U.S. patent application number 10/574626 was filed with the patent office on 2007-07-26 for cerium organic colloidal dispersion and element selected from rhodium and palladium and use thereof as additive to diesel fuel for internal combustion engines.
Invention is credited to Gilbert Blanchard, Bruno Tolla.
Application Number | 20070169406 10/574626 |
Document ID | / |
Family ID | 34307400 |
Filed Date | 2007-07-26 |
United States Patent
Application |
20070169406 |
Kind Code |
A1 |
Blanchard; Gilbert ; et
al. |
July 26, 2007 |
Cerium organic colloidal dispersion and element selected from
rhodium and palladium and use thereof as additive to diesel fuel
for internal combustion engines
Abstract
The inventive colloidal dispersion comprised cerium compound
particles, an acid and an organic phase and is characterized in
that it also comprises a compound of at least one element selected
from rhodium and palladium. According to variants, the dispersion
comprises particles of a compound of cerium, another rare earth
and/or iron. The inventive dispersion can be used as an additive to
diesel fuels for diesel engines
Inventors: |
Blanchard; Gilbert;
(Lagny-Le Sec, FR) ; Tolla; Bruno; (Paris,
FR) |
Correspondence
Address: |
Jean-Louis Seugnet;Rhodia Inc Legal Department
8 Cedar Brook Drive
CN 7500
Cranbury
NJ
08512-7500
US
|
Family ID: |
34307400 |
Appl. No.: |
10/574626 |
Filed: |
October 1, 2004 |
PCT Filed: |
October 1, 2004 |
PCT NO: |
PCT/FR04/02491 |
371 Date: |
November 20, 2006 |
Current U.S.
Class: |
44/354 |
Current CPC
Class: |
B01J 13/0013 20130101;
C10L 1/1881 20130101; B01D 53/9413 20130101; C10L 10/06 20130101;
B01J 13/0026 20130101; C10L 1/10 20130101 |
Class at
Publication: |
044/354 |
International
Class: |
C10L 1/12 20060101
C10L001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 3, 2003 |
FR |
03 11614 |
Claims
1-14. (canceled)
15. A colloidal dispersion comprising particles of a cerium
compound, an acid and an organic phase, and comprising a compound
of at least one element selected from the group consisting of
rhodium and palladium.
16. The dispersion as claimed in claim 15, comprising particles of
a compound of cerium and of another rare earth.
17. The dispersion as claimed in claim 16, wherein it comprises
particles of a compound of cerium, of another rare earth, and of
iron.
18. The dispersion as claimed in claim 17, wherein the element is
presets a content of not more than 5% with respect to the
combination of the elements cerium, other rare earth and iron of
the particles.
19. The dispersion as claimed in claim 17, wherein the content of
the element is not more than 0.5% with respect to the combination
of the elements cerium, other rare earth and iron of the
abovementioned particles.
20. The dispersion as claimed in claim 15, wherein the compound of
the element is bound to the particles.
21. The dispersion as claimed in claim 17, wherein cerium is
present in a proportion of not more than 50%, optionally not more
than 20% in moles of cerium oxide CeO.sub.2 with respect to the
total number of moles of cerium oxide and iron oxide
Fe.sub.2O.sub.3.
22. The dispersion as claimed in claim 16, wherein the other rare
earth is lanthanum or praseodymium.
23. The dispersion as claimed in claim 15, wherein the acid is an
amphiphilic acid.
24. The dispersion as claimed in claim 15, wherein at least 90% of
the particles are single crystal particles.
25. The dispersion as claimed in claim 15, wherein the particles
have a d.sub.50 of between 1 and 5 nm, optionally between 2 and 4
nm.
26. A method for preparing a dispersion as claimed in claim 15,
comprising the steps of: a) preparing an aqueous mixture comprising
at least one cerium salt, optionally a salt of a rare earth other
than cerium and an iron salt, and a salt of at least one element
selected from the group consisting of rhodium and palladium; b)
contacting the aqueous mixture of step (a) with a basic medium to
form a reaction mixture whose pH is maintained at a basic pH,
thereby producing a precipitate; and c) the precipitate obtained in
step b) is contacted with the acid and the organic phase, to obtain
an organic colloidal dispersion.
