Nano-structured particles with high thermal stability

[0001] The present invention relates to the field of nanostructured particles.

Background of the Invention [0002] The two most important parameters during the development of the catalyst are the particle size that contain the catalytic material and the thermal stability of these particles. Particle size is important because it relates to surface area, and increasing surface area can increase performance; larger surface areas will provide more places where the catalytic material can contact the catalysed substance. Thermal stability is important because for many catalytic reactions for higher yields, high temperature processes are required or preferred, and for the catalyst to be effective it must be stable at these temperatures.

[0003] Unfortunately, known technologies for developing particles used as catalysts are not capable of producing particles that have both sufficiently high surface area to mass ratios and sufficiently high thermal stability. For example, porous and mesoporous zirconia products with desirable surface area to mass ratios were used in the catalysis. However, according to current technologies, the very porous structure of these products means that these particles have less than optimal, high temperature processing efficiency. According to other known methods, product particles with high thermal stability can be produced, but these particles have unacceptable surface area to mass ratios.

[0004] Thus, there is a need to develop compositions comprising thermally stable nanoparticles that have high surface area to mass ratios. The present invention provides a solution.

Summary of the Invention [0005] The present invention relates to products of nanostructured particles that have a high specific surface area, which relates to the surface area to mass ratio, as well as high thermal stability. More specifically, the present invention relates to nanostructured metal oxide particle products that have the above-mentioned features.

[0006] In one aspect, the present invention provides a composition consisting of nanostructured metal oxide particles and at least one stabilizing agent, wherein said nanostructured metal oxide particles retain a surface area to weight ratio greater than or equal to 50 m²/ g, consist of basic particles in the size range from 5 nm to 50 nm and are mesoporous, having a pore size distribution between 2 nm and 30 nm, after said composition has been subjected to a heat treatment at a temperature of at least 600 ° C for at least 6 hours, in which the metal oxide in said nanostructured metal oxide particles is titanium oxide or zirconia and in which the stabilizing agent is selected from the group consisting of silicate, phosphate and aluminum phosphate.

[0007] In another aspect, the invention provides a catalyst consisting of the above composition and at least one active ingredient selected from the group consisting of sulfates, vanadates, molybdates, tungstates, alumina, silica, metal oxides, metal salts and metals.

In yet another aspect, the invention provides a method of making a composition consisting of nanostructured metal oxide particles, said method comprising the aging process of nanoparticle precursors comprising at least one oxide selected from the group consisting of zirconium oxide and titanium oxide in a liquid suspension containing ammonia or water-soluble organic bases with a pKa of about 9 or higher, at a temperature greater than or equal to 60 ° C while maintaining a pH greater than or equal to pH 7 and in the presence of at least one stabilizing agent selected from the group consisting of silicate, phosphate and aluminum phosphate.

[0009] Preferred embodiments of the invention are set out in the dependent claims.

[0010] The high surface area and high thermal stability of the particle products of the present invention makes the products useful as, for example, catalysts, catalyst supports, adsorbents and membrane separation materials. They are particularly useful for applications where high temperature operations are preferred or necessary. These applications include DeNOx catalysts, car catalysts and chemical catalysts for high temperature reactions.

[0011] For a better understanding of the present invention, together with other and further embodiments, reference is made to the following description in connection with examples, the scope of which is set out in the appended claims.

Brief description of the drawings [0012]

Figure 1 shows a comparison of the thermal stability of nanostructured zirconia particles, where BET surface area values ​​are plotted versus calcining temperatures.

Figure 2 shows the pore size distribution curves of nanostructured zirconia particles. All samples were calcined under the same conditions, 800 ° C for 6 hours. Figures 3A and 3B show TEM (transmission electron microscopy) images of nanostructured zirconia particles. Figure 3A shows the particles of comparative example 1. Figure 3B shows the particles of example 3. Both particle samples were calcined at 800 ° C for 6 hours. The figures show differences in the morphology and structure of the molecule. Figure 3C also shows the image of the particles of Comparative Example 1 which was taken at a larger magnification than the image in Figure 3A. Figure 3D shows the particles of example 6. Both particle samples were calcined at 800 ° C for 6 hours and show differences in individual crystallites.

Figure 4 is an X-ray powder diffraction pattern of the following products: (A) example 9, calcined at 700 ° C, showing a typical monoclinical phase model; (B) example. 1, calcined at 800 ° C, showing mainly a tetragonal phase model with a small amount of monoclinic phase; and (C) example 2, calcined at 800 ° C showing a typical phase model for the metastable tetragonal phase.

