A preparation method for synthesizing CHA zeolite based on phenol medium

Abstract

The present invention provides a kind of preparation method of synthesizing CHA zeolite based on phenol medium, comprise the steps:Step S1, adds aluminium hydroxide in potassium hydroxide aqueous solution, heated and stirred to clarification, after cooling, adds silica sol and phenol, obtains mixed solution after mixing, wherein the mol ratio of phenol to the aluminium hydroxide is 1:1 3, and silicon-aluminium ratio is 2 3:1;The mixed solution is placed in autoclave, put into homogeneous reactor and be aged, and aging time is no more than 38h;Step S2, after aging, carries out hydrothermal reaction at 160 DEG C, and the time of hydrothermal reaction is 48 144h;Step S3, after reaction terminates, centrifugal washing, drying, obtain product zeolite.The technical scheme of the present invention introduces phenol medium, can regulate the heterogeneity of zeolite, promotes CHA crystallization, and the CHA zeolite obtained has very high CO2adsorption capacity, better storage capacity and excellent selectivity.

Description

Technical Field

[0001] The invention belongs to the field of material technology, and in particular relates to a preparation method for synthesizing CHA zeolite based on a phenol medium. Background Art

[0002] Small-pore SSZ-13 zeolites (CHA topology) have attracted increasing attention because their transition metal ion exchange adsorbents have shown excellent CO2 capture performance, which is attributed to the π-complexation effect. In addition, their copper or iron ion exchange catalysts have also shown extremely high activity for the conversion of NH3 to NO. x The selective catalytic reduction (SCR) of CHA zeolite has excellent selectivity and stability. Therefore, people have been working hard to overcome the difficulties in their synthesis over the past few decades. The typical synthesis of CHA zeolite requires the use of N,N,N-trimethyl-1-adamantyl ammonium hydroxide (TMAdaOH) as an organic structure directing agent (OSDA). But unfortunately, this directing agent is both expensive and toxic. In order to open the molecular sieve channels and cages that are critical to catalysis and separation, the organic TMAdaOH must be removed, which usually requires calcination in air at about 550°C, thereby increasing a lot of energy consumption and environmental impact.

[0003] Despite significant efforts to eliminate the use of OSDA, small-pore CHA zeolites are difficult to synthesize in OSDA-free media within reasonable timescales. Heterogeneity is a common problem during OSDA-free synthesis, resulting from a variety of kinetic factors that can lead to the formation of unwanted phases or crystalline impurities. Summary of the Invention

[0004] In response to the above technical problems, the present invention discloses a preparation method for synthesizing CHA zeolite based on a phenol medium. The CHA zeolite synthesized in the phenol medium has high CO2 adsorption capacity, better storage capacity and excellent selectivity.

[0005] To this end, the technical solution adopted in the present invention is:

[0006] A preparation method for synthesizing CHA zeolite based on a phenol medium comprises the following steps:

[0007] Step S1, adding aluminum hydroxide to a potassium hydroxide aqueous solution, heating and stirring until clear, cooling, adding silica sol and phenol, and mixing uniformly to obtain a mixed solution, wherein the molar ratio of phenol to the aluminum hydroxide is 1:1-3, and the silicon-aluminum ratio is 2-3:1; placing the mixed solution in an autoclave, and placing it in a homogeneous reactor for aging, and the aging time is not more than 38 hours;

[0008] Step S2: after aging, performing a hydrothermal reaction at 155-165° C. for 48-144 hours;

[0009] Step S3: After the reaction is completed, the product is centrifuged, washed, and dried to obtain the zeolite product.

[0010] As a further improvement of the present invention, in step S1, the aging temperature is room temperature, and the rotation speed of the homogeneous reactor is 15-25 rpm. Furthermore, the rotation speed of the homogeneous reactor is 20 rpm.

[0011] As a further improvement of the present invention, in step S1, the aging time is 1-24 hours. Further, in step S1, the aging time is 24 hours.

[0012] As a further improvement of the present invention, in step S1, the molar ratio of phenol to the aluminum hydroxide is 1:1-2; pure CHA can be crystallized into walnut-shaped particles containing embedded nanocrystals.

[0013] As a further improvement of the present invention, the molar ratio of the components in the mixed solution in step S1 is KOH:Al(OH)3:SiO2:phenol:H2O=7:4:10:1~5:150.

[0014] As a further improvement of the present invention, the hydrothermal reaction temperature in step S2 is 160°C.

[0015] As a further improvement of the present invention, in step S2, the hydrothermal reaction time is 72-144 hours. Further, in step S2, the hydrothermal reaction time is 72-96 hours. Further, in step S2, the hydrothermal reaction time is 96 hours.

[0016] As a further improvement of the present invention, the preparation method of CHA zeolite synthesized based on phenol medium also includes step S4, mixing the obtained product zeolite with (NH4)2SO4 solution at 70-90°C for more than 4 hours, and then calcining at 500-600°C to obtain H-type zeolite.

[0017] As a further improvement of the present invention, the concentration of the (NH4)2SO4 solution is 2-3 mol / L, and the ratio of the zeolite to the (NH4)2SO4 solution is 1 g: 25-35 mL. Furthermore, the concentration of the (NH4)2SO4 solution is 2.5 mol / L.

[0018] The present invention also discloses a CHA zeolite, which is prepared by adopting the above-mentioned preparation method for synthesizing CHA zeolite based on a phenol medium.

[0019] The present invention also discloses the application of the CHA zeolite described above for gas adsorption, and further for adsorbing CO2.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The technical solution of the present invention is to introduce phenol as a medium to adjust the heterogeneity of the zeolite, thereby promoting CHA crystallization and changing the dissolution of silicon and aluminum sources. The resulting CHA zeolite has high CO2 adsorption capacity, better storage capacity and excellent selectivity. Further, selecting a suitable aging time is conducive to the formation of the zeolite CHA phase. The phenol medium can make the aluminate dimer Al2O(OH)6 2- The species reappeared. Direct synthesis in a phenol medium is environmentally friendly and readily scalable, as phenol can be removed from the resulting zeolite by simple water washing and recycled. Similar to discrete zeolite nanocrystals treated with mixed cations, the low-silica CHA zeolite obtained in a phenol medium exhibits high CO adsorption capacity, with each CHA single cage capable of almost complete adsorption of nine CO molecules, and exhibits excellent recyclability, with the ability to withstand multiple high-temperature CO adsorption-desorption cycles.

