CS257252B2 - Process for preparing synthetic modified silica-based material - Google Patents

Abstract

The process for preparing a synthetic modified material based on silicon dioxide with a specific surface area greater than 150 m^/g of the general composition 0.0001 - 1 MnOm . 1 SiO2 in which Mn0,„ is an oxide of one or more metals used as chemical elements modifying silicon dioxide, is carried out in an aqueous, alcoholic or aqueous-alcoholic environment, whereby a silicon derivative is reacted with a derivative of the said modifying element in the presence of a substance with a clathrate-forming effect, and optionally in the presence of a mineralizing agent and an inorganic base. The mixture is allowed to crystallize in a closed environment at a temperature of 100 to 220 °C for up to 30 days, while it is cooled, filtered, washed, dried and calcined, which can be repeated if necessary. The products obtained have a crystalline structure, a large specific surface area and are porous, and are suitable as catalysts for a large number of different reactions.

Description

The invention relates to a method for preparing a synthetic modified material based on silica 2 with a specific surface area greater than 150 m/g.

As regards the prior art, a large number of types of amorphous silica with large or small specific surface areas are known, which can be obtained, for example, by known processes of gelation of silica sol or by precipitation and gelation of various silicates, see, for example, United States Patents Nos. 2,715,060, 3,210,273, 3,236,594 and 3,709,833.

In the United States Patent No. 3,983,055, for example, a synthetic amorphous silica with a pre-selected pore distribution and a method for its preparation are disclosed, in which an organic silicon derivative is hydrolyzed and then condensation polymerization and calcination are carried out. A large number of crystalline types of silica are known from practice, such as quartz, cristobalite, tridymite, keatite and many others, the preparation methods of which are described in detail in the technical literature. For example, in the Heidemann process, see Beitr. Min. Petrog 10, 242 (1964), it is possible to obtain by the reaction of amorphous silicon dioxide with 0.55 percent potassium hydroxide, which takes place at a temperature of 180 ° C for two and a half days, a crystalline silicon dioxide, called silica X, which has a specific surface area of about 10 m /g and low stability, this product passing into cristobalite and then into quartz within five days. Flanigen et al. report in Nature, 271, 512 (1978) a procedure for preparing crystalline silicon dioxide, or silica gel, with a large specific surface area, this product can be used for the purification of water polluted with organic substances due to its hydrophobic nature.

The object of the present invention is to modify the character of crystalline silica while maintaining its unchanged stability and thus to prepare a product which would be usable as a catalyst or which would be suitable for the preparation of catalysts.

Catalytic properties can be achieved in silica, for example, by imparting acidic properties to it. It is therefore a further object of the present invention to find a method for preparing crystalline modified silica with these properties.

The essence of the method for preparing a synthetic modified material based on silicon dioxide 2 with a specific surface area greater than 150 m /g of the general formula

0.0001 - 1 M 0 . 1 SiO• nm 2 in which M _n O _m is an oxide of one or more metals used as chemical elements modifying silicon dioxide, selected from the group comprising chromium, beryllium, titanium, vanadium, zinc, silver and boron, according to the said invention, consists in reacting, in an aqueous, alcoholic or aqueous-alcoholic solution, a silicon derivative based on silicon dioxide or tetraalkyl orthosilicate with a derivative of the said modifying element, which has at least partially amphoteric character, in the presence of a substance with a clathrate-forming effect selected from the group comprising tertiary amines, amino alcohols and quaternary ammonium bases NR^OH or NA^OH where R is an alkyl containing 1 to 5 carbon atoms and A is phenyl or alkylphenyl containing 1 to 5 carbon atoms in the alkyl part, optionally in the presence of a mineralizing agent selected from the group comprising hydroxides and halides of alkali metals and alkaline earth metals, to promote crystallization, and optionally in the presence of an inorganic base, the mixture being allowed to crystallize in a closed environment for up to 30 days at a temperature in the range of 100 to 200 °C, then cooled, filtered, washed, dried and calcined in air at a temperature in the range of 300 to 700 °C for 2 to 24 hours, then optionally washed with boiling distilled water containing an ammonium salt and finally calcined again under the same conditions as stated for the first calcination.

