JP2007021438A - Water-repellent noble metal-containing catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for quickly reducing a nitrate ion in water with high selectivity to clean the water and a method for cleaning the water contaminated with the nitrate ion by using the catalyst. <P>SOLUTION: The water-repellent catalyst is manufactured by deposing Pd and one or more metals selected from the group consisting of Cu, Sn and In on one or more carriers selected from the group consisting of activated carbon, Al<SB>2</SB>O<SB>3</SB>, SiO<SB>2</SB>, TiO<SB>2</SB>and ZnO<SB>2</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a noble metal-containing catalyst having water repellency and a method for removing nitrate ions in water using the same.

In recent years, contamination of groundwater by nitrate ions has become apparent all over the world.For example, in order to purify contaminated groundwater for drinking, there is a technology that makes low-concentration nitrate ions contained in water simple and inexpensive. It has been demanded.

Known techniques for removing nitrate ions include biological methods using microorganisms and physicochemical methods such as ion exchange, electrodialysis, and reverse osmosis. Biological methods are becoming widespread as wastewater treatment and are almost established technically. However, this method requires denitrifying bacteria that reduce nitrate ions to nitrogen gas, and organic substances such as ethanol or methanol as an energy source for the denitrifying bacteria. Great care is required for the maintenance of this denitrifying bacterium. Furthermore, in order to make drinking water after removing nitrate ions, remaining organic substances and denitrifying bacteria must be removed, which is not suitable for small-scale treatment. The ion exchange method has a track record of being used to remove nitrate in drinking water at water purification plants. However, coexisting ions such as sulfate ions significantly reduce the removal rate of nitrate ions, necessitate regeneration of ion exchange resins, and generate secondary wastewater during resin regeneration. . The reverse osmosis method and the electrodialysis method have a problem of how to cope with a change in water quality, a problem of treatment of secondary waste liquid, and a problem of high cost. Thus, there are many problems to be solved in the conventional removal method of nitrate ions, and development of a new removal method is desired.

As a new method, so-called catalytic methods are proposed in which nitrate ions are purified to nitrogen by using a solid catalyst and hydrogen as a reducing agent (Patent Documents 1 to 8 and Non-Patent Documents 1 to 4). reference). However, these catalysts are inferior in terms of activity and N ₂ selectivity, and there are many problems such as the need to flow hydrogen in a large excess, and further improvement is necessary for practical use. .

JP 2001-866 JP-A-8-332490 JP 2000-334477 Japanese Patent Laid-Open No. 9-285793 JP 2003-71461 A JP 2005-95784 A Japanese Patent Laid-Open No. 2003-333281 JP 2002-336850 A Catal. Today, No. 17, p. 21, 1993 Catal. Today, 55, 139, 2000 Catal. Today, 55, 79, 2000 J. Catal. 207, 37, 2002

The present invention provides a catalyst capable of purifying water by quickly and highly selectively reducing nitrate ions in water, and a method for purifying water contaminated with nitrate ions using the catalyst. is there.

The inventors of the present invention have made extensive studies in order to improve the activity and N ₂ selectivity of conventionally used catalysts in a catalytic method for reducing nitrate ions in water to nitrogen. As a result, if the catalyst is made water-repellent, the contact between the active site of the catalyst and the hydrogen gas preferably used as the reducing agent can be increased, and a significantly higher catalytic activity can be obtained at a lower hydrogen pressure than in the past. I found out that In addition, if Pd is preferably used as the catalyst metal, the ammonia selectivity of nitric acid contained in water can be remarkably lowered, and if Cu is used preferably, N ₂ selectivity of nitric acid contained in water is increased. It was also found that N ₂ selectivity can be increased by using activated carbon.

That is, the present invention
(1) one or more metals selected from the group consisting of Pd, Pt, Ir, Ru and Rh, and one or more metals selected from the group consisting of Cu, Sn and In are activated carbon, Al ₂ O ₃ , A catalyst having water repellency supported on one or more carriers selected from the group consisting of SiO ₂ , TiO ₂ and ZnO ₂ .