27. A fuel additive for internal combustion engines comprising a
colloidal dispersion as defined in claim 15.
28. A fuel for internal combustion engines, obtained by mixing a
standard fuel with a colloidal dispersion as claimed in claim 15.
Description
[0001] The present invention relates to an organic colloidal
dispersion of cerium and of an element selected from rhodium and
palladium, and the use thereof as a diesel fuel additive for
internal combustion engines.
[0002] It is known that during the combustion of diesel fuel in the
diesel engine, the carbonaceous products tend to form soot, which
is considered to be harmful both to the environment and to health.
Research has been conducted for many years on techniques. for
reducing the emission of these carbonaceous particles.
[0003] One satisfactory solution that is now used in mass-produced
engines consists in collecting the particles on a filter that is
regularly regenerated to prevent the clogging thereof. Filter
regeneration is easier if the autoignition temperature of the soot
is low, and this can be obtained by introducing a catalyst into the
core of the soot during combustion. This technology, known as "Fuel
Borne Catalysis" or FBC, is also widely used. The soot thereby
containing additives has an autoignition temperature that is
sufficiently low to be reached frequently during the normal running
of the engine or during specific regeneration cycles.
[0004] It is known that dispersions of rare earth compounds, used
as fuel additives, can serve to reduce the autoignition temperature
of soot.
[0005] Furthermore, it is also important to limit the emission of
the nitrogen oxides (NO.sub.x) by diesel engines.
[0006] Hence a real need remains for an effective catalyst for both
lowering the soot combustion temperature and reducing the NO.sub.x
content of the diesel engine exhaust gases.
[0007] It is the object of the invention to provide such a
catalyst.
[0008] For this purpose, the colloidal dispersion of the invention
is of the type comprising particles of a cerium compound, an acid
and an organic phase, and is characterized in that it further
comprises a compound of at least one element selected from rhodium
and palladium.
[0009] According to a first variant of the invention, the colloidal
dispersion is characterized in that it comprises particles of a
compound of cerium and of another rare earth.
[0010] According to a further variant, the colloidal dispersion of
the invention is characterized in that it comprises particles based
on a compound of cerium, optionally of another rare earth, and of
iron.
[0011] Other features, details and advantages of the invention will
appear even more completely from a reading of the description that
follows, and of concrete but nonlimiting examples provided to
illustrate it.
[0012] For the rest of the description, rare earth means elements
of the group consisting of yttrium and the elements of the Periodic
Table with atomic numbers from 57 to 71 inclusive.
[0013] The expression "colloidal dispersion" in the present
invention designates any system consisting of fine solid particles
of colloidal size based on a cerium compound and, according to the
abovementioned variants, of a rare earth other than cerium and/or
iron, in suspension in a liquid phase, said particles further
optionally containing residual quantities of bound or adsorbed ions
such as, for example, nitrates, acetates, citrates and ammoniums.
Colloidal size means size between about 1 nm and about 500 nm. The
particles may more particularly have an average size of not more
than about 250 nm, particularly of not more than 100 nm, preferably
of not more than 20 nm, and even more preferably of not more than
15 nm. In such dispersions, the cerium, the other rare earth and/or
the iron may be present either, preferably, completely in colloidal
form, or in colloidal form and partially in ionic form.
[0014] More particularly, if the particles of the dispersion of the
invention are based on a compound of a plurality of elements, that
is, cerium, another rare earth and/or iron, these elements are
mixed within each particle, and generally have the form of mixed
oxides and/or hydrated mixed oxides (oxyhydroxides).
[0015] The cerium is mainly in the form of cerium IV. For example,
the cerium III content with respect to cerium IV (content expressed
by the atomic ratio Ce III/Ce total) is generally not more than
40%. It may vary according to the embodiments of the dispersions
used and may thus be not more than 20%, more particularly not more
than 10%, and even more particularly not more than 1%.
