Process for preparing iron(III)-exchanged zeolite composition
The present disclosure relates to processes for formation of a molecular sieve, particularly a metal-promoted molecular sieve, and more particularly an Iron(III) exchanged zeolite. Preferably, the zeolite is of the chabazite form or similar structure. The processes can include combining a zeolite with Iron(III) cations in an aqueous medium. The process can be carried out at a pH of less than about 7, and a buffering material can be used with the aqueous medium. The processes beneficially result in Iron exchange that can approach 100% along with removal of cations (such as sodium, NH4, and H) from the zeolite. An Iron(III)-exchanged zeolite prepared according to the disclosed processes can include about 2,000 ppm or less of cation and about 1% by weight or greater of Iron(III). The disclosure also provides catalysts (e.g., SCR catalysts) and exhaust treatment systems including the Iron(III)-exchanged zeolite.
1. A process for preparing an Iron-exchanged zeolite, the process comprising combining a zeolite with Iron(III) cations in an aqueous medium such that the Iron(III) cations are exchanged into or onto the zeolite to thus form an Iron(III)-exchanged zeolite;
wherein the zeolite and the Iron(III) cations are combined in an aqueous medium that comprises a buffering agent and that is at a pH of about 2.0 to about 6.0.
2. The process of claim 1 , wherein the zeolite has a double 6-ring (D6R) building unit structure.
3. The process of claim 1 , wherein the zeolite has a chabazite (CHA) structure.
4. The process of claim 1 , wherein the Iron(III) cations are provided from an Iron(III) salt.
5. The process of claim 4 , wherein the Iron(III) salt is selected from the group consisting of Iron(III) halides, Iron(III) citrates, Iron(III) nitrates, Iron(III) sulfates, Iron(III) acetate, and combinations thereof.
6. The process of claim 5 , wherein the Iron(III) salt is selected from the group consisting of Iron(III) nitrates, Iron(III) sulfates, and combinations thereof.
7. The process of claim 1 , wherein the Iron(III) cations are provided in situ via oxidation of an Iron(II) salt.
8. The process of claim 1 , wherein the Iron(III) cations are exchanged with one or more different cations present in or on the zeolite such that about 75% by weight or greater of the different cations present in or on the zeolite are exchanged with the Iron(III) cations.
9. The process of claim 1 , wherein the Iron(III)-exchanged zeolite comprises Iron(III) in an amount of about 1% by weight or greater.
10. The process of claim 9 , wherein the Iron(III)-exchanged zeolite comprises Iron(III) in an amount of about 1% by weight to about 10% by weight.
11. The process of claim 1 , wherein the Iron(III)-exchanged zeolite comprises sodium, NH 4 , or H cations in an amount of about 2,000 ppm or less.
12. The process of claim 1 , wherein the pH is about 3.0 to about 5.0.
13. The process of claim 1 , wherein the buffering agent comprises ammonium acetate.
14. The process of claim 1 , wherein the exchange of Iron(III) into or onto the zeolite is carried out at a temperature that is greater than about 30° C. and is less than the decomposition temperature of an Iron salt that is included in the aqueous medium as a source for the Iron(III) cations.
15. The process of claim 1 , wherein the exchange of Iron(III) cations into or onto the zeolite is carried out at a temperature of about 30° C. to about 80° C.
16. The process of claim 1 , wherein the exchange of Iron(III) cations into or onto the zeolite is carried out at a temperature of about 40° C. to about 70° C.
17. The process of claim 1 , wherein the process results in substantially no ammonium nitrate formation.
18. The process of claim 1 , wherein the process further comprises washing and filtering the Iron(III)-exchanged zeolite to a solution conductivity of about 200 micromhos or less.