Metal colloidal solution and method for producing the same

Abstract

The present invention is a metal colloid solution comprising: colloidal particles consisting of metal particles consisting of one or two or more metal(s) and a protective agent bonding to the metal particles; and a solvent as a dispersion medium of the colloidal particles, wherein: a chloride ion concentration per a metal concentration of 1 mass % is 25 ppm or less; and a nitrate ion concentration per a metal concentration of 1 mass % is 7500 ppm or less. In the present invention, adsorption performance can be improved with adjustment of the amount of the protective agent of the colloidal particles. It is preferable to bind the protective agent of 0.2 to 2.5 times the mass of the metal particles.

Claims

1. A metal colloid solution for producing a catalyst having an inorganic oxide as a carrier, said metal colloid solution consisting of: colloidal particles comprising metal particles of one or more metals and a protective agent consisting of polyvinylpyrrolidone bound to the metal particles; and a solvent as a dispersion medium of the colloidal particles, wherein: a concentration of the metal in the solution is 0.01 to 8.0 mass %, and wherein the protective agent bound to the metal particles is present in the metal colloid solution in an amount from 0.2 to 1.0 times a mass of the metal particles to adsorb the colloidal particles to the inorganic oxide; a chloride ion concentration per metal concentration of 1 mass % is 25 ppm or less; and a nitrate ion concentration per metal concentration of 1 mass % is 7500 ppm or less.

2. The metal colloid solution according to claim 1, wherein the metal particles comprise one or more metals of platinum, palladium, rhodium, ruthenium, gold, silver and iridium.

3. A method of producing the metal colloid solution defined in claim 2, comprising: a step of adding one or more metal salts, a protective agent and a reducing agent to a solvent to form colloidal particles to produce the metal colloid solution; and a stabilization treatment step for removing chloride ion and/or nitrate ion in the metal colloid solution.

4. The method of producing the metal colloid solution according to claim 3, wherein the stabilization treatment step includes a step of subjecting the metal colloid solution to ultrafiltration.

5. The method of producing the metal colloid solution according to claim 3, wherein the stabilization treatment step includes a step of adding alkali to the metal colloid solution.

6. The method of producing the metal colloid solution according to claim 3, wherein the stabilization treatment step includes a step of centrifuging the metal colloid solution to form precipitates and decanting the metal colloid solution.

7. The method of producing the metal colloid solution according to claim 3, wherein the stabilization treatment step includes a step of removing nitrate ion in the metal colloid solution wherein energy of heat, microwave, ultrasound, plasma is imparted to the metal colloid solution to decompose nitrate ion.

8. A method of producing a metal colloid solution for producing a catalyst having an inorganic oxide as a carrier, said metal colloid solution comprising: colloidal particles comprising metal particles of one or more metals and a protective agent consisting of polyvinylpyrrolidone bound to the metal particles; and a solvent as a dispersion medium of the colloidal particles, wherein: a concentration of the metal in the solution is 0.01 to 8.0 mass %, and wherein the protective agent bound to the metal particles is present in the metal colloid solution in an amount from 0.2 to 1.0 times a mass of the metal particles to adsorb the colloidal particles to an inorganic oxide; a chloride ion concentration per metal concentration of 1 mass % is 25 ppm or less; and a nitrate ion concentration per metal concentration of 1 mass % is 7500 ppm or less, said method comprising: a step of adding one or more metal salts, a polyvinylpyrrolidone protective agent and a reducing agent to a solvent to form colloidal particles to produce the metal colloid solution; and a stabilization treatment step for removing chloride ion and/or nitrate ion in the metal colloid solution; wherein the polyvinylpyrrolidone protective agent is 0.2 to 1.0 times the mass of metal in the metal salt, and wherein the reducing agent is an alcohol, a glycol, hydrogen, sodium borohydride, hydrazine, or dimethylamine borane.

9. The method of producing the metal colloid solution according to claim 8, wherein the stabilization treatment step includes a step of subjecting the metal colloid solution to ultrafiltration.

10. The method of producing the metal colloid solution according to claim 8, wherein the stabilization treatment step includes a step of adding alkali to the metal colloid solution.

11. The method of producing the metal colloid solution according to claim 8, wherein the stabilization treatment step includes a step of centrifuging the metal colloid solution to form precipitates and decanting the metal colloid solution.

