Method for manufacturing noble metal fine particles

Abstract

A method for manufacturing noble metal fine particles, by which noble metal fine particles are obtained whose particle diameter and alloy composition are easy to control and whose crystallinity and purity are high, is provided. The method includes the steps of: (1) obtaining a molten mixture containing a noble metal chloride, by insufflating chlorine gas into a mixture of a molten salt of an alkali metal chloride and a noble metal; (2) obtaining a noble metal oxide as a precipitate by adding an alkali metal carbonate to the molten mixture under an inert gas atmosphere; (3) obtaining a mixture containing noble metal oxide fine particles, by pulverizing the noble metal oxide with at least one of an alkali metal carbonate and an alkali earth metal carbonate; and (4) obtaining noble metal fine particles by heating the mixture obtained in step (3) under an atmosphere of gas containing hydrogen, and then treating the heat-treated mixture with acid.

1 . A method for manufacturing noble metal fine particles, the method comprising the steps of:
 (1) obtaining a molten mixture containing a noble metal chloride, by insufflating chlorine gas into a mixture of a molten salt of an alkali metal chloride and a noble metal;   (2) obtaining a noble metal oxide as a precipitate by adding an alkali metal carbonate to the molten mixture under an inert gas atmosphere;   (3) obtaining a mixture containing noble metal oxide fine particles, by pulverizing the noble metal oxide with at least one of an alkali metal carbonate and an alkali earth metal carbonate; and   (4) obtaining noble metal fine particles by heating the mixture obtained in step (3) under an atmosphere of gas containing hydrogen, and then treating the heat-treated mixture with acid.   
   
   
       2 . The method according to  claim 1 , wherein in step (1), a molten mixture A and a molten mixture B, which contain different noble metals, are prepared and mixed together to obtain a molten mixture C. 
   
   
       3 . The method according to  claim 1 , wherein the noble metal is at least one member selected from the group consisting of rhodium, platinum, and palladium. 
   
   
       4 . The method according to  claim 1 , wherein the alkali metal chloride is at least one member selected from the group consisting of LiCl, NaCl, KCl, CsCl, LiCl—NaCl, LiCl—KCl, NaCl—KCl, NaCl—CsCl, LiCl—CsCl, KCl—CsCl, LiCl—KCl—NaCl, LiCl—MgCl 2 , LiCl—CaCl 2 , LiCl—BaCl 2 , NaCl—MgCl 2 , NaCl—CaCl 2 , NaCl—BaCl 2 , KCl—MgCl 2 , KCl—CaCl 2 , KCl—BaCl 2 , KCl—MgCl 2 , KCl—CaCl 2 , KCl—BaCl 2 , CsCl—MgCl 2 , CsCl—CaCl 2 , and CsCl—BaCl 2 . 
   
   
       5 . The method according to  claim 1 , wherein in step (1), the mixture ratio of the noble metal and the alkali metal chloride is 1:5 to 20 in weight ratio. 
   
   
       6 . The method according to  claim 1 , wherein in step (1), the insufflated amount of the chlorine gas is set such that the mole ratio of the chlorine gas to the noble metal is 1:1.5 to 5. 
   
   
       7 . The method according to  claim 1 , wherein in step (2), the added amount of the alkali metal carbonate is set such that the mole ratio of the alkali metal carbonate to the noble metal chloride is 1:1 to 10. 
   
   
       8 . The method according to  claim 1 , wherein in step (3), the noble metal oxide is pulverized so as to have an average particle diameter of 10 nm to 10 μm. 
   
   
       9 . The method according to  claim 1 , wherein said at least one of the alkali metal carbonate and the alkali earth metal carbonate, which are used in step (3), is at least one member selected from the group consisting of sodium carbonate, magnesium carbonate, calcium carbonate, and barium carbonate. 
   
   
       10 . The method according to  claim 2 , wherein the noble metal is at least one member selected from the group consisting of rhodium, platinum, and palladium. 
   
   
       11 . The method according to  claim 2 , wherein the alkali metal chloride is at least one member selected from the group consisting of LiCl, NaCl, KCl, CsCl, LiCl—NaCl, LiCl—KCl, NaCl—KCl, NaCl—CsCl, LiCl—CsCl, KCl—CsCl, LiCl—KCl—NaCl, LiCl—MgCl 2 , LiCl—CaCl 2 , LiCl—BaCl 2 , NaCl—MgCl 2 , NaCl—CaCl 2 , NaCl—BaCl 2 , KCl—MgCl 2 , KCl—CaCl 2 , KCl—BaCl 2 , KCl—MgCl 2 , KCl—CaCl 2 , KCl—BaCl 2 , CsCl—MgCl 2 , CsCl—CaCl 2 , and CsCl—BaCl 2 . 
   
   
       12 . The method according to  claim 3 , wherein the alkali metal chloride is at least one member selected from the group consisting of LiCl, NaCl, KCl, CsCl, LiCl—NaCl, LiCl—KCl, NaCl—KCl, NaCl—CsCl, LiCl—CsCl, KCl—CsCl, LiCl—KCl—NaCl, LiCl—MgCl 2 , LiCl—CaCl 2 , LiCl—BaCl 2 , NaCl—MgCl 2 , NaCl—CaCl 2 , NaCl—BaCl 2 , KCl—MgCl 2 , KCl—CaCl 2 , KCl—BaCl 2 , KCl—MgCl 2 , KCl—CaCl 2 , KCl—BaCl 2 , CsCl—MgCl 2 , CsCl—CaCl 2 , and CsCl—BaCl 2 . 
   
   
       13 . The method according to  claim 2 , wherein in step (1), the mixture ratio of the noble metal and the alkali metal chloride is 1:5 to 20 in weight ratio. 
   
   
       14 . The method according to  claim 3 , wherein in step (1), the mixture ratio of the noble metal and the alkali metal chloride is 1:5 to 20 in weight ratio. 
   
   
       15 . The method according to  claim 4 , wherein in step (1), the mixture ratio of the noble metal and the alkali metal chloride is 1:5 to 20 in weight ratio. 
   
   
       16 . The method according to  claim 2 , wherein in step (1), the insufflated amount of the chlorine gas is set such that the mole ratio of the chlorine gas to the noble metal is 1:1.5 to 5. 
   
   
       17 . The method according to  claim 2 , wherein in step (2), the added amount of the alkali metal carbonate is set such that the mole ratio of the alkali metal carbonate to the noble metal chloride is 1:1 to 10. 
   
   
       18 . The method according to  claim 3 , wherein in step (2), the added amount of the alkali metal carbonate is set such that the mole ratio of the alkali metal carbonate to the noble metal chloride is 1:1 to 10. 
   
   
       19 . The method according to  claim 2 , wherein in step (3), the noble metal oxide is pulverized so as to have an average particle diameter of 10 nm to 10 μm. 
   
   
       20 . The method according to  claim 2 , wherein said at least one of the alkali metal carbonate and the alkali earth metal carbonate, which are used in step (3), is at least one member selected from the group consisting of sodium carbonate, magnesium carbonate, calcium carbonate, and barium carbonate.