[0016] In the case of the abovementioned first variant, the rare
earth other than cerium may be more particularly lanthanum or
praseodymium. Obviously, the present variant covers the case in
which the particle is a compound of cerium and of a plurality of
other rare earths in combination.
[0017] The proportion of rare earth other than cerium is preferably
at least 10%, more particularly at least 20% and even more
particularly not more than 50%, in moles with respect to the total
number of moles of cerium and of rare earth expressed as oxide.
[0018] In the case of the second variant, the proportion of cerium
is preferably not more than 50%, more particularly not more than
20% and even more particularly not more than 10%, this proportion
being expressed as moles of cerium oxide CeO.sub.2 with respect to
the total number of moles of cerium oxide and of iron oxide
Fe.sub.2O.sub.3.
[0019] The two variants may be combined, that is, the particles may
be compounds of cerium, of at least one other rare earth, and of
iron.
[0020] According to the main feature of the invention, the
colloidal dispersion further contains a compound of at least one
element selected from rhodium and palladium. The invention applies
in particular to the case in which rhodium and palladium are
present in combination. Palladium has the additional effect of
favoring the oxidation of CO and unburnt hydrocarbons in exhaust
gases.
[0021] Generally, the rhodium and/or palladium content is not more
than 5%, more particularly not more than 1% and even more
particularly not more than 0.5% with respect to the combination of
the elements cerium, other rare earth and iron in the particles.
This content is expressed as a % by weight of rhodium and/or
palladium metal with respect to the sum of the weights of the
elements cerium, rare earth and iron. The upper limit for the
rhodium and/or palladium content is not critical, but simply of an
economic order, because an excessive quantity of these elements
incurs a higher cost of the dispersion without providing technical
advantages. The lower limit is that below which the rhodium and/or
palladium have no observable effect for reducing the nitrogen oxide
releases. This lower limit is generally about 100 ppm.
[0022] In the case of the dispersions obtained by the preparation
method described below, it is conceivable for the rhodium and/or
palladium to be also mainly present in the form of oxides or
hydrated oxides. In the same case, the rhodium and/or palladium are
moreover present in the dispersion essentially as being bound to
the particles of the cerium compound. This bond between the element
rhodium and/or palladium and the particles may be of a chemical
type and it may be produced by the adsorption of said element on
the particle surface.
[0023] The colloidal dispersion according to the invention
comprises at least one acid, advantageously amphiphilic. The acid
is more particularly selected from organic acids having at least 6
carbon atoms, even more particularly 10 to 60 carbon atoms,
preferably 15 to 25 carbon atoms.
[0024] These acids may be linear or branched. They may be aryl,
aliphatic or arylaliphatic acids, optionally containing other
functional groups provided that these functional groups are stable
in the media in which the dispersions according to the present
invention are to be used. Thus, it is possible to use, for example,
aliphatic carboxylic acids, aliphatic sulfonic acids, aliphatic
phosphonic acids, alkylarylsulfonic acids and alkylarylphosphonic
acids having about 10 to about 40 carbon atoms, whether natural or
synthetic. It is obviously possible to use acid mixtures.
[0025] It is also possible to use carboxylic acids of which the
carbon chain bears ketone functional groups such as pyruvic acids
substituted with the ketone functional group in the alpha position.
They may also be alpha-halocarboxylic acids or
alphahydroxycarboxylic acids. The chain attached to the carboxylic
group may carry unsaturated groups. In general, however, it is
better to avoid too many double bonds because cerium catalyzes the
crosslinking of double bonds. The chain may be interrupted by ether
or ester functional groups provided that this does not excessively
alter the lipophilicity of the chain bearing the carboxylic
group.
