KR20110106884A - Fuel additive containing lattice engineered cerium dioxide nanoparticles - Google Patents

Abstract

The present invention mechanically shears an aqueous mixture comprising an oxidant in an amount effective to oxidize a first cerium ion to a second cerium ion, wherein the transition metal-containing cerium dioxide nanoparticles Ce _{1 - x} M _x O ₂ (where “x Has a value of about 0.3 to about 0.8) to a process for preparing cerium dioxide nanoparticles comprising at least one transition metal (M) using a suspension of cerium hydroxide nanoparticles produced. It is about. The nanoparticles thus obtained have a cubic fluorspar structure, with an average hydrodynamic diameter in the range of about 1 nm to about 10 nm, and a geometric diameter of less than about 4 nm. Transition metal-containing crystalline cerium dioxide nanoparticles can be used to produce dispersions of particles in nonpolar media.

Description

Fuel additive containing lattice engineered cerium dioxide nanoparticles {FUEL ADDITIVE CONTAINING LATTICE ENGINEERED CERIUM DIOXIDE NANOPARTICLES}

Cross Reference to Related Applications

This application is all related to PCT / US07 / 077545 and Cerium Dioxide Nanoparticle-Containing Fuel Additive, filed on September 4, 2007, filed with the method of preparing cerium dioxide nanoparticles, The application is filed in US Provisional Application No. 60 / 824,514, filed Sep. 5, 2006; US Provisional Application No. 60 / 911,159, filed April 11, 2007, entitled Reverse Michel Fuel Additives Composition; And US Provisional Application No. 60 / 938,314, filed May 16, 2007, entitled Reverse Michel Fuel Additives Composition. The disclosures of all these applications are incorporated herein by reference.

Field of invention

The present invention relates generally to cerium dioxide nanoparticles and in particular to cerium dioxide nanoparticles Ce _1-x M _x O ₂ comprising at least one transition metal (M) and to a process for the preparation of said particles. These nanoparticles are useful as components of fuel additive compositions, as washcoats for catalytic converters or as catalysts for reduction / oxidation reactions.

The trucking industry accounts for more than 5% of US GDP and consists of more than 500,000 rental, dedicated and government vehicles, including private truck operators. This is an indicator of the US economy representing nearly 70% of the tonnage carried by all types of domestic cargo traffic, including manufactured and retail goods. This industry is almost entirely powered by diesel engines (compressed ignition engines) characterized by high torque developed at lower rpm and 25% greater thermodynamic efficiency than spark ignition (gasoline) engines. As a result of reduced emissions from nitrogen oxides (NO _x ) and diesel particulate matter (DPM or soot) as mandated by the 2007 EPA, vehicles using diesel fuel must be equipped with diesel oxidation catalyst (DOC) or some form of catalytic converter and Low sulfur diesel fuel ULSD (<15 ppm S) must be used. These and other techniques, such as EGR (Exhaust Gas Recirculation), must meet the EPA-mandated emission standards. The ULSD requirement is the result of sulfur poisoning of precious metals on DOC due to high sulfur concentrations. The legislation is due to the huge consumption of diesel fuel (for pavement) in the United States at 650 M gal / week, the second highest after gasoline (1,300 M gal / week).

The cost of the EPA order is estimated to add about $ 0.39 to the price of one gallon of diesel fuel. This includes increased engine cost ($ 0.11 / gal), particle trap retention ($ 0.05 / gal), reduced fuel cost ($ 0.09 / gal), increased ULSD ($ 0.06 / gal), and lower ULSD fuel energy content ($ 0.08 / gal). It is divided into the following factors.

Clearly, any technology that can provide reductions in DPM and other emissions while simultaneously increasing fuel costs (measured in terms of miles per gallon) is recognized as a huge economic and environmental benefit.

The inclusion of inorganic metal and metal oxide materials in contrast to diesel fuel additives, especially organic materials, offers the potential for reduced DPM and improved fuel costs.

U.S. Patent No. 4,389,220 to Kracklaurer, the disclosure of which is incorporated herein by reference, describes a method of tuning a diesel engine, wherein the carbon deposits are removed from the combustion surface of the diesel engine and the layer of iron oxide on the combustion surface. The diesel engine is operated with diesel fuel containing about 20-30 ppm dicyclopentadienyl iron for a time sufficient to deposit (this layer is effective to prevent further stacking of carbon deposits). The diesel engine is then continuously operated at a maintenance concentration of about 10-15 ppm of dicyclopentadienyl iron or its derivatives. The holding concentration is effective for keeping the catalytic iron oxide layer on the combustion surface, but insufficient to reduce the timing delay of the engine. Added dicyclopentadienyl iron can produce iron oxide (Fe ₂ O ₃ ) on the engine cylinder surface, which reacts with carbon deposits (soot) to form Fe and CO ₂ , thereby removing the deposits. . However, this method has the potential to form rust and accelerate engine aging.

United States Patent Application Publication No. 2003/0148235 (Valentine, et al., The disclosure of which is incorporated herein by reference) describes certain bimetallic or trimetallic fuel based catalysts for increasing fuel combustion efficiency. The catalyst reduces the contamination of the heat transfer surface by unburned carbon, but when used in the form and amount commonly used, the amount of secondary additive ash that can itself cause overloading of particulate collector devices or the release of toxic ultrafine particles. To limit. The use of fuels containing fuel-soluble catalysts consisting of platinum and one or more additional metals including cerium and / or iron reduces the generation of contaminants of the type resulting from incomplete combustion. Ultra low levels of non-toxic metal combustion catalysts can be used to improve heat recovery and reduce emissions of regulated pollutants. However, fuel additives of this type may require months before the engine is “tuned”, in addition to using precious and expensive metals such as platinum. "Adjusted" means that you will not get all the benefits of the additive until the engine is running with the catalyst for some time. Initial adjustment may require 45 days, and an optimal benefit may be obtained after 60 to 90 days. In addition, the free metal can be discharged from the exhaust system into the atmosphere so that the free metal can subsequently react with the organism.

Cerium dioxide is widely used as a catalyst in converters to remove toxic emissions and reduce particulate emissions in motor vehicles using diesel fuel. In catalytic converters, cerium dioxide can act as a chemically active component that acts to release oxygen in the presence of reducing gas, as well as to remove oxygen by interaction with the oxidizing species.

Cerium dioxide can store and release oxygen by the reversible process shown in Scheme 1:

<Scheme 1>

에 의하여 생성된 독성 배기 가스를 감소시키는 촉매로서 작용할 뿐 아니라, 디젤 엔진과 함께 통상적으로 사용되는 미립자 트랩중에 축적되는 미립자의 연소를 촉진하는 작용을 한다:This process is referred to as Ceria's oxygen storage capacity (OSC). Here, ceria acts as an oxygen storage buffer (like a pH buffer), releasing oxygen in space regions with low oxygen concentration or pressure, and absorbing oxygen in space regions with high oxygen pressure. When x is 0.5, ceria is effectively fully reduced to Ce ₂ O ₃ , with a maximum OSC theory of 1,452 micromoles of O ₂ per gram of ceria. The redox potential between Ce ³⁺ and Ce ⁴⁺ ions is between 1.3 and 1.8 V and is highly dependent on the anionic groups present and the chemical environment. CERIUM: A Guide to its Role in Chemical Technology , 1992 by Molycorp, Inc, Library of Congress Catalog Card Number 92-93444. Thereby, the described forward and reverse reactions can easily occur close to the stoichiometric ratio (15: 1) of oxygen required in the exhaust gas. Cerium dioxide can provide oxygen for the oxidation of CO or hydrocarbons in an oxygen deficient environment or, conversely, can absorb oxygen to reduce the concentration of nitrogen oxides (NO _x ) in an oxygen rich environment. Similar catalytic activity can also occur when adding cerium dioxide as an additive to fuels such as diesel or gasoline. However, for this effect to be useful, cerium dioxide must be suspended in the fuel by Brownian motion and have a particle size, ie nanoparticles (less than 100 nm), small enough not to settle. In addition, since the catalytic effect depends on the surface area, the small particle size makes the nanocrystalline material more effective as a catalyst. The incorporation of cerium dioxide in the fuel is fuel combustion, for example the "aqueous gas shift reaction".

In addition to acting as a catalyst to reduce the toxic exhaust gases produced by it, it also serves to promote the combustion of particulates that accumulate in particulate traps commonly used with diesel engines:

As already mentioned, cerium dioxide nanoparticles are particles having an average diameter of less than 100 nm. For the purposes of this disclosure, unless stated to the contrary, the diameter of a nanoparticle refers to its hydrodynamic diameter, which is the diameter measured by dynamic light scattering techniques and refers to the solvated shell of the molecular adsorbate and the accompanying particles. Include. Alternatively, geometric particle diameter can be measured using transmission electron microscopy (TEM).

BACKGROUND ART Onboard addition systems are known which distribute the cerium dioxide in the fuel before the fuel enters the engine, but such systems are complex and require extensive electronic control to supply the appropriate amount of additives to the fuel. To avoid such complex onboard systems, cerium dioxide nanoparticles may be added to the fuel at an early stage to achieve improved fuel efficiency. For example, cerium dioxide nanoparticles can typically be added to refineries with processing additives such as cetane enhancers or lubricants or added in fuel distribution tank facilities.

Cerium dioxide nanoparticles can also be added at fuel distribution centers that can be racked in bulk (approximately 100,000 gal) of fuel, or in smaller fuel company repositories that can be specially tailored to specific individual needs. May be In addition, cerium dioxide can be added during fuel delivery to automobiles at gas stations, which has the potential benefit of improved stabilization of the particle dispersion.

Cerium nanoparticles can form a ceramic layer on the engine cylinders and internal moving parts to convert the engine into a catalytic device. Alternatively, cerium nanoparticles can be recycled in the lubricant in which they accumulate. Its catalytic efficiency derives from the fact that cerium nanoparticles are reduced by Scheme 1 to provide a source of oxygen atoms during combustion, but in general, several months of induction are required for their mpg benefit to be observed. The result is better fuel combustion and reduced concentrations of particulate matter emissions. In addition, when used as fuel additives, these nanoparticles can reduce engine friction to provide improved engine performance. As an alternative dosing mode, cerium dioxide nanoparticles can be added to the lubricating oil and serve to reduce internal friction as a lubricity enhancer. This also improves fuel efficiency.

The following publications are incorporated herein by reference and describe fuel additives containing cerium oxide based compounds.

US Pat. No. 5,449,387 to Hawkins et al. Discloses cerium (IV) oxide based compounds having the general formula:

Wherein the radicals A are the same or different and each is an anion of an organic oxyacid AH with pK _a greater than 1, p is an integer ranging from 0 to 5, n is a number ranging from 0 to 2, m is an integer ranging from 1 to 12). The organic oxyacids are preferably carboxylic acids, more preferably C ₂ -C ₂₀ monocarboxylic acids or C ₄ -C ₁₂ dicarboxylic acids. Cerium-containing compounds can be used as catalysts for the combustion of hydrocarbon fuels.

US Patent No. 7,063,729 (Valentine et al.) Discloses a low emission diesel fuel comprising a bimetallic fuel-soluble platinum group metal and a cerium catalyst, wherein cerium is provided as a fuel-soluble hydroxyl oleate propionate complex. .

US Pat. No. 6,210,451 (Chopin et al.) Contains a stable organic sol comprising particles of cerium dioxide in the form of agglomerates of microcrystals (preferably 3 to 4 nm in size), and at least one acid having a total of 10 or more carbon atoms. A petroleum based fuel comprising an amphoteric acid system and an organic diluent medium is disclosed. The controlled particle size is 200 nm or less.

US Pat. No. 6,136,048 to Birchem et al. Discloses auxiliaries for diesel engine fuels including sol, amphoteric acid system and diluent comprising particles of oxygenated compounds with d ₉₀ of 20 nm or less. Oxygenated metal compound particles are produced by reaction with a basic medium in a solution of rare earth salts, such as cerium salts, followed by recovery of the formed electrolyte by atomization or freeze drying.

US Patent No. 6,093,223 (Lemaire et al.) Discloses the combustion of hydrocarbon fuels in the presence of one or more cerium compounds to produce agglomerates of cerium oxide microcrystals. The soot comprises at least 0.1% by weight of dicerium oxide microcrystalline aggregates with a maximum particle size of 50 to 10,000 kPa, microcrystalline size of 50 to 250 kPa and soot having an ignition temperature of less than 400 ° C.

U.S. Pat.No. 7,195,653B2 (Hazarika et al.) Discloses a method of improving fuel efficiency and / or reducing fuel emissions of a fuel combustion device, which method comprises at least one particulate lanthanide oxide, in particular cerium dioxide. Is dispersed as a tablet, capsule powder or liquid fuel additive at 1 to 10 ppm in fuel, wherein the particulate lanthanum oxide is coated with a surfactant selected from the group consisting of alkyl carboxylic anhydrides and esters having an HLB of 7 or less.

US Patent Application Publication No. 2003/0182848 (Collier et al.) Improves the performance of diesel fuel particulate traps and contains 1 to 25 ppm of metal and 100 to 500 ppm of a useful nitrogen-containing ashless detergent additive in the form of metal salt additives. A diesel fuel composition comprising a combination of is disclosed. The metal may be an alkali metal, alkaline earth metal, IVB, VIIB, VIIIB, IB, Group IIB metal or any rare earth metal of atomic number 57 to 71, in particular cerium or a mixture of any of the above metals.

