JPS605230A - Catalyst for treating combustion exhaust gas - Google Patents

Abstract

PURPOSE:To provide a catalyst capable of effectively treat combustion exhaust gas over a long period of time, obtained by forming a coating layer comprising heat stable oxide to the surface of a catalyst layer supported by a carrier. CONSTITUTION:A honeycomb structure, a porous body or a reticulated structure is formed of a material selected from ceramics, a heat resistant metal and a heat resistant inorg. fiber to prepare a carrier and a catalyst layer formed of a substance selected from platinum, palladium and a mixture of platinum and palladium is supported by said carrier. To the surface of this catalyst layer, a coating layer comprising alumina or a mixture of alumina and at least one oxide selected from silica, titania, celia and zirconia is formed in a thickness of 15- 60mum so as to adjust the total BET surface area of the coating layer and the catalyst layer to 15m<2> or more per one gram of the catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a long-term activity-sustaining combustion exhaust gas treatment catalyst, more specifically, natural carbides such as coal, charcoal, beet charcoal, and coconut charcoal, as well as coke and briquettes made from them. To effectively treat carbon monoxide and other components in the combustion gas, including the combustion gas discharged with a large amount of dust during the combustion of solid fuels such as charcoal and charcoal, over a long period of time. This invention relates to a combustion exhaust gas treatment catalyst with an integrated structure and low ventilation resistance.

Coal, coke, charcoal, briquettes, charcoal, etc. are used as solid fuels for stoves, stoves, hibachi, and kotatsu.

It is used as a heat source for heaters such as Anka and Ondol and for cooking, but the problem is that it often causes poisoning due to the carbon monoxide contained in the combustion gas.

Such solid fuels contain many volatile components of inorganic compounds that easily become dust when burned, sublimable components, ash, etc., which are different from gas and liquid fuels, and the combustion gas contains soot, fumes, Generally 0.
It contains a large amount of dust with a particle size of 0.01 to 100 μm.

For example, in the case of briquettes, depending on the manufacturing method and quality of raw materials,
Smoking gas is dust that mainly contains oxides, halides, and sulfides of sodium, potassium, calcium, lead, zinc, tin, antimony, gallium, silicon, and arsenic.

Contains some or all of sulfates, etc., and these compounds directly impregnate the surface of the oxidation catalyst, reducing the active surface area of # components in the catalyst in a short period of time, thereby improving the performance of the catalyst. It is known to significantly reduce

However, as a method for reducing the concentration of, for example, carbon oxide contained in the combustion gas of these solid fuels, conventionally,
Secondary air is mixed into the combustion gas passage at the top of a combustor such as a stove, and the combustion gas is passed through a reactor made of materials such as ceramics and heat-resistant metals to reduce the concentration of carbon monoxide in the combustion gas. This non-catalytic method for removing carbon monoxide, as well as an oxidation catalyst that is effective for oxidizing carbon monoxide in place of the above reactor, especially platinum or platinum, which has remarkable oxidation activity at low temperatures with respect to -carbon oxide. j Methods have been implemented in which radium catalysts are used in their raw form.

However, in the non-catalytic removal method, the gas temperature is 6.
It has the disadvantage that carbon monoxide cannot be removed unless the temperature reaches a high temperature of 30° C., and the removal rate at high temperatures is also low. On the other hand, as mentioned above, the method using an oxidation catalyst has the drawback that the catalyst poison component contained in the dust in the combustion gas directly coats the active part of the catalyst metal component, causing the loss of the ability to oxidize and remove carbon oxides. have. To address this issue, methods have been proposed in which platinum or radium catalysts, which are particularly active against carbon oxides at low temperatures, are used at high metal concentrations; however, such methods require large amounts of expensive precious metals. Generally speaking, it is not suitable for relatively inexpensive solid fuel combustion devices, and has not been put into practical use.

The present invention has been made in view of the above-mentioned drawbacks of the prior art. Therefore, an object of the present invention is to reduce combustion exhaust gas, including solid fuel combustion gas that is emitted with a large amount of dust, for a long time. It is an object of the present invention to provide a combustion exhaust gas treatment catalyst that can effectively treat combustion exhaust gas over a period of time.

