WO2024104392A1

WO2024104392A1 - Synthesis of zeolitic materials having aft framework structure and scr catalysts comprising the same

Info

Publication number: WO2024104392A1
Application number: PCT/CN2023/131838
Authority: WO
Inventors: Li Hua SHI; Xiao Duo QI; Vivek VATTIPALLI; Hai Tao LIU; Yu DAI; Ming Ming WEI; Jin Li
Original assignee: Basf Corporation; Basf (China) Company Limited
Priority date: 2022-11-16
Filing date: 2023-11-15
Publication date: 2024-05-23

Abstract

A process for preparing an aluminosilicate zeolite having an AFT framework structure, which includes (1) providing a synthesis mixture comprising (A) a source for Al 2O 3, (B) a source for SiO 2, (C1) a source for first organic structure directing agent comprising a N, N, N, N', N', N'-hexaethyl alkylenediammonium cation wherein the alkylene moiety is substituted or unsubstituted straight chain or branched chain having 3 to 10 carbons, and (C2) a source for second organic structure directing agent comprising (C2-i) N, N, N-trimethyl-cyclohexylammonium cation represented by formula (I), or (C2-ii) a spiroquaternary ammonium cation represented by formula (II), or a combination thereof, wherein the formula (I) and formula (II) are as defined in the claims, and (2) subjecting the synthesis mixture to crystallization conditions to form an aluminosilicate zeolite having an AFT framework structure. Meanwhile, the aluminosilicate zeolite obtained and/or obtainable by the process, and use of the aluminosilicate zeolite in catalysts for selective catalytic reduction of nitrogen oxides are also provided.

Description

SYNTHESIS OF ZEOLITIC MATERIALS HAVING AFT FRAMEWORK STRUCTURE AND SCR CATALYSTS COMPRISING THE SAME

Field of the invention

The present invention relates to a process for synthesis of zeolitic materials having an AFT framework structure, use of the zeolitic materials in catalysts for selective catalytic reduction (SCR) of nitrogen oxides, and SCR catalysts comprising the same.

Background

Small-pore zeolites having pore openings of smaller than 5 Angstromssuch as those of CHA, AEI or AFX type, have been found excellent as sorbents or catalysts in various applications, for example for separation of gases, for conversion reaction of organic compounds such as methanol-to-olefins (MTO) , or for treatment of exhaust gases such as exhausts from internal combustion engines. Small-pore zeolites having other framework structures received increasing attention of researchers with the hope of finding more potential candidates for small-pore zeolite sorbents or catalysts.

For example, US patent No. US 10, 343, 927 B2 describes a novel aluminosilicate zeolite of AFT type. The zeolites of AFT type are small-pore zeolites, which were first known as aluminophosphate (AIPO) framework structure. The aluminosilicate zeolite of AFT type, designated as SSZ-112 in US 10, 343, 927 B2, was prepared from a synthesis gel comprising sources of SiO₂, Al₂O₃, Group 1 metal, hydroxide ions, hexamethonium dication ions as the first organic templates (Q1) and one or more of 1-methyl-1-alkylpyrrolidinium cations and 1-methyl-1-alkylpiperidinium cations as the second organic template (Q2) , where each alkyl group is independently C₁-C₅ alkyl. It was mentioned in the patent that the zeolite SSZ-112 may be used as a catalyst for a wide variety of organic or inorganic conversion processes including alkylation, cracking, hydrocracking, isomerization, oligomerization, conversion of organic oxygenates (e.g., methanol and/or dimethyl ether) to olefins (e.g., ethylene, propylene) , synthesis of monoalkylamines and dialkylamines, and the catalytic reduction of nitrogen oxides.

The process for preparing the aluminosilicate zeolite of AFT type as reported is limited to the very particular organic structure directing agents (OSDAs) . There remains a need of more processes for preparing aluminosilicate zeolites of AFT type, particularly processes which could provide aluminosilicate zeolites of AFT type with desirable catalytic activities in selective catalytic reduction (SCR) applications.

Summary of the invention

It is an object of the present invention to provide a novel process for preparing aluminosilicate zeolites having an AFT framework structure.

The object was achieved by using a combination of N, N, N, N', N', N'-hexaethyl alkylenediammonium organic structure directing agent and another organic structure directing agent selected from quaternary ammonium organic structure directing agent and spiro-quaternary ammonium organic structure directing agent.

Another object of the present invention is to provide an SCR catalyst based on a zeolite having an AFT framework structure, which has a desirable catalytic activity, particularly low-temperature catalytic activity.

It has been surprisingly found that the object was achieved by an SCR catalyst composition which comprises an aluminosilicate zeolite having an AFT framework structure and a promoter metal.

Accordingly, in one aspect, the present invention relates to a process for preparing an aluminosilicate zeolite having an AFT framework structure, which includes

(1) providing a synthesis mixture comprising

(A) a source for Al₂O₃,

(B) a source for SiO₂,

(C1) a source for first organic structure directing agent comprising a N, N, N, N', N', N'-hexaethyl alkylenediammonium cation wherein the alkylene moiety is substituted or unsubstituted straight chain or branched chain having 3 to 10 carbons, and

(C2) a source for second organic structure directing agent comprising

(C2-i) N, N, N-trimethyl-cyclohexylammonium cation represented by formula (I) ,

or

(C2-ii) a spiro-quaternary ammonium cation represented by formula (II) ,

wherein

Ra and Rb, represent substituents on the seven-membered ring and the six-membered ring respectively, and independently from each other are hydroxyl or C₁-C₈ alkyl;

m represents number of Ra and is an integer in the range of from 0 to 6,

n represents number of Rb and is an integer in the range of from 0 to 5, and

“-” represents attachment of each Ra to one or more carbon atoms of the seven-membered ring when m is not 0, and attachment of each Rb to one or more carbon atoms of the six-membered ring when n is not 0,

or a combination thereof,

and

(2) subjecting the synthesis mixture to crystallization conditions to form an aluminosilicate zeolite having an AFT framework structure.

In another aspect, the present invention relates to an aluminosilicate zeolite having an AFT framework structure obtained and/or obtainable by the process as described herein.

In still another aspect, the present invention relates to an SCR catalyst composition which comprises an aluminosilicate zeolite having an AFT framework structure obtained and/or obtainable by the process as described herein and a promoter metal.

In yet another aspect, the present invention relates to a catalytic article in form of an extrudate comprising an SCR catalyst composition or in form of a monolith comprising a washcoat containing an SCR catalyst composition on a substrate, wherein the SCR catalyst composition comprises an aluminosilicate zeolite having an AFT framework structure and a promoter metal.

In a further aspect, the present invention relates to an exhaust gas treatment system comprising an internal combustion engine and an exhaust gas conduit in fluid communication with the internal combustion engine, wherein the catalytic article as described herein is present in the exhaust gas conduit.

