JPS6111666B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a catalyst carrier, specifically a catalyst carrier having excellent heat resistance,
The present invention relates to a ceramic catalyst carrier that exhibits little deterioration in catalyst performance even at high temperatures and has high thermal shock resistance. In general, a catalyst supported on a ceramic carrier is usually deposited on the surface of a high-strength ceramic carrier body such as cordierite, mullite, or silicon silicide in an amount of several percent by weight (based on the carrier body).
The catalyst is coated with activated alumina and the active catalyst component is supported on it. There are various properties required of a catalyst carrier, but one of the important conditions for a catalyst carrier used at high temperatures is excellent heat resistance. Various types of ceramics having high heat resistance are used as the catalyst carrier body.
However, for example, automobile exhaust gas purification catalysts
Due to vehicle driving conditions, engine malfunctions, etc., high concentrations of carbon monoxide (CO) and hydrocarbons (HC) are emitted, and it is not uncommon for the catalyst temperature to exceed 1200°C. If exposed to high temperatures,
Although the support body has heat resistance, the active alumina coating phase on the surface undergoes sintering and recrystallization, resulting in a significant decrease in the specific surface area, and the catalyst active component is Particularly in the case of activated alumina coatings, diffusion phenomena from the activated alumina coating phase into the internal support body often occur, causing a deterioration of the activity. The present invention has improved the above-mentioned drawbacks, and is a catalyst carrier having an activated alumina coating phase on the surface of a ceramic catalyst carrier body, and (1) the weight of the activated alumina coating phase is 10 to 10% of the weight of the carrier body. 25%, (2) the water absorption rate of the entire carrier is 12% by weight or more, and (3) the content of Mg, Al, Fe, Mo, W, and Th is 0.1% by weight or more in terms of metal amount based on the entire carrier. A catalyst carrier characterized in that one or more compounds or metals (hereinafter collectively referred to as sintering inhibitors) are substantially uniformly contained at least in the activated alumina coating phase. be. The reason why the amount of active alumina coating is set to 10 to 25% by weight is that if it is less than 10% by weight, the active alumina content is small, so the supporting ability of the catalytic active component is insufficient, and the supporting layer spreads to the carrier body, resulting in the surface This is because the concentration becomes low and sufficient catalytic activity is not achieved.Furthermore, if the catalyst is used for a long time at high temperatures, the catalytic active components will diffuse into the interior of the carrier body, further reducing the concentration of the catalytic components on the carrier surface. The reason for this is that the activity will increase and the activity will continue to decline. As the active alumina content increases, the catalytic active components will be more firmly supported on the surface of the active alumina phase, and as a result, the concentration of the catalytic components on the surface of the carrier will increase, and of course, the initial high performance can be exhibited. The dense activated alumina phase prevents the active components of the catalyst from diffusing inside at high temperatures, making it possible to maintain high performance for a long period of time. However, the amount of activated alumina coating
If it exceeds 25% by weight, the activity will not be further improved, and the manufacturing process will become complicated, and the thermal shock resistance will deteriorate, so the upper limit should be kept at 25% by weight. Also, the water absorption rate of the entire carrier after activated alumina coating (according to the measurement method specified in JIS R2205)
The reason why it is set at 12% by weight or more is because if it is less than 12%, the porosity of the carrier itself will be too low, resulting in poor thermal shock resistance during rapid heating and cooling, and cracks will easily occur in the carrier. In addition, if the sintering inhibitor is contained at least almost uniformly in the activated alumina phase, the amount of the sintering inhibitor is 0.1 in terms of the amount of metal relative to the weight of the entire carrier.
Although the effect is recognized starting from 2% by weight, no particular increase in the effect is observed even when the amount exceeds 2% by weight. The reason why the catalyst carrier of the present invention as described above has higher heat resistance is that by applying an appropriate amount of activated alumina coating to the ceramic carrier body, the active catalytic component is firmly supported near the surface of the carrier, which allows it to withstand high temperatures. It is thought that this is because the fine particles of the sintering inhibitor present at the grain boundaries of the activated alumina particles prevent the sintering and recrystallization of the activated alumina. An example of the method for manufacturing the catalyst carrier of the present invention is as follows. A ceramic carrier body such as cordierite, mullite, or silica silicon is mixed into a liquid composition containing activated alumina or its precursor (hereinafter referred to as alumina sol), for example, Japanese Patent Application No. 138896/1989 "Liquid Composition". Immersion in the described alumina sol under reduced pressure. Next, the carrier body impregnated with alumina sol was taken out from the alumina sol, the excess sol was removed by blowing air, and after drying at 100 to 150℃,
Bake at ~900°C for 5-1 hour. This operation is repeated as many times as necessary so that the water absorption rate of the entire carrier after coating with activated alumina is 12% by weight or more, and the amount of activated alumina coating is 10 to 25% by weight of the weight of the carrier body. The method of containing the sintering inhibitor is that it is easy to contain it almost uniformly at least in the activated alumina coating phase, and that it is easy to process.
A method of impregnating a carrier having an activated alumina coating phase with an aqueous solution of a water-soluble compound as a sintering inhibitor is recommended because of its low cost. That is, the carrier having the activated alumina coating phase is immersed in a solution containing an appropriate amount of these sintering inhibitors, the removed carrier is blown with air to remove excess solution, dried at 100 to 150°C, and then heated to 500 to 900°C. Bake for 5 to 1 hour. In addition, there is also a method in which an appropriate amount of an anti-sintering agent is added to the alumina sol in the form of a solution or fine powder. Next, examples will be shown. Example 1 Commercially available cordierite honeycomb carrier body (76φ
18 test pieces of 20 ^L x 20 ^W x 30 ^H were cut out from the sample (20 L x 20 ^W x 30 H) and immersed in alumina sol under reduced pressure. Regarding the manufacturing method of this alumina sol, 15 parts of Condeia's alumina SC (boehmite) powder of 325 mesh or less (average particle size 30μ) is gradually added to 85 parts of a 0.4 N acetic acid aqueous solution with vigorous stirring. After adding the entire amount, continue stirring for another 20 minutes to thoroughly mix the boehmite and acetic acid solution, and store this mixture in a constant temperature room at 25°C until no boehmite particles are visible to the naked eye (approximately 42°C).
A colloidal alumina sol with a viscosity of 110 cp was prepared by curing (time) and is detailed in Japanese Patent Application No. 138896/1989 entitled "Liquid Composition." Next, the carrier taken out from the alumina sol is blown with air to remove excess sol, dried at 150°C, and then fired at 700°C for 3 hours. By repeating this operation as many times as necessary, three honeycomb carriers each having active alumina coating phases of approximately 5, 10, 15, 20, 25, and 30% by weight (based on the carrier body) were obtained. Next, each of these carriers was mixed with an aqueous magnesium chloride solution (MgCl ₂ .
579g/, 700g/, 840g/, as 6H ₂ O
1050g/, 1400g/, and 1867g/), the removed carrier was blown with air to remove excess solution, dried at 150°C, and then calcined at 700°C for 3 hours. % was included. Next, these supports were impregnated with a Pd impregnating solution of an aqueous palladium chloride hydrochloride solution containing 3.4 g of Pd and 13.6 g of azodicarbonamide (disclosed in Japanese Patent Application No. 1983-9553, "Impregnating Solution Used in the Production of Catalysts for Gas Conversion"). After impregnation with Pd using a 60-70% impregnating solution
Perform wet reduction by immersing in a 3% by weight sodium formate aqueous solution for 30 minutes, washing with water, drying at 150°C, and then heating to 700°C.
The honeycomb catalyst was fired for 3 hours to obtain a honeycomb catalyst in which 3 g/Pd was supported on each honeycomb carrier. 700 each of these catalysts
The oxidation rates of carbon monoxide (CO) and hydrocarbons (HC) were measured using samples heat-treated at 1000°C, 1000°C, and 1200°C for 48 hours. The results are shown in Table 1. The conditions for measuring these oxidation rates are as follows.

