Suspension of cerium oxide particles

Abstract

The present invention relates to a suspension of cerium oxide compound particles having a D50 of 10 to 200 nm and a D90 of less than 1000 nm, determined by laser particle size analysis, in a liquid medium, preferably an aqueous liquid medium, comprising at least one carboxylic acid containing 3 to 9 carbon atoms or at least one functionalized carboxylic acid having 2 carbon atoms or any mixture thereof. The present invention also relates to a process for preparing such a suspension.

Description

Technical Field

[0001] This application claims the priority of European Patent Application Publication No. 22305883.5 filed on June 17, 2022, the entire content of which is incorporated herein by reference for all purposes.

[0002] The present invention relates in particular to a suspension of cerium oxide compound particles useful for the preparation of catalysts and a process for producing said suspension.

Background Art

[0003] Suspensions of cerium compounds have many uses, particularly in heterogeneous catalysis, especially the treatment of exhaust gases from internal combustion engines. In that case, the catalyst reduces the amount of pollutants emitted from internal fuel combustion, namely carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx) and particulate matter (PM).

[0004] Suspensions of cerium compounds may be particularly relevant for the preparation of so-called three-way catalysts or gasoline particulate filters used in stoichiometric gasoline or gas fuel engines. Cerium compounds are oxygen buffers that promote the conversion of CO, HC and NOx around stoichiometry. Suspensions of cerium compounds are also useful for adding some cerium compounds into the formulations of catalysts for lean engines such as diesel engines or lean-burn gasoline engines. Those lean catalysts can be, for example, oxidation catalysts, particulate filters and NOx reduction catalysts (NOx storage or ammonia selective catalytic reduction catalysts). In that case, the cerium compound is considered as an oxygen enhancer that promotes oxidation reactions or a stabilizer that maintains noble metals in small particles.

[0005] These suspensions can also be used as corrosion inhibitors for coatings, or as UV absorbers or moisture control additives in cosmetics, or optionally as mechanical polishing components in polishing applications.

[0006] U.S. Patent Application Publication No. 5,922,330 discloses an aqueous colloidal dispersion of a cerium compound consisting essentially of cerium(IV) oxide and / or hydrated cerium(IV) oxide, having a pH higher than 5 and a conductivity of up to 2 mS / cm, and formed from a cerium nitrate starting product. However, the stability and catalytic properties of the dispersions disclosed in this reference are still not satisfactory.

[0007] U.S. Patent Application Publication No. 7,462,665 discloses a mixture of an aqueous paint and an aqueous colloidal dispersion of a cerium compound, the dispersion comprising an organic acid having at least three acid functional groups or a salt of this acid, having a third pK of up to 10 and showing a pH of at least 7, and aqueous ammonia or an amine. These dispersions do not appear to be suitable for catalytic applications.

[0008] If the disclosure of any patent, patent application, and publication incorporated herein by reference conflicts with the description of this application to the extent that it may obscure a term, the description shall control. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0009] The present invention now provides a suspension of cerium oxide compound particles having good properties for catalytic applications and facilitating use during the preparation of catalysts, and in particular, the suspension exhibits excellent stability when its pH is raised to a basic pH.

[0010] In a first aspect, the present invention relates to a suspension of cerium oxide compound particles having a D50 of 10 to 200 nm and a D90 of less than 1000 nm, as determined by laser particle size analysis, in a liquid medium, preferably an aqueous liquid medium, comprising at least one carboxylic acid containing 3 to 9 carbon atoms, at least one functionalized carboxylic acid having 2 carbon atoms, or any mixture thereof.

[0011] In certain embodiments, the cerium oxide compound particles of the suspension of the present invention have a D10 of 5 nm or more as determined by laser particle size analysis.

[0012] In certain embodiments, the cerium oxide compound particles of the suspension of the present invention are composed of crystallites having a diameter of 30 nm or less as determined by XRD after air calcination at 500 °C for 1 hour.

[0013] In another specific embodiment, the cerium oxide compound particles of the solution of the present invention have a BET specific surface area of at least 50 m2 / g after air calcination at 500 °C for 1 hour.

[0014] In a more specific embodiment, the cerium oxide compound particles of the suspension of the present invention have a total pore volume of at least 0.05 ml / g, preferably at least 1 ml / g, more preferably at least 0.15 ml / g as determined by nitrogen adsorption after air calcination at 500 °C for 1 hour.

[0015] In another embodiment, the suspension of the present invention contains 10 wt% to 40 wt% of cerium oxide compound particles represented as CeO2 based on the total weight of the suspension.

[0016] In a further embodiment, the suspension of the present invention contains at least one carboxylic acid, and the carboxylic acid includes di- or tri-carboxylic acids, preferably citric acid.

[0017] In a further embodiment, in the suspension of the present invention, the molar ratio of the carboxylic acid to the cerium oxide compound is 0.05 to 1.5.

