METHOD FOR PREPARING A NANOMETRIC ZEOLITE Y

Abstract

Preparation of a FAU-structural-type nanometric zeolite Y having a crystal size of less than 100 nm and an Si/Al ratio that is greater than 2: mixing, in aqueous medium, of at least one AO.sub.2 source of at least one tetravalent element A that is silicon, germanium, and/or titanium, at least one BO.sub.b source of at least one trivalent element B that is aluminum, boron, iron, indium, and/or gallium, at least one C.sub.2/mO source of an alkaline metal or alkaline-earth metal C that is lithium, sodium, potassium, calcium, and/or magnesium the C.sub.2/mO source also having at least one hydroxide ion source obtaining a gel, curing of the gel after at least 3 days of curing, with addition of at least one source of at least one tetravalent element A and the hydrothermal treatment of the gel obtained at a to achieve crystallization of the FAU-structural-type nanometric zeolite Y.

Claims

1. Method for preparation of a FAU-structural-type nanometric zeolite Y that has a crystal size of less than 100 nm and an Si/Al ratio that is greater than 2, with said method comprising at least the following steps: i) The mixing, in aqueous medium, of at least one AO.sub.2 source of at least one tetravalent element A that is selected from among silicon, germanium, titanium by itself or in a mixture, at least one BO.sub.b source of at least one trivalent element B that is selected from among aluminum, boron, iron, indium, gallium, by itself or in a mixture, at least one C.sub.2/mO source of an alkaline metal or alkaline-earth metal C selected from among lithium, sodium, potassium, calcium, magnesium by itself or in a mixture, with said C.sub.2/mO source of alkaline metal or alkaline-earth metal C also comprising at least one hydroxide ion source for obtaining a gel, with the reaction mixture having the following molar composition:
vAO.sub.2:wBO.sub.b:xC.sub.2/mO:yH.sub.2O with v being between 1 and 40, with w being between 0.1 and 5, with x being between 1 and 40, with y being between 30 and 1000, with b being between 1 and 3, b being a whole number or a rational number, with m being equal to 1 or 2, ii) the curing of the gel obtained at the end of step (i) at a temperature of between −15° C. and 60° C., with or without stirring, for a time period of between 1 and 60 days, iii) after at least 3 days of curing, the one-time or repeated addition of at least one AO.sub.2 source of at least one tetravalent element A that is selected from among silicon, germanium, titanium, by itself or in a mixture, in said gel, with the molar composition of the gel at the end of the addition being as follows:
vAO.sub.2:wBO.sub.b:xC.sub.2/mO:yH.sub.2O with v being between 5 and 50, with w being between 0.1 and 5, with x being between 1 and 40, with y being between 200 and 1000, with b being between 1 and 3, b being a whole number or a rational number, with m being equal to 1 or 2, (iv) the hydrothermal treatment of the gel that is obtained at the end of step (iii) at a temperature of between 20° C. and 200° C., under autogenous reaction pressure, for a time period of between 1 hour and 14 days, to obtain the crystallization of said FAU-structural-type nanometric zeolite Y.

2. Method according to claim 1, in which A is silicon.

3. Method according to claim 1, in which B is aluminum.

4. Method according to claim 1, in which C is sodium.

5. Method according to claim 1, in which the reaction mixture of the mixing step (i) has the following molar composition:
vAO.sub.2:wBO.sub.b:xC.sub.2/mO:yH.sub.2O with v being between 15 and 20, with w being between 0.2 and 1.5, with x being between 1 and 20, with y being between 100 and 400, with b being between 1 and 3, b being a whole number or a rational number, with m being equal to 1 or 2, where A, B and C have the same definition as above.

6. Method according to claim 1, in which seeds comprising FAU-structural-type zeolite crystals are added during the mixing step (i).

7. Method according to claim 1, in which the tetravalent element A added in the curing step (iii) of the method according to the invention can be identical to or different from the tetravalent element A that is added in the mixing step (i).

8. Method according to claim 1, in which the one-time or repeated addition of at least one source of at least one tetravalent element A is carried out during the curing step (ii).

9. Method according to claim 8, in which the one-time or repeated addition of at least one source of at least one tetravalent element A is carried out after at least 5 days of curing.

10. Method according to claim 1, in which the one-time or repeated addition of at least one source of at least one tetravalent element A is carried out after the curing step (ii).

11. Method according to claim 1, in which the molar composition of the gel at the end of the addition in step (iii) is as follows:
vAO.sub.2:wBO.sub.b:xC.sub.2/mO:yH.sub.2O with v being between 20 and 30, with w being between 0.2 and 1.5, with x being between 1 and 20, with y being between 200 and 500, with b being between 1 and 3, b being a whole number or a rational number, with m being equal to 1 or 2, where A, B and C have the same definition as above.

12. Method according to claim 1, in which the FAU-structural-type nanometric zeolite Y that is formed at the end of step (iv) is filtered, washed, and then dried at a temperature of between 20° C. and 150° C.

