Aerogel and metallic compositions

Abstract

Metallic aerogel compositions comprising an aerogel, e.g., RF or carbon aerogel, having metallic particles dispersed on its surface are disclosed. The aerogel compositions can have a uniform distribution of small metallic particles, e.g., 1 nanometer average particle diameter. Also disclosed are processes for making the aerogel compositions comprising contacting an aerogel with a supercritical fluid containing a metallic compound. The aerogel compositions are useful, for example in the manufacture of fuel cell electrodes.

1 - 32 . (canceled)  
   
   
       33 . A method for producing metal particles or mixed metal particles dispersed on a particulate substrate comprising: 
 a. exposing an organometallic and the particulate substrate to a supercritical or near supercritical fluid under conditions to form a mixture of the fluid and the organometallic;    b. allowing the mixture to remain in contact with the substrate for a time sufficient to deposit dispersed organometallic onto the substrate;    c. venting the mixture;    d. thereby adsorbing the organometallic onto the substrate; and then    e. reducing the dispersed organometallic to dispersed metal particles with a reducing agent.    
   
   
       34 . The method of claim  1 , wherein the substrate comprises a carbonaceous material.  
   
   
       35 . The method of  claim 34 , wherein the metal particles are nanoparticles.  
   
   
       36 . The method of claim  1 , wherein the organometalllic comprises 1,5-cyclooctadiene dimethyl platinum [Pt(COD)Me 2 ].  
   
   
       37 . The method of  claim 33 , wherein the metal particles are nanoparticles.  
   
   
       38 . The method of  claim 37 , whrein the nanoparticles are about 1 nm to about 4 nm in average diameter.  
   
   
       39 . The method of  claim 33 , wherein the metal particles are noble metal particles.  
   
   
       40 . The method of  claim 33 , wherein the metal particles comprise platinum, iridium, ruthenium, rhodium, palladium, chromium, gold, silver, nickel, cobalt, or a mixture thereof, or an alloy thereof.  
   
   
       41 . The method of  claim 33 , wherein the metal particles comprise platinum.  
   
   
       42 . The method of  claim 33 , wherein the metal particles comprise silver.  
   
   
       43 . The method of  claim 33 , wherein the metal particles comprise ruthenium.  
   
   
       44 . The method of  claim 33 , wherein the metal particles are mixed metal particles.  
   
   
       45 . The method of  claim 33 , wherein the fluid comprises carbon dioxide, ethane, or propane.  
   
   
       46 . The method of  claim 33 , wherein the reducing is by addition of a reducing agent.  
   
   
       47 . The method of  claim 46 , wherein the reducing agent comprises hydrogen.  
   
   
       48 . The method of  claim 33 , wherein the organometallic is adsorbed while in the mixture.  
   
   
       49 . The method of  claim 33 , wherein the organometallic is adsorbed when the mixture is vented.  
   
   
       50 . The method of  claim 33 , wherein in step (a), at least some of the organometallic dissolves in the fluid.  
   
   
       51 . The method of  claim 33 , wherein in step (a), all or substantially all of the organometallic dissolves in the fluid.  
   
   
       52 . The method of  claim 33 , wherein the method produces a supported particulate catalyst suitable for use in a fuel cell.  
   
   
       53 . A method for producing particulate substrate-supported dispersed metallic particles comprising: 
 a. mixing an organometallic in a supercritical or near supercritical fluid to form a mixture;    b. exposing a particulate substrate to the mixture of a) under supercritical or near supercritical conditions for a period of time sufficient to deposit dispersed organometallic on the substrate;    c. venting the mixture;    d. thereby adsorbing the organometallic onto the substrate; and then    e. reducing the organometallic to dispersed metal particles with a reducing agent.    
   
   
       54 . A method for producing particulate substrate-supported dispersed metallic particles comprising; 
 a. adding a particulate substrate and an organometallic to a reactor;    b. adding a supercritical fluid to the reactor to form a mixture with the organometallic;    c. allowing the organometallic to remain in contact with the substrate for a time sufficient to deposit dispersed organometallic onto the substrate;    d. venting the reactor;    e. thereby adsorbing the organometallic onto the substrate; and then    f. adding a gaseous reducing agent to the reactor; and    g. contacting the reducing agent and organometallic until the organometallic is reduced to dispersed metal particles.    
   
   
       55 . The method of  claim 33 , wherein the particulate substrate is a porous particulate substrate.  
   
   
       56 . A method for producing metal particles or mixed metal particles dispersed on a surface of a substrate comprising; 
 exposing an organometallic and the surface to a supercritical or near supercritical fluid in a reactor under conditions to form a mixture of the fluid and the organometallic;    allowing the mixture to remain in contact with the surface for a time sufficient to deposit dispersed organometallic onto the surface;    depressurizing the reactor; and then    reducing the dispersed organometallic to dispersed metal or mixed metal particles.    
   
   
       57 . The method of  claim 57 , wherein the substrate is a porous substrate.