[0018] In certain embodiments, the liquid medium of the suspension of the present invention is an aqueous medium having a pH of 7 or less.

[0019] In still a further embodiment, the D50 of the cerium oxide compound particles of the suspension of the present invention measured at pH 10 increases by less than 30% compared to the D50 of the cerium oxide compound particles measured at pH 5.

[0020] In another aspect, the present invention relates to the use of the suspension of the present invention described above in various aspects for the preparation of a catalyst.

[0021] In a further aspect, the present invention relates to a catalyst obtainable by the use of the suspension of the present invention described above, in particular an exhaust gas pollution prevention catalyst for motor vehicles.

[0022] In yet a further aspect, the present invention relates to a catalyst obtained by the use of the suspension of the present invention described above, in particular an exhaust gas pollution prevention catalyst for motor vehicles.

[0023] In another aspect, the present invention relates to the use of the suspension of the present invention as a component of a polishing composition.

[0024] The present invention is a process for producing the suspension of the present invention, comprising: (a) providing a first suspension in a liquid medium comprising a cerium oxide compound and at least one carboxylic acid containing 3 to 9 carbon atoms or a functionalized carboxylic acid having 2 carbon atoms; (b) subjecting the first suspension to mechanical treatment to provide the suspension according to any one of claims 1 to 10. The present invention also relates to a process comprising the above.

[0025] In a more specific aspect of the process, the pH during step (b) is maintained at 4 to 6.

[0026] In a further aspect of the process, mechanical energy is applied using inert metal oxide beads, in particular zirconia beads.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Accordingly, the present invention relates to a suspension of cerium oxide compound particles having a D50 of 10 to 200 nm and a D90 of less than 1000 nm, as determined by laser particle size analysis, in a liquid medium, preferably an aqueous liquid medium, comprising at least one carboxylic acid containing 3 to 9 carbon atoms, at least one functionalized carboxylic acid having 2 carbon atoms or any mixture thereof.

[0028] Surprisingly, it has been found that the suspension according to the present invention has excellent stability of its particle size even when the pH of the suspension is increased to a basic value which can be as high as about 10. This allows for great flexibility, for example, especially when combining the suspension with other components, particularly alkaline solutions or slurries, for catalyst production. For example, some alkaline solutions or suspensions such as basic solutions of noble metals or transition metals can be added. The flexibility of the suspension is also advantageous when adjusting the pH of the suspension, for example, by adding ammonia, to change the rheology of the suspension and facilitate the coating process on a substrate. The use of the suspension according to the present invention can further reduce or avoid the operator's exposure to dust. The cerium oxide compound particles in the suspension can also exhibit high porosity and surface area, which is particularly advantageous for catalytic applications.

[0029] In the suspension according to the present invention, the cerium oxide compound can be suitably selected from cerium oxides, oxyhydroxides and hydroxides or mixtures thereof which may optionally contain one or more dopants.

[0030] The dopant can be selected from the following non-limiting list: any rare earth other than cerium or zirconium, such as lanthanum, yttrium, neodymium or praseodymium.

[0031] Preferably, the cerium oxide compound is cerium oxide. In particular, the cerium oxide compound contains cerium(IV) oxide or consists of cerium(IV) oxide. The content of cerium(IV) oxide in the cerium oxide compound is generally at least 80 mol%, particularly at least 90 mol%, at least 91 mol%, at least 92 mol%, at least 93 mol%, at least 94 mol%, at least 95 mol%, at least 96 mol%, at least 97 mol%, at least 98 mol%, at least 99 mol%, at least 100 mol%.

[0032] Preferably, the cerium oxide compound according to the present invention is the cerium oxide compound according to European Patent Application Publication No. 1435338, the content of which is incorporated herein by reference.

[0033] According to European Patent Application Publication No. 1435338, the cerium oxide compound is cerium oxide, which is an oxide consisting essentially of cerium oxide and has a specific surface area of 30.0 m 2 / g or more after calcination at 900 °C for 5 hours.

[0034] By convention, the content of the cerium oxide compound in the suspension according to the present invention is expressed as the weight% of CeO2.

[0035] Diameter (D) The cerium oxide compound is in the form of particles having a D50 of 10 nm to 200 nm. The D50 can be more particularly 20 nm to 150 nm, more particularly 30 nm to 140 nm, more particularly 40 nm to 120 nm.

[0036] In a more specific embodiment, the cerium oxide compound is in the form of particles having a D50 of 60 to 120 nm as measured by laser diffraction.

