JP2002102701A - Ordinary temperature catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an ordinary temperature catalyst which is activated at ordinary temperature below 50 deg.C so that it can decompose and remove environmentally pollution load materials such as CO, amines and formaldehyde. SOLUTION: This ordinary temperature catalyst is obtained by carrying a noble metal on an oxide with introduced oxygen deficiency, and >=90% of the noble metal is carried in the form of fine particles of <=2 nm particle diameter. Active oxygen contained in the oxygen deficiency reacts with environmentally pollution load materials adsorbed on the surface of the catalyst at ordinary temperature below 50 deg.C to oxidize and decompose the materials. Though the active oxygen is consumed by the reaction, gaseous oxygen contained in the air is incorporated into the catalyst and becomes active oxygen, which reacts further with environmentally pollution load materials. Since the noble metal is carried as the fine particles, numerous active sites are present and the catalyst has very high activity at ordinary temperature below 50 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for easily decomposing environmentally hazardous substances such as carbon monoxide (CO), hydrocarbons (HC), aldehydes, ethylene and ammonia at room temperature (room temperature) of 50 ° C. or less. It relates to a room temperature catalyst that can be removed.

[0002]

2. Description of the Related Art For example, adhesives for plywood or coatings applied to furniture may contain free formaldehyde, which is gradually released into the atmosphere. In addition, formaldehyde is generated from industrial products using adhesives and paints using formaldehyde as a raw material along with deterioration. This formaldehyde has a pungent odor and is pointed out as one of the causative substances of sick house syndrome. For this reason, house manufacturers are making efforts to reduce the formaldehyde concentration by aging the house before handing it over to the owner after the construction of the house, but aging alone does not necessarily meet the standards of the Ministry of Health and Welfare, There is a need for a further reduction in the formaldehyde concentration in the air.

[0003] Therefore, as a method for removing environmentally hazardous substances from the air, a method using ozone or a method using an adsorbent such as activated carbon or zeolite is widely used.
For example, as a deodorant which is placed in a refrigerator, a closet, a shoe box or the like to deodorize, a product in which an adsorbent is stored in a container through which air can flow is commercially available. Also, an air purifier with a built-in adsorbent or photocatalyst is known.

[0004] In addition, ethylene contained in the air promotes the physiological action of the fruits and vegetables to promote ripening and aging, so that it is thought that the freshness of the fruits and vegetables is reduced by ethylene. Therefore, the removal of ethylene from the atmosphere is effective for maintaining the freshness of fruits and vegetables, and methods of decomposing ethylene by ozone and hydrogen peroxide and adsorbing and removing ethylene have been proposed.

[0005] For example, Japanese Patent Application Laid-Open No. 7-260331 discloses that a photocatalyst and an ultraviolet light source are arranged in a storage container for accommodating fresh vegetables, and a gas harmful to freshness maintenance of fresh vegetables such as ethylene and acetaldehyde is provided by the photocatalytic action. An apparatus for disassembly and removal is disclosed.

For example, Japanese Patent Application Laid-Open No. 10-296087 discloses that
A catalyst in which a noble metal is supported on a support containing zirconia or ceria is disclosed. According to this catalyst, trimethylamine can be oxidatively decomposed at a temperature of about 200 ° C.

A catalyst for oxidizing CO or HC, or NO
_As a catalyst for reducing _x , a catalyst in which a noble metal is supported on a carrier such as alumina is known, and is widely used as an exhaust gas purifying catalyst and the like.

[0008]

However, in the method using ozone, an ozone concentration exceeding a regulated value is required in order to exert the effect of ozone, and there is a possibility that ozone will remain even after removing environmental load substances. is there. Therefore, it is not practical because a catalyst for treating residual ozone is required.

In the method of adsorbing and removing environmentally hazardous substances in the air by the adsorbent, it is difficult to adsorb the adsorbent in excess of the adsorbing capacity of the adsorbent. There is a need.