As a preferred embodiment,
(2) The catalyst according to the above (1), comprising 1 to 10% by weight of one or more metals selected from the group consisting of Pd, Pt, Ir, Ru and Rh,
(3) The catalyst according to the above (1), comprising 2 to 5% by weight of one or more metals selected from the group consisting of Pd, Pt, Ir, Ru and Rh,
(4) The catalyst according to any one of (1) to (3) above, wherein one or more metals selected from the group consisting of Pd, Pt, Ir, Ru and Rh are Pd,
(5) The catalyst according to any one of (1) to (4) above, wherein 0.2 to 3 wt% of one or more metals selected from the group consisting of Cu, Sn and In are contained,
(6) The catalyst according to any one of (1) to (4) above, wherein 0.4 to 1.5% by weight of one or more metals selected from the group consisting of Cu, Sn and In are contained,
(7) The catalyst according to any one of (1) to (6) above, wherein one or more metals selected from the group consisting of Cu, Sn and In are Cu,
(8) The catalyst according to any one of (1) to (7) above, wherein the support is activated carbon,
(9) The catalyst according to (8) above, wherein the activated carbon is produced from coconut shells,
(10) The catalyst according to any one of (1) to (9) above, wherein the water repellency is expressed by including a fluorine resin,
(11) Fluorine resin is polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), polyvinylidene fluoride ( PVDF), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene-ethylene copolymer (ETFE), fluoroethylene vinyl ether (FEVE), and ethylene chlorotrifluoroethylene copolymer (ECTFE). The catalyst according to (10) above,
(12) The catalyst according to the above (10), wherein the fluororesin is polytetrafluoroethylene (PTFE),
(13) The catalyst according to any one of (10) to (12) above, wherein 0.1 to 20% by weight of a fluororesin is contained,
(14) The catalyst according to any one of (10) to (12) above, wherein the fluororesin is contained in an amount of 0.2 to 5% by weight,
(15) The catalyst according to any one of (1) to (14) above, for reducing nitrate ions contained in water,
(16) A method for reducing nitrate ions contained in water using the catalyst according to any one of (1) to (15) above,
(17) The method according to (16) above, wherein hydrogen is used as a reducing agent,
(18) The method according to (16) or (17) above, wherein the temperature is 5 to 60 ° C
(19) The method according to any one of (16) to (18) above, wherein the hydrogen pressure is 0.001 to 0.2 MPa.
(20) The method according to any one of (16) to (18) above, wherein the hydrogen pressure is 0.003 to 0.1 MPa.
(21) The method according to any one of (16) to (18) above, wherein the hydrogen pressure is 0.005 to 0.05 MPa.
Can be mentioned.

The catalyst of the present invention has remarkably high catalytic activity and nitrogen selectivity under low hydrogen pressure conditions as compared with a catalyst conventionally used for removing nitrate ions contained in water. Thereby, it is possible to reduce the pressure of the hydrogen gas used as the reducing agent. By being able to react at a low hydrogen pressure, generation of ammonia and nitrite ions, which are undesirable by-products, can be suppressed, and hydrogen consumption can be suppressed.

In the catalyst of the present invention, one or more metals selected from the group consisting of Pd, Pt, Ir, Ru and Rh are used. Of these metals, Pd is preferably used. By using Pd, the selectivity of nitric acid contained in water to ammonia can be remarkably lowered as compared with the case of using other metals. The upper limit of the content of the metal in the catalyst of the present invention is preferably 10% by weight, more preferably 7% by weight, still more preferably 5% by weight, and the lower limit is based on the support weight. , Preferably 1% by weight, more preferably 1.5% by weight, still more preferably 2% by weight. Exceeding the above upper limit results in not only a significant increase in the effect but also high costs. Below the lower limit, sufficient catalytic action is not exhibited.

In the catalyst of the present invention, one or more metals selected from the group consisting of Cu, Sn and In are used. Of these, Cu is preferably used. By using Cu, the activity of the catalyst can be increased and the selectivity of nitric acid contained in water to nitrogen can be increased as compared with the case of using other metals. The upper limit of the content of one or more metals selected from the group consisting of Cu, Sn and In is preferably 3% by weight, more preferably 2% by weight, and even more preferably 1.5% by weight with respect to the weight of the carrier. The lower limit is preferably 0.2% by weight, more preferably 0.3% by weight, and still more preferably 0.4% by weight with respect to the weight of the carrier. Exceeding the above upper limit results in not only a significant increase in the effect but also high costs. Below the lower limit, sufficient catalytic action is not exhibited. As the metal, Cu is preferably used.

