JPH1190239A - Manufacture of palladium catalyst and palladium catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the possibilities that a catalyst layer might come off when an impact, vibration or the like is inflicted to a catalyst by treating the surface of the catalyst by oxidation to form an oxide layer on the surface through a heat history in which the rise and the fall of a temperature in the oxidation atmosphere are alternately repeated when oxidizing a palladium material in the oxidation atmosphere. SOLUTION: The surface of a solid palladium plate is made finely uneven by sandblasting the surface. Next, this solid palladium plate is thermally treated in an atmosphere. The heat treatment history is established by alternately repeating the rise and the fall of an atmospheric temperature. For example, the thermal treatment at 750 deg.C for 10 min. and the thermal treatment at 850 deg.C for 10 min. are alternately repeated three times in an electric furnace and finally, the thermal treatment at 750 deg.C for 10 min. is performed. Further, the solid palladium plate is treated by oxidation through the heat history to form an oxide layer on the surface. In addition, the solid palladium plate is treated at a specified mixed gas temperature in a methane reaction device using a methane mixture gas. Thus it is possible to obtain the palladium catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a palladium catalyst using a palladium material.

[0002]

2. Description of the Related Art As a conventional reaction catalyst, a supported catalyst has been often used. This supported catalyst has been used in combination with a washcoat on a metal honeycomb or ceramic honeycomb serving as a catalyst carrier, dried and calcined to be used as a catalyst body.

[0003] Since the supported catalyst employs the above-described production method, the catalyst layer itself is formed in a layered form with the honeycomb, and the wash coat and the coefficient of thermal expansion between the catalyst layer and the metal honeycomb or ceramic honeycomb which is the carrier of the catalyst are reduced. Because of the difference, the catalyst layer may be peeled off when subjected to a physical shock, a thermal shock, or a vibration. For this reason, various devices have been devised to prevent impact and vibration in devices incorporating a catalyst body.

[0004] In particular, when the supported catalyst is used in a fluid such as water, in addition to physical shock and vibration,
The supported catalyst layer itself is subjected to friction and resistance due to the fluid, and the separation of the catalyst layer is more likely to occur. When the catalyst layer is separated, the catalyst layer is mixed into the fluid solution, which is unreliable. .

[0005] In recent years, environmental issues have become very important, and with the recognition that resources are limited, industrial products are required to have properties as recyclable products. From such a viewpoint, the conventional supported catalyst has a small amount of supported catalyst metal, and therefore has a problem in terms of profitability in terms of recovery rate and economic efficiency even when recycling.

[0006]

SUMMARY OF THE INVENTION Accordingly, the present invention completely eliminates the possibility that a conventional supported catalyst may cause peeling of a catalyst layer when subjected to physical shock, thermal shock, vibration, etc. The purpose was to provide.

[0007]

In order to solve the above-mentioned problems, the present inventor considered using a solid palladium material. However, even if a pure palladium material is used as a catalyst, the same catalytic performance as a conventional supported catalyst cannot be exhibited. The present inventor has conducted intensive studies on this point, and as a result, the surface oxide layer of palladium is closely related to the catalytic ability, and a palladium material having a surface oxide layer formed by heat treatment by a certain method has been conventionally used. It has been revealed that the catalyst can be used as a palladium catalyst capable of exhibiting the same catalytic performance as a supported catalyst.

According to the first aspect of the present invention, in oxidizing a palladium material in an oxidizing atmosphere, an oxidation treatment is performed through a heat history of alternately increasing and decreasing the temperature of the oxidizing atmosphere to form an oxide layer on the surface. This is a method for producing a palladium catalyst to be formed. As used herein, the term “palladium material” refers to a pure palladium material and a palladium-based alloy (such as a Pd-Pt alloy containing a small amount of platinum). What is suitable is to use what is suitable for. The term “oxidizing atmosphere” used herein may be any kind of atmosphere as long as it is an atmosphere in which an oxide layer can be formed on the surface of a palladium material by heating. Heating may be simply performed in an air atmosphere in consideration of economy.

In the process of producing this palladium catalyst, it is very necessary to carry out the oxidation treatment through a heat history in which the temperature of the oxidizing atmosphere is repeatedly increased and decreased alternately, in order to secure the desired catalytic performance. Is important. That is, if the temperature of the oxidizing atmosphere for the oxidizing treatment is different, the properties of the oxide formed on the surface of the palladium material are different, and the fine irregularities on the surface of the oxide layer are different. Therefore, by treating the palladium material through a certain thermal history of repeatedly raising and lowering the temperature of the oxidizing atmosphere, the thickness, properties and fine irregularities of the surface of the oxide layer are controlled. This fine uneven shape can be observed for the first time by using a scanning electron microscope (SEM).

