JP2009061383A - Heat resistant alumina carrier and method for producing the same - Google Patents

Abstract

An alumina carrier having a sufficient surface area even at a high temperature of 1200 ° C. or higher and excellent in heat resistance and a method for producing the same are provided.
A transferable alumina having a purity of 99.9% or more is impregnated with an appropriate amount of lanthanum relative to aluminum, and a LaAlO ₃ phase of 100 nanometers or less coexists.
[Selection] Figure 1

Description

The present invention relates to a carrier used for an automobile exhaust purification catalyst or a combustion catalyst.

As a catalyst for combustion gas treatment and automobile exhaust gas treatment, a catalyst in which a transition metal, a metal oxide or a composite metal composition is supported on a carrier is used. Among the performance required as a carrier for these catalysts, it is important to carry the catalyst components in a highly dispersed manner in order to effectively use the catalyst components such as noble metals. It is desired that the surface area of the carrier is large and that it is high even if it is heat-treated with a high-temperature gas, and that the carrier itself is required to have thermal stability even if it is exposed to a high temperature for a long time. In order to satisfy these requirements, transferable alumina having a low surface area and a high surface area is used. However, as is well known, when this transitional alumina is exposed to a high temperature of 1000 ° C. or higher, it undergoes a transition to the alpha (α) -alumina form and the surface area is significantly reduced. When a transitional alumina is used as a catalyst carrier in a pellet or other shaped product coated bear, the structural change due to the transition to α-alumina may cause mechanical deterioration or detachment of the coating layer or catalyst component sintering. Causes to promote. Conventionally, it is known to add an alkaline earth element or a rare earth element as a method for improving the thermal stability such as preventing the surface area of the transitional alumina from being reduced (Patent Documents 1 to 3). However, it is difficult to obtain sufficient heat resistance by adding conventional alkaline earth element or rare earth element oxide powder as a support for a catalyst exposed to a high temperature of 1000 ° C. or more like a recent automobile catalyst. is there. Among the rare earth elements, 99.95% purity alumina is used as a heat-resistant support in a system to which lanthanum is added, and a specific surface area of 60 m ² / g after heating at 1200 ° C. for 5 hours has been developed (Patent Document 4). However, since it is used in large quantities, the cost of high-purity alumina becomes a problem. Furthermore, combustion catalysts for gas turbines require heat resistance at about 1300 ° C., and the fact is that the heat resistance cannot be maintained with simple transitional alumina alone. Another problem is that it is difficult to mix particle components on an alumina support at the nanometer level. That is, even if alumina as a carrier and a carrier having different properties are mixed to bring about various carrier effects, alumina itself is fine, so other particles cannot be mixed to the inside. For example, perovskite-type composite oxides have excellent catalytic activity and have been pointed out as advantageous as a heat-resistant carrier (Patent Document 5), but the carrier mixed at the nanometer level is unknown.
JP 54-117387 A JP-A-48-14600 USP4021185 Japanese Patent Publication No. 5-21030 Patent 2620624

The present invention intends to solve the above-mentioned problems of the prior art, and is an alumina carrier having a sufficient surface area even at a high temperature of 1200 ° C. or higher and having excellent heat resistance, and a LaAlO ₃ phase having a particle size of 100 nanometers or less. It is intended to provide a highly functional carrier that coexists with the above and a method for producing the same. LaAlO ₃ with a particle size of 100 nanometers or less, impregnated with 1 to 8% of the lanthanum fraction of aluminum in transitional alumina that retains high temperature performance and has a purity of 99.9% or more other than lanthanum. The specific surface area after coexisting phases and heating at 1200 ° C. for 3 hours is at least 60 m ² / g. Further, transitional alumina is impregnated with 3 to 8% of lanthanum to aluminum, coexisting with a LaAlO ₃ phase having a particle size of 100 nanometers or less, and a specific surface area of at least 20 m ² after heating at 1300 ° C. for 3 hours. It is characterized by / g. A support in which alumina and a perovskite complex oxide LaAlO ₃ component are mixed at the nanometer level is a novel alumina support that has not achieved its form control technology.

