JPS6158223B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an impregnating liquid used for producing a catalyst that can simultaneously detoxify nitrogen oxides (NOx), hydrocarbons (HC), carbon monoxide (CO), etc. contained in combustion exhaust gas, particularly exhaust gas between internal combustion engines. Conventionally, when attempting to simultaneously detoxify harmful components such as NOx, HC, and CO in combustion exhaust gas, a catalyst is often used within a certain range close to the stoichiometric air-fuel ratio. Since platinum (Pt)-rhodium (Rh) catalysts have effective catalytic activity, various methods for producing Pt-Rh catalysts have been proposed. A three-way catalyst, which can simultaneously detoxify NOx, HC, and CO, reduces NOx, an oxidizing component in exhaust gas, to harmless nitrogen gas, and also oxidizes HC and CO, which are reducing components. In order to simultaneously carry out the redox reaction of converting carbon dioxide into harmless carbon dioxide and water simultaneously and over a long period of time, (1) First, high catalytic activity against all components of NOx, HC and CO must be achieved. Of course, it also has the ability to maintain its activity for a long time when used in a wide temperature range from low to high temperatures (2) Excellent poisoning resistance against lead, phosphorus, sulfur, etc. catalytic performance is required. However, the three-way catalysts that have been proposed so far
It is difficult to obtain a catalyst that has high catalytic activity against all three components, NOx, HC, and CO. For example, increasing the catalytic activity against NOx lowers the catalytic activity against HC and CO, and conversely increases the catalytic activity against HC and CO. It has been difficult to maintain a high catalytic activity while maintaining the balance of redox reactions, as the catalytic activity against NOx decreases as the temperature increases. Furthermore, under actual usage conditions, the catalyst activity decreases due to poisonous components such as lead, phosphorus, and sulfur contained in the exhaust gas, and on top of that, the catalyst deteriorates due to prolonged contact with high-temperature exhaust gas. In addition to thermal deterioration, the three-way catalyst also had a short lifespan. The present inventors have conducted various studies to overcome these drawbacks, and as a result, we have found a method for producing three-way catalysts containing Pt-Rh, palladium (Pd)-Rh, and Pt-Pd-Rh as catalytically active components. Therefore, catalysts manufactured using an impregnating liquid containing at least one of the organic nitrogen compounds described below are used when supporting these platinum group metals on a carrier.
It has high catalytic activity against NOx, HC, and CO, and has excellent poisoning resistance against lead, phosphorus, and sulfur. It has been found that when a carrier with excellent strength is used, heat resistance and mechanical strength can be sufficiently maintained. The present invention has been made based on this, and will be explained in detail below. The organic nitrogen compound used in the present invention is -N=N
An organic nitrogen compound containing nitrogen (N) or/and an amino group (-NH ₂ ) having at least one multiple bond such as -, >C=N-, -C≡N, -N=O, etc. A few specific examples include cystine, azodicarbonamide, its partial thermal decomposition product cyanuric acid, azobisisobutylnitrile, guanidine, and its partial thermal decomposition product melamine. One or more of these are used. The amount of these organic nitrogen compounds added is considered to be effective in the range of several tenths to several moles per mole of platinum group metal present in the impregnating solution, but in terms of the conspicuousness and improvement of the effect, it is particularly effective. It is preferable to choose a range of 0.5 to 3 mol. The organic nitrogen compound to be added may be in liquid or powder form without any problem in use, and by adding these organic nitrogen compounds to the catalyst impregnating liquid to make a homogeneous solution, the impregnating liquid of the present invention can be prepared. can get. Of course, in order to quickly complete the homogenization of the solution, it is preferable to sufficiently stir and mix the solution, and in some cases, homogenization can be further accelerated by heating. Generally, stirring and mixing for 5 to 10 minutes will sufficiently homogenize the solution. Once the catalyst impregnating solution obtained in this way is impregnated into a honeycomb-shaped, pellet-shaped or other shaped carrier, the subsequent treatment can be carried out according to the usual method for producing impregnated catalysts. The original catalyst is obtained. The treatment method commonly used after impregnation is as follows. i.e. 100 after impregnation
Drying is carried out at ~180°C for 3-24 hours, preferably at 110-150°C for 3-10 hours, followed by gaseous or liquid reduction. In the case of gaseous reduction, hydrogen, ammonia decomposition gas, etc. are used as the reducing gas, and the reduction conditions are 300~
700℃ for 30 minutes to 2 hours, preferably 400 to 500℃
The duration is 30 to 60 minutes. In the case of liquid reduction, formalin, sodium formate, sodium borohydride, N-N diethylglycine, etc. are used as reducing agents, and the reduction conditions are 30 to 100°C for 30 minutes to 2 hours, preferably 60 to 80°C, The duration is 30-60 minutes. Then (in the case of wet reduction, after washing with water and drying), the target catalyst is baked in air or nitrogen atmosphere at 400-800°C for 30 minutes to 4 hours, preferably at 500-700°C for 1-3 hours. is obtained. In addition, when the impregnating liquid contains three of Pt, Pd, and Rh, precipitation may occur when the above-mentioned organic nitrogen compound is added. In this case, if at least one organic acid belonging to the aliphatic saturated dicarboxylic acid or aliphatic oxycarboxylic acid group, such as oxalic acid, succinic acid, tartaric acid, citric acid, or gluconic acid, is added to the impregnating solution, precipitation can be prevented. Re-dissolve to form a homogeneous solution. The amount of these acids to be added can be set as long as no precipitation is observed, but even if a little extra is added, the performance of the resulting catalyst will not be impaired. Usually, the amount is about 0.2 to 2 moles per 1 mole of platinum group metals in the impregnating solution. Examples are shown below to clarify the above effects. Example 1 Four pieces of cordierite honeycomb carrier 1 (bulk specific gravity 0.55) treated with activated alumina were prepared, and an aqueous solution of chloroplatinic acid (H ₂ PtCl ₆ 6H ₂ O),
Pt using rhodium chloride (RhCl ₃ 4H ₂ O) aqueous solution
Four 800 ml acetic acid aqueous solutions containing 0.9 g of Rh and 0.1 g of Rh were prepared. To these four solutions, as an organic additive, azodicarbonamide was added in an amount of 1, 2, 3, and 4 times the mole of Pt and Rh, respectively, and 0.3 times the amount of azodicarbonamide, respectively. One honeycomb carrier was immersed in each of the four types of mixed solutions in which a molar amount of cystine was added and thoroughly mixed to impregnate chloroplatinic acid and rhodium chloride. After the impregnated carrier was dried in a dryer at 130 to 150°C for one day and night, it was kept in a hydrogen stream at 500°C for 30 minutes to reduce the platinum salt and rhodium salt, and then dried in air at 500°C for 1 hour. Catalysts 1 to 4 were prepared by calcination. In addition, one comparative catalyst 1 was prepared using the same procedure as above except that the impregnating solution did not contain any organic additives.
was prepared. The amounts (g) of Pt and Rb supported per carrier of these catalysts were as shown in Table 1.