[0026] By way of example, mention can be made of fatty acids of
tallol, soybean oil, soot, linseed oil, oleic acid, linoleic acid,
stearic acid and isomers thereof, pelargonic acid, capric acid,
lauric acid, myristic acid, dodecylbenzenesulfonic acid,
2-ethylhexanoic acid, naphthenic acid, hexoic acid, toluenesulfonic
acid, toluenephosphonic acid, laurylsulfonic acid, laurylphosphonic
acid, palmitylsulfonic acid, and palmitylphosphonic acid.
[0027] In the context of the present invention, the term
"amphiphilic acid" may also designate other amphiphilic agents such
as, for example, polyoxyethylene alkyl ether phosphates. The
phosphates here are phosphates of the formula: ##STR1##
[0028] or polyoxyethylene dialkyl phosphates of the formula:
##STR2##
[0029] where: [0030] R.sup.1, R.sup.2, R.sup.3, identical or
different, represent a linear or branched alkyl radical,
particularly with 2 to 20 carbon atoms; a phenyl radical, an
alkylaryl radical, more particularly an alkylphenyl radical,
particularly with 8 to 12 carbon atoms; an arylalkyl radical, more
particularly a phenylaryl radical; [0031] n is the number of
ethylene oxide possibly ranging from 0 to 12, for example; [0032] M
represents a hydrogen, sodium or potassium atom.
[0033] The radical R.sup.1 may be in particular a hexyl, octyl,
decyl, dodecyl, oleyl or nonylphenyl radical.
[0034] By way of example of this type of amphiphilic compound,
mention can be made of those marketed under the trademarks
Lubrophos.RTM. and Rhodafac.RTM. sold by Rhodia and particularly
the following products: [0035] polyoxyethylene alkyl (C8-c10) ether
phosphates Rhodafac.RTM. RA 600; [0036] polyoxyethylene tridecyl
ether phosphate Rhodafac.RTM. RS 710 or RS 410 [0037]
polyoxyethylene oleocetyl ether phosphate Rhodafac.RTM. PA 35
[0038] polyoxyethylene nonylphenyl ether phosphate Rhodafac.RTM. PA
17 [0039] polyoxyethylene nonyl(branched) ether phosphate
Rhodafac.RTM. RE 610.
[0040] The dispersions of the invention further comprise a liquid
phase that is an organic phase and in which the particles are in
suspension.
[0041] By way of example of an organic phase, mention can be made
of aliphatic hydrocarbons such as hexane, heptane, octane, nonane,
inert cycloaliphatic hydrocarbons such as cyclohexane,
cyclopentane, cycloheptane, aromatic hydrocarbons such as benzene,
toluene, ethylbenzene, xylenes, liquid naphthenes. Also suitable
are petroleum cuts of the Isopar or Solvesso type (trademarks of
Exxon), particularly Solvesso 100 which essentially contains a
mixture of methyl ethylbenzene and trimethylbenzene, Solvesso 150
which contains a mixture of alkylbenzenes, particularly
dimethylbenzene and tetramethylbenzene and Isopar which essentially
contains C-11 and C-12 isoparaffinic and cycloparaffinic
hydrocarbons. As other petroleum cuts, mention can also be made of
those of the Petrolink.RTM. type marketed by Petrolink and of the
Isane.RTM. type marketed by Total.
[0042] Chlorinated hydrocarbons can also be used for the organic
phase, such as chlorobenzene or dichlorobenzene, and chlorotoluene.
Ethers as well as aliphatic and cycloalophatic ketones such as, for
example, diisopropyl ether, dibutyl ether, methyl ethyl ketone,
methyl isobutyl ketone, diisobutyl ketone, mesityl oxide, can be
considered.
[0043] Esters may also be considered, but their drawback is the
risk of hydrolysis. As ethers suitable for use, mention can be made
of those produced by the reaction of acids with C1 to C8 alcohols,
and particularly palmitates of secondary alcohols such as
isopropanol. By way of example, mention can also be made of butyl
acetate.
[0044] Obviously, the organic phase may be based on a mixture of
two or more hydrocarbons or compounds of the type described
above.
