Molecular sieve abstract
Hybrid mesoporous molecular sieve silica compositions which have
intergrown wormhole domains and lamellar or hexagonal domains and
prepared from mixtures of water soluble silicate precursors and
amine surfactant templates through a neutralization reaction are
described. The silica compositions are stable above 600.degree.
C.
Molecular sieve claims
We claim:
1. A hybrid mesoporous silica composition comprising a framework
structure defining the mesopores which is in one domain lamellar
or hexagonal and in another domain with wormhole pores and wherein
the domains are intergrown together, wherein the silica is defined
in anhydrous form, the silica has the formula:
wherein 1.0.gtoreq.w.gtoreq.0 and 1.5.gtoreq.x.gtoreq.0 and wherein
M when present is one or more metal ions.
2. The composition of claim 1 having at least one resolved X-ray
reflection and an X-ray diffraction pattern selected from the group
consisting of FIGS. 1 4 and 5.
3. The composition of claim 1 having a N.sub.2 adsorption-desorption
isotherm selected from the group consisting of FIGS. 2 and 6.
4. The composition of claim 1 having a BET surface area between
400 and 1400 m.sup.2 /g.
5. The composition of claim 1 having a textural mesopore volume
from 0.01 to 3 cc/g.
6. The composition of claim 1 having TEM micrograph selected from
the group consisting of FIGS. 3A, 7A and 8A.
7. The composition of claim 1 wherein the silica contains a hexagonal
framework structure.
8. The composition of claim 1 wherein said oxide has a composition
as follows:
wherein (SiM.sub.w O.sub.2+x) is written in anhydrous form without
water, wherein R--N is at least one of a selection of neutral aliphatic
amines or polyamine surfactants wherein when R--N is present, n
is between about 0.05 and 2; wherein when M is present at least
one element selected from the group comprising B, Ge, Sb, Zr, W,
P, Ba, Y, La, Ce, Sn, Ti, Cr, Nb, Fe, V, Ga, Al, Zn, Co, Ni, Mo
and Cu and w and 2+x are the molar stoichiometries of M and "O",
respectively, wherein w is 0.00 to 0.30; x is 0.00 to 1.50.
9. The composition of claim 8 having a X-ray diffraction pattern
selected from the group consisting of FIG. 4 wherein the main diffraction
peak corresponds to a basal spacing between 2.0 and 15 nm.
10. The composition of claim 8 in which the surfactant has been
removed from the silica matrix by calcination in air at 600.degree.
C.
11. The composition of claim 10 having a N.sub.2 adsorption-desorption
isotherm, the shape of which is as in FIG. 2.
12. The composition of claim 8 having a TEM micrograph selected
from the group consisting of FIGS. 3A, 7A and 8A.
13. The composition of claim 8 in which the surfactant has been
removed from silica by solvent extraction or by extraction with
an acid.
14. The composition of claim 1 wherein said silica has a composition
as follows:
wherein (SiM.sub.w O.sub.2+x) is written in anhydrous form without
water, wherein when M is present at least one element selected from
the group comprising B, Ge, Sb, Zr, W, P, Ba, Y, La, Ce, Sn, Ti,
Cr, Nb, Fe, V, Ga, Al, Zn, Co, Ni, Mo and Cu and w and 2+x are the
molar stoichiometries of M and "O", respectively, wherein
w is 0.00 to 0.30; x is 0.00 to 1.50.
15. The composition of claim 1 having a X-ray diffraction pattern
as in FIG. 1 or FIG. 5.
16. The composition of claim 1 in which the surfactant has been
removed from the silica by calcination in air.
17. The composition of claim 16 having a N.sub.2 adsorption-desorption
isotherm shape as in FIG. 2 or FIG. 6.
18. The composition of claim 16 having a TEM micrograph image selected
from the group consisting of FIGS. 3A, 7A and 8A.
19. The composition of claim 16 in which the surfactant has been
removed from the silica matrix by solvent extraction or extraction
with an acid.
20. The composition of claim 1 wherein said silica has a composition
expressed in anhydrous form as follows:
where E is one or more exchange ions, q is the weighted molar average
valence of E; n/q is moles of E per mole of Si, n is the charge
on the composition excluding E, and w and 2+x, respectively, are
the molar compositions of M and oxygen in the framework, wherein
1.0.gtoreq.w.gtoreq.0 and 1.5 .gtoreq.x.gtoreq.0.
21. The composition of claim 20 having a X-ray diffraction pattern
selected from the group consisting of FIGS. 1 and 5.
22. The composition of claim 20 in which the surfactant has been
removed from the silica by calcinations in air.
23. The composition of claim 22 having a N.sub.2 adsorption-desorption
isotherm shape as in FIG. 6.
24. The composition of claim 22 having a TEM micrograph selected
from the group consisting of FIGS. 3A, 7A and 8A.
25. The composition of claim 20 in which the surfactant has been
removed from the silica by solvent extraction or by extraction with
acid.
26. The composition of claim 27 having a N.sub.2 adsorption-desorption
isotherm shape selected from the group consisting of FIG. 6.
27. The composition of claim 1 having a TEM micrograph of FIG.
8A showing ordered pore structures in a hexagonal unit cell within
small particle materials and having a selected area electron diffraction
pattern showing polycrystalline ordering in the silica as seen by
multiple diffraction spots as shown in FIG. 8C.
28. The composition of claim 1 derived from a mixture of a neutral
amine, basic silicate and acid in an aqueous solution to produce
a pH between about 5 to 10.5.
29. The composition of claim 1 derived from a mixture of a protonated
amine and a basic silicate in an aqueous solution to produce a pH
between about 5.0 and 10.5.
30. A composition which is a hybrid wormhole and lamellar or hexagonal
framework molecular sieve silica prepared by a neutralizing reaction
in an aqueous solution of amine surfactant; a reactive silica species
of pH between 5.0 and 10.5; aging of the solution to precipitate
the silica and removing of the silica from the solution, wherein
the silica is defined in anhydrous form, the silica has the formula:
wherein 1.0.gtoreq.w.gtoreq.0 and 1.5.gtoreq.x.gtoreq.0 and wherein
M when present is one or more metal ions.
31. A composition which is a hybrid wormhole and lamellar or hexagonal
molecular sieve silica prepared by a process which comprises: (a)
acidifying an aqueous solution of an amine surfactant as a structure
director with an acid selected from the group consisting of organic,
mineral and oxy acids; (b) preparing a reactive silica species in
the aqueous solution by neutralization of a basic soluble silicate
solution by mixing with the acidified amine surfactant aqueous solution
of step (a) reaching a final pH of about 5 to 10.5; (c) aging the
reactive silica species from step (b) at a temperature greater than
-20.degree. C.; (d) recovering a solid product from the aqueous
solution by removal of the solution; and (e) removing the surfactant
from the solid by calcination at 600.degree. C. in air for not less
than 30 minutes, by solvent extraction, or by treatment with a stoichiometric
amount of aqueous acid solution and washing with water, to produce
the molecular sieve silica, wherein silica possesses framework-confined
mesopores with pore diameters ranging from 1.0 to 12.0 nm, the framework-confined
channel structure comprises a hybrid wormhole and lamellar or hexagonal
framework morphology has at least one resolved powder x-ray reflection
corresponding to a pore-pore correlation spacing of 1.5 to 15.0
nm, inorganic oxide wall thickness of greater than 0.5 nm, specific
surface areas of 400 to 1400 m.sup.2 /g and framework pore volumes
of 0.1 to 3 cc/g N.sub.2.
32. The composition of claim 31 wherein the silica in step (b)
is sodium silicate "water glass" with a SiO.sub.2 /Na.sub.2
O=1.5 to 4.0.
33. The composition of claim 31 wherein silica in step (b) is colloidal
silica or fumed silica.
34. The composition of claim 33 wherein soluble silica solution
is prepared with addition of an alkali, or organic base to dissolve
silica at a high pH greater than 12.
35. The composition of claim 31 wherein said acid is selected from
the group consisting of: HX where X.dbd.Cl, Br, I; H.sub.x Y where
Y=NO.sub.3.sup.-, SO.sub.4.sup.-2 PO.sub.4.sup.-3 CO.sub.3.sup.-2
and x equals the charge on Y; and HZ, where Z=an organic carboxylate,
phenolate, citrate, glycolate.
36. A composition which is a hybrid molecular sieve silica prepared
by a process that comprises: (a) preparing an aqueous solution of
a amine surfactant as an organic structure director; (b) adding
a basic soluble silicate to the amine solution; (c) neutralizing
the basic amine and silicate solution with an acid selected from
the group consisting of organic, mineral and oxy acids to a final
pH of about 5.0 to 10.5 to provide a reactive silica; (d) aging
reactive silica from step (b) at temperatures greater than -20.degree.
C.; (e) recovering a solid product from the aqueous solution; and
(f) removing the surfactant by removal of the solution to provide
the molecular sieve silica, wherein the silica possesses framework-confined
mesopores with pore diameters ranging from 1.0 to 12.0 nm, the framework-confined
channel structure comprises the hybrid of a wormhole and lamellar
or wormhole framework morphology, has one resolved powder X-ray
reflection corresponding to a pore-pore correlation spacing of 1.5
to 15.0 nm, inorganic oxide wall thickness of greater than 0.5 nm,
specific surface areas of 400 to 1400 m.sup.2 /g and framework pore
volumes of 0.2 to 3.0 cc/g N.sub.2.
