of 1.7 mol / L necessary for the target ratio of 5% Y2O3 in the final oxide was quickly introduced into the precipitation tank.

[0142] The slurry was washed with water by filtration and repulping in water to reduce the amounts of SO4 2- , Na + and Cl - (each ion less than 200 ppm). After repulping at 100 g solid / L in water, the slurry was aged at 97 °C for 1 hour.

[0143] After aging, an aqueous lanthanum nitrate solution of 2.0 mol / L necessary for the target ratio of 5% wt La2O3 in the final oxide was quickly introduced into the reaction mixture.

[0144] Then, 3.63 kg of lauric acid was added under stirring for 1 hour. Then the suspension was filtered, and the obtained filter cake was calcined in air at 800 °C for 3 hours to obtain a mixed oxide.

[0145] The obtained mixed oxide exhibited the following properties:

[0146] BET specific surface area (1000 °C / 4 h) = 61 m 2 / g

[0147] BET specific surface area (1100 °C / 4 h) = 31 m 2 / g

[0148] After calcination in air at 1100 °C for 4 hours: T max = 578 °C

[0149] After calcination in air at 1100 °C for 4 hours: V H2 = 15.2 mL / g

[0150] TPV (1000 °C / 4 h) = 0.24 mL / g

[0151] Example 2: Mixed oxide prepared by the method of the present invention

[0152] This example aims to prepare a composition based on cerium, zirconium, lanthanum, yttrium, and iron using the same equipment as Comparative Example 1, having the following corresponding oxide ratios: 40 wt%, 49.9 wt%, 5 wt%, 5 wt%, 0.1 wt%.

[0153] First, an aqueous solution was prepared by mixing 42.8 L of DIW and 16.71 L of an aqueous CeCl3 solution ([Ce] = 1.53 mol / L, density 1.33), and 15.40 kg of an aqueous ZrOCl2 solution (36.2 wt% ZrO2) was added thereto. 37.25 L of an aqueous H2SO4 solution (8.77 wt%; d 1.05) was added to this solution.

[0154] After adding sulfuric acid, the solution was continuously mixed for 2 hours. Precipitation was initiated by transferring the obtained aqueous solution to a precipitation tank pre-filled with 100 L of an aqueous NaOH solution (10.8% wt; d 1.099) over 50 minutes. During precipitation, the stirring speed was 220 rpm.

[0155] An aqueous solution containing 1.7 mol / L of yttrium chloride and iron(III) chloride, in an amount necessary for the target ratios of 5 wt% Y2O3 and 0.1 wt% Fe2O3 in the final oxide, was rapidly introduced into the settling tank.

[0156] The slurry was washed by filtration and repulping in water to reduce the amounts of SO4 2- , Na + and Cl - (each ion less than 200 ppm). After repulping at 100 g solid / L in water, the slurry was aged at 97 °C for 1 hour.

[0157] After aging, an aqueous solution of lanthanum nitrate containing 2.0 mol / L in an amount necessary for the target ratio of 5 wt% La2O3 in the final oxide was rapidly introduced into the reaction mixture.

[0158] Then, 3.63 kg of lauric acid was added with stirring for 1 hour. Then the suspension was filtered, and the resulting filter cake was calcined in air at 800 °C for 3 hours to obtain a mixed oxide.

[0159] This mixed oxide exhibited the following properties:

[0160] Ratio of Na: 91 ppm; Ratio of Cl: <20 ppm; Ratio of sulfate: <150 ppm

[0161] BET specific surface area (1000 °C / 4 h) = 58 m 2 / g

[0162] BET specific surface area (1100 °C / 4 h) = 26 m 2 / g

[0163] After calcination in air at 1100 °C for 4 hours: T max = 498 °C

[0164] TPV (1000 °C / 4 h) = 0.34 mL / g

[0165] Example 3: Mixed oxide prepared by the method of the present invention

[0166] This example aims to prepare a composition based on cerium, zirconium, lanthanum, and iron using the same equipment as in Comparative Example 1, which has the following corresponding oxide ratios: 30 wt%, 59.9 wt%, 10 wt%, and 0.1 wt%.

