Coated Composites of Al2O3-CeO2/ZrO2 and a Method for Their Production

Abstract

The present invention relates to a metal oxide coated composite comprising a core consisting of a mixture of a La stabilized Al.sub.2O.sub.3 phase and an Ce/Zr/RE.sub.2O.sub.3 mixed oxide phase, the core having a specific crystallinity, specific pore volume and a specific pore size distribution, and a method for the production of the metal oxide coated composite.

Claims

1. A coated Al/Ce/Zr composite comprising a calcined Al/Ce/Zr core, the core consisting of two phases, a La stabilized Al.sub.2O.sub.3 phase and a Ce/Zr/Re.sub.2O.sub.3 mixed oxide phase, both phases forming a homogeneous mixture, the calcined Al/Ce/Zr core being characterized by having a pore volume above 0.2 ml/g (according to DIN 66133), and a pore size distribution having a maximum between 50 and 200 Å (according to DIN 661333), the core comprising a metal oxide coating wherein the metal oxide coating forms at least 1 to 50 wt, % of the coated Al/Ce/Zr composite and wherein the Al/Ce/Zr core in the coated composite is characterized by an intensity ratio between the characteristic reflection of gamma-alumina at 2θ≈67° and the characteristic reflection of Ce/Zr solid solution at 2θ≈29°, normalized by the Al.sub.2O.sub.3 weight % of equal to or larger than 1.

2. The coated composite of claim 1, wherein the calcined Al/Ce/Zr core in the coated composite has: a) a reflection between 2θ=65° and 69°, and b) a reflection between 2θ=27° and 31°.

3. The coated composite of claim 2, wherein the calcined Al/Ce/Zr core in the coated composite has: a) a reflection between 2θ=66° and 68°, and b) a reflection between 2θ=28° and 30°.

4. The coated composite of claim 1, wherein the metal oxide coating comprises one or more members selected from the group consisting of CeO.sub.2, ZrO.sub.2, mixed oxides of Ceria/Zirconia, and one or more rare earth metal oxide different from Ceria.

5. The coated composite of claim 1, wherein the metal oxide coating comprises CeO.sub.2.

6. The coated composite of claim 5, wherein the metal oxide coating consists of CeO.sub.2.

7. The coated composite of claim 1, wherein the pore volume of the calcined Al/Ce/Zr core is between 0.2 to 1.0 ml/g.

8. The coated composite of claim 7, wherein the pore volume of the calcined Al/Ce/Zr core is between 0.4 to 0.6 ml/g.

9. The coated composite of claim 1, wherein the pore size distribution of the calcined Al/Ce/Zr ore has a maximum between to 70 to 150 Å.

10. The coated composite of claim 9, wherein the pore size distribution of the calcined Al/Ce/Zr core has a maximum between to 80 to 130 Å.

11. The coated composite of claim 1, wherein the calcined Al/Ce/Zr core is obtainable from a boehmite alumina precursor.

12. The coated composite of claim 11, wherein the boehmite alumina precursor has a crystallite size of 4 to 40 nm measured at the (020) reflection.

13. The coated composite of claim 11, wherein the boehmite alumina precursor has a D-value of the (020) reflection of from 6.05 Å to 6.20 Å.

14. The coated composite of claim 13, wherein the boehmite alumina precursor has a D-value of the (020) reflection of 6.11 Å.

15. The coated composite of claim 1, wherein the metal oxide coating forms between 4 to 27 wt. % of the coated Al/Ce/Zr composite.

Description

[0067] The invention will now be further described with reference to the following Figures and non-limiting examples.

[0068] In the Figures

[0069] FIG. 1 represents the comparison of the pore radius distribution curves obtained by mercury intrusion porosimetry measurements of Al/Ce/Zr core B and Al/Ce/Zr core D materials;

[0070] FIG. 2 represents the pore radius distribution curves obtained by mercury intrusion porosimetry measurements of Al/Ce/Zr core C materials having different alumina contents;

[0071] FIG. 3 is an XRD comparing the crystallinity of the Al/Ce/Zr core B of the present invention with that of core D of WO2012/088373 before calcination; and

[0072] FIG. 4 is an XRD comparing the crystallinity of the Al/Ce/Zr core B of the present invention with that of core D of WO2012/088373 after calcination at 700° C. for 5 hours.

