Coated silica shells

Abstract

The disclosure of the invention relates to a high surface area powder composition in which the individual powder particles comprise silica shells which have been coated with finely distributed surface accessible metals, and to a process for preparing the same. Suitable surface accessible metals comprise one or more of Pd, Pt, Ag, among others.

The Following Is Claimed: 
     
       1. A powder composition in which individual particles of the powder comprise: a hollow silica shell having a pre-determined shape, an average diameter in the range of about 0.05 to 15 microns, and a shell thickness in the range of from about 5 to 50 nanometers, at least a portion of said silica shell having a coating comprising a surface accessible metal containing species selected from a group consisting of Pd, Pt, Rh, Re, In, Au, Ag, Cu, Ni; wherein said metal containing species comprises about 0.1 to 90% by weight of the powder composition.   
     
     
       2. A powder composition made by the process comprising the steps of: (a) applying to a slurry comprising core particles, a coating comprising silica,   (b) optionally dissolving the cores to form an aqueous slurry comprising hollow silica shells,   (c) optionally adding a soluble stannous salt,   (d) recovering the silica shells from the slurry, washing and optionally drying the recovered shells;   (e) preparing an aqueous slurry of the recovered silica shells, and;   (f) coating at least a portion of the silica shells with at least one metal containing species, by adding at least one salt of the corresponding metal containing species, and a reducing agent to the slurry.   
     
     
       3. A high surface area and low density catalyst composition made by the process comprising the steps of: (a) preparing an aqueous slurry comprising hollow silica shells,   (b) optionally adding a soluble stannous salt;   (c) applying a coating of at least one catalytic metal upon at least a portion of said shells, by adding at least one salt which corresponds to said metal, and a reducing agent;   (d) recovering the solids from the slurry, and optionally drying the solids.   
     
     
       4. The composition of claims 2 or 3 wherein said metal containing species comprises at least one member selected from the group consisting of Pd, Pt, Rh, Ir Re, In, Au, Ag, Cu, Ni, and alloys thereof. 
     
     
       5. The composition of claim 3 wherein said catalytic metal comprises at least one member selected from the group of Pd and Pt. 
     
     
       6. The composition of claims, 1, 2 or 3 wherein said powder is electrically conductive. 
     
     
       7. The composition of claims 2 or 3, wherein the amount of said metal ranges from about b 0.1 to 90% weight. 
     
     
       8. The composition of claims 2, or 3, further comprising applying an intermediate coating before depositing said metal. 
     
     
       9. The composition of claims 2, or 3, wherein said salt comprises at least one of chlorides and nitrates, and said reducing agent comprises at least one member selected from the group consisting of formaldehyde, hydrazine, alkali metal nitrates, phosphites, and thiosulfates. 
     
     
       10. The composition of claim 1 further comprising an intermediate coating.