JPH07313882A - Diesel engine exhaust gas purification catalyst and method for producing the same - Google Patents

Abstract

(57) [Abstract] [Purpose] There is no problem of secondary pollution due to catalyst, SOF can be removed to reduce particulates, and formation of SO ₂ to sulfate at a catalyst inlet temperature of 400 ° C or higher is possible. To provide means that can be suppressed. [Structure] On a support having an integral structure, zirconium phosphate was supported as a catalyst component to form a diesel engine exhaust gas purification catalyst, and the object could be achieved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to hydrocarbon (HC), carbon monoxide (CO) in exhaust gas discharged from a diesel engine, and an organic solvent-soluble component (SOF) contained in particulates. The present invention relates to a diesel engine exhaust gas-purifying catalyst and a method for producing the same, which can reduce the emission of particulates and suppress the generation of sulfur dioxide (SO ₂ ) to sulfate.

[0002]

2. Description of the Related Art Exhaust gas from diesel engines is HC, C
It contains O, nitrogen oxides (NO _x ), and a large amount of particulates. Here, particulates are soot-based, unburned gas oil and lubricating oil, and a fine particle substance having a structure in which sulfate surrounds, and as a constituent component, a component soluble in an organic solvent. (SOF), a component insoluble in an organic solvent (ISOF), and sulfate. Further, the exhaust gas atmosphere of the diesel engine is in excess of oxygen. Compared to a gasoline engine exhaust gas equipped with a three-way catalyst, the exhaust gas from a diesel engine emits a large amount of HC, CO, especially NO _x , contains a large amount of particulates, and is a type of particulate SO.
Carcinogenic substance is contained in F. Therefore, this is a social issue, and in Japan in 1994 NO
_{In addition to x} , the regulation of particulates was introduced, and the stricter regulation value is set as a long-term target.

To this end, improvements in diesel engines,
The amount of particulate emissions is being reduced. Therefore, as a method for reducing the particulate emission amount, only the diesel particulate filter (DPF) that collects the particulate matter and performs the regeneration process when the collected amount becomes a certain amount and the SOF component in the particulate matter are collected. There are flow-through type catalysts that reduce. DPF
Is because it is possible to reduce the particulates themselves,
Conventionally, the DPF has been the mainstream for reducing particulates.
The SOF in the particulates can be reduced by using an oxidation catalyst such as platinum / alumina. Further, in order to use a flow-through type catalyst as a diesel engine exhaust gas purification catalyst to reduce the particulate emission amount, it is necessary to remove SOF and suppress the production of SO ₂ into sulfate. A platinum / vanadium / alumina diesel engine exhaust gas purification catalyst that removes SOF with a flow-through type catalyst and suppresses the formation of SO ₂ into sulfate has been reported (SA
E Paper No. 930130).

[0004]

However, in a three-way catalyst for a gasoline engine, HC and CO can be removed because the exhaust gas atmosphere of the diesel engine is excessive in oxygen, but it is difficult to remove NO _x . Further, although the SOF in the particulates can be removed by using the three-way catalyst, SO _{2 in} the exhaust gas is oxidized to produce sulfate, and as a result, the emission amount of particulates increases. Therefore, there is a problem that a three-way catalyst such as for a gasoline engine cannot be used.

Further, in the improvement of the diesel engine, it became possible to reduce the ISOF during particulates.
O reduction in the _x and particulate emissions are in a trade-off relationship, only improvement of diesel engines, there is a problem that lowering the respective emissions by regulation value especially long-term target value is difficult, due to the catalyst Reduction of particulate emissions is desired.

Furthermore, the DPF requires a regeneration treatment device, has many problems such as cracking of the catalyst carrier at the time of regeneration, and is capable of reducing ISOF by improving the engine. Through-type catalysts have come to be expected as catalysts for diesel engine exhaust gas.