US Patent Application Publication No. 2003/0221362 to Collier et al. Discloses a fuel additive composition for a diesel engine equipped with a particulate trap, the composition comprising a hydrocarbon solvent and up to 125 carbon atoms. Oil-soluble metal carboxylates or metal complexes derived from acids. The metal may be an alkali metal, alkaline earth metal, IVB, VIIB, VIIIB, IB, Group IIB metal or rare earth metals including cerium or mixtures of any of the above metals.

US Patent Application Publication No. 2004/0035045 (Caprotti et al.) Discloses a fuel additive composition for a diesel engine equipped 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. Upon addition 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.

U.S. Patent Application Publication No. 2005/0060929 to Caprotti et al. Discloses colloidal dispersed or solubilized metal catalyst compounds and lipophilic hydros bound to at least two polar groups, at least one of which is a carboxylic acid or carboxylate group. Disclosed is a diesel fuel composition stabilized against phase separation, comprising from 5 to 1,000 ppm stabilizer, which is an organic compound having a carbyl chain. Metal catalyst compounds include one or more organic or inorganic compounds or complexes of Ce, Fe, Ca, Mg, Sr, Na, Mn, Pt or mixtures thereof.

U.S. Patent Application Publication No. 2006/0000140 (Caprotti et al.) Discloses 1 comprising a hydroxyl substituent and an additional substituent selected from hydrocarbyl, -COOR or -COR where R is hydrogen or hydrocarbyl. A fuel additive composition comprising a stabilizer component that is a condensation product of a compound comprising at least one aromatic moiety and an aldehyde or ketone and at least one colloidal metal compound or species is disclosed. The colloidal metal compound preferably comprises at least one metal oxide, with the preferred oxide being iron oxide, cerium dioxide or cerium-doped iron oxide.

International Patent Application Publication No. WO2004 / 065529 (Scattergood) discloses a method for improving the fuel efficiency of a fuel for an internal combustion engine, comprising adding cerium dioxide and / or doped cerium dioxide and optionally one or more fuel additives to the fuel. Is disclosed.

International Patent Application Publication No. 2005/012465 (Anderson et al.) Discloses a method for improving the fuel efficiency of fuels for internal combustion engines, including lubricating oils and gasoline, which methods include cerium dioxide and / or doped cerium dioxide. To lubricating oil or gasoline.

Cerium-containing nanoparticles can be produced by various techniques known in the art. Regardless of whether synthetic nanoparticles are produced in hydrophilic or hydrophobic media, particles typically require stabilizers to prevent undesirable aggregation. The following publications, the disclosures of which are incorporated herein by reference, describe some of these synthetic techniques.

US Pat. No. 6,271,269 to Chane-Ching et al. Discloses reacting a basic reactant with an aqueous solution of an acidic metal cation salt to form an aqueous colloidal dispersion comprising excess hydroxyl ions; Contacting the aqueous colloidal dispersion with an organic phase comprising an organic liquid medium and an organic acid; A process for preparing a storage stable organic sol is disclosed which comprises separating the resulting aqueous / organic phase mixture into an aqueous phase and a product organic phase. Preferred metal cations are cerium and iron cations. Colloidal particulates have a hydrodynamic diameter in the range of 5-20 nm.

US Pat. No. 6,649,156 (Chane-Ching) discloses cerium dioxide particles produced by a thermal hydrolysis process; Organic liquid phase; An organic sol comprising at least one amphoteric compound selected from polyoxyethylenated alkyl ethers of carboxylic acids, polyoxyethylenated alkyl ether phosphates, dialkyl sulfosuccinates and quaternary ammonium compounds is disclosed. The water content of the sol may be 1% or less. The average microcrystal size is about 5 nm and the particle aggregates of these microcrystals range in size from 200 to 10 nm.

US Pat. No. 7,008,965 (Chane-Ching) discloses an aqueous colloidal dispersion of a cerium compound and one or more other metals, the dispersion having a conductivity of 5 mS / cm or less and a pH of 5-8. .

US Patent Application Publication No. 2004/0029978 (Chane-Ching) (disclosed on December 7, 2005) discloses organics having amphoteric properties, based on metal oxides, hydroxides and / or oxyhydroxides, and having hydrophobic properties. Surfactants are disclosed in which a chain is formed from one or more nanoparticles bound to a surface. The metal is preferably selected from cerium, aluminum, titanium or silicon, the alkyl chains comprising 6 to 30 carbon atoms or polyoxyethylene monoalkyl ethers, the alkyl chains of polyoxyethylene monoalkyl ethers being 8 to 30 A carbon atom, the polyoxyethylene moiety comprising 1 to 10 oxyethylene groups. The particles are isotropic or circular particles having an average diameter of 2 to 40 nm.

U.S. Patent Application Publication No. 2006/0005465 (Blanchard et al.) Includes particles of at least one compound, at least one acid and at least one diluent based on at least one rare earth, wherein at least 90% of the particles are single crystals. Phosphorus organic colloidal dispersions are disclosed. 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 and 80% of the particles range in size from 1 to 4 nm.

United States Patent No. 7,025,943 (Zhou et al.) Discloses mixing a first solution of water soluble cerium salt with a second solution of alkali metal or ammonium hydroxide; Simultaneously passing gaseous oxygen through the solution while stirring the resulting reactant solution under turbulent conditions; A process for the preparation of cerium dioxide crystals is disclosed which comprises precipitating cerium dioxide particles having a major particle size in the range of 3 to 100 nm. In Example 1, the particle size is said to be about 3 to 5 nm. Stabilizers are not mentioned, and the sol is expected to eventually aggregate and settle.

WO2008 / 002223A2 (Sandford et al.) Describes an aqueous precipitation technique for producing cerium dioxide directly without subsequent calcination. Stable agglomeration with first cerium ⁺³ cations gradually oxidized to second cerium ^{+ 4} by nitrate ions and 11 nm of microcrystalline size (and approximately the same grain size) when acetic acid is used as a stabilizer I did not get a sol. Interestingly, EDTA and citric acid produce grains with microcrystal sizes on the order of hundreds of nanometers.

U.S. Patent No. 4,231,893 (Woodhead, James, L.) describes the preparation of an aqueous dispersion of ceria by acid treatment of Ce (OH) ₄ obtained from a peroxide treatment of Ce ^{+3 in} a base. No data on size were provided and at the required pH 1.5 for stabilization, the similar stabilizer is a NO ₃ ⁻ anion.

U.S. Patent Application Publication No. 2004/0241070 to Noh et al. Discloses cerium hydroxide by precipitation of cerium salts in the presence of an organic solvent and a solvent mixture of water, preferably from about 0.1: 1 to about 5: 1 weight ratio. To; A method for producing a single crystalline cerium dioxide nanopowder comprising hydrothermally reacting cerium hydroxide is disclosed. Nanopowders have a particle size of about 30 to 300 nm.

US Patent Application Publication No. 2005/0031517 (Chan) discloses that nanoparticles are formed in the resulting mixture while rapidly mixing an aqueous solution of cerium nitrate with aqueous hexamethylenetetraamine and maintaining the temperature below about 320 ° K; A method for producing cerium dioxide nanoparticles comprising separating the formed nanoparticles is disclosed. The mixing device preferably comprises a mechanical stirrer and a centrifuge. In the illustrative example, the resulting cerium dioxide particles were reported to be about 12 nm in diameter.

U.S. Patent Nos. 6,413,489 (Ying et al.) And 6,869,584 (Ying et al.) Synthesized by reverse micelle techniques of nanoparticles with no aggregation, particle size less than 100 nm and surface areas of 20 m 2 / gm or more. Is disclosed. This method involves introducing a ceramic precursor comprising barium alkoxide and aluminum alkoxide in the presence of an inverse emulsion.

Related publications, US Patent Application Publication No. 2005/0152832 (Ying et al.), Show the absence of agglomeration in emulsions with a water content of 1 to 40% and the synthesis by reverse micelle technique of nanoparticles having a particle size of less than 100 nm. Is disclosed. Nanoparticles are preferably metal oxide particles that can be used to oxidize hydrocarbons.

US Pat. No. 5,938,837 (Hanawa et al.) Discloses a process for the preparation of cerium dioxide particles, mainly for use as abrasives, which has a mixing ratio in which the pH value of the mixture is in the range of 5 to 10, preferably 7 to 9 After mixing an aqueous solution of cerium nitrate with a base, preferably with aqueous ammonia, with stirring, the resulting mixture is quickly heated to a temperature of 70 ° C. to 100 ° C., and the mixture of cerium nitrate and base is Maturing to form grains. The product grains are uniform in size and shape and have an average particle size of 10 to 80 nm, preferably 20 to 60 nm.

European Patent Application No. 0208580, published January 14, 1987, whose inventor is Chane-Ching, and the applicant, Rhone Poulenc, discloses a cerium (IV) compound corresponding to the formula Has been:

(Wherein M represents an alkali metal or quaternary ammonium radical, x is 0.01 to 0.2, y is y = 4-z + x, and z is 0.4 to 0.7). The process for preparing the colloidal dispersion of cerium (IV) compounds produces particles having a hydrodynamic diameter of about 1 nm to about 60 nm, suitably about 1 nm to about 10 nm, preferably about 3 nm to 8 nm. .

S. Sathyamurthy et al., Nano Technology 16, (2005), pp 1960-1964] cerium nitrate using sodium hydroxide as precipitant and n-octane containing surfactant cetyltrimethylammonium bromide (CTAB) and cosurfactant 1-butanol as oil phase Reverse Michel synthesis of CeO ₂ is described. The resulting polyhedral particles have an average size of 3.7 nm and show aggregation when removed from their protective reverse micelle structure. In addition, the reaction is expected to proceed in low yield (for reactants A and B, there are a number of AB collisions resulting in the product as AA and BB which are non-productive collisions).

Seal et al., Journal of Nano Particle Research , (2002), 4, pp 433-448 describe the use of an aqueous microemulsion system comprising AOT as a surfactant and toluene as an oil phase for high temperature oxidation resistant coatings. The preparation of nanocrystalline ceria particles from cerium nitrate and ammonium hydroxide is described. The ceria nanoparticles formed on the upper oil of the reaction mixture have a particle size of 5 nm.

US Pat. No. 7,419,516 (Seal et al., 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. Particles produced by the reverse micelle process using toluene as oil phase and AOT as surfactant have a diameter in the range of about 2 to 7 nm, with an average of about 5 nm.

Pang et al., J. Mater. Chem. , 12 (2002), pp 3699-3704, Al ₂ by a water-in-oil microemulsion method using an oil phase containing cyclohexane and a nonionic surfactant Triton X-114, and an aqueous phase comprising 1.0 M AlClO ₃ . O ₃ nanoparticles were produced. The resulting Al ₂ O ₃ particles having a particle size of 5 to 15 nm were found to be distinctly different from hollow ball-shaped particles having a size of micrometers or less produced by the direct precipitation method.

U. S. Patent No. 6,133, 194 (Cuif et al., The disclosure of which is incorporated herein by reference) includes cerium, zirconium or mixtures thereof, bases, optionally oxidizing agents, and anionic surfactants, nonionic surfactants, polyethylene glycols, carboxes. A method comprising reacting a metal salt solution comprising an additive selected from the group consisting of an acid and a carboxylate salt to form a product is described. The product is then calcined at temperatures above 500 ° C. (which effectively carbonizes the claimed surfactant).

Many authors claim Ceria nanoparticles of less than 5 nm, but understand that they did not present X-ray or electron diffraction data that clearly demonstrates that the grain is virtually cubic CeO ₂ and not hexagonal or cubic Ce ₂ O _3. shall. It is believed that it is not practical that the cubic CeO ₂ is thermodynamically stable at very small grain sizes, and that the grains are actually reduced and more stable hexagonal Ce ₂ O ₃ forms. S. Tsunekawa, R, Sivamohan, S. Ito, A. Kasuya and T. Fukada, Nanostructured Materials , vol 11, no. 1, pp 141-147 (1999).

"Structural Study on Monosize CeO _2-x Nanoparticles" doubts the presence of CeO ₂ especially below 1.5 nm.

Additional proof for the presence of (Ce ₂ O ₃ as and extension) Ce ^{3 +} in a very small grain diameter is found a log-linear relationship between the change Δa and crystal diameter in the lattice constant D as shown in Equation (2) Desphande et al., Applied Physics Letters 87, 133113 (2005) "Size Dependency Variation in Lattice Parameter and Valency States in Nano Crystalline Cerium Oxide":

Δa = aa ₀ (a ₀ = 5.43 μs at CeO ₂ )

<Equation 2>

Thus, a grain diameter of 10 nm undergoes a change in lattice strain or lattice constant of 0.0103 mm 3 or 1.91%, while a 1 nm diameter grain undergoes a change of 0.031 mm 3 or 5.73%.

Degree is CeO ₂ that can act as a catalyst oxygen storage material shown in Scheme 1 are in part influenced by the particle size of CeO _2. At 20 nm particle size and smaller particle sizes, the lattice parameter increases rapidly as the microcrystal size decreases (up to 0.45% at 6 nm, for example, Zhang, et al., Applied Physics Letters , 80 1, 127 (2002)]. Related size-induced lattice strains involve an increase in surface oxygen voids leading to improved catalytic activity. Such reverse size-dependent activity not only provides more efficient fuel cells but also provides better oxidative properties when used in the combustion of petroleum fuels.

