JPS6054730A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To provide the titled catalyst capable of removing CO, HC, NOx in the exhaust gas contg. excess oxygen by specifying the amt. of Pt, Rh, Pd, Ce, Pr, Cu, Ni, and Zr to be supported on a carrier basing on the amt. of alumina supported by the carrier. CONSTITUTION:Alumina contg. oxides of at least one kind of heavy metal selected from Ce, Pr, Cu, Ni, and Zr is prepd., and coated on honeycomb carrier. Then, noble metals i.e. Pt, Rh, and Pd are deposited thereto. In this case, proportions of these metals basing on the alumina layer are by wt%; 0.70-0.90 Pt, 0.07-0.15 Rh, 0.07-0.75 Pd, 4.0-45 Ce, 10-25 Pr, 10-25 Cu, 10-20 Ni, and 10-20 Zr. With this catalyst, CO, HC, and NOx in the exhaust gas are removed simultaneously in an atmosphere contg. excess oxygen with high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical field to which the invention relates
[0] and an exhaust gas purifying catalyst used to purify nitrogen oxides (NOx) with high efficiency in an oxygen-rich atmosphere.

Conventional technology Conventional exhaust gas, especially 00 in exhaust gas from internal combustion engines such as vehicles.
, HC! Many catalysts for removing NOx and NOx have been proposed and are known. Among these, as a catalyst for purifying Co, He, and NoX in the exhaust gas in which the air-fuel ratio (air amount/fuel amount - h1 weight ratio) is large, a platinum catalyst is used in A/F-15~ 19 is used at a low level and purifies 00, He, and NOx on the lean side. A removable platinum-rhodium-germanium catalyst (JP-A-58-187892) is known.

Treating exhaust gas in such an oxygen-rich atmosphere is advantageous in terms of durability of the catalyst because the temperature of the treated gas is low, and it is also advantageous in terms of preventing deterioration of the catalyst due to reaction heat, which can further reduce fuel consumption. However, the above-mentioned conventional catalyst deteriorates when used for a long time, and even if the NOx conversion rate is A/F 1cr, it becomes less than 20%. However, there was a problem in that the purification rate of nitrogen oxides suddenly decreased.

DISCLOSURE OF THE INVENTION This invention was made by focusing on such conventional problems.
Platinum (, pt) -1° Tetradium Bth)
The above-mentioned problems are solved by a catalyst supporting one or more noble metals selected from the group consisting of palladium (Pd) and palladium (Pd).

The amount of noble metals and heavy metals supported in the catalyst of this invention is:
The amount of platinum for the alumina layer attached to the carrier is 0.70~
0.90% by weight, the amount of cerium is 0.07~0.15% by weight, the amount of palladium is 0.07~0.75% by weight, the amount of cerium is 4. ON45 weight section, praseodymium amount is 10~
25% by weight, the amount of copper is 10-25% by weight, the amount of nickel is 1
The amount of zirconium is in the range of 0 to 25% by weight, and the amount of zirconium is in the range of 10 to 20% by weight. The reason for this is platinum, cerium, palladium,
If the amounts of cerium, praseodymium, copper, nickel, and zirconium are below each of the above lower limits, the effect of adding these responsible metals and heavy metals may be insufficient compared to the performance required by the inventors. On the other hand, even if the amount of cerium, praseodymium, copper, nickel, and zirconium is increased beyond the above-mentioned upper limit values, there is almost no effect of increasing the amount of cerium, praseodymium, copper, nickel, and zirconium. . The reason why the purification rate decreases as the amount of cerium, praseodymium, etc. added increases beyond a certain level is thought to be because the surface area of the carrier decreases as the amount of activated alumina decreases relatively.

The catalyst of the present invention has good CjO, H'0, and NOx conversion rates even when the air twisting cost A/F is 25 by supporting the noble metals and the above-mentioned amounts of cerium, praseodymium, nickel, and zirconium on the carrier. shows. The temperature of the exhaust gas to be treated at this time is particularly preferably in the range of 800 to 350°C; if it is higher than 850°C, the conversion rate of NOx will be poor, while if it is lower than 300°C, the
The conversion rate of MO decreases.

In this way, the catalyst of this invention has good C even at A/F 25.
The reason for the high conversion rates of HC, NOx, and NOx has not been fully elucidated, but as described in JP-A-52-144580, whether the exhaust gas purifying catalyst works for oxidation or reduction depends on whether the exhaust gas purification catalyst works for oxidation or reduction. Does CO in the gas react with O3?
Alternatively, it may react with NOx, and if you compare the reaction rate between CO and 02 and the reaction rate between CO and NOx, they tend to be about the same when the catalyst bed temperature is relatively low (500.a9 or less). It is thought that this tendency is further promoted by the addition of heavy metals such as cerium.

