JP7344495B2 - Method for producing VOC removal catalyst, VOC removal catalyst and VOC removal method - Google Patents

Description

The present invention relates to a method for producing a VOC removal catalyst, a VOC removal catalyst, and a VOC removal method.

VOC is an abbreviation for volatile organic compounds, and known examples include toluene, xylene, benzene, ethyl acetate, methanol, and dichloromethane. While these VOCs are widely used in solvents, adhesives, chemical raw materials, etc., they are also known to cause photochemical oxidants or suspended particulate matter (SPM), so they have been widely used in the atmosphere. Its emissions are strictly regulated under the Pollution Prevention Act.

VOCs are emitted through various processes, such as painting (indoors and outdoors), cleaning, refueling, manufacturing of chemical products, printing, and adhesion. Among these, it is said that the greatest amount of VOC is emitted from painting. Emissions from sources account for more than 50%.

From this point of view, in order to further reduce the amount of VOC emissions, it is desired to establish a technology that removes VOCs more efficiently. Various VOC removal methods have been proposed so far. VOC emission control technologies can be broadly classified into four types: (1) recovery and regeneration methods; (2) sealing methods; (3) combustion and decomposition methods; and (4) material substitution methods.

The combustion/decomposition method processes VOCs by decomposing them into carbon dioxide, water, and the like. When using multiple VOCs with different substances and component ratios, as typified by conventional painting and printing, there is little advantage in reusing VOCs even if they are recovered and recycled. It can be said that the disassembly method is realistic.

Among the combustion/decomposition methods, the method of decomposing VOCs by combustion has been used in Japan since around 1960. As combustion methods, for example, a direct combustion method, a catalytic combustion method, and a regenerative combustion method are known. Among them, the catalytic combustion method is a method of oxidatively decomposing VOCs at a low temperature of 200 to 350° C. using a catalyst supporting platinum, palladium, or the like. The characteristics of the VOC removal device used in this method include that it can be operated at low temperatures, that it can be easily made small and lightweight, that there is little risk of explosion, and that there is no by-product of thermal NOx.

However, with the catalytic combustion method, there are issues such as difficulty in ascertaining the degree of catalyst deterioration, so it is necessary to develop new catalysts that are less likely to be poisoned and have a longer lifespan, as well as catalysts with a view to improving heat resistance and reducing costs. development is underway. Recently, inexpensive catalysts that do not use expensive noble metals such as platinum have also been proposed (see, for example, Non-Patent Document 1).

Applied Catalysis B: Environmental 104 (2011) 144-150

However, in recent years, in addition to not using expensive precious metals such as platinum, it has become desirable for VOC removal catalysts to have properties that allow them to remove VOCs more efficiently. It was hoped that a new method would be used to manufacture the product. In particular, there has been a strong demand for a VOC removal catalyst that has excellent VOC removal efficiency even when treated at low temperatures.

The present invention has been made in view of the above, and aims to provide a VOC removal catalyst that can be produced by a simple method and has excellent VOC removal efficiency even when processed at low temperatures, a method for producing the same, and a VOC removal method. purpose.

As a result of extensive research to achieve the above object, the present inventors have discovered that the above object can be achieved by using copper foam as a conductive porous base material, and have completed the present invention.

That is, the present invention includes, for example, the subject matter described in the following sections.
Item 1
A step of performing pulsed electrodeposition treatment in an aqueous solution containing at least two metal compounds using the conductive porous substrate as a cathode ,
The metal compound is a compound of at least one metal selected from the group consisting of Ni, Cu, Co, Mo, W, Ti, Cr, Fe, Mn, V, Zn, Mg and La,
A method for producing a VOC removal catalyst, wherein the conductive porous substrate is a copper foam.
Section 2
It is formed by coating a conductive porous base material with a metal oxide,
The metal oxide is a composite oxide of at least two metals selected from the group consisting of Ni, Cu, Co, Mo, W, Ti, Cr, Fe, Mn, V, Zn, Mg and La,
A catalyst for VOC removal, wherein the conductive porous substrate is a copper foam.
Section 3
A method for removing VOCs, comprising a step of removing VOCs using the VOC removal catalyst obtained by the production method according to Item 1 or the VOC removal catalyst according to Item 2 .

