Process for the production of composites from aluminum oxide and cerium / zirconium mixed oxides

Description

[0001] The present invention relates to a process for producing composites comprising aluminum oxide and cerium / zirconium mixed oxides, hereinafter referred to as Al / Ce / Zr oxide composites. Al / Ce / Zr oxide composites produced in this way exhibit increased thermal stability.

[0002] Al / Ce / Zr oxide composites with embedded catalytically active precious metals are well known and are used, for example, for catalytic exhaust gas aftertreatment, particularly of combustion gases that have left the combustion chamber of vehicles. Such vehicle catalysts usually consist of several components. The carrier is a temperature-stable honeycomb body made of ceramic, usually cordierite or metal foil, which has a large number of thin-walled channels. On top of the carrier is the so-called washcoat. This comprises porous aluminum oxide (Al 2 O 3 ) and oxygen storage components. Catalytically active precious metals are also embedded in the washcoat. In modern exhaust catalysts, these are platinum, rhodium and / or palladium. The ceramic carrier is mounted in a metallic housing using special bearing mats, for example made of high-temperature wool, or less frequently in combination with knitted wire.Washcoats containing Al / Ce / Zr oxide composites are known for exhaust aftertreatment of internal combustion engines, with the cerium / zirconium mixed oxides acting as oxygen storage components. The Al / Ce / Zr oxide composites of this invention are used in the above-mentioned vehicle catalysts.

[0003] WO 2006 / 070201 A2 describes an improved variant for the production of mixed oxides from aluminum oxide, zirconium oxide and optionally at least one representative of CeO 2 , La 2 O 3 , Nd 2 O 3 , Pr 6 O 11 , Sm 2 O 3 , Y 2 O 3 and optionally other rare earth oxides. The production is based on a joint precipitation of the corresponding salts. The production takes place via a joint precipitation of all the oxides involved, starting from a metal salt solution, with the pH being adjusted in the range of 8.5 + / - 1 during the precipitation. The precipitation took place by adding alkali hydroxides, in particular sodium hydroxide solution.

[0004] WO 2008 / 113457 A1 describes the production of Al / Ce / Zr oxide composites based on mixtures of separately produced aluminum oxide and cerium / zirconium mixed oxide.

[0005] US 6306794 B1 discloses a process for producing composites which were not obtained via a boehmite and under hydrothermal aging and accordingly show poorer thermal stability.

[0006] US Pat. No. 5,883,037 addresses the importance of thermal stability in composite materials. The process described therein involves a multi-stage procedure in which Ce, Zr, and possibly Pr salts are first precipitated by increasing the pH, and a precipitate is isolated. The precipitate is brought into contact with alumina while mixing, isolated, and subsequently dried and calcined. The alumina is preferably stabilized by foreign ions from the rare earth group, Ba, Zr, or Si. The Ce / Zr mixed oxides and Ce / Zr / Pr mixed oxides produced by precipitation can optionally be further stabilized, for example, by at least one element from Group VIII, bismuth, and / or another rare earth element. A disadvantage of this production process is the low homogeneity of the resulting material.

[0007] EP 1172139 A1 describes the preparation of homogeneous Al 2 O 3 / CeO 2 / ZrO 2 / Y 2 O 3 / La 2 O 3 mixed oxides via coprecipitation and their thermal stability. In the described process, the Al-Ce-Zr-Y-La hydroxide intermediates resulting from coprecipitation were calcined and thus converted into the oxides.

[0008] WO 2006 / 119549 A1 describes a process in which a solution of metal salts is added to an acidic boehmite suspension to obtain a second suspension. Precipitation occurs by dropwise addition of the second suspension to an alkaline solution. The process of WO 2006 / 119549 A1 leads, as shown by Examples 1 and 2, to the formation of discrete islands of the Ce / Zr / rare earth mixed oxide next to the aluminum oxide. A very similar process is described in Comparative Examples 3, 14, and 15 of US Pat. No. 6,831,036. The stated residual surface areas after calcination at 1000°C for 3 hours are, due to the process, a maximum of 39 m² / g.

[0009] WO 2012 / 67654 A1 describes a process in which Al / Ce / Zr / rare earth oxide composites are produced via a two-stage precipitation process. In the first step, an "aluminum hydrate" and, if necessary, rare earth hydroxide are produced by precipitating aluminum sulfate with sodium aluminate. After re-acidifying the suspension, the Ce / Zr / rare earth component is precipitated by adding the appropriate salt solution to this suspension and raising the pH again. The resulting Al / Ce / Zr / rare earth oxide composites are said to have a surface area (in m 2 / g) after calcination at 1100°C for 5 hours, which is calculated from the formula SA = 0.8235 · [Al] + 11.157. The residual surface area of ​​the materials after calcination at 1200°C for 5 hours is given by the formula SA = 0.3 [Al] + 7. WO 2012 / 67654 A1 is post-published. The associated priority application relates to a different subject matter than that specified above.

[0010] The object of the present invention is to provide improved Al / Ce / Zr / (optionally rare earth) oxide composites that exhibit significantly higher thermal surface stability, particularly at temperatures of 1100°C and above (e.g., for 24 hours or more). Surface stability in this sense is the (largely) preservation of the surface at high temperatures, measured according to BET. At the same time, a maximum degree of homogeneity should be achieved. Homogeneity here means a uniform distribution of the Al 2 O 3 and Ce / Zr / rare earth mixed oxide phases without the formation of discrete islands.

[0011] The object is achieved by a method according to claim 1. Preferred embodiments are the subject of the subclaims and / or described below.

