Isomorphous substitution of metals on synthesized zeolite framework

Abstract

The present disclosure relates to a novel method for introducing various metals in the structure of zeolite frameworks by isomorphous substitution. This new method is based on a hydrothermal reaction of the metal with the zeolite. This method allows obtaining zeolite with a structure and with control of the metal location.

Claims

1. A method for the preparation of a metal-containing synthetic zeolite material comprising at least one metal M selected from W, V, Mo, Sn, Zr, Ag, Co, Ni, Cu, Ti, In, Zn and any mixture thereof, with silicon to metal M molar ratio Si/M ranging from 117 to 65440 as determined by inductively coupled plasma optical emission spectrometry; the method comprising the following steps: a) providing a synthetic zeolite material; b) optionally washing said synthetic zeolite material and drying it at a temperature of at least 50° C. for at least 2h; c) optionally calcining the synthetic zeolite material obtained at the previous step at a temperature of at least 200° C. for at least 1h; d) putting said synthetic zeolite material in a clear solution comprising one source of alkali metal M′ selected from Li, Na, K, or Cs and at least one metal M wherein both M and M′ are fully soluble in water and originate from the same compound; and wherein the molar ratio M′/M is of at least 1 and the weight ratio of said synthetic zeolite over said clear solution containing M and M′ ranges from 0.03 to 0.5; e) optionally stirring the solution obtained at step d) for at least 30 min, preferably at room temperature and/or atmospheric pressure; f) heating the solution for at least 12h and at a temperature of at least 50° C. preferably under autogenous pressure so that the solution does not evaporate; g) separating the liquid from the solid obtained at the previous step and washing the solid obtained; h) drying the solid obtained at the previous step and calcining it at a temperature of at least 200° C. for at least 1h and recovering a metal-containing synthetic zeolite material; wherein the ratio of surface OH groups between the synthetic zeolite material provided in step a) and the metal-containing synthetic zeolite material recovered in step h) is at least 2.0.

2. The method according to claim 1, characterized in that the silicon to metal M molar ratio Si/M is ranging from 179 to 65440 as determined by inductively coupled plasma optical emission spectrometry.

3. The method according to claim 1, characterized in that said synthetic zeolite material has a BEA or an MFI or an FAU framework type, preferably an MFI framework type.

4. The method according to claim 1, characterized in that when the synthetic zeolite material comprises no aluminium, or in that said synthetic zeolite material contains comprises aluminium the Si/Al molar ratio of at least 5 as determined by inductively coupled plasma optical emission spectrometry, preferably the Si/Al molar ratio ranging from 10 to 500 as determined by inductively coupled plasma optical emission spectrometry.

5. The method according to claim 1, characterized in that when the synthetic zeolite material comprises aluminium the Si/Al molar ratio is of at least 10; preferably of at least 50; more preferably of at least 80.

6. The method according to claim 1, characterized in that said synthetic zeolite material comprising aluminium with the Si/Al molar ratio of at least 5 as determined by inductively coupled plasma optical emission spectrometry, is obtained via dealumination.

7. The method according to claim 1, characterized in that said metal M is selected from W, V, Mo, Sn, Zr, Co, Ni, Cu, Ti, In, Zn and any mixture thereof.

8. The method according to claim 1, characterized in that said metal M is selected from Mo, Sn, V and any mixture thereof.

9. The method according to claim 1, characterized in that said metal M is Mo.

10. The method according to claim 1, characterized in that in step d), the source of M and M′ is selected from Na.sub.2WO.sub.4.2H.sub.2O, K.sub.2WO.sub.4, NaVO.sub.3, KVO.sub.3, Na.sub.2MoO.sub.4.2H.sub.2O, Na.sub.2MoO.sub.4.4H.sub.2O, K.sub.2MoO.sub.4, Na.sub.2SnO.sub.3.3H.sub.2O, K.sub.2SnO.sub.3.3H.sub.2O, Na.sub.2ZrO.sub.3, K.sub.2ZrO.sub.3, or any mixture thereof preferably selected from NaVO.sub.3, KVO.sub.3, Na.sub.2MoO.sub.4.2H.sub.2O, Na.sub.2MoO.sub.4.4H.sub.2O, K.sub.2MoO.sub.4, Na.sub.2SnO.sub.3.3H.sub.2O, K.sub.2SnO.sub.3.3H.sub.2O, or any mixture thereof; more preferably is Na.sub.2MoO.sub.4.4H.sub.2O.