According to the method for producing a VOC removal catalyst of the present invention, the VOC removal catalyst can be produced by a simple method, and the obtained VOC removal catalyst can process VOCs at a lower temperature than before. Also has excellent VOC removal efficiency.

According to the VOC removal catalyst of the present invention, the VOC removal efficiency is excellent even when VOCs are treated at low temperatures.

According to the VOC removal method of the present invention, VOCs can be treated at low temperatures, so it is a method suitable for removing VOCs.

FIG. 2 is a schematic diagram illustrating a method of electrochemical oxidation treatment of copper foam. SEM images of VOC removal catalysts obtained in each example and comparative example are shown. It is a graph showing the evaluation test results of the VOC removal catalysts obtained in each example and comparative example, and showing the relationship between temperature and toluene conversion.

Embodiments of the present invention will be described in detail below. Note that, in this specification, the expressions "contain" and "comprising" include the concepts of "containing", "containing", "consisting essentially of", and "consisting only".

1. Method for manufacturing a catalyst for VOC removal The method for manufacturing a catalyst for VOC removal of the present invention includes a step of performing electrodeposition treatment in an aqueous solution containing at least one metal compound using a conductive porous substrate as a cathode . include. Hereinafter, this process will be abbreviated as "electrodeposition process". In particular, in the manufacturing method of the present invention, the conductive porous substrate is a copper foam.

By including the electrodeposition step, the production method of the present invention allows a VOC removal catalyst to be produced in a simple manner, and by using the obtained VOC removal catalyst, VOCs can be treated at low temperatures. I can do it. Therefore, the VOC removal catalyst obtained by the production method of the present invention has excellent VOC removal efficiency.

The copper foam used in the electrodeposition process is a base material mainly made of copper, which has electrical conductivity and is porous. The copper foam plays the role of retaining the metal oxide or metal composite oxide described below that has a catalytic action for VOC removal. The shape of the copper foam is not particularly limited, and may be formed into, for example, a plate shape, a wire shape, a rod shape, a mesh shape, or the like. Note that the copper foam may contain other components (for example, elements such as metals that are unavoidably mixed) as long as the effects of the present invention can be obtained.

The copper foam used in the electrodeposition process can be obtained by a known method, or can be obtained from a commercially available product.

The copper foam used in the electrodeposition process may further have copper nanowires formed on its surface. In this case, the metal tends to be uniformly dispersed and present on the copper foam via the nanowires, and the catalytic activity of the metal oxide or metal composite oxide, which will be described later, formed on the copper foam is further enhanced. As a result, the VOC removal efficiency of the resulting VOC removal catalyst is further increased.

Therefore, the manufacturing method of the present invention preferably includes a step of forming copper nanowires on the surface of the copper foam.

The method for forming copper nanowires on the copper foam is not particularly limited, and for example, a wide variety of known nanowire forming methods can be employed. For example, copper nanowires can be formed on the copper foam by electrochemical oxidation treatment (electrooxidation) of the copper foam. The electrooxidation method is not particularly limited either, and, for example, a known electrooxidation method can be applied. An example is electrooxidation using a galvanostatic method.

FIG. 1 is a schematic diagram illustrating a method of electrochemical oxidation treatment of copper foam, and schematically shows how copper nanowires are formed on copper foam by a constant current method.

When forming copper nanowires on a copper foam using a galvanostatic method, an electrolytic device including a working electrode, a counter electrode, a reference electrode, and an electrolyte is used, as shown in FIG. can be used. As a working electrode, copper foam can be used to form nanowires. As the counter electrode, for example, a known insoluble electrode can be used, such as an electrode made of carbon, platinum group metal, gold, or the like. Platinum group metals include platinum, palladium, ruthenium, rhodium, osmium, and iridium, with platinum being preferred. The platinum group metal contained in the counter electrode may contain one or more of the above metal species. Furthermore, the platinum group metal may be contained in the form of an alloy, metal oxide, or the like. As the reference electrode, a silver/silver chloride electrode (Ag/AgCl electrode), a mercury/mercury chloride electrode (Hg/HgCl ₂ electrode), a standard hydrogen electrode, etc. can be used.

