Zeolites containing gallium in their crystalline framework structure are prepared by treating a zeolite material with a reagent capable of replacing a part of the aluminum of the framework structure of the zeolite material with the gallium. The method is especially applicable for the preparation of faujasitic materials of the formula EQU M.sub.(x+y/n) [ALO.sub.2 ].sub.x [GaO.sub.2 ].sub.y [SiO.sub.2 ].sub.z wherein: PA1 M is a charge balancing ion and n is the oxidation state thereof, PA1 x, y and z are the respective numbers of tetrahedra represented respectively by AlO.sub.2, GaO.sub.2 and SiO.sub.2, PA1 x+y+z=192, for a said faujasitic structure with no missing tetrahedra, PA1 x+y is from 0.1 to 71 inclusive, and PA1 y is from 0.01 to 60 inclusive.

FIELD OF THE INVENTION 
This invention relates to crystalline aluminosilicate zeolites containing 
gallium, their preparation and to catalyst compositions containing them. 
It relates further to hydrocarbon conversion with such catalysts and in 
particular to their use in FCC processing. 
BACKGROUND OF THE INVENTION 
A zeolite may be described generally as a crystalline, three dimensional, 
stable structure enclosing cavities of molecular dimensions. 
Zeolites can be natural or synthetic in origin. Naturally occurring 
zeolites include gmelinite, chabazite, dachiardite, clinoptilolite, 
faujasite, heulandite, analcite, levynite, erionite, sodalite, cancrinite, 
mepheline, lazurite, scolecite, natrolite, offretite, mesolite, mordenite, 
brewsterite and ferrierite. Synthetic zeolites include the zeolites 
A,B,E,F,H,J,L,Q,T,W,X,Y,Z,N-A, beta, omega, rho, the EU types, the Fu 
types, the Nu types, the ZK types, the ZSM types, the ALPO. types, the 
SAPO types, the pentasil types, the LZ series, and other similar 
materials. 
These crystalline zeolitic materials contain well-defined microporous 
systems of channels and cages. Because the dimensions of these pores are 
frequently such as to permit adsorption of molecules up to a certain size, 
with exclusion of larger molecules, zeolites are sometimes referred to as 
molecular sieves. 
Most zeolites are based on aluminosilicate frameworks, the aluminum and 
silicon atoms being tetrahedrally coordinated by oxygen atoms. 
More particularly, these aoluminosilicates are three dimensional networks 
of SiO.sub.4 and AlO.sub.4 tetrahedra which are linked by sharing of 
oxygen atoms to give an overall atomic ratio (Si+Al)/O=2. Each AlO.sub.4 
unit introduces a single negative charge which must be balanced by an 
appropriate cation content. When the charge on AlO.sub.4 is balanced by 
hydrogens or by polyvalent cations such as Ca.sup.2+, Mg.sup.2+ and 
particularly by rare earth cations, zeolites possess acidic properties and 
can function as acid catalysts for various types of hydrocarbon 
conversion. 
In some zeolites, atoms of other elements, such as boron, germanium, 
chromium, iron, phosphorous and gallium, are present in the framework of 
the crystalline structure. They may be present either in the original 
zeolite or be introduced into it. 
The terms "zeolite" and "zeolitic structure" used hereinafter include 
similar materials in which atoms of such other elements are present in the 
framework. Further, they include materials such as pillared interlayered 
clays ("PILCS"), which have many of the catalytically valuable 
characteristics of the aluminosilicate zeolites. We also include all 
modifications to the above materials, whether obtained by ion-exchange, 
impregnation, hydrothermal or chemical treatments, as later described. 
The acid properties of zeolites have been widely utilised in the production 
of gasoline by the cracking of oil fractions, particularly of gas oil, 
using FCC technology. 
The initial activation of pure hydrocarbons in general by zeolites is still 
a matter of discussion and both ionic and radical intermediates and also 
dehydrogenation processes have been proposed in the initial activation. 
However, the typical product distributions at higher conversion of 
hydrocarbons over strongly acid zeolites are consistent with carbocation 
chemistry involving among other reactions typical 8-scission, alkylation, 
cyclisation and bimolecular hydrogen-transfer processes. The optimal 
balance of these processes can lead to optimal amounts and quality of 
gasoline. 
Typically, in FCC technology, wide-pore zeolites having the faujasitic 
structure (X or Y zeolites) have been employed but improvements have been 
achieved by including in the catalyst composition other additional 
zeolites, including medium pore zeolites of the ZSM-5 family, or by adding 
molecular sieves based on AlO.sub.4, PO.sub.4 and SiO.sub.4 tetrahedra 
(e.g. SAPO-37). Various modifications of zeolite Y, including 
ion-exchange, hydrothermal treatment and chemical treatment have provided 
improved catalysts. Hydrothermal treatments and some chemical treatments 
result in replacement of some of the framework AlO.sub.4 by SiO.sub.4 
tetrahedra. 