12. The method of producing the metal colloid solution according to claim 8, wherein the stabilization treatment step includes a step of removing nitrate ion in the metal colloid solution wherein energy of heat, microwave, ultrasound, plasma is imparted to the metal colloid solution to decompose nitrate ion.

13. A method according to claim 8, wherein the metal colloid solution comprises metal particles which comprise one or more metals of platinum, palladium, rhodium, ruthenium, gold, silver and iridium.

14. A metal colloid solution produced according to the method of claim 9.

15. A metal colloid solution produced according to the method of claim 12.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(1) Preferred embodiments of the present invention will be described below. In the present embodiment, various metal colloid solutions were produced, and their stability was evaluated. In addition, for the metal colloid solutions, the adsorption property onto the inorganic oxide carrier was also evaluated.

(2) Various metal colloid solutions were prepared according to similar steps. That is, a metal salt solution comprising a one or more metal salts was provided, to which a protective agent solution with a protective agent dissolved was added, and then a reducing agent was added and the mixture was refluxed at 100 C. for 2 hours to make a metal colloid solution. Then, after treatment for removing chloride ion or nitrate ion in the metal colloid solution, the treated solution was concentrated with heating to afford a metal colloid solution having an increased metal concentration.

(3) The chloride ion or nitrate ion removal treatment was performed with selection of the following kinds of treatment: a. Ultrafiltration: The metal colloid solution is passed through an ultrafiltration filter of 10000 molecular weight cutoff to remove the chloride ion. b. Centrifugation: After 10% by volume of methanol was added to the metal colloid solution, centrifugation was performed at a rotation rate of 6000 rpm for 5 minutes, and the supernatant was removed with decantation, and then water was added to the precipitate to adjust the colloid concentration. c. Heat treatment: For the metal colloid solution produced after the heating reflux treatment (100 C., 2 hours) in which a reducing agent was added, the heat refluxing treatment was continued for 10 hours as it was to decompose and remove nitrate ion. d. Alkali addition: Ammonia was added to the metal colloid solution until the pH became 5 to 7 with pH meter measurement.

(4) Table 1 shows the metal colloid solutions produced in the present embodiment.

(5) TABLE-US-00001 TABLE 1 Protective agent Amount of Desalting/ Metal protective Denitration Final metal colloid Metal salt Type agent treatment concentration Example 1 Pd7Pt3 Palladium Chloroplatinic PVP 1.0 a 4 wt % nitrate acid Example 2 Pd Palladium chloride 2.0 a 4 wt % Example 3 Pt Chloroplatinic acid 0.2 b 4 wt % Example 4 Pd1Pt1 Palladium Chloroplatinic 1.0 a 2 wt % chloride acid Example 5 Pd Palladium nitrate 1.5 c 4 wt % Example 6 Pt Dinitrodiamine platinum 0.2 d 4 wt % Example 7 Au Chloroauric acid 1.0 a 2 wt % Example 8 Rh Rhodium nitrate 1.5 c 4 wt % Example 9 Ru Ruthenium nitrate 0.2 d 4 wt % Example 10 Pt Chloroplatinic acid 2.0 b 4 wt % Example 11 Ag Silver nitrate 2.0 d 4 wt % Example 12 Ir Iridium chloride 1.0 a 2 wt % Example 13 Pd1Ag1 Palladium Silver nitrate 1.5 c 4 wt % nitrate Comparative Pd7Pt3 Palladium Chloroplatinic PVP 5.0 None 2 wt % Example 1 nitrate acid Comparative Pd Palladium chloride 3.0 4 wt % Example 2 Comparative Pt Chloroplatinic acid 1.0 4 wt % Example 3 Comparative Pd Palladium nitrate 1.5 4 wt % Example 4 Comparative Au Chloroauric acid 3.0 4 wt % Example 5 Comparative Rh Rhodium nitrate 5.0 4 wt % Example 6 Comparative Ru Ruthenium nitrate 3.0 4 wt % Example 7 Comparative Ag Silver nitrate 2.0 4 wt % Example 8 Comparative Ir Iridium chloride 3.0 2 wt % Example 9 Comparative Pd1Ag1 Palladium Silver nitrate 3.0 4 wt % Example 10 nitrate In Example 1 and Comparative Example 1, Alloy of Pd:Pt = 7:3; In Example 4, Alloy of Pd:Pt = 1:1; In Example 13 and Comparative Example 10, Alloy of Pd:Ag = 1:1. a: Ultrafiltration b: Decantation c: Heating decomposition d: Anmmonia addition Amount of protective agent represents the mass ratio of PVP to the metal weight.

