CN111871452A - CHA-type molecular sieve and catalyst for diesel vehicle exhaust purification, and preparation method and application thereof - Google Patents

CHA-type molecular sieve and catalyst for diesel vehicle exhaust purification, and preparation method and application thereof Download PDF

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CN111871452A
CN111871452A CN202010797921.0A CN202010797921A CN111871452A CN 111871452 A CN111871452 A CN 111871452A CN 202010797921 A CN202010797921 A CN 202010797921A CN 111871452 A CN111871452 A CN 111871452A
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王志光
王炳春
史振宇
李进
柳海涛
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China Catalyst New Material Co ltd
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    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • 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
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Abstract

The invention discloses a CHA type molecular sieve and a catalyst for purifying diesel vehicle tail gas, and a preparation method and application thereof, belonging to the field of chemical synthesis technology and application thereof. The CHA-type silicon-aluminum zeolite molecular sieve is synthesized by adopting an N, N, N-trimethyl-3, 3, 5-trimethyl cyclohexyl-quaternary ammonium onium compound as an organic template, wherein the molar ratio of silicon dioxide to aluminum oxide is 6-80, the average grain diameter is less than or equal to 500nm, and the total specific surface area is more than or equal to 400m2Per g, total pore volume is not less than0.20ml/g, the pore volume of the micropores is more than or equal to 0.10ml/g, and the diameter of crystal grains in the crystal plane (-210) direction is 50-160 nm. After the molecular sieve is subjected to hydrothermal treatment at 600-850 ℃, the four-coordinate aluminum accounts for more than or equal to 90% of the total aluminum content, and the six-coordinate aluminum accounts for less than or equal to 10% of the total aluminum content. The molecular sieve of the invention has high hydrothermal stability without large crystal grains, and shows high nitrogen oxide reduction characteristics after being exposed under high temperature and high humidity, particularly shows high nitrogen oxide reduction characteristics in a temperature range of 200-550 ℃.

Description

CHA-type molecular sieve and catalyst for diesel vehicle exhaust purification, and preparation method and application thereof
Technical Field
The invention relates to a CHA type molecular sieve and a catalyst for purifying diesel vehicle tail gas, a preparation method and application thereof, belonging to the field of chemical synthesis technology and application thereof.
Background
The silicon-aluminum zeolite molecular sieve is a CHA type topological structure, has a three-dimensional pore structure and orthogonal symmetry, a one-dimensional main channel is formed by double eight-membered rings, the pore size is 0.38nm multiplied by 0.38nm, and the framework density is 14.5. The CHA molecular sieve topological structure is formed by connecting double 6 circular rings (d6r) through 4-membered rings to form a CHA big cage, the crystal face of the d6r faces the CHA big cage, Cu ions can be stabilized in the d6r at high temperature, and the Cu ions are allowed to migrate, so that the CHA molecular sieve has unique physicochemical characteristics of SCR reaction potential. Analysis of dehydrated Cu-SSZ-13 molecular sieves by Rietveld structural refinement in the literature (J.Phys.chem.C 2010,114,1633-2+Unique to the face of d6 r. In subsequent studies dehydrated Cu ions ([ CuOH ] located near the 8-membered ring were also confirmed]Presence of a + active site. The SSZ-13 and SSZ-62 molecular sieves are typical CHA-structure silicoaluminophosphate molecular sieves, and are widely used as cracking catalysts, MTO reaction catalysts, nitrogen oxide reduction catalysts, and as nitrogen oxide reduction catalysts using Selective Catalytic Reduction (SCR). The characteristics of the active sites of the Cu-SSZ-13 molecular sieve catalyst in the NH3-SCR reaction are widely researched, and the active sites of the frameworks of the SSZ-13 molecular sieve are equivalent, so that the catalyst is easier to characterize.
CN201611070989 discloses a molecular sieve material with CHA topology formed by self-assembly of silica tetrahedron and alumina tetrahedron, wherein the Si/Al molar ratio is between 4 and 8, the BET specific surface area is 400 to 800m2/g, and the crystal grain size is 0.8 to 20 μm. In the preparation of the molecular sieve, alkyl ammonium hydroxide and adamantyl ammonium hydroxide are used as double templates, and the molecular sieve can be applied to the technical field of separation of CO2/N2 and N2/O2 mixed gas. Patent CN201780032379 discloses synthesis of CHA-type zeolite with a silica/alumina molar ratio of 10.0 to 55.0 using N, N-trialkyl adamantyl ammonium salt and N, N-trialkyl cyclohexyl ammonium salt as composite templates. In the literature (Microporous and Mesoporous materials 255(2018)192-199), an SSZ-13 molecular sieve with the particle size of 50-300 nm is synthesized by crystallization at low (95 ℃) and high (210 ℃) temperature sections, has obvious hydrothermal stability and has equivalent catalytic performance in the aspect of ammonia selective catalytic reduction (NH3-SCR) nitrogen oxide (NOx).
The synthesis method of SSZ-13 molecular sieve with CHA structure and the catalytic performance of the SSZ-13 molecular sieve as SCR catalyst are disclosed in many documents above, which shows that the catalyst with good thermal stability and good dispersion of supported metal is preferable, and the conventional method adopts N, N, N-trialkyl-1-adamantyl ammonium salt and alkaline combination thereof as template agent, which is expensive, low in utilization rate and difficult to recycle, and needs template agent with low cost and easy post-treatment to synthesize the silicon-aluminum zeolite molecular sieve with small crystal grain, large specific surface area, large pore volume and good thermal stability.