A chemical treatment, applicable to a wide range of zeolites, for replacing 
some of the framework AlO.sub.4 by SiO.sub.4 tetrahedra is described in 
EP-A-0082211. In this process a zeolite, especially zeolite Y and 
preferably in ammonium form, is reacted with an aqueous solution of a 
fluorosilicate salt, especially ammonium silicon hexafluoride. This 
results in a range of faujasitic structures known as the LZ series. 
Such processes can modify the strength and number of the catalytically 
active acid sites and are associated with a decrease in the unit cell 
parameter of the zeolite Y as described in more detail below. The activity 
and selectivity of FCC catalysts can be correlated to the unit cell 
parameter of the zeolite; see Pine, LA and et al, J. Catalysis (1984), 85, 
466. A cell parameter less than that of a typical Y zeolite has been found 
to be advantageous. 
The incorporation of gallium into various zeolite catalysts is known to 
change their behaviour. 
Thus, U.S. Pat. No. 4,377,504 and U.S. Pat. No. 4,415,440 describe the 
impregnation of a zeolite catalyst (of unspecified type), contaminated 
with metals such as vanadium and iron, with gallium. This restores the 
selectivity of the contaminated catalyst. In such catalysts the gallium is 
merely present as a component of a catalyst mixture. 
EP-A-0147111 teaches impregnation and/or ion exchange for introduction into 
zeolite catalysts suitable for cracking of ethane rich low hydrocarbon 
foodstocks. 
EP-A-0292030 describes a process for preparing a modified zeolite Y for 
hydrocracking in which the zeolite is treated with a solution of a gallium 
salt to effect ion exchange and thereafter calcined to provide a product 
having a low unit cell size of from 24.21-24.6 .ANG.. Such products give 
improved catalytic activity in hydroconversion processes. 
Ion exchange processes for introducing gallium ions into zeolites are also 
described in EP-A-0024930 and EP-A-0258726, which latter describes gallium 
ion exchange of zeolites for providing an FCC catalyst giving an increased 
aromatic content. 
In such ion exchange processes, the gallium is present as gallium ions 
which may be attached to the zeolite structure. 
U.S. Pat. No. 4,803,060 and JP-A-62-179593 describe the primary, i.e. 
direct, synthesis of zeolites in which the gallium forms part of the 
crystal framework structure. The zeolites are prepared from solutions 
capable of reacting so as to provide a crystalline zeolite structure 
containing gallia and silica alone (U.S. Pat. No. 4,803,060) or gallia, 
alumina and silica (JP-A-62-179593). The zeolites of U.S. Pat. No. 
4,803,060 are used for hydrocracking, while those of JP-A-62-179563 are 
used for cracking hydrocarbons in general to increase the aromatic 
content, the cracking ability of the zeolites being tested with reference 
mainly to n-hexane. 
U.S. Pat. No. 4,524,140 and U.S. Pat. No. 4,620,921 describe the secondary 
synthesis of zeolites in which boron or iron present in the crystal 
framework structure of a zeolite is replaced by gallium. This substitution 
is achieved by a hydrothermal activation technique using liquid water at 
high temperature and pressure in the presence of gallium chloride. The 
product had an improved c-value for cracking n-hexane. 
EP-A-0134849 describes the reaction of high silica zeolites with various 
volatile metallic compounds having a radius ratio below 0.6, including 
chloride vapour. The zeolite is calcined before reaction with the volatile 
compound to create vacancies in the lattice into which the metal may be 
introduced. No structural data are given to substantiate the presence of 
the metal in the framework structure. 
EP-A-0187496 describes the synthesis of zeolites containing gallium in 
which a high silica zeolite (SiO.sub.2 /Al.sub.2 O.sub.3 =26,000) is 
treated with an aqueous solution containing gallium at a pH of at least 7. 
Again, no structural data are given, so there is no confirmation that the 
gallium enters the framework structure. 
Likewise U.S. Pat. No. 4,891,463 describes the synthesis of ZSM 5 zeolites 
containing gallium in which high silica ZSM 5 zeolites are treated with an 
aqueous alkali solution containing gallium. It is claimed that at least 
some of the gallium is present in the framework structure, though no 
mention is made as to whether the gallium replaces silicon or aluminium. 
