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, NH 4 , 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. An Iron(III)-exchanged molecular sieve comprising a porous zeolite having a double 6-ring (D6R) building unit structure, wherein cations in the zeolite have been exchanged with Iron(III) cations such that the zeolite includes about 1% by weight of the zeolite or greater of Iron(III), wherein the Iron(III)-exchanged molecular sieve is prepared by combining a zeolite with Iron(III) cations in an aqueous media such that the Iron(III) cations are exchanged into or onto the zeolite to form the Iron(III)-exchanged zeolite, and wherein the aqueous medium comprises a buffering agent and is at a pH of about 2.0 to about 6.0.
2. The Iron(III)-exchanged molecular sieve of claim 1 , wherein the zeolite is a sodium-containing zeolite, an NH 4 -containing zeolite, or an H-containing zeolite.
3. The Iron(III)-exchanged molecular sieve of claim 1 , wherein the zeolite includes about 1% to about 10% by weight of the zeolite of Iron(III).
4. The Iron(III)-exchanged molecular sieve of claim 1 , wherein the zeolite has a chabazite (CHA) structure.
5. The Iron(III)-exchanged molecular sieve of claim 1 , wherein the zeolite includes sulfate in an amount of about 400 ppm or greater based on the total weight of the Iron(III)-exchanged zeolite.
6. The Iron(III)-exchanged molecular sieve of claim 1 , wherein the Iron(III) is dispersed on the zeolite.
7. The Iron(III)-exchanged molecular sieve of claim 1 , wherein the Iron(III) cations are exchanged onto the zeolite.
8. A catalyst comprising an Iron(III)-exchanged molecular sieve according to claim 1 combined with a substrate.
9. A catalyst comprising an Iron(III)-exchanged zeolite according to claim 1 .
10. An exhaust treatment system comprising a selective catalytic reduction (SCR)catalyst positioned to receive an exhaust gas stream, the SCR catalyst including an Iron(III)-exchanged zeolite according to claim 1 .
11. The exhaust treatment system of claim 10 , further comprising one or both of a diesel oxidation catalyst (DOC) and a catalyzed soot filter (CSF).
12. The exhaust treatment system of claim 10 , further comprising a reductant injector.