Figure 5 is a graph of the BET surface area value as a function of the transition temperature from tetragonal to monoclinic, derived from differential thermal analysis. The almost straight-line relationship indicates that the thermal stability of nanostructured particles is determined by the stability of the metastable tetragonal phase.

Detailed description [0013] It is not intended that the present disclosure be a scientific dissertation on nanoparticles. Readers are referred to relevant available texts and other materials in the field for additional information on the basics.

Definitions [0014] Certain terms and terms used in the present disclosure are defined as follows, unless otherwise specified.

[0015] The term "range of mesopores sizes" refers to sizes in the range of 50 nm measured by the BET method.

[0016] The term "nanoparticles" refers to particles that have an overall size in the nanoscale range of 1 - 100 nm.

[0017] The term "nanoscale" refers to a substance that at least in one dimension is in the size range of 1 - 100 nm.

[0018] The term "nanostructured particles" refers to particles that consist of one or more subunits (major particles or crystallites according to the present invention) that have a size of 1-100 nm.

[0019] The term "base particle" and the term "crystallite" refers to the smallest discrete units of substance particles in nanostructured particles that bind to each other through aggregation, surface charge, or other forces acting between particles. For example, "base particle" and "crystallite" may refer to a molecule or an assembly of connected elements or molecules such as inorganic metal hydroxides.

Preferred Embodiments [0020] According to the present invention, it is possible to make compositions that contain nanostructured particles that have large surface areas and high thermal stability.

[0021] According to a first embodiment, the present invention provides a composition consisting of nanostructured metal oxide particles that have a surface area greater than or equal to 50 m²/ g and are thermally stable at a temperature of at least 600 ° C. Preferably, the surface area to mass ratio is between 50 m²/ ga 200 m²/ g, more preferably between 70 m²/ ga 150 m²/ G. The surface area is determined by N2 BET adsorption technology, which is well known to the average specialist in the field.

[0022] Nanostructured particles whose total size may be relatively large (up to the micrometer range) and whose shape is mainly spherical, consist of basic particles of nanometric size (crystallites) which are chemically and / or physically connected to each other. The base particles have a size range of 5 to 50 nanometers, and the base particles are produced in such a way that the pore size distribution is in the range of 2 - 30 nm. Nanostructured particles formed by base particles have unique and characteristic mesoporous structures with a large specific surface area and a narrow pore size distribution.

[0023] As noted above, the mesoporous particle structure is thermally stable at a temperature of at least 600 ° C and potentially up to about 1000 ° C, depending on the nature of the metal oxides contained and depending on whether stabilizing agents have been used, as described below.

[0024] The thermal stability of the nanostructured particles according to the present invention refers to the resistance of the structure and porosity of the particles to heating at a given temperature. Stability is measured by given specific surface area values ​​and pore size distribution that the particles retain after treatment. For certain metal oxides, the transformation of the crystalline phases occurs in a temperature range of 500 ° C to 1000 ° C. In these cases, the thermal stability of nanostructured particles can also be quantified by the transition temperature at which the desired crystalline phase (metastable tetragonal phase in the case of zirconia and the anatase phase in the case of titanium oxide) is transformed into a less desirable phase or into a "high-temperature phase" (monoclinic zirconia phase and rutile phase titanium oxide). Thus, the higher the transformation temperature, the greater the thermal stability of the product.

[0025] Thermal stability is also illustrated by the ratio of surface area to mass. The higher the surface area to mass ratio, the higher the thermal stability that the product has when calcining at the desired temperature for a desired period of time. As indicated above, the particle surface area of ​​the present invention refers to the BET specific surface area.

[0026] For example, according to the first embodiment of the present invention, when the composition is thermally stable at 600 ° C, the structure of nanostructured particles will not break down and accordingly the specific surface area of ​​the composition will not be significantly reduced after treatment or application at this temperature or any temperature lower than this. A decrease in specific surface area of ​​at least 10% or more will be considered significant. It should be taken into account that the combined effect of heating on the particles can make them unstable at a certain temperature only after being held at that temperature for a certain amount of time. As used herein, unless otherwise specified, the thermal stability of nanostructured particles refers to stability measured by subjecting them to a specific temperature for at least six hours, for example during calcining. Thus, the composition is described as being thermally stable at this temperature only if it does not disintegrate in any measurable degree and accordingly its specific surface area does not decrease significantly when exposed to these conditions.

[0027] According to an embodiment, the present invention provides a composition consisting of nanostructured zirconia particles in which said nanostructured zirconia particles have a surface area greater than or equal to about 60 m²/ g and are thermally stable at a temperature of at least 600 ° C, more preferably at least 800 ° C. Preferably, the nanostructured zirconia particles have a surface area greater than or equal to about 70 m²/ G.