As a carrier in the catalyst of the present invention, activated _{carbon, Al 2 O 3, SiO 2} , is one or TiO ₂ and the group consisting of ZnO ₂ is used. Activated carbon is preferably used, more preferably activated carbon produced from coconut shells. By using activated carbon, higher activity can be obtained and harmful by-products can be further reduced as compared with the case of using other carriers. In particular, by-product ammonia can be suppressed by using activated carbon produced from coconut shells.

The catalyst of the present invention has water repellency. The water repellency is expressed by including a fluorine resin in the catalyst. As the fluororesin, polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), polyvinylidene fluoride (PVDF) And polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene / ethylene copolymer (ETFE), fluoroethylene vinyl ether (FEVE), and ethylene chlorotrifluoroethylene copolymer (ECTFE). Of these, polytetrafluoroethylene (PTFE) is preferred.

The upper limit of the fluororesin content is preferably 20% by weight, more preferably 10% by weight, still more preferably 5% by weight, based on the carrier weight, and the lower limit is preferably 0.1% with respect to the carrier weight. % By weight, more preferably 0.15% by weight, still more preferably 0.2% by weight. Exceeding the above upper limit results in not only a significant increase in the effect but also high costs. Below the lower limit, sufficient water repellency cannot be applied to the catalyst.

The catalyst of the present invention can be produced using a known method such as an impregnation method or a spray method. Preferably, the support is sequentially impregnated with one or more metals selected from the group consisting of Pd, Pt, Ir, Ru and Rh, and one or more metals selected from the group consisting of Cu, Sn and In, Subsequently, it can manufacture by impregnating a fluororesin.

The catalyst of the present invention can contain, for example, additives such as stabilizers, other metals, and the like, in addition to the above substances, as long as the effects of the present invention are not impaired.

The catalyst of the present invention can be preferably used in a method for reducing nitrate ions contained in water. In the method, a reducing agent is used. As the reducing agent, hydrogen, formic acid, hydrazine or the like is preferably used. When using the reduced water for drinking water, if formic acid, hydrazine or the like is used as a reducing agent, these must be removed after the reduction treatment. Therefore, hydrogen is preferred in the production of drinking water. When hydrogen is used as the reducing agent, nitrate ions are reduced to nitrogen gas by the following reaction.

(Chemical 1)
2NO ₃ ⁻ + 5H ₂ → N ₂ + 4H ₂ O + 2OH ⁻

The upper limit of the hydrogen pressure in the above reaction is preferably 0.2 MPa, more preferably 0.1 MPa, still more preferably 0.05 MPa, and the lower limit is preferably 0.001 MPa, more preferably 0.003 MPa, and still more preferably 0.005 MPa. If the upper limit is exceeded, the pressure resistance of the device due to an increase in pressure is costly, and if it is less than the lower limit, nitrate ions are not sufficiently reduced. Hydrogen can be used alone or mixed with other gases such as helium, argon, nitrogen and the like. Further, carbon dioxide gas can be preferably used as a pH adjuster during the reaction. By using carbon dioxide gas, the amount of OH ⁻ ions generated by the progress of the reduction reaction of nitrate ions can be reduced, and the adsorption reaction of nitrate ions can be prevented by preventing adsorption of OH ⁻ ions to the catalytically active sites. Can be promoted. In addition, the activity of the catalyst can be increased. The pH during the reaction is preferably adjusted to 4.0 to 8.0, more preferably 6.0 to 6.5.

The upper limit of the temperature during the reduction is preferably 80 ° C, more preferably 60 ° C, still more preferably 50 ° C, and the lower limit is preferably 5 ° C, more preferably 10 ° C, and even more preferably 20 ° C. Beyond the above upper limit, it costs for heating, and below the above lower limit, the reduction of nitrate ions becomes insufficient.

