JP6230464B2 - Metal-based fine particle supported catalyst - Google Patents

Description

  The present invention relates to a metal-based fine particle supported catalyst, a method for producing the same, and a method for treating nitrate nitrogen-containing water using the same.

  Nitrate nitrogen is required to be removed from industrial wastewater and the like because it causes eutrophication in lakes and marshes and damages the health of the human body. Methods for removing nitrate nitrogen from wastewater include biological treatment methods using microorganisms, physicochemical treatment methods such as ion exchange methods, and chemical treatment methods that perform reductive decomposition in the presence of a reducing agent and a catalyst. Are known. Among these, chemical treatment for performing reductive decomposition in the presence of a reducing agent and a catalyst is suitable for mass treatment of nitrate nitrogen-containing water, and various treatment methods have been conventionally proposed.

  For example, in Patent Document 1, in a method of treating nitrate nitrogen-containing water in which nitrate nitrogen-containing water and a water treatment catalyst are brought into contact in the presence of a reducing gas, the water treatment catalyst has metal fine particles supported on crystalline carbon particles. A method for treating nitrate-nitrogen-containing water comprising fine particles having an average primary particle diameter in the range of 5 nm to 1 μm, and the supported amount of metal fine particles in the catalyst fine particles being in the range of 1 to 50% by weight as metal. Is described.

  In Patent Document 2, metal particles made of at least one metal selected from the group consisting of a fourth periodic transition metal element, a fifth periodic transition metal element, platinum and gold are supported on an inorganic carrier material. There is described a metal particle-supported catalyst, wherein at least a part of the metal particles are polyhedral metal particles having a polyhedral structure. And the Example which carries out the reduction process of nitrate nitrogen containing water using such a metal particle carrying | support catalyst is described.

  Patent Document 3 describes a method for treating nitrate nitrogen-containing water, which comprises contacting nitrate nitrogen-containing water with a catalyst for treating nitrate nitrogen-containing water in the presence of ultrafine bubble reducing gas. ing.

JP 2007-21289 A JP 2009-172574 A JP 2007-7541 A

As described above, Patent Documents 1 to 3 describe that nitrate-containing water is reduced in the presence of a catalyst, but such a catalyst promotes a reductive decomposition reaction of nitrate nitrogen. It is preferable that the performance (hereinafter also referred to as activity) is high and that the activity is maintained high even after repeated use.
The present invention has a high activity for the reductive decomposition reaction of nitrate nitrogen in nitrate nitrogen-containing water, and maintains a high activity even during repeated use, a method for producing the same, and a method for producing the same It aims at providing the processing method of nitrate nitrogen containing water.

The present inventor has intensively studied to solve the above-described problems and completed the present invention.
The present invention includes the following (1) to (12).
(1) A metal-based fine particle-supported catalyst in which metal-based fine particles containing at least Pd and Cu are supported on an inorganic carrier material,
The inorganic carrier material has an average primary particle diameter of 5 to 200 nm, contains at least one oxide selected from the group consisting of Ti, Al, Si, Sn, and Zn as a main component, and the metal fine particles Is a metal-based fine particle-supported catalyst having an average primary particle size of 1 to 9 nm.
(2) The average pore diameter of the inorganic carrier material is 5 to 100 nm, the average pore volume is 0.1 to 1.5 ml / g, and the specific surface area is 10 to 300 m ² / g. Metal-based fine particle supported catalyst.
(3) The metal-based fine particle-supported catalyst according to (1) or (2), wherein the main component of the inorganic support material is TiO ₂ .
(4) The metal-based fine particle-supported catalyst according to any one of (1) to (3), wherein the inorganic support material is spherical or pellet-shaped.
(5) The metal-based fine particle-supported catalyst according to any one of the above (1) to (4), wherein a mass ratio of Pd: Cu in the metal-based fine particle is 30:70 to 99: 1.
(6) The metal-based fine particle-supported catalyst according to any one of (1) to (5), wherein the content of the metal-based fine particles is 0.1 to 10% by mass.
(7) Carrier preparation for obtaining an inorganic carrier material having an average primary particle diameter of 5 to 200 nm and containing as a main component at least one oxide selected from the group consisting of Ti, Al, Si, Sn, and Zn Process,
A dispersion adjusting step for obtaining a dispersion of metallic fine particles containing at least Pd and Cu and having an average primary particle diameter of 1 to 9 nm;
An immersion step of immersing the inorganic carrier material in the dispersion to obtain a metal-based fine particle / carrier mixture;
And a drying step of drying the metal-based fine particle / carrier mixture to obtain a metal-based fine particle-supported catalyst.
(8) The method for producing a metal-based fine particle-supported catalyst according to (7), wherein the immersion step is performed in the air or under a reduced pressure atmosphere.
(9) The method for producing a metal-based fine particle-supported catalyst according to (7) or (8), wherein a drying temperature in the drying step is 100 to 200 ° C.
(10) The method for producing a metal-based fine particle-supported catalyst according to any one of (7) to (9), wherein the drying step is performed in air, vacuum, inert gas atmosphere, or reducing gas atmosphere.
(11) A method for treating nitrate nitrogen-containing water, wherein the metal-based fine particle-supported catalyst according to any one of (1) to (6) is contacted with nitrate nitrogen-containing water.
(12) Nitrate nitrogen-containing water as described in (11) above, wherein nitrate nitrogen-containing water is passed through a reaction tower packed with the metal-based fine particle-supported catalyst according to any of (1) to (6) above. Processing method.

