Pgm-free washcoats for catalyzed diesel particulate filter applications

Abstract

The present invention provides new platinum group metal (“PGM”) free catalytic compositions that comprise silver and/or cobalt stabilized ceria. These compositions facilitate soot oxidation during the regeneration of diesel particulate filters (DPF) thereby replacing PGM formulations. The compositions of the invention are particularly useful as washcoat compositions for DPFs as part of an automotive after-treatment system. Among the formulations tested, the silver-stabilized ceria and cobalt-stabilized ceria formulations e.g. can oxidize soot at 250-300° C. in the presence of NO 2 and oxygen, while silver-stabilized ceria can oxidize diesel soot even in the presence of oxygen as the sole oxidizing agent at these temperatures. A perovshite composition containing Ag—La—Mn was very active at temperatures above 300° C.

1 . A diesel particulate filter comprising: 
 a substrate; and    a washcoat comprising a component selected from the group consisting of silver stabilized ceria, cobalt stabilized ceria, and mixtures thereof.    
   
   
       2 . The diesel particulate filter of  claim 1  wherein the component selected from the group consisting of silver stabilized ceria, cobalt stabilized ceria, and mixtures thereof is stabilized from sintering.  
   
   
       3 . The diesel particulate filter of  claim 1  wherein the silver stabilized ceria comprises silver oxide and ceria which are present in a molar ratio of cobalt oxide to ceria from about 4:1 to about 1:4.  
   
   
       4 . The diesel particulate filter of  claim 1  wherein the cobalt stabilized ceria comprises cobalt oxide and ceria which are present in a molar ratio of cobalt oxide to ceria from about 1.5:1 to about 1:10.  
   
   
       5 . The diesel particulate filter of  claim 1  wherein the washcoat further comprises oxides of rare earth metals.  
   
   
       6 . The diesel particulate filter of  claim 1  wherein the washcoat coating further comprises oxides of La or Pr.  
   
   
       7 . The diesel particulate filter of  claim 1  wherein the silver is partially or completely substituted with Co or the silver is partially substituted with Cu, Cr, Fe and Mn.  
   
   
       8 . The diesel particulate filter of  claim 1  further comprising an oxide base coating between the washcoat coating and the substrate wherein the base coating comprises an oxide of a metal selected from the group consisting of Mn, Ce, Pr, La, Sr, Zr, Sm, Y, Pr, Nd, Cu, Co, Fe, Cr, Ag and mixtures thereof.