37. A composition which is a hybrid molecular sieve silica prepared
by a process which comprises: (a) acidifying an aqueous solution
of an amine surfactant containing an alkyl chain with 6 to 36 carbon
atoms as the organic structure director with an acid selected from
the group consisting of organic, mineral and oxy acids; (b) preparing
a reactive silica species by addition of a soluble silicate to the
acidified amine surfactant reaching a pH of less than 4; (c) titrating
the reactive silica with a base to a final pH of about 5.0 to 10.5;
(d) aging reactive silica from step (b) at temperatures greater
than -20.degree. C.; (e) recovering a solid product from the aqueous
solution; and (f) removing the surfactant from the solid product
to provide the molecular sieve silica, wherein the resulting inorganic
oxide possesses framework-confined mesopores with pore diameters
ranging from 10 to 12.0 nm, the framework-confined channel structure
comprises the hybrid of a wormhole and lamellar or hexagonal framework
morphology, has at least one resolved powder x-ray reflection corresponding
to a pore-pore correlation spacing of 1.5 to 15.0 nm, inorganic
oxide wall thickness of greater than 0.5 nm, specific surface areas
of 400 to 1400 m.sup.2 /g and framework pore volumes of 0.2 to 3.0
cc/g N.sub.2.
38. A process for the preparation of a hybrid wormhole and lamellar
or hexagonal molecular sieve silica which comprises: (a) reacting
in an aqueous solution, an amine surfactant and a reactive silica
species of pH between 5.0 and 10.5; (b) aging the solution to precipitate
the silica; and (c) removing the silica from the solution.
39. A process for the preparation of a hybrid molecular sieve silica
which comprises: (a) providing a protonated amine surfactant solution
with a pH below 7.0; (b) reacting the protonated amine surfactant
solution with a mixture of a base and a soluble silicate solution
to produce a reactive silica species at a final pH between about
5.0 and 10.5; (c) aging the reactive silica species in the solution
of step (b) at a temperature greater than -20.degree. C. to form
a precipitated product which is the silica in the solution; and
(d) recovering the precipitated product from the solution.
40. The process of claim 39 wherein the surfactant is removed from
the precipitated product.
41. A process for the preparation of a hybrid molecular sieve silica
which comprises: (a) acidifying surfactant solution of a neutral
amine surfactant with an acid thereof to produce a pH below 7.0;
(b) forming a reactive silica species by neutralization of a soluble
silicate solution with the surfactant solution of step (a) to provide
a final pH of about 5.0 to 10.5; (c) aging the reactive silica species
in the solution of step (b) at a temperature greater than -20.degree.
C. to form a precipitated product which is the silica composition
in the solution; and (d) recovering the precipitated product from
the solution.
42. The process of claim 41 wherein soluble silica solution is
a sodium silicate with SiO.sub.2 /OH.sup.- ratio of between 0.7
and 2.
43. The process of claim 41 wherein the acid is an organic acid.
44. The process of claim 43 wherein the acid is selected from the
group consisting of acetic, glycolic, formic and citric acid.
45. The process of claim 41 wherein the surfactant is removed by
calcination, solvent extraction or acid washing.
46. The process of claim 41 with the additional step (d) of removing
the surfactant and by calcination of the precipitated product in
air for not less than 30 minutes.
47. A process for the preparation of a hybrid molecular sieve silica
which comprises: (a) providing an aqueous solution of a water soluble
silicate at a pH greater than 9; (b) combining the aqueous solution
with a neutral amine surfactant and an acid to produce a resulting
mixture wherein the pH of the mixture is between about 5.0 and 10.5;
(c) aging the resulting mixture at a temperature between -20.degree.
and 100.degree. C. until the hybrid molecular sieve silica is formed;
and (d) removing at least the aqueous solution to produce the hybrid
molecular sieve silica.
48. A process for the preparation of a hybrid molecular sieve aluminosilicate
which comprises: (a) providing an aqueous solution of a water soluble
aluminate and silicate in a molar ratio of aluminate to silicate
of between about 0.01 and 1.0 at a pH greater than 9; (b) combining
the aqueous solution with a neutral amine surfactant and an acid
in aqueous solution to produce a resulting mixture wherein the pH
of the mixture to be between about 5.0 and 10.5; (c) aging the resulting
mixture at a temperature between -20.degree. and 100.degree. C.
until the hybrid molecular sieve aluminosilicate is formed; and
(d) removing at least the aqueous solution to produce the hybrid
molecular sieve aluminosilicate.
49. A process for the preparation of a hybrid molecular sieve aluminosilicate
which comprises: (a) providing an aqueous solution of a water soluble
silicate at a pH greater than 9; (b) combining the aqueous solution
with a neutral amine surfactant, an aluminum salt and an acid in
aqueous solution to produce a resulting mixture wherein the aluminum
to silicon molar ratio is between 0.01 and 1.0 and the pH of the
mixture to be between about 5.0 and 10.5; (c) aging the resulting
mixture at a temperature between -20.degree. and 100.degree. C.
until the hybrid molecular sieve aluminosilicate is formed; and
(d) removing at least the aqueous solution to produce the hybrid
molecular sieve aluminosilicate.
50. The process of claim 49 wherein in step (d) the surfactant
and water are removed from the aluminosilicate so that aluminosilicate
is dry.
51. The process of claim 49 wherein the aluminosilicate is calcined.
52. The process of claim 49 wherein the aluminum salt is selected
from the group consisting of aluminum nitrate, aluminum chloride,
aluminum sulfate and a cationic aluminum oligomer.
Molecular sieve description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to thermally stable hybrid molecular
sieve silicas generally having uniform pores, and specifically to
calcined silicas. The silicas have hybrid wormhole and either lamellar
or hexagonal structures intergrown together. In particular, the
present invention relates to the use of water soluble silicates
and preferably neutral amine surfactants surfactants for the preparation
of these thermally stable silicas. In particular the present invention
relates to mesoporous silicas having a pore size between about 1.0
and 12 nm.
(2) Description of Related Art
The disclosure by Mobil in 1992 (Beck, J. S., et al., J. Am. Chem.
Soc. 114 10834 (1992)) of the synthesis of mesoporous aluminosilicate
molecular sieves (M41S materials) utilizing assemblies of cationic
organic molecules (micelles) as structure directors led to a vast
amount of research into this field. To date, the synthesis of mesoporous
molecular sieves can be classified into several general pathways
according to their organic-inorganic interfacial interactions. Electrostatic
charge matching (Beck, J. S., et al., J. Am. Chem. Soc. 114 10834
(1992); Huo, Q., et al., Chem. Mater. 6 1176 (1994); Huo, Q., et
al., Nature 368 317 (1994)), H-bonding (Tanev, P. T., et al., Science
267 865 (1994); and Bagshaw, S. A., et al., Angwen. Chem. Int. Ed.
Engl. 36 516 (1997)), and dative bonding interactions (Antonelli,
D. M., et al., Angwen. Chem. Int. Ed. Engl., 35 426 (1996); and
Antonelli, D. M., et al., Chem. Mater 8 874 (1996)) at the organic
micelle-inorganic interface have all been successfully utilized
in the formation of mesostructured inorganic materials.
Electrostatic charge matching pathways utilize coulombic interactions
between the charged structure directing surfactant assemblies (micelles)
and ionic silica species in the assembly of stable inorganic framework
structures. As reported by Mobil, synthesis of the M41S family of
molecular sieves relies on cooperative assembly between cationic
quaternary ammonium surfactant micelles (S.sup.+) and anionic water-soluble
silicates (I.sup.-). Synthesis under hydrothermal conditions results
in mesoporous silicates that possess a high degree of framework
pore order. M41S materials are generally large particle materials
that have uniform pore diameters, significantly large surface areas
(-800-1200 m.sup.2 /g) and little to no observable textural mesoporosity
(Tanev, P. T., et al., Chem. Mater. 8 2068 (1996)). Due to the strong
coulombic interactions between the surfactant and the silica wall,
however, a simple solvent extraction and recycling of this costly
quaternary ammonium surfactant is not possible. Surfactant removal
is accomplished either by calcinations or by an ion exchange-solvent
extraction method (Whitehurst, D. D. U.S. Pat. No. 6143879 (1992)).
The syntheses of HMS materials rely on H-bonding interactions between
the neutral amine surfactant (S.sup.o) assemblies and molecular
silica precursors (I.sup.o) such as tetraethylorthosilica (TEOS)
(Tanev, P. T., et al., Science 267 865 (1995)). This H-bonding interaction
is significantly weaker than the coulombic interactions of the electrostatic
pathways resulting in the disordered wormhole pore structure typical
of HMS silicas (Tanev, P. T., et al., Science 267 865 (1995); Tanev,
P. T., et al., Chem. Mater. 8 2068 (1996); and Behrens, P., Angew.
Chem. Int. Ed. Engl. 35(5) 515 (1996)). This wormhole pore structure
has significant pore branching and 3-dimensional pore character.
Characteristic properties of HMS silicas, however, are similar to
those of electrostatically assembled mesostructures in their pore
size distributions, surface areas, and pore volumes. Additionally,
synthesis of these silicas in highly polar solvents, where the surfactant
exists in an emulsion phase, results in small particle materials
that possess significant textural, or inter-particle, porosity (Pauly,
T. R., et al., J. Am. Chem. Soc. 121 8835 (1999)). This fact along
with the highly branched pore structure yields a mesoporous material
that exhibits unique catalytic activity due to the enhanced access
to reactive sites (Pauly, T. R., et al., J. Am. Chem. Soc. 121 8835
(1999)).
