WO2021244683A1

WO2021244683A1 - Preparation of hierarchical beta zeolites using monoquaternary structure-directing agent

Info

Publication number: WO2021244683A1
Application number: PCT/CZ2020/050040
Authority: WO
Inventors: Roman BARAKOV; Maksym OPANASENKO; Mariya SHAMZHY; Martin Kubu; Jiri Cejka
Original assignee: Charles University, Faculty Of Science
Priority date: 2020-06-04
Filing date: 2020-06-04
Publication date: 2021-12-09

Abstract

s The present invention provides a method for preparation of hierarchical Beta zeolites, said method comprising the following steps: a) contacting a monoquaternary structure-directing agent with aqueous solution of a protic acid, to form a first mixture with the molar ratio of the components: structure-directing agent : protic acid (expressed as moles of [H+]) : water = 0.55 – 0.65 : 0.15 – 0.25 : 20 – 25; b) adding a source of silica to the first mixture to form a second mixture having the molar ratio of the components: source of silica (SiO2) : structure-directing agent : protic acid [H+] : water = 1 : 0.55 – 0.65 : 0.15 – 0.25 : 20 – 25; c) contacting the second mixture with a source of alumina to form a third mixture with the molar ratio: source of silica (expressed as SiO2) : source of alumina (expressed as Al2O3) : structure-directing agent : protic acid [H+] : water = 1 : 0.005 – 0.05 : 0.55 – 0.65 : 0.15 – 0.25 : 20 – 25; d) optionally subjecting the third mixture to evaporation of water to achieve the molar ratio H2O to SiO2 within the range 3 to 19; e) processing the third mixture having the molar ratio H2O to SiO2 within the range 3 to 25 by hydrothermal treatment at 130 to 150 °C, under autogenic pressure for 6 – 10 days, to form the as-synthesized product; f) calcination of the as-synthesized product at temperatures ranging from 550 to 650 °C, with a heating time 4 – 8 hours. The method allows to prepare catalytically active H-form of hierarchical Beta zeolites with reproducible properties (SiO2/Al2O3 ratio, nanoparticle size, textural properties and acid sites concentration) without i) utilization of complex mesoporogens and ii) necessity to perform extra synthesis steps (ion-exchange followed by thermal treatment).

Description

Preparation of hierarchical Beta zeolites using monoquaternary structure-directing agent

Field of Art

The present invention relates to a method of preparation of hierarchical zeolites consisting of Beta nanoparticles.

Background Art

Zeolites are crystalline aluminosilicates built from TO₄ tetrahedra (T = Si, Al) that are arranged in such a manner that intracrystalline pores and cavities of molecular dimensions (0.3 - 1.5 nm) are present. The presence of Al atoms in the zeolite framework generates negative charges in the structure that require external cations to be balanced, which can be substituted by protons (Bronsted acid sites). Dehydroxylation of these sites leads to the formation of Lewis acid sites. The existence of strong and tunable acidity in zeolites has led to their utilization as catalysts in a large number of acid-catalysed reactions, mainly in organic synthesis, oil refining and petrochemical industries. Hierarchical zeolites are zeolitic materials consisting of a crystalline network of TO₄ tetrahedra that possess, in addition to uniform zeolitic micropores, a secondary porosity, in most cases, mesopores (2 - 50 nm). The presence of mesopores in hierarchical zeolites provides benefits in catalysis such as reduction of the steric limitations for converting bulky molecules exceeding zeolite micropore size, an increase in the rate of intracrystalline diffusion, as well as decrease in the deactivating effect of carbon deposition (D. P. Serrano, J. M. Escola and P. Pizarro, Chem. Soc. Rev., 2013, 42, 4004-4035; K. Moller and T. Bein, Chem. Soc. Rev., 2013, 42, 3689-3707). Zeolite with *BEA framework type was invented by Mobil Research and Development Laboratories in 1967 and denoted as Beta material, which is a large pore zeolite with channels defined by twelve-rings. The estimated pore sizes of *BEA are 0.66 x 0.67 nm and 0.56 x 0.56 nm, while its empirical formula is INa⁺ _yl[Al_ySi_64-y0₁₂₈]-H₂O (y < 7). Due to its improved thermal stability and high acidity this type of zeolite is widely used in industry as a heterogeneous catalyst, mainly in alkylation and acylation processes (K. Tanabe and W. F. Holderich, Appl. Catal. A Gen., 1999, 181, 399-434). Hierarchical Beta zeolites can be obtained by various methods (1 - 6):

1) Direct synthesis as assembly of zeolite nanoparticles with the size of 10 - 50 nm to the material possessing interparticle mesopores, which results from the packing of these particles to form bulk but porous aggregates (W. Schwieger, A. G. Machoke, T. Weissenberger, A. Inayat, T. Selvam, M. Klumpp and A. Inayat, Chem. Soc. Rev., 2016, 45, 3353-3376).

