Zeolite structure synthesized using mixtures of organic structure directing agents
The disclosure provides methods of preparing small pore zeolites, the method including using a first organic structure-directing agent and a second organic structure-directing agent to crystallize the zeolites, wherein the first organic structure-directing agent is bis-quaternary ammonium cations, and the second organic structure-directing agent is mono-quaternary ammonium cations. Further disclosed are small pore zeolites having a controlled framework aluminum distribution, and selective catalytic reduction catalyst compositions, articles, and systems including such zeolites promoted with a metal.
1. A method of synthesizing a small pore zeolite, the method comprising:
preparing a mixture of water, an aluminum source, a silicon source, a source of a first organic structure-directing agent, and a source of a second organic structure-directing agent to form a synthesis gel; and
subjecting the synthesis gel to a crystallization process to crystallize the small pore zeolite;
wherein the first organic structure-directing agent comprises a bis-quaternary ammonium cation, a derivative of the bis-quaternary ammonium cation, or a combination thereof, and the second organic structure-directing agent comprises a mono-quaternary ammonium cation, a derivative of the mono-quaternary ammonium cation, or a combination thereof; and
wherein the small pore zeolite has a crystalline framework structure type selected from the group consisting of AEI, AFT, AFX, AFV, AVL, CHA, EAB, ERI, ITW, KFI, LEV, LTA, MER, SAS, SAT, and SAV.
2. The method of claim 1 , wherein the bis-quaternary ammonium cations are selected from the group consisting of N1,N1,N1,N3,N3,N3-hexaethylpropane-1,3-diaminium, N1,N1,N1,N4,N4,N4-hexamethylbutane-1,4-diaminium, N1,N1,N1,N4,N4,N4-hexaethylbutane-1,4-diaminium, (E)-N1,N1,N1,N4,N4,N4-hexamethylbut-2-ene-1,4-diaminium, N1,N1,N1,N5,N5,N5-hexamethylpentane-1,5-diaminium, (E)-N1,N1,N1,N5,N5,N5-hexamethylpent-2-ene-1,5-diaminium, N1,N1,N1,N6,N6,N6-hexamethylhexane-1,6-diaminium, (E)-N1,N1,N1,N6,N6,N6-hexamethylhex-2-ene-1,6-diaminium, (2E,4E)-N1,N1,N1,N6,N6,N6-hexamethylhexa-2,4-diene-1,6-diaminium, N1,N1,N1,N7,N7,N7-hexamethylheptane-1,7-diaminium, N1,N1,N1,N8,N8,N8-hexamethyloctane-1,8-diaminium, N1,N1,N1,N3,N3,N3-hexamethylcyclohexane-1,3-diaminium, N1,N1,N1,N3,N3,N3-hexamethylbicyclo[2.2.11heptane-1,3-diaminium, N1,N1,N1,N3,N3,N3-hexamethylbenzene-1,3-diaminium, N1,N1,N1,N4,N4,N4-hexamethylcyclohexane-1,4-diaminium, N1,N1,N1,N4,N4,N4-hexamethylbicyclo[2.2.11heptane-1,4-diaminium, N1,N1,N1,N4,N4,N4-hexamethylbicyclo[2.2.21octane-1,4-diaminium, N1,N1,N1,N4,N4,N4-hexamethylbenzene-1,4-diaminium, 1,1,4,4-tetramethylpiperazine-1,4-diium, 1,1,3,3-tetramethylhexahydropyrimidine-1,3-diium, 1,1′-(1,3-phenylene)bis(N,N,N-trimethylmethanaminium), 1,1′-(1,4-phenylene)bis(N,N,N-trimethylmethanaminium), or a combination thereof.
3. The method of claim 1 , wherein the mono-quaternary ammonium cations are selected from the group consisting of tetraethylammonium, 2-hydroxy-N,N,N-trimethylethan-1-aminium, N,N,N-trimethylcyclohexanaminium, N,N,N-trimethyladamantan-1-aminium (TMAda), N,N,N-trimethylbicyclo[2.2.1] heptan-2-aminium, N,N,N-trimethylbenzenaminium, 1,1-dimethylpiperidin-1-ium, 1,1,3,5-tetramethylpiperidin-1-ium, 1-methylquinuclidin-1-ium, 3-hydroxy-1-methylquinuclidin-1-ium, or a combination thereof.
4. The method of claim 1 , wherein the first organic structure-directing agent is a bis-quaternary ammonium compound comprising the bis-quaternary ammonium cations and balancing anions selected from the group consisting of OH—, Cl—, and Br and the source of the second organic structure-directing agent is a mono-quaternary ammonium compound comprising the mono-quaternary ammonium cations and balancing anions selected from the group consisting of OH—, Cl—, and Br.
5. The method of claim 1 , wherein the source of the first organic structure-directing agent is hexamethonium dihydroxide (HMOH) or octamethonium dihydroxide (OMOH), and the source of the second organic structure-directing agent is N,N,N-trimethyladamantan-1-aminium hydroxide (TMAdaOH).
6. The method of claim 1 , wherein the mixture further comprises an inorganic structure-directing agent, wherein the inorganic structure-directing agent is alkali metal cations or alkaline earth metal cations.
7. The method of claim 1 , wherein the source of aluminum comprises one or more of an aluminum salt, aluminum metal, an aluminum oxide, an aluminosilicate, or a zeolite and the source of silicon is colloidal silica, a silicon alkoxide compound, an alkali metal silicate, fumed silica, amorphous silica, or an aluminosilicate.
8. The method of claim 1 , wherein an OH/Si ratio of the synthesis gel is from about 0.03 to about 1.0.
9. The method of claim 1 , wherein the crystallization process comprises maintaining the synthesis gel at a temperature of from about 90° C. to about 250° C.
10. The method of claim 1 , further comprising filtering the crystals formed during the heating step, and further comprising calcining the zeolite at a temperature of from about 450° C. to about 750° C.
11. The method of claim 1 , wherein the small pore zeolite has a silica-to-alumina ratio (SAR) of from about 6 to about 100.
12. The method of claim 1 , wherein the small pore zeolite has a controlled aluminum distribution comprising an altered aluminum siting and pairing arrangement characterized by an altered equilibrium Cu +2 uptake at a Cu +2 concentration greater than 0.25M, as compared to a small pore zeolite synthesized with only a mono-quaternary OSDA, and wherein prior to calcining, at least a portion of the pores of the small pore zeolite are occupied by the bis-quaternary ammonium cations, and at least a portion of the pores are occupied by the mono-quaternary ammonium cations.
13. The method of claim 1 , wherein from about 1 to about 99% of the pores are occupied by the bis-quaternary ammonium cations, and from about 99 to about 1% of the pores are occupied by the mono-quaternary ammonium cations.