Long alkyl chain amine surfactants used in HMS synthesis are significantly
less costly than quaternary ammonium salts used in the synthesis
of M41S and SBA materials. The use of TEOS or other molecular silica
species, however, is considerably more expensive than available
water soluble silicate species. Thus far, however, mesostructure
synthesis using H-bonding mechanisms with neutral amine surfactants
required the use of molecular silica species.
Mesoporous molecular sieve silicas with wormhole framework structures
(e.g., MSU-X (Bagshaw, S. A., et al., Science 269 1242 (1994); Bagshaw,
S. A., et al., Angwen. Chem. Int. Ed. Engl. 35 1102 (1996); Prouzet,
E. et al., Angwen. Chem. Int. Ed. Engl. 36 516 (1997), and HMS (Tanev,
P. t., et al., Science 267 865 (1995)) are generally more active
heterogeneous catalysts in comparison to their ordered hexagonal
analogs (e.g., MCM-41 (Beck, J. S., et al., J. Am. Chem. Soc. 114
10834 (1992); and Huo, Q., et al., Nature 368 317 (1994)), and SBA-15
(Stucky, JACS). The enhanced reactivity has been attributed, in
part, to a pore network that is connected in three dimensions, allowing
the guest molecules to more readily access reactive centers that
have been designed into the framework surfaces (Tanev, P. T., et
al., Chem. Mater. 8 2068 (1996); Whitehurst, D. D. U.S. Pat. No.
6143879 (1992); Behrens, P. Angwen. Chem. Int. Ed. Engl. 35(5),
515 (1996); and Pauly, T. R., et al., J. Am. Chem. Soc. 121 8835
(1999)). All of the wormhole framework structures reported to date
have been prepared through supramolecular S.sup.o I.sup.o (Tanev,
P. T., et al., Science 267 865 (1995) and N.sup.o I.sup.o (Bagshaw,
S. A., et al., Angwen. Chem. Int. Ed. Engl. 35 1102 (1996); Prouzet,
E., et al., Angwen. Chem. Int. Ed. Engl. 36 516 (1997)) assembly
pathways wherein I.sup.o is an electrically neutral silica precursor
(typically, tetraethylorthosilicate, TEOS), S.sup.o is a neutral
amine surfactant, and N.sup.o is a neutral di- or tri-block surfactant
containing polar polyethylene oxide (PEO) segments. One disadvantage
of these pathways, as with other assembly pathways based on TEOS,
is the high cost of the hydrolyzable silicon alkoxide precursor.
Greater use of wormhole framework structures as heterogeneous catalysts
can be anticipated if a more efficient approach to either S.sup.o
I.sup.o or N.sup.o I.sup.o assembly is devised based on the use
of low cost soluble silicate precursors, without sacrificing the
intrinsically desirable processing advantages of these pathways
(e.g., facile removal and recycling of the surfactant).
Recently, Guth and co-workers reported the preparation of disordered
silica mesostructures by precipitation from sodium silicate solutions
over a broad range of pH in the presence of TRITON-X 100 an N.sup.o
surfactant (Sierra, L., et al., Adv. Mater 11(4) 307 (1999); and
Sierra, L., et al., Microporous and Mesoporous Materials 27 243
(1999)). The retention of a mesostructure was observed up to a calcination
temperature of 480.degree. C., but the complete removal of the surfactant
at 600.degree. C. led either to the extensive restructuring of the
silica framework, as indicated by the loss of mesoporosity or the
formation of a completely amorphous material. In contrast wormhole
MSU-X and HMS mesostructures are structurally stable to calcination
temperatures in excess of 800.degree. C.
Of interest is the use of an aqueous acid solution to extract an
amine surfactant template from the as-formed mesoporous silica composition.
This is reported by Cassiers et al., Royal Society of Chemistry
2489-2490 (2000).
U.S. Pat. Nos. 5800799 6027706 5622684 5795559 5855864
5672556 5840264 5800800 5785946 and 5712402 are generally
related to the present invention.
Objects
There is a need for mesoporous silica compositions with improved
properties. There is also a need for mesostructured silica compositions
which are economical to prepare. These and other objects will become
increasingly apparent by reference to the following description
and the drawings.
SUMMARY OF THE INVENTION
The present invention relates to hybrid mesoporous silica compositions
in which the framework pore structure is defined by the intergrowth
of nano-domains of both wormhole framework pore structures and either
lamellar or hexagonal framework pore structures. Typically, the
nano-domains are of 100 nm or less in diameter and do not possess
a distinct boundary between adjacent domains.
The present invention relates to a hybrid molecular sieve silica
composition comprising a framework structure defining the mesopores
which is in one domain lamellar or hexagonal and in another domain
with wormhole pores and wherein the domains are intergrown together.
Typically the domain sizes are 100 nm or less.
The present invention also relates to a composition which is a
hybrid wormhole and lamellar or hexagonal framework molecular sieve
silica prepared by a neutralizing reaction in an aqueous solution
of amine surfactant; a reactive silica species of pH balance 5 and
10.5; aging of the solution to precipitate the silica and removing
of the silica from the solution.
The present invention particularly relates to a composition which
is a hybrid wormhole and lamellar or hexagonal molecular sieve silica
prepared by a process which comprises: (a) acidifying an aqueous
solution of an amine surfactant, preferably containing 6 to 36 carbon
atoms, as a structure director with an acid selected from the group
consisting of organic, mineral and oxy acids; (b) preparing a reactive
silica species in the aqueous solution by neutralization of a basic
soluble silicate solution by mixing with the acidified amine surfactant
aqueous solution of step (a) reaching a final pH of about 5 to 10.5;
(c) aging the reactive silica species from step (b), preferably
for no less than 5 minutes, at a temperature greater than -20.degree.
C. in anhydrous form. The silica has the formula: (c) aging the
reactive silica species from step (b), preferably for no less than
5 minutes, at a temperature greater than -20.degree. C. in anhydrous
form. The silica has the formula:
wherein 1.0.gtoreq.w.gtoreq.0 and 1.5.gtoreq.x.gtoreq.0 and wherein
M when present is one or more metal ions. wherein 1.0.gtoreq.w.gtoreq.0
and 1.5.gtoreq.x.gtoreq.0 and wherein M when present is one or more
metal ions. (d) recovering a solid product from the aqueous solution
by removal of the solution; and (e) removing the surfactant from
the solid by calcination at 600.degree. C. in air for not less than
30 minutes, by solvent extraction, or by treatment with a stoichiometric
amount of aqueous acid solution and washing with water, to produce
the molecular sieve silica, wherein silica possesses framework-confined
mesopores with pore diameters ranging from 1.0 to 12.0 nm, the framework-confined
channel structure comprises a hybrid wormhole and lamellar or hexagonal
framework morphology has at least one resolved powder x-ray reflection
corresponding to a pore-pore correlation spacing of 1.5 to 15.0
nm, inorganic oxide wall thickness of greater than 0.5 nm, specific
surface areas of 400 to 1400 m.sup.2 /g and framework pore volumes
of 0.2 to 2.0 cc/g N.sub.2 preferably with textural pore volumes
of 0.01 to 3 cc/g N.sub.2.
The present invention further relates to a composition which is
a hybrid molecular sieve silica prepared by a process that comprises:
(a) preparing an aqueous solution of a amine surfactant as an organic
structure director; (b) adding a basic soluble silicate to the amine
solution; (c) neutralizing the basic amine and silicate solution
with an acid selected from the group consisting of organic, mineral
and oxy acids to a final pH of about 5.0 to 10.5 to provide a reactive
silica; (d) aging reactive silica from step (b) at temperatures
greater than -20.degree. C.; (e) recovering a solid product from
the aqueous solution; and (f) removing the surfactant by removal
of the solution to provide the molecular sieve silica, wherein the
silica possesses framework-confined mesopores with pore diameters
ranging from 1.0 to 12.0 nm, the framework-confined channel structure
comprises the hybrid, a wormhole and lamellar or wormhole framework
morphology, has one resolved powder X-ray reflection corresponding
to a pore-pore correlation spacing of 1.5 to 15.0 nm, inorganic
oxide wall thickness of greater than 0.5 nm, specific surface areas
of 400 to 1400 m.sup.2 /g and framework pore volumes of 0.2 to 3.0
cc/g N.sub.2 and preferably textural pore volumes of 0.01 to 3
cc/g N.sub.2.
The present invention further relates to a composition which is
a hybrid molecular sieve silica prepared by a process which comprises:
(a) acidifying an aqueous solution of an amine surfactant containing
an alkyl chain with 6 to 36 carbon atoms as the organic structure
director with an acid selected from the group consisting of organic,
mineral and oxy acids; (b) preparing a reactive silica species by
addition of a soluble silicate to the acidified amine surfactant
reaching a pH of less than 4; (c) titrating the reactive silica
with a base to a final pH of about 5.0 to 10.5; (d) aging reactive
silica from step (b) at temperatures greater than -20.degree. C.;
(e) recovering a solid product from the aqueous solution; and (f)
removing the surfactant from the solid product to provide the molecular
sieve silica, wherein the resulting inorganic oxide possesses framework-confined
mesopores with pore diameters ranging from 10 to 12.0 nm, the framework-confined
channel structure comprises the hybrid of a wormhole and lamellar
or hexagonal framework morphology, has at least one resolved powder
x-ray reflection corresponding to a pore-pore correlation spacing
of 1.5 to 15.0 nm, inorganic oxide wall thickness of greater than
0.5 nm, specific surface areas of 400 to 1400 m.sup.2 /g and framework
pore volumes of 0.2 to 2.0 cc/g N.sub.2 and textural pore volumes
of 0.01 to 3 cc/g N.sub.2.
