Sulfur trap in NOx adsorber systems for enhanced sulfur resistance

Abstract

An exhaust gas catalyst system, comprises: a sulfur trap warm-up catalyst, housed within the exhaust stream and comprising: a sulfur scavenger component; and a NO X adsorber catalyst, housed within the exhaust stream downstream from said sulfur trap in an underfloor position. The method of reducing sulfur poisoning of a nitrogen oxide adsorber, housed within an exhaust gas catalyst system, comprises: placing a sulfur trap within the exhaust stream upstream from a NO X adsorber, wherein said sulfur trap comprises: a sulfur scavenger component.

1 . An exhaust gas catalyst system, comprising: 
 a sulfur trap disposed within an exhaust stream, said sulfur trap comprising a sulfur scavenger component; and    a NO X  adsorber catalyst disposed within the exhaust stream, downstream from said sulfur trap.    
     
     
         2 . The exhaust gas catalyst system of    claim 1   , wherein said sulfur scavenging component is an inorganic material having an affinity for sulfur species such that said sulfur scavenging component traps sulfur components within an exhaust stream flowing over said sulfur scavenging component.  
     
     
         3 . The exhaust gas catalyst system of    claim 2   , wherein said sulfur scavenging component is a trapping element selected from the group consisting of Ag, Al, Ba, Ce, Co, Cu, La, Li, Mg, Nd, Rb, Sn, Sr, Zn, and mixtures and alloys comprising at least one of the foregoing trapping elements.  
     
     
         4 . The exhaust gas catalyst system of    claim 1   , wherein said sulfur scavenging component is loaded on a porous support selected from the group consisting of alumina, gamma-alumina, alpha-alumina, zeolite, zirconia, ceria, magnesium oxide, titania, silica, and mixtures comprising at least one of the foregoing supports.  
     
     
         5 . The exhaust gas catalyst system of    claim 1   , further comprising an oxidation catalyst.  
     
     
         6 . The exhaust gas catalyst system of    claim 5   , wherein said oxidation catalyst is selected from the group consisting of platinum, palladium, rhodium, and mixture s comprising at least one of the foregoing catalysts.  
     
     
         7 . The exhaust gas catalyst system of    claim 1   , further comprising a lean NO X  catalyst.  
     
     
         8 . The exhaust gas catalyst system of    claim 7   , wherein said lean NO X  catalyst comprises: a support selected from the group consisting of Al 2 O 3 , SiO 2 , ZrO 2 , CeO 2 , La 2 O 3 , TiO 2 , and mixtures comprising at least one of the foregoing supports; one or more zeolitic materials; and one or more precious metals.  
     
     
         9 . The exhaust gas catalyst system of    claim 1   , further comprising a three-way catalyst positioned downstream of the NO X  adsorber or within the NO X  adsorber washcoat.  
     
     
         10 . The exhaust gas catalyst system of    claim 1   , further comprising a particulate filter, housed in an underfloor position, upstream of said NO X  adsorber.  
     
     
         11 . The exhaust gas catalyst system of    claim 1   , further comprising a sulfur trap bypass valve for spraying injected fuel directly in front of said NO X  adsorber.  
     
     
         12 . The exhaust gas catalyst system of    claim 11   , further comprising a particulate filter, housed in an underfloor position, upstream of said NO X  adsorber.  
     
     
         13 . The exhaust gas catalyst system of    claim 1   , further comprising a three-way valve, between the sulfur trap and the NO X  adsorber, for diverting a short, rich exhaust period around said NO X  adsorber catalyst.  
     
     
         14 . The exhaust gas catalyst system of    claim 13   , further comprising a particulate filter, housed in an underfloor position, upstream of said NO X  adsorber.  
     
     
         15 . The exhaust gas catalyst system of    claim 1   , wherein said sulfur trap is housed in a close-coupled position relative to an internal combustion engine.  
     
     
         16 . A method of reducing sulfur poisoning of a nitrogen oxide adsorber, housed within an exhaust gas catalyst system, comprising: 
 placing a sulfur trap within the exhaust stream upstream from a NO X  adsorber, housed in an underfloor position, wherein said sulfur trap comprises: a sulfur scavenger component;    removing sulfur species from said exhaust stream into said sulfur trap according to the sulfur affinity of said sulfur scavenger component; and    directing the resulting exhaust stream, having a reduced sulfur species concentration, to said NO X  adsorber.    
     
     
         17 . The method of    claim 16   , wherein said sulfur scavenging component is an inorganic material having an affinity for sulfur species such that said sulfur scavenging component traps sulfur components within an exhaust stream flowing over said sulfur scavenging component.  
     
     
         18 . The method of    claim 17   , wherein said sulfur scavenging component comprises a trapping element selected from the group consisting of Ag, Al, Ba, Ce, Co, Cu, La, Li, Mg, Nd, Rb, Sn, Sr, Zn, and mixtures and alloys comprising at least one of the foregoing trapping elements.  
     
     
         19 . The method of    claim 16   , wherein said sulfur scavenging component is loaded on a porous support selected from the group consisting of alumina, gamma-alumina, alpha-alumina, zeolite, zirconia, ceria, magnesium oxide, titania, silica, and a mixture comprising at least one of the foregoing supports.  
     
     
         20 . The method of    claim 16   , wherein said sulfur trap further comprises an oxidation catalyst.  
     
     
         21 . The method of    claim 20   , wherein said oxidation catalyst is selected from the group consisting of platinum, palladium, rhodium, and mixtures and alloys comprising at least one of the foregoing catalysts.  
     
     
         22 . The method of    claim 16   , wherein said sulfur trap further comprises a lean NO X  catalyst.  
     
     
         23 . The method of    claim 22   , wherein said lean NOx catalyst comprises: a support selected from the group consisting of Al 2 O 3 , SiO 2 , ZrO 2 , CeO 2 , La 2 O 3 , TiO 2 , and mixtures comprising at least one of the foregoing supports; one or more zeolitic materials; and one or more precious metals.  
     
     
         24 . The method of    claim 16   , wherein the exhaust gas catalyst system further comprises a three-way catalyst positioned downstream of the nitrogen oxide adsorber or within the NO X  adsorber washcoat.  
     
     
         25 . The method of    claim 16   , further comprising spraying injected fuel directly in front of said NO X  adsorber via a bypass valve such that oxygen is consumed on said NO X  adsorber prior to exposure to a sulfur rich pulse.  
     
     
         26 . The method of    claim 25   , further comprising filtering particulate materials from said exhaust stream via a particulate trap, housed between the sulfur trap and the NO X  adsorber.  
     
     
         27 . The method of    claim 26   , wherein spraying fuel directly in front of said NO X  via said bypass valve occurs during regeneration of said particulate trap.  
     
     
         28 . The method of    claim 16   , further comprising diverting a short, fuel-rich exhaust pulse around said NO X  adsorber catalyst via a three-way valve, located between the sulfur scavenging component and said NO X  adsorber prior to exposure of said NO X  adsorber to a sulfur rich pulse.  
     
     
         29 . The method of    claim 28   , further comprising filtering particulate materials from said exhaust stream via a particulate trap, housed between the sulfur trap and the NO X  adsorber.  
     
     
         30 . The method of    claim 29   , wherein diverting said exhaust gas around said NO X  adsorber by way of said three way valve to said NO X  adsorber occurs immediately prior to regeneration of said particulate trap or of said sulfur trap warm-up catalyst.  
     
     
         31 . The method of    claim 16   , wherein said sulfur trap is housed in a close-coupled position relative to an internal combustion engine.