JP4075412B2 - Particulate combustion catalyst and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a combustion catalyst for particulates contained in exhaust gas of automobiles and the like, and more particularly, to a particulate combustion catalyst suitable for combustion purification of particulates contained in exhaust gas of a lean combustion internal combustion engine, and production thereof. Regarding the method.
[0002]
[Prior art]
Exhaust gas emitted from lean combustion internal combustion engines such as diesel engines generally contains particulate matter particulates, and these particulates are required to reduce emissions early in terms of environmental protection. Has been.
For this reason, various ways of reducing particulates have been studied, and as one of them, a catalyst carrier such as γ-alumina and a catalyst component such as platinum are applied to a filter medium such as a honeycomb substrate in which cells are alternately plugged. The development of particulate filters carrying sapphire is underway.
[0003]
Such a particulate filter filters and captures particulates in the exhaust gas, lowers the combustion temperature by the action of a catalyst, and purifies the captured particulates by combustion.
[0004]
[Problems to be solved by the invention]
However, particulates include carbonaceous particles and soluble organic components (SOF) as flammable components. Carbonaceous particles, in particular, have a high temperature at which combustion starts, so the particulates are filtered while exhaust gas is filtered. There is a problem that it is difficult to continuously burn the particulates, for example, to purify the curates.
[0005]
By the way, the applicant of the present invention disclosed in JP-A-11-347424, JP-A-11-156193 and the like an exhaust gas purifying catalyst carrying an alloy catalyst having high performance for purifying nitrogen oxides and hydrocarbons. is suggesting. However, these publications do not describe any special effects related to particulate combustion.
[0006]
In addition, Japanese Patent Laid-Open No. 2001-98925 proposes an exhaust gas purifying apparatus for purifying particulates carrying an oxide such as Ce and Fe.
It is an object of the present invention to provide a particulate combustion catalyst that greatly facilitates the combustion of particulates, in particular, the combustion of carbonaceous particles, by producing effects different from those of the prior art and / or by using different configurations. And
[0007]
[Means for Solving the Problems]
The above objects, on top of which is supported on the oxide support a noble metal, and one transition metal is directly supported on the at no small, noble metal, platinum, palladium, rhodium, gold, and from the group consisting of ruthenium It is achieved by a particulate combustion catalyst characterized in that the selected and transition metal is selected from the group consisting of iron, nickel, cobalt, and manganese .
[0008]
Such catalysts have been found to significantly reduce the combustion start temperature of the carbonaceous particles, as shown in the Examples below. The reason is presumed as follows.
A noble metal such as platinum has an action of dissociating oxygen molecules O ₂ into active oxygen atoms O ^*, and the oxygen atoms O ^* have an extremely high oxidizing action. Accordingly, a noble metal such as platinum can function as a particulate combustion catalyst. On the other hand, the oxygen atom O ^* has a high affinity with a noble metal, has a property of drifting on the surface of the noble metal and not easily desorbing from the surface.
[0009]
Here, when a transition metal is locally present on the surface of the noble metal, since the affinity of the transition metal with the oxygen atom O ^* is relatively low, the oxygen atom O ^* is easily desorbed at the location where the transition metal exists. Become.
Therefore, the noble metal and the transition metal supported thereon can function as an efficient oxygen donor that dissociates and releases the oxygen molecule O ₂ into the oxygen atom O ^* in the combination of both metals. .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Particulate combustion catalyst of the present invention, on top of which is supported on the oxide support a noble metal, are supported on one transition metal is directly even without small, the noble metal, platinum (Pt), palladium (Pd), A group selected from the group consisting of rhodium (Rh), gold (Au), and ruthenium (Ru), and the transition metal is composed of iron (Fe), nickel (Ni), cobalt (Co), and manganese (Mn) It is characterized by being selected more .
The oxide carrier includes oxides such as alumina, silica, and zirconia, as well as composite oxides such as silica - alumina, zirconia-ceria, alumina - ceria - zirconia, ceria - zirconia - yttria, and zirconia-calcia. Those composed of fine particles having an average particle diameter of 1 μm or less can be suitably used.
[0011]
Precious metals to be supported on the oxide support, good Mashiku is at least one Pt, Pd, Rh. To oxides carrier, the noble metal responsible lifting is accomplished by any method that is capable of supporting the metal on the support. This can be performed, for example, by evaporation to dryness, impregnation, adsorption, ion exchange, reduction precipitation, or the like.
[0012]
Preferably, dinitrodiammine platinum complex Pt (NH ₃ ) ₂ (NO ₂ ) ₂ , chloroplatinic acid H ₂ PtCl ₆ .6H ₂ O, platinum acetylacetonate (acac) ₂ , palladium nitrate Pd (NO ₃ ) ₂ , chloride Using soluble compounds such as palladium PdCl ₂ , rhodium nitrate Rh (NO ₃ ) ₃ , rhodium chloride RhCl ₃ .4H ₂ O, these compounds are dissolved in a slurry in which the above oxide carrier is dispersed in a solvent. Then, the solvent is removed by evaporation or the like, and then supported by a method of baking.