In this invention, the catalyst is prepared using a large amount of ce in advance.

Alumina containing an oxide of one or more heavy metals selected from the group consisting of pr, Ou, Ni, and Zr is prepared, and a large amount of this alumina is coated with a cordon on a honeycomb carrier, and then Pt, Rh, and Preferably, one or more noble metals selected from the group consisting of Pa are attached.

EXAMPLES OF THE INVENTION Next, the present invention will be explained with reference to Examples, Comparative Examples, and Test Examples.

Example 1 Alumina sol (sol obtained by adding 10% by weight of HBTO8 to boehmite alumina 10% by weight suspension) 2478g, activated alumina granular carrier 491g
and commercially available ceria powder 10829 to Ballumi/'-
After mixing and pulverizing for 6 hours, this liquid containing alumina (hereinafter referred to as coating liquid) was applied to a monolithic carrier base material (
0,9), 800 cells) and baked at 650°C for 2 hours. In this case, the amount of adhesion is 18 per carrier base material.
It was set to 0g.

Furthermore, the carrier treated with this coating solution was immersed in a mixed aqueous solution of chloroplatinic acid and rhodium chloride, and the amount of platinum and rhodium deposited was 1.39% for platinum and 0.262% for rhodium.
After supporting the catalyst so as to have the following properties, the catalyst was calcined at 600°C for 2 hours to obtain Catalyst 1.

Example 2 Catalyst 2 was obtained in the same manner as in Example 1, except that alumina sol 24789, 697 g of activated alumina granular carrier, and commercially available ceria powder 8269 were used.

Example 8 Catalyst 8 was obtained in the same manner as in Example 1, except that alumina sol 24789, activated alumina granular carrier 903, and commercially available ceria powder 6199 were used.

・Example 4 Particulate carrier mainly composed of gamma alumina (particle size 2 to 4
B) was impregnated in an aqueous solution of cerium nitrate, dried, and then calcined in air at 600° C. for 1 hour to obtain a carrier containing cerium oxide in an amount of 5% by weight in terms of metal relative to alumina.

The thus obtained cerium-containing activated alumina granular carrier 15229 and alumina sol 2478 were mixed in a ball mill and ground for 6 hours, and then the coating liquid was attached to a monolithic carrier base material (0.9t, aoo1゛□ cell). The mixture was heated at 650° C. for 2 hours.

In this case, the adhesion amount was set at 180 parts per carrier base material.

Further, this adhered carrier was immersed in a mixed aqueous solution of chloroplatinic acid and rhodium chloride, and the amount of platinum and rhodium □ deposited was 1.89 platinum and 0.289 rhodium, and then heated at 600'C for 2 hours. The catalyst 4 was obtained by calcination.

Example 5 Granular carrier mainly composed of gamma alumina (particle size: 2 to 4
i+m) in a cerium nitrate aqueous solution and dried at 600°C.
It was fired in air for 1 hour to obtain a carrier containing 5% by weight of cerium oxide based on alumina in terms of metal.

Activated alumina granular carrier containing cerium thus obtained, alumina sol 24789 and commercially available ceria 10
After mixing 82 in a ball mill and grinding for 6 hours, the resulting coating liquid was applied to the monolithic carrier base (0,9),
800 cells) and baked at 650°C for 2 hours.

The adhesion amount in this case was set to 1809 per carrier base material.

Further, this adhered carrier was immersed in a mixed aqueous solution of chloroplatinic acid and rhodium chloride, and the amount of platinum and rhodium deposited was 1°3 of platinum and 0.269 of rhodium, and then heated at 600°C for 2 hours. The catalyst 5 was obtained by calcination.

Example 6 Catalyst 6 was obtained in the same manner as in Example 1, except that alumina sol 24789, activated alumina granular carrier 13169, and 601 g of brassica oxide were used. Example 7 Alumina sol 2478 and activated alumina granular carrier were used in Example 1. Catalyst 7 was obtained in the same manner except that copper oxide 668 was used instead of copper oxide 668.

Example 8 Catalyst 8 was obtained in the same manner as in Example 1 except that alumina sol 2478, activated alumina granular carrier 1flllfN2, and nickel oxide 500% were used.

Example 9 Catalyst 9 was obtained in the same manner as in Example 1 except that 24789 alumina sol, 1816 g of alumina granular carrier, and 545 g of zirconium oxide were used.

Example 10 Catalyst 1o was obtained in the same manner as in Example 1, except that the noble metal aqueous solution to be immersed was changed to chloroplatinic acid. However, the amount of platinum deposited was set at 1.67 per carrier base material.

