JPS59169534A - Catalyst for removing fine particles in diesel exhaust gas - Google Patents

Abstract

PURPOSE:The titled catalyst for removing fine particles based on carbon in diesel exhaust gas while making the same harmless in good efficiency, obtained by allowing a carrier having a three-dimensional reticulated structure coated with activated alumina to support a specific amount of Rh and a selected metal. CONSTITUTION:The surface of a heat resistance carrier having a three-dimensional reticulated integral structure such as cordierite is coated with 20-200g per 1l of the carrier of activated alumina. This catalyst carrier is allowed to support 0.05-2g per 1l of the carrier of Rh by using an aqueous RhCl3 solution and one or more of elements selected from Cu, Ag, Fe, Mg and Zn. By using this catalyst for removing fine particles in the exhaust gas from a disel engine, the conversion of SO2 to sulfate can be suppressed and particulate can be efficiently removed in a harmless state.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalyst for removing particulates mainly composed of carbon emitted from diesel engines.

Harmful components emitted from diesel engines include:
Gaseous CO (-carbon oxide), HC (hydrocarbon), NO
In addition to X (nitrogen oxides), fine particles whose main component is carbon (
(hereinafter referred to as particulates) and S (sulfur) oxide.

In 1980, the US Environmental Protection Agency (EPA) decided to implement tscutiki rate regulations in the United States. A proposed regulation value of 0.2g/mile for light passenger cars and 0.26p/mile for light trucks is being considered. Therefore, in order to pass these regulatory values in the future, it is inevitable that some sort of post-processing device will be required.

For information on how to remove particulates from diesel exhaust,
Many methods have been proposed so far. For example, Tokuko Sho 5
A method of removing exhaust gas by passing it through a filter made of interlaced metal wires coated with alumina as described in No. 6-29581, and an electrostatic filter as shown in JP-A-56-1201.1. There are various methods such as passing the exhaust gas through, or removing the exhaust gas by passing it through a combination of a filter medium and a heater as disclosed in JP-A-56-72213. In addition, a method of removing exhaust gas by passing it through a heat-resistant material of a three-dimensional network structure coated with a substance having catalytic ability (n-type semiconductor oxide) has been proposed in Japanese Patent Laid-Open No. 137040/1983. There is. However, all of these methods have insufficient performance as methods for removing particulates from diesel exhaust from automobiles, etc., are difficult to install, and have the risk of impairing the function of the internal combustion engine due to clogging with particulates. It has some drawbacks. Among the various methods described above, the most preferable method for a particulate removal device to be installed in an automobile is one in which a three-dimensional network structure is coated with a substance having catalytic ability, from the viewpoint of ease of installation and cost.

By the way, as a catalyst for burning and detoxifying particulates of diesel exhaust, it is preferable to use a catalyst that has excellent combustibility of adsorbed hydrocarbons. In other words, the main component in the fine particles is carbon, but it is extremely difficult to act directly on the carbon to gasify and burn it at high temperatures of 600°C or higher, and it is extremely difficult to do so in practice. It is possible to remove fine particles mainly composed of carbon by using combustion as an ignition source.

Catalytic materials for burning this adsorbed hydrocarbon include platinum (pt), palladium (pa), and rhodium (Rh).
) are the most effective.

However, when conventional PT catalysts and Pd catalysts are used for diesel exhaust removal, a problem arises in that they produce sulfates such as sulfuric acid mist. That is, diesel engines normally use light oil that has a higher S content than gasoline, but the S in the light oil is oxidized in the combustion chamber and is discharged as SO2. Therefore, diesel cars have about 10 times more S than regular gasoline cars.
02 is normally included.

For such diesel exhaust, pt, pt-Pd
When a conventional noble metal catalyst containing components such as XPd is used, su2 in the exhaust gas is oxidized to S03, which combines with water at low temperatures to form acid mist or *acid compounds (sulfates). .

