JPH0813335B2 - Self-cleaning coating layer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a coating layer having an oxidation catalyst action for hydrocarbon compounds.

BACKGROUND ART Conventionally, oxides of noble metals and transition metals have been used as hydrocarbon-based oxidative decomposition catalysts. For example, when considering a triglyceride of a higher fatty acid containing a carboxyl group found in oil stains of cookers as a hydrocarbon compound, each metal oxide such as Mn, Cu, Fe, Co, Ni or each metal oxide is considered. Is known as an oxidative decomposition catalyst, and there is a catalyst coating in which a catalyst material containing these oxides as a main component is added to a enamel or glassy film on the inner wall surface of the cooking chamber. These are those in which a catalyst is dispersed in an inorganic binder and applied to the inner wall surface to form a coating layer, which is intended to catalytically decompose oil and food residues at high temperatures. Since the substance is covered with a coating such as enamel, glass, or paint and the surface is not exposed, a high temperature of 450 ° C. or higher is required, and a coating layer having a catalytic activity at a lower temperature is desired.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the above conventional technique, for example, the catalytic activity of each metal oxide is low with respect to the oxidative decomposition reaction of triglyceride, and when used as a film, the catalyst is dispersed in a heat-resistant binder. Therefore, the problem is that the catalyst surface is not exposed and the activity is reduced. Also, in order to increase the exposure of the catalyst surface, the coating layer must be made as porous as possible, but on the other hand, making it porous reduces the adhesion to the substrate and the corrosion resistance and wear resistance of the coating layer. was there. These problems are the main factors, and secondary problems such as difficulty in practical use occur.

The present invention is intended to solve the above problems and provides a self-cleaning coating layer which lowers the reaction temperature by enhancing the activity of the catalyst itself and also when the catalyst is formed as a coating layer on a substrate. It is a thing.

Means for Solving the Problems In order to solve the above problems, the present invention, by plasma spraying, a rare earth element Ce and a transition metal on the surface of the heat resistant substrate.
Cu, Mn complex oxide coating layer, Ce, in the thickness direction of the coating layer
It is formed with a concentration gradient of Cu and Mn, and it is intended to decompose the oil content scattered from the food on the surface of the coating layer.

Action The action of the catalyst coating layer having the above configuration will be described.
First, the catalyst of the present invention is Ce _A Cu _B Mn _C O _D (where A = 1, B + C
= 1,0 <B <1,0 <C <1, D> 0) is a compound oxide that has never existed before and has a higher activity for the oxidation of triglyceride than the single oxide of each component. Indicates. For example, the oxidation activity is higher than any of CeO ₂ , CuO, Cu ₂ O, Mn ₂ O ₃ , and MnO ₂ . This is because in the three-element system oxide of Ce, Cu, and Mn, the element on the surface of the oxide takes many valences (for example, Mn is trivalent and tetravalent, Cu is monovalent and divalent, etc.). ), That is, valence control between different elements that is not found in a single component is performed, and a surface more suitable for reaction is created. This is confirmed by XPS.

In the present invention, a single film of the catalyst is formed by plasma spraying using the above-mentioned catalyst. Since the film itself is a catalyst, it is not hardened by covering the catalyst with frit or binder like enamel, glass or paint. Therefore, in the coating layer of the present invention, the direct contact between the catalyst and the oil and the supply of oxygen to the reaction interface are sufficiently carried out to improve the catalytic performance. Furthermore, since it is possible to have a concentration gradient of Ce, Cu, Mn in the thickness direction of the coating layer, for example, by increasing the Ce content on the surface side of the heat-resistant substrate of the coating layer, the surface area of the heat-resistant substrate is increased. By increasing the content of Cu and Mn on the surface side of the coating layer, a coating layer having higher oxidation activity can be formed.

Example Hereinafter, an example of the present invention will be described. First, a method for preparing the catalyst will be described.

Ce, Cu, and Mn nitrates were made into an aqueous solution with a predetermined molar ratio, and a precipitate was obtained by the coprecipitation method.
_A Cu _B Mu _C O _D (However, A = 1, B + C = 1,0 <B <1,0 <C <1, D
The composite oxide represented by> 0). For comparison, single and binary transition metal oxides were prepared by the precipitation method.

Using the catalyst powder prepared by the above method, plasma spraying was performed on a blasted stainless steel substrate (plate thickness 1 mm) to form a catalyst spray coating with a film thickness of 20 μm.

For plasma spraying, an NT30 type DC plasma spray device manufactured by Nagata Iron Works Co., Ltd. was used.

Using this as a test piece, the ability to purify oil at 370 ° C was confirmed. A certain amount of salad oil was dropped on the test piece and kept in an oven at 370 ° C. to see the change in salad oil. The results are shown in Table 1.

From the above results, it can be seen that the coating layer obtained by plasma spraying the Ce-Cu-Mn composite oxide has an extremely large promoting effect on the oxidation reaction of triglyceride.