[0045] The dispersions according to the invention have a
concentration of cerium compounds, of the element rhodium and/or
palladium and, optionally of the other rare earth and of iron, that
generally may range up to 40% by weight of oxides of these elements
with respect to the total weight of the dispersion. Above 40%, the
viscosity of the dispersion is liable to be too high, particularly
at low temperature. It is, however, preferable for this
concentration to be at least 5%. Lower concentrations are
economically less advantageous because of the volume of liquid
phase which becomes too large.
[0046] The proportion between the organic phase and the acid or
acids is not critical. The weight ratio between the organic phase
and the acid or acids is selected preferably between 0.3 and
2.0.
[0047] The dispersion of the invention may be in a specific
embodiment.
[0048] According to this embodiment, the dispersion is such that at
least 90% of the particles are single-crystal particles.
"Single-crystal" particles means particles which, when the
dispersion is examined under a TEM (high-resolution transmission
electron microscope), appear to be individualized and consisting of
a single crystallite.
[0049] The cryo-TEM technique can also be used to determine the
state of aggregation of the elementary particles. In this method,
the transmission electron microscope (TEM) is used to observe
samples that are kept frozen in their natural medium, which is
either water or organic diluents such as aromatic or aliphatic
solvents like, for example, Solvesso and Isopar, or certain
alcohols such as ethanol.
[0050] The frozen specimens are thin films about 50 to 100 nm thick
frozen either in liquid ethane for aqueous samples or in liquid
nitrogen for others.
[0051] With cryo-TEM, the state of dispersion of the particles is
well preserved and representative of the state present in the real
medium.
[0052] According to this embodiment, the particles have a fine and
narrow particle size distribution. In fact, they have a d.sub.50 of
between 1 and 5 nm, preferably between 2 and 4 nm.
[0053] In the present description, the particle size distribution
properties refer to notations d, where n is a number from 1 to 99.
This notation represents the particle size such that n % by number
of said particles have a size smaller than or equal to said size.
For example, a d.sub.50 of 3 nanometers means that 50% by number of
the particles have a size of 3 nanometers or smaller.
[0054] The particle size distribution is determined by conventional
transmission electron microscopy (TEM), on a sample previously
dried on a carbon membrane supported on a copper grid.
[0055] This preparation technique is preferred because it allows
for better accuracy of particle size measurement. The zones
selected for the measurements are those that have a state of
dispersion similar to that observed by cryo-TEM.
[0056] The dispersion according to the specific embodiment given
above can be prepared by a method comprising the following
steps:
[0057] a) an aqueous mixture is prepared comprising at least one
cerium salt, optionally a salt of a rare earth other than cerium
and an iron salt, and a salt of at least one element selected from
rhodium and palladium;
[0058] b) the aqueous mixture of step (a) is contacted with a basic
medium to form a reaction mixture of which the pH is maintained at
a basic pH. thereby producing a precipitate;
[0059] c) the precipitate thus obtained is contacted with an acid
and an organic phase, to obtain an organic colloidal
dispersion.
[0060] The first step of the method (step a) consists in preparing
an aqueous mixture, in the usual form of a solution or dispersion,
of element(s) present in the composition of the particles to be
obtained. This mixture comprises salts, preferably soluble, more
particularly an acetate and/or a nitrate, of cerium and rhodium
and/or palladium. In the case of the preparation of the dispersions
according to the different variants described above, this mixture
may further comprise salts of other necessary elements, that is,
salts of a rare earth other than cerium and/or an iron salt.
[0061] The next step (step b) consists in contacting the
abovementioned aqueous mixture with a basic medium. Basic medium
means any medium with a pH above 7. The basic medium is normally an
aqueous solution containing a base. Products of the hydroxide type
can be used as a base in particular. Mention may be made of alkali
metal or alkaline-earth metal hydroxides. Use may also be made of
secondary, tertiary or quaternary amines. However, amines and
ammonia may be preferred insofar as they decrease the risk of
pollution by the alkali or alkaline-earth metal cations. Mention
may also be made of urea.
