Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Mixture is exhaust from internal-combustion engine
Reexamination Certificate
1998-05-08
2001-04-10
Dunn, Tom (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Mixture is exhaust from internal-combustion engine
C423S212000, C502S304000, C502S349000
Reexamination Certificate
active
06214306
ABSTRACT:
The present invention relates to a composition based on zirconium oxide and on cerium oxide, to its processor or preparation and to its use, in particularly in catalysis.
So-called multifunctional catalysts are currently used in the treatment of exhaust gases from internal combustion engines (automobile afterburning catalysis). Multifunctional catalysts is understood to means catalysts capable of carrying out not only oxidation, in particular of carbon monoxide and hydrocarbons present in exhaust gases, but also reduction, in particularly of nitrogen oxides also present in these gases (“three-way” catalysts). Zirconium oxide and cerium oxide today appear as two particularly important and advantages constituents in this type of catalyst. To be effective, these catalysts must have a high specific surface, even at high temperature. Moreover, it is often advantages to use these catalysts in the form of mixed oxides or of solid solutions.
There therefore exists a need for catalysts capable of being able to be used at high temperature and, for this, exhibiting high stability with respect to their specific surface.
The subject of the invention is thus the development of a catalytic composition which can respond to this need.
Another object of the invention is to provide catalysts based on zirconium oxide and on cerium oxide and which are provided in the form of a solid solution.
With this aim, the composition of the invention is based on zirconium oxide and it comprises cerium oxide and it is characterized in that it has a specific surface of at least 30 m
2
/g after calcination for 6 hours at 900° C. and in that it is provided in the form of a pure solid solution of cerium oxide in zirconium oxide.
Moreover, according to another embodiment of the invention, the composition is based on zirconium oxide and it comprises cerium oxide and it is characterized in that it has a specific surface greater than 25 m
2
/g after calcination for 6 hours at 1000° C.
According to a third embodiment of the invention, the composition is based on zirconium oxide and it comprises cerium oxide and at least one doping element and it is characterized in that it has a specific surface of at least 25 m
2
/g, more particularly of at least 30 m
2
/g, after calcination for 6 hours at 1000° C.
The invention also relates to a process for the preparation of the above compositions which is characterized in that it comprises the following stages:
a mixture is prepared, in liquid medium, containing a zirconium compound and a cerium(IV) compound;
the said mixture is heated at a temperature greater than 100° C.;
the reaction mixture obtained on conclusion of the heating is brought to a basic pH;
the precipitate thus obtained is recovered;
the said precipitate is calcined;
the abovementioned doping element being, if appropriate, added either to the starting mixture in liquid medium or to the reaction mixture obtained on conclusion of the heating.
According to another alternative form of the invention, the preparation process is characterized in that it comprises the following stages:
a mixture is prepared, in liquid medium, containing a cerium compound and at least one zirconium oxychloride and, if appropriate, a compound of the doping element;
the said mixture and a basic compound are brought together, whereby the mixture is caused to precipitate;
the precipitate thus obtained is recovered;
the said precipitate is calcined.
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Aubert Maryline
Birchem Thierry
Blanchard Gilbert
Touret Olivier
Burns Doane Swecker & Mathis L.L.P
Dunn Tom
Rhone-Poulenc Chimie
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