[0028] In the compositions of the present embodiment, the nanostructured zirconia particles are formed by basic particles of nanometric size in such a way that a large amount of the surface of the basic particles is available, for example, for adsorbed, isolated, catalyzed substances, etc. In the size range of mesopores, in principle, the entire surface measured using BET technology should be available.

[0029] In addition, the particle structure is held firmly together and remains largely intact even during high temperature processing. The base particles can be held together, for example mainly by chemical bonds, which are formed during heat treatment and the interaction of surface charges between the particles. This unique thermal stability of nanostructures is the result of stabilized surfaces of the base particles that form nanostructured particles, and can be obtained, for example, by aging treatment as described below.

[0030] In addition, nanostructured zirconia particles are porous agglomerates consisting of nano-sized primary particles that have interstitial pores (spaces between the primary particles) in the mesopores size range, 5 to 50 nm, with a pore size distribution between 2 and 30 nm , more preferably between 2 and 20, concentrated at about 10 nanometers.

[0031] As described in more detail below, the compositions comprise a stabilizer or stabilizing agent.

[0032] The present invention provides a method of making a composition consisting of nanoparticles. This method involves the process of aging nanoparticle precursors in a liquid suspension at a temperature higher or equal to 60 ° C while maintaining a pH greater than or equal to pH 7. A "nanoparticle precursor" is a substance that can be processed to produce nanoparticles. Thus, it is a substance that can be converted to metal oxide or which is already a metal oxide that can be processed to produce the composition of the invention.

[0033] The precursors undergo aging for a time that allows the formation of a thermally stable product with the desired surface area. The duration of this "extended period" of aging is partly dependent on the temperature at which the aging process takes place. For example, at higher temperatures, a shorter "extended period" is needed. In addition, a longer aging process may be desirable if greater thermal stability is desired and / or particles with a high surface area to mass ratio are desired. In some embodiments, the method is carried out for a period of between 10 hours and 100 hours. In some preferred embodiments, at least one and more preferably all of the following conditions exist: the aging process is carried out at a temperature of at least 80 ° C; the aging process is carried out for at least 24 hours; and the pH is greater than or equal to pH 9.

[0034] By subjecting the particles to aging at the right temperature, for the right time and under the right conditions, it is possible to produce compositions with high thermal stability that retain high specific surface areas even after high temperature treatments. It is postulated that the aging process makes the surfaces of the particles more inert to heat treatment, and thus the aggressive growth of particles during heat treatment can be prevented or reduced. This allows higher surface area to mass ratios. Surface inertness also reduces the likelihood of removing pores during heat treatment, even at very high temperatures.

[0035] During the aging process, the pH of the suspension is usually reduced due to the continuation of the hydrolysis reaction, which consumes hydroxyl groups, or due to evaporation of basic molecules such as NH3, or for both reasons. An additional base can be added if necessary to maintain the pH in the desired range.

[0036] The method of this embodiment can be used to produce products with a large surface area of ​​metal oxides, mixed metal oxides and complex metal oxides. These products contain zirconium oxide or titanium oxide.

[0037] When the product contains zirconia, the nanoparticle precursors preferably form a colloidal, aqueous zirconia deposit. Furthermore, preferably the colloidal aqueous zirconia precipitate is formed by combining a zirconium salt solution and a base solution at pH 7 or above. The zirconium salt solution may contain, for example, at least one substance selected from the group consisting of zirconium chloride, zirconium oxychloride, zirconium oxynitrate, zirconium sulfate, zirconium sulfate and zirconium oxycarbonate.

[0038] Hydrolyzable organic zirconium compounds, such as zirconium alkoxides, may also be used as precursor materials. Similar salt products and alkoxides can be used as precursor materials for other metal oxides including, but not limited to, titanium oxide or cerium oxide. Examples of precursor materials for titanium and cerium oxide include, but are not limited to, titanium oxychloride, titanium oxosulfate, titanium isopropoxide, cerium (III) nitrate, ammonium cerium (IV) nitrate and ammonium cerium (IV) sulfate.