[0167] First, an aqueous solution was prepared by mixing 44.6 L of H2O and 12.53 L of an aqueous CeCl3 solution ([Ce] = 1.53 mol / L, density 1.33), and 18.49 kg of an aqueous ZrOCl2 solution (36.2 wt% ZrO2) was added thereto. 38.55 L of an aqueous H2SO4 solution (8.77 wt%; d 1.05) was added to this solution.

[0168] After adding sulfuric acid, the solution was continuously mixed for 2 hours. Precipitation was initiated by transferring the obtained aqueous solution to a precipitation tank pre-filled with 100 L of an aqueous NaOH solution (10.8% wt; d 1.099) within 50 minutes. During precipitation, the stirring speed was 220 rpm.

[0169] An aqueous solution containing 1.7 mol / L of iron(III) chloride, which is the necessary amount for the target ratio of 0.1% Fe2O3 in the final oxide, was quickly introduced into the precipitation tank.

[0170] The slurry was washed by filtration and repulping in water to reduce the amounts of SO4 2- 、Na + and Cl - (each ion less than 200 ppm). After repulping at 100 g solid / L in water, the slurry was aged at 97 °C for 1 hour.

[0171] After aging, an aqueous solution of lanthanum nitrate with a concentration of 2.0 mol / L, which is the necessary amount for the target ratio of 10 wt% La2O3 in the final oxide, was quickly introduced into the reaction mixture.

[0172] Then, 3.63 kg of lauric acid was added under stirring for 1 hour.

[0173] Then the suspension was filtered, and the obtained filter cake was calcined in air at 800 °C for 3 hours to obtain a mixed oxide.

[0174] The mixed oxide exhibits the following properties:

[0175] Proportion of Na: 50 ppm; proportion of Cl: <20 ppm; proportion of sulfate: <150 ppm

[0176] BET specific surface area (1000 °C / 4 h) = 45 m 2 / g

[0177] BET specific surface area (1100 °C / 4 h) = 30 m 2 / g

[0178] After calcination in air at 1100 °C for 4 hours: T max = 516 °C

[0179] After calcination in air at 1100 °C for 4 hours: V H2 = 18.9 mL / g

[0180] TPV (1000 °C / 4 h) = 0.27 mL / g

[0181] As can be seen, compared to the mixed oxide of Comparative Example 1 (T max = 578 °C), the mixed oxides of Examples 2 and 3 exhibit lower T max (respectively T max = 498 °C and 516 °C). Also see Figure 1 and 2 the dashed lines on. For the mixed oxide of the present invention, T max ≤ 530 °C, more particularly T max ≤ 500 °C.

[0182] Example 4: Aging of the catalyst

[0183] Catalysts 1 and 2 are aged under severe conditions (1000 °C; lean / rich conditions for 6 hours). As can be seen from the solid curves in Figure 1 and Figure 2 the presence of Rh on the catalyst also results in lower T max and higher H2 consumption.

[0184] It can also be observed that for catalyst 2 containing iron (= Fe + Rh), the peak of H2 consumption is narrower. This is an obvious characteristic of good dispersion of Rh on the homogeneous catalytic sites of this mixed oxide. This ensures better adsorption of O2 on the catalyst surface, enhancing the catalyst activity through faster and higher oxygen delivery.

[0185] Other examples of the mixed oxide prepared according to the disclosed method are provided in Table I.

[0186] Table I

[0187]

[0188] *Determined after calcination in air at 1100 °C for 4 h

[0189] **The composition is given by weight of oxides (wt%).