Each of the above processes provides a zeolite catalyst in which gallium is 
present in some form or other, i.e. either as gallia in admixture with the 
zeolite, as gallium ions or as gallium within the crystal framework 
structure. 
However, we find that in all of the above structures either the gallium is 
not present in a form in which it has maximum effect, especially in FCC 
technology, or it is necessary to use very large amounts of gallium in the 
system to achieve the improved effect. 
In particular, when incorporating gallium into a faujastic structure by 
direct synthesis a particularly large amount of gallium is present in the 
starting reaction medium and yet only a small amount is finally 
incorporated into the crystal framework structure. 
SUMMARY OF THE INVENTION 
Surprisingly, we find that excellent catalytic activity with improved 
selectivity, particularly improved aromatic content can be achieved, 
especially in FCC technology, using only a small amount of gallium if a 
zeolite, especially a faujasitic zeolite, is prepared by secondary 
synthesis. 
Although only a small amount of gallium is used as starting material, the 
synthesis allows larger amounts of gallium to be incorporated into the 
crystalline structure than had previously been achieved. 
The present invention provides zeolites modified by the partial replacement 
of aluminium in the crystal framework structure by gallium and containing 
larger amounts of gallium in the framework structure than had previously 
been achieved. 
This isomorphic substitution may be achieved by a secondary synthesis in 
which the zeolite is reacted with a reagent capable of removing aluminium 
from the crystal framework structure and providing gallium ions for 
replacing the aluminium. 
Reagents which may be used for such partial replacement of aluminium by 
gallium contain gallium and halogen. 
In one method of synthesis which may be used the zeolite is reacted with a 
gallium halide such as gallium trifluoride in the vapour phase. 
However, the reagent with which the zeolite is reacted is preferably a 
fluorogallate salt, more preferably a fluorogallate salt having at least a 
degree of solubility in water, the reaction preferably taking place in an 
aqueous medium. More preferably, the reaction is carried out at a pH which 
at least at the start of the reaction is a roughly neutral pH of 5-8, 
especially 5-6.7, more especially 6-6.5, and at a temperature of 
50.degree.-95.degree. C., especially 70.degree.-80.degree. C. 
It may be possible to carry out the secondary synthesis reaction of the 
invention on any zeolite such as those listed above. 
However, the process is especially suitable for the modification, by 
isomorphic substitution, of wide and medium-pore zeolites which, after 
modification provide catalysts especially suitable for FCC. 
Typical wide-pore zeolites (having a pore size &gt;7 .ANG., usually 7-8 .ANG., 
but possibly 10-12 .ANG.) include zeolites X and Y, especially the LZY, 
such as LZY-210, and USY series, zeolite H-Y, certain ZSMs, especially 
ZSM-20, EM1, EM2, zeolite 8 and mordenite (MOR), and typical medium-pore 
zeolites (having a pore size of about 5-6 .ANG.) including certain ZSMs, 
especially ZSM 5, ZSM 11 and the zeolite theta-1 (sometimes called 
zeolite-TON). 
Particularly preferred zeolite catalysts for FCC are wide pore zeolites 
having a faujasitic structure of cubic form, e.g. zeolite X (having a 
Si/Al ratio of &lt;1.7) or zeolite Y (having a Si/Al ratio &gt;1.7) or of, for 
example, ZSM-20; which is reported to be a mixture of both hexagonal and 
cubic forms of faujasite. 
Subsequent to the isomorphic substitution of the gallium the resultant 
zeolite may be subjected to the usual further modification steps such as 
washing, drying, combining with a mixture of components, usually including 
a matrix for the zeolite material, and calcining (either dry or in the 
presence of steam) to provide a catalyst composition, especially an FCC 
catalyst composition. 
It is especially preferred that the zeolite starting material contains 
replacement ions rendering the zeolite more suitable for the secondary 
synthesis reaction. Suitably the replacement ions are provided by a 
preliminary ion exchange reaction, and an especially preferred replacement 
ion is ammonium. 
The preferred reagent for the secondary synthesis reaction is capable of 
providing GaF.sub.x.sup.(3-x) -ions in aqueous solution, wherein x is 
0.5-6, preferably greater than 2, especially 4 or 5. 
The cation of the reagent may be metallic or non-metallic, but is 
preferably a cation capable of providing an aluminium containing reaction 
product which is soluble in water. An especially preferred cation is 
ammonium. 