The present invention relates to a process for the preparation
of a hybrid wormhole and lamellar or hexagonal molecular sieve silica
which comprises: (a) reacting in an aqueous solution, an amine surfactant
and a reactive silica species of pH between 5 and 10.5; (b) aging
the solution to precipitate the silica; and (c) removing the silica
from the solution.
The present invention further relates to a process for the preparation
of a hybrid molecular sieve silica which comprises: (a) providing
a protonated amine surfactant solution with a pH below 7.0; (b)
reacting the protonated amine surfactant solution with a mixture
of a base and a soluble silicate solution to produce a reactive
silica species at a final pH between about 5 and 10.5; (c) aging
the reactive silica species in the solution of step (b) at a temperature
greater than -20.degree. C. to form a precipitated product which
is the silica in the solution; and (d) recovering the precipitated
product from the solution.
The present invention further relates to a process for the preparation
of a hybrid molecular sieve silica which comprises: (a) acidifying
a surfactant solution of a neutral amine surfactant with an acid
thereof to produce a pH below 7.0; (b) forming a reactive silica
species by neutralization of a soluble silicate solution with the
surfactant solution of step (a) to provide a final pH of about 5.0
to 10.5; (c) aging the reactive silica species in the solution of
step (b) at a temperature greater than -20.degree. C. to form a
precipitated product which is the silica in the solution; and (d)
recovering the precipitated product from the solution.
The present invention further relates to a process for the preparation
of a hybrid molecular sieve silica which comprises: (a) providing
an aqueous solution of a water soluble silicate at a pH greater
than 9; (b) combining the aqueous solution with a neutral amine
surfactant and an acid to produce a resulting mixture wherein the
pH of the mixture is between about 5.0 and 10.5; (c) aging the resulting
mixture at a temperature between -20.degree. and 100.degree. C.
until the hybrid molecular sieve silica is formed; and (d) removing
at least the aqueous solution to produce the hybrid molecular sieve
silica.
The present invention further relates to a process for the preparation
of a hybrid molecular sieve aluminosilicate which comprises: (a)
providing an aqueous solution of a water soluble aluminate and silicate
in a molar ratio of aluminate to silicate of between about 0.01
and 1.0 at a pH greater than 9; (b) combining the aqueous solution
with neutral amine surfactant and an acid in aqueous solution to
produce a resulting mixture wherein the pH of the mixture to be
between about 5.0 and 10.5; (c) aging the resulting mixture at a
temperature between -20.degree. and 100.degree. C. until the hybrid
molecular sieve aluminosilicate is formed; and (d) removing at least
the aqueous solution to produce the hybrid molecular sieve aluminosilicate.
Further the present invention relates to a process for the preparation
of a hybrid molecular sieve alumino-silicate which comprises: (a)
providing an aqueous solution of a water soluble silicate at a pH
greater than 9; (b) combining the aqueous solution with a neutral
amine surfactant, an aluminum salt and an acid in aqueous solution
to produce a resulting mixture wherein the aluminum to silicon molar
ratio is between 0.01 and 1.0 and the pH of the mixture to be between
about 5.0 and 10.5; (c) aging the resulting mixture at a temperature
between -20.degree. and 100.degree. C. until the hybrid molecular
sieve aluminosilicate is formed; and (d) removing at least the aqueous
solution to produce the hybrid molecular sieve aluminosilicate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an X-ray powder diffraction pattern of the calcined product
of Example 1.
FIG. 2 is a graph showing a N.sub.2 adsorption-desorption isotherm
of the calcined product of Example 1.
FIGS. 3A and 3B are TEM micrographs of the calcined product of
Example 1.
FIG. 4 is an X-ray powder diffraction pattern of the as-synthesized
product of Example 2.
FIG. 5 is an X-ray powder diffraction pattern of the calcined product
of Example 3.
FIG. 6 is a graph showing a N.sub.2 adsorption-desorption isotherm
of the calcined product of Example 3.
FIGS. 7A and 7B are TEM micrographs of the calcined product of
Example 3.
FIGS. 8A and 8B are TEM micrographs and selected area electron
diffraction pattern (SAED) pattern of the calcined product of Example
15.
FIG. 8C is a selected area electron diffraction pattern (SAED).
DESCRIPTION OF PREFERRED EMBODIMENTS
A particular objective of this invention is to provide for new
classes of mesoporous silica compositions with hybrid framework
structures. In one embodiment of the invention, the mesoporous framework
combines the structural characteristics of a wormhole framework
with those of a lamellar framework. In another embodiment, the framework
structure integrates a wormhole framework with the structural characteristics
of a hexagonal framework. These hybrid structures cannot be described
as simple physical mixtures of wormhole and lamellar or wormhole
and hexagonal structures. Instead, the hybrid compositions of this
invention are intergrowths of mesoscopic domains that are structurally
best described as wormhole frameworks intergrown with either lamellar
or hexagonal frameworks through intergrowth of domains. Thus, a
physical separation of the intergrown domains is not possible. Another
objective of this invention is to provide a cost-efficient process
for forming the said hybrid structures using soluble silicates as
the silica precursors and amine surfactants as the structure-directing
agents. One particularly preferred silica precursor is the silica-sodium
hydroxide solution generally known as "water glass". Other
silica sources such as fumed silica can also be used in place of
soluble silicate salts, but the soluble silicates are preferred
in view of their low cost. The synthesis of the hybrid structure
are carried out under conditions of pH (between 5.0 and 10.5) where
the amine surfactant exists in solution primarily in the electronically
neutral form. To achieve the desired pH conditions, it is necessary
to add an amount of acid to the basic soluble silicate precursor
solution in order to neutralize most, if not all, of the hydroxide
ions that are initially present in the starting soluble silicate
solution. The acid used to neutralize hydroxide ions in the silicate
precursor solution can be either an organic acid, a mineral acid
or an oxyacid. The control of pH in the range 5.0 to 10.5 more
preferably in the range 6.5 to 8.5 allows the amine surfactant
and silica precursor to exist primarily in electrically neutral
form to allow for H-bonding interactions at the surfactant-silica
interface.
In particular the process uses:
(a) increased temperatures to increase pore size and (b) increased
temperatures to increase framework cross-linking and dehydroxylation
of the pore surface. Control of particle size and morphology also
is achieved by adjustment of these synthesis conditions. The compositions
of the present invention contain: Variable alkali (metal) ions or
quaternary ammonium ions in the final product. These ions originate
from the counter-cations of the soluble silicate precursors. Variable
amine surfactant to SiO.sub.2 ratios (0.10 to 1.0). Uniform framework
pore sizes and correlated pore spacings leading to unique disordered
wormhole hybrid structures intergrown with lamellar or hexagonal
framework structures over domains of mesoscopic size. Framework
pore diameters from 1.0 to 12.0 nm formed from amine templated solutions.
Short-range lamellar and hexagonal pore order intergrown with wormhole
frameworks obtained through judicious choices of amine surfactant,
synthesis pH, reaction stoichiometry and reaction temperature. Divalent
and Trivalent hetero-atom substitution (Ba, Cr, Ni, Zn, Co, Cu,
Al, B, Ga, Fe, etc.) in a mesostructured silica framework. Tetravalent
hetero-atom substitution (Ge, Ti, V, Sb, Zr, Sn, etc.) in a mesostructured
silica framework. Penta- or Hexavalent hetero-atom substitution
(P, V, W, Mo, etc.) in a mesostructured silica framework. The compositions
of the present invention are generally referred to as "hybrid
molecular sieve silicas", or simply "silicas" or
occasionally "silicates". In using such terms the meaning
is mesostructured oxide compositions in which at least 50% of the
oxide on a mole basis is silica (SiO.sub.2) when written in anhydrous
form. The remaining portion of the framework composition may be
other metal oxides or even organosilyl groups that are integrated
into the framework structure through covalent bond formation. Exchange
cations that balance the framework charge and guest molecules, such
as water, that occupy the framework pores are not considered to
be part of the framework composition within the scope of this definition.
The framework may be negatively charged, particularly when the framework
contains aluminum and other metal ions co-condensed with SiO.sub.4
units in the framework. In this case protons, alkali metal, transition
metal or organic cations can be introduced in the framework pores
or be electrostatically linked to the framework walls to balance
the framework charge.
Further, the compositions of the present invention exhibit at least
one x-ray reflection corresponding to a d-spacing .gtoreq.3.0 nm.
Still further, TEM (transmission electron microscopy) images reveal
a framework structure that integrates the structural characteristics
of a wormhole framework with the structural characteristics of either
a lamellar framework or a hexagonal framework through intergrowth
of mesoscopic domains of said structures.
The term "surfactant" means a surface active molecule
with one polar water soluble end and a non-polar oil soluble end,
thus enabling the molecule to reduce the surface tension of water.
The term "neutral amine surfactant" means a composition
which is a surface active agent initially absent of any formal charge
which acts as a template or structure director. The template is
provided with a proton from an acid during acidification to form
an onium ion in a first aqueous solution which is neutralized in
the process by the basic silica species in a second aqueous solution.
Particularly included are the neutral amine surfactants. The template
is in one preferred embodiment a neutral primary, secondary, tertiary
or polyamine or mixtures thereof, preferably having at least one
alkyl chain of from 6 to 36 carbon atoms or mixtures thereof. The
amines can also be aliphatic or aromatic amines. The amine or polyamine
surfactant may be initially protonated but upon reaction with basic
solutions of the preferred soluble silicate precursors the protons
are neutralized by reaction with the basic component of the silicate
source, thus generating a predominately neutral amine or polyamine
as the structure-directing surfactant.