Claims

1. A mixed oxide of zirconium, cerium, lanthanum, iron, and optionally at least one rare earth element RE other than cerium and lanthanum, having one of the following compositions C1 - C3: ■ Composition C1 ■ Cerium between 18.0 wt% and 22.0 wt%; ■ Lanthanum between 3.0 wt% and 7.0 wt%; ■ Yttrium between 3.0 wt% and 7.0 wt%; ■ Iron between 0.05 wt% and 0.25 wt% by weight; ■ Optionally, hafnium less than or equal to 2.5 wt%; ■ The balance being zirconium; ■ Composition C2 ■ Cerium between 28.0 wt% and 32.0 wt%; ■ Lanthanum between 3.0 wt% and 7.0 wt%; ■ Yttrium between 3.0 wt% and 7.0 wt%; ■ Iron between 0.05 wt% and 0.25 wt%; ■ Optionally, hafnium less than or equal to 2.5 wt%; ■ The balance being zirconium; ■ Composition C3 ■ Cerium between 38.0 wt% and 42.0 wt%; ■ Lanthanum between 3.0 wt% and 7.0 wt%; ■ Yttrium between 3.0 wt% and 6.0 wt%; ■ Iron between 0.05 wt% and 0.25 wt%; ■ Optionally, hafnium less than or equal to 2.5 wt%; ■ The balance being zirconium; These ratios are given by weight of the oxides relative to the total mixed oxide, The mixed oxide exhibits the following properties after calcination in air at 1100 °C for 4 hours: ■At least 25 m 2 / g BET specific surface area; ■Maximum reduction temperature T of up to 530 °C max .

2. The mixed oxide according to claim 1, wherein, In composition C1, the amount of lanthanum is between 1.0 wt% and 7.0 wt%.

3. The mixed oxide according to claim 2, wherein In composition C1, the amount of lanthanum is between 1.0 wt% and 5.0 wt%.

4. The mixed oxide according to claim 1, characterized in that, In composition C1, the amount of iron is between 0.05 wt% and 0.20 wt%.

5. The mixed oxide according to claim 4, characterized in that, In composition C1, the amount of iron is between 0.05 wt% and 0.15 wt%.

6. The mixed oxide according to claim 1, characterized in that, In composition C2, the amount of lanthanum is between 1.0 wt% and 7.0 wt%.

7. The mixed oxide according to claim 6, wherein, In composition C2, the amount of lanthanum is between 1.0 wt% and 5.0 wt%.

8. The mixed oxide according to claim 1, characterized in that, In composition C2, the amount of iron is between 0.05 wt% and 0.20 wt%.

9. The mixed oxide according to claim 8, characterized in that, In composition C2, the amount of iron is between 0.05 wt% and 0.15 wt%.

10. The mixed oxide according to claim 1, characterized in that, In composition C3, the amount of lanthanum is between 1.0 wt% and 7.0 wt%.

11. The mixed oxide according to claim 10, characterized in that, In composition C3, the amount of lanthanum is between 1.0 wt% and 5.0 wt%.

12. The mixed oxide according to claim 1, wherein In composition C3, the amount of iron is between 0.05 wt% and 0.20 wt%.

13. The mixed oxide according to claim 12, characterized in that, In composition C3, the amount of iron is between 0.05 wt% and 0.15 wt%.

14. The mixed oxide according to claim 1, characterized in that, The mixed oxide exhibits a BET specific surface area of at least 26 m 2 / g after calcination in air at 1100 °C for 4 hours.

15. The mixed oxide according to claim 1, wherein The mixed oxide exhibits a BET specific surface area of at least 28 m 2 / g after calcination in air at 1100 °C for 4 hours.

16. The mixed oxide according to claim 1, characterized in that, The mixed oxide exhibits a BET specific surface area of at least 30 m 2 / g after calcination in air at 1100 °C for 4 hours.

17. The mixed oxide according to claim 1, characterized in that, The mixed oxide exhibits a maximum reduction temperature T of up to 500 °C after calcination in air at 1100 °C for 4 hours max .

18. The mixed oxide according to claim 1, characterized in that, It contains hafnium.

19. The mixed oxide according to claim 1, characterized in that, It contains hafnium, and the ratio of hafnium is less than or equal to 2.0 wt%, this ratio being given by weight of the oxide relative to the total mixed oxide.

20. The mixed oxide according to any one of claims 1 to 19, wherein, The elements Zr, optionally Hf, Ce, La, Fe, and Yb that make up the mixed oxide are present in the mixed oxide as oxides.