[0022] Furthermore, the present invention also provides an anion-tuning strategy for manipulating OSDA-free zeolite phase selection, complementing existing toolboxes employing mixed inorganic cations. Another advantage of the phenol-mediated anion-tuning strategy is its mild etching properties. Therefore, the synthesis recipe and conditions can be tailored to maximize its nucleophilic etching-assisted growth mechanism, generating intracrystalline mesopores that accompany the formation of hierarchically porous zeolites. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the XRD pattern of the blank sample of pure MER zeolite in Comparative Example 2 of the present invention.

[0024] Figure 2 These are scanning electron microscope images of the blank sample of pure MER zeolite in Comparative Example 2 of the present invention, wherein (a) and (b) are at different magnifications.

[0025] Figure 3 The microstructures of the K-nPhe samples obtained in Examples 1-5 of the present invention and Comparative Examples 1-2, wherein (a) is the XRD diagram, and (b) is the functional relationship between the relative crystallinity change of CHA zeolite compared with K-4.0Phe and the amount of phenol added.

[0026] Figure 4These are scanning electron microscope images of the samples obtained in Examples 1 to 5 of the present invention; among them, (a) K-0.1Phe, (b) K-1.0Phe, (c) K-2.0Phe, (d) K-3.0Phe, (e) K-4.0Phe, and (f) K-5.0Phe; the insets are magnified surface features.

[0027] Figure 5 This is a microscopic characterization of samples obtained at different aging times according to the present invention; wherein, (a) is an XRD pattern, and the arrow indicates the peak generated by MER impurities; (b) to (e) are scanning electron microscope images of CHA zeolite products synthesized by aging K-4.0Phe for 0h, 24h, 38h, and 96h, respectively, and the insets are magnified surface features; (f) is the nitrogen adsorption-desorption isotherm of phenol-mediated CHA, i.e., K-4.0Phe, after ion exchange to H-type; and (g) is the BJH pore size distribution.

[0028] Figure 6 The effect of phenol dosage on the performance of K-nPhe synthesized CHA zeolite in Examples 2-4 of the present invention; wherein, (a) particle size, (b) crystallite size.

[0029] Figure 7 1 is the performance curve of H-nPhe of the embodiment of the present invention, wherein (a) is the nitrogen adsorption-desorption isotherm at -196°C, and (b) is the BJH pore size distribution of zeolites synthesized with different phenol contents after ion exchange into H type.

[0030] Figure 8 These are SEM images of CHA zeolite products obtained at different aging times according to the examples of the present invention, where (a) 0 h, (b) 24 h (K-4.0 Phe), (c) 38 h, and (d) 96 h; the circles represent MER impurities with a rod-like morphology.

[0031] Figure 9 The results of the analysis of the sample K-4.0Phe of Example 4 of the present invention are shown in Figures 1 and 2. (a) and (b) are low-resolution and high-resolution TEM images of the K-4.0Phe zeolite, respectively, and the inset shows the selected area electron diffraction (SAED) pattern corresponding to the CHA type zeolite and the diffraction spot 0.93 nm ((100) plane); the crack image in the cross-sectional transmission electron microscope is produced by ultrathin sectioning, which slightly cuts the zeolite crystal; (c) is the Raman spectrum of K-4.0Phe before and after washing; (d)-(f) are the solid MAS nuclear magnetic resonance spectra of K-4.0Phe, respectively; (d) is 29 Si MAS NMR, (e) 27 Al MAS NMR, (f) 13 C MAS NMR.

[0032] Figure 10 3 and 4 are Raman spectra of pure phenol, SiO2 source, Al(OH)3 and KOH according to an embodiment of the present invention.

[0033] Figure 11 This is the 1H NMR of the K-4.0Phe washing solution synthesized for cleaning in an embodiment of the present invention.

[0034] Figure 12 This is the XRD analysis of K-nNaPhe (K-2NaPhe and K-4NaPhe) samples synthesized in the presence of sodium phenolate in Comparative Example 8 of the present invention. The final gel had a molar composition of KOH:Al(OH)3:SiO2:NaPhe:H2O = 7:4:10:n (n = 2, 4):150. The gel was aged at room temperature for 24 hours at 20 rpm and hydrothermally synthesized at 160°C for 4 days.

[0035] Figure 13 : In situ ReactRaman monitoring of the synthesis mixture before the hydrothermal step of an embodiment of the present invention; wherein, (a) is the spectrum of the K-0.0Phe synthesis system during the aluminate precursor, the addition of silica and the 24-hour aging period (the time interval is 3 hours); (b) is the spectrum of the K-4.0Phe synthesis system during the 72-hour aging period (the time interval is 9 hours); (c) is the enlarged spectrum of (b) to further show the peaks of the aluminate dimer and monomer, and (d) is the peak at 543 cm in (b). -1 / 615cm -1 Peak intensity ratio curve.

[0036] Figure 14 The in-situ ReactRaman spectra of the initial stage of K-4.0Phe synthesis in the embodiment of the present invention are shown; wherein (a) is the time-resolved Raman spectrum of K-4.0Phe synthesis in the aging stage, with a time interval of 9 hours, and (b) is the 543cm during the precursor addition process during the pre-aging process. -1 and 614cm -1 Spectrum of peaks versus time.

[0037] Figure 15 The in-situ reaction diagrams of zeolite synthesis during the aging process of K-0.0Phe and K-4.0Phe in the present invention are shown; (a) and (b) are the three-dimensional surfaces of the synthesis system after aging for 24 hours and 72 hours, respectively, and (c) and (d) are the 543 cm-1 of the K-0.0Phe and K-4.0Phe synthesis systems during aging. -1 *10(535cm -1 *10) and 614cm -1 (620cm -1 ) peak intensity variation spectrum over time.

[0038] Figure 16 The present invention uses 532nm laser Raman technology to analyze the time series samples collected during the aging of K-4.0Phe, K-0Phe and K-1.0Phe. (a) is the process Raman spectrum of the precursor mixture of K-0.0Phe, K-1.0Phe and K-4.0Phe at different aging times, and the right y-axis represents the final product stage after hydrothermal synthesis; (b) is the Al2O(OH)6 in the K-4.0Phe precursor mixture at different aging times. 2- Aluminate dimer and Al(OH)4 - Peak area ratio of monomers.