The neutral amine surfactant preferably has the structural formula:
##STR1##
R.sub.1 is a hydrophobic group preferably containing 6 to 36 carbon
atoms;
R.sub.2 R.sub.4 R.sub.5 are alkyl or aryl groups or hydrogen;
R.sub.3 is an organic linker group containing one to six carbon
atoms; and
x is 0 to 6. Synthesis of polyamine surfactants comprises reacting
tallow (animal) fatty acids with ammonia (NH.sub.3) at high temperatures
followed by the subsequent reduction of the resultant nitrile with
H.sub.2 over a ReNi catalyst at high pressures. Continued reaction
of the reduced amine with acrylonitrile (CH.sub.2 CHCN), followed
by subsequent reduction with H.sub.2 results in polyamine whose
amine content and number of amine repeat units is dependent on the
number of continued alkylations of the amine with acrylonitrile.
Those skilled in the art will recognize that any amine or protonated
onium surfactants capable of bonding to inorganic precursors through
complexation or through hydrogen bonds to Si--OH or Si--O linkages
can be suitable surfactants. Polyamine based surfactants have the
advantage of low cost.
The term "soluble silicate solution" means a basic solution
of an alkali metal or organic quaternary ammonium ion silicate.
The soluble silica solution is prepared with addition of an alkali,
or organic base to dissolve silica at a high pH greater than 12.
Preferably the solution has a SiO.sub.2 /M.sub.2 O ratio of between
about 1.5 and 4.0 where M is an alkali metal ion or an organic
quaternary ammonium ion.
The aluminum salts are aluminum nitrate, aluminum chloride, aluminum
sulfate and a cationic aluminum oligomer.
The reaction mixture can include an organo silane selected from
the group consisting of X.sub.3 SiR.sub.1 X.sub.2 SiR.sub.2 or
XSiR.sub.3 and mixtures thereof. X is a hydrolyzable moiety (e.g.
alkoxide or halide), which reacts with the hydroxylated silica.
The acid used in the neutralization of the reaction mixture can
be either an inorganic or organic acid. Generally this includes
organic acids, mineral acids and oxyacids. Inorganic acids are HNO.sub.3
HCl, H.sub.2 SO.sub.4 and the like. Specific organic acids are acetic,
glycolic, formic and citric acids, although other acids with similar
properties are suitable.
The acid is selected from the group consisting of:
HX where X.dbd.Cl, Br, I;
H.sub.x Y where Y=NO.sub.3.sup.-, SO.sub.4.sup.-2 PO.sub.4.sup.-3
CO.sub.3.sup.-2 and x equals the charge on Y; and
HZ, where Z=an organic carboxylate, phenolate, citrate, glycolate.
The hydroxylated silica composition of the present invention preferably
has the formula:
wherein [SiM.sub.w O.sub.2+x ] is written in anhydrous form without
water, wherein R-N is at least one of a selection of neutral aliphatic
amines or polyamine surfactants wherein when R-N is present, n is
between about 0.05 and 2; wherein when M is present at least one
element selected from the group comprising P, Ba, Y, La, Ce, Sn,
Ti, Cr, Nb, Fe, V, Ga, Al, Zn, Co, Ni, Mo and Cu and w and 2+x are
the molar stoichiometries of M and "O", respectively,
wherein w is 0.00 to 0.30; x is 0.00 to 1.50.
After removal of the structure-directing RN amine surfactant by
calcination, solvent extraction, or treatment with a stoichiometric
amount of acid, the compositions of the present invention also are
described in anhydrous form as SiM.sub.w O.sub.2+x wherein w and
x are as above. They may be used as adsorbents, molecular sieves,
catalysts and catalyst supports. When the calcined framework appropriately
contains M, one or more functional metallic, non-metallic or metalloid
elements, or subsequently impregnated as taught in Ger. Pat. (DD)
No. 286522 with the correct amount of a catalytically active element,
selected from the group comprising Sn, Al, Ga, Al, Rh, Nb, Re, Ag,
Cu, Cr, Pt, Pd, Ti, V, Zr, Zn, Co, Mo, Ni, Cu or mixtures thereof,
or when intercalated with transition metal inorganic metallocycles,
it can be used as a catalyst component for cracking, hydrocracking,
hydrogenation-dehydrogenation, isomerization, alkylation or oxidations
involving large and small organic substrates. Preferably the molar
ratio of deposited metal to silica is between 0.005 and 0.20 to
1. The compositions of this invention are also useful as adsorbents
for molecular separations and chromatography.
The composition with exchange counter ions is defined in anhydrous
form by the formula:
where E is one or more exchange ions, q is the weighted molar average
valence of E; n/q is moles of E per mole of Si, n is the charge
on the composition excluding E, and w and x, respectively, are the
molar compositions of M and oxygen in the framework.
The synthetic process toward the new compositions of this invention
involve the preparation of solutions or emulsions of a structure-directing
surfactant and co-surfactant compound and reaction of this solution
with the inorganic silica precursor under stirring, sonication,
shaking, or quiescent conditions until formation of the desired
product is achieved and recovered as the mesoporous silica product.
The assembled mesostructured silicas of the present invention can
be combined with other components, for example, zeolites, clays,
inorganic oxides, carbon, graphite, or organic polymers or mixtures
thereof. In this way adsorbents, ion-exchangers, catalysts, catalyst
supports or composite materials with a wide variety of properties
can be prepared. Additionally, one skilled in the art can impregnate
or encapsulate transition metal macrocylic molecules such a porphyrins
or phthalocyanines containing a wide variety of catalytically active
metal centers.
Additionally, the surfaces of the compositions can be chemically
functionalized in order to produce catalytic, hydrophilic or hydrophobic
surfaces. The surfaces may be functionalized by directly incorporating
the functionalizing agent into the mesostructure assembly process
or after synthesis of the mesostructure by reaction with various
metal salts, organometallic reagents, silylation reagents, or alkylating
reagents.
Wide-angle powder x-ray diffraction (XRD) patterns are obtained
using a Rigaku Rotaflex Diffractometer with Cu K.alpha. radiation
(.lambda.=0.154 nm). Counts were accumulated every 0.02 degrees
(20) at a scan speed of 1 degree (2.theta.)/min. X-ray scattering
provides structural data on the spatial arrangement of mesoporous
channels within the porous oxide on one length scale, and the atomic
ordering of the oxide itself on a smaller length scale. Periodically
ordered channels within an oxide and/or the crystalline oxide itself,
will provide Bragg scattering indicative of the corresponding symmetry.
Coherent X-ray scattering from disordered channel structures, however,
results in correlation peaks whose scattering intensity versus angle
is dependent on the average pore to pore distance and the uniformity
of the pore separation distance within the oxide. Differences in
the positions of the correlation peak for disordered pore systems
indicate changes in the average pore-pore separation.
N.sub.2 adsorption-desorption isotherms are obtained at -196.degree.
C. on a Micromeritics ASAP 2010 Sorptometer (Norcross, Ga.) using
static adsorption procedures in order to characterize the pore structure.
Samples were out gassed at 150.degree. C. and 10.sup.-6 Torr for
a minimum of 12 hours prior to analysis. BET surface areas were
calculated from the linear part of the BET plot according to IUPAC
(Sing, K. S. W., et al., Pure Appl. Chem. 57 603 (1985)) recommendations.
Pore size distribution was estimated from the adsorption branch
of the isotherm by the method of Horvath and Kawazoe (Horvath, G.,
et al., J. Chem. Eng. Jpn. 16 470 (1983)). The framework pore volume
(V.sub.f) for each mesostructured sample is taken as the volume
adsorbed at the completion of capillary condensation within the
framework pores (mid-P/Po N.sub.2 uptake), whereas the total pore
volume (V.sub.t) is the volume adsorbed at 0.99 P/Po. The textural
pore volume (V.sub.tx) is the difference (V.sub.t -V.sub.f). Pore
wall thickness for disordered pore oxides is determined by subtracting
the Horvath-Kawazoe (HK) pore size from the pore-pore correlation
distance determined from x-ray scattering. Pore wall thickness for
periodically ordered pore oxides is determined by subtracting the
Horvath-Kawazoe (HK) pore size from the unit cell parameter, a.sub.o,
determined from x-ray scattering.
TEM images were obtained on a JEOL JEM-100CX.TM. II electron microscope
(JEOL, USA, Peabody, Mass.) with a CeB.sub.6 filament on accelerating
voltage of 120 KV, a beam size of approx. 5 .mu.m and objective
lens aperture of 20 .mu.m. Samples were prepared by sonicating the
powdered sample for 20 minutes in ETOH, and then evaporating 2 drops
onto carbon coated copper grids. The electron diffraction patterns
were recorded by using an acceleration voltage of 120 kV, a beam
size of approx. 5 .mu.m, and a diffraction aperture of 20 .mu.m.
The thermogravimetric analyses (TGA) of all samples were performed
on a CAHN system TG analyzer using heating rate of 5.degree. C./min
to a maximum value of 1000.degree. C.
.sup.29 Si MAS NMR spectrums were recorded on a Varian VXR-400.TM.
(Palo alto, Calif.) solid-state NMR Spectrometer at 79.5 MHz under
single pulse mode with a 7-mm Zirconia rotor, a spinning frequency
of 4 kHz, pulse width of 8.5 .mu.s and a pulse delay of 800 seconds.
The chemical shifts were externally referenced to Talc (-98.1 ppm).
.sup.27 Al MAS NMR spectra were obtained using a VARIAN VXR-400.TM.