[0012] It was found that the Al / Ce / Zr oxide composites obtained by the process according to the invention, optionally containing other rare earth oxide components, contain at least the Ce / Zr oxide in the form of a solid solution. This can be verified by X-ray powder diffraction. Furthermore, Al 2 O 3 and the Ce-Zr (or rare earth) mixed oxides are present in a completely homogeneous distribution alongside one another, as demonstrated by EDX (energy-dispersive X-ray analysis) and element mapping. No domains for individual metal oxides were detected. The indication of the components Al 2 O 3 and Ce-Zr mixed oxides or Ce-Zr (or rare earth) mixed oxides or Al / Ce / Zr / (or rare earth) oxide composites does not exclude the possibility that other metal oxides are components of the mixed oxide or composite. Preferably, the composites consist exclusively of Al 2 O 3 and Ce-Zr (possibly rare earth) mixed oxide.

[0013] The process described in this invention differs from the prior art described above in that an aqueous, alkaline boehmite suspension (slurry) is used, and precipitation occurs in this suspension in the presence of soluble metal salts to form a Ce-Zr (or rare earth) hydroxide precipitate. The Ce-Zr (or rare earth) hydroxide precipitate (as well as the subsequent solid solution) is homogeneously distributed in the boehmite matrix. The degree of homogeneity and the associated effective separation of the Ce-Zr (or rare earth) mixed oxide crystallites by the aluminum oxide is achieved by a very homogeneous precipitation, in which the boehmite particles do not sediment within the suspension, even in an alkaline environment. The constantly high pH value ensures a uniform precipitation of the Ce / Zr / (possibly rare earth) hydroxides, which means that after calcination they are present in the form of a homogeneous "solid solution".

[0014] The process described here eliminates the use of alkali, especially caustic soda. The removal of alkali or sodium hydroxide from the composite material is essential for the application, and thus eliminating this component represents a significant advantage.

[0015] The method according to the invention comprises in particular the following steps: (a) Providing a suspension comprising boehmite as an alumina precursor and adjusting the pH to 8 to 11.5 or 9 to 10.5, e.g., with an aqueous solution of ammonia. In a preferred embodiment, this is an aqueous suspension of boehmites modified with organic compounds containing at least one carboxyl group and one or more further groups selected from hydroxy (-OH), oxo (O), carboxyl (-COO), and / or amine (-NH) groups, e.g., tartaric acid or citric acid, preferably in weight proportions of 0.1 to 50 wt.%, in particular 3 to 12 wt.%, based on the dry weight of the boehmite. (b) Producing an aqueous metal salt solution comprising metal salts of cerium and zirconium and optionally one or more rare earth elements. All water-soluble salts (e.g., acetates, nitrates, chlorides) are suitable for production.Soluble in this sense means that, upon stirring at the reaction temperature, a stable solution of at least 5 g of salt (based on the oxide form of the metal) in 100 g of water is formed. In a preferred embodiment, metal nitrates are used. In particular, ammonium cerium(IV) nitrate is used as the cerium source. According to another preferred embodiment, cerium(III) nitrate can be used if the resulting metal salt solution is oxidized, e.g., with an aqueous H 2 O 2 solution.(c) bringing the suspension from (a) together with the metal salt solution from (b), preferably at pH values ​​of 6.5 to 11, in particular 8 to 10.5, particularly preferably 8.5 to 10, and independently thereof in particular at temperatures of 5 to 95°C, preferably 80 to 95°C, or exposing the slurry thus obtained to these temperatures, wherein the suspension from (c) is hydrothermally aged in an aqueous environment at at least 90°C for at least 1 h, in particular: (c1) introducing the metal salt solution and dropwise adding the alumina precursor suspension and subsequently adjusting the pH to 6.5 to 11, in particular 8 to 10.5, particularly preferably 8.5 to 10. (c2) introducing the metal salt solution and dropwise adding the alumina precursor suspension and simultaneously adjusting the pH to 6.5 to 11, in particular 8 to 10.5 , particularly preferably 8.5 to 10.(c3) Initially introducing the alumina precursor and simultaneously adding dropwise the metal salt solution and the ammonia solution to maintain a pH of 6.5 to 11, in particular 8 to 10.5, particularly preferably 8.5 to 10. (d) Separating off the aqueous solution and washing the solid from (c) with water. (d1) Optionally, the suspension from (c) is hydrothermally aged (autoclaved), then filtered and the solid washed with deionized water. (d2) Drying the solid from (d), e.g. by (d2.1) drying the solid, e.g. at 120°C for 16 h, under the action of heat. (d2.2) Redispersing the solid from (d or d1) and subsequent spray drying. In a particular embodiment, one or more further soluble compounds are added before spray drying, and in particular only after step (c) or after redispersion. Preferred salts are acetates, e.g.La acetate and / or salts of alkaline earth elements, rare earth elements, zirconium, or silicon are used. (e) Calcining the solid from (d or d1 or d2), e.g., in the temperature range of 550-1200°C, preferably in the range of 600-1000°C, in particular for at least 1 h.

[0016] Nitrogen bases can be used to adjust the pH. These include, for example, ammonia, urea, or urotropine. In particular, the suspension containing boehmite is adjusted to the required pH value.

[0017] The composite may further comprise one or more alkaline earth elements / compounds, rare earth elements / compounds, zirconium and / or silicon, in particular rare earth elements / compounds, these being added preferably before drying, and in particular only after step (c) or even (d) in the form of one or more further soluble compounds.

[0018] According to one embodiment, the suspension from (c) is hydrothermally aged in an aqueous environment, preferably at at least 90°C and for at least 1 h, in particular at at least 120°C and for at least 4 h.

[0019] In particular, water-soluble metal salts, such as acetates, nitrates, and / or chlorides, are used to prepare the metal salt solution. In the process according to the invention, the addition of alkali and / or alkaline earth salts is preferably avoided, with the exception of barium salts, which may be used if desired.