Disclosure of Invention
The invention aims to provide a CHA type molecular sieve for purifying diesel vehicle tail gas, which is used for removing NO by selective reductionxThe molecular sieve has high Al content, small grain size, large specific surface area and pore volume, can provide more ion exchange sites and solid acid amount, forms the SCR catalyst after exchanging with transition metal ions such as copper ions, iron ions and the like, has high reduction rate of nitrogen oxides in a low-temperature area compared with the prior SCR catalyst, and has high hydrothermal stability at high temperature. The present invention relates to removal of nitrogen oxides emitted from internal combustion engines, and provides a nitrogen oxide removal catalyst composed of a silicoaluminophosphate zeolite molecular sieve having a CHA structure, a production method of the catalyst, and a nitrogen oxide removal method in which nitrogen oxides are reacted with at least one of ammonia water, urea, and an organic amine using the catalyst.
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 provides a CHA-type molecular sieve for purifying tail gas of diesel vehicles, which is synthesized by adopting N, N, N-trimethyl-3, 3, 5-trimethylcyclohexyl-quaternary ammonium as an organic template agent, wherein the molar ratio of silicon dioxide to aluminum oxide of the CHA-type silicon-aluminum molecular sieve is 6-80, the average grain diameter is less than or equal to 500nm, and the total specific surface area (S) is measured by a BET methodBET)≥400m2G, total pore volume (V)total) Not less than 0.20ml/g, micropore volume (V)micro) Not less than 0.10 ml/g; the silicon-aluminum zeolite molecular sieve has at least one XRD diffraction peak in each range of the following table within the range of 4-40 degrees of 2 theta, and has the characteristics of the following table:
Figure BDA0002626338960000031
relative intensity is intensity relative to peak intensity of 20.40-20.90 [ theta ]
The molecular sieve has a CHA topological structure, the range of the half-value width (FWHM) of a crystal plane of X-ray crystal diffraction (-210) is 0.1-0.2 degrees, and the diameter size of a crystal grain in the crystal plane (-210) direction is 50-160 nm calculated by a Debye-Scherrer formula. After the molecular sieve is treated by saturated steam at 600-850 ℃, the four-coordinate aluminum accounts for more than or equal to 90 percent of the total aluminum content, and the six-coordinate aluminum accounts for less than or equal to 10 percent of the total aluminum content.
The structural formula of the N, N, N-trimethyl-3, 3, 5-trimethylcyclohexyl-quaternary ammonium compound is shown as a formula I:
Figure BDA0002626338960000041
wherein R1 and R2 are independently selected from methyl or deuterated methyl, C2-C4 straight-chain or branched-chain alkyl, and R3 is selected from C1-C5 straight-chain or branched-chain alkyl; x-Counter anions which are N, N-trimethyl-3, 3, 5-trimethylcyclohexyl-quaternary ammonium ions include any of hydroxide, halide, sulfate, bisulfate, carbonate, bicarbonate, oxalate, acetate, phosphate, carboxylate, alkyl-substituted sulfate, carbonate or oxalate.
Further, in the above technical solution, the halide includes chloride ion, bromide ion, or iodide ion; carboxylates include formate, acetate, propionate; alkyl substituted sulphate, carbonate or oxalate including methyl sulphate, ethyl sulphate, methyl carbonate, ethyl carbonate, methyl oxalate or ethyl oxalate; the N, N, N-trimethyl-3, 3, 5-trimethyl cyclohexyl-quaternary ammonium salt compound is synthesized by taking isophorone as a raw material, firstly performing ammoniation hydrogenation, and finally performing alkylation reaction.
The pore structure data of the molecular sieve was determined using a Micromeritics ASAP 2460 model static nitrogen adsorption apparatus. And (3) testing conditions are as follows: the sample was placed in a sample handling system and evacuated to 1.33X 10 at 350 deg.C-2Pa, keeping the temperature and the pressure for 15h, and purifying the sample. Measuring the specific pressure p/p of the purified sample at-196 deg.C under liquid nitrogen0And (3) obtaining a nitrogen adsorption-desorption isothermal curve according to the adsorption quantity and the desorption quantity of the nitrogen under the condition. Then, the BET total specific surface area (S) is calculated using the BET equationBET) Calculating the specific surface area (S) of the sample micropore by adopting a t-plot methodmicro) And micropore volume (V)micro) Total pore volume in P/P0Calculated as adsorption at 0.98: specific surface area of outer pores (S)exter)＝SBET–Smicro(ii) a External pore volume (V)exter)＝Vtotal-Vmicro)。
The invention also provides a synthesis method of the CHA-type molecular sieve for purifying the tail gas of the diesel vehicle, which comprises the following steps:
1) fully dissolving and dispersing zeolite molecular sieve with the molar ratio of silicon dioxide to aluminum oxide of 2-30, NaOH and deionized water to obtain slurry with the molar ratio of nNa2O:nSiO2:nAl2O3:nH2O (0.5-2.5): 1 (0.0333-0.5): 5-20), aging in a crystallization kettle at 60-120 ℃ for 6-48 hours to obtainTo silica-alumina gel;
2) adding a silicon source, an organic template agent OSDA, a metal salt M and deionized water into the silicon-aluminum gel obtained in the step 1), fully and uniformly mixing, supplementing NaOH according to the system alkalinity requirement, and mixing the components of the slurry according to the molar ratio of nNa2O:nSiO2:nA12O3:nOSDA:nM:nH2O is (0.05-0.5) 1, (0.0125-0.20), (0.01-0.5), (0.05-0.5) and (10-100); adding acid solution to control alkali hydroxyl OH in mixed slurry-With SiO2The molar ratio nOH-/nSiO2 is 0.1-1.0; adding CHA molecular sieve seed crystal with SiO in the slurry2And A12O30.5-15% of the total mass; the metal salt M is NaCl and NaNO3、Na2SO4、Na3PO4、NaBr、NaF、KCl、KNO3、K2SO4、KBr、KF、K3PO4Any of them, preferably NaCl and NaNO3、Na2SO4、Na3PO4Any one of the above; wherein the CHA molecular sieve seed crystal is a CHA molecular sieve synthesized by adopting N, N, N-trimethyl-1-adamantyl ammonium hydroxide as a template according to the method of an example of a patent US 6709644.
