JP2863568B2 - Exhaust gas purifying material and exhaust gas purifying method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying material and a method for purifying exhaust gas using the exhaust gas purifying material, and more particularly to an exhaust gas comprising a foam type filter carrying a catalyst. The present invention relates to a purifying material and a method for purifying exhaust gas using the purifying material.

[Problems to be solved by conventional technology and invention]

In recent years, nitrogen oxides and particulate carbon substances (particulates) in exhaust gas of diesel engines have become environmentally problematic. In particular, particulates easily float in the air and are easily taken into the human body by breathing.Therefore, reduction of particulates is urgently needed.A method of capturing and burning particulates using a heat-resistant filter from an early stage, or a method using a catalyst A method of burning particulates at a lower temperature using a heat-resistant filter to regenerate the filter has been proposed. In particular, the latter method is considered to be a better method because the filter can be regenerated at a lower temperature, the regeneration time of the filter is shortened, and the heat resistance of the filter is considered.

However, the exhaust gas temperature of a diesel engine is lower than that of a gasoline engine, the oxygen concentration in the exhaust gas is high, and the amount of SO ₂ in the exhaust gas is high because light oil is used as fuel. A regeneration method that satisfactorily ignites and burns the fine particles accumulated under such exhaust gas conditions and does not cause secondary pollution has yet been established.

For example, when a noble metal catalyst is supported on a filter,
Lowering of the ignition temperature of the particulate, it is effective for purification of unburned hydrocarbons or CO,, and to produce an SO ₃ to oxidize the SO ₂ in the exhaust gas, it is such as characteristic deterioration of the catalyst due to ash problem Wake up. On the other hand, the use of a base metal-based catalyst is effective in lowering the ignition temperature of particulates, and the generation of SO ₃ is small, but the purification ability of CO is low.

Therefore, an object of the present invention is to provide a function of effectively burning and purifying particulates contained in exhaust gas having a relatively high oxygen concentration found in diesel engines and the like, and an unburned hydrocarbon (hereinafter referred to as HC) by suppressing SO ₃ generation. And a method of purifying exhaust gas having a function of reacting CO with residual oxygen and purifying the exhaust gas effectively, and an exhaust gas purifying method using the purifying material.

[Means for solving the problem]

In view of the above problems, as a result of intensive research, the present inventors have found that a foam-type heat-resistant porous filter having two layers with different densities, a base metal-based catalyst that improves particulate combustion characteristics, and a similar increase in particulate combustion characteristics, HC and
By supporting a platinum group-based catalyst having a CO purifying ability, it has been found that an exhaust gas purifying material having a good particulate removing ability and an HC and CO purifying ability and a method thereof can be obtained. completed.

That is, the exhaust gas purifying material of the present invention is an exhaust gas purifying material using a heat-resistant porous foam type filter as a carrier, wherein the filter is located at a high-density thin layer portion located at an inlet side of an exhaust gas flow and at an outlet side. The high-density thin layer portion carries a platinum group element, and the relatively low-density portion includes (a)
Alkali metal elements and (b) groups IB, IIB, VA of the periodic table
One or two members selected from the group consisting of Group VIII transition elements except for Group VIA, Group VIA, Group VIIA, and Platinum group elements, and Sn
It is characterized in that more than one kind of element is supported.

The exhaust gas purifying method of the present invention is a method of purifying exhaust gas using an exhaust gas purifying material comprising the heat-resistant porous foam type filter, wherein the high-density thin layer portion is an exhaust gas inlet side, The low-density filter portion is the outlet side of the exhaust gas, and the high-density thin-layer portion burns or ignites most of the particulates in the exhaust gas at a low temperature and oxidizes and removes HC and CO, thereby removing the low-density filter. Particulates burn the particulates that have passed through the high-density thin layer portion.

 Hereinafter, the present invention will be described in detail.