[0010] The fine concavo-convex shape plays a role in increasing the contact reaction area when the palladium catalyst reacts with hydrogen gas, carbon monoxide gas, and other hydrocarbon gases in general. The reason that even if a solid material of palladium that is not heat-treated is used as a catalyst as it is, it cannot exhibit the same catalytic performance as a conventional supported catalyst, is due to the difference in the contact reaction area. That is, the palladium material is subjected to an oxidation treatment to form a fine uneven shape of the oxide, so that the total oxide amount and the contact reaction area equivalent to the supported catalyst can be secured for the first time, and the catalyst ability equivalent to the supported catalyst is obtained. It is possible to obtain a palladium catalyst that exerts its effect. Further, if a surface roughening treatment such as sandblasting is previously performed on the palladium material to be oxidized, the contact reaction area can be more easily increased.

According to the second aspect of the present invention, the heat history in which the temperature of the oxidizing atmosphere is repeatedly raised and lowered alternately is such that the temperature is raised and lowered alternately with the thermal dissociation temperature of PbO therebetween. A method for producing a palladium catalyst according to claim 1. The present invention has been made by paying attention to the thermal dissociation property of PdO, which is a palladium oxide. This Pd
The thermal dissociation temperature of O is about 780 ° C. in the atmosphere. Although it is possible to form an oxide layer on the surface of the palladium material by heating at a certain temperature, even if the heating is continued as it is, if the oxide layer is formed uniformly, a local battery may be formed. When there is no oxide, the progress of oxidation slows down, and it becomes difficult to increase the fine irregularities of the oxide.

Therefore, when the temperature rise and fall of the ambient temperature are alternately repeated with the PdO dissociation temperature interposed therebetween, the oxide formed by the oxidation reaction at a temperature of 780 ° C. or less under the atmospheric pressure becomes 780 ° C. When the temperature is maintained at the above temperature, oxygen is dissociated. At this time, once the fine irregularities of the oxide are formed by the oxidation reaction, the fine irregularities remain on the surface of the palladium material even if reduced by dissociation of oxygen, and the fine irregularities are maintained. When the temperature is again kept at 780 ° C. or lower, palladium oxide is further formed on the fine irregularities, and it is possible to form finer and higher-density fine irregularities. By repeating such a heat treatment a plurality of times as the thermal history, a palladium catalyst having the desired fine irregularities can be obtained.

According to a third aspect of the present invention, a palladium material is heated and oxidized in an air atmosphere to form an oxide layer on the surface.
This is a method for producing a palladium catalyst in which a combustion gas is catalytically burned on the surface of the palladium material to form an oxide layer on the surface of the palladium material. According to the present invention, an oxide layer is formed in advance by oxidizing a palladium material in an air atmosphere, and a target oxide layer is formed in a short time by utilizing the catalytic combustion reaction of a combustion gas. It is a palladium catalyst obtained by.

The combustion gas used here may be any combustion gas as long as it can oxidize the palladium material by the combustion reaction, but methane is preferred. Methane is Pd-free with no oxide layer compared to other combustion gases
Combustion is difficult with the catalytic activity of, combustion apparently stops,
This is because excessive temperature rise is unlikely to occur and temperature control is easy. By utilizing the combustion reaction of methane, Pd
The same effect can be obtained by repeatedly raising and lowering the ambient temperature across the O dissociation temperature.

That is, the palladium material having an oxide layer formed by oxidizing the palladium material in an air atmosphere is treated in a methane reactor at a mixture temperature of about 500 ° C. using a methane mixture. The reason is that an appropriate thickness of the oxide layer is obtained.

At this time, in the methane reactor, the oxidation activity of the palladium material gradually increases, and a catalytic combustion reaction of methane is performed on the palladium material. When the oxidation reaction of methane proceeds in this way, the surface temperature of the palladium material increases due to the heat of the oxidation reaction, and when the temperature reaches 780 ° C., PdO on the surface of the palladium material undergoes thermal dissociation and changes to Pd. When it changes to Pd, apparently catalytic combustion reaction does not occur, the surface temperature of the palladium material drops, and PdO is formed again on the surface of the palladium material. When a certain amount of PdO is reformed, a catalytic combustion reaction occurs again, and the above-described series of reactions occurs repeatedly, so that a palladium catalyst having a large reaction surface area can be obtained.

According to a fourth aspect of the present invention, an oxide layer is formed on a surface of a palladium material.
Is a palladium catalyst obtained by any one of the production methods. In this palladium catalyst, the surface of a palladium material is covered with a very dense and dense oxide layer.
Therefore, the contact reaction area as a catalyst is high, and the concern of falling off of a catalyst layer such as a supported catalyst can be solved.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment which is considered to be the best invention of the present invention will be described.

