COMPLEX OXIDE, METHOD FOR PRODUCING SAME, AND EXHAUST GAS PURIFYING CATALYST

Abstract

Disclosed are a composite oxide which is capable of maintaining a large volume of pores even used in a high temperature environment, and which has excellent heat resistance and catalytic activity, as well as a method for producing the composite oxide and a catalyst for exhaust gas purification employing the composite oxide. The composite oxide contains cerium and at least one element selected from aluminum, silicon, or rare earth metals other than cerium and including yttrium, at a mass ratio of 85:15 to 99:1 in terms oxides, and has a property of exhibiting a not less than 0.30 cm.sup.3/g, preferably not less than 0.40 cm.sup.3/g volume of pores with a diameter of not larger than 200 nm, after calcination at 900° C. for 5 hours, and is suitable for a co-catalyst in a catalyst for vehicle exhaust gas purification.

Claims

1. A composite oxide comprising (A) cerium and (B) at least one element selected from the group consisting of aluminum, silicon, and rare earth metals other than cerium, wherein a mass ratio of (A):(B) in the composite oxide is 85:15 to 99:1 in terms oxides, and wherein the composite oxide has a property of exhibiting a not less than 0.30 cm.sup.3/g volume of pores with a diameter of not larger than 200 nm, after calcination at 900° C. for 5 hours.

2. The composite oxide according to claim 1, having a property of exhibiting a not less than 0.40 cm.sup.3/g volume of pores with a diameter of not larger than 200 nm, after calcination at 900° C. for 5 hours.

3. The composite oxide according to claim 1, having a property of exhibiting a not less than 0.50 cm.sup.3/g volume of pores with a diameter of not larger than 200 nm, after calcination at 900° C. for 5 hours.

4. The composite oxide according to claim 1, having a property of exhibiting a not less than 0.32 cm.sup.3/g volume of pores with a diameter of not larger than 200 nm, after calcination at 800° C. for 5 hours.

5. The composite oxide according to claim 1, comprising at least silicon as (B), and having a property of exhibiting a not less than 0.60 cm.sup.3/g volume of pores with a diameter of not larger than 200 nm, after calcination at 900° C. for 5 hours.

6. The composite oxide according to claim 1, comprising at least one element selected from the group consisting of yttrium, lanthanum, praseodymium, and neodymium as (B).

7. A catalyst for exhaust gas purification comprising the composite oxide according to claim 1.

8. The composite oxide according to claim 1, obtained by a method containing the steps of: (e) neutralizing a suspension containing (A) and (B), (f) adding a surfactant to the suspension neutralized in step (e), followed by a retention time of 10 minutes to 6 hours to obtain a precipitate, without subjecting the suspension to washing between step (e) and step (f), and (g) calcining the precipitate.

9. The composite oxide according to claim 8, wherein the suspension used in step (e) is obtained by the steps of: (a) providing a cerium solution not less than 90 mol % of which cerium ions are tetravalent, (b) heating and maintaining the cerium solution obtained from step (a) up to and at not lower than 60° C., (c) adding an oxide precursor of (B) to a cerium suspension obtained through the heating and maintaining, and (d) heating and maintaining the cerium suspension containing the oxide precursor of (B) up to and at not lower than 100° C.

10. The composite oxide according to claim 9, wherein a cerium content of the cerium solution in step (a) is 5 to 80 g/L in terms of CeO.sub.2.

11. The composite oxide according to claim 1, consisting of (A) cerium, (B) at least one element selected from the group consisting of silicon and rare earth metals other than cerium, and (C) oxygen.

12. The composite oxide according to claim 11, consisting of (A) cerium, (B) at least one element selected from the group consisting of silicon, yttrium, lanthanum, praseodymium, and neodymium, and (C) oxygen.

13. The composite oxide according to claim 12, consisting of (A) cerium, (B) at least one element selected from the group consisting of silicon, lanthanum, and praseodymium, and (C) oxygen.

