PROCESS FOR THE PREPARATION OF ZEOLITES ENCAPSULATING TRANSITION METAL NANOPARTICLES FROM LAYERED SILICATE PRECURSORS

Abstract

The present invention relates to a process for the production of a transition metal containing zeolite comprising expanding a layered silicate with a swelling agent and introducing the transition metal into the interlayer expanded silicate prior to calcination thereof for obtaining the transition metal containing zeolite. The present invention further relates to a zeolite containing transition metal nanoparticles as obtainable or obtained according to the inventive process, as well as to a zeolite containing nanoparticles per se. Finally the present invention relates to the use of a zeolite containing transition metal nanoparticles as obtainable or obtained according to the inventive process, as well as to the use of a zeolite containing nanoparticles per se.

Claims

1. A process for the production of a transition metal-containing zeolite, the process comprising: (i) providing a layered silicate; (ii) treating the layered silicate provided in (i) with one or more swelling agents and obtaining an interlayer expanded silicate; (iii) treating the interlayer expanded silicate obtained in (ii) with one or more cationic transition metal complexes and obtaining a transition metal-containing interlayer expanded silicate; (iv) calcining the transition metal-containing interlayer expanded silicate obtained in (iii) and obtaining a transition metal-containing zeolite; and (v) optionally reducing the transition metal-containing zeolite obtained in (iv), wherein the framework structure of the zeolite obtained in (iv) comprises YO.sub.2 and optionally X.sub.2O.sub.3, wherein Y is a tetravalent element, and X is a trivalent element.

2. The process of claim 1, wherein the tetravalent element Y is at least one selected from the group consisting of Si, Sn, Ti, Zr, Ge, and mixtures thereof.

3. The process of claim 1, wherein the trivalent element X is at least one selected from the group consisting of Al, B, In, Ga, and mixtures thereof.

4. The process of claim 1, wherein the layered silicate provided in (i) is at least one selected from the group consisting of MCM-22P, PREFER, Nu-6(2), PLS-3, PLS-4, MCM-47, ERS-12, MCM-65, RUB-15, RUB-18, RUB-20, RUB-36, RUB-38, RUB-39, RUB-40, RUB-42, RUB-51, BLS-1, BLS-3, ZSM-52, ZSM-55, kanemite, makatite, magadiite, kenyaite, revdite, montmorillonite, and mixtures thereof.

5. The process of claim 1, wherein the transition metal of the one or more cationic transition metal complexes is at least one selected from the group consisting of group 8 to 11 transition metals of the periodic table.

6. A transition metal-containing zeolite obtained according to the process of claim 1.

7. A zeolite comprising transition metal nanoparticles, wherein the framework structure of the zeolite comprises YO.sub.2 and optionally X.sub.2O.sub.3, wherein Y is a tetravalent element, and X is a trivalent element, and wherein the micropores of the zeolite comprise 0.15 to 5 wt.-% of the transition metal nanoparticles calculated as the metal element and based on 100 wt.-% of the total weight of X, Y, O, and of the transition metal contained in the zeolite calculated as the respective element, wherein the mean particle size d50 of the transition metal nanoparticles is in the range of from 0.5 to 4 nm, and wherein the transition metal is at least one selected from groups 8 to 11 of the periodic table.

8. The zeolite of claim 7, wherein the particle size d90 of the transition metal nanoparticles is in the range of from 1 to 7 nm.

9. The zeolite of claim 7, wherein the particle size d10 of the transition metal nanoparticles is in the range of from 0.3 to 2.5 nm.

10. The zeolite of claim 7, wherein the transition metal of the transition metal nanoparticles is at least one selected from groups 8 to 11 of the periodic table, and mixtures and/or alloys thereof.

11. The zeolite of claim 7, wherein the transition metal nanoparticles are in elemental form.

12. The zeolite of claim 7, wherein the zeolite has a framework type selected from the group consisting of FER, MWW, SOD, RWR, CDO, and RRO.

13. The zeolite of claim 7, wherein the tetravalent element Y is at least one selected from the group consisting of Si, Sn, Ti, Zr, Ge, and mixtures thereof.

