CA1131206A - Aluminum - modified silica and its uses as catalyst - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE:

The present invention is directed to a process for producing an aluminum-modified silica having a porous crystal-line structure, a specific surface area wider than 150 square metres per gram and the formula: 1 Si.(0.0012 - 0.0050) Al.Oy wherein y varies from 2.0018 to 2.0075, comprising the steps of: reacting in an aqueous, alcoholic or hydroalcoholic solu-tion a derivative of silicon and derivative of aluminum with a substance having an archivolt or clathrating effect selected from the group consisting of tertiary amines, aminoalcohols, amioacids and polyalcohols; crystallizing the reaction product in an enclosure for a period of from a few hours to several days at a temperature of from 100°C to 200°C; cooling, filter-ing and drying the crystallizate; firing in air at a tempera-ture comprised between 300°C to 700°C for a time of from 2 hours to 24 hours; washing the calcined product with distilled water, and firing once again in air at a temperature comprised between 300°C and 700°C for a time of from 2 hours to 24 hours.
The modified silicas thus obtained are efficient catalyst for a large number of reactions.

Description

1~L3~LZV~

"ALU~ MODIFIED SILICA ~ USES I~S A CATl~LYST"
Thls invention rela-tes to a crystalline silica mo-dified with ~l~ninurn, ~Iany materials~ basccl on silica and alumina, are known, a few of natural occurrence and 5 others man made, ~ lore particularly are known9 amon~r such materials~
those ~rhich are callecl zeoli.tes~ which have absorbent, molecular sieve and catalyti.c properties.
Such material have a content of alumina ~rhich va-ries 1rithin a wide ran~e of ratios relative to silic~,the ma~imum silica/alumina ratio being 100:1, but this ratio is ~enerally much smaller ancl is ~referably in the neighborhood of 2.
These materials~ which contain aluminum in tetrahe-dral coordination as replacen1ent for silicon must poss~ss, in order that they may reach elec.tric neutrality, cations capable of balancing the charges clue to the presence of the tetrahedrally coordinated aluminum ~toms.
; The protonic acidity of such zeolites can be attri~
b~lted to the hydrogen atoms ~rhich have ~een introcluced to e~change such cation.s. On the other hand, crystallino silicas~ due to their intri.nsi.c nature9 do not possess protonic charges so that they cannot display any acidic character which is not that inherent in the silicic acid, A number of crystalline silicas are known7 in fact, from cristobalitc to tridymite "~eatito, and many others, 1rhich are prepared acco~din~ to ~rocedures which ha~e been 1~idely disclosed by thc scientific litcrature~
For ex~nplc Heidcmann; in ~oitr, Min, ~etro~, 10, 30 2~2 (1~6~) obtai.ns, by r~actin~ a1l amorpho-ls silica~.th .
$~

~3~Z~

0.55~, of I~OI-I at 1S0C ~or two days and a half, a c~ystal-lino silica, called silica ~, wllich llas, ho~ever~ a spc-ci.fic sur~ace area of about 10 m~/~ (sq~tare metre pe-r ~rarn) and has a poor stabi:Lity since it becomes altered to cristobalite ~ thin five days and is subse~uently chan~red into q-lartz.
~ Iore reccnt:Ly, Flani~en et al, Nature, 2~, 51~
(197S) have obtained a crystalli.ne silica, tha silicali-te~ ~1hich has a high specific snrface area and which, due to its hydrophobic proper-ties, they have sug~estcd its use for the purification of .~aters ~hich had bcon poll~lt-ed by organic s~bstances.
~ n object o~ the present inven-tion is to modi~y thc nat1lre of a crystalline silica by the a~oncy of aluminum, ~hile leavill~ tho stability of s~lch a silica unaltered 30 as to permit its use as a catalyst~ or for the l~repa-ration of catalysts~
; ~s a matter of fact, it has surprisingly been found that it is possible to obtain ~aterials having a very high silica-to~alumina ratio but l~hich cannot be zeoli-tes since the minimum amounts of aluminull1 contained the-rein cannot justi~y a structure Or the type o~ a crystal-line silicoaluminateO
On the othcr hand, these novel materials distin~lish ovor the crystalline silicas sharply in that the intro-d~lction of tiny amounts of al~unimuD induces a wide varia tion of aciclity.
Such materials~ in point of ract, pOSSQSS a proto-nic acidity equal to, or ~reater than, that of the p~o-tonic forms o~ the zeolites themselves while ~a-intaiIling th~ very ni~h str~ctural stability prope. of a crystal-line silica, con'crary to ~hat is experi.enccd for the pro--tonic forms of the zcolites ~,X~Y (thc only oxception bcin, that o~ the mordenita family) ~1hich are rather la- -bilo as they ten~ to be rcadjly converted into thc stab-ler silica al~lminas~
Thc s~ ica al~lm:inas, as such, possess a~l ~ciclit)r ~L:3L3~L~o~

which is somewhat lower: -for example, a commercial silica alumina containing the 25~ by wt of alumina has a concentration, in terms of H~ milliequivalents (meq) per gram of catalyst in the order of magnitude of 1. 10 It has been surprisingly found, furthermore, that by properly metering the quantity of aluminum in the materials, it is possible to adjust the acidity thereof so as to adapt it particularly to the range required by the kind of reaction for ; which the material concerned is to be employed.

An object of the present invention is to provide a silica, modified by the introduction of aluminum atoms in such a way as to display those properties of acidity and ca~talytic . activity which is the most suitable for certain reactions.
Another object of the present invention is to sug-gest a procedure which lends itself well to the preparation of materials of the kind referred to above.
The silica modified by the introduction of aluminum ~- atoms has the following general formula:

1 Si.(0.0012 - 0~0050) Al.Oy wherein y is from 2.0018 to 2.0075.

Consistently with the calcination (firing) tempera-ture, greater or smaller amounts of crystallization water can be present.
In order that the aluminum-modified silica of the present invention may be obtained, it is possible to adopt, with advantage, the preparation procedure to be outlined here-under.
A derivative of silicon and a derivative of aluminum are caused to react in an aqueous, alcoholic or hydroalcoholic solution with a substance having a clathrating or archivolt eect, selected from the group consisting of tertiary amines, aminoalcohols, aminoacids and polyalcohols, possibly adding ,l ,, I

