JPS6147576B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to catalysts used in the non-pollution removal of various harmful gases, in particular carbon monoxide and hydrocarbon compounds as an oxidation catalyst, nitrogen oxides as a reduction catalyst, and ammonia as an oxygen or nitrogen oxidation catalyst. The present invention relates to the structure of a catalyst that is effective when applied as an oxidation catalyst in a reaction with a substance. For example, nitrogen oxides (hereinafter referred to as NOx) in exhaust gas
It is said that the catalytic reduction method, which does not require post-treatment, is economically and technically advantageous as a method for removing oxidants, and the selective reduction method, which is not affected by the oxygen concentration in the exhaust gas, is particularly advantageous. ing. Conventionally, as catalysts applied to this type of reduction method, porous refractories such as alumina, titania, zirconia, etc. are used alone or in combination as carriers, but all of them are expensive because they are used in granulated form. Furthermore, when the gas to be treated is exhaust gas containing a large amount of dust, such as exhaust gas from a boiler fueled by heavy oil, coal, etc., there is a problem of performance deterioration due to accumulation of dust on the catalyst. In order to solve this problem, methods are being considered, such as making the catalyst shape cylindrical or honeycomb-like to make it easier for dust to pass through, and making the catalyst granular and moving the granular catalyst to scatter the adhering dust. In addition, there is a method in which the catalyst is formed into a plate or structure layer and the exhaust gas flows parallel to the catalyst layer.As the catalyst for the plate structure, a nonmetallic fireproof board made of an inorganic material that can be manufactured at low cost is used. something is proposed. However, due to strength issues, it is necessary to increase the thickness of this type of board made of inorganic materials as the size of the board increases, and when the board is used as a catalyst for a plate-like structure, the catalyst becomes larger. However, there are problems such as restrictions on the installation location and increased costs for the denitrification equipment. Therefore, in order to make such plate-shaped catalysts thinner, progress is being made in developing catalysts based on metals. Although the metal itself has a high specific gravity, it has enough strength to withstand use even if the board thickness is reduced to about 0.6 to 10 mm, and compared to the case where the base material is a non-metallic fireproof board made of inorganic materials, it is easier to use. It has the advantage of being compact. Various manufacturing methods are known for not only the above-mentioned NOx reduction catalysts but also various metal-based catalysts, but most of them involve supporting catalyst components on the surface of a metal base material. . However, since most of the catalyst components are metal oxides, their coefficient of thermal expansion is different from that of the base metal, and their adhesion to the base material is often poor. For this reason, various manufacturing methods have been proposed for the purpose of improving the adhesion between the base material and the catalyst component. Among them, there are those that utilize enamel as a means to improve the adhesion between the metal base material and the catalyst component. For example, (1) a method of baking a glassy substance on the surface of a metal substrate, holding this glassy substance at a temperature above its softening point, and fixing catalyst component particles to it (Japanese Patent Application Laid-open No. 127913/1989); (2) ) A method of making a slip by mixing a frit for enamel and a catalyst component and baking this onto an enamel (enamel) substrate formed on a metal base material (Special Publication No. 17832/1983), (3) Metal base material The surface of the enamel slip is glazed, and before the slip is dried, refractory fine powder is uniformly sprinkled thereon, and after drying and firing, the catalyst component is adhered and supported. However, method (1) above has poor workability because the catalyst component particles are deposited at a high temperature (approximately 500°C) above the softening point of glass, and it is difficult to uniformly disperse the catalyst component. Moreover, the catalyst produced by this method, as shown in the cross section in Figure 1,