Brief description of the drawings

Figure 1A, 1 B and 1 C shows SEM images of the zeolites from Examples 1 to 3 (Materials A to C) respectively.

Figure 2 shows XRD patterns of the zeolites from Examples 1 to 3 (Materials A to C) respectively.

Detailed description of the invention

The present invention will be described in detail hereinafter. It is to be understood that the present invention may be embodied in many different ways and shall not be construed as limited to the embodiments set forth herein.

Herein, the singular forms “a” , “an” and “the” include plural referents unless the context clearly dictates otherwise. The terms “comprise” , “comprising” , etc. are used interchangeably with “contain” , “containing” , etc. and are to be interpreted in a non-limiting, open manner. That is, e.g., further components or elements may be present. The expressions “consists of” or “consists essentially of” or cognates may be embraced within “comprises” or cognates.

The term “AFT” as used herein refer to AFT framework type as recognized by the International Zeolite Association (IZA) Structure Commission.

The term “aluminosilicate” as used within the context of zeolite is intended to mean the framework constructed primarily of alumina and silica, which may or may not comprise a framework metal other than aluminum and silicon. When a framework metal other than aluminum is present in place of one or more aluminum or silicon framework atoms, the aluminosilicate zeolite may be referred to as “metal-substituted” .

The terms “zeolite having an AFT framework structure” , “zeolite of AFT type” , “AFT zeolite” and the like as used herein are intended to refer to a material which shows an XRD pattern of an AFT framework structure, and will be used interchangeably with each other hereinbelow. Those terms are also intended to include any forms of the zeolite, for example as-synthesized form, calcined form, NH₄ ⁺-exchanged form, H-form and metal-substituted form.

The term “as-synthesized” as used herein is intended to refer to a zeolite in its form after crystallization and drying, prior to removal of the organic structure directing agents.

The term “calcined form” as used herein is intended to refer to a zeolite in its form upon calcination.

In the first aspect, the present invention provides a process for preparing an aluminosilicate zeolite having an AFT framework structure, which includes

(1) providing a synthesis mixture comprising

(A) a source for Al₂O₃,

(B) a source for SiO₂,

(C1) a source for first organic structure directing agent comprising a N, N, N, N', N', N'-hexaethyl alkylenediammonium cation (OSDA1) wherein the alkylene moiety is substituted or unsubstituted straight chain or branched chain having 3 to 10 carbons, and

(C2) a source for second organic structure directing agent comprising the following cation (OSDA2) ,

(C2-i) N, N, N-trimethyl-cyclohexylammonium cation represented by formula (I) ,

or

(C2-ii) a spiro-quaternary ammonium cation represented by formula (II) ,

wherein

Ra and Rb, represent substituents on the seven-membered ring and the six-membered ring respectively, and independently from each other are hydroxyl or C₁-C₈ alkyl; ;

m represents number of Ra and is an integer in the range of from 0 to 6,

n represents number of Rb and is an integer in the range of from 0 to 5, and

or a combination thereof,

The first organic structure directing agent particularly comprises a N, N, N, N', N', N'-hexaethyl alkylenediammonium cation (OSDA1) wherein the alkylene moiety is selected from substituted or unsubstituted straight chain or branched chain C₃-C₁₀ alkanediyl, preferably unsubstituted straight chain or branched C₃-C₁₀ alkanediyl.

Particularly, the first organic structure directing agent comprises a N, N, N, N', N', N'-hexaethyl alkylenediammonium cation (OSDA1) represented by the following formula (III) :
(C₂H₅) ₃N⁺ (CH₂) _nN⁺ (C₂H₅) ₃ (III)

wherein

n is an integer in the range of from 3 to 10, preferably from 4 to 7, most preferably 5.

In some embodiments, the first organic structure directing agent comprises a cation selected from the group consisting of N, N, N, N', N', N'-hexaethyl-1, 3-propanediammonium, N, N, N, N', N', N'-hexaethyl-1, 4-butanediammonium, N, N, N, N', N', N'-hexaethyl-1, 5-pentane-diammonium, N, N, N, N', N', N'-hexaethyl-1, 6-hexanediammonium, N, N, N, N', N', N'-hexaethyl-1, 7-heptanediammonium, and any combinations thereof. Preferably, the first organic structure directing agent comprises a cation selected from the group consisting of N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium, N, N, N, N', N', N'-hexaethyl-1, 6-hexane-diammonium, N, N, N, N', N', N'-hexaethyl-1, 7-heptanediammonium, and any combinations thereof, more preferably N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium.

In some embodiments, the second organic structure directing agent particularly comprises (C2-i) N, N, N-trimethyl-cyclohexylammonium cation represented by formula (I) :

In some other embodiments, the second organic structure directing agent particularly comprises (C2-ii) a spiro-quaternary ammonium cation represented by formula (II) ,

wherein

Ra and Rb, represent substituents on the seven-membered ring and the six-membered ring respectively, and independently from each other are hydroxyl or C₁-C₈ alkyl such as C₁-C₃ alkyl;

m represents number of Ra and is an integer in the range of from 0 to 6, preferably from 0 to 3,

n represents number of Rb and is an integer in the range of from 0 to 5, preferably from 0 to 2, and

“-” represents attachment of each Ra to one or more carbon atoms of the seven-membered ring when m is not 0, and attachment of each Rb to one or more carbon atoms of the six-membered ring when n is not 0.

Particularly, the second organic structure directing agent comprises (C2-ii) a spiro-quaternary ammonium cation represented by formula (II) wherein Ra and Rb independently from each other are C₁-C₃ alkyl, m is an integer in the range of from 0 to 3, and n is an integer in the range of from 0 to 2.

Preferably, the second organic structure directing agent comprises (C2-ii) a spiro-quaternary ammonium cation represented by formula (II) wherein m and n are 0, i.e., 6-azaspiro [5.6] dodecan-6-ium.

In some preferable embodiments of the process according to the present invention, the first organic structure directing agent comprises N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium cation and the second organic structure directing agent comprises (C2-i) N, N, N-trimethyl-cyclohexylammonium cation, or (C2-ii) a spiro-quaternary ammonium cation represented by formula (II) wherein Ra and Rb independently from each other are C₁-C₃ alkyl, m is an integer in the range of from 0 to 3, and n is an integer in the range of from 0 to 2, or any combinations thereof.

Particularly, in the process according to the present invention, the first organic structure directing agent comprises N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium cation and the second organic structure directing agent comprises (C2-i) N, N, N-trimethyl-cyclohexylammonium cation. Alternatively, in the process according to the present invention, the first organic structure directing agent comprises N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium cation and the second organic structure directing agent comprises (C2-ii) a spiro-quaternary ammonium cation represented by formula (II) wherein Ra and Rb independently from each other are C₁-C₃ alkyl, m is an integer in the range of from 0 to 3, and n is an integer in the range of from 0 to 2.