  According to the present invention, a metal-based fine particle-supported catalyst having high activity for the reductive decomposition reaction of nitrate nitrogen in nitrate nitrogen-containing water and maintaining the activity high even in repeated use, a method for producing the same, and a method for producing the same A method for treating nitrate-containing water used is provided.

It is a schematic diagram of the reactor in a batch type activity test. 4 is a SEM image of the catalyst of Example 2. 4 is a graph showing the activity characteristics of the catalyst of Example 2.

The present invention will be described.
The present invention is a metal-based fine particle-supported catalyst in which metal-based fine particles containing at least Pd and Cu are supported on an inorganic carrier material, wherein the inorganic carrier material has an average primary particle diameter of 5 to 200 nm, Ti, The metal-based fine particle is a metal-based fine particle-supported catalyst containing at least one oxide selected from the group consisting of Al, Si, Sn, and Zn as a main component, and having an average primary particle diameter of 1 to 9 nm.
Hereinafter, such a metal-based fine particle-supported catalyst is also referred to as “the catalyst of the present invention”.

<Inorganic carrier material>
The inorganic carrier material in the catalyst of the present invention will be described.
The inorganic carrier material contains at least one oxide selected from the group consisting of Ti, Al, Si, Sn, and Zn as a main component. Examples of these oxides include SiO ₂ , Al ₂ O ₃ , TiO ₂ , SnO ₂ , and ZnO. Further, it may be a composite oxide such as SiO ₂ —Al ₂ O ₃ , SiO ₂ —TiO _2, or may contain both an oxide and a composite oxide.

In the present invention, TiO ₂ is preferably included as a main component of the inorganic carrier material. This is because impurities (organic matter, Fe, etc.) other than nitrate nitrogen in the nitrate nitrogen-containing water are difficult to adsorb, and thus prevent a decrease in catalytic activity due to the adsorption of impurities. Here, the main component is 70% by mass or more in the whole inorganic carrier substance, preferably 80% by mass or more, more preferably 90% by mass or more, and 100% by mass, ie, inorganic. More preferably, the system support material consists essentially of TiO ₂ . Here, “substantially” means that impurities that are inevitably contained from the raw materials and the production process may be contained, but other than that are not contained. Unless otherwise specified, “main component” and “substantially” are used in this meaning in the description of the present invention.

Further, it is preferable that TiO ₂ is contained in the main component of the inorganic carrier material, and in addition, at least one oxide selected from the group consisting of Al, Si, Sn, and Zn is contained. In this case, the content of at least one oxide selected from the group consisting of Al, Si, Sn, and Zn in the main component is preferably 30% by mass or less, more preferably 20% by mass or less, and more preferably 10% by mass. % Or less is more preferable.
When such an oxide is used, even in nitrate nitrogen-containing water containing organic matter, adsorption of the organic matter to the inorganic carrier material can be further suppressed due to the low affinity between the oxide and the organic matter, As a result, the activity of the catalyst can be maintained higher.

  The average primary particle diameter of the inorganic carrier material is 5 to 200 nm, preferably 10 to 180 nm, and more preferably 20 to 150 nm. When the average primary particle diameter is in such a range, the specific surface area is high, and the metal-based fine particles can be supported in a highly dispersed state, so that the activity of the catalyst is improved.

  Here, the average primary particle diameter of the inorganic carrier material means a value determined as follows. The image of the inorganic carrier material particles taken with a transmission electron microscope is analyzed to determine the projected area equivalent circle diameter. Then, the projected area equivalent circle diameter for 50 randomly selected particles is simply averaged, and the obtained value is taken as the average primary particle diameter of the inorganic carrier material.

  The average pore diameter of the inorganic carrier material is preferably 5 to 100 nm, more preferably 10 to 95 nm, more preferably 20 to 85 nm, and still more preferably 20 to 70 nm. When the average pore diameter is in such a range, the supported metal-based fine particles are distributed in the pores and can be supported uniformly, and in addition to maintaining a high surface area, more sufficient catalytic activity can be obtained. An inorganic carrier material having an average pore diameter of less than 5 nm is difficult to obtain in the synthesis.

The average pore volume of the inorganic carrier material is preferably 0.1 to 1.5 ml / g, more preferably 0.15 to 1.3 ml / g, and 0.2 to 1.0 ml / g. More preferably.
When the average pore volume is in such a range, the supported metal-based fine particles are less likely to aggregate and a more sufficient catalytic activity can be obtained. Moreover, since sufficient intensity | strength of a catalyst can be obtained, problems on use, such as catalyst pulverization, can be prevented.

Preferably the specific surface area of the inorganic support material is 10 to 300 m ² / g, more preferably 10~250m ² / g, more preferably 15~150m ² / g, 20~100m ² More preferably, it is / g. When the specific surface area is in such a range, the adsorption of impurities to the inorganic carrier material can be suppressed, and high catalytic activity can be maintained.