)6 one or more mineralizing agents to encourage crystallization, and possibly also an inorganic base, allowing the resultant mixture to crystallize in an enclosure for a period of time of from a few hours to several days at a temperature of from 100C
to 220C, preferably at a temperature from 150C to 200C for a week, allowing to cool, filtering and drying the crystalli-zate,firing in air at a temperature comprised between 300C and 700C, preferably at 550C, for a time between 2 hours to 24 hours, then washing the calcined product with distilled water and firing once again in air at a temperature comprised between 300C and 700C for a time of from 2 hours to 24 hours.
The derivatives of silicon can be selected from among a silica-gel (no matter how obtained) or a tetraalkyl ortho-silicate, such as tetraethyl orthosilicate and tetramethyl orthosilicate.
The derivatives of aluminum can preferably be selec-ted from among the salts of aluminum, such as nitrates and acetates.
The substances having a archivolt action have the function of originating a crystalline structure with pores having a determined size and thus are composed by adé~uately large molecules.
The mineralizing agents can be selected from among the group consisting of LiOH, NaOH, KOH, Ca(OH)2, KBr, NaBr, NaI, CaI2 and CaBr2O
The added inorganic base can be selected from among the group consisting of NaOH, KOH and Ca(OH~2.
As regards the amount to be used of the inorganic base and/or of clathrating substance, they are generally

2~3~

lower than the stoichlometrlc amount relative to silica and are preferably from 0.05 and 0.50 mol per mol of silica.
The product thus obtained are characterized by an acidity of the protonic type which can be monitored by varying the Sl-replacing cation which is introduced. For a pure silica there is a number of milliequivalents of hydrogen ions per gram of sample, of 1 . lO 3, but this acidity can be increased by the introduction of aluminum until reaching a number of ~; milliequivalents of hydrogen ions per gram of sample of about 10 1 10~1 '' The materials according to the present invention are characterized by`a well defined crystalline structure as can be seen in the X-ray diffraction spectra reported on Figures 1 and 2 of the accompanying drawings and possess a high specific surface area which is over 150 m2/g and is generally comprised between 300 m2/g and 500 m2/g.
The presence of aluminum, which so deeply modifies the acidity of the silica, gives rise to the formation of crystalline materials the spectra of wh~ich can either be consider-ably resembling those reported by the literature for the crystal-line silica called silicalite (Nature, ~71~ 512 (1978), or, conversely, remarkably different therefrom.
The silica which has been aluminum-modified according to the present invention can be employed for catalytic or absorption uses, either a]one or dispersed on a more or less inert supporting body, with a high and a 1QW specific surface area and porosity.
The supporting body has the task of improving the physical and mechanical stability and possibly also the catalytic properties of the material concerned. The procedure which can be used for obtaining a supported material can be selected from among those known in the art and to the skilled artisans.
The quantity of supporting bGdy can be comprised ~ 5 zo~

between 1p' and 90,~ but the range ~rom 5~0 to 60~' is pre-~erred.
Among the preferred supporting bodies, there can be cited clays~ silica, aluminag diatomaoeous earth~ sili-5 ca-alumina ancl many others.
The aluminum-modifi~d silica accordin~ to this in-vention can profitably be employed as a catalyst for a large number of reactions among which there can bc indi-cat~d the alkylatlon of benzene, more particularly the alkylation of benze~e with ethylene~ the alkylation of benzene with ethanol.
Other ~ossible uses are:
1. Alkylation of toluene with methanol to produce .~ylene, prevailingly para~Yylene.
2. Disproportionation of toluene to produce para,Yylene predominantly.

3. Conve~sion of dimethyl ether and/or methanol or other lower alcohols into hydrocarbons (olefines and aroma-tics), l~ Craclcing and hydrocrackin~. -5. Isomeri~ation of nor,paraffins and naphthenes.
6. Pol~erization of compo~mds which contain olefine or acetylene bonds. - -7 r R~forming 8. Isomerization of ~olyalkyl substituted aromatics, such as o.sylene, 9. Disproportionation of aromatics~ especially toluene.
10.Conrersion o~ aliphatic carbonyl compounds into at least partially aromatic hydrocarbons~
11.Separation of ethylben~ene from other C~ aromatic hy-drocarbons.
12.~Iydrogenation and dehydrogcnation of hydrocarbons.
13.Methanation~ ~
A few e~amplQs will now be given which ha~e the pur-~ose of better illustratin~ the invention without limi-tation~
E,~L~ 1 ~3~Z~36 : This example is illustrative o~ the preparation of the porous crystalline silica T~S-22 in the crystalline lattice of ~fhich there has been introduced alumi~m as silicon-ropl~cin~ element.
A Pyrex~lass vessel ~fhich is constantly l~ept in a nitrogen atmosphere, is charged with ~0 g of tetraethyl orthosilicate (T~OS) lfhich are ncated ~ith stirrin.~ -to a temperature of 80C. There is added then a solution1 in 80 mls of dlst. waterJ of 20 ~ of tetrapropylammonium hydro~ide (obtained from tetraprop~rlammonium and moisten-ed silver o lde so as to have a product free of inorga-nic all~aline bases) and stirrinO is continued at 80C un-til the mi~ture is homo~eneous and clear, that ~fhich takes about one hour.
- There are added subsequently ~0 mg (milligrams) of ~l(N03)3.9H20 dissolved in 50 mls of abs. ethanol.
A coAmpact gel i5 formed almost immediately, and dist. ~fater is ad.ded theroto to make up to an overall vo-lume of ~00 mls~ stirring being activatcd if necossary and tho mi~ture is brou~lt to a boil so as -to complete the hydrolysis and to clrive off all -th~3 c-thanol~ i.e.
the one ~Yhich has been addecl and the one set free by the hydrolysis.
The time taken by these steps is from 2 to 3 hours-: 25 and the gel is converted, slo~ and gradually into a ~hite po~lder~ ~Jhich is the pr-3cursor of thQ modified crystalline silica.
~he mi~turc is made up to 150 mls with d.-i.st. water alld ~ then the Pyre~-glass vessel is introduced in an autocla ; 30 ve and it is maintainecl therein at tho temperature of : 155~C durin~ 7 days. Upon coolin~, the solid which has been formed is centrifugecl at a speed of 10,000 r-pm for 15 mins.~ is reslurried in dist ~fater and centrifuO~ed once morc and this washin~ s-tcp i5 repeatecl four timcs~
The procluct is ovon dried at 12QC ancl it is seen that it is ~-ray crystallinc.
The chomical anal.ysis of the sample, driecl at 120C, ~3~6 gives the composition:
~0 ~t SiO2 83.0 S wt ~l203 0.2 /o~-t Na20 0.18 ; 5 ,' wt Lrzo 0002 ; Loss on firin~ at 1100C = 16~6f~J
The molar ratio of SiO2 to ~l203 is 70~.
The allali metals which are prescnt come from the reactants and from the ~lass, since they havG not deli-berately bsen added, In order that the all~aline impurities which are pre-sent may com~letf-~ly be removed from the compound, ths latter can be fired for 16 hours at 550C in an air stream and subscqucntely it can repcatfdly bee l~ashecl with boil-in~ dist. watfr containing, clissolved thcrein 7 arnmoniumacctate and fircd again at 550C for 6 hours.
The s~ecific s~lrface area, as dctermined ~ith the BET method is 1~ m2/g~
The concentration of protonic milliequivalen-ts per gram of sa~ple is 1.5 4 1 0 E~MPJ.E 2 This e~.ampl~ is illustrative of the prepar~tion of the porous crystalline silica T~S-O, in the crystallinc lattice of lJhich traces o~ aluminum have been introduced as replacemfnts for thf~ silicon~
A Pyre~ lass fla5k equipped ~rith reflux condenser and maintained in a nitrogen atmosphere~ is charged with 40 ~ of tctraethyl orthosilicate ~T~OS) and 12~ mls of a 20f/o aq~eous solution of tetrapropylammonium hydro~ide (conc, by ~rt~ and tho mixture is heated to the boil.
Thc fina~ result is a clear, colorlcss solution which remains limpid cven after a long refluxing, At this stagr, there are addcd 30 m~ (milli~rams) of Al(~03)3~9~12o ancl the llquor bc~comes opalrsccnt and, 3~ by continuinO thc administration of heat, a whitc po~rrlor is separatod thcrcfrom~
~olling is continuc~fl durin~ 6 da~rs, ~ihcreaftor thc .