The substances obtained according to this process are characterized by a defined crystalline structure, as will be further described in connection with the attached figures, and have a large specific surface area, exceeding 150 m ² /g and typically reaching values of 200 to 500 m ² /g. The products obtained by the process according to the invention are also characterized by a porous structure with a pore diameter of 0.4 to 0.7 nm. Other metals can be added to the silica prepared in this way, containing a cation that is either a substitute for silicon or is capable of forming a polysilicic acid salt with silicon, which are capable of contributing to the special catalytic properties of these products. Examples of these metals include platinum, palladium, nickel, cobalt, tungsten, copper, zinc and others. The method by which these metals are added may be, for example, impregnation or any other known process using solutions of salts of the selected metals, for example, in a preferred embodiment, nitrates, acetates or oxides, and other compounds.

The synthetic silica-based materials obtained by the process according to the invention can be advantageously used as catalysts for a large number of reactions, for example for the alkylation of benzene, in particular the alkylation of benzene with ethylene and the alkylation of benzene with ethanol, with the following reactions being mentioned as further possible uses:

- alkylation of toluene with methanol to xylene, mainly p-xylene, - disproportionation of toluene to form mainly p-xylene,

- conversion of dimethyl ether and/or methanol or other (lower) alcohols to hydrocarbons, such as olefins and aromatics,

- cracking and hydrocracking,

- isomerization of normal paraffins and naphthenes,

- polymerization of compounds containing olefinic or acetylenic bonds,

- reforming,

- isomerization of polyalkyl-substituted aromatics such as o-xylene,

- disproportionation of aromatics, especially toluene,

- conversion of aliphatic carbonyl compounds into at least partially aromatic hydrocarbons,

- separation of ethylbenzene from other C _g aromatic hydrocarbons,

- hydrogenation and dehydrogenation of hydrocarbons,

- methanization,

- oxidation, especially of exhaust gases from combustion engines, >

- dehydration of oxygenated aliphatic compounds,

- conversion of olefins to high-octane fuels. ,

In a preferred embodiment of the process according to the invention, silica gel, tetraethyl orthosilicate or tetramethyl orthosilicate is used as the silicon derivative, and a nitrate, oxide, hydroxide, alkoxy derivative or salt of chromium, beryllium, titanium, vanadium, zinc and boron is used as the derivative of the modifying element.

Preferably, the mineralizing agent used in this process is lithium hydroxide, potassium hydroxide, sodium hydroxide, calcium hydroxide, potassium bromide, sodium bromide, sodium iodide, calcium iodide and calcium bromide, wherein the inorganic base compound is preferably selected from the group consisting of alkali metal and alkaline earth metal hydroxides. Most preferably, the inorganic base is potassium hydroxide, sodium hydroxide and calcium hydroxide.

• 1 . '

The above-mentioned inorganic basic compound and/or clathrate-forming agent is preferably used in an amount ranging from 0.05 to 0.5 mol per mol of silica in the preferred embodiment of the invention.

The new materials obtained by the process according to the invention, which will be referred to hereinafter as TRS substances, are composed of silicon dioxide modified with elements that can enter the crystal lattice either as a substitute for silicon or in the form of salts of polysilicic acids, depending on the nature and relative amount of the reactants.

•

Elements that can be used to obtain the above-mentioned modified silicas include all metal cations, with a preferred embodiment, as already mentioned, using elements that are at least partially amphoteric in nature, such as chromium, beryllium, titanium, vanadium, manganese, iron, cobalt, zinc, zirconium, rhodium, silver, tin, antimony and boron, in order to simplify the process.