14. The composite oxide according to claim 13, consisting of (A) cerium, (B) silicon, and (C) oxygen.

Description

EXAMPLES

[0064] The present invention will now be explained in more detail with reference to Examples and Comparative Examples, which are not intended to limit the present invention.

Example 1

[0065] This example relates to a composite oxide of cerium oxide and lanthanum oxide at a mass ratio of 90:10.

[0066] 50 g of a ceric nitrate solution in terms of CeO.sub.2 containing not less than 90 mol % tetravalent cerium ions was measured out, and adjusted to a total amount of 1 L with pure water. The obtained solution was heated to 100° C., maintained at this temperature for 30 minutes, and allowed to cool down to the room temperature, to thereby obtain a cerium suspension.

[0067] After the mother liquor was removed from the cerium suspension thus obtained, 20.8 ml of a lanthanum nitrate solution (5.2 g in terms of La.sub.2O.sub.3) was added, and the total volume was adjusted to 1 L with pure water.

[0068] Then the cerium suspension containing a precursor of lanthanum oxide was maintained at 120° C. for 2 hours, allowed to cool, and neutralized to pH 8.5 with aqueous ammonia.

[0069] To a slurry resulting from the neutralization, an ammonium laurate solution prepared by dissolving 10.4 g of lauric acid in 1.2% aqueous ammonia was added, and stirred for 30 minutes. The obtained slurry was subjected to solid-liquid separation through a Nutsche filter to obtain a filter cake. The cake was calcined in the air at 300° C. for 10 hours to obtain composite oxide powder mainly composed of cerium oxide with 10% by mass of lanthanum oxide.

[0070] For determination of its properties, the obtained composite oxide powder was calcined in the air at 800° C. for 5 hours or at 900° C. for 5 hours, and then subjected to measurement of the volume of pores with a diameter of not larger than 200 nm, by means of mercury porosimetry. The results are shown in Table 1.

Example 2

[0071] This example relates to a composite oxide of cerium oxide and lanthanum oxide at a mass ratio of 85:15.

[0072] Composite oxide powder mainly composed of cerium oxide with 15% by mass of lanthanum oxide was prepared in the same way as in Example 1, except that the amount of the lanthanum nitrate solution was 33.2 ml (8.3 g in terms of La.sub.2O.sub.3). The properties of the composite oxide powder thus obtained were evaluated in the same way as in Example 1. The results are shown in Table 1.

Example 3

[0073] This example relates to a composite oxide of cerium oxide and praseodymium oxide at a mass ratio of 90:10.

[0074] Composite oxide powder mainly composed of cerium oxide with 10% by mass of praseodymium oxide was prepared in the same way as in Example 1, except that the lanthanum nitrate solution was replaced with 20.5 ml of a praseodymium nitrate solution (5.2 g in terms of Pr.sub.6O.sub.11). The properties of the composite oxide powder thus obtained were evaluated in the same way as in Example 1. The results are shown in Table 1.

Example 4

[0075] This example relates to a composite oxide of cerium oxide, lanthanum oxide, and praseodymium oxide at a mass ratio of 90:5:5.

[0076] Composite oxide powder mainly composed of cerium oxide with 5% by mass each of lanthanum oxide and praseodymium oxide was prepared in the same way as in Example 1, except that the amount of the lanthanum nitrate solution was 10.4 ml (2.6 g in terms of La.sub.2O.sub.3), and 10.3 ml of a praseodymium nitrate solution (2.6 g in terms of Pr.sub.6O.sub.11) was added at the same time. The properties of the composite oxide powder thus obtained were evaluated in the same way as in Example 1. The results are shown in Table 1.

Example 5

[0077] This example relates to a composite oxide of cerium oxide and neodymium oxide at a mass ratio of 90:10.