Further, even with a flow-through type platinum / vanadium / alumina catalyst, it is difficult to completely suppress the formation of SO ₂ into sulfate. Especially, when the catalyst inlet temperature is 400 ° C. or higher, the formation of sulfate causes the formation of sulfate. There is a problem that the curate increases. In addition, since vanadium, which is a heavy metal, is used, when used as a catalyst for purifying exhaust gas from diesel engines, vanadium may scatter into the exhaust gas, resulting in secondary pollution.

The present invention does not have the problem of secondary pollution caused by the catalyst and can remove SOF for reducing particulates,
Moreover, it is an object of the present invention to provide a means capable of suppressing the formation of SO ₂ into sulfate at a catalyst inlet temperature of 400 ° C. or higher.

[0009]

DISCLOSURE OF THE INVENTION As a result of repeated studies to solve the above problems and achieve the above object, the present inventors have found that the object can be achieved by using zirconium phosphate as an active substance. The inventors have found the present invention and completed the present invention. That is, the first embodiment of the present invention is a diesel engine exhaust gas purification catalyst in which zirconium phosphate is supported as a catalyst component on a support having an integral structure, and the second embodiment is zirconium phosphate. Is a method for producing a diesel engine exhaust gas-purifying catalyst, which comprises a step of preparing a slurry containing the above, a step of supporting the slurry on a support having an integral structure, and a step of firing the slurry.

[0010]

The present invention will be described in detail below.

The support having an integral structure is made of a refractory metal oxide or a refractory metal, and the shape thereof is a honeycomb, a foam having a three-dimensional network structure, or the like. Examples of the refractory metal oxide that constitutes the support having an integral structure include cordierite, mullite, α-alumina, sillimanite, magnesium silicate, zirconia, pentalite, spodumene, and alumina silicate. The refractory metal is one type, and examples thereof include a refractory iron-based alloy, a refractory nickel-based alloy, and a refractory chrome-based alloy, and at least one of them is used. Among these supports having an integrated structure, the honeycomb support made of cordierite is most preferably used.

Zirconium phosphate has a unique pore structure, and the molar ratio P / Zr is 0.1 to 10, preferably 0.5 to 5. In addition, its crystal structure is amorphous,
It has a two-dimensional layered structure or a three-dimensional network structure. As amorphous, Zr (HPO ₄ ) ₂ · nH ₂ O, ZrO
_{(H 2 PO 4) · 2H} 2 O, and the like. The two-dimensional layered _{structure, Zr (HPO 4) 2 ·} 2
H ₂ O, Zr and the like _{(HPO 4) 2.} Further, as a three-dimensional network structure, (H ₃ O) Zr
₂ (PO ₄ ) ₃ .nH ₂ O and the like can be mentioned.
The amount of zirconium phosphate supported on the support is not particularly limited, but preferably 20 to 200 per liter of the support.
g, and more preferably 60 to 150 g. .

Such a catalyst can be manufactured as follows. That is, adjustment of slurry: zirconium phosphate, pure water, and
As a binder, a zirconium compound such as zirconyl acetate and a phosphoric acid compound such as ammonium phosphate trihydrate are ground with a grinder to form a slurry.
The amount of pure water is from 500 to 1 kg of zirconium phosphate.
1600 ml is preferred. By pulverization, the average particle size of zirconium phosphate in the slurry is preferably 0.1 to 10 μm.

The produced slurry is transferred to a container and pure water is added to obtain a slurry having a predetermined specific gravity. This specific gravity is
For example, it is preferably 1.20 to 1.75 g / ml.

Support of Slurry on Support Having Integrated Structure: A support having an integrated structure as described above is dipped in the slurry prepared as described above, for example, 1 to
After dipping and adhering for 60 seconds, excess slurry in the cell is removed by air flow. Next, the support to which the slurry is attached is heated with, for example, hot air, preferably 20 to 100 ° C.,
Remove at least 50% water, preferably 90% water. After removing the water in this way, 200
~ 900 ° C, preferably 10 at a temperature of 300-800 ° C
Baking is performed for 10 minutes, preferably 15 to 60 minutes, for example, in air. When the temperature of the support is gradually raised during firing, the drying (removal of water) may be omitted.

