JPS6231982B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a mixed catalyst made by mixing two or more types of catalysts with different characteristics. Specifically, in at least two types of catalysts to be mixed,
It is characterized by containing at least one type of platinum group metal as a common catalyst substance supported under different supporting conditions. Platinum group metals consisting of platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os) are all expensive metals, but they have extremely high activity as catalyst materials. has the ability. Therefore, when a platinum group metal is used as a catalyst, the platinum group metal is dispersed and supported on a carrier having a large specific surface area in order to widen the contact area with the reaction article.
In general, the catalytic reaction proceeds at a high rate on the apparent surface of the catalyst, and the rate of effective utilization decreases as it goes deeper into the surface pores of the catalyst. In addition, the catalysts may wear out due to collisions with each other, the surface may be coated with poisonous components that harm the catalyst, and the structure of the catalyst may change due to exposure to high temperatures. For example, when a catalyst is used to oxidize unburned hydrocarbons (HC) and carbon monoxide (CO) contained in exhaust gas from an automobile internal combustion engine, or to reduce nitrogen oxides (NOx), the use of a catalyst The temperature range extends from room temperature to over 800℃, and the catalyst is exposed to ever-changing conditions such as air fuel consumption (A/F) and space velocity (SV), so a catalyst is required to have an extremely wide range of action. be done. Also, the exhaust gas contains lead,
It contains poisonous components such as phosphorus and sulfur, and must have sufficient durability against poisoning by these substances. Many methods have been proposed for supporting platinum group metals on carriers. Furthermore, in order to support platinum group metals, various platinum group compounds are used as supporting materials. When these various platinum group compounds are used as raw materials for catalysts, catalysts having different characteristics depending on the raw materials can be obtained. For example, if platinum is supported on an activated alumina carrier using an acidic dinitrodiaminoplatinum nitric acid aqueous solution, a platinum distribution on the surface of the carrier as shown in FIG. 1 can be obtained. Further, when a platinum hexacine tetrahydroxide aqueous solution is used, a platinum distribution as shown in FIG. 2 is obtained.
In this way, it is thought that when the supported raw materials are different, the state of the catalyst substance supported on the carrier is different. Therefore, as shown in Table 2, they each have different characteristics in exhaust gas purification, and there are also differences in durability. The present inventors have focused on the fact that catalyst performance, particularly durability, differs depending on the raw material compound used for supporting. According to the inventors' considerations, the cause of the difference in durability is mainly due to the difference in the distribution of the catalyst material, and if the distribution of the catalyst material is average over a wide range, the durability will be higher even if the initial performance is slightly lower. It was found that when a large amount of catalyst material is distributed on the surface, the initial performance is excellent even if the durability is somewhat inferior. The present invention relates to a catalyst in which a desired effect can be obtained by mixing and using catalysts in which catalytic substances are supported by these various raw material compounds according to their characteristics. In other words, in the present invention, a mixture of the same catalyst materials but with different supporting conditions is used in combination with other catalyst materials as necessary. As a result, even when using the same catalytic material, substances in different supported states work together to perform the catalytic action, resulting in more useful effects than when using a single supported catalyst. That will happen. Furthermore, depending on the reaction of interest, catalyst substances that have good fusion properties may be used in combination even if they are supported on the same carrier, if necessary. For example, in the present invention, in addition to the platinum group catalyst, catalyst components such as iron, nickel, steel, and chromium may be included. A granular carrier is suitable for use in the present invention, and examples of the material include alumina and silica. In addition, examples of the platinum group compound as a catalyst-supporting raw material used in the present invention include chlorine-containing compounds such as chloroplatinic acid, palladium chloride, and rhodium chloride; ansine complexes such as dinitrodiaminoplatinum and diaminopalladium chloride; palladium sulfate; and nitric acid. Examples include mineral acid salts such as rhodium, and these platinum group compounds have their own characteristics when used as supporting materials. The present invention will be explained below using examples. Example 1 (i) Made of γ-alumina and δ-alumina, with an average specific surface area of 70 to 120 m ² /g and an average bulk density
A 0.64 kg/~0.70 kg/carrier (hereinafter referred to as "carrier A") 1 was impregnated by spraying 0.35 ml of dinitrodiaminoplatinum acidic aqueous solution containing 1.0 g of Pt. Next, it was dried at about 120°C for 2 hours and then calcined at about 500°C for 1 hour to obtain catalyst 1a. (ii) Immerse the carrier A1 in 0.8 g of platinum hexamine tetrahydroxide aqueous solution containing 1.0 g of Pt,
After standing for 30 minutes with occasional stirring, excess solution was removed. Next, it was dried at about 120°C for 2 hours and then calcined at about 500°C for 1 hour to obtain catalyst 2a. Next, catalyst 1A was obtained by mixing catalyst 1a, 0.5 with catalyst 2a, 0.5. Example 2 Support A1 was a mixed solution of chloroplatinic acid and palladium chloride hydrochloric acid aqueous solution containing 0.5 g of Pt and 0.5 g of Pd.
0.8 and allowed to stand for 30 minutes with occasional stirring, then excess solution was removed. Next, aqueous solution 1 containing 3 g of NaBH ₄ was added and left to stand for about 20 minutes with occasional stirring, and then excess liquid was removed. Furthermore, washing with water 1 was repeated three times, followed by drying at about 120°C for 2 hours and calcining at about 40°C for 30 minutes to obtain catalyst 3a. Next, catalyst 2a, 0.2 and catalyst 3a, 0.8 in Example 1 were mixed to obtain catalyst 1B. Example 3 Palladium chloride hydrochloric acid aqueous solution containing 1.0 g of Pd
Using 0.8, the same treatment as in catalyst 3a was carried out to obtain catalyst 4a. Next, catalyst 4a, 0.4 was mixed with catalyst 1a, 0.3 and catalyst 2a, 0.3 in Example 1 to obtain catalyst 1C. Example 4 Catalyst 1a, 1 was impregnated with 0.35% of an aqueous rhodium nitrate solution containing 0.1g of Rh by spraying. Then about
It was dried at 120°C for 2 hours and calcined at about 600°C for 30 minutes to obtain catalyst 5a. Next, 0.6 of catalyst 5a was mixed with 0.4 of catalyst 2a in Example 1 to obtain catalyst 1D. Comparative Example 1 Catalyst 6a was obtained by the same treatment as in Example 4 using 0.8 g of a mixed solution of chloroplatinic acid and palladium chloride hydrochloric acid aqueous solution containing 0.6 g of Pt and 0.4 g of Pd. Comparative Example 2 Catalyst 1a in Example 1, Catalyst 4 in 0.6
A and 0.4 were mixed to obtain catalyst 7a. Comparative Example 3 Catalyst 5 was added to catalyst 1a, 0.4 in Example 1.
A and 0.6 were mixed to obtain catalyst 7b. The mixing states of the catalysts of Examples 1 to 4 and Comparative Examples 2 and 3 are shown in Table 1 for convenience of comparison.