The type of electrolytic solution is not particularly limited either, and a wide variety of known electrolytic solutions that can be used in the constant current method can be used, and for example, alkaline aqueous solutions such as potassium hydroxide and sodium hydroxide can be used. When the electrolyte is an alkaline aqueous solution, its concentration is not particularly limited and can be, for example, 2 to 6M.

The conditions for electrooxidation using the constant current method (current, voltage, electrolysis time, etc.) are not particularly limited, and conditions for known constant current methods can be widely applied.

By galvanostatic method, copper nanowires are formed on the copper foam, as shown in FIG. 1. The size of the copper nanowires is not particularly limited, and for example, the diameter can be about 1 to 150 nm.

In the electrodeposition step, electrodeposition is performed in an aqueous solution containing at least one metal compound. The type of metal contained in the metal compound is not particularly limited, and for example, metals used in VOC removal catalysts can be widely used. Hereinafter, the metal in the metal compound will be referred to as "metal M". Examples of the type of metal M include various metals used in VOC removal catalysts.

Specifically, the metal compound is a compound of at least one metal M selected from the group consisting of Ni, Cu, Co, Mo, W, Ti, Cr, Al, Fe, Mn, V, Zn, Mg, and La. It is preferable. In this case, it is easy to manufacture the VOC removal catalyst, and the resulting VOC removal catalyst also has excellent VOC removal efficiency.

The type of metal compound is not particularly limited, and for example, known inorganic acid salts of metal M, organic acid salts of known metal M, hydroxides of known metal M, halides of known metal M, etc. are widely used. can do. The compound of metal M may be a hydrate.

Examples of the inorganic acid salt of metal M include one or more selected from the group consisting of nitrates, sulfates, hydrochlorides, carbonates, hydrogen carbonates, phosphates, hydrogen phosphates, etc. of metal M. .

Examples of the organic acid salt of metal M include one or more selected from the group consisting of metal M acetates, oxalates, formates, succinates, and the like.

It is preferable that the metal M compound used in the electrodeposition process is easily dissolved in water to form an aqueous solution, and in this case, it is easy to produce a VOC removal catalyst. Among these, the compound of metal M used in the electrodeposition step is preferably a nitrate of metal M, a sulfate of metal M, a chloride of metal M, etc., and a nitrate of metal M is more preferable.

The metal compounds used in the electrodeposition process may be used alone or in combination of two or more different metal compounds. It is preferable to use two or more different types of metal compounds in the electrodeposition process, since the resulting VOC removal catalyst tends to have excellent VOC removal efficiency. When two or more different metal compounds are used together, each metal compound is preferably the same type of salt. For example, each metal compound can all be a nitrate.

When two or more types of metal compounds are used in the electrodeposition step, it is preferable that at least one metal compound is at least one type of compound selected from the group consisting of Ni, Cu, and Co. In this case, since Ni, Cu, and Co are metals that are easily electrodeposited, metal oxides or metal composite oxides are likely to be formed on the copper foam. In this case, the other metal compound is at least one compound selected from the group consisting of Mo, W, Ti, Cr, Al, Fe, Mn, V, Zn, Mg, and La, which are considered to be difficult to deposit. can include. By combining easily electrodepositable metal compounds such as Ni, Cu, Co, etc. with difficult electrodepositable metal compounds, electrodeposition can easily occur even on metals that are difficult to electrodeposit on their own. Because it will be.

When two or more types of metal compounds are used in the electrodeposition process, it is particularly preferable to employ a combination of a metal compound containing Co and a metal compound containing Mn. In this case, the resulting VOC removal catalyst is more It becomes possible to remove VOCs at low temperatures.

In the electrodeposition step, when two or more different metal compounds are used together, the proportion of each metal compound used is not particularly limited. For example, when two types of metal compounds are used together, the molar ratio of metal M in one compound to metal M in the other compound can be 1:0.1 to 1:20, and 1:1 to 1:20. A ratio of 1:10 is particularly preferred. In particular, when the metal compound includes a combination of a metal compound containing Co and a metal compound containing Mn, the molar ratio of Co and Mn (Co:Mn) can be 1:0.1 to 1:20, A ratio of 1:1 to 1:10 is particularly preferred.