According to the present invention, there is provided a combustion exhaust gas treatment catalyst comprising a catalyst layer and a coating layer made of a thermally stable oxide formed on the surface of the catalyst layer.

Hereinafter, the present invention will be explained regarding a carbon monoxide oxidation removal catalyst according to an embodiment of the present invention.

The above-mentioned conventional method of using an oxidation catalyst to remove carbon monoxide from the combustion gas of inexpensive solid fuels such as briquettes uses corzoerite (2Mg0.2At2) as a carrier.
03.5SiO2), mullite (3At205.2S
10□).

Alumina (At203) #Zircon (zro2-sto
2), zirconia (Zr02), aluminum titanate (At203/Tl02), spinel (Mg
O-At20. ), Sponnoyumen (L1□0・At
203/48102), silicon carbide (stc)
Ceramics such as δ: Heat-resistant metals such as iron and stainless steel:
Alternatively, the entire structure, porous body, or network structure formed of heat-resistant fibers may be used, and in order to increase the BET surface area on this carrier and make it easier to support the catalytic metal component, activated alumina, which has a large BET surface area, or a A catalyst is coated with silica, and this active surface layer is further supported with catalyst V, which is effective in oxidizing and removing carbon monoxide, as a catalyst metal component, especially platinum or palladium, which has remarkable low-temperature activity. I am trying to let it pass.

The oxidation catalyst used in the prior art has a porous, monolithic support with a BET surface weight of 1 gram.
Om2 or less, and the catalyst component cannot be supported as it is, so the surface of the carrier is coated with activated alumina, but even with such a coating, the BET surface area is approximately 15 m2 or less per 1 gram heavy surface area. It is. In addition, in the case of this activated alumina surface coating, the presence of microbore with a pore diameter of 300X or less as determined by the pore distribution measurement method using the nitrogen adsorption method was 90.01 per gram weight for the entire oxidation catalyst.
ml or less. In this way, conventional acid conversion catalysts have the following problems: the alumina coating layer and the catalyst metal component are in the same layer and the metal component is exposed on the surface, the BET surface area is small, and the volume of pores with a diameter of 300X or less This has the disadvantage that it is not possible to prevent the catalyst metal components and active surface area from being covered by dust caused by the dust contained in the combustion gas.

In view of the shortcomings of the prior art, the inventors of the present invention have made extensive studies and found that the particle size of dust in the combustion gas of solid fuel is approximately 0.01 μm (xooX) to 100 μm, as described above.
On the other hand, the molecular cross-sections of carbon monoxide, oxygen, carbon dioxide, water vapor, etc. involved in the reaction are all 20×2
(square angstrom) or less, therefore, if the surface of the catalytically active metal component is coated with a thermally stable oxide containing abundant pores of 100X or less and dust is captured by this coating layer, the combustion gas The present invention was completed based on the knowledge that the catalytic metal component can effectively maintain its catalytic activity over a long period of time because the components pass through the pores and react on the surface of the catalytic metal component. did.

Alumina is a suitable thermally stable oxide that can be used in the present invention. As the alumina, for example, γ-alumina, η-alumina, δ-alumina, ni-alumina, χ-alumina, and θ-alumina can be used. Formed amorphous alumina is also suitable for use. In this case, the BET surface area of the alumina component of the coating layer is 1 gram per gram of alumina.
00 m2 or more, and the pore volume of microbore with a pore diameter of 100X or less as determined by pore distribution measurement method using nitrogen adsorption method is pQ, 2 m per 1 gram weight of alumina.
It is preferable that it is 1 or more. Furthermore, as the thermally stable oxide, a mixture of such alumina and other thermally stable oxides can also be used. Examples of such other oxides include silica (StO□), titania (TiO□), and ceria (CeO2)-zirconia (ZrO2).Such oxides have an M area ratio of 0.1 to alumina. Commercially available products can be used for each of these oxides. Relatively large oxides can also be used.The BIT surface area of these oxides is 50 m2 per gram weight.
The above is preferable. Alternatively, a mixture of such oxides is
It is also possible to load a water-soluble titanium, cerium or zirconium compound together with alumina into a Zeel mill, mix and grind the compound, support it on alumina, coat it on an oxidation catalyst, and then sinter it to finally form an oxide.