)6 mixture is allo~red to cool, the solid lS collected on a filter and ~ashed ~rith dist, water and dricd at 100C.
The prodttct, drled at 100C, is X-ray crystallinc, It is fired for 16 hours at 550C in ~n air stream and is subsequently repeatedly ~Yashed with boiling dist. ~ra-ter ~rhich contains, dissolved therein, ammonium acetate, ~hereafter the solid is fired at 550C once more for 6 hours~
The chemical analysis on the procluet thus obtained ~ives the compositioll reported hereunder:
wt of SiO2 96.2 wt o~ ~l203 002 o~ wt of ~2~2 0.02 1~cight loss on ~irin~ at 1100C - 3,58~
The molar ratio of SiO2 to ~l203 is 816-The traces of alkali metals which are present come from the reactants and the glass si~lco they have not de-liberately been aclded. The 5pQCifiC surfac~ area~ as de-terrnined with the BET method is ~20 m /g~
The concentration in protonic milliequi~alents per gram of sample is 1.9 . 10 1.
, X~MFL'~
This e~amp~e is illustrative of the preparation of a porous cry~talline silica, called TP~S-23, in the cry-sta1line lattice of which alurninum has been introducecl as a r~placernent for silicon and in the preparation of sueh silica an organic base has been used, tetraethylam-monium hydro~lde, clifferent from thc base used for the ~xamples 1 and 2 hereof.
The procedure is as in ~xarnple 1, by reactin~ 80 ~
of tetraethyl orthosilicate~ 68 mls o~ ~ 25,' (by ~rt) a-queous solution of tetraethylammonium hydro~ide1 80 mO~
of ~ T03)3,9H~0 dissolved in 50 ~S of abs. ethanol a~d 2 g of ~aOH pellets dissolvcd in 10 mls of dist~ ~ater~
this mixt~lrc b~in~ mantained at the te~peraturc of 155C
~or 18 days.
The pro~llct, wherl dricd at 120C~ is ,~-ray crys-tal--- lo --line, The conccntration of pro-tonic milliequivalen-ts per gram o~ s~mple (~ircd at 550C) is 1,1 ~ 10 6.
The cho~ical analysis, made on a thoroughly washcd sample which has then been fired at 550C, gives -the com position:
by wt SiO2 96~3 p by wt ~l203 0~2 c/~ by wt Na20 -3 ~Jeight loss on firing at 1100C -- 3~7~
The molar ratio SiO2 to ~1203 is 81~.
The specific surface area, as determined with the BET method, is 1~70 m2/g.
The cGnccntration o~ protonic milLiequiva1en-ts pcr gram of sample is ~,3 ~ 10 3.
This example is illus*rative of the preparation of a porous crystaIline silica9 initiallcd TRS-19, in the cryst~lline lattice of which aluminum has be~n introduc-ed as a replacement for silicon: in the preparatio3l of this silica, an or~anic base has been used, which is dif-ferent from those used in the ~revious e~amples~ and is tetrabutylammonium hydro-Yide, The procedure is the same as in E~ample 1, by react-ing ~0 g of tetraethyl orthosilicate (T~OS), a solution 25 of 100 mg of Al~03~3,~l-I2o in 50 mls of abs~ ethanol, a solution o~ 29 g o~ tetrabutylammonium hydro~id~ (ob*ain-ed from tetrabutylammonium bromide and moistened silver o~idc) in 1~0 mls of dist. water and 2 ~ of MaOtI dissolv-ed in 20 mls of dist~ water.
This mi~tu~e is placed in an auto~la~e and h~ld for 16 d~ys at the tem~erature of 155C.
The product, dried at 1~0C i~ ~_r~r crystallinc.
Thc co~centration of protonic milliequivaleIlts per gram of sample (fired at5~0C) is 4.5 . 10 ~0 The chemiea1 analysis on a thorou~hly washed sample gives the following composition:
p by wt SiO~ ~6.0 .3~

/0 by wt ~l203 0.3 7' by wt Na~0 0,03 Wei~ht loss on firin~ at 1100~ = 3.67' The molar ratio SiO2 to ~l203 is 5~3.
The speci~ c sur~ace area, as measured with the B~T
method is 3S0 M2/g.
'~he concentration of milliec~uivalcnts ~I~ per gram of sample is 2~5 . 10 1, ~ Fi~lrc 1 of the accompanying drawings shows the ~-ray diflraction spectrum of the product of this e-ca~nnle.
~L~ 5 This cxample is illustrative of the preparation of a porous crystalline silica, initjalled TRS-20, in -the crystalline lattice of which aluminum has been introduced as the modifyin~ element in renlacement for silicon. The preparation of this silica has bee~carried out without any inorganic all~aline basc being present: the only alka-line cations might con1e from the traces of impurities which aro present in the usecl reactants.
By adopting the same procedure as in ~cample 1, thcre are reacted 40 g of tetraethyl orthosilicate~ a so-lution o~ 100 m~ of ~ 03)3.9H20 in 50 mls of abs. e-thanol3 50 mls of a 407' (by wt) aqueous solution of te~
trapropylamrnonium hydroxicle (obtained from tetra~ropyl-ammonium bromicle and moistened sil~er o~cide~ in orcler -to obtain a product free of alI~aline inorganic bases and the mi~t~trs is maintainéd at 155~C for 10 days, The X-ray analysis indicatcs the crystallino charac-ter o* the sample dried at 120C~
For the use as a cataly~t, the product is fired at 550C in air -for 16 hours and then repeatedly washecl with boili~c~st. ~ater contain:in~ disso~vecl therein am-monium acetate and lastly the solid is fired once a~ain at 550C for 6 hours.
'~he procluct thus obtained has the following c~lemical analytical composition:
~ by wt SiO2 96 0 ~O by Itt ~l203 o,3 c~ by wt Na20 0.01 Weight loss on firing at 1100C = 3.59~,~
The molar ~tio Si2 to ~l203 is 51~
The s~ecific surface area as determined with the BET
methocl is as high as 500 m2/g.
The concentration of H~ions per gram of sample is

