COMPOSITION BASED ON OXIDES OF CERIUM, OF NIOBIUM AND, OPTIONALLY, OF ZIRCONIUM AND USE THEREOF IN CATALYSIS

Abstract

A composition based on cerium and niobium oxide in a proportion of niobium oxide of 2% to 20% is described. This composition can include zirconium oxide, optionally 50% of cerium oxide, 2% to 20% of niobium oxide, and at most 48% of zirconium oxide. Also described, is the use of the composition for treating exhaust gases.

Claims

1. A composition comprising niobium oxide with the following proportions by weight: niobium oxide: from 2% to 20%; and the remainder as cerium oxide.

2. The composition as claimed in claim 1, wherein the composition further comprises zirconium oxide with the following proportions by weight: cerium oxide: at least 50%; niobium oxide: from 2% to 20%; and zirconium oxide: up to 48%.

3. The composition as claimed in claim 2, wherein the composition further comprises at least one oxide of an element M selected from the group consisting of tungsten, molybdenum, iron, copper, silicon, aluminum, manganese, titanium, vanadium and a rare earth metal other than cerium, with the following proportions by weight: cerium oxide: at least 50%; niobium oxide: from 2% to 20%; oxide of the element M: up to 20%; and the remainder as zirconium oxide.

4. The composition as claimed in claim 1, wherein after calcination at 800 C. for 4 hours, the composition exhibits an acidity of at least 610.sup.2 this acidity being expressed in ml of ammonia per m.sup.2 of composition.

5. The composition as claimed in claim 1, wherein the composition comprises niobium oxide in a proportion by weight of between 3% and 15%.

6. The composition as claimed in claim 2, wherein the composition comprises cerium oxide in a proportion by weight of at least 65% and niobium oxide in a proportion by weight between 2% and 12%.

7. The composition as claimed in claim 6, wherein the composition comprises cerium oxide in a proportion by weight of at least 70%.

8. The composition as claimed in claim 6, wherein the composition comprises niobium oxide in a proportion by weight of less than 10%.

9. The composition as claimed in claim 6, wherein the composition exhibits an acidity, measured by TPD analysis, of at least at least 610.sup.2 ml of ammonia per m.sup.2.

10. The composition as claimed in claim 4, wherein after calcination at 800 C. for 4 hours, the composition exhibits a surface area of at least 15 m.sup.2/g.

11. The composition as claimed in claim 4, wherein after calcination at 800 C. for 4 hours, the composition exhibits a surface area of at least 20 m.sup.2/g.

12. The composition as claimed in claim 4, wherein after calcination at 1000 C. 4 hours, the composition exhibits a surface area of at least 2 m.sup.2/g.

13. A catalytic system comprising a composition as defined in claim 1.

14. A method for treating a gas, comprising treating the gas using as catalyst for the oxidation of CO and hydrocarbons present in the gas, a catalytic system as claimed in claim 13.

15. A process for the treatment of a gas comprising using a catalytic system as claimed in claim 13 for the decomposition of N.sub.2O, for the adsorption of NO.sub.x and CO.sub.2.

16. A process employing one of the following reactions: a water gas reaction, a steam reforming reaction, an isomerization reaction or a catalytic cracking reaction, the process comprising using a catalytic system as claimed in claim 13 in the process.

17. A three-way catalysis process for the treatment of gasoline engine exhaust gases, the process comprising using a catalytic system as claimed in claim 13 for carrying out the process.

Description

EXAMPLE 1

[0106] This example relate to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 63.0/27.0/10.0.

[0107] First of a niobium hydroxide suspension prepared according to the following process.

[0108] 1200 g of anhydrous ethanol are introduced into a 5 liter reactor equipped with a stirrer and a reflux condenser. 295 of niobium(V) chloride powder are added over 20 minutes with stirring. 625 g of anhydrous ethanol are subsequently added. The medium is left standing for 12 hours.

[0109] 50 g of deionized water are introduced into the reactor and the medium is brought to reflux at 70 C. for 1 hour. Cooling is allowed to take place. This solution is named A.