[0039] Figure 17 3 is a characterization diagram of the hydrothermal synthesis reaction stage of an embodiment of the present invention; wherein (a) is the reaction Raman spectrum of the K-0.0Phe blank sample during the crystallization stage, (c) is the reaction Raman spectrum of the phenol-mediated K-4.0Phe crystallization stage, (b) and (d) are curves of the corresponding intensities of the characteristic peaks representing the zeolite bicyclic structural unit and the aluminate dimer during the crystallization stage of K-0.0Phe and K-4.0Phe, respectively, over time.

[0040] Figure 18 3. The figures are comparisons of scanning electron microscope images of the K-0.0Phe and K-4.0Phe synthesis systems after aging for 24 hours in the embodiments of the present invention; wherein, (a1) to (a3) ​​are SEM images of K-4.0Phe at different magnifications, and (b1) to (b3) are SEM images of K-0.0Phe at different magnifications.

[0041] Figure 19 Characterization results for K-4.0Phe-t samples obtained from different hydrothermal synthesis times according to an embodiment of the present invention; (a) is the XRD pattern, (b) is the relative crystallinity, and (c)-(j) are SEM images at 2h, 12h, 24h, 48h, 72h, 96h, 120h, and 144h, respectively. The inset shows a magnified view of the surface features.

[0042] Figure 20 These are the EDX results of samples obtained from K-4.0Phe-t of the present invention at different hydrothermal synthesis times; wherein (a)-(e) are 2h, 12h, 24h, 48h, 72h, 96h, 120h, and 144h, respectively.

[0043] Figure 21These are the gas physical adsorption results of samples obtained at different hydrothermal synthesis times of K-4.0Phe-t in Example 1 of the present invention; wherein, (a) is the nitrogen adsorption-desorption isotherm of the sample after ion exchange into H-type at different hydrothermal crystallization times, and (b) is the BJH pore size distribution.

[0044] Figure 22 This is a possible synthetic route for the phenol medium of the present invention to adjust the phase selection of CHA and MER zeolites.

[0045] Figure 23 These are characterization diagrams of MER zeolite, the final product obtained when MER seed crystals are added to a mixture without phenol according to the present invention; wherein, (a) is an XRD diagram, and (b) is an SEM diagram.

[0046] Figure 24 Characterization diagrams of the products obtained by adding seed crystals in the phenol-mediated synthesis of CHA zeolite in an embodiment of the present invention; among them, (a) is the XRD pattern, (b) to (e) are SEM images of MER+4.0Phe, 4.0Phe+CHA, CHA+4.0Phe, and CHA / 4.0Phe, respectively, and the inset shows the magnified surface features.

[0047] Figure 25 This is a characterization of the product synthesized by adding CHA seeds under phenol-free conditions of the present invention; (a) is an XRD pattern, (b) is an SEM pattern, and the inset is an enlarged surface feature.

[0048] Figure 26 1 is the gas adsorption isotherm of K-nPhe at 0°C obtained in an embodiment of the present invention, (a) is CO2, and (b) is N2.

[0049] Figure 27 This is the TGA curve of K-4.0Phe obtained in an embodiment of the present invention after continuous adsorption / desorption cycles; (a) is the temperature and zeolite mass curve in 10 consecutive CO2 adsorption / desorption cycles, (b) and (c) are the N2 nitrogen curve display and the change curve during CO2 adsorption, respectively. DETAILED DESCRIPTION

[0050] The preferred embodiments of the present invention are described in further detail below.

[0051] Materials All chemicals were used as received. Aluminum hydroxide (AR, Macklin), JN-30 silica sol (30 wt.% SiO2, Guangzhou Huixin Chemical Co., Ltd.), phenol (99%, Aladdin) and potassium hydroxide (95%, Aladdin) were used to synthesize zeolites.

[0052] Zeolite Synthesis: The synthesis of K-type CHA zeolite in phenol medium was carried out by a hydrothermal method without the need for any organic structure-directing agent.

[0053] Example 1

[0054] A preparation method for synthesizing CHA zeolite based on a phenol medium comprises the following steps:

[0055] A certain proportion of aluminum hydroxide and potassium hydroxide aqueous solution was heated at 100°C and stirred for 3 hours until the solution became clear.

[0056] After cooling to room temperature, the calculated amounts of JN-30 silica sol and phenol were added and thoroughly mixed for 10 minutes to produce a mixture with a molar ratio of KOH:Al(OH)3:SiO2:phenol:H2O = 7:4:10:1.0:150. The polytetrafluoroethylene (PTFE)-lined container containing the mixture was then secured in a stainless steel autoclave and transferred to a homogeneous reactor (rotary oven) for aging at room temperature for 24 hours at 20 rpm.

[0057] After aging, the temperature was raised to 160°C at a rate of 10°C / min and hydrothermal synthesis was carried out in a homogeneous reactor at a rotation speed of 10 rpm for 96 hours. The temperature was then cooled to room temperature, washed several times by centrifugation with deionized water, and dried at 80°C for 12 hours to obtain the product zeolite, named K-1.0Phe.

[0058] On the basis of this example, if KOH is replaced by NaOH, sodium phenolate, potassium phenolate, etc., the target product CHA zeolite cannot be obtained.

[0059] Example 2

[0060] Based on Example 1, this example differs in that the molar ratio of the components in the mixture is KOH:Al(OH)3:SiO2:phenol:H2O=7:4:10:2.0:150. The resulting zeolite is named K-2.0Phe.

[0061] Example 3

[0062] Based on Example 1, this example differs in that the molar ratio of the components in the mixture is KOH:Al(OH)3:SiO2:phenol:H2O=7:4:10:3.0:150. The resulting zeolite is named K-3.0Phe.

[0063] Example 4

[0064] Based on Example 1, this example differs in that the molar ratio of the components in the mixture is KOH:Al(OH)3:SiO2:phenol:H2O=7:4:10:4.0:150. The resulting zeolite is named K-4.0Phe.

[0065] Example 5

[0066] Based on Example 1, this example differs in that the molar ratio of the components in the mixture is KOH:Al(OH)3:SiO2:phenol:H2O=7:4:10:0.1:150. The resulting zeolite is named K-0.1Phe.