When the starting zeolite material for the secondary synthesis reaction has 
a faujasitic structure, the anhydrous zeolite material so synthesised has 
a framework unit cell composition characterised by the formula 
EQU M.sub.(x+y)/n [AlO.sub.2 ].sub.x [GaO.sub.2 ].sub.y [SiO.sub.2 ].sub.z(I) 
wherein 
M is a charge balancing ion and n is the oxidation state thereof. 
x, y and z are the respective numbers of tetrahedra represented 
respectively by AlO.sub.4, GaO.sub.2 and SiO.sub.2, 
x+y+z=192 for a faujasitic structure with no missing tetrahedra, 
x+y is from 0.1 to 71 inclusive, preferably from 10 to 56 inclusive, and 
y is from 0.01 to 60 inclusive, preferably from 0.1 to 15 inclusive. 
The corresponding aluminosilicate starting material has the formula 
EQU M.sub.x/n [AlO.sub.2 ].sub.x [SiO.sub.2 ].sub.y 
wherein 
M, n, x and y are as defined above, 
x+y=192 for a faujasitic structure with no missing tetrahedra, and 
x/(x+y) is from 0.01 to 0.5. 
A zeolite Y in particular is a cubic structure for which a unit cell 
parameter is measurable. The unit cell size of a particular zeolite Y 
gives an indication of the degree of substitution of the aluminium by 
another element. 
For example, silicon is smaller than aluminium, so replacement of aluminium 
by silicon will cause a decrease in the unit cell size. As mentioned above 
such a decrease in unit cell size was considered previously to provide 
improved selectively. 
On the other hand, gallium is larger than aluminium, so replacement of 
aluminium by gallium will cause an increase in the unit cell size. 
Furthermore, the more gallium substituted into the crystal framework 
structure, the greater is the unit cell size. Since an increase in cell 
size obtained by incorporation of additional aluminium leads to reduced 
activity in these aluminium-rich faujasites, it is surprising that an 
increase in cell size achieved by increased gallium substitution provides 
improved catalytic activity. 
The unit cell size of NH.sub.4 Y, an ammonium ion exchanged zeolite Y, is 
24.68 .ANG., as compared with a unit cell size of 24.70 .ANG. for a GaY 
prepared by direct synthesis (as described for example in JP-A-62-179593 
and U.S. Pat. No. 4,803,060), and at least 24.72 and possibly 24.79 .ANG. 
or higher (and even possibly 24.8 .ANG. or higher) for a GaY prepared by 
secondary synthesis in accordance with the method of the invention. 
Indeed, the method can be so controlled as to provide an increased unit 
cell size within the range 24.76-24.79 .ANG.. 
Similarly, for a modified zeolite Y of related structure, containing 
gallium and having a molar ratio of silica/(alumina+gallia) of at least 
5/1, the unit cell size is from 0.01 to 0.15 .ANG. inclusive greater than 
that of the corresponding gallium free zeolite, i.e. the gallium free 
zeolite having a silica/alumina molar ratio which is the same as the 
silica/(alumina+gallia) molar ratio of the gallium containing zeolite Y. 
Examples of the increase in unit cell size achievable are as follows 
______________________________________ 
Unit cell size of 
Unit cell size of 
Zeolite Ga free zeolite (.ANG.) 
Ga zeolite (.ANG.) 
______________________________________ 
CSY 24.50 24.53 
USY 24.31 24.36 
ZSM20 24.52 24.72 
______________________________________ 
The method allows a predetermined, very small, amount of gallium to be 
provided in discrete locations in the zeolite at positions exactly where 
it is required to provide a catalyst the effect of which is maximised 
during FCC, namely at a position within the crystal framework structure. 
Although not wishing to be bound by theory, it is believed that, in use, 
the gallium will be dislodged from the framework structure (as is 
aluminium) and so provide a fine dispersion of the gallium having 
excellent catalytic properties. This leads to particularly efficient 
gallium usage. 
Moreover, the zeolite has two different distinct types of acid site 
provided respectively by the framework aluminium and the framework 
gallium, rendering the zeolite useful for example, for different 
respective catalytic reactions, in particular, the gallium, especially 
gallium dislodged during use, can promote dehydrogenation reactions. 
In a typical method embodying the invention a zeolite such as a zeolite X, 
Y, MOR, .beta., ZSM-20, ZSM-5 or zeolite TON is subjected to ion exchange 
to provide the corresponding NH.sub.4 zeolite. 
A slurry of the zeolite in an aqueous medium buffered at pH 6 with ammonium 
acetate is then formed and a solution of an ammonium gallofluoride, e.g. 
(NH.sub.4).sub.3 GaF.sub.6, is added over a suitable period of time, 
typically 4 hours, to the stirred slurry at 70.degree. C. This allows the 
reaction of zeolite and gallofluoride salt to take place. 
