PRIMER WASHCOATS FOR METAL SUBSTRATES
Metal substrates suitable for use as catalyst supports for catalytic converters are disclosed, as well as methods of making such substrates. A coating of boehmite particles in aqueous suspension is applied to the metal substrate and calcined. Any further desired washcoats can then be applied to the resulting calcined boehmite-coated metal substrate. One exemplary metal for use as a substrate is stainless steel.
1 . A coated metal substrate comprising a metal substrate and a primer layer comprising boehmite disposed directly on the metal substrate, wherein the primer layer comprises at least 80% boehmite.
2 . The coated metal substrate of claim 1 , wherein the metal substrate has a honeycomb structure or corrugated metal foil structure.
3 . The coated metal substrate of claim 1 , wherein the primer layer on the metal substrate has been calcined.
4 . The coated metal substrate of any one of claims 1 - 3 , wherein the primer layer is present in an amount of about 1 g/L to about 4 g/L.
5 . The coated metal substrate of claim 4 , wherein the primer layer is present in an amount of about 3 g/L.
6 . The metal substrate of any one of claims 1 - 5 , wherein the metal substrate is stainless steel.
7 . The metal substrate of claim 6 , wherein the stainless steel comprises at least 16% chromium.
8 . The metal substrate of claim 6 or claim 7 , wherein the stainless steel comprises at least 3% aluminum.
9 . The coated metal substrate of any one of claims 1 - 8 , further comprising an additional washcoat layer disposed directly on top of the primer layer.
10 . A method of making the coated substrate of claim 1 , comprising:
a) providing a metal substrate;
b) forming an aqueous suspension of boehmite particles;
c) applying the boehmite particle suspension to the metal substrate; and
d) drying and calcining the metal substrate having the applied boehmite.
11 . The method of claim 10 , wherein the metal substrate comprises stainless steel.
12 . The method of claim 10 or claim 11 wherein deionized water is used for forming the aqueous suspension of boehmite particles.
13 . The method of any one of claims 10 - 12 , wherein the aqueous solution further comprises a dispersant.
14 . The method of claim 13 , wherein the dispersant comprises a nonionic polymeric dispersant.
15 . The method of any one of claims 10 - 14 , wherein the boehmite particle suspension is sonicated before applying to the metal substrate.
16 . The method of claim 15 , where the boehmite particle suspension is centrifuged after sonication, and the supernatant of the centrifuged suspension is applied to the metal substrate.
17 . The method of any one of claims 10 - 16 , wherein the calcining is performed for at least about two hours at a temperature between 500° C. and 600° C.
18 . The method of any one of claims 10 - 17 , wherein after calcining, the primer layer on the coated substrate has a thickness of about 1 g/L to about 4 g/L.
19 . The method of any one of claims 10 - 17 , wherein after calcining, the primer layer on the coated substrate has a thickness of about 3 g/L.
20 . The method of any one of claims 10 - 19 , further comprising:
e) depositing an additional washcoat layer directly on top of the primer layer.