[0037] The cerium oxide compound particles exhibit a D90 of less than 1000 nm. D90 can be more particularly from 50 nm to 1000 nm, more particularly from 50 nm to 800 nm, even more particularly from 50 nm to 500 nm, even more particularly from 50 nm to 400 nm, even more particularly from 50 nm to 300 nm, even more particularly from 60 nm to 300 nm, even more particularly from 70 nm to 400 nm, even more particularly from 80 nm to 300 nm, even more particularly from 90 nm to 200 nm, even more particularly from 100 nm to 200 nm, even more particularly from 110 nm to 200 nm, even more particularly from 120 nm to 200 nm, even more particularly from 130 nm to 200 nm, even more particularly from 140 nm to 200 nm.

[0038] The cerium oxide compound particles preferably exhibit a D10 of 5 nm or more. D10 can be more particularly 10 nm or more, even more particularly 15 nm or more, even more particularly 20 nm or more, even more particularly 25 nm or more, even more particularly 30 nm or more, even more particularly 35 nm or more, even more particularly 40 nm or more, and even more particularly 45 nm or more.

[0039] The cerium oxide compound particles preferably exhibit a D10 of 150 nm or less, more particularly 140 nm or less, more particularly 130 nm or less, more particularly 120 nm or less, more particularly 110 nm or less, and more particularly 100 nm or less.

[0040] D50 corresponds to the median diameter as conventionally understood statistically, which is determined from the volume distribution of the diameters of the particles obtained by means of laser diffraction technology. Thus, this is the value at which 50% of the particles in the cumulative curve of the distribution have a diameter greater than D50 and 50% of the particles have a diameter less than D50.

[0041] According to the present invention, D10, D50 and D90 are determined by laser diffraction using a Beckman Coulter LS 13320 laser diffraction particle size analyzer (Beckman Colter, Inc.) using standard procedures predetermined by the instrument software.

[0042] The Fraunhofer mode can be used according to the manufacturer's guidelines (https: / / www.beckmancoulter.com / wsrportal / techdocs?docname=B05577AB.pdf). A relative refractive index of 1.6 is used. The method disclosed in the examples can be conveniently used.

[0043] The measurement can optionally be carried out in water in the presence of a dispersant.

[0044] According to the present invention, D10, D50 and D90 referred to in this specification and the claims refer to the D values measured using a Beckman Coulter LS 13320 laser diffraction particle size analyzer (except when certain other methods are used (see Example 2).

[0045] Stability A particularly preferred property of the suspension according to the present invention is its stability when the pH is increased. This stability property can be tested, for example, by providing an initial suspension according to the present invention, adjusting its pH to pH 5, measuring the D50 of the particles in the sample, adding a basic compound or solution to the initial suspension to achieve a pH increase up to pH 10, and measuring the D50 of the particles in the basic suspension.

[0046] For the purpose of the test method, the pH increase is achieved by adding the volume of 4N aqueous ammonia solution required to adjust the pH of the suspension to pH 10. The test method is carried out under substantially isothermal conditions while maintaining the temperature at 25 °C ± 5 °C.

[0047] The pH measurement was carried out using a WTW SetTix pH electrode based on a liquid electrolyte reference.

[0048] In this stability test, it is possible to define a "stability index" (referred to as SF) by the following formula. SF = (D50 at pH 10 - D50 at pH 5) / D50 at pH 5 × 100 The D50 at pH 10 is the D50 in micrometers measured on the suspension at pH 10. The D50 at pH 5 is the D50 in micrometers measured on the suspension at pH 5. The lower the SF, the higher the stability of the suspension.

[0049] For example, the SF is generally less than 30%, preferably less than 25%, preferably less than 20%, preferably less than 15%, more preferably less than 10%. The SF can be equal to 0 or about 0. When the SF is about 0, a slightly negative value may be obtained due to the standard deviation of the various measurement methods applied.

[0050] The suspension according to the present invention exhibits very good stability in its particle size, which constitutes an advantage of the processing steps in catalyst preparation.

[0051] According to one specific feature of the suspension of the present invention, when the suspension according to the present invention is maintained in the temperature range of 5°C to 50°C, the stability index does not show significant fluctuations.

[0052] Therefore, the fluctuations within this temperature range are less than 10%, preferably less than 5% with respect to the stability index (SF).

[0053] Ratio of cerium oxide The ratio of cerium oxide in the suspension is 10% to 40% by weight, more particularly 15% to 35% by weight, even more particularly 20% to 30% by weight.

[0054] This ratio in percentage (%) is represented by the weight of CeO2 corresponding to the cerium oxide compound with respect to the total weight of the suspension.

[0055] For example, a ratio of 40% by weight of cerium oxide corresponds to 40 g of CeO2 per 100 g of the suspension.

[0056] Carboxylic acid The suspension of the present invention also contains at least one carboxylic acid containing 3 to 9 carbon atoms, at least one functionalized carboxylic acid having 2 carbon atoms, or any mixture thereof.

[0057] According to a particular embodiment, the suspension also contains a mixture of carboxylic acids containing 3 to 9 carbon atoms.