2) In the presence of hard templates, e.g., carbon nanoparticles and nanofibers, polystyrene spheres (S. Soltanali and J. T. Dariana, Microporous Mesoporous Mater., 2019, 286, 169-175). Rigid and typically non-porous templates are incorporated into crystals and/or interparticle space during zeolite crystallization process with the formation of intracrystalline or interparticle mesopores after calcination of the material. The general procedure includes the following main steps: preparation of the solution by mixing structure-directing agent, sources of silica and alumina, alkali, distilled water; impregnation of hard templates with this solution; aging of the mixture followed by its further hydrothermal treatment at 150 °C for 2 - 4 days in static conditions; filtration, washing and drying of the product; removal of the template and structuredirecting agent by calcination (550 °C, 5 h). The structure-directing agent is a molecule that guides the formation of particular types of pores and channels during the synthesis of zeolite. The disadvantages of this method are high cost of hard templates, difficulties with the removal of a large amount of carbon species after the crystallization step and difficulty to tune the textural properties of the obtained materials.

3) The use of non-ionic (polyethylene glycol, polyacrylamide, polyvinyl butyral, polyvinyl alcohol) and cationic polymers (polydialyldimethylammonium chloride, epichlorohydrin- dimethylamine polyamine) as templates allows to obtain materials consisting of zeolite nanoparticle agglomerates characterized by the presence of interparticle mesopores (L. Wang, Z. Zhang, C. Yin, Z. Shan and F.-S. Xiao, Microporous Mesoporous Mater., 2010, 131, 58- 67). For obtaining the hierarchical Beta zeolite, source of alumina, alkali, structure-directing agent and distilled water are mixed, followed by addition of silica source. Then the polymer is added into the reaction mixture. After stirring for 12 - 24 h at room temperature, the mixture is subjected to hydrothermal treatment at 140 °C for 5 - 7 days in static conditions. The product is calcined to remove the template and the structure-directing agent. The materials obtained using this method are characterized by a relatively broad mesopore size distribution and low crystallinity.

4) Amphiphilic organosilanes ([3-(trimethoxysilyl)propyl]hexadecyldimethylammonium chloride) and silylating agents (phenylaminopropyltrimethoxysilane) can be used as mesoporogens to prevent zeolite crystal growth, and thereby to stabilize zeolite nanoparticles (V. P. S. Caldeira, A. Peral, M. Linares, A. S. Araujo, R. A. Garcia- Munoz and D. Serrano, Appl. Catal. A Gen., 2017, 531, 187-196). The mesoporogen also contributes to organisation of zeolite nanoparticles on the mesoscale and after removal of the mesoporogen the material contains mesopores. Amphiphilic organosilanes contain a hydrolysable methoxysilyl moiety, a zeolite structure-directing group such as quaternary ammonium, and a hydrophobic alkyl chain moiety. The silanol groups resulting from the hydrolysis of methoxysilyl moiety strongly interact with silanol groups of growing crystal domains, while the hydrophobic alkyl moieties of organosilane limit the growth of zeolite crystallites. For the synthesis of hierarchical Beta zeolite in the presence of amphiphilic organosilane, this compound is added to a zeolite synthesis mixture containing sources of silica and alumina, alkali, structure-directing agent and distilled water. After stirring for 2 h at room temperature, the mixture is subjected to hydrothermal treatment at 140 °C for 6 - 8 days under tumbling conditions. Hierarchical zeolites are also synthesized using silylating agent. This agent is added into a zeolite synthesis mixture and left reacting at 90 °C for 6 h under reflux. The resulting mixture is subjected to hydrothermal treatment at 135 °C for 7 days in static conditions. Both solid products are calcined to remove the mesoporogen and the structure-directing agent. The materials obtained using silylating agents and amphiphilic organosilanes consist of relatively large zeolite particles (ca. 40 - 50 nm) and therefore are characterized by a small volume and surface area of interparticle mesopores.