The specific surface area of the inorganic carrier material means a value obtained from an adsorption isotherm obtained by a nitrogen adsorption method. Furthermore, an average pore diameter and an average pore volume mean the value calculated | required from the desorption isotherm in BJH (Barret-Joyner-Halenda) method.
Here, the nitrogen adsorption method will be described.
First, the dried measurement object is placed in a measurement cell as a sample, degassed in a nitrogen gas stream at 250 ° C. for 40 minutes, and then the sample is mixed with 30% by volume of nitrogen and 70% by volume of helium. A liquid nitrogen temperature is maintained in a gas stream, and nitrogen is adsorbed on the sample to obtain a nitrogen adsorption isotherm / desorption isotherm. Using this nitrogen adsorption isotherm, the specific surface area is determined by BET theory. Further, a pore diameter distribution curve of a sample is obtained by a BJH (Barret-Joyner-Halenda) method using a desorption isotherm, and mesopores (pores on the particle surface) side and macropores (interparticle fine particles) appearing on the curve Of the peaks on the (pore) side, the pore diameter of the peak on the mesopore side is determined as the average pore diameter. Similarly, a pore distribution curve is obtained by the BJH method, and a peak appearing in the curve is obtained as an average pore volume. This nitrogen adsorption method can be performed using, for example, a conventionally known pore distribution measuring apparatus.

  The inorganic carrier material is preferably in the form of a sphere or pellet, but may be in various forms such as a columnar shape, a crushed piece shape, a honeycomb shape, and a powder shape.

<Metallic fine particles>
The metal-based fine particles in the catalyst of the present invention will be described.
The metal-based fine particles contain at least Pd and Cu. This is because it is excellent in activity against the reductive decomposition reaction of nitrate nitrogen. In addition to Pd and Cu, other metals may be included. Examples of other metals include Pt, Au, Ag, Ru, Ni, W, V, Mo, and Fe.

  Furthermore, the mass ratio of Pd: Cu in the metal-based fine particles is preferably 30:70 to 99: 1. Further, the total content of Pd and Cu in the metal-based fine particles is preferably 90% by mass or more, more preferably 95% by mass or more, more preferably 98% by mass or more, and substantially 100%. More preferably, it is mass%.

  The average primary particle diameter of the metal-based fine particles is 1 to 9 nm. By setting the average primary particle size in such a range, it is difficult to agglomerate and the catalytic activity can be kept high. In addition, the average primary particle diameter of metal-type fine particles shall mean the value calculated | required with the following method. The image of the metal-based fine particles taken with a transmission electron microscope is analyzed to determine the projected area equivalent circle diameter. Then, the projected area equivalent circle diameters of 50 randomly selected particles are simply averaged, and the obtained value is used as the average primary particle size of the metal-based fine particles.

<Metal-based fine particle supported catalyst>
The metal-based fine particle-supported catalyst, that is, the catalyst of the present invention is one in which metal-based fine particles are supported on the above inorganic carrier material.
The content of the metal-based fine particles in the metal-based fine particle supported catalyst is preferably 0.1 to 10% by mass, more preferably 0.3 to 7% by mass, and 0.5 to 3% by mass. More preferably. When the content of the metal-based fine particles is within such a range, high catalytic activity can be obtained.
When the content of the metal-based fine particles is within such a range, the metal-based fine particles are difficult to aggregate and a more sufficient catalytic activity can be obtained.

  The average primary particle size of the metal-based fine particle supported catalyst is preferably 5 to 200 nm. In addition, an average primary particle diameter shall mean the value obtained by measuring with the same method as the case of an inorganic type carrier substance.

<Method for producing metal-based fine particle supported catalyst>
The present invention provides a carrier preparation for obtaining an inorganic carrier material having an average primary particle size of 5 to 200 nm and containing at least one oxide selected from the group consisting of Ti, Al, Si, Sn, and Zn as a main component A step of preparing a dispersion of metal-based fine particles containing at least Pd and Cu and having an average primary particle diameter of 1 to 9 nm; and immersing the inorganic carrier substance in the dispersion A method for producing a metal-based fine particle-supported catalyst, comprising: an immersing step for obtaining a fine particle / carrier mixture; and a drying step for drying the metal-based fine particle / carrier mixture to obtain a metal-based fine particle-supported catalyst.
Hereinafter, such a method for producing a metal-based fine particle-supported catalyst is also referred to as “the production method of the present invention”. The catalyst of the present invention can be produced by the production method of the present invention.

The carrier adjustment process will be described.
In the carrier adjustment step, an inorganic carrier material having an average primary particle diameter of 5 to 200 nm and containing at least one oxide selected from the group consisting of Ti, Al, Si, Sn, and Zn as a main component is prepared. To do. This step is not particularly limited as long as the desired inorganic carrier material is obtained. For example, an oxide mixture obtained by a conventionally known method (solid phase mixing method, liquid phase mixing method, coprecipitation method, impregnation method, etc.) is used. If necessary, it can be dried and then calcined.