As described above, for the preparation of cerium nanoparticles, US Pat. No. 5,017,352 (Chane-Ching, et al.), US Pat. No. 5,938,837 (Hanawa, et al.), US Pat. No. 4,786,325 (Melard, et al., US Pat. No. 5,712,218 to Chopin, et al., US Patent Application Publication No. 2005/0031517 (Chan) and US Pat. No. 7,025,943 (Zhou, et al.). And devices are reported, the disclosures of which are incorporated herein by reference. However, conventional methods are not economical, not easy (i.e. not calcined), and at very high suspension densities [more than 0.5 moles, i.e. 9 wt% of sufficiently small size (less than 5 nm at average geometric diameter)]. The production of cubic CeO ₂ nanoparticles with high yields within a short time is unclear, uneven in size frequency distribution (coefficient of variation [COV], where COV is the standard deviation divided by the average diameter), Not stable for the preferred application. In addition, it is highly desirable to produce particles that are crystalline, i.e., single crystals rather than agglomerates of microcrystals of various sizes as taught in the art and technical literature described above.

While it is advantageous to include substantially pure cerium dioxide nanoparticles in the fuel additive, it may be further advantageous to use cerium dioxide doped with components that result in the formation of additional oxygen voids formed (Scheme 1). In order for this to occur, the dopant must be divalent or trivalent, ie a rare earth metal, a transition metal, or a divalent or trivalent ion of an element that is an IIA, IIIB, VB or VIB metal of the Periodic Table of the Elements. The requirement for crystal charge neutrality with these lower valence cations causes Scheme 1 to proceed to the right, i.e., to form a higher degree of oxygen voids. Metal dopant ions with an ionic radius of less than Ce ⁺⁴ (0.97 kPa in octahedral structure) also aid in the formation of oxygen voids, which can cause two neighboring Ce ⁺⁴ ions (one surface and one surface). This is because it is reduced to Ce ⁺³ with a larger ion radius of 1.143 kPa, which causes the lattice to expand and cause lattice deformation. Thus, the substituted Zr ⁺⁴ (ion radius 0.84 kW) or Cu ⁺² (the ion radius of the six-coordinate octahedral structure is 0.73 kPa and the ion radius of the four-coordinate tetrahedral structure is 0.57 kPa) alleviates some of these lattice deformations. Let's go. In addition, Zr will form two neighboring surface Ce ^{+ 3} species (rather than one surface and one surface), which may be important for very small particles where about 50% of the ions are surface ions. Thus, substituted ion doping is preferred for gap ion doping, where the dopant occupies the space between normal lattice positions.

For this discussion, one must distinguish what doping means as opposed to lattice engineered crystals. In semiconductor physics, the term doping refers to n or p type impurities present in the range of 1 part per million. The term doped crystal is used to refer to a crystal in which one or more metal dopant ions are present at a concentration of less than 2 mol% (20,000 ppm). Conversely, the lattice engineered crystals may have one or more metal dopant ions present in the CeO ₂ crystals at concentrations above 20,000 ppm up to 800,000 ppm (or 80% of the cerium sublattice). Thus, lattice engineered cerium dioxide crystals may have cerium present as a minor metal component.

Doping cerium dioxide with metal ions to improve ion transport, reaction efficiency and other properties is described, for example, in " Doped Ceria as a Solid Oxide Electrolyte, HL Tuller and AS Nowick, J. Electrochem Soc. , 1975, 122 (2), 255], "Point Defect Analysis and Microstructural Effects in Pure and Donor Doped Ceria", MR DeGuire, et. Al., Solid State Ionics , 1992, 52, 155; and "Studies on Cu / CeO ₂ : A New NO Reduction Catalyst "Partha sarathi Bera, ST Aruna, KC Patil and MS Hegde, Journal of Catalysis , 186, 36-44 (1999). The resulting dopant effect on electron and oxygen diffusion properties. Are described in Trovarelli, Catalysis by Ceria and Related Materials , Catalytic Science Series , World Scientific Publishing Co., 37-46 (2002) and references cited therein.

Trovarelli et al., Catalysis Today , 43 (1998), 79-88, discuss the preparation of ceria-zirconia mixed oxides with fairly good composition homogeneity using an approach with surfactants. High specific surface area 230 m 2 / gm is obtained after calcination of the composition at 723 ° K, but sintering occurs at 1,173 ° K as the specific surface area drops to 40 m 2 / gm (about 20 nm diameter).

Pulse neutron diffraction techniques are described in E. Mamontov, et al., J. Phys. Chem. B 2000, 104, 1110-1116, to study ceria and ceria-zirconia solid solutions. These studies were the first to establish a correlation between the concentration of void-gap oxygen deficiency and oxygen storage capacity. This document argues that preservation of oxygen deficiency assisted by Zr is essential to improve the degradation of OSC against thermal aging. ZrO ₂ is present at 30.5 mol% and the calcined particles are about 40 nm in diameter based on the BET surface area measurements.

Z. Yang et al., Journal of Chemical Physics , (2006) 124 (22), 224704 / (1-7)] calculate from the first principle using density functional theory, in which oxygen pores are close to the center of Zr. Most easily generated, so that these centers act as nucleation sites for pore assemblies. The released oxygen provides two electrons to the Ce ⁺⁴ centers adjacent to the voids, creating two Ce ⁺³ centers.

R. Wang et al., J. Chem. Phys. B , 2006, 110, 18278-18285 studied the spatial distribution of Zr in Ce _0.5 Zr _0.5 O ₂ produced by spray freezing followed by calcination. This document found that particle nanounit heterogeneity characterized by Ce-rich cores and Zr-rich shells in particles with particle sizes between 5.4 and 25 nm is associated with materials with greater redox activity. This finding implies that a homogeneous distribution of Zr and Ce reduces the activity and is therefore undesirable.

S. Bedrane et al., Catalysis Today , 75, 1-4, 401-405 July 2002] 11 noble metals (PM = Rh, Pt, Rd, Ru and Ir) doped ceria (CeO ₂ ) and ceria-zirconia ( Ce _0.63 Zr _0.37 O ₂ ) The oxygen storage capacity (Scheme 1) of the composition was measured. In this document, Ce-Zr materials have OSCs that are almost independent of PM concentration, and observe a leveling effect that is 2-4 times greater than PM-loaded Ce alone materials.

H. Sparks et al. Of Nanophase Technologies, Corp., using vapor phase synthesis, prepared ceria mixed with rare earth oxide nanomaterials. Mat. Res. Soc. Symp. Proc , Vol 788, 2004. In this document an improved thermal stability of nanocrystalline particle size and an increase in OSC for Zr-doped ceria (1: 1) were observed, but adding La or Pr to the Zr composition was superior to ceria itself. It is worse than the zirconium ceria combination. From the reported specific surface areas, it can be estimated that the particle size is 10 nm at 600 ° C. and increased to 40 nm at 1,050 ° C.

The catalytic effect of Zr and Fe doped CeO ₂ in the combustion of diesel soot has been studied in Aneggi et al., Catalysis Today , 114, (2006), 40-47. This document repeats the fact that Zr improves the thermal stability and OSC of pure ceria, and Fe ₂ O ₃ led to better new results, but confirmed that there is a net loss of activity after calcination. A series of highly systematic levels of Zr and Zr and Fe, including crystallographic data for these calcined particles of about 21 nm, were studied. This document measured the nanoparticle specific area limit of 35 m 2 / gm (corresponding to a diameter of less than 24 nm), where the new versus aged activity was unchanged.

Copper based catalyst systems have also received much attention. In a very thorough structural analysis of 3 and 5 atomic% Cu / CeO ₂ , MS Hegde et al., Chem. Mater . 2002, 14, 3591-3601 demonstrated that Cu forms a distinct solid solution of Ce _1-x Cu _x O ₂ without discontinuous CuO phase. In these 50 nm aggregated grains produced by the combustion synthesis, Cu is in the +2 state, and the catalytic activity is much greater than Cu in CuO. In addition, oxygen ion voids are produced around the Cu ⁺² cation.

A. Martinex-Arias et al., J. Phys. Chem. B , 2005, 109, 19595-19603], the reduction of Ce _1-x M _x O ₂ fluorspar nanoparticles (x = 0.05, 0.1 and 0.2) is reversible and the oxidation state of Cu is at its steady state (+1 or Higher than +2). Dopants cause large lattice strains at about 6 nm particles in the oxide sublattices, which is beneficial for the formation of oxygen voids. These materials were produced using an inverse microemulsion method followed by calcination at 500 ° C.

Iron is another metal infused with CeO ₂ nanoparticles with improved catalytic activity. I. Melian-Cabrera et al., Journal of Catalysis , 239, 2006, 340-346, reports the optimum catalytic decomposition and improved activity (relative to undoped material) of N ₂ O, an oxygen-limited reaction with a 50/50 composition of cerium and iron oxide. Fe-doped ceria is produced by the coprecipitation method which produces particles in the 30 nm diameter range.

T. Campenon and colleagues, SAE special publication SP 2004, SP-1860, "Diesel Exhaust Emission Control", use iron doped ceria to control ash buildup in diesel particulate filters.

R. Hu and colleagues, Shiyou Huagong (2006), 35 (4), 319-323, studied Fe-doped cerium dioxide produced by solid phase milling followed by calcination at various high temperatures. Iron doping improved the catalytic activity for the combustion of methane and at the same time reduced the particle size.

Examples 9 and 10 of US Patent Application Publication No. 2005/0152832 describe the preparation of cerium-doped and cerium-coated barium hexaaluminate particles, respectively. Example 13 describes the oxidation of methane using cerium-coated particles.

U.S. Patent No. 6,752,979 (Talbot et al., The disclosure of which is incorporated herein by reference) discloses a mixture of a surfactant and a solution comprising at least one metal cation under conditions such that the surfactant micelle is formed in solution. A method for producing metal oxide particles with nano-sized grains is described which forms a micelle liquid, heats the micelle liquid to remove the surfactant, and forms metal oxide particles having an irregular pore structure. The metal cation is selected from the group consisting of cations from the Periodic Tables IA, 2A, 3A, 4A, 5A and 6A, transition metals, lanthanides, actinides and mixtures thereof. The preparation of particles of cerium dioxide and mixed oxides containing cerium and one or more other metals is included in the examples.

Example 9 of US Pat. No. 6,413,489 and US Pat. No. 6,869,584, the disclosures of which are incorporated herein by reference, include cerium-doped hexaalu, collected by freeze drying and calcined at 500 ° C. and 800 ° C. under air. It has been described to include cerium nitrate in the emulsion mixture to produce barium nitrate particles. The resulting particles have grain sizes of less than 5 nm and 7 nm at 500 ° C. and 800 ° C., respectively. Example 10 describes the synthesis of cerium-coated barium hexaaluminate particles. After calcination, the cerium-coated particles have grain sizes of less than 4 nm, 6.5 nm and 16 nm at 500 ° C, 800 ° C and 1,100 ° C, respectively.

US Patent No. 7,169,196B2 to Wakefield, the disclosure of which is incorporated herein by reference, includes divalent or trivalent metals or metalloids which are rare earth metals, transition metals or Group IIa, IIIB, VB or VIB metals of the Periodic Table. A fuel comprising doped cerium dioxide particles is described. Copper is disclosed as a preferred dopant.

US Pat. No. 7,384,888B2 to Oji Kuno, the disclosure of which is incorporated herein by reference, describes cerium-zirconium composite metal oxides having a ceria core and a zirconia shell with improved high temperature stability and OSC stability. However, calcination at 700 ° C. is required for the preparation of the material, and the catalytic activity for hydrocarbon and carbon monoxide oxidation has been shown to be 10-20% improved. There is no data on the size to support claims of 5 to 20 nm particles, no mention of direct OSC measurements, and no analytical data to support claims on core-shell geometry.

With respect to 10 nm diameter or smaller nanoparticles, there is doubt about the ability to incorporate metal ion dopants into the small particles. For example, 8.1 nm particles are less than 10% of Ce ions on the surface, while 2.7 nm particles (5 unit cells on the edge of each 0.54 nm / unit cell) are 46.6% of 500 Ce ions on the surface. Surface ions are incorporated into the lattice by one half (for the front) or one eighth (the corners), so that the binding energy is substantially reduced and its coordination requirements are not met. Difficulties associated with the doping of (semiconductor) nanocrystals are discussed in Science , 319, March 28, 2008 by Norris et al. Properties such as the relative solubility of the dopant in crystals versus solution, the diffusion of the dopant into the lattice, the energy of its formation, the size and valences for the ions to be substituted, and the kinetic barrier as can be added by adsorbed surface stabilizers are all If desired, dopant metal ions can serve to determine the extent to which they can be incorporated into nanocrystals having these sizes.

From the preceding literature, most of the doping operations occur at relatively large particle sizes (20 nm, etc.), and micelle synthesis is a process that is not readily used for the production of large-scale materials, either by calcination of the initial cerium-metal dopant mixture. It is obvious that it is implemented by. In the work of describing particles less than 10 nm in size, no crystallographic form has been demonstrated or no definitive evidence of specification has been provided.

Thus, it is easy to incorporate various metal dopant ions into the cerium sublattice of cubic CeO ₂ for very small nanoparticles (diameter less than about 10 nm) in an easy manner that does not require calcination (above 500C), and dopants In contrast to the preparation of separately nucleated populations of metal oxide grains there is a need to clearly demonstrate incorporation. Since single crystal grains of ceria are unique, so will the metal lattice engineered variants of ceria. In addition, it is desirable to produce significant available amounts of these materials in an economical manner and in a relatively short time.