[0078] Composite oxide powder mainly composed of cerium oxide with 10% by mass of neodymium oxide was prepared in the same way as in Example 1, except that the lanthanum nitrate solution was replaced with 23.5 ml of a neodymium nitrate solution (5.2 g in terms of Nd.sub.2O.sub.3). For determination of its properties, the composite oxide powder thus obtained was subjected to the evaluation of the volume of pores with a diameter of not larger than 200 nm after calcination at 900° C. for 5 hours in the same way as in Example 1. The results are shown in Table 1.

Example 6

[0079] This example relates to a composite oxide of cerium oxide and yttrium oxide at a mass ratio of 90:10.

[0080] Composite oxide powder mainly composed of cerium oxide with 10% by mass of yttrium oxide was prepared in the same way as in Example 1, except that the lanthanum nitrate solution was replaced with 22.9 ml of a yttrium nitrate solution (5.2 g in terms of Y.sub.2O.sub.3). For determination of its properties, the composite oxide powder thus obtained was subjected to the evaluation of the volume of pores with a diameter of not larger than 200 nm after calcination at 900° C. for 5 hours in the same way as in Example 1. The results are shown in Table 1.

Example 7

[0081] This example relates to a composite oxide of cerium oxide and aluminum oxide at a mass ratio of 90:10.

[0082] Composite oxide powder mainly composed of cerium oxide with 10% by mass of aluminum oxide was prepared in the same way as in Example 1, except that the lanthanum nitrate solution was replaced with 38.2 g of aluminum nitrate nonahydrate (5.2 g in terms of Al.sub.2O.sub.3). For determination of its properties, the composite oxide powder thus obtained was subjected to the evaluation of the volume of pores with a diameter of not larger than 200 nm after calcination at 900° C. for 5 hours in the same way as in Example 1. The results are shown in Table 1.

Example 8

[0083] This example relates to a composite oxide of cerium oxide, lanthanum oxide, praseodymium oxide, and aluminum oxide at a mass ratio of 85:5:5:5.

[0084] Composite oxide powder mainly composed of cerium oxide with 5% by mass each of lanthanum oxide, praseodymium oxide, and aluminum oxide was prepared in the same way as in Example 1, except that the amount of the lanthanum nitrate solution was 11.2 ml (2.8 g in terms of La.sub.2O.sub.3), and 11.1 ml of a praseodymium nitrate solution (2.8 g in terms of Pr.sub.6O.sub.11) and 20.6 g of aluminum nitrate nonahydrate (2.8 g in terms of Al.sub.2O.sub.3) were added at the same time. For determination of its properties, the composite oxide powder thus obtained was subjected to the evaluation of the volume of pores with a diameter of not larger than 200 nm after calcination at 900° C. for 5 hours in the same way as in Example 1. The results are shown in Table 1.

Example 9

[0085] This example relates to a composite oxide of cerium oxide and silicon oxide at a mass ratio of 90:10.

[0086] Composite oxide powder mainly composed of cerium oxide with 10% by mass of silicon oxide was prepared in the same way as in Example 1, except that the lanthanum nitrate solution was replaced with 25.4 g of colloidal silica (5.2 g in terms of SiO.sub.2). For determination of its properties, the composite oxide powder thus obtained was subjected to the evaluation of the volume of pores with a diameter of not larger than 200 nm after calcination at 900° C. for 5 hours in the same way as in Example 1. The results are shown in Table 1.

Example 10

[0087] This example relates to a composite oxide of cerium oxide, lanthanum oxide, praseodymium oxide, and silicon oxide at a mass ratio of 85:5:5:5.

[0088] Composite oxide powder mainly composed of cerium oxide with 5% by mass each of lanthanum oxide, praseodymium oxide, and silicon oxide was prepared in the same way as in Example 1, except that the amount of the lanthanum nitrate solution was 11.2 ml (2.8 g in terms of La.sub.2O.sub.3), and 11.1 ml of praseodymium nitrate solution (2.8 g in terms of Pr.sub.6O.sub.ii) and 13.7 g of colloidal silica (2.8 g in terms of SiO.sub.2) were added at the same time. For determination of its properties, the composite oxide powder thus obtained was subjected to the evaluation of the volume of pores with a diameter of not larger than 200 nm after calcination at 900° C. for 5 hours in the same way as in Example 1. The results are shown in Table 1.