[0039] Ammonia and any water-soluble organic bases with pKa at about 9 or higher can be used to form the precipitate. Organic bases include, but are not limited to, methylamine (pKa = 10.657), ethylamine (pKa = 10.807), diethylamine (pKa = 10.489), ethylenediamine (pKa1 = 10.712), n-butylamine (pKa = 10.77), piperidine (pKa = 11,123), n-hexylamine (pKa = 10,56) and cyclohexylamine (pKa = 10,66). Urea can also be used, although it is not itself a strong organic base, because when heated, the urea molecules break down to form ammonia. Ammonia and organic bases are preferred compared to inorganic bases such as sodium hydroxide, potassium hydroxide. e.t.c. Ammonia and organic bases can be easily removed during the calcining step, whereas if inorganic metal hydroxides were used, if sufficient residue was left after washing as would be the case with inorganic bases such as sodium hydroxide and potassium hydroxide, sintering of particles would be promoted. As a result, with inorganic bases such as sodium hydroxide and potassium hydroxide, nanostructure stability would be reduced and surface area values ​​would be lower.

[0040] Although without intending to be bound by theory, it is postulated that the above-mentioned useful bases act not only as Bronsted bases, providing OH groups^- for the precipitation of salts as hydroxide or aqueous oxide (for example, they can provide OH groups^- during the precipitation of zirconium salts as zirconium hydroxide or as aqueous zirconia) but also as Lewis bases that can replace water or hydroxyl groups on the surface of precipitated particles. The latter function is believed to be the driving force that makes ammonia and organic bases effective in increasing the thermal stability of the particles of the present invention, compared to inorganic alkali metal hydroxides.

[0041] Precipitation can be carried out by any method that is currently known or is beginning to be known, and by the method of reading this disclosure when one of ordinary skill in the art considers that it would be beneficial to use it in connection with the present invention. For example, precipitation can be carried out using the "double stream" method "double-jet" method), which refers to the simultaneous addition of salt solutions, for example a zirconium salt solution and a base solution, to the reactor under constant agitation, with a controlled flow rate of the base solution so that a constant pH can be maintained during precipitation (typically pH equal to or greater than 9). It can also be carried out by means of a single stream process that involves adding a salt solution to a suitable amount of a base solution or adding a base solution to a suitable amount of a salt solution in the reactor while constantly stirring. Precipitation can be stopped when the desired pH is reached or more base can be added if necessary to keep the pellet at the desired level before the precipitation is completed. The desired pH may be referred to as "final pH".

[0042] In addition, the method may further comprise: (a) sludge recovery; (b) drying the precipitate to produce dry particles; and (c) calcining the dry particles to produce calcined particles.

[0043] The recovery step may be carried out, for example by filtration, decanting or centrifugation. After recovery, the sludge will usually be washed with a solvent suitable to remove unwanted parts. For example, water may be used as the solvent.

[0044] The drying step may be carried out, for example, by placing a deposit in an oven. Preferably, this occurs after the washing step. Alternatively, the washed sludge can be resuspended at the desired concentration and spray dried.

[0045] The calcining step may be carried out at the desired temperature. The nanostructured zirconia particles of the present invention may be preferably calcined at a temperature of at least 600 ° C, more preferably at least 700 ° C, and most preferably at least 800 ° C for further processing and measuring the thermal stability of the particles. In addition, preferably the calcining step is carried out for at least six hours. The calcined particles may themselves be the desired nanostructured particles themselves, or may be further processed to produce nanoparticles with the desired properties. Further processing after the calcining step may include, for example, milling of the calcinated particles. Milling is a technique well known to those skilled in the art and can be used to obtain particles of the desired size.

[0046] Prior to the aging process, the deposits are amorphous. However, after aging, especially after an aging time of 24 hours or more, the material acquires some crystallinity. High resolution TEM imaging (transmission electron microscopy) reveals that after aging, when the nanoparticles are based on zirconia, material subjected to sufficient aging may contain crystallites of about 2-5 nanometers in size. The edges of the lattice of individual crystallites corresponding to certain crystallographic additions are clearly observed. Due to the very small size, XRD (X-ray diffraction) powder diffraction patterns only show very wide lines.

[0047] After the calcining step, the material is transformed into highly crystalline, porous aggregates of nanostructured particles that have a crystallite size of about 550 nm. In addition, the pore size distributions are concentrated preferably at about 230 nm.

[0048] According to a particularly preferred embodiment, the present invention provides a method for producing a composition consisting of nanoparticles, said method comprising: (a) combining a zirconium salt solution and a base solution, said zirconium salt solution comprising a compound selected from the group consisting of chloride zirconium, zirconium oxychloride, zirconium oxynitrate, zirconium sulfate, zirconium sulfate and oxygen zirconium carbonate; (b) precipitation of a colloidal aqueous zirconia deposit; (c) subjecting said sludge to aging at a temperature greater than or equal to 60 ° C while maintaining a pH greater than or equal to pH 7; (d) recovering said precipitate by filtration or centrifugation; (e) drying said precipitate to produce dry particles; and (f) calcining said dry particles to produce calcined particles. These calcined particles can be either nanoparticles that are used in the desired applications or can be further processed to produce nanoparticles with any desired properties. Further processing may include, for example, milling of calcined particles.

