Zeolite-Containing SCR Catalyst

Abstract

The present disclosure provides a selective catalytic reduction (SCR) catalyst composition prepared from a first un-promoted zeolite having a first silica-to-alumina ratio (SAR) from about 5 to about 100, a promoter precursor, and a second un-promoted zeolite having a second silica-to-alumina ratio (SAR) from about 5 to about 100. The present disclosure further provides a method of forming the SCR catalyst composition, a catalytic article comprising the SCR catalyst composition, an engine exhaust gas treatment system comprising the SCR catalyst composition, and a method of removing nitrogen oxides from exhaust gas from a lean burn engine using the SCR catalyst composition.

Claims

1. A method of forming a selective catalytic reduction (SCR) catalyst composition, comprising: mixing a first un-promoted zeolite with a promoter precursor, wherein the first un-promoted zeolite and the promoter precursor react in situ to form a metal-promoted zeolite; and mixing the metal-promoted zeolite with a second un-promoted zeolite to form the catalyst composition.

2. The method of claim 1, wherein the first un-promoted zeolite and the second un-promoted zeolite are both in hydrogen-form or are both in ammonium-form, wherein one of the first un-promoted zeolite and the second un-promoted zeolite is in hydrogen-form and the other of the first un-promoted zeolite and the second un-promoted zeolite is in ammonium-form.

3.-4. (canceled)

5. The method composition of claim 1, wherein the first un-promoted zeolite and the second un-promoted zeolite do not contain transition metals.

6. The method of claim 1, wherein the first un-promoted zeolite and the second un-promoted zeolite have the same framework structure or have different framework structures.

7. (canceled)

8. The method of claim 1, wherein at least one of the first un-promoted zeolite and the second un-promoted zeolite has a CHA framework structure.

9. The method of claim 1, wherein at least one of the first un-promoted zeolite and the second un-promoted zeolite has an “8-ring” framework structure chosen from AEI, AFT, AFV, AFX, AVL, CHA, DDR, EAB, EEI, ERI, IFY, IRN, KFI, LEV, LTA, LTN, MER, MWF, NPT, PAU, RHO, RTE, RTH, SAS, SAT, SAV, SFW, TSC, UFI, and combinations thereof.

10. The method of claim 1, wherein at least one of the first un-promoted zeolite and the second un-promoted zeolite has a “10-ring” framework structure chosen from AEL, AFO, AHT, BOF, BOZ, CGF, CGS, CHI, DAC, EUO, FER, HEU, IMF, ITH, ITR, JRY, JSR, JST, LAU, LOV, MEL, MFI, MFS, MRE, MTT, MVY, MWW, NAB, NAT, NES, OBW, PAR, PCR, PON, PUN, RRO, RSN, SFF, SFG, STF, STI, STT, STW, SVR, SZR, TER, TON, TUN, UOS, VSV, WEI, WEN, and combinations thereof.

11. The method of claim 1, wherein at least one of the first un-promoted zeolite and the second un-promoted zeolite has a “12-ring” framework structure chosen from AFI, AFR, AFS, AFY, ASV, ATO, ATS, BEA, BEC, BOG, BPH, BSV, CAN, CON, CZP, DFO, EMT, EON, EZT, FAU, GME, GON, IFR, ISV, ITG, IWR, IWS, IWV, IWW, JSR, LTF, LTL, MAZ, MEI, MOR, MOZ, MSE, MTW, NPO, OFF, OKO, OSI, RON, RWY, SAF, SAO, SBE, SBS, SBT, SEW, SFE, SFO, SFS, SFV, SOF, SOS, STO, SSF, SSY, USI, UWY, VET and combinations thereof.

12. The method of claim 1, wherein the first un-promoted zeolite has a first silica-to-alumina ratio (SAR) from about 2 to about 50, and wherein the second un-promoted zeolite has a second silica-to-alumina ratio (SAR) from about 2 to about 50, or wherein the first SAR and the second SAR are the same, or, wherein the first SAR and the second SAR are different.