In some further preferable embodiments of the process according to the present invention, the first organic structure directing agent comprises N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium cation and the second organic structure directing agent comprises (C2-i) N, N, N-trimethyl-cyclohexylammonium cation, (C2-ii) 6-azaspiro [5.6] dodecan-6-ium cation, or any combinations thereof.

Particularly, in the process according to the present invention, the first organic structure directing agent comprises N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium cation and the second organic structure directing agent comprises (C2-i) N, N, N-trimethyl-cyclohexylammonium cation. Alternatively, in the process according to the present invention, the first organic structure directing agent comprises N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium cation and the second organic structure directing agent comprises (C2-ii) 6-azaspiro [5.6] dodecan-6-ium cation.

The first and second organic structure directing agents may be used in a molar ratio of the first organic structure directing agent to the second organic structure directing agent, in terms of respective cations, in the range of from 10 : 1 to 1 : 20, or from 5 : 1 to 1 : 10, or from 2 : 1 to 1: 7.

In some exemplary embodiments of the process according to the present invention, the second organic structure directing agent comprises (C2-i) N, N, N-trimethyl-cyclohexylammonium cation, and the molar ratio of the first organic structure directing agent to the second organic structure directing agent in terms of respective cations is in the range of from 5 : 1 to 1 : 10, or from 1 : 1 to 1 : 7, preferably from 1 : 2 to 1 : 6. Preferably, the first organic structure directing agent comprises N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium cation and the second organic structure directing agent comprises (C2-i) N, N, N-trimethyl-cyclohexylammonium cation.

In some other exemplary embodiments of the process according to the present invention, the second organic structure directing agent comprises (C2-ii) a spiro-quaternary ammonium cation represented by formula (II) as described herein, and the molar ratio of the first organic structure directing agent to the second organic structure directing agents in terms respective cations is in the range of from 5 : 1 to 1 : 10, or from 3 : 2 to 1 : 3, preferably from 1 : 1 to 1 : 2. Preferably, the first organic structure directing agent comprises a N, N, N, N', N', N'-hexaethyl- 1, 5-pentanediammonium cation and the second organic structure directing agent comprises (C2-ii) a spiro-quaternary ammonium cation represented by formula (II) wherein Ra and Rb independently from each other are C₁-C₃ alkyl, m is an integer in the range of from 0 to 3, and n is an integer in the range of from 0 to 2, among which 6-azaspiro [5.6] dodecan-6-ium cation is preferable.

The synthesis mixture may or may not comprise an additional organic structure directing agent. In some embodiments, the synthesis mixture comprises no organic structure directing agent other than the first and second organic structure directing agents. In other words, the organic structure directing agent and thus the synthesis mixture provided in step (1) comprises no cation of OSDA other than those described hereinabove for OSDA1 and OSDA2.

Suitably, the first and second organic structure directing agents, independently from each other, are in form of halide such as fluoride, chloride and bromide, hydroxide, sulfate, nitrate and carboxylate such as acetate of respective cations as described herein above, preferably chloride, bromide, hydroxide and sulfate.

Preferably, the first and second organic structure directing agents, independently from each other, are hydroxides of respective cations as described herein above.

The first and second organic structure directing agents may be present in the synthesis mixture in a total molar ratio relative to source (s) for SiO₂, calculated as the sum of the cations (OSDA1 + OSDA2) to SiO_2, in the range of from 0.01 to 1.0, preferably from 0.02 to 0.5, more preferably from 0.04 to 0.3.

There is no particular restriction to the sources for Al₂O₃ and SiO₂. Suitable examples of the source for Al₂O₃ may include, but are not limited to alumina, aluminates, aluminum alkoxides and aluminum salts, preferably alumina, aluminum tri (C₁-C₅) alkoxides, AlO (OH) , Al (OH) ₃, aluminum halides, aluminum sulfate, aluminum phosphate and aluminum fluorosilicate. Suitable examples of the source for SiO₂ may include, but are not limited to fumed silica, precipitated silica, silica hydrosols, silica gels, colloidal silica, silicic acid, silicon alkoxides, alkali metal silicates, sodium metasilicate hydrate, sesquisilicate, disilicate and silicic acid esters. Combined sources for Al₂O₃ and SiO₂ may be used alternatively or additionally, for example aluminosilicate zeolite such as FAU zeolite.

In some embodiments of the process for preparing an aluminosilicate zeolite having an AFT framework structure, an FAU zeolite as the combined sources for Al₂O₃ and SiO₂ and an additional source for SiO₂ are used. Particularly the FAU zeolite is zeolite Y, which may be in Na⁺-form, H-form or NH₄ ⁺-exchanged form. Zeolite Y having a molar ratio of SiO₂ to Al₂O₃ of no more than 40, no more than 30, no more than 20, or even no more than 10 is more preferable. The additional source for SiO₂ is selected from the group consisting of fumed silica, precipitated silica, silica hydrosols, silica gels or colloidal silica.

The synthesis mixture provided in step (1) may comprise the source (s) for SiO₂ and the source (s) for Al₂O₃ in a molar ratio calculated as SiO₂ to Al₂O₃ in the range of from 5 to 100, preferably from 10 to 50, more preferably from 15 to 40.

The synthesis mixture provided in step (1) may further comprise a source for alkali metal and/or alkaline earth metal cations (AM) , preferably alkali metal cations. The alkali metal is preferably selected from the group consisting of Li, Na, K, Cs and any combinations thereof, more preferably Na and/or K, and most preferably Na. The alkaline earth metal is preferably selected from the group consisting of Mg, Ca, Sr and Ba. Suitable sources for alkali metal and/or alkaline earth metal cations (AM) are typically halide such as fluoride, chloride and bromide, hydroxide, sulfate, nitrate and carboxylate such as acetate of the alkali metal and/or alkaline earth metal, or any combinations thereof. Preferably, the sources for the alkali metal and/or alkaline earth metal cations (AM) include chloride, bromide, hydroxide or sulfate of the alkali metal and/or alkaline earth metal, or any combinations thereof. More preferably, hydroxide of the alkali metal is used in the synthesis mixture.

The alkali metal and/or alkaline earth metal cations (AM) may be present in the synthesis mixture in a molar ratio relative to the source (s) for SiO₂, calculate as AM to SiO₂, in the range of from 0.01 to 1.0, preferably from 0.05 to 1.0, more preferably from 0.1 to 0.8.