3) Stirring the mixture obtained in the step 2), transferring the mixture into a hydrothermal crystallization reaction kettle, crystallizing for 8-120 hours at the self-generated pressure and the temperature of 125-200 ℃, and filtering, washing, drying and roasting the obtained crystallized product to obtain molecular sieve raw powder;
4) mixing the molecular sieve raw powder obtained in the step 3) with an ammonium salt solution with the concentration of 0.1-5.0 mol/L according to a solid-liquid mass ratio of 1: (5-50) carrying out ion exchange at 60-100 ℃, wherein each time of exchange is 0.5-6 hours, and repeatedly exchanging the obtained filter cake with an ammonium ion solution for 1-3 times until the Na ion content in the molecular sieve is lower than 500 ppm; and then filtering and separating out a solid product, repeatedly washing the solid product by using deionized water until the solid product is neutral, drying a filter cake at the temperature of 100-130 ℃ for 12-48 hours, and roasting the filter cake at the temperature of 400-600 ℃ for 2-16 hours to obtain the CHA-type molecular sieve. After the molecular sieve raw powder prepared in the step 3) and the CHA type molecular sieve are treated by saturated steam at 600-850 ℃, the content of tetra-coordinated aluminum in the total aluminum is more than or equal to 90 percent, and the content of hexa-coordinated aluminum in the total aluminum is less than or equal to 10 percent.
The invention adopts27The Al MAS NMR characterization method observed the formation of non-framework aluminum and the reduction of framework aluminum, as well as the discrimination of the coordination state of aluminum. In the zeolite molecular sieve aluminum spectrum, signals between 55 and 65ppm come from framework four-coordinate aluminum, signals at 0ppm come from non-framework six-coordinate aluminum, and resonance peaks of non-framework four-coordinate aluminum and non-framework five-coordinate aluminum belonging to signals about 30 to 45ppm are superposed. For characterizing molecular sieves in the invention27Fitting the peaks of the Al MAS NMR spectrogram into a Gaussian curve by using a generally adopted Gaussian fitting mode, wherein the abscissa position represents the chemical shift of the four-coordinate aluminum, namely the four-coordinate aluminum in different chemical environments; and the corresponding peak areas represent the amount of the corresponding tetracoordinated aluminum. It is composed of27In the Al MAS NMR spectrum, characteristic peaks are all at 55-65ppm, while no characteristic peaks of hexacoordinated aluminum are present at 0ppm, which indicates that the coordination of Al exists in a four-coordinate form, Al is connected with four surrounding Si through O, and no connection of Al with Al through O (hexacoordinated aluminum) or Al with a terminal hydroxyl group (defect) occurs.
Further, in the above technical means, the zeolite molecular sieve in the molar ratio range of 2 to 30 of silica to alumina in step 1) is any one of FAU type zeolite, MFI type zeolite, BEA type zeolite, MOR type zeolite, LTA type zeolite, and EMT type zeolite, preferably any one of FAU type zeolite, MFI type zeolite, BEA type zeolite, and MOR type zeolite, and more preferably any one of X molecular sieve, Y molecular sieve, and USY molecular sieve having FAU type structure; in the step 2) of the synthesis method, the silicon source is selected from one or more of silica sol, water glass, white carbon black, sodium metasilicate, column chromatography silica gel, macroporous silica gel, fine pore silica gel, amorphous silica gel, B-type silica gel, methyl silicate, ethyl silicate, propyl silicate, butyl silicate, ultrafine silica powder, activated clay, organosilicon, diatomite and gas phase method silica gel, and preferably any one or more of silica sol, water glass, column chromatography silica gel, white carbon black, macroporous silica gel, coarse pore silica gel, microporous silica gel, amorphous silica gel, B-type silica gel, methyl silicate and ethyl silicate.
Further, in the above technical solution, the acid solution in step 2) is selected from any one or more of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, propionic acid, citric acid, carbolic acid, oxalic acid, and benzoic acid.
Further, in the above technical solution, the ammonium salt in step 4) includes a mixture of any one, two or more of ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium carbonate and ammonium acetate mixed in any ratio.
The invention provides an SCR catalyst for denitration, wherein a CHA-type molecular sieve is subjected to ion exchange with a soluble metal salt solution, then forms slurry with the solid content of 25.0-48.0 wt% with a binder and deionized water, and is coated on a carrier of a porous regular material or an integral filter substrate to form a proper coating, so that the SCR catalyst of the CHA molecular sieve promoted by metal is obtained.
Further, in the above technical solution, the soluble metal salt is selected from one or a combination of several 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 a copper salt and an iron salt, and further preferably a 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 water solution of the soluble salt of copper is 0.1-0.5 mol/L.
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; the porous regular material or the monolithic filter base material is prepared from any one of cordierite, alpha-alumina, silicon carbide, aluminum titanate, silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia or zirconium silicate.
The invention also provides application of the catalyst in purifying the tail gas of the diesel vehicle.