13.-14. (canceled)

15. The method of claim 1, wherein the first un-promoted zeolite has a first D90 particle size of about 2 microns to about 20 microns, and wherein the second un-promoted zeolite has a second D90 particle size of about 2 microns to about 20 microns, or wherein the first D90 particle size is the same as the second D90 particle size, or wherein the first D90 particle size is different from the second D90 particle size.

16.-17. (canceled)

18. The method of claim 1, wherein the first un-promoted zeolite and the second un-promoted zeolite are present with a weight ratio ranging from about 1:0.05 to about 1:1.

19. The method of claim 1, wherein the first un-promoted zeolite and the second un-promoted zeolite are present in the catalyst composition in a total amount ranging from about 1.0 g/in.sup.3 to about 5.0 g/in.sup.3.

20. The method of claim 1, wherein the promoter precursor comprises at least one chosen from copper oxide, copper acetate, copper nitrate, copper formate, copper oxalate, copper sulphate, and copper carbonate basic.

21. A catalytic article comprising a catalyst composition prepared according to the method of claim 1, wherein the catalyst composition is disposed on a flow-through honeycomb substrate or a wall-flow filter substrate.

22. An engine exhaust gas treatment system comprising a catalyst composition prepared according to the method of claim 1, and an exhaust gas conduit in fluid communication with a lean burn engine, wherein the catalyst composition is downstream of the exhaust gas conduit.

23. The engine exhaust gas treatment system of claim 22, wherein the engine is a diesel engine.

24. The engine exhaust gas treatment system of claim 22, wherein the catalyst composition is downstream of a DOC or CSF catalyst, wherein the system optionally further comprises a downstream SCR catalyst or an ammonia oxidation catalyst (AMOx), and wherein the downstream SCR catalyst or the AMOx catalyst comprises Cu-CHA.

25. A method of removing nitrogen oxides from exhaust gas from a lean burn engine, the method comprising contacting an exhaust gas stream from a lean burn engine with a catalyst composition prepared according to the method of claim 1.

26. A method of preparing a selective catalytic reduction (SCR) catalyst composition according to the method of claim 1.

27. A selective catalytic reduction (SCR) catalyst composition, comprising: a metal-promoted zeolite prepared from a first un-promoted zeolite having a first silica-to-alumina ratio (SAR) from about 2 to about 50 and reacts in situ with a promoter precursor; and a second un-promoted zeolite having a second silica-to-alumina ratio (SAR) from about 2 to about 50.

Description

EXAMPLES

[0071] Aspects of the present disclosure are further illustrated by the following examples, which are set forth to illustrate certain aspects of the present disclosure and are not to be construed as limiting thereof.

Example 1

[0072] A first slurry containing Chabazite-A having a silica to alumina ratio (SAR) of 19, CuO in a quantity sufficient to produce 3.7% CuO of the total quantity of zeolite and CuO, zirconium acetate, and deionized water was milled to a target particle size of D90 2 microns-20 microns. The first slurry was mixed for 24 hours at room temperature to allow copper ions to exchange into the zeolite framework.

[0073] A second slurry containing Chabazite-B having a silica to alumina ratio of 26 and deionized water was milled to a target particle size.

[0074] The second slurry was mixed into the first slurry. The weight ratio of Chabazite-A and Chabazite-B was 1:0.2. The final slurry was coated onto cellular ceramic monoliths having a cell density of 400 cpsi and a wall thickness of 6 mil (e.g., 0.006 inch or 152.4 microns), followed by drying at 130° C., and calcination at 550° C. for 1 hour.

Comparative Example 1

[0075] A slurry containing Chabazite-A having a silica to alumina ratio of 19, CuO in a quantity sufficient to produce 3.7% CuO of the total quantity of zeolite and CuO, zirconium acetate, and deionized water was milled to a target particle size of D90 2 microns-20 microns. The slurry was mixed for 24 hours at room temperature to allow copper ions to exchange into the zeolite framework. The slurry was coated onto cellular ceramic monoliths having a cell density of 400 cpsi and a wall thickness of 6 mil (e.g., 0.006 inch or 152.4 microns), followed by drying at 130° C., and calcination at 550° C. for 1 hour.