The synthesis mixture provided in step (1) may also comprise a source for the anion OH^-. Useful source for OH^-may be for example a metal hydroxide such as alkali metal hydroxide or ammonium hydroxide. Preferably, the anion OH^-may be originated from one or more of the sources for alkali metal and/or alkaline earth metal cations (AM) and the sources for the first and/or second organic structure directing agents.

The OH^-anions may be present in the synthesis mixture in a molar ratio relative to the source (s) for SiO₂, calculated as OH^-to SiO₂, in the range of from 0.02 to 2.0, more preferably from 0.05 to 1.0, more preferably from 0.1 to 0.5.

The synthesis mixture provided in step (1) may also comprise at least one solvent, preferably water, more preferably deionized water. The solvent may be comprised in one or more of starting materials of the synthesis mixture, such as the sources for Al₂O₃, SiO₂, and the first and/or second organic structure directing agents and thus be carried into the synthesis mixture, and/or may be incorporated into the synthesis mixture separately.

In some embodiments, the synthesis mixture has a molar ratio of water to the source (s) for SiO₂, calculated as H₂O to SiO₂, in the range of from 3 to 100, preferably from 10 to 80, more preferably from 10 to 40.

In some exemplary embodiments, the synthesis mixture provided in step (1) have a molar composition as shown in the Table 1 below:

Table 1

1) the amounts of the sources for Al₂O₃ and SiO₂ are calculated as respective oxides, and the amounts of OSDA1 and OSDA2 are calculated as respective cations

In some embodiments, the synthesis mixture provided in step (1) may further comprise an amount of seed crystals of AFT zeolite. The seed crystals of AFT zeolite may be obtained from the process as described herein without using seed crystals or from conventional process using other organic structure directing agent (s) .

The synthesis mixture may be subjected to crystallization conditions to form an aluminosilicate zeolite having an AFT framework structure in step (2) with no particular restriction. The crystallization may be carried out at an elevated temperature in the range of from 80 to 250 ℃, more preferably from 100 to 200 ℃ for a period sufficient for crystallization, for example 0.5 to 12 days, 1 to 6 days, or 2 to 5 days. Typically, the crystallization is carried out under autogenous pressure, for example in a pressure tight vessel such as an autoclave. Further, the crystallization is preferably carried out without agitation.

The aluminosilicate zeolite as formed may be subjected to a work-up procedure including isolating for example by filtration, optionally washing, and drying to obtain the as-synthesized AFT zeolite. Accordingly, step (2) in the process according to the present invention optionally further comprises the work-up procedure.

The first and/or second organic structure directing agents remaining, if any, in the filtrate liquid from the filtration and optionally the washed liquid from the washing may be recycled, and used for further sythesis of the AFT zeolite.

The as-synthesized AFT zeolite typically comprises within its structure pores at least a portion of the first and second organic structure directing agents as described hereinabove.

In some embodiments, the as-synthesized AFT zeolite from step (2) may be subjected to a calcination procedure. Accordingly, the process according to the present invention further comprises step (3) of calcination of the as-synthesized AFT zeolite.

In some embodiments, the as-synthesized or the as-calcined AFT zeolite may be subjected to an ion-exchange procedure such that one or more of ionic non-framework elements contained in the zeolite are exchanged to H⁺ and/or NH₄ ⁺. Accordingly, the process according to the present invention further comprises (4) exchanging one or more of ionic non-framework elements contained in the zeolite obtained in step (2) or (3) to H⁺ and/or NH₄ ⁺, preferably NH₄ ⁺.

Generally, the zeolite having been exchanged to H⁺ and/or NH₄ ⁺ in step (4) may be subjected to a work-up procedure including isolating for example by filtration, optionally washing, and drying, and/or subjected to a calcination procedure. Accordingly, step (4) in the process according to the present invention optionally further comprises the work-up procedure and/or calcination procedure.

The calcination in step (3) and/or step (4) may be carried out at a temperature in the range of from 300 to 900 ℃, for example 350 to 700 ℃, or 400 to 650 ℃. Particularly, the calcination may be performed in a gas atmosphere having a temperature in the above-described ranges, which may be air, oxygen, nitrogen, or a mixture of two or more thereof. Preferably, the calcination is performed for a period in the range of from 0.5 to 10 hours, for example 3 to 7 hours, or 4 to 6 hours.

Aluminosilicate zeolites having an AFT framework structure could be successfully obtained from the process as described in the first aspect, as determined by X-ray powder diffraction (XRD) analysis.

Accordingly, in the second aspect, the present invention provides an aluminosilicate zeolite having an AFT framework structure obtainable and/or obtained from the process as described in the first aspect.

The aluminosilicate zeolite having an AFT framework structure has a molar ratio of silica to alumina (SAR) in the range of from 10 to 25, preferably from 11 to 20, as determined in its calcined H-form.

The aluminosilicate zeolite having an AFT framework structure according to the present invention may have an average crystal size of up to 2 μm, for exmaple up to 1 μm or up to 500 nm. The average crystal size may be determined via scanning electron microscopy (SEM) . Particularly, the average crystal size was determined via SEM by measuring the crystal sizes for at least 30 different crystals selected at random from multiple images covering different areas of the sample.

The aluminosilicate zeolite having an AFT framework structure according to the present invention is preferably at least 90%phase pure, i.e., at least 90%of the zeolite framework is of AFT type, as determined by X-ray powder diffraction (XRD) analysis. More preferably, the aluminosilicate zeolite having an AFT framework structure is at least 95%phase pure, or even more preferably at least 98%or at least about 99%.

In some embodiments, the aluminosilicate zeolite having an AFT framework structure may contain some other framework like AFX or CHA as intergrowth in minor amounts, for example less than 10%, preferably less than 5%, even more preferably less than 2%or less than 1%.

It has been surprisingly found that the aluminosilicate zeolite having an AFT framework structure as obtained from the process as described in the first aspect exhibits a higher low-temperature catalytic activity in the application of selective catalytic reduction (SCR) of NOx, compared with the zeolite having the same framework type but prepared otherwise.

Accordingly, in the third aspect, the present invention further provides an SCR catalyst composition which comprises the aluminosilicate zeolite having an AFT framework structure according to the present invention and a promoter metal.

The term “promoter metal” as used herein refers to a non-framework metal capable of improving the catalytic activity of a zeolite. The “non-framework metal” is intended to mean that the metal does not participate in constituting the zeolite framework structure. The promoter metal may reside within the zeolite and/or on at least a portion of the zeolite surface, preferably in form of ionic species.

Particularly, the SCR catalyst composition according to the present invention comprises the aluminosilicate zeolite having an AFT framework structure and a promoter metal present within and/or on the aluminosilicate zeolite having an AFT framework structure.