【table】

[Table] Example 2 A test piece of cordierite honeycomb carrier body of the same type and size as that used in Example 1 (20 ^L
×20 ^W ×30 ^H ) 18 pieces were coated with 20% by weight of activated alumina in the same manner as shown in Example 1, and then divided into 6 groups of 3 pieces each, and the appropriate concentration was adjusted for each of 5 groups. Five kinds of magnesium chloride solutions (53g/as MgCl ₂ 6H ₂ O,
263g/, 525g/, 1050g/ and 1575g/
) and in exactly the same manner as shown in Example 1 to produce honeycomb carriers impregnated with 0, 0.1, 0.5, 1.0, 2.0, and 3.0% by weight in terms of Mg. subsequent
The Pd loading operation was carried out in exactly the same manner as in Example 1.
A honeycomb catalyst on which Pd was supported was prepared, and the oxidation rate of CO and HC was measured in the same manner as shown in Example 1. The results are shown in Table 2. Example 3 An aqueous solution of ferrous chloride, aluminum chloride, ammonium molybdate, ammonium tungstate, and thorium nitrate was used instead of the aqueous magnesium chloride solution in Example 2, except that 2% by weight of each metal was supported. A honeycomb carrier-supported Pd catalyst of the present invention was prepared in exactly the same manner as in Example 2, and CO,
The HC oxidation rate was measured. The results are shown in Table 3.

【table】

[Table] Example 4 Commercially available cordierite honeycomb carriers of A, B, and C types with different water absorption rates, each having a size of 76〓×75 ^L , were divided into 2 pieces of 76〓×37 ^L , as shown in Example 1. Activated alumina coating was applied in exactly the same manner as described above to produce carriers having water absorption rates as shown in Table 4 after coating. These honeycomb carriers having an activated alumina coating phase were held in a Matsufuru furnace at 700°C for 15 minutes, and then immediately taken out of the furnace and allowed to cool in a room. After cooling for about 15 minutes, it was placed into a 700°C furnace again, and this thermal cycle was repeated 5 times. The results of these tests are shown in Table 4, and it can be seen from these results that if the water absorption rate of the carrier after coating with activated alumina is 12% or more, it has excellent thermal shock resistance.

【table】

Claims (1)

[Scope of Claims] 1. A catalyst carrier having an activated alumina coating phase on the surface of a ceramic catalyst carrier body, wherein (1) the weight of the activated alumina coating phase is 10 to 25% of the weight of the carrier body, and ( 2) The water absorption rate of the entire carrier is 12% by weight or more, and (3) 0.1% by weight or more of a compound of Mg, Al, Fe, Mo, W, or Th or one type of metal based on the entire carrier in terms of metal content. Or a catalyst carrier characterized in that two or more types are contained substantially uniformly at least in the active alumina coating phase. 2. The catalyst carrier according to claim 1, wherein the ceramic catalyst carrier has a honeycomb shape.