Reformer assisted lean NOx catalyst aftertreatment system and method

A method for reducing NOx contained in a gas stream resulting from a combustion process, said method comprising the steps of:

• passing said gas stream through a combination catalyst having first and second catalysts positioned in a staged arrangement for catalytically reducing the NOx, said combination catalyst comprising:
• said first catalyst far catalytically processing the gas stream being selected from the group consisting of metal-containing alumina, metal oxide-containing alumina, or a combination thereof, wherein the metal is selected from the group consisting of silver, indium, gallium, tin and cobalt and mixtures thereof, said first catalyst having a first temperature at which peak catalytic activity occurs, said first catalyst being for both converting a portion of NOx directly to N2 and another portion to nitrogen-containing intermediates with a portion of NOx remaining;
• and
• said second catalyst being located downstream from the first catalyst for catalytically processing the gas stream subsequent to the first catalyst, said second catalyst being selected from the group consisting of a metal-containing zeolite, metal oxide-containing zeolite, or a combination thereof, wherein the metal is selected from the group consisting of copper, iron, cobalt, and silver and mixtures thereof, said second catalyst having a second temperature at which peak activity occurs, said second catalyst being adapted to facilitate the reaction of the remaining NOx and intermediates for further reduction into N2, wherein the value of the second temperature is lower than the value of the first temperature;
• injecting a reductant from a reductant source into said gas stream upstream of said combination catalyst;
• reforming a portion of a reductant from the reductant source to obtain an activator selected from the group consisting of hydrogen (H2), oxygenated hydrocarbon, or a combination thereof;
• and
• injecting the activator into said gas stream upstream of said combination catalyst, to activate said reductant to improve low temperature NOx conversion.

A method for catalytically processing the exhaust gas stream from an internal combustion engine to reduce the presence of NOx therein, said method comprising the steps of:

• delivering the gas stream to a first catalyst being selected from the group consisting of metal-containing alumina, metal oxide-containing alumina, or a combination thereof, wherein the metal is selected from the group consisting of silver, indium, gallium, tin and cobalt and mixtures thereof for catalytically processing the gas stream, said first catalyst having a first temperature at which peak catalytic activity occurs, said first catalyst being adapted for both converting a portion of NOx directly to N2 and another portion to nitrogen-containing intermediates with a portion of NOx remaining;
• conveying the gas stream from the first catalyst to a second catalyst located downstream from the first catalyst in a staged arrangement, said second catalyst being selected from the group consisting of a metal-containing zeolite, metal oxide-containing zeolite, or a combination thereof, wherein the metal is selected from the group consisting of copper, iron, cobalt, and silver and mixtures thereof, for catalytically further processing the gas stream subsequent to the first catalyst, said second catalyst having second temperature at which peak activity occurs, said second catalyst being adapted to facilitate the reaction of the remaining NOx and intermediates for further reduction into N2, wherein the value of the second temperature is lower than the value of the first temperature;
• injecting a hydrocarbon compound reductant from a hydrocarbon reductant source into said exhaust gas stream upstream of said first catalyst;
• reforming a portion of a hydrocarbon reductant from the hydrocarbon reductant source to obtain an activator selected from the group consisting of hydrogen (H2), oxygenated hydrocarbon, or a combination thereof;
• and
• injecting the activator into said exhaust gas stream upstream of said first catalyst to activate said reductant in a low temperature range relative to said exhaust gas stream to facilitate the reduction of NOx in the gas stream.

An apparatus for catalytically processing the exhaust gas stream from a lean burn internal combustion engine to reduce the presence of NOx therein, said apparatus comprising:

• a combination catalyst having first and second catalysts positioned in a staged arrangement for catalytically processing the gas stream, said combination catalyst including:
• said first catalyst for catalytically processing the gas stream, being selected from the group consisting of metal-containing alumina, metal oxide-containing alumina, or a combination thereof, wherein the metal is selected from the group consisting of silver, indium, gallium, tin and cobalt and mixtures thereof, said first catalyst having a first temperature at which peak catalytic activity occurs, said first catalyst being adapted for both converting a portion of NOx directly to N2 and another portion to nitrogen-containing intermediates with a portion of NOx remaining;
• and
• said second catalyst being located downstream from the first catalyst for catalytically processing the gas stream subsequent to the first catalyst, being selected from the group consisting of a metal-containing zeolite, metal oxide-containing zeolite, or a combination thereof, wherein the metal is selected from the group consisting of copper, iron, cobalt, and silver and mixtures thereof, said second catalyst having a second temperature at which peak activity occurs, said second catalyst being adapted to facilitate the reaction of the remaining NOx and intermediates for further reduction into N2, wherein the value of the second temperature is lower than the value of the first temperature;
• a source of hydrocarbon compound reductant for injecting the same into said gas stream upstream of said first catalyst;
• an activator selected from the group consisting of hydrogen (H2), oxygenated hydrocarbon, or a combination thereof, for injection into said gas stream upstream of said first catalyst, for activating said reductant to improve NOx reduction in a low temperature range of said exhaust gas stream relative to the overall temperature range thereof;
• a reformer adapted for reforming a portion of said reductant into said activator;
• and
• a controller for individually adjusting the amounts of said reductant and activator injected as a function of both the temperature of the exhaust gas stream and engine speed.