The method for producing the metal compound is not particularly limited, and, for example, it can be obtained by a known production method. Alternatively, metal compounds can also be obtained from commercial products.

The method for preparing the aqueous solution containing the metal compound used in the electrodeposition process is not particularly limited, and can be prepared, for example, by mixing at least one metal compound and a solvent. As the solvent, water or a mixture of water and a lower alcohol (for example, an alcohol having 1 to 4 carbon atoms such as methanol or ethanol) can be used, and water is particularly preferred. Various kinds of water can be used as water, such as distilled water, tap water, industrial water, ion exchange water, deionized water, pure water, and electrolyzed water. The solvent may contain a pH adjuster, a viscosity adjuster, a fungicide, etc., as long as the effects of the present invention are not impaired.

The concentration of the aqueous solution containing the metal compound used in the electrodeposition process is not particularly limited. For example, in the aqueous solution, the concentration of metal M (if two or more metals are present, the concentration of each metal M) is preferably 0.1 to 1000 mmol/L. In this case, a structurally stable VOC removal catalyst can be easily formed. The concentration of the metal M (if two or more metals are present, each metal M) is more preferably 0.5 to 500 mmol/L, particularly preferably 1 to 100 mmol/L.

The aqueous solution used in the electrodeposition process may contain other additives as long as the effects of the present invention are not impaired. Other additives include, for example, pH adjusters.

In the electrodeposition step, the electrodeposition treatment method is not particularly limited, and a wide variety of known electrodeposition treatment methods can be employed. For example, the electroconductive porous base material can be immersed in the aqueous solution to perform electrodeposition treatment.

In the manufacturing method of the present invention, in the electrodeposition process, copper foam, which is a conductive porous base material, is used as an anode to perform the electrodeposition process. The copper foam may be formed with copper nanowires as described above.

In the electrodeposition process, various electrodeposition methods can be employed. Examples of the electrodeposition method include a constant current method (GM), a constant voltage method (PM), a cyclic voltammetry method (CV), and a pulsed electrodeposition method. The pulsed electrodeposition method is an electrodeposition method that can control the electrodeposition rate of metal ions, and includes, for example, the pulsed voltage method (PPM) in which a high end voltage and a low end voltage are applied at a constant cycle, and a high end current and a low end voltage method. Examples include the pulsed current method (PGM) in which a current is applied at a constant cycle, and the unipolar pulsed voltage method (UPED) in which the application of a high-end voltage and an open circuit state are repeated at a constant cycle.

The electrodeposition method is preferably a pulsed electrodeposition treatment method, and among them, a unipolar pulsed voltage method (UPED) is more preferred.

When employing the unipolar pulse voltage method (UPED) as the electrodeposition method in the electrodeposition process, the conditions for the unipolar pulse voltage method are not particularly limited. For example, the following conditions can be adopted: the applied voltage is -0.6 to 1.8 V, the constant current is 0 to 15 mA, the pulse on/off time is 0.5 to 1 second, and the number of cycles is 100 to 1000. As a more specific example, the unipolar pulse voltage method can be performed under the conditions of an applied voltage of -1 V, a constant current of 10 mA, and an on/off time of 1 s.

The temperature of the aqueous solution during electrodeposition treatment is not particularly limited, and can be, for example, about 0 to 50°C, preferably 20 to 30°C.

In the electrodeposition process, in addition to the cathode , an anode , a reference electrode, an electrolyzer, a power source, control software, etc. can be used. These types are not particularly limited, and known types can be used depending on the purpose. For example, as the reference electrode, a silver/silver chloride electrode (Ag/AgCl electrode), a mercury/mercury chloride electrode (Hg/HgCl ₂ electrode), a standard hydrogen electrode, etc. can be used.

As the anode used in the electrodeposition process, for example, a known insoluble electrode can be used. As the anode , for example, an electrode made of carbon, platinum group metal, gold, or the like can be used. Platinum group metals include platinum, palladium, ruthenium, rhodium, osmium, and iridium, with platinum being preferred. The platinum group metal contained in the anode may contain one or more of the above metal species. Furthermore, the platinum group metal may be contained in the form of an alloy, metal oxide, or the like.