In the carrier adjustment step, at least one oxide selected from the group consisting of Ti, Al, Si, Sn, and Zn is wet-pulverized to form a slurry, and then dried as necessary, and then fired. Thus, it is preferable to obtain an inorganic carrier material. The wet pulverization is a method in which the raw material is dispersed, pulverized, pulverized or mixed in a state where the raw material is immersed in water or an organic solvent. For example, the raw material and water are put in a ball mill and pulverized.

  Moreover, it is preferable to dry the slurry-like raw material. Drying can be performed using, for example, a conventionally known stationary dryer, spray dryer, vacuum dryer, or vacuum dryer. Furthermore, it is preferable to dry at a temperature of 100 to 200 ° C. for 2 to 10 hours.

  Next, it is preferable to fire the dried raw material. The method for firing is not particularly limited, and can be performed by, for example, a conventionally known method. For example, an inorganic carrier material can be obtained by baking for about 2 to 10 hours in an atmosphere at a temperature of about 500 to 1000 ° C. using a conventionally known baking furnace (a tunnel furnace, a muffle furnace, a rotary kiln or the like).

  The inorganic carrier material obtained in the above process is usually in powder form. The inorganic carrier material is preferably formed into a spherical shape or a pellet shape.

The dispersion liquid adjusting step will be described.
In the dispersion liquid adjusting step, a dispersion liquid of metal-based fine particles containing the specific metal component and having the specific average primary particle diameter range is adjusted. This step is not particularly limited as long as a desired dispersion of metal-based fine particles can be obtained. For example, a conventionally known method can be used.

  For example, a metal salt containing a predetermined amount of Pd metal salt and Cu metal salt is dissolved in water to obtain an aqueous metal salt solution. These metal salts preferably have a Pd: Cu mass ratio of 30:70 to 99: 1. As the Pd metal salt, for example, palladium nitrate, palladium chloride, palladium acetate, or tetraammine palladium can be used. Moreover, copper nitrate, copper chloride, etc. can be used as Cu metal salt. In addition to Pd and Cu, other metal salts such as platinum chloride, silver nitrate and nickel nitrate can be added. At this time, in the total metal elements including Pd and Cu, the content of other metal salts is preferably 5% by mass or less, more preferably 1% by mass or less, and 0.5% by mass or less. More preferably.

  Moreover, it is preferable to add a stabilizer and a reducing agent to the aqueous metal salt solution. A conventionally known stabilizer can be used, but trisodium citrate is preferably used. Although a conventionally well-known thing can be used for a reducing agent, It is preferable to use ferrous sulfate. The addition amount of the reducing agent is preferably 1 to 3 times the total number of moles of the metal salt. Then, it is preferable to stir for 1 to 30 hours in inert gas atmosphere, such as N2. In this way, a dispersion of metal-based fine particles is obtained.

The dipping process will be described.
In the dipping step, an inorganic carrier material is immersed in a dispersion of metal fine particles to obtain a metal fine particle / carrier mixture.

  It is preferable to remove impurities in the dispersion of metal-based fine particles before the immersion. As a method for removing impurities, it is preferable to precipitate the metal-based fine particles with a centrifuge and then remove the supernatant. Preferably, water is newly added to the precipitate of the metal fine particles to form a dispersion of 1 to 10% by mass of the metal fine particles.

  Next, the inorganic carrier material is immersed in a dispersion of metal fine particles. This immersion is preferably performed in the air or in a reduced pressure atmosphere. The immersion is preferably performed for 0.1 to 2 hours. Thereby, a metallic fine particle / carrier mixture is obtained. The embodiment of the metallic fine particle / carrier mixture is a liquid or a solid.

The drying process will be described.
In the drying step, the metal-based fine particle-supported catalyst is obtained by drying the metal-based fine particle / carrier mixture.

For the drying, a conventionally known method such as freeze drying, spray drying, or stationary drying can be used. When the metal-based fine particle / carrier mixture is solid, static drying can be used, and when it is liquid, spray drying or freeze drying can be used. The drying temperature is preferably 100 to 200 ° C. The drying time is preferably 1 to 20 hours. Furthermore, the drying step is preferably performed in air, vacuum, inert gas atmosphere, or reducing gas atmosphere.
After the drying, for example, a powdered metal-based fine particle-supported catalyst is obtained.

<Method of treating nitrate-containing water>
The present invention is a method for treating nitrate nitrogen-containing water by contacting the catalyst of the present invention with nitrate nitrogen-containing water.
Such a treatment method for nitrate nitrogen-containing water is hereinafter also referred to as “treatment method of the present invention”.

The processing method of the present invention will be described.
In the treatment method of the present invention, reductive decomposition treatment is performed on nitrate nitrogen in nitrate nitrogen-containing water using the catalyst of the present invention.

Nitrate nitrogen-containing water refers to an aqueous solution containing nitrate nitrogen, and examples thereof include domestic wastewater and industrial wastewater. Nitrate nitrogen is NO ₃ , NO ₂ or the like, and usually exists as ions in an aqueous solution. The concentration of nitrate nitrogen in the nitrate nitrogen-containing water is preferably 100 to 100,000 ppm, more preferably 300 to 60,000 ppm as N. The concentration of nitrate nitrogen can be measured, for example, by a conventionally known method (UV method, ion chromatography method).
The nitrate nitrogen-containing water may contain substances other than nitrate nitrogen. Examples thereof include inorganic substances such as NH ₃ , ClO ₃ , ClO ₂ , ClO, Na, Cl, Fe, and Ni, and organic substances such as citric acid, oxalic acid, EDTA, and EDDS.