11. The method according to claim 1, characterized in that the alkali metal M′ selected from Na and/or K.

12. The method according to claim 1, characterized in that in the composition of the solution of step d) the molar ratio M′/M ranges from 1 to 200, preferably from 2 to 100.

13. The method according to claim 1, characterized in that the ratio of surface OH groups between the synthetic zeolite material provided in step a) and the metal-containing synthetic zeolite material recovered in step h) is at least 2.5.

14. The method according to claim 1, characterized in that the metal-containing synthetic zeolite material comprises a metal M with a content ranging from 0.1 to 1.5 wt. % with respect to the total mass of the material measured according via EDS-TEM.

15. The method according to claim 1, characterized in that the metal-containing synthetic zeolite material comprises a metal M with a content ranging from 0.3 to 1.2 wt. % with respect to the total mass of the material measured according via EDS-TEM.

16. The method according to claim 1, characterized in that the metal-containing synthetic zeolite material comprises a metal M with a content ranging from 0.4 to 1.0 wt. % with respect to the total mass of the material measured according via EDS-TEM.

17. The method according to claim 1, characterized in that the metal-containing synthetic zeolite material has an average crystal size ranging from 10 to 800 nm preferably from 10 to 600 nm measured by scanning electron microscopy (SEM).

18. The method according to claim 1, characterized in that the metal-containing synthetic zeolite material has dispersed nanocrystals.

19. The method according to claim 1, characterized in that one or more of the following is true: the drying of the steps b) and/or h) is performed at 60° C.; and/or the drying of the steps b) and/or h) is performed for at least 4 h; and/or the drying of the steps b) and/or h) is performed via freeze-drying for 48 h.

20. The method according to claim 1, characterized in that one or more of the following is true: the calcination of steps c) and/or h) is carried out at a temperature ranging from 400° C. to 800° C., under an air, oxygen or inert atmosphere; and/or the calcination of steps c) and/or h) is carried out for 8 h.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 represents the XRD pattern of sample Mo-Silicalite-1 obtained from step h). Splitting of diffraction peaks at 23.30, 23.75, and 24.50° 20 is clearly observed and indicates a monoclinic symmetry of the MFI structure instead of the orthorhombic cell.

(2) TABLE-US-00001 TABLE 1 Sample Mo-Silicalite-1 Symmetry P21/n (monoclinic) a  19.9243(5) b  20.1433(8) c  13.3985(2) β  90.6087(3) Volume (Å.sup.3) 5377.10(7) GOF.sup.a   1.70 Rp.sup.b   2.47 wRp.sup.c   3.42 .sup.aGoodness of fit .sup.bExpected R-factor .sup.cWeight Profile R-factor

(3) Additionally, using Le Bail profile refinement of the diffraction pattern (Table 1), the space group transition towards monoclinic symmetry was confirmed, alongside a unit cell volume expansion at 5377.1 Å.sup.3 (to be compared with a volume of average 5330.0 Å.sup.3 for purely siliceous MFI (Silicalite-1) zeolite). Both observations indicate the successful introduction of Mo atoms in the Silicalite-1 structure.

(4) FIG. 2 shows the SEM picture of sample Mo-Silicalite-1 obtained from step h). Particles of approximately 100 to 150 nm are obtained.

(5) FIG. 3 represents (a) the .sup.29Si MAS NMR spectrum of sample Mo-Silicalite-1 obtained from step h), as well as (b) the {.sup.1H} .sup.29Si CP MAS NMR experiment.

(6) No signal is observed on the cross-polarization experiment, indicative of the absence of any silanol species for this sample. This is further supported by the absence of Q3 species in the .sup.29Si MAS NMR spectrum. Additionally, very high resolution of the Q4 species is achieved, indicative of the very high local homogeneity of the sample, and of the absence of silanol defects.

(7) FIG. 4 represents the XRD pattern of sample Mo-ZSM-5 obtained from step h); Splitting of diffraction peaks at 23.30, 23.75, and 24.50° 2θ is clearly observed indicating the transformation from orthorhombic to monoclinic symmetry of the sample.

(8) TABLE-US-00002 TABLE 2 Sample Mo-ZSM-5 Symmetry P21/n (monoclinic) a  19.9101(1) b  20.1388(3) c  13.3915(7) β  90.6088(3) Volume (Å.sup.3) 5369.26(6) GOF.sup.a   1.60 Rp.sup.b   2.89 wRp.sup.c   3.97 .sup.aGoodness of fit .sup.bExpected R-factor .sup.cWeight Profile R-factor

(9) In addition, using Le Bail profile refinement of the following XRD pattern (Table 2), the space group transition towards monoclinic symmetry is confirmed, and expansion of the unit cell volume with regards to the initial material from 5353.81 to 5369.27 Å.sup.3 is measured. The higher unit cell volume of the initial ZSM-5 sample used in the preparation of Mo-ZSM-5 is attributed to the presence of aluminium.