The practice of the present invention was carried out using solid palladium plates. First, the solid palladium plate was subjected to sandblasting to form fine irregularities on the surface. Subsequently, the solid plate of palladium was heat-treated in the air. The history of heat treatment is 750 ° C in an electric furnace.
The heat treatment of × 10 minutes and the heat treatment of 850 ° C. × 10 minutes were alternately repeated three times, and finally the heat treatment of 750 ° C. × 10 minutes was performed.

The solid palladium plate which has been subjected to the heat treatment in the atmosphere is mixed in a methane reactor with a mixture of methane at a concentration of 4% (adiabatic combustion temperature of 1380 ° C.) and a mixture temperature of 50%.
The mixture was treated at 0 ° C. for 30 minutes to obtain a palladium catalyst.
At this time, the formation of PdO and the generation of Pd by dissociation of O are repeated a plurality of times.

Through the above heat treatment step, a palladium catalyst was obtained from a solid palladium plate. In order to confirm the performance of the palladium catalyst, the following performance comparison test was performed. As comparative catalyst bodies used in the performance comparison test, was used Pd / ZrO ₂ carrier cordierite ceramic catalyst body and untreated heat-treated Pd foil honeycomb catalyst body. Here, the palladium catalyst body using the palladium catalyst according to the present invention is referred to as a heat-treated Pd foil honeycomb catalyst body.

First, the catalyst ignition temperatures of methane were compared. The Pd / ZrO ₂ -supported cordierite ceramic catalyst body used here was ZrO ₂ wash-coated with a size of 50 mm diameter × 50 mm length, and a general catalyst having a considerably high Pd loading amount of 1 mg / cm ² was used. . The unheated Pd foil honeycomb catalyst body is 50
A Pd foil having a diameter of 50 mm and a diameter of 50 mm and a thickness of 100 μm is spirally wound. The heat-treated Pd foil honeycomb catalyst body is a Pd foil having a thickness of 100 μm, which is subjected to a predetermined heat treatment step to form a palladium catalyst, which is spirally wound into a size of 50 mm diameter × 50 mm length. The ignition temperature measurement conditions are as follows.

Conditions for measuring catalyst ignition temperature with methane Air flow rate: 500 SLPM (Standard Liter Per Minute, the same applies hereinafter) Linear velocity 4.2 Nm / sec Methane flow rate: 21.5 SLPM (methane concentration 4.3%) Mixed air heating method: air After mixing methane into the mixture, the air before mixing with methane is heated by an electric heater so that the temperature reaches a predetermined level. Catalyst ignition determination method: The catalyst wall temperature rises rapidly, and the catalyst outlet wall temperature rises to 600 ° C or higher. The mixture temperature at the inlet to the catalyst ignition temperature

Under the above conditions, the result of the measurement was that Pd / Z
The catalyst ignition temperature of the rO ₂ -supported cordierite ceramic catalyst is 358 ° C., the catalyst ignition temperature of the unheated Pd foil honeycomb catalyst is 550 ° C. or higher, and the catalyst ignition temperature of the heat-treated Pd foil honeycomb catalyst is 351 ° C. Equivalent performance was shown. It is also clear that the catalytic performance of the unheated Pd foil honeycomb catalyst body cannot be sufficiently exhibited.

Next, the catalyst ignition temperatures of hydrogen were compared. The Pd / ZrO ₂ -supported cordierite ceramic catalyst body, the unheated Pd foil honeycomb catalyst body, and the heat-treated Pd foil honeycomb catalyst body used here had a size 30 times smaller than that used in the test of the catalyst ignition temperature with methane.
The difference is only the mm diameter × 50 mm length, and the others are the same. The ignition temperature measurement conditions are as follows.

Conditions for measuring catalyst ignition temperature with hydrogen Air flow rate: 150 SLPM Linear velocity 3.5 Nm / sec Methane flow rate: 3.0 SLPM (hydrogen concentration 2.0%) Mixed air heating method: After mixing hydrogen with air, a predetermined Heat the air before hydrogen mixing with an electric heater to reach the temperature. Catalyst ignition determination method: The catalyst mixture temperature is set so that the temperature of the catalyst wall rises rapidly and the temperature of the hottest part becomes 400 ° C or higher. Temperature

Measurements were made under these conditions, and as a result, Pd / Z
The catalyst ignition temperature of the rO ₂ -supported cordierite ceramic catalyst body is 30 ° C. or less, the catalyst ignition temperature of the unheated Pd foil honeycomb catalyst body is 140 ° C., and the catalyst ignition temperature of the heat-treated Pd foil honeycomb catalyst body is 30 ° C. or less. It showed the same performance as. It was also found here that the catalytic performance of the unheated Pd foil honeycomb catalyst body was poor.

