Catalytic soot filter and use thereof in treatment of lean exhaust gases

Abstract

The invention provides a process for reducing the amounts of carbon monoxide, hydrocarbons and soot particles in the lean exhaust gas from an internal combustion engine using a particle filter, wherein the soot particles have a soot ignition temperature T Z and the particle filter is regenerated from time to time by raising the temperature of the particle filter to above the soot ignition temperature and burning the soot particles, wherein the temperature of the filter is increased to the temperature required to initiate soot ignition by burning additional fuel on the catalytic coating when the exhaust gas back pressure reaches a predetermined value. The process is characterised in that the particle filter is provided with a catalytic coating comprising a first group of components for reducing the ignition temperature of soot, said first group of components contains at least one oxygen storage component and at least one platinum group metal selected from the group consisting of platinum, palladium and rhodium. In a preferred embodiment of the process the catalytic coating further comprises a second group of components for oxidising carbon monoxide and hydrocarbons, said second group of components comprises at least a support material selected from the group consisting of aluminium oxide, silicon oxide, titanium oxide, zirconium oxide and zeolite and at least one platinum group metal selected from the group consisting of platinum, palladium and rhodium deposited on said support materials.

1 . A process for reducing the amounts of carbon monoxide, hydrocarbons and soot particles in the lean exhaust gas from an internal combustion engine using a particle filter, wherein the soot particles have a soot ignition temperature T Z  and the particle filter is regenerated from time to time by raising the temperature of the particle filter to above the soot ignition temperature and burning the soot particles, wherein the temperature of the filter is increased to the temperature required to initiate soot ignition by burning additional fuel on the catalytic coating when the exhaust gas back pressure reaches a predetermined value, 
 characterised in that 
 the particle filter is provided with a catalytic coating comprising a first group of components for reducing the ignition temperature of soot, said first group of components contains at least one oxygen storage component and at least one platinum group metal selected from the group consisting of platinum, palladium and rhodium.  
   
     
     
         2 . A process according to  claim 1 , 
 characterised in that 
 the at least one oxygen storage component is selected from the group consisting of cerium oxide, cerium/zirconium mixed oxide, manganese oxide, iron oxide, copper oxide, zinc oxide, lanthanum oxide, bismuth oxide, niobium oxide and tantalum oxide.  
   
     
     
         3 . A process according to  claim 2 , 
 characterised in that 
 the first group of components further comprises a compound of an alkaline earth metal selected from the group consisting of magnesium, calcium, barium, strontium or mixtures thereof  
   
     
     
         4 . A process according to  claim 3 , 
 characterised in that, 
 the first group of components comprises platinum, cerium oxide, manganese oxide and calcium oxide.  
   
     
     
         5 . A process according to  claim 4 , 
 characterised in that, 
 the catalytic coating further comprises a second group of components for oxidising carbon monoxide and hydrocarbons, said second group of components comprises at least a support material selected from the group consisting of aluminium oxide, silicon oxide, titanium oxide, zirconium oxide and zeolite and at least one platinum group metal selected from the group consisting of platinum, palladium and rhodium deposited on said support materials.  
   
     
     
         6 . A process according to  claim 5 , 
 characterised in that, 
 the particle filter comprises a wall flow filter ( 1 ) having inflow ( 2 ) and outflow ( 3 ) flow channels for the exhaust gases separated from each other by porous channel walls ( 5 ).  
   
     
     
         7 . A process according to  claim 6 , 
 characterised in that, 
 the catalytic coating comprises two layers one upon the other wherein the first layer is coated directly on or into the channel walls of the inflow channels of the particle filter and comprises the second group of components and the second layer lies on said first layer and comprises the first group of components.  
   
     
     
         8 . A process according to  claim 7 , 
 characterised in that, 
 the catalytic coating comprises two layers wherein the first layer is coated on or into the channel walls of the inflow channels and comprises the first group of components and the second layer is coated on the channel walls of the outflow channels and comprises the second group of components.  
   
     
     
         9 . A process according to  claim 5 , 
 characterised in that, 
 the concentration of the first group of components lies between 20 and 150 g/l of the particle filter and the concentration of the second group of components lies between 40 and 150 g/l of the particle filter.  
   