[0020] The Ce / Zr (possibly rare earth) oxide is present in the form of a solid solution in the composite and Al 2 O 3 and the Ce-Zr (possibly rare earth) mixed oxides / solid solution are homogeneously distributed next to each other.

[0021] The Al / Ce / Zr oxide composite preferably comprises 20 to 80 wt.%, preferably 40 to 70 wt.%, aluminum, 5 to 80 wt.%, preferably 5 to 40 wt.%, zirconium, 5 to 80 wt.%, preferably 5 to 40 wt.% cerium, 0 to 12 wt.%, preferably 0.1 to 9 wt.% rare earth metal(s) (RE), calculated as Al 2 O 3 , ZrO 2 , CeO 2 , RE 2 O 3 . The proportion of the further soluble compounds added in step (d2.2) after redispersion is preferably 0.1 - 15 wt.% (calculated as oxide) based on the mass of Al 2 O 3 . Preferred rare earth metals are neodymium, praesodymium, yttrium and / or lanthanum.

[0022] The Al / Ce / Zr oxide composites preferably still have surface areas of at least 20 m 2 / g, preferably at least 40 m 2 / g, even after 4 h and 1200°C.

[0023] The aluminum / cerium / zirconium mixed oxides can be used in vehicle catalysts such as three-way catalysts (TWCs) or in other components such as NOx traps, diesel oxidation catalysts (DOCs), and diesel particulate filters (DPFs). Their structure is described above.

[0024] Boehmites in the sense of this invention are compounds of the general formula AlO(OH) x H 2 O. Boehmites produced by the hydrolysis of an aluminum alkoxide are preferably used, see US Patent 5055019 ("Process for the Production of Boehmitic Aluminas"). According to this process, boehmitic aluminas with a purity of at least 99.95% Al 2 O 3 and defined pore radii in a range between 3 and 100 nm are obtained by salt-free, aqueous, neutral aluminum alkoxide hydrolysis, wherein the alumina suspension obtained from the aluminum alkoxide hydrolysis is aged in an autoclave a) at a steam pressure of 1 to 30 bar corresponding to a temperature of 100 to 235°C, b) for a period of 0.5 to 20 hours and c) with stirring at a peripheral speed of 1.0 to 6.0 m / s.

[0025] According to the invention, aluminum alcoholates are used to produce the boehmitic clays in order to obtain high-purity products. The aluminum alcoholates can be produced, for example, by the Ziegler process, which preferably includes a purification step by filtration. For the production of the aluminum alcoholates, C1 to C24 alcohols or mixtures thereof can be used, for example.

[0026] The boehmites used are characterized, among other things, by their particularly high purity (contents of: SiO 2 < = about 0.01%, Fe 2 O 3 < = about 0.01%, Na 2 O < = about 0.002%, K 2 O < = about 0.002%, TiO 2 < = 0.005%, other elements < = 0.01%). Independently of this, in a further preferred form, boehmites are used which have a pore volume of 0.4 to 1.2 ml / g and / or crystallite sizes of 4 to 40 nm, preferably 4 to 16 nm, measured at the (120) reflection.

[0027] According to a particularly preferred embodiment, the boehmites are modified with organic compounds which have at least one carboxyl group and one or more further groups selected from hydroxyl (-OH), carboxyl (-COO or -COOH) and / or amine (-NH, including -NH 2 ) groups, such as tartaric acid or citric acid, in particular with 2 to 12 C atoms, particularly preferably 4 to 8 C atoms, preferably in weight proportions of 0.1 to 50 wt.%, in particular 5 to 15 wt.%, based on the dry weight of the boehmite. These prevent the agglomeration and sedimentation of the boehmite in alkaline environments. Further suitable substituted carboxylic acids within the meaning of the invention are, for example, 2-hydroxypropionic acid, 2-oxopropanoic acid, hydroxybutanedicarboxylic acid, dihydroxybutanedicarboxylic acid, 2-hydroxypropane-1,2,3-tricarboxylic acid (citric acid), L-aspartic acid, L-serine, glycine, L-leucine, L-tyrosine or L-tryptophan.

[0028] The composites produced according to the invention comprising aluminum oxide and cerium / zirconium (possibly rare earth) mixed oxides further comprise platinum, rhodium and / or palladium when configured as catalysts.

[0029] Based on the present invention, it was further discovered that precipitation in the presence of an alkaline suspension of boehmite modified by the addition of the above polyfunctional organic acids, particularly in combination with the use of ammonium cerium(IV) nitrate as the cerium source, leads to end products with particularly high thermal stability. Surprisingly and independently, this effect is particularly pronounced when the alkaline suspension is added dropwise to the metal salt solution.

[0030] The invention is explained in more detail by the figures. They show: Fig. 1 Particle size distributions of examples A1 and A2 in aqueous suspensions Fig. 2: X-ray powder diffractograms of the material from Example 2 after calcination

[0031] The following test examples show that a) higher residual surface areas are obtained compared to the production methods in EP 1172139 B1 and WO 2012 / 067654 A1, b) high residual surface areas are obtained even after calcination under particularly harsh conditions (1150°C / 36 h, 1200°C / 4 h). c) In Comparative Example 3, surface areas are obtained which are also very high and are in the range of the composites according to the invention which were produced using the process described here (Comparative Example 3 and Example 6). However, the process described here does not require the use of sodium, which represents a significant process-related advantage, since sodium leads to the poisoning of noble metal catalysts. d) In Comparative Example 5, high residual surface areas are also obtained, which are also in the range of the composites produced using the process described here (Comparative Example 5, Examples 7 and 8).