21. The mixed oxide according to any one of claims 1 to 19, wherein, The elements Zr, optionally Hf, Ce, La, Fe, and Yb that make up the mixed oxide are present in the mixed oxide as oxides and partly also in the form of hydroxides or hydroxyoxides.

22. The mixed oxide according to claim 1, wherein, The ratio of lanthanum is between 3.0 wt% and 7.0 wt%.

23. The mixed oxide according to any one of claims 1 to 19, wherein, The proportion of iron is between 0.10 wt% and 0.20 wt%.

24. The mixed oxide according to claim 23, wherein the proportion of iron is between 0.10 wt% and 0.15 wt%.

25. The mixed oxide according to any one of claims 1 to 19, wherein, The proportion of iron is higher than 0.10 wt%.

26. The mixed oxide according to any one of claims 1 to 19, characterized in that, The proportion of zirconium is at least 45.0 wt%.

27. The mixed oxide according to claim 26, wherein, The proportion of zirconium is at least 49.0 wt%.

28. The mixed oxide according to claim 27, wherein, The proportion of zirconium is at least 50.0 wt%.

29. The mixed oxide according to claim 28, wherein, The proportion of zirconium is at least 54.0 wt%.

30. The mixed oxide according to claim 29, characterized in that, The proportion of zirconium is at least 55.0 wt%.

31. The mixed oxide according to any one of claims 1 to 19, characterized in that, The amount of Na in the mixed oxide is less than 150 ppm, this amount being by weight and given relative to the whole of the mixed oxide.

32. The mixed oxide according to claim 31, wherein, The amount of Na in the mixed oxide is less than 100 ppm, this amount being by weight and given relative to the whole of the mixed oxide.

33. The mixed oxide according to any one of claims 1 to 19, characterized in that, The amount of Na in the mixed oxide is included between 10 ppm and 150 ppm, this amount being by weight (ppm) and given relative to the whole of the mixed oxide.

34. The mixed oxide according to claim 33, characterized in that, The amount of Na in the mixed oxide is included between 20 ppm and 150 ppm, this amount being by weight (ppm) and given relative to the whole of the mixed oxide.

35. The mixed oxide according to claim 34, characterized in that, The amount of Na in the mixed oxide is included between 20 ppm and 100 ppm, this amount being by weight (ppm) and given relative to the whole of the mixed oxide.

36. The mixed oxide according to any one of claims 1 to 19, characterized in that, The amount of Cl in the mixed oxide is less than 100 ppm, this amount being by weight (ppm) and given relative to the whole of the mixed oxide.

37. The mixed oxide according to claim 36, characterized in that, The amount of Cl in the mixed oxide is less than 50 ppm, this amount being by weight (ppm) and given relative to the whole of the mixed oxide.

38. The mixed oxide according to any one of claims 1 to 19, characterized in that, The amount of Cl in the mixed oxide is included between 1 ppm and 100 ppm, this amount being by weight (ppm) and given relative to the whole of the mixed oxide.

39. The mixed oxide according to claim 38, characterized in that, The amount of Cl in the mixed oxide is included between 1 ppm and 50 ppm, this amount being by weight (ppm) and given relative to the whole of the mixed oxide.

40. The mixed oxide according to claim 39, characterized in that, The amount of Cl in the mixed oxide is included between 5 ppm and 50 ppm, this amount being by weight (ppm) and given relative to the whole of the mixed oxide.

41. The mixed oxide according to any one of claims 1 to 19, characterized in that, The amount of SO4 2- in the mixed oxide is less than 200 ppm, this amount being given by weight and relative to the whole of the mixed oxide.

42. The mixed oxide according to claim 41, characterized in that, The amount of SO4 2- in the mixed oxide is less than 150 ppm, this amount being given by weight and relative to the whole of the mixed oxide.

43. The mixed oxide according to claim 42, characterized in that, The amount of SO4 2- in the mixed oxide is less than 100 ppm, this amount being given by weight and relative to the overall mixed oxide.

44. The mixed oxide according to any one of claims 1 to 19, characterized in that, The amount of SO4 2- in the mixed oxide is between 5 ppm and 200 ppm, this amount being in ppm by weight and given relative to the whole of the mixed oxide.

