GB2102779A - Crystalline gallosilicate - Google Patents

Abstract

A crystalline gallosilicate having the chemical composition, in terms of mole ratios of oxides:- 0.9 + 0.25 M2/nO:Ga2O3:1 to 6 SiO2:zH2O in which M represents a cation of valence n and z has a value of from 0 to 50, and an X-ray powder diffraction pattern characterised by the lines substantially as set forth in Table 1.

Description

SPECIFICATION A novel crystalline gallosilicate and its use as a catalyst or a catalyst support The present invention relates to a novel crystalline gallosilicate and the use of such a crystalline gallosilicate as a conversion catalyst or as a catalyst support.

Crystalline aluminosilicates, or zeolites, occur both naturally and also as a result of crystallising gels containing aluminium and silicon oxides. Examples of crystalline gallosilicates useful in catalytic applications have also been disclosed; for example US Patent No 3431219 discloses the preparation of a gallosilicate having the same crystal structure as the mineral faujasite or the synthetic zeolite Y.

We have now synthesised a novel crystalline gallosilicate having the same crystal structure as the natural mineral aluminosilicate analcite.

Accordingly the present invention provides a crystalline gallosilicate having the chemical composition, in terms of mole ratios of oxides: 0.9 + 0.25 M2/,O : Ga2O3 1 to 6 SiO2: zH2O in which M represents a cation of valence n and z has a value of from 0 to 50, and an X-ray powder diffraction pattern characterised by the lines substantially as set forth in Table 1 hereinafter.

A preferred crystalline gallosilicate has the chemical composition in terms of mole ratios of oxides as follows: 0.9 + 0.25 M2/n : Ga2O3:1.5 to 3.0 SiO2 : 2 to 3 H2O The gallosilicate may suitably be produced by mixing a source of silicon, a source of gallium, a source of alkali metal and water, and maintaining the mixture under conditions of elevated temperature and pressure for a time such that crystallisation occurs.

Suitable sources of silicon include, for example, sodium silicate, silica hydrosol, silica gel, silica sol and silicic acid. The preferred source of silica is an aqueous colloidal dispersion of silica particles. A suitable commercially available source of silica is LUDOX Colloidal Silica manufactured by Du Pont (LUDOX is a Registered Trade Mark).

Suitable sources of alkali metal include metal hydroxides and oxides. Preferably the alkali metal is sodium.

Suitable sources of gallium include inorganic salts, such as the nitrate, chloride and sulphate, and the oxide or hydroxide. The preferred source of gallium is the oxide (Ga2O3).

It will be appreciated that each source of silicon, gallium and alkali metal may be supplied by one or more initial reactants and then mixed together in any order. For example sodium silicate is a source of both sodium and silicon.

The source of silicon, the source of gallium, the source of alkali metal and water may be mixed together in quite wide proportions. Suitably the composition of the mixture in terms of mole ratios of oxides may fall within the following ranges: SiO2 : Ga203 from 2:1 to 20:1 M2/nO : Ga203 from 1 :5to 20:1, and H2O :Ga203 from 1:1 to 500:1.

Suitably the mixture may be maintained at an elevated temperature in the range 100 to 200"C, prefer ably from 140 to 180"C. However, as is well known in the art the use of particularly advantageous conditions, such as seeding, ie the introduction of a small amount of the desired crystalline gallosilicate from a previous batch, may allow the use of lower temperatures if so desired. The mixture may be maintained at a pressure in the range from autogenous, ie the pressure generated within a closed reactor at the particular temperature employed, to 25 bars, preferably from autogenous to 10 bars, even more preferably autogenous. Pressures above autogenous pressure may be achieved for example by pressurising with a suitable gas, eg nitrogen.The mixture may suitably be maintained underthe aforesaid conditions for a time not less than 4 hours, preferably at least 20 hours. Generally a time of about 60 hours will be found suitable, though times up to and in excess of 7 days may be employed.

The mixture may suitably be maintained underthe aforesaid conditions within a closed vessel capable of withstanding the elevated pressure generally employed. Furthermore the mixture is preferably agitated during crystalline of the gallosilicate. The crystalline gallosilicate so-produced is preferably separated from the mother liquid by filtration, though other methods of recovery may be employed if so desired. After recovery the gallosilicate is preferably washed, suitably with water, at a temperature in the range, for example, of from 15 to 950C and dried at a temperature in the range 100 to 250"C for 8 hours to 24 hours. As will be readily apparent to persons skilled in the art milder conditions may be employed if so desired; for example drying may be effected at room temperature under vacuum.