The sulfate generated in this way is captured by a filter for particulate measurement, so that the 5 particulates (
is detected as part of the conventional p
When a large amount of sulfate is produced, such as in the case of a T catalyst or a Pd catalyst, a disadvantage arises in that the amount of furnace tiki rate in the outlet gas becomes larger than that of the fine particle component in the catalyst inlet gas. Ma7'r, Rh catalyst is pt catalyst,
Does it have the disadvantage of producing a large amount of sulfate like Pd catalysts, or does it have the disadvantage of being expensive due to the small amount of resource produced?

In view of these circumstances, the present inventor, Akira et al., has developed a method of fine particles in diesel exhaust that can efficiently detoxify and remove the tikilate, which prevents the conversion of S02 to sulfate. We succeeded in providing a removal catalyst.

However, in the catalyst of the present invention, activated alumina is applied to the surface of a heat-resistant integrated structure support having a three-dimensional network structure.
A catalyst carrier coated with 20 to 200 g of rhodium per catalyst carrier 11 is coated with 0.05 to 2 g of rhodium per catalyst carrier 11, and at least one element selected from copper, silver, iron, magnesium, and zinc is supported on the catalyst carrier. That's what happens.

The three-dimensional network structure carrier used in the present invention is desirably a cornoelite ceramic which is heat resistant and has a low coefficient of thermal expansion, but a heat resistant metal carrier may also be used. Regarding ceramic three-dimensional network structures, for example, JP-A No. 56-50165 and JP-A No. 56-62509
No. 56-418b8. Regarding the manufacturing method, please refer to Japanese Patent Application Laid-Open No. 13956-5
No. 0165 describes a solid product in which a slurry consisting of ceramic raw materials, water, and a bubble stabilizer is mixed with air and stirred to create a foamy slurry, and this foamy slurry is poured into a mold and then dried to remove moisture. A method for manufacturing a porous ceramic molded article is disclosed, which is characterized by forming a solid article and firing the solid article to make it porous. In addition, JP-A-5
No. 6-62509 discloses that on the lattice surface of a ceramic porous skeleton having a three-dimensional network structure with an internal communication space and having an electrical ratio of 0.3 to 0.6, a lattice of 3 to 40
A method for producing porous ceramic structures by coating an active layer consisting of 7% by weight of activated alumina and 0.5 to 10% by weight of 7 lux for aluminum has been shown and is still disclosed in JP-A-56-41868. contains an organic polyisocyanate compound, a compound having at least two active hydrogen atoms in the molecule, a ceramic raw material, water, a surfactant with high cell openness, and a blowing agent if necessary. A method for producing a reticulated porous ceramic is disclosed, which comprises mixing, foaming, and firing the foam.

For example, a heat-resistant three-dimensional metallic network structure is disclosed in Japanese Patent Application Laid-Open No. 56-55504, and a method for manufacturing the same is described in which the inside is three-dimensionally communicated in multiple directions and the outside is also connected. A step of embedding a prototype made of an organic substance having a communicating space in a liquid investment material that does not decompose at the sintering temperature of the tombstone, filling it to the inside with liquid investment material, and drying and solidifying the investment material; Following the process, the investment material is heated to decompose and eliminate the original mold made of organic matter, and a mold made of the investment material that has a hole in the same shape as the original mold is created inside the investment material, and after this step, sintering is performed. If it has metal powder or ceramic powder and organic binder and further organic solvent.

A step of pouring a fluid suspension mixed with water into the hole of the mold made of the investment material and drying and solidifying it, and then sintering the metal powder or ceramic powder in the fluid suspension. Production of a porous body, comprising the steps of: sintering these powders at high temperature while extinguishing the binder; and following this step, removing a mold made of investment material from the sintered body. A method is disclosed in Japanese Patent Application Laid-Open No. 56-55504. In the case of a cornoelitic structure, the apparent bulk density is preferably 0.2 to 0.6 and the pore diameter is preferably 6 to 30 mesh. The activated alumina used to coat the surface of the carrier may be γ, δ, η, ρ, θ, etc., but inert alumina with an extremely small specific surface area such as α alumina is a hydrocarbon. It cannot be used because of its low adsorption power and low ticulate collection rate. Activated alumina coating on the surface of the carrier is 20 to 20011 per 11 of the carrier.
is appropriate. When the coating t,1 is less than 209 per carrier 11, the particulate removal rate is small;
If the weight exceeds 200g per unit, the pressure loss will increase significantly.