[0058] According to a particular embodiment, the suspension also contains a mixture of functionalized carboxylic acids having 2 carbon atoms.

[0059] According to a particular embodiment, the suspension also contains a mixture of at least one carboxylic acid containing 3 to 9 carbon atoms and at least one functionalized carboxylic acid having 2 carbon atoms.

[0060] The carboxylic acid may also contain at least one functional group other than COOH.

[0061] The functional group may be selected, for example, from the group consisting of OH, C=O, acid anhydride, and ester groups.

[0062] According to a specific embodiment, at least one carboxylic acid containing 3 to 9 carbon atoms in the solution of the present invention may suitably be a monocarboxylic acid, di- or tri-carboxylic acid, or alpha-hydroxy-carboxylic acid.

[0063] More particularly, the carboxylic acid may be of the formula: R1-COOH, where R1 is a linear or branched alkyl group containing 2 to 8, more particularly 2 to 7 carbon atoms.

[0064] More particularly, the carboxylic acid of the present invention may be selected from the group consisting of propionic acid, butanoic acid, hexanoic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, and citric acid.

[0065] In the suspension according to the present invention, at least one carboxylic acid preferably includes a di- or tri-carboxylic acid having 3 to 9 carbon atoms. Citric acid is more particularly preferred.

[0066] In another aspect, the suspension according to the present invention includes at least one functionalized carboxylic acid containing two carbon atoms. According to this aspect, the carboxylic acid is appropriately selected from oxalic acid, hydroxyacetic acid, and glyoxylic acid.

[0067] In a more specific aspect of the present invention, the molar ratio of the carboxylic acid to the cerium oxide compound in the suspension is 0.05 to 1.5. This molar ratio is preferably 0.1 to 1, more preferably 0.1 to 0.5.

[0068] aqueous liquid medium The suspension of the present invention is in an aqueous liquid medium. This aqueous liquid medium contains water.

[0069] According to one embodiment, water is the main constituent of the liquid medium. In a specific aspect of the present invention, the aqueous liquid medium is water.

[0070] According to another embodiment, the aqueous liquid medium may include at least one other liquid that is miscible with water.

[0071] The other liquid can be, for example, an organic liquid such as an alcohol, an ester, or a ketone. The nature and amount of the other liquid should preferably be such that it does not affect the stability of the suspension.

[0072] The weight ratio of water / other liquid is preferably 100 / 0 to 80 / 20, more preferably 100 / 0 to 90 / 10, and even more preferably 100 / 0 to 95 / 5.

[0073] In a specific aspect of the present invention, the liquid medium, particularly the aqueous liquid medium, also includes at least one carboxylic acid containing 3 to 9 carbon atoms and / or at least one functionalized carboxylic acid having two carbon atoms.

[0074] While not wishing to be bound by any theory, it is understood that at least one carboxylic acid containing 3 to 9 carbon atoms and / or at least one functionalized carboxylic acid having 2 carbon atoms can be present in a coordinated form in a solution in an aqueous liquid medium and also on the surface of the particles of the cerium oxide compound.

[0075] In one embodiment, the liquid medium contains in particular an inorganic acid such as nitric acid. The inorganic acid helps to adjust the pH and has an additional stabilizing effect.

[0076] The liquid medium can also contain impurities present in the cerium oxide compound being mechanically treated. The impurities can be released during the mechanical treatment.

[0077] In another embodiment, the liquid medium contains in particular a base such as ammonia. The base can be used to adjust the pH to a desired value.

[0078] The pH of the suspension is from 2.0 to 7.0. In a preferred embodiment, the pH of the suspension is from 3.0 to 6.0, preferably from 4.0 to 6.0. In a more preferred embodiment, the pH is about 5. When referring to a pH value, "about" means that the numerical value of the pH can vary plus or minus 4% of the numerical value, preferably plus or minus 2% above or below the numerical value.

[0079] solid According to a further aspect, the invention depends on a solid. After calcining the suspension in air at 500 °C for 1 hour, the solid can be isolated from the suspension.

[0080] This calcination treatment can be carried out by placing the suspension directly into an electric furnace. In one embodiment, the temperature of the furnace is then raised at a temperature ramp of 4 °C per minute. The solid recovered by this treatment consists mainly of the cerium oxide compound particles according to the invention.

[0081] Composition of the cerium oxide compound particles in the suspension The cerium oxide compound particles in the suspension according to the present invention are composed of crystallites having a diameter of 30 nm or less.

[0082] Preferably, the crystallite diameter is 20 nm or less. More preferably, the crystallite diameter is 10 nm or less.

[0083] In a specific embodiment of the present invention, the cerium oxide compound particles in the suspension according to the present invention are composed of crystallites having a diameter of 3 nm or more.

[0084] According to another aspect of the present invention, the crystallite diameter is 5 nm or more.