[0062] The above mixture is contacted with the basic medium under
conditions such that the pH of the reaction mixture formed remains
basic. Thus, the pH of the reaction mixture is maintained at a
value of at least 7, more particularly of at least 7.5 and even
more particularly of between 7.5 and 11.
[0063] The aqueous mixture can be contacted with the basic medium
by introducing the above mixture into the basic medium. Contact can
be continuous, provided that the pH is controlled by adjusting the
respective flow rates of the mixture and the basic medium.
[0064] According to a particular embodiment of the invention, it is
possible to operate in conditions such that when the mixture is
contacted with the basic medium, the pH of the reaction medium thus
formed is kept constant. Constant pH means a pH variation of not
more than .+-.0.2 pH units from the set value. Such conditions can
be obtained by introducing an additional quantity of base into the
reaction mixture formed, during the introduction of the mixture
into the basic medium.
[0065] The contacting is normally carried out at ambient
temperature. This contacting can advantageously be obtained under
an atmosphere of air or nitrogen or a nitrogen-air mixture.
[0066] A precipitate is recovered on completion of the
reaction.
[0067] This precipitate can optionally be separated from its mother
liquor by filtration, centrifugation or any other means known to a
person skilled in the art for such a separation. The separated
product can be washed.
[0068] Preferably, the precipitate is left in wet form, that is, it
is not subjected to a drying or a freeze-drying step or any
operation of this type.
[0069] In the rest of the method, the precipitate can be used as
such, or optionally after being placed again in aqueous
suspension.
[0070] The precipitate is then contacted with at least one acid and
one organic phase, as defined above (step c).
[0071] During step (c), the precipitate is used in its wet form,
and the proportion of oxides of cerium, of the other element
rhodium and/or palladium and optionally of another rare earth
and/or iron, of said precipitate may vary between 10 and 50% by
weight of the weight of the wet precipitate. The percentages of
total oxides can be determined by loss on ignition, for example, by
calcination at 1000.degree. C.
[0072] To obtain an organic colloidal dispersion in step (c), the
optionally redispersed precipitate is contacted with at least one
acid and one organic phase like those described above. The quantity
of acid to be incorporated may be defined by the molar ratio r:
number of moles of acid/number of moles of cerium and/or optionally
of the other rare earth and/or of iron.
[0073] This molar ratio may be between 0.2 and 0.8, preferably
between 0.3 and 0.6.
[0074] The quantity of organic phase to be incorporated is adjusted
in order to obtain a total oxide concentration such as that
mentioned above.
[0075] At this stage, it may be advantageous to add a promoter to
the organic phase, its function being to accelerate the transfer of
the particles of compound(s) from the aqueous phase to the organic
phase and to improve the stability of the organic colloidal
dispersions obtained.
[0076] Promoters that are suitable include compounds with an
alcohol function and particularly linear or branched aliphatic
alcohols with 6 to 12 carbon atoms. By way of specific examples,
mention can be made of 2-ethylhexanol, decanol, dodecanol or
mixtures thereof.
[0077] The proportion of said agent is not critical and may vary
within wide limits. However, a proportion of between 2 and 15% by
weight is generally suitable.
[0078] The order of introduction of the various reagents is
immaterial. The precipitate or its aqueous suspension, the acid,
the organic phase, and optionally the promoter, can be mixed
simultaneously. The acid, the organic phase and optionally the
promoter can also be premixed.
[0079] The aqueous colloidal dispersion can be contacted with the
organic phase in a reactor that is under an atmosphere of air,
nitrogen or an air-nitrogen mixture.
[0080] Although the aqueous colloidal dispersion can be contacted
with the organic phase at ambient temperature, about 20.degree. C.,
it is preferable to operate at a temperature selected in an
interval ranging from 60.degree. C. to 150.degree. C.,
advantageously between 80.degree. C. and 140.degree. C.
[0081] In certain cases, due to the volatility of the organic
phase, it is necessary to condense its vapors by cooling to a
temperature below its boiling point.