[0049] As in the previous embodiment, according to this embodiment, preferably the method is carried out under at least one and preferably under all of the following conditions: the aging process is carried out at a temperature of at least 80 ° C; the aging process is carried out for at least 24 hours; and the pH is greater than or equal to pH 9.

[0050] For zirconia based nanoparticles, after calcining, the material becomes highly crystalline nanostructured particles with a crystallite size of about 5-50 nm (Figure 3). Measurements with powder XRD reveal that the nanostructured particles are mainly in the tetragonal phase, although a small amount of monoclinical phase is also observed when a stabilizing agent is used as described below, the amount of stabilizing agent is small, or the processing time is not long enough (Figure

4). Nanostructured particles formed after calcination are porous aggregates of nanometer-sized crystallites. Both crystallites and pores inside the particle are rather uniform in size. As noted above, the pores are usually in the range of mesopores and the pore size distribution is about 2 to 30 nanometers (Figure 2).

[0051] The present invention provides nanostructured products whose surfaces have been stabilized by a stabilizer. The stabilizer gives increased thermal stability to nanoparticles. The stabilizer is selected from the group consisting of silica, alumina, aluminum phosphate.

[0052] Preferably, the effective stabilizing agent is negatively charged under alkaline conditions and has high binding power to the zirconia surface or other oxide surface to which it is to be connected. For example, silica may become soluble under strongly basic conditions or at high temperatures, forming negatively charged silicate moieties. Presumably, these moieties can effectively replace H2O and OH- groups on the oxide surface and reduce surface activity, and thus stabilize nanoparticles and prevent their rapid growth. Stabilizing moieties on the zirconia surface can also inhibit or delay the nucleation of the monoclinic phase during calcining and, as a result, increase the temperature of the phase transition of the tetragonal phase into the monoclinic phase, and thus increase the thermal stability of nanostructured particles. When the nanostructured particles contain zirconia, the stabilizer is preferably selected such that the phase transition temperature is 600 ° C or more.

[0053] The effectiveness of some stabilizing agents against the thermal stability of nanostructured zirconia particles is summarized in Figure 1. As can be seen, aluminum silicate, phosphate and phosphate are high efficiency stabilizing agents. The BET surface area values ​​of the samples stabilized by these agents are in the range of about 80 m²/ g to as large as 140 m²/ g after calcining them at 800 ° C for 6 hours.

[0054] The proposed mechanism for stabilizing nanostructured zirconia particles involves modifying the surface of nanoparticles by a stabilizing agent to increase inertness to intermolecular condensation and reduce particle growth during calcining at high temperatures. This can be proved by comparing the size of the crystallites shown in the TEM images (Figure 3). As can be seen from the images in Figure 3, the size of the crystallites in the comparative example (image A and C) is about 50 nm, while the size of the crystallites from the examples with stabilizers is about 10 times smaller and is about 5 nm. Another aspect of the stabilizing effect is based on the fact that the stabilizing agent can effectively delay the phase transition between the metastable tetragonal phase and the monoclinic phase. Figure 5 shows the correlation of the BET surface area value of samples calcined under the same conditions (800 ° C for 6 hours) but prepared using different stabilizing agents as a function of the transition temperatures of the tetragonal to monoclinic phase derived from the respective maximum exotherms on their thermal differential analysis curves (DTA). The near-linear relationship clearly shows that thermal stability and surface area values ​​are frequent nanostructured are closely related to the stability of the metastable tetragonal phase. Higher phase transition temperature correlates with higher thermal particle stability and higher surface area values. Therefore, the phase transition temperature can be used to quantitatively measure the thermal stability of the products of nanostructured zirconia particles. In addition, the phase transition temperature may exhibit the effectiveness of the stabilizing agent.

[0055] The production of thermally stable nanostructured particles according to this embodiment can be carried out in the following steps: (a) combining the precursor solution and the base solution; (b) precipitation of colloidal aqueous oxide by mixing the precursor solution with a base solution with a final pH of 7 or above, preferably 9 or above; (c) treating the sludge in the presence of at least one surface stabilizing agent at a temperature of 60 ° C or higher, preferably 80 ° C or higher, with a pH of the aging process of the precipitate at 7 or above constantly controlled with a base solution, preferably at 9 or above, for a period of about 10 hours or longer; (d) isolating the particles after treatment by filtration or centrifugation and washing, and producing mainly spherical particles by means of spray drying; and (e) calcining at the desired temperature, typically 600 ° C to 1000 ° C, for 6 hours or more.