The aluminosilicate zeolite having an AFT framework structure useful in the SCR catalyst composition according to the present invention is the one obtained and/or obtainable by the process as described in the first aspect or are those as described in the second aspect. Any general and particular description with respect to the process in the first aspect or the aluminosilicate zeolite having an AFT framework structure in the second aspect are incorporated here by reference.

The promoter metal may be any metals known useful for improving catalytic performance of zeolites in the application of selective catalytic reduction (SCR) of NOx. Generally, the promoter metal may be selected from transition metals, for example precious metals such as Au, Ag and platinum group metals, base metals such as Cr, Zr, Nb, Mo, Fe, Mn, W, V, Ti, Co, Ni, Cu and Zn, alkali earth metals such as Ca and Mg, and Sb, Sn and Bi, and any combinations thereof.

In a preferable embodiment, the SCR catalyst composition comprises at least Cu and/or Fe as the promoter metal. In some particular embodiments, the SCR catalyst composition comprises Cu as the promoter metal.

The promoter metal may be present in the SCR catalyst composition at an amount of 0.1 to 10 %by weight, preferably 0.5 to 10 %by weight, more preferably 1 to 7 %by weight, particularly 2 to 6 %by weight, on an oxide basis, based on the total weight of the promoter metal and the aluminosilicate zeolite having an AFT framework structure. In some particular embodiments wherein copper, iron or the combination thereof is used as the promoter metal, the promoter metal is preferably present in the SCR catalyst composition at an amount of 1 to 5 %by weight, more preferably 2 to 5%by weight, on an oxide basis, based on the total weight of the promoter metal and the aluminosilicate zeolite having an AFT framework structure.

Alternatively, the promoter metal may be present in the SCR catalyst composition at an amount of 0.1 to 1.0 moles, preferably 0.2 to 0.7 moles, more preferably 0.3 to 0.5 moles, per mole of framework aluminum of the aluminosilicate zeolite having an AFT framework structure. In some particular embodiments wherein copper, iron or the combination thereof is used as the promoter metal, the amount of the promoter metal is 0.2 to 0.7 moles, preferably 0.3 to 0.5 moles per mole of framework aluminum of the aluminosilicate zeolite having an AFT framework structure.

In some preferable embodiments, the SCR catalyst composition according to the present invention comprises

- an aluminosilicate zeolite having an AFT framework structure, which has a molar ratio of silica to alumina (SAR) in the range of from 10 to 25, and

- a promoter metal present within and/or on the aluminosilicate zeolite, which is Cu and/or Fe, particularly Cu,

wherein the promoter metal is present at an amount of 0.2 to 0.7 moles per mole of framework aluminum of the aluminosilicate zeolite.

In some other preferable embodiments, the SCR catalyst composition according to the present invention comprises

- a promoter metal present within and/or on the aluminosilicate zeolite, which is Cu and/or Fe, wherein the promoter metal is present at an amount of 0.3 to 0.5 moles per mole of framework aluminum of the aluminosilicate zeolite.

In some more preferable embodiments, the SCR catalyst composition according to the present invention comprises

- a promoter metal Cu present within and/or on the aluminosilicate zeolite,

wherein Cu is present at an amount of 0.3 to 0.5 moles per mole of framework aluminum of the aluminosilicate zeolite.

In an exemplary embodiment, the SCR catalyst composition according to the present invention comprises

- an aluminosilicate zeolite having an AFT framework structure, which has a molar ratio of silica to alumina (SAR) in the range of from 11 to 20, and

- a promoter metal Cu present within and/or on the aluminosilicate zeolite,

The promoter metal may be incorporated into the aluminosilicate zeolite having an AFT framework structure via any known processes, for example ion exchange and impregnation. For example, the promoter metal may be incorporated into the aluminosilicate zeolite having an AFT framework structure by mixing the aluminosilicate zeolite into a solution of a soluble precursor of the promoter metal. The zeolite upon ion-exchanging with the promoter metal typically in form of cation may be conventionally washed, dried and calcined. Useful soluble precursors of the promoter metal may be for example salts of the promoter metal, complexes of the promoter metal and a combination thereof. Alternatively, the promoter metal may be incorporated into the aluminosilicate zeolite having an AFT framework structure in situ during the preparation of catalytic articles such as extrudate or coated monolith as described hereinbelow.

It has been found that the SCR catalyst composition according to the present invention has a desirable activity in applications for selective catalytic reduction (SCR) of NOx. Moreover, it has been surprisingly found that the SCR catalyst composition according to the present invention has an improved low-temperature activity in applications for selective catalytic reduction (SCR) of NOx.

In the fourth aspect, the present invention provides use of the aluminosilicate zeolite having an AFT framework structure obtained and/or obtainable by the process as described herein in catalysts for selective catalytic reduction (SCR) of NOx.

For the SCR applications, the aluminosilicate zeolite having an AFT framework structure, preferably loaded with the promoter metal as described hereinabove, may be applied in form of an extrudate or in form of a washcoat on a monolithic substrate.

Accordingly, in the fifth aspect, the present invention provides a catalytic article in form of an extrudate comprising a catalyst composition or in form of a monolith comprising a washcoat containing a catalyst composition on substrate, wherein the catalyst composition comprises the aluminosilicate zeolite having an AFT framework structure as described in the second aspect and a promoter metal, or the catalyst composition is the SCR catalyst composition as described in the third aspect.

The term “extrudate” generally refers to shaped body formed by extrusion. According to the present invention, the extrudate comprising the aluminosilicate zeolite having an AFT framework structure and the promoter metal typically has a honeycomb structure.

The term “washcoat” has its usual meaning in the art, that is a thin, adherent coating of a catalytic or other material applied to a substrate.

The term “substrate” generally refers to a monolithic material onto which a catalytic coating is disposed, for example monolithic honeycomb substrate, particularly flow-through monolithic substrate and wall-flow monolithic substrate.

The aluminosilicate zeolite having an AFT framework structure and the promoter metal may be processed into the application forms by any known processes with no particular restriction. In a further aspect, the present invention relates to an exhaust gas treatment system comprising an internal combustion engine and an exhaust gas conduit in fluid communication with the internal combustion engine, wherein the catalytic article as described herein is present in the exhaust gas conduit.

The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as “The …according to any one of embodiments 1 to 4” , every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to “The …according to any one of embodiments 1, 2, 3, and 4” . Further, it is explicitly noted that the following set of embodiments is not the set of claims determining the extent of protection, but represents a suitably structured part of the description directed to general and preferred aspects of the present invention.