A conventional chemical reactor to be used to produce cerium dioxide is a reaction chamber comprising a mixer (see, eg, FIG. 1 of Zhou et al., The disclosure of which is incorporated herein by reference). It includes. The mixer typically includes a shaft, a propeller or turbine blade attached to the shaft, and a motor that rotates the shaft so that the propeller rotates at high speed (1,000 to 5,000 rpm). The shaft can drive a flat blade turbine for good meso mixing (micro units) and a pitch blade turbine for macro mixing (pumping fluid out through the reactor).

Such a device is described in US Pat. No. 6,422,736 (Antoniades), the disclosure of which is incorporated herein by reference. The disclosed reactors are useful for high speed reactions, for example represented by the following schemes, where the product AgCl is a crystalline material with a diameter of several hundred nanometers to several thousand nanometers:

Cerium dioxide particles produced using this type of mixing are often too large to be useful for certain applications. It is highly desirable to have the smallest possible cerium dioxide particles as the catalyst tendency, especially for particles with an average diameter of less than 10 nm because the ability to provide oxygen to the combustion system (see Scheme 1) increases with decreasing particle size. to be.

PCT / US2007 / 077545, filed on September 4, 2007, entitled Process for Making Cerium Dioxide Nanoparticles, describes a mixing device capable of producing CeO ₂ nanoparticles up to 1.5 nm in high yield and very high suspension density. It is. The reactor includes an input port for adding reactants, a propeller, a shaft and a motor for mixing. The reaction mixture is received in a reactor vessel. The addition of reactants such as cerium nitrate, oxidant and hydroxide ions to the vessel can lead to the formation of CeO ₂ nanoparticles initially formed as very small nuclei. Mixing causes the nucleus to circulate, and as the nucleus circulates through the reactive mixing zone continuously, they grow incorporating new reactants (increasing in diameter). Thus, after enrichment of the initial stationary state of the nucleus is formed, this nuclear population is subsequently grown into larger particles. If the growth phase is not terminated using a grain growth inhibitor, this nucleation and growth process is undesirable when it is desired to limit the final size of the particles while still maintaining a high particle suspension density.

Examples of such nucleation and growth processes applied to aqueous precipitation of CeO ₂ are described in Zhang et al., J. Appl. Phys. , 95, 4319 (2004) and Zhang, et al., Applied Physics Letters , 80, 127 (2002). Using cerium nitrate hexahydrate (very dilute to 0.0375 M) as cerium source and 0.5 M hexamethylenetetraamine as ammonia precursor, 2.5 to 4.25 nm cerium dioxide particles are formed in less than 50 minutes. These particles are subsequently grown to 7.5 nm or larger, depending on growth conditions, using a reaction time of about 250 or 600 minutes. Restrictions on particle size, concentration and reaction time preclude this process from consideration as an economically viable route to bulky industrial quantities of CeO ₂ nanoparticles.

IH Leubner, Current Opinion in Colloid and Interface Science , 5, 151-159 (2000), Journal of Dispersion Science and Technology , 22, 125-138 (2001) and Hom., 23, 577-590 ( 2002) and the literature cited therein provide theoretical treatments related to the molar addition rate of the reactants, the solubility of the crystals and the number of stable crystals formed by the temperature. This model also accounts for the effects of diffusion, dynamically regulated growth processes, Ostwald ripening agents and growth inhibitors / stabilizers on the number of crystals. High molar addition rates, low temperatures, low solubility and the presence of growth inhibitory all benefit many nuclei and thus smaller final grains or particle sizes.

In contrast to a batch reactor, a colloidal mill typically has a flat blade turbine that rotates at 10,000 rpm to pass through a screen with holes that can be varied from one millimeter to several millimeters in size. In general, no chemical reaction occurs, but a change in particle size caused by milling occurs. In certain cases, particle size and stability can be thermodynamically controlled by the presence of surfactants. For example, US Pat. No. 6,368,366 and US Pat. No. 6,363,237, both of which disclosures are incorporated herein by reference, describe aqueous microemulsions in hydrocarbon fuel compositions produced under high shear conditions. . However, the aqueous particle phase (discontinuous phase in the fuel composition) is as large as 1,000 nm in size.

Colloid mills are not useful for reducing the particle size of large cerium dioxide particles because the particles are so hard that they are not sheared within a reasonable amount of time by the mill. A preferred method of reducing large agglomerated cerium dioxide particles from micrometer size to nanometer size is to mill in the presence of a stabilizer on a ball mill for several days. This is an expensive and time consuming process that invariably produces a wide distribution of particle sizes. Thus, for an economical and easy method to synthesize large quantities of very small nanometer particles of cerium dioxide incorporating one or more transition metal ions with a uniform size distribution at high suspension densities and still maintaining a CeO ₂ cubic fluorite structure Demand exists.

Aqueous precipitation can provide an easy route to cerium nanoparticles. However, to be useful as a fuel based catalyst for fuels, cerium dioxide nanoparticles must be stable in nonpolar media, such as diesel fuel. Most stabilizers used to prevent aggregation in aqueous environments are inadequate for the task of stabilization in nonpolar environments. When placed in a nonpolar solvent, these particles aggregate immediately and lose some, but not all, desirable nanoparticulate properties. Thus, cerium dioxide particles that are stable in an aqueous environment and having the same stabilizer on the particle surface can then be delivered to a nonpolar solvent, where the particles remain stable and can form a homogeneous mixture or dispersion. It is desirable to have. In this simple and economical way, the affinity of the surface stabilizer can be eliminated from the need to change from polar to nonpolar. Changing the stabilizer may involve difficult substitution reactions or separate, tedious separation and redispersion methods, such as precipitation and subsequent use of new stabilizers and redispersion using ball milling.

Thus, there is a need for an efficient and economical method of synthesizing stable transition metal-containing cerium dioxide nanoparticles in a polar aqueous environment and then transferring these particles to a nonpolar environment in which a stable homogeneous mixture is formed.

The use of cerium nanoparticles to provide high temperature oxidation resistant coatings is described, for example, in "Synthesis Of Nano Crystalline Ceria Particles For High Temperature Oxidization Resistant Coating," S. Seal et al., Journal of Nanoparticle Research , 4, 433-. 438 (2002). The adhesion of cerium dioxide on various surfaces including Ni, chromia and alumina alloys, and stainless steel, and on Ni and Ni-Cr coated alloy surfaces has been studied. Cerium dioxide with a particle size of 10 nm or less has been found to be preferred. Ceria particle incorporation subsequently inhibits oxidation of the metal surface.

U.S. Patent No. 6,892,531 (Rim), the disclosure of which is incorporated herein by reference, discloses an engine lubricating oil for a diesel engine comprising a lubricant and a catalyst additive comprising 0.05 to 10% by weight of cerium carboxylate.

As described above, currently available cerium oxide- and doped cerium oxide based fuel additives have improved fuel combustion in diesel engines, but further improvements are still needed. It is desirable to formulate fuel additives for diesel engines that provide further improved fuel combustion using nanoparticles of much smaller cubic CeO _{2 while having} a much smaller specific surface area of less than 5 nm. The increased oxygen storage capacity made possible by including transition metals with such grain size is also highly desirable. In addition, protection of the engine from wear, reduction of engine friction, greater lubricity and at the same time improved fuel efficiency would be very beneficial.

Summary of the Invention

The present invention

(a) an aqueous reaction comprising a first cerium ion source, at least one transition metal ion (M) source, a hydroxide ion source, at least one nanoparticle stabilizer, and an oxidant at an initial temperature ranging from about 20 ° C to about 95 ° C. Providing a mixture;

(b) mechanically shearing the mixture and passing through a perforated screen to form a suspension of cerium hydroxide nanoparticles; And

(c) providing a temperature condition effective to oxidize the first cerium ion to the second cerium ion to form a product stream comprising transition metal-containing cerium dioxide nanoparticles Ce _1-x M _x O ₂ . And a process for preparing lattice engineered cerium dioxide nanoparticles comprising at least one transition metal (M). The cerium dioxide nanoparticles thus obtained have a cubic fluorspar structure, with an average hydrodynamic diameter in the range of about 1 nm to about 10 nm, and a geometric diameter in the range of about 1 nm to about 4 nm.

The present invention further

(a) Stabilized transition metal-containing cerium dioxide nanoparticles Ce _1-x M having a cubic fluorspar structure and having an average hydrodynamic diameter in the range of about 1 nm to about 10 nm and a geometric diameter of about 1 nm to about 4 nm. providing an aqueous mixture comprising _x O ₂ ;

(b) concentrating the aqueous mixture comprising the stabilized transition metal-containing cerium dioxide nanoparticles to form an aqueous concentrate;

(c) removing substantially all of the water from the aqueous concentrate to form a substantially water-free concentrate of the stabilized transition metal-containing cerium dioxide nanoparticles;

(d) adding an organic diluent to the substantially water free concentrate to form an organic concentrate of the stabilized transition metal-containing cerium dioxide nanoparticles; And

(e) transition metal-containing 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, wherein "x" has a value from about 0.3 to about 0.8 And a method for forming a homogeneous dispersion comprising stabilized transition metal-containing cerium dioxide nanoparticles Ce _1-x M _x O ₂ .

1A and 1B show TEM image and particle size frequency analysis by TEM of CeO ₂ nanoparticles produced by non-isothermal precipitation as described in Example 1, respectively.
2 shows the X-ray powder diffraction spectrum of the cerium dioxide nanoparticles produced as described in Example 1. FIG.
3A shows a TEM image of 1.1 nm CeO ₂ nanoparticles produced as described in Example 2. FIG. 3B shows the electron diffraction pattern of the 1.1 nm particles. FIG. 3C shows Table 1 including theoretical versus measured values of electron diffraction intensities for cubic and hexagonal CeO ₂ and Ce ₂ O ₃ lattice.
4A and 4B show TEM image and particle size frequency analysis by TEM of isothermally precipitated CeO ₂ nanoparticles produced by a triple jet process as described in Example 3, respectively.
5A and 5B show TEM image and particle size frequency analysis by TEM of isothermally precipitated Cu-containing CeO ₂ nanoparticles produced as described in Example 4, respectively.
6A and 6B show TEM image and particle size frequency analysis by TEM of isothermally precipitated Fe-containing CeO ₂ nanoparticles produced as described in Example 5, respectively.
7A and 7B show TEM image and particle size frequency analysis by TEM of isothermally precipitated Zr-containing CeO ₂ nanoparticles produced as described in Example 6, respectively.
8A and 8B show TEM image and particle size frequency analysis by TEM of isothermally precipitated CeO ₂ nanoparticles comprising Zr and Fe produced as described in Example 7, respectively. Figure 8C shows an X-ray diffraction spectrum of the isothermal precipitated CeO ₂ nanoparticles including a an isothermal precipitated CeO ₂ nanoparticles and, Zr and Fe generated as described in Example 7.
9 shows field emission total TEM lattice images of CeO ₂ nanoparticles comprising Zr and Fe produced as described in Example 7. FIG.

Detailed description of the invention

In the present application, the term “transition metal” is to be understood to encompass 40 chemical elements 21-30, 39-48, 72-80, which are included in the 4, 5, 6 cycles of the periodic table of the elements, respectively.

The present invention

(a) providing an aqueous reaction mixture comprising a first cerium ion source and at least one transition metal ion, a hydroxide ion source, at least one nanoparticle stabilizer and an oxidant;

(b) mechanically shearing the mixture and passing through a perforated screen to form a suspension of cerium hydroxide nanoparticles; And

(c) has a cubic fluorite structure providing a temperature condition effective to oxidize the first cerium ion to the second cerium ion, having an average hydrodynamic diameter in the range of about 1 nm to about 10 nm, and a geometric diameter of about 1 nm. Preparation of transition metal ion-containing cerium dioxide (CeO ₂ ) nanoparticles comprising forming a product stream comprising transition metal-containing cerium dioxide nanoparticles Ce _1-x M _x O ₂ in a range from about 4 nm. Provide a method. Crystalline cerium dioxide particles comprising one or more transition metal ions and having a monomodal size distribution and a monodisperse size frequency distribution can be selectively produced in this size range. Single crystalline particles comprise two unit cells per edge for 1.1 nm particles or up to five unit cells per edge for 2.7 nm particles, depending on the production conditions. The term crystalline here does not consist of a plurality of aggregated microcrystals of various sizes, but rather refers to particles consisting of a single crystal having a predetermined dimension indicated by the number of component unit cells.

The present invention further includes one or more transition metal ions comprising mixing in a continuous reactor a first cerium ion, one or more transition metal ions, an oxidant, one or more nanoparticle stabilizers and a hydroxide ion. And continuously produce crystalline cerium dioxide CeO ₂ nanoparticles having an average hydrodynamic diameter of about 1 nm to about 10 nm.

The invention also

(a) providing an aqueous first reaction mixture comprising a first source of cerium ions, at least one transition metal ion and at least one nanoparticle stabilizer;

(b) stirring the first reaction mixture while adding an oxidant to produce a second reaction mixture;

(c) adding a source of hydroxide ions to the second reaction mixture while performing mechanical shearing to form a third reaction mixture; And

(d) heating the third reaction mixture to a temperature of about 50 ° C. to about 100 ° C. to produce crystalline cerium dioxide nanoparticles comprising one or more transition metal ions, which are substantially monomodal and have a uniform size frequency distribution. It provides a method for producing a cerium dioxide nanoparticles, comprising the step.