The modified silicas obtained by the process according to the invention are characterized by the presence of a single crystalline phase and these substances correspond to a molar ratio of 0.0001 to 1 M _n O _m . 1 SiO ₂ , where M _n O _m is an oxide of one or more of the metals mentioned above.

The products obtained may contain a small amount of water, this amount of water depending on the calcination temperature. The products obtained by the process according to the invention have a very high thermal stability and are characterized by their composition, preparation method and crystalline structure, these characteristics will be described below, and also by a large specific surface area and acidity in the sense of the Lewis and Bronsted systems, which is adjustable depending on the nature of the cations introduced as a modifying element.

Since the modifying element has a predominant influence on the catalytic properties of silica, the addition of this element causes the formation of crystalline materials whose spectrum can be either very similar to that of silicalite or completely different, as is evident from Fig. 1 and Fig. 2 below.

The silicon oxides designated according to the invention TRS, modified by the addition of the elements mentioned, are characterized by their crystalline structure, their composition corresponding to the stated molar _{ratio of silicon dioxide and Mn} ^oxide , where this oxide is an oxide of a metal cation capable of entering the crystalline lattice of silicon dioxide as a substitute for silicon or as a salt of silicic acid or polysilicic acid. As already mentioned, depending on the calcination temperature, a greater or lesser amount of water may be present.

•

As already mentioned, a large number of various metal cations can be used to obtain the modified silica according to the invention, with preference being given to elements having an amphoteric character.

The process according to the invention can generally be carried out in the following manner. The silicon derivative is reacted in an aqueous, alcoholic or aqueous-alcoholic solution with a derivative of the modifying element and with a substance acting as a clathrate, and optionally one or more mineralizing agents are added to promote crystallization and optionally an inorganic base. The crystallization of the mixture is allowed to proceed in a closed environment for a period of from several hours to many days, at a temperature in the range from 100 to 220 ° C, preferably about one week at a temperature in the range from 150 to 200 ° C. The mixture obtained is then cooled, washed and collected on a filter. The calcination, which is carried out in air at a temperature in the range from 300 to 700 ° C, in a preferred embodiment at a temperature of about 550 ° C, takes place in the range from 2 hours to 24 hours. The product is then optionally washed to remove possible ion-exchangeable cationic impurities, for example with boiling distilled water containing dissolved ammonium salt, preferably acetate or nitrate, and the above-mentioned calcination is then repeated.

The silicon derivatives used as basic starting materials for the process according to the invention can be selected from the group comprising any silicon dioxide-based material, silica gel (regardless of its preparation method) and tetraalkyl orthosilicates, such as tetraethyl orthosilicate and tetramethyl orthosilicate.

Derivatives of the modifying element can be selected from the group comprising oxides, hydroxides and salts of alkoxy derivatives of the above-mentioned elements, with nitrates and acetates being particularly preferred salts.

Substances with clathrate-forming or archivolt-forming activity can be selected from the group comprising amines, amino alcohols, amino acids, polyalcohols and quaternary ammonium bases, such as tetraalkylammonium bases NR^OH, where R is an alkyl containing 1 to 5 carbon atoms, or tetraarylammonium bases NA^OH, where A is a phenyl or alkylphenyl radical containing 1 to 5 carbon atoms in the alkyl part.

The purpose of clathrate-forming substances is to provide a crystalline structure with pores of defined size, and therefore the substances specified above, which have relatively large molecules, are used.

The above-mentioned mineralizing additives may be hydroxides or halides of alkali metals or alkaline earth metals, which have already been specified.

The added inorganic base may be selected from the group comprising alkali metal or alkaline earth metal hydroxides and ammonia.

The products obtained are characterized by a protonic type acidity, which can be controlled by varying the introduced modifying cation. For pure silica, the number of milliequivalents of hydrogen ions is 1.10 per gram of sample. This acidity can be increased by introducing a modifying element in such an amount that the number of milliequivalents of hydrogen ions per gram of sample can reach approximately 5.10 ^-1 milliequivalents of hydrogen ions H ⁺ .