5) Multi-quaternary ammonium surfactants have also been used for direct synthesis of hierarchical Beta zeolite (K. Na, C. Jo, J. Kim, K. Cho, J. Jung, Y. Seo, R. J. Messinger, B. F. Chmelka and R. Ryoo, Sci., 2011, 333, 328-332). The hydrophilic head groups of these surfactants - quaternary nitrogen atoms - act as a structure-directing agent to form zeolite domains, while the hydrophobic alkyl chains limit the growth of zeolite crystals. In a typical hierarchical zeolite synthesis, sources of silica and alumina, alkali, multi-quaternary ammonium surfactant, ethanol and distilled water are mixed to obtain a gel. The resultant gel mixture is agitated at 60 °C for 6 h and subjected to hydrothermal treatment at 140°C for 4 d under tumbling conditions. The product is calcined in order to remove the organic surfactants. The use of multi-quaternary ammonium surfactants allows to obtain materials with well-developed mesoporosity and high accessibility of acid sites. However, the synthesis of multi-quaternary ammonium surfactants is costly and labor-consuming process.

6) Hierarchical zeolite Beta can also be obtained without additional mesoporogens by careful choice of the synthesis conditions (composition and pH of the reaction mixture, temperature and duration of hydrothermal treatment) (A. Petushkov, G. Merilis, S. C. Larsen, Microporous Mesoporous Mater., 2011, 143, 97-103). For the synthesis of hierarchical Beta zeolite, source of alumina, alkali, structure-directing agent and distilled water are mixed, followed by addition of silica source. After stirring for 14 - 16 h at room temperature, the mixture is rotary evaporated at 65 °C until 50 % of the initial volume is removed. Then the mixture (H₂O/SiO₂ molar ratio of 20, pH = 12.2) is subjected to hydrothermal treatment at 120 - 150 °C for 20 - 96 h in static conditions. However, these methods have several drawbacks such as relatively broad mesopore size distribution, low crystallinity, and limited concentration of strong Bronsted acid sites in the obtained materials.

The methods known in the art for producing hierarchical Beta zeolites suffer from the above- described drawbacks. Thus, there is a need for developing a simple, cheap, effective and reproducible method for direct preparation of hierarchical H-Beta zeolites with well-developed mesoporosity and high acidity using direct hydrothermal treatment without utilization of complex mesoporogens.

Disclosure of the Invention

The present invention provides a method for preparation of hierarchical Beta zeolites, comprising the following steps: a) contacting a monoquatemary structure-directing agent with aqueous solution of a protic acid, to form a first mixture with the molar ratio of the components: structure-directing agent : protic acid (expressed as moles of [H⁺]) : water = 0.55 - 0.65 : 0.15 - 0.25 : 20 - 25; b) adding a source of silica to the first mixture to form a second mixture having the molar ratio of the components: source of silica (SiO₂) : structure-directing agent : protic acid [H⁺] : water = 1 : 0.55 - 0.65 : 0.15 - 0.25 : 20 - 25; c) contacting the second mixture with a source of alumina to form a third mixture with the molar ratio of the components: source of silica (expressed as SiO₂) : source of alumina (expressed as Al₂O₃) : structure-directing agent : protic acid [H⁺] : water = 1 :0.005- 0.05 : 0.55 -0.65 : 0.15 - 0.25 : 20 - 25; d) optionally subjecting the third mixture to evaporation of water to achieve the molar ratio H₂O to SiO₂ within the range 3 to 19; e) processing the third mixture having the molar ratio H₂O to SiO₂ within the range 3 to 25 by hydrothermal treatment at 130 to 150 °C for 6 - 10 days to form an as-synthesized product; f) calcination of the as-synthesized product at temperatures ranging from 550 to 650 °C, with a heating time 4 - 8 hours.

In the present invention, the concentrated reaction mixtures (H₂O/SiO₂ molar ratio of 3 - 25) obtained either by direct preparation or by drying the initial mixture, are used for the synthesis of hierarchical Beta zeolites. A large number of zeolite nuclei is formed during hydrothermal treatment of the concentrated reaction mixtures in the presence of monoquatemary structure-directing agent, followed by their agglomeration resulting in the packing of the particles preventing their further growth and formation of highly porous material consisting of zeolite Beta nanoparticles. The addition of protic acid to the reaction mixture contributes to a decrease in its pH, that slows down the crystallization process and limits the growth of zeolite nanoparticles. The use of alkali metal-free mixtures (the reagents do not contain alkali metals) allows to obtain H-form of hierarchical Beta zeolites directly after calcination, without additional operations of ion-exchange. The preparation procedure is simple, straightforward, and hierarchical zeolites with variable SiO₂/Al₂O₃, ratio, nanoparticle size, textural properties (micropore volume, mesopore volume, mesopore diameter, total specific surface area, external surface area) and acid sites concentration can be prepared in a reproducible way.

