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CN110961145A - Symbiotic composite molecular sieve with CHA/AFX structure, preparation method thereof and SCR application thereof - Google Patents

Symbiotic composite molecular sieve with CHA/AFX structure, preparation method thereof and SCR application thereof Download PDF

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CN110961145A
CN110961145A CN201911287107.8A CN201911287107A CN110961145A CN 110961145 A CN110961145 A CN 110961145A CN 201911287107 A CN201911287107 A CN 201911287107A CN 110961145 A CN110961145 A CN 110961145A
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molecular sieve
ssz
silicon
aluminum
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王志光
柳海涛
王贤彬
王炳春
李进
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China Catalyst New Material Co ltd
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
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    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
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    • B01J29/00—Catalysts comprising molecular sieves
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    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/70—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65
    • B01J29/72—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65 containing iron group metals, noble metals or copper
    • B01J29/76—Iron group metals or copper
    • B01J29/763—CHA-type, e.g. Chabazite, LZ-218

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Abstract

The invention discloses a preparation method of an intergrowth composite molecular sieve and an SCR catalyst with a CHA/AFX structure, which are formed by intergrowth of CHA and AFX topological structure molecular sieves, wherein a phase spectrogram of an X-ray diffraction of the molecular sieve with the intergrowth structure has a characteristic diffraction peak at a specific 2 theta angle; the molar ratio of silicon oxide to aluminum oxide in the intergrowth composite molecular sieve is 10-200. In the preparation of the symbiotic composite molecular sieve, a composite template agent is adopted, FAU type silicon-aluminum molecular sieves are used as an aluminum source and a silicon source, or other silicon sources and alkali sources are combined to form a mixed sol, and the CHA/AFX symbiotic composite molecular sieve is synthesized by dynamic temperature-section crystallization; and exchanging with soluble metal salt cations, and coating the carrier with the exchange solution to obtain the SCR molecular sieve catalyst. The symbiotic composite molecular sieve obtained by the invention has more reasonably distributed acidity and good hydrothermal stability, has good catalytic activity and excellent service life in SCR reaction of NOx-containing gas discharged by a mobile source and a fixed source, and can well meet the standard requirement of tail gas emission.

Description

Symbiotic composite molecular sieve with CHA/AFX structure, preparation method thereof and SCR application thereof
Technical Field
The invention relates to an intergrowth composite molecular sieve with a CHA/AFX structure, a preparation method thereof and SCR (Selective catalytic reduction) application, in particular to synthesis of an SSZ-13/SSZ-16 intergrowth composite molecular sieve and preparation of a catalyst thereof, belonging to the fields of chemical synthesis technology and application thereof.
Background
The SSZ-13 molecular sieve belongs to a CHA type topological structure and has orthogonal symmetry, a one-dimensional main channel is formed by double eight-membered rings, the size of an orifice is 0.38nm multiplied by 0.38nm, and the framework density is 14.5. The SSZ-16 molecular sieve belongs to AFX topological configuration type molecular sieve, and has three-dimensionally intersected eight-membered ring pore channel and relatively smaller pore channel size (
Figure BDA0002318313230000011
) The framework density was 14.7 and consisted of elongated larger aft cages (0.55X 1.35nm) and smaller gme cages (0.33X 0.74 nm). The Cu-SSZ-16 keeps the NOx conversion rate higher than 90 percent at the high temperature ranging from 400 ℃ to 550 ℃ all the time, and has slightly better high-temperature NOx compound SCR reaction conversion rate than the Cu-SSZ-13 molecular sieve.
For copper supported molecular sieve catalysts, the structure of the molecular sieve also has an effect on the distribution of copper species, and through the association of copper species with activity and topology, the d6r building block in the small pore cage molecular sieve is believed to be the key to the generation of highly active copper species. Meanwhile, the existence of pores with proper size can also better reduce the formation of low-activity CuO cluster particles and effectively limit the generation of byproducts, namely NH3The SCR process brings about advantageous effects.
Generally, the SCR catalyst is a molecular sieve having a crystal structure prepared by using zeolite as a carrier and loading an SCR active component, wherein the zeolite is an aluminosilicate crystal material having a fairly regular pore size, and patents EP1961933a1, EP1147801a1, EP 2123614a2, US7332148B2, EP1579911a1 and US20030143141a1 disclose X zeolite, Y zeolite, β zeolite, mordenite, ferrierite, a zeolite, erionite, L zeolite, ZSM-5, ZSM-8, ZSM-11 and ZSM-12 zeolite molecular sieves and the like as SCR catalyst carriers, and these zeolites can be exchanged with metals such as Cu, Fe, Mn, Ag, V, Ti and Co, or the zeolite itself contains a part of metals such as Cu and Fe.
Disclosure of Invention
The invention aims to solve the technical problem of overcoming the defect that the activity of an SCR catalyst for synthesizing a molecular sieve by using supported iron and copper is lower at low temperature through a hydrothermal durability test in the prior art, and provides a copper-based SCR catalyst which still has higher activity at low temperature after the hydrothermal durability test and a preparation method thereof.
The invention aims to provide a metal-loaded SSZ-13/SSZ-16 symbiotic composite molecular sieve catalyst which is used for catalytic reduction (SCR) treatment of waste gas NOx of internal combustion engines, gas turbines, coal or fuel oil power generation and the like, and improves hydrothermal stability and ignition activity. In a particular embodiment of the invention, the method is used for treating a NOx-containing exhaust gas of a lean-burn internal combustion engine, such as a diesel engine, a lean-burn gasoline engine or an engine powered by liquid petroleum gas or natural gas, the NOx-containing exhaust gas of which is preferably an exhaust gas stream emitted by a motor vehicle, more preferably an exhaust gas stream obtained from a lean-burn engine, even more preferably a diesel exhaust gas stream.
The molecular sieve catalysts of the present invention can also be used to treat gases from industrial processes such as refining, NOx-containing gases from refining heaters and boilers, furnaces, chemical processing industries, coke ovens, municipal waste treatment plants, and incinerators. Nitrogen oxides (NOx), including various compounds, such as nitrous oxide (N)2O), Nitric Oxide (NO), nitrogen dioxide (NO)2) Dinitrogen trioxide (N)2O3) Dinitrogen tetroxide (N)2O4) And dinitrogen pentoxide (N)2O5) And the like.