Salts used to support Rh, a catalyst component, include rhodium chloride, rhodium nitrate, rhodium sulfate, rhodium ammine compounds, etc. These salts can be made into acidic or basic aqueous solutions, or dissolved in organic solvents. , a given Rh
After adjusting the concentration, Rh can be applied by impregnating and adsorbing these solutions. The amount of Rh supported is preferably 0.05 to 2y per activated alumina coated catalyst carrier 11. If the supported amount is less than 0.05 g per catalyst carrier, the catalyst performance will be insufficient, while if the supported amount is less than 2 g per catalyst carrier, no increase in effectiveness will be seen due to an increase in the supported amount. . As the salts used for supporting other supported components, chlorides, nitrates, sulfates, etc. are suitable.

Examples of this invention will be described below along with comparative examples.

Comparative Example 1 Corsoelite three-dimensional network structure] Shi body (diameter 120
m, length 130+mn, particle size 13 mesh, apparent bulk specific gravity 0.35), activated alumina 110 gC carrier 11/7
5g) was coated, dried at 110°C, and calcined at 700°C to obtain a catalyst carrier. Then, 0.1 per V catalyst carrier 11
RhCt whose concentration was adjusted so that g of Rh was supported
The catalyst carrier coated with activated alumina was impregnated in the 5 solution, dried at 100°C, and then soaked in the air at 500°C.
A completed catalyst B was obtained by calcination for a period of time. Catalyst B was subjected to catalyst performance evaluation tests (tests for particulate removal rate, sulfate generation lid, and catalyst pressure loss increase) using the equipment and method described later, and the results are shown in Figures 2 to 4. Ta.

Example 1 Per 11 catalyst carriers of catalyst B obtained in Comparative Example 1, 0.
Cu whose concentration is adjusted so that 1 mol of Cu is supported
After the nuclear catalyst B was immersed in the (NO3)2 solution, it was taken out from the solution, dried at 100°C, and further calcined in air at 500°C for 2 hours to obtain a completed catalyst H. A catalyst performance evaluation test was conducted on this catalyst H in the same manner as in Comparative Example 1, and the results are shown in FIGS. 2 to 4.

Example 2 Per 11 catalyst carriers of catalyst B obtained in Comparative Example 1, 0.01
AgN whose concentration is adjusted so that moles of Ag are supported
After immersing the catalyst B in an O3 solution, it was taken out from the solution, dried at 100°C, and further calcined in air at 500°C for 2 hours to obtain a completed catalyst I. A catalyst performance evaluation test was conducted on this catalyst I in the same manner as in Comparative Example 1, and the results are shown in FIGS. 2 to 4.

Example 3 01 per 11 catalyst carriers of catalyst B obtained in Comparative Example 1
The concentration was adjusted so that moles of Fe were supported.
After impregnating the catalyst B in the NO3)2 solution, the bath solution was poured out, dried at 100°C, and further calcined in air at 500°C for 2 hours to obtain the finished catalyst J. A catalyst performance evaluation test was conducted on this catalyst J in the same manner as in Comparative Example 1, and the results are shown in FIGS. 2 to 4.

Example 4, per 11 catalyst carriers of catalyst B obtained in Comparative Example 1, 0.
Mg concentration adjusted so that 1 mol of Mg is supported
After immersing the catalyst B in the (NOx)2 solution, it was taken out from the M solution, dried at 100°C, and further calcined in air at 500°C for 2 hours to obtain the finished catalyst K. A catalyst performance evaluation test was conducted on this catalyst K in the same manner as in Comparative Example 1, and the results are shown in FIGS. 2 to 4.