The reaction can be performed continuously or batchwise, but a continuous method is more preferable. The catalyst can be a fixed bed or a fluidized bed. As the reaction apparatus, it is preferable to use a fixed bed continuous apparatus. In addition, any one-stage or two-stage or more multistage reaction can be used. In the case of the continuous type, the upper limit of the liquid space velocity (LHSV) is preferably 5000 hours ⁻¹ , more preferably 1000 hours ⁻¹ , even more preferably 100 hours ⁻¹ , and the lower limit of the feed rate of the raw material liquid is preferably 5 hr ^-1, more preferably 10 hr ^-1, more preferably from 20 hr ^-1. If the upper limit is exceeded, nitrate ions are not sufficiently reduced, and if it is less than the lower limit, a large treatment facility is required.

As the water subjected to reduction treatment in the method of the present invention, for example, ground water, waste water, industrial water or the like having a nitrate ion concentration of 40 to 5000 mg / liter is used. In particular, it is suitable for converting groundwater into drinking water. According to the method of the present invention, the nitric acid concentration can be lowered to preferably 0 to 20 milligram / liter, more preferably about 0 to 5 milligram / liter.

In the following examples, the present invention will be described in more detail, but the present invention is not limited to these examples.

(Example)

(Example 1)
Preparation of catalyst Activated carbon (AC, wood chips and rice husks as raw materials) (Wako Pure Chemical Industries, Ltd., activated carbon, powder, 037-02115) and PdCl ₂ (Wako Pure Chemical Industries, Ltd.) And an aqueous solution of Cu (NO ₃ ) ₂ · 3H ₂ O (Wako Pure Chemical Industries, Ltd.) were successively impregnated so that the supported amounts of Pd and Cu were 5% by weight and 0.6% by weight, respectively. The activated carbon thus obtained was dried at 100 ° C. overnight under a nitrogen stream to produce activated carbon carrying Pd and Cu (5 wt% Pd-0.6 wt% Cu / AC). Next, a dispersion obtained by dispersing polytetrafluoroethylene (PTFE) in water (manufactured by Nagoya Synthesis Co., Ltd., PTFE dispersion NS-01), the Pd and Cu after drying so that the supported amount becomes 5% by weight. The loaded activated carbon was impregnated. The obtained sample was calcined at 250 ° C. for 2 hours in an air atmosphere, and then reduced for 2 hours at 250 ° C. in a hydrogen stream, and a catalyst (5 wt% PTFE) further supporting PTFE on activated carbon supporting Pd and Cu. /5wt%Pd-0.6wt%Cu/AC).

Reaction test 0.3 gram of 5 wt% PTFE / 5 wt% Pd-0.6 wt% Cu / AC produced as described above was added to a continuous reactor (pyrex (registered trademark) glass cylindrical tube, inner diameter 8 mm x length 10 cm, the catalyst was fixed with absorbent cotton).

Next, water having a nitrate ion concentration of 200 milligrams / liter was supplied to the reactor at 33 cm ³ / hour, and at the same time, both hydrogen gas and carbon dioxide gas were supplied to the reactor at 98 cm ³ / hour. At this time, nitrate ion-containing water, hydrogen gas, and carbon dioxide gas were all introduced from the lower part of the reactor. In addition, the temperature of the water was adjusted in advance through a glass tube having an inner diameter of 4 mm and a length of 1 m so that the temperature of the water became the same as the temperature in the reactor when it was introduced into the reactor. The pressure in the reactor was 0.1 MPa, and the hydrogen partial pressure was 0.05 MPa. Carbon dioxide gas was used to adjust the pH in the reactor. As a result, PH was adjusted to about 6.0 to 6.5. The temperature in the reactor was 60 ° C., and the LHSV was 110 hours− ¹ .

Water from the reactor was collected and the concentrations of N ₂ , N ₂ O, NO ₃ ⁻ , NO ₂ ⁻ and NH ₃ were measured. Here, gas chromatography (manufactured by Shimadzu Corporation, model GC-8A) is used for N ₂ and N ₂ O measurements, and absorptiometry (FIA method, Sanuki) is used for NO ₃ ⁻ , NO ₂ ⁻ and NH ₃ measurements. A model FI-710 manufactured by Kogyo Co., Ltd. was used.

The conversion rate of nitrate ion was 100%.

The reaction rate was determined as follows. The catalyst loading was 0.012 grams of 0.025 g, and the catalyst loading of each, except for using a feed rate of nitrate-containing water 59cm ^{3 /} time and 83cm ^{3 /} time, similarly to the reduction reaction with the reaction test Carried out. Next, from these two experimental results, the relationship between the contact time and the conversion rate was plotted on a graph, and the reaction rate was calculated from the slope. The results are shown in Table 1.