13. Method according to claim 12, in which said zeolite that is obtained at the end of the drying step undergoes at least one calcination step and at least one ion exchange step.

Description

DESCRIPTION OF THE FIGURES

[0070] FIGS. 1 and 2 show the X-ray diffraction diagrams of the FAU-structural-type nanometric zeolites Y that are synthesized in Examples 1 and 2, in the diffraction angle range 2θ=5° to 40°.

EXAMPLES

[0071] The invention is illustrated by the following examples that do not in any case have a limiting nature.

Example 1: Preparation of a FAU-Structural-Type Nanometric Zeolite X and an Si/Al Molar Ratio that is Equal to 1.4 According to a Method that is not in Compliance with the Invention

[0072] A FAU-structural-type nanometric zeolite X that contains the elements Si and Al, with an Si/Al molar ratio equal to 1.4, is synthesized according to a preparation method known to one skilled in the art. Typically, the aluminum source (sodium aluminate, Strem Chemicals, 99%) and the mineralizing agent (sodium hydroxide, Fluka, 99%) are dissolved in deionized water, while being stirred. The silicon source (Ludox AS-40, 40%, Sigma Aldrich) is then added drop by drop, so as to obtain a reaction mixture whose molar composition is 15.2 SiO.sub.2: 1 Al.sub.2O.sub.3: 17 Na.sub.2O: 360 H.sub.2O. The reaction mixture is continuously stirred vigorously for 17 days at ambient temperature. The product is then filtered and washed, before being dried in the oven for one night at 100° C. No silicon source or any other tetravalent element is added during the curing step.

[0073] The X-ray diffraction diagram of the material shown in FIG. 1 can be indexed in the cubic system of the FAU-structural-type zeolite. The analysis of the X-ray diffractogram provides an Si/Al molar ratio that is equal to 1.4 according to the Fichtner-Schmittler equation. These characteristics correspond to a FAU-structural-type zeolite X. The size of the zeolite crystals obtained, measured in 8 transmission electron microscopy images, is between 15 and 50 nm.

Example 2: Preparation of the FAU-Structural-Type Nanometric Zeolite Y and an Si/Al Molar Ratio Equal to 2.7 According to a Method in Compliance with the Invention

[0074] A FAU-structural-type nanometric zeolite Y that contains the elements Si and Al, with an Si/Al molar ratio equal to 2.7, is synthesized according to a preparation method that is described in Example 1 relative to the mixing step (i). Typically, the aluminum source (sodium aluminate, Strem Chemicals, 99%) and the mineralizing agent (sodium hydroxide, Fluka, 99%) are dissolved in deionized water, while being stirred. The silicon source (Ludox AS-40, 40%, Sigma Aldrich) is then added drop by drop, so as to obtain a reaction mixture whose molar composition is 15.2 SiO.sub.2: 1 Al.sub.2O.sub.3: 17 Na.sub.2O: 360 H.sub.2O. The gel that is thus formed is stirred vigorously at ambient temperature. At the end of 7 days of curing, a silicon source (Ludox AS-40, 40%, Sigma Aldrich) is added drop by drop. The operation is repeated the next day and the day after that. After the three additions of silicon source, the gel that is thus formed has the following composition: 25 SiO.sub.2: 1 Al.sub.2O.sub.3: 18.4 Na.sub.2O: 480 H.sub.2O. The reaction mixture is continuously stirred vigorously for 4 additional days at ambient temperature, and then is transferred into a polypropylene flask. This flask is placed in an oven at 60° C. for 24 hours under autogenous pressure and without adding gas. After having cooled the flask to ambient temperature, the product is filtered and washed, before being dried in the oven for one night at 100° C.

[0075] The X-ray diffraction diagram of the material shown in FIG. 2 can be indexed in the cubic system of the FAU-structural-type zeolite. The analysis of the X-ray diffractogram provides an Si/Al molar ratio that is equal to 2.7 according to the Fichtner-Schmittler equation. These characteristics also correspond to a FAU-structural-type zeolite Y. The size of the zeolite crystals obtained, measured in 8 transmission electron microscopy images, is between 15 and 50 nm.

Example 3: Not in Compliance with the Invention

[0076] According to a method that is not in compliance with the invention, there is prepared—from the first mixing step—a gel with a composition that is identical to the one described in Example 3 after the three additions of silicon source: 25 SiO.sub.2: 1 Al.sub.2O.sub.3: 18.4 Na.sub.2O: 480 H.sub.2O. This gel is stirred vigorously at ambient temperature for 13 days, corresponding to the total curing period of the gel that is prepared in Example 3. The reaction mixture is then transferred into a polypropylene flask. This flask is placed in an oven at 60° C. for 24 hours under autogenous pressure and without the addition of gas. After having cooled the flask to ambient temperature, the product is filtered and washed, before being dried in the oven for one night at 100° C.

[0077] The X-ray diffraction diagram of the material shown in FIG. 4 shows that no crystallized product is formed at the end of the crystallization step at 60° C. The preparation method described in this example therefore does not make it possible to obtain a FAU-structural-type nanometric zeolite.