Embodiments

1. A process for preparing an aluminosilicate zeolite having an AFT framework structure, which includes

(1) providing a synthesis mixture comprising

(A) a source for Al₂O₃,

(B) a source for SiO₂,

(C2) a source for second organic structure directing agent comprising

(C2-i) N, N, N-trimethyl-cyclohexylammonium cation represented by formula (I) ,

or

(C2-ii) a spiro-quaternary ammonium cation represented by formula (II) ,

wherein

Ra and Rb, represent substituents on the seven-membered ring and the six-membered ring respectively, and independently from each other are hydroxyl or C₁-C₈ alkyl,

m represents number of Ra and is an integer in the range of from 0 to 6,

n represents number of Rb and is an integer in the range of from 0 to 5, and

or a combination thereof,

and

2. The process according to embodiment 1, wherein the alkylene moiety in the N, N, N, N', N', N'-hexaethyl alkylenediammonium cation is selected from substituted or unsubstituted straight chain or branched chain C₃-C₁₀ alkanediyl.

3. The process according to embodiment 2, wherein the alkylene moiety in the N, N, N, N', N', N'-hexaethyl alkylenediammonium cation is selected from unsubstituted straight chain or branched chain C₃-C₁₀ alkanediyl.

4. The process according to embodiment 3, wherein the N, N, N, N', N', N'-hexaethyl alkylenediammonium cation is of following formula (III) :
(C₂H₅) ₃N⁺ (CH₂) _nN⁺ (C₂H₅) ₃ (III)

wherein

5. The process according to embodiment 4, wherein the N, N, N, N', N', N'-hexaethyl alkylenediammonium cation is selected from the group consisting of N, N, N, N', N', N'-hexaethyl-1, 3-propanediammonium, N, N, N, N', N', N'-hexaethyl-1, 4-butanediammonium, N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium, N, N, N, N', N', N'-hexaethyl-1, 6-hexanediammonium, N, N, N, N', N', N'-hexaethyl-1, 7-heptanediammonium, and any combinations thereof, preferably N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium, N, N, N, N', N', N'-hexaethyl-1, 6-hexanediammonium, N, N, N, N', N', N'-hexaethyl-1, 7- heptanediammonium, and any combinations thereof.

6. The process according to embodiment 5, wherein the N, N, N, N', N', N'-hexaethyl alkylenediammonium cation is N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium.

7. The process according to any of embodiments 1 to 6, wherein in formula (II) , Ra and Rb independently from each other are C₁-C₃ alkyl, m is an integer in the range of from 0 to 3, and n is an integer in the range of from 0 to 2.

8. The process according to any of embodiments 1 to 7, wherein in formula (II) , m and n are 0.

9. The process according to any of embodiments 1 to 6, wherein the first organic structure directing agent comprises the N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium cation and the second organic structure directing agent comprises (C2-i) the N, N, N-trimethyl-cyclohexylammonium cation.

10. The process according to any of embodiments 1 to 8, wherein the first organic structure directing agent (C1) comprises the N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium cation and the second organic structure directing agent comprises (C2-ii) the spiro-quaternary ammonium cation represented by formula (II) .

11. The process according to any of embodiments 1 to 10, wherein the first and second organic structure directing agents are used in a molar ratio of the first organic structure directing agent to the second organic structure directing agent in terms of respective cations in the range of from 10 : 1 to 1 : 20.

12. The process according to embodiment 11, wherein the molar ratio is in the range of from 5: 1 to 1 : 10.

13. The process according to embodiment 12, wherein the molar ratio is in the range of from 2: 1 to 1 : 7.

14. The process according to embodiment 9, wherein the first and second organic structure directing agents are used in a molar ratio of the first organic structure directing agent to the second organic structure directing agent in terms of respective cations in the range of from 5: 1 to 1 : 10.

15. The process according to embodiment 14, wherein the molar ratio is in the range of from 1: 1 to 1 : 7.

16. The process according to embodiment 15, wherein the molar ratio is in the range of from 1: 2 to 1 : 6.

17. The process according to embodiment 10, wherein the first and second organic structure directing agents are used in a molar ratio of the first organic structure directing agent to the second organic structure directing agent in terms of respective cations in the range of from 5 : 1 to 1 : 10.

18. The process according to embodiment 17, wherein the molar ratio is in the range of from 3: 2 to 1 : 3.

19. The process according to embodiment 18, wherein the molar ratio is in the range of from 1: 1 to 1 : 2.

20. The process according to any of embodiments 1 to 19, wherein the sources for Al₂O₃ and SiO₂ comprise FAU zeolites, particularly zeolite Y, more preferably zeolite Y having a molar ratio of SiO₂ to Al₂O₃ of no more than 40, no more than 30, no more than 20, or even no more than 10.

21. The process according to embodiment 20, wherein an additional source for SiO₂ is used.

22. The process according to any of embodiments 1 to 21, wherein the synthesis mixture has a molar ratio of SiO₂ to Al₂O₃ in the range of from 5 to 100, for example from 10 to 50, preferably from 15 to 40.

23. An aluminosilicate zeolite having an AFT framework structure obtained and/or obtainable by the process according to any of embodiments 1 to 22.

24. The aluminosilicate zeolite according to embodiment 23, which has a molar ratio of silica to alumina in the range of from 10 to 25, preferably from 11 to 20.

25. The aluminosilicate zeolite according to embodiment 23 or 24, which has an average crystal size of up to 2 μm.

26. Use of the aluminosilicate zeolite according to any of embodiments 23 to 25 in catalysts for selective catalytic reduction of nitrogen oxides.

27. An SCR catalyst composition, which comprises the aluminosilicate zeolite according to any of embodiments 23 to 25 and a promoter metal.

28. The SCR catalyst composition according to embodiment 27, wherein the promoter metal is selected from transition metals, alkali earth metals, Sb, Sn and Bi, and any combinations thereof, preferably comprising Cu and/or Fe, preferably Cu.

29. The SCR catalyst composition according to embodiment 28, wherein the promoter metal consists of Cu and/or Fe.

30. A catalytic article, which is in form of an extrudate comprising a catalyst composition or in form of a monolith comprising a washcoat containing a catalyst composition on a substrate, wherein the catalyst composition is the SCR catalyst composition as defined in any of embodiments 27 to 29.

31. An exhaust gas treatment system, which comprises an internal combustion engine and an exhaust gas conduit in fluid communication with the internal combustion engine, wherein the catalytic article according to embodiment 30 is present in the exhaust gas conduit.

32. A method for selective catalytic reduction of nitrogen oxides, which includes contacting a gas stream comprising nitrogen oxides with an SCR catalyst composition according to any of embodiments 27 to 29 or the catalytic article according to embodiment 30.

The invention will be further illustrated by following Examples, which set forth particularly advantageous embodiments. While the Examples are provided to illustrate the present invention, they are not intended to limit the present invention.

Examples

Scanning electron microscopy (SEM) measurements were performed by a scanning electron microscope (Hitachi SU1510) .