(6) For each of the produced metal colloid solutions, it was first examined whether dissolution of the colloidal particles and precipitation generation were present or not as a stability evaluation. In this stability evaluation test, for the metal colloid solutions after production, the colloidal solution was sampled at each predetermined period (the day of production, 1 day, 7 days, 30 days later), and then 100 mL of the solution was put in an ultrafiltration device (10000 molecular weight cutoff) and filtered under pressure with Ar gas of 4 atm. Then, the filtrate was subjected to ICP analysis to calculate a proportions of dissolved metal ions (the amount of metal charged, by mass). Further, the precipitation generation was determined based on whether precipitation remained on the filter paper or not after the sampled solution was filtered through a membrane filter having a pore size of 0.2 m. The results of this evaluation are shown in Table 2.

(7) TABLE-US-00002 TABLE 2 Desalting/ Anion concentration (ppm) Metal dissolution rate, Presence of precipitation Metal Denitration Chloride ion Nitrate ion Manufacturation After 1 After 30 colloid treatment concentration concentration day day After 7 days days Example 1 Pd7Pt3 a 4 420 ND ND ND ND Example 2 Pd a 3 ND ND ND ND ND Example 3 Pt b 23 ND ND ND ND ND Example 4 Pd1Pt1 a 2 ND ND ND ND ND Example 5 Pd c ND 7230 ND ND ND ND Example 6 Pt d ND 2850 ND ND ND ND Example 7 Au a 5 ND ND ND ND ND Example 8 Rh c ND 7410 ND ND ND ND Example 9 Ru d ND 2090 ND ND ND ND Example 10 Pt b 21 ND ND ND ND ND Example 11 Ag d ND 2020 ND ND ND 0.02% Example 12 Ir a 3 ND ND ND ND ND Example 13 Pd1Ag1 c ND 2650 ND ND ND ND Comparative Pd7Pt3 None 540 17840 ND 0.10% 0.45% 0.63% Example 1 Comparative Pd 5850 ND ND 0.12% 0.52% 0.82% Example 2 Comparative Pt 10810 ND ND ND Precipitation Precipitation Example 3 generation generation Comparative Pd ND 18880 ND 0.11% 0.51% 0.76% Example 4 Comparative Au 7290 ND ND ND 0.01% 0.03% Example 5 Comparative Rh ND 22060 ND 0.03% 0.04% 0.07% Example 6 Comparative Ru ND 19580 ND 0.05% 0.08% 0.25% Example 7 Comparative Ag ND 15020 1.05% 2.52% 5.63% 12.30% Example 8 Comparative Ir 7860 ND ND 0.01% 0.05% 0.12% Example 9 Comparative Pd1Ag1 ND 12250 0.95% 2.33% 4.24% 8.45% Example 10 In Example 1 and Comparative Example 1, Alloy of Pd:Pt = 7:3; In Example 4, Alloy of Pd:Pt = 1:1; In Example 13 and Comparative Example 10, Alloy of Pd:Ag = 1:1. a: Ultrafiltration b: Decantation c: Heating decomposition d: Anmmonia addition ND: Not detected Anion concentration represents a concentration of 1 mass % of the metal.

(8) It has been found from Table 2 that in the metal colloid solution of Examples 1 to 13 in which various kinds of desalting and denitration treatment were performed, dissolution of the metal ions scarcely occurred and precipitation generation was not observed even 30 days later, and thus the metal colloid solution had excellent stability. It is considered that this result is due to the decrease in chloride ion and nitrate ion with the stabilization treatment. Meanwhile in the respective Comparative Examples, it can be confirmed that although there was a difference in degree, dissolution of the metal ions occurred. It is considered that the precipitate formed in the Pt colloid of Comparative Example 3 is derived from the metal of the colloidal particle, and this is considered because the quantity of the protective agent was relatively small under a circumstance of extremely high chloride ion concentration. Optimization of the amount of the protective agent is considered to be required in view of the results of the after-mentioned confirmation test on an effect of improving the adsorption property. However, it is believed that the decrease in the anion concentration must be given priority.

