Method and system for the purification of exhaust gas from an internal combustion engine

Abstract

The invention provides a method and system for the purification of exhaust gas from an internal combustion engine, comprising a filter and a SCR catalyst. The filter is periodically regenerated increasing the temperature of the exhaust gas up to 850 C. and the water vapor content up to 100% by volume. The SCR catalyst comprises a hydrothermally microporous stable zeolite and/or zeotype having the AEI type framework and being promoted with copper.

Claims

1. Method for the purification of exhaust gas from an internal combustion engine, comprising reducing the content of soot in the exhaust gas by passing the gas through a filter; subsequently reducing the content of nitrogen oxides in presence of ammonia or a precursor thereof in contact with a catalyst being active in NH.sub.3-SCR; periodically regenerating the filter by burning of soot captured in the filter and thereby increasing temperature of the exhaust gas up to 850 C. and water vapour content up to 100% by volume; and passing the exhaust gas from the filter through the catalyst during the regeneration of the filter, wherein the catalyst comprises a hydrothermally microporous stable zeolite and/or zeotype having the AEI type framework and being promoted with copper, and maintains 80% of the initial reduction of nitrogen oxides at 250 C. after the catalyst has been exposed to a water vapour content of 100% in the exhaust gas for 13 hours.

2. The method of claim 1, wherein the atomic copper to aluminium ratio is between about 0.01 and about 1 for the zeolite and the atomic copper to silicon ratio is between 0.01 and about 1 for the zeotype.

3. The method of claim 1, wherein the atomic ratio of silicon to aluminium is between 5 and 50 for the zeolite and between 0.02 and 0.5 for the zeotype.

4. The method of claim 1, wherein 80% of the initial reduction of nitrogen oxides at 250 C. is maintained after the catalyst has been exposed to a temperature of 750 C.

5. The method of claim 1, wherein at least 80 to 90% of the initial microporosity is maintained after aging at 600 C., and at least 30 to 40% is maintained after aging at 750 C.

6. The method of claim 3, wherein the catalyst is an aluminosilicate zeolite SSZ-39 and/or silicoaluminum phosphate SAPO-18.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A shows the powder X-ray diffraction (PXRD) pattern of treated Cu-SSZ-39 samples.

(2) FIG. 1B shows the powder X-ray diffraction (PXRD) pattern of treated CHA samples.

(3) FIG. 2 is a summary of the results of Examples 1-4 with the Cu-SSZ-39 and CHA catalysts.

(4) FIG. 3 shows the results of Example 5 with the Cu-SSZ-39 catalyst.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) The Cu-SSZ-39 catalyst system has shown an improved performance compared to the typical state-of-the-art Cu-SSZ-13 when similar Si/Al ratios are compared.

Example 1

Cu-SSZ-39 Catalyst Preparation

(6) The zeolite SSZ-39 with the framework type code AEI was synthesized in a similar way as given in U.S. Pat. No. 5,958,370 using 1,1,3,5-tetramethylpiperidinium as the organic template. A gel with the following composition: 30 Si:1.0 Al:0.51 NaOH:5.1 OSDA:600 H.sub.2O, was autoclaved at 135 C. for 7 days, the product filtered, washed with water, dried and calcined in air. The final SSZ-39 had a Si/Al=9.1 measured by ICP-AES.

(7) To obtain the Cu-SSZ-39 the calcined zeolite was ion exchanged with Cu(CH.sub.3COO).sub.2 to obtain the final catalyst with a Cu/Al=0.52 after calcination.

(8) The powder X-ray diffraction (PXRD) pattern of Cu-SSZ-39 after calcination is shown in FIG. 1.

Example 2

Catalytic Testing

(9) The activity of the samples for the selective catalytic reduction of NO.sub.x was tested in a fixed bed reactor to simulate an engine exhaust stream using a total flow rate of 300 mL/min consisting of 500 ppm NO, 533 ppm NH.sub.3, 7% O.sub.2, 5% H.sub.2O in N.sub.2 in which 40 mg catalyst was tested.

(10) The NO.sub.x present in the outlet gases from the reactor were analyzed continuously and the conversion is shown in FIG. 2.

Example 3

Test of Hydrothermal Durability

(11) In order to test the hydrothermal stability of the zeolites, steaming treatments were done to the samples. They were exposed to a water feed (2.2 mL/min) at 600 or 750 C. during 13 hours in a conventional oven and afterwards tested similarly to Example 2.

(12) The catalytic results can also be seen in FIG. 2. The samples that underwent a hydrothermal treatment have been marked with 600 or 700 C., depending on the temperature used during the hydrothermal treatment.

(13) Additional characterization has also been performed to all treated samples. PXRD patterns after hydrothermal treatments are shown in FIG. 1, and BET surface areas, micropore areas, and micropore volumes of treated samples are summarized in Table 1 below.

Example 4

Comparative Example with Cu-CHA (Cu-SSZ-13)

(14) A Cu-CHA zeolite was prepared from a gel with the molar composition: SiO.sub.2:0.033 Al.sub.2O.sub.3:0.50 OSDA:0.50 HF:3 H.sub.2O, where the OSDA is N,N,N-trimethyl-1-adamantamonium hydroxide.

(15) The gel was autoclaved at 150 C. for 3 days under tumbling to give a final zeolite product with a Si/Al=12.7 after washing, drying and calcination.

(16) To obtain the Cu-CHA the calcined zeolite was ion exchanged with Cu(CH.sub.3COO).sub.2 to obtain the final catalyst with a Cu/Al=0.54.

(17) The powder X-ray diffraction (PXRD) pattern of Cu-CHA after calcination is shown in FIG. 1.

(18) This catalyst was also tested according to example 2, and the hydrothermal durability evaluated similarly to example 3. The catalytic results are summarized in FIG. 2 of the drawings. PXRD patterns of treated-CHA samples are shown in FIG. 1, and textural properties (BET surface area, micropore volume, and micropore area) are summarized on Table 1.

(19) TABLE-US-00001 TABLE 1 Volume BET surface Micropore micropore Sample area (m.sup.2/g) area (m.sup.2/g) (cm.sup.3/g) SSZ-39_Calc 571 568 0.28 SSZ-39_600 C. 554 551 0.28 SSZ-39_750 C. 565 563 0.28 Cu-SSZ-39_600 C. 465 463 0.24 Cu-SSZ-39_750 C. 158 152 0.09 CHA_calc 675 637 0.32 CHA_600 C. 687 645 0.32 CHA_750 C. 674 623 0.31 Cu-CHA_600 C. 633 585 0.29 Cu-CHA_750 C. 50 35 0.02

Example 5

Cu-SAPO-18

(20) Silicoaluminophosphate SAPO-18 with the framework type code AEI was synthesized according to [J. Chen, J. M. Thomas, P. A. Wright, R. P. Townsend, Catal. Lett. 28 (1994) [241-248] and impregnated with 2 wt. % Cu. The final Cu-SAPO-18 catalyst was hydrothermally treated in 10% H.sub.2O and 10% O.sub.2 at 750 C. and tested under the same conditions as given in Example 2. The results are shown in FIG. 2 of the drawings.