[0085] The average diameter of the above crystallites is determined by X-ray diffraction (XRD) technology. The X-ray powder diffraction pattern is obtained with an X'pertPro MPD powder diffractometer (PANAlytical Company) equipped with a Cu Kα (1.5406 angstrom) radiation source and a linear detector X Celerator Detector. Scattering intensity data was collected from 2θ values of 19 to 85° by scanning at 0.017° steps using a counting time of 28 seconds per step. The crystal phase was identified by matching with the International Centre for Diffraction Data Powder Diffraction File (ICDD-PDF). The average crystallite diameter (DXRD) of the sample was determined using the Scherrer equation from the line broadening considering the instrument width, and the lattice parameter was estimated by the standard cubic indexing method using the intensity of the main reflection (111).

[0086] XRD is generally performed on the solid isolated from the suspension as described in the previous section.

[0087] Specific surface area (SSA) The cerium oxide compound particles of the suspension of the present invention exhibit a specific surface area (BET) of at least 50 m 2 / g, particularly at least 70 m2 / g, more particularly at least 90 m2 / g.

[0088] This specific surface area is 250 m 2 / g or less, particularly 200 m 2 / g or less, more particularly 170 m 2 / g or less.

[0089] According to the present invention, the "specific surface area (BET) of the cerium oxide compound particles" refers to the specific surface area (BET) of the solid isolated from the suspension, that is, the cerium oxide compound, particularly cerium oxide.

[0090] The term "specific surface area (BET)" is understood to mean the BET specific surface area determined by nitrogen adsorption.

[0091] The specific surface area is well known to those skilled in the art and is measured according to the Brunauer-Emmett-Teller method. The theory of this method was first described in the journal "The Journal of the American Chemical Society, 60, 309 (1938)". More detailed information on this theory can also be found in Chapter 4 of "Powder surface area and porosity", 2nd edition, ISBN 978-94-015-7955-1. The method of nitrogen adsorption is disclosed in the standard ASTM D 3663-03 (re-approved in 2008). In practice, the specific surface area (BET) can be automatically measured using a Micromeritics apparatus Flowsorb II 2300 or apparatus Tristar 3000 according to the manufacturer's guidelines. They can also be automatically measured using a Mountech Macsorb analyzer model I-1220 according to the manufacturer's guidelines. Before measurement, the sample is optionally degassed by heating at a temperature of up to 300 °C under vacuum to remove adsorbed volatile species. More specific conditions can be found in the examples.

[0092] Total pore volume The cerium oxide compound particles used in the suspension according to the present invention can also be further characterized by their total pore volume determined by nitrogen porosimetry. The measurement was carried out as described in Example 1.

[0093] The total pore volume can be determined after firing the solid isolated from the suspension in air at 500 °C for 1 hour as described above.

[0094] In the suspension according to the present invention, the cerium oxide compound particles have a total pore volume of at least 0.05 ml / g, preferably at least 0.1 ml / g, more preferably 0.15 ml / g, determined by nitrogen adsorption.

[0095] In the suspension according to the present invention, the cerium oxide compound particles have a total pore volume of at most 1.00 ml / g, preferably at most 0.70 ml / g, determined by nitrogen adsorption.

[0096] Regarding the determination of nitrogen porosity, a TRISTAR II 3020 analyzer manufactured by Micromeritics is used according to the manufacturer's guidelines.

[0097] To determine the nitrogen porosity, the Barrett, Joyner, and Halenda (BJH) method of the Harkins-Jura law is used. The analysis of the results is carried out on the desorption curve. Before any measurement, the sample was pretreated in a vacuum oven at 300 °C for 60 minutes as done for the specific surface area evaluation to remove physically adsorbed volatile species.

[0098] Process for producing the suspension The present invention relates to (a) providing a first suspension in a liquid medium comprising a cerium oxide compound and at least one carboxylic acid containing 3 to 9 carbon atoms or a functionalized carboxylic acid containing at least 2 carbon atoms; (b) subjecting the first suspension to mechanical treatment to provide a suspension according to the present invention; and also relates to a process for producing a suspension according to the present invention, comprising the above steps.

[0099] Preferably, the cerium oxide compound according to the present invention is a cerium oxide compound according to European Patent Application Publication No. 1435338, the content of which is incorporated herein by reference.

[0100] The amounts of the cerium oxide compound, carboxylic acid and liquid medium applied in step (a) are appropriately adjusted to produce a suspension having the desired proportions of cerium oxide compound and carboxylic acid in the final suspension recovered after step (b), such proportions being as described above.

[0101] The first suspension of the cerium oxide compound obtained in step (a) is subjected to mechanical treatment (step (b)) to reduce the particle size. A device is used that provides sufficient energy / shear to reduce the particle size without significantly affecting the specific surface area. The particles of the cerium oxide compound are thought to be in the form of agglomerates broken into primary particles or smaller aggregates of primary particles. Where appropriate, impurities contained in the primary particles are released into the liquid medium. In one aspect, the impurity is a basic impurity and the pH of the suspension increases during mechanical treatment.

