Exhaust gas treatment system and method with reductant injection and close-coupled treatment element

1. An exhaust gas treatment system for an internal combustion engine, the system comprising:

an exhaust gas pathway configured to receive exhaust gas from the internal combustion engine;

a first treatment element positioned within the exhaust gas pathway such that the first treatment element is close coupled to the engine, the first treatment element including a NOx storage element and a first selective catalytic reduction (SCR) element coated under or over the NOx storage element;

a first injector configured to selectively introduce a first reductant into the exhaust gas pathway upstream of the first treatment element;

a second injector configured to introduce a second reductant into the exhaust gas pathway downstream of the first treatment element; and

a second treatment element positioned within the exhaust gas pathway downstream of the second injector, the second treatment element including a second SCR element.

2. The exhaust gas treatment system of claim 1 , wherein the NOx storage element includes a passive NOx adsorber.

3. The exhaust gas treatment system of claim 1 , wherein the NOx storage element includes a NOx storage catalyst.

4. The exhaust gas treatment system of claim 1 , wherein the first injector is configured to introduce the first reductant into the exhaust gas in response to a sensed temperature of the exhaust gas being within a predetermined temperature range.

5. The exhaust gas treatment system of claim 4 , wherein the predetermined temperature range is about 100 degrees Celsius to about 300 degrees Celsius.

6. The exhaust gas treatment system of claim 1 , wherein the first reductant includes ammonia gas, and wherein the second reductant includes diesel exhaust fluid.

7. The exhaust gas treatment system of claim 1 , wherein the first treatment element includes a diesel particulate filter (DPF), and wherein the NOx storage element is coated on the DPF.

8. The exhaust gas treatment system of claim 1 , wherein the second injector is configured to introduce the second reductant into the exhaust gas in response to a temperature of the exhaust gas exceeding a predetermined temperature.

9. An exhaust gas treatment system for an internal combustion engine, the system comprising:

an exhaust gas pathway configured to receive exhaust gas from the internal combustion engine;

a first treatment element positioned within the exhaust gas pathway such that the first treatment element is close coupled to the engine, the first treatment element including a diesel particulate filter (DPF) coated with a precious metal catalyst;

a first injector configured to selectively introduce a first reductant into the exhaust gas pathway upstream of the first treatment element;

a second injector configured to introduce a second reductant into the exhaust gas pathway downstream of the first treatment element, wherein the second reductant has a different composition than the first reductant; and

a second treatment element positioned within the exhaust gas pathway downstream of the second injector, the second treatment element including a selective catalytic reduction (SCR) element.

10. The exhaust gas treatment system of claim 9 , wherein the first reductant includes ammonia gas, and the second reductant includes diesel exhaust fluid.

11. The exhaust gas treatment system of claim 9 , wherein the first treatment element includes a selective catalytic reduction (SCR) element.

12. The exhaust gas treatment system of claim 11 , wherein the first treatment element includes a NOx storage element.

13. The exhaust gas treatment system of claim 11 , wherein the first second treatment element includes an ammonia oxidation catalyst (AOC).

14. An exhaust gas treatment system for an internal combustion engine, the system comprising:

an exhaust gas pathway configured to receive exhaust gas from the internal combustion engine;

a first treatment element positioned within the exhaust gas pathway such that the first treatment element is close coupled to the engine, the first treatment element including a selective catalytic reduction (SCR) element and a NOx storage element;

a first injector configured to selectively introduce a first reductant into the exhaust gas pathway upstream of the first treatment element;

a second injector configured to introduce a second reductant into the exhaust gas pathway downstream of the first treatment element; and

a second treatment element positioned within the exhaust gas pathway downstream of the second injector.

15. The exhaust gas treatment system of claim 14 , wherein the NOx storage element is configured to selectively adsorb NOx.

16. The exhaust gas treatment system of claim 15 , wherein the first injector is configured to introduce the first reductant into the exhaust gas in response to a sensed temperature of the exhaust gas being within a predetermined temperature range.

17. The exhaust gas treatment system of claim 14 , wherein the first treatment element includes a diesel particulate filter (DPF), and wherein the SCR element and the NOx storage element are coated on the DPF.

18. The exhaust gas treatment system of claim 14 , wherein the second treatment element includes a selective catalytic reduction (SCR) element and an ammonia oxidation catalyst (AOC).

19. The exhaust gas treatment system of claim 14 , wherein the first reductant includes ammonia gas, and wherein the second reductant includes diesel exhaust fluid.