The present invention further provides a method of forming a homogeneous mixture comprising the aforementioned crystalline cerium dioxide nanoparticles, at least one nanoparticle stabilizer, at least one surfactant, a glycol ether mixture, and a nonpolar medium. This way

(a) providing an aqueous mixture comprising stabilized crystalline cerium dioxide nanoparticles produced by intimate bonding of a nanoparticle stabilizer and crystalline cerium dioxide nanoparticles;

(b) concentrating the aqueous mixture comprising stabilized crystalline cerium dioxide nanoparticles to form an aqueous concentrate; And

(c) removing almost all of the water by solvent transfer from the aqueous environment to the glycol ether environment, and mixing the surfactant and optionally the cosurfactant with the solvent transferred concentrate in the presence of a nonpolar medium to form a homogeneous mixture. Include.

In the presence of hydroxide ions, the second cerium ions react to form cerium hydroxide, which is converted to crystalline cerium dioxide upon heating. The temperature in the reaction vessel is maintained at about 50 ° C to about 100 ° C, more preferably about 65 ° C to 95 ° C, most preferably about 85 ° C. Time and temperature can be controlled, and higher temperatures typically shorten the time required to convert hydroxide to oxide. After a lapse of about 1 hour or less and suitably about 0.5 hours at high temperature, cerium hydroxide is converted to crystalline cerium dioxide and the temperature of the reaction vessel is reduced to about 15 ° C to 25 ° C. The crystalline cerium dioxide nanoparticles are then concentrated and the unreacted cerium and waste by-products such as ammonium nitrate are most conveniently removed, for example by diafiltration.

In one aspect of the invention, a method of making crystalline cerium dioxide nanoparticles comprising one or more transition metal ions comprises a first cerium ion, one or more transition metal ions, a hydroxide ion, a stabilizer or a combination of stabilizers and oxidants. Providing an aqueous reaction mixture comprising the reaction producing a small nucleus size, conducting at a temperature effective to subsequently oxidize the first cerium ion to a second cerium ion and to grow the nucleus to nanosized cerium dioxide. Include. The reaction mixture undergoes mechanical shearing, preferably through a perforated screen to form a suspension of crystalline cerium dioxide nanoparticles having an average hydrodynamic diameter in the range of about 1 nm to about 10 nm. The particle diameter can be adjusted in the range from 1.5 nm to 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, most preferably about 6 nm. . Preferably the nanoparticles comprise one or at most two primary microcrystals per particle edge, with each microcrystal an average of 2.5 nm (about 5 unit cells). Thus, the resulting nanoparticle size frequency is substantially simple dispersion, ie, the coefficient of variation (COV) is less than 25%, where COV is defined as the standard deviation divided by the mean value.

Mechanical shear includes the movement of a fluid on a surface, such as the movement of a rotor, thereby creating a shear stress. In particular, the laminar flow on the surface is zero in velocity, and shear stresses occur between the zero-velocity surface and the high velocity flow away from the surface.

In one embodiment, the present invention uses, as a chemical reactor to produce cerium dioxide nanoparticles, a colloid mill commonly used for milling microemulsions or colloids. Examples of useful colloid mills include those described in US Pat. No. 6,745,961 (Korstvedt) and US Pat. No. 6,305,626 (Korstvedt), the disclosures of which are incorporated herein by reference.

The reactant may be a first cerium ion source such as cerium nitrate; Oxidizing agents such as hydrogen peroxide or molecular oxygen; And stabilizers such as aqueous solutions of 2- [2- (2-methoxyethoxy) ethoxy] acetic acid. Typically, a 2-electron oxidant, such as a peroxide, is preferably present at least half of the molar concentration of cerium ions. The hydroxide ion concentration may preferably be at least 2 times, more preferably 3 times or even 5 times the molar concentration of cerium ions.

Initially, the reaction chamber is maintained at a temperature low enough to produce a small cerium hydroxide nucleus size, which can then be grown to nanometer crystalline cerium dioxide particles after being transferred to a higher temperature. The first cerium ion is converted into the second cerium ion state. Initially, although higher temperatures can be used without a significant increase in particle size, temperatures of about 25 ° C. or less are appropriate.

In one embodiment, a first cerium ion source, one or more transition metal ions, nanoparticle stabilizers, and an oxidant are placed in a reactor and a period of time, preferably up to about 10 minutes, with stirring the hydroxide ion source such as ammonium hydroxide Add over. Under certain conditions, for example, under conditions in which a single jet of ammonia is added to the metal ions, about 20 seconds or less are preferred, and about 15 seconds or less are even more preferred. In an alternative embodiment, a hydroxide ion source and an oxidant are placed in a reactor and a first cerium ion source and one or more transition metal ions are added over about 15 seconds to 20 minutes. In a third and preferred embodiment, a stabilizer is placed in the reaction vessel and the first cerium nitrate having at least one transition metal ion is added 2: 2, 3: 1 or even 5: 1 with a separate jet of ammonium hydroxide. Are introduced simultaneously into the reaction chamber at an optimal stoichiometric molar ratio of OH: Ce.

The first cerium ion reacts with the oxidant in the presence of hydroxide ions to form cerium hydroxide, which can be converted to crystalline cerium dioxide by heating. The temperature in the reaction vessel is maintained at about 50 ° C to about 100 ° C, preferably about 65 ° C to 85 ° C, more preferably about 70 ° C. Incorporation of certain transition metal ions, such as Zr and Cu, typically requires a higher temperature of about 85 ° C. At this high temperature, preferably after about 1 hour or less, more preferably after about 0.5 hours, the doped cerium hydroxide is substantially converted to crystalline cerium dioxide, and the temperature of the reaction vessel is reduced to about 15 ° C to 25 ° C. Time and temperature parameters can be adjusted, and higher temperatures generally require shorter reaction times. It can be achieved simply by concentrating the suspension of cerium dioxide nanoparticles, removing unreacted cerium and waste by-products such as ammonium nitrate, and by diafiltration.

Nanoparticle stabilizers are important components of the reaction mixture. Nanoparticle stabilizers are water soluble and preferably form weak bonds with cerium ions. K _BC represents the binding constant of the nanoparticle stabilizer to cerium ions in water. The log K _BC is 1 for nitrate ions and 14 for hydroxide ions. Most preferably log K _BC is in this range, preferably in the middle of this range. Examples of useful nanoparticle stabilizers include alkoxy substituted carboxylic acids, α-hydroxy carboxylic acids, α-ketocarboxylic acids such as pyruvic acid and small organic polyacids such as tartaric acid and citric acid. Examples of alkoxylated carboxylic acids include methoxy acetic acid, 2- (methoxy) ethoxy acetic acid and 2- [2- (2-methoxyethoxy) ethoxy] acetic acid (MEEA). Examples of α-hydroxycarboxylic acids include lactic acid, gluconic acid and 2-hydroxybutanoic acid. Examples of polyacids include ethylenediaminetetraacetic acid (EDTA), tartaric acid and citric acid. Combinations of compounds with a high 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 concentrations or in conjunction with slightly K _BC stabilizers, such as lactic acid.

In one preferred embodiment, nanoparticle stabilizers include compounds of formula (Ia). In formula la, R represents hydrogen or a substituted or unsubstituted alkyl group or an 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 formula la, n represents an integer from 0 to 5, preferably 2, and Y represents H or a counterion such as an alkali metal, for example Na ⁺ or K ⁺ . Stabilizers bind to nanoparticles and interfere with the agglomeration of particles and the formation of large chunks of subsequent particles:

<Formula Ia>

In another embodiment, the nanoparticle stabilizer is represented by Formula Ib, wherein 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 counterion such as Na ⁺ or K ⁺ , p is 1 or 2:

<Formula Ib>

Useful nanoparticle stabilizers also include, for example, gluconic acid in α-hydroxysubstituted carboxylic acids such as lactic acid and polyhydroxysubstituted acids.

Nanoparticle stabilizers preferably do not contain elemental sulfur, since sulfur-containing materials may not be desirable for certain applications. For example, when incorporating cerium dioxide particles into a fuel additive composition, the use of sulfur-containing stabilizers such as AOT is undesirable because it can release sulfur oxides after combustion.

The size of the resulting cerium dioxide particles can be measured by dynamic light scattering, a measurement technique for measuring the hydrodynamic diameter of the particles. Hydrodynamic diameters [BJ Berne and R. Pecora, " Dynamic Light Scattering: With Applications to Chemistry, Biology and Physics ", John Wiley and Sons, NY 1976] and [" Interactions of Photons and Neutrons with Matter ", SH Chen and M Kotlarchyk, World Scientific Publishing, Singapore, 1997] is slightly larger than the particle's geometric diameter and includes both the original particle size and the solvated shell around the particle. As the beam of light passes through the colloidal dispersion system, the particles or droplets scatter some of the light in all directions. When the particles are very small compared to the wavelength of the light, the intensity of the scattered light is uniform in all directions (Rayleigh scattering). If the light is coherent and monochromatic light from a laser, for example, a suitable detector such as a photomultiplier tube which can be operated in the photon counting mode can be used and the time dependent variation in the scattering intensity can be observed. This variation is due to the fact that the particles are small enough to undergo random thermal Brownian motion, and therefore the distance between the particles is constantly changing. Since the constructive and destructive interference of light scattered by neighboring particles in the irradiated area is caused by particle motion, intensity variations occur in the detector plane that contain information about this motion. Hence, a time dependent analysis of the intensity variation can yield the diffusion coefficient of the particles, from which the hydrodynamic radius or diameter of the particles can be calculated by the Stokes Einstein equation and the known viscosity of the medium.

In another aspect of the invention, a process for continuously preparing small transition metal ion-containing crystalline cerium dioxide nanoparticles, ie, particles having an average diameter of less than about 10 nm, comprises a first cerium ion, at least one transition metal ion, an oxidant, a nano Mixing the particle stabilizer or stabilizer combination and hydroxide ions in a continuous reactor, wherein the reactants and other components are introduced continuously into the reactor where the product is continuously removed. Continuous methods are described, for example, in US Pat. No. 6,897,270 (Ozawa, et al.), US Pat. No. 6,723,138 (Nickel, et al.), US Pat. No. 6,627,720 (Campbell, et al.), US Pat. No. 5,097,090 ( Beck) and US Pat. No. 4,661,321 to Byrd, et al., The disclosure of which is incorporated herein by reference.

Solvents such as water are often used in the process. The solvent can control the process by dissolving the reactants and controlling the flow of the solvent. Advantageously, a mixer can be used to stir and mix the reactants.

Any reactor that can accommodate a continuous flow of reactants to deliver a continuous flow of product can be used. Such reactors include continuous stirred tank reactors, plug-flow reactors, and the like. The reactants required to effect the nanoparticle synthesis are preferably charged into the reactor in a flow state, ie it is preferably introduced as a liquid or solution. The reactants may be charged in separate flows or certain reactants may be mixed prior to filling the reactor.

The reactants are introduced into the reaction chamber equipped with the stirrer through one or more inlets. Typically the reactants are a source of cerium ions such as cerium nitrate, transition metal ions such as ferric nitrate or cupric nitrate; Oxidizing agents such as molecular oxygen, including hydrogen peroxide or ambient air; And stabilizers such as an aqueous solution of 2- [2- (2-methoxyethoxy) ethoxy] acetic acid. Preferably, a two-electron oxidant, such as hydrogen peroxide, is present at at least half the molar concentration of cerium ions. Alternatively, molecular oxygen can be bubbled through the mixture. The hydroxide ion concentration is preferably at least two times the cerium molar concentration.

In one embodiment of the present invention, the method of forming small cerium dioxide nanoparticles forms a first aqueous reactant stream comprising a first cerium ion, such as cerium nitrate, at least one transition metal ion and an oxidant. It includes a step. Suitable oxidizing agents capable of oxidizing Ce (III) to Ce (IV) include, for example, hydrogen peroxide or molecular oxygen. Optionally, the first reactant stream also includes nanoparticle stabilizers that bind to the doped cerium dioxide nanoparticles and interfere with the aggregation of the particles. Useful examples of nanoparticle stabilizers are mentioned above.

The process of the present invention includes forming a second aqueous reactant stream comprising a source of hydroxide ions, for example ammonium hydroxide or potassium hydroxide. Optionally, the second reactant stream further comprises a stabilizer, examples of which are described above. However, at least one of the first or second reactant streams must comprise a stabilizer or stabilizer combination.

The first and second reactant streams combine to form a reaction stream. Initially, the temperature of the reaction stream is kept low enough to form small cerium hydroxide nuclei. The oxidation of Ce (III) to Ce (IV) then takes place in the presence of an oxidant and the temperature is raised so that the hydroxide is converted to an oxide to produce a product stream comprising crystalline cerium dioxide. The temperature for converting the hydroxide into an oxide is preferably about 50 ° C to 100 ° C, more preferably about 60 ° C to 90 ° C. In one embodiment, the first and second reactant streams are combined at a temperature of about 10 ° C. to 20 ° C., after which the temperature is raised to about 60 ° C. to 90 ° C. Isothermal precipitation at high temperatures, for example 90 ° C., is an alternative method for producing small nanoparticles as long as the growth step can be inhibited by appropriate molecular adsorbates (growth inhibitors).

It is desirable to concentrate the lattice engineered crystalline cerium dioxide nanoparticles in the product stream using one or more semi-porous membranes, for example by diafiltration techniques. In one embodiment, the product stream comprises an aqueous suspension of transition metal-containing crystalline cerium dioxide nanoparticles reduced to a conductivity of about 5 mS / cm or less by one or more semi-porous membranes.