[0032] However, one embodiment of the process described here involves the use of modified boehmite, which enables dispersibility in alkaline media. Thus, agglomeration and sedimentation of the boehmite do not occur, but rather a particularly homogeneous precipitation and distribution of the CeO2 / ZrO2 / (possibly rare earth oxide) component at elevated pH in the presence of finely dispersed boehmite, which is evident from the particle sizes in the aqueous suspension at high pH values. This is demonstrated in Examples A1 and A2.

[0033] Surface area measurements (BET) were performed using a Micromeritics TriStar 3000 in accordance with DIN ISO 9277. X-ray diffractograms were measured using a Panalytical X'Pert Pro MDB diffractometer. Percentages are by weight unless otherwise stated. Particle distribution was determined using a Malvern Mastersizer 2000 with the Hydro-S dispersion unit in water. The measurements were performed according to ISO 13320:2009, with the Fraunhofer method used for evaluation. Comparison example 1 Preparation analogous to Example 27 of EP 1172139 B1 Composition: 61.5% Al 2 O 3 , 21% CeO 2 , 15% ZrO 2 , 2.5% Y 2 O 3

[0034] A mixture consisting of 96.43 g of an aqueous solution of zirconyl nitrate (ZrO 2 content = 7%), 52.5 g of an aqueous solution of cerium(III) nitrate (CeO 2 content = 18%), 6.32 g of an aqueous solution of yttrium nitrate (Y 2 O 3 content = 17.80%) and 205.61 g of aluminum nitrate nonahydrate in crystalline form was mixed with 600 ml of water and stirred until a clear solution was obtained.

[0035] To this solution was added 7.47 g of a 35% H 2 O 2 solution (equivalent to 1.2 times the molar amount of cerium), and the mixture was stirred for approximately 25 minutes. The resulting solution was then adjusted to pH 7 by adding a 24% ammonia solution and stirred for 15 minutes. The resulting mixture was filtered, and the filter residue was washed with deionized water at 60°C. This filter cake was then dried at 120°C for 16 hours. The dried filter cake was then calcined, first at 300°C for 5 hours and then at 700°C for 5 hours.

[0036] The measured surface is shown in Table 1. BET after 300°C / 5 hours + 700°C / 5 hours (starting material): 168 m 2 < / g BET after 950°C / 5 hours: 109 m 2 < / g BET after 1000°C / 4 hours: 84 m 2 < / g BET after 1100°C / 2 hours: 32 m 2 < / g Comparison example 2 Preparation analogous to Example 1 of EP 1172139 B1 Composition: 41% Al 2 O 3 , 30% CeO 2 , 23% ZrO 2 , 2.5% Y 2 O 3 , 3.5% La 2 O 3

[0037] A mixture consisting of 145.93 g of an aqueous solution of zirconyl nitrate (ZrO 2 content = 7%), 72.25 g of an aqueous solution of cerium(III) nitrate (CeO 2 content = 18%),

[0038] 6.07 g of an aqueous solution of yttrium nitrate (Y 2 O 3 content = 17.80%), 10.81 g of an aqueous solution of lanthanum nitrate (La 2 O 3 content = 14.57%) and 138.08 g of aluminum nitrate nonahydrate in crystalline form were mixed with 600 ml of water and stirred until a clear solution was obtained.

[0039] This solution was treated with 10.71 g of a 35% H 2 O 2 solution (equivalent to 1.2 times the molar amount of cerium), and the mixture was stirred for approximately 25 minutes. The resulting solution was then adjusted to pH 7 by adding a 24% ammonia solution and stirred for 15 minutes. The resulting mixture was filtered, and the filter residue was washed with deionized water at 60°C.

[0040] This filter cake was then dried at 120°C for 16 hours. The dried filter cake was then calcined first at 300°C for 5 hours and then at 700°C for 5 hours.

[0041] The measured surface is shown in Table 2. Comparison example 3 Preparation analogous to Example 6 of WO 2006 / 070201 A2. Composition: 51%Al 2 O 3 , 14.2% CeO 2 , 34.8% ZrO 2

[0042] An aluminum nitrate solution was prepared by stirring 112.5 g of aluminum nitrate monohydrate into 1500 ml of water. To this solution were added 14.77 g of a cerium(III) nitrate solution (CeO2 content = 28.85%) and 149.16 g of a zirconyl nitrate solution (ZrO2 content = 7%). This mixed solution was then stirred at room temperature for 15 minutes. By adding 25% sodium hydroxide solution, a pH value of 10 was adjusted and maintained at this value during the precipitation process. 5 g of a 35% H2O2 solution were added and the pH value was readjusted to 10. The resulting suspension was then stirred for 60 minutes. The pH value was then adjusted to 8 by adding 30% nitric acid and the suspension was stirred again for 60 minutes.

[0043] The resulting mixture was filtered off, and the filter residue was washed with deionized water at 60°C. This filter cake was then suspended in 850 ml of deionized water and adjusted to pH 10 by adding 25% sodium hydroxide solution. Autoclaving was then carried out at 120°C for 6 hours. The aged suspension was cooled to room temperature, adjusted to pH 8 by adding nitric acid, and stirred for 30 minutes.

[0044] The suspension was then stirred again at 60°C for one hour, and the liquid was then filtered off. The resulting filter cake was then washed with deionized water at 60°C and subsequently calcined at 850°C for 4 hours. The measured surface area is shown in Table 3. Comparison example 4 Preparation analogous to Example 12 of WO 2012 / 067654 A1. Composition: 50% Al 2 O 3 , 30% CeO 2 , 15% ZrO 2 , 3.5% La 2 O 3 , 1.5% Y 2 O 3

[0045] Solution A was prepared by adding 6.0 g of a solution of lanthanum nitrate (La 2 O 3 content 14.57%) to 53 g of a 24% ammonia solution and 110 g of distilled water.