Monoquatemary structure-directing agent is preferably selected from tetraethylammonium hydroxide, methylpropylpyrrolidinium hydroxide, butylmethylpyrrolidinium hydroxide, methylpropylpiperidinium hydroxide and mixtures thereof. A particularly preferred structure- directing agent is tetraethylammonium hydroxide.

Protic acid acts as a pH adjusting agent, and it is preferably selected from hydrochloric acid, sulfuric acid, nitric acid and a mixture thereof. A particularly preferred protic acid is hydrochloric acid.

Sources of silica are known to a person skilled in the art; suitable sources of silica are listed, e.g., in M. W. Kasture, P.S. Niphadkar, S. R. Kate, P. D. Godbole, K. R. Patil, G. M. Chaphekar, P. N. Joshi, Stud. Surf. Sci. Catal, 2004, 154, 3081-3087. Preferably, the source of silica is selected from fumed silica (0.2-0.3 μm average particle size, aggregate), colloidal silica, silicon dioxide nanopowder (D50 NMT 100 nm), AEROSIL®380 (AEROSIL®380 is a hydrophilic fumed silica with a specific surface area in the range of 350-410 m²/g) and mixtures thereof. A particularly preferred source of silica is fumed silica (0.2-0.3 μm average particle size, aggregate).

In this text, the ratio of the source of silica to other components of the mixture is expressed as a molar ratio of SiO₂ to the other components. This means that the amount of the source of silica is re-calculated to moles of SiO₂ in order to determine its ratio to the other components of the reaction mixture. Sources of alumina are known to a person skilled in the art; suitable sources of alumina are listed, e.g., in M. Hadi, H. R. Aghabozorg, H. R. Bozorgzadeh, M. R. Ghasemi, Bull. Chem. React. Eng. Catal., 2018, 13, 543-552. Preferably, the source of alumina is selected from aluminum hydroxide, aluminum nitrate nonahydrate, aluminum sulfate hexadecahydrate, aluminum isopropylate and mixtures thereof. A particularly preferred source of alumina is aluminum hydroxide.

In this text, the ratio of the source of alumina to other components of the mixture is expressed as a molar ratio of Al₂O₃ to the other components. This means that the amount of the source of silica is re-calculated to moles of Al₂O₃ in order to determine its ratio to the other components of the reaction mixture.

In step a), water is preferably distilled water.

In step b), the second mixture is preferably stirred for 30 - 60 min.

In step c), Al₂O₃/SiO₂ molar ratio in the third mixture is preferably within the range of 0.014 to 0.05. The third mixture, typically having a pH of 13.5 to 14.5, is preferably stirred for 60 - 90 min.

In the optional step d), the third mixture is preferably dried at a temperature of 40 - 100 °C, more preferably 60 - 80 °C to H₂O/SiO₂ molar ratio in the mixture within the range 3 to 19.

In the hydrothermal treatment step e), the third mixture or the partially evaporated third mixture is preferably kept at a temperature within the range of 130 to 150 °C, under autogenic pressure (in the range of 5 to 15 atm) for 6 - 8 days. The hydrothermal crystallization may be carried out in an autoclave under static conditions.

The hydrothermal crystallization may be quenched for example by cold water (laboratory temperature or colder), and the product may be centrifuged and washed with distilled water, and dried (for example, at a temperature ranging from 60 to 100 °C). The product of the hydrothermal crystallization is then calcined in a furnace at temperatures ranging from 550 to 650 °C, with a temperature rate preferably ranging from 1 °C to 10 °C/min and with a heating time 4 - 8 hours.

The present invention allows to obtain highly porous hierarchical zeolites consisting of Beta nanoparticles in the presence of only monoquatemary structure-directing agent (such as tetraethylammonium hydroxide), without utilization of mesoporogens which are expensive and complex. Thanks to this invention, catalytically active H-form of hierarchical Beta zeolites can be directly obtained after removal of the structure-directing agent.