The molecular sieve catalysts of the invention are also useful for treating gases from industrial processes such as refining, NO-containing gases from refining heaters and boilers, furnaces, chemical processing industries, coke ovens, municipal waste treatment plants and incinerators, and the likexA gas. Nitrogen Oxides (NO)x) Including a variety of 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 treatment comprises NOxWherein prior to contacting said catalyst with said gas stream, is contacted with NOxMeasured as 100% by weight of NO2The content is 80 wt% or less, wherein NO is preferably contained in an amount of 5 to 70 wt%, more preferably 10to 60 wt%, more preferably 15 to 55 wt%, even more preferably 20 to 50 wt%2And (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: NO2Volume ratio.
Reducing agents (urea, NH) are generally used3Etc.) in a Selective Contact Reduction (SCR) system, several chemical reactions take place, all of which represent the reaction of NOxReduction 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)
The invention relates to an SCR catalyst for denitration, which is an SCR catalyst for obtaining a metal-promoted SSZ-13 eutectic molecular sieve by carrying out ion exchange on synthesized silicon-aluminum zeolite molecular sieve raw powder and a soluble metal salt solution.
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 0.1-1.5 mol/L.
The amount of Cu in the copper-based SCR molecular sieve catalyst 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 certain embodiments of the invention, the washcoat of the eutectic molecular sieve SCR catalyst is preferably a solution, suspension or slurry that is applied to a porous structured material (i.e., a honeycomb monolithic catalyst support structure having a plurality of parallel channels running axially through the entire assembly) or a monolithic filter substrate, such as a wall-flow filter, etc., 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 porous regular material comprises a honeycomb flow-through regular carrier which is prepared from cordierite, alpha-alumina, silicon carbide, aluminum titanate, silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia or zirconium silicate materials; the carrier is preferably a cordierite porous honeycomb flow-through type monolith carrier, and the carrying capacity of the carrier is 170-270 g/L.
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-structure 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 more proper pore structure and grain size distribution, 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 molecular sieve has more reasonably distributed acidity and good hydrothermal stability, overcomes the limitations of the components, and the provided SCR catalyst is subjected to durable treatment at high temperature in an atmosphere containing hydrothermal steam, particularly NO at low temperaturexThe reducibility is still excellent. Better meets the requirements of industrial application and has wide application prospect.
The silicoaluminophosphate zeolite molecular sieve of the present invention is more suitable for a high-crystallinity CHA-type zeolite as a catalyst or a catalyst carrier than a conventional CHA-type zeolite, and particularly suitable for a nitrogen oxide reduction catalyst or a carrier thereof, and further a nitrogen oxide reduction catalyst or a carrier thereof in the presence of ammonia or urea.
The molecular sieve of the present invention is a silicoaluminophosphate zeolite molecular sieve having high heat resistance without having a large crystal grain size, and is a catalyst which exhibits high nitrogen oxide reduction characteristics even after exposure to high temperature and high humidity, particularly high nitrogen oxide reduction characteristics at a temperature range of 200 to 550 ℃.
Drawings
FIG. 1 is an XRD diffractogram of the SSZ-13 molecular sieve synthesized in example 1.
FIG. 2 is an XRD diffractogram of the SSZ-13 molecular sieve synthesized in example 2.
FIG. 3 is an XRD diffractogram of the SSZ-13 molecular sieve synthesized in example 3.
FIG. 4 is an SEM topography of the SSZ-13 molecular sieve synthesized in example 1.
FIG. 5 is an SEM topography of the SSZ-13 molecular sieve synthesized in example 2.
FIG. 6 is an SEM topography of the SSZ-13 molecular sieve synthesized in example 3.
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 eutectic 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 Data 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). As XRD measurement conditions in the embodiment of the present invention, the following conditions may be mentioned:
ray source: CuK α ray λ 1.540598, measurement mode: step scan 2 θ step scan scale: 0.02626 °, measurement range: 2 theta is 5-60 degrees.
And substituting X-ray diffraction data into a Debye-Scherrer formula to calculate the grain size Dhkl, wherein the Debye-Scherrer formula is as follows: d (hkl) ═ k λ/β cos θ; wherein D (hkl) is the grain diameter along the direction vertical to the crystal face hkl, and the unit is nm; k is the Scherrer constant; λ is the incident X-ray wavelength in nm; theta is the Bragg diffraction angle in degrees; beta is the half-peak broadening of the diffraction peak. The wavelength λ is 0.15406nm when Cuka is used as the X-ray source and 0.15418nm when Cuka1 is used as the X-ray source. The measurement was carried out by a PANalytical X-ray diffractometer under CuK alpha monochromatic light irradiation at a tube voltage of 45kV and a current of 40mA in a 2 theta range of 15 to 35 degrees.