There is a problem that the catalyst component particles 3 can be deposited in only one layer on the enamel 2 formed on the metal base material 1, and the amount of the catalyst component particles 3 deposited is small. In addition, in the method (2) above, as the cross section is shown in FIG. 2, the catalyst component particles 3 on the surface contributing to the reaction are mixed with the enamel frit 4, so the amount thereof is small. It has the problem of low performance. Furthermore, as shown in the cross section of FIG. 3, the method (3) above allows the formation of a thick layer 3' of catalyst components on the surface, which poses no problem in terms of performance. The refractory fine powder 5 must be sprinkled after coating and before drying, which not only imposes time constraints, but also makes it difficult to uniformly distribute the fine powder 5, and the process is time-consuming. The drawback is that it is complicated and therefore costly. In view of the above circumstances, the present inventors conducted intensive research to provide a catalyst with excellent performance through a simple process, and as a result, formed a layer of a mixture of enamel and catalyst components on a metal base material, and created a layer of the mixture of enamel and catalyst components. The present invention was achieved by discovering that an excellent catalyst can be obtained by depositing and supporting a catalyst component layer on the layer. FIG. 4 is a sectional view for explaining the catalyst of the present invention. As is clear from FIG. 4, the mixture layer α formed on the surface of the metal base material 1 is composed of enamel grains 4 and catalyst component grains 3, and is porous and has fine irregularities on the surface. Since it is rich in carbon dioxide, it has a high adhesive force with the catalyst component layer 3'. In addition, since the porous mixture layer α has water absorption properties, it is compatible with (does not repel) the catalyst slurry for forming the catalyst component layer 3', and moreover, the catalyst component particles 3 in the mixture layer α and the catalyst Since it has the same physical properties as the component layer 3', it is strongly bonded to the component layer 3', and the overall state is as if the catalyst component is embedded in the enamel, thus exhibiting a strong bonding force. In addition, the mixture layer α
Needless to say, the enamel grains 4 inside are firmly bonded to the metal base material 1. In this way, in the catalyst of the present invention, the catalyst component and the metal base material, which originally have a weak bonding force,
Both of them are firmly bonded by a mixture layer with a strong bonding force. In the catalyst of the present invention, the mixing ratio of the enamel component and the catalyst component in the mixture layer is such that when the enamel component is large, the bonding force between the mixture layer and the metal base material increases, but the bonding force between the mixture layer and the catalyst component layer increases. Usually, the enamel component: catalyst component = 4:6.
The ratio is preferably about 6:4 (weight ratio), but it does not need to be within this range if the mixture layer is made into multiple layers. That is, the lower layer may be a layer containing many enamel components, and the upper layer may be a layer containing many catalyst components. Most ideally, it would have a enamel layer on the surface of the metal substrate, a mixture layer above which the enamel component gradually decreases, and a catalyst component layer on the outermost surface. Enamelable metal base materials for the catalyst of the present invention include iron, steel, stainless steel, aluminum, aluminum alloys, aluminum-plated steel plates, etc.
Moreover, you can use materials that can withstand the usage environment.
Any shape can be used, such as a plate, rod, line, tube, or wire mesh shape. Further, as the enamel, any enamel may be selected depending on the material of the metal base material, such as enamel for mild steel, enamel for aluminum, and enamel for stainless steel. In the conventional method (2) mentioned above, a mixture of enamel and catalyst components is baked onto the enamel substrate to form the catalyst surface layer. However, when enamel with a high firing temperature is used, the catalyst is There are restrictions on the types of enamel that can be used because the performance of the ingredients may deteriorate. On the other hand, since the mixture layer in the catalyst of the present invention is an intermediate layer, it is not subject to such restrictions.