For carrying out certain catalytic reactions, it may be advantageous to reduce the acidity by introducing an alkaline substance in order to achieve a neutral or even basic product.

Depending on the metal (or metals) added, catalytic properties can be induced or improved in this silica, so that, for example, these substances can be used to carry out hydrogenation, hydration, hydrosulfurization, cracking, reforming, oxidation, isomerization, disproportionation, polymerization, etc., as already detailed above.

The silica-based materials prepared by the process of the present invention may be for catalytic reactions or dispersed on a support material which is more or less inert and which has a high or low specific surface area and porosity.

The carrier material has the task of increasing the physical stability and mechanical resistance and optionally the catalytic properties of the material. Any known preparation of these materials can be used for the preparation process of the active material with the carrier.

The amount of modified silica in the mixture with the carrier material may be 1 to 90% by weight, preferably 5 to 60% by weight.

Examples of suitable carrier materials include clays, silica, alumina, diatomaceous earths, silica and alumina, and other materials.

The attached figures relate to the embodiments according to the following examples, wherein Fig. 1 shows the diffraction X-ray pattern of a sample obtained by the process according to Example 1, Fig. 2 shows the diffraction X-ray pattern of a sample obtained by the process according to Example 2, Fig. 3 shows graphically the values relating to the alkylation of benzene with ethylene, wherein the molar amount of ethylbenzene formed in percent is a function of the reaction time in hours and the dashed line corresponds to 100% conversion of ethylene, and Fig. 4 shows graphically the values relating to the alkylation of benzene with ethanol, wherein the molar amount of ethylbenzene formed is a function of the time in hours and the dashed line corresponds to 100% conversion of ethanol. In the alkylations mentioned, the product prepared by the process according to the present invention was used as a catalyst.

In the following, practical examples of the implementation of the method according to the invention will be given, which are intended to illustrate this method in more detail without limiting it in any way.

Example

This example illustrates the preparation of porous crystalline silica, designated TRS-27, in which silicon has been replaced by beryllium in the crystal lattice.

According to this embodiment, 40 grams of tetraethyl orthosilicate (TEOS) was placed in a Pyrex glass vessel, which was constantly kept under a nitrogen atmosphere, and the resulting mixture was heated with stirring to a temperature of 80 °C. Then 100 milliliters of a 20% aqueous solution of tetrapropylammonium hydroxide (% by weight) were added and the mixture was then further stirred and heated until homogenous and clear, which took about 1 hour. At this stage, 4 grams of beryllium nitrate Be(NO ₃ > ₂ · 4H ₂ O) were added, which was dissolved in 80 milliliters of ethanol.

In the subsequent phase, a white precipitate formed rapidly, which was heated to boiling with stirring in order to remove all ethanol, i.e. both added and formed by hydrolysis.

This mixture was then made up to 150 milliliters with distilled water, after which the glass vessel was placed in an autoclave, where it was maintained for 17 days at a temperature of 155 ° C. After cooling, the resulting solid was centrifuged, which was carried out at a speed of 10,000 min ^-3 , the obtained cake was resuspended in distilled water and the centrifugation was repeated, this washing procedure was repeated four times. The obtained product was then dried in a drying oven at a temperature of 120 ° C. This product was analyzed by X-ray diffraction, and it was found to have a crystalline structure.

To completely remove the alkaline impurities contained in the compounds used, the product was calcined for 16 hours at 550°C in a stream of air, and the solid obtained was repeatedly washed with boiling distilled water containing dissolved ammonium acetate. Finally, the calcination was repeated, this time at 550°C for 6 hours.

A chemical analysis of the product was then performed, with the sample obtained having the following composition:

_SiO2 96.65% by weight

BeO 3.33% by weight

At ₂ 0 0.02% by weight.