[0073] In the figure it is indicated the gamma-alumina reflection at 2θ≈67° and the Ce/Zr solid solution reflection at 2θ≈29°, the intensities of both reflections being used to calculate the normalized I.sub.γ-Al2O3/I.sub.CZ ratio compiled in Table III.

Experimental

[0074] The test used for the La-leaching suppression is included hereunder:

[0075] La-Leaching Test: Experimental Details:

[0076] La-leaching test of the core materials of the present invention without metal oxide surface layer and the core materials of the present invention coated with a metal oxide or mixed metal oxide surface layer were performed by treating the powder in aqueous HNO.sub.3 solution at pH=3. This mixture was stirred for 1 h at room temperature and then it was centrifuged and filtered. The filtered solution was analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the lanthanum % that leaches from the sample (La-leaching %).

[0077] From the La-leaching (%) results it was calculated the La-leaching suppression (%) parameter that means how much the La-leaching % decreases after coating the calcined Al/Ce/Zr core surface with the metal oxide (MO.sub.x). The formula used to carry out this calculation is the following:

[00003]$\mathrm{La}-\mathrm{leaching}\mathrm{suppression}\left(\%\right)\left(\mathrm{hereunder}\mathrm{given}\mathrm{as}a\mathrm{wt}./\mathrm{wt}.\mathrm{relationship}\right)=\frac{\begin{array}{c}\left(\mathrm{La}-\mathrm{leaching}\left(\%\right)\mathrm{of}\mathrm{the}\mathrm{Al}/\mathrm{Ce}/\mathrm{Zr}\mathrm{core}\right)-\\ \left(\mathrm{La}-\mathrm{leaching}\left(\%\right)\mathrm{of}\mathrm{the}x\%{\mathrm{MO}}_x/\mathrm{Al}/\mathrm{Ce}/\mathrm{Zr}\mathrm{core}\right)\end{array}}{\left(\mathrm{La}-\mathrm{leaching}\left(\%\right)\mathrm{of}\mathrm{the}\mathrm{Al}/\mathrm{Ce}/\mathrm{Zr}\mathrm{core}\right)}$

[0078] A higher value of the La-leaching suppression parameter therefore indicates a more effective metal oxide layer formation on the surface of the calcined Al/Ce/Zr core.

[0079] Preparation of Core Materials:

[0080] The preparations of the different Al/Ce/Zr core materials were performed according to prior art and are described in detail hereunder.

[0081] Al/Ce/Zr Core A Preparation:

[0082] The preparation of the Al/Ce/Zr composite core material was performed according to WO 2013/007809 A1.

[0083] Firstly, La-acetate solution was added to a Disperal® HP14 suspension (boehmite) with a Al.sub.2O.sub.3 content of 5 wt. % to obtain a 96% Al.sub.2O.sub.3: 4% La.sub.2O.sub.3 weight ratio. This mixture was stirred for 30 minutes. Secondly, a Ce/Zr/Nd-hydroxides wetcake (composition: CeO.sub.2=44 wt. %; ZrO.sub.2=50 wt. %; Nd.sub.2O.sub.3=6 wt. %) was re-suspended in deionized water and then mixed with an external stirrer (Ultraturrax) for 5 minutes to obtain a suspension. This Ce/Zr/Nd-hydroxides suspension was added under stirring to the previous La-doped boehmite suspension at room temperature and then stirred for 30 minutes. The aqueous suspension obtained was spray dried. The powder obtained was calcined at 800° C. for 1 h to get the final calcined Al/Ce/Zr core material.

[0084] The composition of this Al/Ce/Zr core material checked by ICP was: Al.sub.2O.sub.3=46 wt. %; La.sub.2O.sub.3=2 wt. %; CeO.sub.2=23 wt. %; ZrO.sub.2=26 wt. %; Nd.sub.2O.sub.3=3 wt. %. The specific surface area is 83 m.sup.2/g.

[0085] Al/Ce/Zr Core B Preparation:

[0086] The Al/Ce/Zr core material was prepared according to Example 4 of WO2013/007242 A1.