[0102] In the process according to the invention, the pH of the suspension during step (b) is maintained at 4 - 6, preferably about 5. Where appropriate, the pH of the suspension is maintained by the addition of an acid. In particular, the pH can be maintained by the addition of a carboxylic acid as described above. More particularly, the pH is maintained by the addition of at least one of the same carboxylic acids used to provide the suspension in step (a).

[0103] The device used for the mechanical treatment in step (b) should also provide good mixing to ensure a homogeneous treatment of the dispersion. The device can be a high-pressure homogenizer, a wet jet mill, an agitator bead mill, a high-shear stirrer, an ultrasonic homogenizer.

[0104] A high-pressure homogenizer (HPH) involves forcing a dispersion through a narrow gap (e.g., a nozzle with a diameter of 0.1 - 0.2 mm) at a high pressure of about 1500 - 4000 bar, and then relaxing the dispersion through this nozzle to atmospheric pressure. The dispersion is then subjected to very high shear stress, cavitation, and turbulent flow that causes agglomerate deagglomeration. Shear is induced by the sudden restriction of the flow through a restrictive nozzle.

[0105] The technology of wet jet mills shows some similarities to the technology of HPH. In a wet jet mill, the dispersion is usually compressed in a chamber at 1500 - 2500 bar, divided into two streams, and they pass through two respective nozzles with a diameter of 0.1 - 0.2 mm. Then, the dispersion discharged from the nozzles at atmospheric pressure forms two jets of liquid. The two nozzles are in opposite positions, and the two jets collide with each other at high speed. The collision generates high shear stress on the particles and causes their deagglomeration.

[0106] The technology of agitator bead mills is based on the grinding of solids with hard beads that come into contact with the solids and move at high speed. The beads are often made of hard materials, such as inert metal oxides like zirconia. The beads preferably exhibit a diameter of less than 500 μm, more particularly 50 - 500 μm, and even more particularly 200 - 500 μm. The smaller the diameter, the more beads can be added in contact with the solids, which enables obtaining more collisions between the beads and the solid particles. More details regarding this technology can be found in the examples. A person skilled in the art can obtain a suspension as claimed using the conditions of wet milling disclosed in the examples. An agitator bead mill consists of a grinding container containing beads and means for moving the beads inside the container. The means ensures vigorous movement of the beads inside the container. Various agitator bead mills available on the market can be used in the process of the present invention. The technology of agitator beads has been conveniently used for the preparation of the suspensions disclosed in the examples.

[0107] Use of the suspension The present invention also relates to the use of the suspension according to the invention for the preparation of catalysts, in particular catalysts for preventing motor vehicle exhaust pollution. The invention also relates to devices, catalytic converters, comprising an anti-pollution catalyst obtained by using the suspension according to the invention.

[0108] The present invention also relates to the use of the suspension according to the invention as a component of a polishing composition for the polishing of substrates such as, for example, glass or semiconductor substrates. In particular, the suspension according to the invention can be used in a chemical mechanical planarization (CMP) process for the polishing of semiconductor substrates.

[0109] The following examples in this specification are intended to illustrate the invention but not to limit it.

Examples

[0110] Example 1: Materials and methods Milled suspension According to the required analysis, the milled suspension is - Used "as is" for particle size analysis and dynamic light scattering, - Fired in an electric furnace for 1 hour at 500 °C (4 °C / min ramp) to obtain the solid fraction used for XRD, SBET and N2 porosimetry.

[0111] Particle size analysis of the suspension by laser diffraction A Beckman-Coulter laser particle size analyzer LS13320 was used. A relative refractive index of 1.6 was used.

[0112] Approximately 20 mL of the suspension is placed in a 50 mL beaker. The pH is then adjusted to 5, 8 or 10 by introducing droplets of 4N ammonia. After subjecting the suspension to ultrasonic treatment at over 120 W for 5 minutes in an external US bath, the suspension is placed under mechanical stirring for 5 minutes. The pH of the Beckman-Coulter bath is also adjusted to the desired pH by using 5N ammonia. The suspension is then introduced drop by drop into the measurement batch until 40% < PIDS < 50. When this condition is met, the measurement is carried out.

[0113] Particle size analysis of the suspension by dynamic light scattering (DLS) DLS is performed on a Zetasizer nano ZS manufactured by Malvern.

[0114] Add 5 drops of the suspension to 80 mL of deionized water. Sonicate the as-prepared suspension in a bath at 120 W for 5 minutes. Then add 1 drop of the as-prepared suspension to a DLS cell (12.5×12.5×45 mm). Fill the cell with 2.5 mL of water and analyze.