[0046] Solution B was prepared by combining 22.19 g of zirconyl nitrate (ZrO 2 content = 33.80%), 35.89 g of cerium(III) nitrate (CeO 2 content = 41.80%), 4.21 g of a solution of yttrium nitrate (Y 2 O 3 content = 4.21%), 100 g of distilled water and hydrogen peroxide, the molar ratio H 2 O 2 / CeO 2 being 3.

[0047] Solution C was prepared by dissolving 46.3 g of sodium aluminate in 200 g of distilled water.

[0048] 2 l of distilled water were initially introduced and heated to 65°C. Solution A was added dropwise over a period of 25 minutes, while solution C was added at the same time to maintain the pH at 7.3. After complete addition of solution A, the remainder of solution C was added in full, thus adjusting the pH to 9.8. The resulting suspension was then adjusted to pH 4 with dilute nitric acid. Solution B was then added over a period of 20 minutes. During this time, the pH was maintained at 4 by adding 10% ammonia solution. After complete addition of solution B, the pH was raised to 8.2 by adding concentrated ammonia solution. The suspension was filtered, and the solid was washed with 2 liters of an aqueous solution of ammonium bicarbonate (120 g / 1 H 2 O) heated to 60°C. The resulting surface areas are shown in Table 4. Comparison example 5 Preparation analogous to comparative example 3 of US 6,831,036 or example 7 of WO 2006 / 119549 A1. Composition: 50% Al 2 O 3 , 30% CeO 2 , 15% ZrO 2 , 3.5% La 2 O 3 , 1.5% Y 2 O 3

[0049] 15 g CeO 2 , 7.5 g ZrO 2 , 1.75 g La 2 O 3 and 0.75 g Y 2 O 3 were dissolved in water in the form of their nitrates. 31.53 g DISPERAL HP 14 (boehmite, Al 2 O 3 content = 79.3%) were added to this acidic solution and the resulting suspension was stirred for 30 minutes. 300 g concentrated ammonia solution was diluted with 750 ml water and placed at room temperature. The acidic boehmite / metal nitrate suspension was slowly added dropwise to the ammonia solution and, after the addition was complete, the mixture was stirred for a further 30 minutes. The solid was separated by filtration, washed with 1.5 l water and then dried for 16 hours at 100°C.

[0050] The obtained surfaces are given in Table 4. Example A1 - Preparation of an alkaline boehmite suspension using pure boehmite.

[0051] A suspension with an Al 2 O 3 content of 5% was prepared by stirring DISPERAL HP14 (boehmite) into deionized water at pH 7. Subsequently, the pH was adjusted to 10 by adding a 24% ammonia solution. The particle sizes in the suspension were determined by laser diffraction (Mastersizer): D 10 = 0 , 96 μ m ; D 50 = 5 , 11 μ m ; D 90 = 28 , 34 μm

[0052] The measured particle size distributions are in Fig. 1 shown. Example A2 - Preparation of an alkaline boehmite suspension using a modified boehmite.

[0053] A suspension with an Al 2 O 3 content of 5% was prepared by stirring DISPERAL HP14 / 7 (boehmite modified with citric acid) into deionized water at pH 7. Subsequently, the pH was adjusted to 10 by adding a 24% ammonia solution. The particle sizes in the suspension were determined by laser diffraction (Mastersizer): D 10 = 0 , 09 μ m ; D 50 = 0 , 23 μ m ; D 90 = 0 , 67 μm

[0054] The measured particle size distributions are in Fig. 1 shown. Example 1 (not according to the invention) Composition: 61.5% Al 2 O 3 , 21% CeO 2 , 15% ZrO 2 , 2.5% Y 2 O 3 (according to Comparative Example 1)

[0055] A metal salt solution consisting of 81.4 g of a solution of ammonium cerium(IV) nitrate (CeO 2 content = 12.90%), 103.30 g of a solution of zirconyl nitrate (ZrO 2 content = 7.26%) and 7.0 g of a solution of yttrium nitrate (Y 2 O 3 content = 17.80%) was introduced and heated to 90°C.

[0056] A suspension consisting of 615.0 g of DISPERAL HP14 / 7 (boehmite modified with citric acid) (Al 2 O 3 content = 5%) was prepared by stirring the solid into deionized water and subsequently adding 24% ammonia solution to a pH of 10. This suspension was slowly added dropwise to the metal salt solution and, after the addition was complete, the pH was adjusted to 8.7 by adding 24% ammonia solution. This mixture was then stirred at 90°C for 30 minutes. The mixture was then filtered off and the filter residue was washed with deionized water at 60°C. The filter cake was resuspended in deionized water with stirring and then spray-dried (inlet temperature = 220°C, outlet temperature = 110°C). The dried material was calcined at 850°C for 4 hours. Example 2 (not according to the invention) Composition: 41% Al 2 O 3 , 30% CeO 2 , 23% ZrO 2 , 2.5% Y 2 O 3 , 3.5% La 2 O 3 (according to Comparative Example 2)

[0057] A metal salt solution consisting of 96.9 g of a solution of ammonium cerium(IV) nitrate (CeO 2 content = 12.90%), 131.96 g of a solution of zirconyl nitrate (ZrO 2 content = 7.26%), 10.02 g of a solution of lanthanum nitrate (La 2 O 3 content = 14.57%) and 5.84 g of a solution of yttrium nitrate (Y 2 O 3 content = 17.80%) was introduced and heated to 90°C.