(9) Then, in the adsorption property evaluation test, a solution in such an amount that the metal content was 0.05 g was collected from each of the metal colloid solutions, and 500 mL of purified water was added thereto. Then, this metal colloid solution was stirred for 5 minutes, and 5 g of each of various inorganic oxide carriers was added thereto (when the all amount of the metal is adsorbed, the supporting amount is 1 mass %.). The pH of the solution was 5 to 7 at this point. After addition of the inorganic oxide, the solution was stirred for 2 hours and then was suction-filtered through a filter paper of 5C of the JIS standard. The filtrate was subjected to ICP analysis to measure metal concentrations, and an adsorption rate per 2 hours which was a duration of stirring was calculated (taken as 100 mass % when all amount of the charged metal is supported). Table 3 shows the results.

(10) TABLE-US-00003 TABLE 3 Amount of protective agent Adsorption rate (%) Metal colloid PVP/Metal Titania Zirconia Alumina Ceria Example 1 Pd7Pt3 1.0 100 100 100 100 Example 2 Pd 2.0 100 100 100 100 Example 3 Pt 0.2 100 100 100 100 Example 4 Pd1Pt1 1.0 100 100 100 100 Example 5 Pd 1.5 100 100 100 100 Example 6 Pt 0.2 100 100 100 100 Example 7 Au 1.0 100 100 100 100 Example 8 Rh 1.5 100 100 100 100 Example 9 Ru 0.2 100 100 100 100 Example 10 Pt 2.0 100 96 92 89 Example 11 Ag 2.0 100 100 100 100 Example 12 Ir 1.0 100 100 100 100 Example 13 Pd1Ag1 1.5 100 100 100 100 Comparative Pd7Pt3 5.0 74 42 34 30 Example 1 Comparative Pd 3.0 84 74 65 54 Example 2 Comparative Pt 1.0 64 49 44 42 Example 3 Comparative Pd 1.5 93 95 93 90 Example 4 Comparative Au 3.0 80 77 63 61 Example 5 Comparative Rh 5.0 66 45 33 29 Example 6 Comparative Ru 3.0 91 82 85 70 Example 7 Comparative Ag 2.0 82 75 70 64 Example 8 Comparative Ir 3.0 69 61 54 44 Example 9 Comparative Pd1Ag1 3.0 88 78 72 63 Example 10 In Example 1 and Comparative Example 1, Alloy of Pd:Pt = 7:3; In Example 4 Alloy of Pd:Pt = 1:1; In Example 13 and Comparative Example 10, Alloy of Pd:Ag = 1:1. Amount of protective agent represents the mass ratio of PVP to the metal weight.

(11) From Table 3, it is found that the amount of the protective agent (the mass of the protective agent to that of the metal) affects the adsorption performance of the metal colloid. In the metal colloids of Examples 1 to 13, the amount of the protective agent is set to 2.0 times or less, and the metal colloid is adsorbed on all of the inorganic oxide carriers at the adsorption rate of 100%. Comparative Examples 1 to 7 mainly involve the colloids having a relatively large amount of the protective agent, and the adsorption rate is low. In Comparative Example 3, the adsorption rate was low in spite of a small amount of the protective agent and it is considered because the precipitation generation was observed as described above. Also in Comparative Example 8, despite a small amount of the protective agent, the dissolution amount of the metal dissolved is large because of nitrate ion and thus it is considered that the adsorption rate was measured lower. From the above, it is understood that it is preferable to pay attention to the amount of protective agent as well as a decrease in amount of chloride ion and the like in the solution in order to make a metal colloid solution having excellent adsorptive property in addition to stability.

INDUSTRIAL APPLICABILITY

(12) As described above, the metal colloid solution according to the present invention has excellent stability and the metal composition of the colloidal particles changes only a little bit even after long period of time. Further, the present invention can improve the adsorption ability for various carriers with adjustment of the amount of the protective agent. Because of these properties, the present invention is useful for producing a material such as a catalyst that requires strict adjustment of the composition.