FIG. 1 shows the XRD patterns of calcined hierarchical Beta (HB) zeolites synthesized in the reaction mixture with SiO₂/Al₂O₃ molar ratio of 70 and H₂O/SiO₂ molar ratio of 20 (HB-1, Example 1), 15 (HB-2, Example 2), 10 (HB-3, Example 3), 5.5 (HB-4, Example 4) and 3 (HB- 5, Example 5).

FIG. 2 shows the XRD patterns of calcined hierarchical Beta zeolites synthesized in the reaction mixture with SiO₂/Al₂O₃ molar ratio of 40 and H₂O/SiO₂ molar ratio of 20 (HB-6, Example 6), 15 (HB-7, Example 7), 10 (HB-8, Example 8), 5.5 (HB-9, Example 9) and 3 (HB-10, Example 10).

FIG. 3 shows the XRD patterns of calcined hierarchical Beta zeolites synthesized in the reaction mixture with H₂O/SiO₂ molar ratio of 20 and SiO₂/Al₂O₃ molar ratio of 35 (HB-11, Example 11), 30 (HB-12, Example 12), 25 (HB-13, Example 13) and 20 (HB-14, Example 14).

FIG. 4 shows TEM image of calcined hierarchical Beta zeolite HB-1 (Example 1) synthesized in the reaction mixture with SiO₂/Al₂O₃ molar ratio of 70 and H₂O/SiO₂ molar ratio of 20.

FIG. 5 shows nitrogen ad(de)sorption isotherms at -196 °C (a, c) and mesopore size distribution curves (b, d) of calcined hierarchical Beta zeolites synthesized in the reaction mixture with SiO₂/Al₂O₃ molar ratio of 70 and H₂O/SiO₂ molar ratio of 20 (HB-1, Example 1), 15 (HB-2, Example 2), 10 (HB-3, Example 3), 5.5 (HB-4, Example 4) and 3 (HB-5, Example 5).

FIG. 6 shows nitrogen ad(de)sorption isotherms at -196 °C (a, c) and mesopore size distribution curves (b, d) of calcined hierarchical Beta zeolites synthesized in the reaction mixture with SiO₂/Al₂O₃ molar ratio of 40 and H₂O/SiO₂ molar ratio of 20 (HB-6, Example 6), 15 (HB-7, Example 7), 10 (HB-8, Example 8), 5.5 (HB-9, Example 9) and 3 (HB-10, Example 10). FIG. 7 shows nitrogen ad (de) sorption isotherms at -196 °C (a) and mesopore size distribution curves (b) of calcined hierarchical Beta zeolites synthesized in the reaction mixture withH₂O/SiO₂ molar ratio of 20 and SiO₂/Al₂O₃, molar ratio of 35 (HB-11, Example 11), 30 (HB- 12, Example 12), 25 (HB-13, Example 13) and 20 (HB-14, Example 14).

Examples

Materials and Methods

Products were analyzed by X-ray powder diffraction method to confirm the *BEA topology. X-ray diffraction patterns were obtained on diffractometer D8 ADVANCE (Bruker AXS) with a graphite monochromator using CuK_α-radiation in Bragg-Brentano geometry. An average Beta crystallite size (average size of coherent scattering regions) was calculated by the Scherrer’s equation.

The content of Si and A1 in the products was determined by ICP-OES (Thermo Scientific iCAP 7000) analysis. Firstly, the mixture of 1.8 ml of HF, 5.4 ml of HC1, 1.8 ml of HNO₃ and 50 mg of product was transferred into a closed vessel, placed in the microwave, and heated. After cooling down, the surplus of HF was disposed of by adding 13.5 ml of H₃BO₃ and by treatment in microwave. Then, the solutions were diluted before analysis.

The inner structure of products is determined by Transmission Electron Microscopy (TEM) using NEOARM 200 F (JEOL) with a Schottky-type field emission gun at accelerating voltage of 200 kV. Microscope was equipped with TVIPS XF416 CMOS camera. The alignment was performed using standard gold nanoparticles film method. Due to low beam- stability of the sample the dose of electrons was kept below current density of 2 pA/cm².