(Example 2)
The same operation as in Example 1 was performed except that helium gas was mixed with hydrogen gas and the hydrogen partial pressure in the reactor was 0.005 MPa. The conversion rate of nitrate ion was 100%.

The reaction rate was determined as follows. The catalyst loading was 0.025 grams, except the feed rate of nitrate ion-containing water having a 60cm ^{3 /} time and 82cm ^{3 /} time, it was determined by same as above. The results are shown in Table 1.

(Comparative Examples 1 and 2)
The procedure was the same as in Examples 1 and 2, except that a catalyst containing no polytetrafluoroethylene was used. The conversion rate of nitrate ions was 100%.

The reaction rate was determined as follows. Except the catalyst loading was 0.05 grams, and the Comparative Example 1 the feed rate of nitrate ion-containing water 83cm ^{3 /} time and 177cm ^{3 /} time, which was Comparative Example 2 60cm ^{3 /} time and 83cm ^{3 /} time, Calculated in the same manner as above. The results are shown in Table 1.

Examples 1 and 2 have different hydrogen partial pressures. When the hydrogen partial pressure was lowered, the amount of produced nitrogen could be remarkably increased without reducing the reaction rate, and the amount of produced ammonia could be remarkably reduced. On the other hand, Comparative Examples 1 and 2 had a remarkably low reaction rate. It has been found that using the catalyst of the present invention, high N ₂ selectivity can be obtained at a significantly higher reaction rate.

Example 3
Preparation of catalyst Activated carbon made from coconut shell (made by Wako Pure Chemical Industries, Ltd., activated carbon, granular, 034-02125) is used in granular form, and the supported amounts of Pd and Cu are 2 respectively. A catalyst (5 wt% PTFE / 2 wt% Pd-0.4 wt% Cu / AC) identical to that of Example 1 was produced except that the weight was reduced to 0.4 wt% and the reduction treatment was performed with sodium borohydride.

Reaction test 0.3 grams of 5 wt% PTFE / 2 wt% Pd-0.4 wt% Cu / AC prepared as described above was charged to the same continuous reactor used in Example 1.

Next, water with a nitrate ion concentration of 200 milligrams / liter is supplied to the reactor at 39 cm ³ / hour, and at the same time, both hydrogen gas (mixed gas including helium gas) and carbon dioxide gas are reacted at 98 cm ³ / hour. Was supplied to the vessel. The pressure in the reactor was 0.1 MPa, and the hydrogen partial pressure was 0.005 MPa. The reactor temperature was 25 ° C. and the LHSV was 130 hours− ¹ .

The conversion rate of nitrate ion was 58.1%. The results are shown in Table 2.

(Comparative Example 3)
The same procedure as in Example 3 was performed except that a catalyst containing no polytetrafluoroethylene was used.

The conversion rate of nitrate ion was 42.8%. The results are shown in Table 2.

From Example 3 and Comparative Example 3, when the catalyst of the present invention is used, the conversion rate of nitrate ions can be remarkably increased. Although the ammonia / nitrite ion selectivity was somewhat high, the conversion rate was remarkably increased, so the effects of the present invention were not impaired.

In Examples 4 to 7 below, the effect of the activated carbon as the carrier was changed and the effect was examined.

(Examples 4 to 6)
Preparation of catalyst: Activated charcoal, using wood chips and rice husks as raw materials, coal as raw materials (Kuraray Chemical Co., Ltd., Kuraray Coal GWC-H, crushed pieces used in mortar) The catalyst (5 wt% PTFE / 5 wt% Pd-0.6 wt% Cu / AC) was used in the same manner as in Example 1 except that the one using coconut shell as a raw material (granulated in a mortar) was used. Manufactured.

Reaction test 0.5 grams of 5 wt% PTFE / 5 wt% Pd-0.6 wt% Cu / AC prepared as described above was charged to the same continuous reactor used in Example 1.

Next, water with a nitrate ion concentration of 200 milligrams / liter is supplied to the reactor at 27 cm ³ / hour, and at the same time, both hydrogen gas (mixed gas including helium gas) and carbon dioxide gas are reacted at 98 cm ³ / hour. Was supplied to the vessel. The pressure in the reactor was 0.1 MPa, and the hydrogen partial pressure was 0.005 MPa. The reactor temperature was 60 ° C. and the LHSV was 54 hours− ¹ .