4.7 . 10 1meq.
PXA~IPL~ 6 0 This e~ample is illustrative of the prepRration of the porous crystalline silica TRS-5~7 in the crystalline lattice of ~hich alumin~un has been introduced as the rno-difier. In the preparation of the silica in questi~n, triet~anolamine has been used~
lS There are reacted ~0 g of tetraethyl orthosilicate, 80 mg of ~l~N03)3.9H20 dissolved in 50 mls o~ abs. etha~
nol~ a solution of 27 g of triethanolamine in 50 mls of distS water~ -the procedure being as disclosed in ~arnple 1 hereo~. -There are now a~decl 7 g of sodium hydro~ide and the Pyrex-glass ~essel is laced in an autocla~e and maintan-ed at the tcm era-ture of 194C ~or 7 days.
It is ascertained that the product dried at 120C
is X-ray c~ystallinec The X-ray ~iffraction spectrum ~ this product is de-pieted in ~igure 2 of the accornpanyin~ drawings.
~he chemieal analysis on the sampleg fired at 550C~
gi~es the following results:
,~ ~y wt SiOz ~602 30 fjo by wt ~l203 0~2 7b ~y wt Ma20 0.05 Weight loss on firing at 1100C - 3 i55~ob The molarratio SiO2 to ~1~03 is ~l6.
The speci~ic surface area is, when measured ~th the B~T methodg 3~ m /g~ and the concentration of ~I~meq ?er gram o~ sample is 1~5 . 10 ~ -~) .

This e~ample is illustrative of the lacl; of dehydrat-i~ catalytic properties of the modified crystalline 5i-lica TRS-~2 preparcd acc~ling to ~:am,)le 1 here~of but containing sodium cations 3 SO that the concentration of protonic.milliequi~alents per gram of sample is as low a s 4 .1 . 1 0 The for~ation of dimethyl ether from methanol has been selected as the e,~emplary dehydration reaction, - An electrically heated tubular reactor having the inside diameter o~ 8 mm has been char~ed with ~ mls (-2 g) of catalyst; in the ~rit fracti.on com~rised between 30 mesh and ~0 mesh of the ~S'rM US~ series~
~ sampler ~or the e~fluent of the reaction is posi-tioncd downstream o, the reactor and the analysis are ~ade ~aschromatographicallyO
The catalyst is initially fired at 500C for t~ro hours in a nitro~en ~tream to remove the absorbed water.
~Iethanol is thon fed in at a wei~ht hourly space ~e-locity (I~JI-ISV) 1.5 ~/~ an hour with an o~en tempcrature 20 o~ 275C and subsequently of 4000C~ , .
The analysis of the reaction o~fluent shows the pre- .
sence of methanol only at both the temperatures indicat-ed above.' ~IPL~ 8 (~ comparativo e~am~le¦
2~ I`his e~ample is illustrativ~ of the absonce of de-hydratinO~ propcrties o-~ the modi~ied crystallin~ silica TRS-23 as pre~arcd accordin~ to.~ample 3 an ~ot thorou~
1~ washed, BO that tIIe concentration of protonic millie-qui~alents per ~ram of catalyst is as low as lo1 , 10 5 Ey operatirg ~ith the procedura and with the appa-ratus~escribcd in ~;ample 7 hereo~ thc reactor is chargcd with ~ m],s (-2.8 ~) of cata,lyst the grit si~e o:~ which is comprised between 30 and ~0 mesh, ~ST~I US~ series, and the cata].yst is heated ~or two hours at 500C in a stream of anh,~drous nitrogen O
~ Iethanol is ~cd in at the temperatures o~ 2l~0C and 300~C and also l~oooc at a wcight hourl~ sp~cc ~clocity ISV) of 1075 ~rams per ~ram an hour.
In all thrce cases J no dimethyl cther is iound in the reaction efflucnt and only the fed in methanol is founcl.
~ IP~ 9 This e amplc is illustrativc of the e~.ccllent cata-lytic dchydratin~ properties of the moclified c~ystalline silica TRS-22 as prepared according to E~ample 1 hereof and having a concontration of protonic milliequlva1ents per ~ram of 1.5 . 10 . By operatin~^ with thc procedure and the appar~tus as dcscribed in E~ample 7 hcreol~ the reactor is c~ar~ed with ~ mls (-3,5 g) of ca~aly3t in the grit fraction comprised between 30 mesh and S0 mesh of the US~ series o~ ~AST~I~
Upon firing for 2 ho~trs under an anhydrous nitro~en strcam to~remoYe the adsorbed water~ ~ethanol is ~ed in at a weight hourly space velocity (1~ISV~ of 1.5 ~/~ an hour at the reactor temperatures of 250C and 255C
The anal~sis o~ the reactor ef~`luent, which is com-posed by dimcthyl ether3 unreactecl methanol and water,w~hout ascertainin~ thc presencc of by-products c1ekocta-ble gaschro~ato~raphically~ gives thc r~sults cabulated in Tablc 1 h~reof It can be seen that the crystalline silica accordin~ to the present invention has an e~celleIlt dehydrating acti-vity~ with convorsion ~ercentages hi~h~r than those de-scribcd in the by thc same ~ssi~nee hereof relating to active al~minas which have been treated 1~ith silicon compounds.
; 30 It is sufficient t~note that by operatin~ with TRS-22 at 250C and ~T 2650C~ thero aro o~t~i ned~ with a InISV
of 1.5 convcrsion of methanol ~thich arc~ res~ectively, equal to~ and hi~cr than~ tnose whic~ can be obtaincd at 300C and with a ~ISV of 1 on active alumina which has been treatcd l~lth silicon compo~mds.
T ~ B L ~
., D ~