The process for treating a gas stream comprising NOx wherein prior to contacting the catalyst with the gas stream, NO2 is present in an amount of 80 wt.% or less, based on NOx, based on 100 wt.% and preferably comprising 5 to 70 wt.%, more preferably 10to 60 wt.%, more preferably 15 to 55 wt.%, even more preferably 20 to 50 wt.% NO2And (4) content. An oxidation catalyst located upstream of the catalyst oxidizes nitrogen monoxide in the gas to nitrogen dioxide and then mixes the resulting gas with a nitrogenous reductant prior to the mixture being added to the zeolite catalyst, wherein the oxidation catalyst is adapted to produce a gas stream entering the zeolite catalyst, the gas stream having a ratio of 4: 1 to 1: 3 NO: NO2 volume ratio.
In a Selective Catalytic Reduction (SCR) system, which generally uses a reducing agent (urea, NH3, etc.), several chemical reactions occur, all of which represent reactions that reduce NOx to elemental nitrogen. In particular, the dominant reaction mechanism at low temperature is represented by formula (1).
4NO+4NH3+O2→4N2+6H2O (1)
Non-selective reaction with competing oxygen, or formation of 2-fold products, or non-productive consumption of NH3. As such a non-selective reaction, for example, NH represented by the formula (2)3Is completely oxidized.
4NH3+5NO2→4NO+6H2O (2)
Furthermore, NO present in NOx2And NH3The reaction of (3) is considered to proceed by means of the reaction formula.
3NO2+4NH3→(7/2)N2+6H2O (3)
And NH3With NO and NO2The reaction between (a) and (b) is represented by the reaction formula (4).
NO+NO2+2NH3→2N2+3H2O (4)
The reaction rates of the reactions (1), (3) and (4) are greatly different depending on the reaction temperature and the kind of the catalyst used, and the rate of the reaction (4) is usually 2 to 10 times the rate of the reactions (1) and (3).
In the SCR catalyst, in order to improve NOx purification ability at low temperature, it is necessary to make the reaction of formula (4) dominant, not the reaction of formula (1). The reaction of formula (4) is dominant at low temperatures, preferably increasing NO2This is obvious.
Therefore, at a low temperature of 150-300 ℃, copper has excellent adsorption capacity to NO and has stronger NO oxidation capacity. The oxidation reaction of NO is represented by formula (5).
NO+1/2O2→NO2(5)
In order to solve the problems, the technical scheme provided by the invention is as follows: the preparation method comprises the steps of taking an intergrowth composite molecular sieve containing a CHA structure molecular sieve and an AFX structure molecular sieve as a main matrix component of the catalyst, and effectively introducing active metal components such as copper, iron and the like to prepare the copper-based or iron-based SCR molecular sieve catalyst.
The invention provides an intergrowth composite molecular sieve with a CHA/AFX structure, which is characterized in that: the composite material is formed by intergrowth of CHA and AFX topological structure molecular sieves, wherein the CHA structure molecular sieve accounts for 60-99% of the total weight, and the AFX structure molecular sieve accounts for 1.0-40% of the total weight; the intergrowth composite molecular sieve has a silica to alumina molar ratio (nSiO)2/nAl2O3) 10to 200; the molecular sieve X-ray diffraction phase spectrogram of the intergrowth structure has characteristic peaks at the 2 theta angles of 7.42 +/-0.2, 8.64 +/-0.2, 9.40 +/-0.2, 11.56 +/-0.2, 12.86 +/-0.2, 13.80 +/-0.2, 15.54 +/-0.2, 15.90 +/-0.2, 17.52 +/-0.2, 17.76 +/-0.2, 20.20 +/-0.2, 20.44 +/-0.2, 21.66 +/-0.2, 24.60 +/-0.2, 25.80 +/-0.2, 27.82 +/-0.2, 30.38 +/-0.2, 30.70 +/-0.2, 31.30 +/-0.2, 34.24 +/-0.2 and 33.50 +/-0.2.
The intergrowth composite molecular sieve with the CHA/AFX topological structure is characterized in that: the CHA structure molecular sieve specifically comprises any one or more of SSZ-13, SAPO-34, chabazite, MeAPO-47, CoAPO-44, AlPO-34 and SSZ-62, and preferably is an SSZ-13 silicon-aluminum molecular sieve; the AFX structure molecular sieve specifically comprises any one or more of SAPO-56 and SSZ-16, and preferably is an SSZ-16 silicon-aluminum molecular sieve.
Further, in the above technical solution, the synthesis method of the intergrowth composite aluminosilicate molecular sieve having CHA/AFX topology of the present invention is characterized in that:
1) mixing FAU type molecular sieve, silicon source, NaOH, composite organic template agent and deionized water under ultrasonic stirring condition, wherein FAU type silicon-aluminum molecular sieve provides aluminum source and partial silicon source, mixing in slurry, and SiO is used as silicon source2The aluminum source is A12O3The composite template agent is calculated by OSDA, NaOH is calculated by Na2Calculated by O, the component molar ratio is nNa2O:nSiO2:nA12O3:nOSDA:nH2O＝(0.05～0.25):1:(0.005～0.1):(0.05～0.5):(10～100)；
2) Stirring the mixture obtained in the step 1), transferring the mixture into a hydrothermal crystallization reaction kettle, performing two-section or multi-section crystallization at the autogenous pressure and the temperature of 120-200 ℃ for 48-168 hours in total, and filtering, washing, drying and roasting the obtained crystallized liquid to obtain raw powder of a symbiotic composite silicon-aluminum molecular sieve;
further, mixing the raw powder of the symbiotic composite silicon-aluminum molecular sieve obtained in the step 2) with an ammonium salt solution with the concentration of 0.1-5.0 mol/L according to the solid-liquid mass ratio of 1: (5-50) carrying out ion exchange at 80-120 ℃, wherein each time of exchange is 0.5-6 hours, and repeatedly exchanging the obtained filter cake with a fresh ammonium ion solution for 1-3 times until the Na content in the molecular sieve sample is lower than 500 ppm; and then filtering and separating out a solid product, repeatedly washing the solid product with deionized water to be neutral, drying a filter cake at 100-130 ℃ for 12-48 hours, and roasting the filter cake at 400-600 ℃ for 2-8 hours to obtain the H-type SSZ-13/SSZ-16 symbiotic composite silicon-aluminum molecular sieve.