In the method using a photocatalyst, an artificial light source is required as an excitation source of the photocatalyst. If the light source is constantly irradiated with the light source, an electricity cost for operating the light source is also required, which is expensive. I have.

Further, in the method using a catalyst, the temperature must be raised to the activation temperature of the noble metal, and a catalyst that activates at a normal temperature of 50 ° C. or less has not yet been known.

The present invention has been made in view of such circumstances, and has as its object to provide a catalyst which can be activated at room temperature of 50 ° C. or lower to decompose and remove environmentally harmful substances such as CO, amines and formaldehyde. And

[0013]

The room temperature catalyst of the present invention which solves the above-mentioned problems is characterized in that a noble metal is supported on an oxide into which oxygen deficiency has been introduced, and 90% or more of the noble metal has a particle diameter of 2%.
That is, it is supported in the state of fine particles of nm or less.

This oxide is preferably at least one selected from transition metal oxides and rare earth oxides.
Transition metal oxide is at least one selected from oxides of Zr, Fe, Mn, Co, Ni, Cu, Cr, Mo and Nb, and rare earth oxides are oxides of Ce, Y, Nd, Pr and Sm And CeO ₂ -Zr
Desirably, it is at least one selected from O ₂ .
Pt, Pd, Rh, Ir, Ru and Au are desirable as the noble metal, and Pt is particularly desirable.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The room temperature catalyst of the present invention has a noble metal supported on an oxide into which oxygen deficiency has been introduced. Oxygen deficiency refers to a highly active state in which part of oxygen forming an oxide is eliminated, and a state in which the molar amount of oxygen bonded as an oxide is smaller than a specified value. For example, in the case of Ce oxide, CeO ₂ has no oxygen deficiency. Therefore, if the oxygen atom is less than twice the mole of Ce atom, it means that oxygen deficiency has been introduced.

This oxygen deficiency contains active oxygen, and this active oxygen reacts with the environmental load substance adsorbed on the catalyst surface at a room temperature of 50 ° C. or lower, and oxidatively decomposes the environmental load substance. The active oxygen contained in the catalyst is consumed by the reaction with environmentally harmful substances, but the oxygen gas contained in the air is taken into the catalyst to become active oxygen, which further reacts with the environmentally harmful substances . As described above, the oxidation reaction proceeds catalytically, whereby the environmentally hazardous substance can be oxidatively decomposed and removed.

The room temperature catalyst of the present invention carries a noble metal on the oxide into which the oxygen deficiency has been introduced. The activity of the oxide itself is enhanced by the oxygen deficiency, and as a result, the ability of the environmentally hazardous substance to be adsorbed on the noble metal is reduced. As a result, the activity of the noble metal is increased, and the oxidation reaction of the environmentally hazardous substance proceeds using active oxygen activated via the oxygen deficient portion.

For example, CO is oxidized by active oxygen to form CO.
₂ and formaldehyde (HCHO) or ethylene (C ₂ H ₄ ) is oxidized to CO ₂ and H ₂ O and made harmless.

Further, in the room temperature catalyst of the present invention, 90% or more of the noble metal is supported in the form of fine particles having a particle size of 2 nm or less. Since the noble metal is carried in such a fine state, its active sites are extremely large and its activity at room temperature of 50 ° C. or less is extremely high.

As the oxide, any oxide can be introduced as long as it can introduce oxygen deficiency, and an oxide of at least one transition metal selected from Zr, Fe, Mn, Co, Ni, Cu, Cr, Mo and Nb;
Alternatively, an oxide of at least one rare earth element selected from Ce, Y, Nd, Pr and Sm is preferable. One of these may be used, or a plurality of them may be used in combination.

Among them, Ce oxide is a particularly preferred oxide because it easily introduces oxygen deficiency and can stably maintain the oxygen deficiency state. If Ce oxide and Zr oxide are used together, the stability of the oxygen deficiency state of Ce oxide is further improved. In this case, it is more desirable that the Ce oxide and the Zr oxide form a composite oxide or a solid solution. By using a composite oxide or a solid solution, more oxygen vacancies can be formed, and the stability of the oxygen deficiency state is further improved.