(10) FIG. 5 represents (a) the .sup.29Si MAS NMR spectrum of sample Mo-ZSM-5 obtained from step h), as well as (b) the {.sup.1H} .sup.29Si CP MAS NMR spectrum.

(11) The absence of any silanol species for this sample is confirmed: no peaks corresponding to Q2 and Q3 are present in the {.sup.1H} .sup.29Si CP MAS NMR spectrum (FIG. 5). Additionally, the Q4 species are present with high resolution indicating the high local homogeneity of the sample, and the absence of silanol defects, as they are cured by the addition of Mo.

(12) FIG. 6 represents .sup.1H MAS NMR of dehydrated zeolite samples silicalite-1, Mo-silicaliste-1, ZSM-5 and Mo-ZSM-5.

EXAMPLES

(13) The starting materials used in the examples are as follow: Tetraehtylorthosilicate (TEOS), 98%, from Aldrich Tetrapropylammonium hydroxyl (TPAOH), 20 wt. % in water (1 M), from Alfa Aesar Sodium molybdate tetrahydrated (Na.sub.2MoO.sub.4, 4H.sub.2O), 98%, from Alfa Aesar Aluminum nitrate (Al(NO.sub.3).sub.3, 9H.sub.2O) from Alfa Aesar Double distilled water

(14) These materials were used as received from manufacturers without any further purification. The zeolite samples described in the following examples are characterized by various methods as listed below:

(15) Scanning Electron Microscopy (SEM):

(16) Scanning electron microscopy images of examples after step h) were recorded using a MIRA\LMH (TESCAN) microscope, with an electron beam of 30 kV.

(17) Powder X-Ray Diffraction (XRD):

(18) Powder samples of zeolites obtained after step h) were measured using a PANalytical X'Pert Pro X-ray diffractometer equipped with a monochromator specific to CuKα radiation (A=1.5418 Å, 45 kV, 40 mA). Samples were measured from 3 to 70° 2θ, with a step size of 0.016°. Le Bail profile refinement of each XRD patterns was also performed.

(19) Solid-state nuclear magnetic resonance of silicon (.sup.29Si MAS NMR):

(20) Powder samples obtained after step h) are packed into zirconia rotor of 4 mm outer diameter spun at 12 kHz, in a Bruker Avance III-HD 500 (11.7 T) spectrometer operating at 99.3 MHz. .sup.29Si MAS NMR spectra are recorded from a single pulse excitation (30° flip angle), used with a recycle delay of 30 s. {1H} .sup.29Si cross-polarization (CP) solid-state MAS NMR was acquired using a contact time of 5 ms and a recycle delay of 2 s. Chemical shifts were referenced to tetramethyl silane (TMS).

(21) 1H MAS NMR of Dehydrated Zeolite Samples

(22) Zeolite samples were dehydrated at 200° C. overnight and directly measured in MAS NMR. Measurement performed using liquid water as a reference for the amount of hydrogen. Error for the calculated absolute values: less than 0.5 mmol/g.

(23) Scanning Transmission Electron Microscopy with Energy Dispersive X-Ray Analysis (STEM/EDS or EDS-TEM) and High Angle Annular Dark Field Imaging (HAADF-STEM):

(24) Experiments were performed on an Analytical double (objective and probe) corrected JEOL ARM200CF equipped with a 100 mm Centurio EDS detector, and a Quantum GIF for the EELS. A probe of 0.1 nm was used to scan the sample in STEM mode and Bright Field and High Angle Annular Dark Field detectors were simultaneously employed for imaging. Camera length was 8 cm, and two different accelerating voltages of 200 and 80 kV were used in the STEM mode for imaging and chemical analysis respectively. Owing to the enhanced Z-contrast developed at 200 kV, this configuration was used for imaging and a high-speed scanning protocol (10 μsec/px) was employed in order to prevent sample degradation under the electron beam. To avoid such degradation, STEM-EDS analytical assays were carried out at 80 kV, with a scanning speed of 3 μs/px for a mean duration of 60 minutes. A cross-correlation algorithm implemented in the Jeol Analysis Station software was applied every 30 seconds in an effort to compensate for the special drift occurring during the test. The microstructure of samples was checked prior and after each EDS scan.