Catalyst : TRS-22 Temporature~ ~C 250C 265~C
Prossure, bar ~-ISV in g/g hourly1~5 -105 Conversion of CM30~I
molar ~ ~2 ~ - 88~1 ~lPL~ 10 ~ com~arative exam~e) This e~a~ple is illustrative of t e convorsion of . tho ~imethyl ethcr in-to hydrocarbons, with a special at-tention to tho light olefines, on the modified crystal-line silica TRS-22 as prepared accordin~ to ~.am21e 1 hereof and con-taining sodium cations, so that the con~en-tration o~ protonic milliequivalents per ~ram of catalyst is ~.] . 10 ~. -An electrically heated tubular reactor having a dia-- meter of S mm (inside) is char~od with 2 ml (=1 g) of a catalyst havin~ a ~rit size ratin~ between 30 mesh and 80 mcsh of the US~ series o~ AST~I~
The catalyst is heated~ at the outsot, to 550C for 2 hours in a nitro~en stream to remove -the absorbed water, if anyD Gascous dimethyl ether.is fed by maintaining all the pi~in~is heated to prevent condonsat-ion. Do~rnstream of the reactor~ a properly hcated sampling appliance is installed~ to permit -the introduction o~ the reactor ef-fluent into a gaschromato~raph.in which the complete a-nalysis of the reaction ?roducts is carTied outO
30 ~s regards the calculatior of the conversion,.it is to be borne in mind that the methanol ~rhich is formed by - partial hydration of the dimethyl ether is consider3d as an unreacted prodt~ct~ so that the molar conversion is referred to the dimethyl ethor which has beon converted into hydrocarbons and carbon mono~idc ~lld carbon dio~ide.
The molar sclrec-tivities on tho products aro rcfcr-rod to the n~bor of mols of dimcthyl ethor which havo bcen _ 16 -convcrted into the inclicated produc~, relative to the total n~lmber of reacted mols.
The results thus obtainccl are tabulated in Taole ~;
the latter clearly shows that the catalyst in question is not very active and not vory selectivc 9 too inasmuch as considerablo amounts of carbon mono~idc and carbon dio~ide a~cl methane have been formecl~
T ~ ~ L ~ 2 Convorsion of ~lmeth~rl ~th _ drocarbons Catalyst : TRS-22 .
Test TempO Press. 1~ISV Conversion S~LECTIVITY IM TI~ PR0-per pass~ DUCTS, molar ' No. ~ bar molar ~CO-~C0 ~C~ C ~IL-C II6-C~
1 375 1 oO652.35.0 14.9 30.1 50.0 2 1~75 1 0.2097.010.9 6.5 2601 56~5 ~L~ 11 This example is illustrative of the con~ersion of the dimethyl ether into hydrocarbons~ with s~ecial at-; tention to the light olcfines on the modi iod c~rstalli-nc silica TPS-22 as preparcd accordin~ to e~amplc 1 and haYin~ a co~centration of 1~5 . 10 protonic milliequi-valents per ~ram of sample, By operating with the procedure and the apparatus as disclosecl in ~xample 9 hereo~, tho reactor is char~ed with 3 mls (=1~5 g) of catalyst in the grit size range o~ ~rom 30 mesh and 80 mesh of the ~ST~I US~ series.
The catalyst is pre~io~ls3y heatecl to 550C for 2 hours under a nitrogen stream to remo~e thc absorbecl wa-ter.
The results which have be~en obtained are tabulatod in Table 3. The comparison ~lith Table 2 clearl,~ shows that, as the acidity is varied, the beha~ior of the ca talyst is ~os;.ti~oly im~rovedO

~3~

T,~ E L ~ ~
Conversion of Dimet1~ thc-r into II~-clrocarbons Catalyst : TRS-22 Test Tenl~. Press. I~SV Conversion SEL~C~IVITY IN '~ PR0-per pass. ~UCTS, molar ~0 No. C bar molar ~' C'~C~CHI~-C2~ -C3II6-C4 1 305 1 207 3808 0.5 30.1 2t~,3 L15.1 2 335 1 2.7 ~7.9 -5 23.0 1909 56.6 3 365 1 4.7 97.3 -5 19.0 18.8 61~7 365 ~ 6.7 ~7.1~ 0.5 23,.2 19,7 5~.6 l~85 1 6.7 9~.1 0.5 18.3 18.7 61~9 6 l~85 1 ,8.7 87-1 0.5 20.1 1~.2 61.2 7 L~40 1 9.0 92,1 0-5 1~o5 15.2 67.8 E~IPL~ 12 This e~ample is illustrative o~ the acti~ity~ in,the reaction of alkylation of bcnzene with ethyle~ne, o~ the c~talyst TRS-22 (1.5 . 10 meq H* per gram).
~ l electrically heated tubular reactor havin~ the in~ide diameter of 8 mm is chargcd with 1.2 mls (~0.8 g) o~ catalyst TRS-22 ha~in~ a grit size ~ating from 30 mesh and 50 mesh, Thrcllgh a meterin~ pump benzene is *irst in-troduccd in a preheater system-wherein lt mects a prese-lected rate o~ flo~ of ethyle}le ancl then into thc reac--tor, The reaction proclucts are gaschromatogra~hically analy~ecl. Table l~ tabulates the clata relatin~ tc the tests which have been carried out.
~ 30' ; Alkylation o:~ ~en~enc with ~th~,~lene C~t~lyst : ~S-22 Pressure . 20 1~/cm2 Liquid ~Iour1y Space ~elocity~ LI-ISV : l~
35 ~50~ar ratic~ C6I-16:C2~ = 7 z~

~ _ 18 -Run TempO ,~ molar o~ /~ Molar O:e conversion r~
hours C ethylbenzene diethylbenzcne o~ ethylene in pr~ducts in products lO L~l~o13.8 1.50 100.0

5 44013.7 1-55 100~0 100 4413.9 1.l~5 100.0 150 ~'413~9 1,1~ 100,0 200 ~413.8 1.50 100.0 10 250 l~4011.~ 0~80 80.S
300 L~408.2 0.25 51.8 320 1~7011,5 o.7o 76.7 ; 350 47010.9 o.65 72.6 400 47010,3 o.60 68.2 1 ) - , ' . ' ~XA~L~ 1~
This e~ample is intended to illustrate thc regcnera-tion o~ the catalysts in question.
More particularly, the catalyst o~ the previotls e-~ample 12 (TRS-22), af-ter 400 hours of operation, has been regencrated at 550C, in a properly acljusted air stream for 5 hours~
On completion o~ the regen~ration run, the system - is pur~od ~ith nitro~en clurin~ onc hour~ still at 550C, ~hereafter the reac-tion is restartecl under the sam~ con-di*ions as reported previously.
Tablc 5 reports the clata rclativc to the tests l~hich have been conducted~