It is advantageous for a thermally stable oxide or alumina, which forms its main component, to have a large BET surface area and a large pore volume so as to provide many places for dust to be deposited on its surface. Preferably, the surface area is at least 9100 m'' per gram weight, and the volume of pores with a diameter of 100X or less is at least pQ,2 m1 per gram weight h1-.

Such thermally stable oxides can be deposited on the silicon oxidation catalyst by a variety of methods. For example, by adding a filtrate or a mixture thereof to an aqueous solution of a surfactant? - Perform pulverization treatment in Lumir for more than 50 hours to completely form a slurry with an average particle size of 10 μm or less, and then immerse, for example, an oxidation catalyst supported on a carrier in a slurry, and then remove excess by using an air flow. The catalyst can be coated with a layer of oxide by drying after removal of the slurry and final calcination at temperatures above 500°C. In this case, the thickness of the coating layer can be controlled by adjusting the concentration of coating layer components in the slurry or the viscosity of the slurry with water.

An example of the oxidation catalyst thus formed is shown enlarged in FIG. In FIG. 1, reference numeral 1 indicates a honeycomb structure carrier, 2 a catalyst layer, and 3 an oxide coating layer. Support 1 is made of cordierite, similar to conventional catalysts.
Mullite, alumina.

Ceramics such as zircon, zirconia, aluminum titanate, spinel, stainless steel, and silicon carbide; heat-resistant metals such as iron and stainless steel; or honeycomb structures, porous bodies, or mesh structures formed from heat-resistant fibers. I can do it.

The oxide coating layer in the present invention is formed on the surface of the oxidation catalyst to a thickness of 15 to 60 μm.

When the thickness becomes thinner than 15 μm, it becomes difficult to obtain the effect of prolonging the life of the catalyst.On the other hand, as the thickness exceeds 60 μm, there is formation of the coating layer, which can also be measured by observing the cross section of the catalyst with a metallurgical microscope or a scanning electron microscope.

As described above, the oxidation catalyst of this example, which is provided with an oxide coating layer on the surface, can remove carbon monoxide contained in combustion gas containing a lot of dust, such as combustion exhaust gas of briquettes. It can be maintained for a long period of time. This is because the dust is captured by the coating layer having a high BET surface area, which prevents catalyst poisonous substances in the dust from being deposited on the catalyst surface.

Hereinafter, the present invention will be further explained with reference to examples.

Example cordierite (2Mg0・2At203・58 to
□) coated with γ-alumina on a honeycomb structure carrier made of
A carbon monoxide catalyst having a known structure (conventional example 1) with /4' radium supported thereon, and a γ-alumina coating with a thickness of 14 μm applied to the catalyst surface of this conventional example 1. A catalyst having a known configuration (Conventional Example 2) was formed. Further, oxidation catalysts according to the present invention were prepared by forming γ-alumina coating layers on the surface of Conventional Example 1 to thicknesses of 21 μm, 135 μm, and 60 μm, respectively, by the method described above. The physical properties of these catalysts were as shown in Table 1.

Table 1*l...The palladium concentration is the weight in grams of radium supported on catalyst container 11.

Summer 2...The thickness of the alumina coating layer was determined by measuring the cross section of the catalyst using an X-ray microanalyzer (EMX-8 manufactured by Shimadzu Corporation).
M7) f: was used to scan with palladium and aluminum, and measurements were made to distinguish between the alumina layer containing palladium and the aminum oxide layer newly coated on the surface.

*8... Pore volume and distribution are measured using SOAPTOMATIC 1670-3 manufactured by Carloerba, which is a measuring instrument based on nitrogen adsorption.
Measured using a mold.

Each of the catalysts described above was subjected to a long-term carbon monoxide treatment test using the apparatus shown in FIG. 2, using briquette combustion gas as the combustion exhaust gas containing dust. In the apparatus shown in FIG. 2, reference numeral 4 is a catalyst, 5 is charcoal, 6 is a primary air inlet, and 7 is a secondary air inlet. The smoked charcoal 5 used had a diameter of 1501 m.
Height: 140++Ims Weight: 3.4-3.5 kg
The calorific value was 3,200 to 4,600 kcat.