The shape of the anode is not particularly limited, and can be appropriately selected depending on the purpose of use and required performance. Examples of the shape include metal wire, sheet shape, plate shape, rod shape, mesh shape, and the like. Specifically, a spiral platinum wire, a platinum plate, etc. can be exemplified.

In the electrodeposition treatment, the pH of the aqueous solution is not particularly limited, and is, for example, less than 6, preferably about 2 to 5, more preferably about 3 to 4.

The hydroxide of metal M is formed on the copper foam by the electrodeposition process in the electrodeposition process. When two or more metal compounds containing different metals M are used, a double hydroxide containing two or more metals M is formed on the copper foam.

After the electrodeposition process, the copper foam with the hydroxide or double hydroxide formed thereon can be subjected to a firing process. As a result, the hydroxide or double hydroxide on the conductive porous substrate is fired and changed into an oxide. If a double hydroxide has been formed on the conductive porous substrate, it can be transformed into a composite oxide by firing.

That is, the manufacturing method of the present invention can include, after the electrodeposition step, a step of firing the copper foam electrodeposited in the electrodeposition step. Hereinafter, this process will be abbreviated as a firing process.

In the firing step, the method of firing treatment is not particularly limited, and a wide variety of known firing methods can be employed. For example, the temperature of the firing treatment can be 100°C or higher, preferably 150 to 450°C, and more preferably 200 to 400°C. The firing time may be appropriately selected depending on the firing temperature, and can be, for example, 1.5 to 5 hours. In step 1, the rate of temperature increase during firing is not particularly limited, and can be appropriately set to a level at which a desired oxide is formed.

The firing process may be performed either in air or in an inert gas atmosphere. Preferably, the firing treatment is performed in air. For the firing process, for example, a known heating device such as a commercially available heating furnace can be used.

Before the firing treatment, if necessary, the copper foam that has been electrodeposited in the electrodeposition process can be dried at 50° C. to 150° C. in air or vacuum.

By the above baking treatment, the metal hydroxide or double hydroxide on the copper foam is changed into an oxide or composite oxide, and the copper foam is coated with the metal oxide or composite oxide. In particular, when copper nanowires are formed on a copper foam, the oxide or composite oxide produced in the firing process is formed to cover the copper nanowires.

By including the electrodeposition step, the manufacturing method of the present invention can shorten the synthesis time compared to conventional chemical synthesis methods. In contrast to conventional chemical synthesis methods, which required a long reaction time and a high reaction temperature, and also required cleaning after the reaction, the production method of the present invention, which includes an electrodeposition step, The reaction time is short, and cleaning after the reaction is not necessarily required.

In addition, the production method of the present invention eliminates the post-synthesis granulation step that was necessary in conventional chemical synthesis methods, which also reduces the overall production time and improves the quality of the obtained product. can be used as is as a VOC removal catalyst.

Furthermore, in the manufacturing method of the present invention, by including the electrodeposition step, the metal oxide or metal composite oxide can be easily distributed uniformly on the carrier (copper foam). When a metal that is easy to electrodeposit, such as a metal that is easy to electrodeposit, can be electrodeposited together with a metal that is difficult to electrodeposit, for example, it becomes easy to form a composite oxide containing Mn and Co.

Furthermore, in the manufacturing method of the present invention, by using copper foam as the conductive porous base material that is the carrier, VOC is reduced compared to the case where a base material such as a known nickel foam is used. It becomes possible to remove it at a lower temperature. As a result, VOCs can be efficiently removed using a smaller amount of catalyst than the catalyst obtained by conventional chemical synthesis methods.

2. VOC Removal Catalyst The VOC removal catalyst of the present invention is formed by coating a conductive porous base material with a metal oxide. In particular, in the VOC removal catalyst of the present invention, the conductive porous substrate is a copper foam. The VOC removal catalyst of the present invention can be obtained, for example, by the method for producing the VOC removal catalyst of the present invention described above.

In the VOC removal catalyst, the type of copper foam is the same as the type of copper foam used in the production method of the present invention. Therefore, copper nanowires may be formed in the copper foam.

The metal oxide formed on the copper foam is an oxide of the metal M. As a precautionary note, the metal oxide may be a composite metal oxide containing two or more types of metal M.