[0082] The resulting reaction mixture (mixture of aqueous colloidal
dispersion, acid, organic phase and optionally promoter) is
maintained with stirring throughout the duration of the heating,
which may vary.
[0083] When the heating is stopped, the presence of two phases is
observed: an organic phase containing the colloidal dispersion, and
a residual aqueous phase.
[0084] The presence of a third emulsified phase may sometimes be
observed.
[0085] The organic phase and the aqueous phase are then separated
by conventional separation techniques: settling,
centrifugation.
[0086] As indicated above, the method described applies to the
preparation of a dispersion according to the abovementioned
specific embodiment. It is also possible to implement a method
different from the one given above by the fact that it comprises,
between steps (b) and (c), a drying of the precipitate
particularly. by spray drying or freeze drying. This method leads
to a dispersion according to the invention but the particles of the
specific embodiment do not have the characteristic of being single
crystals.
[0087] The organic colloidal dispersions described above can be
employed as additives for motor fuels, particularly diesel, for
internal combustion engines, more particularly as a diesel fuel
additive for a diesel engine.
[0088] Finally, the invention relates to a fuel for internal
combustion engines that contains a colloidal dispersion of the type
described above. This fuel is obtained by mixing a standard fuel,
particularly of the diesel type, with the dispersion of the
invention, generally in a proportion such that the ratio of element
Ce+element Rh and/or Pd metal+optionally the rare earth element and
iron, to the mass of fuel, is between 5 and 200 ppm.
[0089] The presence of the dispersions of the invention in fuels
has the effect of lowering the autoignition temperature of the soot
and reducing the emission of nitrogen oxides in the engine exhaust
gases, and it can also contribute to the oxidation of the carbon
monoxide and unburnt hydrocarbons.
[0090] Examples will now be provided.
EXAMPLE 1
[0091] This example relates to the preparation of a dispersion
according to the invention, based on cerium, iron and rhodium. This
preparation is made in two steps: the first leads to the formation
of a solid precipitate in the aqueous phase, and the second relates
to the transfer of this precipitate to the organic phase.
[0092] 1) Synthesis of a solid precipitate in aqueous phase
[0093] a) Preparation of an iron acetate solution
[0094] 206.1 g of ferric (III) nitrate nonahydrate
(Fe(NO.sub.3).sub.3.9H.sub.2O of 98% purity from Prolabo) is
dissolved in 1 l of purified water in order to prepare a solution
containing 0.5 mol/l of Fe. 270 ml of a 10% by volume ammonia
solution is added to the ferric nitrate solution thus prepared and
stirred, using a peristaltic pump, at the rate of 10 ml/min.
[0095] The neutral pH suspension obtained is centrifuged at 4500
rpm for 12 minutes. The precipitate recovered is replaced in
suspension of the initial volume with purified water. The
suspension is stirred for 15 minutes, the precipitate is separated
again under the same conditions, and again replaced in suspension
with an equivalent final volume.
[0096] A dispersion with pH 6.5 is thereby obtained, to which 100
ml of acetic acid (CH.sub.3COOH 100% from Prolabo) is added, to
yield an iron acetate solution with pH 2.7 and oxide concentration
of 2.8% of Fe.sub.2O.sub.3 (determined by loss on ignition).
[0097] b) Preparation of a coacetate solution
[0098] 139.7 g of crystallized cerium (III) acetate
(Ce(CH.sub.3COO).sub.3 from Rhodia Electronics and Catalysis
comprising 49.29% of oxide CeO.sub.2) is dissolved in 0.8 l of
purified water. 6.7 g of acetic acid (CH.sub.3COOH 100% from
Prolabo), 3 g of a rhodium (III) nitrate solution
(Rh(NO.sub.3).sub.3 concentrated to 10% of Rh from Aldrich) and
1124.6 g of the previously prepared iron acetate solution, are
added to this solution. The mixture is made up to 2.5 l with
purified water.