Textural properties of hierarchical Beta zeolites were evaluated from nitrogen ad(de)sorption isotherms measured using ASAP 2020 (Micromeritics) static volumetric apparatus at -196 °C. Before the sorption measurements, all samples were degassed in a Smart Vac Prep instrument (Micromeritics) under vacuum at 250 °C (heating rate 1 °C/min) for 8 h. Specific surface area S_BET was evaluated by BET equation; the mesopore size (D_meso) was determined from the desorption branch of the isotherm, using the method of Barret-Joyner-Hallenda (BJH). The micropore volume (V_micro) and external surface area (S_ext) were determined by the comparative t-plot method. The adsorbed amount at relative pressure p/p₀=0.98 reflects the total pore volume. The mesopore volume (V_meso) was determined as the difference between the total pore volume and micropore volume. The concentration and type of acid sites in the products were determined by adsorption of pyridine as a probe molecule and observed by FTIR spectroscope Nicolet 6700 AEM (Thermo Fischer Scientific) equipped with DTGS detector, using the self-supported wafer technique. Prior to adsorption of the probe molecule, self-supported wafers of zeolite samples were activated in-situ by overnight evacuation at temperature 450 °C. Pyridine adsorption proceeded at 150 °C for 20 min at partial pressure 3 Torr, followed by 20 min evacuation at 150 °C. The concentrations of Bronsted and Lewis acid sites in aluminosilicate samples were calculated from integral intensities of individual bands characteristic of pyridine on Br0nsted acid sites at 1545 cm^-1 and band of pyridine on Lewis acid site at 1455 cm^-1 and molar absorption coefficients of ε(Β)=1.67±0.1 cm/μmol and ε(L)=2.22±0.1 cm/μmol, respectively.

The present invention is further illustrated by the following examples which should not be construed as further limiting. EXAMPLE 1

In Example 1, hierarchical Beta zeolite was prepared from the reaction mixture with SiO₂/Al₂O₃ molar ratio of 70 and H₂O/SiO₂ molar ratio of 20.

Tetraethylammonium hydroxide solution (40 wt. %, 6.42 g) and 0.57 g of hydrochloric acid (37 wt. %) were added to distilled water. Then 1.74 g of fumed silica (0.2-0.3 μm average particle size, aggregate) was added under vigorous stirring. After stirring for 30 min, 0.064 g of aluminum hydroxide (63.5 wt. % Al₂O₃) was added and the reaction mixture was stirred for 60 min. Then the reaction mixture was placed in a Teflon-lined stainless-steel autoclave and subjected to hydrothermal treatment at 140 °C for 7 days in static conditions. The product was then centrifuged and washed with 80 ml of distilled water (with portions of 20 ml) until the pH of filtrate was below 8, dried in an oven at 60 °C, and calcined in a furnace at 550 °C with a temperature rate 2 °C/min and with a heating time 5 hours.

The product obtained in Example 1 consists of Beta nanoparticles with size of 10 nm (calculation by the Scherrer's equation). Obtained product is characterized by following parameters of porous structure: V_micro = 0.15 cm³/g, V_meso = 0.60 cm³/g, D_meso = 9±1.3 nm, S_BET = 620 m²/g, S_ext = 290 m²/g. SiO₂/Al₂O₃ molar ratio in the product is 87. Bronsted acid sites concentration in the product is 0.10 mmol/g, Lewis acid sites concentration is 0.11 mmol/g.

EXAMPLES 2-5 In Examples 2 - 5, hierarchical Beta zeolites were prepared from reaction mixtures with the same SiO₂/Al₂O₃, molar ratio (70) and various H₂O/SiO₂ molar ratios.

Tetraethylammonium hydroxide solution (40 wt. %, 6.42 g) and 0.57 g of hydrochloric acid (37 wt. %) were added to distilled water. Then 1.74 g of fumed silica (0.2-0.3 μm average particle size, aggregate) was added under vigorous stirring. After stirring for 30 min, 0.064 g of aluminum hydroxide (63.5 wt. % Al₂O₃) was added and the reaction mixture was stirred for 60 min. Then obtained reaction mixture with H₂O/SiO₂ molar ratio of 20 was dried at 60 °C to H₂O/SiO₂ molar ratio in the mixture 15 (Example 2), 10 (Example 3), 5.5 (Example 4) and 3 (Example 5). Then the reaction mixture was placed in a Teflon-lined stainless-steel autoclave and subjected to hydrothermal treatment at 140 °C for 7 days in static conditions. The product then centrifuged and washed with 80 ml of distilled water (with portions of 20 ml) until the pH of filtrate was below 8, dried in an oven at 60 °C, and calcined in a furnace at 550 °C with a temperature rate 2 °C/min and with a heating time 5 hours. Particle size calculated by the Scherrer’s equation and characteristics of porous structure of the obtained products are shown in Table 1.