[0058] A suspension consisting of 341.6 g of DISPERAL HP14 / 7 (boehmite modified with citric acid) (Al 2 O 3 content = 5%) was prepared by stirring the solid into deionized water and subsequently adding a 24% ammonia solution to pH 10. Table 1 Measured BET surface areas from Comparative Example 1 and Example 1 after calcination [m 2 < / g]. Comparative example 1 (analogous to EP 1 172 139) Example 1 (according to the invention) 5 h / 300°C + 5 h / 700°C (starting material) 168 126 5 hours / 950 °C 109 95 4 h / 1000 °C 84 89 2 hours / 1100°C 32 70

[0059] This suspension was slowly added dropwise to the metal salt solution, and after the addition was complete, the pH was adjusted to 8.5 by adding 24% ammonia solution. This mixture was then stirred at 90°C for 30 minutes. The mixture was then filtered, and the filter residue was washed with deionized water at 60°C. The filter cake was resuspended in deionized water with stirring and then spray-dried (inlet temperature = 220°C, outlet temperature = 110°C). The dried material was calcined at 850°C for 4 hours.

[0060] In Fig. 2 The X-ray powder diffractograms of the material from Example 2 after calcination are shown. a) after calcination 4h / 850°C b) after calcination 4h / 850°C + 4h 1100°C c) after calcination 4h / 850°C + 24h 1100°C d) Simulated diffractogram of CeO 2 (cubic) e) Simulated diffractogram of ZrO 2 (tetragonal). Example 3 (according to the invention) The composition corresponds exactly to that of comparative example 2 41% Al 2 O 3 , 30% CeO 2 , 23% ZrO 2 , 2.5% Y 2 O 3 , 3.5% La 2 O 3

[0061] 220.4 g of a suspension of PURAL SB (boehmite, Al 2 O 3 content = 9.3%) (pH 9.5) were brought to pH 9.5 with a 24% ammonia solution and then introduced into a reaction vessel. At room temperature, a mixture consisting of 300 g of a solution of cerium acetate (CeO 2 content = 5.0%), 50.3 g of a solution of zirconium acetate (ZrO 2 content = 22.88%), 24.0 g of a solution of lanthanum acetate (La 2 O 3 content = 7.3%), and 31.3 g of a solution of yttrium acetate (Y 2 O 3 content = 4.0%) was slowly added. The pH was kept constant at pH 9.5 by the simultaneous addition of a 24% ammonia solution. The resulting mixture was stirred for 45 minutes. The suspension was then autoclaved at 140°C for 3 hours. The resulting mixture was filtered off, and the solid was washed with deionized water at 60°C. This filter cake was dried in a drying oven for 16 hours and then calcined at 850°C. Example 4 (not according to the invention) Composition: 41% Al 2 O 3 , 30% CeO 2 , 23% ZrO 2 , 2.5% Y 2 O 3 , 3.5% La 2 O 3 (corresponds to comparative example 2)

[0062] A boehmite suspension consisting of 492.0 g of DISPERAL HP14 / 7 (boehmite modified with citric acid) (Al 2 O 3 content = 5%) was prepared by stirring the solid into deionized water and subsequently adding a 24% ammonia solution to pH 10.

[0063] At 90°C, a metal salt solution consisting of 139.53 g of a solution of ammonium cerium(IV) nitrate (CeO 2 content = 12.90%), 190.1 g of a solution of zirconyl nitrate (ZrO 2 content = 7.26%), 14.41 g of a solution of lanthanum nitrate (La 2 O 3 content = 14.57%), and 5.45 g of a solution of yttrium nitrate (Y 2 O 3 content = 27.54%) was slowly added dropwise to this suspension. The pH was kept constant at 9.0 by simultaneous addition of a 24% ammonia solution. This mixture was then stirred at 90°C for 30 minutes. The mixture was then filtered off, and the filter residue was washed with deionized water at 60°C. The filter cake was resuspended in deionized water with stirring and then spray-dried (inlet temperature = 220°C, outlet temperature = 110°C). The dried material was calcined at 850°C for 4 hours. Example 5 Composition: 41% Al 2 O 3 , 30% CeO 2 , 23% ZrO 2 , 2.5% Y 2 O 3 , 3.5% La 2 O 3 corresponds to comparative example 2, but using cerium(III) nitrate + H 2 O 2

[0064] A metal salt solution consisting of 58.34 g of a solution of cerium(III) nitrate (CeO 2 content = 18.00%), 131.96 g of a solution of zirconyl nitrate (ZrO 2 content = 7.26%), 10.02 g of a solution of lanthanum nitrate (La 2 O 3 content = 14.57%) and 5.84 g of a solution of yttrium nitrate (Y 2 O 3 content = 17.80%) was introduced.

[0065] At room temperature, 25.74 g of a 30% H 2 O 2 solution, cooled to 5°C, are added. The resulting suspension is stirred for 10 minutes and then heated to 90°C. A suspension consisting of 341.6 g of DISPERAL HP14 / 7 (boehmite modified with citric acid) (Al 2 O 3 content = 5%) was prepared by stirring the solid into deionized water and subsequently adding a 24% ammonia solution to pH 10.

[0066] This suspension was slowly added dropwise to the metal salt solution, and after the addition was complete, the pH was adjusted to 8.3 by adding 24% ammonia solution. This mixture was then stirred at 90°C for 30 minutes. The mixture was then filtered, and the filter residue was washed with deionized water at 60°C. The filter cake was resuspended in deionized water with stirring and then spray-dried (inlet temperature = 220°C, outlet temperature = 110°C). The dried material was calcined at 850°C for 4 hours. Table 2. Measured surface areas (BET) from Examples 2-6 and Comparative Example 2 after calcination in m 2 < / g. See 2, analogous to EP 1 172 139 Example 2 Example 3 Example 4 Example 5 according to the invention 4 h / 850°C (starting material) 112 98 89 88 85 4 hours / 1100 °C 18 49 34 46 51 24 hours / 1100°C 12 45 34 39 37 36 hours / 1150 °C 20 25 4 hours / 1200°C 16 21 Example 6 (not according to the invention) Composition: 51%Al 2 O 3 , 14.2% CeO 2 , 34.8% ZrO 2 (corresponds to comparative example 3)

[0067] A metal salt solution consisting of 55.0 g of a solution of ammonium cerium(IV) nitrate (CeO 2 content = 12.90%) and 239.7 g of a solution of zirconyl nitrate (ZrO 2 content = 7.26%) was introduced and heated to 90°C.

