Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Mixture is exhaust from internal-combustion engine
Reexamination Certificate
2001-04-13
2003-04-15
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Mixture is exhaust from internal-combustion engine
C423S213500, C423S213700, C423S235000
Reexamination Certificate
active
06548032
ABSTRACT:
The present invention relates to a process for the treatment of gases, in particular exhaust gases of internal-combustion engines, with high oxygen content, with a view to controlling nitrogen oxide emissions.
It is known that the emissions of nitrogen oxides (NOx) in exhaust gases of motor-vehicle engines, in particular, are controlled using three-way catalysts which use stoichiometrically the reducing gases present in the mixture. Any excess of oxygen results in a drastic reduction in the performance of the catalyst.
Moreover, some engines, such as diesel engines or lean-burn petrol engines, are economical in terms of fuel but emit exhaust gases which continuously contain a large excess of oxygen, for example at least 5%. A standard three-way catalyst therefore has no effect on the NOx emissions of these engines. Furthermore, limitating the NOx emissions has become an imperative requirement because of the tightening of motor-vehicle afterburn standards, which are now extended to this type of engine.
Therefore there is a real need for an effective catalytic converter to control NOx emissions for this type of engine, and more generally to treat this type of gas.
The object of the invention is therefore to find a catalytic converter which can be used for the treatment of exhaust gases with high oxygen content.
To this end, the method according to the invention, for the treatment of gases with high oxygen content, with a view to controlling nitrogen oxide emissions, is characterized in that use is made of a catalytic composition comprising manganese oxide and at least one oxide chosen from cerium oxide and zirconium oxide.
The invention furthermore relates to a catalytic system for the same treatment of the same type of gas, which is characterized in that it comprises a catalytic composition of the above type.
Finally, the invention relates to a process for the preparation of such a catalytic system, which is characterized in that use is made of a catalytic composition as mentioned above.
Other characteristics, details and advantages of the invention will emerge yet more fully on reading the following description, as well as various concrete but non-limiting examples intended to illustrate it.
As indicated above, the catalytic composition used in the scope of the present invention comprises manganese oxide and at least one oxide chosen from cerium oxide and zirconium oxide.
This composition may furthermore contain an additional element, which is also generally present in oxide form in the composition. This element may be chosen from those in groups VIII, IB, IVB and VB.
The Periodic Table of the Elements to which reference is made is the one published in “le Supplément au Bulletin de la Société chimique de France” [Supplement to the Journal of the Chemical Society of France] No. 1 (January 1966).
All elements in group IB are suitable in the scope of the present invention. Tin may more particularly be mentioned in the case of group IVB, and antimony and bismuth in the case of group VB.
As regards cerium and zirconium, use is preferably made of an oxide suitable for catalysis applications, that is to say an oxide capable, in particular, of retaining a sufficient specific surface at elevated temperature.
By way of example, mention may be made of the cerium oxides described in French patent applications FR-A-2559754 and FR-A-2640954.
Manganese is present in a quantity, expressed as atomic manganese content relative to the number of moles of cerium oxide and zirconium oxide, which is preferably at most 50%. This content may, more particularly, be at most 20%. The minimum manganese content is usually at least 0.5%. The manganese content is generally between 5 and 20%.
The respective proportions of cerium and zirconium are arbitrary. The other element or elements is/are present in a quantity, expressed as atomic element content relative to the number of moles of cerium oxide and zirconium oxide, which is preferably at most 20% and, in particular, at most 10%. This content may more particularly be at most 5%.
With regard to the method of using manganese and the other element or elements with cerium and/or zirconium, there are several embodiments of the invention.
According to a first embodiment, the cerium and/or zirconium may constitute a support onto which the manganese, and optionally at least one aforementioned additional element, is deposited.
According to a second embodiment, the cerium and/or zirconium, with the manganese, may constitute a support onto which at least one element of the aforementioned type is deposited.
According to a variant of the invention, the cerium and/or zirconium, with the manganese, are present in the form of a solid solution. This variant is particularly applicable to the case in which the cerium and/or zirconium, with the manganese, all form the support of the composition. The term “solid solution” is intended to mean that the X-ray diffraction spectra of the cerium and/or zirconium/manganese mixture actually reveal the existence, within the latter, of only one single identifiable phase (absence of a detectable parasitic secondary phase), this phase corresponding, for example in the case of a mixture containing only cerium, to that of a ceric oxide which is crystallized in the cubic system and whose lattice parameters are to some extent shifted relative to a pure ceric oxide, thus manifesting the fact that manganese is incorporated in the crystal lattice of the cerium oxide, and therefore that a true solid solution is obtained.
The compositions which can be used in the scope of the present invention may be prepared in various ways. Various methods will be given below without implying any limitation.
According to a first method, the following operations are carried out:
a mixture in a liquid medium is prepared, containing a cerium and/or zirconium compound and a manganese compound;
the said mixture is heated;
the precipitate thus obtained is recovered;
the said precipitate is calcined.
The first operation therefore consists in preparing a mixture in a liquid medium, generally in the aqueous phase, containing at least one cerium and/or zirconium compound and a manganese compound. These compounds are preferably soluble compounds. The mixture may equally well be obtained either from compounds initially in the solid state, which will then be introduced into an aqueous stock solution, or directly from solutions of these compounds, then mixing the said solutions in an arbitrary order.
Water-soluble cerium compounds which may be mentioned are, in particular, cerium(IV) salts such as nitrates or cerium-ammonium nitrates, for example, which are particularly suitable in this case. Ceric nitrate is preferably used. The cerium(IV) salt solution may contain cerium in the cerous state without causing problems, but it is desirable for it to contain at least 85% of cerium(IV). An aqueous ceric nitrate solution may, for example, be obtained by reacting nitric acid with a hydrated ceric oxide prepared conventionally by reacting a solution of a cerous salt, for example cerous carbonate, with an ammonia solution in the presence of aqueous hydrogen peroxide solution. It is also possible, and preferable, to use a ceric nitrate solution obtained by the process of electrolytic oxidation of a cerous nitrate solution, as described in document FR-A-2 570 087, which here constitutes the starting material of choice.
It will be noted here that the aqueous solution of cerium(IV) salts may have some degree of initial free acidity, for example a normality varying between 0.1 and 4N. According to the present invention, it is possible both to use an initial cerium(IV) salt solution which actually has some degree of free acidity, as mentioned above, and to use a solution which has been neutralized beforehand to a greater or lesser extent by adding a base such as, for example, an ammonia solution or alkali metal (sodium, potassium, etc.) hydroxide solution, but preferably an ammonia solution, so as to limit this acidity. In the latter case, a degree of neutralization (r) of the i
Barthe Philippe
Hedouin Catherine
Seguelong Thierry
Medina Maribel
Rhodia Chimie
Silverman Stanley S.
LandOfFree
Process for the treatment of gases with high oxygen content,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the treatment of gases with high oxygen content,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the treatment of gases with high oxygen content,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3083704