The present invention is based on the discovery of a unique tissue state found as a result of earnest research in order to control solid reaction between alumina and lanthanum and impart heat resistance. The alumina of the present invention is obtained by impregnating transitional alumina having a purity of 99.9% or more with 1 to 10% of lanthanum in atomic percent relative to aluminum, and has a surface area of at least 60 m ² / g after heating at 1200 ° C. for 3 hours. It is a heat-resistant alumina carrier that is characterized by a certain characteristic, and is particularly a composite carrier in which a LaAlO ₃ phase having a particle diameter of 100 nanometers or less coexists in a dispersed manner. Furthermore, it is a heat-resistant alumina support characterized by having a specific surface area of at least 20 m ² / g after heating at 1300 ° C. for 3 hours, and also specifically disperses a LaAlO ₃ phase having a particle size of 100 nanometers or less The present invention provides a composite carrier that coexists with the above. In the present invention, the purity of the transitional alumina does not require a special high-purity state, but it needs to be 99.9% or more, and if this is the case, the effect of impregnation with lanthanum becomes remarkable, and LaAlO ₃ fine particles are generated. It occurs quickly and does not form coarse particles. Examples of the transferable alumina include alumina having phases such as gamma (γ), delta (δ), eta (η), key (χ), theta (θ), and kappa (κ). Or use 2 or more. However, gamma, delta, and theta type alumina are most desirable among the above transitional aluminas. Further, the so-called particle size of these transitional aluminas is preferably fine particles of 0.5 μm or less. In addition to commercially available products of alumina, a product obtained by inducing a water-soluble aluminum solution with aluminum nitrate, aluminum halide, aluminum sulfate, an organoaluminum compound, etc., coprecipitating from the solution, and then heat-treating it may be used. Further, lanthanum is impregnated with the above transferable alumina, and the impregnation of this lanthanum suppresses the transferable alumina from being transferred to α-alumina even at a high temperature to reduce its surface area, and LaAlO ₃ Of fine particles are dispersedly included. As described above, when the purity of the transferable alumina is 99.9% or more, the above effect is promoted. In addition, it is difficult to achieve the above-mentioned heat resistance effect by simply adding lanthanum to the above-mentioned transitional alumina containing many impurities. The amount of the lanthanum impregnated into the transferable alumina needs to be in the range of 0.3 to 10% with respect to the alumina. Desirably, it is 1 to 8% at 1200 ° C and 3 to 8% at 1300 ° C depending on the heat resistance index temperature. If the impregnation amount of lanthanum is less than 0.3%, it seems that the LaAlO ₃ phase is not formed, but it cannot be determined because the dispersion amount is small. If it exceeds 10%, a large amount of lanthanum that is not sorbed by the alumina reacts with the alumina, and a large amount of complex oxide such as LaA1O ₃ or LaA ₁₁ O ₁₉ forms coarse particle aggregates or grows grains. It causes the surface area to rise. Further, the superior effect of impregnation with lanthanum is that the impregnation amount is in the range of 1 to 8% after heat treatment at 1200 ° C. The carrier according to the invention has a surface area of at least 60 m ² / g after heating at 1200 ° C. for 3 hours. Furthermore, in the state where the LaAlO ₃ phase coexists, a composite in which LaAlO ₃ particles have a particle size of 100 nanometers or less and generally 50 nanometers or less is formed. After heating at 1300 ° C for 3 hours, impregnation with 3 to 8% lanthanum to aluminum and LaAlO ₃ phase with a particle size of 100 nanometers or less should coexist and the specific surface area should be at least 20m ² / g A heat-resistant alumina support is provided. This heating is a test condition performed for specifying the properties of the carrier of the present invention and is not a production condition, but does not conflict with the production condition and should not be excluded. As a method for producing the carrier according to the present invention, there is a method using an impregnation method. As this method, for example, an aqueous solution containing lanthanum such as lanthanum nitrate is used, with a water absorption of 40 to 80% as a guide, soaking the transferable alumina in the aqueous solution, stirring sufficiently, drying, and then temporarily It is something to be baked. The calcination is preferably performed at a temperature not higher than the transition temperature of the alumina and not lower than the reaction start temperature, more preferably not lower than 750 ° C. in order to sorb the lanthanum uniformly in the alumina and generate fine particles of LaAlO _3. It should be fired in air at 1100 ° C. or lower and a holding time of about 1 to 10 hours. A detailed experiment was carried out by changing the heat treatment temperature from 600 ° C to 1300 ° C for the solid phase reaction, and the LaAlO ₃ phase began to form at 750 ° C. The amount increased with the increase of the heat treatment temperature and peaked at 1100 ° C. Although it decreased, a considerable amount remained even at 1200 ° C. The size of the particles was estimated from observation with an electron microscope and was found not to exceed 100 nanometers at most. In general, such a reaction causes a sintering phenomenon and lowers heat resistance. However, in the alumina support of the present invention, LaAlO ₃ particles are dispersed in the alumina secondary particles and have a good effect on the heat resistance. ing. In other words, it absorbs excess lanthanum as a stable substance in advance and is itself a nanometer-sized fine particle equivalent to alumina particles. It plays the role of stopping further solid-phase reaction, and forms the most stable structure in the composite structure. ing. Furthermore, at a high temperature of 1300 ° C., these LaAlO ₃ prevent densification due to sintering of alumina and maintain a high surface area. In the production method of the present invention, the impregnation operation requires a more careful operation than usual. In other words, it is necessary to grasp the water absorption amount with sufficient accuracy in advance under each condition so that lanthanum is adsorbed to alumina very uniformly. Although it is considered that there is currently no index for measuring the homogeneity of lanthanum adsorption during impregnation, the formation of dispersed LaAlO ₃ fine particles of the present invention was rather a result of the homogeneous adsorption, leading to the present invention. This is the result of a microstructure controlled manufacturing method brought about by numerous experiments and operational precision. Therefore, although the material is specified in the resulting form and surface area of the alumina support, the manufacturing conditions are specified as claims from the results of the solid-phase reaction investigation on the assumption that the lanthanum adsorption operation is performed homogeneously. In the present invention, the shape, form, and structure of the carrier using this include a granular body, a pellet-like body, a porous body, and a honeycomb structure. The carrier formed by impregnating or adhering lanthanum with the transferable alumina according to the present invention may be coated on the surface of a molded body made of ceramics or a porous metal body as a substrate. However, since the body of the present invention can be used as an assembly of an automobile exhaust purification catalyst, a combustion catalyst, etc., and is particularly excellent in heat resistance, it is exposed to a high temperature of 1000 ° C. or higher or used in a high temperature. Useful as a carrier.