14. The zeolite of claim 7, wherein the trivalent element X is at least one selected from the group consisting of Al, B, In, Ga, and mixtures thereof.

15. A process, comprising employing a transition metal-containing zeolite according claim 6 as a molecular sieve, catalyst, catalyst component, catalyst support, absorbents, and/or for ion-exchange.

Description

DESCRIPTION OF THE FIGURES

[0150] FIG. 1 shows the X-ray diffraction patterns of (a) RUB-36; (b) swollen RUB-36; (c) deswollen material obtained by ion exchange with Pd(en).sub.2.sup.2+; (d) Pd@ZSM-35 obtained after calcination and H.sub.2 reduction according to Example 1. In the figure, the angle 2 theta in degrees is shown along the abscissa and the intensities are plotted along the ordinate.

[0151] FIG. 2 shows the TEM in figures (a) and (b) and the STEM in figure (c) of the Pd@ZSM-35 obtained after calcination and H.sub.2 reduction according to Example 1.

[0152] FIG. 3 shows the particle size distribution of the Pd nanoparticles in Pd@ZSM-35 obtained after calcination and H.sub.2 reduction according to Example 1 as determined from the TEM images. In the figure, the particle size in nm is shown along the abscissa and the distribution in % is plotted along the ordinate.

EXAMPLES

Characterization Methods

[0153] XRD patterns were collected on the PANalytical X'Pert3 Powder X-ray diffractometer with Cu K.sub.α radiation in the 2θ range of 0.5-10° and 5-50° and scan step size of 0.026°.

[0154] Nitrogen adsorption/desorption measurements were carried out on a Micromeritics 2020 analyzer at 77 K after the samples were degassed at 350° C. under vacuum.

[0155] Pd contents of the resulted catalysts were determined by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES, Optima 2000 DV, USA).

[0156] SEM and STEM images were obtained using a Hitachi S-5500 SEM equipped with a scanning transmission electron microscope (STEM), operating at an accelerating voltage of 30 kV.

[0157] Transmission electron microscopy (TEM) images were recorded on Hitachi HT 7700 microscope operated at an acceleration voltage of 100 kV. The mean particle size (d50) of the palladium nanoparticles in the samples was determined by analysis of a 100×100 nm area in the TEM image of a given sample. More specifically, the size (diameter) of the particles within that area was measured according to the scale bar with a margin of error of ±0.2 nm, wherein the threshold for the determination of the particles was a size of 0.8 nm. Thus, only particles having a diameter 0.8 nm or greater were taken into consideration for the determination of the particle size distribution and the calculation of the mean particle size. For the measurement of non-spheroidal nanoparticles, the largest dimension was recorded as the particle diameter. The mean particle size determined was accordingly the mean particle size by number.

Reference Example 1: Preparation of diethylenediamine palladium (II) acetate (Pd(en).SUB.2.(Ac).SUB.2.) and Ethylenediamine Acetic Acid (En-HAc) Solutions

[0158] 0.3 g palladium acetate (Aladdin Reagent) was dispersed into 9 ml ethanol containing 0.5 g ethylenediamine (Tianjin Bodi Chemical Co., Ltd.). After sonification for 10 min, a clear ethanol solution of Pd(en).sub.2(Ac).sub.2 was obtained.

[0159] 1.0 g acetic acid (Tianjin Fuyu Fine Chemical Co., Ltd.) was dissolved into 9.0 ml ethanol containing 1.0 g ethylenediamine and 0.6 g deionized H.sub.2O to get a clear solution of en-HAc.

Example 1: Preparation of ZSM-35 Encapsulating Pd Nanoparticles (Pd@ZSM-35)

[0160] The layered silicate RUB-36 was prepared as respectively described in W. M. H. Sachtler, Acc. Chem. Res., 1993, 26, 383-387 and N. Wang et al., J. Am. Chem. Soc., 2016, 138, 7484-7487, using diethyldimethylammonium hydroxide as the structure-directing agent (DEDMAOH, 20 wt % solution in water, Sachem Inc.). In general, it was crystallized from the gel with a composition of SiO.sub.2:0.5 SDA:10H.sub.2O. Aerosil 200 was utilized as the silica source. Crystallization was carried out in an autoclave without stirring for 14 days. The resulting product was filtered, washed with deionized water and dried at 100° C.