Of course, even though it is an intermediate layer, if it has a certain level of catalytic performance, the thickness of the catalyst component layer can be made thinner, so it is preferable to use enamel that has a firing temperature close to the firing temperature of the catalyst component. Needless to say. The catalyst component used in the mixture layer of the catalyst of the present invention may be the same as the catalyst component layer, but if the catalyst performance in the mixture layer cannot be expected, the catalyst component used in the mixture layer may be the same as the catalyst component layer. may be used, leading to cost reduction. This is because the active-imparting component is generally in a trace amount, and its physical properties hardly change even if this component is removed. The method for coating the metal base material with the mixture layer of enamel and the catalyst component can be carried out in exactly the same manner as for ordinary enamel coating, and can be carried out by any method such as coating, spraying, dipping, etc. The slip containing the catalyst component may be coated, dried, and calcined using a method. If the catalyst component layer is adhered and supported on the surface of the mixture layer coated on the metal base material in this manner, it is possible to obtain the catalyst of the present invention having a metal base material with excellent adhesive strength. This catalyst component is composed of porous refractories such as alumina, silica, titania, zirconia, and calcium sulfate, and noble metal elements such as platinum, palladium, rhodium, and ruthenium, alone or in combination, or copper, vanadium, chromium, manganese, It supports oxides or sulfate compounds of base metal elements such as iron, cobalt, nickel, niobium, molybdenum, and tungsten, singly or in combination, as the main active ingredient, and is effective against CO in automobile and other various exhaust gases. It can be provided as an oxidation catalyst that removes hydrocarbon compounds and NOx, a reduction catalyst, or a three-way catalyst (a catalyst that simultaneously oxidizes CO, oxidizes hydrocarbon compounds, and reduces NOx). In addition, in addition to the above-mentioned activation-imparting components, a small amount of oxides such as tin, zinc, cerium, lanthanum, barium, etc. can be added in order to suppress SO ₂ oxidation and stabilize the catalyst _. to be
It can be used as a NOx removal catalyst or as a _NH3 decomposition catalyst using NOx and oxygen in exhaust gas. The method for depositing and supporting the catalyst component on the mixture layer is as follows:
Although not particularly limited, a slurry in which active ingredients, etc. are added to porous refractory powder by a kneading method or an impregnation method is applied by coating, dipping, spraying, etc., and then dried or baked as necessary. do it. Note that if the firing temperatures of the catalyst component and the enamel are the same, it is also possible to fire the mixture layer and the catalyst component at the same time. The catalyst of the present invention will be specifically explained below with reference to Examples. Example 1 (Catalyst Preparation Example) SiO ₂ : 45.2wt%, Al ₂ O ₃ : 8.5wt%, B ₂ O ₃ :
17.1wt%, CaO: 3.0wt%, _K2O : 4.1wt%,
_Na2O : 15.0wt%, NiO: 1.2wt%, CoO: 2.9wt
%, MnO: 2.5 wt%, ZnO: 0.5 wt%, 100 parts by weight of frit, 5 parts by weight of clay, 15 parts by weight of silica powder, 0.5 parts by weight of borax, 0.3 parts by weight of sodium nitrite, water.
Slip 1 was prepared by adding 50 parts by weight and mixing. Next, 8 parts by weight of vanadium pentoxide, 3 parts by weight of tungsten oxide, and 150 parts by weight of water were added to 100 parts by weight of anatase-type titanium oxide powder and mixed to prepare catalyst slurry 1. Mixed slurry 1 consisting of 50 parts by weight of slip 1 and 50 parts by weight of catalyst slurry was prepared, and this was mixed into a 1 mm
A thick cold-rolled steel plate (SPCC) was applied to a base material that had been pretreated by degreasing, pickling, nickel treatment, etc., dried, and then baked at 820°C for 2 minutes to obtain treated base material 1. . Next, catalyst slurry 1 was applied onto the treated substrate 1 and dried at 150° C. for 5 hours to obtain catalyst 1. When Catalyst 1 was subjected to a scratch test using a cutter, no peeling was observed on both sides of the scratch, indicating good adhesion. Example 2 (Catalyst preparation example) SiO ₂ : 20wt%, TiO ₂ : 25wt%, PbO: 28wt
%, _Na2O : 15wt%, _K2O : 5wt%, _B2O3 : _5wt
%, CaO: prepared slip 2 consisting of 5 wt%,