The loss on annealing at 1100 °C was 4.1% by weight, the molar ratio of _SiO2 :BeO in the obtained product was 12, and the diffraction diagram is shown in Fig. 1. The concentration of hydrogen ions was 1.5.1032 milliequivalents/g and the specific surface area was 400 m2/g.

Example 1 and 2

This example will illustrate the preparation of crystalline silica designated TRS-28, into whose crystal lattice chromium was introduced as a modifying element.

According to this example, 40 grams of tetraethyl orthosilicate (TEOS) were placed in a glass vessel (Pyrex glass) maintained under a nitrogen atmosphere and then this substance was heated to a temperature of 80 ° C with stirring. In the next procedure, 20 grams of a 20% aqueous solution of tetrapropylammonium hydroxide were added and this mixture was then maintained at a temperature of 80 ° C with stirring until it was clear, which took about 1 hour. Then 4 grams of chromium nitrate Cr(NOj) ₃ ·9H ₂ O were added, which was dissolved in 50 milliliters of anhydrous methanol. Almost immediately a compact light ^- green gel was formed, to which 0.25 grams of potassium hydroxide, dissolved in 20 milliliters of water, was then added and the mixture was brought to a boil with constant stirring in order to complete the hydrolysis and remove the ethanol both added and formed by the hydrolysis. The latter phase was carried out over a period of 2 to 3 hours. The gel obtained then slowly transformed into a light green powder, which was a precursor of crystalline silica modified with chromium.

This substance was then made up to 150 milliliters with distilled water and the container was then placed in an autoclave at 155 °C for 13 days. After cooling the autoclave, the resulting solid was centrifuged for 15 minutes at 5,000 ^rpm , the resulting precipitate was washed four times by suspending in distilled water and then the product was dried at 120 °C.

The product thus obtained was X-ray crystalline.

In order to remove the last traces of alkaline impurities contained in the product thus obtained, this product was calcined for 16 hours at a temperature of 550 °C in a stream of air, after which the solid was repeatedly washed by suspending it in boiling distilled water containing dissolved ammonium acetate. The final step was calcination, which was carried out at a temperature of 550 °C for 6 hours.

Chemical analysis of the obtained product revealed the following composition:

SiO ₂ 93.78% by weight

_Cr2O2 6.22% by _weight .

The loss on annealing at 1100 °C was 3.5% by weight, with a molar ratio of _Si02 : _Cr203 in this product of _38. This sample was X-ray crystalline, the X-ray diffraction pattern of which is shown in Fig. 2. The proton concentration in this sample was “3 + 2

5.8.10 milliequivalents H/g and the specific surface area was 380 m/g.

Example 3

This example will illustrate the preparation of porous crystalline silica, designated TRS-66, into the crystal lattice of which zinc has been introduced.

According to this example, 40 grams of tetraethylorthosilicate were placed in a glass vessel (made of Pyrex glass) kept under a carbon dioxide-free atmosphere, and then a solution of 4 grams of zinc nitrate Ζη(ΝΟ ₃ ) ₂ ·Η ₂ Ο in 40 milliliters of ethanol (95%) was added with stirring. Then a solution of 20 grams of tetrapropylammonium hydroxide was added with stirring and the mixture obtained was heated until a homogeneous and compact gel was formed. This gel was then crushed and water was added in which 2 grams of potassium bromide were dissolved, obtaining a suspension which was heated with stirring until all the ethanol present (that is, both added and formed by hydrolysis) had evaporated. This mixture was then made up to 150 milliliters with distilled water and the mixture was transferred to a glass container (made of Pyrex glass), which was then placed in an autoclave and left in this autoclave for 6 days at a temperature of 197 °C.

After cooling, the resulting solid was collected on a filter, then washed until the basic reaction completely disappeared and dried at 120° C. X-ray diffraction showed the product to be crystalline.

In order to completely eliminate the alkaline impurities present in the said substance, this product was calcined in a stream of air at a temperature of 550 °C for 16 hours and then repeatedly washed with boiling distilled water with dissolved ammonium acetate, after which the obtained solid was calcined for 6 hours at a temperature of 550 °C.