X-ray powder diffraction (XRD) patterns were measured with PANalytical X'pert³ Powder Diffractometer (40kV, 40 mA) using CuKαradiation to collect data in Bragg-Brentano geometry.

Example 1 Preparation of aluminosilicate AFT zeolite with N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium hydroxide and tetraethylammonium hydroxide as the organic structure directing agents (Material A, calcined H-form)

147 g of an aqueous solution of tetraethylammonium hydroxide (20 wt%) and 289 g of an aqueous solution of N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium hydroxide (20 wt%) were mixed with 4169 g of D.I. water, followed by addition of 255.9 g of sodium hydroxide (99%, solid) . After sodium hydroxide dissolved, 131.2 g of Zeolite HY (SAR = 7.2, from Shandong Duoyou) and 1368.9 g ofAS-40 colloidal silica were added. After stirring at room temperature for 30 mins, the synthesis mixture was transferred into an autoclave for crystallization. The crystallization was carried out at 150 ℃ for 3 days under static condition. After cooling to room temperature, the zeolite product was collected by filtration and dried at 120 ℃ overnight. The as-synthesized zeolite was calcined at 550 ℃ for 6 hours to remove the organic structure directing agents.

The calcined zeolite was crushed and ion-exchanged in a 10 wt%aqueous NH₄Cl solution at a solid/liquid ratio of 1: 10. The ion exchange process was carried out at 80 ℃ for 2 hours and repeated twice. After the ion exchange, the product was collected by filtration, washed with D. I. water, dried at 120 ℃ overnight, and calcined at 450 ℃ for 6 hours to obtain the calcined H-form zeolite.

The zeolite has a SiO₂/Al₂O₃ molar ratio of (SAR) of 16, as measured on the calcined H-form by XRF.

The crystal morphology of the zeolite observed from the SEM image and the XRD pattern of the zeolite are shown in Figure 1A and Figure 2 respectively. It was confirmed by the XRD pattern that the zeolite has a typical AFT framework.

Example 2 Preparation of aluminosilicate AFT zeolite with N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium hydroxide and 6-azaspiro [5.6] dodecan-6-ium hydroxide as the organic structure directing agents (Material B, calcined H-form)

74 g of an aqueous solution of 6-azaspiro [5.6] dodecan-6-ium hydroxide (20 wt%) and 86.7 g of an aqueous solution of N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium hydroxide (20 wt%) were mixed with 110.4 g of D. I. water, followed by addition of 8 g of sodium hydroxide (99%, solid) . After sodium hydroxide dissolved, 35.57 g of Zeolite HY (SAR = 7.2, from Shandong Duoyou) and 144.3 g ofAS-40 colloidal silica were added. After stirring at room temperature for 30 mins, the synthesis mixture was transferred into an autoclave for crystallization. The crystallization was carried out at 150 ℃ for 3 days under static condition. After cooling to room temperature, the zeolite product was collected by filtration and dried at 120 ℃ overnight. The as-synthesized zeolite was calcined at 550 ℃ for 6 hours to remove the organic structure directing agents.

The zeolite has a SiO₂/Al₂O₃ molar ratio of (SAR) of 19, as measured on the calcined H-form by XRF.

The crystal morphology of the zeolite observed from the SEM image and the XRD pattern of the zeolite are shown in Figure 1 B and Figure 2 respectively. It was confirmed by the XRD pattern that the zeolite has a typical AFT framework.

Example 3 Preparation of aluminosilicate AFT zeolite with N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium hydroxide and N, N, N-trimethyl-cyclohexylammonium hydroxide as the organic structure directing agents (Material C, calcined H-form)

39.2 g of an aqueous solution of N, N, N-trimethyl-cyclohexylammonium hydroxide (20 wt%) and 14.4 g of an aqueous solution of N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium hydroxide (20 wt%) were mixed with 196.2 g of D.I. water, followed by addition of 7.9 g of sodium hydroxide (99%, solid) . Then, 35.8 g of Zeolite HY (SAR = 7.2, from Shandong Duoyou) and 114.3 g ofAS-40 colloidal silica were added. After stirring at room temperature for 30 mins, the synthesis mixture was transferred into an autoclave for crystallization. The crystallization was carried out at 150 ℃ for 3 days under static condition. After cooling to room temperature, the zeolite product was collected by filtration and dried at 120 ℃ overnight. The as-synthesized zeolite was calcined at 550 ℃ for 6 hours to remove the organic structure directing agents.

The zeolite has a SiO₂/Al₂O₃ molar ratio of (SAR) of 18, as measured on the calcined H-form by XRF.

The crystal morphology of the zeolite observed from the SEM image and the XRD pattern of the zeolite are shown in Figure 1C and Figure 2 respectively. It was confirmed by the XRD pattern that the zeolite has a typical AFT framework.

Example 4 Preparation of Cu-loaded AFT zeolite material (SCR catalyst)

The H-form zeolite powder as obtained was impregnated with an aqueous copper (II) nitrate solution by incipient wetness impregnation and maintained at 50 ℃ for 20 hours in a sealed container. The obtained solid was dried and calcined in air in a furnace at 450 ℃ for 5 hours, to obtain a Cu-loaded zeolite.

The Cu-loaded AFT zeolite materials as prepared in accordance with the above general procedure are summarized in the Table 2 below.

Table 2

Example 5 Test of Catalyst Performance

For test of SCR performance, each Cu-loaded zeolite materials was slurried with an aqueous solution of Zr-acetate and then dried at ambient temperature in air under stirring, and calcined at 550 ℃ for 1 hour to provide a product containing 5 wt%ZrO₂ as the binder based on the amount of the product. The product was crushed and the powder fraction of 250 to 500 microns was aged at 650 ℃ for 50 hours or 820 ℃ for 16 hours in a flow of 10 vol%steam/air to provide the sample for the test.

The selective catalytic reduction (SCR) test was carried out in a fixed-bed reactor with loading 120 mg of the test sample together with corundum of the same sieve fraction as diluent to about 1mL bed volume, in accordance with following conditions:

Gas feed: 500 vppm NO, 500 vppm NH₃, 5 vol%H₂O, 10 vol%O₂ and balance of N₂, with gas hourly space velocity (GHSV) of 120,000 h^-1;

Temperature: RUN1 -200, 400, 575 ℃ (first run for degreening) RUN2 -175, 200, 225, 250, 350, 450, 550, 575 ℃.

NOx conversions as measured from RUN 2 at 200 ℃ and 575 ℃ are reported as the test results, which are summarized in Table 3 below.

Table 3

It can be seen that the catalysts comprising Cu-loaded AFT zeolite according to the present invention are effective for selective catalytic reduction (SCR) of nitrogen oxides, especially exhibit improved NOx removal activity at the lower temperature.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It will be apparent to those of skill in the art that various modifications and variations can be made to the method and apparatus of the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention include modifications and variations that are within the scope of the appended claims and their equivalents.

