Continuous diesel soot control with minimal back pressure penatly using conventional flow substrates and active direct soot oxidation catalyst disposed thereon

Abstract

There is disclosed high cell density or tortuous/turbulent flow through monolithic catalyst devices for the direct catalytic, and (semi) continuous oxidation of diesel particulate matter. The catalysts relate to OIC/OS materials having a stable cubic crystal structure, and most especially to promoted OIC/OS wherein the promotion is achieved by the post-synthetic introduction of non-precious metals via a basic (alkaline) exchange process. The catalyst may additionally be promoted by the introduction of Precious Group Metals.

1 . A catalyst system for the direct catalytic oxidation of particulate matter in the off-gas of an internal combustion engine wherein the system comprises a standard flow through monolith device, upon which is coated an active oxidation catalyst formulation for the direct, low temperature oxidation of aforementioned particulate matter, with the active catalyst containing an active redox oxide disposed therein. 
     
     
         2 . The catalyst system of  claim 1 , wherein the monolith is a flow through monolith with >900 cells per square inch. 
     
     
         3 . The catalyst system of  claim 1 , wherein the monolith is a flow through monolith with >600 cells per square inch. 
     
     
         4 . The catalyst system of  claim 1 , wherein the monolith is a flow through monolith with >400 cells per square inch. 
     
     
         5 . The catalyst system of  claim 1 , wherein the monolith is a metal monolith capable of introducing turbulent flow in the exhaust stream. 
     
     
         6 . The catalyst system of  claim 1 , wherein the monolith is a metal or ceramic foam presenting a flow path of highly tortuous nature. 
     
     
         7 . The catalyst system of  claim 1 , wherein the catalyst system is a refractory oxide. 
     
     
         8 . The catalyst system of  claim 1 , wherein the catalyst system contains cerium. 
     
     
         9 . The catalyst system of  claim 1 , wherein the oxide is a cerium oxide in the form of a solid solution of cerium and zirconium oxide (Ce—Zr oxide). 
     
     
         10 . The redox active oxide of  claim 1 , wherein the oxide is a cerium oxide in the from of a Ce—Zr oxide solid solution that is substantially phase pure cubic fluorite solid solution (as determined by conventional XRD method) with oxygen ion conducting properties and comprises
 a. up to about 95% zirconium   b. up to about 95% cerium   c. up to about 20% of a stabiliser selected from the group consisting of rare earths, yttrium and mixtures thereof.   
     
     
         11 . The catalyst system of  claim 1 , wherein the catalyst system is a substantially phase pure cubic fluorite solid solution additionally modified by the introduction of one or more base metal dopant species selected from the group consisting of a transition metal, an alkali metal, an alkaline earth metal and a group IIIb metal. 
     
     
         12 . The catalyst system of  claim 11 , wherein the redox oxide is a base metal doped cerium containing cubic fluorite solid solution produced by contacting redox active material with a precursor solution of dissolved cations under conditions of high ph/low hydronium ion (H 3 O + )/low proton (H + ) content. 
     
     
         13 . The catalyst system of  claim 12 , wherein the base metal is introduced into the redox active oxide by means of an ammonium hydroxide/ammoniacal complex of the metal cation. 
     
     
         14 . The catalyst system of  claim 12 , wherein the base metal is introduced into the redox oxide by means of an organic amine complex of the metal cation. 
     
     
         15 . The catalyst system of  claim 12 , wherein the base metal is introduced into the redox oxide by means of a hydroxide compound of the metal cation. 
     
     
         16 . The catalyst system of  claim 12 , wherein the concentration of metal species introduced is about 0.01 weight % to about 10 weight %. 
     
     
         17 . The catalyst system of  claim 16 , wherein the concentration of metal species introduced is most preferably 0.1 wt % to about 2.5 wt % 
     
     
         18 . The catalyst system of  claim 12 , wherein the base metal doped solid solution contains metal at high levels of dispersion such that phase analysis by conventional XRD methods retains a substantially phase pure cubic fluorite phase (>95%), with bulk metal oxide dopant phase being recorded at <5% and dopant metal oxide particle size, as determined by line-broadening/Scherrer equation method, is about 30 A to about 100 A. 
     
     
         19 . The catalyst system of  claim 12 , wherein the base metal doped solid solution contains metal at high levels of dispersion such that phase analysis by XRD reveals the promoted material maintains at least 95% cubic fluorite phase after hydrothermal oxidising aging at 1100° C. 
     
     
         20 . The catalyst system of  claim 12 , wherein the base metal doped solid solution contains metal at high levels of dispersion such that phase analysis by XRD reveals the promoted material maintains at least 99% cubic fluorite phase after hydrothermal oxidizing aging at 1100° C. 
     
     
         21 . A device for the direct catalytic oxidation of soot comprising the catalyst system of  claim 1 , and a housing wherein the temperature of required for soot oxidation is about 100 to about 650° C. 
     
     
         22 . A device for the direct catalytic oxidation of soot comprising the catalyst system of  claim 1 , and a housing wherein the temperature of required for soot oxidation is about 200 to about 400° C. 
     
     
         23 . A device for the direct catalytic oxidation of soot comprising the catalyst system of  claim 1 , and a housing wherein continuous soot oxidation occurs for temperatures of about 100 to about 650° C. 
     
     
         24 . A catalytic system for the direct catalytic oxidation of soot according to  claim 1 , wherein the catalyst system is free of a platinum group metal. 
     
     
         25 . The catalyst system for the direct catalytic oxidation of soot according to  claim 1 , further comprising a platinum group metal. 
     
     
         26 . The catalyst system for the direct catalytic oxidation of soot according to  claim 25 , wherein the platinum group metal is selected from the group consisting of platinum, palladium, rhodium and mixtures thereof. 
     
     
         27 . The catalyst system for the direct catalytic oxidation of soot according to  claim 25 , further comprising a catalytically active washcoat disposed upon the monolith as a single layer washcoat which additionally contains Al 2 O 3 , modified Al 2 O 3 , SiO 2 , ZrO 2 , or combinations thereof or other suitable refractory oxide as an additional support or binding agent. 
     
     
         28 . The catalyst system for the direct catalytic oxidation of soot according to  claim 25 , further comprising a catalytically active washcoat disposed upon the monolith in two or more layers with a first layer containing substantially Al 2 O 3 , modified Al 2 O 3 , SiO 2 , ZrO 2 , combinations thereof or other suitable refractory oxide as a support or binding agent and a second layer comprising the active oxidation catalyst formulation, including a base metal doped mixed oxide. 
     
     
         29 . A method of treating exhaust gas comprising passing an exhaust gas over the catalyst system of  claim 1 .