A schematic diagram of a continuous reactor suitable for the practice of the present invention is shown in FIG. 3 of PCT / US2007 / 77545, entitled Process for the Preparation of Cerium Dioxide Nanoparticles, filed September 4, 2007. Reactor 40 comprises a first reactant stream 41 comprising aqueous cerium nitrate. An oxidant such as hydrogen peroxide is added to the reactant stream by inlet 42 and the reactants are mixed by mixer 43a. The stabilizer is added to the resulting mixture via the inlet 45 and then mixed by the mixer 43b. The mixture from mixer 43b is then introduced into mixer 43c where it is combined with a second reactant stream comprising ammonium hydroxide from inlet 44. The first and second reactant streams may be mixed using a mixer 43c to form a reaction stream, which may be passed through a perforated screen to effect mechanical shear. In a further embodiment, the mixer 43c comprises a colloid mill reactor as described above, provided with an inlet port and an outlet port 45 for receiving the reactant stream. In further embodiments, the temperature of the mixer 43c is maintained at a temperature in the range of about 10 ° C to about 25 ° C.

The mixture from the mixer 43c is introduced into a reactor tube 45 comprising a constant temperature bath 46 which maintains the tube 45 at a temperature of about 60 ° C to 90 ° C. Crystalline cerium dioxide nanoparticles are formed in the reactor tube 45, which may include a coil 50. The product stream is then fed to one or more diafiltration units 47 where the crystalline cerium dioxide nanoparticles are concentrated using one or more semi-porous membranes. One or more diafiltration units may be connected in series to achieve a single pass concentration of the product or the units may be arranged in parallel for very high volume throughput. Diafiltration units can be arranged in series and in parallel to achieve both very high volume and rapid throughput. Concentrated crystalline cerium dioxide nanoparticles are discharged from the diafiltration unit via outlet port 49, and excess reactants and water are removed from diafiltration unit 47 via outlet port 48. In alternative embodiments, stabilizers may be added to the second reactant stream via port 51 rather than via port 45 to the first reactant stream.

In one embodiment of the invention, the product stream of concentrated lattice engineered crystalline cerium dioxide nanoparticles exiting diafiltration unit 47 is solvent transferred to an environment of at least one glycol ether substantially free of water. This can be accomplished by running the aqueous nanoparticles with an organic diluent, preferably using a dialysis bag or via diafiltration column, preferably with one or more glycol ethers. The organic diluent may further comprise an alcohol. Useful diluents include mixtures of diethylene glycol monomethyl ether and 1-methoxy-2-propanol.

The resulting solvent-shifted organic concentrate is combined with a surfactant such as oleic acid and then combined with a stream comprising a nonpolar solvent such as kerosene or ultra low sulfur diesel fuel to form a lattice engineered crystalline cerium dioxide nano that is miscible with a hydrocarbon fuel such as diesel. To form a homogeneous dispersion of particles.

The use of a continuous method for producing lattice engineered crystalline cerium dioxide nanoparticles provides better control over the generation of particle nuclei and their growth as provided by a batch reactor. Nucleus size can be controlled by initial reagent concentration, temperature, and the ratio of nanoparticle stabilizer to agent concentration. Small nuclei are aided by low temperatures below about 20 ° C. and high ratios of nanoparticle stabilizer to reagent concentration. In this method, very small nanoparticles having an average hydrodynamic diameter of less than about 10 nm and a geometric particle diameter of less than about 3 nm can be produced in an economical manner.

The present invention provides a method of combining a homogeneous mixture comprising cerium dioxide (CeO ₂ ) nanoparticles comprising one or more transition metal ions, nanoparticle stabilizers, surfactants, glycol ethers, and nonpolar solvents. 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 diameter (measured by TEM) is less than about 4 nm. .

As described above, lattice engineered crystalline cerium dioxide nanoparticles can be produced in a variety of procedures. A common synthetic route uses water as solvent and yields an aqueous mixture of nanoparticles and one or more salts. For example, cerium dioxide particles can be produced by reacting a hydrate of cerium (III) nitrate with hydroxide ions from, for example, aqueous ammonium hydroxide, to form cerium (III) hydroxide, as shown in Scheme 3a below. Cerium hydroxide can be oxidized to cerium dioxide (IV) using an oxidizing agent such as hydrogen peroxide, as shown in Scheme 3b. Similar Tris hydroxide stoichiometry is shown in Schemes 4a and 4b:

<Scheme 3a>

<Scheme 3b>

<Scheme 4a>

<Scheme 4b>

Complexes formed at very high base concentrations, such as 5: 1 OH: Ce, also provide a route to cerium oxide despite much larger grain sizes if growth is not adequately inhibited.

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

Transition metal containing crystalline cerium dioxide particles are formed in an aqueous environment and combined with one or more nanoparticle stabilizers. The cerium dioxide nanoparticles are preferably formed in the presence of stabilizer (s) or the stabilizer (s) is added immediately after its formation. Examples of useful nanoparticle stabilizers include alkoxysubstituted carboxylic acids, α-hydroxyl carboxylic acids such as pyruvic acid and small organic polycarboxylic acids. Examples of the alkoxy substituted carboxylic acid include methoxy acetic acid, 2- (methoxy) ethoxy acetic acid and 2- [2- (2-methoxyethoxy) ethoxy] acetic acid (MEEA). Examples of α-hydroxy carboxylic acid include lactic acid, gluconic acid and 2-hydroxybutanoic acid. Examples of polycarboxylic acids include ethylenediaminetetraacetic acid (EDTA), tartaric acid and citric acid. In a preferred embodiment, the nanoparticle stabilizer comprises a compound of formula (la) or formula (lb) as described above.

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

In one preferred embodiment, the transition metal containing crystalline cerium dioxide particles are concentrated by diafiltration. Diafiltration techniques use ultrafiltration membranes, which can be used to completely remove, replace or reduce the concentration of salts in the nanoparticle-containing mixture. This method optionally uses a semipermeable (semi-porous) membrane filter to separate components from the reaction mixture based on their molecular size. Thus, suitable ultrafiltration membranes retain most of the nanoparticles formed, while smaller molecules such as salts and water are sufficiently porous to pass through the membrane. In this way, nanoparticles and associated bound stabilizers can be concentrated. The material retained by the filter, including stabilized nanoparticles, is referred to as concentrate or retentate, and the discarded salt and unreacted material are referred to as filtrate.

Pressure may be applied to the mixture to accelerate the rate (flow rate) of small molecules passing through the membrane and to facilitate the concentration process. Other means of increasing the flow rate include using large membranes with large surface areas and increasing the pore size of the membranes, but there should be no unacceptable loss of nanoparticles.

In one embodiment, the membrane is selected such that the average pore size of the membrane is about 30% or less, 20% or less, 10% or even 5% or less of the average diameter of the nanoparticles. However, the pore diameter must be sufficient to allow water and salt molecules to pass through. For example, ammonium nitrate and unreacted cerium nitrate must be completely or partially removed from the reaction mixture. In one preferred embodiment, the average membrane pore size is small enough to retain particles of at least 1.5 nm in diameter in the retentate. This corresponds to a protein size of about 3 kilodaltons.

The concentrate preferably contains stabilized nanoparticles and residual water. In one embodiment, the concentration of cerium dioxide nanoparticles is preferably greater than about 0.5 mole, more preferably greater than about 1.0 mole, even more preferably greater than about 2.0 mole (about 35% solids in the dispersion).

Once the concentrate is formed, most but not all of the water is removed by dialysis with glycol ether. It is placed in a 2 kilodalton dialysis bag with a mixture of diethylene glycol methyl ether and 1-methoxy-2-propanol, and the water is the glycol ether medium while the glycol ether medium replaces the water in the nanoparticle dispersion. Is achieved by exchanging Several exchanges may be necessary (exchange of glycol ether media). Alternatively, the glycol ether mixture can be run with aqueous transition metal containing crystalline cerium dioxide particles through a diafiltration column and solvent migration can be carried out in this way.

Glycol ether surfactants comprising both ether and alcohol groups include compounds of the general formula (Ic):

<Formula Ic>

(Wherein R ³ represents a substituted or unsubstituted alkyl group, m is an integer from 1 to 8).

Other useful surfactants for carrying out solvent transfer include nonylphenyl ethoxylates having the formula C ₉ H ₁₉ C ₆ H ₄ (OCH ₂ CH ₂ ) _n OH, where n is 4 to 6. .

If the transition metal-containing crystalline cerium dioxide particles are still stabilized with the initial stabilizers used for manufacturing in organic media but complexed with glycol ethers, the mixture is a nonpolar medium, such as affinity with most hydrocarbon fuels such as diesel and biodiesel, such as Can be dispersed in kerosene. The surface of the particles is first functionalized with a surfactant such as oleic acid and optionally a cosurfactant such as 1-hexanol prior to addition to the hydrocarbon diluent. The composition of this material is not a reverse micelle water-in-oil emulsion since there is little water present; Rather it is important to recognize that the positive charge on the surface of the cerium nanoparticles is complexed by ether oxygen atoms and conversely bound to the charged carboxylic acid. The carboxylic acid is present in the chemisorbed state and promotes miscibility of the nanoparticles with the nonpolar hydrocarbon diluent. Other surface functionalizing materials such as linoleic acid, stearic acid and palmitic acid can be used in place of oleic acid. Generally preferred materials are carboxylic acids having a length of carbon chain that is less than 20 carbon atoms and more than 8 carbon atoms. Other suitable nonpolar diluents include hydrocarbons having about 8 to 20 carbon atoms, such as octane, nonane, decane and toluene and hydrocarbon fuels such as gasoline, biodiesel and diesel fuel.

For optimum miscibility and stability with nonpolar hydrocarbons, it is desirable to have very little ions present in the cerium dioxide concentrate to conduct electricity. This situation can be achieved by concentrating the nanoparticles via diafiltration to a conductivity level of less than about 5 mS / cm, preferably up to about 3 mS / cm.

Resistivity is the inverse of conductivity, the ability of a material to conduct current. The conductivity device includes two plates disposed on the sample, and applies electrical potential to the plates (typically sinusoidal voltage) and measures the current by measuring the current. The conductivity (G), which is the inverse of the resistivity (R), is determined from the voltage and current values according to Ohm's law, G = 1 / R = I / E, where I is the current in amperes and E is the volt The unit voltage. Since the charge of ions in the solution promotes the conductivity 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 cell geometry affects conductivity values, standardized measurements are presented in non-conductivity units (mS / cm) to compensate for variations in electrode dimensions.

The invention further provides a homogeneous mixture comprising transition metal-containing cerium dioxide nanoparticles, one or more nanoparticle stabilizers, one or more solvent transferred media such as glycol ethers, one or more surfactants and nonpolar diluents or solvents. It relates to a method for compounding. The first step provides an aqueous mixture comprising stabilized cerium dioxide nanoparticles, wherein the molecules of the nanoparticle stabilizer are closely related to the nanoparticles. The second step involves concentrating the stabilized crystalline cerium dioxide nanoparticles while minimizing the ionic strength of the suspension to form an aqueous concentrate that is relatively free of anions and cations. The third step uses a nonionic surfactant to remove the water bound to the nanoparticles. The final step involves combining the solvent transferred concentrate with a nonpolar solvent comprising a surfactant to form a substantially homogeneous mixture that is thermodynamically stable and is a multicomponent, biphasic dispersion.

The substantially homogeneous thermodynamic dispersion preferably comprises a minimum amount of water at a concentration of about 0.5% by weight or less.

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.

Cerium dioxide nanoparticles have a major microcrystal size of about 2.5 nm ± 0.5 nm and preferably include one or at most two microcrystals per particle edge length.

The aqueous mixture is advantageously formed in a colloid mill reactor and the nanoparticle stabilizer may comprise a compound comprising an ionic surfactant, preferably a carboxylic acid group and an ether group. Nanoparticle stabilizers can include surfactants of Formula Ia:

<Formula Ia>

Wherein R represents hydrogen or a substituted or unsubstituted alkyl group or a substituted or unsubstituted aromatic group; R ¹ represents a hydrogen or alkyl group; Y represents H or a counterion; n is 0 to 5. R represents a substituted or unsubstituted alkyl group, R ¹ represents hydrogen, Y represents hydrogen, n is 2.

Another suitable nanoparticle stabilizer includes dicarboxylates of Formula Ib:

<Formula 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 counterion; p is 1 or 2.

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

Concentration of the aqueous mixture is preferably carried out using diafiltration, so that the conductivity of the concentrated aqueous mixture is reduced to about 5 mS / cm or less.

Surfactants used to transfer stabilized transition metal containing crystalline cerium dioxide particles from an aqueous environment to a non-aqueous environment include nonionic surfactants, preferably compounds comprising alcohol groups and ether groups, in particular compounds of formula (Ic) It may be beneficial to:

<Formula Ic>

Wherein R ³ represents a substituted or unsubstituted alkyl group; m is an integer from 1 to 8.

Nonionic surfactants may also include compounds of Formula Id:

<Formula 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).

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

The introduction of such solvent transferred concentrates is facilitated by surfactants that surface functionalize the nanoparticles. Preferred surfactants are carboxylic acids such as oleic acid, linoleic acid, stearic acid and palmitic acid. In general, preferred materials are carboxylic acids having a carbon chain length of less than 20 carbon atoms and more than 3 carbon atoms.

The nonpolar diluent included in the substantially homogeneous dispersion is advantageously selected from hydrocarbons containing about 6 to 20 carbon atoms, for example octane, decane, kerosene, toluene, naphtha, diesel fuel, biodiesel and mixtures thereof. . When used as a fuel additive, one part of the homogeneous dispersion is used with at least 100 parts of fuel.