Example 1
A CHA type SSZ-13 molecular sieve and an SCR catalyst preparation method are disclosed:
1) mixing 45.59g HY molecular sieve (Si/Al to nSiO)2/nAl2O35.20 dry basis, 78.1 percent of dry basis), 26.68g of NaOH flake caustic soda and 69.98g of deionized water are fully dissolved and dispersed to obtain slurry with the molar ratio of nNa2O:nSiO2:nAl2O3:nH2Aging in a crystallization kettle at 85 ℃ for 36 hours to obtain silicon-aluminum gel, wherein O is 0.75:1.0:0.192: 10;
2) 507.51g of silica gel solution (Na) were added to the mixed silica-alumina gel mixture obtained in step 1)2O：0.24wt％，SiO2: 30.36 wt%), 275.29g N, N-diethyl-N' -methyl-3, 3, 5-trimethylcyclohexylammonium hydroxide (concentration 20 wt%, expressed as OSDA), 56.31g NaOH flake alkali, 21.25g NaCl and 156.10g deionized water were thoroughly and ultrasonically stirred and mixed uniformly so that the mixed slurry components had a molar ratio of nNa2O:nSiO2:nA12O3:nOSDA:nNaCl:nH2O ═ 0.35:1.0:0.0286:0.08:0.12: 15; adding 5% HCl solution to adjust nOH in the system-/nSiO2Adding SiO into the mixed slurry with the ratio of 0.782And A12O3Taking 9.45g of CHA molecular sieve accounting for 5.0 percent of the total mass as seed crystal; stirring the mixture, transferring the mixture into a hydrothermal crystallization reaction kettle, crystallizing for 36 hours at the self-generated pressure and the temperature of 140 ℃, then quenching to stop crystallization, filtering and washing the product until the pH value is nearly neutral, drying for 12 hours at the temperature of 120 ℃, and roasting for 4 hours at the temperature of 540 ℃ to obtain SSZ-13 molecular sieve raw powder;
3) performing ion exchange on the SSZ-13 molecular sieve raw powder in the step 2) and an ammonium nitrate solution with the concentration of 1.0mol/L for 2 hours at the temperature of 60 ℃ according to the solid-liquid mass ratio of 1:10, and then repeatedly exchanging the filter cake obtained by filtering with a fresh ammonium nitrate solution twice under the same condition so as to ensure that the Na ion content in the sample is lower than 500 ppm. Then filtering and separating the solid product, repeatedly washing the solid product to be neutral by using deionized water, and drying the obtained filter cake at 110 ℃ for 12h to obtain the ammonium type molecular sieve NH4SSZ-13, then heating to 500 ℃ and roasting for 8 hours to obtain the H-type SSZ-13 molecular sieve (namely the CHA-type molecular sieve).
4) Adding 50.0g of the H-type SSZ-13 molecular sieve obtained in the step 3) into a copper nitrate aqueous solution with the concentration of 0.15mol/L, dropwise adding dilute nitric acid into the solution to adjust the pH value to 6.5, uniformly stirring, placing into a heat-resistant container, and placing 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 copper-modified SSZ-13 molecular sieve is obtained, and the catalyst prepared according to XRF analysis results contains 3.2% of copper (II) ions in the total weight of the molecular sieve catalyst, namely the copper loading is 3.2 wt%.
5) Taking 40.0g of the copper-modified molecular sieve obtained in the above 4), and 20.0g of silica Sol (SiO)2The content is as follows: 30.0 wt%) and 93.33g of deionized water are uniformly mixed to prepare catalyst slurry with the solid content of 30.0 wt%, the catalyst slurry is coated on a honeycomb-shaped porous regular material (#400cpsi, the diameter is 20mm, and the length is 40mm) made of cordierite through an impregnation method, redundant slurry drops are blown off by compressed air, the catalyst slurry is dried for 24 hours at 105 ℃, the catalyst slurry is coated for 2 times under the same condition, the catalyst slurry is calcined for 2 hours at 500 ℃, the loading on the regular material is 227.7g/L (the weight of the regular material after calcination is divided by the space volume occupied by the regular material, the definitions of the subsequent examples and comparative examples are the same with respect to the loading), and in order to obtain the SCR catalyst, the preparation parameters and the material types are shown in tables 1, 2, 3 and 4.
Example 2
The process for synthesizing the CHA-type SSZ-13 molecular sieve is similar to that of example 1, except that the slurry components in step 1) are present in a molar ratio (nNa)2O:nSiO2:nAl2O3:nH2O), zeolite molecular sieve type, zeolite molecular sieve silicon-aluminum ratio, aging temperature and aging time, wherein in the step 2), the mixed slurry component molar ratio, the organic template agent type, the silicon source type, the seed crystal adding amount, the acid adding type, the metal salt M type, the crystallization temperature and the crystallization time are adopted, in the step 4), 50.0g of H-type SSZ-13 molecular sieve is taken, different soluble metal salt types, different concentrations, different solution volumes and different metal loading amounts are adopted, in the step 5), 40.0g of copper modified CHA-type SSZ-13 molecular sieve and 20.0g of silica Sol (SiO)2The content is as follows: 30.0 wt%) and 97.53g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 29.2 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, 3 and 4.
Example 3
The process for synthesizing the CHA-type SSZ-13 molecular sieve is analogous to the examples1, except that the molar ratio of the components of the slurry in step 1) (nNa)2O:nSiO2:nAl2O3:nH2O), zeolite molecular sieve type, zeolite molecular sieve silicon-aluminum ratio, aging temperature and aging time, wherein in the step 2), the mixed slurry component molar ratio, the organic template agent type, the silicon source type, the seed crystal adding amount, the acid adding type, the metal salt M type, the crystallization temperature and the crystallization time are adopted, in the step 4), 50.0g of H-type SSZ-13 molecular sieve is taken, different soluble metal salt types, different concentrations, different solution volumes and different metal loading amounts are adopted, in the step 5), 40g of copper modified CHA-type SSZ-13 molecular sieve and 20.0g of silica Sol (SiO) are taken2The content is as follows: 30.0 wt%) and 88.87g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 30.9 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, 3 and 4.
Example 4
The process for synthesizing the CHA-type SSZ-13 molecular sieve is similar to that of example 1, except that the slurry components in step 1) are present in a molar ratio (nNa)2O:nSiO2:nAl2O3:nH2O), zeolite molecular sieve type, zeolite molecular sieve silicon-aluminum ratio, aging temperature and aging time, wherein in the step 2), the mixed slurry component molar ratio, the organic template agent type, the silicon source type, the seed crystal adding amount, the acid adding type, the metal salt M type, the crystallization temperature and the crystallization time are adopted, in the step 4), 50.0g of H-type SSZ-13 molecular sieve is taken, different soluble metal salt types, different concentrations, different solution volumes and different metal loading amounts are adopted, in the step 5), 40g of copper modified CHA-type SSZ-13 molecular sieve and 20.0g of silica Sol (SiO) are taken2The content is as follows: 30.0 wt%) and 84.65g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 31.8 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, 3 and 4.