Example 5 Per 11 catalyst carriers of catalyst B obtained in Comparative Example 1, 0.
Zn concentration adjusted so that 1 mol of Zn is supported
After immersing the catalyst B in the (NO3)2 solution, it was taken out from the solution, dried at 100°C, and further calcined in air at 500°C for 2 hours to obtain a finished catalyst. A catalyst performance evaluation test was conducted on this catalyst using Comparative Example 1 and the specific method, and the results are shown in FIGS. 2 to 4.

Comparative Example 2 01 per catalyst carrier of catalyst B obtained in Comparative Example 1
The concentration of Mn (
After immersing the catalyst B in the NO3)2 solution, it was taken out from the solution, dried at 100°C, and further calcined in air at 500°C for 2 hours to obtain a completed catalyst Mk. A catalyst performance evaluation test was conducted on this catalyst M in the same manner as in Comparative Example 1, and the results are shown in FIGS. 2 to 4.

Comparative Example 3 Per 11 catalyst carriers of catalyst B obtained in Comparative Example 1, 0.
Cr whose velocity is adjusted so that 1 mol of Cr is supported
After immersing the catalyst B in the (NO3)3 solution, it was taken out from the bath liquid, dried at 100°C, and further calcined in air at 500°C for 2 hours to obtain a finished catalyst N. A catalyst performance evaluation test was conducted on this catalyst N in the same manner as in Comparative Example 1, and the results are shown in FIGS. 2 to 4.

Comparative Example 4 Corsoelite three-dimensional network structure carrier (W diameter 120+
in, length 130 wn, particle size 13 mesh, apparent specific gravity 0.35) was coated with 110 g activated alumina (75 g per 1 carrier), dried at 110°C, and further heated at 700°C.
A catalyst carrier was obtained by calcination. Then, 0.05 g, 0.5, 9, 1.09 and 2.0 g per 11 of the catalyst carriers.
The concentration of RhCt3 is adjusted so that Rh is supported.
After immersing the catalyst carrier coated with activated alumina in the solution, it was taken out from the solution, dried at 100°C, and further calcined in air at 500°C for 2 hours to obtain the completed catalyst AXCX.
D and E were obtained. Catalysts A, C, D, and E were subjected to performance evaluation tests in the same manner as in Comparative Example 1, and the results are shown in FIGS. 2 to 4.

Comparative Example 5 Cordierite three-dimensional network structure carrier (diameter 1201
11I++1 length 130III++1 particle size 13 mesh, apparent specific gravity 0.35) was coated with activated alumina 11oN' (75 g per 11 carrier), dried at 110°C, and further calcined at 700°C to obtain a catalyst carrier. Next, the catalyst carrier coated with activated alumina was immersed in a nonitrosaminoplatinum solution whose concentration was adjusted so that 042 g of pt was supported on each catalyst carrier 11, and then taken out from the solution and dried at 100°C. Then, the catalyst was further calcined in air at 400° C. for 3 hours to obtain a completed catalyst F. A catalyst performance evaluation test was conducted on this catalyst F in the same manner as in Comparative Example 1, and the results are shown in FIGS. 2 to 4.

Comparative Example 6 Cordierite three-dimensional network structure carrier (@120 m diameter
mX length 130 scale, particle size 13 mesh, apparent specific gravity 0.3
5) was coated with 110 g of activated alumina (75 g per 11 carriers), dried at 110°C, and further calcined at 700°C to obtain a catalyst carrier. Next, the activated alumina-coated catalyst carrier r was placed in a baradium chloride solution whose concentration was adjusted so that 1 g of Pd was supported per catalyst carrier 11.
After immersion, the catalyst was reduced with sodium borohydride, washed with hot water, dried at 100°C, and calcined in air at 500°C for 1 hour to obtain a completed catalyst G.

A catalyst performance evaluation test was conducted on this catalyst G in the same manner as in Comparative Example 1, and the results are shown in FIGS. 2 to 4.