[Table] Example 2 Granular activated alumina carrier 3 (bulk specific gravity 0.73) was prepared, and 800 ml of an acidic hydrochloric acid solution containing 0.9 g of Pd and 0.1 g of Rh was prepared using a palladium chloride (PdCl ₂ ) aqueous solution and a rhodium chloride aqueous solution. I prepared three. Pd was added as an organic additive to these three solutions.
1 times the molar amount of azodicarbonamide, 1 times the molar amount of guanidine, and 1 times the molar amount of melamine were sequentially added per 1 molar amount of the total amount of Rh and Rh, and the above-mentioned granules were added to the three mixed solutions that were well mixed. Each carrier was dipped to impregnate it with palladium chloride and rhodium chloride. After impregnation, the carrier is heated in a dryer at 130 to 150℃ for 5 minutes.
After drying for an hour, wet reduction with sodium formate solution,
After washing with water and drying, bake at 700℃ for 3 hours and catalyst 5~
7 was prepared. Comparative catalyst 2 of 1 was prepared using the same procedure as above except that the impregnating solution did not contain any organic additives.
was prepared. The support for these catalysts contains Pd and Rh per 1
The supported amount (g) of was as shown in Table 2.

[Table] Example 3 Four cordierite honeycomb carriers treated with activated alumina (bulk specific gravity 0.55) were prepared, and Pt was 0.6 using a chloroplatinic acid aqueous solution, a palladium chloride aqueous solution, and a rhodium chloride aqueous solution.
800ml containing 0.3g as g, Pd and 0.1g as Rh
Four acetic acidic aqueous solutions were prepared. A total of 1% of Pt, Pd and Rh was added to these 4 solutions as organic additives.
In order per molar amount, 1 times molar amount of azodicarbonamide, 1 times molar amount of guanidine, 1 times molar amount of melamine, 1 times molar amount of alanine, each of 0.3 times molar amount of cystine, and further in the above order. One honeycomb carrier each was immersed in four types of mixed solutions in which 0.5 times the molar amount of oxalic acid, succinic acid, tartaric acid, and citric acid were added and mixed well to add chloroplatinic acid, palladium chloride, and rhodium chloride. Impregnated. The impregnated carrier was treated in the same manner as in Example 1 to prepare catalysts 8 to 8.
11 was prepared. In addition, one comparative catalyst 3 was prepared using the same procedure as above except that the impregnating solution did not contain any organic additives.
was prepared. Pt, Pd and
The amount of Rh supported (g) was as shown in Table 3.

[Table] Example 4 Catalyst activity determination tests were conducted on catalysts 1 to 11 prepared in Examples 1 to 3 and comparative catalysts 1 to 3.
Judgment tests were conducted on new catalysts and on catalysts (durable catalysts) that had been operated for 250 hours at a constant speed of 100 km/h with the catalyst installed in the exhaust system of an engine dynamometer equipped with an 1800 c.c. engine. was evaluated. Sample gas composition CO 1.05% H ₂ 0.35% C ₃ H ₆ 330ppm C ₃ H ₈ 170ppm NO 1000ppm O ₂ 0.83% CO ₂ 10% H ₂ O 10% N ₂ balance % and ppm are both volume reducing components/ Oxidizing component = CO + H ₂ + 9C ₃ H ₆ + 10C ₃ H ₈ /NO
+2O ₂ =1 Space velocity 60000Hr ^-1 The test results are shown in Table 4. From this table, the effect of the present invention can be clearly seen.

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Claims (1)

[Claims] 1. At least one organic nitrogen compound containing nitrogen having at least one multiple bond and/or an amino group is added to an aqueous solution containing at least one compound of palladium and platinum and a compound of rhodium. Impregnation liquid for manufacturing redox catalysts for combustion exhaust gas purification.