The ammonium salt is a mixture formed by mixing any one, two or more than two of ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium carbonate and ammonium acetate in any proportion;
the composite template agent OSDA in the step 1) comprises organic template agents R1 and R2, wherein the molar ratio of the two organic template agents nR1 to nR2 is 1 (0.05-0.8);
the organic template R1 in the step 1) comprises the following types: one or more of N, N, N-trimethyl-1-adamantane ammonium hydroxide, benzyltrimethyl ammonium hydroxide, N, N-dimethyl-N '-ethylcyclohexylammonium onium, N, N-ethyl-N' -methylcyclohexylammonium, N, N, N-triethylcyclohexylammonium onium, and N, N, N-trimethylcyclohexylammonium onium;
the organic template R2 in the step 1) is a compound containing a structure of alkane substituted by double six-membered ring or double five-membered heterocyclic group, and comprises the following 11 chemical formulas:
Figure BDA0002318313230000061
n is 4-8 formula I;
Figure BDA0002318313230000062
n is 4-8 chemical formula II;
Figure BDA0002318313230000063
n is 4-8 chemical formula III;
Figure BDA0002318313230000064
n is 4-8 chemical formula IV;
Figure BDA0002318313230000065
n is a chemical formula of 4-8; v
Figure BDA0002318313230000066
n is 4-8 formula VI;
Figure BDA0002318313230000071
n is 4-8 formula VII;
Figure BDA0002318313230000072
n is 4-8 formula VIII;
Figure BDA0002318313230000073
n is 4-8 chemical formula IX;
Figure BDA0002318313230000074
n is 4-8 chemical formula X;
Figure BDA0002318313230000075
n is 4-8 chemical formula XI;
further, in the above technical solution, the molar ratio of silicon to aluminum in the intergrowth composite molecular sieve is 10to 200, preferably 10to 100, and more preferably 10to 50.
Further, in the above technical solution, the synthesis method of the present invention is characterized in that: the aluminum source is selected from four-coordinate aluminum in FAU type silicon-aluminum zeolite, wherein the FAU type molecular sieve comprises an X molecular sieve, a Y molecular sieve and a USY molecular sieve.
Further, in the above technical solution, the synthesis method of the present invention is characterized in that: the silicon source in the step 1) is selected from one or more of white carbon black, macroporous silica gel, coarse porous silica gel, fine porous silica gel, thin layer chromatography silica gel, B type silica gel, sodium metasilicate, silica sol, water glass, alkyl silicate, diatomite and gas phase method silica gel, and preferably chromatography silica gel, white carbon black, silica sol, water glass and alkyl silicate.
Further, in the above technical solution, the synthesis method of the present invention is characterized in that: the organic template R2 is of the following types: any one or more of 1, 4-bis ([ 4-aza-1-azoniabicyclo [2.2.2]) butane, 1, 4-bis (quinuclidinium) butane, 1, 4-bis (N-methylpiperidinium) butane, 1, 4-bis (N-methylpiperazinium) butane, 1, 4-bis (N-methylmorpholinium) butane, 1, 4-bis (N-methylpiperidinium) butane, 1, 4-bis (N-methylpyrrolidium) butane, 1, 4-bis (N-methylimidazolium) butane, 1, 4-bis (2, 3-dimethylimidazolium) butane and 1, 4-bis (N-methylimidazolium) butane.
The invention provides an SCR catalyst for denitration, which is characterized in that ion exchange is carried out on the symbiotic composite silicon-aluminum molecular sieve and a soluble metal salt solution, then slurry with the solid content of 25.0-48.0 wt% is formed by the symbiotic composite silicon-aluminum molecular sieve and a binder and deionized water, and the slurry is coated on a carrier of a porous regular material or an integral filter substrate to form a proper coating, so that the metal-promoted SCR catalyst with the symbiotic composite molecular sieve with the CHA/AFX topological structure is obtained.
Further, in the above technical solution, the binder is selected from any one or a mixture of several of silica sol, aluminum sol or pseudo-boehmite; SiO in sol2Or Al2O3The mass of the supported metal intergrowth CHA/AFX molecular sieve catalyst is 8.0-25.0 wt%.
Further, in the technical scheme, the porous regular material or the monolithic filter base material is prepared from any one of cordierite, α -alumina, silicon carbide, aluminum titanate, silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia or zirconium silicate, and the carrier material is preferably a cordierite porous honeycomb flow-through monolith carrier, and the carrying capacity of the carrier material is 170-270 g/L.
The soluble metal salt used in the preparation process of the catalyst is selected from one or a combination of more of soluble salts of copper, iron, cobalt, tungsten, nickel, zinc, molybdenum, vanadium, tin, titanium, zirconium, manganese, chromium, niobium, bismuth, antimony, ruthenium, germanium, palladium, indium, platinum, gold or silver, preferably any one or two of copper salt and iron salt, and further preferably copper salt. The copper salt is one or more of copper nitrate, copper chloride, copper acetate or copper sulfate; the concentration of copper ions in the copper salt aqueous solution is 0.1-0.5 mol/L. The amount of Cu in the copper-based SCR molecular sieve catalyst of the present invention is 0.03 to 20 wt%, based on the weight of the copper-based SCR catalyst, wherein the amount of Cu is preferably 0.2 to 15 wt%, more preferably 0.5 to 10 wt%, more preferably 1.0 to 8.0 wt%, more preferably 1.5 to 5.0 wt%, more preferably 2.0 to 4.0 wt%, more preferably 2.5 to 3.5 wt%, more preferably 2.7 to 3.3 wt%, more preferably 2.9 to 3.1 wt%.
In embodiments of the invention, the washcoat of the intergrowth composite molecular sieve SCR catalyst is preferably a solution, suspension or slurry that is coated onto a porous structured material (i.e., a honeycomb monolithic catalyst support structure having a plurality of parallel small channels running axially through the entire assembly) or a monolithic filter substrate such as a wall-flow filter or the like, with suitable coatings including a surface coating, a coating that penetrates a portion of the substrate, a coating that penetrates the substrate, or some combination thereof.