In order to form oxygen vacancies in the oxide, a method of reducing the oxide is exemplified. For example, the above oxide may be treated in a reducing gas stream at a temperature of 100 ° C. to 800 ° C. for about 1 hour. When the oxide comes in contact with the reducing gas at a high temperature, part of the oxygen of the oxide is combined with the reducing gas and removed, and as a result, part of the oxide becomes an oxygen-deficient state and oxygen deficiency may be introduced. it can. When the temperature of the reduction treatment is lower than 100 ° C., the reduction reaction does not proceed, and it is difficult to form a desired oxygen deficiency state. On the other hand, if the treatment temperature exceeds 800 ° C., the specific surface area of the oxide becomes small, and the catalytic activity is undesirably reduced. Hydrazine,
The reduction treatment can also be performed using a reducing agent represented by aluminum borohydride or the like.

The reducing gas used in the reduction treatment includes:
In addition to reducing gases such as hydrogen and carbon monoxide, hydrocarbons such as methane and aldehydes may be mentioned. The concentration of the reducing gas at the time of the reduction treatment is preferably 0.1% by volume to 100% by volume, more preferably 1% by volume to 100% by volume.

By knowing the relationship between the amount of active oxygen contained and the amount of oxygen deficiency in advance, the amount of oxygen deficiency can be easily adjusted by adjusting the temperature and time of the reduction treatment. . For example, 40 μmol / g of active oxygen
It is desirable to contain the above. Active oxygen content is 40μ
If it is less than mol / g, the reaction with the environmentally harmful substance at room temperature of 50 ° C. or less is not sufficient. The amount of active oxygen is 40 μmol /
When the amount is greater than or equal to g, the oxidation reaction of the environmentally harmful substance proceeds rapidly, and the activity of purifying the environmentally harmful substance in a normal temperature range becomes extremely high. Although oxidative purification of environmentally harmful substances is possible even at a high temperature exceeding 50 ° C., it is desirable to use it at 50 ° C. or lower, more preferably 10 to 40 ° C., because oxygen deficiency may be lost.

As the noble metal supported on the room temperature catalyst of the present invention, at least one selected from Pt, Pd, Rh, Ir, Au and Ru can be used. One of these may be
A plurality of types can be carried. Highly active Pt is particularly desirable. The amount of the noble metal carried is preferably 0.1 to 10% by weight based on the oxide into which oxygen vacancies have been introduced.
If the content is less than 0.1% by weight, the catalytic activity at 50 ° C. or less cannot be obtained, which is not preferable. Further, even if the precious metal is supported in an amount exceeding 10% by weight, the purification efficiency is not improved for the addition, and a large amount of expensive precious metal is used, resulting in an increase in cost.

For supporting the noble metal, a known supporting method such as an adsorption supporting method, an evaporation to dryness method and a supercritical fluid method can be used. In order to support the noble metal in a fine particle state in which 90% or more of the noble metal has a particle size of 2 nm or less, it is easy to adjust the firing conditions after supporting the noble metal as a chemical solution or to adjust the specific surface area of the oxide. Can be. When firing in the air, for example, the firing temperature may be set to 500 ° C. or lower. Also for example, when supported on CeO ₂ -ZrO ₂ solid solution, the specific surface area of CeO ₂ -ZrO ₂ solid solution is preferably used as more than 100 m ² / g. By preserving a noble metal before reducing the oxide and subjecting the noble metal to a reducing treatment, oxygen vacancies can be more effectively introduced.

Hereinafter, the structure of the room temperature catalyst of the present invention will be described in detail when CeO ₂ -ZrO ₂ which is a solid solution or a composite oxide is used as the oxide.