Further, before adding the catalyst, the pH of the nitrate nitrogen-containing water is preferably 6 to 12, more preferably 7 to 11. By adjusting the pH to such a range, it is possible to prevent elution of metal fine particles of the catalyst, a decrease in catalytic activity, and an increase in the amount of by-product NH ₃ .

The addition amount of the catalyst of the present invention is preferably such that the metal-based fine particles in the catalyst are 0.00001 to 0.5% by mass in nitrate nitrogen-containing water, and 0.0001 to 0.1% by mass. It is more preferable to add so that it may become%.
When the addition amount is within such a range, more sufficient catalytic activity can be obtained and it is economically preferable.

The contact time between the catalyst of the present invention and nitrate nitrogen-containing water is the amount of nitrate nitrogen-containing water, the concentration of nitrate nitrogen before treatment, the target concentration of nitrate nitrogen after treatment, and the nitrate nitrogen-containing water. Depending on the concentration of impurities (organic matter or metal), the content of metal-based fine particles in the catalyst, the particle size of the inorganic carrier catalyst, etc., it is preferably about 20 hours or less, usually 3 to 15 hours.
The temperature during the contact is preferably 20 ° C to 100 ° C, more preferably 40 ° C to 80 ° C. When the temperature at the time of contact is in such a range, sufficient catalyst activity can be obtained, and the progress of catalyst deterioration can be further delayed.

  The contact between the nitrate nitrogen-containing water and the catalyst of the present invention is preferably carried out in the presence of a reducing agent. As the reducing agent, hydrazine, sodium borohydride, sodium hypophosphite, quinone, hydroquinone, hydrogen gas and the like can be used. The addition amount of the reducing agent is preferably 1 to 3 mol times the amount of N of nitrate nitrogen in the nitrate nitrogen-containing water, and more preferably 1 to 2 mol times.

  In the processing method of this invention, if the catalyst of this invention can be contacted with nitrate nitrogen containing water, it will not restrict | limit in particular, For example, the conventional processing equipment can be used. For example, complete mixing tank type, distribution type, multistage type, batch type processing equipment, etc. may be mentioned.

The contact between the catalyst of the present invention and the nitrate nitrogen-containing water is preferably a flow-through system in which the nitrate nitrogen-containing water is passed through the metal-based fine particle-supported catalyst. This is because continuous operation is possible in the treatment facility, nitrate-nitrogen-containing water can be efficiently treated, and further, separation of the catalyst and nitrate-nitrogen-containing water is unnecessary, and the catalyst can be easily replaced.
Specifically, nitrate nitrogen-containing water is introduced from one of the reaction towers filled with the metal-based fine particle-supported catalyst and brought into contact with the catalyst held inside the reaction tower. At this time, it is preferable to mix the reducing agent with the nitrate nitrogen-containing water and then flow into the reaction tower. Thereby, nitrate nitrogen is reduced and decomposed, and nitrate nitrogen-containing water becomes a treatment liquid and flows out from the other side of the reaction tower.
Moreover, 5-30 L / h is preferable and, as for the liquid transmission speed | rate (SV value) at the time of letting it pass in a counter response, 10-25 L / h is more preferable.
Furthermore, the reducing agent in the flow type may be premixed with nitrate nitrogen-containing water and then flowed into the reaction tower. At the same time, nitrate nitrogen-containing water is allowed to flow into the reaction tower, and at the same time, the reducing agent is fed into the reaction tower. It may be allowed to flow.

  In systems other than the circulation type, the catalyst can be repeatedly used by separating the catalyst from the treated water, but it can also be regenerated and used as necessary. The separation means is not particularly limited, and for example, an ultrafiltration membrane or a ceramic filter can be used.

  Examples of the present invention will be described. In addition, this invention is not limited to a following example.

[Example 1]
<Adjustment of carrier>
As a carrier, TiO ₂ powder (TMB-AA1514) manufactured by JGC Catalysts & Chemicals Co., Ltd. was used. The used TiO ₂ powder had a pore diameter of 34 nm, a pore volume of 0.27 nm, and a specific surface area of 30 m ² / g.
The same TiO ₂ powder was used in the following examples and comparative examples.

<Preparation of metal-based fine particles>
A metal salt aqueous solution in which 3 g of palladium nitrate dihydrate and 1.15 g of copper nitrate trihydrate are dissolved in 100 g of pure water so that the mass ratio of Pd and Cu constituting the metal-based fine particles is 80/20. It was adjusted. To this metal salt aqueous solution, 20 g of a 30% by mass trisodium citrate aqueous solution as a stabilizer and 15 g of a 25% by mass ferrous sulfate aqueous solution as a reducing agent are added and stirred for 10 hours in a nitrogen atmosphere. A dispersion (A) was obtained. The average primary particle diameter of the metal-based fine particles in this dispersion (A) was 4 nm.