[0087] Firstly a boehmite suspension with Al.sub.2O.sub.3 content of 5 wt. % was prepared by stirring a commercially available Disperal® HP14/7 (boehmite modified with citric acid) with deionized water and then a solution of ammonia was added up to a pH of 10. This suspension was heated at 90° C. and a metal salts solution containing (NH.sub.4).sub.2Ce(NO.sub.3).sub.6, ZrO(NO.sub.3).sub.2, Nd(NO.sub.3).sub.3 and La(NO.sub.3).sub.3 was added slowly to this suspension. After that ammonia solution was added to keep the pH at 9.0. This mixture was then stirred for 40 minutes at 90° C. Following that the mixture was filtered and the filter residue was washed with deionized water. The filter cake was re-suspended in deionized water using an external stirrer (Ultraturrax) for 10 minutes and then spray dried. The dry powder was calcined at 850° C. for 4 h to obtain the fresh calcined Al/Ce/Zr core material.

[0088] The composition of this Al/Ce/Zr core material checked by ICP was: Al.sub.2O.sub.3=75.6 wt. %; La.sub.2O.sub.3=2.5 wt. %; CeO.sub.2=10.9 wt. %; ZrO.sub.2=10.6 wt. %; Nd.sub.2O.sub.3=0.5 wt. %. The specific surface area is 119 m.sup.2/g.

[0089] Al/Ce/Zr Core C Preparations with Three Different Al.sub.2O.sub.3 Contents:

[0090] The preparation of the Al/Ce/Zr composite core C materials with varying alumina contents was performed according to the method described in WO 2013/007809 A1.

[0091] La-acetate solution was added to a Disperal® HP14 suspension (boehmite) with a Al.sub.2O.sub.3 content of 5 wt. % to obtain a 96% Al.sub.2O.sub.3:4% La.sub.2O.sub.3 weight ratio. This mixture was stirred for 30 minutes. On the other hand, a Ce/Zr/Nd-hydroxides wetcake (composition: CeO.sub.2=28 wt. %; ZrO.sub.2=66.4 wt. %; Nd.sub.2O.sub.3=5.6 wt. %) was re-suspended in deionized water and then mixed with an external stirrer (Ultraturrax) for 5 minutes to obtain a suspension. This Ce/Zr/Nd-hydroxides suspension was added under stirring to the previous La-doped boehmite suspension at room temperature and then stirred for 30 minutes. The aqueous suspension obtained was spray dried. The dry powder was calcined at 850° C. for 4 h to obtain the fresh Al/Ce/Zr core material.

[0092] The compositions of the three different materials were checked by ICP (Table I). The pore volume is increasing with increasing alumina content between 0.23 and 0.83 ml/g, with the pore radius distribution curves (FIG. 2) showing pronounced maxima in the range between 80 and 130 Å.

[0093] Al/Ce/Zr Core D Preparation:

[0094] This Al/Ce/Zr core material was prepared following the same steps of Example 1 from WO 2012/088373 A2.

[0095] Firstly a NaAlO.sub.2 basic solution having a pH of 13 was placed in a flask under stirring and heated at 48° C. To this solution was added (NH.sub.4).sub.2Ce(NO.sub.3).sub.6, ZrO(NO.sub.3).sub.2, Nd(NO.sub.3).sub.3 and La(NO.sub.3).sub.3 dropwise and after that a HNO.sub.3 solution was added to the mixture until reaching pH 8.5. A precipitate formed and the aqueous slurry was stirred 1 h at 48° C. Then the aqueous slurry was filtered and the filter residue obtained was washed with ammonia water of pH 9.5-10. After washing, the filter cake was resuspended in deionized water with PEG-200 solution (1L water: 8.3 ml PEG-200 ratio) using an external stirrer (Ultraturrax) for 30 minutes, then spray dried and the resulting powder was calcined at 700° C. for 5 h to obtain the fresh Al/Ce/Zr core material.

[0096] The composition of this Al/Ce/Zr core material checked by ICP was: Al.sub.2O.sub.3=72 wt. %; La.sub.2O.sub.3=2.8 wt. %; CeO.sub.2=12.6 wt. %; ZrO.sub.2=11.9 wt. %; Nd.sub.2O.sub.3=0.6 wt. %. The specific surface area is 157 m.sup.2/g.