The smoky charcoal 5 is stacked in two layers and burned, and when the smoky charcoal in the lower tier burns out, the smoldering charcoal in the upper tier is moved to the lower tier, the ashed smoldering charcoal is discarded, and a new smoldering charcoal is placed in the upper tier. The analysis was performed using a Horiba fJ MEXA-201F non-dispersive infrared (NDIR)-carbon oxide analyzer. The test results were as shown in Figure 3.

In the conventional catalyst without a coating layer (Conventional Example 1), dust in the smoky charcoal exhaust gas adhered to the catalyst surface, causing a rapid loss of catalytic activity.

Further, the catalyst in which the γ-alumina coating layer was formed to a thickness of 14 μm (Conventional Example 2) also had an insufficient effect of extending the life.

On the other hand, all the catalysts of the present invention can withstand long-term use of 1,600 hours or more without causing any practical problems.

The large difference in catalytic activity between the oxidation catalyst having the coating layer of the present invention and the conventional oxidation catalyst is due to the fact that in the former catalyst, no catalytic metal component is present in the surface layer, and only the coating layer forming component is present. This is due to

Although the combustion exhaust gas treatment catalyst of the present invention has been mainly described with respect to a carbon monoxide oxidation catalyst as an example thereof, the present invention is not limited to such an oxidation catalyst. For example, the combustion exhaust gas treatment catalyst of the present invention can be implemented as a catalyst for purifying hydrocarbons, malodor-producing organic substances, etc. in exhaust gas containing a large amount of dust by catalytic combustion, or for recovering heat by oxidation.

[Brief explanation of drawings]

Fig. 1 is a partially enlarged cross-sectional view showing an embodiment of the combustion exhaust gas treatment catalyst according to the present invention, and Fig. 2 is a schematic cross-sectional view of a test device used to compare the performance of the catalyst according to the present invention and a conventional catalyst. 3 are graphs showing comparative test results. DESCRIPTION OF SYMBOLS 1...Carrier, 2...Catalyst layer, 3...Coating layer, 4...
・Touch 5...Smoky charcoal, 6...Next air inlet, 7.
...Secondary air inlet. Agent Patent Attorney Hide Matsumoto 11Ono234567B Smoked Charcoal Suzenyaki Saima (Murama)

Claims (1)

[Scope of Claims] (1) A combustion exhaust gas treatment catalyst comprising a catalyst layer and a coating layer made of a thermally stable oxide formed on the surface of the catalyst layer. (2) The catalyst layer is made of a material selected from the group consisting of platinum, mother radium, and a mixture of platinum and palladium, and is supported on a carrier, and the coating layer is alumina or alumina and silica. The combustion exhaust gas treatment catalyst according to claim 1, characterized in that it is formed from a mixture with at least one oxide selected from the group consisting of titania, ceria, and zirconia. (3) Claims characterized in that the carrier is a honeycomb structure, a porous body, or a network structure formed of a material selected from the group consisting of ceramics, heat-resistant metals, and heat-resistant inorganic fibers. The combustion exhaust gas treatment catalyst according to item 2. (4) The combustion exhaust gas treatment catalyst according to claim 1 or 2, wherein the coating layer has a thickness of 19 to 60 μm. (5) The coating layer is coated so that the total BET surface area of the coating layer and the catalyst layer is 1) 15 mzW or more per 1 gram of catalyst weight. Claim 1 or 2, characterized in that the coating layer is applied so that the pore volume of the microbore having a pore diameter of 300X or less is 0.02 m1 or more per gram weight of the catalyst. combustion exhaust gas treatment catalyst. (7) The alumina of the coating layer is a BET of alumina component.
The surface area is 100 m" or more per gram of alumina, and the pore volume of microbore with a pore diameter of 100X or less as measured by pore distribution measurement using nitrogen adsorption is 0.0 m" per gram of alumina. The combustion exhaust gas treatment catalyst according to claim 1 or 2, wherein the combustion exhaust gas treatment catalyst has a volume of 2 m1 or more.