In the VOC removal catalyst, the metal oxide is at least one metal selected from the group consisting of Ni, Cu, Co, Mo, W, Ti, Cr, Al, Fe, Mn, V, Zn, Mg, and La. Preferably, it is an oxide or a composite oxide. In this case, the VOC removal catalyst tends to have improved VOC removal performance.

Among them, Ni, Cu, and Co are metals that are easily electrodeposited, so it is preferable that the metal M contained in the metal oxide contains at least one selected from the group consisting of Ni, Cu, and Co. In this case, the metal M further includes at least one selected from the group consisting of Mo, W, Ti, Cr, Al, Fe, Mn, V, Zn, Mg, and La, which are considered to be difficult to deposit. I can do it. Since the metal M contains Ni, Cu, Co, etc., which are easily electrodepositable, when the electrodeposition method is adopted as the catalyst production method, it becomes possible to electrodeposit even difficult-to-electrodeposit metals. , it is possible to obtain a VOC removal catalyst in which each metal is uniformly dispersed.

It is particularly preferable that the metal oxide is a composite metal oxide containing both Co and Mn. In this case, the resulting VOC removal catalyst can remove VOCs at a lower temperature.

The shape of the metal oxide (including composite metal oxide) formed on the copper foam is not particularly limited. For example, metal oxides are formed in any shape such as nanowires, nanorods, petal-shaped particles, spherical particles, porous particles, etc., and have particularly excellent VOC removal performance. Preferably, the shape is

The VOC removal catalyst of the present invention has the above-mentioned structure, so it has excellent VOC removal efficiency even when VOC is treated at low temperature, and in particular, when the VOC removal catalyst is obtained by the production method of the present invention, Even more efficient.

Furthermore, since the VOC removal catalyst of the present invention can easily distribute the metal oxide or metal composite oxide uniformly on the carrier (copper foam), it can be used less than the catalyst obtained by conventional chemical synthesis methods. amount, VOCs can be efficiently removed. In particular, when a VOC removal catalyst is obtained by the production method of the present invention, the metal oxide or metal composite oxide is more likely to be more uniformly distributed on the carrier, further increasing the VOC removal efficiency.

3. VOC Removal Method The VOC removal method of the present invention includes a step of removing VOC using the VOC removal catalyst obtained by the production method of the present invention. Alternatively, the VOC removal method of the present invention includes a step of removing VOC using the VOC removal catalyst of the present invention.

For example, the VOC removal catalyst of the present invention is housed in a container, and VOCs such as toluene are introduced into the container and treated at a predetermined temperature to burn the VOCs. This allows VOCs to be removed. If desired, one or both of nitrogen and oxygen can be flowed into the container, and the VOCs can be combusted in the presence of one or both of nitrogen and oxygen. The type of container is not particularly limited, and for example, a wide variety of known containers used for catalytic combustion of VOCs can be used.

The VOC treatment temperature within the container is not particularly limited, and may be the same as the treatment temperature set for known VOC removal. In particular, in the present invention, by using the above-mentioned VOC removal catalyst, VOC removal efficiency is excellent even at low temperatures. can treat VOCs at temperatures below 280°C.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the embodiments of these Examples.

