Catalytic structure

Abstract

Foil, wire and similar coherent bodies of catalytic metal are provided with catalytically active surfaces by diffusing a chemically removable metal such as aluminum or zinc into those surfaces and then selectively dissolving out at least about a third of the removable metal. Platinum wire screens activated in this way make effective exhaust catalysts for automotive engines.

What is claimed: 
     
       1. A self-supported coherent structure essentially of metal selected from the class consisting of a platinum family metal .[.and nickel.]. having its surface in the form of a three-dimensional micro-fissured fragmentation into cells principally ranging from about 500 Angstroms to about 5000 Angstroms in size and produced by dissolving out from that surface a different metal introduced into that surface by activated pack diffusion. 
     
     
       2. The structure of claim 1 in which the metal is platinum and contains an amount of aluminum about 0.5 to about 10% by weight of the platinum. 
     
     
       3. The structure of claim 1 in which the metal is platinum and contains an amount of zinc about 0.5 to about 10% by weight of the platinum. 
     
     
       4. In the preparation of a highly active platinum catalyst, the improvement according to which aluminum is diffused into the platinum by activated pack diffusion, and the aluminum-containing platinum has at least about one-third of its aluminum leached out by a first treatment with aqueous caustic and a second treatment with aqueous acid. 
     
     
       5. A stirrer propeller whose surface is nickel catalytically activated by first diffusing into it a chemically leachable alloying metal and then chemically leaching at least about a third of that leachable metal. 
     
     
       6. A platinum catalyst in the form of a platinum screen produced by the process of claim 4 in which essentially all the aluminum was leached out of the platinum. 
     
     
       7. The structure of claim 1 in which the metal is a wire screen in which the wire has a thickness from about one mill or less to about 10 mils. 
     
     
       8. The structure of claim 7 in which the .[.metal is a platinum family metal and the.]. wire is about 4 mils thick. 
     
     
       9. The structure of claim 1 in which the metal is platinum having a thickness from about 1 mil or less to about 10 mils, and it also has pores less than 100 Angstroms wide in a density of at least 10 8  per square centimeter of gross surface, the diffusion having been effected at about 800° to 850° F. 
     
     
       10. A stack of catalytic screens in which each screen is made of platinum hardened with rhodium and having the structure of claim 1. 
     
     
       11. The preparation of claim 4 in which the aqueous caustic leaching is effected until it is essentially completed, and the treatment with aqueous acid is a one-minute contact with strong acid. 
     
     
       12. The structure of claim 7 in which the .[.metal is a platinum family metal and the.]. wire is about 1 mil thick. 
     
     
       13. The metal structure of claim 1 containing about 0.5 to about 10% of the dissolved-out metal. .Iadd. 
     
     
       14.  A self-supporting nickel web that has a visibly active pyrophoric surface in the form of a three-dimensional micro-fissured fragementation into cells principally ranging from about 500 Angstroms to about 5000 Angstroms in size, and produced by dissolving out from that surface a different metal introduced by low-temperature activated pack diffusion into the surface of a starting web not over about 50 mils thick. .Iaddend. .Iadd.15. The combination of claim 14 in which the starting web is not over 20 mils thick. .Iaddend. .Iadd.16. The combination of claim 14 in which the starting web is not over 2 mils thick. .Iaddend. .Iadd.17. The combination of claim 14 in which the visibly active pyrophoric surface is dry. .Iaddend. .Iadd.18. The combination of claim 14 in which the different metal is aluminum. .Iaddend. .Iadd.19. The combination of claim 14 in which the different metal is zinc. .Iaddend.