45. The mixed oxide according to claim 44, characterized in that, The amount of SO4 2- in the mixed oxide is between 5 ppm and 150 ppm, this amount being in ppm by weight and given relative to the whole of the mixed oxide.

46. The mixed oxide according to claim 45, characterized in that, The amount of SO4 2- in the mixed oxide is between 5 ppm and 100 ppm, this amount being in ppm by weight and given relative to the whole of the mixed oxide.

47. The mixed oxide according to any one of claims 1 to 19, which exhibits a BET specific surface area of at least 50 m 2 / g after calcination in air at 1000 °C for 4 hours.

48. The mixed oxide according to claim 47, which exhibits a BET specific surface area of at least 55 m 2 / g after calcination in air at 1000 °C for 4 hours.

49. The mixed oxide according to claim 48 exhibits a BET specific surface area of at least 60 m 2 / g after calcination in air at 1000 °C for 4 hours.

50. The mixed oxide according to any one of claims 1 to 19, characterized in that, T max is between 460 °C and 530 °C.

51. The mixed oxide according to claim 50, characterized in that, T max is between 460 °C and 500 °C.

52. The mixed oxide according to claim 50, characterized in that, T max is between 490 °C and 530 °C.

53. The mixed oxide according to any one of claims 1 to 19, characterized in that, After calcination in air at 1100 °C for 4 hours, the mixed oxide exhibits a total hydrogen consumption of at least 17 mL (V H2 ) / g of mixed oxide, this volume being determined between 200 °C and 800 °C.

54. The mixed oxide according to any one of claims 1 to 19, characterized in that, After calcination in air at 1000 °C for 4 hours, the mixed oxide exhibits a total pore volume (TPV) between 0.20 and 0.40 mL / g, this total pore volume being measured by N2 porosimetry.

55. The mixed oxide according to claim 54, characterized in that, After calcination in air at 1000 °C for 4 hours, the mixed oxide exhibits a total pore volume (TPV) between 0.30 and 0.40 mL / g, this total pore volume being measured by N2 porosimetry.

56. The mixed oxide according to any one of claims 1 to 19 exhibits a specific surface area of at least 70 m 2 / g.

57. The mixed oxide according to claim 56 exhibits a specific surface area of at least 75 m 2 / g.

58. A method for preparing a mixed oxide according to any one of claims 1 to 57, the method comprising the following steps: (a1) An aqueous solution containing sulfate anions (SO4 2- ) and zirconium chloride salt and cerium(III) chloride is introduced into a stirred tank containing an aqueous alkaline solution containing sodium hydroxide to form a precipitate; (b1) Then, an aqueous solution of iron(III) chloride and optionally a salt of at least one rare earth element (RE) other than cerium and lanthanum is introduced into the stirred tank; (c1)Separate the precipitate obtained at the end of step (b1) from the liquid medium and repulp it in water to reduce the amounts of SO4 2- , Na + and Cl - ; (d1) Heating the precipitate obtained at the end of step (c1) in an aqueous medium; (e1) Adding a lanthanum salt to the suspension of the precipitate; (f1) Add an organic texturant to the mixture obtained at the end of step (e1); (g1) Separate the solid material obtained at the end of step (e1) from the liquid medium and calcine it in air.

59. A composition comprising the mixed oxide according to any one of claims 1 to 57 mixed with at least one mineral material.

60. The composition according to claim 59, wherein, The mineral material is selected from the group consisting of: alumina, titanium oxide, cerium oxide, zirconium oxide, silica, spinel, zeolite, silicate, crystalline silicoaluminophosphate and crystalline aluminum phosphate.

61. A catalytic converter for treating motor vehicle exhausts, comprising a catalytically active coating formed from the composition according to claim 59 or 60 and deposited on a solid support.

62. Use of the mixed oxide according to any one of claims 1 to 57 for the preparation of a catalytic converter for treating motor vehicle exhausts.

63. Use of the mixed oxide according to any one of claims 1 to 57 for the preparation of a catalyst for treating motor vehicle exhausts.

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