Air-injection system to improve effectiveness of selective catalytic reduction catalyst for gasoline engines

A method of improving the durability of a catalyst system for reducing emissions from lean-burn gasoline engine exhaust emissions, comprising the following steps:

• providing a catalyst system that includes a light-off catalyst closely coupled to the engine and a selective catalytic reduction catalyst positioned downstream from the light-off catalyst;
• injecting air between the light-off catalyst and the selective catalytic reduction catalyst at certain designated conditions that could harm the durability of the selective catalytic reduction catalyst;
• and
• injecting a reductant upstream of the selective catalytic reduction catalyst.

A durable catalyst system for the reduction of emissions from a gasoline engine exhaust stream, comprising:

• a light-off catalyst closely coupled to the engine;
• a selective catalytic reduction catalyst positioned downstream of the light-off catalyst;
• a reductant injection system positioned between the light-off catalyst and the selective catalytic reduction catalyst;
• and
• a diverter valve positioned downstream of the location for reductant injection and upstream of the SCR, the diverter valve being connected to a bypass arm that includes a reduction catalyst, which can be utilized to bypass the SCR and improve NOx conversion under high load conditions.

A method of improving the durability of a catalyst system for reducing emissions from lean-burn gasoline engine exhaust emissions, comprising the following steps:

• providing a catalyst system that includes a light-off catalyst closely coupled to the engine and a selective catalytic reduction catalyst positioned downstream from the light-off catalyst;
• injecting a reductant upstream of the selective catalytic reduction catalyst;
• and
• providing a diverter valve positioned between the location for reductant injection and the selective catalytic reduction catalyst, wherein the diverter valve is connected to a bypass arm that includes a reduction catalyst, to allow the exhaust emissions to bypass the selective catalytic reduction catalyst during high load conditions, so that the exhaust emissions are directed through the reduction catalyst in the bypass arm to improve NOx conversion during high load conditions.

A durable catalyst system for the reduction of emissions from a gasoline engine exhaust stream, comprising:

• a light-off catalyst closely coupled to the engine;
• a selective catalytic reduction catalyst positioned downstream of the light-off catalyst;
• a lean NOx trap positioned between the light-off catalyst and the selective catalytic reduction catalyst, wherein the lean NOx trap has a low oxygen storage capacity to stimulate ammonia production for use by the selective catalytic reduction catalyst;
• and
• an air injection system positioned between the lean NOx trap and the selective catalytic reduction catalyst to inject air into the exhaust stream at designated engine conditions to improve the durability of the selective catalytic reduction catalyst.