A performance evaluation test was conducted on the catalysts A-N obtained in the above-mentioned Examples to 5 and Comparative Examples to 6. A schematic diagram of the performance evaluation test equipment is shown in Figure 1. ennon 1
A 2.2.00 cc L-type engine manufactured by Toyota Motor Corporation was used. Engine operating condition is 2.00 Or
pm, and the load was 8 kg-m. Collection container 2 filled with the catalyst in the middle of the exhaust system of this engine 1
A sampling pipe was installed before and after the collection container 2, and a three-way cock 4, a filter case 6, a suction pump 7, and a gas meter 8 were installed in the middle of each pipe.

A heating heater 3 was wrapped around the sampling pipe leading to the filter case.

If the sampling gas temperature is low, moisture will condense and particulates will adhere to the sampling pipe, making it impossible to accurately measure the amount of particulates. The heating heater 3 was wrapped to prevent moisture condensation. A suction pump 7 was installed to flow the exhaust gas at a constant flow rate, and a gas meter 8 was installed to measure the capacity of the exhaust gas to pass through. The filter case 6 contained a Teflon-coated filter with a diameter of 47 cm. Note that the manometer 5 was installed as shown in the figure in order to measure the increase in pressure loss of the catalyst, as will be described later.

The measurement was carried out by switching on and off the exhaust gas by switching the three-way cock 4, but the particulate amount was measured by passing the 40A exhaust gas through a Teflon-coated filter in the filter case 6, This was done by measuring the weight of particulates in the exhaust gas collected before and after the test.

- The ticulate removal rate was calculated using the following formula, and the results are shown in Figure 2.

Particulate removal rate (porridge)Next, we measured the amount of sulfate in the exhaust gas when catalyst A-N was used.The measurement was carried out using barium phosphorus luminosity using a filter sampled in the same manner as the particulate measurement. Quantitative analysis was performed using the titration method.The results are shown in Figure 3.Furthermore, to measure the increase in pressure drop, the performance evaluation test equipment shown in Figure 1 was used.
A mercury manometer was installed in front of the catalyst container [L, the front pressure of the catalyst container when the engine was started at 2.00 rpm and the front pressure after 24 hours of engine operation were measured, and the differential pressure was calculated. It was calculated on the assumption that this corresponds to the increase in pressure loss of the catalyst.

The results obtained are shown in FIG.

Based on the results of the above examples and comparative examples, the table below shows
・Guticulate removal rate, sulfate amount,
A comprehensive evaluation of pressure drop increase and cost is shown. As is clear from these, the catalysts shown in the comparative examples have drawbacks in terms of particulate rate removal rate, amount of sulfate produced, increase in pressure loss, and cost, whereas the catalysts of the present invention (example) It can be seen that the particulate removal rate, the amount of sulfate produced, the increase in pressure drop, and the cost are satisfactory, and that it is extremely useful.

table ○...Good, △...Town, ×...Not acceptable

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a performance evaluation device for a catalyst for removing particulates from diesel exhaust, and Fig. 2 shows catalysts of the present invention (H, I, JXK, and L) and comparative catalysts (A, BX).
Figure 3 is a straight line diagram and a bar diagram showing the removal rate of the zeti-key rate in the exhaust gas using catalysts H, I, and CXDXEXF, G, M, and N.
, JXK, LXA, B, C, D, E, F, G, M and N. JXK,L
, AXB, C, DXE. 24 at 2,000 rpm using FXGXM and N
FIG. 2 is a curve diagram and a bar diagram showing an increase in pressure loss of the catalyst with respect to the start of operation when the engine is operated for an hour. DESCRIPTION OF SYMBOLS 1... Ennon, 2... Collection container, 3... Heating heater, 4... Three-way cock, 5... Manometer, 6... Filter case, 7... Suction bonde, 8
...Gas meter.

Claims (1)

[Claims] A catalyst carrier formed by coating the surface of a heat-resistant monolithic structure carrier having a three-dimensional network structure with 20 to 200 g of activated alumina per carrier 11 was coated with 0.0 g of rhodium per catalyst carrier 11.
A catalyst for removing particulates from diesel exhaust, which supports 5 to 2y and at least one selected from copper, silver, iron, magnesium and zinc.