| abstract |
A multi-layered catalyst on a metal substrate and a method for its preparation is provided. The catalyst includes a substrate, an adhesive sublayer whose improved adhesion to the substrate is obtained by the formation of a diffusion layer between the substrate and adhesive layer, a catalytically active layer deposited on the adhesive sublayer characterized by a smooth compositional gradient of the catalytically active component such that the catalytically active layer ranges from substantially 0.0 wt % at the adhesive sublayer interface to substantially 100 wt % at the outermost portion of the catalytically active layer and a porous layer containing at least the catalytically active component. An activator coating can be applied to the porous layer. The catalyst is prepared by plasma spraying a thermally reactive powder onto the substrate to form the adhesive sublayer, whereby the heat generated by the thermally reactive powders causes diffusion of the sublayer into the substrate and a diffusion bonded layer is formed resulting in a strong adhesion of the sublayer to the substrate, subsequently introducing at least alumina and a second powder into a plasma torch at separately controllable variable feed rates and co-depositing alumina and the second powder, adjusting the relative feed rates of alumina and second powder into the plasma torch such that a catalytically active layer with a smooth compositional gradient is achieved, whereby the alumina content of the catalytically active layer ranges from substantially 0 wt % at the adhesive sublayer interface to substantially 100 wt % at the uppermost portion of the catalytically active layer, subsequently introducing at least alumina and an additional metal carbonate or hydroxide into the plasma torch; and co-depositing a porous layer of at least alumina and the additional metal carbonate or hydroxide, whereby the metal carbonate or hydroxide decomposes with a release of gas or vapor resulting in an outer coating with a high surface area. |