As prepared by the method hereinbefore described the crystalline gallosilicate has a skeletal structure which is made up of a three-dimensional network of Si04 and GaO4 tetrahedra corner-linked to each other by shared oxygen atoms. There are no unshared oxygen atoms in the frame-work, so that the ratio of the total number of gallium and silicon atoms (Ga + Si) to the number of oxygen atoms is 1:2 and the negative charges created by the replacement of Si(lV) atoms by Ga(lll) atoms are neutralised by an electrochemical equivalent of cations. In the gallosilicate produced by the aforesaid method these cations (M) are generally alkali metal cations.The crystalline gallosilicate of the present invention has a characteristic X-ray powder diffraction pattern in which the significant lines in the range 4to 32" theta are given in the foilowing Table 1.

TABLE 1 Interplanar Relative 20 Value Spacing d(A) lntensity 15.28t2" 5.8i0.5 W 15.68i20 5.65+0.5 S 17.96 +2 4.9+0.5 W 18.14+2 4.9rut0.5 W 24.09+2 3.7+0.5 W 25.80+2 3.45+0.5 S 30.36+2 2.90.5 M 31.76~2 2.8+0.5 W The values in Table 1 were determined using stan dard techniques.The radiation was the K-alpha doublet of copper and a scintillation counter spec trometer with a strip chart pen recorder was used.

The peak heights, I, and the positions as a function of 2 theta, where theta is the Bragg angle, were read from the spectrometer chart. From these relative intensities 100 x Illo, where loins the intensity of the strongest line or peak, and d, the interplanar spacing in A corresponding to the recorded lines or peaks, were calculated. In the Table, the relative intensities of the peaks are given in terms of the symbols S =strong, M =medium and W = weak.

The crystalline gallosilicates ofthe present invention may be used as catalysts or as catalyst supports.

The catalytic properties of the crystalline gallosilicate can be modified by partial or complete replacement of alkali metal cations generally present in the as-synthesised gallosilicate by other cations.

Examples of suitable cationic forms of the crystalline gallosilicate are those in which the cation M is the hydrogen ion, the ammonium ion or a cation of one or more metals belonging to Groups IB, IIB, IIIA, IVA, VA or VIII of the Periodic Table of the Elements as published in the Handbook of Chemistry and Physics. Particularly preferred forms are those in which the cation M is the hydrogen ion, the ammonium ion or a cation of one or more of the rare earth metals, copper, silver, zinc, gallium, aluminium, indium, thallium, lead, antimony, bismuth, iron, cobalt, nickel, manganese, ruthenium, thorium, rhodium, palladium, iridium and platinum. The gallosilicate may contain a mixture of the cations (M) provided that the electroneutrality of the solid is preserved. The various cationic forms may be produced by ionexchanging the gallosilicate.Ion-exchange is a well known technique which usually involves contacting the material to be exchanged at ambient temperature or above with a solution containing the desired cations.

Alternatively, or in addition, the aforesaid metals may be incorporated in and/or on, the gallosilicate by other methods, such as by impregnation. The gallosilicate may thus be impregnated with an aqueous solution of a compound of the desired metal and the impregnated mass thereafter calcined to produce the metal oxide 'in situ' deposited in the interstices and/or on the surface of the gallosilicate structure.

The compounds of the metals used are suitably those compounds which will decompose on the application of heat to form the corresponding oxides and which are soluble in water, eg the nitrates or chlorides. The impregnated gallosilicate preferably contains from 0.1 to 5.0% by weight of the metal or metals.

Furthermore the crystalline gallosilicate may be admixed with another support material such as silica, alumina, thoria, titania etc., or a zeolite or another gallosilicate.

Before catalytic use it is preferred to activate the crystalline gallosilicate, suitably by heating in air at a temperature in the range 400 to 700"C for a period of from 2 to 48 hours.

The X-ray diffraction pattern disclosed in Table 1 is characteristic of all samples of the crystalline gal losilicate. Some minor shifts in interplanar spacing and variations in relative intensity may occur as the cation (M) is varied or as a result of activation, but overall the pattern remains substantially the same.

