METHOD OF FORMING AN INORGANIC OXIDE COATING ON A MONOLITH ARTICLE
A method of forming an inorganic oxide coating on a monolith article is disclosed. The coated monolith article is suitable for the treatment of an exhaust gas. The method comprises spraying, as a dry particulate aerosol, inorganic particles comprising an aluminosilicate zeolite having a SAR of greater than 100:1 and a silicone resin to form a coating layer. The present invention also provides an uncalcined porous monolith article for use in forming a monolith article for the treatment of an exhaust gas. The uncalcined monolith article comprises a dry particulate composition comprising inorganic particles and a silicone resin.
1 . A method of forming an inorganic oxide coating on a monolith article for the treatment of an exhaust gas, the method comprising:
providing a porous monolith article comprising a plurality of channels for the passage of an exhaust gas, each channel having a gas-contacting surface;
spraying onto the gas-contacting surface, as a dry particulate aerosol, inorganic particles comprising an aluminosilicate zeolite having a silica-to-alumina molar ratio (SAR) of greater than 100:1 and a silicone resin to form a coating layer; and
calcining the coating layer to provide a coated monolith article.
2 . The method according to claim 1 , wherein the aluminosilicate zeolite having a SAR of greater than 200:1, preferably greater than 300:1, more preferably greater than 400:1.
3 . The method according to claim 1 , wherein the aluminosilicate zeolite is selected from the group consisting of AEI, BEA, CHA, and MFI.
4 . The method according to claim 1 , wherein the monolith article is a monolith filter.
5 . The method according to claim 1 , wherein either:
(i) the inorganic particles are sprayed onto the gas-contacting surface as a first dry particulate aerosol to form an inorganic particle layer and the silicone resin is then sprayed onto the inorganic particle layer as a second dry particulate aerosol to form the coating layer; or
(ii) a mixture of the inorganic particles and silicone resin is sprayed onto the gas-contacting surface as a dry particulate aerosol to form the coating layer.
6 . The method according to claim 1 , wherein the silicone resin has a molecular weight of greater than 1,000, preferably greater than 2,000, preferably greater than 5,000, preferably greater than 10,000, and/or a molecular weight of less than 500,000, preferably less than 200,000.
7 . The method according to claim 1 , wherein the silicone resin has a glass transition temperature (Tg) of greater than 30° C., preferably greater than 35° C., and/or less than 100° C., preferably less than 80° C.
8 . The method according to claim 1 , wherein the silicone resin has the formula [R x SiX y O z ] n , wherein R is an alkyl or aryl, X is a functional group bonded to silicon, and wherein z is more than 1 and less than 2.
9 . The method according to claim 1 , wherein the silicone resin has a degree of crosslinking of greater than 55% and less than 80%.
10 . The method according to claim 1 , wherein the silicon dioxide content of the silicone resin is greater than 50 wt %, preferably greater than 60 wt %, preferably greater than 70 wt %, preferably greater than 80 wt %.
11 . The method according to claim 1 , wherein the inorganic particles have a d 50 by volume of greater than 0.2 μm and less than 50 μm.
12 . The method according to claim 1 , wherein calcining comprises heating to a temperature of at least 400° C. and at most 600° C.
13 . An uncalcined porous monolith article for use in forming a monolith article for the treatment of an exhaust gas, the uncalcined porous monolith article comprising a plurality of channels and comprising a dry particulate composition comprising inorganic particles comprising an aluminosilicate zeolite having a SAR of greater than 100:1 and a silicone resin, the dry particulate composition being located within the channels and/or pores of said uncalcined porous monolith.
14 . The uncalcined porous monolith article according to claim 13 , wherein the mass loading of the dry particulate composition is less than 50 g/L.
15 . An uncalcined porous monolith article for use in forming a monolith article for the treatment of an exhaust gas, the monolith article obtainable by a method comprising:
providing a porous monolith article comprising a plurality of channels for the passage of an exhaust gas, each channel having a gas-contacting surface;
spraying onto the gas-contacting surface, as a dry particulate aerosol, inorganic particles comprising an aluminosilicate zeolite having a SAR of greater than 100:1 and a silicone resin to form a coating layer.
16 . A coated monolith article for the treatment of an exhaust gas obtainable by the method of any of claim 1 .
17 . A vehicular exhaust system comprising the coated monolith article according to claim 16 .