The two most common substrate designs to which the SCR catalyst of the invention can be applied are plate and honeycomb. Preferred substrates, particularly for mobile applications, include flow-through monoliths having a so-called honeycomb geometry comprising a plurality of adjacent, parallel channels that are open at both ends and generally extend from an inlet face to an outlet face of the substrate, and that result in a high surface area to volume ratio. For certain applications, the honeycomb flow-through monolith preferably has a high pore density, for example, about 600 to 800 pores per square inch, and/or an average internal wall thickness of about 0.18 to 0.35mm, preferably about 0.20 to 0.25 mm. For certain other applications, the honeycomb flow-through monolith preferably has a low pore density of about 150 to 600 pores per square inch, more preferably about 200 to 400 pores per square inch.
The catalyst in the embodiments of the invention shows that high NOx conversion is obtained in a much wider temperature window. The temperature range for improving the conversion efficiency may be about 150 to 650 ℃, preferably 200 to 500 ℃, more preferably 200 to 450 ℃, or most significantly 200 to 400 ℃. Within these temperature ranges, the conversion efficiency after exposure to a reducing atmosphere, even after exposure to a reducing atmosphere and high temperatures (e.g., up to 850 ℃) can be greater than 55% to 100%, more preferably greater than 90% efficiency, and even more preferably greater than 95% efficiency.
The SCR catalyst prepared by the CHA/AFX structure symbiotic composite molecular sieve has better hydrothermal stability and wider ignition activity window temperature (200-500 ℃), has good low-temperature and high-temperature ignition activity, has a proper pore structure, is beneficial to the diffusion of NOx molecules, enhances the adhesion of metal copper ions, and reduces the possibility of aggregation caused by the hydrothermal action.
The intergrowth composite zeolite molecular sieve is formed by SSZ-16 with an AFX structure and SSZ-13 with a CHA structure, has two molecular sieve structural characteristics, generates structural particularity, has more reasonably distributed acidity and good hydrothermal stability, overcomes the limitations of components, better meets the requirements of industrial application, and has wide application prospect.
Description of the drawingsthe invention will now be further described with reference to the accompanying drawings and examples:
FIG. 1: XRD diffractogram of the intergrown SSZ-13/SSZ-16 molecular sieve synthesized in example 1;
FIG. 2: XRD diffractogram of the intergrown SSZ-13/SSZ-16 molecular sieve synthesized in example 2;
FIG. 3: XRD diffractogram of the intergrown SSZ-13/SSZ-16 molecular sieve synthesized in example 3;
FIG. 4: XRD diffractogram of the intergrown SSZ-13/SSZ-16 molecular sieve synthesized in example 4;
FIG. 5: XRD diffractogram of the intergrown SSZ-13/SSZ-16 molecular sieve synthesized in example 5.
Detailed Description
The embodiments and the effects of the present invention are further illustrated by examples and comparative examples, but the scope of the present invention is not limited to the contents listed in the examples.
The intergrowth composite molecular sieve of the present invention is identified by finding the lattice plane spacing (d) from the XRD pattern by the Powder method of X-ray Diffraction (X-ray Diffraction) analysis, and comparing the obtained lattice plane spacing (d) with Data collected from the XRD database of the International society for synthetic zeolites or the PDF (Powder Diffraction File) of ICDD (International centre for Diffraction Data).
Mechanically and uniformly mixing and grinding the SSZ-13 molecular sieve and the SSZ-16 molecular sieve which are pure in phase and have high relative crystallinity according to the mass ratio of 50:50, 60:40, 70:30, 80:20 and 90:10, and determining the XRD characteristic peak area. The SSZ-13 molecular sieve is corresponding to five characteristic peaks at the 2 theta angle of 9.40 plus or minus 0.2, 13.80 plus or minus 0.2, 15.90 plus or minus 0.2, 20.44 plus or minus 0.2 and 24.60 plus or minus 0.2, and the total area of the SSZ-13 molecular sieve is related to the mass percentage of SSZ-13; the five characteristic peaks at the 2 theta angle of 7.42 +/-0.2, 8.64 +/-0.2, 11.56 +/-0.2, 12.86 +/-0.2 and 21.66 +/-0.2 correspond to the SSZ-16 molecular sieve, and the total area of the five characteristic peaks is related to the SSZ-16 mass percentage content. Thereby obtaining a function curve of the SSZ-13/SSZ-16 peak area ratio and the SSZ-13/SSZ-16 molecular sieve mass ratio, and taking the function curve as a reference curve to be used for calculating the relative proportion value of the two molecular sieves in the sample to be measured.
Example 1
A preparation method of an SSZ-13/SSZ-16 symbiotic composite silicon-aluminum molecular sieve and an SCR catalyst comprises the following steps:
1) mixing 8.66g HY (nSiO)2/nAl2O378 wt% dry basis) molecular sieve, 12.27g water glass (Na)2O：7.48wt％，SiO2: 24.61 wt%), 60.87g of silica gel solution (Na)2O：0.23wt％，SiO2: 29.49 wt%), 32.46g of N, N, N-trimethyl-1-adamantane ammonium hydroxide (25 wt%), 27.34g of 1, 4-bis ([ 4-aza-1-azoniabicyclo [ 2.2.2)]) Butane (weight concentration 25 wt%) and 191.01g deionized water were mixed uniformly under ultrasonic agitation, and the mixture slurry components were mixed in a molar ratio of nNa2O:nSiO2:nA12O3:nOSDA:nH2O＝0.07:1.0:0.0313:0.077:0.0432:30；
2) Stirring the mixture obtained in the step 1), transferring the mixture into a hydrothermal crystallization reaction kettle, stirring the mixture under the autogenous pressure and the speed of 80rpm, crystallizing the mixture for 24 hours at the temperature of 140 ℃, and then heating the mixture to 170 ℃ for crystallizing the mixture for 72 hours. And after complete crystallization, quickly cooling the product, performing suction filtration separation and washing until the pH value is 8.0-9.0, drying at 120 ℃ for 12 hours, and roasting at 540 ℃ for 4 hours to obtain SSZ-13/SSZ-16 symbiotic composite silicon-aluminum molecular sieve raw powder.
The molecular sieve raw powder and an ammonium nitrate solution with the concentration of 1.0mol/L are subjected to ion exchange for 2 hours at 90 ℃ according to the solid-liquid mass ratio of 1:10, and then a filter cake obtained by filtering is subjected to ion exchange twice with a fresh ammonium nitrate solution again under the same condition, so that the Na ion content in a sample is lower than 500 ppm. The filter cake obtained by subsequent filtration is dried at 110 ℃ overnight to obtain ammonium type molecular sieve NH4Heating to 450 ℃ and roasting for 16 hours to obtain the H-type SSZ-13/SSZ-50 molecular sieve.
