Process for reducing diesel enigne emissions

Abstract

The present invention discloses a system and a process for removing diesel engine emissions. The system comprises two honeycomb-type oxidation catalysts and a catalyzed flow-through filter configured such that the filter sandwiched between the honeycombs. The system is effective for the continuous removal of carbon monoxide and hydrocarbon particulate matter, and has high efficiency and low pressure drop.

1 . An exhaust cleaning system for treating diesel exhaust, said system comprising; 
 (a) at least a first and a second catalyst, each comprising a honeycomb substrate washcoated with a support material and treated with a metal known in the art to facilitate total particulate matter oxidation; and    (b) a catalyzed flow-through filter;    wherein said exhaust cleaning system is mounted between an engine cylinder exhaust manifold and an exhaust pipe, and said diesel exhaust can pass through the exhaust manifold, and then into said cleaning system where the exhaust first contacts said first honeycomb catalyst, and then contacts said filter, and then contacts said second honeycomb catalyst, and then exits said cleaning system and enters said exhaust pipe.    
     
     
         2 . The exhaust cleaning system of  claim 1  wherein said honeycomb substrate is ceramic or metallic.  
     
     
         3 . The exhaust cleaning system of  claim 1  wherein said honeycomb substrate is selected from the group consisting of ceramic, cordierite, mullite, silicon carbide, alumina, titania, zirconia, silica, alumina-silica, alumina-zirconia, stainless steel, Fe—Cr—Al alloy, other materials typically used for diesel oxidation catalysts, and combinations thereof.  
     
     
         4 . The exhaust cleaning system of  claim 1  wherein said honeycomb substrate is washcoated with a high surface area support.  
     
     
         5 . The exhaust cleaning system of  claim 4  wherein said high surface area support is selected from the group consisting of alumina, silica, titania, zirconia, alumina-silica, zeolites, and combinations thereof.  
     
     
         6 . The exhaust cleaning system of  claim 1  wherein said metal catalyst is selected from the group consisting of an alkaline metal, an alkaline earth metal, vanadium, a precious metal, platinum, palladium, rhodium and combinations thereof.  
     
     
         7 . The exhaust cleaning system of  claim 1  wherein said first and said second honeycomb-type oxidation catalysts have essentially the same compositions.  
     
     
         8 . The exhaust cleaning system of  claim 1  wherein said first and said second honeycomb-type oxidation catalysts have different compositions.  
     
     
         9 . The exhaust cleaning system of  claim 1  wherein said filter is a particulate filter with a foam, wire-mesh, or other non-wall-flow type structure.  
     
     
         10 . The exhaust cleaning system of  claim 1  wherein said filter is made of a material selected from the group consisting of ceramic, alumina, tiatania, zirconia, cordierite, mullite, silicon carbide, stainless steel, iron chromium alloy, and combinations thereof.  
     
     
         11 . The exhaust cleaning system of  claim 1  wherein said filter comprises a high surface area support and a catalyst.  
     
     
         12 . The filter of  claim 11  wherein said high surface area support is selected from the group consisting of alumina, titania, zirconia, zeolite, and combinations thereof.  
     
     
         13 . The filter of  claim 11  wherein said catalyst is selected from the group consisting of precious metals, base metals, vanadium-comprising complexes, alkaline metals, alkaline earth metals, alkaline vanadates, MoO 3 —V 2 O 5 , platinum, palladium, rhodium and combinations thereof.  
     
     
         14 . The exhaust cleaning system of  claim 1  further comprising a catalyst housing having an exhaust manifold end and an exhaust pipe end, said honeycomb catalysts and said filters being contained within said housing such that said first honeycomb catalyst is positioned near said exhaust manifold end, and said second honeycomb catalyst is positioned near said exhaust pipe end, and said filter is positioned between the first and second honeycomb catalysts.  
     
     
         15 . The exhaust cleaning system of  claim 1  wherein said first honeycomb catalyst, said filter, and said second honeycomb catalyst are each contained within a housing and are arranged such that the housing containing said first honeycomb catalyst is connected via piping to an exhaust manifold, and the housing containing said second honeycomb catalyst is connected via piping to an exhaust pipe, and the housing containing said filter is positioned between the first and second honeycomb catalysts so as to receive exhaust from said first catalyst and send exhaust to said second catalyst.  
     
     
         16 . An exhaust cleaning system for treating diesel exhaust, said system comprising; 
 (a) at least a first and a second catalyst, each comprising a honeycomb substrate washcoated with a support material and treated with a metal known in the art to facilitate total particulate matter oxidation; and    (b) a catalyzed flow-through filter;    wherein said exhaust cleaning system is mounted between an engine cylinder exhaust manifold and an exhaust pipe, and said diesel exhaust can pass through the exhaust manifold, and then into said cleaning system where the exhaust first contacts said first honeycomb catalyst, and then contacts said filter, and then contacts said second honeycomb catalyst, and then exits said cleaning system and enters said exhaust pipe.    
     
     
         17 . The exhaust cleaning system of  claim 16  wherein said honeycomb substrate is selected from the group consisting of ceramic, cordierite, mullite, silicon carbide, alumina, titania, zirconia, silica, alumina-silica, alumina-zirconia, stainless steel, Fe—Cr—Al alloy, other materials typically used for diesel oxidation catalysts, and combinations thereof; and wherein said honeycomb substrate is washcoated with a high surface area support selected from the group consisting of alumina, silica, titania, zirconia, alumina-silica, zeolites, and combinations thereof; and wherein said metal catalyst is selected from the group consisting of an alkaline metal, an alkaline earth metal, vanadium, a precious metal, platinum, palladium, rhodium and combinations thereof.  
     
     
         18 . The exhaust cleaning system of  claim 16  wherein said filter is a particulate filter with a foam, wire-mesh, or other non-wall-flow type structure made of a material selected from the group consisting of ceramic, alumina, tiatania, zirconia, cordierite, mullite, silicon carbide, stainless steel, iron chromium alloy, and combinations thereof; said filter further comprising a high surface area support selected from the group consisting of alumina, titania, zirconia, zeolite, and combinations thereof, and a catalyst selected from the group consisting of precious metals, base metals, vanadium-comprising complexes, alkaline metals, alkaline earth metals, alkaline vanadates, MoO 3 —V 2 O 5 , platinum, palladium, rhodium and combinations thereof.  
     
     
         19 . A process of treating diesel exhaust comprising passing said exhaust through an exhaust manifold, and then into an exhaust cleaning system where said exhaust first contacts a first honeycomb catalyst and then contacts a filter and then contacts a second honeycomb catalyst, and then said exhaust exits through an exhaust pipe.  
     
     
         20 . The process of  claim 19  wherein said first honeycomb catalyst comprises a honeycomb substrate washcoated with a support material and treated with a metal known in the art to facilitate total particulate matter oxidation, and said filter comprises a particulate filter having a high surface area support and a catalyst, and said second honeycomb catalyst comprises a honeycomb substrate washcoated with a support material and treated with a metal known in the art to facilitate total particulate matter oxidation.