The conversion rate of nitrate ions was 100%. The results are shown in Table 3.

(Example 7)
The same procedure as in Example 6 was performed except that the supported amounts of Pd and Cu were 2% by weight and 0.4% by weight, respectively, and the metal was supported on the granular activated carbon.

The conversion rate of nitrate ion was 100%. The results are shown in Table 3.

From Examples 4 to 6, when using activated carbon made from coconut husks, the selectivity of ammonia can be significantly reduced compared to when using activated carbon made from wood chips and rice husks and activated carbon made from coal. I understood that I could do it. Further, from Example 7, it was found that ammonia generation can be suppressed by supporting a metal in a granular form and reducing the amount of metal supported.

In Examples 8 to 10 below, the effect of changing the type of metal used together with Pd was investigated. Cu, In, or Sn was used as the metal, and the molar ratio of Pd / Cu, Pd / In, or Pd / Sn was 0.6.

(Example 8)
Preparation of catalyst Activated carbon (AC, wood chips and rice husks as raw materials) (manufactured by Wako Pure Chemical Industries, Ltd., activated carbon, powder, 037-02115) and PdCl ₂ (Wako Pure Chemical Industries, Ltd.) Manufactured) and Cu (NO ₃ ) ₂ · 3H ₂ O (manufactured by Wako Pure Chemical Industries, Ltd.) aqueous solution were successively impregnated so that the supported amounts of Pd and Cu were 1% by weight and 1% by weight, respectively. The activated carbon thus obtained was dried at 100 ° C. overnight under a nitrogen stream to produce activated carbon carrying Pd and Cu (1 wt% Pd-1 wt% Cu / AC). Next, a dispersion in which polytetrafluoroethylene (PTFE) (manufactured by Nagoya Synthesis Co., Ltd., NS-01, trademark) is dispersed in water is loaded with the Pd and Cu after drying so that the loaded amount is 5% by weight. Impregnated into activated carbon. The obtained sample was calcined in an air atmosphere at 250 ° C. for 2 hours, and then reduced at 300 ° C. for 2 hours in a hydrogen stream, and a catalyst in which PTFE was further supported on activated carbon supporting Pd and Cu (5 wt% PTFE / 1wt% Pd-1wt% Cu / AC).

Reaction test 0.5 gram of 5 wt% PTFE / 1 wt% Pd-1 wt% Cu / AC prepared as described above was charged to the same continuous reactor used in Example 1.

Next, a reduction reaction was carried out in the same manner as in Example 1 except that nitrate ion-containing water was supplied to the reactor at 117 cm ³ / hour, carbon dioxide was not supplied, and LHSV was set to 234 hours− ^1. The concentration of each component was measured.

(Example 9)
Example 8 and Example 8 were used except that an In (NO ₃ ) ₂ (Kishida Chemical Co., Ltd.) aqueous solution was used instead of the Cu (NO ₃ ) ₂ · 3H ₂ O aqueous solution and the In supported amount was changed to 1.8% by weight. A catalyst (5 wt% PTFE / 1 wt% Pd-1.8 wt% In / AC) was produced in the same manner, and then a reaction test was performed.

(Example 10)
Except that the aqueous solution of SnCl ₂ · 2H ₂ O (manufactured by Wako Pure Chemical Industries, Ltd.) was used in place of the Cu (NO ₃ ) ₂ · 3H ₂ O aqueous solution, the Sn loading was 1.9 wt%. A catalyst (5 wt% PTFE / 1 wt% Pd-1.9 wt% Sn / AC) was produced in the same manner as in 8, and then a reaction test was performed.

The results of Examples 8 to 10 are shown in Table 4.

*：転化率が低く測定不能

*: Low conversion and cannot be measured

From the results of Examples 8 to 10, it was found that when Cu was used as a metal, a significantly higher conversion rate was obtained and ammonia selectivity was lower than when In or Sn was used. Although In was not as high as Cu, high conversion and low ammonia selectivity were obtained as well. When Sn was used as the metal, the conversion was significantly lower than when Cu or In was used. However, it is possible to increase the conversion rate by reducing the supply amount of nitrate ions per unit time.