[0067] Comparative Example 1

[0068] Based on Example 1, this comparative example differs in that the molar ratio of the components in the mixture is KOH:Al(OH)3:SiO2:phenol:H2O=7:4:10:5.0:150. The obtained product is named K-5.0Phe.

[0069] Comparative Example 2

[0070] This comparative example differs from Example 1 in that phenol was not added. Specifically, the molar ratio of the mixture was KOH:Al(OH)₃:SiO₂:phenol:H₂O = 7:4:10:0:150. The resulting zeolite was designated K-0.0Phe. This comparative example represents a blank sample synthesized under identical conditions without phenol.

[0071] Example 6

[0072] Based on Example 4, the difference of this example is that the aging time is 38 hours.

[0073] Comparative Example 3

[0074] Based on Example 4, the difference of this comparative example is that the aging time is 0 h, that is, no aging.

[0075] Comparative Example 4

[0076] Based on Example 4, this comparative example is different in that the aging time is 96 h.

[0077] Example 7

[0078] Based on Example 4, the difference of this example is that the hydrothermal synthesis time is 48 hours.

[0079] Example 8

[0080] Based on Example 4, the difference of this example is that the hydrothermal synthesis time is 72 hours.

[0081] Example 9

[0082] Based on Example 4, the difference of this example is that the hydrothermal synthesis time is 120 hours.

[0083] Example 10

[0084] Based on Example 4, the difference of this example is that the hydrothermal synthesis time is 144 hours.

[0085] Comparative Example 5

[0086] Based on Example 4, the difference of this comparative example is that the hydrothermal synthesis time is 2 h.

[0087] Comparative Example 6

[0088] Based on Example 4, the difference of this comparative example is that the hydrothermal synthesis time is 12 hours.

[0089] Comparative Example 7

[0090] Based on Example 4, the difference of this comparative example is that the hydrothermal synthesis time is 24 hours.

[0091] Example 11

[0092] In order to verify the effect of water washing, the K-4.0Phe obtained in Example 4 was calcined at 550° C. for 6 hours, and the sample was named K-4.0Phe-calcined.

[0093] The performance analysis of the embodiments and comparative examples is as follows. Among them, in order to better monitor the crystallization kinetics and understand the role of organic small molecules, we used an autoclave coupled to Mettler-Toledo ReactRaman 785 to monitor the entire crystallization process in situ. We also used an Invia confocal Raman spectrometer (Renishaw Qontor Raman spectrometer, excitation wavelength of 532nm, laser power of 5%, objective lens of 100×) to track time-resolved structural transitions. Among them, except for the Micromeritics Tristar II 3020v1.03 analyzer for H-nPhe, the others are all for K-nPhe.

[0094] Liquid samples 1 H NMR spectra were obtained using an AVANCE-III (400 MHz, Bruker) spectrometer. Powder X-ray diffraction (XRD) patterns of the crystals were obtained using a Rigaku D / Max-2200 PC diffractometer with Cu Kα radiation in the diffraction angle range of 2θ = 4°–55°. The XRD patterns were recorded at 40 kV and 40 mA. The average crystal size was estimated using the Scherrer equation based on the XRD patterns. The relative crystallinity was estimated based on the peak intensities at 9.5° and 12.8° in the XRD patterns of each zeolite sample normalized to the peak intensities of K-4.0Phe as a standard. Scanning electron microscopy (SEM) measurements were performed using a JEOL JSM-7800F electron microscope at 5.0 kV. An Oxford Instruments X-Max N A Falcon energy dispersive X-ray spectrometer (EDX) was used to analyze the elements contained in the samples. Transmission electron microscopy (TEM) was performed on a 300 kV JEM-3200FS field emission source transmission electron microscope. The zeolite samples were embedded in Spurr epoxy resin and ultrathinly sliced ​​to 80 nm thick for TEM measurements. The calcined zeolite powder was recorded at 199.13 and 156.25 MHz on an Agilent 600DD2 spectrometer with a magnetic field strength of 14.1 T using a 4 mm diameter zirconia rotor. 29 Si and 27 Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) Spectroscopy The rotor was rotated at 8 kHz in dry air. 29 Si MAS NMR used 4 μs pulses, 3 s recycle delay, and 1024 scans to accumulate the spectrum; 27 Al MAS NMR was performed using a 3.6 μs pulse, a 1 s recycle delay, and 128 scans to accumulate the spectrum. 29 Si or 27 The Al chemical shifts were referenced to the 0 ppm tetramethylsilane (TMS) Si signal or the 0.9 ppm AlCl3 Al signal, respectively. The C 13 MAS NMR spectroscopy. The sample was mounted in a 4 mm ZrO2 rotor and spun at 8000 Hz with a 2 s relaxation time, 1600 scans, and cross-polarization. Physical properties were obtained using a Micromeritics Tristar II 3020 v1.03 analyzer at -196°C using nitrogen adsorption-desorption isotherms. Based on these properties, the BET surface area, micropore volume, mesopore volume, and BJH pore size distribution (for H-nPhe) were calculated.

[0095] The adsorption experiments involved calcining the K-nPhe sample at 550°C for 6 hours and then degassing at 300°C for at least 3 hours before measurement. Adsorption measurements of pure CO2, N2, and CH4 were performed at 0°C and 100 kPa, and the separation factors were calculated based on the ratio of the equilibrium molar amounts of the adsorbed pure gases. Thermogravimetric analysis (TGA) was performed on a Shimadzu TGA-50 analyzer. The sample was heated from 25°C to 600°C at a heating rate of 5°C / min under CO2 or N2 (flow rate: 40 mL / min). TGA monitored 10 consecutive CO2 adsorption / desorption cycles by alternating cycles of activation at 350°C for 2 hours under N2 (flow rate: 40 mL / min) and adsorption under CO2 (flow rate: 40 mL / min) for 2 hours at room temperature.