~}
Catalyst : Re~cnerated TI~S-22 Pressure : 203;~/cm2 Licluid lIourly Space Yolocity, Tl-lSV
-~lolar ratio C6h~6:C2II~ : 7 ~L3 R~ Tomp . ,' molar o~ ~ molar o~ conversion c' hours C ethylbenzene diethylbonzenc of ethylene in products in products 5 10 4l~o 13~ 1 a55 100.0 5 4~0 13.6 1.40- 97-6 100 l~o 13~8 1~,50 100.0 150 1~40 13 ~ 5 100.0 200 ~4 13~7 1~55. 100dO
10250 l~l~o12.2 0.95 83-~
3 ~ 0 10~3 o~60 6S~5 350 ~ O 9 ~ 8 0 ~ 38 62~5 ' E~ ' This e:a~ple illustrates the activity~ in the reac-tion of alkylation of benzene ~ith ethanol, of the cata-lyst TRS-0.
An ~lectrica].ly heatec1 tubular rcactor of the diame-ter (inslde) of 8 ~m is char~ecl wi-th 1.Z ~ls (-O.S ~ o~
catalyst havin~ a rit size ran~e o~ fro~ 30 mesh to 50 mesh. Throu~h a meterin~ pt~p thc reaction mi~t~rs is in~
trodueed, ~hich consists o~ ben~ens and ethanol~ in a mo-lar ratio o~ 5:1~ first in a prehcater and then in the reactor The reaction is carried out at 4l~ooC and the reac-tion products are gaschromato~raphically analy~ed.
In T~ble 6 tho data relative to ths tests ~hich ha~e been carried out are ta~ulated d ~ -tio Catalyst : TRS~0 Temperature 1~ 0C
Pressur- ~ 20 l;g/cm2 ~ :
Liqvicl I-Iourly Space Volocity, LIISV : 10 3~ ~Iolar ratio C6II6 C2II~~

1~-3~

Run hours ~ molar of ~ molar of conversion c' othylbenzene dietihylbenzene of C2II50II
in produets in produets , 5 50 19.0 1.2 100 100 19~,0 1,,2 100 150 19~0 1~2 100 200. 19~0 1"2 100 - 300 19~0 1 o2 100 10 400 19~0 1.2 100 5 mls of the alumin~-modified silica TRS-20 prepar-ed as su~ested in ~ample 5 are impre~rnated with an a-15 queous solution of II2PtCl6 in sueh a ~ay that the contentof Pt in the catalyst is 0.2 ,' by ~t.
Platir~m~ is reduced to the elemental state at 600C
in a hydro~cn stream ancl is introducecd in an electrical-ly heatecl tubular reaetor havingr an inside diameter of 20 mm.
The capacity of abatin~ the exhaust gases o~ a mo-tor car is ellecked ~ith two typieal reactions, that is~
oxidation of propylelle to carbon dioxide and o~idation of earbon monoxide to earbon dioxide.
Test~
The fed in ~ases .~hich are composecl by S00 ppm (parts per million) of propylene, 8~' of oxygen and the balance nitro~en~ are preheated to 120C and passecl on the eata-lyst ~ith Gaseous Hourly Spaee Veloeity, GIISV of ~0~000 hours (reeiproeal hours). Propylenc is convortecl for ~9,~
The same ~aseous ~i~r-ture~ prehcated to 90C i5 fed to the catalyst at a GHS~ of ~0,000 reciprocal hours and a eon-version of ~9C~ for pro~ylene is obtaincdO
Te.st E!
The fed in ~ases are eomposed by ~.S ,' of C0, Sf~ of oxygen and tlle balance nitrogen and are preheatecl to S0.C
and pas3ed on the catalyst at ~ GHS~ of ~O~OOO.reeiproea'.

~3~ )6 hours, the conversion o~ 59,' of C0 being thus obt~ined.
The same ~aseous mi~ture~ prehcatcd to the same tom-perature is fed to the catalyst at a G~ISV o 50,000 rc-ciprocal hours and a conversion o~ 99' is obtained for CO. Thc temperatures indicated abovc~ i.c. from ~0C to 120C~ r..ust be corrcctly rngarded as e:;ceptional since the best commcrcial catalyst as used in the catalytic muf~lers carry out the same conversion ratin~s o~ prop~-lenc and carbon dio~ide at the same space velocities re-portecl above but at a ~mperature which is nevcr below 150~C.
; E~-~2ll~L~ 16 This cx~ple is for illustrating the activity, in the reaction of all~ylation of benzene with ethylene~ of the catalyst T~S-57 as pre~ared accor~ing to the proce-dure o~ ~ample 6 hereo~.
The reaction i3 carried out in a tubular rcactor of - the fi~cd-bed type having an inside diameter o~ ~ mm and electrically heated.
There is introduced in the reactor 1.2 ml ~=0.~5 ~) of the catalyst, having a grit size rating from 30 mesh to 50 mesh.
Throu~h a metering pump benzcne is introduced, first into a prchcater system (where it merges with a preselec~
ted rate of flow of ethylene) ~nd then into the reactor.
The reactor o~fluents are gaschromato~rapIlically analyz-ed. Table 7 reports the data rela-tive to the tests which ha~e been carried out.
~Z
~ ylation of Ben~cne wi ~ y~
Catalyst : TRS-57 Prcssure : 20 1~/cm2 Te~erature : ~L~o oc Liquid EIourly Space Velocity~ ~ISV
~lolar ratio C6I-I6:C~ 7 ~31~