About 1 μ of salad oil was dropped on the catalyst powder and heated to confirm the temperature at which the combustion of the salad oil started. Ce-Cu
In the -Mn system, the onset of combustion was observed at about 240-250 ℃.

With Mn oxides and Cu oxides, such a phenomenon does not occur even at 300 ° C, and the difference in catalytic activity is clear, indicating that the Ce-Cu-Mn system is particularly suitable for oil decomposition. Since this is a complex oxide, it accelerates the oxidation reaction due to the complex effect, Ce
It is considered that the high activity for the decomposition of oil is exerted as described above, due to its function as a source of oxygen for Mn and the like particularly in the bulk.

Furthermore, considering the function of each element in the Ce-Cu-Mn-based composite oxide, as shown in Table 2, the Ce oxide is
It can be seen that the surface area as a single oxide is also large, and that a catalyst with a larger surface area is made by combining with a Cu-Mn-based composite oxide. Ce oxide in bulk
As described above, it is a source of oxygen supply to Mn and the like.

Next, CeO _X , MnO _X , CuO _X (X:
(Undetermined), each powder and salad oil were mixed at a constant weight ratio, and the weight change of the salad oil due to the temperature rise was followed using a thermobalance. The results are shown in FIG. From Figure 3, it can be seen that MnO _X and CuO _X have higher catalytic activity than CeO _X for the oxidation of salad oil. In the case of Ce-Cu-Mn-based complex oxides, the compounding of them causes a synergistic effect, and shows a high activity that has never been seen before.

Therefore, based on the above results, an attempt was made to form a coating layer having higher activity by taking advantage of plasma spraying.
In plasma spraying, two or more kinds of powders can be simultaneously sprayed from different spray ports onto the same base material to form a film. Therefore, as shown in FIG. 1, CeO _X and Cu—MnO _X were sprayed onto the heat-resistant substrate 1 from separate spray ports 2 and 3 to form a coating layer 4. At that time, as shown in FIG. 2, the respective thermal spraying amounts were changed with time, the thermal spraying was stopped after T time, and a Ce, Cu, Mn concentration gradient was provided in the thickness direction of the coating layer. When salad oil was dropped on the coating layer 4 formed with a concentration gradient of Ce, Cu, Mn and the temperature was raised, the oil completely decomposed after about 20 minutes at 350 ° C. and no residue remained. In the coating layer formed without the concentration gradient, as shown in Table 1,
The oil decomposes in about 30 to 35 minutes at 370 ° C. This means that by increasing CeO _X on the base material side, a catalyst layer with a larger surface area is formed, and by increasing Cu-Mn, which has high catalytic activity, in the surface layer, it is possible to prevent oxidation of oil overall. This is probably because it exhibits high catalytic activity.

As described above, according to the present invention, the self-cleaning coating layer of the catalyst alone is formed on the surface of the base material by the plasma spraying using the catalyst of the extremely high catalytic activity Ce-Cu-Mn composite oxide. Therefore, the contact area between the catalyst and oil is large, and since the plasma spray coating is a porous film having a suitable porosity, oxygen is sufficiently supplied to the reaction interface between the catalyst and oil. Therefore, the oxygen consumed in the oxidation reaction is also replenished from the inside of the film and from the air, so that the catalytic activity can be maintained for a long period of time without deterioration in performance. Further, since a Ce, Cu, Mn concentration gradient can be freely provided in the film thickness direction, a more highly active film can be formed. Also Ce
O _X has good adhesion to the base material and is strong against acid. Therefore, increasing the CeO _X content on the base material side of the coating layer improves the adhesion to the base material, and It is possible to prevent the base material from being corroded by acid even if it is touched.

When the self-cleaning coating layer of the present invention is applied to the inner wall surface of an oven or the like, it is necessary to maintain the temperature at 500 to 550 ° C. in the case of thermal self-cleaning in a conventional oven of the burning-off method. It is possible to reduce the temperature to below ℃, which has a great effect on energy saving and heat insulation. In addition, since oil stains can be completely decomposed, the inside of the oven can be kept in a state like a new one for a long time.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a coating layer according to an embodiment of the present invention,
FIG. 2 is a correlation graph showing an example of a spraying amount control method in plasma spraying, and FIG. 3 is a thermogravimetric change curve of a mixture of various oxides and salad oil. 1 ... Heat resistant base material, 2, 3 ... Plasma spray port, 4 ... Plasma spray catalyst film.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mamoru Isoya 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-1-304049 (JP, A)

Claims (1)

[Claims] 1. Ce, Cu, formed on a substrate by plasma spraying,
A coating layer of a complex oxide composed of Mn, wherein the complex oxide is Ce _A Ce _B Mn _C O _D (where A = 1, B + C = 1, O <B <1, O <C <
1, D> 0), and the coating layer has a concentration gradient of Ce, Cu, Mn in the thickness direction, and is formed by a plasma spraying method for self-cleaning. .