Example 5
The process for synthesizing the CHA-type SSZ-13 molecular sieve is similar to that of example 1, except that the slurry components in step 1) are present in a molar ratio (nNa)2O:nSiO2:nAl2O3:nH2O), zeolite molecular sieve type, zeolite molecular sieve silicon-aluminum ratio, aging temperature and aging time, wherein in the step 2), the mixed slurry component molar ratio, the organic template agent type, the silicon source type, the seed crystal adding amount, the acid adding type, the metal salt M type, the crystallization temperature and the crystallization time are adopted, in the step 4), 50.0g of H-type SSZ-13 molecular sieve is taken, different soluble metal salt types, different concentrations, different solution volumes and different metal loading amounts are adopted, in the step 5), 40g of copper modified CHA-type SSZ-13 molecular sieve and 30.0g of aluminum sol (Al) are taken2O3The content is as follows: 20.0 wt%) and 98.97g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 29.0 wt%, which was coated on a cordierite structured material by an impregnation method. Specific parameters in this example are shown in tables 1, 2, 3 and 4.
Example 6
The process for synthesizing the CHA-type SSZ-13 molecular sieve is similar to that of example 1, except that the slurry components in step 1) are present in a molar ratio (nNa)2O:nSiO2:nAl2O3:nH2O), zeolite molecular sieve type, zeolite molecular sieve silicon-aluminum ratio, aging temperature and aging time, wherein in the step 2), the mixed slurry component molar ratio, the organic template agent type, the silicon source type, the seed crystal adding amount, the acid adding type, the metal salt M type, the crystallization temperature and the crystallization time are adopted, in the step 4), 50.0g of H-type SSZ-13 molecular sieve is taken, different soluble metal salt types, different concentrations, different solution volumes and different metal loading amounts are adopted, in the step 5), 40g of copper modified CHA-type SSZ-13 molecular sieve and 30.0g of aluminum sol (Al) are taken2O3The content is as follows: 20.0 wt%) and 84.36g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 29.8 wt%, which was coated on a cordierite structured material by an impregnation method. Specific parameters in this example are shown in tables 1, 2, 3 and 4.
Example 7
The process for synthesizing the CHA-type SSZ-13 molecular sieve is similar to that of example 1, except that the slurry components in step 1) are present in a molar ratio (nNa)2O:nSiO2:nAl2O3:nH2O), the type of the zeolite molecular sieve, the silicon-aluminum ratio of the zeolite molecular sieve, the aging temperature and the aging time, and the mixing in the step 2)The method comprises the following steps of (1) taking 50.0g of H-type SSZ-13 molecular sieve, adopting different soluble metal salt types, concentrations, solution volumes and metal loading amounts, and taking 40g of copper modified CHA-type SSZ-13 molecular sieve and 30.0g of aluminum sol (Al) in step 5)2O3The content is as follows: 20.0 wt%) and 106.25g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 26.1 wt%, which was coated on a cordierite structured material by an impregnation method. Specific parameters in this example are shown in tables 1, 2, 3 and 4.
Example 8
The process for synthesizing the CHA-type SSZ-13 molecular sieve is similar to that of example 1, except that the slurry components in step 1) are present in a molar ratio (nNa)2O:nSiO2:nAl2O3:nH2O), zeolite molecular sieve type, zeolite molecular sieve silicon-aluminum ratio, aging temperature and aging time, wherein in the step 2), the mixed slurry component molar ratio, the organic template agent type, the silicon source type, the seed crystal adding amount, the acid adding type, the metal salt M type, the crystallization temperature and the crystallization time are adopted, in the step 4), 50.0g of H-type SSZ-13 molecular sieve is taken, different soluble metal salt types, different concentrations, different solution volumes and different metal loading amounts are adopted, in the step 5), 40g of copper modified CHA-type SSZ-13 molecular sieve and 30.0g of aluminum sol (Al) are taken2O3The content is as follows: 20.0 wt%) and 107.61g of deionized water were mixed uniformly to prepare a catalyst slurry having a solid content of 25.9 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, 3 and 4.
TABLE 1 selection of parameters in the Synthesis of molecular sieves step 1)
Examples nNa2O:nSiO2:nAl2O3:nH2O Zeolite molecular sieve species Zeolite molecular sieve silica-alumina ratio Ageing temperature/. degree.C Aging time/h
Example 1 0.75:1.0:0.192:10 HY 5.20 85 36
Example 2 1.25:1.0:0.189:10 NaY 5.29 120 8
Example 3 1.05:1.0:0.417:6 NaX 2.40 100 24
Example 4 2.45:1.0:0.040:20 ZSM-5 22.0 110 40
Example 5 1.35:1.0:0.139:15 USY 7.20 85 48
Example 6 2.05:1.0:0.085:20 MOR 11.8 105 36
Example 7 1.15:1.0:0.208:12 NaY 4.80 90 16
Example 8 1.85:1.0:0.074:18 USY 12.1 105 12
TABLE 2 selection of parameters in molecular Sieve Synthesis step 2)
Figure BDA0002626338960000191
TABLE 3 tables of molecular sieve performance parameters obtained in examples 1 to 8
Figure BDA0002626338960000201
*: the sample is used after the hydrothermal treatment for 16 hours by saturated water vapor at 800 DEG C27And testing the aluminum proportioning ratio by Al MAS NMR solid nuclear magnetic resonance.