CeO ₂ -ZrO ₂ was precipitated by a co-precipitation method, an alkoxide method, or the like, using a solution in which at least one of a Ce compound and a Zr compound was dissolved, mixing the other oxide powder as necessary. Thereafter, it can be formed by firing. Further, a mixture of CeO ₂ powder and ZrO ₂ powder may be fired at a high temperature.

The molar ratio of Ce and Zr in CeO ₂ —ZrO ₂ is
e: Zr = 100: 1 to 1: 100 is preferable, and Ce: Zr
= 20: 1 to 1:10, more preferably Ce: Zr = 5:
A range of 1 to 1: 1 is more preferred. By setting it in this range, the oxygen deficiency state can be more stably maintained.
It is desirable that the molar amount of Ce be larger than the molar amount of Zr. This makes it possible to more easily form an oxygen deficiency state and increase the amount of active oxygen.

CeO ₂ -ZrO ₂ has, as a third component, oxides of rare earth elements such as Y, La, Nd, Pr, Fe, Mn, C
1 selected from transition metal oxides such as o, Cr, Ni, and Cu
May contain seeds. By blending these third components, the oxygen-deficient state of CeO ₂ —ZrO ₂ can be more stably maintained. The content of the third component is 1 to
Preferably it is 30 mol%. If the amount is less than this range, the effect of containing the compound cannot be obtained, and if the amount exceeds 30 mol%, it may be difficult to form oxygen vacancies.

The introduction of oxygen deficiency into CeO ₂ —ZrO ₂ can be carried out by a reduction treatment using a reducing gas as described above. As a result, oxygen vacancies are mainly introduced into CeO ₂ . In this case, the composition ratio of _n in CeOn is 1.5 ≦ n
If the oxygen deficiency state is in the range of <2, more preferably 1.5 ≦ n ≦ 1.8, a particularly excellent effect on the purification of formaldehyde is exhibited. A state where the n value is less than 1.5 is considered to be difficult to form by ordinary reduction treatment, and even if it is, it is difficult to identify it under ordinary elemental analysis conditions. The oxygen deficiency state of the oxide can be measured by, for example, X-ray diffraction. From the viewpoint of catalytic activity, it is desirable that the composition ratio in the surface layer of about 100 nm from the surface of the catalyst particles be in the range of 1.5 ≦ n ≦ 1.8 rather than the inside of the catalyst particles.

The noble metals supported on CeO ₂ —ZrO ₂ include:
At least one of Pt, Pd, Rh, Au, and Ru is preferable, and Pt is particularly preferable. The supported amount of the noble metal is 1 of CeO ₂ -ZrO ₂ .
The amount is preferably 0.1 g to 20 g, more preferably 0.5 g to 5 g per 50 g. To support precious metals,
It is carried before the reduction treatment, and the reduction treatment is carried out after the noble metal is carried. When producing CeO ₂ -ZrO ₂ by a coprecipitation method or the like,
After coprecipitation in the coexistence of a noble metal, baking can be carried.

The catalyst of the present invention is prepared as a powder, which can be formed into pellets for use. In addition, a coat layer can be formed from the catalyst powder on the surface of the honeycomb substrate in the same manner as in the usual method.

[0034]

The present invention will be specifically described below with reference to examples and comparative examples.

Example 1 CeO ₂ powder (specific surface area: 120 m ² /
g) Impregnating 150 g with a predetermined amount of a dinitrodiammine platinum aqueous solution having a predetermined concentration, heating after stirring, and evaporating to dryness;
Then, it was calcined in the air at 500 ° C. for 3 hours to carry Pt.
The supported amount of Pt is ₂ g per 150 g of CeO ₂ powder.

Next, the obtained Pt-supported CeO ₂ powder was
A normal temperature catalyst of Example 1 was prepared by placing it in a nitrogen stream containing volume% and performing a reduction treatment at 500 ° C. for 15 minutes to introduce oxygen vacancies.