     
     
         10 . A process according to  claim 9 , 
 characterised in that, 
 the concentration of the platinum group metals of the first and second group of components lies within the range between 0.5 and 10 g/l of particle filter.  
   
     
     
         11 . A process according to  claim 1 , 
 characterised in that, 
 the material of the particle filter is selected from the group consisting of silicon carbide, silicon nitride, cordierite or sodium zirconium phosphate.  
   
     
     
         12 . A process according to  claim 1 , 
 characterised in that 
 the additional fuel required to heat the particle filter is added to the exhaust gas stream upstream of the particle filter.  
   
     
     
         13 . A process according to  claim 1 , 
 characterised in that 
 the additional fuel required to heat the particle filter is injected into the cylinders of the internal combustion engine during the expansion phase.  
   
     
     
         14 . A process according to  claim 13 , 
 characterised in that 
 an oxidation catalyst is located upstream of the particle filter, in a position close to the engine, this being of such a size that it converts only a small proportion of the additional fuel injected.  
   
     
     
         15 . A particle filter for use in the process according to one of the preceding claims selected from the group consisting of a wall flow filter, a wire mesh filter and an open pore ceramic or metallic foam filter, 
 characterised in that 
 the particle filter is provided with a catalytic coating comprising a first group of components for reducing the ignition temperature of soot, said first group of components contains at least one oxygen storage component and at least one platinum group metal selected from the group consisting of platinum, palladium and rhodium.  
   
     
     
         16 . The particle filter according to  claim 15 , 
 characterised in that 
 the at least one oxygen storage component is selected from the group consisting of cerium oxide, cerium/zirconiumn mixed oxide, manganese oxide, iron oxide, copper oxide, zinc oxide, lanthanum oxide, bismuth oxide, niobium oxide and tantalum oxide.  
   
     
     
         17 . The particle filter according to  claim 16 , 
 characterised in that 
 the first group of components further comprises a compound of an alkaline earth metal selected from the group consisting of magnesium, calcium, barium, strontium or mixtures thereof.  
   
     
     
         18 . The particle filter according to  claim 17 , 
 characterised in that, 
 the first group of components comprises platinum, cerium oxide, manganese oxide and calcium oxide.  
   
     
     
         19 . The particle filter according to  claim 18 , 
 characterised in that, 
 the catalytic coating further comprises a second group of components for oxidising carbon monoxide and hydrocarbons, said second group of components comprises at least a support material selected from the group consisting of aluminium oxide, silicon oxide, titanium oxide, zirconium oxide and zeolite and at least one platinum group metal selected from the group consisting of platinum, palladium and rhodium deposited on said support materials.  
   
     
     
         20 . The particle filter of  claim 19 , 
 characterised in that,    the particle filter comprises a wall flow filter ( 1 ) having inflow ( 2 ) and outflow ( 3 ) flow channels for the exhaust gases separated from each other by porous channel walls ( 5 ).    
     
     
         21 . The particle filter of  claim 20 , 
 characterised in that, 
 the catalytic coating comprises two layers one upon the other wherein the first layer lies directly on the channel walls of the inflow channels of the particle filter and comprises the second group of components and the second layer lies on said first layer and comprises the first group of components.  
   
     
     
         22 . The particle filter of  claim 20 , 
 characterised in that, 
 the catalytic coating comprises two layers wherein the first layer is coated on the channel walls of the inflow channels and comprises the first group of components and the second layer is coated on the channel walls of the outflow channels and comprises the second group of components.  
   
     
     
         23 . The particle filter of  claim 19 , 
 characterised in that, 
 the concentration of the first group of components lies between 20 and 150 g/l of the particle filter and the concentration of the second group of components lies between 40 and 150 g/l of the particle filter.  
   
     
     
         24 . The particle filter of  claim 23 , 
 characterised in that, 
 the concentration of the platinum group metals of the first and second group of components lies within the range between 0.5 and 10 g/l of particle filter.  
   
     
     
         25 . The particle filter of  claim 15 , 
 characterised in that, 
 the material of the particle filter is selected from the group consisting of silicon carbide, cordierite or sodium zirconium phosphate.