(Palo Alto, Calif.) NMR spectrometer equipped with a VARIAN MAS
probe and Zirconia rotor. The spectrometer frequency was 104.22
Mhz pulse width 2 ms, pulse delay of 1 s, and sample spinning rate
4000 Hz.
Alumina-substituted and other metal-substituted derivatives of
the mesoporous silicas of the invention are preferably made by (a)
direct assembly, or (b) post-synthesis treatment of a mesoporous
silica with an aluminum or other metal ion reagent. Organo-functionalized
derivatives of silicas can be prepared directly or by post-synthesis
treatment of the silica with organosilane reagents.
In a typical synthesis of the silica compositions of this invention,
the surfactant and an amount of acid equivalent to the hydroxide
content of the basic silicate solution (e.g., 27% SiO.sub.2 14%
NaOH) are mixed at ambient temperature and then added to the basic
silicate to form a reactive silica in the presence of the structure
directing surfactant. This allows for the assembly of the framework
under slightly alkaline pH conditions. The assembly process continues
at the desired temperature for a period of 10 to 20 hours. The surfactant
is then removed from the washed and air-dried products either by
solvent extraction with hot ethanol acid extraction or by calcination
in air at 600.degree. C.
Materials List Silica sources: Aldrich (Milwaukee, WI) Sodium Silicate,
27% SiO.sub.2 14% NaOH from Aldrich. Ludox Colloidal, Ludox HS-40
39.5% SiO.sub.2 0.5% NaOH from Dupont via Aldrich Aldrich (Milwaukee,
WI) Fumed Silica, 99.5% SiO.sub.2 P.Q. Corp (Valley Forge, PA) silicas
D Sodium Silicate, 29% SiO.sub.2 19% NaOH RU Sodium silicate, 34%
SiO.sub.2 18% NaOH K Sodium Silicate, 32% SiO.sub.2 14% NaOH N
Sodium Silicate, 28% SiO.sub.2 12% NaOH
Surfactant Templates
Surfactant specifications
The neutral organic amine surfactants include those of the general
formula R.sub.1 R.sub.2 R.sub.3 N in which at least one of R.sub.1
R.sub.2 R.sub.3 group is preferably a hydrophobic group. The remainder
of the R.sub.1 R.sub.2 R.sub.3 group being selected from various
groups.
The neutral organic polyamine surfactants include those of the
general formula ##STR2##
in which at least one of R.sub.1 to R.sub.5 is preferably a hydrophobic.
R.sub.1 is a hydrophobic group preferably containing 6 to 36 carbon
atoms;
R.sub.2 R.sub.4 R.sub.5 are alkyl or aryl groups or hydrogen;
R.sub.3 is an organic linker group containing one to six carbon
atoms; and x is 0 to 6.
Acidified, or protonated amine surfactants include those of the
previous general formulas, R.sub.1 R.sub.2 R.sub.3 N and R.sub.1
R.sub.2 (NR.sub.3).sub.x NR.sub.4 R.sub.5 in which an additional
proton is temporarily associated with the basic amine creating a
labile cationic charge.
Aliphatic and aryl amines including polyamines, most preferably
in which one hydrophobic segment contains 6 to 36 carbon atoms.
Specific examples include:
DDA Dodecylamine, C.sub.12 H.sub.25 NH.sub.2 from Aldrich Tallow
Amines from Tomah Industries (Milton, WI). TA Tallow Amine, C.sub.14-18
NH.sub.2 TDA Tallow Diamine, C.sub.14-18 NH(CH.sub.2).sub.3 NH.sub.2
TTA Tallow Triamine, C.sub.14-18 NH(CH.sub.2).sub.3 NH(CH.sub.2).sub.3
NH.sub.2 TTeA Tallow Tetraamine, C.sub.14-18 NH(CH.sub.2).sub.3
NH(CH.sub.2).sub.3 NH(CH.sub.2).sub.3 NH.sub.2
where C.sub.14-18 designates the carbon number of the hydrophobic
hydrocarbon chain attached to polar amine head group of the surfactant.
Acids HX where X.dbd.Cl, Br, I H.sub.x Y where Y=SO.sup.2-.sub.4
NO.sup.-.sub.3 CO.sup.2-.sub.3 PO.sup.3-.sub.4 and x equals the
charge on Y. HZ where Z=organic carboxylate, phenolate citrate,
glucolate.
EXAMPLE 1
Example 1 demonstrates the ability to form mesoporous silica with
stable hybrid lamellar and wormhole framework pore structures from
water-soluble silicate and primary amine surfactants. The surfactant
solution was prepared by adding 0.58 gram of dodecylamine (C.sub.12
H.sub.25 NH.sub.2 DDA) to 10 milliliters of H.sub.2 O. 10 milliliters
of 1.0 M acetic acid was added to the surfactant solution and stirred
for 10 minutes. A 2.7-gram quantity of sodium silicate (27% SiO.sub.2
.about.14% NaOH) in 30 milliliters of water was added to the surfactant-acid
mixture. The reaction vessel was sealed and stirred at room temperature
for 20 hours. The reaction stoichiometry expressed in terms of moles
per mole SiO.sub.2 corresponded to the following:
0.25 DDA
0.77 NaOH
0.80 CH.sub.3 O.sub.2 H
230 H.sub.2 O
The resulting solid product was recovered by filtration and calcined
at 600.degree. C. for 4 hours in air to remove the incorporated
template.
The X-ray diffraction pattern of the calcined product (FIG. 1)
exhibited an intense peak at 3.5 nm and a broad shoulder between
4-6 degrees (2.theta.). The shoulder arises due to scattering from
a wormhole pore topology and not from a broadening of higher order
Bragg reflections of a long-range ordered material. This characteristic
of scattering is not apparent from prior art synthesized mesostructured
materials. A value of 3.5 nm was obtained for the average pore-pore
correlation distance from the initial XRD peak, signifying a very
uniform spatial separation of pores within the oxide matrix. The
N.sub.2 adsorption-desorption isotherm of the calcined product (FIG.
2) exhibited a step-like N.sub.2 adsorption uptake at P/Po 0.15-0.30
and again at P/Po>0.9 indicating capillary condensation within
both framework confined mesopores and intra-particle textural pores,
respectively.
TEM images of the calcined product (FIGS. 3A and 3B) show small
mesostructured grains. The existence of intra-particle or textural
pores as deduced by N.sub.2 adsorption is clearly seen in FIG. 4A
as the pores formed between the grains of the mesostructured silicas
as these grains aggregate and intergrow into a sponge-like particle.
Evident within the grains is the disordered mesoporous channel structure
and the curved nature of the wormhole channel topology. The uniform
pore to pore correlation distance of these wormhole pores as seen
in TEM are in agreement of values determined by powder X-ray diffraction
(FIG. 1). Additionally, superimposed upon the disordered wormhole
framework structure, and observable through TEM imaging, is a distinguishing
lamellar structure indicated by arrows in FIGS. 3A and 3B. These
molecular sieves with hybrid lamellar and wormhole pore structure
are distinct compositions. These compositions are only attainable
through the current process using neutral mesostructure assembly
of water-soluble silicates by aliphatic amine surfactants.
Comparative Example 2
Example 2 demonstrates the ability to form end member mesoporous
silica with a lamellar structure from water-soluble silicate and
aliphatic amine surfactants through control of interfacial surfactant-silica
interactions. This example reveals the dependence of mesophase formation
on H-bonding between surfactant and the neutralized silicate, and
the control of this H-bonding by controlling assembly pH. The surfactant
solution was prepared by adding 0.58 gram of dodecylamine (C.sub.12
H.sub.25 NH.sub.2 DDA) to 10 milliliters of H.sub.2 O. Ten milliliters
of 0.25 M acetic acid was added to the surfactant solution and stirred
for 10 minutes. A 2.7-g quantity of sodium silicate (27% SiO.sub.2
.about.14% NaOH) in 30 milliliters of water was added to the surfactant-acid
mixture. The reaction mixture at a pH above about 12 was stirred
at room temperature for 20 hours in a sealed reaction vessel. The
reaction stoichiometry expressed in terms of moles per mole SiO.sub.2
corresponded to the following:
0.25 DDA
0.77 NaOH
0.20 CH.sub.3 O.sub.2 H
230 H.sub.2 O
The resulting solid product was recovered by filtration and calcined
at 600.degree. C. for 4 hours in air to remove the incorporated
template.
The X-ray diffraction patterns of the as-made product synthesized
under high pH conditions (FIG. 4) exhibits a lamellar pattern with
d.sub.001 =4.4 nm. Although this structure is not stable to the
removal of template and undergoes collapse upon calcination, the
end member lamellar structure is clearly identifiable. This example
illustrates that the formation of the framework mesophase is directly
related to the ability of the reactive silica to H-bond the organic
structure director. At high pH values (>10.0) the silicate wall
contains significant negative charge. The counter ions needed to
match this negative charge interfere in the H-bonding between the
inorganic and organic arrays resulting in a mesophase of little
or no surface curvature and the resulting lamellar mesophase. This
interaction is not apparent from the prior art synthetic strategies.
Direct control of the pH of the system, and, therefore indirect
control of the H-bonding interactions at the organic-inorganic interface,
results in a structure directing interface with a variable surface
curvature and, consequently, formation of hybrid structures with
variable mesophases unique to this methodology.
EXAMPLES 3-5
The following examples indicate the suitability of long alkyl chain
polyamine surfactants as the structure directing surfactant in the
synthesis of silicas with hybrid lamellar and wormhole mesophases.
Additionally, these surfactants can be combined with low cost mineral
or oxy acids for neutralizing the NaOH content of the sodium silicate
starting solution.