As a catalyst for oxidizing particulates, HC and CO, a catalyst containing a platinum group element having high oxidizing ability is used. This may be a Pt-based catalyst or a Pd-based catalyst, or a Pt-based and Pd-based mixed catalyst, or a Pt-based, Pd- and Rh-based mixed catalyst. Further, the platinum group element-based catalyst may be further loaded with gold or silver.

On the other hand, the particulate oxidation catalyst supported on the low-density filter portion includes (a) an alkali metal, and (b) elements IB, IIB, VA (V, Nb, Ta) and VIA (Cr , Mo,
W), VIIA (Mn, Tc, Re) and VIII not containing platinum group elements
And at least one element selected from the group consisting of group elements (Fe, Co, Ni) and Sn. These catalysts work effectively to increase the burning rate of particulates and to lower the ignition temperature. When an alkali metal and another element described above are used in combination, the catalytic effect can be expected to be further improved.

In the present invention, the above two types of catalysts are separately supported on two parts of the filter. Particulates and H
The platinum group catalyst for oxidizing C and CO is supported on the high-density thin layer portion of the filter, and this portion serves as the exhaust gas inlet side. The catalyst for particulate oxidation is supported on a relatively low-density portion of the filter, and this portion is set on the exhaust gas outlet side.

By providing the filter and the catalyst in this way, the action of purifying the exhaust gas is further improved. The reasons include the following (1) to (5).

(1) Since the exhaust gas inlet side has a high density, the particulates are effectively trapped in the thin layer portion at the filter inlet.

(2) Since the exhaust gas comes into contact with the catalyst supported on the inlet side of the filter more frequently, HC and CO are oxidized on the surface of the catalyst supported on the inlet side of the filter, and the particulates are effective. Burned or ignited.

(3) Even if the back pressure increases, the particulates are captured without being blown out. Then, the particulates that have passed through the high-density layer on the inlet side enter pores inside the filter on the outlet side, and are effectively burned on the catalyst surface there.

(4) Since the exhaust gas is efficiently purified by the above (2), no abrupt pressure loss occurs.

(5) The platinum group catalyst in the high-density thin layer on the inlet side of the exhaust gas gives priority to particulates, oxidation of HC and CO, and SO
₃ Generation is suppressed.

The foam-type heat-resistant filter is required to have a required particulate collection performance while providing a pressure loss within an allowable range, and alumina, silica, zirconia, silica-alumina, and alumina-usually used as a carrier are required. Examples of the ceramic foam include zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, mullite, cordierite, and the like.

There are several methods for forming a high-density thin layer on one surface of the heat-resistant porous foam type filter. (A) Glycerin, water, and a surfactant are formed on the bottom of a mold having a desired shape. A method of applying a release agent, pouring a slurry of cordierite or the like into the mold, separating the mold, drying and firing, or (b) first forming a uniform filter, and powdering an organic binder and cordierite or the like. Is mixed, applied to one surface of the filter, dried, and fired.

In this way, the porosity of the formed high-density thin layer portion is 40 to 85%, and the pore size is 3 to 800 (300 μm on average).
m). In order to avoid ash deposition, the pore size is preferably 30 μm or more. The thickness of the high-density thin layer itself is preferably 0.2 to 2 mm.

As a method of impregnating the foam-type heat-resistant filter with the catalyst for removing the paticute, carbonates, nitrates,
A known method such as a method of immersing the heat-resistant filter in a solution such as acetate or hydroxide can be employed. A method is also possible in which the filter is immersed in a solution of a compound containing a plurality of base metal-based metals such as alkali ferrocyanide to impregnate the catalyst.

Similarly, as a method of impregnating the high density thin layer portion of the filter with the platinum group catalyst, a method of immersing only the high density thin layer portion on the exhaust gas inlet side of the filter in a solution of platinum group chloride or the like is used. Can be adopted.