Example 11 Catalyst 11 was obtained in the same manner as in Example 1 except that the noble metal aqueous solution to be immersed was changed to chloroplatinic acid and palladium chloride. However, the amount of platinum and palladium deposited is 1.8 platinum and 0 palladium per carrier base material.
．． It was set to 269.

Example 12 Catalyst 12 was obtained in the same manner as in Example 1, except that the noble metal aqueous solution to be immersed was changed to chloroplatinic acid, rhodium chloride, or palladium chloride. However, the amount of platinum, rhodium and palladium deposited is 1.8'9N of platinum per carrier base material.
"Dium was set at 0.13 g and palladium at 0.189 g.

Example 18 Catalyst 13 was prepared in the same manner as in Example 1 except that palladium chloride and rhodium chloride were used as the noble metal aqueous solution to be immersed.
I got it. However, the amount of palladium and rhodium deposited is
1.89 palladium and 0 rhodium per carrier substrate
．． It was set to 269.

Example 14 In Example 1, alumina sol 24789, activated alumina granular carrier 1B], 69, praseodymium oxide 2
@medium 14 was obtained in the same manner except that it was changed to 00no.

Example 15 Catalyst 15 was obtained in the same manner as in Example 1 except that alumina sol 24789, activated alumina granular carrier 18169, and copper oxide 220 were used instead.

Example 16 Catalyst 16 was obtained in the same manner as in Example 1, except that 2478 L of alumina sol, 1816 g of activated alumina granular carrier, and 28 L of nickel oxide were used.

Example 17 Catalyst 17 was obtained in the same manner as in Example 1 except that the alumina sol 2478L; ii, alumina granular carrier 18169, and zirconium oxide 239L were used.

Comparative Example 1 Alumina Sol 2568. (1, activated alumina granular carrier 1
After mixing 4879 into a ball mill and grinding for 6 hours,
The obtained coating liquid was applied to the monolith carrier base material (0,9)
, 800 cells) and fired. The amount of adhesion in this case was set at 1.80° per carrier base material.

Further, the 11 bodies subjected to the adhesion treatment were immersed in an aqueous solution of chloroplatinic acid to support the platinum so that the amount of platinum deposited was 1°6, and then calcined at 600°C for 2 hours to obtain catalyst A.

Comparative Example 2 In Comparative Example 1, when immersed in a mixed aqueous solution of chloroplatinic acid and rhodium chloride, the amount of platinum and rhodium deposited was 1.3 platinum.
Catalyst B was obtained in the same manner except that rhodium was supported so that the amount of rhodium was 0.267.

Comparative Example 3 Catalyst C was obtained in the same manner as in Example except that alumina sol 24789, activated alumina granular carrier 13169, and germanium oxide 1082 were used instead.

Comparative Example 4 A catalyst was obtained in the same manner as in Comparative Example 3, except that the noble metal aqueous solution to be immersed was changed to a chloroplatinic acid aqueous solution. However, the amount of platinum deposited was set at 1.69 per carrier base material.

, Comparative Example 5 Catalyst E was obtained in the same manner as in Comparative Example 8 except that the noble metal aqueous solution to be immersed was changed to a mixed aqueous solution of chloroplatinic acid and palladium chloride. However, the amount of platinum and palladium deposited is 1.89 platinum and 0 palladium per carrier base material.
．． It was set to 269.

Comparative Example 6 Catalyst F was obtained in the same manner as in Comparative Example 3, except that the noble metal aqueous solution to be immersed was changed to a mixed aqueous solution of chloroplatinic acid, rhodium chloride, and palladium chloride. However, the supported amounts of platinum, rhodium, and palladium are 1.89 g of platinum, 0.18 g of rhodium, and 0.1 g of palladium per carrier base material.
It was set to 189.

Comparative example? Catalyst G was obtained in the same manner as in Comparative Example 8, except that the noble metal aqueous solution to be immersed was changed to a mixed aqueous solution of palladium chloride and rhodium chloride. However, the amounts of palladium and rhodium deposited were set to 1.87 palladium and 0.269 rhodium per carrier substrate.

Comparative Example 8 Catalyst (2) was obtained in the same manner as in Example 10 except that the amount of platinum deposited was changed to 0.90 g of platinum.

Comparative Example 9 A catalyst material was obtained in the same manner as in Example 10 except that the amount of platinum deposited was 1.8 to 5. - Comparative Example 1O In Example 12, the amount of rhodium deposited was 0,0
Catalyst J was obtained in the same manner except that 9i7 was used.