[0110] 870 q of aqueous ammonia solution (29.8% of NH.sub.3) are introduced into a 6 liter reactor equipped with a stirrer. All of the solution A and 2250 ml of deionized water are simultaneously introduced over 15 minutes with stirring. The suspension is recovered and washed several times by centrifuging. The centrifugate is named B.

[0111] 2.4 liters of a 1 mol/l nitric acid solution are introduced into a 6 liter reactor equipped with a stirrer. The centrifugate B is introduced into the reactor with stirring. Stirring is maintained for 12 hours. The pH is 0.7. The concentration of Nb.sub.2O.sub.5 is 4.08%. This suspension is named C.

[0112] An aqueous ammonia solution D is subsequently prepared by introducing 1040 g of a concentrated aqueous ammonia solution (29.8% of NH.sub.3) into 6690 g of deionized water.

[0113] A solution E is prepared by mixing 4250 g of deionized water, 1640 g of a cerium(III) nitrate solution (30.32% of CeO.sub.2), 1065 a of a zirconium oxynitrate solution (20.04% of ZrO.sub.2), 195 g of an aqueous hydrogen peroxide solution (50.30% of H.sub.2O.sub.2) and 1935 g of the suspension C (4.08% of Nb.sub.2O.sub.5). This solution E is set stirring.

[0114] The solution D and the solution E are simultaneously added at a flow rate of 3.2 liters/hour to a stirred 4 liter reactor equipped with an overflow. After starting up the plant, the precipitate is recovered in a keg. The pH is stable and in the vicinity of 9.

[0115] The suspension is filtered and the solid product obtained is washed and calcined at 800 C. for 4 hours.

Example 2

[0116] This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 55.1/40.0/4.9.

[0117] The preparation is carried out of an aqueous ammonia solution D as in example 1 and with the same compounds but in the following proportions:

concentrated aqueous ammonia solution: 978 g
deionized water: 6760 g.

[0118] The preparation is also carried out of a solution E as in example 1 and with the same compounds but in the following proportions:

deionized water: 5000 g
cerium(III) nitrate solution: 1440 g
zirconium oxynitrate solution: 1580 g
aqueous hydrogen peroxide solution: 172 g
suspension C: 950 g

[0119] The subsequent procedure is as in example 1.

Example 3

[0120] This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight 54.0/39.1/6.9.

[0121] The preparation is carried out of an aqueous ammonia solution C as in example 1 and with the same compounds but in the following proportions:

concentrated aqueous ammonia solution: 1024 g
deionized water: 6710 g.

[0122] The preparation is also carried out of a solution E as in example 1 and with the same compounds but in the following proportions:

deionized water: 4580 g
cerium(III) nitrate solution: 1440 g
zirconium oxynitrate solution: 1580 g
aqueous hydrogen peroxide solution: 172 g
suspension C: 1370 g

[0123] The subsequent procedure is as in example 1.

Example 4

[0124] This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide the following respective proportions by weight: 77.9/19.5/2.6.

[0125] The preparation is carried out of an aqueous ammonia solution D as in example 1 and with the same compounds but in the following proportions:

concentrated aqueous ammonia solution: 966 g
deionized water: 6670 g.

[0126] The preparation is also carried out of a solution E as in example 1 and with the same compounds but in the following proportions:

deionized water: 5620 g
cerium(III) nitrate solution: 2035 g
zirconium oxynitrate solution: 770 g
aqueous hydrogen peroxide solution: 242 g
suspension C: 505 g

[0127] The subsequent procedure is as in example 1.

Example 5

[0128] This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 76.6/19.2/4.2.

[0129] The preparation is carried out of an aqueous ammonia solution D as in example 1 and with the same compounds but in the following proportions:

concentrated aqueous ammonia solution: 1002 g
deionized water: 6730 g.

[0130] The preparation is also carried out of a solution E as in example 1 and with the same compounds but in the following proportions:

deionized water: 5290 g
cerium(III) nitrate solution: 2635 g
zirconium oxynitrate solution: 770 g
aqueous hydrogen peroxide solution: 242 g
suspension C. 836 g

[0131] The subsequent procedure is as in example 1.