[0056] Alternatively, the above step (c) may be carried out using a sealed pressure reactor. In this case, the precipitated nanoparticle precursors are processed under virtually hydrothermal conditions. Due to the use of higher pressure in addition to the elevated temperature, the processing time can be significantly reduced. The preferred hydrothermal treatment time is 2 to 12 hours and the treatment temperature is 80 ° to 150 ° C. Higher processing temperatures and longer processing times are not preferred because under hydrothermal conditions the crystals grow much faster than under ambient pressure; high temperature and long processing time can produce overgrown crystals with low surface area values. The advantage of hydrothermal treatment in a sealed pressure reactor is that no additional base is needed, while this is necessary for the normal aging process described above.

[0057] The above production step (c) is particularly advantageous for particles to increase thermal stability. As noted above, high thermal stability indicates the desired crystalline phase and indicates that high surface area values ​​are maintained even after high temperature calcination. This can be demonstrated by the fact that the specific surface area values ​​of the particles are changed drastically by the treatment conditions in step (c), such as the addition of a stabilizing agent (see data in Table 1 and curves in Figure 1), its concentration as in the case of mol% SiO2 vs. 10 mol% SiO2 (Table 1 and Figure 1), and other processing conditions (e.g., hydrothermal treatment produces more stable products than aging at ambient pressure as shown by the data in Table 1 and Figure 1).

[0058] Generally speaking, the production method according to this embodiment can be used to produce products with a large surface area of ​​zirconia, as well as TiO2, mixed metal oxides such as ZrO2 / TiO2. The large surface area and high thermal stability of the particle products make them useful as catalysts, catalyst supports, adsorbents, membrane separation materials, etc., especially for applications where high temperature operations are necessary. These applications include DeNOx catalysis, autocatalysis and chemical catalysis for high temperature reactions.

[0059] Particularly favorable properties of the large surface area and high thermal stability of nanostructured particles produced in accordance with this embodiment are believed to result from the presence of basic particles at the nanoscale, whose surfaces are stabilized by stabilizing agents and from the unique, obtained mesoporous structure of the particle products. Each of the particles is formed by basic particles of nanometric size in such a way that a large amount of the surface area of ​​the primary particles is still available, while the structure of the particles is strongly held together and remains largely intact even during high temperature processing.

[0060] As noted above, according to this embodiment, the obtained sludge is treated at 60 ° C or above, preferably at 80 ° C to reflux temperature (about 102 ° C), for a period of about 10 hours to several days. Higher processing temperatures will speed up the machining process. In addition, under hydrothermal conditions, the processing time can be reduced, because both temperature and pressure assist in the treatment process. In addition, if it is first necessary to dissolve the stabilizing agent during the treatment process, for example SiO2, AlPO4, etc., the time required for complete dissolution should be considered when determining the treatment time. Typically, dissolution is a slower process than the binding of dissolved individuals to the oxide surface, which is why the first of these determines the treatment time. In practice, the optimal machining time can be determined by routine experimental research, which includes changing the machining time and monitoring changes in surface area. The optimal machining time is the period of time during which the maximum surface area is achieved. Thus, the additional treatment does not further increase the surface area.

[0061] For example, in an open reactor system at 80 ° C and with 5 mol% fumed silica as a stabilizer, nanostructured particles are completely stabilized after treatment for about 10 hours. Typically, during treatment, the pH of the slurry decreases due to the continuation of the hydrolysis reaction, which consumes hydroxyl groups, dissolution of a stabilizing agent (e.g. silica) and / or evaporation of base molecules such as NH3. An additional base is added to the system when it is necessary to maintain the system pH at 7 or above, preferably 9 or above. Under hydrothermal conditions, the treatment time can be reduced to 2-3 hours and no additional base is needed.

[0062] After treatment, the products can be isolated and washed by filtration or centrifugation. Washed products are usually spray dried and then calcined at 700 ° C or higher for about 6 hours. The optimal calcination time can be determined by performing many calcination tests over various periods of time. However, the inventors have found that after 6 hours of calcining, the specific surface area value is substantially stabilized.

[0063] Spray drying is preferred to control particle geometry and total particle size. Spray drying produces particles of micrometer sizes with highly spherical geometry. However, it seems that checking the total particle size and geometry does not change the thermal stability and surface value of the nanostructured particles. Both oven dried and spray dried particles show similar thermal stability and surface area.