[0096] The XRD of the blank sample of comparative example 2 is as follows Figure 1 As shown, scanning electron microscopy Figure 2 The XRD patterns of the K-nPhe zeolite samples obtained in Examples 1-5 and Comparative Examples 1-2 are shown in FIG. Figure 3 As shown in the scanning electron microscope image Figure 4 As shown. It can be seen that in Comparative Example 2, under the same conditions without phenol, pure MER zeolite was obtained, and its nano-rod-shaped crystals aggregated into bouquet-shaped particles of about 3 μm. MER is a typical impurity phase observed in the CHA synthesis process. Strontium metal can be used as an alkali source to inhibit its growth, but it is expensive. Figure 3 As shown in the XRD pattern in (a), when the phenol / Al molar ratio is 1 / 4 or lower, that is, the addition of a small amount of phenol does not affect the selection of this phase, a similar MER phase will still be produced, but the crystallinity is slightly increased and the morphology is more like aggregated rods ( Figure 4 (a)-(b)).

[0097] Further addition of phenol to a phenol / Al molar ratio of 1 / 2 allowed the pure CHA to crystallize into walnut-shaped particles containing embedded nanocrystals ( Figure 4 (c)-(e)). When an excessive amount of phenol is used, such as in Comparative Example 1 where the phenol / Al molar ratio reaches 5 / 4, excessive etching by phenol results in crystallization failure, resulting in only an amorphous product ( Figure 4 (f)), which indicates that too high a phenol dosage would strongly interfere with the synthesis of zeolite.

[0098] The zeolite obtained in Example 2-4, that is, when the amount of phenol was between 2.0 and 4.0, the calculated CHA crystallinity increased with the increase of the amount of phenol (e.g. Figure 3 (b)). As the crystallinity increases, the particle and crystal size of CHA also increases (e.g. Figure 6The crystal size observed in the SEM image is consistent with the size estimated from the peak width of the XRD pattern. + , K + and Cs + ) is equivalent to the zeolite obtained in the colloidal suspension of .

[0099] Furthermore, ion exchange can be used to convert potassium-type zeolite (K-nPhe) into H-type zeolite (H-nPhe), which removes the kinetic limitations of using nitrogen adsorption at −196 °C to probe the pore structure and surface area of ​​K-type CHA.

[0100] Specifically, the zeolite (K-nPhe) obtained in the previous example was subjected to cation exchange. First, the obtained K-nPhe sample was mixed with a 2.5 mol / L (NH4)2SO4 solution (1 g of zeolite was added to prepare a 30 mL solution) at 80°C for 8 hours to exchange it with NH4 + The H-type zeolite is prepared by calcining NH4-nPhe at 550°C for 6 hours at a heating rate of 3°C / min and is named H-nPhe. The corresponding examples 1-5 and comparative example 2 are H-1.0Phe, H-2.0Phe, H-3.0Phe, H-4.0Phe, H-0.1Phe and H-0.0Phe, respectively. The composition and texture characteristics of the H-nPhe series were detected by EDX and nitrogen adsorption-desorption isotherms. The results are as follows: Figure 7 shown.

[0101] Table 1 shows the composition and textural properties of H-nPhe products obtained at different phenol addition levels. As shown in Table 1, adding an appropriate amount of phenol increases the BET surface area and micropore volume of the zeolite product, which is consistent with the improved crystallinity shown in the XRD pattern.

[0102] Table 1 Composition and texture characteristics of H-nPhe products obtained at different phenol addition amounts

[0103]

[0104] a The silicon / aluminum ratios of the synthesized samples were measured by EDX.

[0105] b BET surface area obtained from N2 adsorption isotherms in the relative pressure range of 0.05-0.30.

[0106] c Micropore volume obtained by t-plot method.

[0107] dThe total pore volume was calculated based on the adsorbed N2 when P / P0 = 0.98.

[0108] e The average mesopore diameter was calculated from the desorption branches using the BJH method.

[0109] In addition to the phenol content in the synthesis formula playing a key role in phase selection, the aging time prior to hydrothermal synthesis is also a significant factor. The composition and physical properties of H-CHA zeolites prepared with different aging times are shown in Table 2. Specifically, the H-nPhe products obtained after cation exchange using the aforementioned method were analyzed for composition and texture, as shown in Table 2.

[0110] Table 2 Composition and texture characteristics of H-CHA zeolites prepared at different aging times

[0111]

[0112] like Figure 5 and Figure 8 It is shown that at a short aging time of 0 h, the CHA product contains a small amount of MER impurity, which is barely visible in the XRD pattern, but trace amounts can be identified in the SEM images. Extending the aging time to 24 h helps to eliminate the MER impurity, resulting in higher crystallinity, and the N2 adsorption-desorption isotherm ( Figure 5 (f)-(g)) can be judged to have higher specific surface area and pore volume. However, with 38 hours and 96 hours of aging,

[0113] As the aging time increases, the heterogeneous MER phase reappears, and the crystallinity and specific surface area decrease. The optimal aging time is 24 hours, at which the BET surface area of ​​the generated CHA (417 m 2 / g) and micropore volume (0.21 cm 3 / g) was the highest (Table 2). Therefore, under the action of phenol, a competitive and cooperative relationship exists between framework assembly and in situ dissolution. Therefore, during the 24-hour aging process, the competition and cooperation between framework assembly and phenol-enabled in situ dissolution may be well balanced, thereby eliminating the emergence of defective cores or impurity phases.

[0114] Since the sample K-4.0Phe of Example 4 has the highest crystallinity and specific surface area, further TEM (such as Figure 9 (a)-(b)), Raman (e.g. Figure 9 (c))、 29 4. 27 Al and 13 C solid-state MAS NMR (such as Figure 9(d)-(f)) Analysis. TEM images show that the tiny particles are assembled from nanoscale CHA crystals with plate-like morphology. Clearly visible intracrystalline mesopores of approximately 5 nm are embedded within the nanocrystals, consistent with the results of N2 physical adsorption. The lattice spacing of 0.93 nm corresponds to the (100) plane of CHA zeolite. 29 Si MAS NMR spectroscopy showed that K-4.0Phe zeolite contained 2.62% Q 0 (4Al) (-94.6ppm), 13.65% Q 1 (3Al)(-98.17 ppm), 39.88%Q 2 (2Al)(-103.54 ppm, 33.98%Q 3 (1Al), -108.84 ppm, 9.88%Q 4 (0Al), -114.22 ppm (as Figure 9 (d), Table 3), from which the Si / Al ratio was estimated to be 2.4. 27 Al MAS NMR spectroscopy (e.g. Figure 9 (e)) shows a strong peak at 50-55 ppm associated with tetrahedrally coordinated Al in the framework and a weak peak at 0 ppm associated with octahedral Al atoms. 13 C MAS NMR spectroscopy (e.g. Figure 9 (f)) shows no observable peak, indicating that no phenol is incorporated into the zeolite structure. Therefore, water washing can effectively remove phenol and subsequently recover phenol from the mother liquor of CHA zeolite synthesis, as confirmed by the comparative Raman spectra of the solid product (e.g. Figure 9 c).