SiO₂/Al₂O₃ molar ratio and Bronsted and Lewis acid sites concentrations in the products (Examples 2-5) are shown in Table 2.

EXAMPLE 6

In Example 6, hierarchical Beta zeolite was prepared from the reaction mixture with SiO₂/Al₂O₃ molar ratio of 40 and H₂O/SiO₂ molar ratio of 20.

Tetraethylammonium hydroxide solution (40 wt. %, 6.42 g) and 0.57 g of hydrochloric acid (37 wt. %) were added to distilled water. Then 1.74 g of fumed silica (0.2-0.3 μm average particle size, aggregate) was added under vigorous stirring. After stirring for 30 min, 0.113 g of aluminum hydroxide (63.5 wt. % Al₂O₃) was added and the reaction mixture was stirred for 60 min. Then the reaction mixture was placed in a Teflon-lined stainless- steel autoclave and subjected to hydrothermal treatment at 140 °C for 7 days in static conditions. The product then centrifuged and washed with 80 ml of distilled water (with portions of 20 ml) until the pH of filtrate was below 8, dried in an oven at 60 °C, and calcined in a furnace at 550 °C with a temperature rate 2 °C/min and with a heating time 5 hours.

The product obtained in Example 6 consists of Beta nanoparticles with size of 18 nm (calculation by the Scherrer’s equation). Obtained product is characterized by following parameters of porous structure: V_micro = 0.25 cm³/g, V_meso = 0.22 cm³/g, D_meso = 31+8.0 nm, S_BET = 670 m²/g, S_ext = 125 m²/g. SiO₂/Al₂O₃ molar ratio in the product is 36. Bronsted acid sites concentration in the product is 0.30 mmol/g, Lewis acid sites concentration is 0.19 mmol/g.

EXAMPLES 7-10

In Examples 7-10, hierarchical Beta zeolites were prepared from the reaction mixtures with the same SiO₂/Al₂O₃ molar ratio (40) and various H₂O/SiO₂ molar ratios.

Tetraethylammonium hydroxide solution (40 wt. %, 6.42 g) and 0.57 g of hydrochloric acid (37 wt. %) were added to distilled water. Then 1.74 g of fumed silica (0.2-0.3 μm average particle size, aggregate) was added under vigorous stirring. After stirring for 30 min, 0.113 g of aluminum hydroxide (63.5 wt. % Al₂O₃) was added and the reaction mixture was stirred for 60 min. Then obtained reaction mixture with H₂O/SiO₂ molar ratio of 20 was dried at 60 °C to H₂O/SiO₂ molar ratio in the mixture 15 (Example 7), 10 (Example 8), 5.5 (Example 9) and 3 (Example 10). Then the reaction mixture was placed in a Teflon-lined stainless-steel autoclave and subjected to hydrothermal treatment at 140 °C for 7 days in static conditions. The product then centrifuged and washed with 80 ml of distilled water (with portions of 20 ml) until the pH of filtrate was below 8, dried in an oven at 60 °C, and calcined in a furnace at 550 °C with a temperature rate 2 °C/min and with a heating time 5 hours. Particle size calculated by the Scherrer’s equation and characteristics of porous structure of the obtained products (Example 7-10) are shown in Table 3.

SiO₂/Al₂O₃ molar ratio and Bronsted and Lewis acid sites concentrations in the products (Examples 7-10) are shown in Table 4.

EXAMPLES 11-14

In Examples 11-14, hierarchical Beta zeolites were prepared from the reaction mixtures with the same H₂O/SiO₂ molar ratio (20) and various SiO₂/Al₂O₃ molar ratios (Table 5). Tetraethylammonium hydroxide solution (40 wt. %, 6.42 g) and 0.57 g of hydrochloric acid (37 wt. %) were added to distilled water. Then 1.74 g of fumed silica (0.2-0.3 μm average particle size, aggregate) was added under vigorous stirring. After stirring for 30 min, the appropriate amount of aluminum hydroxide (63.5 wt. % Al₂O₃) according to the Table 3 was added and the reaction mixture was stirred for 60 min. Then the reaction mixture was placed in a Teflon-lined stainless-steel autoclave and subjected to hydrothermal treatment at 140 °C for 7 days in static conditions. The product then centrifuged and washed with 80 ml of distilled water (with portions of 20 ml) until the pH of filtrate was below 8, dried in an oven at 60 °C, and calcined in a furnace at 550 °C with a temperature rate 2 °C/min and with a heating time 5 hours. TABLE 5 SiO₂/Al₂O₃ molar ratio Aluminum _ in the reaction mixture hydroxide [g]