[0076] NO.sub.x conversions and N.sub.2O selectivity of Example 1 and Comparative Example 1 were measured at a gas hourly volume-based space velocity of 80,000 h.sup.−1 under pusedo-steady state conditions in a gas mixture of 500 ppm NO, 525 ppm NH.sub.3, 10% O.sub.2, 10% H.sub.2O, balance N.sub.2 in a temperature range from 200° C. to 600° C. NO.sub.x conversion was reported as mol % and measured as NO and NO.sub.2. N.sub.2O selectivity was reported as mol % and measured as follows:

[00001]$N_{2}O\mathrm{Selectivity}\left(\%\right)=\frac{N_{2}O÷2\times 100\%}{\left(\mathrm{NO}+{\mathrm{NO}}_2+{\mathrm{NH}}_3\right)\mathrm{inlet}-\left(\mathrm{NO}+{\mathrm{NO}}_2+{\mathrm{NH}}_3+N_{2}O÷2\right)\mathrm{outlet}}$

[0077] The samples were hydrothermally aged at 800° C. for 16 hours in the presence of 10% steam before testing. NO.sub.x conversion and N.sub.2O selectivity of Example 1 and Comparative Example 1 are shown in FIGS. 4 and 5. FIG. 4 depicts a graph of NO.sub.x conversion over a range of temperatures for the SCR catalyst samples according to Example 1 and for the SCR catalyst samples according to Comparative Example 1. FIG. 5 depicts a graph of N.sub.2O formation over a range of temperatures for the catalyst samples according to Example 1 and for the SCR catalyst samples according to Comparative Example 1. As illustrated in FIGS. 4 and 5, the catalytic article prepared according to Example 1 provided improved high-temperature NO.sub.x conversion and reduced N.sub.2O formation, without compromising low-temperature NO.sub.x conversion, as compared with Comparative Example 1, which does not have the second, un-promoted zeolite.

Example 2

[0078] A first slurry containing Chabazite-A having a silica to alumina ratio of 19, CuO in a quantity sufficient to produce 5.2% CuO over the total quantity of zeolite and CuO, zirconium acetate, and deionized water was milled to a target particle size of D90 2 microns-20 microns. The first slurry was mixed for 24 hours at room temperature to allow copper ions to exchange into the zeolite framework.

[0079] A second slurry containing Chabazite-A and deionized water was milled to a target particle size.

[0080] The second slurry was mixed into the first slurry. The weight ratio of Chabazite-A in the first slurry and Chabazite-A in the second slurry was 1:0.1. The final slurry was coated onto cellular ceramic monoliths having a cell density of 400 cpsi and a wall thickness of 6 mil (e.g., 0.006 inch or 152.4 microns), followed by drying at 130° C., and calcination at 550° C. for 1 hour.

Comparative Example 2

[0081] A slurry containing Chabazite-A having a silica to alumina ratio of 19, CuO in a quantity sufficient to produce 5.2% CuO over the total quantity of zeolite and CuO, zirconium acetate, and deionized water was milled to target particle size of D90 2 microns-20 microns. The slurry was mixed for 24 hours at room temperature to allow copper ions to exchange into the zeolite framework. The slurry was coated onto cellular ceramic monoliths having a cell density of 400 cpsi and a wall thickness of 6 mil (e.g., 0.006 inch or 152.4 microns), followed by drying at 130° C., and calcination at 550° C. for 1 hour.

[0082] NO.sub.x conversions and N.sub.2O selectivity of Example 2 and Comparative Example 2 were measured according to the same method described above for Example 1 and Comparative Example 1. The samples were hydrothermally aged at 800° C. for 16 hours in the presence of 10% steam before testing. NO.sub.x conversion and N.sub.2O selectivity of Example 1 and Comparative Example 1 are shown in FIGS. 6 and 7. FIG. 6 is a graph of NO.sub.x conversion over a range of temperatures for the SCR catalyst samples according to Example 2 and for the SCR catalyst samples according to Comparative Example 2. FIG. 7 is a graph of N.sub.2O formation over a range of temperatures for the catalyst samples according to Example 2 and for the SCR catalyst samples according to Comparative Example 2. As illustrated in FIGS. 6 and 7, the catalytic article prepared according to Example 2 provided improved high-temperature NO.sub.x conversion and reduced N.sub.2O formation, without compromising low-temperature NO.sub.x conversion, as compared with Comparative Example 2, which does not have the second un-promoted zeolite.