Further, in order to increase the area for carrying the catalyst, it is practical to use it by indirectly supporting it on a heat resistant filter via a carrier powder having a large surface area, such as alumina, silica, and titania, as described above. . In particular, since the high-density thin layer portion has almost no thickness, it is desirable to support the catalyst at a high concentration, and titania, titania-alumina, titania-coated with a carrier powder having a large surface area such as titania-based porous silica, It is preferable to immerse in a chloride aqueous solution such as Pt, Pd, Rh, and Au. Also, in order to carry the catalyst at a high concentration,
Furthermore, a solution containing a high concentration of catalyst can be applied only to the surface of the high-density thin layer portion to increase the amount of supported catalyst.

Further, when a filter immersed in a chloride aqueous solution of Pt, Pd, Rh, Au or the like is irradiated with light, the catalyst can be supported very effectively. Alternatively, a method in which a platinum group element-based catalyst is first supported on a titania-based carrier by light irradiation, and the titania-based carrier is coated on a filter thin film is also possible. When this light irradiation method is used, it is highly dispersed and well fixed to the titania carrier, the coating layer of the filter can be made thin, and the pressure loss can be reduced when the catalyst is carried on a thin layer having a high density. It is valid.

 The present invention is described in more detail by the following examples.

〔Example〕

Example 1 A high density (2.2 g / ml) thin layer portion was formed on one side of a cordierite ceramic foam filter (apparent volume 2 l, density 0.65 g / ml) by the above-described method.

Γ-alumina is applied to the portion except the thin layer portion with respect to the foam filter to be coated at 10% (% by weight, the same applies hereinafter)
This was impregnated with potassium carbonate using potassium carbonate and 2.5% of γ-alumina, and then with CrCl ₃ using 2.5% of Cr. The thin layer portion was coated with 1% of γ-alumina based on the weight of the thin layer, and then Pt was converted to γ-alumina from an aqueous H ₂ PtCl ₆ solution.
The alumina was impregnated with 0.2%. (Al ₂ O ₃ / K / Cr-Al ₂ O ₃
/ Pt: Example 1) For this purifying material, the ignition temperature of particulates (temperature at which pressure loss decreases) and the exhaust gas purification characteristics were evaluated using a 510 cc single cylinder diesel engine. At this time, the engine was operated at 1500 rpm and a load of 90%. Under these conditions, CO was about 460 ppm and oxygen concentration was 5%. Table 1 shows the ignition temperature of the purifying material, Table 2 shows the particulate collection efficiency, and Table 3 shows the change in CO concentration.

Examples 2 to 8 In the same manner as in Example 1, except that the thin layer portion was impregnated with 2.5% of Na using sodium carbonate and 2.5% of Cu using CuCl ₂ (Example 2), or potassium carbonate was used. Using K to 2.
Mn was impregnated with 5% and MnCl ₂ , respectively, at 2.5% (Example 3), or potassium carbonate was impregnated with 2.5%, and V was impregnated with NH ₄ VO ₃ , respectively (Example 4). ). Further, each thin layer portion was impregnated with 0.2% of Pt to produce the following exhaust gas purifying material.

(Al ₃ O ₃ / Na / Cu-Al ₂ O ₃ / Pt: Example 2) (Al ₂ O ₃ / K / Mn-Al ₂ O ₃ / Pt: Example 3) (Al ₂ O ₃ / K / V-Al ₂ O ₃ / Pt: Example 4) Similarly, the same impregnation was performed as in the above example except for the thin layer portion, and the thin layer portion was filtered with TiO ₂ instead of Al ₂ O _3. After coating 1% by weight of H ₂ PtCl ₆ and / or P
The thin layer portion was immersed in an aqueous solution of dCl ₂ and irradiated with light using a 500 W Hg lamp, impregnated with 0.2% of Pt and Pd, respectively, to produce the following exhaust gas purifying materials.

(Al ₂ O ₃ / K / Cr-TiO ₂ / Pt: Example 5) (Al ₂ O ₃ / Na / Cu-TiO ₂ / Pd: Example 6) (Al ₂ O ₃ / K / Mn-TiO ₂ / Pt / Pd: Example 7) (Al ₂ O ₃ / K / V-TiO ₂ / Pt: Example 8) The exhaust gas purifying materials of Examples 2 to 8 were also produced in the same manner as in Example 1. The ignition temperature of particulates and the exhaust gas purification characteristics were evaluated. Table 1 shows the ignition temperature (Examples 1 to 4) of each purifying material, Table 2 shows the particulate collection efficiency at 300 ° C (Examples 1, 2, and 5), and Table 3 shows the results.
Changes in the concentration of CO at 400 ° C. (Examples 1 to 8) are shown respectively.

Comparative Examples 1 to 4 For comparison, the following four purifying materials were experimentally manufactured, and the ignition temperature, the particulate collection efficiency, and the CO concentration change were measured in the same manner as in the examples. The respective results are similarly calculated for the first to third
It is shown in the table.

Comparative Example 1: Filter with no catalyst supported.

Comparative Example 2: A filter having the same catalyst as in Example 1, but without a high-density thin layer portion.

Comparative Example 3: A filter that does not carry a platinum group catalyst in the high-density thin layer portion, and has a catalyst of Al ₂ O ₃ / K / Cr for particulate purification.

Comparative Example 4: A filter in which a platinum group catalyst is not supported on a high-density thin layer portion, and has a catalyst of Al ₂ O ₃ / Na / Cu for particulate purification.

Each of the purifying materials of Examples 1 to 4 showed an ignition temperature of 400 ° C. or less, and the particulate purifying characteristics were high. In the particulate collection efficiency measured at 300 ° C., the filter with a thin layer showed 80% or more, while the filter without a thin layer showed only 50% at most. Regarding the purification characteristics of CO, a purification material having no platinum group element carried in a thin layer has little CO purification ability and tends to have a slightly higher CO. %, And the purification material carried by light irradiation showed a purification characteristic of 45% or more. In addition, when these purifying materials were used, SO ₃ was hardly generated.

〔The invention's effect〕

When the exhaust gas purifying material of the present invention is used, the collection efficiency of particulates in exhaust gas is improved, and an excellent action for purifying CO and HC is also exhibited. Such exhaust gas purifying materials are
It can be expected to be particularly effective for purifying exhaust gas containing a large amount of particulates such as diesel engines and having a relatively high oxygen concentration.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 23/42 B01J 23/44 A 23/44 23/78 A 23/78 35/02 P 35/02 F01N 3/02 321A F01N 3/02 321 B01D 53/36 104Z (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 39/14 B01J 23/00-23/96, 35/02

Claims (3)

(57) [Claims] An exhaust gas purifying material comprising a heat-resistant porous foam type filter as a carrier, wherein the filter comprises a high-density thin layer located on the inlet side of the exhaust gas flow, and a relatively low-density layer located on the outlet side. A platinum group element is supported on the high-density thin layer portion, and the relatively low-density portion includes (a) an alkali metal element;
(B) at least one member selected from the group consisting of Sn, IB, IIB, VA, VIA, VIIA, and VIII transition elements excluding platinum group elements; An exhaust gas purifying material characterized by carrying an element. 2. The exhaust gas purifying material according to claim 1, wherein
An exhaust gas purifying material, wherein the high-density thin layer portion further supports gold or silver. 3. The method for purifying exhaust gas using the exhaust gas purifying material according to claim 1 or 2, wherein the high-density thin layer portion is an exhaust gas inlet side, and the relatively low-density portion is an exhaust gas purifying material. At the exit side, the particulates in the exhaust gas are burned or ignited at a low temperature in the high-density thin layer portion, and unburned hydrocarbons and CO are oxidized and removed. A method for purifying exhaust gas, comprising burning particulates that have passed through a layer portion.