The following values were found by chemical analysis of the obtained product:

SiO ₂ 91.68% by weight

ZnO 8.30% by weight

_K2O 0.02% by weight.

For this sample, the loss on annealing at 1,100 °C was 3.7% by weight, the molar ratio of SiO ₉ /ZnO was 15.0, the hydrogen ion concentration was 2.2.10 milliequivalents/g ^of Zn 2 and the specific surface area determined by the BET method (Brunauer, Emmett, Teller) was 380 m /g.

Attached

This example will illustrate the preparation of crystalline silicon dioxide designated TRS-42, into whose crystal lattice beryllium was introduced as a modifying element.

In carrying out the procedure according to this example, the same procedure was followed as in Example 1, using 83 grams of tetraethyl orthosilicate, 59.6 grams of triethanolamine, 1.1 grams of beryllium nitrate Be(NO3) _2.4H2O and 2 grams _of sodium hydroxide.

This mixture was then made up to 200 milliliters with distilled water, placed in an autoclave and left in this autoclave for 6 days at a temperature of 200 °C.

After drying at 120 °C, the product obtained was X-ray crystalline. Chemical analysis of the product, which was calcined at 550 °C for 4 hours, revealed the following values:

SiO 99.56% by weight

BeO 0.41% by weight

At ₂ 0 0.03% by weight.

For the product thus obtained, the loss on annealing at a temperature of 1,100 °C corresponded to 3.5% by weight, the ~3 molar ratio of SiO^iBeO corresponded to 100, the hydrogen ion concentration was 1.2.10 meq./g ^of 2 and the specific surface area, determined by the BET method, was 380 m /g.

Example 5

This embodiment example will illustrate the process of preparing porous crystalline silicon dioxide designated TRS-45, into the crystal lattice of which boron has been introduced as a modifying element.

In this example, the same procedure as in Example 1 was followed, with 30.5 grams of tetramethyl orthosilicate, 14.6 grams of triethyl borate and 60 milliliters of water being added to the reaction, and the mixture was then heated to boiling for 1 hour. Then 6 grams of tetrapropylammonium hydroxide were added. After this addition, a gel was immediately formed, which was crushed and suspended in water, and 2 grams of potassium hydroxide were then added to the suspension obtained. This boiling suspension was then stirred for 20 hours and then transferred to an autoclave, where it was left for 6 days at a temperature of 175 ° C.

The product thus obtained, dried at 120°C, was X-ray crystalline.

After annealing at 550 °C for 5 hours, the following chemical composition was found:

SiO ₂ 77.84% by weight

BjOj 22.14% by weight

K ₂ 0 0.02% by weight.

The loss on ignition at 1,100 °C for this product was 3.8% by weight, the molar ratio of SiO ₂ :B ₂ O ₃ was 4, and the specific surface area, determined by the BET method, was 410 m /g.

Example

This example will illustrate the preparation of porous crystalline silica designated TRS-64, into whose crystal lattice titanium was introduced as a modifying element.

In this example, the same procedure was followed as in Example 1, whereby 40 grams of tetraethyl orthosilicate, 10 grams of tetraethyl orthotitanate (separately hydrolyzed with water and boiled in 100 milliliters of 30% hydrogen peroxide until a clear yellow-orange solution was obtained), 20 grams of tetrapropylammonium hydroxide (10% aqueous solution) and 2 grams of potassium bromide were added to the reaction. This mixture was left in an autoclave at 145°C for 10 days. The product thus obtained was X-ray crystalline after drying at 120°C. After calcination at 550°C for 4 hours, a chemical analysis of the product was carried out, and the following composition was found:

_SiO2 96.74% by weight

_TiO2 3.24% by weight

K ₂ 0 0.02% by weight.