By such a method, the noble metal can be supported on the oxide support in the form of extremely fine particles or an extremely thin film.
[0013]
The transition metal is supported on a noble metal supported on such an oxide support . Good Mashiku is supported transition metal, adding a reducing agent to an aqueous solution of compounds that form ions of transition metals in aqueous solution, and insoluble by reducing the ions of the transition metals, precipitate particles of a transition metal The reduction precipitation method is performed.
[0014]
Specifically, compounds such as transition metal nitrates, sulfates, chlorides, acetates, carbonates and the like are dissolved in an aqueous slurry of an oxide carrier supporting the above-mentioned noble metal, and trisodium citrate is added to the slurry. dihydrate _{C 6 H 5 Na 3 O 7} · 2H 2 O, hydrazine N ₂ H _4, sodium thiosulfate Na ₂ S ₂ O _3, potassium thiosulfate K ₂ S ₂ O _3, ammonium thiosulfate (NH _{4) 2} Reducing agents such as S ₂ O ₃ , sodium sulfite Na ₂ SO ₃ , borohydrides such as sodium borohydride NaBH ₄ , hypophosphite, citrate, formic acid CH ₂ O ₂ , oxalic acid CH ₂ O ₄ Then, a buffering agent such as sodium L-ascorbate C ₆ H ₇ O ₆ Na or ethylenediaminetetraacetate is added to reduce transition metal ions and precipitate transition metal fine particles.
According to such reductive precipitation, it is relatively easy to deposit transition metal fine particles having a diameter of about 1 nm (nanometer) on substantially all precious metal particles or thin films.
[0016]
In such a method, the particulate combustion catalyst of the present invention preferably has a transition metal / noble metal mass ratio of 0.005 to 0.3, more preferably 0.01 to 0.1. It is prepared by adjusting the raw material ratio. In addition, the transition metal is prepared by adjusting the type and concentration of the reducing agent in the reduction precipitation so that the particle diameter of the transition metal is 0.5 to 10 nm, more preferably 0.5 to 5 nm.
[0017]
This is because the mass ratio of transition metal / noble metal and the particle diameter of the transition metal are within these ranges, thereby providing a more effective particulate combustion catalyst.
Even if the metal component other than the noble metal and the transition metal is contained on the oxide support in an amount of several mass% or less based on the total mass of the noble metal and the transition metal, it is acceptable for the purpose and effect of the present invention. be able to.
[0018]
The particulate combustion catalyst of the present invention can form a particulate filter by, for example, coating cells on a honeycomb substrate alternately plugged, or has a high particulate combustion action. A non-clogged honeycomb substrate can be coated or pelletized to form a flow-through particulate purification catalyst.
[0019]
FIG. 1 schematically shows a particulate combustion catalyst of the present invention. When the noble metal is supported on the oxide support using a soluble compound such as dinitrodiammine platinum complex as described above, the noble metal is extremely thin on the oxide support as shown in FIG. It can be supported in the form of a thin film at an atomic level thickness.
The particulate combustion catalyst of the present invention is constituted by a transition metal supported in the form of particles on such a noble metal.
[0020]
When the catalyst is exposed to a high-temperature exhaust gas atmosphere exceeding about 500 ° C. over a long period of time, the noble metal is supported in a thin film state and has a property of changing to a particulate form. In this case, as shown in FIG. 1B, the transition metal is in a state of being supported in the form of particles on the noble metal particles.
The particulate combustion catalyst of the present invention includes both the supported states shown in FIGS. 1 (a) and 1 (b).
Hereinafter, the present invention will be described more specifically with reference to examples.
[0021]
【Example】
Example 1
Using γ-alumina powder as a carrier, this was impregnated with a dinitrodiammine platinum solution, then dried and heat-treated at 500 ° C. for 2 hours in the atmosphere, and 2.00 parts by mass with respect to 100 parts by mass of γ-alumina powder. Of Pt was obtained.
[0022]
30 g of this Pt-supported γ-alumina powder is dispersed in 200 cc of ion-exchanged water at 30 ° C., and the following reagents are sequentially added in the following amounts to the resulting slurry and placed under gentle stirring for 24 hours. Then, Fe was reduced and precipitated from iron chloride FeCl ₃ .6H ₂ O.
FeCl ₃ · 6H ₂ O 0.29g
C ₆ H ₇ O ₆ Na 21.28 g
NaBH ₄ 0.65 g
[0023]
After this reduction precipitation, the slurry is filtered and washed, dried in air at 120 ° C. for 2 hours, and further heat-treated in air at 500 ° C. for 2 hours to support Fe on Pt / γ-alumina. Thus, a catalyst of the present invention having a mass ratio of Al ₂ O ₃ /Pt/Fe=97.8/2/0.2 was obtained.