Example 6

[0132] This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 74.2/18.6/7.2.

[0133] The preparation is carried out of an aqueous ammonia solution D as in example 1 and with the same compound but in the following proportions:

concentrated aqueous ammonia solution: 1068 g
deionized water: 6650 g.

[0134] The preparation is also carried out of a solution E as in example 1 and with the same compounds but in the following proportions:

deionized water: 4680 g
cerium(III) nitrate solution: 2035 g
zirconium oxynitrate solution: 770 g
aqueous hydrogen peroxide solution: 242 g
suspension C: 1470 g

[0135] The subsequent procedure is as in example 1.

Example 7

[0136] This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 72.1/18.0/9.9.

[0137] An ammonium niobium(V) oxalate solution is prepared by dissolving 192 g of ammonium niobium(V) oxalate in 300 g of deionized water under hot conditions.

[0138] This solution is maintained at 50 C. The concentration of Nb.sub.2O.sub.5 in this solution is 14.2%.

[0139] This solution is subsequently introduced onto a powder formed of a mixed oxide of cerium and zirconium (composition by weight CeO.sub.2/ZrO.sub.2 80/20, specific surface, after calcination at 800 C. for 4 hours, of 59 m.sup.2/g) until the pore volume is saturated.

[0140] The impregnated powder is subsequently calcined at 800 C. (stationary phase of 4 hours).

Example 8

[0141] This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 68.7/17.2/14.1.

[0142] The preparation is carried out of an aqueous ammonia solution D as in example 1 and with the same compounds but in the following proportions:

concentrated aqueous ammonia solution: 1148 g
deionized water: 6570 g.

[0143] The preparation is also carried out of a solution E as in example 1 and with the same compounds but in the following proportions:

deionized water: 3400 g
cerium(III) nitrate solution: 1880 g
zirconium oxynitrate solution: 710 g
aqueous hydrogen peroxide solution: 224 g
suspension C: 2870 g

[0144] The subsequent procedure is as in example 1.

Example 9

[0145] This example relates to the preparation of a composition according to the invention comprising cerium oxide and niobium oxide in the following respective proportions by weight: :96.8/3.2.

[0146] The preparation is carried out of an aqueous ammonia solution D as in example 1 and: with the same compounds but in the following proportions:

concentrated aqueous ammonia solution: 990 g
deionized water: 6750 g.

[0147] The preparation is also carried out of solution E as in example 1 and with the same compounds but without zirconium oxynitrate and in the following proportions:

deionized water: 5710 g
cerium(III) nitrate solution: 2540 g
aqueous hydrogen peroxide solution: 298 g
suspension C: 625 g

[0148] The subsequent procedure is as in example 1.

Example 10

[0149] This example relates to the preparation of a composition according to the invention comprising cerium oxide and niobium oxide in the following respective proportions by weight: 91.4/8.6.

[0150] The preparation is carried out of an aqueous ammonia solution D as in example 1 and with the same compounds but in the following proportions:

concentrated aqueous ammonia solution: 1110 g
deionized water: 6610 g

[0151] The preparation is also carried out of a Solution E as in example 1 and with the same compounds but without zirconium oxynitrate and in the following proportions:

deionized water: 4570 g
cerium(III) nitrate solution: 2540 g
aqueous hydrogen peroxide solution: 298 g
suspension C: 1775 g

[0152] The subsequent procedure is as in example 1.

Example 11

[0153] This example relates to the preparation of a composition according to the invention comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 63.0/27.0/10.0.

[0154] A solution of zirconium and cerium(IV) nitrates is prepared by mixing 264 g of deionized water, 238 g of cerium(IV) nitrate solution (252 g/l of CeO.sub.2) and 97 g of zirconium oxynitrate solution (261 g/l of ZrO.sub.2. The concentration of oxide in this solution is 120 g/l.

[0155] 373 g of deionized water and 111 g of aqueous ammonia solution (32% of NH.sub.3) are introduced into a stirred 1.5 l reactor.

[0156] The solution of nitrates is introduced over 1 hour. The final pH is in the vicinity of 9.5.