Example 2 Except that CeO ₂ -ZrO ₂ solid solution powder (specific surface area: 120 m ² / g) of Ce: Zr = 5: 1 produced by a coprecipitation method was used instead of CeO ₂ powder. In the same manner as in Example 1, a room temperature catalyst of Example 2 was prepared.

(Example 3) The sintering temperature at the time of carrying Pt was 300 ° C.
A normal temperature catalyst of Example 3 was prepared in the same manner as in Example 1 except that

(Comparative Example 1) A CeO ₂ -ZrO ₂ solid solution powder (specific surface area: 30 m ² / g) of Ce: Zr = 5: 5 produced by a coprecipitation method was used instead of the CeO ₂ powder. In the same manner as in Example 1, a room temperature catalyst of Comparative Example 1 was prepared.

Comparative Example 2 A room temperature catalyst of Comparative Example 2 was prepared in the same manner as in Example 1 except that CeO ₂ powder having a low specific surface area (specific surface area: 3 m ² / g) was used.

(Comparative Example 3) The sintering temperature at the time of carrying Pt was 700 ° C.
A room temperature catalyst of Comparative Example 3 was prepared in the same manner as in Example 1 except that

(Comparative Example 4) The firing temperature at the time of carrying Pt was 800 ° C.
A normal temperature catalyst of Comparative Example 4 was prepared in the same manner as in Example 1 except that

(Comparative Example 5) The firing temperature at the time of carrying Pt was 900 ° C.
A normal temperature catalyst of Comparative Example 5 was prepared in the same manner as in Example 1 except that

Comparative Example 6 The room temperature catalyst of Comparative Example 6 was prepared in the same manner as in Example 1 except that a Pt colloid solution having a controlled particle size of about 5 nm was used instead of the dinitrodiammine platinum aqueous solution. Prepared.

Comparative Example 7 The room temperature catalyst of Comparative Example 7 was prepared in the same manner as in Example 1 except that a Pt colloid solution having a controlled particle diameter of about 10 nm was used instead of the dinitrodiammine platinum aqueous solution. Prepared.

Comparative Example 8 The ordinary temperature catalyst of Comparative Example 8 was used in the same manner as in Example 1 except that a Pt colloid solution having a controlled particle size of about 15 nm was used instead of the dinitrodiammine platinum aqueous solution. Prepared.

Comparative Example 9 A coconut shell activated carbon (specific surface area: 700 m ² / g), which is generally used as an adsorbent, was used in Comparative Example 9.
And

<Test / Evaluation> (Test Example 1) The particle size of Pt carried on the catalysts of Examples 1 to 3 and Comparative Examples 1 to 8 was measured. The measurement of the Pt particle size was mainly performed by observation with a transmission electron microscope. In addition, the measurement based on the amount of adsorbed CO and the measurement based on X-ray diffraction were simultaneously performed, and the average value was calculated. Table 1 shows the results.

5 g of each of the catalysts of Examples 1 to 3 and Comparative Examples 1 to 8 were placed in an evaluation device, and a model gas consisting of a CO concentration of 250 ppm, an O ₂ concentration of 20% by volume and a balance of N ₂ was supplied at a gas flow rate of 10 liter / liter. Min, and the CO conversion at room temperature (25 ° C.) was measured. Table 1 shows the results.

The relationship between the Pt particle size and the CO conversion in Table 1 was plotted, and the results are shown in FIG.

[0051]

[Table 1]

As shown in Table 1 and FIG. 1, the catalyst of each embodiment has a Pt particle size of 2 nm or less. When the Pt particle size is 2 nm or less, the CO conversion at room temperature is clearly as high as 90% or more, and it is understood that the catalyst activity at room temperature decreases as the Pt particle size increases.

(Test Example 2) The catalyst of Example 1 and the adsorbent of Comparative Example 9 were selected, and 0.1 g of each was placed in a 5 liter closed container filled with an atmosphere containing 900 ppm of methyl mercaptan at room temperature (25 ° C.). The change over time of the methyl mercaptan concentration in the closed container was measured by gas chromatography. The results are shown in FIG.

