Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Mixture is exhaust from internal-combustion engine
Patent
1997-09-09
1999-11-02
Straub, Gary P.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Mixture is exhaust from internal-combustion engine
4232135, 423231, 423605, 423632, 502102, 502303, B01J 802, B01J 3100, C01B 1716, C01G 4502
Patent
active
059764767
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a catalytic composition based on cerium oxide and on manganese, iron or praseodymium oxide, to a process for its preparation and to its use in automobile afterburning catalysis.
So-called multifunctional catalysts are currently used for the treatment of exhaust gases from internal combustion engines (automobile afterburning catalysis). Multifunctional catalysts in understood to mean catalysts capable of carrying out not only oxidation, in particular of carbon monoxide and hydrocarbons present in exhaust gases, but also reduction, in particular of nitrogen oxides also present in these gases ("three-way" catalysts).
For this type of catalyst, cerium oxide is a commonly used component. This oxide is generally present on a support, such as alumina.
As fuels contain sulphur, cerium oxide and the support become sulphated. When the atmosphere of the catalyst becomes reducing, for example when the power demand of the engine suddenly ceases, the sulphates attached to the oxide and the support are reduced to H.sub.2 S which causes the emission of nauseating smells.
In point of fact, for obvious environmental reasons, it is important to reduce H.sub.2 S emissions.
One solution proposed is to add nickel oxide to the catalytic formulation. However, in certain countries, especially in Europe, nickel is banned by the standards enforced in this technical field, so this solution cannot be applied.
There exists therefore a real need for a catalytic composition which can be used in automobile afterburning catalysis which makes it possible to control H.sub.2 S emissions.
With this aim, the catalytic composition according to the invention in characterized in that it is based on a cerium oxide and on at least one other oxide chosen from iron, manganese and praseodymium oxides.
Moreover, according to a first embodiment, the process for the preparation of a composition according to the invention in characterized in that it comprises the following stages: least one iron, manganese or praseodymium compound;
According to a second embodiment, the process for the preparation of a composition according to the invention is characterized in that it comprises the following stages: least one iron, manganese or praseodymium compound; caused to precipitate;
According to a third embodiment, the process for the preparation of a composition according to the invention is characterized in that it comprises the following stages: one iron, manganese or praseodymium compound;
Finally, according to a fourth embodiment, the process for the preparation of a composition according to the invention in characterized in that a cerium oxide is impregnated with a solution of at least one iron, manganese or praseodymium compound and the impregnated cerium oxide is then calcined.
Other characteristics, details and advantages of the invention will become still more completely apparent on reading the description which will follow, as well as the various concrete but non-limiting examples intended to illustrate it.
As indicated above, the catalytic compositions of the invention are based on cerium and on at least one other oxide chosen from iron, manganese and praseodymium oxides. The invention therefore relates to the composition based on all the possible combinations of these elements. Mention will more particularly be made of compositions based on cerium and on manganese and based on cerium, on iron and on praseodymium.
According to a specific alternative form of the invention, the compositions exhibit a major phase of solid solution or mixed oxide type. According to yet another alternative for, the composition of the invention exist entirely in the form of a solid solution. Solid solution is understood to mean that the X-ray diffraction spectra of these compositions in fact reveal, within the latter, the existence of only a single identifiable phase (absence of detectable secondary phase) which corresponds in fact to that of a ceric oxide crystallized in the cubic system in which the unit cell parameters are more or less offset
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Blanchard Gilbert
Quemere Eric
Touret Olivier
Visciglio Valerie
Carleton Katherine L.
Nguyen Cam N.
Rhodia Chimie
Straub Gary P.
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