The amount of ammonium acetate per gram of anhydrous NH.sub.4 zeolite in 
the slurry is preferably in the region of from 0.8-1 g, especially 
0.85-0.95 g, and the ammonium acetate is preferably added in the form of 
an aqueous solution at a concentration of 1-1.1M. Typically NH.sub.4 
zeolite is added in the form of a hydrate containing from 10-18% H.sub.2 
O, and the desired concentration of ammonium acetate by weight of the 
anhydrous NH.sub.4 zeolite can be achieved by adding about 10 ml of a 
1.02M ammonium acetate solution per 1 g NH.sub.4 zeolite hydrate. 
The amount of ammonium gallofluoride solution providing the desired gallium 
fluoride ion: NH.sub.4 zeolite weight ratio is preferably around 
8.times.10.sup.-4 to 2.2.times.10.sup.-3 moles of ammonium gallofluoride 
per 1 g hydrated NH.sub.4 zeolite and the concentration of added ammonium 
gallofluoride solution is preferably around 1.7.times.10.sup.-3 molar. 
Although the above amounts of ammonium acetate and ammonium gallofluoride 
by weight of zeolite are frequently effective, these values can be 
modified for optional reaction in any given instance. 
The reaction product may be washed free of excess fluoride and then dried. 
Where the resultant products have the required structure, catalysts, 
especially FCC catalysts, can be prepared from those products by 
conventional procedures such as combining with a matrix and calcining. 
Such catalysts are found to be much more active than corresponding FCC 
catalysts prepared from parent Y-zeolites in the conversion of 
hydrocarbons such as n-hexane in the temperature range 
200.degree.-600.degree. C. Moreover, hydrocarbon product distributions are 
also modified. At lower conversions more olefins and alkane isomers are 
observed and at higher conversions such products contain more aromatics. 
Isomers and aromatics can be desirable components in gasoline because they 
increase the motor octane number (MON). Catalysts of this type are also 
useful in similar processes such as hydrocracking, isomerisation, 
polymerisation and cyclisation. 
In particular, the invention provides a process for preparing a gasoline 
from a hydrocarbon feed which process comprises subjecting the hydrocarbon 
feed to catalytic cracking under FCC conditions, using a catalyst 
comprising a zeolite material of the formula (I) as hereinbefore defined. 
The invention also provides such a process in which the catalyst comprises 
zeolite Y having a unit cell size of at least 24.72 .ANG., or a modified 
zeolite having a molar ratio of silica/(alumina+gallia) of at least 5/1 in 
which the unit cell size is from 0.01 to 0.15 .ANG. greater than that of 
the corresponding gallium free zeolite. 
The catalyst may comprise from 0.1 to 60 wt % of the Ga zeolite material 
and a matrix binder therefor, which matrix binder may constitute the 
remainder of the catalyst. 
Typically, the binder matrix may be for example, a silica sol, an alumina 
sol and/or clay. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
The invention will now be described in more detail with reference to the 
following Examples, Tables and accompanying drawings in which 
Examples 1 and 2 illustrate respective large and small laboratory scale 
procedures embodying the invention for secondary synthesis of zeolite GaY 
from zeolite NH.sub.4 Y, 
Examples 3 and 4 are respective comparative examples illustrating the 
introduction of gallium into zeolite Y by impregnation and ion exchange 
respectively, 
Example 5 is a comparative example illustrating the direct synthesis of 
zeolite GaY, 
Example 6 illustrates the preparation of a starting material, ZSM-20, for 
the secondary synthesis of a Ga ZSM-20 embodying the invention, 
Example 7 illustrates a procedure embodying the invention for the secondary 
synthesis of a Ga ZSM-20 from the product of Example 6, 
Example 8 illustrates a procedure embodying the invention for cracking 
n-hexane using the Ga-Y of Examples 1 and 2, 
Example 9 illustrates a procedure embodying the invention for cracking of a 
gas oil using the Ga-Y of Example 1 and, for comparison, a commercially 
available zeolite Y, 
Tables A-E give the X-ray diffraction patterns of the starting material, 
zeolite NH.sub.4 Y, of Example 1 (Table A) and the reaction products of 
respective Examples 1,2,6 and 7 (Tables B-E), 
Table 1 gives a summary of the unit cell size and % crystallinity values of 
the starting material of Example 1 and the reaction products of Examples 
1-7, 
Table 2 gives a summary of the molecular structures of the starting 
material of Example 1 and the reaction products of Examples 1,2,6 and 7, 
Table 3 gives the results for n-hexane cracking for Example 8, and 
Table 4 gives the results from gas oil cracking from Example 9,