According to the slurry supporting step, for example, 20 to 200 g of zirconium phosphate, and optionally 0.1 to 20 g of zirconium compound in terms of zirconium oxide, and phosphoric acid compound of phosphorus oxide per liter of the support having an integral structure are obtained. It can carry 0.1 to 20 g in terms of conversion.

[0017]

EXAMPLES Next, examples of the present invention will be described. Example 1 Preparation of Slurry: 1 amorphous zirconium phosphate
Kg, 251 g of zirconyl acetate (zirconium oxide equivalent; 50 g), 2 g of triammonium phosphate trihydrate
(Phosphorus oxide conversion; 1 g) and 700 ml of pure water were put into a pulverizer and mixed and pulverized to obtain a slurry. The grinding time is
It was set that 90% or more of the particle diameter in the slurry became 9.0 μ or less. Pure water was added to this slurry to adjust the specific gravity to 1.51 g / ml to obtain a diluted slurry.

Preparation of catalyst: In the slurry obtained in
A cylindrical cordierite monolithic carrier having a diameter of 143.8 mm and a length of 152.4 mm (volume: 2.5 liter, 4
(00 cells / in ² ) was immersed for 5 seconds, and this was pulled up from the diluted slurry, and then the excess slurry was removed by an air flow. Further, after drying at 30 to 60 ° C., it was calcined at 400 ° C. for 30 minutes to obtain a catalyst A. The obtained catalyst A is
120 g of amorphous zirconium phosphate, zirconium compound (zirconium oxide conversion; 6 g), and phosphorus compound (phosphorus oxide conversion; 0.1) per liter of the finished catalyst.
g) was included.

Performance Evaluation: The catalyst A obtained in the above was used as a naturally aspirated direct injection diesel engine (4 cylinders, 4000 cc)
It is installed in the exhaust system of and has a sulfur content of 0.05 as fuel.
The engine speed is 3200 r.
p. m. By adjusting the torque to be constant, the exhaust gas temperature at the catalyst inlet is set to 400 ° C. and 600 ° C., and HC, CO, and CO at the catalyst inlet and outlet at the respective temperatures are set.
The particulates, SOF, and sulfates were measured, and the removal rates of HC, CO, particulates and SOF, and the incidence of sulfates were determined. In addition, the measurement of the particulates in the exhaust gas uses a split-flow partial dilution tunnel (manufactured by Horiba), and the SOF extracts the particulates supplemented by the split-flow partial dilution tunnel with a dichloromethane solution, and before and after the extraction of the particulates. Calculated from the weight difference. Further, the sulfate was converted from SO ₄ ²⁻ which was obtained by putting the particulates after SOF extraction in pure water, extracting with ultrasonic waves, and analyzing using an ion chromatograph (Yokogawa). The results are shown in Table 1. Example 2 In the process of Example 1, the same amount of zirconium phosphate having a two-dimensional layered structure was used in place of the amorphous zirconium phosphate, and zirconyl acetate and triammonium phosphate trihydrate were added. And the amount of pure water added was 7
The same process as in Example 1 was carried out except that the amount was changed to 1000 ml instead of 00 ml, and
A catalyst B containing 120 g of zirconium phosphate having a two-dimensional layered structure was obtained.

The performance of the obtained catalyst B was evaluated in the same manner as in Example 1 and the results are shown in Table 1. Example 3 In the process of Example 1, the same amount of zirconium phosphate having a three-dimensional network structure was used instead of amorphous zirconium phosphate, and triammonium phosphate trihydrate was not added. Except for the above, the same treatment as in Example 1 was carried out to obtain a catalyst C containing 120 g of zirconium phosphate having a three-dimensional network structure and a zirconium compound (calculated as zirconium oxide; 6 g) per liter of the finished catalyst.