TABLE-US-00001 TABLE I Characterization of Al/Ce/Zr core materials before calcination. Crystal size measured at the D-spacing of the Composition Alumina (020) reflection (020) reflection Designation (wt. % oxide base) precursor phase (nm) (Å) Core A Al46La2 Boehmite 12 6.11 Ce23Zr26Nd3 Core B Al75.6La2.5 Boehmite 14 6.11 Ce10.9Zr10.6Nd0.5 Core D acc. Al72La2.8 Pseudoboehmite <4 6.54 WO2012/088373 A2 Ce12.6Zr11.9Nd0.6 Core C80 Al80La3 Ce5Zr11Nd1 Boehmite 14 6.11 Core C44 Al44.3La1.7 Boehmite 12 6.11 Ce16.1Zr35.2Nd2.7O2 Core C23 Al23La1 Boehmite 12 6.11 Ce21.4Zr50.5Nd4.3

TABLE-US-00002 TABLE II Characterization of calcined Al/Ce/Zr core materials by mercury intrusion porosimetry Pore volume Pore Designation (ml/g) radius (Å) Core A 0.57  98 Core B 0.83 128 Core D acc. 0.35 n.a. WO2012/088373 A2 Core C80 0.83  98 Core C44 0.45 105 Core C23 0.23  86

TABLE-US-00003 TABLE III I.sub.γ-Al2O3/I.sub.CZ ratio comparison of Al/Ce/Zr core B and core D after 700° C.-5 h calcination. Intensity γ-AL.sub.2O.sub.3 Intensity CZ Normal- reflection at reflection at ized Al.sub.2O.sub.3 2θ = 67° 2θ = 29° I.sub.γ-Al2O3/I.sub.CZ I.sub.γ-Al2O3/ Designation wt. % (from FIG. 4) (from FIG. 4) ratio.sup.*1 I.sub.CZ ratio.sup.*2 Core B 75.6 0.8 1 0.80 1.06 Core D acc. 72 0.56 1 0.56 0.78 WO2012/ 088373 A2 .sup.*1I.sub.γ-Al2O3/I.sub.CZ ratio: relative intensities of γ-AL.sub.2O.sub.3 reflection at 2θ = 67° with regard to the Ce/Zr solid solution reflection at 2θ = 29°. .sup.*2Normalized I.sub.γ-Al2O3/I.sub.CZ ratio: [(I.sub.γ-Al2O3/I.sub.CZ)/(Al.sub.2O.sub.3 weight %)] * 100

[0097] Table I summarizes the composition, the alumina precursor phase, the crystal size of the alumina precursor measured at the (020) reflection and a (020) D-value of the (020) reflection of the different Al/Ce/Zr core materials before calcination.

[0098] Table II summarizes the pore volume and pore radius of the different calcined Al/Ce/Zr core materials.

[0099] In order to further evidence the differences in crystallinity of Al/Ce/Zr cores provided herein and the Al/Ce/Zr core D according to WO 2012/088373 A2, the relative intensities of gamma-alumina reflection at 2θ≈67° with regard to the Ce/Zr solid solution reflection at 2θ≈29° after calcination of the cores at 700° C. for 5 hours have been analysed. Table III includes this I.sub.γ-Al2O3/I.sub.CZ ratio and the normalization of this ratio by the Al.sub.2O.sub.3 weight % of the Al/Ce/Zr core, as the intensity of these reflections depend on the Al.sub.2O.sub.3 content of the Al/Ce/Zr material.

[0100] From Table III a higher I.sub.γ-Al2O3/I.sub.CZ normalized ratio for the Al/Ce/Zr core B with regard to the Al/Ce/Zr core D is shown, being this normalized I.sub.γ-Al2O3/I.sub.CZ ratio larger than 1 for the Al/Ce/Zr cores according to the present invention.

[0101] Furthermore, the crystallinity of Al/Ce/Zr Core B was compared with the crystallinity of Al/Ce/Zr core D as per FIGS. 3 and 4. From the FIG. 3 it is clear that the pseudoboehmite core D shows a poor crystallinity when compared with core B which has a well crystallized boehmite structure before calcination.