Comparative Examples 1 to 4

[0089] Various composite oxide powders were prepared in the same way as in Examples 1 to 4, except that the treatment with the ammonium laurate solution was eliminated. That is, these composite oxides were prepared by the production method disclosed in Patent Publication 1. The properties of the composite oxide powders thus obtained were evaluated in the same way as in Example 1. The results are shown in Table 1.

Comparative Example 5

[0090] Composite oxide powder mainly composed of cerium oxide with 10% by mass of lanthanum oxide was prepared in the same way as in Example 1, except that the ammonium laurate solution was added immediately after the addition of the lanthanum nitrate solution. For determination of its properties, the composite oxide powder thus obtained was subjected to the evaluation of the volume of pores with a diameter of not larger than 200 nm after calcination at 900° C. for 5 hours in the same way as in Example 1. The results are shown in Table 1.

Comparative Example 6

[0091] Composite oxide powder mainly composed of cerium oxide with 10% by mass of lanthanum oxide was prepared in the same way as in Example 1, except that the ammonium laurate solution was added immediately before the neutralization with aqueous ammonia. For determination of its properties, the composite oxide powder thus obtained was subjected to the evaluation of the volume of pores with a diameter of not larger than 200 nm after calcination at 900° C. for 5 hours in the same way as in Example 1. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Composition of Ce + Volume of pores (cm.sup.3/g) ME in terms of oxides (≦200 nm) (mass %) 800° C./5 h 900° C./5 h Example 1 Ce/La = 90/10 0.64 0.53 Example 2 Ce/La = 85/15 0.36 0.32 Example 3 Ce/Pr = 90/10 0.41 0.36 Example 4 Ce/La/Pr = 90/5/5 0.50 0.44 Example 5 Ce/Nd = 90/10 — 0.33 Example 6 Ce/Y = 90/10 — 0.31 Example 7 Ce/Al = 90/10 — 0.38 Example 8 Ce/La/Pr/Al = 85/5/5/5 — 0.35 Example 9 Ce/Si = 90/10 — 0.68 Example 10 Ce/La/Pr/Si = 85/5/5/5 — 0.70 Comp. Ex. 1 Ce/La = 90/10 0.22 0.21 Comp. Ex. 2 Ce/La = 85/15 0.21 0.22 Comp. Ex. 3 Ce/Pr = 90/10 0.23 0.23 Comp. Ex. 4 Ce/La/Pr = 90/5/5 0.26 0.25 Comp. Ex. 5 Ce/La = 90/10 — 0.15 Comp. Ex. 6 Ce/La = 90/10 — 0.21 ME stands for one or more elements selected from aluminum, silicon, and rare earth metals other than cerium and including yttrium.

[0092] As clearly seen from the results in Table 1, the composite oxides of Examples prepared by the method of the present invention exhibited larger volumes of pores compared to the composite oxides of Comparative Examples 1 to 4 prepared by the method disclosed in Patent Publication 1, after calcination under the same conditions. It is assumed that, in Comparative Examples 1 to 4, during the course of calcining the filter cake to obtain a composite oxide, evaporation of moisture present at the interface of the particles in the precipitate induced aggregation of the particles, and sufficient volume of pores could not be achieved. In contrast, in the composite oxides of Examples prepared by the method of the present invention, the surfactant was adsorbed uniformly on the surface of the particles in the precipitate to hydrophobize the particle surface, which prevented aggregation of the particles caused by the moisture evaporation during calcining. As a result, the composite oxides of Examples were able to maintain, even after the calcination at high temperature, large volumes of pores which cannot be achieved by the composite oxides disclosed in Patent Publication 1.