The performance of the obtained catalyst C was evaluated in the same manner as in Example 1 and the results are shown in Table 1. Comparative Example 1.2 kg of activated alumina having a BET surface area of 150 m ² / g and an average particle size of 30 μ was put in a mixer.
While stirring the activated alumina, 420 ml of an amine aqueous solution of hydroxyplatinic acid containing 5 g of platinum was dropped little by little and dispersed uniformly. Next, 160 ml of 10 wt% acetic acid was dropped little by little and uniformly dispersed to prepare an alumina powder containing platinum.

1000 g of the activated alumina containing platinum obtained in the above step, 142 ml of 90% by weight acetic acid, and 800 ml of pure water were put into a pulverizer and mixed and pulverized to obtain a slurry. The pulverization time was until 90% or more of the particle diameter in the slurry became 9.0 μ or less. Pure water was added to the obtained slurry to adjust the specific gravity to 1.54 g / ml to obtain a diluted slurry.

In the diluted slurry obtained in the step 1, a cylindrical cordierite monolith carrier having a diameter of 143.8 mm and a height of 152.4 mm (volume: 2.5 liter, 400
(Cell / in ² ) was immersed for 5 seconds and pulled out from the diluted slurry, and then excess slurry was removed by air flow. Further, after drying at 30 to 60 ° C., it was calcined at 400 ° C. for 30 minutes to obtain a catalyst D. This catalyst D contained 0.5 g of platinum and 120 g of activated alumina per liter of the finished catalyst.

Regarding the obtained catalyst D, Example 1-
The performance was evaluated in the same manner as in, and the results are shown in Table 1.

[0025]

[Table 1]

From these results, the catalyst inlet temperature is 400 ° C.
Then, the catalyst D of the comparative example has a relatively small amount of particulates because the amount of sulfate is small and the amount of SOF is reduced, while the catalysts A, B and B of Examples 1 to 3 and It is recognized that C has a reduced particulate because SOF is reduced without generation of sulfate.

At the catalyst inlet temperature of 600 ° C., the catalyst D of the comparative example has a large amount of sulfate, and the SOF increases.
On the other hand, in the catalysts A, B, and C of Examples 1 to 3, since the generation of sulfate was suppressed and was small, it was confirmed that the particulates did not increase.

It was confirmed that HC and CO were reduced in the catalyst D of the comparative example, while the catalysts A and C of Examples 1 and 3 were less reduced, but were reduced in the catalyst B of Example 2. To be

[0029]

Since the present invention uses zirconium phosphate as an active substance, it is possible to remove HC, CO and SOF contained in particulates in exhaust gas discharged from a diesel engine, and to remove particulates. Remarkable effects such as the reduction of the amount of curate discharged and the suppression of the formation of SO ₂ into sulfate can be observed.

Claims (5)

[Claims] 1. A catalyst for purifying exhaust gas of a diesel engine, comprising zirconium phosphate as a catalyst component supported on a support having an integral structure. 2. The catalyst for purifying exhaust gas from a diesel engine according to claim 1, wherein the support having an integral structure is made of a refractory metal oxide or a refractory metal. 3. A zirconium phosphate having a P / Zr molar ratio of 0.1 to 10, and a crystal structure thereof having an amorphous structure, a two-dimensional layered structure, or a three-dimensional network structure. The catalyst for purifying exhaust gas from a diesel engine according to claim 1. 4. The amount of zirconium phosphate supported on a support having an integral structure is 20 to about 1 liter of the support.
The catalyst for purifying diesel engine exhaust gas according to claim 1, wherein the catalyst is 200 g. 5. A catalyst for purifying diesel exhaust gas, which comprises a step of preparing a slurry containing zirconium phosphate, a step of supporting the slurry on a support having an integral structure, and a step of firing the slurry. Manufacturing method. .