[0157] The suspension thus prepared is matured at 95 C. for 2 hours. The medium is subsequently allowed to cool.

[0158] A niobium(V) oxalate solution is prepared by dissolving 44.8 g of niobium(V) oxalate in 130 g of deionized water under hot conditions.

[0159] This solution is maintained at 50 C. The concentration of Nb.sub.2O.sub.5 in this solution is 3.82%.

[0160] The niobium (V) oxalate solution is introduced over 20 minutes into the cooled suspension.

[0161] The suspension is filtered and washed.

[0162] The cake is subsequently introduced into a furnace and calcined at 800 C. (stationary phase of 4 hours).

Example 12

[0163] This example relates to the preparation of a composition comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 63.3/26.7/10.0.

[0164] A solution of zirconium and cerium(IV) nitrates is prepared by mixing 451 g of deionized water, 206 g of cerium(IV) nitrate solution (252 g/l of CeO.sub.2) and 75 g of zirconium oxynitrate solution (288 g/l of ZrO.sub.2). The concentration of oxide in this solution is 80 g/l.

[0165] This solution of nitrates is introduced into an autoclave.

[0166] The temperature is raised to 100 C. The medium is kept stirred at 100 C. for 1 hour.

[0167] Cooling is allowed to take place.

[0168] The suspension is transferred into a stirred 1.5 l reactor.

[0169] A 6 mol/l aqueous ammonia solution is introduced with stirring until a pH in a vicinity of 9.5 is obtained.

[0170] The suspension is matured at 95 C. for 2 hours.

[0171] The medium is subsequently allowed to cool.

[0172] A niobium(V) oxalate solution is prepared by dissolving 39 g of niobium(V) oxalate in 113 g of deionized water under hot conditions.

[0173] This solution is maintained at 50 C. The Concentration of Nb.sub.2O.sub.5 in this solution is 3.84%.

[0174] The niobium oxalate solution is introduced over 20 minutes into the cooled suspension.

[0175] The pH is subsequently brought back to pH 9 by addition of an aqueous ammonia solution (32% of NH.sub.3).

[0176] The suspension is filtered and washed. The cake is subsequently introduced into a furnace and calcined at 800 C. (stationary phase of 4 hours).

Example 13

[0177] This example relates to the preparation of a composition comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 64.0/27.0/9.0.

[0178] The same procedure is employed as in example 12.

[0179] However, the niobium(V) oxalate solution is prepared by dissolving 35.1 g of niobium(V) oxalate in 113 g of deionized water under hot conditions. The concentration of Nh.sub.2O.sub.5 in this solution is 3.45%.

Comparative Example 14

[0180] This example relates to the preparation of a composition comprising cerium oxide, zirconium oxide and niobium oxide in the following respective proportions by weight: 19.4/77.6/3.0.

[0181] The preparation is carried out of an aqueous ammonia solution as in example 1 and with the same compounds but in the following proportions:

concentrated aqueous ammonia solution: 940 g
deionized water: 6730 g.

[0182] The preparation is also carried out of a solution E as in example 1 and with the same compounds but in the following proportions:

deionized water: 5710 g
cerium(III) nitrate solution: 2540 g
aqueous hydrogen peroxide solution: 298 g
suspension C: 625 g

[0183] The subsequent procedure is as in example 1.

[0184] Mention is made, in the following table, for each of the compositions of the examples above, of:

the BET specific surface after calcination at 800 C. and 900 C. for 4 hours;
the acidity properties;
the reducibility properties.

[0185] Acidity

[0186] The acidity properties are measured by the TPD method, which is described below.

[0187] The probe molecule used to characterize the acid sites in TPD is ammonia.

Preparation of the Sample:

[0188] The sample is brought to 500 C. under a stream of helium (30 ml/min) according to a temperature rise of 20 C./min and is maintained at this temperature for 30 minutes in order to remove the water vapor and to thus prevent the pores from blocking. Finally, the sample is cooled to 100 C. under a stream of helium at a rate of 10 C./min.

Adsorption:

[0189] The sample is subsequently subjected to a stream (30 ml/min; of ammonia (5 vol % of NH.sub.3 in helium at 100 C.) at atmospheric pressure for 30 minutes (up to saturation). The sample is subjected to a stream of helium for a minimum of 1 hour.

Desorption

[0190] The TPD is carried out by performing a rise in temperature of 10 C./min until 700 C. is reached.

[0191] During the rise in temperature, the concentration of the desorbed entities, that is to say of ammonia, is recorded. The concentration of ammonia during the desorption phase is deduced by virtue of the calibration of the variation in the thermal conductivity of the gas stream measured at the outlet of the cell using a thermal conductivity detector (TCD).

[0192] In table 1, the amounts of ammonia are expressed in ml (standard temperature and pressure conditions)/m.sup.2 (surface area at 800 C.) of composition.

[0193] The higher the amount of ammonia, the higher the surface acidity of the product.

[0194] Reducibility

[0195] The reducibility properties a e measured by carrying out a temperature programmed reduction (TPR) on a Micromeritics Autochem 2 device. This device makes it possible to measure the hydrogen consumption of a composition as a function of the temperature.

[0196] More specifically, hydrogen is used as reducing gas at 10% by volume in argon with a flow rate of 30 ml/min.

[0197] The experimental protocol consists in weighing out 200 mg of the sample into a pretared container.

[0198] The sample is subsequently introduced into a quartz cell containing quartz wool in the bottom. Finally, the sample is covered with quartz wool and positioned in the furnace of the measuring device.

[0199] The temperature program s as follows.:

rise in temperature from ambient temperature up to 900 C. with a rise gradient at 20 C./min under H.sub.2 at 10 vol % in Ar.

[0200] During this program, the temperature of the sample is measured using a thermocouple placed in the quartz cell above the sample.

[0201] The hydrogen consumption during the reduction phase is deduced by virtue of the calibration of the variation in the thermal conductivity of the gas stream measured at the outlet of the cell using a thermal conductivity detector (TCD).

[0202] The hydrogen consumption is measured between 30 C. and It is given in table 1 in ml (standard temperature and pressure conditions) of H.sub.2 per g of product.

[0203] The higher this hydrogen consumption, the better the reducibility properties of the product (redox properties).

TABLE-US-00001 TABLE 1 Example No. TPD TPR Ce/Zr/Nb Specific surface m.sup.2/g ml/m.sup.2/ ml H.sub.2/q in % 800 C. 900 C. 1000 C. (acidity) (reducibility) No. 1 35 17 4 6.5 10.sup.2 32.9 63.0/27.0/10.0 No. 2 41 19 7.8 6.4 10.sup.2 29.7 55.1/40.0/4.9 No. 3 38 16 6.2 7.3 10.sup.2 29.4 54.0/39.1/6.9 No. 4 37 12 5.8 8.7 10.sup.2 30.7 77.9/19.5/2.6 No. 5 30 14 5.6 6.9 10.sup.2 29.8 76.6/19.2/4.2 No. 6 28 15 3.9 9.4 10.sup.2 32.3 74.2/18.6/7.2 No. 7 31 17 3.7 8.3 10.sup.2 32.5 72.1/18.0/9.9 No. 8 32 12 3.9 7.8 10.sup.2 33.9 63.7/17.2/14.1 No. 9 19 15 4.5 9.1 10.sup.2 19.5 96.8/0/3.2 No. 10 34 15 4.1 8.9 10.sup.2 21 91.4/0/8.6 No. 11 36 16 4.3 7.5 10.sup.2 30.4 63.0/27.0/10.0 No. 12 47 15 4 7 10.sup.2 31.0 63.3/26.7/10.0 No. 13 48 16 4 7 10.sup.2 31.2 64.0/27.0/9.0 No. 14 52 31 4.1 7.6 10.sup.2 12.6 comparative 19.4/77.6/3.0

[0204] It should be remembered that the reducibility values in the table are given for compositions which have been subjected to a calcination at 800 C. for 4 hours.

[0205] It is seen, from table 1, that the compositions according to the invention simultaneously exhibit good reducibility properties and good acidity properties. The composition of the comparative example exhibits good acidity properties but the reducibility properties are far inferior to those of the compositions of the invention.