[0102] After calcination at 700° C. for 5 hours the superior crystallinity of Al/Ce/Zr core B compared with Core D is exhibited from the more intensive and pronounced gamma-alumina reflection at 2θ≈67° (FIG. 4). As a result of these differences in crystallinity, the Al/Ce/Zr Core B was able to be better coated than Core D.

TABLE-US-00004 TABLE IV Example Al/Ce/Zr metal oxide wt. % of coated metal oxide # core coated metal oxide precursor 1 A CeO.sub.2 4, 8, 17, 27 Ce-nitrate 2 A CeO.sub.2 17 Ce-acetate 3 CeO.sub.2 4, 8, 16 Ce-citrate complex 4 A CeO.sub.2 1, 4, 10, 17 Ce-EDTA complex 5 A CeO.sub.2 46 Ce-acetate 6 A ZrO.sub.2  9 Zr-acetate 7 (CeZrNd)O.sub.2 39 Ce, Zr, Nd- acetates 8 B CeO.sub.2 17 (NH.sub.4).sub.2Ce(NO.sub.3).sub.6 comp. D CeO.sub.2 17 (NH.sub.4).sub.2Ce(NO.sub.3).sub.6 Ex. 1

[0103] Example 1—Incipient Wetness Impregnation (IWI) Using Ce(NO.sub.3).sub.3

[0104] An aqueous solution of Ce(NO.sub.3).sub.3 was added under continuous mixing to the Al/Ce/Zr core A material until the point of incipient wetness was reached, i.e. the pore volume of the Al/Ce/Zr core material is completely filed with solution.

[0105] Four samples were prepared following this procedure having 4, 8, 17 and 27 wt. % CeO.sub.2 impregnated onto the Al/Ce/Zr core material (as verified by ICP analysis) by adjusting the concentration of the Ce(NO.sub.3).sub.3 solution. All samples were dried at 120° C. overnight and calcined at 550° C. for 3 h.

[0106] La-leaching suppression (%) results are included in Table V hereunder:

TABLE-US-00005 TABLE V La leaching Sample suppression (%)  4 wt. % CeO.sub.2/Al/Ce/Zr 23 core A  8 wt. % CeO.sub.2/Al/Ce/Zr 26 core A 17 wt. % CeO.sub.2/Al/Ce/Zr 37 core A 27 wt. % CeO.sub.2/Al/Ce/Zr 64 core A

[0107] The results in Table V shows that a progressive increase of the La-leaching suppression (%) with increasing amount of impregnated CeO.sub.2 on the surface of the Al/Ce/Zr core is observed. This La-leaching suppression is used as a prove for the existence of an uniform CeO.sub.2 surface layer on the Al/Ce/Zr core material which reduces the Al and La contact to aqueous phase.

[0108] Example 2—Equilibrium Deposition Filtration (EDF) Using Ce-acetate

[0109] The Al/Ce/Zr core A material was re-suspended in the required volume of a Ce-acetate aqueous solution with a concentration of 1 wt. % CeO.sub.2. To the resulting suspension under stirring was added ammonia solution to reach pH 9.0. Then the mixture was heated at 50° C. for 3 h under stirring. After that the sample was filtered, dried at 120° C. overnight and calcined at 550° C. for 3 h. The ICP analysis of the final material indicated a CeO.sub.2 incorporation of 17 wt. % onto the Al/Ce/Zr core material.

[0110] The above described Al/Ce/Zr core A coated with a 17 wt. % CeO.sub.2 shows a La-leaching suppression result of 81%, indicating an effective coating.

[0111] Example 3—Wet Impregnation (WI) Using a Ce-citrate Complex

[0112] The ammonium citrate dibasic salt was dissolved in deionized water and the pH was adjusted to 10 with the addition of ammonia solution. To this citrate solution was incorporated drop-wise a Ce-acetate solution using a molar ratio citrate:CeO.sub.2 of 1:1 in order to prepare the Ce-citrate complex. The complex was aged for 2 h at room temperature. Then, the Al/Ce/Zr core A material was added to this solution and the obtained suspension was aged for 24 h at room temperature with constant stirring. After that the suspension was dried in a rotary evaporator by applying temperature and vacuum and the dry powder was finally calcined at 550° C. for 3 h.

[0113] Three samples were prepared following this procedure having 4, 8 an 16 wt. % CeO.sub.2 impregnated onto the Al/Ce/Zr core material (as verified by ICP analysis).