According to the 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 combined with Zr or Y, more preferably Fe.

It may be advantageous to form a ceramic oxide coating on site on the inner surface of a diesel engine cylinder. Potential benefits of coatings include the additional protection of the engine from thermal stress; For example, CeO ₂ is melted at 2,600 ° C, while cast iron, a common material used in the manufacture of diesel engines, is melted at about 1,200 ° C to 1,450 ° C. Even 5 nm ceria particles exhibit the ability to protect the steel from oxidation for 24 hours at 1,000 ° C., thus size dependent melting phenomenon is expected to lower the melting point of the cerium dioxide nanoparticles of the invention below the combustion temperature encountered in the engine. It doesn't work. See, eg, Patil et al., Journal of Nanoparticle Research , vol. 4, pp 433-438 (2002). The engine thus protected can be operated at higher temperatures and compression ratios, thus producing greater thermodynamic efficiency. Diesel engines whose cylinder walls are coated with cerium dioxide are resistant to further oxidation (CeO ₂ is already fully oxidized), thereby preventing the engine from "rusting". This is because certain additives used to reduce carbon emissions or to improve fuel economy, such as oxygenated MTBE, ethanol and other cetane improvers such as peroxides, also increase corrosion upon entering the combustion chamber, forming rust and This is important because it can lead to deterioration of engine life and performance. The coating should not be too thick to interfere with the 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 of less than about 10 nm, preferably less than about 8 nm, more preferably up to 6 nm, useful as fuel additive for diesel engines. to provide. The surface of the cerium dioxide nanoparticles is modified to promote bonding to the iron particles, and when included in the fuel additive composition it is desirable to quickly form a ceramic oxide coating on the surface of the diesel engine cylinder.

In one embodiment, a transition metal having a binding affinity for iron is incorporated on the surface of the cerium dioxide nanoparticles. Examples of metal surfaces include those present in many internal components of the engine. Examples of suitable transition metals include Mn, Fe, Ni, Cr, W, Co, V, Cu, Zr and Y. Transition metal ions occupying cerium ion lattice sites in the crystal and incorporated into cerium dioxide nanoparticles can be introduced during the final stage of cerium dioxide precipitation. The transition metal ions can be added in combination with the first cerium ions, for example, in a single jet manner in which both the first cerium ion and the transition metal ions are fed together into a reactor comprising ammonium hydroxide. Alternatively, transition and first cerium ions may be added with simultaneous addition of hydroxide ions. The transition metal-containing particles may also be formed by a double jet reaction of dissolved transition metal ions and first cerium ions titrated against ammonium hydroxide vapors introduced simultaneously by a second jet. Importantly, it is understood that sufficient nanoparticle stabilizer is present to interfere with the aggregation of immature particles.

Surfactant / stabilizer combinations may have additional advantages to assist in the process of solvent migration from aqueous polar media to nonpolar oil media. In a combination of charged and uncharged surfactants, charged surfactant compounds play a major role in aqueous environments. However, when solvent migration occurs, the charged compound is solubilized and washed with the aqueous phase, and the uncharged compound becomes more important in stabilizing the reverse Michel emulsion.

Dicarboxylic acids and derivatives thereof, so-called "gemini-type carboxylates" in which carboxyl 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 acids are advantageous stabilizers.

According to the present invention, nanoparticle stabilizer compounds are composed of organic carboxylic acids such as 2- [2- (2-methoxyethoxy) ethoxy] acetic acid (MEEA) and ethylenediaminetetraacetic acid (EDTA), lactic acid, It is preferred to include gluconic acid, tartaric acid, citric acid and mixtures thereof.

Motor oils are used as lubricants in various internal combustion engines in automobiles and other vehicles, boats, lawn mowers, trains, airplanes and the like. Engines often include contacts that run against each other at high speed for long periods of time. This frictional motion causes friction to form temporary welds that prevent the moving parts from moving. Breaking this temporary weld otherwise absorbs the useful power generated by the motor and converts energy into useless heat. Friction also wears on the contact surfaces of these parts, thereby increasing fuel consumption, lowering the efficiency of the motor, and leading to lowering the motor's performance. In one aspect of the invention, the motor oil comprises lubricating oil, transition metal-containing crystalline cerium dioxide nanoparticles having an average diameter of preferably less than about 10 nm, more preferably about 5 nm and optionally surface adsorbed stabilizers. .

Diesel lubricating oil is substantially free of water (preferably less than 300 ppm), but it is preferred that the cerium dioxide can be modified by the addition of a cerium dioxide composition in which solvent transfer from its aqueous environment to an organic or nonpolar environment. The cerium dioxide composition comprises nanoparticles with an average diameter of less than about 10 nm, more preferably about 5 nm, as described above. Diesel engines operated with modified diesel fuel and modified lubricating oil provide greater efficiency, in particular improved fuel economy, reduced engine wear or reduced pollution or a combination of these features.

Metal polishing polish, also referred to as buffing, is a process of smoothing metals and alloys and polishing polishing with a bright smooth mirror finish. Metal polishing varnishes are often used to improve automobiles, motorcycles, antiques and the like. Many medical instruments are polished and polished to prevent contamination from irregularities on the metal surface. Abrasive polishers are also used to polish polish to surface smoothness within a portion of the wavelength of light handled by optical elements such as lenses and mirrors. The smooth, rounded, and uniform cerium dioxide particles of the present invention advantageously can be used as abrasive polishes, and can be used in addition to planarization (smooth the surface at the atomic level) of semiconductor substrates for subsequent processing of integrated circuits. Can be.

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

Example 1

Preparation of Cerium Dioxide Nanoparticles by Single-Jet Addition

To a 3 L round bottom stainless steel reactor vessel was added 1.267 L of distilled water followed by 100 ml of Ce (NO ₃ ) ₃ .6H ₂ O solution (600 gm / L Ce (NO ₃ ) ₃ .6H ₂ O). The solution is clear and has a pH of 4.2 at 20 ° C. 30.5 gm of 2- [2- (2-methoxyethoxy) ethoxy] acetic acid (MEEA) was then added to the vessel. The solution remained clear and the pH at 20 ° C. was 2.8. Lower the high shear mixer, colloid mill made by Silverson Machines, Inc., modified by the peristaltic tube pump to feed the reactants directly into the mixer blade, and lower the mixer head. Is placed slightly above from the bottom of the reactor vessel. The mixer was set at 5,000 rpm and 8.0 gm of 30% H ₂ O ₂ was added to the reactor vessel. Then 16 ml of 28% -30% NH ₄ OH diluted to 40 ml were pumped into the reactor vessel by the mixer head within about 12 seconds. Initially the clear solution turned orange / brown. The high shear mixer was removed and the reactor vessel was transferred to a temperature controlled water jacket where the solution was stirred at 450 rpm using a mixer with R-100 propeller. The pH was 3.9 at 25 ° C. in 3 minutes after NH ₄ OH was pumped into the reactor. The temperature of the reactor vessel was then raised to 70 ° C. over 25 minutes, with a pH of 3.9. The solution temperature was maintained at 70 ° C. for 20 minutes, at which time the solution turned from orange brown to clear dark yellow. pH was 3.6 at 70 ° C. The temperature was then reduced to 25 ° C. over 25 minutes, with a pH of 4.2 at 25 ° C. Particle size analysis by dynamic light scattering revealed a cerium dioxide strength weighted hydrodynamic diameter of 6 nm. The dispersion was then diafiltered at a conductivity of 3 mS / cm and concentrated by nominally 1 mole in CeO ₂ particles by about 10 times.

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

Cerium dioxide particles were analyzed using transmission electron microscopy (TEM). 9 μl solution (0.26 M) was dried on a grid and image processed to produce the image shown in FIG. 1. The particles showed no signs of aggregation even in this dried state. In solution the particles are expected to show a much less tendency for aggregation. The size frequency distribution (shown in FIG. 1) of the cerium dioxide particles measured by transmission electron microscopy (TEM) yielded a geometric diameter of about 2.6 nm. In addition, the size distribution is substantially monomodal, i.e., only one maximum and uniform 19% COV, and most of the particles fall in the 2 nm to 4 nm range.

FIG. 2 shows an X-ray diffraction pattern 70 of a sample of dried cerium dioxide nanoparticles with a control spectrum 71 of cerium dioxide provided by the National Institute of Standards and Technology (NIST) library. The position of the line in the sample spectrum is consistent with that of the standard spectrum. The 2θ peak width is very wide in the sample spectrum, which is consistent with very small primary microcrystal size and particle size. X-ray data (Cu K alpha line at about 8,047 ev) and the Scherrer equation d = 0.9 * λ / δ * cos (θ) [where λ is the X-ray wavelength and δ is the full width at half maximum, θ Is the scattering angle corresponding to the X-ray peak], the primary microcrystal size was calculated to be 2.5 ± 0.5 nm (95% confidence in 5 replicates). Since the particles themselves are sized with such microcrystals, there is only one crystal per particle, so such compositions are referred to as crystalline cerium dioxide in order to distinguish the nanoparticles from all prior art consisting of agglomerates of microcrystals of various sizes. do.

Example 2

About 1.5 nm CeO ₂  Precipitation of Nanoparticles

This precipitation is followed by Example 1, except that a combination of a ratio of 20:80 and a stabilizer of EDTA and lactic acid at 76.4 gm EDTA disodium salt and 85% lactic acid concentration of 74.0 gm is used in place of the MEEA stabilizer. 3A is a high magnification TEM showing grain size that is substantially smaller than 5 nm and is estimated to be 1.1 ± 0.3 nm. 3B shows the electron diffraction pattern of a representative sample of precipitation. FIG. 3C is a table 1 analyzing the intensities of various diffraction rings {311}, {220}, {200} and {111} within a framework of cubic CeO ₂ , cubic and hexagonal Ce ₂ O ₃ and Ce (OH) ₃ . To show. It is evident that the variation ratio of the analyzed ring strength with crystal habits is minimal for the cubic fluorspar structure of CeO ₂ , thereby setting up a polymorph of the polymorph to such grain diameter.

Example 3

Isothermal Double Jet Precipitation CeO ₂ By CeO ₂  Preparation of Nanoparticles

1,117 g of distilled water was added to a 3 L round bottom stainless steel reactor vessel. Lower the standard Rv 100 propeller into the reactor vessel and place the mixer head slightly above from the bottom of the reactor vessel. The mixer is set at 700 rpm and the temperature of the reactor is about 70 ° C. Thereafter, 59.8 g (98%) of methoxyacetic acid were added to the reactor. A 250 ml solution containing 120.0 g of Ce (NO ₃ ) ₃ .6H ₂ O was pumped into the reactor simultaneously with a solution containing 69.5 g (28-30%) of ammonium hydroxide to give a double jet precipitation in 5 minutes. It was carried out over. Distilled water tracing to the reactor removed the reactant line of residual material. 10.2 g of 50% non-stabilized hydrogen peroxide was then added to the reactor and its contents were added over 40 seconds. Initially, the reaction mixture was an opaque dark orange brown liquid at a pH in the range of 6-7. The reaction mixture was heated for an additional 60 minutes, at which time the pH dropped to 4.25 (consistent with the release of hydronium ions through reactions (3a) and (3b)) and the mixture became a clear yellow orange color. The reaction was cooled to 20 ° C. and diafiltered to a conductivity of 3 mS / cm to remove excess water and unreacted material. The dispersion was thus concentrated by about 10 times or nominally 1 mole in CeO ₂ particles. Particle size-frequency analysis by transmission electron microscopy (FIG. 4) revealed that the average particle size was 2.2 nm and the size frequency distribution (one standard deviation divided by the average diameter) with the variation coefficient COV was 23%. Yield theory is 62.9%.

Example 4

Copper-containing CeO ₂  Nanoparticles Ce _{0 .9} Cu _{0 .One} O _{One .95}

The conditions of Example 3 were repeated except that the cerium nitrate solution contained 108.0 g of cerium nitrate hexahydrate and 6.42 g of Ce (NO ₃ ) ₃ .2.5H ₂ O. These metal salts were dissolved separately and then combined to make 250 mL of solution. The reaction proceeded as described in Example 3 except for adding hydrogen peroxide over 40 seconds after the addition of cerium and ammonia. Particle size-frequency analysis by transmission electron microscopy (FIG. 5) revealed a mean frequency distribution with an average particle size of 2.5 nm and a coefficient of variation COV (one standard deviation divided by the average diameter) of 25%. Note that there is no bimodal distribution, the second peak indicates that Cu is not incorporated into the CeO ₂ lattice but instead exists as a separate Cu ₂ O ₃ population.

Example 5

Iron-containing CeO ₂  Nanoparticle Ce _0.9 Fe _0.1 O _1.95 (CeO-255)

The conditions of Example 4 were repeated except that the metal salt solution contained 108.0 g of cerium nitrate hexahydrate and 11.16 g of Fe (NO ₃ ) ₃ .9H ₂ O. These metal salts were dissolved separately and then combined to form a 250 mL solution. The reaction proceeded as described in Example 4. TEM (FIG. 6A) and particle size-frequency analysis (FIG. 6B) of the precipitated particles showed an average particle size of 2.2 ± 0.7 nm and a coefficient of variation COV (one standard deviation divided by the average diameter). It was found to have a size frequency distribution of 32%. Yield theory is 55.1%.