[0115] Specific surface area (BET) The surface area was measured by the BET flow method (multi-point) with N2 adsorption at liquid N2 temperature (77 K) using a Micromeritics TRISTAR II 3020 analyzer. The specific surface area was calculated by the well-known Brunauer-Emmett-Teller (BET) method. Before measurement, the sample was pretreated in a vacuum oven at 300 °C for 60 minutes to remove any residual moisture and adsorbed species.

[0116] Nitrogen porosity A TriStar II 3020 analyzer manufactured by Micromeritics was used to determine the nitrogen porosity according to the manufacturer's guidelines.

[0117] To determine the nitrogen porosity, the Barrett, Joyner, and Halenda (BJH) method of the Harkins-Jura law was used. The analysis of the results was performed on the desorption curve. Before any measurement, the sample was pretreated in a vacuum oven at 300 °C for 60 minutes as done for the specific surface area evaluation to remove physically adsorbed volatile species.

[0118] XRD of the recovered powder The X-ray powder diffraction pattern was obtained using an X’pertPro MPD powder diffractometer (PANAlytical Company) equipped with a Cu Kα (1.5406 Å) radiation source and a linear detector, the X Celerator Detector. Scattering intensity data were collected from 2θ values of 19 to 85° by scanning at 0.017° steps using a counting time of 28 seconds per step. The crystal phase was identified by matching with the International Centre for Diffraction Data Powder Diffraction File (ICDD-PDF). The average crystallite size of the sample (DXRD) was determined using the Scherrer equation from the line broadening taking into account the instrumental width, and the lattice parameter was estimated by the standard cubic indexing method using the intensity of the main reflection (111).

[0119] For Examples 2 to 4 and the Comparative Example below, the cerium oxide particles used in step (a) were prepared according to the process disclosed in European Patent No. 1435338 B1. This cerium oxide had a specific surface area of 155 m2 / g after calcination at 700 °C for 2 hours in air and 83 m2 / g after calcination at 800 °C for 2 hours in air. The particle size was D50 of 4.0 μm and D90 of 6.6 μm. The crystallite size measured by XRD was approximately 8 nm. It was observed that the crystallite size of the cerium oxide after mechanical treatment was substantially the same.

[0120] For Example 5 below, the cerium oxide particles used in step (a) were prepared in the same manner as the cerium oxide particles of Examples 2 to 4, except that the product was spray-dried and not calcined in air.

[0121] Example 2 The cerium oxide (40 g) prepared above was added to distilled water (158 g) under mechanical stirring. The pH of the suspension was 6.6. Next, citric acid (8.9 g) was added to give a ratio of citric acid / cerium oxide of 0.2. The suspension was further homogenized for 15 minutes under mechanical stirring.

[0122] Next, 150 mL of a homogeneous dispersion was placed into a bowl (500 ml capacity, bowl diameter 10 cm) of a laboratory bead mill containing zirconia beads (605.5 g, average diameter 350 μm). This dispersion was milled in the bowl at 1500 rpm for 60 minutes using a bead stirrer, and finally 7.9 mL of 4N NH4OH solution was added to raise the pH to pH 5.

[0123] The properties of the milled suspension are reported in Table 1.

[0124] The resulting suspension is ceria at a concentration of 20 wt%. The particle size of the suspension was measured by laser diffraction using a D50 of 63 nm. When the particle size is measured by another method (diffusing wave spectroscopy (DLS)), the D50 also becomes as high as a value of 133 nm.

[0125] Next, 4N NH4OH solution is added to the suspension to raise the pH from 5 to 10. Table 1 demonstrates that there is no effect on the particle size and the stabilization factor SF is equal to 0.

[0126] Example 3 Example 3 was carried out according to the procedure of Example 2, except that the solid content of the suspension was 25 wt%.

[0127] As can be seen from Table I, a D50 of 61 nm, which is equivalent to that of Example 2, and the concentration effect do not adversely affect the stability of the suspension. At pH 10, the particle size (D50 = 61 nm) remains very stable with a "stability index" (SF) of 0.

[0128] Example 4 Example 4 was carried out according to the protocol of Example 2, except that the solid content of the suspension was 33 wt% instead of 20 wt%, and 14.7 g of citric acid solution was added to the initial suspension of cerium oxide. The final pH of the solution was 1.9. Milling was carried out under these conditions, and finally the pH was raised to pH 5 by adding 4N NH4OH solution.

[0129] The properties of the prepared suspension are reported in Table 1. Similar to Examples 2 and 3, the particle size does not change even when the pH is increased to 10 (D50 is 62 nm at pH 5 and pH 10), and as a result, SF is equal to 0.

[0130] Example 5: Example 4 was carried out according to the protocol of Example 1, but the solid content of the suspension was 30 wt% and different zirconia beads with an average particle size of 105 μm were used.

