Exhaust system promoting decomposition of reductants into gaseous products

Abstract

An engine exhaust treatment system. The treatment system includes and a reductant injector adapted to deliver a reductant composition into an exhaust stream moving along an exhaust flow path. A selective catalytic reduction device is disposed downstream from the reductant injector. The selective catalytic reduction device is adapted to reduce an amount of NOx in exhaust gases produced by an engine by reaction of the NOx with ammonia. A basic and/or amphoteric oxide contact surface is disposed along the exhaust flow path.

1 . An engine exhaust treatment system, comprising:
 a reductant injector adapted to deliver a reductant composition into an exhaust stream moving along an exhaust flow path defined by an exhaust conduit;   a selective catalytic reduction device disposed downstream from the reductant injector, the selective catalytic reduction device being adapted to reduce an amount of NOx in exhaust gases produced by an engine by reaction of the NOx with ammonia; and   a contact surface of a material selected from the group consisting of basic metal oxide, amphoteric metal oxide and blends thereof disposed along the exhaust flow path.   
   
   
       2 . The engine exhaust treatment system as recited in  claim 1 , wherein the contact surface includes ZnO. 
   
   
       3 . The engine exhaust treatment system as recited in  claim 1 , wherein the contact surface is selected from the group consisting of CaO, MgO, SrO, BaO, and La 2 O 3 . 
   
   
       4 . The engine exhaust treatment system as recited in  claim 1 , wherein the contact surface includes a ZnO coating. 
   
   
       5 . The engine exhaust treatment system as recited in  claim 4 , wherein the ZnO coating is disposed at walls of the exhaust conduit in surrounding relation to an opening for the reductant injector. 
   
   
       6 . The engine exhaust treatment system as recited in  claim 4 , wherein the ZnO coating is disposed at one or more elbows of the exhaust conduit. 
   
   
       7 . The engine exhaust treatment system as recited in  claim 1 , wherein the contact surface is a coating selected from the group consisting of CaO, MgO, SrO, BaO, and La 2 O 3 . 
   
   
       8 . The engine exhaust treatment system as recited in  claim 7 , wherein the coating is disposed at walls of the exhaust conduit in surrounding relation to an opening for the reductant injector. 
   
   
       9 . The engine exhaust treatment system as recited in  claim 7 , wherein the coating is disposed at one or more elbows of the exhaust conduit. 
   
   
       10 . An engine exhaust treatment system, comprising:
 a reductant injector adapted to deliver a reductant composition into an exhaust stream moving along an exhaust flow path defined by an exhaust conduit;   a reductant mixer in fluid communication with the reductant injector;   a selective catalytic reduction device disposed downstream from the reductant injector, the selective catalytic reduction device being adapted to reduce an amount of NOx in exhaust gases produced by an engine by reaction of the NOx with ammonia; and   a basic oxide coating disposed within each of the reductant mixer and the exhaust conduit.   
   
   
       11 . The engine exhaust treatment system as recited in  claim 10 , wherein the basic oxide coating is disposed at walls of the exhaust conduit in surrounding relation to an opening for the reductant injector. 
   
   
       12 . The engine exhaust treatment system as recited in  claim 11 , wherein the basic oxide coating is disposed at walls of the exhaust conduit in substantially opposing relation to an opening for the reductant injector. 
   
   
       13 . The engine exhaust treatment system as recited in  claim 12 , wherein the basic oxide coating is disposed at one or more elbows of the exhaust conduit. 
   
   
       14 . An engine exhaust treatment system, comprising:
 a reductant injector adapted to deliver a reductant composition into an exhaust stream moving along an exhaust flow path defined by an exhaust conduit;   a selective catalytic reduction device disposed downstream from the reductant injector, the selective catalytic reduction device being adapted to reduce an amount of NOx in exhaust gases produced by an engine by reaction of the NOx with ammonia; and   a coating layer defining a contact surface disposed along the exhaust flow path, the coating layer including a first oxide-forming metal of basic or amphoteric character in combination with at least one alloy element characterized by a Gibbs free energy of oxide formation more positive than the Gibbs free energy of oxide formation of the first oxide-forming metal.   
   
   
       15 . The engine exhaust treatment system as recited in  claim 14 , wherein the first oxide-forming metal is zinc. 
   
   
       16 . The engine exhaust treatment system as recited in  claim 15 , wherein the at least one alloy element is selected from the group consisting of Ni, Co, Fe and combinations thereof. 
   
   
       17 . A method of reducing an amount of NOx in exhaust gases produced by an engine by treatment of the exhaust gases in an exhaust treatment system, the exhaust treatment system including a reductant injector adapted to deliver a reductant composition into an exhaust stream moving along an exhaust flow path defined by an exhaust conduit, and a selective catalytic reduction device disposed downstream from the reductant injector, the selective catalytic reduction device being adapted to reduce an amount of NOx in the exhaust gases by reaction of the NOx with ammonia, the method comprising:
 providing a contact surface of a material selected from the group consisting of basic oxide, amphoteric oxide and blends thereof disposed along the exhaust flow path upstream from the selective catalytic reduction device.   
   
   
       18 . The method as recited in  claim 17 , wherein the contact surface is a coating having an oxide surface layer including at least one of the group consisting of ZnO, CaO, MgO, SrO, BaO, and La 2 O 3 . 
   
   
       19 . The method as recited in  claim 18 , wherein the coating is disposed at walls of the exhaust conduit in surrounding relation to an opening for the reductant injector. 
   
   
       20 . The method as recited in  claim 19 , wherein the coating is disposed at walls of the exhaust conduit in substantially opposing relation to an opening for the reductant injector. 
   
   
       21 . The method as recited in  claim 17 , wherein the contact surface is a thermal spray coating. 
   
   
       22 . The method as recited in  claim 21 , wherein the thermal spray coating is applied by a plasma transferred wire arc process. 
   
   
       23 . The method as recited in  claim 18 , wherein the coating is disposed at one or more elbows of the exhaust conduit. 
   
   
       24 . The method as recited in  claim 18 , wherein the coating has a thickness of about 50 to about 400 microns. 
   
   
       25 . The method as recited in  claim 18 , wherein the coating is disposed at walls of the exhaust conduit in substantially opposing relation to an opening for the reductant injector and at one or more elbows of the exhaust conduit at a thickness of about 50 to about 400 microns.