Texturized purification structure incorporating an electrochemical catalyst system

Abstract

A structure for the purification of a polluted gas comprising a porous matrix of an inorganic material, in the form of interconnected grains and an electrochemical system for the treatment of said gas, formed by a reduction catalyst A for reducing the polluting species of the NO x type, an oxidation catalyst B for oxidizing the polluting species of the hydrocarbon HC type or CO type, an electron-conductive compound C and an ion-conductive compound D, said structure being characterized in that catalysts A and B are placed in the pores of the inorganic material, in that the grains and possibly the grain boundaries of the inorganic material constituting the matrix are covered over at least part of their surface with a texturizing material, and in that said texturizing material is an ionic, electronic or ionic/electronic conductor and constitutes, respectively, the element C, the element D or the elements C and D of the electrochemical gas treatment system.

1 . A structure for the purification of a polluted gas selected from the group consisting of an exhaust gas of a diesel or gasoline engine, comprising:
 a porous matrix of an inorganic material, in the form of grains that are interconnected so as to provide cavities between them, the open porosity of which is between 20 and 70% and the median diameter of its pore distribution is between 5 and 40 μm; and   an electrochemical system for the treatment of said gas comprising:   a. a reduction catalyst A for reducing a polluting species of the NO x  type,   b. an oxidation catalyst B for oxidizing a polluting species of the hydrocarbon HC type or CO type,   c. an electron-conductive compound C and   d. an ion-conductive compound D,   said catalysts A and B being in electronic contact via compound C and in ionic contact via compound D, wherein:   catalysts A and B are placed in the pores of the inorganic material;   the grains and possibly the grain boundaries of the inorganic material constituting the matrix are covered over at least part of their surface with a texturizing material, said texturizing consisting of irregularities having dimensions between 10 nm and 5 microns; and   said texturizing material is an ionic, electronic or ionic/electronic conductor and constitutes, respectively, the element C, the element D or the elements C and D of the electrochemical gas treatment system.   
   
   
       2 . The structure as claimed in  claim 1 , in which said texturizing consists of irregularities taking the form of beads, crystallites, polycrystalline clusters, rods or acicular structures, hollows or craters, said irregularities having a mean diameter d of between about 10 nm and about 5 microns and a mean height h or a mean depth p of between about 10 nm and about 5 microns. 
   
   
       3 . The structure as claimed in  claim 1 , in which the mean equivalent diameter d and/or the mean height h or the mean depth p of the irregularities are/is smaller than the mean size of the grains of the inorganic material constituting the matrix by a factor of between ½ and 1/1000. 
   
   
       4 . The structure as claimed in  claim 1 , in which the texturizing material covers at least 10% of the total surface of the grains and possibly of the grain boundaries of the inorganic material constituting the porous matrix. 
   
   
       5 . The structure as claimed in  claim 1 , in which the texturizing material is of the same nature as the inorganic material constituting the matrix. 
   
   
       6 . The structure as claimed in  claim 1 , in which the inorganic material constituting the matrix is based on silicon carbide, SiC. 
   
   
       7 . The structure as claimed in  claim 6 , in which the inorganic material is based on SiC doped with aluminum or with nitrogen, and is doped in such a way that its electronic resistivity is less than 20 Ω·cm at 400° C. 
   
   
       8 . The structure as claimed in  claim 1 , in which the irregularities are formed by crystallites or by a cluster of crystallites of a fired or sintered material on the surface of the grains of the porous matrix. 
   
   
       9 . The structure as claimed in  claim 1 , in which the irregularities essentially consist of beads of an electron-conductive and/or ion-conductive material. 
   
   
       10 . The structure as claimed in  claim 1 , in which the irregularities take the form of craters hollowed out in a fired or sintered material on the surface of the grains of the porous matrix. 
   
   
       11 . The structure as claimed in  claim 1  for the purification and filtration of an exhaust gas of a diesel engine, comprising at least one honeycomb monolith, said monolith(s) comprising a plurality of adjacent ducts or channels having mutually parallel axes separated by porous walls, said ducts or channels being closed off by plugs at one or other of their ends in order to define inlet ducts opening onto a gas intake face and outlet ducts opening onto a gas discharge face, in such a way that the gas passes through the porous walls.