3) Adding 50.0g of the H-type SSZ-13/SSZ-16 symbiotic composite silicon-aluminum molecular sieve in the step 2) into a 0.15mol/L copper nitrate aqueous solution, dropwise adding dilute nitric acid into the solution to adjust the pH value to 6.5, uniformly stirring, putting into a heat-resistant container, and putting into a dryer with a pressure reducing valve; vacuumizing the pressure in the dryer to be below 10Torr by using a vacuum pump, degassing at room temperature for 1 hour, heating to 90 ℃, drying for 12 hours, and roasting the dried sample at the temperature of 500 ℃ for 4 hours under normal atmospheric pressure; the obtained copper modified SSZ-13/SSZ-16 intergrowth composite silicon-aluminum molecular sieve is prepared according to XRF analysis results, wherein copper (II) ions account for 2.9% of the total weight of the molecular sieve catalyst, namely the copper loading is 2.9 wt%.
4) Taking 40.0g of the copper-modified molecular sieve obtained in the above 3), and 33.3g of silica Sol (SiO)2The content is as follows: 30.0 wt%) and 118.2g of deionized water were uniformly mixed to prepare a catalyst slurry having a solid content of 26.1 wt%, and the catalyst slurry was coated on a cordierite honeycomb porous structured material (#400cpsi, 20mm in diameter and 40mm in length) by an impregnation method, excess slurry droplets were blown off with compressed air, dried at 105 ℃ for 24 hours, coated 2 times under the same conditions, and calcined at 500 ℃ for 2 hours to prepare an SCR catalyst, wherein the loading amount on the structured material was 233.9g/L (the mass of the weight gain of the structured material after calcination divided by the volume of the space occupied by the structured material, and the definitions of the subsequent examples and comparative examples with respect to the loading amount were the same), and in order that the obtained SCR catalyst was denoted as a, the preparation parameters and the species were as shown in tables 1, 2 and 3.
Example 2
The process for synthesizing the SSZ-13/SSZ-16 intergrowth composite molecular sieve is similar to the example 1, except that the molar ratio of the mixed sol, the type of the organic template agent, the type of the silicon source, the type of the FAU zeolite, the silicon-aluminum ratio, the crystallization temperature, the crystallization time and the like in the step 1) and the step 2) are adopted, 50.0g of H-type SSZ-13/SSZ-16 intergrowth composite silicon-aluminum molecular sieve is taken in the step 3), different types, concentrations, solution volumes and metal loading amounts of soluble metal salts are adopted, and 40.0g of copper modified SSZ-13/SSZ-16 intergrowth composite molecular sieve and 33.3g of silica Sol (SiO) are taken in the step 4)2The content is as follows: 30.0 wt%) and 57.9g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 38.1 wt%, which was coated on a cordierite structured material by an impregnation method. Specific parameters in this example are shown in tables 1, 2 and 3.
Example 3
The process for synthesizing the SSZ-13/SSZ-16 intergrowth composite molecular sieve is similar to that in example 1, except that the molar ratio of the mixed sol, the type of the organic template agent, the type of the silicon source, the type of FAU zeolite, the silicon-aluminum ratio, the crystallization temperature, the crystallization time and the like in the step 1) and the step 2) are adopted, 50.0g of H-type SSZ-13/SSZ-16 intergrowth composite silicon-aluminum molecular sieve is taken in the step 3), different types, concentrations, solution volumes and metal loading amounts of soluble metal salts are adopted, and 40g of copper modified SSZ-13/SSZ-16 intergrowth composite molecular sieve and 33.3g of silica sol (SiO 2) are taken in the step 4)2The content is as follows: 30.0 wt%) and 45.7g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 42.0 wt%, which was coated on a cordierite structured material by an impregnation method. Specific parameters in this example are shown in tables 1, 2 and 3.
Example 4
The process for synthesizing the SSZ-13/SSZ-16 intergrowth composite molecular sieve is similar to that in example 1, except that the molar ratio of the mixed sol, the type of the organic template agent, the type of the silicon source, the type of FAU zeolite, the silicon-aluminum ratio, the crystallization temperature, the crystallization time and the like in the step 1) and the step 2) are adopted, 50.0g of H-type SSZ-13/SSZ-16 intergrowth composite silicon-aluminum molecular sieve is taken in the step 3), different types, concentrations, solution volumes and metal loading amounts of soluble metal salts are adopted, and 40g of copper modified SSZ-13/SSZ-16 intergrowth composite molecular sieve and 33.3g of silica sol (SiO 2) are taken in the step 4)2The content is as follows: 30.0 wt%) and 74.6g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 33.8 wt%, which was coated on a cordierite structured material by an impregnation method. Specific parameters in this example are shown in tables 1, 2 and 3.
Example 5
The process for synthesizing the SSZ-13/SSZ-16 intergrowth composite molecular sieve is similar to that in the embodiment 1, except that the molar ratio of the mixed sol, the type of the organic template agent, the type of the silicon source, the type of the FAU zeolite, the silicon-aluminum ratio, the crystallization temperature, the crystallization time and the like in the steps 1) and 2) are adopted, 50.0g of H-type SSZ-13/SSZ-16 intergrowth composite silicon-aluminum molecular sieve is taken in the step 3), and different types, concentrations, solution volumes and metal loads of soluble metal salts are adoptedAmount, and 4) step of taking 40g of the copper modified SSZ-13/SSZ-16 intergrown composite molecular sieve and 50.0g of alumina sol (Al)2O3The content is as follows: 20.0 wt%) and 69.9g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 34.4 wt%, and the catalyst slurry was coated on a cordierite structured material by an impregnation method. Specific parameters in this example are shown in tables 1, 2 and 3.
Example 6
The process for synthesizing the SSZ-13/SSZ-16 intergrowth composite molecular sieve is similar to the example 1, except that the molar ratio of the mixed sol, the type of the organic template agent, the type of the silicon source, the type of the FAU zeolite, the silicon-aluminum ratio, the crystallization temperature, the crystallization time and the like in the step 1) and the step 2) are adopted, 50.0g of H-type SSZ-13/SSZ-16 intergrowth composite silicon-aluminum molecular sieve is taken in the step 3), different types, concentrations, solution volumes and metal loading amounts of soluble metal salts are adopted, and 40g of copper modified SSZ-13/SSZ-16 intergrowth composite molecular sieve and 50.0g of aluminum sol (Al) are taken in the step 4)2O3The content is as follows: 20.0 wt%) and 50.9g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 35.5 wt%, which was coated on a cordierite structured material by an impregnation method. Specific parameters in this example are shown in tables 1, 2 and 3.