[0083] According to the present disclosure, the use of the two separate un-promoted zeolites in the catalyst compositions can trap CuOx clusters (e.g., which reduce high-temperature NO.sub.x conversion), and allow for reaction of the CuOx clusters with the un-promoted zeolite for enhanced SCR activity. As described above, during preparation of the catalyst compositions, the first un-promoted zeolite can react with the promoter precursor in situ to form a metal-promoted zeolite with a relatively low amount of CuO.sub.x clusters. That is, the first zeolite can react with CuO during catalyst preparation. The second un-promoted zeolite present in the catalyst compositions can be effective to trap metal oxide clusters that form under hydrothermal conditions. For example, the second zeolite functions as a CuO.sub.x trap during hydrothermal aging. The CuOx described here is different from the CuO used in catalyst preparation (e.g., which has a low surface area and low NH.sub.3 oxidation activity). CuO.sub.x clusters generated during hydrothermal aging are active for NH.sub.3 oxidation, which reduces high temperature NO.sub.x conversion.

EXAMPLE EMBODIMENTS

[0084] Without limitation, some embodiments of the present disclosure include:

[0085] 1. A method of forming a selective catalytic reduction (SCR) catalyst composition, comprising:

[0086] mixing a first un-promoted zeolite with a promoter precursor, wherein the first un-promoted zeolite and the promoter precursor react in situ to form a metal-promoted zeolite; and

[0087] mixing the metal-promoted zeolite with a second un-promoted zeolite to form the catalyst composition.

[0088] 2. The method of Embodiment 1, wherein the first un-promoted zeolite and the second un-promoted zeolite are both in hydrogen-form.

[0089] 3. The method of Embodiment 1, wherein the first un-promoted zeolite and the second un-promoted zeolite are both in ammonium-form.

[0090] 4. The method of Embodiment 1, wherein one of the first un-promoted zeolite and the second un-promoted zeolite is in hydrogen-form and the other of the first un-promoted zeolite and the second un-promoted zeolite is in ammonium-form.

[0091] 5. The method composition of any one of Embodiments 1-4, wherein the first un-promoted zeolite and the second un-promoted zeolite do not contain transition metals.

[0092] 6. The method of any one of Embodiments 1-5, wherein the first un-promoted zeolite and the second un-promoted zeolite have the same framework structure.

[0093] 7. The method of any one of Embodiments 1-5, wherein the first un-promoted zeolite and the second un-promoted zeolite have different framework structures.

[0094] 8. The method of any one of Embodiments 1-7, wherein at least one of the first un-promoted zeolite and the second un-promoted zeolite has a CHA framework structure.

[0095] 9. The method of any one of Embodiments 1-7, wherein at least one of the first un-promoted zeolite and the second un-promoted zeolite has an “8-ring” framework structure chosen from AEI, AFT, AFV, AFX, AVL, CHA, DDR, EAB, EEI, ERI, IFY, IRN, KFI, LEV, LTA, LTN, MER, MWF, NPT, PAU, RHO, RTE, RTH, SAS, SAT, SAV, SFW, TSC, UFI, and combinations thereof.

[0096] 10. The method of any one of Embodiments 1-7, wherein at least one of the first un-promoted zeolite and the second un-promoted zeolite has a “10-ring” framework structure chosen from AEL, AFO, AHT, BOF, BOZ, CGF, CGS, CHI, DAC, EUO, FER, HEU, IMF, ITH, ITR, JRY, JSR, JST, LAU, LOV, MEL, MFI, MFS, MRE, MTT, MVY, MWW, NAB, NAT, NES, OBW, PAR, PCR, PON, PUN, RRO, RSN, SFF, SFG, STF, STI, STT, STW, SVR, SZR, TER, TON, TUN, UOS, VSV, WEI, WEN, and combinations thereof.