[0028]

The palladium catalyst according to the present invention is different from a supported catalyst in that a palladium material itself is catalyzed by a predetermined heat treatment as represented by a solid palladium plate.
Poor peeling of the catalyst layer due to vibration, impact, thermal shock, fluid friction, etc. generated in the supported catalyst was eliminated, so that its application range could be expanded, and catalytic performance equivalent to that of the supported catalyst could be obtained. Moreover, the use of a palladium material such as a solid palladium plate makes it easy to recover and purify, and can improve the recovery efficiency compared to attempting to recover the palladium contained in the supported catalyst,
Recycling with high economic efficiency becomes possible, and the economic effect and environmental conservation effect when viewed from a long-term perspective are great. When the palladium catalyst according to the present invention is used,
Hydrogen gas can be oxidized safely and easily to water, and it can also be used as a combustion catalyst for general CO and hydrocarbons.

[Procedure amendment]

[Submission date] November 6, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 2

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

According to the first aspect of the present invention, in oxidizing a palladium material in an oxidizing atmosphere, an oxidation treatment is performed through a heat history of alternately increasing and decreasing the temperature of the oxidizing atmosphere to form an oxide layer on the surface. This is a method for producing a palladium catalyst to be formed. As used herein, the term “palladium material” refers to a pure palladium material and a palladium-based alloy (such as a Pd-Pt alloy containing a small amount of platinum). What is suitable is to use what is suitable for. The oxidizing atmosphere referred to here may be any kind of atmosphere as long as it can be broadly regarded as an atmosphere in which an oxide layer can be formed on the surface of a palladium material by heating. Heating may be simply performed in an air atmosphere in consideration of economy.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

In the process of manufacturing the palladium catalyst, the oxidation treatment through a heat history of alternately increasing and decreasing the temperature of the oxidizing atmosphere is very important for securing the desired catalytic performance. It becomes important. That is, if the temperature of the oxidizing atmosphere for the oxidizing treatment is different, the properties of the oxide formed on the surface of the palladium material are different, and the fine irregularities on the surface of the oxide layer are different. Therefore, by treating the palladium material through a certain thermal history of repeatedly raising and lowering the temperature of the oxidizing atmosphere, the thickness, properties and fine irregularities of the surface of the oxide layer are controlled. This fine uneven shape can be observed for the first time by using a scanning electron microscope (SEM).

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

[0010] The fine concavo-convex shape plays a role in increasing the contact reaction area when the palladium catalyst reacts with hydrogen gas, carbon monoxide gas, and other hydrocarbon gases in general. The reason that even if a solid material of palladium that is not heat-treated is used as a catalyst as it is, the catalyst ability equivalent to that of the conventional supported catalyst cannot be exhibited is due to the difference in the contact reaction area. That is, the palladium material is subjected to an oxidation treatment to form a fine uneven shape of the oxide, so that the total oxide amount and the contact reaction area equivalent to the supported catalyst can be secured for the first time, and the catalyst ability equivalent to the supported catalyst is obtained. It is possible to obtain a palladium catalyst that exerts its effect. Further, if a surface roughening treatment such as sandblasting is previously performed on the palladium material to be oxidized, the contact reaction area can be more easily increased.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

According to the second aspect of the present invention, the heat history in which the temperature of the oxidizing atmosphere is repeatedly raised and lowered alternately is such that the temperature is raised and lowered alternately with the thermal dissociation temperature of PdO therebetween. A method for producing a palladium catalyst according to claim 1. The present invention has been made by paying attention to the thermal dissociation property of PdO, which is a palladium oxide. This Pd
The thermal dissociation temperature of O is about 780 ° C. in the atmosphere. Although it is possible to form an oxide layer on the surface of the palladium material by heating at a certain temperature, even if heating is continued further, the oxide layer is formed uniformly and there is no place to form a local battery Then, the progress of oxidation slows down, and it becomes difficult to increase the fine irregularities of the oxide.

Claims (4)

[Claims] 1. A method of oxidizing a palladium material in an oxidizing atmosphere, wherein the palladium material is oxidized through a heat history of alternately increasing and decreasing the temperature of the oxidizing atmosphere to form an oxide layer on the surface. Method for producing catalyst. 2. The palladium according to claim 1, wherein the thermal history of alternately raising and lowering the temperature of the oxidizing atmosphere alternately increases and decreases the temperature with the thermal dissociation temperature of PbO interposed therebetween. Method for producing catalyst. 3. A palladium material, wherein a palladium material is heated and oxidized in an air atmosphere to form an oxide layer on the surface, and a combustion gas is catalytically burned on the surface of the palladium material to form an oxide layer on the surface of the palladium material. Method for producing catalyst. 4. A palladium catalyst obtained by the production method according to claim 1, wherein an oxide layer is formed on a surface of a palladium material.