Comparative Example 11 The amount of rhodium deposited in Example 12 was changed to 0.8 rhodium.
Catalyst K was obtained in the same manner except that 62 was used.

Comparative Example 12 In Example 12, the amount of palladium deposited was changed to 0 palladium.
．． A catalyst was obtained in the same manner except that 099 was used.

Comparative Example 18 Catalyst M was obtained in the same manner as in Example 12, except that the amount of palladium deposited was changed to 0.69 g of palladium.

Comparative Example 14 A Nt-catalyst was obtained in the same manner as in Example 1 except that the amount of cerium was changed to 20% by weight based on the amount of deposited metal.

Comparative Example 15 Catalyst O was obtained in the same manner as in Example 1, except that the amount of cerium was changed to 50% by weight based on the amount of deposited metal.

Comparative Example 16 Catalyst P was obtained in the same manner as in Example 6 except that the amount of praseodymium oxide was changed to 25% by weight based on the amount of attached praseodymium metal.

Comparative Example 17 Catalyst Q was obtained in the same manner as in Example 6, except that the amount of praseodymium oxide was changed to 80% by weight based on the amount of attached praseodymium metal.

Comparative Example 18 Catalyst R was obtained in the same manner as in Example 7 except that copper oxide was changed to 5% by weight based on the coaching amount in terms of copper metal.

Comparative Example 19 Catalyst S was obtained in the same manner as in Example 7, except that the amount of oxidized steel was changed to 30 weight ff14 in terms of the amount of deposited copper metal.

Comparative Example 20 Catalyst T was obtained in the same manner as in Example 8, except that the amount of nickel oxide was changed to 5 times the amount of adhesion in terms of nickel metal.

Comparative Example 21 Catalyst U was prepared in the same manner as in Example 8 except that nickel oxide was changed to 25% by weight based on the amount of nickel metal deposited.
I got it.

Comparative Example 22 Catalyst V was obtained in the same manner as in Example 9, except that zirconium oxide was changed to 5% by weight based on the amount of deposited zirconium metal.

Comparative Example 23 Catalyst W was obtained in the same manner as in Example 9, except that the amount of zirconium oxide was changed to 25% by weight based on the amount of adhered zirconium oxide in terms of silconium ram metal.

Test Examples Catalysts 1 to 17 obtained in Examples 1 to 17 and Comparative Examples 1 to 2
A durability test was conducted on the catalysts AW obtained in 8 under the following conditions.

Thermal durability test conditions Atmosphere Air Temperature Temperature 600°C Durability time Zoo hours After conducting the durability test in this way, the catalyst was evaluated under the following evaluation conditions for hydrocarbons (CHC), -carbon oxides (CO), and nitrogen oxides ( The purification rate of NOx) was measured in the laboratory, and the results are shown in Table 1 below.

Evaluation conditions: scum flow ffi '85'/min, contact amount 60f! Lt Inlet log gas temperature 820℃ Gas composition 028.6% No 300 ppm 00 0.32% HO6500ppm C H2O, 11% Co 7.7% H2 10% N2 Remainder Table 1 Table 1 (continued) Table 1 (continued) ) As described in detail, the catalyst of the present invention has a structure in which specific amounts of specific noble metals and heavy metals are supported, so that even after durability, Co in the exhaust gas in an oxygen-rich atmosphere is
, the purification rate of He and NOx does not decrease, and these harmful components can be removed with high efficiency. Also, as shown in Table 1 showing the test results, the catalyst of the present invention has a lower reduction rate than the catalyst of the comparative example. It is clear that the NOx purification rate was significantly improved despite the atmosphere.

Patent applicant: Nissan Motor Co., Ltd.

Claims (1)

[Claims] L: One or more noble metals selected from the group consisting of platinum, rhodium, and palladium, and one or more heavy metals selected from the group consisting of cerium, praseodymium, copper, nickel, and zirconium. Two or more types are supported on the refractory carrier, and the supported amount is 0.70 to 0.90% by weight of platinum and 0% of rhodium based on the alumina layer attached to the carrier.
．． 07-0.15% by weight, palladium amount 0.07-0
．． 75% by weight, 4.0-45% by weight of cerium, 10-25% by weight of praseodymium, 10-25% by weight of copper, 10-20% by weight of nickel, 10-20% by weight of zirconium. A catalyst for exhaust gas purification that can simultaneously remove carbon monoxide, hydrocarbons, and nitrogen oxides in exhaust gas with high efficiency in an oxygen-rich atmosphere. 2. The exhaust gas purification catalyst according to claim 1, wherein the oxygen-excess atmosphere has an air-fuel ratio of 25 or less.