[0115] Table 3 29Si MAS NMR spectrum peak deconvolution and curve fitting results of K-4.0Phe sample

[0116]

[0117] The K-4.0Phe-unwashed sample showed peaks at ∼993 and ∼1022 cm -1 The obvious Raman peaks at 998 and 1023 cm-1 are attributed to the two prominent ring stretching vibrations of phenol. -1 Compared with pure phenol, these peak positions shifted to lower wavelengths (such as Figure 10 ), which may be due to the hydrogen bond between the silicon oxygen of SiO2 and the π cloud of phenol. -1 A weak ring deformation peak is also shown at ∼828 cm -1There is a slight shoulder at the bottom, which is derived from dimers and higher oligomers. After washing the K-4.0Phe sample with water, these phenol-related Raman peaks disappeared. 1 H NMR analysis of the washing solution (e.g. Figure 11 ) further confirmed the effectiveness of water in removing phenol. In the first to third rounds of washing, the washing solution showed obvious phenol peaks at chemical shifts of ~6.6 and ~7.1 ppm, but they completely disappeared after the fourth round of washing.

[0118] Comparative Example 8

[0119] During the competitive growth of MER / CHA zeolites, the phenol medium not only quantitatively modulates their physicochemical properties (including size, morphology, and porosity), but also significantly controls the primary phase. To reveal the role of phenol, we synthesized the zeolites in the presence of sodium phenolate (NaPhe) at similar molar amounts. Specifically, we replaced phenol with sodium phenolate, following the same procedures as in Examples 2 and 4.

[0120] The obtained comparative example 8 sample was subjected to microscopic analysis, and the results were as follows: Figure 12 As shown, only MER crystals were obtained, indicating that phenol is not an OSDA (organic structure-directing agent) for the synthesis of CHA zeolites. Since CHA synthesis is carried out at a pH of approximately 13, phenol deprotonates and in situ cleaves the framework Si-O / Al-O bonds. Therefore, phenol is a mild etchant that can be used to adjust the phase selectivity of CHA. Following phenol deprotonation, the ligand coordinated to Al is likely a phenolate. To further clarify the underlying mechanism, we used laser Raman spectroscopy to monitor the comparative synthesis in situ.

[0121] Before the hydrothermal step, Figures 13 to 15 The pre-aging and aging stages of K-0.0Phe (without phenol) and K-4.0Phe (with phenol) were studied. The pre-aging stage (the process of adding raw materials) and the aging stage were studied. Operando 785-nm Raman spectra of the reaction mixtures showed that the formation of CHA crystal phase could be selected by appropriate phenol etching agent. The balanced dissolution of silica and alumina during aging played a key role. The initial potassium aluminate solution was at ~615cm -1 A strong Raman signal is shown at the - Due to stretching. And at ~535cm -1 The side band at the 2- The dimer is probably the oxygen bond (OH)3Al-O-Al(OH)3 in the alkaline system 2- After adding silica source, at ~733cm -1A new peak with silica characteristics appeared at 400-500 cm -1 A broad peak appears in the range, which comes from the silicon-oxygen vibration in silica. This is accompanied by the suppression of the aluminate peak, especially Al2O(OH)6 2- Aluminate dimer v s Al-O mode at ~535 cm -1 In the K-0.0Phe synthesis process, where no phenol was used, the aluminate dimer peak weakened throughout the aging process, e.g. Figure 13 (a) As shown. In the synthesis of K-4.0Phe, the addition of phenol immediately suppressed the main peaks of aluminate and silica, but promoted the reappearance of the aluminate dimer peak ( Figure 14 and Figure 15 As time goes by, the dimer peak changes from ∼535 cm -1 Move slightly to ~543cm -1 Higher wavelengths ( Figure 13 (b)-(c)), indicating the possible existence of substitution doping. The intensity ratio of the Raman dimer / monomer peak ( Figure 13 (d) shows a stable trend with a slight hump after aging for about 24 h.

[0122] To obtain higher spectral resolution for further confirmation, 532 nm laser Raman technology was used to analyze time series samples collected during the aging stages of K-4.0Phe, K-0Phe, and K-1.0Phe. Figure 16 As shown in Figure 2, the blank K-0.0Phe precursor showed a peak at ∼615 cm-1 at 0-h and 24-h aging. -1 The obvious monomer aluminate Al(OH)4 - peak, and at 543 cm -1 There is no dimer aluminate peak at ∼615 cm-1. Similarly, the K-1.0Phe precursor aged for 24 hours has a peak at ∼615 cm-1. -1 It also shows a strong peak at 543 cm -1 No peak was detected at . These precursors all produced MER zeolites after hydrothermal treatment. However, for the K-4.0Phe system involving phenol (which ultimately gave the desired pure CHA topology), the synthetic mixtures after aging for 0 and 24 hours showed that the monomer aluminate peak was suppressed, but the dimer peak was greatly enhanced ( Figure 16 (a)). Interestingly, as the aging time increased to 38 h and 96 h, the aluminate peaks of the synthesized mixtures decreased, with the decrease of the dimer aluminate peak being the most significant ( Figure 6 (b)). Al(OH)4 - Monomer and Al2O(OH)62- The relative abundance of aluminate dimers was based on the 615 cm -1 and 543cm -1 The ratio of the peak area to the total area is shown in Table 4. When the aging time increases from 0 to 24 hours, the monomer aluminate ratio increases slightly from 75% to 77%, and then rapidly decreases to 40% as the aging time extends to 96 hours (as shown in Table 4). Consistent with this observation, in the synthesis of K-4.0Phe, the precursor aged for 24 hours produces pure CHA, the precursor aged for 0 hours cannot be detected by XRD, but MER can be observed by SEM, and the precursors aged for 38 and 96 hours produce a clear MER phase.

[0123] Table 4 Voigt fitting of the aluminate spectral region of the K-4.0Phe Raman spectrum

[0124]

[0125] Among them, peaks A and B correspond to Al2O(OH)6 2- and Al(OH)4 - .

