Cerium oxide particles and production method thereof

Abstract

The present invention relates to cerium oxide particles having excellent heat resistance and / or pore volume, which are particularly useful for catalysts, functional ceramics, solid electrolytes for fuel cells, polishing, ultraviolet absorbers, etc., and are particularly suitable for use as catalysts or co-catalyst materials in catalysis for purifying vehicle exhaust gas, for example. The present invention also relates to a method for preparing such cerium oxide particles, and a catalyst for purifying exhaust gas using these cerium oxide particles, for example.

Description

[0001] The present invention relates to cerium oxide particles having excellent heat resistance and / or pore volume, which are particularly useful for catalysts, functional ceramics, solid electrolytes for fuel cells, polishing, ultraviolet absorbers, etc., and are particularly suitable for use as catalysts or co-catalyst materials in catalysis for purifying vehicle exhaust gas, for example. The present invention also relates to a method for preparing such cerium oxide particles, and a catalyst for purifying exhaust gas using these cerium oxide particles, for example.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Provisional Application No. 62 / 338,372 filed on May 18, 2016, the contents of which are incorporated herein by reference in their entirety for all purposes. In the event of any inconsistency between this application and the US application that would affect the clarity of terminology or expression, reference should be made only to this application. Background Art

[0004] The following discussion of the prior art is provided in order to place the present invention in the proper technical context and enable its advantages to be more fully understood. However, it should be understood that any discussion of the prior art throughout the specification should not be taken as an explicit or implicit admission that such prior art is widely known or forms part of the common general knowledge in the art.

[0005] The catalyst for purifying vehicle exhaust gas is composed of a catalytic metal such as platinum, palladium, or rhodium and a co-catalyst for enhancing the catalytic action of such metal, both of which are supported on a catalyst carrier made of, for example, aluminum oxide or cordierite. As such a co-catalyst material, a cerium oxide-containing material having the characteristics of absorbing oxygen in an oxidizing atmosphere and desorbing oxygen in a reducing atmosphere (i.e., oxygen absorption and desorption capacity) derived from cerium oxide is used. With such oxygen absorption and desorption capacity, these cerium oxide-containing materials purify harmful components in exhaust gas, such as hydrocarbons, carbon monoxide, and nitrogen oxides, with excellent efficiency. In this way, a large amount of cerium oxide-containing materials are used as co-catalysts.

[0006] The key to activating the function of such a cerium oxide-containing co-catalyst material is to keep the co-catalyst at a high temperature. Low temperatures of the exhaust gas (e.g., at engine start-up) will result in low purification efficiency. Vehicle manufacturers are currently trying to solve this problem by placing the catalyst system close to the engine to introduce the hot exhaust gas from the engine to the catalyst system immediately after discharge. There is also a need for a co-catalyst material that is activated at lower temperatures.

[0007] In general, the efficiency of exhaust gas treatment with a catalyst is proportional to the contact area between the active phase of the catalyst and the exhaust gas, and the oxygen absorption and desorption capacity of the co-catalyst material (such as cerium oxide). Therefore, the co-catalyst material needs to have a sufficiently large specific surface area and a sufficiently high oxygen absorption and desorption capacity, as well as high activity at a relatively low temperature. In addition, the co-catalyst material is generally required to have a sufficiently large pore volume, especially a pore volume with a pore diameter of not more than 200 nm, to increase gas diffusion and thereby obtain a high gas purification efficiency.

[0008] In order to solve these problems, US Pat. No. 7,361,322 B2 proposes a method for obtaining cerium oxide having good heat resistance, the cerium oxide having a strength of more than 30.0 m / s after calcination at 900° C. for 5 hours. 2 / g, especially about 40m 2 / g-50m 2 / g specific surface area, the method comprises the following steps:

[0009] (a) providing a cerium solution, wherein not less than 90 mol % of cerium is a tetravalent cerium cation, the cerium solution having a cerium concentration of 10 to 60 g / L calculated as cerium oxide;

[0010] (b) maintaining the cerium solution prepared in step (a) at 60° C. to 220° C. under heating;

[0011] (c) cooling the heated cerium solution;

[0012] (d) adding a precipitant to the cooled cerium solution to obtain a precipitate; and

[0013] (e) calcining the precipitate.

[0014] However, it seems that the heat resistance of the specific surface area of ​​these cerium oxides obtained by this method is still insufficient. In addition, the method disclosed in US 7,361,322 B2 does not disclose the addition of an organic texturizing agent in one of the steps. Therefore, the mesoporosity of these particles is different from the mesoporosity of the particles of the present invention.

[0015] In addition, in addition to the heat resistance of the specific surface area of ​​the catalyst support, the heat resistance of the total pore volume is also required. High heat resistance of the total pore volume generally refers to a small reduction ratio of the pore volume in a comparison of two different aging conditions such as fresh and 900°C catalyst supports. In the case where an active substance (e.g., an active metal) is loaded onto a catalyst support in the form of a noble metal, the noble metal is loaded into the pores with good dispersibility. Therefore, cerium oxide having a large pore volume even at high temperatures is desired.

[0016] There is still a need to provide cerium oxide having high heat resistance and oxygen absorption and desorption capabilities, which can be used as a catalyst or a promoter material suitable for a catalyst such as a catalyst for purifying exhaust gas. Summary of the invention

[0017] Therefore, the object of the present invention is to provide cerium oxide (cerium (IV) oxide) having excellent heat resistance and adsorption and desorption capacity and / or pore volume, which cerium oxide is useful for catalysts, functional ceramics, solid electrolytes for fuel cells, polishing, ultraviolet absorbers, etc., and is particularly suitable for use as a catalyst or co-catalyst material, especially in catalysis for purifying vehicle exhaust gas. The cerium oxide particles of the present invention also provide high heat resistance of total pore volume and specific surface area. The cerium oxide particles of the present invention are particularly capable of maintaining a large specific surface area even when used in a high temperature environment under air and certain gas conditions (see claim 1). These cerium oxide particles are also able to exhibit high oxygen absorption and desorption capacity in a lower temperature range. In addition, the cerium oxide particles according to the present invention can have excellent pore volume values ​​and / or pore volume values ​​of pores with a pore diameter of no more than 200 nm. The present invention also relates to a method for preparing these cerium oxide particles, and a catalyst for purifying exhaust gas using the cerium oxide particles.

[0018] The cerium oxide particles of the present invention also provide high NO x Capture performance, thus allowing reduction of NO from vehicles x emissions in order to comply with strict pollutant regulations. These cerium oxide particles then also x Trapping (LNT) catalysts are useful.

[0019] The present invention then relates to cerium oxide particles having the following characteristics:

[0020] - After calcination at 900°C for 5 hours in air, including at 45m 2 / g and 80m 2 / g, more particularly between 50m 2 / g and 80m 2 / g, and even more particularly between 55m 2 / g and 80m 2 Specific surface area between 1000 and 2000 μg (SBET); and

[0021] - After calcination at 700°C for 4 hours in a gaseous atmosphere containing 10% by volume of O2, 10% by volume of H2O and the balance of N2, including at 75m 2 / g and 90m 2 / g, more particularly between 78m 2 / g and 90m 2 / g between the specific surface area (SBET).

[0022] More specifically, these particles have the following properties:

[0023] - After calcination at 900°C for 5 hours in air, including at 55m 2 / g and 80m 2 Specific surface area between 1000 and 2000 μg (SBET); and

[0024] - After calcination at 700°C for 4 hours in a gaseous atmosphere containing 10% by volume of O2, 10% by volume of H2O and the balance of N2, including at 75m 2 / g and 90m 2 / g between the specific surface area (SBET).

