Catalyst design for selective-catalytic-reduction (scr) filters

Abstract

Provided is an improved selective catalytic reduction filtering (SCRF) device that separates reduction of nitrogen oxides (NOx) from oxidation of soot, hydro-carbon (HC) and carbon monoxide (CO). The SCRF device has a diesel oxidation catalyst unit for oxidizing HC and CO and oxidizing diesel fuel to support DPF regenerations, and a SCR filtering unit, including at least one inlet channel and being connected to the diesel oxidation catalyst unit, for controlling (soot) emission, cleaning-up slipped HC and CO during a DPF regeneration, and reducing nitrogen oxides in the diesel exhaust gas. At least one inlet channel is coated with an ammonia-neutral oxidation catalyst, and at least one outlet channel is coated with a selected catalytic reduction catalyst.

What is claimed is: 
     
         1 . An exhaust gas treatment apparatus comprising:
 a diesel oxidation catalyst unit for receiving exhaust gas; and   a selective catalyst reduction filtering unit, having at least one inlet channel and being connected to the diesel oxidation catalyst unit, for oxidizing hydrocarbon and carbon monoxide, reducing nitrogen oxide, and controlling particulate matters emission in the exhaust gas,   wherein the at least one inlet channel is coated with an ammonia-neutral oxidation catalyst.   
     
     
         2 . The exhaust gas treatment apparatus of  claim 1 , further comprising at least one outlet channel coated with a selective catalytic reduction catalyst. 
     
     
         3 . The exhaust gas treatment apparatus of  claim 2 , wherein the selective catalytic reduction catalyst includes a zeolilte-based catalyst. 
     
     
         4 . The exhaust gas treatment apparatus of  claim 1 , further comprising a selective catalytic reduction catalyst connected to the selective catalyst reduction filtering unit, for reducing the nitrogen oxides. 
     
     
         5 . The exhaust gas treatment apparatus of  claim 4 , wherein the selective catalyst reduction unit is coated with a zeolilte-based catalyst. 
     
     
         6 . The exhaust gas treatment apparatus of  claim 1 , further comprising a diesel exhaust fluid injector for injecting a urea solution into the exhaust gas. 
     
     
         7 . The exhaust gas treatment apparatus of  claim 6 , wherein the diesel exhaust fluid injector is located between the diesel oxidation catalyst unit and the selective catalyst reduction filtering unit. 
     
     
         8 . A selective catalytic reduction filter comprising:
 at least one inlet channel for receiving exhaust gas; and   at least one outlet channel connected to the at least one inlet channel,   wherein the at least one inlet channel is coated with an ammonia-neutral oxidation catalyst.   
     
     
         9 . The selective catalytic reduction filter of  claim 8 , wherein the at least one outlet channel is coated with a selective catalyst reduction catalyst. 
     
     
         10 . The selective catalytic reduction filter of  claim 9 , wherein the selective catalytic reduction filter is coated with a zeolilte-based catalyst. 
     
     
         11 . The selective catalytic reduction filter of  claim 8 , wherein, when the selective catalytic reduction filter is in operation, nitrogen oxides in the exhaust gas pass through the at least one inlet channel substantially unaffected by the ammonia-neutral oxidation catalyst. 
     
     
         12 . The selective catalytic reduction filter of  claim 9 , wherein, when the selective catalytic reduction filter is in operation, the exhaust gas is mixed with ammonia and nitrogen oxides in the exhaust gas is reduced when nitrogen oxides react with ammonia when the exhaust gas passes through the at least one outlet channel coated with the SCR catalyst. 
     
     
         13 . The selective catalytic reduction filter of  claim 8 , wherein the exhaust gas is from a diesel engine. 
     
     
         14 . The selective catalytic reduction filter of  claim 8 , wherein the exhaust gas is from a lean-burn gasoline engine. 
     
     
         15 . A method for reducing nitrogen oxides from an exhaust gas, comprising:
 feeding an exhaust gas with ammonia into a selective catalytic reduction filtering device comprising at least one inlet channel coated with an ammonia-neutral oxidation catalyst and at least one outlet channel coated with a selective catalytic reduction catalyst;   passing the ammonia through the at least one inlet channel to the at least one outlet channel; and   reducing, in the at least one outlet channel, nitrogen oxides in the exhaust gas.   
     
     
         16 . The method of  claim 15 , further comprising injecting a urea solution into the exhaust gas to produce the ammonia. 
     
     
         17 . The method of  claim 15 , further comprising oxidizing, in the at least one inlet channel, hydro-carbon and carbon-monoxide in the exhaust gas. 
     
     
         18 . The method of  claim 15 , wherein reducing the nitrogen oxides occurs at temperatures below about 400C. 
     
     
         19 . The method of  claim 15 , wherein the selective catalytic reduction catalyst comprises a zeolilte-based catalyst. 
     
     
         20 . The method of  claim 15 , further comprising receiving the exhaust gas a diesel oxidation catalyst.