The following tallow amines were obtained from Tomah Industries:
TDA Tallow Diamine, C.sub.14-18 NH(CH.sub.2).sub.3 NH.sub.2..about.MW
298 g/mole TTA Tallow Triamine, C.sub.14-18 NH(CH.sub.2).sub.3 NH(CH.sub.2).sub.3
NH.sub.2 .about.MW 355 g/mole TTeA Tallow Tetraamine, MW .about.412
g/mole C.sub.14-18 NH(CH.sub.2).sub.3 NH(CH.sub.2).sub.3 NH(CH.sub.2).sub.3
NH.sub.2.
The designation C.sub.14-18 indicates the carbon number range of
the hydrocarbon chain attached to the head group of each surfactant.
An appropriate amount of tallow amine surfactant (see Table 1)
was added to 5 ml of EtOH, as a co-surfactant. A 10-ml quantity
of 1.0 M HCl was added to the surfactant/EtOH solution while stirring.
25 ml of H.sub.2 O was then added to surfactant-acid solution (Solution
A). A 2.8-g quantity of sodium silicate (27% SiO.sub.2 .about.14%
NaOH) was added to 10 ml H.sub.2 O (Solution B) Solution B was added
to solution A dropwise while stirring. The reaction vessel was sealed
and stirred at ambient temperature for 20 hours. The reaction stoichiometry
expressed in terms of moles per mole SiO.sub.2 corresponded to the
following:
0.20 moles TDA, TTA, or TteA
198.0 moles H.sub.2 O
6.80 moles EtOH
0.79 moles HCl
0.79 moles NaOH
The resulting solid products were recovered by filtration. The
surfactant was removed from mesostructured silica by calcination
at 600.degree. C. for 4 hours.
TABLE 1 Amount of Example Template Template (g) d.sub.100 HK BET
3 TDA 0.751 4.6 4.3 977 4 TTA 0.845 4.6 3.7 1063 5 TTeA 1.038 4.7
4.3 998
The X-ray diffraction pattern of the calcined product of Example
3 (FIG. 5) exhibited an intense peak at 4.6 nm and a broad shoulder
between 3-4 degrees (2.theta.). As in Example 1 the X-ray diffraction
pattern indicated a disordered framework pore structure. The significant
intensity of both the primary peak and that of the shoulder results
from the uniformity of the framework pores. The shoulder arises
due to scattering from a wormhole pore topology, and not from a
broadening of higher order Bragg reflections of a long-range ordered
material. This scattering behavior is not apparent from prior art
synthesized mesostructured materials. The N.sub.2 adsorption-desorption
isotherm of the calcined product of Example 3 (FIG. 6) shows step-like
N.sub.2 adsorption uptakes at P/Po=0.40-0.50 and >0.9 indicating
capillary condensation within framework confined mesopores and intra-particle
textural pores, respectively.
TEM images (FIGS. 8A and 8B) confirmed both the disorder of the
framework pore channels indicated by powder X-ray diffraction and
uniformity of the pore diameters seen in N.sub.2 adsorption. In
addition, the images show the presence of small grained mesostructured
silicas that have aggregated and intergrown into a sponge-like particle
with significant intra-particle textural pore volume. Observable
in the TEM images is the presence of a wormhole pore topology. As
in Example 1 there are areas within the TEM images, FIG. 8A (arrow),
which indicate the presence of a lamellar mesostructure. Again,
this hybrid lamellar and wormhole structure is unique to the current
methodology.
EXAMPLES 6-9
The following examples are chosen to illustrate the use of different
silica sources with a wide range of SiO.sub.2 to alkali metal (Na.sup.+)
hydroxide ratios as precursors to mesoporous materials assembled
through H-bonding interactions with aliphatic amine surfactant structure
directors. With increasing ratio of SiO.sub.2 /Na.sub.2 O, the pH
of the silicate source decreases, yet the silicate species increases
in polymeric size. The silica sources were provided by P.Q. Corporation
(Valley Forge, Pa.) and used according to the grade indicated by
the supplier (see Table 2).
TABLE 2 Silicate Wt. % SiO.sub.2 / Example Grade SiO.sub.2 Na.sub.2
O 6 D 29.5 2.06 7 RU 33.7 2.51 8 K 32.2 3.02 9 N 28.4 3.29
A 0.750-g quantity of TDA was added to 5 mL of EtOH. Molar quantities
of HCl equal to the NaOH content of each silicate solution grade
was added to the surfactant solution along with 35 mL of H.sub.2
O (Solution A). An appropriate amount of the silicate source (Table
3) was added to 10 mL of H.sub.2 O (Solution B). Solution B was
added to solution A dropwise while stirring. The reaction stoichiometry
expressed in terms of moles per mole SiO.sub.2 corresponded to the
values given in Table 3.
TABLE 3 Mass SiO.sub.2 Stoichiometry/mole SiO.sub.2 Example Brand
(g) TDA H.sub.2 O EtOH NaOH HCl 6 D 2.56 0.20 198 6.8 0.97 0.97
7 RU 2.24 0.20 198 6.8 0.79 0.79 8 K 2.35 0.20 198 6.8 0.66 0.66
9 N 2.66 0.20 198 6.8 0.61 0.61
The reaction vessels were sealed and shaken at 240 rpm for 20 hours
at 45.degree. C. The products were recovered by filtration, washed
and air-dried at ambient temperatures for 24 hours. The products
then were calcined at 600.degree. C. for 4 hours in order to remove
the incorporated template.
TABLE 4 HK (nm) BET (m.sup.2 /g) Example d.sub.100 nm Pore Size
Surface area 6 4.8 4.9 949 7 4.8 4.9 916 8 4.7 4.8 793 9 4.9 4.8
877
Table 4 lists the physico-chemical properties for Examples 6 to
9. Regardless of the NaOH to SiO.sub.2 ratio of the silicate source,
the mesopore structure formed by this procedure remained virtually
identical to Example 3. In each of the examples, independent of
ratio, the structures were very similar in pore diameter, pore to
pore spacing and BET surface area. Each sample exhibited powder
X-ray diffraction patterns similar to FIG. 5 N.sub.2 adsorption
desorption isotherms as seen in FIG. 6 and TEM images similar to
those in FIG. 7.
With increasing ratio of SiO.sub.2 /Na.sub.2 O, the pH of silicate
source decreases, yet the silicate oligomers increase in size. Neutralization
of the silicate source with equal molar amounts of acid, regardless
of the total hydroxide concentration and oligomeric size, results
in a silica that is efficiently structured into a stable hybrid
wormhole topology.
EXAMPLES 10 AND 11
Examples 10 and 11 demonstrate the ability to form hybrid lamellar
and wormhole mesoporous silica from water-soluble silicate and aliphatic
diamine surfactants through control of interfacial interactions.
This example reveals the dependence of mesophase formation on H-bonding
between surfactant and neutralized silicate and a method of controlling
this H-bonding by controlling the assembly temperature. The following
examples demonstrate that increasing the assembly temperature increases
the framework pore diameter, along with increasing the inorganic
crosslinking within the silicate wall structure. This structural
behavior is not apparent from prior art and is a characteristic
property of the current H-bonding assembly mechanism.
A 0.750-g amount of TDA was added to 5 mL of EtOH. A 10-ml amount
of 1.0 M HCl was added to the surfactant/EtOH solution while stirring.
25 ml of H.sub.2 O then was added to the solution (Solution A).
A 2.8-g amount of sodium silicate (27% SiO.sub.2 .about.14% NaOH)
was added to 10 ml H.sub.2 O (solution B). Solution B was added
to solution A dropwise while stirring. The reaction stoichiometry
expressed in terms of moles per mole SiO.sub.2 corresponded to the
following:
0.20 moles TDA
198.0 moles H.sub.2 O
6.80 moles EtOH
0.79 moles HCl
0.79 moles NaOH
The resulting gels were stirred at 45.degree. C. (Example 11) or
65.degree. C. (Example 12) for 20 hours to obtain products. The
resulting solid products were recovered by filtration and calcined
at 600.degree. C. for 4 hours in air to remove the incorporated
template.
TABLE 5 HK BET pore surface Example .degree. C. d.sub.100 size
area Q.sup.4 /(Q.sup.3 + Q.sup.2) 3 Ambient 4.6 4.3 1063 2.1 11
45.degree. C. 4.9 4.8 906 3.2 12 65.degree. C. 5.1 5.4 754 3.8
Table 5 lists the physico-chemical properties for Examples 3 11
and 12. Clearly, increasing the synthesis temperature has a profound
affect on the Horvath-Kawazoe (HK) mesopore diameter. As the temperature
increases, the pore diameter assembled by the polyamine surfactant
systematically increases from approximately 4.3 to 5.4 nm and the
surface area decreases from 1063 to 754 m.sup.2 /g. Also the framework
crosslinking parameter Q.sup.4 /(Q.sup.3 +Q.sup.2) increases with
increasing assembly temperature. Each sample exhibits powder X-ray
diffraction patterns similar to FIG. 5 N.sub.2 adsorption desorption
isotherms as seen in FIG. 6 and TEM images similar to those in FIGS.
7A and 7B.
The increasing diameter of the framework pore structure is initiated
by a temperature-induced decrease in H-bonding at the interface.
The decreasing degree of H-bonding is due to the increased thermal
energy at the surfactant-silica interface, combined with the deceasing
silanols present at the interface for H-bonding with the amine.