Table 4 SCR catalyst metal ion parameters and metal loadings prepared in examples 1-8
Figure BDA0002626338960000202
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 80 ℃ according to the solid-liquid mass ratio of 1:10, and then filter cakes obtained by filtration are repeatedly exchanged with fresh ammonium nitrate solution twice 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 raw powder was added to 100g of Cu (NO) having a concentration of 0.3mol/L3)2·3H2In an aqueous O solutionAnd dropwise adding dilute nitric acid into the 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
The SSZ-13 molecular sieve is synthesized and the SCR catalyst is prepared according to the method in CN 103328385:
to 13.9g N, N-trimethylamantadine ammonium hydroxide solution (TMADAOH, 25%), pure water 31.4g, an aqueous potassium hydroxide solution (concentration 48%), and an amorphous aluminosilicate gel 9.0g prepared from sodium silicate and aluminum sulfate were added and mixed thoroughly to obtain a raw material composition. The composition of the raw material composition is SiO2：0.048Al2O3：0.124TMADAOH：0.054Na2O：0.081K2O：18H2And O. The raw material composition was sealed in an 80ml stainless steel autoclave and crystallized at 150 ℃ for 72 hours at a rotation speed of 55 rpm. Filtering or centrifuging the crystallized product, washing with deionized water to approach neutrality, and drying at 110 deg.C to obtain SSZ-13 molecular sieve product, SiO2/Al2O3The molar ratio is 14.9, and the particle size is 1.0-3.0 μm.
Mixing the SSZ-13 molecular sieve raw powder with 1.0mol/L nitreAnd carrying out ion exchange on the ammonium nitrate solution at 90 ℃ for 2 hours according to the solid-liquid mass ratio of 1:10, and then repeatedly exchanging the filter cake obtained by filtering with a fresh ammonium nitrate solution twice under the same condition to ensure 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 raw powder was added to 100g of Cu (NO) having 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 3.0% 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 216.6g/L and is marked as VS-2.
Examples 9 to 14
Testing of the SCR catalyst:
SCR catalysts prepared in examples 1 to 6 and comparative examples 1 to 2 were installed in a reactor
Figure BDA0002626338960000231
In the mixed gas flow, a mixed gas flow containing 500ppm NO, 500ppm NH3, 10 vol% O2, 5 vol% steam and Ar as balance gas is 160mL/min, and the mixed gas flow firstly passes through a preheater (set at 25%0 deg.C) and then 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 was determined under steady state conditions by measuring NOx, NH3, and N2O concentrations at the outlet using a Bruker EQUINOX model 55 FT-IR spectrometer.
Figure BDA0002626338960000241
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 5.
TABLE 5 preparation of catalyst NO for examples 1-6 and comparative examples 1-2xEvaluation index of Selective reduction Performance
Figure BDA0002626338960000242
800 ℃ in an atmosphere of 10% moisture + 10% oxygen concentration, at a space velocity of 30000/h, for 16 hours.
As can be seen from Table 5, the Cu-SSZ-13 or Fe-SSZ-13 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 or Fe-SSZ-13 catalyst materials of the present invention and the catalysts obtained therewith have improved SCR catalytic activity, especially at low conversion temperatures characteristic of cold start conditions when treating NOx, for example, in diesel locomotive applications. For other SCR applications, the Cu-SSZ-13 or Fe-SSZ-13 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. A CHA-type molecular sieve for purifying diesel vehicle tail gas, which is characterized in that: the CHA-type silicon-aluminum molecular sieve is synthesized by adopting N, N, N-trimethyl-3, 3, 5-trimethyl cyclohexyl-quaternary ammonium as an organic template, wherein the mole ratio of silicon dioxide to aluminum oxide of the CHA-type molecular sieve is 6-80, the average grain diameter is less than or equal to 500nm, and the total specific surface area is more than or equal to 400m2The total pore volume is more than or equal to 0.20ml/g, and the micropore volume is more than or equal to 0.10 ml/g; the molecular sieve has a CHA topological structure, the range of the half-value width (FWHM) of a crystal face of X-ray crystal diffraction (-210) is 0.1-0.2 degrees, and the diameter size of crystal grains in the crystal face (-210) direction is 50-160 nm calculated by a Debye-Scherrer formula; after the molecular sieve is treated by saturated steam at 600-850 ℃, the four-coordination aluminum accounts for more than or equal to 90 percent of the total aluminum content, and the six-coordination aluminum accounts for less than or equal to 10 percent of the total aluminum content; the structural formula of the N, N, N-trimethyl-3, 3, 5-trimethylcyclohexyl-quaternary ammonium compound is shown as a formula I:
Figure FDA0002626338950000011
wherein R1 and R2 are independently selected from methyl or deuterated methyl, C2-C4 straight chain or branchChain alkyl, R3 is selected from C1-C5 straight chain or branched chain alkyl; x-Counter anions which are N, N-trimethyl-3, 3, 5-trimethylcyclohexyl-quaternary ammonium ions include any of hydroxide, halide, sulfate, bisulfate, carbonate, bicarbonate, oxalate, acetate, phosphate, carboxylate, alkyl-substituted sulfate, carbonate or oxalate.
2. The CHA-type molecular sieve for diesel vehicle exhaust purification of claim 1, wherein: the CHA-type molecular sieve has at least one XRD diffraction peak in each of the following tables in the range of 4-40 DEG 2 theta and has the characteristics as set forth in the following tables:
Figure FDA0002626338950000021
the relative intensity is an intensity relative to a peak intensity of 20.40 to 20.90 in terms of 2 θ.
