NOx reduction using zeolite catalysts

Abstract

A high-surface-area (greater than 600 m 2 /g), large-pore (pore size greater than 6.5 angstroms), basic zeolite having a structure such as an alkali metal cation-exchanged Y-zeolite is employed to convert NO x contained in an oxygen-rich exhaust to N 2 and ON 2 . Preferably, the invention relates to a two-stage method and apparatus for NO x reduction in an oxygen-rich engine exhaust that includes a plasma oxidative stage and a selective reduction stage. The first stage employs a non-thermal plasma treatment of NO x gases in an oxygen-rich exhaust and is intended to convert NO to NO 2 in the presence of O 2 and added hydrocarbons. The second stage employs a lean-NO x catalyst including the basic zeolite at relatively low temperatures to convert such NO 2 to environmentally benign gases that include N 2 , CO 2 , and H 2 O.

We claim:  
     
         1 . An apparatus comprising a catalytic converter, said apparatus comprising: 
 an oxygen rich engine-exhaust gas inlet;    a diesel fuel inlet; and    a reductive stage convert of NO x  connected to receive a mixture of NO x  from the engine-exhaust gas inlet and diesel fuel from the diesel fuel inlet, said convert comprising an alkali metal cation-exchanged faujasite-type zeolite catalyst that further serves to convert NO x  to gases that include N 2 , CO 2 , and H 2 O.    
     
     
         2 . The apparatus of  claim 1  further comprising a plasma converter upstream of said catalyst capable of converting at least a portion of said NO x  to NO 2 .  
     
     
         3 . The apparatus of  claim 1  wherein said zeolite comprises an X-zeolite or Y-zeolite.  
     
     
         4 . The apparatus of  claim 1  wherein said zeolite wherein said zeolite comprises a pore volume above about 0.20 ml/gram.  
     
     
         5 . The apparatus of  claim 1  wherein said zeolite comprises a pore volume above about 0.30 ml/gram.  
     
     
         6 . The apparatus of  claim 1  wherein said zeolite comprises a pore size greater than about 6.5 angstroms.  
     
     
         7 . The apparatus of  claim 1  wherein said zeolite comprises a silicon/aluminum ratio in the range of about 1 to about 3.  
     
     
         8 . The apparatus of  claim 1  wherein said zeolite comprises a silicon/aluminum ratio in the range of about 1 to about 3.  
     
     
         9 . A vehicle with reduced NO x  engine exhaust emissions, comprising: 
 a fuel supply of diesel fuel;    an internal combustion engine operably connected to receive a major portion of said fuel supply of diesel fuel and to propel a vehicle, and having an oxygen-rich exhaust comprising NO x ;    a first reactor operably connected to receive pulsed inletted minor portions of said fuel supply of diesel fuel, said first reactor comprising a catalyst that further comprises an alkali metal cation-exchanged faujasite-type zeolite for NO x  reduction gas treatment and wherein said first reactor is further operably connected to receive said oxygen-rich exhaust comprising NO x , and operably connected to output therefrom a product comprising N 2  that has been converted from said NO x  and noncombusted hydrocarbons from said diesel fuel, and    a second reactor for collection and combustion of said noncombusted hydrocarbons connected to receive said product of the first reactor with said NO x  and connected to receive said noncombusted hydrocarbons, and operably connected to output a second exhaust with reduced NO x  emissions.    
     
     
         10 . The vehicle of  claim 9  wherein said zeolite comprises an X-zeolite or Y-zeolite.  
     
     
         11 . The vehicle of  claim 9  wherein said first reactor is adapted to receive said minor portion of said fuel supply in an amount less than 10% of said fuel supply of a diesel fuel requirement that initially produces said diesel engine exhaust prior to said injecting.  
     
     
         12 . The vehicle of  claim 11  wherein said minor portion of said fuel supply of diesel fuel comprises less than 5% of said fuel supply of diesel fuel.  
     
     
         13 . The vehicle of  claim 9  further comprising a plasma converter upstream of said catalyst capable of converting at least a portion of said NO x  to NO 2 .  
     
     
         14 . The vehicle of  claim 9  wherein said zeolite comprises a pore volume above about 0.20 ml/gram.  
     
     
         15 . The vehicle of  claim 9  wherein said zeolite comprises a pore volume above about 0.30 ml/gram.  
     
     
         16 . The vehicle of  claim 9  wherein said zeolite comprises a pore size greater than about 6.5 angstroms.  
     
     
         17 . The vehicle of  claim 9  wherein said zeolite comprises a silicon/aluminum ratio in the range of about 1 to about 3.  
     
     
         18 . The apparatus of  claim 9  wherein said zeolite comprises a silicon/aluminum ratio in the range of about 1 to about 3.