From FIG. 2, it is clear that the catalyst of Example 1 is superior to the adsorbent of Comparative Example 9 in the removal characteristics of methyl mercaptan, and it is understood that the catalyst has a high normal-temperature purification activity.

(Test Example 3) The procedure of Test Example 2 was repeated except that the catalyst of Example 1 and the adsorbent of Comparative Example 9 were selected, and instead of methyl mercaptan, air containing 900 ppm of triethylamine or ethylene was used. The changes over time in the triethylamine concentration and the ethylene concentration were measured. Fig. 3 shows the results.
And FIG.

3 and 4, it is clear that the catalyst of Example 1 is superior to the adsorbent of Comparative Example 9 in removing triethylamine and ethylene, and has a high normal-temperature purifying activity. I understand.

[0057]

According to the room temperature catalyst of the present invention, 50
Environmentally hazardous substances such as CO, amines and formaldehyde can be efficiently decomposed and removed at room temperature of not more than ℃.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the Pt particle size and the CO conversion at room temperature of the catalysts of Examples and Comparative Examples of the present invention.

FIG. 2 is a graph showing the change over time in the concentration of methyl mercaptan at room temperature in a closed container containing the catalyst of Example 1 and the adsorbent of Comparative Example 9.

FIG. 3 is a graph showing a time-dependent change in the concentration of triethylamine at room temperature in a closed container containing the catalyst of Example 1 and the adsorbent of Comparative Example 9.

FIG. 4 is a graph showing the change over time of the ethylene concentration at room temperature in a closed vessel containing the catalyst of Example 1 and the adsorbent of Comparative Example 9.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) // A61L 9/00 B01D 53/36 104Z (72) Inventor Kenichiro Suzuki Ken-ichiro Suzuki 41, Yokomichi No. 1, Toyota Central Research Laboratory Co., Ltd. (72) Inventor J. Sasaki 41, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Yokomichi No. 41 Inside Toyota Central Research Laboratory Co., Ltd. (72) Akira Morikawa Aichi Aichi 41, Toyoda Central Research Institute Co., Ltd. (72) Inventor Hiroaki Hayashi Hiroaki Hayashi 41st, Toyoda Central Research Institute Co., Ltd. Sugiura Masaki Sugiura 41, Nagakute-machi, Aichi-gun, Aichi-gun, 41-cho, Yokomichi Yokomichi F-term in Toyota Central R & D Laboratories, Inc. 4C080 AA07 AA09 BB02 CC05 CC08 CC09 HH05 KK08 LL03 LL10 MM07 NN01 QQ03 4D048 AA01 AA08 AA13 AA17 AA19 AB01 BA08X BA08Y BA18Y BA19X BA19Y BA24Y BA25A BA26Y BA28Y BA30A BABAYA33 BA33ABABAY BA33A BAAY BC BC44A BC51A BC51B BC55A BC58A BC59A BC62A BC66A BC67A BC68A BC69A BC70A BC71A BC72A BC74A BC75A BC75B CA07 CA11 CA14 CA15 CA17 DA05 FA02 FB09 FB14 FB44

Claims (4)

[Claims] 1. A room-temperature catalyst comprising a noble metal supported on an oxide into which oxygen deficiency has been introduced, wherein 90% or more of the noble metal is supported in the form of fine particles having a particle size of 2 nm or less. 2. The room temperature catalyst according to claim 1, wherein the oxide is at least one selected from transition metal oxides and rare earth oxides. 3. The transition metal oxide is zirconium,
At least one selected from oxides of iron, manganese, cobalt, nickel, copper, chromium, molybdenum and niobium, wherein the rare earth oxide is selected from oxides of cerium, yttrium, neodymium, praseodymium and samarium and ceria-zirconia The room-temperature catalyst according to claim 2, which is at least one of the following. 4. The room temperature catalyst according to claim 1, wherein the noble metal is at least one selected from Pt, Pd, Rh, Ir, Ru and Au.