In Examples 11 to 15 below, the influence of various types of carriers was examined. In addition to activated carbon (same as used in Example 8) as a support, TiO ₂ (Nippon Aerosil Co., Ltd., P-25, trademark), ZrO ₂ [Zr hydroxide (Daiichi Rare Element Industrial Co., Ltd.) Baked at 450 ° C.], SiO ₂ (manufactured by Nippon Aerosil Co., Ltd., Aerosil 300, trademark) and Al ₂ O ₃ (JRC-ALO-4) were used.

(Examples 11 to 15)
Each carrier Preparation <br/> above catalyst, PdCl _{2 (Wako} Pure Chemical Industries, Ltd.) and _{Cu (NO 3) 2 · 3H} 2 O ( Wako Pure Chemical Industries, Ltd.) aqueous solution sequentially impregnated with, The supported amounts of Pd and Cu were 5% by weight and 0.6% by weight, respectively. The material thus obtained was dried overnight at 100 ° C. under a nitrogen stream, and each carrier was supported with Pd and Cu (5 wt% Pd-0.6 wt% Cu / AC, TiO ₂ , ZrO ₂ , SiO ₂ , Al ₂ O ₃ ) was produced. Next, a dispersion in which polytetrafluoroethylene (PTFE) (manufactured by Nagoya Gosei Co., Ltd., NS-01, trademark) is dispersed in water is loaded with the dried Pd and Cu so that the loaded amount is 5% by weight. The impregnated material was impregnated. The obtained sample was calcined at 250 ° C. for 2 hours in an air atmosphere, and then subjected to reduction treatment at 300 ° C. for 2 hours in a hydrogen stream, and a catalyst in which PTFE was further supported on a material supporting Pd and Cu (5 wt% PTFE _{/5wt%Pd-0.6wt%Cu/AC,TiO 2, ZrO 2, SiO 2} , Al 2 O 3) was prepared.

Response study <br/> was prepared as described above 5wt% PTFE / 5wt% Pd- 0.6wt% Cu / AC, using 1.0 grams of _{TiO 2, ZrO 2, SiO 2} , Al 2 O 3 in Example 1 The same continuous reactor was charged.

Next, a reduction reaction was carried out in the same manner as in Example 1 except that nitrate ion-containing water was supplied to the reactor at 39 cm ³ / hour, carbon dioxide was not supplied, and LHSV was 39 hours- ^1. The concentration of each component was measured.

The results of Examples 11 to 15 are shown in Table 5.

From the results of Examples 11 to 15, it was found that when activated carbon was used as the carrier, it could have a significantly higher conversion rate and a significantly lower ammonia selectivity than when other carriers were used. When TiO ₂ or ZrO ₂ was used as a support, a high conversion rate was obtained. Although the ammonia selectivity was higher than that of activated carbon, the effect of the present invention was not impaired. When SiO ₂ was used, a remarkably high conversion was obtained, and when Al ₂ O ₃ was used, a remarkably low ammonia selectivity was obtained.

The catalyst of the present invention is effective in a method of removing ground ions containing nitrate ions from the ground water into drinking water. It can also be used for wastewater treatment or industrial water purification.

Claims (7)

One or more metals selected from the group consisting of Pd, Pt, Ir, Ru and Rh, and one or more metals selected from the group consisting of Cu, Sn and In are activated carbon, Al ₂ O ₃ , SiO ₂ , A water repellent catalyst supported on one or more supports selected from the group consisting of TiO ₂ and ZnO ₂ . One or more metals selected from the group consisting of Pd, Pt, Ir, Ru and Rh are Pd, one or more metals selected from the group consisting of Cu, Sn and In are Cu, and the support is activated carbon. The catalyst according to claim 1, wherein 3. The catalyst according to claim 1, wherein the water repellency is expressed by including a fluorine-based resin. 4. The catalyst according to claim 3, wherein the fluororesin is polytetrafluoroethylene. The catalyst according to any one of claims 1 to 4, wherein the activated carbon is produced from coconut shells. A method for reducing nitrate ions contained in water using the catalyst according to any one of claims 1 to 5. 7. The method according to claim 6, wherein hydrogen is used as the reducing agent.