[0064] As noted above, a method of producing zirconia-based particles with high thermal stability can be used to produce other metal oxide products with high thermal stability. Examples include, but are not limited to, hafnium dioxide, titanium oxide, tin oxide, cerium dioxide, niobium oxide and tantalum oxide, mixed oxides of these types of metals, and complex oxides. Nanostructured zirconia products with high thermal stability have great potential for use as catalysts, catalyst supports and support materials, adsorbents, porous membranes for separation or filtration, etc., especially for those applications where high temperature operations are necessary or advantageous under in terms of performance, efficiency, etc.

[0065] Carriers or carrier materials may be further treated with active ingredients by depositing active ingredients on their surfaces. Examples of active ingredients include, but are not limited to, sulfates, vanadates, molybdates, tungstates, silica, alumina and other metal oxides, metal salts and metals. Methods for combining active ingredients with a catalytic substance are well known to those of ordinary skill in the art.

[0066] The compositions described above and compositions prepared according to the methods described above can be used to prepare catalysts for the removal of commercially generated toxic substances. These poisonous substances include, but are not limited to, substances that are produced during the operation of cars and power plants. Therefore, the present invention can be used in automotive equipment and power plants as well as other applications where the use of catalysts is desired.

[0067] After a detailed description of the invention, examples will now be given. These examples are not intended and should not be interpreted in any way as limiting the scope of the claims. Although the invention can be readily understood by reference to the following examples, they are provided for the purpose of illustration and are not intended to limit the present invention, unless otherwise specified.

Examples

Example 1 [0068] 1000 ml of 0.8 mol / l zirconium chloride solution prepared by dissolving the crystalline powder ZrOCl ^ 6H₂O in deionized water was introduced into a 3 liter double wall reactor containing 1000 g 20 wt. ammonia solution. The reactor was equipped with a programmable heat-circulating bath, a pH regulator with a pH electrode, an upper stirrer and liquid pumps, if necessary. Delivery was completed in 60 minutes (about 16.7 ml / min) with vigorous stirring and at a constant temperature of 30 ° C. The pH decreased from pH 11.2 ammonia solution before providing the zirconium solution to about pH 9.6 after precipitation of the zirconium. After precipitation, fumed SiO2 fumed silica (5 mol% zirconia) was added and the temperature increased to 85 ° C. After constant stirring, the pellet was aged at approximately 85 ° C for 48 hours with a controlled pH at or above 9.0 by automatic pumping into an ammonia solution, while the liquid pump was controlled by a pH regulator. Then, the aging pellet was filtered and washed several times with deionized water until the conductivity of the filtrate was less than 1 mS / cm. The washed material was suspended and spray dried. Portions of the sample were calcined at 700 ° C, 800 ° C and 900 ° C, respectively, for 6 hours. The BET surface area values ​​are summarized in Table 1.

Example 2 [0069] The precipitation of zirconium oxychloride was the same as that of Example 1. However, 10 mol% of fumed SiO2 colloidal silica was added prior to aging. Portions of the samples were also calcined at 700 ° C, 800 ° C and 900 ° C, respectively, for 6 hours. The BET surface area results are given in Table 1.

Example 3 [0070] The method of precipitation of zirconium oxychloride and the percentage of silica used were the same as for Example 2. However, before aging the sediment pH was adjusted to 11, and the aging process was carried out in a sealed, mixed pressure reactor at 90 ° C for 12 hours. No base added during the hydrothermal aging process. The product was processed in the same manner and calcined at 700 ° C, 800 ° C and 900 ° C in small portions as described above. The BET results are given in Table 1.

Example 4 [0071] The precipitation of zirconium oxychloride and the percentage of silica used were the same as for Example 1. However, tetraethylorthosilicate (TEOS) was used as the silicate precursor. TEOS hydrolyzes in water under basic conditions to form single or oligomeric silicate moieties. The aging process and finishing processes used were the same as for Example 1. Portions of the sample were also calcined at 700 ° C, 800 ° C and 900 ° C for 6 hours, respectively. The BET surface area results are given in Table 1.

Example 5 [0072] The precipitation of zirconium oxychloride was the same as for Example 1. However, 5 mol% aluminum phosphate (AIPO4) was added before aging at elevated temperature. The aging process and finishing processes were carried out in the same manner as for Example 1. Portions of the sample were calcined at 600 ° C, 700 ° C, 800 ° C and 900 ° C for 6 hours. BET surface area data are given in Table 1.

Example 6 [0073] Zirconium oxychloride precipitation and stabilizing agent (5 mol% AIPO4) were the same as for Example 5. However, the aging process was carried out under hydrothermal conditions as for Example 3, i.e. at 90 ° C for 12 hours and no addition no additional rule during hydrothermal treatment. Portions of the sample were also calcined at 600 ° C, 700 ° C, 800 ° C and 900 ° C, respectively. BET surface area data are given in the Table

1.

