Gasoline engine with an exhaust system for combusting particulate matter

Abstract

A gasoline engine having an exhaust system comprises means for trapping particulate matter (PM) from the exhaust gas and a catalyst for catalysing the oxidation of the PM by carbon dioxide and/or water in the exhaust gas, which catalyst comprising a supported alkali metal. The invention further includes a method of combusting PM from a gasoline engine in CO 2 and/or H 2 O from the exhaust gas at temperatures in excess of 500° C., which method comprising trapping the PM and contacting it with a catalyst comprising a supported alkali metal.

1 . A system comprising a three-way catalyst (TWC) adapted for simultaneously oxidizing CO and HC and reducing NO x  of an exhaust gas from a gasoline engine, means for trapping particulate matter (PM) of <100 nm from the exhaust gas and a catalyst for catalysing the oxidation of the PM by at least one of carbon dioxide (CO 2 ) and water (H 2 O) in the exhaust gas, which catalyst comprising a supported alkali metal, wherein the supported alkali metal is disposed downstream of the TWC and is disposed relative to the means for trapping in order to effect contact between the supported alkali metal and the particulate matter. 
     
     
         2 . A system according to  claim 1 , wherein the alkali metal is selected from the group consisting of lithium, sodium, potassium, rubidium, caesium and a mixture of any two or more thereof. 
     
     
         3 . A system according to  claim 2 , wherein the alkali metal is the mixture and the mixture is a eutectic mixture. 
     
     
         4 . A system according to  claim 1 , wherein the alkali metal is present in the catalyst at from 1% to 20% by weight of the total catalyst. 
     
     
         5 . A system according to  claim 1 , wherein the support is selected from the group consisting of alumina, ceria, zirconia, titania, a silica-alumina, a zeolite, a mixture thereof and a mixed oxide of any two or more thereof. 
     
     
         6 . A system according to  claim 1 , wherein the support is alumina selected from the group consisting of alpha-alumina, theta-alumina, gamma-alumina and a mixture of any two or more thereof. 
     
     
         7 . A system according to  claim 1 , wherein the alkali metal is potassium and the support is selected from the group consisting of alpha-alumina, zirconia, ceria and a mixture of any two or more thereof. 
     
     
         8 . A system according to  claim 5 , wherein the support comprises the mixed oxide and each component of the mixed oxide is present in an amount of from 10 wt % to 90 wt % by total catalyst weight. 
     
     
         9 . A system according to  claim 8 , wherein the mixed oxide is a binary mixed oxide and the ratio of the cationic components present is in a ratio of from 20:80 to 50:50. 
     
     
         10 . A system according to  claim 1 , wherein the trapping means comprises a filter. 
     
     
         11 . A system according to  claim 10 , wherein the filter comprises a wall-flow filter, a foam or a wire mesh. 
     
     
         12 . A system according to  claim 11 , wherein the filter is the foam and the foam is a metal oxide. 
     
     
         13 . A system according to  claim 1 , wherein the trapping means is coated, at least in part, with the catalyst. 
     
     
         14 . A method of combusting PM of <100 nm comprising contacting an exhaust gas from a gasoline engine with a three-way catalyst adapted for simultaneously oxidizing CO and HC and reducing NO x  of the exhaust gas, trapping the PM and contacting the trapped PM with a catalyst comprising a supported alkali metal, said catalyst adapted to oxidize the PM by at least one of carbon dioxide (CO 2 ) and water (H 2 O) at temperatures in excess of 500° C. 
     
     
         15 . A method according to  claim 14 , wherein the trapping step is by electrophoresis or filtration. 
     
     
         16 . A system according to  claim 1 , wherein the support is a mixed oxide of any two or more selected from the group consisting of alpha-alumina, zirconia and ceria. 
     
     
         17 . A system according to  claim 16 , wherein each component of the mixed oxide is present in an amount of from 10 wt % to 90 wt % by total catalyst weight. 
     
     
         18 . A system according to  claim 12 , wherein the metal oxide is selected from the group consisting of alpha Al 2 O 3 , ZrO 2 /MgO, ZrO 2 /CaO/MgO and ZrO 2 /Al 2 O 3 . 
     
     
         19 . A system according to  claim 1 , wherein the elemental alkali metal is present in the catalyst at from 5% to 15% by weight of the total catalyst. 
     
     
         20 . A method according to  claim 14 , wherein said catalyst is adapted to oxidize the PM at temperatures in excess of 550° C.