The loss on ignition at 1,100 °C for this sample was 3.9% by weight, the molar ratio of

SiO ₂ :TiO ₂ corresponded to 3, the specific surface area, determined by the BET method, was 430 m /g.

Example7

This embodiment example will illustrate the preparation of porous crystalline silica designated TRS-48, into the crystal lattice of which vanadium has been introduced as a modifying element.

In this example, the same procedure was followed as in Example 1, whereby 8 grams of ammonium vanadate NH4VO4 was reacted with 200 milliliters of water containing 20 grams of tetrapropylammonium hydroxide and the mixture was then heated until the solids were completely dissolved. 88 grams of tetramethyl orthosilicate was then added and the gel obtained was then suspended in water to form a suspension which was treated for several hours at boiling. After adding 0.25 grams of potassium hydroxide, the mixture was placed in an autoclave and left there for 6 days at a temperature of 175 °C.

The product thus prepared was X-ray crystalline after drying at 120 °C. Chemical analysis of this product after annealing at 550 °C for 4 hours revealed the following results:

_SiO2 84.83% by weight,

V ₂ O ₅ 15.16% by weight,

_K2O 0.01% by weight.

The loss on ignition of this product at a temperature of 1,100 °C was 3.7% by weight, the molar ratio of SiO ₂ :V ₂ O 2 was 17, and the specific surface area, determined by the BET method, was 410 m 2 /g.

Example 8

This example will illustrate the preparation of porous crystalline silica designated TRS-41, into whose crystal lattice beryllium was introduced as a modifying element.

In this example, the same procedure was followed as in Example 1, except that 38 grams of 30% silica sol was used instead of tetraethyl orthosilicate, and the other reactants and reaction conditions were unchanged.

The product thus obtained was X-ray crystalline after drying at 120 °C. The chemical analysis of this product, which was carried out after annealing at 550 °C for 5 hours, revealed the following values:

_SiO2 96.66% by weight,

BeO 3.32% by weight,

_K2O 0.02% by weight.

The loss on ignition at 1100°C was 3.7% by weight for this product, the _SiO2 /BeO molar ratio was 12, and the properties of this product were the same as those of the product prepared according to Example 1.

Examples 9-12

In these examples, the same procedure was followed as in Example 6, with the difference that the silicon source used was colloidal silicon dioxide containing 40% by weight of SiO ₂ , and no potassium bromide was added.

The following table shows both the molar ratios of the starting reactants (expressed as SiO:TiO ratios) and the amount of tetrapropylammonium cation (expressed as the ratio RN ⁺ :SiO ₂ ).

The modified silica thus obtained can be characterized by the molar fraction of titanium dioxide contained therein, the chemical composition, expressed in weight percentage, and also the specific surface area.

In addition, the table below shows the ratio of the absorbances of the infrared band at 950 cm ^-1 (titanium) and the infrared band at 800 cm"^ (silicon). The value of the ratio decreases with decreasing titanium dioxide content, i.e. with decreasing value of its molar ratio, since titanium dioxide replaces silicon dioxide in its crystal lattice structure.

Table

Example 9 10 11 12 SiOj/TiOj ratio (reaction components) 5 30 65 130 Ratio RN ⁺ /SiO ₂ (reaction components) 0.89 0.80 0.75 0.70 Product: molar ratio of titanium dioxide TiO ₂ 0.017 0.012 0.0080 0.005 SiO (% by weight) 97.75 98.40 98.94 99.33 ' _TiO2 (% by weight) 2.25 1.60 1.06 0.67 loss on ignition at 1100 °C 2.80 3.00 3.20 2.90 specific surface area (m/g) 110 390 420 380 ratio of band intensities at 950 and 800 cm’·'' in the infrared spectrum 0.61 0.35 0.21 0.15

Example 13

This example will illustrate the utility of a synthetic modified silica-based material prepared by the process of the present invention for catalytic purposes.