EXAMPLE 11 35 0.130

EXAMPLE 12 30 0.151

EXAMPLE 13 25 0.179

EXAMPLE 14 20 0.219

Particle size calculated by the Scherrer’s equation and characteristics of porous structure of the obtained products (Example 11-14) are shown in Table 6.

TABLE 6

Particle

V_micro D_meso S_BET Sext size

(cm³/g) (cm³/g) (nm) (m²/g) (m²/g)

(nm)

EXAMPLE 11 15 0.22 0.23 24+3.8 630 175 EXAMPLE 12 17 0.23 0.17 24+4.5 610 105 EXAMPLE 13 18 0.25 0.24 23+5.8 660 120 EXAMPLE 14 17 0.23 0.51 15+8.8 660 180 SiO₂/Al₂O₃ molar ratio and Br0nsted and Lewis acid sites concentrations in the products

(Examples 11-14) are shown in Table 7. TABLE 7 Bronsted acid sites Lewis acid sites SiO₂/Al₂O₃ concentration concentration

_ (mmol/g) _ (mmol/g)

EXAMPLE 11 33 0.28 0.20 EXAMPLE 12 27 0.42 0.23 EXAMPLE 13 24 0.36 0.22 EXAMPLE 14 22 0.34 0.23

Claims

1. A method for preparation of hierarchical Beta zeolites, said method comprising the following steps: a) contacting a monoquatemary structure-directing agent with aqueous solution of a protic acid, to form a first mixture with the molar ratio of the components: structure-directing agent : protic acid (expressed as moles of [H⁺]) : water = 0.55 - 0.65 : 0.15 - 0.25 : 20 - 25; b) adding a source of silica to the first mixture to form a second mixture having the molar ratio of the components: source of silica (SiO₂) : structure-directing agent : protic acid [H⁺] : water = 1 : 0.55 - 0.65 : 0.15 - 0.25 : 20 - 25; c) contacting the second mixture with a source of alumina to form a third mixture with the molar ratio: source of silica (expressed as SiO₂) : source of alumina (expressed as Al₂O₃) : structure- directing agent : protic acid [H⁺] : water = 1 : 0.005 - 0.05 : 0.55 - 0.65 : 0.15 - 0.25 : 20 - 25; d) optionally subjecting the third mixture to evaporation of water to achieve the molar ratio H₂O to SiO₂ within the range 3 to 19; e) processing the third mixture having the molar ratio H₂O to SiO₂ within the range 3 to 25 by hydrothermal treatment at 130 to 150 °C, under autogenic pressure for 6 - 10 days, to form the as-synthesized product; f) calcination of the as-synthesized product at temperatures ranging from 550 to 650 °C, with a heating time 4 - 8 hours.

2. The method according to claim 1, wherein the monoquatemary structure-directing agent is selected from tetraethylammonium hydroxide, methylpropylpyrrolidinium hydroxide, butylmethylpyrrolidinium hydroxide, methylpropylpiperidinium hydroxide and mixtures thereof.

3. The method according to any one of the preceding claims, wherein the protic acid is selected from hydrochloric acid, sulfuric acid, nitric acid and a mixture thereof.

4. The method according to any one of the preceding claims, wherein the source of silica is selected from fumed silica, colloidal silica, silicon dioxide nanopowder, AEROSIL®380 and mixtures thereof.

5. The method according to any one of the preceding claims, wherein the source of alumina is selected from aluminum hydroxide, aluminum nitrate nonahydrate, aluminum sulfate hexadecahydrate, aluminum isopropylate and mixtures thereof.

6. The method according to any one of the preceding claims, wherein in step b), the second mixture is stirred for 30 to 60 min.

7. The method according to any one of the preceding claims, wherein in step c), the third mixture is stirred for 60 to 90 min.

8. The method according to any one of the preceding claims, wherein in step d), the third mixture is dried at a temperature of 40 - 100 °C.