Example 7 [0074] Zirconium oxychloride precipitation was carried out in the same manner as for Example 1. However, 10 mol% ammonium hydrogen phosphate ((NH4) 2HPOa) was used as the stabilizing agent and added before aging. The aging and finishing processes were carried out in the same manner as for Example 1. Again, aliquots of the sample were calcined at 600 ° C, 700 ° C, 800 ° C and 900 ° C, respectively. BET surface area data are given in Table 1.

Example 8 (references) [0075] Zirconia oxychloride precipitation was carried out in the same manner as for

Example 1. However, 5 mol% (by weight) of ammonium para-tungstate ((NH₄)₁₀IN₁₂ABOUT₄₁^ 5H₂O) and was added before the aging process. The aging process and finishing processes were the same as for Example 1. Portions of the sample were calcined at 500 ° C, 600 ° C, 700 ° C and 800 ° C for 6 hours, respectively. BET surface area data are given in Table 1.

Example 9 (comparative) [0076] Zirconia oxychloride precipitation was carried out in the same manner as for Example 1. The pellet was aged at elevated temperature under the same conditions as for Example 1. However, no stabilizing agent was added prior to aging treatment. Since the chloride salt was used as the zirconia precursor and ammonia was used as the base for precipitation, ammonium chloride can be considered a stabilizing agent. After aging treatment, the sample was finished by washing and drying. Portions of the sample were calcined at 500 ° C, 600 ° C, 700 ° C, 800 ° C and 900 ° C respectively for 6 hours. BET surface area data are given in Table 1.

Comparative Example 1 [0077] Zirconium oxychloride precipitation was carried out in the same manner as for Example 1. However, the precipitate was not aged and no stabilizing agent was added. The product was finished by washing and drying. Portions of the sample were calcined at 600 ° C, 700 ° C, 800 ° C and 900 ° C, respectively, for 6 hours. BET surface area data are given in Table 1.

Table 1

<td colspan="7">BET surface area values ​​in m2²/ G.</td>

<td colspan="2">All samples calcined at the given temperature for 6 hours</td><td></td><td></td><td></td><td></td><td></td>

<td></td><td>Stabilizer</td><td>500 ° C</td><td>600 ° C</td><td>700 ° C</td><td>800 ° C</td><td>900 ° C</td>

<td>Comparative Example 1</td><td>without stabilizer / without aging</td><td> --</td><td> 49,8</td><td> 20,3</td><td> 14,2</td><td> 8,4</td>

<td>Comparative Example 9</td><td>without stabilizer / with aging</td><td> 76,5</td><td> 60,5</td><td> 44,9</td><td> 36,4</td><td> 24,9</td>

<td>Example 1</td><td>5 mol% colloidal SiO2 fumed / with aging</td><td> --</td><td> --</td><td> 96,6</td><td> 77,5</td><td> 44,7</td>

<td>Example 2</td><td>10 mol% matte colloidal SiO2 / with aging</td><td> --</td><td> --</td><td> 126,8</td><td> 96,1</td><td> 61,9</td>

<td>Example 3</td><td>10 mol% matte colloidal SiO2, with aging under conditions hydrothermal</td><td> --</td><td> --</td><td> 156,2</td><td> 139,5</td><td> 108,4</td>

<td>Example 4</td><td>5 mol% TEOS * / with aging</td><td> --</td><td> --</td><td> 96,3</td><td> 71,1</td><td> 45,9</td>

<td>Example 5</td><td>5 mol% AIPO4 / with aging</td><td> --</td><td> 136,2</td><td> 103,2</td><td> 82,9</td><td> 59,0</td>

<td>Example 6</td><td>5 mol% AIPO4, with aging in hydrothermal conditions</td><td> --</td><td> 199,8</td><td> 144,0</td><td> 128,8</td><td> 104,0</td>

<td>Example 7</td><td>10 mol% (NH4) 2HPO4 / with aging</td><td> --</td><td> 147,2</td><td> 121,8</td><td> 100,8</td><td> 57,0</td>

<td>Reference example 8</td><td>20 mol% (as WO₃) APT **</td><td> 117,6</td><td> 90,7</td><td> 73,8</td><td> 58,2</td><td> --</td>

<td colspan="7">* TEOS means tetraethoxysilane; ** APT stands for ammonium paratungstate. No value specified at temperature means that the specified sample was not calcined at that temperature.</td>

[0078] The review of the data in Table 1 shows that the aging process only increases the BET surface area and that the addition of a stabilizer in combination further increases the BET surface area. In addition, increasing the stabilizer concentration further increases the BET surface area.