[0025] The cerium oxide particles may have at least one of the following characteristics:

[0026] - After calcination at 900°C for 24 hours in air, including at 30m 2 / g and 60m 2 / g, more particularly between 37m 2 / g and 60m 2 / g, and even more particularly at 40m 2 / g and 60m 2 Specific surface area between 1000 and 2000 μg (SBET);

[0027] - After calcination at 1000°C for 5 hours in air, including 22m 2 / g and 40m 2 / g, more particularly between 26m 2 / g and 40m 2 Specific surface area between 1000 and 2000 μg (SBET);

[0028] a total pore volume comprised between 1.5 ml / g and 4.0 ml / g after calcination at 400° C. for 10 hours in air;

[0029] a total pore volume comprised between 1.5 ml / g and 3.8 ml / g after calcination at 900° C. for 24 hours in air;

[0030] a pore volume comprising pores having a pore diameter in the range of not more than 200 nm, after calcination at 400° C. for 10 hours in air, of between 0.3 ml / g and 1.5 ml / g;

[0031] a pore volume comprising pores having a pore diameter in the range not exceeding 200 nm of between 0.25 ml / g and 1.0 ml / g after calcination at 900° C. for 24 hours in air.

[0032] They may also have at least one of the following characteristics:

[0033] - After calcination at 900°C for 24 hours in air, including at 37m 2 / g and 60m 2 Specific surface area between 1000 and 2000 μg (SBET);

[0034] - After calcination at 1000°C for 5 hours in air, including 26m 2 / g and 40m 2 Specific surface area between 1000 and 2000 μg (SBET);

[0035] a total pore volume comprised between 1.5 ml / g and 4.0 ml / g after calcination at 400° C. for 10 hours in air;

[0036] a total pore volume comprised between 1.5 ml / g and 3.8 ml / g after calcination at 900° C. for 24 hours in air;

[0037] a pore volume comprising pores having a pore diameter in the range of not more than 200 nm, after calcination at 400° C. for 10 hours in air, of between 0.3 ml / g and 1.5 ml / g;

[0038] a pore volume comprising pores having a pore diameter in the range not exceeding 200 nm of between 0.25 ml / g and 1.0 ml / g after calcination at 900° C. for 24 hours in air.

[0039] The present invention also relates to a method for preparing cerium oxide particles, in particular the cerium oxide particles of the present invention, the method comprising at least the following steps:

[0040] (a) providing a cerium salt solution comprising anions and cations, wherein between 90 mol % and 100 mol % of the cerium cations are tetravalent cerium cations;

[0041] (b) heating the cerium salt solution at a temperature comprised between 60° C. and 220° C. to obtain a suspension comprising a liquid medium and a precipitate;

[0042] (c) reducing the concentration of anions from the cerium salt present in the liquid medium by between 10 mol % and 90 mol % compared to said anions contained in the liquid medium in step (b);

[0043] (d) heating the suspension obtained in step (c) at a temperature comprised between 100° C. and 300° C.;

[0044] (e) optionally cooling the suspension obtained in step (d);

[0045] (f) contacting the suspension with a basic compound;

[0046] (g) heating the suspension from step (f) at a temperature comprised between 60° C. and 300° C.;

[0047] (h) optionally separating the precipitate from the liquid medium;

[0048] (i) optionally adding an organic texturizing agent to the suspension obtained in step (g) or the precipitate obtained in step (h);

[0049] (j) optionally separating the precipitate from the liquid medium; and

[0050] (k) calcining the precipitate obtained at the end of step (g) or obtained in step (h), (i) or (j) to obtain cerium oxide particles; the method comprising at least step (h) and / or step (j),

[0051] The trivalent cerium (III) cation must be present in one of the steps preceding the precipitation step (f).

[0052] The invention also relates to cerium oxide particles readily obtainable by this process.

[0053] Other characteristics, details and advantages of the invention will appear even more fully on reading the following description.

[0054] definition

[0055] Throughout this description, including the claims, the term "comprising one / an" should be understood to be synonymous with the term "comprising at least one / an", unless otherwise indicated, and "between..." should be understood to include the limits.

[0056] It should be noted that, for the sake of continuity of the present description, the limiting values ​​are included in the range of given values ​​unless otherwise indicated.

[0057] Unless otherwise indicated, the amounts are given as oxides. Cerium oxide is in the form of cerium oxide (CeO2).

[0058] For the sake of continuity of the present description, the term "specific surface area" is understood to mean the BET specific surface area determined by nitrogen adsorption according to the standard ASTM D3663-78, based on the Brunauer-Emmett-Teller method described in the journal "The Journal of the American Chemical Society, 60, 309 (1938)". The specific surface areas can be determined with the device Flowsorb II 2300 from Micromeritics, according to the constructor's instructions. They can also be determined with the Macsorb analyzer model I-1220 from Mountech, according to the constructor's instructions. Before the measurement, the samples are degassed under vacuum and adsorbed substances are removed by heating at temperatures of up to 200° C. The conditions can be found in the examples.

[0059] According to standard ASTM-D-4284-83 ("Standard method for pore volume distribution of catalysts by mercury intrusion porosimetry"), the porosity curve and its derived values ​​(such as average size or total pore volume) are determined by mercury intrusion.

[0060] The porosity measurement method given above makes it possible to obtain a pore size graph which gives the pore volume as a function of the pore diameter (V=f(d), V representing the pore volume and d representing the pore diameter). From this pore size graph, it is possible again in a known manner to obtain the curve (C) which gives the derivative dV / dlogD. From the cumulative curve and the data obtained, it is possible to read off the pore volume, in particular the total pore volume and the total pore volume of pores in the range not exceeding 200 nm.

[0061] The Micromeritics Autopore IV 9500 can be used according to the conditions presented in the equipment manual. The total pore volume is determined directly on the porosity curve.

[0062] As used herein, the term "alkyl" is intended to refer to a hydrocarbon having the formula C n H 2n+1The alkyl group is a saturated aliphatic hydrocarbon group containing between 1 and 22 carbon atoms, advantageously between 1 and 10 carbon atoms. The alkyl group may be straight or branched. For example, the alkyl groups include saturated hydrocarbons having one or more carbon atoms, including straight chain alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl; cyclic alkyl groups (or "cycloalkyl" or "alicyclic" or "carbocyclic" groups) such as cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl; branched alkyl groups such as isopropyl, tert-butyl, sec-butyl, and isobutyl; and alkyl-substituted alkyl groups such as alkyl-substituted cycloalkyl and cycloalkyl-substituted alkyl groups. In complex structures, the chains may be branched or bridged. DETAILED DESCRIPTION

[0063] About the preparation method of cerium oxide

[0064] The method for preparing cerium oxide of the present invention comprises using Ce IV and Ce III According to the method of the present invention, firstly in step (a) an aqueous solution of a cerium salt is provided, wherein between 90 mol % and 100 mol % of the cerium cations are tetravalent. IV and optional Ce III The aqueous solution of the cation is characterized by Ce IV The molar ratio of cerium to total cerium is at least 0.9. The ratio may be 1.0.