<Catalyst adjustment>
The dispersion (A) is separated into a supernatant and a precipitate by a centrifuge, and impurities are removed by removing the supernatant. Then, pure water is added to the precipitate, and 2% by mass of metallic fine particles. A dispersion (B) was obtained. The carrier was immersed in this dispersion (B) at 25 ° C. for 1 hour to obtain a Pd—Cu colloid / carrier powder mixture. Next, the Pd—Cu colloid / carrier powder mixture was dried in a vacuum dryer at 150 ° C. for 12 hours to prepare a metal-based fine particle supported catalyst (hereinafter referred to as catalyst). The amount of metal supported in this catalyst was 1.0% by mass.

[Comparative Example 1]
Activated carbon was used as a carrier instead of TiO ₂ powder. Otherwise, the catalyst was prepared in the same manner as in Example 1.

[Comparative Example 2]
Al ₂ O ₃ powder was used as a carrier instead of TiO ₂ powder. Otherwise, the catalyst was prepared in the same manner as in Example 1.

The catalysts of Example 1 and Comparative Examples 1 and 2 prepared by the above method were reacted with the simulated waste liquid (A), and the activity of each catalyst for the reductive decomposition reaction of nitrate nitrogen was examined. The simulated waste liquid (A) is an aqueous solution containing 990 ppm NO ₃ , 460 ppm NO ₂ , 83 ppm Fe, 0.46 mass% Na, 0.57 mass% Cl, and 750 ppm COD.
The activity of each catalyst for the reductive decomposition reaction of nitrate nitrogen was examined by the following method.

<Batch activity test>
FIG. 1 shows a reactor 1 for examining catalyst activity and its persistence. In a separable flask 9 maintained at 80 ° C. with hot water in the thermostat 7, nitrogen gas (purity 99.9%, 200 ml / min) was purged to the simulated waste liquid (A) 3 to which the catalyst was added. The mixture was heated and stirred with a magnetic stirrer 6. At this time, the amount of the catalyst added was 9.1 g, the simulated waste liquid (A) was 200 ml, and the stirring speed was 200 rpm. The 2.5 mass% hydrazine aqueous solution 15 was supplied to the roller pump 17 at a dropping rate of 16.5 ml / h for 2 hours, and after the supply was completed, the mixture was further heated and stirred for 1 hour to simulate a catalyst waste liquid. (A) was reacted. During the reaction, by-product NH ₃ is exhausted from the cooling pipe 19. Next, the simulated waste liquid (A) reacted with this catalyst was cooled and filtered to separate the catalyst to obtain a treatment liquid. Furthermore, the above test was repeated 3 or 4 times using the catalyst separated from the treatment liquid.
This test method is called a batch activity test.

In the above test, to measure the N content of each processing solution when repeated 3-4 times nitrate nitrogen (NO ₃ + NO _2). The N amount of nitrate nitrogen was measured by HPLC (Nihon Dionex Co., Ltd., ICS-90). The results are shown in Table 1.

  From Table 1, it was confirmed that the catalyst of Example 1 has high activity for the reductive decomposition reaction of nitrate nitrogen even in repeated use.

Next, only the carrier used for the catalyst of Example 1, Comparative Example 1 or 2 was added to the simulated waste liquid (A), and reacted in the same manner as in the batch type activity test. Then, each composition component shown in Table 2 was measured about the obtained processing liquid. The measurement of NO ₃ amount, NO ₂ amount and Cl amount was performed by HPLC (Nihon Dionex Co., Ltd., ICS-90). The amount of Na was measured by atomic absorption analysis, and the amount of Fe was measured by ICP emission spectroscopic analysis. The amount of COD was measured by oxidation-reduction titration using potassium permanganate and oxalic acid.
Here, the test was not repeated, and the reaction between the simulated waste liquid (A) and the carrier was performed only once.

Table 2 shows that the TiO ₂ carrier used in Example 1 has a low adsorption amount of Fe and organic matter in the simulated waste liquid (A).

  Next, the average pore diameter, average pore volume, and specific surface area of various carriers used in the catalysts of Example 1 and Comparative Examples 1 and 2 were examined. The average pore diameter, average pore volume, and specific surface area of the support were measured by the aforementioned nitrogen adsorption method using a pore distribution measuring device (BELSORP-mini (II), manufactured by Nippon Bell Co., Ltd.). The measurement results are shown in Table 3.

Next, the catalytic activity of the catalyst using the TiO ₂ support having various physical properties was examined.

[Example 2]
<Adjustment of carrier>
50 g of TiO ₂ powder was added to 100 g of pure water and suspended. Then, it was dried by heating to 80 ° C. under reduced pressure to remove moisture, and this dried product was used as a carrier.

<Preparation of metal-based fine particles>
A metal salt in which 7.4 g of palladium nitrate dihydrate and 4.9 g of copper nitrate trihydrate are dissolved in 100 g of pure water so that the mass ratio of Pd and Cu constituting the metal-based fine particles is 70/30. An aqueous solution was prepared. In this metal salt aqueous solution, 265 g of 30% by mass trisodium citrate aqueous solution as a stabilizer and 129 g of 25% by mass ferrous sulfate aqueous solution as a reducing agent (twice the total number of moles of palladium nitrate and copper nitrate) (Corresponding to the number of moles) was added and stirred under a nitrogen atmosphere for 20 hours to obtain a dispersion (A) of metal-based fine particles. The average primary particle diameter of the metal-based fine particles in this dispersion (A) was 4 nm.