[0024]
Example 2
In the same manner as in Example 1, except that Pt was supported on γ-alumina powder using dinitrodiammine platinum, and then nickel chloride NiCl ₂ .6H ₂ O was used instead of iron chloride FeCl ₃ .6H ₂ O. In the same manner as in Example 1, Ni was reduced and precipitated to obtain a catalyst of the present invention having an Al ₂ O ₃ / Pt / Ni mass ratio of 97.8 / 2 / 0.2.
[0025]
Example 3
As in Example 1, Pt was supported on γ-alumina powder using dinitrodiammine platinum, and then cobalt chloride CoCl ₂ was used instead of iron chloride FeCl ₃ .6H ₂ O. Then, Co was reduced and precipitated to obtain a catalyst of the present invention having a mass ratio of Al ₂ O ₃ /Pt/Co=97.8/2/0.2.
[0026]
Example 4
In the same manner as in Example 1, except that Pt was supported on γ-alumina powder using dinitrodiammine platinum, and then manganese chloride MnCl ₂ .4H ₂ O was used instead of iron chloride FeCl ₃ .6H ₂ O. Mn was reduced and precipitated in the same manner as in Example 1 to obtain a catalyst of the present invention having a mass ratio of Al ₂ O ₃ /Pt/Mn=97.8/2/0.2.
[0027]
Comparative Example 1
In the same manner as in Example 1, a catalyst having a mass ratio of Al ₂ O ₃ / Pt in which Pt was supported using γ-alumina powder using dinitrodiammine platinum = 100/2 was used as a catalyst of the comparative example.
[0028]
-Evaluation of catalyst performance-
The performance of each of the above catalysts as a particulate combustion catalyst was evaluated as follows.
Each catalyst and commercially available carbon black (Carbon Granular, manufactured by Kishida Chemical Co., Ltd.) were weighed at a mass ratio of 10: 1, and these were carefully mixed using a mortar to prepare each sample.
[0029]
Next, 0.5 g of each sample was placed in an infrared heating furnace capable of controlling the atmosphere, and 100 cc of model gas containing 80% by volume N ₂ and 20% by volume O ₂ was supplied from the model gas generator. The temperature of the sample region was increased from 30 ° C. to 700 ° C. at a rate of 10 ° C./min.
In conjunction with this temperature raising operation, the outlet gas in the sample region was led to the mass spectrometer, and the relative concentration of CO ₂ corresponding to the mass number 44 was measured with respect to the temperature in the sample region. The results are shown in FIGS.
[0030]
FIG. 2 is a chart of the relative concentration of CO ₂ with respect to the temperature of the sample area, measured using a mass spectrometer. FIG. 3 is a graph comparing the CO ₂ production start temperature obtained from the measurement chart for each catalyst.
From these results, it can be seen that the catalysts of Examples 1 to 4 have a CO ₂ production starting temperature that is about 50 ° C. lower than that of the catalyst of Comparative Example 1 that does not carry a transition metal. The combustion promoting effect is remarkable.
[0031]
-Observation of catalyst morphology-
For each of the catalysts of Examples 1 to 4, morphological observation with a transmission electron microscope (TEM) and elemental analysis in the spot region of an electron microscope image by energy dispersive X-ray spectroscopic analysis (EDX) were performed.
As a result, in each of the catalysts, Pt as particles was not observed in a TEM having a resolution of about 1 nm, and it was observed that the transition metal was present as particles having a particle diameter of 2 to 3 nm.
[0032]
On the other hand, from elemental analysis at various locations in a spot region having a diameter of about 1 nm by EDX, it is analyzed that Pt atoms are present on almost all surfaces of Al ₂ O ₃ and the presence of transition metals is analyzed. In the spot region having a diameter of about 1 nm, Pt was always analyzed simultaneously.
From these results, it is judged that Pt is present in the form of a very thin film on the surface of γ-alumina particles, and the transition metal is present in the form of fine particles on the thin film of Pt.
[0033]
【The invention's effect】
It is possible to provide a particulate combustion catalyst that greatly facilitates the combustion of particulates.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a configuration of a catalyst of the present invention.
FIG. 2 is a chart in which the CO ₂ production start temperature is measured by a mass spectrometer.
FIG. 3 is a graph comparing the CO ₂ production start temperature for each catalyst.

Claims (5)

On top of which is supported on the oxide support a noble metal, and one transition metal is directly supported on the at no small, the noble metal is platinum, palladium, selected from the group consisting of rhodium, gold, and ruthenium, and The particulate combustion catalyst , wherein the transition metal is selected from the group consisting of iron, nickel, cobalt, and manganese . The mass ratio of the transition metal / the noble metal is 0.005 to 0.3, particulate combustion catalyst according to claim 1. The particle size of the transition metal is 0.5 to 10 nm, particulate combustion catalyst according to claim 1 or 2. The particulate combustion catalyst according to any one of claims 1 to 3, wherein the particulate combustion catalyst is produced by reducing and precipitating the transition metal after supporting the noble metal on the oxide support. After carrying the noble metal on the oxide support, characterized in that to reduction precipitation of the transition metal, the production method of the particulate combustion catalyst according to any one of claims 1-4.

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