[0126] During the hydrothermal synthesis, the crystallization behaviors of K-0.0Phe and K-4.0Phe precursors after 24 h aging were further monitored in situ using ReactRaman. Figure 17 As shown in Figure 2, the composite building unit (CBU) formation rate of the K-4.0Phe system is slower than that of the blank K-0.0Phe. For the K-0.0Phe system, the zeolite double ring structure unit is at 480 cm -1 The bending mode, d6r or d8r, appears at around 160°C. Interestingly, at the same time, the 544cm -1 Dimer Al2O(OH)6 2- For the K-4.0Phe system, the CBU peak appears after 26 hours, and its intensity increases sharply. -1 Dimer Al2O(OH)6 2- The peak shows an obvious upward trend and then further decreases. Comparison of SEM images of K-0.0Phe and K-4.0Phe after aging (e.g. Figure 18 This observation is also confirmed by the results of Figure 3. Aged K-4.0Phe contains some aggregated particles, while aged K-0.0Phe only shows amorphous precursors.

[0127] In addition, a series of offline experimental characterizations were performed, including XRD ( Figure 19 (a)-(b))、SEM( Figure 19 (c)-(j))、EDX( Figure 20 ) and gas physical adsorption ( Figure 21 As shown), in order to track the crystallization behavior of K-4.0Phe precursor to hierarchical pore CHA zeolite after 24 hours of aging, samples with different hydrothermal synthesis times were analyzed. Figure 19 It shows that the nucleation process occurs between 0 and 48 hours, and the relative crystallinity increases from almost 0 to 87%, which is similar to the curve of in situ Raman monitoring. After 48 hours, all characteristic CHA peaks appear in the X-ray diffraction pattern, and cubic crystals that grow mutually begin to appear in the scanning electron microscope image, with an average particle size of about 5.50 microns. When the crystallization time is extended to 72 hours, the average particle size increases to about 10.85 microns. Further extending the hydrothermal synthesis time will reduce the relative crystallinity and the crystal surface will become rough, which indicates the presence of a continuous etching effect ( Figure 19 (b), (g)-(j)). The peak of the (100) crystal plane in the synthesized CHA zeolite gradually shifts to lower angles, indicating that the d-spacing increases with the extension of crystallization time. Time-resolved composition and structural analysis of the sample (Table 5) shows that the Si / Al ratio decreases from 2.6 to 2.2. At the same time, the BET surface area and porosity reach a maximum of 416.6 cm after 96 hours of synthesis. 2 / g and 0.24cm / g 3 .

[0128] Table 5 Structure and texture properties of H-4.0Phe-t products at different crystallization times

[0129]

[0130] Based on the above observations, we propose the following mechanism, such as Figure 22 As shown in Figure 2, the concentration of the precursor dissolved in water is controlled by phenol, which is crucial for the preparation of CHA zeolite. In the absence of phenol, the Al(OH)4 - The addition of phenol changes the solubility of zeolite and promotes the formation of Al2O(OH)6 2- Aluminate dimers, such as (OH)3Al-O-Al(OH)3 2- or (OH)3Al-(OH)-Al(OH)3 2-, bridged by oxygen or hydroxyl groups, leading to their recovery in precursor solutions of silicon and aluminum sources. These dimerized aluminates are key intermediates in the formation of CHA. According to the theory proposed by Breynaert and colleagues, for a specific framework silicon / aluminum ratio, the topology with the highest cation site occupancy is preferred. The formation of binuclear aluminum complexes may mean that there are fewer available aluminum sites than viable cation sites, resulting in more vacant cation sites to maintain charge neutrality. Under similar Si / Al ratios (Table 1), the CHA zeolite framework can accommodate the same number of cations, but with more vacancies than the MER topology. Therefore, under synthetic conditions where the dimerized aluminate species persists during the early nucleation process, CHA will appear preferentially. As the aging time is extended to more than 24 hours, Al2O(OH)6 2- The Raman peak intensity of the zeolite was significantly weakened, and MER impurities appeared in the zeolite product after hydrothermal synthesis ( Figure 5 The slowly released Al is likely incorporated into the framework, resulting in a lower Si / Al ratio in the product. Although the Raman spectrum of the precursor during the aging stage does not reveal zeolite-specific composite structural units, the early formation of specific Si and Al aggregates may have determined the subsequent phase selection. The mild etching of phenol during the optical decomposition of the amorphous phase plays a dominant role in regulating the distribution of Al-containing species in the nucleation mixture and their coordination state with Si in a dynamic equilibrium with the alkaline Si-Al source, thereby affecting the kinetic formation of the zeolite product. Appropriate control of phenol content and aging time can form pure, high-quality CHA zeolite.

[0131] Example 12

[0132] In this example, seed-assisted synthesis of zeolite was used based on Example 4. The results of different unusual seed-assisted synthesis are shown in Table 6, which further demonstrates the effect of changing the specifications of silicon and aluminum on polycrystalline selection.

[0133] Table 6 List of zeolites synthesized with seed assistance

[0134]

[0135] In this embodiment, when MER seeds are added to a mixture without phenol, the final product is MER zeolite (such as Figure 23 However, when MER seeds were added to an appropriate phenolic system, the CHA phase was promoted, as shown in Figure 24As shown. Therefore, in the presence of phenol, the added MER crystals are sacrificed and are dissolved instead of accelerating the nucleation and growth kinetically. The CHA topology is a metamorphic phase, while the MER zeolite is thermodynamically more stable. In addition, CHA and MER zeolites do not have a common CBU and they lack structural similarity in crystal topology. According to the Ostwald stage rule, the initial thermodynamically stable framework will be transformed into a stable framework as the interzeolite transformation (IZT) process proceeds. This apparently contradictory result indicates that phenol can change the dissolution rate (i.e. stability) of the parent zeolite despite its high framework density. Therefore, it is not surprising that the MER product can still be obtained by adding CHA crystals to the precursor without phenol ( Figure 25 The promoting effect of CHA seeds in the presence of phenol depends largely on the synthesis process. When 0.5 wt% of CHA seeds and phenol were added simultaneously to the synthesis mixture (CHA + 4.0 Phe sample), a highly crystalline CHA zeolite with a BET surface area of ​​433.5 m 2 / g, pore volume 0.25cm 3 / g. However, if CHA seeds (4.0Phe+CHA sample) or phenol (CHA / 4.0Phe sample) were added after aging for 24 hours, lower surface area and pore volume were obtained, as shown in Table 7. Therefore, controlling the dissolution of silicon and aluminum in the early stage of nucleation and changing the size and relative distribution of silicon and aluminum are very important in determining the final quality of the zeolite.