[0099] c) Precipitation of the coacetate solution
[0100] The precipitation is carried out in a continuous assembly
comprising: [0101] a 1 l reactor equipped with a propeller stirrer,
set at 400 rpm, with a stock of 0.5 l of basic solution (NH.sub.4OH
at pH=10.5) and an electrode servocontrolled by a pH control pump
with a setpoint at pH 10.5; [0102] two feed bottles, one containing
the coacetate solution previously prepared and the other a 6N
ammonia solution. The flow rate of the coacetate solution is set at
500 ml/h and the flow rate of ammonia is servocontrolled by the pH
regulation; [0103] a drawoff system that is used to adjust the
volume in the reactor to 0.5 l and connected to a second reactor
placed in series with the first; [0104] a second reactor for
recovering the precipitate formed.
[0105] The precipitate is recovered by centrifugation at 3000 rpm
for 12 minutes and then replaced in suspension in purified water in
a concentration of 50 g/l of total oxide.
[0106] 2) Transfer to organic phase
[0107] 340 ml of the previously described aqueous suspension is
placed in a 2 liter double jacket reactor equipped with a
controlled temperature bath. An organic phase containing 129.9 g of
Isopar L (paraffinic solvent from Exxon) and 23.1 g of isostearic
acid (Prisorine 3501 solution from Uniquema) previously dissolved,
are added at ambient temperature.
[0108] The two-phase mixture is then heated to 95.degree. C. in 1 h
30 min, with the stirrer speed set at 220 rpm. The mixture is kept
at 95.degree. C. for 4 hours, and then left to cool at ambient
temperature. The coalescence obtained when stirring is stopped
reveals the formation of a black organic phase, above a clear
aqueous phase. The oxide concentration of the aqueous phase,
determined by loss on ignition, is negligible, attesting to a
quantitative transfer.
[0109] 3) Characterization of the organic colloidal dispersion
based on cerium, iron and rhodium.
[0110] The concentration of the organic colloidal phase, determined
after evaporation of the Isopar L and calcination at 1000.degree.
C., is equal to 9.9% of total oxide. The composition of the oxide
dispersed in the organic phase, determined by potentiometric
methods (Ce) and polarographic methods (Fe), is equimolar in Ce/Fe
and contains 0.26% of rhodium (mass of rhodium metal/mass of
elemental cerium and iron), the rhodium being determined by
ICP/OES. Analysis by cryo-transmission electron microscopy of the
organic colloidal phase reveals perfectly individualized particles
with a diameter of 3 to 5 nm.
EXAMPLE 2
[0111] This example relates to the evaluation on an engine test
bench of the product obtained in the previous example.
[0112] The evaluation is made using a Peugeot 2.2 l cubic capacity
diesel engine, reference DW 12 TED4/L4, placed on a dynamometric
test bench. The exhaust line is equipped with a silicon carbide
particulate filter produced by Ibiden (5.66.times.6200 cpsi).
[0113] The dispersion of the invention is added as an additive to a
diesel containing 7 ppm of sulfur to obtain a proportion of 10 ppm
(Ce+Fe+Rh metal) with respect to the diesel containing
additive.
[0114] The particulate filter is then loaded under the following
conditions: [0115] engine speed: 3000 rpm [0116] torque: 30 Nm
[0117] loading time: 10 hours.
[0118] During this loading phase, the nitrogen oxide NO and
NO.sub.2 emissions are measured continuously using an Ecophysic CLD
700 analyzer.
[0119] The results obtained are given below. The comparative test
is the test performed with, as the additive, a dispersion prepared
following the procedure of example 1 but without rhodium.
TABLE-US-00001 NO + NO.sub.2 emissions measured at end of filter
loading (t = 10 h) Test in ppm Example 2 100 Comparative 125
[0120] A 20% reduction of nitrogen oxide releases is observed when
the dispersion according to the invention is used.
[0121] All the soot accumulated in the filter during 10 hours is
then burned at 500.degree. C. in 320 seconds.
* * * * *