[0065] In step (a), the cerium salt solution may preferably be a cerium nitrate solution, a cerium ammonium nitrate solution, a cerium sulfate solution and / or a cerium ammonium sulfate solution. The cerium salt may be an ionic compound generally produced by a neutralization reaction of an acid and a base or by dissolving a cerium compound (such as cerium hydroxide) with an acid. They are composed of cerium cations and anions, so that the product is electrically neutral.

[0066] Advantageously, a cerium salt having a purity of at least 99.5%, more particularly at least 99.9%, is used. The cerium salt solution may be an aqueous cerium nitrate solution. The solution is obtained by reacting nitric acid with hydrated cerium oxide, which is obtained by reacting a solution of a cerium salt with an aqueous ammonia solution in the presence of aqueous hydrogen peroxide to convert Ce to nitrate. III Cations are converted to Ce IV Also particularly advantageous is a cerium nitrate solution obtained using the electrolytic oxidation method of a cerium nitrate solution disclosed in FR 2570087. The cerium nitrate solution obtained according to the teaching of FR 2570087 may have an acidity of about 0.6N.

[0067] The cerium salt solution of the present invention may have a cerium cation concentration expressed as cerium oxide comprised between 5 g / L and 150 g / L. For example, a concentration of 225 g / L of cerium nitrate is equivalent to 100 g / L of CeO2; a concentration of 318 g / L of ammonium cerium nitrate is equivalent to 100 g / L of CeO2; a concentration of 193 g / L of cerium sulfate is equivalent to 100 g / L of CeO2; a concentration of 270 g / L of ammonium cerium sulfate is equivalent to 100 g / L of CeO2. The cerium salt concentration of the cerium solution may be adjusted between 10 and 120 g / L, more preferably between 15 and 100 g / L, in terms of cerium oxide, usually with water, preferably with deionized water.

[0068] The cerium salt solution may be acidic. Acidity may be produced by dissolving the salt in water or an acid, for example HNO3 and H2SO4 may be added. + The amount can be from 0.01N and 1N.

[0069] Typical cerium salt solutions contain Ce IV , optional Ce III , H + and NO3 - It can be obtained by mixing an appropriate amount of Ce IV and Ce III and optionally adjusting the acidity. Examples of aqueous solutions that can be used are disclosed in Example 1.

[0070] According to the method of the present invention, the cerium salt solution prepared in step (a) is then maintained at between 60°C and 220°C under heating to cause the reaction of the cerium solution in step (b) to obtain a suspension comprising a liquid medium and a precipitate. The precipitate may be in the form of cerium hydroxide. Any reaction vessel may be used in step (b) without strict restrictions, and a sealed container or an open container may be used. In particular, an autoclave reactor may preferably be used.

[0071] In step (b), the temperature is included between 60°C and 220°C, preferably between 80°C and 180°C, more preferably between 90°C and 160°C. The duration of the heat treatment is generally between 10 minutes and 48 hours, preferably between 30 minutes and 36 hours, more preferably between 1 hour and 24 hours. As described in detail in these examples, the temperature can be between 90°C and 140°C. The duration can be between 30 minutes and 1 hour. Without wishing to be bound by any particular theory, the effect of the heating step is to improve the crystallinity of the precipitate and cause the cerium oxide of the present invention to have better heat resistance.

[0072] In the present invention, steps (a) and (b) can be carried out in one step. In this case, the combined step comprises heating the cerium salt solution comprising anions and cations to obtain a suspension comprising a liquid medium and a precipitate, wherein between 90 mol% and 100 mol% of the cerium cations are tetravalent cerium cations at a temperature of 60°C to 220°C.

[0073] In step (c), water is added to reduce the concentration of anions present in the liquid medium. Compared with the anions contained in the liquid medium in step (b), the concentration of anions from the cerium salt present in the liquid medium is reduced between 10mol% and 90mol%, preferably between 15mol% and 85mol%. If the same amount of anions are present in steps (a) and (b), the reduction of anions in the liquid medium in step (c) can be calculated compared with the anions contained in the liquid medium in step (a) or (b). Therefore, [anions] in step (c) / [anions] in step (b) is between 10%-90%, preferably 15%-85%. When the method includes the typical aqueous solution disclosed above, [NO3 - ] / [NO3 - ] is between 10%-90%, preferably between 15%-85%.

[0074] The anion from the cerium salt may be, for example, a nitrate from cerium nitrate or a sulfate from cerium sulfate.

[0075] This reduction in the concentration of anions present in the liquid medium can be obtained by at least one of the following methods:

[0076] - adding water, preferably deionized water, to the suspension obtained in step (b); and / or

[0077] - removing at least a portion of the liquid medium from the suspension obtained in step (b) and then adding water, preferably deionized water, to the medium. The medium is defined according to the partial removal or complete removal of the liquid medium as previously stated; i.e. the medium may be a precipitate in the case of complete removal of the liquid medium in the step, or conversely a mixture of precipitate and liquid medium in the case of partial removal of the liquid medium.

[0078] The separation of the liquid medium from the precipitate can be carried out, for example, by Nutsche filtration, centrifugation, filter pressing or decantation.

[0079] According to the invention, partial or complete removal of the liquid medium is understood to mean that the liquid medium is partially or completely removed from the precipitate. For example, between 10% and 100% by weight, preferably between 10% and 90% by weight, more preferably between 15% and 95% by weight, in particular between 20% and 90% by weight of the liquid medium present in step (b) can be removed in step (c).

[0080] The reduction in concentration can be determined by mass balance and calculation of the amount of anions in the liquid medium of step (b) and step (c). In the case of cerium nitrate, the reduction in the concentration of anions present in the liquid medium in step (c) compared to the anions contained in the liquid medium in step (b) can be calculated in the case of cerium nitrate as follows:

[0081] The materials at the start of step (a) are Ce(IV)(NO3)4 and Ce(III)(NO3)3 and optionally HNO3.

[0082] 1. NO3 - Calculation of the total number of ions (mol)

[0083] NO3 - (mol)=A / 172.12x[B / 100x 4+(100-B) / 100x 3]+C=D

[0084] in:

[0085] - A is the amount of cerium cations in step (a) calculated as CeO2 (grams)

[0086] - B is the percentage of tetravalent cerium cations per total cerium cations at the start of step (b)

[0087] - C is the amount (mol) of HNO3 in step (a) (if any)

[0088] 2. NO3 in step (b) - Calculation of concentration

[0089] [NO3 - ](mol / l)=D / E

[0090] Wherein E is the volume (liters) of the reaction medium in step (b). B can be measured, for example using a graduated cylinder or meter.

[0091] 3. NO3 in step (c) - Calculation of concentration

[0092] [NO3 - ](mol / l)=F / G

[0093] -F is NO3 - Amount of ions (mol). If the liquid medium is not removed, then F = D. If the liquid medium is removed, then F = D x the removal rate of the liquid medium.

[0094] -G is the volume after adding water (liters).

[0095] 4. NO3 - Concentration reduction ratio

[0096] -[NO3 - ] reduction ratio (%) = [NO3 - ] / [NO3 - ]x100=(F / G) / (D / E)x100.

[0097] The anion concentration can be controlled by directly measuring the anion concentration in steps (b) and (c). - The concentration can be analyzed by ion chromatography or adsorption determination, both of which are commonly used to analyze NO3 in liquid media. - concentration. Place a portion of the liquid medium into the analyzer to automatically measure NO3 - concentration. The two concentrations can then be compared to calculate NO3 - The reduction ratio of concentration.