Claims

A process for preparing an aluminosilicate zeolite having an AFT framework structure, which includes

(1) providing a synthesis mixture comprising

(A) a source for Al₂O₃,

(B) a source for SiO₂,

(C1) a source for first organic structure directing agent comprising a N, N, N, N', N', N'-hexaethyl alkylenediammonium cation wherein the alkylene moiety is substituted or unsubstituted straight chain or branched chain having 3 to 10 carbons, and

(C2) a source for second organic structure directing agent comprising

(C2-i) N, N, N-trimethyl-cyclohexylammonium cation represented by formula (I) ,

or

(C2-ii) a spiro-quaternary ammonium cation represented by formula (II) ,

wherein

Ra and Rb, represent substituents on the seven-membered ring and the six-membered ring respectively, and independently from each other are hydroxyl or C₁-C₈ alkyl,

m represents number of Ra and is an integer in the range of from 0 to 6,

n represents number of Rb and is an integer in the range of from 0 to 5, and

“-” represents attachment of each Ra to one or more carbon atoms of the seven-membered ring when m is not 0, and attachment of each Rb to one or more carbon atoms of the six-membered ring when n is not 0,

or a combination thereof,

and

(2) subjecting the synthesis mixture to crystallization conditions to form an aluminosilicate zeolite having an AFT framework structure.
The process according to claim 1, wherein the alkylene moiety in the N, N, N, N', N', N'- hexaethyl alkylenediammonium cation is selected from substituted or unsubstituted straight chain or branched chain C₃-C₁₀ alkanediyl, preferably unsubstituted straight chain or branched chain C₃-C₁₀ alkanediyl.
The process according to claim 2, wherein the N, N, N, N', N', N'-hexaethyl alkylenediammonium cation is of following formula (III) :
(C₂H₅) ₃N⁺ (CH₂) _nN⁺ (C₂H₅) ₃ (III)

wherein

n is an integer in the range of from 3 to 10, preferably from 4 to 7, most preferably 5.
The process according to claim 3, wherein the N, N, N, N', N', N'-hexaethyl alkylenediammonium cation is selected from the group consisting of N, N, N, N', N', N'-hexaethyl-1, 3-propanediammonium, N, N, N, N', N', N'-hexaethyl-1, 4-butanediammonium, N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium, N, N, N, N', N', N'-hexaethyl-1, 6-hexanediammonium, N, N, N, N', N', N'-hexaethyl-1, 7-heptanediammonium, and any combinations thereof, preferably N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium, N, N, N, N', N', N'-hexaethyl-1, 6-hexanediammonium, N, N, N, N', N', N'-hexaethyl-1, 7-heptanediammonium, and any combinations thereof.
The process according to claim 4, wherein the N, N, N, N', N', N'-hexaethyl alkylenediammonium cation is N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium.
The process according to any of claims 1 to 5, wherein in formula (II) , Ra and Rb independently from each other are C₁-C₃ alkyl, m is an integer in the range of from 0 to 3, and n is an integer in the range of from 0 to 2.
The process according to any of claims 1 to 6, wherein in formula (II) , m and n are 0.
The process according to any of claims 1 to 5, wherein the first organic structure directing agent comprises the N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium cation and the second organic structure directing agent comprises (C2-i) the N, N, N-trimethyl-cyclohexylammonium cation.
The process according to any of claims 1 to 7, wherein the first organic structure directing agent (C1) comprises the N, N, N, N', N', N'-hexaethyl-1, 5-pentanediammonium cation and the second organic structure directing agent comprises (C2-ii) the spiro-quaternary ammonium cation represented by formula (II) .
The process according to any of claims 1 to 9, wherein the first and second organic structure directing agents are used in a molar ratio of the first organic structure directing agent to the second organic structure directing agent in terms of respective cations in the range of from 10 : 1 to 1 : 20, or from 5 : 1 to 1 : 10, or from 2 : 1 to 1 : 7.
The process according to claim 8, wherein the first and second organic structure directing agents are used in a molar ratio of the first organic structure directing agent to the second organic structure directing agent in terms of respective cations in the range of from 5 : 1 to 1 : 10, or from 1 : 1 to 1 : 7, preferably from 1 : 2 to 1 : 6.
The process according to claim 9, wherein the first and second organic structure directing agents are used in a molar ratio of the first organic structure directing agent to the second organic structure directing agent in terms of respective cations in the range of from 5 : 1 to 1 : 10, or from 3 : 2 to 1 : 3, preferably from 1 : 1 to 1 : 2.
The process according to any of claims 1 to 12, wherein the sources for Al₂O₃ and SiO₂ comprise FAU zeolites, particularly zeolite Y, more preferably zeolite Y having a molar ratio of SiO₂ to Al₂O₃ of no more than 40, no more than 30, no more than 20, or even no more than 10.
The process according to claim 13, wherein an additional source for SiO₂ is used.
The process according to any of claims 1 to 14, wherein the synthesis mixture has a molar ratio of SiO₂ to Al₂O₃ in the range of from 5 to 100, for example from 10 to 50, preferably from 15 to 40.
An aluminosilicate zeolite having an AFT framework structure obtained and/or obtainable by the process according to any of claims 1 to 15.
The aluminosilicate zeolite according to claim 16, which has a molar ratio of silica to alumina in the range of from 10 to 25, preferably from 11 to 20.
The aluminosilicate zeolite according to claim 16 or 17, which has an average crystal size of up to 2 μm.
Use of the aluminosilicate zeolite according to any of claims 16 to 18 in catalysts for selective catalytic reduction of nitrogen oxides.
An SCR catalyst composition, which comprises the aluminosilicate zeolite according to any of claims 16 to 18 and a promoter metal.
The SCR catalyst composition according to claim 20, wherein the promoter metal is selected from transition metals, alkali earth metals, Sb, Sn and Bi, and any combinations thereof, preferably comprising Cu and/or Fe, preferably Cu.
The SCR catalyst composition according to claim 21, wherein the promoter metal consists of Cu and/or Fe.
A catalytic article, which is in form of an extrudate comprising a catalyst composition or in form of a monolith comprising a washcoat containing a catalyst composition on a substrate, wherein the catalyst composition is the SCR catalyst composition as defined in any of claims 20 to 22.
An exhaust gas treatment system, which comprises an internal combustion engine and an exhaust gas conduit in fluid communication with the internal combustion engine, wherein the catalytic article according to claim 23 is present in the exhaust gas conduit.
A method for selective catalytic reduction of nitrogen oxides, which includes contacting a gas stream comprising nitrogen oxides with an SCR catalyst composition according to any of claims 20 to 22 or the catalytic article according to claim 23.