Example 7
The process for synthesizing the SSZ-13/SSZ-16 intergrowth composite molecular sieve is similar to the example 1, except that the molar ratio of the mixed sol, the type of the organic template agent, the type of the silicon source, the type of the FAU zeolite, the silicon-aluminum ratio, the crystallization temperature, the crystallization time and the like in the step 1) and the step 2) are adopted, 50.0g of H-type SSZ-13/SSZ-16 intergrowth composite silicon-aluminum molecular sieve is taken in the step 3), different types, concentrations, solution volumes and metal loading amounts of soluble metal salts are adopted, and 40g of copper modified SSZ-13/SSZ-16 intergrowth composite molecular sieve and 50.0g of aluminum sol (Al) are taken in the step 4)2O3The content is as follows: 20.0 wt%) and 73.9g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 30.5 wt%, and the catalyst slurry was coated on a cordierite structured material by an impregnation method. Specific parameters in this example are shown in tables 1, 2 and 3.
Example 8
Synthesis of SSZ-13/SSZ-16 symbiotic complexesThe process of the molecular sieve is similar to that of example 1, except that the molar ratio of the mixed sol, the type of the organic template, the type of the silicon source, the type of the FAU zeolite, the silicon-aluminum ratio, the crystallization temperature, the crystallization time and the like in step 1) and step 2), 50.0g of H-type SSZ-13/SSZ-16 intergrowth composite silicon-aluminum molecular sieve is taken in step 3), different soluble metal salt types, concentrations, solution volumes and metal loading amounts are adopted, and 4) 40g of copper-modified SSZ-13/SSZ-16 intergrowth composite molecular sieve and 50.0g of aluminum sol (Al) are taken in step 4)2O3The content is as follows: 20.0 wt%) and 62.4g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 32.8 wt%, which was coated on a cordierite structured material by an impregnation method. Specific parameters in this example are shown in tables 1, 2 and 3.
TABLE 1
Figure BDA0002318313230000161
TABLE 2
Figure BDA0002318313230000162
Figure BDA0002318313230000171
TABLE 3
Figure BDA0002318313230000172
Comparative example 1
17.0g of SB powder was dissolved in 50.0g of a 50 wt% aqueous NaOH solution, and 200.0g of white carbon was then added thereto and mixed thoroughly. An aqueous solution of N, N, N-trimethyladamantane ammonium hydroxide (TMADA +) (25 wt% concentration) was slowly added to the mixture while mixing. 80.0g of deionized water was slowly added and the resulting mixture was mixed well for 1 hour. The molar composition of the synthesis mixture was:
0.21Na2O：SiO2：0.0286Al2O3：0.18TMADa+：26.8H2O
and then transferring the obtained gel into a stainless steel reaction kettle to crystallize at 170 ℃ for 168 hours, after the reaction is finished, washing the product with deionized water, drying at 120 ℃ for 12 hours, and roasting at 540 ℃ for 4 hours to obtain the SSZ-13 molecular sieve raw powder. The molecular sieve raw powder and ammonium nitrate solution with the concentration of 1.0mol/L are subjected to ion exchange for 2 hours at the temperature of 90 ℃ according to the solid-liquid mass ratio of 1:10, and then filter cakes obtained by filtration are subjected to ion exchange twice with fresh ammonium nitrate solution again under the same condition, so that the Na ion content is lower than 500 ppm. The filter cake obtained by subsequent filtration is dried at 110 ℃ overnight to obtain ammonium type molecular sieve NH4Heating to 450 ℃ and roasting for 16 hours to obtain the H-type SSZ-13 molecular sieve.
10g of SSZ-13 molecular sieve type H was added to 100g of Cu (NO) at a concentration of 0.3mol/L3)2·3H2And (3) dripping dilute nitric acid into the O aqueous solution to adjust the pH value to 5.8, and uniformly stirring. After stirring was stopped for 1 hour, the supernatant was siphoned off when SSZ-13 zeolite settled. The exchange with fresh copper nitrate solution was repeated once, and finally the exchanged SSZ-13 zeolite was filtered and washed with deionized water. Drying at 90 ℃ for 12 hours under the low pressure of 10Torr, and then roasting at 500 ℃ for 4 hours under normal atmospheric pressure to obtain the copper modified SSZ-13 molecular sieve powder. According to XRF analysis, copper (II) ions accounted for 2.9% of the total weight of the molecular sieve catalyst.
15g of the resulting copper-modified SSZ-13 molecular sieve were taken and mixed with 5.56g of silica sol (30 wt% SiO)2) And 22.80g of deionized water are uniformly mixed to prepare catalyst slurry with the solid content of 38.44 wt%, the catalyst slurry is coated on a honeycomb-shaped porous regular material (400 cpsi, the diameter of 20mm and the length of 40mm) made of cordierite through an impregnation method, redundant slurry drops are blown off by compressed air, the drying is carried out for 12 hours at the temperature of 110 ℃, then, the slurry is coated again, the SCR catalyst is prepared after the calcination is carried out for 2 hours at the temperature of 500 ℃, and the measured catalyst loading capacity on the regular material is 228.4g/L and is marked as VS-1.
Comparative example 2
SSZ-16 molecular sieve is synthesized and prepared into SCR catalyst according to the method in the patent US 5194235:
1) 35.0g of sodium metasilicate aqueous solution (1.39g/ml), 8.5g of organic template 1, 4-bis (triethylenediamine) butane bromide and 1.25g of sodium hydroxide were dissolved in 80ml of deionized water, and the mixture was stirred sufficiently for 1 hour to prepare a mixed solution. And adding 3.5g of NaY molecular sieve into the mixed solution, and quickly stirring for 1h to form a sol precursor.