Run hours O molar of ~' molar of cor.~.version cO
eth~rlben~ene dicthyl1~cnzcne of ethylene in products in products 13~9 1.35 100.0 13.9 1'~3$ 100.0 100 11~o 1.30 100.0 150 1308 1~30 98.
200 13.9 1.35 ' 100.0 10 250 13,~ 1~28 . 97.9 300 12.5 1.02 ~7.6 350, 11.3 0.90 '78.9 E~I~L~ 1~
Thc same catalyst T~S~ hich had bcen uscd ~or thc reaction o~ al1~ylation o~ benzene ~ith ethylcnc as dis-closed in 1~ample 16~ has bccn subjcctcd to an in situ rcgcneration run with a stre~m o~ air diluted ~tith ni-trogon at 500C, On comnletion o~'the rQ~eneration r~m, -the catalyst has been sub~ected a,ne~ to the r~action o~ al1~ylation o* benzene ~ith. ethylcnc. The data tabulatcd in Table S
.are a clear sho~in~ o:~ ho~ simple and advanta~eous is to regenerate such a catalystO
T ~ 8 L E 8 ~ Y____- ~ BenY~ it~ Y1~3 Catalyst : P~e~encrated T~S-57 Pressur^ : 20 l;g/cm2 Tcmperatur~ o C
Liquid IIourly Snace Velocity, LI-ISV
~Iolar ratio C6~I6:C2~I4 : 7 R~1~ hours ~' mvlar of ,~ molar of conversion c'~
ethylbcnæene diethylben~cne of cthylene in products in products 10 . 1l~0 1.30 lOOoO

13~9 1.35 100.0 100 1308 ~-4 100~0 150 13.9 1035 100~0 20~ 13~8 1~0 100~0 5 250 13~2 1~19 93.8 300 1208 Or95 88~5 ~L~ 18 This e~a~plo illustrates tho acti~ity of the cata-lyst T~S-~7 as clescribed in F~;am~le 6 for tho reaction of all~lation of bonzene with ethanol~

~ ~3~2~i . 24.

The reaction is carried out by introducing in an electrically heated~ fixed-bed~ tubular reactor~ 1.2 ml (0.85 g) of the catalyst, ha~ing a grit size r~nge of from 30 mesh and 50 mesh. ~ia a metering pump~ the reaction mixture~ which is comprised of benzene, ethanol, is introduced first into a preheater assembly and then into the reactor. The effluents are gaschromatographi-cally analyzed. Table 9 reports the data relative to the tests which have been carried out.
: 10 T A B L E 9 . ~
`.. -: . ALKYLATION OF BENZENE WITH ETHANOL . -Catalyst : TRS-57 . Pressure : 20 kg/cm2 Temperature : 440C
Liquid Hourly Space Velocity, LHSV = 10 Molar ratio : C6 6 2 5 Run % molar of ethyl- % molar of diethyl- % conver-benzene in the benzene in the sion of products produets C~H50H

18.8 1~3 100 100 19.0 ~.2 100 150 18.8 1.3 100 200 19.0 1~2 100 250 19.0 1.2 100 25 3~ 19.0 1.~ 100 400 19.0 1.~ 100 Quite particular an aspect of application of the modified silicas according to the present invention~ is the use of such aluminum-modified silicas as eatalysts ~13~

25~

~n the alkylation of the C4 hydrocarbons~ olefines and/or paraffins, to hydrocarbons having a high octane numbers.
As outlined above, such modified silicas are porous and have a specific surface area greater than 150 m /g and correspond to the general formula reported in the foregoing.
The following Example 19 is illustrative of this particular application of the present invention.

For alkylating isobutane with nor.butenes~ a porous crystalline silica such as obtained in Example 5 hereof, the crystalline lattice of which aluminum has been introduced as a replacement for silicon~ is employ-ed as the catalystO
A small reactor such that described in Example 7 hereo is charged with 3 mls of catalyst ( = 1.9 g)~
having a grit size of from 30 mesh to 50 mesh-. -The operative condi-tions and the results which ha~e been ob-tained are tabulated in Table 10 hereunder Pressure : 20 kg/cm Molar ratio of isobutene to the nor.butenes = 15 _ _ _ _ Temp. LHS~ % alkylation with Composition of C rec.hrs respect to the the products butenes .. _ . . . .
250 1.3 100 about 90% iso-paraffins ~ about 20% aromatics _ 350 1.3 100 aboùt 50% iso-paraffins ~ about 50% aromatics ~ . . _ ~
350 5~o 9~ about 70~ iso-paraffins ~ about 30% a~onlatics 26.

Yet another practical application of the pre-sent invention is the preparation and use of a zeolite-type ca-talyst of the class ZSM~5.
It is known from a patent assigned to Mobil, US 3 702 886, that zeolites of the class ZSM-5 can be prepared by exploiting deri~atives of silicon, such as silica-sols, aerosyl-type amorphous silicas, te-traalkyl orthosilicates, or deriva-tives of aluminum such as sodium aluminate~ aluminum sulfate~ aluminum acetate, in con-junction with a quaternary ammonium base such as tetra-propylammonium hydroxideO
According to a modified embodiment of the present invention it has been ascertained that zeolites of the ZSM-5 type can be prepared by exploiting the general teachings of the invention whenever the material which monitors the crystallization is an aminoalcohol and appropriate amounts of compounds of silicon, germanium, aluminum and gallium are used so that the molar ratios SiO Al Ge2 A123 Si2 2 3 2 2 3 are comprised between 5 and 100 and are preferably in the vicinity of 35.
A z~olite prepared according to the present in-v~ntion has an X-ray diffraction spectrum akin to that of zeolite ZSM-5 and corresponds to the general formula :
. 25 .9 ~ 0.2 ~2/n W203 5-100 Y02 : ~H20 wherein M is a cation selected from among H and/or NH4 and/or metallic cations and/or cations deriving from - amino alcohols~ especially ethanolamines~ n is the va--lency of such cation, W is selected from the group con-3o sisting of aluminum and gallium, Y is selected f~om the group consisting of silicon or germanium and z is between 0 and 40.

27.

The preferred form of this zeolite provides W
as aluminum, Y as silicon with a ratio of silica to alumina comprised between 10 and 60.
The preparation of the preferred zeolite accord-ing to the present invention is carried out by admix-ing the reactants within the following ra~ios~ express-ed in terms of mols of oxides.
Ratios Broad interval Preferred Interval OH /SiO2 0.2 - o.8 o.3 - o.6 T.~.T.A./T.E.T.A.+Na o.3 - o.8 Oo4 - o.6 H20/OH- 10 ~ 100 20 - 40 wherein T.E.T.A. stands for the amino alcohols~ more par-- ticularly triethanolamine.
~he process according to this particular aspect of the present invention provides for the following - step sequence :
A derivative of silicon or of germanium and a derivative of aluminum or gallium is reacted, in an aqueous~ alcoholic of hydroalcoholic solution~ with an ami~o alcoholj such as the e-thanolamines anl more par-ti-cularly triethanolamine, adding possibly one or more mine-ralizing agents such as hydroxides andfor halides of al-kali metals or alkaline earth mstals to encourage cry-stallization.
The mixture is allowed to crystallize in an enclo--~ sure for a period from a few hours to many days at a high temperature, from 150C to 250C and preferably from 170C
to 210C for a period o-E time of from 2 to 10 days~ gene- -rally one week, allowed to cool and, upon collection on a filter and washing with deionized water~ the crystals ~L~3~2~

28.

are dried and fired in air at a temperature comprised betwcen 300C and 700C, preerably a-t 550C, for a period of from 2 hours to 24 hours, whereafter a re-peated cationic exchange is effected with an ammonium S salt, preferably ammonium nitrate or acetate~ washing with dist. water and fired once again as described above, if the product is desired in the form H .
The zeolite thus preparsd can be used as such, or diluted in an appropriate dilution ratio and supple-mented with one or more elements having catalytic promo-ting actlvity, according to the procedures and other methods provirled for the zeolites of the ZSM-5 class.
A few examples~ numbered from 20 to 22 inclusive are intended better to illustrate -this particular embo-diment of the invention which is connected with the zeolite-type catalysts.