(25) The method provides results in atomic % that are converted in wt. % using Tecnai Microscope control software.

(26) Inductively coupled plasma (ICP) optical emission spectrometry was used to determine the chemical compositions using a Varian ICP-OES 720-ES. The Si/Al molar ratio or the Si/M molar ratio are determined using the said method.

Example 1

(27) Preparation of Molybdenum (Mo) Containing Silicalite-1 Zeolite with a Fully Crystalline, Purified and Calcined Sample as Starting Material

(28) The steps 1) to 4) correspond to the normal synthesis of the Silicalite-1 zeolite. The steps 5) to 10) correspond to the isomorphous substitution of the MFI with molybdenum.

(29) Step 1):

(30) In a polypropylene synthesis bottle (125 mL), solution A is prepared by adding 24.591 g of TPAOH (1M) and 42.581 g of double-distilled water, under agitation performed using a magnetic stirrer. To this solution A is then added drop-wise 18.0 g of TEOS, under stirring performed by a magnetic stirrer. The solution should be water clear and liquid. Upon preparation, the gel might be slightly inhomogeneous, but the solution should end up being water-like during the ageing step (beginning of step 2). The molar composition of the as-prepared precursor suspension is the following: 0.28 TPAOH:1 SiO.sub.2:40 H.sub.2O

(31) Step 2):

(32) The bottle containing the solution prepared in step 1) is air-tightly closed with a cap. The as-made synthetic suspensions are left for ageing under magnetic stirring for 1 h, and then on an orbital shaker (225 rpm) for an additional 18 h. All the steps up to this point are performed at room temperature and ambient pressure.

(33) Step 3):

(34) The synthesis mixture is water-like at this point. The synthetic mixture, still in its air-tightly closed bottle, is then subjected to static hydrothermal treatment at 90° C., for a duration of 48 h.

(35) Step 4):

(36) The sample is removed from the oven after step 3), and cooled down to room temperature. The solid phase is then separated from the liquid phase using centrifugation. The solid is dispersed in distilled water and centrifugation is performed again. This washing procedure is repeated until the pH of the liquid separated from the solid phase is around 7-8.

(37) Step 5) correspond to step b) and c):

(38) The obtained solid sample is then dried in a static oven at 80° C. overnight.

(39) The dried sample retrieved is then subjected to the following calcination procedure: In ambient atmospheric conditions (composition of the atmosphere, and atmospheric pressure), the sample is placed in a muffle furnace. The furnace heats up from room temperature to 550° C. in 5 h, holds at 550° C. for an additional 5 h, before the furnace is allowed to cool down to room temperature in 5 h.

(40) Step 6):

(41) 300 mg of the obtained purely siliceous and fully crystalline Silicalite-1 zeolite that was calcined in step 5), is then introduced in a sealed container containing a solution composed by 0.208 g of sodium molybdate (Na.sub.2MoO.sub.4.4H.sub.2O) dissolved in 8.0 g of distilled water.

(42) Step 7) (Corresponds to Step e):

(43) The obtained suspension is mixed with a magnetic stirrer for 1 h at room temperature.

(44) Step 8) (Corresponds to Step f):

(45) The obtained suspension from step 7) is then placed in a static oven at 90° C. for 96 h.

(46) Step 9) (Corresponds to Step g):

(47) The sample is removed from the oven after step 8), and cooled down to room temperature.

(48) The solid phase is then separated from the liquid phase using centrifugation. The solid is dispersed in distilled water and centrifugation is performed again. This washing procedure is repeated several times (around 3 to 6 times) in order to remove any unreacted species.

(49) Step 10) (Corresponds to Step h):

(50) The obtained solid sample is then dried in a static oven at 80° C. overnight.

(51) The dried sample retrieved is then subjected to the following calcination procedure: In ambient atmospheric conditions (composition of the atmosphere, and atmospheric pressure), the sample is placed in a muffle furnace. The furnace heats up from room temperature to 550° C. in 5 h, holds at 550° C. for an additional 5 h, before the furnace is allowed to cool down to room temperature in 5 h. The as-obtained sample from step 8) is called Mo-Silicalite-1

Example 2

(52) Preparation of Molybdenum (Mo) Containing ZSM-5 Zeolite with a Fully Crystalline, Purified and Calcined ZSM-5 Zeolite as Starting Material (Sample Mo-ZSM-5)

(53) The steps 1) to 4) correspond to the synthesis of the ZSM-5 zeolite. The steps 5) to 10) correspond to the isomorphous substitution of the ZSM-5 with molybdenum.