The carrier of the present invention is excellent in heat resistance without deterioration even when used at a high temperature of 1000 ° C. or higher. Lanthanum is added to the transitional alumina, and the purity of the transitional alumina is high, and since the pre-reacted LaAlO ₃ is present in fine particles, further solid reaction and sintering are prevented. . Even at high temperatures, the initial state of carrier preparation is easily maintained, and the form of a fine particle composite of transitional alumina and LaAlO ₃ is maintained, and the surface area is unlikely to decrease. Furthermore, the unique catalytic activity of perovskite type LaAlO ₃ can be utilized.

Examples of the present invention will be described below, but the present invention is not limited thereto.

Transposable alumina (γ-alumina) having a purity of 99.9% or more was impregnated with an aqueous solution of lanthanum nitrate (La (NO ₃ ) ₃ · 6H ₂ O). The amount of lanthanum was adjusted to a ratio of 0, 0.3, 1.5, 3, 5, 7.5, and 10 mol% by the above-mentioned ratio of alumina to lanthanum (lanthanum / aluminum). Further, the impregnation was performed by immersing the above-mentioned alumina in an aqueous solution of lanthanum nitrate so that the entire amount was soaked in the alumina in consideration of the water absorption rate of alumina being 60%. Transposable alumina was impregnated with an aqueous lanthanum nitrate solution, dried, and then calcined in the atmosphere at 1000 ° C. for 3 hours to obtain a carrier. This was further heat-treated at 1200 ° C and 1300 ° C for 3 hours each. Table 1 shows the specific surface area of this carrier measured from nitrogen adsorption at 77K. In addition, Table 2 shows the product phase examined by powder X-ray diffraction.