[0114] La-leaching suppression (%) results are included in Table VI hereunder:

TABLE-US-00006 TABLE VI La-leaching Sample suppression (%)  4 wt. % CeO.sub.2/Al/Ce/Zr core A 31  8 wt. % CeO.sub.2/Al/Ce/Zr core A 36 16 wt. % CeO.sub.2/Al/Ce/Zr core A 52

[0115] The results in Table VI show that a progressive increase of the La-leaching suppression (%) with increasing amount of impregnated CeO.sub.2 on the surface of the Al/Ce/Zr core is observed.

[0116] Example 4—Wet Impregnation (WI) Using a Ce-EDTA Complex

[0117] Firstly the ethylenediaminetetraacetic acid (EDTA) was dissolved in deionized water after adjusting the pH at 10 with ammonia solution. To this EDTA solution was incorporated drop-wise a Ce-acetate solution using a molar ratio EDTA:CeO.sub.2 of 1:1 in order to prepare the Ce-EDTA complex. The complex was aged for 2 h at room temperature.

[0118] Then, the Al/Ce/Zr core A material was added to this solution and the obtained suspension was aged for 24 h at room temperature with constant stirring. After that the suspension was dried in a rotary evaporator by applying temperature and vacuum and the dry powder was finally calcined at 550° C. for 3 h.

[0119] Four samples were prepared following this procedure having 1, 4, 10 and 17 wt. % CeO.sub.2 impregnated onto the Al/Ce/Zr core material (as verified by ICP analysis).

[0120] La-leaching suppression (%) results are included in Table VII hereunder:

TABLE-US-00007 TABLE VII La leaching Sample suppression (%)  1 wt. % CeO.sub.2/Al/Ce/Zr core A 19  4 wt. % CeO.sub.2/Al/Ce/Zr core A 35 10 wt. % CeO.sub.2/Al/Ce/Zr core 38 A 17 wt. % CeO.sub.2/Al/Ce/Zr core 55 A

[0121] The results in Table VII show that a progressive increase of the La-leaching suppression (%) with increasing amount of impregnated CeO.sub.2 on the surface of the Al/Ce/Zr core is observed.

[0122] Example 5—Wet Impregnation (WI) in Volume Excess Using Ce-acetate

[0123] The Al/Ce/Zr core A material was resuspended in the required volume of a Ce-acetate aqueous solution with a concentration of 6.4 wt. % CeO2 in order to finally incorporate 50 wt. % of CeO.sub.2. This suspension was dried in a rotary evaporator by applying temperature and vacuum and the dry powder was finally calcined at 550° C. for 3 h. The ICP analysis of the final material verified an actual CeO.sub.2 incorporation onto the Al/Ce/Zr core material of 46 wt. %.

[0124] The above described Al/Ce/Zr core A coated with a 46 wt. % CeO.sub.2 shows a La-leaching suppression result of 77%, indicating an effective coating.

[0125] Example 6—Equilibrium Desposition Filtration (EDF) Using Zr-acetate

[0126] The Al/Ce/Zr core A material was re-suspended in the required volume of a Zr-acetate aqueous solution with a concentration of 1 wt. % ZrO.sub.2 in order to incorporate a total amount of 10 wt. % of ZrO.sub.2 onto the Al/Ce/Zr core material. To the resulting suspension under stirring was added ammonia solution to reach pH 9.0. Then the mixture was heated at 50° C. for 3 h under stirring. After that the sample was filtered, dried at 120° C. overnight and calcined at 550° C. for 3 h. The ICP analysis of the final material indicated a ZrO.sub.2 incorporation of 9 wt. % onto the Al/Ce/Zr core material.

[0127] The above described Al/Ce/Zr core A coated with a 9 wt. % ZrO.sub.2 shows a La-leaching suppression result of 46%, indicating an effective coating.

