Patent Application
20080020925
This example concerns a composition with 60% zirconium and 40% praseodymium, these proportions being expressed as weight percentages of the oxides ZrO2 and Pr6O11.
In a stirred beaker, 500 ml of zirconium nitrate (120 g/l) and 80 ml of praseodymium nitrate (500 g/l) are introduced. Distilled water is then added to make up to a volume of 1 liter of a solution of nitrates.
In a stirred reactor, 224 ml of an aqueous ammonia solution (12 mol/l) are introduced and distilled water added to make up to a total volume of 1 liter.
The nitrate solution is introduced in one hour into the reactor with constant stirring.
The solution obtained is placed in a stainless steel autoclave equipped with a stirrer. The temperature of the medium is raised to 150° C. with stirring for 2 hours.
The suspension thus obtained is filtered on a Büchner funnel. A precipitate containing 19% by weight of oxide is recovered.
100 g of this precipitate are taken.
Simultaneously, an ammonium laurate gel is prepared under the following conditions: 250 g of lauric acid are introduced into 135 ml of aqueous ammonia (12 mol/l) and 500 ml of distilled water, and the mixture blended using a spatula.
22.7 g of this gel are added to 100 g of the precipitate and the combination is mixed until a uniform paste is obtained.
The product obtained is then heated to 500° C. for 4 hours in steps.
It has the following surface characteristics:
The XR analyses show that between 900° C. and 1000° C., the product has a majority cubic phase and a minority quadratic phase.
The total pore volume measured is 0.81 ml/g of oxide. The pores between 10 nm and 500 nm in diameter constitute 39% of the total pore volume.
This example concerns a composition with 85% zirconium and 15% praseodymium, these proportions being expressed as weight percentages of the oxides ZrO2 and Pr6O11.
In a stirred beaker, 708 ml of zirconium nitrate (120 g/l) and 30 ml of a solution of praseodymium nitrate (500 g/l) are introduced. Distilled water is added to make up to a total volume of 1 liter of a solution of nitrates.
In a stirred reactor, 220 ml of an aqueous ammonia solution are introduced and distilled water added to make up to a total volume of 1 liter.
The solution obtained is placed in a stainless steel autoclave equipped with a stirrer. The temperature of the medium is raised to 150° C. with stirring for 2 hours.
The suspension thus obtained is filtered on a Büchner funnel. A precipitate containing 17.9% by weight of oxide is recovered.
100 g of this precipitate are taken.
Simultaneously, an ammonium laurate gel is prepared under the following conditions: 250 g of lauric acid are introduced into 135 ml of aqueous ammonia (12 mol/l) and 500 ml of distilled water, and the mixture blended using a spatula.
21.4 g of this gel are added to 100 g of the precipitate and the combination is mixed until a uniform paste is obtained.
The product obtained is then heated to 500° C. for 4 hours in steps.
It has the following surface characteristics:
The XR analyses show that between 900° C. and 1000° C., the product has a single quadratic phase.
This example concerns a composition containing 90% zirconium and 10% praseodymium, these proportions being expressed as weight percentages of the oxides ZrO2 and Pr6O11.
The same procedure is followed as in Example 1.
The surface characteristics are given in Table 3 below. The XR analyses show that between 900° C. and 1000° C., the product has a single quadratic phase.
This example concerns a composition containing 90% zirconium and 10% lanthanum, these proportions being expressed as weight percentages of the oxides ZrO2 and La2O3.
The same procedure is followed as in Example 1.
The surface characteristics are given in Table 3 below.
This example concerns a composition containing 90% zirconium and 10% neodymium, these proportions being expressed as weight percentages of the oxides ZrO2 and Nd2O3.
The same procedure is followed as in Example 1.
The surface characteristics are given in Table 3 below.
This example describes a catalytic test for a catalyst prepared using a composition according to the invention.
a) Preparation of the Catalyst
The catalyst containing 0.1% by weight of metal rhodium element with respect to the total weight of catalyst is prepared by wet impregnation of rhodium nitrate on the product of Example 3 obtained after 4 h of calcination at 500° C. The impregnated product is then subjected to slow evaporation, drying, and finally, calcination in air for 4 h at 500° C.
The catalyst in powder form is then aged for 6 hours at 1100° C. in a redox mixture (alternating streams of 5 minutes of 1.8% CO and 10% H20, and of 1.8% O2 and 10% H2O). The catalyst is then aged in a quartz tubular fired heater, traversed by the gas stream.
b) Test Conditions
Gas flow rate: 30 l/h
Catalyst weight: 20 mg (grain size fraction 100-200 microns) diluted with 150 mg of SiC.
The composition of the gases is given in Table 4 below.
The following results are observed.
In a rich mixture, the initiation temperature at 20% conversion for NO is 345° C., for C3H6 it is 350° C. Hence these are low temperatures in both cases.
Furthermore, the half-conversion (50% conversion) temperature for NO and C3H6 is only 360° C. 100% of NO and C3H6 are converted before 400° C.
In the lean mixture, the initiation temperatures at 20% conversion for NO, for C3H6 and for CO are 310° C., 325° C. and 285° C. respectively. Moreover, for C3H6 80% conversion is obtained at 500° C.
All these results reveal the low temperature effectiveness of the catalysts based on compositions of the invention.
In this example, a composition is prepared based on zirconium and cerium oxides, with a specific surface area stabilized by lanthanum and neodymium oxides. This composition answers to the formula ZrO2/CeO2/La2O3/Nd2O3 with respective weight proportions of these oxides of 75/20/2.5/2.5.
The same procedure is followed as in Example 2, using the following quantities of solutions per 100 g of product:
The method of preparation is identical to the one described in Example 2. However, the precipitate is not mixed with the surfactant, but is directly calcined. The product obtained after calcination for 4 hours at 1000° C. has a specific surface area of 44 m2/g and, after calcination for 4 hours at 1100° C., a specific surface area of 18 m2/g. A catalyst containing 0.1% by weight of metal rhodium element with respect to the total weight of catalyst is also prepared by the wet impregnation of rhodium nitrate on the composition prepared as described above and obtained after 4 hours of calcination at 500° C.
This catalyst thereby prepared is subjected to the same aging at 1100° C. and the same test as described above in Example 6.
Table 5 below gives the results for initiation temperatures at 20% (Ta) for the products of Examples 6 and 7.
The initiation temperatures are much higher in the case of the product of the comparative example.
This example concerns a composition containing 80% zirconium and 20% praseodymium, these proportions being expressed as weight percentages of the oxides ZrO2 and Pr6O11.
In a stirred beaker, 276 ml of zirconium nitrate (290 g/l) and 40 ml of praseodymium nitrate (500 g/l) are introduced. Distilled water is added to make up the volume to a total of 1 liter of a solution of nitrates.
In a stirred reactor, 193 ml of an aqueous ammonia solution (12 mol/l) are introduced and distilled water then added to make up to a total volume of 1 liter.
The nitrate solution is introduced in one hour into the reactor with constant stirring.
The solution obtained is placed in a stainless steel autoclave equipped with a stirrer. The temperature of the medium is raised to 150° C. for 4 hours with stirring.
40 grams of lauric acid is added to the suspension thereby obtained. This suspension is maintained with stirring for 1 hour.
This suspension is then filtered on a Büchner funnel and the equivalent in volume of the filtration mother liquors is added to the filter precipitate. A precipitate is finally recovered.
The product obtained is then heated to 700° C. for 4 hours in steps.
It has the following surface area characteristics:
The XR analyses show that between 900° C. and 1000° C., the product has a majority cubic phase and a minority quadratic phase.
This example concerns a composition containing 90% zirconium and 10% praseodymium, these proportions being expressed as weight percentages of the oxides ZrO2 and Pr6O11.
The same procedure is followed as in Example 1, with two exceptions: the surfactant is added in the form of lauric acid (33 grams) directly to the suspension issuing from the autoclave and after cooling, and the initial calcination is carried out at 800° C. for 3 hours.
The product has the following surface characteristics:
The total pore volume measured is 1.32 ml/g of oxide. The pores between 10 nm and 500 nm in diameter constitute 48% of the total pore volume.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04 01948 | Feb 2004 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR05/00455 | 2/25/2005 | WO | 00 | 5/14/2007 |