In this example, the catalyst designated TRS-28 (product prepared according to the procedure of Example 2) was used for the alkylation of benzene with ethylene. 1 milliliter of the above catalyst was used for the alkylation of benzene with ethylene, which was carried out in a fixed bed reactor.

The reaction was carried out under the following conditions:

a) space velocity of the liquid phase 14 h ¹ molar ratio benzene : ethylene 7.5 temperature 440 °C pressure 2 MPa

b) space velocity of the liquid phase 2 h ' molar ratio benzene : ethylene 7.5 temperature 400 °C pressure 4 MPa

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The products obtained were analyzed by gas chromatography, the results according to the above embodiments a) and b) are shown in Fig. 3, where the molar percentages of ethylbenzene are plotted as a function of the reaction time in hours. The dashed line corresponds to 100% ethylene conversion.

Example 14

This example will illustrate the utility of the product obtained by the process of the present invention as a catalyst for alkylation reactions.

In this example, the catalyst designated TRS-28 (product prepared according to the procedure of Example 2) was used for the alkylation of benzene with ethanol. 1 milliliter of the catalyst was used for the alkylation of benzene with ethanol, which was carried out in a fixed bed reactor.

The reaction was carried out under the following conditions:

space velocity of the liquid phase 10 h ^-1 molar ratio CgHg/C ₂ HgOH 5 temperature 440 °C pressure 2 MPa.

The obtained products were analyzed by gas chromatography. Fig. 4 shows the dependence of the molar content of ethylbenzene in percent, which is contained in the reaction product, on the reaction time in hours. The dashed line corresponds to 100% ethanol conversion.

Claims (7)

A process for preparing a synthetic modified silica-based material having a specific surface area greater than 150 m / g of composition 0.0001 - 1 MO. 1 SiO, nm 2 wherein M _n O _m is the oxide of one or more metals used as the chemical modifying silicon dioxide selected from the group consisting of chromium, beryllium, titanium, vanadium, zinc and boron, characterized in that an alcoholic or aqueous-alcoholic solution reacts a silica derivative of silicon dioxide or tetraalkyl orthosilicate with a derivative of said modifying element having at least partially amphoteric character, in the presence of a clathrating agent selected from tertiary amines, aminoalcohols, and quaternary ammonium bases NR 4 OH or NA 4 OH, wherein R is a C 1 -C 5 alkyl group and A is a phenyl or C 1 -C 5 alkylphenyl group, optionally in the presence of a mineralizing agent selected from the group consisting of alkali hydroxides and halides metals and alkaline earth metals, pr to promote crystallization, and optionally in the presence of an inorganic base, wherein the mixture is left to crystallize in an enclosed environment for up to 30 days at a temperature ranging from 100 to 220 ° C, then cooled, filtered, washed, dried and calcined in air at in the range of 300 to 700 ° C for a time in the range of 2 to 24 hours, then optionally washing with boiling distilled water containing the ammonium salt and finally annealing again with the same aforesaid for the first calcination. 2. The method of claim 1, wherein the silicon derivative is a silica gel, tetraethyl orthosilicate or tetramethyl orthosilicate. 3. The process of claim 1 wherein the modifying derivative is a nitrate, oxide, hydroxide, alkoxy derivative or a salt of chromium, beryllium, titanium, vanadium, zinc, and boron. 4. The process of claim 1 wherein the mineralizing agent is lithium hydroxide, potassium hydroxide, sodium hydroxide, calcium hydroxide, potassium bromide, sodium bromide, sodium iodide, calcium iodide, and calcium bromide. 5. The process of claim 1 wherein the inorganic base is selected from the group consisting of alkali and alkaline earth metal hydroxides and ammonia. 6. The process of claim 5 wherein the inorganic base is potassium hydroxide, sodium hydroxide, and calcium hydroxide. 7. A method according to claim 1, characterized in that the amount of the inorganic basic compound and / or klatrátotvorného agent is from 0.05 to 0.5 mol per mol of SiO ₂ · 3 drawings