[0068] A suspension consisting of 510.0 g of DISPERAL HP14 / 7 (boehmite modified with citric acid) (Al 2 O 3 content = 5%) was prepared by stirring the solid into deionized water and subsequently adding a 24% ammonia solution to pH 10.

[0069] This suspension was slowly added dropwise to the metal salt solution, and after the addition was complete, the pH was adjusted to 8.7 by adding 24% ammonia solution. This mixture was then stirred at 90°C for 30 minutes. The mixture was then filtered, and the filter residue was washed with deionized water at 60°C. The filter cake was resuspended in deionized water with stirring and then spray-dried (inlet temperature = 220°C, outlet temperature = 110°C). The dried material was calcined at 850°C for 4 hours.

[0070] The values ​​from comparative example 3 are given in brackets. BET after 850°C / 4 hours (starting material): 97 m 2 / g (107) BET after 1100°C / 2 hours: 62 m 2 / g (47) BET after 1100°C / 24 hours: 36 m 2 / g (35) Table 3. Measured surface areas (BET) of Comparative Example 3 and Example 7 after calcination [m 2 < / g]. Comparative Example 3 (analogous to WO 2006 / 070201) Example 6 (according to the invention) 850°C / 4 hours (starting material) 107 97 2 hours / 1100 °C 47 62 24 hours / 1100°C 35 36 Example 7 (not according to the invention) Composition: 50% Al 2 O 3 , 30% CeO 2 , 15% ZrO 2 , 3.5% La 2 O 3 , 1.5% Y 2 O 3 (corresponds to comparative examples 4 and 5)

[0071] A metal salt solution consisting of 116.3 g of a solution of ammonium cerium(IV) nitrate (CeO 2 content = 12.90%), 103.3 g of a solution of zirconyl nitrate (ZrO 2 content = 7.26%), 12.1 g of a solution of lanthanum nitrate (La 2 O 3 content = 14.50%) and 4.2 g of a solution of yttrium nitrate (Y 2 O 3 content = 17.80%) was introduced and heated to 90°C.

[0072] A suspension consisting of 500g DISPERAL HP14 / 7 (boehmite modified with citric acid) (Al 2 O 3 content = 5%) was prepared by stirring the solid into deionized water and subsequently adding a 24% ammonia solution to pH 10.

[0073] This suspension was slowly added dropwise to the metal salt solution, and after the addition was complete, the pH was adjusted to 8.3 by adding 24% ammonia solution. This mixture was then stirred at 90°C for 30 minutes. The mixture was then filtered, and the filter residue was washed with deionized water at 60°C. The filter cake was dried at 120°C for 16 hours and then calcined at 850°C for 4 hours. Example 8 (not according to the invention) Composition: 50% Al 2 O 3 , 30% CeO 2 , 15% ZrO 2 , 3.5% La 2 O 3 , 1.5% Y 2 O 3 (corresponds to comparative examples 4 and 5)

[0074] A metal salt solution consisting of 116.3 g of a solution of ammonium cerium(IV) nitrate (CeO 2 content = 12.90%), 103.3 g of a solution of zirconyl nitrate (ZrO 2 content = 7.26%), 12.1 g of a solution of lanthanum nitrate (La 2 O 3 content = 14.50%) and 4.2 g of a solution of yttrium nitrate (Y 2 O 3 content = 17.80%) was introduced and heated to 90°C.

[0075] A suspension consisting of 500 g of DISPERAL HP14 / 7 (boehmite modified with citric acid) (Al 2 O 3 content = 5%) was prepared by stirring the solid into deionized water and then adding a 24% ammonia solution to a pH of 10. This suspension was slowly added dropwise to the metal salt solution and, after the addition was complete, the pH was adjusted to 9.0 by adding 24% ammonia solution. This mixture was then stirred at 90°C for 30 minutes. The mixture was then filtered off and the filter residue was washed with deionized water at 60°C. The filter cake was resuspended in deionized water with stirring and then spray-dried (inlet temperature = 220°C, outlet temperature = 110°C). The dried material was calcined at 850°C for 4 hours. Example 9 (not according to the invention) Composition: 70% Al 2 O 3 , 20% CeO 2 , 7% ZrO 2 , 3.0% La 2 O 3

[0076] A boehmite suspension consisting of 420.0 g of DISPERAL HP14 / 7 (boehmite modified with citric acid) (Al 2 O 3 content = 5%) was prepared by stirring the solid into deionized water and subsequently adding a 24% ammonia solution to a pH of 10. At 90°C, a metal salt solution consisting of 46.51 g of a solution of ammonium cerium(IV) nitrate (CeO 2 content = 12.9%), 30.0 g of a solution of zirconyl nitrate (ZrO 2 content = 7.0%) and 6.18 g of a solution of lanthanum nitrate (La 2 O 3 content = 14.57%) was slowly added dropwise to this suspension. The pH was kept constant at 9.0 by simultaneously adding a 24% ammonia solution. This mixture was then stirred at 90°C for 30 minutes. The mixture was then filtered, and the filter cake was washed with deionized water at 60°C. The filter cake was resuspended in deionized water with stirring and then dried at 120°C for 16 hours.The dried material was then calcined at 850°C. Table 4. Measured surface areas (BET) from comparative examples 4 and 5 and examples 8-10 in m 2 < / g. See 4 calculated* Vg1.5 Example 7 Example 8 Example 9 4 h / 850°C (starting material) 130 96 92 96 101 4 hours / 1200°C 17 22 (5 h) 23 23 25 40 Surfaces calculated using the formulas in WO2012 / 067654 A1