(Example 1)
A Cu foam (1.5 cm x 1.5 cm) was immersed in 40 mL of KOH solution with a concentration of 3 M and subjected to electrooxidation treatment (electrolytic oxidation) using a galvanostatic method with an applied current of 40 mA and a duration of 1200 seconds. (See Figure 1). In this electrooxidation treatment, a platinum thread was used as a counter electrode, a Cu foam was used as a working electrode, and a silver/silver chloride electrode (Ag/AgCl electrode) was used as a reference electrode. After electrolytic oxidation, the Cu foam was washed with distilled water. As a result, a Cu foam (hereinafter referred to as "Cu foam A") having nanowires formed on its surface was prepared.
Meanwhile, 0.28704 g of Mn(NO ₃ ) _{2.3H 2 O} and 0.29103 g of Co(NO ₃ ) 2.6H ₂ O were simultaneously dissolved in 100 mL of distilled water and stirred until it became transparent _. An aqueous solution having a Mn concentration of 0.01 mol/L and a Co concentration of 0.01 mol/L was prepared. The Mn:Co ratio in this aqueous solution was 1:1. Cu foam A was immersed in this aqueous solution as a cathode , and electrodeposition was performed using a unipolar pulse voltage method. The unipolar pulse voltage method was performed with an applied voltage of -1 V, a pulse on/off time of 1 second, and 1000 cycles. Further, a platinum electrode was used as an anode (counter electrode), and Ag/AgCl was used as a reference electrode. By this electrodeposition treatment, a double hydroxide of Co and Mn was formed on the Cu foam A. The electrodeposited Cu foam A was vacuum-dried overnight in an atmosphere of 80°C, and then the conductive porous substrate was baked in the air at 350°C for 2 hours. Processed. In this firing process, the temperature increase rate was 5° C./min. Through this firing treatment, a conductive porous substrate coated with a composite of Co and Ni was obtained as a catalyst for VOC removal. This VOC removal catalyst was named "0.01Mn-0.01Co/Cu foam."

(Example 2)
A VOC removal catalyst was obtained in the same manner as in Example 1 except that the amount of Mn(NO ₃ ) _{2.3H 2} O used was changed to 1.4352 g. This VOC removal catalyst was named "0.05Mn-0.01Co/Cu foam."

(Example 3)
A VOC removal catalyst was obtained in the same manner as in Example 1 except that the amount of Mn(NO ₃ ) _{2.3H 2} O used was changed to 2.8704 g. This VOC removal catalyst was named "0.10Mn-0.01Co/Cu foam."

(Comparative example 1)
A VOC removal catalyst was obtained in the same manner as in Example 1 except that nickel foam (1.5 cm x 1.5 cm) was used instead of Cu foam A. This VOC removal catalyst was named "0.10Mn-0.01Co/nickel foam."

<Evaluation method>
(SEM measurement)
Observation of SEM (scanning electron microscope) images was performed using "Scanning Electron Microscope SU8010" manufactured by Hitachi High Technologies.

(Elemental analysis)
Elemental analysis of the VOC removal catalyst was performed using an "energy dispersive X-ray analyzer" manufactured by HORIBA.

(VOC removal test)
A toluene removal test was conducted on the VOC removal catalysts obtained in each Example and Comparative Example. In this test, a VOC removal catalyst was packed in a reactor so as to be sandwiched between quartz wool, and toluene was introduced into the reactor at a predetermined flow rate to cause a reaction, thereby removing toluene. The reactor was connected to an oxygen cylinder and a nitrogen cylinder so that oxygen and nitrogen could flow into the reactor. As the conditions for the toluene removal test, a glass reactor with an inner diameter of 8 mm was used, and 100 mg of the VOC removal catalyst was filled therein, so that the toluene concentration in the reactor was 913 to 1027 ppm by volume. Further, the flow rate of nitrogen gas for carrier into the reactor was set to 35 mL/min, the flow rate of nitrogen gas for introducing toluene was set to 5 mL/min, and the flow rate of oxygen gas was set to 10 mL/min. The reaction temperature in the reactor was adjusted to various temperatures in the range of 150 to 350° C., and toluene removal characteristics were evaluated. At this time, from 100 to 350°C, sampling is performed twice every 10°C temperature change, from 210 to 270°C, sampling is performed twice every 5°C temperature change, and from 270 to 300°C, sampling is performed twice every 10°C temperature change. Two samples were taken at each temperature change. The VOC concentration was measured using "GC-2014 Gas Chromatograph" manufactured by Shimadzu Corporation. In addition, the concentration of carbon dioxide discharged from the reactor outlet was measured using an FT-IR gas analyzer "FG-120" manufactured by HORIBA.

(Evaluation results)
FIG. 2 shows SEM images of the VOC removal catalysts obtained in Examples and Comparative Examples. FIG. 2(a) shows SEM images of the VOC removal catalysts of Comparative Example 1, and FIGS. 2(b) to 2(d) show SEM images of the VOC removal catalysts of Examples 1 to 3, respectively. Furthermore, a partially enlarged image (indicated by the broken line) is inserted into each SEM image in FIG. 2 .