[0136] Table 7 Composition and structural properties of seed-assisted synthesized zeolites

[0137]

[0138] Example 13

[0139] Small-pore CHA zeolites are excellent CO2 adsorbents with extremely high selectivity for larger gas molecules (such as N2 and CH4), thanks to the cation gate effect known as the trap gate mechanism. Shang et al. summarized a rule that ensures that the gatekeeper cations completely occupy the pores by adjusting the silicon / aluminum ratio and cation type, thereby achieving a molecular trap gate. The equilibrium adsorption isotherms of CO2 and N2 of K-nPhe are shown in Figure 2. Figure 26As shown. In the K-nPhe series, K-nPhe with CHA topology (n = 2, 3, 4) has a significantly higher CO2 adsorption capacity than K-nPhe with MER topology (n = 0, 1). Due to the low Si / Al ratio of about 2, K-4.0Phe synthesized in phenol medium shows the highest CO2 adsorption capacity of 3.8 mmol / g at 100 kPa, which is almost the same as the previously reported low-silicon CHA zeolite prepared using mixed cations. In contrast, the affinity for N2 is much lower, with an absorption capacity of only 0.3 mmol / g. Therefore, compared with K-type CHA synthesized using OSDA (2.1 mmol / g and ~80, respectively), K-4.0Phe shows higher CO2 adsorption and lower pure gas CO2 / N2 selectivity.

[0140] like Figure 27 As shown in Figure 8, thermogravimetric analysis (TGA) of K-4.0Phe in a CO2 atmosphere demonstrated the adsorption stability of CHA zeolite synthesized in a phenol medium. Combining NMR and EDX composition analysis, the single cage was calculated as shown in Table 8.

[0141] Table 8 Chemical composition of nano CHA zeolite samples obtained by combining NMR (Si / Al ratio), EDX (cations) and TGA (H2O and CO2), assuming 72 oxygen atoms in the CHA framework.

[0142]

[0143] according to Figure 12 The TG analysis shown calculates the amount of CO2 per unit zeolite cage. Dehydrated sample K 10.58 (Si 25.42 Al 10.58 )O 72 (M zeolite =2562.04g / mol) of CO2 absorption is 15.85wt.% (from 0.82 to 0.95). The coordination number n of CO2 is calculated by the following formula:

[0144] n(CO2).M(CO2)=zeolite*(M(CO2) / M(dehydrated))-zeolite

[0145] n(CO2).44.01=2562.04*(0.95 / 0.82)-2562.04

[0146] n(CO2)=9.23 molecules

[0147] Where n(CO2) is the number of CO2 in a unit zeolite cage, M(CO2) is the molar mass of CO2, and M zeoliteis the molar mass of the dehydrated CHA zeolite, M(CO2) is the mass of CO2 contained in the CHA zeolite, and M(dehydrated) is the mass of the dehydrated CHA.

[0148] Before CO2 introduction, the initial weight loss was associated with CHA dehydration, indicating 29.15 water molecules per cage. Subsequently, weight changes during CO2 adsorption-desorption cycles confirmed near-complete absorption of 9.23 CO2 molecules per unit cage, consistent with the results from the physical adsorption isotherm, equivalent to near-complete storage of 9 CO2 molecules per CHA unit cage. CO2 adsorption was fully maintained over multiple temperature cycles, demonstrating the excellent stability and regenerability of K-CHA zeolite.

[0149] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A preparation method for synthesizing CHA zeolite based on phenol medium, characterized in that: The steps include: Step S1, adding aluminum hydroxide to a potassium hydroxide aqueous solution, heating and stirring until clear, cooling, adding silica sol and phenol, and mixing uniformly to obtain a mixed solution, wherein the molar ratio of phenol to the aluminum hydroxide is 1:1-3, and the silicon-aluminum ratio is 2-3:1; placing the mixed solution in an autoclave, and placing it in a homogeneous reactor for aging, and the aging time is not more than 38 hours; Step S2: after aging, performing a hydrothermal reaction at 155-165° C. for 48-144 hours; Step S3: After the reaction is completed, the product is centrifuged, washed, and dried to obtain the zeolite product.

2. The method for preparing CHA zeolite based on phenol medium synthesis according to claim 1, characterized in that: In step S1, the aging temperature is room temperature, and the rotation speed of the homogeneous reactor is 15-25 rpm.

3. The method for preparing CHA zeolite based on phenol medium synthesis according to claim 2, characterized in that: In step S1, the aging time is 1-24 hours.

4. The method for preparing CHA zeolite based on phenol medium synthesis according to claim 1, characterized in that: In step S1, the molar ratio of phenol to the aluminum hydroxide is 1:1-2; pure CHA can be crystallized into walnut-shaped particles containing embedded nanocrystals.

5. The method for preparing CHA zeolite based on phenol medium synthesis according to claim 4, characterized in that: The molar ratio of the components in the mixed solution of step S1 is KOH:Al(OH)3:SiO2:phenol:H2O=7:4:10:1~5:

150.

6. The method for preparing CHA zeolite based on phenol medium synthesis according to claim 5, characterized in that: In step S2, the hydrothermal reaction time is 72-144 hours.

7. The method for preparing CHA zeolite based on phenol medium according to any one of claims 1 to 6, characterized in that: The method further includes step S4, mixing the obtained product zeolite with (NH4)2SO4 solution at 70-90°C for more than 6 hours, and then calcining at 500-600°C to obtain H-type zeolite.

8. The method for preparing CHA zeolite based on phenol medium synthesis according to claim 7, characterized in that: The concentration of the (NH4)2SO4 solution is 2-3 mol / L, and the usage ratio of the zeolite to the (NH4)2SO4 solution is 1 g: 25-35 mL.

9. A CHA zeolite, characterized in that: The zeolite is prepared by the method for synthesizing CHA zeolite based on phenol medium as described in any one of claims 1 to 8.

10. The use of the CHA zeolite according to claim 9, characterized in that: Used for adsorption of gases.

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