[0097] 11. The method of any one of Embodiments 1-7, wherein at least one of the first un-promoted zeolite and the second un-promoted zeolite has a “12-ring” framework structure chosen from AFI, AFR, AFS, AFY, ASV, ATO, ATS, BEA, BEC, BOG, BPH, BSV, CAN, CON, CZP, DFO, EMT, EON, EZT, FAU, GME, GON, IFR, ISV, ITG, IWR, IWS, IWV, IWW, JSR, LTF, LTL, MAZ, MEL, MOR, MOZ, MSE, MTW, NPO, OFF, OKO, OSI, RON, RWY, SAF, SAO, SBE, SBS, SBT, SEW, SFE, SFO, SFS, SFV, SOF, SOS, STO, SSF, SSY, USI, UWY, VET and combinations thereof.

[0098] 12. The method of any one of Embodiments 1-1l, wherein the first un-promoted zeolite has a first silica-to-alumina ratio (SAR) from about 2 to about 50, and wherein the second un-promoted zeolite has a second silica-to-alumina ratio (SAR) from about 2 to about 50.

[0099] 13. The method of any one of Embodiments 1-12, wherein the first SAR and the second SAR are the same.

[0100] 14. The method of any one of Embodiments 1-12, wherein the first SAR and the second SAR are different.

[0101] 15. The method of any one of Embodiments 1-14, wherein the first un-promoted zeolite has a first D90 particle size of about 2 microns to about 20 microns, and wherein the second un-promoted zeolite has a second D90 particle size of about 2 microns to about 20 microns.

[0102] 16. The method of any one of Embodiments 1-15, wherein the first D90 particle size is the same as the second D90 particle size.

[0103] 17. The method of any one of Embodiments 1-15, wherein the first D90 particle size is different from the second D90 particle size.

[0104] 18. The method of any one of Embodiments 1-17, wherein the first un-promoted zeolite and the second un-promoted zeolite are present with a weight ratio ranging from about 1:0.05 to about 1:1.

[0105] 19. The method of any one of Embodiments 1-18, wherein the first un-promoted zeolite and the second un-promoted zeolite are present in the catalyst composition in a total amount ranging from about 1.0 g/in.sup.3 to about 5.0 g/in.sup.3.

[0106] 20. The method of any one of Embodiments 1-19, wherein the promoter precursor comprises at least one chosen from copper oxide, copper acetate, copper nitrate, copper formate, copper oxalate, copper sulphate, and copper carbonate basic.

[0107] 21. A catalytic article comprising a catalyst composition prepared according to the method of any one of Embodiments 1-20, wherein the catalyst composition is disposed on a flow-through honeycomb substrate or a wall-flow filter substrate.

[0108] 22. An engine exhaust gas treatment system comprising a catalyst composition prepared according to the method of any one of Embodiments 1-20, and an exhaust gas conduit in fluid communication with a lean burn engine, wherein the catalyst composition is downstream of the exhaust gas conduit.

[0109] 23. The engine exhaust gas treatment system of Embodiment 22, wherein the engine is a diesel engine.

[0110] 24. The engine exhaust gas treatment system of Embodiment 22, wherein the catalyst composition is downstream of a DOC or CSF catalyst, wherein the system optionally further comprises a downstream SCR catalyst or an ammonia oxidation catalyst (AMOx), and wherein the downstream SCR catalyst or the AMOx catalyst comprises Cu-CHA.

[0111] 25. A method of removing nitrogen oxides from exhaust gas from a lean burn engine, the method comprising contacting an exhaust gas stream from a lean burn engine with a catalyst composition prepared according to the method of any one of Embodiments 1-20.

[0112] 26. A method of preparing a selective catalytic reduction (SCR) catalyst composition according to the method of any one of Embodiments 1-20.

[0113] 27. A selective catalytic reduction (SCR) catalyst composition, comprising:

[0114] a metal-promoted zeolite prepared from a first un-promoted zeolite having a first silica-to-alumina ratio (SAR) from about 2 to about 50 and reacts in situ with a promoter precursor; and

[0115] a second un-promoted zeolite having a second silica-to-alumina ratio (SAR) from about 2 to about 50.

[0116] While the disclosure herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the disclosure set forth in the claims. Furthermore, various aspects of the disclosure may be used in other applications than those for which they were specifically described herein.