[0128] Example 7—Equilibrium Deposition Filtration (EDF) Ce-, Zr-, Nd-acetate

[0129] The Al/Ce/Zr core A material was re-suspended in the required volume of an aqueous solution containing Ce-acetate, Zr-acetate and Nd-acetate with a total concentration of 1 wt. % M.sub.xO.sub.y (M.sub.xO.sub.y=CeO.sub.2+ZrO.sub.2+Nd.sub.2O.sub.3) in order to incorporate a total amount of 40 wt. % of mixed oxide onto the Al/Ce/Zr core material. To the resulting suspension under stirring was added ammonia solution to reach pH 9.0. Then the mixture was heated at 50° C. for 3 h under stirring. After that the sample was filtered, dried at 120° C. overnight and calcined at 550° C. for 3 h. The ICP analysis of the final material indicated a mixed oxide incorporation of 39 wt. % onto the Al/Ce/Zr core material.

[0130] The above described Al/Ce/Zr core A coated with 39 wt. % mixed oxide shows a La-leaching suppression result of 68%, indicating an effective coating.

[0131] Example 8—Impregnation Using (NH.sub.4).sub.2Ce(NO.sub.3).sub.6 of Core B

[0132] 20 g of Al/Ce/Zr Core B material is impregnated in two steps by adding an aqueous solution of (NH.sub.4).sub.2Ce(NO.sub.3).sub.6. For each impregnation step a solution consisting of 6.9 g (NH.sub.4).sub.2Ce(NO.sub.3).sub.6 salt in water having a total volume of 16.6 ml was used, in order to incorporate around 10 wt. % of CeO.sub.2 in each impregnation step. In between the impregnation steps the powder was dried at 120° C. for 2 h. After the second impregnation the sample was dried at 120° C. for 16 h and calcined at 550° C. for 3 h.

[0133] The ICP analysis confirmed a total amount of 17 wt. % of CeO.sub.2incorporated to the Al/Ce/Zr core B material after the whole impregnation process.

[0134] Comparative Example 1—Impregnation Using (NH.sub.4).sub.2Ce(NO.sub.3).sub.6 of Core D

[0135] 20 g of the Al/Ce/Zr core D material prepared according to WO2012/088373 A2 is impregnated in two steps by adding an aqueous solution at (NH.sub.4).sub.2Ce(NO.sub.3).sub.6. For each impregnation step a solution consisting of 6.9 g (NH.sub.4).sub.2Ce(NO.sub.3).sub.6 salt in water having a total volume of 16.6 ml was used, in order to incorporate around 10 wt. % of CeO.sub.2 in each impregnation step. In between the impregnation steps the powder was dried at 120° C. for 2 h. After the second impregnation the sample was dried at 120° C. for 16 h and calcined at 550° C. for 3 h.

[0136] The ICP analysis confirmed a total amount of 17 wt. % of CeO.sub.2 incorporated on the Al/Ce/Zr core D material after the whole impregnation process.

[0137] La-leaching suppression (%) results are included in Table VIII hereunder:

TABLE-US-00008 TABLE VIII La leaching Sample suppression (%) Example 8 38 17 wt. % CeO.sub.2/Al/Ce/Zr core B Comparative Example 1 11 17 wt. % CeO.sub.2/Al/Ce/Zr core D

[0138] The significantly higher La-leaching suppression value of the coated Al/Ce/Zr composite made in Example 8 as compared to the material made in the Comparative Example 1 indicates an enhanced effectiveness of the cerium oxide surface layer of the material of the present invention. As the impregnation procedure, cerium oxide precursor and the amount of coated metal oxide that are applied in Example 8 and Comparative Example 1 are equal, the findings of Table VIII prove that a high effectiveness of the metal oxide coating can only be achieved by applying an appropriate Al/Ce/Zr core material having a specific alumina precursor having a specific crystallite size, specific pore volume and pore radius distribution.

TABLE-US-00009 TABLE IX Example 8 Comparative Example 1 BET Pore volume BET Pore volume (m.sup.2/g) (ml/g) (m.sup.2/g) (ml/g) 4 h 72 0.53 51 0.19 1000° C. 4 h 57 0.45 29 0.17 1100° C. 4 h  3 0.32 15 0.14 1200° C.

[0139] Table IX shows superior thermal stability of the coated Al/Ce/Zr composites of the present invention compared to prior are material. This is in addition to the enhanced effectiveness of the cerium oxide coating a beneficial property achieved by applying an appropriate Al/Ce/Zr core material having a specific alumina precursor having a specific crystallite size, a specific pore volume and pore radius distribution.

[0140] Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope.