JP5438772B2 - Lattice engineered cerium dioxide nanoparticles containing fuel additives - Google Patents

Description

Cross-reference of related applications This application is based on International Application No. PCT / US07 / 077454 “METHOD OF PREPARING CERIUM DIOXIDE NANOPARTICLES” and International Application No. PCT / US07 / 0777535 Filed on September 4). These applications include “CERIUM-CONTAINING FUEL ADDITIVE” (provisional date: September 5, 2006) of provisional application No. 60/824514, and “REVERSE MICELLAR FUEL ADDITION COMPOSITION” (2007) of provisional application No. 60/911159. Claimed on 11 April) and provisional application No. 60/934314 “REVERSE MICELLAR FUEL ADDITION COMPOSTION” (filed May 16, 2007). The disclosures of all these applications are incorporated herein by reference.

The present invention relates generally to cerium dioxide nanoparticles, in particular cerium dioxide nanoparticles Ce _1-x M _x O ₂ containing one or more transition metals (M) and methods for preparing such particles. These nanoparticles are useful as components of fuel additive compositions, washcoats for catalytic converters, or catalysts for reduction / oxidation reactions.

The trucking industry accounts for more than 5% of US gross domestic product, comprising over 500,000 rental private and government vehicles (including self-owned drivers). This is a barometer for the US economy, representing nearly 70% of the total tonnage, including products and retail goods, carried by all forms of domestic freight transport. The industry mostly uses only diesel engines (compression ignition engines) as power, and diesel engines are characterized by high torque at low rpm and 25% higher thermodynamic efficiency than spark ignition (gasoline) engines. . EPA nitrogen oxides in 2007 (NO _X) and diesel exhaust: results ordered emission reductions (diesel particulate matter DPM or soot), currently diesels, diesel oxidation catalyst (diesel oxidation catalyst: DOC) or There is a need to equip some form of catalytic converter and to burn ultra low sulfur diesel fuel (ULSD) (<15 ppm sulfur content). A wide variety of techniques, such as emissions gas recirculation (EGR), are required to meet emission standards mandated by the EPA. The ULSD requirement is the result of sulfur poisoning of DOC precious metals with high sulfur levels. This regulation affected every direction. This is because in the United States (on the road) diesel fuel is consumed at an extraordinary rate of 650M gallons / week and is second only to gasoline (1300M gallons / week).

  It is estimated that the additional cost of EPA orders will add about $ 0.39 to the cost per gallon of diesel fuel. The breakdown is as follows: increase in engine cost ($ 0.11 / gallon), particle capture maintenance cost ($ 0.05 / gallon), reduced fuel economy ($ 0.09 / gallon), ULSD increase ($ 0.06 / gallon) and low ULSD fuel energy capacity ($ 0.08 / gallon).

  A technology that can reduce DPM and other emissions while simultaneously improving fuel economy (measured in increase in miles per gallon) is considered extremely beneficial both financially and environmentally. Of course it is done.

  Diesel fuel additives, particularly those containing inorganic metals and metal oxide materials rather than organic materials, promise to reduce DMP and improve fuel economy.

Krakuraurer (US Pat. No. 4,389,220, the disclosure of which is incorporated herein by reference) describes a method for conditioning a diesel engine that removes carbon deposits from the combustion surface of the engine. And a diesel containing about 20-30 ppm dicyclopentadienyl iron for a time sufficient to deposit a layer of iron oxide (effective in preventing further accumulation of carbon deposits) on the combustion surface Operate with fuel. Subsequently, the diesel engine is continuously operated with a maintenance concentration of dicyclopentadienyl iron of about 10-15 ppm or an equivalent thereof. This maintenance concentration is effective to maintain an iron oxide catalyst layer on the combustion surface, but is insufficient to reduce timing delays in the engine. The added dicyclopentadienyl iron produces iron oxide (Fe ₂ O ₃ ) on the engine cylinder surface, and this iron oxide reacts with carbon deposits (smoke) to produce Fe and CO _2. Thus, the deposit is removed. However, this method may accelerate the aging of the engine due to the generation of rust.

  Valentine et al. (US Patent Application Publication No. 2003/0148235, the disclosure of which is incorporated herein by reference) describes certain binary or ternary metal fuel addition catalysts for increasing the combustion efficiency of fuels. Yes. This catalyst reduces fouling of the heat transfer surface due to unburned carbon, while itself overloads the particulate collection device or discharges toxic ultrafine particles when used in typical configurations and quantities. Reduce the amount of secondary additive ash that can be caused. By utilizing a fuel containing a fuel-soluble catalyst comprising platinum and at least one additional metal, including cerium and / or iron, the generation of the type of pollutants generated by incomplete combustion is reduced. Ultra-low levels of non-toxic metal combustion catalysts can be used to improve heat recovery and reduce regulated pollutant emissions. However, this type of fuel additive may require months of engine “tuning” in addition to using rare and expensive metals (such as platinum). “Conditioning” means that the full effect of the additive cannot be obtained unless the engine is operated over this period of time. The initial adjustment takes 45 days, and if 60 to 90 days have not passed, the effect may not be obtained in the best condition. In addition, free metals may be released from the exhaust system into the atmosphere, and the released free metals can subsequently react with organisms.

  Cerium dioxide is widely used as a catalyst in converters in diesel vehicles to remove toxic exhaust gases and reduce particulate emissions. Within the catalytic converter, cerium dioxide acts as a chemically active component, releasing oxygen in the presence of reducing gas and removing oxygen by interaction with oxidizing species.

Cerium dioxide can occlude and release oxygen by the reversible process shown in Scheme 1.
[Formula 1]
CeO ₂ ← → CeO _2-X + x / 2O ₂

[0010] This process is referred to as ceria's oxygen storage capability (OSC). Here, ceria acts as an oxygen storage buffer (much like a pH buffer), releasing oxygen in a spatial region where the oxygen concentration or pressure is low, and absorbing oxygen in a spatial region where the oxygen pressure is high. When X = 0.5, ceria is effectively fully reduced to Ce ₂ O ₃ and the highest theoretical OSC is 1452 micromoles O ₂ per gram of ceria. The redox potential between Ce ³⁺ and Ce ⁴⁺ ions is 1.3-1.8 V, and depends greatly on the anion groups present and the chemical environment (CERIUM: A Guide to it Role in Chemical Technology, 1992 by Mollycorp, Inc, Library of Congress Catalog Card Number 92-93444). As a result, the above-described normal reaction and reverse reaction are rapidly performed in the exhaust gas near the required stoichiometric ratio of oxygen (15: 1). Cerium dioxide may provide oxygen for the oxidation of CO or hydrocarbons in an oxygen deficient environment. Or, conversely, in a high oxygen concentration environment, oxygen can be absorbed to reduce the level of nitrogen oxides (NO _x ). Similar catalytic activity can occur when cerium dioxide is added as an additive to a fuel (eg, diesel, gasoline). However, in order to make this effect useful, the added cerium dioxide is sufficiently small in particle size, i.e. nanoparticles (less than 100 nm) to be suspended in the fuel and not settled by Brownian motion. It must be. In addition, since the catalytic action depends on the surface area, the nanocrystalline material becomes more effective as a catalyst when the particle size is small. Formulation of cerium dioxide into fuel is, for example, “water gas shift reaction”:
CO + H ₂ O → CO ₂ + H ₂
This not only serves as a catalyst to reduce toxic exhaust emissions generated by fuel combustion, but also promotes complete combustion of particulates that are accumulated in particulate traps typically used in diesel engines.

[0011] As described above, cerium dioxide nanoparticles are particles having an average diameter of less than 100 nm. For the purposes of this disclosure, unless otherwise stated, the diameter of a nanoparticle is its hydrodynamic diameter, which is measured by dynamic light scattering and also includes molecular adsorbates and associated molecules. It is the diameter including the solvation shell of the particles. Alternatively, the geometric particle size can be estimated using transmission electron microscope analysis (TEM).

[0012] Although an in-vehicle supply system that dispenses cerium dioxide into the fuel in front of the engine is known, such a system is complex and is too large to supply an appropriate amount of additive to the fuel. Requires electronic control. In order to avoid such a complicated in-vehicle system, cerium dioxide nanoparticles can be added to the fuel at an earlier stage to improve fuel efficiency. For example, cerium dioxide can be formulated in refineries, typically with processing additives (eg, cetane improvers, lubricants). Alternatively, it can be added at a fuel distribution tank farm.

[0013] Cerium dioxide nanoparticles can also be added to large quantities (~ 100,000 gallons) of fuel by rack injection at the fuel distribution center. Alternatively, cerium dioxide nanoparticles can be added at smaller fuel company repositories and can be customized to specific individual requirements. In addition, cerium dioxide can be added at the gas station while supplying fuel to the vehicle, which may provide the advantage of more stable particle dispersion.

[0014] By the formation of a ceramic layer on the engine cylinder and internal moving parts by the cerium nanoparticles, the engine can essentially turn into a catalytic device. Alternatively, cerium nanoparticles can be reused in the lubricating oil where it accumulates. The catalytic efficiency is derived from the fact that the cerium nanoparticles undergo a reduction of the reaction formula (1) to become a supply source of oxygen atoms during combustion. However, it usually takes several months of induction before benefits can be seen in miles per gallon. This ultimately results in better fuel combustion and lowers particulate material emission levels. In addition, when used as a fuel additive, these nanoparticles can also improve engine performance by reducing engine friction. As another introduction mode, cerium dioxide nanoparticles can be added to the lubricating oil, and the cerium dioxide nanoparticles function as a lubricity improver to reduce internal friction. This also improves fuel efficiency.

[0015] The following publications (the disclosures of which are all incorporated herein by reference) describe fuel additives containing cerium oxide compounds.

(0016-0018) Hawkins et al. (US Pat. No. 5,449,387) has the formula:
(H ₂ O) _p [CeO (A) ₂ (AH) _n ] _m
(In the formula, radicals A are the same or different and are anions of organic oxyacid AH each having _a pKa greater than 1, p is an integer of 0-5, n is a number of 0-2, and m is A cerium (IV) oxide compound having an integer of 1 to 12 is disclosed. The organic oxyacid is preferably carboxylic acid, more preferably a C ₂ -C ₂₀ monocarboxylic acid or a C ₄ -C ₁₂ dicarboxylic acids. Cerium-containing compounds can be used as catalysts for the combustion of hydrocarbon fuels.

Valentine et al. (US Pat. No. 7,063,729) discloses a low emission diesel fuel comprising a bimetallic fuel soluble platinum group metal and a cerium catalyst, where cerium is a fuel soluble hydroxyl oleate propionate. Provided as a complex.

[0020] Chopin et al. (US Pat. No. 6,210,451) contains cerium dioxide particles in the form of microcrystalline aggregates (preferred size is 3-4 nm), containing at least one acid having a total carbon number of at least 10. A petroleum-based fuel comprising a stable organic sol composed of an amphiphilic acid-based and organic diluent medium is disclosed. The controlled particle size does not exceed 200 nm.

Birchem et al. (US Pat. No. 6,136,048) describes an adjuvant for diesel engine fuels comprising a sol composed of particles of an oxygenated compound having an ad ₉₀ of 20 nm or less, an amphiphilic acid system and a diluent. Is disclosed. Oxygenated metal compound particles are prepared by reaction with a basic medium in a solution of a rare earth salt (such as a cerium salt) and subsequent recovery of the resulting precipitate by spraying or lyophilization.

[0022] Lemaire et al. (US Pat. No. 6,093,223) describes a process for producing aggregates of ceric oxide microcrystals by burning a hydrocarbon fuel in the presence of at least one cerium compound. Is disclosed. The soot contains at least 0.1% by weight of ceric oxide microcrystal aggregates, the maximum particle size is 50-10000 angstroms, the microcrystal size is 50-250 angstroms, and the soot is below 400 ° C. Has ignition temperature.

(0023) Hazarika et al. (US Pat. No. 7,195,653 B2) discloses a method for improving fuel efficiency and / or reducing fuel emissions of a fuel combustion device. The method comprises dispersing at least one particulate lanthanide oxide, particularly cerium dioxide, in a fuel at 1-10 ppm as a tablet, capsule, powder or liquid fuel additive, wherein the particulate lanthanum oxide is 7 Coated with a surfactant selected from the group consisting of alkyl carboxylic anhydrides and esters having the following HLB: A preferred coating agent is dodecyl succinic anhydride.

[0024] Collier et al. (US Patent Publication No. 2003/0182848) improve the performance of diesel fuel particulate traps and also have 1-25 ppm metal and 100-500 ppm oil solubility in the form of metal salt additives. A diesel fuel composition containing a combination of a nitrogen-containing ashless detergent additive is disclosed. The metal is either an alkali metal, an alkaline earth metal, a group IVB, VIIB, VIIIB, IB, IIB metal, a rare earth metal having an atomic number of 57-71 (especially cerium) or any of the metals mentioned above It can be a mixture.

[0025] Collier et al. (US 2003/0221362) discloses a fuel additive composition for a diesel engine with a particulate trap. The composition includes a hydrocarbon solvent and an oil-soluble metal carboxylate or metal complex derived from a carboxylic acid having no more than 125 carbon atoms. The metal can be an alkali metal, alkaline earth metal, IVB, VIIB, VIIIB, IB, IIB metal, a rare earth metal including cerium, or a mixture of any of the foregoing metals.

[0026] Caprotti et al. (US 2004/0035045) discloses a fuel additive composition for a diesel engine with a particulate trap. The composition comprises an oil-soluble or oil-dispersible metal salt of an acidic organic compound and a stoichiometric excess of metal. When added to the fuel, the composition provides 1 to 25 ppm of metal selected from the group consisting of Ca, Fe, Mg, Sr, Ti, Zr, Mn, Zn and Ce.

(0027) Caprotti et al. (US 2005/0060929) discloses a diesel fuel composition stabilized against phase separation, which composition was colloidally dispersed. Or a solubilized metal catalyst compound and 5-1000 ppm of stabilizer, which is a lipophilic hydrocarbyl bound to at least two polar groups, at least one of which is a carboxylic acid or carboxylate group An organic compound having a chain. The metal catalyst compound comprises one or more organic or inorganic compounds or complexes of Ce, Fe, Ca, Mg, Sr, Na, Mn, Pt or mixtures thereof.

[0028] Caprotti et al. (US 2006/0000140) discloses a fuel additive composition comprising at least one colloidal metal compound or species and a stabilizer component. The stabilizer component comprises an aldehyde or ketone and one or more aromatics having a further substituent selected from among a hydroxyl substituent and a hydrocarbyl group, -COOR or -COR (where R is hydrogen or hydrocarbyl). It is a condensation product with a compound containing a group moiety. The colloidal metal compound preferably comprises at least one metal oxide, the preferred oxide being iron oxide, cerium dioxide or cerium-doped iron oxide.

Scattergood (International Publication No. WO 2004/065529) discloses a method for improving the fuel efficiency of a fuel for an internal combustion engine, the method comprising cerium dioxide and / or doped cerium dioxide, and optionally Adding one or more fuel additives to the fuel.

[0030] Anderson et al. (International Publication No. WO 2005/012465) discloses a method for improving the fuel efficiency of internal combustion engine fuels, including lubricating oils and gasoline, which includes cerium dioxide and / or Or adding doped cerium dioxide to lubricating oil or gasoline.

[0031] Cerium-containing nanoparticles can be prepared by various techniques known in the art. Regardless of whether the synthetic nanoparticles are formed in a hydrophilic or hydrophobic medium, the particles typically require a stabilizer to prevent undesired aggregation. The following publications, the entire disclosures of which are incorporated herein by reference, describe some of these synthetic techniques.

[0032] Chane-Ching et al. (US Pat. No. 6,271,269) discloses a process for preparing a storage-stable organic sol, which comprises converting a basic reactant to an acidic metal cation salt. An aqueous colloidal dispersion containing excess hydroxyl ions is produced by reacting with an aqueous solution, the aqueous colloidal dispersion is contacted with an organic phase comprising an organic liquid medium and an organic acid, and the resulting aqueous / organic phase mixture Separating the water phase into the product organic phase. Preferred metal cations are cerium cation and iron cation. Colloidal microparticles have a hydrodynamic diameter of 5-20 nanometers.

(0033) Chan-Ching (US Pat. No. 6,649,156) describes cerium dioxide particles formed by a thermal hydrolysis process, an organic liquid phase and at least one amphiphilic compound (polyoxyethylenated alkyl of carboxylic acid). Organic sols containing ethers, polyoxyethylenated alkyl ether phosphates, selected from dialkyl sulfosuccinates and quaternary ammonium compounds are disclosed. The water content of this sol cannot exceed 1%. The average crystallite size is about 5 nm, and the size of the particle aggregates of these crystallites is 200-10 nm.

(0034) Chan-Ching (US Pat. No. 7,0089,965) discloses an aqueous colloidal dispersion of a cerium compound and at least one other metal, which has a conductivity of up to 5 mS / cm. And a pH of 5-8.

[0035] Chane-Ching (U.S. Patent Application Publication No. 2004/0029978, abandoned on December 7, 2005) is amphiphilic and metal oxide, hydroxide and / or oxyhydroxide. A surfactant produced from at least one kind of nanoparticles based on an object is disclosed, and a hydrophobic organic chain is bonded to the surface of the nanoparticles. The metal is preferably selected from cerium, aluminum, titanium or silicon, the alkyl chain containing 6-30 carbon atoms or the alkyl chain containing 8-30 carbon atoms, and the polyoxyethylene moiety is 1-10. Polyoxyethylene monoalkyl ethers containing oxyethylene groups. The particles are isotope or spherical particles having an average diameter of 2 to 40 nm.

(Blanchard et al., US 2006/0005465) discloses particles of at least one compound based on at least one rare earth, at least one acid and at least one diluent. An organic colloidal dispersion is disclosed that includes at least 90% of the particles are monocrystalline. Example 1 describes the preparation of a cerium dioxide colloidal solution from an organic phase comprising cerium acetate and an Isopar hydrocarbon mixture and isostearic acid. The resulting cerium dioxide particles have a d ₅₀ of 2.5 nm, the size of 80% of the particles was 1 to 4 nm.

[0037] Zhou et al. (US Pat. No. 7,025,943) discloses a method for producing cerium dioxide crystals. In this method, a first solution of a water-soluble cerium salt is mixed with a second solution of alkali metal or ammonium hydroxide, and the resulting reactant solution is stirred under turbulent conditions, while gaseous oxygen is added to the solution. Passing and precipitating cerium dioxide particles with a dominant particle size of 3 to 100 nm. In Example 1, the particle size is described to be about 3-5 nm. No mention is made of stabilizers, and the sol is expected to eventually aggregate and settle.

[0038] Sandford et al. (WO 2008/002223 A2 pamphlet) describes an aqueous precipitation technique that directly produces cerium dioxide without subsequent calcination. The trivalent cerium cation Ce ⁺³ is slowly oxidized by the nitrate ion to the tetravalent cerium cation Ce ⁺⁴ , and when acetic acid is used as a stabilizer, the crystallite size is 11 nm (and roughly the same grain size). A stable, non-agglomerated sol. Interestingly, EDTA and citric acid form crystallite size grains on the order of several hundred nanometers.

(0039) James L. Woodhead (US Pat. No. 4,231,893) teaches the preparation of an aqueous dispersion of ceria by acid treatment of Ce (OH) ₄ (obtained by treatment of Ce ⁺³ with peroxide in a base). doing. Sizing data has not been provided, stabilizers may be considered in pH1.5 required for regulation NO ₃ ^- is an anion.

[0040] Noh et al (US 2004/0241070) discloses a method for preparing single crystalline cerium dioxide nanopowders. This method prepares cerium hydroxide by precipitating a cerium salt in the presence of a solvent mixture of an organic solvent and water (preferably in a ratio of about 0.1: 1 to about 5: 1 by weight). Including hydrothermal reaction of cerium hydroxide. The nanopowder has a particle size of about 30-300 nm.

[0041] Chan (US 2005/0031517) discloses a method for preparing cerium dioxide nanoparticles, which rapidly mixes an aqueous cerium nitrate solution with an aqueous hexamethylenetetramine solution. However, the temperature is maintained at a temperature of about 320 ° K. (46.85 ° C.) or less, while nanoparticles are formed in the resulting mixture, including separating the formed nanoparticles. The mixing device preferably comprises a mechanical stirrer and a centrifuge. In the illustrative examples, the prepared cerium dioxide particles are reported to have a diameter of about 12 nm.

(0042) Ying et al. (US Pat. Nos. 6,413,489 and 6,869,584) describe the synthesis of nanoparticles having a particle size of less than 100 nm and a surface area of at least 20 m ² / g without agglomeration by the reverse micelle method. Disclosure. The method includes introducing a ceramic precursor comprising barium alkoxide and aluminum alkoxide in the presence of an inverse emulsion.

[0043] In a related publication (US Patent Application Publication No. 2005/0152832 to Ying et al.), 100 nm without agglomeration by reverse micelle method in an emulsion having a water content of 1-40%. The synthesis of nanoparticles having a particle size of less than is disclosed. The nanoparticles are preferably metal oxide particles that can be used for the oxidation of hydrocarbons.

[0044] Hanawa et al. (US Pat. No. 5,938,837) discloses a method for preparing cerium dioxide particles primarily intended for use as an abrasive. In this method, the aqueous cerium nitrate solution is mixed with a base (preferably an aqueous ammonia solution) with stirring at a mixing ratio such that the pH value of the mixture is in the range of 5-10, preferably 7-9, The method includes rapidly heating the resulting mixture to a temperature of 70 to 100 ° C. and ripening the mixture of cerous nitrate and base at that temperature to form crystal grains. The product crystal grains are uniform in size and shape, and have an average particle size of 10 to 80 nm, preferably 20 to 60 nm.

(0045-0047) European Patent Application No. EP 0208580 (published Jan. 14, 1987. Inventor Chane-Ching, applicant Rhone Poulenc).
Ce (M) _x (OH) _y (NO ₃ ) ₂
(Wherein M represents an alkali metal or quaternary ammonium radical, x is from 0.01 to 0.2, y is such that y = 4-z + x, and z is from 0.4 to Cerium (IV) compounds corresponding to 0.7) are disclosed. Processes for preparing colloidal dispersions of cerium (IV) compounds produce particles having a hydrodynamic diameter of about 1 to about 60 nm, suitably about 1 to about 10 nm, desirably about 3 to 8 nm. .

(0048) S.E. Satyamurthy et al. (Nano Technology 16 (2005), pp 1960-1964) describe the reverse micelle synthesis of CeO ₂ from cerium nitrate, using sodium hydroxide as the precipitating agent and the surfactant cetyltrimethylammonium bromide. N-octane containing (CTAB) and cosurfactant 1-butanol is used as the oil phase. The resulting polyhedral particles had an average size of 3.7 nm, but showed aggregation when separated from their protective reverse micelle structure. In addition, the reaction is expected to proceed in low yield (for reactants A and B, the number of AB collisions that yields the product is comparable to the collisions of AA and BB where no product is produced) .

(0049) Seal et al. (Journal of Nano Particle Research (2002), pp 433-448) describes the preparation of nanocrystalline ceria particles for high temperature oxidation resistant coatings from cerium nitrate and ammonium hydroxide. In the preparation, an aqueous microemulsion system containing AOT as a surfactant and toluene as an oil phase is used. The ceria nanoparticles formed in the upper oil phase of the reaction mixture had a particle size of 5 nm.

(0050) Seal et al. (US Pat. No. 7,419,516, the disclosure of which is incorporated herein by reference) describes the use of rare earth metal oxides, preferably ceria nanoparticles, as fuel additives to reduce soot. Describes use. Particles prepared by the reverse micelle process using toluene as the oil phase and AOT as the surfactant have a diameter of about 2-7 nm and an average diameter of about 5 nm.

(0051) Pang et al. (J. Mater. Chem., 12 (2002), pp 3699-3704) prepared Al ₂ O ₃ nanoparticles by a water-in-oil microemulsion method. An oil phase containing cyclohexane and the nonionic surfactant Triton X-114 and l. An aqueous phase containing 0M AlClO ₃ was used. The resulting Al ₂ O ₃ particles (which had a particle size of 5-15 nm) appeared to be clearly different from the submicron sized hollow ball-like particles formed by the direct precipitation process.

(0052) Cuif et al. (US Pat. No. 6,133,194, the disclosure of which is incorporated herein by reference) includes cerium, zirconium or mixtures thereof, bases, optional oxidizing agents and additives (anionic surfactants, Describes a process comprising obtaining a product by reacting a metal salt solution containing a nonionic surfactant, selected from the group consisting of polyethylene glycol, carboxylic acid and carboxylate salts. The product is subsequently calcined at a temperature above 500 ° C. (this effectively carbonizes the claimed surfactant).

[0053] Although many authors allege about ceria nanoparticles much smaller than 5 nm, to clearly demonstrate that the grains are really cubic CeO ₂ and not hexagonal or cubic Ce ₂ O ₃ . It should be understood that no X-ray or electron diffraction data is presented. It is not believed that cubic CeO ₂ is thermodynamically stable at very small grain sizes, and that the grains are actually in the form of reduced, more stable hexagonal Ce ₂ O _3. Questions remain (S. Tsunekawa, R. Sivamohan, S. Ito, A. Kasuya and T. Fukuda, Nanostructured Materials, vol. 11, No. 1, pp 141-147 (1999)).

(0054) “Structural Study on Monosize CeO _2-x Nanoparticulars” is specifically described in 1.5. Questions are raised about the presence of sub-nm CeO ₂ .

(0055-0056) Further evidence for the presence of Ce ³⁺ (and thus Ce ₂ O ₃ ) at very small grain diameters is found in “Size Dependency Variation” published in Desphande et al., Applied Physics Letters 87, 133113 (2005). in Lattice Parameter and Valuency States in Nano Crystalline Ceria Oxide, Deshande et al., change in lattice constant: Δa = a−a ₀ (a ₀ = 5.43 Å (in CeO ₂ )) and crystal diameter D. We found a log-linear relationship between and. It is as follows.
[Formula 2] (0057)
log Δa = −0.4763 log D−1.5029

Accordingly, when the crystal grain diameter is 10 nm, a change of 0.0101% or 1.91% in the lattice distortion or lattice constant occurs, and when the crystal grain diameter is 1 nm, 0.031% or 5.73%. Changes occur.

(0059) represented by formula 1, the degree operable CeO ₂ as a catalytic oxygen storage material is guided in part by the particle size of CeO _2. For grain sizes below 20 nm, the lattice parameters increase dramatically and the crystallite size decreases (up to 0.45% at 6 nm. See, eg, Zhang et al. Applied Physics Letters, 80 1, 127 (2002). ) Crystal distortion due to the associated size is accompanied by an increase in surface oxygen vacancies, resulting in enhanced catalytic activity. This inverse size-dependent activity provides not only more efficient fuel tanks but also better oxidation characteristics when used for petroleum fuel combustion.

[0060] As mentioned above, various methods and apparatus have been reported for the preparation of cerium nanoparticles, such as Chane-Ching et al. US Pat. No. 5,017,352, Hanawa et al. US Pat. No. 5,938,837, Melard. U.S. Pat. No. 4,786,325, Chopin et al. U.S. Pat. No. 5,712,218, Chan U.S. Patent Application Publication No. 2005/0031517, and Zhou et al. U.S. Pat. No. 7,025,943. The disclosures of these documents are incorporated herein by reference. However, current methods produce an economical, easy (ie, non-calcined) and straightforward preparation of cubic CeO ₂ nanoparticles in a high yield, short time, very high suspension density (greater than 0.5 moles). 9% by weight in sufficiently small size (average geometric diameter less than 5 nm), uniform particle size distribution (coefficient of variation [COV] less than 25%. COV is the standard deviation divided by the average diameter. In addition to crystallinity (ie, not agglomerates of various sizes of microcrystals as taught in the prior art and technical literature above). It is highly desirable to produce single crystal) particles.

[0061] While it is beneficial to include substantially pure cerium dioxide nanoparticles in the fuel additive, the use of cerium dioxide doped with components that result in the formation of more oxygen vacancies can be further beneficial ( Formula 1). For this purpose, the dopant ion should be divalent or trivalent, i.e. a divalent or trivalent ion of an element which is a rare earth metal, a transition metal or a metal of group IIA, IIIB, VB or VIB of the periodic table. It is. The reaction of Formula 1 goes to the right due to the requirements regarding the charge neutrality of the crystals using these low valent cations. That is, more oxygen vacancies are formed. Metal dopant ions whose ionic radii are smaller than Ce ⁺⁴ (0.97 で in octahedral configuration) also help to form oxygen vacancies. This is because this process reduces two adjacent Ce ⁺⁴ ions (one on the surface and one below the surface) to Ce ⁺³ , resulting in a larger ion radius (1.143 Å) of Ce ⁺³ This is because the lattice expands to cause lattice distortion. For this reason, Zr ⁺⁴ (ion radius 0.84 Å) or Cu ⁺² (the ionic radius of the hexacoordinate octahedral configuration is 0.73 あ り and 0.57 場合 in the case of tetracoordinate tetrahedra) This lattice distortion is slightly relieved by replacing with. In addition, Zr forms two adjacent surface Ce ⁺³ species (one surface, not the other), which is important for very small particles where about 50% of the ions are surface ions. obtain. For this reason, it turns out that substitution type ion doping is more preferable than interstitial ion doping in which a dopant occupies a space between normal lattice positions.

[0062] In making this consideration, it is necessary to distinguish between doping and lattice-engineered crystals. In semiconductor physics, the term doping refers to an n- or p-type impurity present at a ratio of 1 part per million. The inventors use the term doped crystal when referring to a crystal having one or more metal dopant ions present at a concentration of less than 2 mole percent (20000 ppm). On the other hand, the lattice engineered crystal may have one or more metal dopant ions present in the CeO ₂ crystal at a concentration higher than 20000 ppm and up to 800000 ppm (or 80% of the cerium sublattice). For this reason, lattice-operated cerium dioxide crystals may have cerium as a small amount of metal component.

[0063] Doping of cerium dioxide with metal ions to improve ion transport, reaction efficiency and other properties is described, for example, in H.C. L. Tuller and A.M. S. Nowick, “Doped Ceria as a Solid Oxide Electrolyte” (J. Electrochem Soc., 1975, 122 (2), 255), M.C. R. DeGuire et al., "Point Defect Analysis and Microstructural Effects in Pure and Donor Doped Ceria" (Solid State Ionics, 1992, 52, 155) and PartazaaraSathiBath. T. T. et al. Aruna, K .; C. Patil and M.M. S. Hegde's “Studies on Cu / CeO ₂ : A New NO Reduction Catalyst” (Journal of Catalysis, 186, 36-44 (1999). The resulting dopant effects on electron diffusivity and oxygen diffusivity are: Described in Trovalelli's “Catalysis by Ceria and Related Materials” (Catalytic Science Series, World Scientific Publishing Co., 37-46 (2002)) and references cited therein.

[0064] Trovarielli et al., In Catalysis Today, 43 (1998), 79-88, discusses the preparation of ceria / zirconia mixed oxides with very good compositional homogeneity by a surfactant-based approach. After firing the composition at 723 ° K. (449.85 ° C.), a high specific surface area of 230 m ² / g is obtained. However, when the specific surface area is reduced to 40 m ² / g (diameter ˜20 mm), sintering occurs at 1173 ° K. (899.85 ° C.).

(0065) The pulsed neutron diffraction technique is described in E.I. Used by Mamontov et al. (J. Phys. Chem. B 2000, 104, 1110-1116) to study ceria and ceria / zirconia solid solutions. For the first time, these studies demonstrated a correlation between the concentration of vacancies / interstitial oxygen defects and oxygen storage capacity. E. Mamontov et al. Argue that Zr-assisted maintenance of oxygen vacancies is necessary to improve OSC degradation in response to thermal degradation. ZrO ₂ was present at 30.5 mol% and the calcined particles had a diameter of about 40 nm (based on BET surface area measurements).

(0066) Z. Yang et al., In Journal of Chemical Physics (2006), 124 (22), 224704 / (1-7), from the first principle, using oxygen density functional theory, oxygen vacancies are most easily near the Zr center. It was predicted that these centers would serve as nucleation sites for hole clustering. The released oxygen donates two electrons to the Ce ⁺⁴ center close to the vacancies, and two Ce ⁺³ centers are obtained.

(0067) R.A. Wang et al. Chem. Phys. B, 2006, 110, 18278-18285 investigated the spatial distribution of Zr in Ce _0.5 Zr _0.5 O ₂ formed by spray freezing technique followed by calcination. R. Wang et al. Have reported that the nanoscale heterogeneity of particles characterized by a Ce-rich core and Zr-rich shell in particles with a particle size range of 5.4-25 nm is related to materials with higher redox activity. I found out. This finding suggests that a homogeneous distribution of Zr and Ce results in decreased activity and is undesirable.

(0068) S.M. Bedrane et al., Catalysis Today, 75, 1-4, 401-405 (July 2002), doped ceria (CeO ₂ ) doped with 11 types of noble metals (noble metals = Rh, Pt, Rd, Ru, Ir) and The oxygen storage capacity of the ceria / zirconia (Ce _0.63 Zr _0.37 O ₂ ) composition was measured (Formula 1). S. Bedrane et al. Have observed a leveling effect in which the Ce / Zr material has an OSC that is approximately independent of the noble metal concentration and is 2-4 times higher than the noble metal doped Ce-only material.

(0069) H. Sparks et al. (Nanophase Technologies, Corp.) used gas phase synthesis to produce ceria mixed with rare earth oxide nanomaterials (Mat. Res. Soc. Symp. Proc., Vol. 788, 2004). . H. Sparks et al. Observed an increase in nanocrystalline particle size thermal stability and an increase in OSC for ceria doped with Zr (1: 1). However, adding more La or Pr to the Zr composition was better than using ceria alone, but worse than combining only zirconium with ceria. From the reported specific surface area, it can be inferred that the particle size is 10 nm at 600 ° C., and this particle size increases to 40 nm at 1050 ° C.

[0070] The catalytic action of Zr and Fe doped CeO ₂ in the combustion of diesel soot was investigated by Aneggi et al. (Catalysis Today, 114 (2006), 40-47). Aneggi et al. Again reiterated the fact that Zr improves the thermal stability and OSC of pure ceria, and found that Fe ₂ O ₃ gives better new results, but Fe ₂ O ₃ Then there was a final loss in activity after firing. A very systematic level system in Zr with Zr and Fe was investigated. Includes crystallographic data for these calcined particles of about 21 nm. Aneggi et al. Determined a nanoparticle specific surface area threshold of 35 m ² / gm (corresponding to a diameter of less than 24 nm). There was no change in the activity of the new catalyst, the activity of the catalyst over time.

[0071] Copper-based catalyst systems are also attracting much attention. In a very thorough structural analysis of 3-5 atomic percent Cu / CeO ₂ , S. Hegde et al. (Chem. Mater. 2002, 14, 3591-3601) demonstrated that Cu forms a unique solid solution of Ce _1-x Cu _x O _{2 and} no separate CuO phase is formed. In these 50 nm aggregated grains formed by combustion synthesis, Cu is +2, which is much more catalytically active than Cu in CuO. In addition, oxygen ion vacancies are formed around the Cu ⁺² cations.

(0072) A. Martinex-Arias et al. Phys. Chem. B, 2005, 109, 19595-19603, the reduction of Ce _1-x Cu _x O ₂ fluorite-type nanoparticles (x = 0.05, 0.1, 0.2) is reversible, and Cu Was found to be higher than its normal state (+1 or +2). The dopant induced large lattice distortions in these ˜6 nm particles in the oxide sublattice, which promoted the formation of oxygen vacancies. These materials were prepared utilizing the inverse microemulsion method followed by calcination at 500 ° C.

(0073) Iron is another metal ions imparted with high catalytic activity by CeO ₂ nanoparticles. I. Melian-Cabrera et al., In Journal of Catalysis, 239, 2006, 340-346, are more active (compared to undoped materials) and optimal for N ₂ O in a 50/50 composition of cerium and iron oxide. Report on catalytic decomposition (oxygen-limited reaction). The ceria doped with Fe is formed by a coprecipitation method in which particles having a diameter of 30 nm are formed.

(0074) T.W. Campenon and colleagues control ash accumulation in diesel particulate filters by using iron-doped ceria in “Diesel Exhaust Emission Control” of SAE special publication SP 2004, SP-1860.

(0075) R.M. Hu and colleagues in Shiyou Huagang (2006), 35 (4), 319-323 described Fe-doped cerium dioxide formed by solid-phase milling techniques followed by various high-temperature firings. investigated. Doping with iron improved the catalytic activity for methane combustion while reducing the particle size.

[0076] Examples 9 and 10 for illustration of US Patent Application Publication No. 2005/0152832 include preparation of cerium-doped barium hexaaluminate particles and cerium-coated barium hexaaluminate particles, respectively. Have been described. Example 13 describes the oxidation of methane using cerium-coated particles.

(0077) Talbot et al. (US Pat. No. 6,752,797, the disclosure of which is incorporated herein by reference) describes a method for producing metal oxide particles having nano-sized grains, A solution containing one or more metal cations is mixed with a surfactant under conditions such that surfactant micelles are formed in the solution to produce a micellar liquid, and the micelle liquid is heated. By removing the surfactant and forming metal oxide particles having an irregular pore structure. The metal cation is selected from the group consisting of cations of groups 1A, 2A, 3A, 4A, 5A and 6A of the periodic table, transition metals, lanthanides, actinides and mixtures thereof. The preparation of mixed oxide particles containing cerium dioxide particles, cerium and one or more other metals is also included in the illustrative examples.

Example 9 for illustration of US Pat. Nos. 6,413,589 and 6,869,584, the disclosure of which is incorporated herein by reference, was doped with cerium by including cerium nitrate in the emulsion mixture. The preparation of barium hexaaluminate particles is described. The particles were recovered by lyophilization and fired to 500-800 ° C. under air. The resulting particles had a grain size of less than 5 nm at 500 ° C. and less than 7 nm at 800 ° C. Illustrative Example 10 describes the synthesis of barium hexaaluminate particles coated with cerium. After firing, the cerium coated particles had grain sizes of less than 4 nm, less than 6.5 nm and less than 16 nm at 500 ° C., 800 ° C. and 1100 ° C., respectively.

Wakefield (US Pat. No. 7,169,196 B2, the disclosure of which is incorporated herein by reference) is a divalent metal that is a rare earth metal, transition metal, or group IIa, IIIB, VB or VIB metal of the periodic table Alternatively, a fuel containing cerium dioxide particles doped with a trivalent metal or metalloid is described. Copper is disclosed as a preferred dopant.

[0080] Oji Kuno has improved high temperature stability and stable OSC consisting of a ceria core and a zirconia shell in US Pat. No. 7,384,888 B2, the disclosure of which is incorporated herein by reference. The cerium / zirconium composite metal oxide is described. However, preparation of this material exhibiting improved catalytic activity of 10-20% for the oxidation of hydrocarbons and carbon monoxide requires calcination at 700 ° C. There is no sizing data to support the claims of 5-20 nm particles, no direct OSC measurement results are shown, and there is no analytical data to support the claim of core / shell shape.

[0081] Regarding nanoparticles with a diameter of 10 nm or less, there are multiple concerns that raise the question of whether such small particles can incorporate metal ion dopants. For example, 8.1 nm particles have less than 10% Ce ions on the surface, and 2.7 nm particles (0.54 nm / unit cell × 5 unit cells on each side) have 46 Ce of 46 Ce ions on the surface. .6%. Surface ions are incorporated into the lattice at 1/2 (in the case of faces) or 1/8 (corners). Therefore, its binding energy is substantially reduced and its coordination requirement is not met. Difficulties associated with doping (semiconductor) nanocrystals are discussed by Norris et al. In Science, 319, March 28, 2008. Features such as the specific solubility of the dopant in the crystal-to-solution, the diffusivity of the dopant into the lattice, its formation energy, the size and valence for the displaced ions, the kinetic barriers that can be imposed by the adsorbed surface stabilizer, etc. It serves to determine the extent to which dopant metal ions can be incorporated (if incorporated) into nanocrystals of these dimensions.

[0082] From the references just mentioned, most of the doping work is done with relatively large particle sizes (around 20 nm), and the first cerium / metal dopant mixture firing or micelle synthesis (large scale materials) Obviously, it was done by any of the processes that were not immediately useful in manufacturing. In the literature describing particles less than 10 nm in size, the crystallographic morphology is not revealed and there is no definitive evidence that the dopant has been incorporated.

Therefore, for very small nanoparticles (less than about 10 nm in diameter), a wide range of metal dopant ions can be rapidly incorporated into the cerium sublattice of cubic CeO _{2 in} an easy manner that does not require firing (above 500 ° C.). Also, it is necessary to clearly demonstrate the uptake as opposed to the production of separately nucleated dopant metal oxide grains. Because ceria single crystal grains are unique, deformations that are latticed with ceria metal are also unique. In addition, it is desirable to manufacture these materials in large quantities for distribution in a relatively short time in an economical manner.

[0084] A typical chemical reactor that may be used to prepare cerium dioxide includes a reaction chamber with a mixer (see, eg, FIG. 1 of Zhou et al. US Pat. No. 7,025,943, the disclosure of which is hereby incorporated by reference). Incorporated herein by reference). A mixer typically includes a shaft, a propeller or turbine blade attached to the shaft and a motor that rotates the shaft, and the propeller is rotated at high speed (1000-5000 rpm). The shaft can drive flat blade turbines for good mesomixing (microscale) and tilted blade turbines for macromixing (pumping fluid across the reactor).

[0085] Such an apparatus is described in US Pat. No. 6,422,736 to Antoniades, the disclosure of which is incorporated herein by reference. The described reactor is useful for fast reactions as shown by the following reaction equation. In the reaction formula, the product AgCl is a crystalline material having a diameter on the order of several hundred nanometers up to several thousand nanometers.
[Formula 3] (0086)
AgNO ₃ + NaCl → AgCl + NaNO ₃

[0087] Cerium dioxide particles prepared using this type of blend are often too large to be useful for certain applications. It is highly desirable to obtain as small a cerium dioxide particle as possible. This is because the catalytic propensity of cerium dioxide particles (ie, the ability to donate oxygen to the combustion system, see Equation 1) increases with decreasing particle size, especially for particles having an average diameter of less than 10 nm. It is.

International Application No. PCT / US2007 / 0775545 (METHOD OF PREPARING CERIUM DIOXIDE NANOPARTICLES) (filed on Sep. 4, 2007) has CeO ₂ nanoparticles reaching 1.5 nm with high yield and very high suspension. A mixing device that can be produced at turbidity is described. The reactor comprises an inlet for adding reactants, a propeller, a shaft and a motor for mixing. The reaction mixture is placed in a reactor vessel. CeO ₂ nanoparticles can be formed by adding reactants (cerium nitrate, oxidant, hydroxide ions, etc.) to the bath, which nanoparticles are initially formed as very small nuclei. Mixing causes a circular motion of the nucleus, and the nucleus grows (increases in diameter) as it continuously moves through the reaction mixing regime, because the nucleus takes in new reactants. Thus, when a steady state concentration of nuclei is first formed, the nuclei continue to grow into larger particles. Unless grain growth inhibitors are used to end this growth phase, this nucleation and growth process is undesirable if one wants to limit the final size of the particles while still maintaining a high particle suspension density.

An example of applying this nucleation and growth process to aqueous precipitation of CeO ₂ is the work of Zhang et al. (J. Appl. Phys., 95, 4319 (2004) and Applied Physics Letters, 80, 127 ( 2002)). Using cerium nitrate hexahydrate as the cerium source (very dilute at 0.0375M) and 0.5M hexamethylenetetramine as the ammonia precursor, 2.5 to 4.25 nm cerium dioxide particles were grown for 50 minutes. Formed in less than. These particles subsequently grow to 7.5 nm or more with a reaction time of about 250-600 minutes (depending on the growth conditions). Limitations in particle size, concentration and reaction time exclude this process from consideration as an economically viable means for producing large commercial quantities of CeO ₂ nanoparticles.

(0090) I.I. H. Leubner (Current Opinion in Colloid and Interface Science, 5, 151-159 (2000), Journal of Dispersion Science and Technology, 22, 125-138 (2001), ibid. (Ref.) Provides a theoretical treatment that relates the number of stable crystals formed to the molar addition rate of the reactants, crystal solubility, and temperature. The model also describes the effects of diffusion, kinetically controlled growth processes, Ostwald ripening agents and growth inhibitors / stabilizers on the number of crystals. Fast molar addition rates, low temperatures, low solubility and the presence of growth inhibitors all help to obtain a large number of nuclei and thus a smaller final grain or particle size.

In contrast to batch reactors, colloid mills typically have a flat blade turbine rotating at 10,000 rpm, which allows the material to be screened (its pores are a fraction of a millimeter in size). Can be varied from 1 to several millimeters). In general, no chemical reaction occurs and only the particle size changes due to milling. In certain cases, particle size and stability can be thermodynamically controlled by the presence of surfactant. For example, Langer et al., In US Pat. No. 6,368,366 and US Pat. No. 6,363,237, the disclosures of which are incorporated herein by reference, show aqueous properties in hydrocarbon fuel compositions produced under high shear conditions. Describes microemulsions. However, the aqueous particle phase (discontinuous phase in the fuel composition) has a large size on the order of 1000 nm.

A colloid mill is not useful for reducing the particle size of large cerium dioxide particles. This is because the particles are too hard to be sheared by the mill within a reasonable time. A preferred method for reducing the highly agglomerated cerium dioxide particles from micron to nanometer size is to mill for several days on a ball mill in the presence of a stabilizer. This is a time consuming and expensive process and always results in a broad particle size distribution. For this reason, very small nanometer particles of cerium dioxide having a uniform size distribution and incorporating one or more transition metal ions are highly suspended in large quantities while still maintaining the CeO ₂ cubic fluorite structure. There remains a need for an economical and easy way to synthesize at density.

[0093] Aqueous precipitation can be a convenient way to obtain cerium nanoparticles. However, in order to be useful as a fuel addition catalyst for fuels, cerium dioxide nanoparticles must exhibit stability in nonpolar media (eg, diesel fuel). Most of the stabilizers used to prevent aggregation in an aqueous environment are not suitable for the stabilization problem in a nonpolar environment. When placed in a non-polar solvent, such particles tend to aggregate quickly and consequently lose some, if not all, of their desirable nanoparticulate properties. For this reason, it is desirable to be able to form stable cerium dioxide particles in an aqueous environment, hold the same stabilizer on the particle surface, and then transfer these particles to a nonpolar solvent, where the particles are It remains stable and forms a homogeneous mixture or dispersion. In this simplified and economical manner, it is not necessary to change the affinity of the surface stabilizer from polar to nonpolar. Changing the stabilizer may involve a difficult substitution reaction or a separate monotonic isolation and redispersion method (eg, precipitation followed by redispersion with a new stabilizer using ball milling).

[0094] For this reason, it is efficient to synthesize stable transition metal-containing cerium dioxide nanoparticles in a polar aqueous environment and then move these particles to a non-polar environment where a stable homogeneous mixture is produced. Economic methods are still needed.

[0095] The use of cerium nanoparticles to obtain high temperature oxidation resistant coatings is described, for example, in S.H. Reported in Seal et al., “Synthesis Of Nano Crystalline Particles For High Temperature Resistant Coating” (Journal of Nanoparticular Research, 4, 433-4). The deposition of cerium dioxide on various surfaces including Ni, chromia alloys, alumina alloys, stainless steel and Ni, Ni-Cr coated alloy surfaces has been studied. A cerium dioxide particle size of 10 nm or less has been found desirable. Incorporation of ceria particles subsequently inhibits metal surface oxidation.

Rim (US Pat. No. 6,892,531, the disclosure of which is incorporated herein by reference) describes an engine lubricating oil composition for a diesel engine, the composition comprising a lubricating oil and a. 05 to 10% by weight of catalyst additive (including cerium carboxylate).

As described above, currently available cerium oxide and doped cerium oxide fuel additives have improved fuel combustion in diesel engines. However, further improvements are still needed. It would be desirable to formulate these fuel additives for diesel engines that further improve fuel combustion by utilizing smaller, less than 5 nm cubic CeO ₂ nanoparticles with a larger specific surface area. The high oxygen storage capability made possible by incorporating transition metals with these grain sizes is also highly desirable. In addition, protecting the engine from wear, reducing engine friction, higher lubricity and higher fuel efficiency are believed to be extremely beneficial.

The present invention is directed to a process for forming lattice-engineered cerium dioxide nanoparticles containing at least one transition metal (M), the process comprising: (a) a source of trivalent cerium ions; An aqueous reaction mixture comprising a source of one or more transition metal ions (M), a source of hydroxide ions, at least one nanoparticle stabilizer and an oxidizing agent is obtained at an initial temperature of about 20 to about 95 ° C. (B) mechanically shearing the mixture and passing through a perforated screen to produce a suspension of cerium hydroxide nanoparticles, and (c) oxidizing trivalent cerium ions to tetravalent cerium ions. Producing a product stream comprising transition metal-containing cerium dioxide nanoparticles Ce _1-x M _x O ₂ by bringing the temperature conditions to be effective. The cerium dioxide nanoparticles thus obtained have a cubic fluorite structure, an average hydrodynamic diameter of about 1 to about 10 nm and a geometric diameter of about 1 to about 4 nm.

[0099] The present invention is further directed to a process for producing a homogeneous dispersion containing stabilized transition metal-containing cerium dioxide nanoparticles Ce _1-x M _x O ₂ comprising: Stabilized transition metal-containing cerium dioxide nanoparticles Ce _1-x M _x O ₂ having a cubic fluorite structure, an average hydrodynamic diameter of about 1 to about 10 nm and a geometric diameter of about 1 to about 4 nm And (b) producing an aqueous concentrate by concentrating the aqueous mixture comprising the stabilized transition metal-containing cerium dioxide nanoparticles, and (c) substantially all of the aqueous concentrate from the aqueous concentrate. Removing the water produces a substantially water-free concentrate of the stabilized transition metal-containing cerium dioxide nanoparticles, and (d) converting the organic diluent into the substantially water-free concentrate. To produce an organic concentrate of stabilized transition metal-containing cerium dioxide nanoparticles, and (d) stabilized by mixing the organic concentrate with a surfactant in the presence of a nonpolar medium. Producing a homogenous dispersion containing the transition metal-containing cerium dioxide nanoparticles Ce _1-x M _x O ₂ (wherein x has a value of about 0.3 to about 0.8).

(0100-0108)
₂ is a TEM image of CeO ₂ nanoparticles prepared by non-isothermal precipitation as described in Example 1. FIG. _{2 is} a TEM particle size distribution analysis of CeO ₂ nanoparticles prepared by non-isothermal precipitation as described in Example 1. 2 is a powder X-ray diffraction spectrum of cerium dioxide nanoparticles prepared as described in Example 1. FIG. 2 is a TEM image of 1.1 nm CeO ₂ nanoparticles prepared as described in Example 2. FIG. It is an electron diffraction pattern of these 1.1 nm particles. Table 1 shows the calculated and measured electron diffraction intensities for cubic and hexagonal CeO ₂ , Ce ₂ O ₃ lattices. It is a TEM image. 4 is a particle size distribution analysis by TEM of isothermally precipitated CeO ₂ nanoparticles prepared by a triple jet process as described in Example 3. 4 is a TEM image of isothermally precipitated Cu-containing CeO ₂ nanoparticles prepared as described in Example 4. FIG. 4 is a particle size distribution analysis by TEM of isothermally precipitated Cu-containing CeO ₂ nanoparticles prepared as described in Example 4. 6 is a TEM image of isothermally precipitated Fe-containing CeO ₂ nanoparticles prepared as described in Example 5. FIG. 6 is a particle size distribution analysis by TEM of isothermally precipitated Fe-containing CeO ₂ nanoparticles prepared as described in Example 5. 7 is a TEM image of isothermally precipitated Zr-containing CeO ₂ nanoparticles prepared as described in Example 6. FIG. 7 is a particle size distribution analysis by TEM of isothermally precipitated Zr-containing CeO ₂ nanoparticles prepared as described in Example 6. 7 is a TEM image of isothermally precipitated Zr / Fe-containing CeO ₂ nanoparticles prepared as described in Example 7. FIG. 4 is a particle size distribution analysis by TEM of isothermally precipitated Zr / Fe-containing CeO ₂ nanoparticles prepared as described in Example 7. _{2 is} an X-ray diffraction spectrum of isothermally precipitated CeO ₂ nanoparticles and isothermally precipitated Zr / Fe-containing CeO ₂ nanoparticles prepared as described in Example 7. FIG. 8 is a field emission electron gun TEM grid image of Zr / Fe-containing CeO ₂ nanoparticles prepared as described in Example 7. FIG.

In the present application, the term “transition metal” is understood to include 40 chemical elements 21-30, 39-48 and 72-80, respectively contained in periods 4, 5, 6 of the periodic table.

(0110) The present invention is a transition metal ion containing cerium dioxide (CeO ₂₎ provides a process for forming nanoparticles, the process, (a) a source of trivalent cerium ions, one or more transition Obtaining an aqueous reaction mixture comprising a source of metal ions, a source of hydroxide ions, at least one nanoparticle stabilizer and an oxidant; (b) mechanically shearing the mixture; To produce a suspension of cerium hydroxide nanoparticles by passing through, and (c) by making the temperature conditions effective to oxidize trivalent cerium ions to tetravalent cerium ions, structure, a product stream comprising a transition metal-containing cerium dioxide particles Ce _1-x M _x O ₂ having a geometric diameter of the average hydrodynamic diameter and about 1 to about 4nm to about 1 to about 10nm Including that formed. Crystalline cerium dioxide particles containing one or more transition metal ions and having a unimodal size distribution and a monodisperse particle size distribution can be selectively prepared within this size range. Single crystalline particles include 2 unit cells per side for 1.1 nm particles up to 5 unit cells per side with up to 2.7 nm particles, depending on the preparation conditions. Here, the term crystallinity is composed of a single crystal with a well-defined dimension determined by the number of lattice cells that are constituent units, not from a plurality of aggregated microcrystals of various sizes. It is a particle.

The present invention further provides a continuous process for producing crystalline cerium dioxide CeO ₂ nanoparticles containing one or more transition metal ions and having an average hydrodynamic diameter of about 1 to about 10 nm. The process includes mixing trivalent cerium ions, one or more transition metal ions, an oxidizing agent, at least one nanoparticle stabilizer, and hydroxide ions in a continuous reactor.

[0112] The present invention also provides a process for forming cerium dioxide nanoparticles comprising: (a) a source of trivalent cerium ions, one or more transition metal ions and at least one nanoparticle. An aqueous first reaction mixture containing a stabilizer is obtained, (b) a second reaction mixture is produced by stirring the first reaction mixture while adding an oxidizing agent, and (c) hydroxylation while subjecting to mechanical shearing. Generating a third reaction mixture by adding a source of product ions to the second reaction mixture; and (d) heating the third mixture at about 50 to about 100 ° C. to produce one or more transition metal ions. And forming a uniform crystalline cerium dioxide nanoparticle having a particle size distribution that is substantially monomodal.

The present invention further provides for producing a homogeneous mixture comprising the crystalline cerium dioxide nanoparticles described above, at least one nanoparticle stabilizer, at least one surfactant, a glycol ether mixture and a nonpolar medium. Provide a process. This process provides (a) an aqueous mixture comprising stabilized crystalline cerium dioxide nanoparticles formed by the close association of nanoparticle stabilizers and crystalline cerium dioxide nanoparticles, and (b) stabilized crystals. An aqueous concentrate is produced by concentrating this aqueous mixture containing the soluble cerium dioxide nanoparticles, (c) removing substantially all the water from the aqueous environment to the glycol ether environment by solvent shift, surfactants and optional A co-surfactant and a solvent-shifted concentrate in the presence of a nonpolar medium to produce a homogeneous mixture.

[0114] In the presence of hydroxide ions, tetravalent cerium ions react to produce cerium hydroxide, which is converted to crystalline cerium dioxide when heated. The temperature in the reaction vessel is maintained at about 50 to about 100 ° C, more preferably about 65 to 95 ° C, and most preferably about 85 ° C. Time and temperature can be balanced, and high temperatures typically reduce the time required to convert hydroxide to oxide. After exposure to these elevated temperatures for a period of time (less than about 1 hour, suitably about 0.5 hours), the cerium hydroxide is converted to crystalline cerium dioxide and the reactor temperature is about 15-25 ° C. Can be lowered. Subsequently, the crystalline cerium dioxide nanoparticles are concentrated and unreacted cerium and unwanted by-products (such as ammonium nitrate) are most conveniently removed, for example, by diafiltration.

[0115] In one embodiment of the present invention, a method of forming crystalline cerium dioxide nanoparticles containing one or more transition metal ions includes a trivalent cerium ion, one or more transition metal ions, a hydroxide ion, Obtaining an aqueous reaction mixture comprising a stabilizer or combination of stabilizers and an oxidizing agent, wherein the reaction generates a small nucleus size and subsequently oxidizes trivalent cerium ions to tetravalent cerium ions and Performed at a temperature effective to grow nuclei into metric cerium dioxide. Subjecting the reaction mixture to mechanical shear (preferably by passing the reaction mixture through a perforated screen) produces a suspension of crystalline cerium dioxide nanoparticles having an average hydrodynamic diameter of about 1 to about 10 nm. . Although the particle size can be controlled within the range of 1.5-25 nm, preferably the crystalline cerium dioxide nanoparticles have an average hydrodynamic diameter of about 10 nm or less, more preferably about 8 nm or less, and most preferably about 6 nm. Have Desirably, the nanoparticles comprise one or up to two primary crystallites per particle edge, with each crystallite averaging 2.5 nm (approximately 5 unit cells). For this reason, the particle size distribution of the resulting nanoparticles is substantially monodisperse, that is, has a coefficient of variation (COV) of less than 25%, where COV is the standard deviation divided by the average. Defined as a thing.

[0116] Mechanical shear involves the movement of fluid on a surface (such as the surface of a rotor), resulting in shear stress. In particular, laminar flow over the surface has zero velocity, and shear stress occurs between the zero velocity surface and a higher velocity flow away from the surface.

[0117] In one embodiment, the present invention utilizes a colloid mill, usually used to mill microemulsions or colloids, as a chemical reactor for producing cerium dioxide nanoparticles. Examples of useful colloid mills include those described in Korstvedt US Pat. No. 6,745,961 and US Pat. No. 6,305,626, the disclosure of which is incorporated herein by reference.

Desirably, the reactants include a source of trivalent cerium ions (eg, cerous nitrate), an oxidizing agent (hydrogen peroxide, molecular oxygen, etc.) and a stabilizer (eg, 2- [2 -(2-methoxyethoxy) ethoxy] acetic acid) in aqueous solution. Typically, a two-electron oxidant such as a peroxide is preferably present at a molar concentration of at least one-half that of cerium ions. The hydroxide ion concentration is preferably at least twice, more preferably 3 times, and even 5 times the cerium ion molar concentration.

[0119] Initially, the reaction chamber is maintained at a temperature sufficiently low to produce small sized cerium hydroxide nuclei. This nucleus can grow into nanometer-sized crystalline cerium dioxide particles after the subsequent transition to higher temperatures, and trivalent cerium ions are converted to tetravalent cerium ions. Initially, the temperature is suitably about 25 ° C. or lower, although higher temperatures may be employed without a significant increase in particle size.

[0120] In one embodiment, a source of trivalent cerium ions, one or more transition metal ions, a nanoparticle stabilizer and an oxidizing agent are placed in a reactor and a source of hydroxide ions (ammonium hydroxide) Etc.) rapidly with stirring, preferably in about 10 minutes or less. Under certain conditions (such as single jet addition of ammonia to metal ions), about 20 seconds or less is preferred, and even more preferred is about 15 seconds or less. In an alternative embodiment, a source of hydroxide ions and an oxidant are placed in the reactor and the source of trivalent cerium ions and one or more transition metal ions are added for about 15 seconds up to 20 minutes. Add. In a third preferred embodiment, the stabilizer is placed in a reactor and cerium nitrate and 1 at an optimal stoichiometric molar ratio of 2: 1, 3: 1, or even 5: 1 OH: Ce. More than one species of transition metal ion is introduced into the reaction chamber simultaneously with another ammonium hydroxide jet.

[0121] Trivalent cerium ions react with an oxidant in the presence of hydroxide ions to produce cerium hydroxide, which can be converted to crystalline cerium dioxide by heating. The temperature of the reaction vessel is maintained at about 50 to about 100 ° C, preferably about 65 to 85 ° C, more preferably about 70 ° C. Incorporation of certain transition metal ions (Zr, Cu, etc.) typically requires high temperatures (about 85 ° C.). After exposure to these high temperatures for a period of time (preferably less than about 1 hour, more preferably about 0.5 hour), the doped cerium hydroxide has been substantially converted to crystalline cerium dioxide. The temperature of the reaction vessel is lowered to about 15-25 ° C. Time and temperature variables can be balanced, and reaction times are generally shorter at higher temperatures. The suspension of cerium dioxide nanoparticles is concentrated to remove unreacted cerium and unwanted by-products (eg, ammonium nitrate). This can conveniently be achieved by diafiltration.

[0122] Nanoparticle stabilizers are an essential component of the reaction mixture. Desirably, the nanoparticle stabilizer is water soluble and forms a weak bond with cerium ions. K _BC represents the binding constant of the nanoparticle stabilizer to cerium ions in water. The log K _{BC for} nitrate ions is 1, and 14 for hydroxide ions. Most desirably, log K _BC is in this range, preferably in the middle of this range. Useful nanoparticle stabilizers include alkoxy-substituted carboxylic acids, α-hydroxylcarboxylic acids, α-ketocarboxylic acids (such as pyruvic acid) and small organic polyacids (such as tartaric acid, citric acid). Examples of alkoxylated carboxylic acids include methoxyacetic acid, 2- (methoxy) ethoxyacetic acid and 2- [2- (2-methoxyethoxy) ethoxy] acetic acid (MEEA). Among α-hydroxycarboxylic acids, examples include lactic acid, gluconic acid and 2-hydroxybutanoic acid. Polyacids include ethylenediaminetetraacetic acid (EDTA), tartaric acid and citric acid. Combinations of compounds with large K _BC such as EDTA and weak K _BC stabilizers (such as lactic acid) are also useful at certain ratios. Large K _BC stabilizers (such as gluconic acid) can be used at low levels or with weak K _BC stabilizers (such as lactic acid).

[0123] In certain desirable embodiments, the nanoparticle stabilizer comprises a compound of formula (Ia). In the formula (Ia), R represents hydrogen, a substituted or unsubstituted alkyl group or a substituted or unsubstituted aromatic group, for example, a methyl group, an ethyl group, or a phenyl group. More preferably, R represents a lower alkyl group (such as a methyl group). R ¹ represents hydrogen or a substituent (such as an alkyl group). In the formula (Ia), n represents an integer of 0 to 5, preferably 2. Y represents a counter ion such as H or an alkali metal (for example, Na ⁺ , K ⁺ ). The stabilizer binds to the nanoparticles and prevents agglomeration of particles and subsequent formation of large masses of particles.
[Formula 4]
RO (CH ₂ CH ₂ O) _n CHR ¹ CO ₂ Y (Ia)

[0124] In another embodiment, the nanoparticle stabilizer is represented by formula (Ib). In the formula, each R ² independently represents a substituted or unsubstituted alkyl group or a substituted or unsubstituted aromatic group. X and Z independently represent H or a counter ion (Na ⁺ , K ⁺ etc.), and p is 2 or 2.
[Formula 5]
XO ₂ C (CR ² ) _P CO ₂ Z (Ib)

Useful nanoparticle stabilizers are also found in α-hydroxy substituted carboxylic acids (such as lactic acid) and polyhydroxy substituted acids (such as gluconic acid).

[0126] Preferably, the nanoparticle stabilizer does not contain elemental sulfur. This is because sulfur-containing materials may not be desirable for certain applications. For example, when cerium dioxide particles are included in the fuel additive composition, use of a sulfur-containing stabilizer (such as AOT) may cause sulfur oxides to be emitted after combustion, which is undesirable.

The size of the resulting cerium dioxide particles can be measured by dynamic light scattering (a measurement technique for measuring the hydrodynamic diameter of particles). Hydrodynamic Diameter (BJ Berne and R. Pecora, “Dynamic Light Scattering: With Applications to Chemistry, Biology and Physics” (John Wiley and Sons. NY 1976). Interactions of Photons and Neutrons with Matter (see World Scientific Publishing, Singapore, 1997) is slightly larger than the geometric diameter of the particle and includes both the original particle size and the solvating shell surrounding the particle. As the light passes through the colloidal dispersion, the particles or droplets scatter part of the light in all directions. When the particles are very small relative to the wavelength of light, the intensity of the scattered light is uniform in all directions (Rayleigh scattering). If the light is coherent and monochromatic, e.g. from a laser, time-dependent variations in scattering intensity can be observed using a suitable detector such as a photomultiplier tube that can operate in photon counting mode. . This variation arises from the fact that the particles are small enough to cause random thermal Brownian motion, and thus the distance between the particles is constantly changing. Intense and destructive interference of light scattered by adjacent particles in the illuminated area causes intensity variations at the detector surface, which arise from the movement of the particles. Contains information about this exercise. Therefore, it is possible to obtain the particle diffusion coefficient by analyzing the time dependence of the intensity variation, and from this diffusion coefficient, using the Stokes-Einstein equation and the known viscosity of the medium, the particle fluid The mechanical radius or diameter can be calculated.

In another aspect of the present invention, a continuous process for producing small transition metal ion-containing crystalline cerium dioxide nanoparticles, ie particles having an average diameter of less than about 10 nm, comprises trivalent cerium ions, one or more Of mixing transition metal ions, oxidants, nanoparticle stabilizers or combinations of stabilizers and hydroxide ions in a continuous reactor, with reactants and other raw materials being continuously introduced into the reactor. And the product is continuously removed therefrom. Continuous processes are described, for example, by Ozawa et al. US Pat. No. 6,897,270, Nickel et al. US Pat. No. 6,723,138, Campbell et al. US Pat. No. 6,627,720, Beck US Pat. No. 5,097,090 and Byrd et al. U.S. Pat. No. 4,661,321, the disclosures of which are incorporated herein by reference.

[0129] Solvents such as water are often used in the process. The solvent dissolves the reactants and the process can be controlled by adjusting the solvent flow. Advantageously, the mixer can be used to stir and mix the reactants.

[0130] Any reactor capable of accepting a continuous stream of reactants and delivering a continuous stream of products can be used. These reactors can include continuous stirred tank reactors, plug flow reactors, and the like. The reactants required to carry out the nanoparticle synthesis are preferably charged by flowing into the reactor. That is, the reactant is preferably introduced as a liquid or solution. The reactants can be charged separately and the specific reactants can be mixed prior to charging to the reactor.

[0131] The reactants are introduced through one or more input ports into a reaction chamber equipped with a stirrer. Typically, the reactants are a source of trivalent cerium ions (eg, cerous nitrate), transition metal ions (eg, ferric nitrate, cupric nitrate, etc.), oxidizing agents (hydrogen peroxide). , Molecular oxygen, etc., including ambient air) and an aqueous solution of a stabilizer (eg, 2- [2- (2-methoxyethoxy) ethoxy] acetic acid). A two-electron oxidant such as hydrogen peroxide is preferably present at a concentration of at least one-half the molar concentration of cerium ions. Alternatively, molecular oxygen can be bubbled through the mixture. The hydroxide ion concentration is preferably at least twice the cerium molar concentration.

In one embodiment of the present invention, a method for forming small cerium dioxide nanoparticles comprises trivalent cerium ions (eg, as cerium (III) nitrate), one or more transition metal ions and an oxidizing agent. Producing a first aqueous reactant stream comprising. Suitable oxidizing agents that can oxidize Ce (III) to Ce (IV) include, for example, hydrogen peroxide or molecular oxygen. Optionally, the first reactant stream also includes a nanoparticle stabilizer that prevents aggregation of the particles by binding to the doped cerium dioxide nanoparticles. Examples of useful nanoparticle stabilizers are described above.

The method further includes generating a second aqueous reactant stream that includes a source of hydroxide ions (eg, ammonium hydroxide, potassium hydroxide). Optionally, the second reactant stream further comprises a stabilizer, examples of which have already been mentioned. However, at least one of the first or second reactant streams must contain a stabilizer or combination of stabilizers.

[0134] The first reactant stream and the second reactant stream are mixed to generate a reactant stream. Initially, the temperature of the reaction stream is kept low enough to form small cerous hydroxide nuclei. Subsequently, when the temperature is raised, Ce (III) is oxidized to Ce (IV) in the presence of an oxidant, and the hydroxide is converted to an oxide, thereby producing a product stream containing crystalline cerium dioxide. Generated. The temperature for converting the hydroxide to the oxide is preferably about 50-100 ° C, more preferably about 60-90 ° C. In one embodiment, the first reactant stream and the second reactant stream are mixed at about 10-20 ° C and the temperature is subsequently increased to about 60-90 ° C. If the growth stage can be inhibited with a suitable molecular adsorbate (growth inhibitor), isothermal deposition at high temperature (eg, 90 ° C.) is an alternative method for forming small nanoparticles.

Desirably, the lattice engineered crystalline cerium dioxide nanoparticles in the product stream are concentrated by a diafiltration technique using, for example, one or more semi-porous membranes. In one embodiment, the product stream comprises an aqueous suspension of transition metal-containing crystalline cerium dioxide nanoparticles that has been reduced to a conductivity of about 5 mS / cm or less by one or more semi-porous membranes.

A continuous reactor suitable for the practice of the present invention is schematically illustrated in FIG. 3 of “METHOD OF PREPARING CERIUM DIOXIDE NANOPARTICLES” (filed on Sep. 4, 2007) of International Application No. PCT / US2007 / 77545. It is shown in the figure. The reactor 40 contains a first reaction stream 41 containing an aqueous cerium nitrate solution. An oxidizing agent (hydrogen peroxide or the like) is added to the reaction stream from the inlet 42, and the reactant is mixed by the mixer 43a. A stabilizer is added to the obtained mixture from the inlet 45, and then mixed by the mixer 43b. Next, the mixture from mixer 43b enters mixer 43c where it is mixed with the second reactant stream containing ammonium hydroxide from input 44. A reaction stream is generated by mixing the first and second reactant streams using mixer 43c. This reaction stream can be subjected to mechanical shearing by passing it through a perforated screen. In a further embodiment, the mixer 43c includes a colloid mill reactor as described above with an inlet and outlet 45 for receiving the reactant stream. In a further embodiment, the temperature of the mixer 43c is maintained at about 10 to about 25 ° C.

[0137] The mixture from 43c enters the reactor tube 45, which is contained in a constant temperature bath 46 that maintains the tube 45 at about 60-90 ° C. Crystalline cerium dioxide nanoparticles are formed in reactor tube 45, which may include a coil 50. The product stream then enters one or more diafiltration units 47 where the crystalline cerium dioxide nanoparticles are concentrated using one or more semiporous membranes. One or more diafiltration units may be connected in series to achieve product concentration in a single pass. Alternatively, units can be placed in parallel to handle ultra high volume volumes. Diafiltration units can also be arranged in combination with series and parallel to process high volumes at high speed. Concentrated crystalline cerium dioxide nanoparticles leave the diafiltration unit via outlet 49 and excess reactants and water are removed from diafiltration unit 47 via outlet 48. The In an alternative embodiment, the stabilizer may be added to the second reaction stream via port 51 rather than to the first reaction stream via port 45.

In one embodiment of the present invention, the product stream of concentrated lattice engineered crystalline cerium dioxide nanoparticles exiting diafiltration unit 47 is substantially free of one or more glycol ethers. Solvent shifted to the environment. This can be accomplished using a dialysis bag or by flowing aqueous nanoparticles through a diafiltration column, preferably with an organic diluent containing one or more glycol ethers. The organic diluent can further comprise an alcohol. Useful diluents include a mixture of diethylene glycol monomethyl ether and 1-methoxy-2-propanol.

Carbonization by mixing the resulting solvent-shifted organic concentrate with a surfactant (such as oleic acid) followed by a stream containing a nonpolar solvent (such as kerosene) or an ultra-low sulfur diesel fuel. Produces a homogeneous dispersion of lattice-operated crystalline cerium dioxide nanoparticles that is miscible with hydrogen fuel (such as diesel).

[0140] Utilizing a continuous process to produce lattice engineered crystalline cerium dioxide nanoparticles can better control the formation of particle nuclei and their growth than in a batch reactor. The nucleus size can be controlled by the ratio of the nanoparticle stabilizer to the initial reagent concentration, temperature and reagent concentration. A low temperature below about 20 ° C. and a high nanoparticle stabilizer to reagent concentration ratio favors small nuclei. In this way, very small nanoparticles having an average hydrodynamic diameter of less than about 10 nm and a geometric particle size of less than about 3 nm can be economically produced.

The present invention is for formulating a homogeneous mixture comprising cerium dioxide (CeO ₂ ) nanoparticles, nanoparticle stabilizers, surfactants, glycol ethers and nonpolar solvents containing one or more transition metal ions. Provide a way. Preferably, the nanoparticles have an average hydrodynamic diameter of less than about 10 nm, more preferably less than about 8 nm, most preferably about 6 nm and a geometric particle size (measured with TEM) of less than about 4 nm.

As described above, lattice engineered crystalline cerium dioxide nanoparticles can be prepared by a variety of procedures. In a typical synthetic route, water is used as a solvent, resulting in an aqueous mixture of nanoparticles and one or more salts. For example, as shown in the reaction formula (3a), cerium dioxide particles are obtained by reacting cerium (III) nitrate hydrate with hydroxide ions from, for example, an aqueous ammonium hydroxide solution, thereby converting cerium (III) hydroxide. It can be prepared by producing. As shown in the reaction formula (3b), cerium hydroxide can be oxidized to cerium dioxide (IV) with an oxidizing agent (hydrogen peroxide or the like). Similar stoichiometric ratios of trishydroxide are shown in reaction formulas (4a) and (4b).
[Formula 6]
Ce (NO ₃ ) ₃ (6H ₂ O) + 2NH ₄ OH → Ce (OH) ₂ NO ₃ + 2NH ₄ NO ₃ + 6H ₂ O (3a)
[Formula 7]
2Ce (OH) ₂ NO ₃ + H ₂ O ₂ → 2CeO ₂ + 2HNO ₃ + 2H ₂ O (3b)
[Formula 8]
Ce (NO ₃ ) ₃ (6H ₂ O) + 3NH ₄ OH → Ce (OH) ₃ + 3NH ₄ NO ₃ + 6H ₂ O (4a)
[Formula 9]
2Ce (OH) ₃ + H ₂ O ₂ → 2CeO ₂ + 4H ₂ O (4b)

[0143] Complexes produced at very high base levels (eg, 5: 1 OH: Ce) are also pathways for cerium oxide formation. However, if the growth is not properly suppressed, the grain size will be much larger.

In some cases, especially when ammonium hydroxide is not present in excess relative to the trivalent cerium ion, the species Ce (OH) ₂ (NO ₃ ) or (NH ₄ ) ₂ Ce (NO ₃ ) ₅ is It can be present first and is subsequently oxidized to cerium dioxide.

[0144] Transition metal-containing crystalline cerium dioxide particles are formed in an aqueous environment and are mixed with one or more nanoparticle stabilizers. Desirably, the cerium dioxide nanoparticles are formed in the presence of a stabilizer or the stabilizer is added immediately after particle formation. Useful nanoparticle stabilizers include alkoxy-substituted carboxylic acids, α-hydroxylcarboxylic acids (such as pyruvic acid) and small organic polycarboxylic acids. Examples of alkoxy substituted carboxylic acids include methoxyacetic acid, 2- (methoxy) ethoxyacetic acid and 2- [2- (2-methoxyethoxy) ethoxy] acetic acid (MEEA). Examples of α-hydroxycarboxylic acid include lactic acid, gluconic acid and 2-hydroxybutanoic acid. Polycarboxylic acids include ethylenediaminetetraacetic acid (EDTA), tartaric acid and citric acid. In desirable embodiments, the nanoparticle stabilizer comprises a compound of formula (Ia) or formula (Ib) as described above.

[0145] In addition to the transition metal-containing crystalline cerium dioxide particles, the reaction mixture comprises one or more salts (eg, ammonium nitrate) and unreacted cerium nitrate. Stabilized particles can be separated from these materials and salts by washing with 18 megaohm water in an ultrafiltration or diafiltration apparatus. Low ionic strength (<5 mS / cm) is highly desirable for particle formation and stabilization in nonpolar media. The washed, stabilized cerium dioxide nanoparticles can be optionally concentrated, for example using a semi-porous membrane, to produce an aqueous concentrate of the nanoparticles. The particles can also be concentrated by other means (eg, centrifugation).

In certain preferred embodiments, the transition metal-containing crystalline cerium dioxide particles are concentrated by diafiltration. Diafiltration techniques utilize an ultrafiltration membrane that can be used to completely remove, replace, or reduce the concentration of salts in the nanoparticle-containing mixture. In this process, the components of the reaction mixture are separated according to their molecular size by selectively utilizing a semi-permeable (semi-porous) membrane filter. Thus, a suitable ultrafiltration membrane allows the passage of smaller molecules such as salt, water, etc. while being porous enough to retain most of the formed nanoparticles. In this way, the nanoparticles and associated stabilizers can be concentrated. The material remaining in the filter, including the stabilized nanoparticles, is referred to as the concentrate or retentate, and the discarded salt and unreacted material is referred to as the filtrate.

By applying pressure to the mixture, the rate at which small molecules pass through the membrane (flow rate) can be accelerated and the concentration process can be facilitated. Other means of increasing the flow rate include the use of large membranes with large surface areas and expansion of the membrane pore size without unacceptable loss of nanoparticles.

In one embodiment, the membrane is selected such that the average pore size of the membrane is no more than about 30%, 20%, 10%, or even 5% of the average diameter of the nanoparticles. However, the pore diameter must be sufficient for water and salt molecules to pass through. For example, ammonium nitrate and unreacted cerium nitrate should be completely or partially removed from the reaction mixture. In certain preferred embodiments, the average membrane pore size is small enough to retain particles having a diameter of 1.5 nm or greater in the retentate. This is thought to correspond to a protein size of about 3 kilodaltons.

[0149] Desirably, the concentrate comprises stabilized nanoparticles and residual water. In one embodiment, the concentration of cerium dioxide nanoparticles is preferably greater than about 0.5 moles, more preferably greater than about 1.0 mole, and even more preferably greater than about 2.0 moles (solids in a given dispersion). Min. 35%).

[0150] Once the concentrate is formed, most if not all water is removed by dialysis with glycol ether. This uses a mixture of diethylene glycol methyl ether and 1-methoxy-2-propanol, puts the concentrate in a 2 kilodalton dialysis bag, exchanges water into the glycol ether medium, while the glycol ether medium Is replaced by water in the nanoparticle dispersion. Several exchanges may be necessary (exchange of glycol ether medium). Alternatively, the glycol ether mixture can be flowed through a diafiltration column with an aqueous transition metal-containing crystalline cerium dioxide particle solution, and the solvent shift is thus performed.

(0151) Glycol ether surfactants having both ether and alcohol groups include compounds of formula (Ic), wherein R ³ represents a substituted or unsubstituted alkyl group, and m is 1-8. Is an integer.
[Formula 10]
R ³ (OCH ₂ CH ₂ ) _m OH (Ic)

Other useful surfactants for performing solvent shifts include the formula: C ₉ H ₁₉ C ₆ H ₄ (OCH ₂ CH ₂ ) _n OH, where n is 4-6. Having nonylphenyl ethoxylate.

[0153] Once the transition metal-containing crystalline cerium dioxide particles are in the organic medium (still stabilized with the original stabilizer used in its manufacture, but complexed with glycol ether) It is possible to disperse the mixture in a nonpolar medium (such as kerosene) that is compatible with most hydrocarbon fuels (diesel, biodiesel, etc.). Prior to addition to the hydrocarbon diluent, the surface of the particles is first functionalized with a surfactant (such as oleic acid) and an optional co-surfactant (such as 1-hexanol). It is important to realize that the composition of this material is not a reverse micelle oil-in-water emulsion. This is because there is almost no water, and the positive charge on the surface of the cerium nanoparticles is complexed with ether oxygen atoms and bound to the oppositely charged carboxylic acid. Carboxylic acid exists in a chemisorbed state and promotes miscibility of the nanoparticles with the nonpolar hydrocarbon diluent. Other surface functionalized materials (linoleic acid, stearic acid, palmitic acid, etc.) can also be used in place of oleic acid. In general, preferred materials are carboxylic acids having a carbon chain length of less than 20 carbon atoms but greater than 8 carbon atoms. Other suitable nonpolar diluents include, for example, hydrocarbons having about 8-20 carbon atoms (eg, octane, nonane, decane, toluene) and hydrocarbon fuels (gasoline, biodiesel, diesel fuel, etc.). .

For optimal miscibility and stability with nonpolar hydrocarbons, it is desirable that very small amounts of ions be present in the cerium dioxide concentrate to conduct electricity. This situation can be achieved by concentrating the nanoparticles through diafiltration to a conductivity level below about 5 mS / cm, preferably below about 3 mS / cm.

[0155] Resistivity is the reciprocal of conductivity (the ability of a substance to pass current). The conductivity meter comprises two plates placed in a sample, and the conductivity can be measured by applying a potential between the plates (usually a sinusoidal voltage) and measuring the current. Conductivity (G), which is the reciprocal of resistivity (R), is Ohm's law: G = 1 / R = I / E where I is the current in amperes and E is the voltage in volts ) According to the voltage and current values. Since the charge of ions in the solution promotes the conductance of the current, the conductivity of the solution is proportional to its ion concentration. The basic unit of conductivity is Siemens (S) or Milli-Siemens (mS). Since the shape of the cell affects the conductivity value, standardized measurements are expressed in specific conductivity units (mS / cm) to correct for variations in electrode dimensions.

The present invention further includes transition metal-containing cerium dioxide nanoparticles, at least one nanoparticle stabilizer, one or more solvent-shifted media (such as glycol ethers), at least one surfactant and a nonpolar diluent. Alternatively, it is directed to a method for preparing a homogeneous mixture containing a solvent. In the first step, an aqueous mixture containing stabilized cerium dioxide nanoparticles is obtained, in which the nanoparticles stabilizer molecules are intimately associated with the nanoparticles. The second step involves producing an aqueous concentrate that is relatively free of anions and cations by concentrating the stabilized crystalline cerium dioxide nanoparticles while minimizing the ionic strength of the suspension. In the third step, water associated with the nanoparticles is removed using a nonionic surfactant. The final step is to mix this solvent-shifted concentrate with a non-polar solvent containing a surfactant to produce a substantially homogeneous mixture that is thermodynamically stable and a multi-component two-phase dispersion. Including doing.

This substantially homogeneous thermodynamic dispersion contains a minimum amount of water, preferably at a level not exceeding about 0.5% by weight.

The transition metal-containing cerium dioxide nanoparticles preferably have an average hydrodynamic diameter of less than about 10 nm, more preferably less than about 8 nm, most preferably about 6 nm and a geometric diameter of about 4 nm or less.

Desirably, the cerium dioxide nanoparticles have a primary crystallite size of about 2.5 nm ± 0.5 nm and include one or up to two crystallites per particle edge length.

[0160] The aqueous mixture is advantageously produced in a colloid mill reactor and the nanoparticle stabilizer may comprise an ionic surfactant, preferably a compound having a carboxylic acid group and an ether group. The nanoparticle stabilizer has the formula (Ia):
[Formula 11]
RO (CH ₂ CH ₂ O) _a CHR ¹ CO ₂ Y (Ia)
Wherein R represents hydrogen, a substituted or unsubstituted alkyl group or a substituted or unsubstituted aromatic group, R ¹ represents hydrogen or an alkyl group, Y represents H or a counter ion, and n represents 0 to 5 Certain surfactants. Preferably, R represents a substituted or unsubstituted alkyl group, R ¹ represents hydrogen, Y represents hydrogen, and n is 2.

Another suitable nanoparticle stabilizer is of formula (Ib):
[Formula 12]
XO ₂ C (CR ² ) _P CO ₂ Z (Ib)
Wherein each R ² independently represents hydrogen, a substituted or unsubstituted alkyl group or a substituted or unsubstituted aromatic group, X and Z independently represent H or a counter ion, and p is 1 or 2. Some) dicarboxylates.

Other useful nanoparticle stabilizers are included in the group consisting of lactic acid, gluconic acid enantiomers, EDTA, tartaric acid, citric acid and combinations thereof.

The concentration of the aqueous mixture is preferably performed using diafiltration, so that the conductivity of the concentrated aqueous mixture is reduced to about 5 mS / cm or less.

The surfactant used to shift the stabilized transition metal-containing crystalline cerium dioxide particles from an aqueous environment to a non-aqueous environment is advantageously a non-ionic surfactant, preferably an alcohol group and Compounds containing an ether group, in particular the formula (Ic):
[Formula 13]
R ³ (OCH ₂ CH ₂ ) _m OH (Ic)
(Wherein R ³ represents a substituted or unsubstituted alkyl group, and m is an integer of 1 to 8).

[0165] The nonionic surfactant has the formula (Id):
[Formula 14]
R ³ Φ (OCH ₂ CH ₂ ) _m OH (Id)
(Wherein R ³ represents a substituted or unsubstituted alkyl group, Φ is an aromatic group, and m is an integer of 4 to 6).

[0166] The reaction mixture may further comprise a cosurfactant, preferably an alcohol.

The introduction of this solvent shifted concentrate is facilitated by a surfactant that surface functionalizes the nanoparticles. Preferred surfactants are carboxylic acids (oleic acid, linoleic acid, stearic acid, palmitic acid, etc.). In general, preferred materials are carboxylic acids having a carbon chain length of less than 20 carbon atoms and greater than 3 carbon atoms.

The apolar diluent contained in the substantially homogeneous dispersion is advantageously a hydrocarbon having about 6 to 20 carbon atoms (eg octane, decane, kerosene, toluene, naphtha, diesel fuel) , Biodiesel and mixtures thereof). When used as a fuel additive, there is at least about 100 parts of fuel per part of homogeneous dispersion.

In the present invention, the transition metal is preferably selected from the group consisting of Fe, Mn, Cr, Ni, W, Co, V, Cu, Mo, Zr, Y and combinations thereof. Preferred transition metals are Zr or Y, more preferably in combination with Fe.

[0170] It may be beneficial to form a ceramic oxide coating in situ on the inner surface of a diesel engine cylinder. Potential benefits of this coating include further protection of the engine from thermal stress. For example, CeO ₂ melts at 2600 ° C., and cast iron, a common material used in diesel engine manufacturing, melts at about 1200-1450 ° C. Even the 5 nm ceria particles showed the ability to protect the steel from oxidation for 24 hours at 1000 ° C., so the size dependent melting phenomenon caused the melting point of the cerium dioxide nanoparticles of the present invention to face the combustion in the engine. It is not expected to drop below the temperature. See, for example, Patil et al., Journal of Nanoparticle Research, vol. 4, pp 433-438 (2002). Engines protected in this way may be able to operate at higher temperatures and compression ratios, resulting in higher thermodynamic efficiency. Diesel engines with cylinder walls coated with cerium dioxide withstand further oxidation (CeO ₂ is already fully oxidized), which prevents engine “rust”. This is important. Certain additives used to reduce carbon emissions or improve fuel economy (eg oxygenate MTBE, ethanol and other cetane improvers (peroxides, etc.)) will also corrode when introduced into the combustion chamber. This is because it can lead to the occurrence of rust and a decrease in engine life and performance. The coating should not be so thick as to prevent cooling of the engine wall by the water recirculation cooling system.

In one embodiment, the present invention provides transition metal-containing crystalline cerium dioxide nanoparticles having an average hydrodynamic diameter that is less than about 10 nm, preferably less than about 8 nm, more preferably 6 nm or even less. The particles are useful as a fuel additive for diesel engines. The surface of the cerium dioxide nanoparticles can be modified to promote its binding to the iron surface, and desirably, the nanoparticles are ceramic on the surface of the diesel engine cylinder when added to the fuel additive composition. An oxide coating can be formed rapidly.

[0172] In one embodiment, a transition metal having binding affinity for iron is incorporated on the surface of the cerium dioxide nanoparticles. Examples of iron surfaces include those present in many engine internal components. Suitable transition metals include Mn, Fe, Ni, Cr, W, Co, V, Cu, Zr and Y. Transition metal ions incorporated into the cerium dioxide nanoparticles by occupying cerium ion lattice sites in the crystal can be introduced later in the precipitation of cerium dioxide. Transition metal ions can be added in combination with trivalent cerium ions, for example, in a single jet mode. In the single jet mode, both trivalent cerium ions and transition metal ions together contain ammonium hydroxide. Introduced into the reactor. Alternatively, transition metal ions and trivalent cerium ions can be added together with the addition of hydroxide ions. Transition metal-containing particles can also be formed by a double jet reaction of trivalent cerium ions and dissolved transition metal ions that are titrated against an ammonium hydroxide stream that is simultaneously introduced by a second jet. Importantly, it is understood that sufficient nanoparticle stabilizer is present to prevent initial particle aggregation.

[0173] Surfactant / stabilizer combinations may have the additional advantage of supporting a solvent shift process from an aqueous polar medium to a nonpolar oil medium. In the combination of charged and uncharged surfactants, charged surfactant compounds play a dominant role in the aqueous environment. However, as solvent shifts occur, charged compounds become solubilized and flowed into the aqueous phase, and uncharged compounds become more important in the stabilization of reverse micelle emulsions.

Dicarboxylic acids and their derivatives (so-called “geminicarboxylates”) in which the carboxylic acid groups are separated by up to two methylene groups are also useful cerium dioxide nanoparticle stabilizers. In addition, C ₂ -C ₈ alkyl, alkoxy and polyalkoxy substituted dicarboxylic acid is preferred stabilizers.

In the present invention, the nanoparticle stabilizer compound preferably contains an organic carboxylic acid, such as 2- [2- (2-methoxyethoxy) ethoxy] acetic acid (MEEA), ethylenediaminetetraacetic acid (EDTA), lactic acid, glucone. Acids, tartaric acid, citric acid and mixtures thereof.

[0176] Motor oil is used as a lubricant for various types of internal combustion engines in automobiles and other vehicles, boats, lawnmowers, trains, airplanes and the like. Engines often have contacts that move at high speed relative to each other over a long period of time. Such a rubbing motion causes friction, a temporary weld is formed, and the movable part stops moving. When this temporary weld is broken, the force that was originally useful by the motor is absorbed and the energy is converted to useless heat. Friction also wears the contact surfaces of these parts, which can lead to increased fuel consumption, reduced motor efficiency, and degradation. In one aspect of the invention, the motor oil comprises a lubricating oil, desirably transition metal-containing crystalline cerium dioxide nanoparticles having an average diameter of less than about 10 nm, more preferably about 5 nm, and optionally a surface adsorbed stabilizer.

Diesel lubricants are essentially free of water (preferably less than 300 ppm), but desirably cerium dioxide has been solvent shifted from its aqueous environment to that of organic or non-polar environments. It can be modified by the addition of a composition. The cerium dioxide composition includes nanoparticles having an average diameter of less than about 10 nm, more preferably about 5 nm, as described above. Higher efficiencies are obtained with diesel engines that operate with modified diesel fuels and modified lubricants, especially when fuel economy is improved, engine wear is reduced, pollution is reduced, or a combination of these features. Can be brought.

[0178] Metal polishing, also called buffing, is a process of smoothing metals and alloys until they have a glossy, smooth mirror finish. Metal polishing is often used to increase the value of automobiles, motorcycles, antique works, and the like. Many medical devices are also polished to prevent dirt from adhering to the irregularities on the metal surface. Abrasives are also used to polish optical elements (lenses, mirrors, etc.) to a surface smoothness that is a fraction of the wavelength of light they will handle. The smooth, round and uniform cerium dioxide particles of the present invention can be advantageously used as an abrasive. It can also be used to planarize the semiconductor substrate (smooth the surface at the atomic level) for subsequent integrated circuit processing.

The present invention is further illustrated by the following examples. These examples are not intended to limit the invention in any way.

(0180-0181) Example 1. Preparation of cerium dioxide nanoparticles by single jet addition A 3 liter round bottom stainless steel reactor vessel is charged with 1.267 liter distilled water followed by 100 ml Ce (NO ₃ ) ₃ .6H ₂ O solution (600 g / liter Ce (NO ₃ ) ₃ · 6H ₂ O) was added. The solution was clear and had a pH of 4.2 at 20 ° C. Subsequently, 30.5 g of 2- [2- (2-methoxyethoxy) ethoxy] acetic acid (MEEA) was added to the vessel. The solution remained clear and the pH was 2.8 at 20 ° C. A high shear mixer (from Silverson Machines, a colloid mill modified so that the reactants can be introduced directly into the mixer blade by a peristaltic tubing pump) is lowered into the reactor vessel and the mixer head is placed at the bottom of the reactor vessel. Positioned slightly above. The mixer was set at 5000 rpm and 8.0 g of 30% H ₂ O ₂ was added to the reactor vessel. Then, 28 to 30% NH ₄ OH in 16ml diluted up to 40 ml, was pumped into the reactor vessel at about 12 seconds by a mixer head. The initially clear solution turned orange / brown. The high shear mixer was removed, the reactor vessel was moved to a temperature controlled water jacket and the solution was stirred at 450 rpm using a mixer equipped with an R-100 propeller. Three minutes after pumping NH ₄ OH into the reactor, the pH was 3.9 at 25 ° C. Over the next 25 minutes, the reactor vessel temperature was raised to 70 ° C. At this time, the pH was 3.9. The solution temperature was maintained at 70 ° C. for 20 minutes. During this time, the color of the solution changed from orange brown to clear dark yellow. The pH was 3.6 at 70 ° C. The temperature was lowered to 25 ° C. over the next 25 minutes. At this time, the pH was 4.2 at 25 ° C. Particle size analysis by dynamic light scattering showed a cerium dioxide strength weighted hydrodynamic diameter of 6 nm. The dispersion was then subjected to diafiltration to a conductivity of 3 mS / cm and concentrated approximately 10 times with CeO ₂ particles to nominally 1 mole.

The cerium dioxide particles were recovered, excess solvent was removed by evaporation and the weight yield (corrected for the weight of MEEA) was measured to be 62.9%.

A transmission electron microscope (TEM) was also used to analyze the cerium dioxide particles. A 9 microliter solution (0.26M) was dried on a grid and the image of FIG. 1 was taken. The particles show no signs of aggregation even in this dry state. The tendency of particles to agglomerate in solution is expected to be even lower. From the particle size distribution of cerium dioxide particles determined by transmission electron microscopy (TEM) (plotted in FIG. 1), a geometric diameter of about 2.6 nm is obtained. In addition, the size distribution is substantially unimodal (ie, there is only one maximum) and is uniform (COV 19%) and most of the particles are in the 2-4 nm range.

FIG. 2 shows a powder X-ray diffraction pattern 70 of a dried cerium dioxide nanoparticle sample with a control spectrum 71 of cerium dioxide provided from a library of NIST (National Institute of Standards and Technology). The position of the sample spectrum line matches that of the standard spectrum. The 2θ peak width was very wide in the sample spectrum, which is consistent with very small primary crystallite and particle sizes. X-ray data (approximately 8047 ev CuKα ray) and Scherrer's equation (d = 0.9 ^* λ / Δ ^* cos (θ), where λ is the X-ray wavelength, Δ is the full width at half maximum, and θ is From the scattering angle corresponding to the X-ray peak)), the primary crystallite size was calculated to be 2.5 ± 0.5 nm (95% confidence in 5 iterations). Since the particles themselves are the size of this microcrystal, there is only one crystal per particle, so by calling this composition crystalline cerium dioxide, the nanoparticle has different sizes of microcrystals. A distinction will be made from all prior art composed of crystalline aggregates.

Example 2: Precipitation of ˜1.5 nm CeO ₂ nanoparticles This precipitation is carried out according to Example 1. However, a combination of EDTA and lactic acid stabilizers (ratio 20:80, 76.4 g EDTA disodium salt and 74.0 g 85% lactic acid) is used in place of the MEEA stabilizer. FIG. 3A is a high magnification TEM image showing the grain size estimated to be 1.1 ± 0.3 nm, substantially less than 5 nm. FIG. 3B is an electron diffraction pattern of a typical precipitation sample. FIG. 3C includes Table 1, where the intensity of the various diffractive rings {311}, {220}, {200}, {111} is cubic CeO ₂ , cubic and hexagonal Ce ₂ O ₃ , Ce. Analyzed within the framework of (OH) ₃ . Apparently, the percent deviation of the analyzed ring strength including crystal habit was minimal with respect to the cubic fluorite structure of CeO ₂ , thus demonstrating the presence of this polymorph at this grain diameter. The

Example 3: Preparation of CeO ₂ nanoparticles by isothermal double jet precipitation (CeO ₂ )
To a 3 liter round bottom stainless steel reactor tank was added 1117 grams of distilled water. A standard Rv100 propeller was lowered into the reactor vessel and the mixer head was positioned slightly above the bottom of the reactor vessel. The mixer was set at 700 rpm and the reactor temperature was about 70 ° C. Next, 59.8 grams (98%) of methoxyacetic acid was added to the reactor. 250 ml of a solution containing 120.0 grams of Ce (NO ₃ ) ₃ .6H ₂ O is pumped into the reactor simultaneously with a solution containing 69.5 grams (28-30%) of ammonium hydroxide. The double jet precipitation was carried out over a period of 5 minutes. Residual material was removed from the reactant feed tube by flushing the reactor with distilled water for rinsing. Next, 10.2 grams of 50% unstabilized hydrogen peroxide was added to the reactor and its contents in 40 seconds. Initially, the reaction mixture was an opaque, dark orange brown pH 6-7 liquid. The reaction mixture is heated for an additional 60 minutes, during which time the pH drops to 4.25 (consistent with the release of hydronium ions by reactions (3a) and (3b)) and the mixture becomes clear yellow-orange. became. The reaction mixture was cooled to 20 ° C. and excess water and unreacted material were removed by diafiltration to a conductivity of 3 mS / cm. This concentrated the dispersion to about 10 times or nominally 1 mole with CeO ₂ particles. Particle size distribution analysis by transmission electron microscope analysis (FIG. 4) reveals that the average particle size is 2.2 nm and the particle size distribution has a coefficient of variation COV (standard deviation divided by average diameter) 23%. did. The calculated yield was 62.9%.

Example 4: Copper-containing CeO ₂ nanoparticles (Ce _0.9 Cu _0.1 O _1.95 )
The conditions of Example 3 were repeated. However, the cerium nitrate solution contained 108.0 grams of cerium nitrate hexahydrate and 6.42 grams of Ce (NO ₃ ) ₃ .2.5H ₂ O. These metal salts were dissolved separately and then mixed to form a 250 ml solution. The reaction proceeded as described in Example 3. However, hydrogen peroxide was added 40 seconds after cerium and ammonia were added. Particle size distribution analysis by transmission electron microscope analysis (FIG. 5) reveals that the average particle size is 2.5 nm and the particle size distribution has a coefficient of variation COV (standard deviation divided by average diameter) 25%. did. Note that there is no bimodal distribution. The secondary peak is believed to indicate that Cu is not incorporated into the CeO ₂ lattice and exists as a separate Cu ₂ O ₃ .

(0189-0190) Example 5: Iron-containing CeO ₂ nanoparticles (Ce _0.9 Fe _0.1 O _1.95 ) (CeO-255)
The conditions of Example 4 were repeated. However, the metal salt solution contained 108.0 grams of cerium nitrate hexahydrate and 11.16 grams of Fe (NO ₃ ) ₃ .9H ₂ O. These metal salts were dissolved separately and then mixed to form a 250 ml solution. The reaction proceeded as described in Example 4. By TEM image of the precipitated particles (FIG. 6A) and particle size distribution analysis by transmission electron microscope analysis (FIG. 6B), the average particle size is 2.2 ± 0.7 nm and the particle size distribution is a coefficient of variation COV (standard Deviation divided by average diameter) was found to have 32%. The calculated yield was 55.1%.

(0191-0192) Example 6: Zirconium-containing CeO ₂ nanoparticles (Ce _0.9 Zr _0.15 O ₂ ) (CeO-257)
The conditions of Example 4 were repeated. However, the metal salt solution contained 101.89 grams of cerium nitrate hexahydrate and 9.57 grams of ZrO (NO ₃ ) ₂ .6H ₂ O. These metal salts were dissolved separately and then mixed to form a 250 ml solution. The reaction proceeded as described in Example 4. However, the reaction was carried out at 85 ° C. According to particle size distribution analysis by transmission electron microscope analysis (FIG. 7A), the average particle size is 2.4 ± 0.7 nm, and the particle size distribution is a coefficient of variation COV (standard deviation divided by average diameter) 29% Was found to have. Inductively coupled plasma atomic emission spectroscopy revealed the stoichiometric ratio of Ce _0.82 Zr _0.18 O _1.91 , and given the relative insolubility of ZrO ₂ to CeO ₂ , this is a higher Zr content (18% vs. 15% ).

Example 0a: Zirconium and iron-containing CeO ₂ nanoparticles (Ce _0.9 Zr _0.15 Fe _0.1 O _1.95 ) (CeO-270)
The conditions of Example 4 were repeated. However, the metal salt solution was 84.0 grams of cerium nitrate hexahydrate, 11.16 grams of Fe (NO ₃ ) ₃ .9H ₂ O and 12.76 grams of ZrO (NO ₃ ) ₂ .6H ₂ O. Contained. These metal salts were dissolved separately and then mixed to form a 250 ml solution. The reaction proceeded as described in Example 4. However, the reaction was carried out at 85 ° C., and the hydrogen peroxide solution (50%) was increased to 20.4 g and added in 10 minutes. By means of a TEM image of the particles (FIG. 8A) and particle size distribution analysis by transmission electron microscopy (FIG. 8B), the average particle size is 2.2 ± 0.6 nm and the particle size distribution is expressed by a coefficient of variation COV (standard deviation). (Divided by the average diameter) was found to have 27%. Again, the monodisperse, unimodal distribution supports the concept that ZrO ₂ and Fe ₂ O ₃ grains are incorporated together rather than being renucleated separately. The calculated yield was 78%. Inductively coupled plasma atomic emission spectroscopy revealed a stoichiometric ratio of Ce _0.69 Fe _0.14 Zr _0.17 O _0.915 . Again, Fe and Zr, which are more concentrated relative to the nominal amount, reflect a higher insolubility than that of its hydroxide precursor, cerium hydroxide. FIG. 8C is also the powder X-ray diffraction pattern of this sample (upper curve) compared to transition metal free CeO ₂ . The lack of a peak at 32 degrees 2θ (indicated by the arrow) means that there is no free ZrO ₂ . That is, they are all incorporated into the cerium lattice. Also, the lack of peaks at 50, 52 degrees 2θ indicates that there is no separate Fe ₂ O ₃ (ie, incorporation of Fe into the cerium lattice). Note the shift to larger 2θ at large 2θ scattering angles. This indicates strain or shrinkage of the lattice (nλ / 2d = sin θ), with smaller ionic radii of Fe ³⁺ (0.78 Å) and Zr ⁴⁺ (0.84 Å) for replacing Ce ⁴⁺ (0.97 Å). It matches. For this reason, the inventor concluded that the transition metal was incorporated into the CeO ₂ lattice and that pure ZrO ₂ and Fe ₂ O ₃ nanoparticles were not present separately. Unimodal particle size distributions support this conclusion.

(0195-0196) Examples 7b-f: CeO ₂ nanoparticles containing zirconium and iron (if zirconium is 15% and the amount of iron is systematically different (15%, 20%, 25%, 30%) and iron is 20% and 20% zirconium)
The conditions of Example 7a were followed. However, using the appropriate metal-containing salt solution, the amount of iron or zirconium was adjusted to obtain the stated nominal stoichiometric ratio. On the other hand, the entire cerium nitrate hexahydrate was reduced to accommodate increased concentrations of iron or zirconium transition metals.

FIG. 9 is a field emission electron gun TEM grid image of the particles formed in Example 1. For clarity, the two particles are circled. Note the small number of lattice planes that delineate a single crystal with a diameter of less than 5 nm. Aqueous sols of various materials were heated at 1000 ° C. in a muffle furnace for 30 minutes. The OSC of these fully dried samples, the kinetics when the maximum OSC was reached, was described by Sarkas et al. , L 4.8.1 (2004)) as measured by thermogravimetric techniques. Typically, a very fast initial reduction rate in nitrogen gas containing 5% hydrogen followed by a second slower rate is observed.

(The latter half of 0197) The accompanying Table 2 shows the oxygen storage capacity (in parentheses) for the reduction in 700 ° C. nitrogen gas containing 5% H ₂ of various lattice-engineered ceria nanoparticles (all 2 nm except Sigma Aldrich control). In the figure, 1σ reproducibility) and fast (k1) and slow (k2) rate constants (1 standard deviation in parentheses) are shown. These values are for the second TGA instrument (average 2.6% difference), gas flow difference (average 1% deviation) and repeated test sample preparation (average 1.54 deviation) at 1000 ° C. for 30 minutes. Cross checked. From the contents of Table 2, it can be seen that the OSC of the cerium dioxide particles is not considered to be size-dependent in the range of about 2 nm to 20 μm. This can be the result of sintering to larger particles. Note that the addition of zirconium increases the OSC by about 50% and is accompanied by a 10-fold rate increase. Furthermore, the addition of iron to the Zr-containing material results in nearly three times the OSC at a rate ten times that of cerium dioxide particles that do not contain transition metal ions. These values are more than three times the values in the described reference. The beneficial effect of citric acid on the reduction rate constant is believed to suggest that the stabilizer can affect particle surface area or morphology even after pyrolysis.

Although the present invention has been described with reference to various specific embodiments, it should be understood that numerous modifications can be made within the spirit and scope of the described inventive concept. Accordingly, the invention is not intended to be limited to the described embodiments but is to have the full scope defined by the language of the following claims.

Claims (14)

A process for forming lattice engineered crystalline cerium dioxide nanoparticles containing at least one transition metal (M) comprising:
(A) an aqueous reaction mixture comprising a source of trivalent cerium ions, a source of one or more transition metal ions (M), a source of hydroxide ions, at least one nanoparticle stabilizer and an oxidizing agent the obtained at an initial temperature of up to 95 ° C. from greater than 25 ° C.,
(B) mechanically shearing the mixture and passing it through a perforated screen to produce a homogeneously distributed suspension of cerium hydroxide nanoparticles;
(C) By making the temperature conditions effective for oxidizing trivalent cerium ions to tetravalent cerium ions, transition metal-containing cerium dioxide nanoparticles Ce _1-x M _x O ₂ (wherein x is 0 includes generating a product stream comprising a) a value of .3～ 0.8, said temperature conditions include a temperature of 50 to 100 ° C., wherein the nanoparticles, crystalline cubic fluorite structure, 1 process characterized by having a geometric diameter of an average hydrodynamic diameter of ~ 1 0 nm and 1 ~ 4 nm.   The process of claim 1, wherein the mechanical shearing is performed in a colloid mill. Effective said temperature conditions to oxidize the trivalent cerium ions to tetravalent cerium ions including temperature of 6 0~ 9 0 ℃, The process of claim 1.   The process of claim 1, wherein the source of ions is introduced into the reaction mixture simultaneously or sequentially during the mechanical shear. The process of claim 1, wherein the cerium dioxide nanoparticles have an average hydrodynamic diameter of 6 nm. Grid operation in the transition metal-containing crystalline cerium dioxide particles _{Ce 1-x M x O 2} ( wherein the stabilized formed by the process of claim 1, x has a value of 0.3 to 0.8 ) a process for producing a homogeneous dispersion containing,
(A) obtaining an aqueous mixture comprising stabilized transition metal doped cerium dioxide nanoparticles Ce _1-x M _x O ₂ having a cubic fluorite-type structure, wherein the nanoparticles have an average hydrodynamics of 1 to 10 nm And a geometric diameter of less than 4 nm,
(B) producing an aqueous concentrate by concentrating the aqueous mixture comprising the stabilized transition metal-containing cerium dioxide nanoparticles;
(C) by removing the water of all hand from the aqueous concentrate to produce the free water of the stabilized transition metal containing cerium dioxide particles concentrate,
(D) generating an organic concentrate of the stabilized transition metal-containing cerium dioxide nanoparticles by adding an organic diluent to the water- free concentrate;
(E) Homogeneous containing the transition metal-containing crystalline cerium dioxide nanoparticles Ce _1-x M _x O ₂ stabilized by mixing the organic concentrate with a surfactant in the presence of a nonpolar medium. A process comprising forming a dispersion. The group in which the transition metal M in the transition metal-containing cerium dioxide nanoparticles Ce _1-x M _x O ₂ is composed of Fe, Mn, Cr, Ni, W, Co, V, Cu, Zr, Y, Mo, and combinations thereof The process according to claim 6 , selected from: x is 0 . 30-0. The process of claim 7 having a value of 80. x is 0 . 40-0. The process of claim 8 having a value of 60. The process according to claim 7 , wherein the transition metal M comprises Zr or Y. The process of claim 10 , wherein the transition metal M further comprises Fe. The process of claim 6 , wherein the organic diluent comprises a glycol ether. Washcoat for catalytic converters of internal combustion engine exhaust systems, characterized in that it is formed using a homogeneous dispersion containing stabilized transition metal-containing crystalline cerium dioxide nanoparticles formed according to claim 6. Wash coat. A catalyst effective in accelerating a reduction or oxidation reaction, produced using a homogeneous dispersion containing stabilized transition metal-containing crystalline cerium dioxide nanoparticles formed according to claim 6 A catalyst characterized by.

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