(54) Step 1):

(55) In a polypropylene bottle (125 mL), solution A is prepared by adding 41.804 g of TPAOH (1M) and 0.346 g of aluminium nitrate (Al(NO.sub.3).sub.3, 9H.sub.2O), under agitation using a magnetic stirrer until complete dissolution of the salt. To this solution A is then added drop-wise 24.0 g of TEOS, under stirring using a magnetic stirrer. The solution becomes water clear after 30 min (beginning of step 2). The molar composition of the as-prepared precursor suspension is the following: 0.357 TPAOH:0.004 Al.sub.2O.sub.3:1 SiO.sub.2:16.189 H.sub.2O

(56) Step 2):

(57) The bottle containing the precursor suspension prepared in step 1) is air-tightly closed with a cap. The as-made synthetic suspensions are left foraging on a magnetic stirrer for 1 h, and then on an orbital shaker for an additional 18 h (225 rpm). All the steps up to this point are performed at room temperature and ambient pressure.

(58) Step 3):

(59) The precursor suspension is water-like at this point. Then it is transferred into Teflon-lined autoclaves, and subjected to static hydrothermal treatment at 180° C., for a duration of 72 h.

(60) Step 4):

(61) The sample is removed from the oven after step 3), and cooled down to room temperature. The solid phase is then separated from the liquid phase using centrifugation. The solid is dispersed in distilled water after reaching the pH of the liquid separated from the solid phase of 7-8.

(62) Step 5):

(63) The obtained solid sample is then dried in a static oven at 80° C. overnight.

(64) The dried sample retrieved is then subjected to the following calcination procedure: In ambient atmospheric conditions (composition of the atmosphere, and atmospheric pressure), the sample is placed in a muffle furnace and heated at 550° C. in 5 h, holds at 550° C. for an additional 5 h and cooled down to room temperature in 5 h. The ZSM-5 zeolite has a Si/Al molar ratio of 112 based on ICP analysis.

(65) Step 6):

(66) 1.2 g of the fully crystalline calcined ZSM-5 zeolite (after step 5), is then introduced in a sealed container containing a solution composed by 0.800 g of sodium molybdate (Na.sub.2MoO.sub.4.4H.sub.2O) dissolved in 25 mL of double-distilled water.

(67) Step 7):

(68) The obtained suspension is mixed with a magnetic stirrer for 1 h at room temperature.

(69) Step 8):

(70) The obtained suspension from step 7) is then placed in a static oven at 90° C. for 9 days.

(71) Step 9):

(72) The sample is removed from the oven after step 8), and cooled down to room temperature. The solid phase is then separated from the liquid phase using centrifugation. The solid is dispersed in distilled water and purified by centrifugation again. This washing procedure is repeated several times (3 to 6 times) in order to remove any unreacted species.

(73) Step 10):

(74) The obtained solid sample is then dried in a static oven at 80° C. overnight.

(75) The dried sample retrieved is then subjected to the following calcination procedure: In ambient atmospheric conditions (composition of the atmosphere, and atmospheric pressure), the sample is placed in a muffle furnace and heated at 550° C. in 5 h, holds at 550° C. for an additional 5 h and cooled down to room temperature in 5 h. The as-obtained sample from step 8) is called Mo-ZSM-5. The analysis showed a Mo content of 0.4 wt. % with respect to the total mass of the material measured according via EDS-TEM and a Si/Mo molar ratio of 438 as determined by inductively coupled plasma optical emission spectrometry.

Example 3

(76) Characterizations of Mo-Silicalite-1 and Mo-ZSM-5 Samples:

(77) The XRD pattern together with the .sup.29Si MAS NMR spectra of samples Mo-Silicalite-1 and Mo-ZSM-5 show that Mo is perfectly substituted on the MFI structure.

(78) The .sup.1H MAS NMR of dehydrated zeolite samples allows calculating a ratio of the concentration of surface OH when Mo is present or not. It appears that the ratio are the following:
nOH(Silicalite-1)/nOH(Mo-Silicalite-1)=3.6
nOH(ZSM-5)/nOH(Mo-ZSM-5)=2.8

(79) There is consequently respectively 3.6 and 2.8 OH groups in the initial Mo free samples for every OH groups in the corresponding Mo-containing sample.