Rare-Earth Phosphate Alumina Composite for Use in Emission Control Catalysts and Method for Making the Same

Abstract

The present invention relates to a composition for use in a catalyst system in emission control systems comprising a transition alumina based material and rare earth phosphates and to a method for making same.

Claims

1. A composition for use as a support in a catalyst system comprising: i) a transition alumina based material; and ii) a rare-earth phosphate, the rare earth phosphate being characterized by having a crystallite size that is lower than 50 nm after calcination at 1000 C. for 3 hours.

2. The composition of claim 1, wherein the transition alumina based material comprises transition alumina derived from boehmite, silica-alumina, doped alumina or mixtures thereof.

3. The composition of claim 1 including at least 50 wt. % of the transition alumina based material.

4. The composition of claim 1, wherein the rare-earth phosphate comprises LaPO.sub.4, YPO.sub.4, NdPO.sub.4 or mixtures thereof.

5. The composition of claim 1 comprising between 3 and 50 wt. % of the rare earth phosphate.

6. The composition of claim 1, wherein the rare earth phosphate has a crystallite size that is lower than 15 nm after calcination at 1000 C. for 3 hours.

7. The composition of claim 1, wherein the rare earth phosphate has a crystallite size that is lower than 10 nm after calcination at 1000 C. for 3 hours.

8. The composition of anyone of claim 1 having a BET specific surface area of at least 50 m.sup.2/g.

9. The composition of claim 1 having a pore volume between 0.2 and 1.2 ml/g.

10. A method to prepare a composition for use as a support in a catalyst system, the method comprising: i) providing a transition alumina rare earth oxide material wherein the transition alumina rare earth oxide material is prepared by a method comprising the following steps: a) preparing a suspension including a transition alumina precursor; b) preparing an aqueous solution including a rare earth salt, wherein the transition alumina precursor includes alumina hydrates of general formulas Al(OH).sub.3 or AlOOH*xH.sub.2O or mixtures thereof; c) combining the suspension with the rare-earth salt solution to form a alumina rare-earth salt mixture; d) drying the alumina rare earth salt mixture to form a dried alumina rare earth salt mixture; e) calcining the dried alumina rare earth salt mixture to form a transition alumina rare earth oxide material; ii) impregnating the transition alumina rare earth oxide material with an aqueous solution including phosphate ions to form an impregnated alumina rare earth oxide material; and iii) calcining the impregnated transition alumina rare earth oxide material.

11. The method of claim 10, wherein the rare earth salt is a rare earth acetate.

12. The method of claim 10 wherein the impregnated transition alumina rare earth oxide material is calcined at a temperature of 600 C. to 1100 C. for 0.5 to 5 hours.

13. The method of claim 10, wherein the composition comprises: i) a transition alumina based material; and ii) a rare-earth phosphate, the rare earth phosphate being characterized by having a crystallite size that is lower than 50 nm after calcination at 1000 C. for 3 hours.

Description

[0054] The invention will now be described with reference to the non-limiting examples and Figures in which:

[0055] FIG. 1 is a powder XRD of the composition obtained in Example 1 compared to Comparative Example 1 showing the difference in crystallinity of LaPO.sub.4;

[0056] FIG. 2 (inventive material) is an SEM of Example 1 and shows homogeneous white spots; and

[0057] FIG. 3 is an SEM of Comparative Example 1 and shows white spots in a grey matrix, which means that there are RE rich (white area) and Al rich domains (grey area).

EXAMPLES

[0058] The crystallite size is determined by the Scherrer method as described above.

[0059] The Surface area is measured by BET and the pore volume by N.sub.2 adsorption as described above.

Experiments

Example 1

[0060] A transition alumina rare earth oxide material made of 20 wt. % lanthanum oxide containing transition alumina having a specific surface area (BET) of 130 m.sup.2/g and a pore volume of 0.97 ml/g was impregnated with an aqueous solution of phosphoric acid (14.4 wt. % H.sub.3PO.sub.4). The product was dried at 120 C. and finally calcined at 1000 C. for 3 hours.