Claims

1. A method for producing composites comprising aluminum oxide and cerium / zirconium (optionally rare earth) mixed oxides comprising the following steps: (a) providing a suspension comprising boehmite as the alumina precursor and adjusting the pH to 8 to 11.5; (b) producing an aqueous metal salt solution comprising metal salts of cerium and of zirconium; (c) bringing in contact the suspension of (a) with the metal salt solution from (b) at temperatures of 5 to 95°C or exposing the resulting slurry to these temperatures, wherein the suspension from (c) is hydrothermally aged in an aqueous environment at a temperature of at least 90°C and for at least one hour; (d) isolating the solids from (c) and (e) calcining the solids from (d).

2. The method according to claim 1, wherein the isolation (d) comprises separation of the aqueous solution, washing of the solids from (c) with water and drying the solids.

3. The method according to claim 1 or 2, wherein the isolation (d) comprises the drying and (re-)dispersing of the solids from (c) and the subsequent spray drying.

4. The method according to at least one of the preceding claims, wherein the composite further comprises one or more alkaline earth elements / compounds, rare earth elements / compounds, zirconium and / or silicon, in particular rare earth elements / compounds, wherein these are added before drying and in particular only after step (c) or even (d) in the form of one or more further soluble compounds.

5. The method according to at least one of the preceding claims, wherein bringing in contact comprises: (c1) providing the metal salt solution and dropwise addition of the alumina precursor suspension and then adjustment of the pH to 6.5 to 11, in particular 8 to 10.5, especially preferably 8.5 to 10; (c2) providing the metal salt solution and dropwise addition of the alumina precursor suspension and at the same time adjusting the pH to 6.5 to 11, in particular 8 to 10.5, especially preferably 8.5 to 10 or (c3) providing the alumina precursor suspension and at the same time dropwise addition of the metal salt solution and of the ammonia solution to maintain a pH of 6.5 to 11, in particular 8 to 10.5, especially preferably 8.5 to 10.

6. The method according to at least one of the preceding claims, wherein the suspension of (c) is hydrothermally aged in an aqueous environment at at least 120°C and for at least four hours and / or the suspension from (c) is filtered after being hydrothermally aged and preferably the solid matter is washed using deionised water.

7. The method according to at least one of the preceding claims, wherein water-soluble salts of the metals are used to prepare the metal salt solution, in particular for example acetates, nitrates and / or chlorides.

8. The method according to at least one of the preceding claims, wherein Ce / Zr (optionally rare earth) oxide is present in the form of a solid solution in the composite, and Al2O3 and the Ce / Zr (optionally rare earth) mixed oxides are present homogeneously distributed side by side.

9. The method according to at least one of the preceding claims, wherein the addition of alkali and / or alkaline earth salts is omitted, except for optionally barium salts.

10. The method according to at least one of the preceding claims, wherein the boehmites are provided with organic compounds having at least one carboxyl group (-COO and / or -COOH) and one or more other groups selected from hydroxy(-OH), oxo(-O), carboxy(-COO and / or -COOH) and / or amine(-NH and / or - NH2) groups, in particular with 2 to 12 carbon atoms, especially preferably 4 to 8 carbon atoms, preferably in amount by weight of 0.1% to 50% by weight, in particular 5% to 15% by weight based on the dry weight of the boehmite.

11. The method according to at least one of the preceding claims, wherein the suspension comprising boehmite is adjusted to the pH by a nitrogen base, in particular ammonia, urea and / or urotropin.

12. The method according to at least one of the preceding claims, wherein the mixed oxide / composite composition comprises 20% to 80% by weight aluminum, 5% to 80% by weight zirconium, 5% to 80% by weight cerium and optionally 0% to 12% by weight rare earth metal(s) (RE), calculated as Al2O3, ZrO2, CeO2, RE2O3.

13. The method according to at least one of the preceding claims, wherein the boehmite and / or the boehmite suspension are prepared by hydrolysis of an aluminum alkoxide, preferably with separation of the alcohol.

14. An Al / Ce / Zr oxide composite comprising aluminum oxide and cerium / zirconium mixed (optionally rare earth) oxide in the form of a "solid solution", verifiable by x-ray powder diffraction, wherein a) Al2O3 and the Ce / Zr (optionally rare earth) mixed oxides are present homogeneously distributed side by side, and b) the Al / Ce / Zr oxide composite is obtainable according to at least one of the claims 1 to 13.

15. The Al / Ce / Zr oxide composite according to claim 14 comprising • 20% to 80% by weight, preferably 40% to 70% by weight, aluminum, calculated as Al2O3; • 5% to 80% by weight, preferably 5% to 40% by weight, zirconium, calculated as ZrO2; • 5% to 80% by weight, preferably 5% to 40% by weight, cerium, calculated as CeO2; and • 0% to 12% by weight, preferably 0,1% to 9% by weight, rare earth metal(s) (RE) calculated as RE2O3.

16. The Al / Ce / Zr oxide composite according to claims 14 and 15 having after 4h at 1200°C surface areas of at least 20 m2 / g, preferably 40 m2 / g, measured according to BET.

17. The Al / Ce / Zr oxide composite according to at least one of claims 14 to 16, wherein the Al / Ce / Zr oxide composite is an Al / Ce / Zr rare earth oxide composite comprising as rare earth oxides the oxides of neodymium, praseodymium, yttrium and / or lanthanum.

18. The Al / Ce / Zr oxide composite according to at least one of claims 14 to 17 further comprising platinum, rhodium and / or palladium.