Example 6

Zirconium-containing CeO ₂  Nanoparticle Ce _0.9 Zr _0.15 O ₂ (CeO 257)

The conditions of Example 4 were repeated except that the metal salt solution contained 101.89 g of cerium nitrate hexahydrate and 9.57 g of ZrO (NO ₃ ) ₂ .6H ₂ O. These metal salts were dissolved separately and then combined to form a 250 ml solution. The reaction proceeded as described in Example 4 except that the temperature of the reaction was carried out at 85 ° C. Particle size-frequency analysis by transmission electron microscopy (FIG. 7A) revealed a size frequency distribution with an average particle size of 2.4 ± 0.7 nm and a coefficient of variation COV (one standard deviation divided by average diameter) of 29%. lost. Inductively coupled plasma atomic emission spectroscopy revealed that the stoichiometry of Ce _0.82 Zr _0.18 O _1.91 , which provides the relative insolubility of ZrO ₂ to CeO ₂ , accounts for the improved Zr content (18% vs. 15%).

Example 7a

Zirconium- and Iron-containing CeO ₂  Nanoparticle Ce _0.9 Zr _0.15 Fe _0.1 O _1.95 (CeO-270)

The conditions of Example 4 except the metal salt solution comprises 84.0 g of cerium nitrate hexahydrate, 11.16 g of Fe (NO ₃ ) ₃ .9H ₂ O and 12.76 g of ZrO (NO ₃ ) ₂ .6H ₂ O Was repeated. These metal salts were dissolved separately and then combined to form a 250 ml solution. The reaction proceeded as described in Example 4 except the temperature of the reaction was carried out at 85 ° C. and the hydrogen peroxide solution (50%) was increased to 20.4 gm and added over 10 minutes. Particle size-frequency analysis (FIG. 8B) by particle TEM (FIG. 8A) and transmission electron microscopy showed an average particle size of 2.2 ± 0.6 nm and a coefficient of variation COV (one standard deviation divided by average diameter) of 27%. It was found to have a size frequency distribution. Again, the monodisperse, monomodal distribution supports the concept of co-incorporation as opposed to the separately renucleated ZrO ₂ and Fe ₂ O ₃ grain populations. Yield theory is 78%. Inductively coupled plasma atomic emission spectroscopy revealed a stoichiometry of Ce _0.69 Fe _0.14 Zr _0.17 O _1.915 . Again, relatively more concentrated Fe and Zr compared to the nominal amount reflect the greater insolubility of the hydroxide precursors for cerium hydroxide. 8C also shows the X-ray powder diffraction pattern (upper curve) of this sample as compared to CeO ₂ without transition metal. The lack of peak at 32 ° 2θ (indicated by arrow) means that free ZrO ₂ is absent, ie it has all been incorporated into the cerium lattice. In addition, the lack of peaks at 50 and 52 ° 2θ indicates that there is no separate population of Fe ₂ O ₃ (ie incorporation of Fe into the cerium lattice). A smaller ionic radius of Fe ³⁺ (0.78 mm 3) and a lattice- (nλ / 2d = sin θ) corresponding to Zr ⁴⁺ (0.84 mm 3) for the substituted Ce ⁴⁺ (0.97 mm 3) Note the shift from the large 2θ scattering angle to the larger 2θ. Thus, it can be concluded that the transition metal has been incorporated into the CeO ₂ lattice and does not represent a separate population of neat ZrO ₂ or Fe ₂ O ₃ nanoparticles. The single-mode size-frequency distribution also supports this conclusion.

Example 7b-f

Zirconium- and iron-containing CeO which systematically changes the amount of iron in 15% zirconium (15%, 20%, 25%, 30%) and 20% zirconium in 20% iron ₂  Nanoparticles

The conditions of Example 7a are as follows, but the appropriate nominal stoichiometry is calculated by adjusting the amount of iron or zirconium using an appropriate metal containing salt solution, and reducing the total cerium nitrate hexahydrate to increase the iron or zirconium transition metal. The concentration was planned.

9 shows the field emission total TEM grid image of the particles produced in Example 1. FIG. Circles are shown to clearly show two of the particles. Note that the number of lattice planes defining a single crystal with a diameter of less than 5 nm is small. An aqueous sol of various materials was heated at 1,000 ° C. in a muffle furnace for 30 minutes. Such thoroughly dried samples are described in Sarkas et al., "Nanocrystalline Mixed Metal Oxides-Novel Oxygen Storage Materials," Mat. Res. Soc. Symp. Proc. Vol. 788, L4.8.1 (2004), using OSC and thermogravimetric techniques to measure the kinetics reaching its maximum OSC. Typically, a very fast initial reduction rate in nitrogen gas containing 5% hydrogen was followed by a slower second rate.

Table 2 below shows the oxygen storage capacity for reduction of various lattice engineered ceria nanoparticles (2 nm except Sigma Aldrich control) in nitrogen gas at 5 ° C. containing 5% H ₂ ( 1 sigma reproducibility) and fast (kl) and slow (k2) rate constants (in parentheses are 1 standard deviation). These values were compared and checked for a second TGA instrument (mean 2.6% difference) against gas flow difference (mean 1% deviation) and sample preparation was repeated for 30 minutes at 1,000 ° C. (mean 1.54% deviation). From the description of Table 2 below, it can be seen that the OSC of the cerium dioxide particles does not appear to have size dependency in the range of about 2 nm-20 μm. This will be the result of sintering to larger particles. Note that OSC is increased approximately 50% with the addition of zirconium, with a 10-fold rate increase. In addition, the addition of iron to the Zr-containing material provides nearly three times the OSC at a rate of ten times that of cerium dioxide particles that do not contain transition metal ions. This value is greater than three times that of the cited literature. The beneficial effect of citric acid on this reduction rate constant appears to suggest that even after the stabilizer is pyrolyzed, it can affect particle surface area or morphology.

TABLE 2

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

Claims (47)

(a) a first cerium ion source, at least one transition metal ion (M) source, a hydroxide ion source, at least one nanoparticle stabilizer, and an oxidant at an initial temperature ranging from about 20 ° C. to about 95 ° C. Providing an aqueous reaction mixture;
(b) mechanically shearing the mixture and allowing it to pass through a perforated screen to form a homogeneously distributed suspension of cerium hydroxide nanoparticles; And
(c) providing transitional metal-containing cerium dioxide nanoparticles Ce _{1 - x} M _x O ₂ , wherein “x” is from about 0.3 to about 37 to provide temperature conditions effective to oxidize the first cerium ion to a second cerium ion. Having a value of about 0.8), wherein the nanoparticles have a crystalline cubic fluorspar structure, with an average hydrodynamic diameter in the range of about 1 nm to about 10 nm, and a geometric diameter of about 1 nm to In the range of about 4 nm
A method of making a lattice engineered crystalline cerium dioxide nanoparticles comprising at least one transition metal (M) comprising a. The method of claim 1, wherein the mechanical shearing is performed in a colloid mill. The method of claim 1, wherein the temperature condition effective to oxidize the first cerium ion to the second cerium ion comprises a temperature of about 50 ° C. to about 100 ° C. 7. The method of claim 3, wherein the temperature condition effective to oxidize the first cerium ion to the second cerium ion comprises a temperature of about 60 ° C. to about 90 ° C. 5. The method of claim 1, wherein the ion source is introduced into the reaction mixture simultaneously or sequentially in the mechanical shear. The method of claim 1, wherein the mean hydrodynamic diameter of the cerium dioxide nanoparticles is about 6 nm. The method of claim 1, wherein the mean geometric (TEM) diameter of the cerium dioxide nanoparticles is less than about 4 nm. The method of claim 1, wherein the cerium dioxide nanoparticles have a substantially monomodal size distribution and a substantially simple distributed size frequency distribution. The method of claim 1, wherein the cerium dioxide nanoparticles are crystalline and have a microcrystalline size in a range from about 1.1 nm to about 2.5 nm ± 0.5 nm. The method of claim 1, wherein the first cerium ion source comprises cerium nitrate. The method of claim 1, wherein the transition metal-containing cerium dioxide nanoparticles Ce _1-x M _x O ₂ The transition metal M is Fe, Mn, Cr, Ni, W, Co, V, Cu, Zr, Y, Mo and combinations thereof. The method of claim 11, wherein the value of “x” is from about 0.30 to about 0.80. The method of claim 12 wherein the value of “x” is from about 0.40 to about 0.60. 12. The method of claim 11, wherein the transition metal M comprises Zr or optionally Y. The method of claim 14, wherein the transition metal M further comprises Fe. The method of claim 1, wherein the hydroxide ion source comprises ammonium hydroxide and the molar stoichiometric ratio of the hydroxide ions to the first cerium ion is from about 2: 1 OH: Ce to about 5: 1 OH: Ce. The method of claim 1, wherein the oxidant comprises hydrogen peroxide or molecular oxygen. The method of claim 1, wherein the nanoparticle stabilizer is selected from the group consisting of alkoxy substituted carboxylic acids, α-hydroxycarboxylic acids, α-ketocarboxylic acids, and combinations thereof. The method of claim 1, wherein the nanoparticle stabilizer is selected from the group consisting of di-, tri-, tetra-carboxylic acids and combinations thereof. The method of claim 1, wherein the nanoparticle stabilizer is selected from the group consisting of 2- [2- (2-methoxyethoxy) ethoxy] acetic acid, methoxyacetic acid, and combinations thereof. The method of claim 1, wherein the nanoparticle stabilizer is selected from the group consisting of ethylenediaminetetraacetic acid, gluconic acid, lactic acid, tartaric acid, pyruvic acid, citric acid, and combinations thereof. The method of claim 21, wherein said nanoparticle stabilizer is citric acid. The method of claim 8, wherein the substantially monomodal and monodisperse size frequency distribution is adjustable by variables selected from the group consisting of nucleation temperature, nanoparticle stabilizer selection, nanoparticle stabilizer concentration, and combinations thereof. The method of claim 1, wherein the method is a continuous process or a batch process. The method of claim 1,
(d) concentrating the product stream to a suspension whose density does not exceed about 35% (solid weight / suspension weight) and whose conductivity does not exceed about 5 mS / cm. The method of claim 25, wherein the concentration of the product stream is carried out using one or more semipermeable membranes. (a) Stabilized transition metal doped cerium dioxide nanoparticles Ce _1-x M _x O ₂ having a cubic fluorspar structure and having an average hydrodynamic diameter in the range of about 1 nm to about 10 nm and a geometric diameter of less than about 4 nm. Providing an aqueous mixture comprising;
(b) concentrating the aqueous mixture comprising the stabilized transition metal-containing cerium dioxide nanoparticles to form an aqueous concentrate;
(c) removing substantially all of the water from the aqueous concentrate to form a substantially water-free concentrate of the stabilized transition metal-containing cerium dioxide nanoparticles;
(d) adding an organic diluent to the substantially water free concentrate to form an organic concentrate of the stabilized transition metal-containing cerium dioxide nanoparticles; And
(e) mixing the organic concentrate with a surfactant in the presence of a nonpolar medium to form a homogeneous dispersion comprising stabilized transition metal-containing crystalline cerium dioxide nanoparticles Ce _{1 - x} M _x O ₂ .
A method of forming a homogeneous dispersion comprising stabilized lattice engineered transition metal-containing crystalline cerium dioxide nanoparticles Ce _{1 - x} M _x O ₂ . The method of claim 27, wherein the transition metal M in the transition metal-containing cerium dioxide nanoparticles Ce _1-x M _x O ₂ is Fe, Mn, Cr, Ni, W, Co, V, Cu, Zr, Y, Mo and combinations thereof. The method of claim 28, wherein the value of “x” is from about 0.30 to about 0.80. The method of claim 29, wherein the value of “x” is from about 0.40 to about 0.60. 29. The method of claim 28, wherein the transition metal M comprises Zr or Y. 32. The method of claim 31, wherein the transition metal M further comprises Fe. The method of claim 27, wherein said organic diluent comprises a glycol ether. The method of claim 27, wherein the organic diluent further comprises an alcohol. The method of claim 27, wherein the organic diluent comprises diethylene glycol monomethyl ether and 1-methoxy-2-propanol. The method of claim 27, wherein the surfactant further comprises a cosurfactant. The method of claim 27, wherein the surfactant comprises oleic acid. 37. The method of claim 36, wherein said cosurfactant comprises 1-hexanol. The method of claim 27, wherein the surfactant does not comprise sulfur. The method of claim 27, wherein the homogeneous dispersion comprises the nanoparticles at a concentration of at least about 2% by weight and water at a maximum concentration of about 0.5% by weight. 41. The method of claim 40, wherein said homogeneous dispersion comprises said nanoparticles in a concentration of at least about 9% by weight. The method of claim 41, wherein the homogeneous dispersion comprises the nanoparticles at a concentration of about 35% by weight. The method of claim 27, wherein the nonpolar medium comprises a hydrocarbon containing about 6 to about 20 carbon atoms. The method of claim 27, wherein the nonpolar medium is selected from the group consisting of octane, decane, toluene, kerosene, naphtha, ultra low sulfur diesel fuel, biodiesel and mixtures thereof. The method of claim 27,
(f) diluting 1 part of said homogeneous dispersion to at least about 100 parts of hydrocarbon fuel. A washcoat for a catalytic converter of an internal combustion engine exhaust device, produced using a homogeneous dispersion containing a stabilized transition metal-containing crystalline cerium dioxide nanoparticle formed according to claim 27. A catalyst effective for accelerating a reduction or oxidation reaction produced using a homogeneous dispersion containing a stabilized transition metal-containing crystalline cerium dioxide nanoparticle formed according to claim 27.

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