2) Transferring the sol precursor obtained in the step 1) to a stainless steel hydrothermal reaction kettle with a polytetrafluoroethylene lining, putting the stainless steel hydrothermal reaction kettle into a 150 ℃ oil bath kettle, and reacting for 6 days under the condition of dynamic stirring. And filtering and washing a product after the reaction by using deionized water until a filtrate is neutral, drying the obtained white powder at 100 ℃ in vacuum for 24 hours, roasting the powder at 550 ℃ for 8 hours, and measuring the product as the SSZ-16 molecular sieve by X-ray diffraction. The molecular sieve raw powder and ammonium nitrate solution with the concentration of 1.0mol/L are subjected to ion exchange for 2 hours at the temperature of 90 ℃ according to the solid-liquid mass ratio of 1:10, and then filter cakes obtained by filtration are subjected to ion exchange twice with fresh ammonium nitrate solution again under the same condition, so that the Na ion content is lower than 500 ppm. The filter cake obtained by subsequent filtration is dried at 110 ℃ overnight to obtain ammonium type molecular sieve NH4Heating to 450 ℃ and roasting for 16 hours to obtain the H-type SSZ-16 molecular sieve.
3) 10g of SSZ-16 molecular sieve type H was added to 100g of Cu (NO) at a concentration of 0.2mol/L3)2·3H2And (3) dripping dilute nitric acid into the O aqueous solution to adjust the pH value to 4.0, and uniformly stirring. After stirring was stopped for 1 hour, the supernatant was siphoned off when the SSZ-16 molecular sieve had settled. And repeatedly using a fresh copper nitrate solution for exchange once, and finally filtering and washing the exchanged SSZ-16 molecular sieve by deionized water. Drying at 90 ℃ for 12 hours under the low pressure of 10Torr, and then roasting at 500 ℃ for 4 hours under normal atmospheric pressure to obtain the copper modified SSZ-16 molecular sieve powder. According to XRF analysis, copper (II) ions accounted for 2.7% of the total weight of the molecular sieve catalyst.
4) 15g of the resulting copper-modified SSZ-16 molecular sieve were taken and mixed with 5.48g of silica sol (30 wt% SiO)2) And 26.6g of deionized water are uniformly mixed to prepare catalyst slurry with the solid content of 35.35 wt%, and the catalyst slurry is coated on a honeycomb-shaped porous regular material prepared from cordierite by an impregnation method (400 cpsi and the diameter of 20 mm)40mm in length), blowing off the excess slurry droplets with compressed air, drying at 110 ℃ for 12 hours, then recoating the slurry once again, calcining at 500 ℃ for 2 hours to prepare the SCR catalyst, and measuring the catalyst loading on the structured material to be 228.5g/L, which is recorded as VS-2.
Examples 9 to 16
Testing of the SCR catalyst:
the SCR catalysts prepared in examples 1 to 6 and comparative examples 1 to 2 were placed in a reactor (
Figure BDA0002318313230000201
) In (1), contains 500ppm of NO and 500ppm of NH 310% by volume of O2160mL/min of a mixed gas stream containing 5 vol% of steam and Ar as an equilibrium gas was passed through a preheater (set at 250 ℃ C.) and then fed into the SCR reactor. At a reaction temperature of 150-650 ℃ for 48000h-1The test specimens were tested at a volumetric gas hourly space velocity. The temperature is monitored by an internal thermocouple located at the sample site.
The used fresh SCR catalysts of the above examples and comparative examples were subjected to a hydrothermal durability treatment under the conditions of the hydrothermal durability treatment test to obtain aged SCR catalysts:
space velocity SV: 30000/h, temperature: 800 ℃, time: 16 hours, water concentration: 10%, oxygen concentration: 10%, nitrogen concentration: and (4) balancing.
After hydrothermal aging treatment is carried out according to the parameters, the catalyst is continuously used as an SCR catalyst for NOx catalytic reduction reaction evaluation test:
NO conversion or "DeNOx" Activity NOx, NH at the outlet were measured under steady state conditions by using a Bruker EQUINOX 55 type FT-IR spectrometer3And N2The concentration of O.
Figure BDA0002318313230000211
The SCR catalyst activity laboratory evaluation device described above was used to evaluate the selective catalytic reduction performance of NOx on the Cu-supported SCR catalysts prepared in examples and comparative examples, and the results are shown in table 4.
TABLE 4
Figure BDA0002318313230000212
As can be seen from Table 4, the Cu-SSZ-13/SSZ-16 or Fe-SSZ-13/SSZ-16 catalysts obtained in examples 1 to 6 evaluated in examples 9 to 14 showed better low-temperature ignition properties and high-temperature activity, and the SCR activity was significantly better than the catalytic performance of catalysts VS-1 and VS-2 obtained in comparative example 1 shown in examples 15 to 16, regardless of their "fresh" state or "aged" state. Thus, the results obtained from examples 9-14 clearly show that the Cu-SSZ-13/SSZ-16 or Fe-SSZ-13/SSZ-16 catalyst materials of the present invention and the catalysts obtained therewith have improved SCR catalytic activity, especially at low conversion temperatures typical of cold start conditions when treating NOx in, for example, diesel locomotive applications. For other SCR applications, the Cu-SSZ-13/SSZ-16 or Fe-SSZ-13/SSZ-16 catalyst materials of the present invention allow for higher conversion at lower temperatures, thus allowing for higher efficiency and thus, at comparable conversion, high energy efficiency in the treatment of NOx-containing exhaust gases, such as exhaust gases obtained from industrial processes.
The above-mentioned embodiments are only for illustrating the technical idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims (10)

1. An intergrowth composite molecular sieve having a CHA/AFX structure, characterized by: the composite material is formed by intergrowth of CHA and AFX topological structure molecular sieves, wherein the CHA structure molecular sieve accounts for 60-99% of the total weight, and the AFX structure molecular sieve accounts for 1.0-40% of the total weight; the molar ratio of silicon oxide to aluminum oxide in the intergrowth composite molecular sieve is 10-200; the molecular sieve X-ray diffraction phase spectrogram of the intergrowth structure has characteristic peaks at the 2 theta angles of 7.42 +/-0.2, 8.64 +/-0.2, 9.40 +/-0.2, 11.56 +/-0.2, 12.86 +/-0.2, 13.80 +/-0.2, 15.54 +/-0.2, 15.90 +/-0.2, 17.52 +/-0.2, 17.76 +/-0.2, 20.20 +/-0.2, 20.44 +/-0.2, 21.66 +/-0.2, 24.60 +/-0.2, 25.80 +/-0.2, 27.82 +/-0.2, 30.38 +/-0.2, 30.70 +/-0.2, 31.30 +/-0.2, 34.24 +/-0.2 and 33.50 +/-0.2.