Example 2

[0061] A transition alumina, rare earth oxide material made of 20 wt. % yttrium oxide containing transition alumina having a specific surface area (BET) of 134 m.sup.2/g and a pore volume of 0.98 ml/g was impregnated with an aqueous solution of phosphoric acid (13.2 wt. % H.sub.3PO.sub.4). The product was dried at 120 C. and finally calcined at 1000 C. for 3 hours.

Example 3

[0062] A transition alumina, rare earth oxide material made of 20 wt. % neodymium oxide containing transition alumina having a specific surface area (BET) of 130 m.sup.2/g and a pore volume of 0.97 ml/g was impregnated with an aqueous solution of phosphoric acid (14.4 wt. % H.sub.3PO.sub.4). The product was dried at 120 C. and finally calcined at 1000 C. for 3 hours.

Example 4

[0063] A transition alumina, rare earth oxide material made of 15 wt. % lanthanum oxide containing transition alumina having a specific surface area (BET) of 145 m.sup.2/g and a pore volume of 0.94 ml/g was impregnated with an aqueous solution of phosphoric acid (9.7 wt. % H.sub.3PO.sub.4). The product was dried at 120 C. and finally calcined at 1000 C. for 3 hours.

Comparative Example 1

[0064] LaPO.sub.4 was prepared according to Example 3 from EP 2754489 A1:

[0065] Phosphoric acid solution was added a to Lanthanum nitrate solution in an amount yielding a 1:1 molar ratio of La and P. A pH value of 8 was adjusted by the addition of ammonia solution. The precipitate was separated by filtration and finally calcined at 900 C. for 5 hours.

[0066] The LaPO.sub.4 obtained was combined with alumina. The LaPO.sub.4 powder and a 4 wt. % lanthanum doped alumina having a specific surface area (BET) of 151 m.sup.2/g and a pore volume of 1.02 ml/g were made into a slurry and wet milled. Then the suspension was spray dried and calcined at 1000 C. for 3 hours to obtain the comparative composite.

Comparative Example 2

[0067] CePO.sub.4 was prepared according to Example 6 of GB 1431868 by evaporating (NH.sub.4).sub.2Ce(NO.sub.3).sub.6 on aluminum oxide, using commercially available PURALOX TH100/150, and heating to 400 C. overnight. Then phosphoric acid was added to the cooled mixture. After calcination for 3 h at 1000 C. the comparative product was tested and no CePO.sub.4 was found; only AlPO.sub.4 was found. The specific surface area (BET) of the comparative product was 45 m.sup.2/g.

[0068] The Results are included in Table 1 hereunder:

TABLE-US-00001 TABLE 1 Example Example Example Example Comparative Comparative 1 2 3 4 Example 1 Example 2 Rare-earth phosphate LaPO.sub.4 YPO.sub.4 NdPO.sub.4 LaPO.sub.4 LaPO.sub.4 (CePO.sub.4) Content 26 wt. % 26 wt. % 26 wt. % 18 wt. % 26 wt. % n/a Crystallite* size (nm) 8 10 7 8 64 n/a - no CePO.sub.4 found, only AlPO.sub.4 BET* (m.sup.2/g) 95 106 114 97 83 45 Pore Volume* (ml/g) 0.6 0.84 0.77 0.84 0.64 0.34 Crystallite** size (nm) 11 84 BET** (m.sup.2/g) 59 53 Pore Volume** (ml/g) 0.56 0.37 *as is **after additional calcination for 3 h at 1200 C. (for thermostability)

[0069] FIG. 1 shows the XRD pattern of materials obtained in Example 1 and Comparative Example 1. The difference in crystallinity of LaPO.sub.4 is clearly revealed by the width of the diffraction lines. The values extracted by the Scherrer method are listed in Table 1.

[0070] Further, the SEM cross-section pictures in FIGS. 2 and 3 show the materials obtained in Example 1 (FIG. 2) and Comparative Example 1 (FIG. 3). To be noted is the difference in homogeneity of the 2 samples by the appearance of well-defined white spots corresponding to LaPO.sub.4 rich areas indicating a lower homogeneity.