A mixed slurry 2 consisting of 50 parts by weight of slip 2 and 50 parts by weight of catalyst slurry 1 was prepared. This mixed slurry 2 was applied to a degreased base material of a 1 mm thick molten aluminum plated steel plate (fabric weight 40 g/m ² on one side) and a 1 mm thick stainless steel plate (SUS 304), and after drying, it was heated at 550℃ for 5 minutes. Firing and processing base material 2
and 3 were obtained. Next, catalyst slurry 1 was applied onto the treated substrates 2 and 3 and dried at 150° C. for 5 hours to obtain catalysts 2 and 3. Catalysts 2 and 3 both had good adhesion similar to catalyst 1. Example 3 (Catalyst Preparation Example) 15 parts by weight of monoethanolamine and 30 parts by weight of water were added to 2.5 parts by weight of ammonium metavanadate and 10 parts by weight of ammonium paratungstate, and 80 parts by weight of water was added to the heated solution. and 100 parts by weight of titanium oxide powder were added and stirred to prepare catalyst slurry 2. Next, slip 2: catalyst slurry 2 = 8:2
A mixed slurry 3 consisting of (weight ratio) and a mixed slurry 4 consisting of slip 2:catalyst slurry 2 = 2:8 (weight ratio) were prepared. Degreased stainless steel plate (SUS 304, 1mm
First, mix slurry 3 was applied on top of the slurry (thickness) and dried, then mixed slurry 4 was applied on top of this, dried, and then catalyst slurry 2 was applied, and after drying, it was fired at 550°C for 3 hours to obtain catalyst 4. Ta. This Catalyst 4 also had good adhesion with no peeling observed in the stick test. Example 4 (Catalyst performance evaluation example) Catalysts 1 to 4 are used as denitration catalysts using ammonia as a reducing agent, and their denitration performance was evaluated in the following manner. For each catalyst, 18 test pieces of 1 mm thickness x 10 mm x 100 mm were packed into a 22 mmφ x 100 mm stainless steel reactor, NO: 200 ppm, NH ₃ : 200 ppm,
_SO2 : 150ppm, _O2 : 2vol%, _CO2 : 12vol%,
_H2O : 10vol%, _N2 : Remaining gas volume 220N
/H, and the denitrification rate was measured at a temperature of 360°C. The results showed that all catalysts had high denitrification rates of over 90%. Example 5 (Catalyst Preparation Example and Catalyst Performance Evaluation Example) Catalysts 5 to 17 were obtained in the same manner as in Example 1 using Slip 1 and the catalyst components shown in Table 1.

[Table] Shows the content of each substance.
Catalysts 5, 15, and 16 are used as oxidation catalysts for CO and hydrocarbon compounds, catalyst 6 is used as a catalyst for purifying NOx emitted from internal combustion engines such as automobiles, and catalyst 17 is used as a three-way catalyst that simultaneously reduces these three components. Performance evaluation tests were conducted using automobile exhaust gas. The results showed that all catalysts exhibited good performance. Of course, the granular catalyst used as a conventional exhaust gas purification catalyst,
Since the amount of catalyst is small compared to honeycomb-shaped catalysts, it is difficult to achieve the same performance as conventional products, but by using the catalyst of the present invention in the exhaust pipe and other pipes through which exhaust gas passes, it is possible to improve the performance by 20 to 30%. This method has the advantage that the amount of catalyst used can be reduced compared to the conventional method. Catalysts 7 to 14 are used as denitration catalysts using ammonia as a reducing agent, and a denitration performance evaluation test was conducted using the same exhaust gas source as in Example 4. At this time, each catalyst was arranged in three stages with 10 sheets/stage of 1 mm thick x 50 mm x 200 mm at 7 mm intervals, and the gas amount
The conditions were 10Nm ³ /H, gas temperature 350°C, and NH ₃ /NOx = 1.0. The results were as shown in Table 2.

[Table] As explained above, the catalyst of the present invention has a wide range of uses and is an excellent catalyst with great practicality in various fields.

[Brief explanation of the drawing]

Figures 1 to 3 are schematic diagrams showing cross sections of conventional catalysts;
FIG. 4 is a schematic diagram showing a cross section of the catalyst of the present invention. In Figs. 1 to 4, 1 is a metal base material, 2 is an enamel layer, 3 is a catalyst component grain, 3' is a catalyst component layer, 4 is an enamel grain, and 5 is a refractory fine particle.

Claims (1)

[Claims] 1. A metal-based catalyst comprising a metal base material, a catalyst component layer formed on the base material, and a mixture layer of enamel and a medium component formed between the metal base material and the catalyst component layer.