The crystalline gallosilicates of the present invention may be used as catalyst or catalyst supports in a wide range of chemical reactions. Examples of such reactions are (i) cracking and hydrocracking, (ii) disproportion of toluene to produce xylene, (iii) reforming, (iv) isomerisation, and (v) methanation. In particularthe rhodium and/or palladium impregnated and/or exchanged gallosilicate may suitably be used as catalyst in the conversion of synthesis gas to simple organic compounds, eg ethanol, and the cobalt, ruthenium, nickel or iron impregnated gallosilicate may be used as catalyst in the conversion of synthesis gas to hydrocarbons.

The invention will now be more particularly described by reference to the following Examples.

Example 1 Gallium oxide (delta Ga203, 3.92g) was dissolved in a solution of sodium hydroxide (6.67 g) in deionised water (50 ml) by warming. this solution was then added, with stirring, to Ludox silica sol Grade AS40 (37.5 g, containing 40% wt/wt silica). After rapid stirring at room temperature for 20 minutes, the whole was placed in a stainless steel autoclave and heated at 170"C for 72 hours. The crystalline product was filtered off. It had an X-ray powder diffraction pattern in the range 2 theta = 4 -32 as shown in Table 2. The X-ray diffraction pattern was obtained in the manner hereinbefore described. In Table 2 the relative intensities of the peaks, 1001/lois expressed in figures rather than symbols.Analysis by X-ray fluorescence indicated that it contained 22% silicon by weight, 24% gallium by weight and 6.8% sodium by weight.

Example 2 The method of Example 1 was followed except that the source of silica was Ludox HS40 and the whole was heated to 170"C for 80 hours. The crystalline product obtained had an X-ray powder diffraction pattern in the range 2 theta = -32"substantially the same as that shown in Table 2 and a similar chemical composition.

Table2

Relative Interplanar intensity 20 value spacing dtA) 100 1/lo 15.28 5.8 5 15.68 5.65 98 17.96 4.9 5 18.14 4.9 9 24.09 3.7 4 25.80 3.45 100 30.36 2.9 37 31.76 2.8 7

Claims (1)

1. A crystalline gallosilicate having the chemical composition, in terms of mole ratios of oxides 0.9 + 0.25 M2/,O : Ga202 1 to 6 Six2: zH2O in which M represents a cation of valence n andz has a value of from 0 to 50, and an X-ray powderdiffrac- tion pattern characterised by the lines substantially as set forth in Table 1.

2. A crystalline gallosilicate according to claim 1 wherein the chemical composition in terms of mole ratios of oxides is: 0.9 + 0.25 M2/,O:Ga203: 1.5 to 3.0 SiO2:2 to 3H20

3. A crystalline gallosilicate according to either claim 1 or claim 2 wherein the cation M is an alkali metal cation.

4. A crystalline gallosilicate according to either claim 1 or claim 2 wherein the cation M is a hydrogen ion, an ammonium ion or a cation of one or more metals belonging to Groups IB, lIB, IIIA, IVA, VA orVIll of the Periodic Table of the Elements.

5. A crystalline gallosilicate according to claim 4 wherein the cation M is a hydrogen ion.

6. A crystalline gallosilicate according to claim 4 wherein the metal is a rare earth metal, copper, silver, zinc, gallium, aluminium, indium, thallium, lead, antimony, bismuth, iron, cobalt, nickel, manganese, ruthenium, thorium, rhodium, palladium, iridium and platinum.

7. A process for the production of a crystalline gallosilicate as claimed in any one of the claims 1 to 6 which process comprises mixing a source of silicon, a source of gallium, a source of alkali metal and water and maintaining the mixture under conditions of elevated temperature and pressure for a time such that crystallisation occurs.

9. A process according to either claim 7 or claim 8 wherein the conditions of elevated temperature and pressure are a temperature in the range 100 to 200"C and autogenous pressure.

10. A process according to any one of claims 7 to 9 wherein the crystalline gallosilicate is impregnated with a compound of one or more of the rare earth metals, copper, silver, zinc, gallium, aluminium, indium, thallium, lead, antimony, bismuth, iron, cobalt, nickel manganese, ruthenium, thorium, rhodium, palladium, iridium and platinum.

11. A process according to any one of claims 7 to 10whereinthe crystalline gallosilicate is activated by heating in air at a temperature in the range 400 to 700"C for a period of from 2 to 48 hours.

12. A process for the production of a crystalline gallosilicate substantially as hereinbefore described with reference to Examples 1 and 2.

13. Crystalline gallosilicates whenever prepared by a process as claimed in any one of claims 7 to 12.

14. A crystalline gallosilicate substantially as hereinbefore described with reference to Examples 1 and 2.