<Catalyst adjustment>
A catalyst was prepared by the same method as in Example 1 using the carrier (dried product) and metal fine particles obtained in this manner.

Example 3
A catalyst was prepared in the same manner as in Example 2 except that the Pd—Cu colloid / carrier powder mixture was air-dried at 150 ° C. for 12 hours using a stationary dryer (manufactured by Yamato, model number DS400). .

Example 4
The Pd—Cu colloid / carrier powder mixture is dried at 150 ° C. for 12 hours in an atmosphere of nitrogen gas (purity 99.9%, 5 L / min) using a high-temperature dryer (manufactured by Yamato, model number DN410I). Except that, the catalyst was prepared in the same manner as in Example 2.

Example 5
In preparing the carrier, a catalyst was prepared in the same manner as in Example 2 except that 190 g of TiO ₂ powder and 10 g of Al ₂ O ₃ powder were suspended in 1000 g of pure water.

Example 6
In the preparation of the carrier, the same method as in Example 2 was used except that 190 g of TiO ₂ powder and 33 g of silica sol (manufactured by JGC Catalysts & Chemicals Co., Ltd., model number: 1SI-30) were suspended in 1000 g of pure water. The catalyst was prepared.

Example 7
In preparing the carrier, the powdery carrier was formed into a pellet. Otherwise, the catalyst was prepared in the same manner as in Example 5.

Example 8
In preparing the carrier, the powdery carrier was formed into a pellet. Otherwise, the catalyst was prepared in the same manner as in Example 6.

Example 9
In preparing the carrier, a catalyst was prepared in the same manner as in Example 2 except that 190 g of TiO ₂ powder and 20 g of tin (II) nitrate hydrate were suspended in 1000 g of pure water.

Example 10
In preparing the carrier, a catalyst was prepared in the same manner as in Example 2 except that 190 g of TiO ₂ powder and 20 g of zinc nitrate hexahydrate were suspended in 1000 g of pure water.

<SEM observation of catalyst particles>
The catalyst particles of Example 2 were photographed using a scanning electron microscope. An SEM image (magnification, 300,000 times) is shown in FIG.

[Comparative Example 3]
In the preparation of the carrier, a dried product obtained by the same method as in Example 2 was further calcined at 1200 ° C. to obtain a carrier. Otherwise, the catalyst was prepared in the same manner as in Example 2.

[Comparative Example 4]
A catalyst was prepared in the same manner as in Example 2 except that the concentration of palladium and copper was tripled in the adjustment of the metal-based fine particles.

[Comparative Example 5]
In preparing the support, a catalyst was prepared in the same manner as in Example 2 except that activated carbon was used instead of TiO ₂ powder.

[Comparative Example 6]
The catalyst was prepared in the same manner as in Example 2 except that the metal-based fine particle supported catalyst was prepared by drying at 400 ° C. for 12 hours in a vacuum dryer.

  Next, the physical properties of Examples 2 to 10 and Comparative Examples 3 to 6 were examined.

The average primary particle diameter of the carrier and the metal-based fine particles was measured by the method described above. H-800 manufactured by Hitachi, Ltd. was used as the transmission electron microscope.
Further, the average pore diameter, average pore volume, and specific surface area of the support were measured by the above-described nitrogen adsorption method using a pore distribution measuring device (BELSORP-mini (II) manufactured by Nippon Bell Co., Ltd.).

Furthermore, the activity with respect to the reductive decomposition reaction of nitrate nitrogen in Examples 2 to 10 and Comparative Examples 3 to 6 was examined by the following method.
Sodium nitrate (Kanto Chemical Co., Ltd., special grade) and sodium nitrite (Kanto Chemical Co., Ltd., special grade) are dissolved in pure water so that the content of nitrate nitrogen is 400 ppm as N. 25 kg of water was adjusted.
Next, the catalyst of each Example and the comparative example was made to react with nitrate nitrogen containing water by the batch type activity test mentioned above. Nitrate nitrogen concentration (NO ₃ and NO ₂ ) contained in each treatment solution obtained was measured by HPLC (manufactured by Nippon Dionex Co., Ltd., ICS-90) and [1-measured nitrate nitrogen concentration (ppm ) / Nitrate nitrogen content in nitric acid-containing water (400 ppm)] × 100 was determined as a nitrogen decomposition rate (%). Further, the treated catalyst was recovered, and the above measurement was repeated 5 times.
Moreover, in measuring the nitrogen decomposition rate of the catalyst obtained in Example 2, the heating temperature of the reactor 1 in the batch type activity test was 40 ° C. (Example 2-1), 60 ° C. (Example 2-2). , 80 ° C. (Example 2-3) was also tested.

  Table 4 shows physical properties and nitrogen decomposition rates of Examples 2 to 10 and Comparative Examples 3 to 6. The nitrogen decomposition rate shown in Table 4 is an average value of the measurement results for five times obtained by the above measurement.

  From Table 4, a high nitrogen decomposition rate of 80% or more was observed in all examples.