[0161] RUB-36 was then swollen using cetyltrimethylammonium hydroxide (CTAOH, 10 wt % solution in water, TCI) at room temperature (RT). More specifically, 0.5 g RUB-36 was dispersed in 35.0 g CTAOH solution (4 wt % solution in water). The mixture was stirred for 48 h, then filtered and washed with deionized water, and finally dried at RT to obtain an interlayer expanded silicate. The deswelling process with Pd(en).sub.2Ac.sub.2 was conducted by mixing 0.5 g swollen sample with a mixture of 10 ml ethanol, 0.31 ml Pd(en).sub.2Ac.sub.2 solution and 1.25 ml en-HAc solution from Reference Example 1, respectively, then stirred for 4 h at RT. The transition metal containing interlayer expanded silicate product was recovered by filtration, repeated washing with deionized water and ethanol, and then dried at RT. Calcination of the obtained sample was conducted at 500° C. in static air for 4 h. The calcined sample was then reduced at 330° C. under 30 ml/min 30% H.sub.2/N.sub.2 for 1 h for obtaining ZSM-35 encapsulating Pd nanoparticles (Pd@ZSM-35).

[0162] As shown in FIG. 1, after calcination in air and reduction with hydrogen, the obtained Pd@FER (see XRD pattern (d)) has the same diffraction pattern as FER zeolite with very good crystallinity. Moreover, the absence of the diffractions of Pd metal crystals near 40.1° and 46.6° means that Pd metal nanoparticles are ultrafine without significant aggregated bulk ones. ICP-AES analysis shows that the Pd loading amount is 1.4 wt.-% based on the total weight of Si, 0, and Pd in the sample. It's worth noting that the introduction of a too large amount of Pd precursors should be avoided between the FER layers since this may hinder the ordered condensation of the silanol groups between the FER layers. For avoiding this, a certain amount of ethylenediamine-acetic acid (En-HAC) solution was co-added with the Pd precursors during the deswelling process.

[0163] N.sub.2 adsorption/desorption isotherms of Pd@FER shows a typical Langmuir-type adsorption, indicating the presence of uniform micropores with a Brunauer-Emmett-Teller (BET) surface area of 325 m.sup.2/g.

[0164] TEM and STEM images shown in FIG. 2 indicate ultrafine and well dispersed Pd nanoparticles with mean particle size of 1.4 nm intensively distributed on the zeolite support, and only very minor bulk ones near the edge of zeolite sheet for Pd@FER, which is reasonable due to the migration of Pd atoms near the edges during high temperature calcination. The particle size distribution of the Pd nanoparticles as obtained from TEM is displayed in FIG. 3.

[0165] It's worth noting that the 1.4 nm mean particle size of the Pd nanoparticles embedded in the FER zeolite is actually much larger than the pore diameters of 5.4×4.2 Å and the side-cages (about 7 Å). It can be explained by the fact that both the formation of 3-D zeolite and Pd nanoparticles occurs during the calcination process, and once Pd nanoparticles were formed larger than the pore size before the ordered condensation of silanol groups, the defects may be created. It's also the case when too many Pd(en).sub.2.sup.2+ were introduced between the FER layers, as a result of which the ordered FER structure could not be obtained. The homogeneous distribution of Pd nanoparticles with extremely high density in FER zeolite without significant aggregation may result from its distinctive two-dimensional structure. Pd precursors or nanoparticles are separated by the FER layers, which hinders the particle aggregation among different layers, and therefore enhance the stability of Pd nanoparticles.

[0166] Therefore, the inventive method allows for the production of zeolites having very high loadings of the transition metal nanoparticles encapsulated within their micropores.

CITED PRIOR ART LITERATURE

[0167] L. Liu et al., Nat Mater, 2017, 16, 132-138 [0168] Z. Zhao et al., Chem. Mater., 2013, 25, 840-847 [0169] W. M. H. Sachtler, Acc. Chem. Res., 1993, 26, 383-387 [0170] N. Wang et al., J. Am. Chem. Soc., 2016, 138, 7484-7487