[0131] The properties of the prepared suspension are reported in Table 1. D50 is 120 nm at pH 5.0, and a slight increase in D50 was observed at pH 10 (127 nm), but SF remained very low at 5.8%.

[0132] Comparative Example 1 A suspension was prepared in the same manner as in Example 2, but acetic acid was used instead of citric acid.

[0133] The particle size of the suspension at pH 5 (i.e., D50 is 66 nm) is within the target close to that of Example 2 (i.e., D50 is 63 nm).

[0134] NH4OH was added to evaluate the stability of the suspension when the pH was increased from 5 to 10. A significant increase in particle size was observed (D50 at pH 10 is 16300 compared to 63 in Example 2), resulting in a very high stability index "sF" exceeding 20000%.

[0135] Therefore, the suspension prepared in this Comparative Example 1 is not stable when the pH increases.

[0136] Comparative Example 2 A suspension was prepared under the same conditions as in Comparative Example 1 at a solid content of 20 wt%, except that the suspension was milled without adding any carboxylic acid and fixed at a pH of 8 by adding 4N NH4OH before the start of milling.

[0137] Table 1 shows that the particle size of the suspension after pulverization is much larger, with D50 exceeding 2000 nm (i.e., 2060 nm).

[0138] Comparative Example 3 A suspension was prepared according to European Patent No. 0208580. When measured by either laser diffraction or DLS, the particle size is much lower, with D50 less than 10 nm (i.e., 9.4 nm), so the suspension is different. The surface area and N2 porosity of the solid fraction recovered during firing at 500 °C / 1 hour in air are much smaller than those of any of the examples according to the present invention (13 m 2 / g compared to 119, 117, 125, and 117 m 2 / g for Examples 2 - 5 respectively).

[0139] The characteristics of the suspensions according to different examples and comparative examples are shown in Table 1 below.

[0140]

Table 1

Claims

1. A suspension of cerium oxide compound particles having a D50 of 10 to 200 nm and a D90 of less than 1000 nm, as determined by laser particle size analysis, in a liquid medium, preferably an aqueous liquid medium, comprising at least one carboxylic acid containing 3 to 9 carbon atoms or at least one functionalized carboxylic acid having 2 carbon atoms or any mixture thereof.

2. The suspension according to claim 1, wherein the cerium oxide compound particles have a D10 of 5 nm or more as determined by laser particle size analysis.

3. The suspension according to claim 1 or 2, wherein the cerium oxide compound particles are composed of crystallites having a diameter of 30 nm or less as determined by XRD after air calcination at 500 °C for 1 hour.

4. The cerium oxide compound particles have a BET specific surface area of at least 50 m ２ / g after air calcination at 500°C for 1 hour, and the suspension according to any one of claims 1 to 3.

5. The suspension according to any one of claims 1 to 4, wherein the cerium oxide compound particles have a total pore volume of at least 0.05 ml / g, preferably at least 0.1 ml / g, more preferably 0.15 ml / g as determined by nitrogen adsorption after air calcination at 500 °C for 1 hour.

6. 10% to 40% by weight, based on the total weight of the suspension, of cerium oxide compound particles represented as CeO ２ The suspension according to any one of claims 1 to 5, containing cerium oxide compound particles represented as CeO

7. The suspension according to any one of claims 1 to 6, wherein the carboxylic acid includes di- or tri-carboxylic acid, preferably citric acid.

8. The suspension according to any one of claims 1 to 7, wherein the molar ratio of the carboxylic acid to the cerium oxide compound is 0.05 to 1.

5.

9. The suspension according to any one of claims 1 to 8, wherein the liquid medium is an aqueous medium having a pH of 7 or less.

10. The suspension according to any one of claims 1 to 9, wherein the D50 of the cerium oxide compound particles measured at pH 10 increases by less than 30% compared to the D50 of the cerium oxide compound particles measured at pH 5.

11. Use of the suspension according to any one of claims 1 to 10 for the preparation of a catalyst.

12. A catalyst obtainable by the use according to claim 11, in particular an exhaust gas pollution prevention catalyst for motor vehicles.

13. Use of the suspension according to any one of claims 1 to 10 as a component of a polishing composition.

14. A process for producing the suspension according to any one of claims 1 to 10, comprising providing a first suspension in a liquid medium, the first suspension comprising a cerium oxide compound and at least one carboxylic acid containing 3 to 9 carbon atoms or a functionalized carboxylic acid having 2 carbon atoms; subjecting the first suspension to mechanical treatment to provide a suspension according to any one of claims 1 to 10; A process comprising:

15. The process according to claim 14, wherein the pH during step (b) is maintained between 4 and 6.

16. The process according to claim 14 or 15, wherein the mechanical energy is applied using inert metal oxide beads, particularly zirconia beads.

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