This example illustrates the preparation of the zeolite ZSM-5 by using triethanoamine~
A Pyrex-glass vessel rnaintained in a G02-free atmosphere is charged with 60 g of Al(N03)3.9H20 dis-sol~ed in 400 mls of 95%-ethanol~ then there are added uith stirring 600 g of tetraethyl orthosilicate. As soon as the solution becomes limpid, there are added 200 g of triethanolamine dissolved in 400 mls of dist~
water and the mixture is heated~ s~ill with stirring, to 600Co After 30 additional minutes, there is added a solution of 13 g of NaOH in 200 mls of dist. water, and~ after 30 further minutes there are added 22 g of an NaOH supplement (total 35 g of NaOH) dissolved in 400 mls water. ~ massive formation of gel is observed : a z~

29.

~vigorous stirring is started and is maintained during a few hours~ while concurrently raising the temperature to 90C so as to dispel all the ethanol, both intro-duced in the reaction and formed by h~drolysis. At this stage, the reaction mixture is transferred to a 3-litre stainless steel autoclave and the hydrothermal treatment at 195C is started~ to be maintained for the duration of 9 days.
The resultant product is then allowed to cool at room temperature, collected on a filter, washed many-a time with very hot distilled water and dried at 120C.
The solid is then fired at 550C for 16 hours and is shifted to the ~1 form by repeated e~change in ; hot condikion t950C) with ammonium acetate (or nitrate) and by firing again at 550C for 6 hours.
The X-ray d~ffraction spectrum corresponds to that reported by Table I of the US pat Specn~ 3 ,02 886.
~XAMPLE 21 _ By adopting the same procedure as in Example 20, there are reacted 880 g of tetramethyl orthosillcateg 120 g of Al(N03)3.9H20, 400 g of triethanolamine which had previously been dissolved in 800 mls of water~ 7~ g -of NaOH in 700 mls of water and the mixture is made up to a volume of about 9 litres by adding dist~ water with very vigorous a stirring. The mixture is concentrated at the temperature of 80C for about 30 hours until re-ducing the volume of the liquor to about 5 litres in total.
The hydrothermal treatment is effected during 8 days at 190C in a stainless steel autoclave, equipped with a stirrer.
The X-ray diffraction spectrum corresponds to that 3L2(~

- 30.

of ZSM-5 and the specific surface area is 380 m /g.
The ratio SiO2 : A1203 is 38-EXA~LE 22 9.6 g of sodium aluminate and 10 g o potas-sium hydroxide are dissolved in 200 mls of water. Theclear solution is supplemented with 208 g of triethanol-amine~ dissolved in 1~000 mls of water. The solution thus obtained is allowed to stand, with stirring, under an inert gas blanket~ for two hours at 80C. There are now added~ as a ¢rystallization-encouraging agent, 40 g of potassium bromide dissolved in 150 mls of water.
There are now added slowly 345 g of Ludox colloi-dal silica (40% SiO2) dissolved in 1~500 mls of water.
The resultant gel is allowecl to age ~or 24 hours at 90C
under an inert gas stream.
The gel thus treated is then crystallized in a stainless steel autocla~e for 10 days at 198C.
~ The procedure illustrated in Example 20 is comple-; ted and zeolite ZSM-5 is thus obtained.

Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A process for producing an aluminum-modified silica having a porous crystalline structure, a specific sur-face area wider than 150 square metres per gram and the formula:
1 Si.(0.0012 - 0.0050) Al.0y wherein y varies from 2.0018 to 2.0075, comprising the steps of:
- reacting in an aqueous, alcoholic or hydroalcoholic solution a derivative of silicon and a derivative of aluminum with a substance having an archivolt or clathrating effect selected from the group consisting of tertiary amines, aminoalcohols, aminoacids and polyalcohols, - crystallizing the reaction product in an enclosure for a period of from a few hours to several days at a temperature of from 100°C to 200°C, - cooling, filtering and drying the crystallizate, - firing in air at a temperature comprised between 300°C to 700°C for a time of from 2 hours to 24 hours, - washing the calcined product with distilled water, and - firing once again in air at a temperature comprised between 300°C and 700°C for a time of from 2 hours to 24 hours.

2. A process according to claim 1, wherein the derivative of silicon is selected from among a silica-gel no matter how obtained and a tetraalkyl orthosilicate.

3. A process according to claim 2, wherein the tetraalkyl orthosilicate is tetraethyl orthosilicate or tetra-methyl orthosilicate.

4. A process according to claim 1, wherein the derivative of aluminum is aluminum nitrate or acetate.

5. A process according to claim 1, wherein a miner-alizing agent is added, which is a member selected from the group consisting of LiOH, NaOH, KOH, Ca(OH)2, KBr, NaBr, NaI, CaI2 and CaBr2.

6. A process according to claim 1, wherein an inorganic base is added, which is a member selected from the group consisting of NaOH, KOH and Ca(OH)2.

7. A process according to claim 6, wherein the quantities of the inorganic base and/or of the substances having an archivolt or clathrating effect are less than the stoichiometric amount with respect to silica.

8. A process according to claim 7, wherein the quantities of the inorganic base and/or substance having an archivolt or clathrating effect are between 0.05 and 0.50 mol per mol of silica.

9. A method for the alkylation of hydrocarbons having four carbon atoms, olefines and/or saturated hydro-carbons, to obtain high-octane hydrocarbons, characterized in that use is made of a catalyst selected from among the alumi-num-modified silicas having a porous crystalline structure, and a specific surface area over 150 m2/g and corresponding to the general formula:

1. Si.(0.0012 - 0.0050) Al.Oy wherein y varies from 2.0018 to 2.0075.