[Table] Furthermore, the results of measuring the distribution state of Pt from the surface to the inside of the catalysts 1a and 2a are shown in FIGS. 1 and 2. It can be seen that in catalyst 1a, Pt is distributed more near the surface and supported at a shallower depth than in catalyst 2a. Next, catalysts 1A to 1C of the present invention and catalysts 1a and 2
Durability tests were conducted on samples a, 6a, 7a, and 7b. The conditions for the durability test are as follows. Durability test time 600 hours Engine displacement 1600c.c. Engine speed 3200rpm Engine load -200mmHg (intake pipe negative pressure) Air fuel consumption 14.6 Fuel used Unleaded gasoline Oxidation performance of each catalyst before and after the durability test The results of the test are shown in Table 2. The oxidation test was conducted using C ₂ H ₄ 600ppm, C ₃ H ₆ 300ppm, CO1
This was done by measuring the oxidation performance when a gas containing 1.6% O ₂ was flowed at a flow rate of 5/min.

[Table] From the results shown in Table 2, looking at the analytical values, there is no difference in the content of platinum group metal, which is a catalytic material, between the catalyst according to the present invention and other catalysts. That is, the content of Pt between catalysts 1A, 1a, and 2a is 1
There is no difference in the content of Pt and Pd between B, 1C, 6a and 7a, and the content of Pt and Rh between 1D and 7b. Comparing the purification performance between these catalysts, the catalyst 1A of the present invention before the durability test was compared with the catalyst 2a.
It has superior performance in purifying CO, C ₂ H ₄ , etc. compared to Catalyst 1a, and has almost the same initial performance as Catalyst 1a. Moreover, after the durability test, the catalyst of the present invention 1A
The C ₃ H ₈ purification rate is much better than that of Catalyst 1a, and the CO and C ₂ H ₄ purification rate is also superior to that of Catalyst 2a. In other words, the catalyst of the present invention compensates for the drawbacks of the individual catalysts 1a and 2a, and has an effect greater than the simple sum of the two catalysts. Furthermore, catalysts 1B and 1C of the present invention are also catalyst 6.
Compared to A and 7a, the C ₃ H ₈ purification rate after the durability test is particularly excellent. The same applies to the catalyst 1D of the present invention. As mentioned above, the catalyst according to the present invention uses different forms of raw material compounds to produce catalysts with different supported states of catalyst substances, and has complementary characteristics and a synergistic effect, and is different from conventional catalysts. It improves the shortcomings of the above and provides excellent characteristics.

[Brief explanation of the drawing]

FIG. 1 shows the distribution of platinum from the surface to the inside of the catalyst 1a, and FIG. 2 shows the distribution of platinum in the catalyst 2a.

Claims (1)

[Claims] 1 A mixed catalyst produced by mixing two or more catalysts containing at least one common platinum group metal, characterized in that at least two of the common platinum group metals are supported under different supporting conditions. A mixed catalyst containing a platinum group metal for oxidation or reduction in exhaust gas.