3. The CHA-type molecular sieve for diesel vehicle exhaust purification of claim 1, wherein: the halide comprises chloride, bromide or iodide; carboxylates include formate, acetate, propionate; alkyl substituted sulphate, carbonate or oxalate including methyl sulphate, ethyl sulphate, methyl carbonate, ethyl carbonate, methyl oxalate or ethyl oxalate; the N, N, N-trimethyl-3, 3, 5-trimethyl cyclohexyl-quaternary ammonium salt compound is synthesized by taking isophorone as a raw material, firstly performing ammoniation hydrogenation, and finally performing alkylation reaction.
4. The method of synthesizing the CHA-type molecular sieve for diesel vehicle exhaust purification of any of claims 1 to 3, wherein the method comprises the steps of: the method comprises the following steps:
1) fully dissolving and dispersing zeolite molecular sieve with the molar ratio of silicon dioxide to aluminum oxide of 2-30, NaOH and deionized water to obtain slurry with the molar ratio of nNa2O:nSiO2:nAl2O3:nH2O (0.5-2.5): 1, (0.0333-0.5): 5-20) inAging in a crystallization kettle at 60-120 ℃ for 6-48 hours to obtain silicon-aluminum gel;
2) adding a silicon source, an organic template agent OSDA, a metal salt M and deionized water into the silicon-aluminum gel obtained in the step 1), fully and uniformly mixing, supplementing NaOH according to the system alkalinity requirement, and mixing the components of the slurry according to the molar ratio of nNa2O:nSiO2:nA12O3:nOSDA:nM:nH2O is (0.05-0.5) 1, (0.0125-0.20), (0.01-0.5), (0.05-0.5) and (10-100); adding acid solution to control alkali hydroxyl OH in mixed slurry-With SiO2The molar ratio nOH-/nSiO2 is 0.1-1.0; adding CHA molecular sieve seed crystal with SiO in the slurry2And A12O30.5-15% of the total mass;
3) stirring the mixture obtained in the step 2), transferring the mixture into a hydrothermal crystallization reaction kettle, crystallizing for 8-120 hours at the self-generated pressure and the temperature of 125-200 ℃, and filtering, washing, drying and roasting the obtained crystallized product to obtain molecular sieve raw powder;
4) mixing the molecular sieve raw powder obtained in the step 3) with an ammonium salt solution with the concentration of 0.1-5.0 mol/L according to a solid-liquid mass ratio of 1: (5-50) carrying out ion exchange at 60-100 ℃, wherein each time of exchange is 0.5-6 hours, and repeatedly exchanging the obtained filter cake with an ammonium ion solution for 1-3 times until the Na ion content in the molecular sieve is lower than 500 ppm; and then filtering and separating out a solid product, repeatedly washing the solid product by using deionized water until the solid product is neutral, drying a filter cake at the temperature of 100-130 ℃ for 12-48 hours, and roasting the filter cake at the temperature of 400-600 ℃ for 2-16 hours to obtain the CHA-type molecular sieve.
5. The method of synthesis according to claim 4, characterized in that: the zeolite molecular sieve in the mole ratio range of 2-30 of the silicon dioxide and the alumina in the step 1) is any one of FAU type zeolite, MFI type zeolite, BEA type zeolite, MOR type zeolite, LTA type zeolite and EMT type zeolite, preferably any one of FAU type zeolite, MFI type zeolite, BEA type zeolite and MOR type zeolite, and further preferably any one of an X molecular sieve, a Y molecular sieve and a USY molecular sieve with FAU type structures; in the step 2), the silicon source is selected from silica sol, water glass, white carbon black, sodium metasilicate and column chromatography silica gelOne or more of macroporous silica gel, coarse porous silica gel, fine porous silica gel, amorphous silica, B-type silica gel, methyl silicate, ethyl silicate, propyl silicate, butyl silicate, superfine silica powder, activated clay, organic silicon, diatomite and gas-phase silica gel, and preferably one or more of silica sol, water glass, column chromatography silica gel, white carbon black, macroporous silica gel, coarse porous silica gel, fine porous silica gel, amorphous silica, B-type silica gel, methyl silicate and ethyl silicate; the metal salt M is NaCl and NaNO3、Na2SO4、Na3PO4、NaBr、NaF、KCl、KNO3、K2SO4、KBr、KF、K3PO4Any of them, preferably NaCl and NaNO3、Na2SO4、Na3PO4Any one of the above; the acid solution is selected from one or more of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, propionic acid, citric acid, carbolic acid, oxalic acid and benzoic acid.
6. The method of synthesis according to claim 4, characterized in that: the ammonium salt in the step 4) comprises 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.
7. A catalyst, characterized by: ion exchange is carried out on the CHA-type molecular sieve of any one of claims 1 to 3 and a soluble metal salt solution, then the CHA-type molecular sieve and a binder and deionized water form slurry with the solid content of 25.0-48.0 wt%, and the slurry is coated on a proper coating formed on a carrier of a porous regular material or a monolithic filter substrate to obtain the metal-promoted catalyst.
8. The catalyst of claim 7, 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 water solution of the soluble salt of copper is 0.1-0.5 mol/L.
9. The catalyst of claim 7, wherein: the binder is selected from any one or mixture of silica sol, aluminum sol or pseudo-boehmite; the porous regular material or the monolithic filter base material is prepared from any one of cordierite, alpha-alumina, silicon carbide, aluminum titanate, silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia or zirconium silicate.
10. Use of a catalyst according to any one of claims 7 to 9 for the purification of diesel vehicle exhaust gases.
CN202010797921.0A 2020-08-10 2020-08-10 CHA-type molecular sieve and catalyst for diesel vehicle exhaust purification, and preparation method and application thereof Pending CN111871452A (en)

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