[0098] In step (d), the suspension is heated at a temperature comprised between 100° C. and 300° C., preferably comprised between 110° C. and 150° C. Any reaction vessel may be used without strict limitation, and a sealed vessel or an open vessel may be used. In particular, an autoclave reactor may preferably be used. The duration of the heating treatment is typically between 10 minutes and 48 hours, preferably between 30 minutes and 36 hours.

[0099] After step (d), the heated suspension can be cooled in optional step (e). The suspension can be cooled usually under stirring. The means for cooling is not critical, and the suspension can be cooled in the atmosphere or forced to cool with a cooling tube. The temperature of the suspension after cooling can be included between 20 ℃ and 90 ℃.

[0100] According to step (f), then add basic compound in suspension or the suspension having cooled.This basic compound can be for example sodium hydroxide, potassium hydroxide, ammonia solution, ammonia or its mixture, wherein preferred ammonia solution.Can be by first preparing the aqueous solution of basic compound with suitable concentration and under agitation adding the solution into the cooling suspension prepared in step (e) to add basic compound, or when using ammonia by under agitation blowing ammonia into the reaction vessel to add basic compound.The amount of basic compound can be easily determined by tracking the pH change of solution.Usually, sufficient amount is to make the pH of solution not less than 7, and preferred amount is to make pH between 7 and 9.Basic compound is for the precipitate Ce dispersed in the suspension at the end of step (d) or (e). 3+ ions are particularly useful to form Ce(OH)3 precipitates.

[0101] In the process according to the invention, the suspension prepared according to step (f) is maintained in step (g) at a temperature between 60° C. and 300° C. Without wishing to be bound by a particular theory, it is believed that this step can modify the crystallinity of the cerium oxide precursor present in the solution obtained by step (f) so as to increase its crystal size.

[0102] Any reaction vessel can be used in step (b) without strict limitation, and a sealed vessel or an open vessel can be used. In particular, an autoclave reactor can be preferably used.

[0103] In step (g), the temperature is included between 60°C and 220°C, preferably between 90°C and 200°C, more preferably between 90°C and 160°C. The duration of the heat treatment is generally between 10 minutes and 48 hours, preferably between 30 minutes and 36 hours, more preferably between 1 hour and 24 hours. In the present invention, the temperature of step (g) may be between 90°C and 120°C. In the present invention, the duration of the heat treatment in step (g) may be from 1 hour to 2 hours.

[0104] In step (h), the separation of the liquid medium and the precipitate can be carried out, for example, by Nutsche filtration, centrifugation, filter pressing or decantation. The precipitate can optionally be washed with water, preferably with water at an alkaline pH (e.g., aqueous ammonia solution). In addition, the precipitate can optionally be dried.

[0105] It is also possible to add a metal compound other than a cerium compound at any point after step (c) and before step (i) of the process, for example a metal element (other than cerium) in the form of a nitrate, chloride, oxide, hydroxide, carbonate, halide, oxyhalide, oxynitrate, and / or sulfate. Examples of metal elements (other than cerium) include (1) metal elements of Group 4A of the Periodic Table, such as silicon (Si) and tin (Sn), (2) metal elements of Group 4B of the Periodic Table, such as titanium and zirconium, (3) metal elements of Group 3A of the Periodic Table, such as aluminum, (4) alkali metal elements, such as barium and strontium, and (5) rare earth elements (REE) or rare earth metals, which are one of a group of 17 chemical elements in the Periodic Table, meaning the fifteen lanthanide elements plus scandium and yttrium. Preferably, the rare earth element oxide is selected from the group consisting of lanthanum oxide (La2O3), praseodymium oxide (Pr6O3), vanadium oxide (Pr6O3), tantalum oxide (T ... 11 ), neodymium oxide (Nd2O3) and yttrium oxide (Y2O3).

[0106] The cerium oxide particles obtained by the process of the invention may then contain, in addition to cerium oxide, for example in a proportion comprised between 1% and 40% by weight of the oxide, preferably in a proportion comprised between 1% and 20% by weight of the oxide, at least one metal oxide. The oxide here refers to the final mixed oxide defined as the integration of cerium oxide and other metal oxides.

[0107] In step (i), an organic texturizing agent is added to the suspension obtained in the preceding step (g) or to the precipitate obtained in step (h) once separated from the liquid medium. According to one embodiment of the present invention, the method of the present invention is carried out without step (i). According to another embodiment of the present invention, the method of the present invention is carried out including step (i).

[0108] Organic texturizers generally refer to organic compounds, such as surfactants, that are capable of controlling or modifying the mesoporous structure of cerium oxide. "Mesoporous structure" essentially describes a structure that contains, inter alia, pores having an average diameter comprised between 2 and 50 nm, described by the term "mesopores". Typically, these structures are amorphous or crystalline compounds, in which the pores are generally distributed in a random manner with a very wide pore size distribution.

[0109] The organic texturizing agent can be added directly or indirectly. It can be added directly to the suspension or precipitate produced by the previous step. It can also be first added to a composition, for example a solvent containing the organic texturizing agent, and then the composition is added to the suspension or precipitate as obtained above.

[0110] The amount of organic texturizing agent used, expressed as percentage by weight of additive relative to the weight of cerium expressed as CeO2, is generally between 5% and 100%, more particularly between 15% and 60%, preferably between 20% and 30%.

[0111] The organic texturizing agent may be adsorbed on the surface of the secondary particles and primary particles of the precipitate. For example, the organic texturizing agent adsorbed on the primary particles will lead to an increase in the size of the mesopores and the pore volume of the precipitate.

[0112] The organic texturizing agent is preferably selected from the group consisting of anionic surfactants, nonionic surfactants, polyethylene glycols, carboxylic acids and their salts, and carboxymethylated fatty alcohol ethoxylate type surfactants. Regarding this additive, reference may be made to the teaching of application WO-98 / 45212, and the surfactants described in this document may be used.

[0113] As surfactants of the anionic type, mention may be made of ethoxycarboxylates, ethoxylated fatty acids, sarcosinates, phosphates, sulfates such as alcohol sulfates, alcohol ether sulfates and sulfated alkanolamide ethoxylates, and sulfonates such as sulfosuccinates, and alkylbenzene or alkylnaphthalenesulfonates.

[0114] As nonionic surfactants, mention may be made of acetylenic surfactants, alcohol ethoxylates, alkanolamides, amine oxides, ethoxylated alkanolamides, long-chain ethoxylated amines, ethylene oxide / propylene oxide copolymers, sorbitan derivatives, ethylene glycol, propylene glycol, glycerol, polyglycerol esters and ethoxylated derivatives thereof, alkylamines, alkylimidazolines, ethoxylated oils and alkylphenol ethoxylates. In particular, mention may be made of the compounds sold under the trademark ETHOXYL®. and Products for sale.

[0115] Regarding carboxylic acids, in particular aliphatic monocarboxylic acids or dicarboxylic acids may be used, and among these, more particularly saturated acids. Fatty acids and more particularly saturated fatty acids may also be used. Therefore, mention may be made in particular of formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid and palmitic acid. As dicarboxylic acids, mention may be made of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid.

[0116] Salts of carboxylic acids, especially ammonium, may also be used.

[0117] By way of example, mention may more particularly be made of lauric acid and ammonium laurate.

[0118] Finally, use may be made of surfactants chosen from those of the carboxymethylated fatty alcohol ethoxylate type.

[0119] The expression “product of the carboxymethylated fatty alcohol ethoxylate type” is intended to mean a product consisting of ethoxylated or propoxylated fatty alcohols comprising a CH2-COOH group at the end of the chain.

[0120] These products can correspond to the following formula:

[0121] R1-O-(CR2R3-CR4R5-O) n -CH2-COOH

[0122] wherein R1 represents a saturated or unsaturated carbon-based chain, the length of which is generally up to 22 carbon atoms, preferably at least 12 carbon atoms; R2, R3, R4 and R5 may be identical and may represent hydrogen or else R2 may represent an alkyl group such as a CH3 group and R3, R4 and R5 represent hydrogen; n is a non-zero integer which may be up to 50 and more particularly between 5 and 15 (these values ​​are inclusive). It will be noted that the surfactant may consist of a mixture of products having the above formula (wherein R1 may be saturated or unsaturated, respectively) or, alternatively, of products containing both -CH2-CH2-O- and -C(CH3)-CH2-O- groups.

[0123] Optionally, in step (j), the precipitate is separated from the liquid medium, for example by Nutsch filtration, centrifugation, or filter press. The precipitate may optionally be washed with an aqueous solution, preferably water at an alkaline pH (e.g., aqueous ammonia solution). In addition, the precipitate may optionally be dried to an appropriate degree to improve the efficiency of subsequent steps.

[0124] In step (k), the precipitate obtained in the above step is calcined to obtain the cerium oxide particles as the object of the present invention. The calcination is preferably carried out in air.

[0125] The process of the invention then comprises a step (h) of separating the liquid medium from the precipitate, or a step (j) of separating the precipitate from the liquid medium, or both steps (h) and (j); so as to carry out calcination of the precipitate obtained at the end of step (g) or obtained in steps (h), (i) or (j) to obtain cerium oxide particles.

[0126] In step (k), the calcination temperature may be suitably selected from a range generally between 250°C and 900°C. The selection of temperature may be carried out as desired, depending on the required values ​​of specific surface area and bulk density. From a practical point of view of preparing a catalyst or co-catalyst material in which specific surface area is important, the calcination temperature in step (k) may preferably be between 250°C and 800°C, more preferably between 250°C and 700°C, most preferably between 280°C and 450°C. The duration of calcination may be appropriately determined depending on the temperature, and may preferably be between 1 and 20 hours.

[0127] After step (k), the obtained cerium oxide particles can generally be crushed. The crushing can be fully carried out in a conventional crusher (such as a hammer mill) to obtain a powder with a desired particle size. The cerium oxide obtained by the method of the present invention can be produced to a desired particle size by the above-mentioned crushing. In order to be used as a co-catalyst in a catalyst for purifying exhaust gas, for example, the preferred average particle size D50 of the cerium oxide is between 0.05 μm and 50 μm, and D50 is measured by laser diffraction as a volume distribution. The measurement can be carried out on a suspension of cerium oxide particles in water. For example, the distribution can be obtained using the LA-920 particle size analyzer commercialized by Horiba, Ltd.

[0128] In the method according to the invention, trivalent Ce III The cation must be present in one of the steps prior to the precipitation step (f). For example, Ce III The cation may be present in the cerium salt solution of step (a). According to a preferred embodiment, Ce III The cation is present after step (c). Ce III The presence of cations can be enhanced by adding Ce III Salt, such as Ce III It can also be obtained by adding a reducing agent to reduce the existing Ce IV After step (c) or before step (f), Ce III The molar ratio of the cations relative to the amount of cerium (III) cations and cerium (IV) cations may be from 5 to 30. III The molar ratio of cations is preferably at least 7. Ce III The molar ratio of the cation is preferably controlled to be no more than 20, more preferably no more than 15.

[0129] The conditions of Examples 1-3 can be used to prepare the cerium oxide particles of the present invention. The cerium oxide particles of the present invention can be preferably prepared by the method according to the present invention.

[0130] About Cerium Oxide Granules

[0131] Cerium oxide particles can be obtained by the process of the present invention, which unexpectedly have excellent heat resistance, especially high heat resistance under "humid" conditions (700° C.; gaseous atmosphere containing 10% by volume of O2, 10% by volume of H2O and the balance N2). Therefore, the present invention relates to cerium oxide particles as defined in claim 1.

[0132] The cerium oxide particles preferably have a particle size of 75 m / s after calcining at 700° C. for 4 hours in a gaseous atmosphere containing 10% by volume of O 2 , 10% by volume of H 2 O and the balance of N 2 . 2 / g and 90m 2 / g, more particularly between 78m 2 / g and 90m 2 The specific conditions of the "wet" condition can also be found in the examples.

[0133] The cerium oxide particles preferably have a strength of about 60 m 2 / g and 80m 2 / g between the specific surface area (SBET).

[0134] The cerium oxide particles are also characterized by comprising a total pore volume between 0.8 ml / g and 4.0 ml / g, more specifically between 0.8 ml / g and 2.5 ml / g, even more specifically between 0.8 ml / g and 2.0 ml / g after calcination at 400° C. for 10 hours in air.

[0135] The cerium oxide particles are also characterized by comprising a total pore volume of between 0.70 ml / g and 1.9 ml / g after calcination at 900° C. for 24 hours in air.

[0136] The cerium oxide particles are also characterized by a pore volume comprising pores having a pore diameter in the range of not more than 200 nm, after calcination at 400° C. in air for 10 hours, between 0.27 ml / g and 0.9 ml / g, more specifically between 0.27 ml / g and 0.7 ml / g.

[0137] The cerium oxide particles are also characterized by a pore volume comprising pores having a pore size in the range of not more than 200 nm of between 0.23 ml / g and 0.65 ml / g after calcination at 900° C. in air for 24 hours.

[0138] The cerium oxide particles can be obtained from the method of the present invention, especially the method wherein the addition of an organic texturizing agent in step (i) is not performed, but the present invention is not limited thereto.

[0139] The total pore volume or the pore volume of pores having a pore size in the range of up to 200 nm can be measured by a conventional mercury porosimeter, as further detailed in the examples below.

[0140] In addition, the inventors of the present invention have unexpectedly found that the cerium oxide particles have a certain porosity, excellent pore volume and thermal stability associated therewith. Therefore, according to one embodiment, the product of the present invention also relates to a cerium oxide particle having a porosity of 37 m / s after calcination at 900°C for 24 hours in air. 2 / g and 60m 2 / g, more particularly between 40m 2 / g and 60m 2 / g, and even more particularly at 45m 2 / g and 60m 2 / g of cerium oxide particles with a specific surface area (SBET) between 2.17 and 2.13 mm.

[0141] The cerium oxide particles according to this embodiment may have a particle size of 26 m / s after being calcined at 1000° C. in air for 5 hours. 2 / g and 40m 2 / g between the specific surface area (SBET).

[0142] The cerium oxide particles according to this embodiment may have a total pore volume comprised between 1.5 ml / g and 4.0 ml / g, more specifically comprised between 1.7 ml / g and 4.0 ml / g, after calcination at 400° C. for 10 hours in air.

[0143] The cerium oxide particles according to this embodiment may have a total pore volume comprised between 1.5 ml / g and 3.8 ml / g, more specifically between 1.7 ml / g and 3.8 ml / g, after calcination at 900° C. in air for 24 hours.

[0144] The cerium oxide particles according to this embodiment may have a pore volume of pores having a pore diameter within a range of not more than 200 nm, after calcination at 400° C. in air for 10 hours, between 0.3 ml / g and 1.5 ml / g, more specifically between 0.4 ml / g and 1.5 ml / g.

[0145] The cerium oxide particles according to this embodiment comprise, after calcination at 900° C. in air for 24 hours, a pore volume of pores having a pore diameter in the range of not more than 200 nm of between 0.25 ml / g and 1.0 ml / g, more particularly between 0.4 ml / g and 1.0 ml / g.

[0146] The cerium oxide particles according to this embodiment preferably have a particle size of at least 40 m 2 / g, more preferably at least 43m 2 / g, still more preferably 45m 2 / g specific surface area (SBET).

[0147] The cerium oxide particles according to this embodiment have a particle size of at least 25 m 2 / g, more particularly at least 28m 2 / g, more preferably at least 30m 2 / g, still more preferably 32m 2 / g specific surface area (SBET).

[0148] The cerium oxide particles according to this embodiment preferably have a total pore volume of at least 1.6, more preferably at least 1.7, still more preferably at least 1.8, yet more preferably at least 1.9, further more preferably at least 2.0, particularly more preferably at least 2.1, still particularly more preferably at least 2.2, yet particularly more preferably at least 2.3, especially preferably at least 2.4, especially preferably at least 2.5, and most preferably at least 2.6 ml / g after calcination at 400° C. in air for 10 hours.

[0149] The cerium oxide particles according to this embodiment preferably have a total pore volume of at least 1.6, more preferably at least 1.7, still more preferably at least 1.8, yet more preferably at least 1.9, further more preferably at least 2.0, still more preferably at least 2.1, still more preferably at least 2.2, yet more preferably at least 2.3, particularly preferably at least 2.4, and particularly preferably at least 2.5 ml / g after calcination at 900° C. in air for 24 hours.

[0150] The cerium oxide particles according to this embodiment preferably have a pore volume of pores having a pore diameter in the range of not more than 200 nm of at least 0.35, more preferably at least 0.40, still more preferably at least 0.45, yet more preferably at least 0.50, further more preferably at least 0.55, still more preferably at least 0.60, still yet more preferably at least 0.65, yet yet more preferably at least 0.70 ml / g after calcination at 400° C. in air for 10 hours.

[0151] The cerium oxide particles according to this embodiment preferably have a pore volume of pores having a pore diameter within a range of not more than 200 nm of at least 0.30, more preferably at least 0.35, still more preferably at least 0.40, and yet more preferably at least 0.45 ml / g after calcination at 900° C. in air for 24 hours.

[0152] The cerium oxide particles according to this embodiment can be obtained from the method of the present invention, particularly the method wherein the method includes adding an organic texturizing agent in step (i), but the present invention is not limited thereto.

[0153] The cerium oxide particles of the present application may contain, in addition to cerium oxide, at least one metal oxide, for example, in a proportion between 1% and 40% by weight of the oxide, preferably in a proportion between 1% and 20% by weight of the oxide. The oxide here refers to the final mixed oxide defined as the integration of cerium oxide and metal oxide.

[0154] The cerium oxide particles as described above or as obtained by the previously described preparation method may be in the form of a powder, but they may optionally be shaped so as to be in the form of particles, granules, foams, beads, cylinders or honeycombs having variable sizes.

[0155] The invention also relates to a catalyst comprising at least cerium oxide particles as defined above, for example a catalyst for purifying exhaust gases. The cerium oxide particles of the invention can be applied as such or in a composition to any support commonly used in the field of catalysis, that is to say in particular a thermally inert support. Such a support can be chosen from alumina, titanium oxide, cerium oxide, zirconium oxide, silicon dioxide, spinel, zeolite, silicate, crystalline silicoaluminophosphate or crystalline aluminum phosphate.

[0156] The catalyst for purifying exhaust gas according to the present invention may be of any type as long as the catalyst has a promoter comprising the cerium oxide of the present invention.The catalyst may be produced, for example, by a generally known method and with generally known other materials.

[0157] The present invention also relates to a composition, preferably a liquid composition, comprising at least cerium oxide particles as previously obtained and defined. More preferably, the composition is a suspension comprising at least a liquid medium as previously obtained and defined and cerium oxide particles.

[0158] According to an embodiment of the invention, the invention also relates to the use of cerium oxide particles as defined and / or as obtained in the above-determined method for polishing applications. For example, a composition for polishing, such as a suspension, containing at least cerium oxide particles of the invention can be obtained. This composition can be used, for example, for polishing glass in crystal manufacturing or mirror industry, flat glass, television screens or glasses, or for polishing ceramics or other materials of glassy type. This composition can also be used most particularly for CMP-type polishing in the electronics industry and therefore for polishing the metal substrates constituting microprocessors, as well as for polishing the insulating layers or interlayer dielectric (ILD) layers of these same microprocessors, the suspension of the invention being particularly suitable for polishing the layers. Chemical mechanical planarization (CMP) is a key process that enables shallow trench isolation (STI), which is used in current integrated circuit manufacturing methods to achieve device isolation. These layers are typically made of silicon dioxide (such as doped silicon dioxide or porous silicon dioxide). This suspension can also be used for metal CMP, which is used for wiring and barriers in integrated circuits, polishing photomask substrates (especially made of synthetic quartz glass). In the present invention, the term "polishing" is understood to include conventional polishing (such as glass polishing) and polishing of surfaces of semiconductor materials (such as silicon wafers in semiconductor applications), which is generally referred to as "planarization".

[0159] Generally, such compositions contain, in addition to compounds having abrasive properties, such as the cerium oxide particles, additives such as dispersants and / or oxidizing agents.

[0160] The present invention also relates to a method for removing a portion of a substrate, for example in a CMP operation, the method comprising:

[0161] - providing at least a composition, such as a suspension, comprising the cerium oxide particles of the invention,

[0162] - bringing at least the composition into contact with the substrate to be polished, and

[0163] - Polishing is performed on the substrate.

[0164] The following examples are included to illustrate embodiments of the invention. It goes without saying that the invention is not limited to the examples described.

[0165] Experimental Section

[0166] Specific surface area

[0167] The specific surface area (BET) by adsorption of N2 is automatically determined on a Flowsorb II 2300 or Macsorb analyzer model I-1220 (Mountech Co., LTD.). Before any test, the sample is carefully degassed to desorb any adsorbed substances. For this purpose, the sample can be heated in a furnace at 200°C for 2 hours and then in a cell at 300°C for 15 minutes.

[0168] Hg porosity

[0169] Porosity measurements are performed on a Micromeritics Autopore IV 9500 equipped with a penetrometer suitable for powders following the Micromeritics guidelines. Similarly, before any test, the samples are carefully degassed to desorb any adsorbed substances. The following parameters can be used: penetrometer 3.2 ml; capillary volume: 0.412 ml; water head pressure: 4.68 psi; contact angle: 130°; mercury surface tension: 485 dynes / cm; mercury density: 13.5335 g / ml. A vacuum is first applied to the sample (50 mm Hg; 5 minutes). The duration of equilibrium is: low pressure (1.3 psi-30 psi): 20 s; (30 psi-60000 psi): 30 s. Before measurement, the sample is heated at 400°C for 10 hours. The total pore volume is determined directly on the porosity curve.

[0170] “ Wet ” condition

[0171] The cerium oxide particles were evaluated under "wet" conditions (700° C.; gaseous atmosphere containing 10% by volume O2, 10% by volume H2O and the balance N2). The samples were prepared in the following manner.

[0172] - compacting the solid into the form of cylindrical pellets of 32 mm diameter by applying a pressure of 30 tons to the powder for 2 minutes;

[0173] - the granules thus obtained are then deagglomerated in a mortar to obtain a powder which is sieved so as to retain only the portion of powder which passes through a 250 μm sieve and is retained by a 125 μm sieve;

[0174] - the powder thus obtained (2.2 g) was hydrothermally aged at 700° C. for 4 hours in a synthesis gas containing 10% by volume of O 2 , 10% by volume of H 2 O and the remainder of N 2 (24 L / h flow rate on the powder (20° C.; 1 atm));

[0175] - The SBET is then measured according to the BET measurement method explained above.

[0176] The same conditions can be applied to cerium oxide particles with platinum, which can be prepared as follows:

[0177] - 9.9 g of cerium oxide in powder form was impregnated with an amine solution of platinum hydroxide (containing 0.1 g of Pt). The product was dried at about 120° C. and further calcined at 500° C. for 4 hours;

[0178] - The whole solid is then compacted into the form of cylindrical pellets of 32 mm diameter by applying a pressure of 30 tons to the powder for 2 minutes;

[0179] - the granules are then deagglomerated in a mortar to obtain a powder which is sieved so as to retain only the fraction of powder which passes through a 250 μm sieve and is retained by a 125 μm sieve;

[0180] - the cerium oxide thus obtained with Pt (2.2 g) was hydrothermally aged at 700° C. for 4 h in a synthesis gas containing 10% by volume of O 2 , 10% by volume of H 2 O and the remainder N 2 (24 L / h flow rate on the powder (20° C.; 1 atm));

[0181] - The SBET is then measured according to the BET measurement method explained above.

[0182] Example 1

[0183] 50 g of a cerium nitrate solution containing not less than 90 mol% of tetravalent cerium ions as CeO2 was dosed and adjusted with deionized water to a total amount of 1 L. The obtained solution was heated to 100°C, maintained at this temperature for 30 minutes, and cooled to 25°C, thereby obtaining a cerium suspension.

[0184] After removing the mother liquor from the cerium suspension thus obtained, the total volume was adjusted to 1 L with deionized water; the anion concentration was thus reduced by 44% compared to the anions contained in the liquid medium after heating. After removing the mother liquor, trivalent Ce in the form of nitrate (Ce(NO3)3) was added. III cation solution to allow Ce III The amount of cations was controlled to 6 mol% based on the total amount of cerium cations.

[0185] The cerium suspension was then kept at 120° C. for 2 hours, allowed to cool, and neutralized to pH 8.5 with aqueous ammonia.

[0186] The obtained mixture was heated to 120° C., maintained at this temperature for 1 hour, and cooled to 25° C. to obtain a slurry. The obtained slurry was subjected to solid-liquid separation through a Nutsche filter to obtain a filter cake. The cake was calcined in air at 400° C. for 10 hours to obtain a cerium oxide powder.

[0187] After calcination at 900°C for 5 hours and at 700°C for 4 hours in air under humid conditions as described above, the obtained composite oxide powder was measured by the BET method for specific surface area, total pore volume (before and after calcination at 900°C for 24 hours in air), and pore volume of pores with a size of not more than 200 nm (before and after calcination at 900°C for 24 hours in air).

[0188] Example 2

[0189] Cerium oxide powder was prepared in the same manner as in Example 1, except that after heat aging at a temperature of 120° C. for 1 hour, the obtained slurry was cooled to 40° C., and then 12.5 g of lauric acid was added to the slurry.

[0190] After calcination at 900°C in air for 5 hours, calcination at 900°C in air for 24 hours, and calcination at 1000°C in air for 5 hours, the specific surface area, total pore volume (before and after calcination at 900°C in air for 24 hours), and pore volume of pores with a size of no more than 200 nm (before and after calcination at 900°C in air for 24 hours) of the obtained composite oxide powder were measured by the BET method.

[0191] Example 3

[0192] Cerium oxide powder was prepared in the same manner as in Example 2, except that Ce III The amount of cations was controlled to 8 mol % instead of 6 mol % based on the total amount of cerium cations.

[0193] The properties of the oxide powder thus obtained were evaluated in the same manner as in Example 2, except for SBET at 1000° C. / 5 hours in air.

[0194] Comparative Example 1

[0195] Cerium oxide powder was prepared according to the method disclosed in patent publication US 7,361,322 B2. Thus, 20 g of a cerium nitrate solution containing not less than 90 mol% of tetravalent cerium cations in terms of CeO2 was dosed and adjusted to a total amount of 1 L with deionized water. The obtained solution was heated to 100°C, maintained at this temperature for 24 hours, and allowed to cool to room temperature. Ammonia water was then added to neutralize to pH 8 to obtain a cerium oxide hydrate in the form of a slurry.

[0196] The slurry was then subjected to solid-liquid separation using a Nutsche filter to obtain a filter cake. The filter cake was calcined in air at 300° C. for 10 hours to obtain a cerium oxide powder.

[0197] The oxide powders thus obtained were evaluated in the same manner as those properties measured in Examples 1 and 2. The properties of the cerium oxides prepared in the above defined examples are mentioned in Table 1.

[0198] Table 1

[0199]

[0200] SBET, unit is m2 / g; pore volume, unit is ml / g

[0201] Example 4: Low temperature NO x Storage capacity test

[0202] The cerium oxides of Example 1 and Comparative Example 1 were calcined in a synthesis gas (24 L / h flow rate on 2.2 g of catalyst) containing 10% by volume of O2, 10% by volume of H2O and the remainder of N2. NO was then measured as follows x Storage capacity: A synthesis gas mixture (30 L / h) representing the catalytic process using composition A given below was flushed at 120° C. during 90 min through 150 mg of cerium oxide placed in a fixed bed reactor. The stored NO was monitored online as a function of time thanks to an Antaris IGS FTIR spectrometer. x The amount.

[0203] Composition A

[0204]

[0205]

[0206] The NOx adsorption of the two cerium oxides of Example 1 and Comparative Example 1 at 90 min is shown in Table 2:

[0207] Table 2

[0208]

[0209] It then appears that the cerium oxide of the present invention has a higher NO content than conventional cerium oxide after hydrothermal aging. x Capture performance. NSC(NO x Storage capacity) is to evaluate NO x An indicator of emission performance.

Claims

1. A method for preparing cerium oxide particles, wherein the cerium oxide particles have the following characteristics: - After calcination at 900°C for 5 hours in air, including at 55m 2 / g and 80m 2 Specific surface area SBET between / g; - After calcination at 700°C for 4 hours in a gaseous atmosphere containing 10% by volume of O2, 10% by volume of H2O and the balance of N2, including at 75m 2 / g and 90m 2 / g between the specific surface area SBET, and - after calcination at 400° C. for 10 hours in air, it has a total pore volume comprised between 1.5 ml / g and 4.0 ml / g, the method comprising at least the following steps: (a) providing a cerium salt solution comprising anions and cations, wherein between 90 mol % and 100 mol % of the cerium cations are tetravalent cerium cations; (b) heating the cerium salt solution at a temperature comprised between 60° C. and 220° C. to obtain a suspension comprising a liquid medium and a precipitate; (c) reducing the concentration of anions from the cerium salt present in the liquid medium by between 10 mol % and 90 mol % compared to said anions contained in the liquid medium in step (b); (d) heating the suspension obtained in step (c) at a temperature comprised between 100° C. and 300° C.; (e) optionally cooling the suspension obtained in step (d); (f) contacting the suspension with a basic compound; (g) heating the suspension from step (f) at a temperature comprised between 60° C. and 300° C.; (h) optionally separating the precipitate from the liquid medium; (i) optionally adding an organic texturizing agent to the suspension obtained in step (g) or the precipitate obtained in step (h); (j) optionally separating the precipitate from the liquid medium; as well as (k) calcining the precipitate obtained at the end of step (g) or obtained in step (h), (i) or (j) to obtain cerium oxide particles; the method comprising at least step (h) and / or step (j), The trivalent cerium (III) cation must be present in one of the steps preceding the precipitation step (f).

2. The method according to claim 1, wherein: The reduction in the anion concentration in step (c) is obtained by adding water to the suspension obtained in step (b), or by removing at least a portion of the liquid medium from the suspension obtained in step (b) and then adding water to the medium.

3. The method according to claim 1, wherein: The addition of the organic agent in step (i) is carried out and the organic texturizing agent is selected from the group consisting of anionic surfactants, nonionic surfactants, polyethylene glycols, carboxylic acids and their salts, and carboxymethylated fatty alcohol ethoxylate type surfactants.

4. The method according to claim 1, wherein: The presence of cerium (III) cations is obtained by adding a cerium (III) salt or by adding a reducing agent to reduce a portion of the cerium (IV) cations already present.

5. The method according to claim 4, wherein: The source of trivalent cerium (III) cations is selected from the group consisting of nitrates, chlorides, hydroxides, carbonates, and sulfates of cerium (III).

6. The method according to claim 1, wherein: The heating temperature in step (g) is in the range from 90°C to 200°C.

7. The method according to claim 1, wherein: The cerium salt solution contains Ce IV , optional Ce III , H + and NO3 - .

8. The method according to claim 1, wherein the cerium oxide particles have a thickness of 78 m / s after calcination at 700° C. for 4 hours in a gaseous atmosphere containing 10% by volume of O2, 10% by volume of H2O, and the balance of N2. 2 / g and 90m 2 / g between the specific surface area SBET.

9. The method according to claim 1, wherein the cerium oxide particles have a total pore volume comprised between 1.7 ml / g and 4.0 ml / g after calcination at 400°C for 10 hours in air.

10. The method according to claim 1, wherein: In addition to cerium oxide, the cerium oxide particles further include at least one metal oxide selected from the group consisting of: (1) metal elements of Group 4A in the periodic table, (2) metal elements of Group 4B in the periodic table, (3) metal elements of Group 3A in the periodic table, (4) alkali metal elements, and (5) rare earth elements or rare earth metals selected from lanthanum, scandium and yttrium.

11. The method according to claim 1, wherein (1) the metal element of Group 4A of the periodic table is selected from silicon and tin.

12. The method according to claim 1, wherein (2) the metal element of Group 4B of the periodic table is selected from titanium and zirconium.

13. The method according to claim 1, wherein (3) the metal element of Group 3A of the periodic table is selected from aluminum.

14. The method according to claim 1, wherein (4) the alkali metal element is selected from barium and strontium.

15. The method according to any one of claims 1 to 14, wherein the cerium oxide particles further comprise, in addition to cerium oxide, at least one metal oxide selected from the group consisting of lanthanum oxide La2O3, praseodymium oxide Pr6O 11 , neodymium oxide Nd2O3 and yttrium oxide Y2O3.

16. The method according to any one of claims 1 to 14, wherein after calcination at 900°C in air for 24 hours, the cerium oxide particles have a particle size of at least about 30 m 2 / g and 60m 2 / g between the specific surface area SBET.

17. The method according to claim 16, wherein after calcination at 900°C for 24 hours in air, the cerium oxide particles have a 2 / g and 60m 2 / g between the specific surface area SBET.

18. The method according to claim 16, wherein after calcination at 900°C for 24 hours in air, the cerium oxide particles have a 2 / g and 60m 2 / g between the specific surface area SBET.

19. The method according to claim 16, wherein after calcination at 900°C for 24 hours in air, the cerium oxide particles have a 2 / g and 60m 2 / g between the specific surface area SBET.

20. The method according to any one of claims 1 to 14, wherein after calcination at 1000°C for 5 hours in air, the cerium oxide particles have a particle size of 22 m 2 / g and 40m 2 / g between the specific surface area SBET.

21. The method according to claim 20, wherein after calcination at 1000°C for 5 hours in air, the cerium oxide particles have a 2 / g and 40m 2 / g between the specific surface area SBET.

22. The method according to any one of claims 1 to 14, wherein the cerium oxide particles have a total pore volume comprised between 0.70 ml / g and 1.9 ml / g after calcination at 900°C for 24 hours in air.

23. The method according to any one of claims 1 to 14, wherein the cerium oxide particles have a pore volume comprising pores having a pore diameter in the range of not more than 200 nm between 0.23 ml / g and 0.65 ml / g after calcination at 900°C for 24 hours in air.

24. The method according to any one of claims 1 to 14, wherein: After calcination at 900° C. for 24 hours in air, the cerium oxide particles have a total pore volume comprised between 1.5 and 3.8 ml / g.

25. The method according to claim 24, wherein: After calcination at 900° C. for 24 hours in air, the cerium oxide particles have a total pore volume comprised between 1.7 ml / g and 3.8 ml / g.

26. The method according to any one of claims 1 to 14, wherein the cerium oxide particles have a pore volume comprising pores having a pore diameter in the range of not more than 200 nm between 0.3 ml / g and 1.5 ml / g after calcination at 400°C for 10 hours in air.

27. The method according to any one of claims 1 to 14, wherein the cerium oxide particles have a pore volume comprising pores having a pore diameter in the range of not more than 200 nm between 0.25 ml / g and 1.0 ml / g after calcination at 900°C for 24 hours in air.

28. The method of claim 27, wherein the cerium oxide particles have a pore volume comprising pores having a pore size in the range of not more than 200 nm between 0.4 ml / g and 1.0 ml / g.

29. The method according to any one of claims 1 to 14, wherein the cerium oxide particles have a particle size of at least 40 m 2 / g specific surface area SBET.

30. The method of claim 29, wherein the cerium oxide particles have a particle size of at least 43 m 2 / g specific surface area SBET.

31. The method of claim 29, wherein the cerium oxide particles have a 45 m 2 / g specific surface area SBET.

32. The method according to any one of claims 1 to 14, wherein after calcination at 1000°C for 5 hours in air, the cerium oxide particles have a particle size of at least 25 m 2 / g specific surface area SBET.

33. The method of claim 32, wherein the cerium oxide particles have a particle size of at least 28 m 2 / g specific surface area SBET.

34. The method of claim 32, wherein the cerium oxide particles have a particle size of at least 30 m 2 / g specific surface area SBET.

35. The method of claim 32, wherein the cerium oxide particles have a 2 / g specific surface area SBET.

36. The method according to any one of claims 1 to 14, having a NO content of greater than or equal to 22 μg after calcination at 700° C. for 4 hours in a gaseous atmosphere containing 10% by volume O2, 10% by volume H2O and the balance N2. x / gCeO2 NO x Adsorption amount.

37. Cerium oxide particles obtained by the method according to any one of claims 1 to 36.

38. Cerium oxide particles obtained by the method according to any one of claims 1 to 36, wherein the addition of an organic texturizing agent in step (i) is not performed.

39. Cerium oxide particles obtained by the process according to any one of claims 1 to 36, comprising the addition of an organic texturizing agent in step (i).

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