  Next, in order to examine the activity for the reductive decomposition reaction of nitrate nitrogen when the catalyst treatment of the present invention was continuously performed, the following test was performed.

<Column type activity test>
The catalytic activity of the catalyst of the present invention was examined using a column type reaction tower. This reaction tower has a structure that allows liquid to pass through the reaction tower while keeping the catalyst inside. Thereby, since the liquid which passed through the inside of a reaction tower contacts a catalyst inside, it becomes a processing liquid reductively decomposed and flows out from a reaction tower.
A cylindrical column type reaction tower (outer diameter 12 mm, inner diameter 10 mm, length 100 mm) is filled with 7 g of the catalyst obtained in Example 2 so that the longitudinal direction of the column type reaction tower becomes the vertical direction. installed. The reaction was carried out from the upper side of the reaction tower while maintaining the nitrogen-containing water in the reaction tower at 40 ° C. (Example 2-4), 60 ° C. (Example 2-5), and 80 ° C. (Example 2-6). A mixed solution of nitrate nitrogen-containing water and hydrazine was injected into the tower and allowed to pass through the reaction tower at a liquid flow rate of 12.9 L / h (SV value). The nitrate nitrogen-containing water was adjusted so that the nitrate nitrogen content was 400 ppm as N. The mixed solution is obtained by adding hydrazine equivalent to 1.2 mol times the nitric acid in the nitrate nitrogen in the nitrate nitrogen-containing water to the nitrate nitrogen-containing water over 2 hours, and 140 ml thereof was used. . A mixed solution that passed through the reaction tower and flowed out from the lower side of the reaction tower was used as a treatment liquid.

The nitrate nitrogen concentration (NO ₃ and NO ₂ ) of this treatment solution was measured by HPLC (manufactured by Nippon Dainex Co., Ltd., ICS-90) to determine the nitrogen decomposition rate (%).
The results are shown in Table 5.

Next, the test of reacting the catalyst of the present invention with the simulated waste liquid (B) was repeated to examine the sustainability of the catalyst activity. The simulated waste liquid (B) is an aqueous solution containing 1000 ppm NO ₃ , 500 ppm NO ₂ , 10 g / L NaCl, 100 mg / L Fe, and 1000 mg / L EDTA. The same catalyst as in Example 2 was used for the reaction with the simulated waste liquid (B). The amount of metal supported on this catalyst was 1.2% by mass.

  For the sustainability of the catalyst activity, two types of tests, a batch type activity test and a column type activity test, were performed.

  In the batch type activity test, 9.1 g of the catalyst of Example 2 was added to 200 ml of the simulated waste liquid (B) and reacted. The catalyst was recovered from the obtained treatment liquid, and the same test was repeated 10 times.

In the column-type activity test, 200 ml of simulated waste liquid (B) was passed through a column-type reaction tower packed with 9.1 g of the catalyst of Example 2 to obtain a treatment liquid.
Thereafter, 200 ml of a simulated waste liquid was newly passed through the same column type reaction tower, and a test for obtaining a treatment liquid was further repeated 10 times.

The N amount of nitrate nitrogen (NO ₃ + NO ₂ ) was measured for the treatment solutions of each repetition test in the batch type and column type activity test methods. The N amount of nitrate nitrogen was measured by HPLC (Nihon Dionex Co., Ltd., ICS-90). FIG. 3 shows changes in the N amount of nitrate nitrogen at each repetition.

  From FIG. 3, even if the above test was repeated 10 times, the N amount of nitrate nitrogen in the treatment liquid showed a low value, so that it was confirmed that the catalytic activity of Example 2 had high durability.

1 Reactor 3 Simulated waste liquid with catalyst added (A)
5 Stirrer bar 6 Magnetic stirrer 7 Constant temperature bath 9 Separable flask 11 Temperature controller 17 Roller pump 19 Cooling tube 21 Nitrogen gas cylinder

Claims (5)

A metal-based fine particle-supported catalyst in which metal-based fine particles containing at least Pd and Cu are supported on an inorganic carrier material,
The inorganic carrier material has an average primary particle diameter of 5 to 200 nm, and contains at least one oxide selected from the group consisting of Ti, Al, Si, Sn, and Zn as a main component,
The inorganic carrier material has an average pore diameter of 5 to 100 nm, an average pore volume of 0.1 to 1.5 ml / g, and a specific surface area of 10 to 300 m ² / g,
The metal-based fine particles having an average primary particle size Ri 1~9nm der,
A metal-based fine particle-supported catalyst , which is a catalyst used for the reductive decomposition reaction of nitrate nitrogen in nitrate nitrogen-containing water . Metallic fine particles supported catalyst according to claim 1 the main component of the inorganic carrier material is TiO _2. 3. The metal-based fine particle-supported catalyst according to claim 1, wherein the inorganic support material is spherical or pellet-shaped. The metal-based fine particle-supported catalyst according to any one of claims 1 to 3 , wherein a mass ratio of Pd: Cu in the metal-based fine particle is 30:70 to 99: 1. The metal-based fine particle-supported catalyst according to any one of claims 1 to 4 , wherein a content of the metal-based fine particles is 0.1 to 10% by mass.