Titania-coated honeycomb catalyst matrix for UV-photocatalytic oxidation of organic pollutants, and process for making

Abstract

A titania-coated honeycomb catalyst matrix is provided for the ultraviolet-photocatalytic oxidation of organic pollutants in a flowing fluid. A honeycomb-shaped skeletal structure ( 12 ) has a thin, lightweight substrate ( 18 ) of metal or ceramic, typically an aluminum alloy, and a surface coating ( 20 ) of photocatalyst, such as titania. The photocatalyst ( 20 ) is bonded to the substrate ( 18 ) via a thin oxide layer ( 18 ′) on the substrate. The oxide layer ( 18 ′) may be grown on the substrate. The photocatalyst coating ( 20 ) is made by mixing ( 30 ) titania powder in a TiO 2 sol-gel to form a titania slurry. The substrate with oxide layer is coated ( 30 ) with the titania slurry and then heat treated ( 31 ). The photocatalyst coating ( 20 ) is typically applied to substrate sheets ( 40, 60, 62 ) preformed for assembly into a honeycomb-shaped skeletal structure ( 12 ) having an array of parallel cells ( 46, 46 ′). The coated sheets ( 40 ) may have troughs ( 42 ) and crests ( 42 ), and be stacked ( 34 ) with intermediate parting sheets ( 48 ). Alternatively, the coated sheets ( 60, 62 ) may be notched ( 64 ) and interfitted in “eggcrate” fashion. The honeycomb-shaped structure ( 12 ) is housed in a frame ( 50 ), and one or more stabilizer members ( 52 ) fastened to the frame serve to limit displacement of the structure as may be caused by the flowing fluid ( 14 ).

What is claimed is:  
     
         1 . A honeycomb photocatalyst matrix for purifying fluid flowing therethrough, comprising: 
 a) a honeycomb-shaped skeletal structure ( 12 ) of material selected from the group consisting of metal and ceramic, said honeycomb structure comprising an array of multiple, substantially parallel, cells ( 46 ,  46 ′) open at opposite ends for fluid flow ( 14 ) therethrough and illumination therewithin, and having respective cell surfaces; and    b) a coating ( 20 ) of photocatalyst on the surfaces of the cells of the honeycomb structure, whereby the coated surfaces ( 20 ) of the cells are activated by ultraviolet illumination ( 16 ) to promote photocatalytic chemical reaction of contaminants contained in a fluid flowing ( 14 ) through the cells.    
     
     
         2 . The honeycomb photocatalyst matrix of  claim 1  wherein the honeycomb-shaped skeletal structure ( 12 ) comprises a plurality of sheets ( 40 ) of lightweight metal, each of said sheets being formed to provide an alternating series of crests ( 44 ) and troughs ( 42 ), said sheets being oriented in stacked arrangement with one another such that said crests and troughs define the respective said cells ( 46 ,  46 ′).  
     
     
         3 . The honeycomb photocatalyst matrix of  claim 2  wherein the honeycomb-shaped skeletal structure ( 12 ) further includes a plurality of planar sheets ( 48 ) of lightweight metal, respective ones of said planar sheets of lightweight metal being interposed between respective adjacent pairs of said stacked sheets ( 40 ) having said crests ( 44 ) and troughs ( 42 ), whereby said planar sheets comprise parting sheets between said sheets having crests and troughs and form a respective surface of said cells, and wherein said sheets having said troughs and crests and said parting sheets are of aluminum.  
     
     
         4 . The honeycomb photocatalyst matrix of  claim 1  wherein the honeycomb-shaped skeletal structure ( 12 ) comprises an array of substantially planar metal sheets ( 60 ,  62 ), with a portion of said sheets ( 60 ) being oriented orthogonally to and interfitted with, the remainder of said sheets ( 62 ) in substantially “eggcrate” fashion to define said cells.  
     
     
         5 . The honeycomb photocatalyst matrix of  claim 1  wherein the honeycomb-shaped skeletal structure ( 12 ) includes an outer perimeter, and further comprising a frame ( 50 ) formed about the outer perimeter of the honeycomb-shaped skeletal structure to maintain the stability thereof transverse to the direction of fluid flow through the cells.  
     
     
         6 . The honeycomb photocatalyst matrix of  claim 5  wherein the frame ( 50 ) and the honeycomb-shaped skeletal structure ( 12 ) are assembled and fastened with means having neither adhesives nor organic materials, thereby eliminating a source of volatile organic compounds (VOCs).  
     
     
         7 . The honeycomb photocatalyst matrix of  claim 5  further including at least one stabilizer member ( 52 ) that is fastened to the frame ( 50 ) and positioned to resist displacement of the honeycomb-shaped skeletal structure ( 12 ) relative to the frame in the direction of fluid flow therethrough.  
     
     
         8 . The honeycomb photocatalyst matrix of  claim 7  comprising at least two stabilizer members ( 52 ), and wherein the stabilizer members are positioned adjacent the opposite ends of the cells to also resist displacement of the honeycomb-shaped skeletal structure ( 12 ) relative to the frame in a direction opposite to the direction of fluid flow therethrough.  
     
     
         9 . The honeycomb photocatalyst matrix of  claim 7  wherein a plurality of stabilizer members ( 52 ) extend through the honeycomb-shaped skeletal structure ( 12 ) transverse to the direction of fluid flow ( 14 ) therethrough.  
     
     
         10 . The honeycomb photocatalyst matrix of  claim 3  wherein said crests ( 44 ) and troughs ( 42 ) in the respective said sheets are substantially rectilinear.  
     
     
         11 . The honeycomb photocatalyst matrix of  claim 10  wherein the thickness of the aluminum forming the honeycomb-shaped skeletal structure is about 0.002 inch.  
     
     
         12 . The honeycomb photocatalyst matrix of  claim 11  wherein the honeycomb-shaped skeletal structure ( 12 ) is about one inch thick in the direction of fluid flow ( 14 ) therethrough, and the cells have an equivalent diameter transverse to the fluid flow of about 0.125 inch.  
     
     
         13 . The honeycomb photocatalyst matrix of  claim 10  wherein the surfaces of the respective cells have an oxide layer ( 18 ′) thereon and the photocatalyst coating ( 20 ) is formed on said oxide layer, to thereby enhance adhesion between the photocatalyst and the skeletal structure.  
     
     
         14 . The honeycomb photocatalyst matrix of  claim 1  wherein the surfaces of the respective cells have an oxide layer ( 18 ′) thereon and the photocatalyst coating ( 20 ) is formed on said oxide layer, to thereby enhance adhesion between the photocatalyst and the skeletal structure.  
     
     
         15 . The honeycomb photocatalyst matrix of  claim 2  wherein said sheets ( 40 ) formed to provide the alternating series of crests ( 44 ) and troughs ( 42 ) include said coating of photocatalyst ( 20 ) thereon prior to said sheets ( 40 ) being oriented in said stacked arrangement.  
     
     
         16 . The honeycomb photocatalyst matrix of  claim 3  wherein said sheets ( 40 ) formed to provide the alternating series of crests ( 44 ) and troughs ( 42 ) and said planar parting sheets ( 48 ) include said coating of photocatalyst ( 20 ) thereon prior to said sheets ( 40 ,  48 ) being oriented in said stacked arrangement.  
     
     
         17 . The honeycomb photocatalyst matrix of  claim 4  wherein said metal sheets ( 60 ,  62 ) include said coating of photocatalyst ( 20 ) thereon prior to said sheets being interfitted in substantially “eggcrate” fashion to define said cells.