Nanoporous Metal Layer Formation on Stainless Steel Substrates Used as Metal Monoliths for Catalytic Converters

For the first time, this research reports the formation of nanoporous layers of metals on the surface of metal substrates by Raney method and their conversion to corresponding porous perovskite layers. The noble metals doped perovskites are used as catalytic converter for reducing automotive pollutants. The use of perovskite as a substrate for the noble metals can reduce the need for such metals by as much as 70%. The metal surface is treated by plastic deformation at high pressures or quenching to create microstructures, and then an aluminum-metal alloy layer is formed on the surface of the metal by its hot dip aluminizing at 750oC. At the same temperature, the aluminum is diffused into the metal surface layer as deep as 30nm for 1h. Subsequently the sample is gradually quenched or cooled and the aluminum is extracted by soda solution. Nanostructures of about 30 nm are obtained by combined Raney method together with the plastic deformation process. Quenching of the alloy creates even smaller nanostructures. The porous metal layer is impregnated with lanthanum nitrate for one or more times and calcined at 900oC to create the porous perovskite layer on the surface of the metal substrate as monolith. The perovskite completely converts CO and C2H6 (as representative of the exhaust unburned hydrocarbons).