From FIG. 2, in the VOC removal catalyst of Comparative Example 1, Mn--Co species were partially aggregated on the nickel foam catalyst carrier. On the other hand, in the VOC removal catalysts of Examples 1 to 3, it was confirmed that Mn--Co species were uniformly formed on the Cu foam nanowires.

Table 1 shows the results of elemental analysis by EDS of the VOC removal catalysts obtained in Examples and Comparative Examples.

From Table 1, it was found that in the VOC removal catalyst obtained in the example, a composite oxide containing Mn and Co was formed on the copper foam. It was also found that the composition of Mn and Co is influenced by the catalyst support (foam) and the initial solution concentration of the aqueous solution used during production. In particular, when nickel foam was used, the amount of Mn electrodeposited was small.

FIG. 3 shows the results of VOC removal tests using the VOC removal catalysts obtained in Examples 1 to 7. FIG. 3 is a plot showing the relationship between temperature (X-axis) and toluene removal rate (Y-axis).

Table 2 shows the results of VOC removal tests using the VOC removal catalysts obtained in Examples and Comparative Examples.

From the results shown in FIG. 3 and Table 2, it was found that all of the VOC removal catalysts can remove toluene when used as a catalyst for catalytic combustion of toluene, which is a typical VOC substance. In Examples 1 to 3, optimal catalytic performance was obtained when the Mn:Co ratio in the aqueous solution used during production was 10:1 (0.10:0.01). Furthermore, the complete combustion temperature of toluene when using a VOC removal catalyst equipped with copper foam as in Examples 1 to 3 is higher than the complete combustion temperature of toluene when using a VOC removal catalyst equipped with nickel foam. It was low. In addition, as shown in Table 2, no matter which VOC removal catalyst was used, the amount of CO ₂ produced corresponded to the amount of toluene introduced within the error range, so all toluene was converted to CO ₂ . It was found that no by-products such as CO were produced.

From the above, it seems that the VOC removal catalyst made of the composite oxide of Co and Mn has synergistically enhanced VOC removal performance due to the so-called alloying effect. The alloying effect here refers to the effect of alloying, which improves catalytic functions (activity, selectivity, stability, etc.) by improving geometrical effects (ensemble effects) and electronic effects (ligand effects) that are different from those of single metals. ) means to give.

Since the composite oxide of Co and Mn exhibits excellent VOC removal performance, it is presumed that composite oxides made from combinations of other metals also exhibit similar performance. Among them, a composite metal oxide containing at least two metals selected from the group consisting of Ni, Cu, Co, Mo, W, Ti, Cr, Al, Fe, Mn, V, Zn, Mg and La is used in Examples It can be said that it shows the same VOC removal effect as the metal oxide catalyst. In particular, since composite oxides of Co and Mn exhibit excellent VOC removal effects, they can be combined with any one of Mn, Mo, W and V, which have excellent oxygen activation ability, and which have hydrocarbon activation ability. It is presumed that any composite oxide in combination with any one of Fe, Co, Ni, and Cu exhibits an excellent VOC removal effect.

Claims (5)

A step of performing pulsed electrodeposition treatment in an aqueous solution containing at least two metal compounds using the conductive porous substrate as a cathode,
The metal compound is at least a compound of Mn and a compound of at least one metal selected from the group consisting of Ni, Cu and Co,
A method for producing a VOC removal catalyst, wherein the conductive porous substrate is a copper foam. It is formed by coating a conductive porous base material with a metal oxide,
The metal oxide is a composite oxide containing at least Mn and at least one metal selected from the group consisting of Ni, Cu and Co,
A catalyst for VOC removal, wherein the conductive porous substrate is a copper foam. A method for removing VOCs, comprising a step of removing VOCs using the VOC removal catalyst obtained by the production method according to claim 1 or the VOC removal catalyst according to claim 2. The production of the VOC removal catalyst according to claim 1, wherein the aqueous solution further contains a compound of at least one metal selected from the group consisting of Mo, W, Ti, Cr, Fe, V, Zn, Mg, and La. Method. The VOC removal catalyst according to claim 2, wherein the metal oxide further contains at least one metal selected from the group consisting of Mo, W, Ti, Cr, Fe, V, Zn, Mg, and La.