As is apparent from Tables 1 and 2, transitional alumina and LaAlO ₃ coexist at 1 to 8% at 1200 ° C. and the specific surface area is 60 m ² / g or more. Also, at 1300 ° C, when impregnating with 3 to 8% lanthanum to aluminum, the LaAlO ₃ phase coexists and the specific surface area after heating at 1300 ° C for 5 hours is at least 20 m ² / g It becomes a functional alumina carrier.
In order to examine the generated particles of LaAlO ₃ , observation with an electron microscope was performed. FIGS. 1 and 2 show a photograph of the alumina produced at 1000 ° C. when the amount of lanthanum to aluminum is 5 mol%. White spots indicating the presence of heavy elements were observed in the backscattered electron image. According to the powder X-ray diffraction method, the phase other than alumina was only LaAlO ₃ . Furthermore, when examined with a transmission electron microscope, a fine LaAlO ₃ crystal of about 20 nm (nm is nanometer) was detected by electron diffraction. These particles are formed in alumina particles and dispersed in an extremely fine state of about 20 nm without aggregation. Such an alumina carrier is achieved for the first time by the provision of the carrier according to the present invention, and has been made possible by the production method of the present invention. FIGS. 3 and 4 show photographs when heat treatment is performed at 1200 ° C. with alumina when the amount of lanthanum relative to aluminum is 5 mol%. Similarly, white spots indicating the presence of heavy elements were observed in the backscattered electron image with a size of 50 nm or less. The specific surface area was 60 m ² / g. Further, after heat treatment at 1300 ° C., particles having a diameter of 100 nm or less were observed by a similar microscopic observation of a sample having 20 m ² / g. From the results of these Examples, it is clear that the heat-resistant carrier of the present invention is a novel composite material having a high specific surface area and a unique composite in which LaAlO ₃ fine particles are dispersed in alumina.

  The heat-resistant alumina carrier and the production method thereof of the present invention can be used in the fields of high-temperature exhaust gas purification and combustion purification.

Photo of the lanthanum aluminum content of 5 mol% when made with alumina at 1000 ° C (electron microscope image (secondary electron image) of 5 mol% lanthanum-containing alumina support heat-treated at 1000 ° C for 3 hours) Photo of the lanthanum with respect to aluminum when it is made at 1000 ° C with alumina when the amount is 5 mol% (reflected electron of electron microscope of 5 mol% lanthanum-containing alumina carrier heat-treated at 1000 ° C for 3 hours taken in the same field of view image) Photo of the lanthanum-aluminum with 5 mol% of alumina produced at 1200 ° C. (electron microscope image (secondary electron image) of 5 mol% lanthanum-containing alumina support heat-treated at 1200 ° C. for 3 hours) Photo of the lanthanum with respect to aluminum when it was made at 1200 ° C with alumina (reflected electron of electron microscope of 5 mol% lanthanum-containing alumina carrier heat-treated at 1200 ° C for 3 hours taken in the same field of view as Fig. 3 image)

Claims (3)

Transposed alumina with a purity of 99.9% or more is impregnated with 1 to 8% of the lanthanum fraction of aluminum, and LaAlO ₃ phase with particle size of 100 nanometers or less coexists, after heating at 1200 ° C for 3 hours A heat-resistant alumina support characterized in that the specific surface area of at least 60 m ² / g. Transposed alumina with a purity of 99.9% or more is impregnated with 3 to 8% of lanthanum to aluminum, and LaAlO ₃ phase with particle size of 100 nanometers or less coexists, after heating at 1300 ° C for 3 hours A heat-resistant alumina support characterized in that the specific surface area of at least 20 m ² / g. Claims in which a transitional alumina having a purity of 99.9% or more is impregnated at a fraction of lanthanum to aluminum and then heat-treated at 750 ° C to 1200 ° C for 1 hour or longer to coexist with a LaAlO ₃ phase having a particle size of 100 nanometers or less. A method for producing 1 or 2 heat-resistant alumina support.