2. The intergrowth composite molecular sieve having the CHA/AFX structure of claim 1, wherein: the CHA structure molecular sieve specifically comprises any one or more of SSZ-13, SAPO-34, chabazite, MeAPO-47, CoAPO-44, AlPO-34 and SSZ-62, and preferably is an SSZ-13 silicon-aluminum molecular sieve; the AFX structure molecular sieve specifically comprises any one or more of SAPO-56 and SSZ-16, and preferably is an SSZ-16 silicon-aluminum molecular sieve.
3. The method of synthesizing an intergrown composite molecular sieve having the CHA/AFX structure of claim 1 or 2, wherein:
1) mixing FAU type molecular sieve, silicon source, NaOH, composite organic template agent and deionized water under ultrasonic stirring condition, wherein FAU type silicon-aluminum molecular sieve provides aluminum source and partial silicon source, mixing in slurry, and SiO is used as silicon source2The aluminum source is A12O3The composite template agent is calculated by OSDA, NaOH is calculated by Na2Calculated by O, the component molar ratio is nNa2O:nSiO2:nA12O3:nOSDA:nH2O＝(0.05～0.25):1:(0.005～0.1):(0.05～0.5):(10～100)；
2) Stirring the mixture obtained in the step 1), transferring the mixture into a hydrothermal crystallization reaction kettle, performing two-section or multi-section crystallization at the autogenous pressure and the temperature of 120-200 ℃ for 48-168 hours in total, and filtering, washing, drying and roasting the obtained crystallized liquid to obtain raw powder of a symbiotic composite silicon-aluminum molecular sieve;
the composite template agent OSDA in the step 1) comprises organic template agents R1 and R2, wherein the molar ratio of the two organic template agents nR1 to nR2 is 1 (0.05-0.8);
the organic template R1 in the step 1) comprises the following types: one or more of N, N, N-trimethyl-1-adamantane ammonium hydroxide, benzyltrimethyl ammonium hydroxide, N, N-dimethyl-N '-ethylcyclohexylammonium onium, N, N-ethyl-N' -methylcyclohexylammonium, N, N, N-triethylcyclohexylammonium onium, and N, N, N-trimethylcyclohexylammonium onium;
the organic template R2 in the step 1) is a compound containing a structure of alkane substituted by double six-membered ring or double five-membered heterocyclic group, and comprises the following 11 chemical formulas:
Figure FDA0002318313220000021
Figure FDA0002318313220000031
the molar ratio of silicon to aluminum in the intergrowth composite molecular sieve is 10-200, preferably 10-100, and more preferably 10-50.
4. The method of synthesis according to claim 3, characterized in that: the aluminum source is selected from four-coordinate aluminum in FAU type silicon-aluminum zeolite, wherein the FAU type molecular sieve comprises an X molecular sieve, a Y molecular sieve and a USY molecular sieve.
5. The method of synthesis according to claim 3, characterized in that: the silicon source in the step 1) is selected from one or more of white carbon black, macroporous silica gel, coarse porous silica gel, fine porous silica gel, thin layer chromatography silica gel, B type silica gel, sodium metasilicate, silica sol, water glass, alkyl silicate, diatomite and gas phase method silica gel, and preferably chromatography silica gel, white carbon black, silica sol, water glass and alkyl silicate.
6. A synthesis method according to claim 3, characterized in that: the organic template R2 is of the following types: any one or more of 1, 4-bis ([ 4-aza-1-azoniabicyclo [2.2.2]) butane, 1, 4-bis (quinuclidinium) butane, 1, 4-bis (N-methylpiperidinium) butane, 1, 4-bis (N-methylpiperazinium) butane, 1, 4-bis (N-methylmorpholinium) butane, 1, 4-bis (N-methylpiperidinium) butane, 1, 4-bis (N-methylpyrrolidium) butane, 1, 4-bis (N-methylimidazolium) butane, 1, 4-bis (2, 3-dimethylimidazolium) butane and 1, 4-bis (N-methylimidazolium) butane.
7. A synthesis method according to claim 3, characterized in that: mixing the intergrowth composite molecular sieve raw powder obtained in the step 2) with an ammonium salt solution with the concentration of 0.1-5.0 mol/L according to the solid-liquid mass ratio of 1: (5-50) carrying out ion exchange at 80-120 ℃, wherein each time of exchange is 0.5-6 hours, and repeatedly exchanging the obtained filter cake with a fresh ammonium ion solution for 1-3 times until the Na content in the molecular sieve sample is lower than 500 ppm; then filtering and separating out a solid product, repeatedly washing the solid product with deionized water to be neutral, drying a filter cake at 100-130 ℃ for 12-48 hours, and roasting the filter cake at 400-600 ℃ for 2-8 hours to obtain an H-type symbiotic composite silicon-aluminum molecular sieve;
the ammonium salt is a mixture formed by mixing any one, two or more than two of ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium carbonate and ammonium acetate in any proportion.
8. An SCR catalyst for denitration, which is prepared by carrying out ion exchange on the intergrowth composite molecular sieve with the CHA/AFX structure and a soluble metal salt solution according to any one of claims 1 or 2, forming slurry with the solid content of 25.0-48.0 wt% with a binder and deionized water, and coating the slurry on a carrier of a porous regular material or an integral filter substrate to form a suitable coating to obtain the metal-promoted SCR catalyst of the intergrowth composite molecular sieve with the CHA/AFX topological structure.
9. The catalyst of claim 8, wherein: the soluble metal salt is selected from one or a combination of more of soluble salts of copper, iron, cobalt, tungsten, nickel, zinc, molybdenum, vanadium, tin, titanium, zirconium, manganese, chromium, niobium, bismuth, antimony, ruthenium, germanium, palladium, indium, platinum, gold or silver, preferably any one or two of copper salt and iron salt, and further preferably copper salt; the copper salt is one or more of copper nitrate, copper chloride, copper acetate or copper sulfate; the concentration of copper ions in the copper salt aqueous solution is 0.1-0.5 mol/L.
10. The SCR catalyst according to claim 8, wherein the binder is selected from the group consisting of silica sol, alumina sol and pseudo-boehmite, or a mixture thereof, and the porous structured material or monolithic filter substrate is made of cordierite, α -alumina, silicon carbide, aluminum titanate, silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia or zirconium silicate.
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