Consequently, the decrease in H-bonding results in a decreasing
surface curvature of the organic micelle-inorganic interface. Additionally,
the deceasing H-bonding between silica and surfactant causes the
surfactant micelle to undergo a self-swelling process in which the
non-H-bonded surfactant penetrates the core of the micelle. The
decreasing surface curvature of the interface combined with the
self-swelling of the micelle results in the significant increase
in pore diameter with increasing temperature. This structural behavior
is not apparent from prior art and is a characteristic property
of the current H-bonding assembly mechanism.
As determined by .sup.29 Si MAS NMR spectroscopy, increasing the
synthesis temperature increases the degree on silica condensation,
reducing the silanols present in the silica framework and increasing
the degree of silica framework cross-linking. The extent of the
cross-linking of the silica wall structure is quantified by the
ratio of fully cross-linked Q.sup.4 silica sites (.about.-110 ppm)
to incompletely cross-linked silica sites (Q.sup.3 .about.-98 ppm,
Q.sup.2 .about.-90 ppm). As is seen in Table 5 the ratio of Q.sup.4
/(Q.sup.3 +Q.sup.2) increases 81% from 2.1 to 3.8 with increasing
synthesis temperature from ambient (.about.20.degree. C.) to 65.degree.
C.
EXAMPLE 13
The following example is selected to stress the ability to remove
the surfactant from the pore structure by a straightforward solvent
extraction. Additionally, simple removal of the surfactant by solvent
extraction further confirms the existence of solely H-bonding between
the surfactant and silica wall structure.
(Product A) A 0.04-g quantity of the air-dried and non-calcined
product of Example 3 was subjected to thermogravimetric analysis
(TGA) at a heating rate of 5.degree. C./minute. The total weight
loss of this sample was approximately 53%. Four distinguishable
weight loss steps were centered at temperatures of 40.degree. C.,
187.degree. C., 290.degree. C. and 540.degree. C. which could be
attributed to the loss of excess H.sub.2 O, adsorbed pore H.sub.2
O, desorption or decomposition of template, and de-hydroxylation
of the silicate surface, respectively.
(Product B) One gram of the air-dried and non-calcined product
of Example 3 was mixed with 100 mL of EtOH and refluxed while stirring
for 1 hour. Product was filtered, washed with another portion of
EtOH. The above washing procedure was repeated twice and the filtered
product was air-dried for 24 hours at ambient temperature. 0.04
grams of product B was subjected to TGA analysis. In contrast to
product A, product B reveals only a 17% total weight loss with 14%
corresponding to H.sub.2 O desorption and de-hydroxylation. Analysis
of the two samples shows that more than 85% of the surfactant amine
has been removed from the mesostructure with this simple alcohol
extraction procedure. The mesostructure retains its x-ray diffraction
pattern with relative intensity greater than that of the surfactant
occluded sample. This shows that the neutral amine surfactant has
been removed from the neutral framework of the inorganic compositions
by ethanol extraction. The extracted organic template in the form
of EtOH solution can be recycled and reused after simple concentration
of the solution. In order to confirm the thermal stability of the
extracted product B, calcination was performed in air at 600.degree.
C. for 7 hours. The X-ray analysis of the calcined product shows
that the correlation distance is retained even after prolonged calcination.
EXAMPLE 14
Mesoporous silica from Example 3 were synthesized to have varying
amounts of alkali metal present in the calcined materials. All metal
ions can be removed from the product with thorough washing of the
material in H.sub.2 O as determined from Inductively Coupled Plasma
(ICP) analysis.
EXAMPLE 15
The following example uses a polyamine surfactants as the structure
directing surfactant in the assembly of a hybrid wormhole and hexagonally
ordered molecular sieve silicas. As in previous hybrid structures
Examples 1 and 3 the degree of curvature at the organic micelle-inorganic
interface is variable and, therefore, controllable through H-bonding
interactions unique to the present methodology. The amine surfactant
used in preparing these compositions was TTeA Tallow Tetraamine,
MW .about.412 g/mole C.sub.14-18 NH(CH.sub.2).sub.3 NH(CH.sub.2).sub.3
NH(CH.sub.2).sub.3 NH.sub.2.
A 1.038-g quantity of tallow tetraamine surfactant (TTeA) was added
to 5 ml of EtOH. A 12 ml volume of 1.0 M HCl was added to the surfactant/EtOH
solution while stirring. 25 ml of H.sub.2 O then was added to the
surfactant-acid solution (Solution A). 2.8 g of sodium silicate
(27% SiO.sub.2 .about.14% NaOH) was added to 10 ml H.sub.2 O (Solution
B). Solution B was added to solution A dropwise while stirring,
reaction vessel sealed and stirred at 45.degree. C. for 20 hours.
The reaction stoichiometry expressed in terms of moles per mole
SiO.sub.2 corresponded to the following:
0.20 moles TTeA
198.0 moles H.sub.2 O
6.80 moles EtOH
0.95 moles HCl
0.79 moles NaOH
The resulting solid products were recovered by filtration. Surfactant
was removed from mesostructured silica by calcination at 600.degree.
C. for 4 hours.
TABLE 6 Amount of Template .sup.d 100 HK BET Example Template (g)
(nm) (nm) m.sup.2 /g 15 TTeA 1.038 4.7 4.2 940
The X-ray diffraction pattern of the calcined product of Example
15 exhibited an intense peak at 4.7 nm and a resolved second peak
between 3-4 degrees (20) (FIG. 5). Unlike Example 5 the resolved
second peak in the X-ray diffraction pattern indicates a small domain
hexagonally ordered framework pore structure. TEM images (FIGS.
8A and 8B) and selected area electron diffraction (FIG. 10C) confirm
the hexagonal order of the pore channels with very small domain
sizes. The ordered domains are clearly observed in the TEM images,
although there exists a significant fraction of the pore structure
resembling a wormhole structure as seen in FIGS. 8A and 8B. There
exists no clear phase boundary between the ordered and disordered
mesopore phases. The N.sub.2 adsorption-desorption isotherm of the
calcined product of Example 15 (see FIG. 6 Table 6) shows step-like
N.sub.2 adsorption uptakes at P/Po=0.40-0.50 and >0.9 indicating
capillary condensation within uniform framework confined mesopores
and extra-particle textural pores, respectively.
EXAMPLE 16
The following example indicates the ability to directly substitute
hetero-atoms, such as aluminum, into the silica framework of these
hybrid silica framework mesostructures using basic (pH>7) reagent
conditions using a polyamine surfactant as the structure director.
TDA Tallow Diamine, C.sub.14-18 NH(CH.sub.2).sub.3 NH.sub.2 where
C.sub.14-18 indicates the range of carbon atoms in the hydrophobic
chain, .about.MW 298 g/mole
TDA (0.75 g) was added to 5 mL of ethanol. A 10-mL portion of 1.0
M HCl in 25 mL of H.sub.2 O was then added to yield acidified amine
solution (Solution A). A 2.7-g quantity of sodium silicate (27%
SiO.sub.2 .about.14% NaOH, Aldrich) and 0.067 g of NaAlO.sub.2.
H.sub.2 O was added to 10 Ml H.sub.2 O and stirred for 10 min (Solution
B). Solution B was added to solution A dropwise while stirring.
The reaction vessel was sealed and stirred at ambient temperature
for 20 hours. The reaction stoichiometry expressed in terms of moles
per mole Si/Al corresponded to the following:
0.20 moles TDA
6.80 moles EtOH
0.79 moles HCl
0.79 moles NaOH
Si/Al=20 SiO.sub.2 /Al.sub.2 O.sub.3 =40
The resulting solid products were recovered by filtration. Surfactant
was removed from mesostructured silica by calcination at 600.degree.
C. for 4 hours.
The X-ray diffraction pattern of the calcined product of Example
16 was similar to that seen in FIG. 6 and exhibited an intense peak
at 4.6 nm and a broad shoulder between 3-4 degrees (2e). As in Example
3 the X-ray diffraction pattern indicated a disordered framework
pore structure. The significant intensity of both the primary peak
and that of the shoulder results from the uniformity of the pores
and their spacing.
The N.sub.2 adsorption-desorption isotherm of the calcined product
of Example 16 are also similar to those of Example 3 (FIG. 7) and
showed N.sub.2 adsorption uptakes at P/Po 0.40-0.50 and >0.9
indicating capillary condensation within framework confined mesopores
and intra-particle textural pores respectively.
The TEM images were similar to those shown in FIGS. 8A and 8B and
confirmed both the disorder of the pore channels indicated by powder
X-ray diffraction and the uniformity of the pore diameters seen
in N.sub.2 adsorption. They also confirmed the presence of small
grained mesostructured silicas that aggregate and intergrow into
a sponge-like particle with significant intra-particle textural
pore volume. Observable in the TEM images was the presence of a
wormhole pore topology.
Elemental analysis confirms the Si/Al value equal to 20.
EXAMPLE 17
The following example indicated the ability to directly substitute
hetero-atoms, such as aluminum, into the silica framework of these
hybrid silica framework mesostructures using acidic (pH<7) reagent
conditions and a polyamine surfactant as the structure-directing
agent. TDA Tallow Diamine, C.sub.14-18 NH(CH.sub.2).sub.3 NH.sub.2
where C.sub.14-18 indicates the range of carbon atoms in the hydrophobic
chain, .about.MW 298 g/mole
TDA (0.75 g) was added to 5 mL of ethanol. A 8-mL quantity of 1.0
M HCl in 25 mL of H.sub.2 O was then added along with 0.24 g of
Al(NO.sub.3).sub.3.9H.sub.2 O to yield an acidified amine/Al.sup.+3
solution (Solution A). A 2.7-g quantity of sodium silicate (27%
SiO.sub.2 .about.14% NaOH, Aldrich) was added to 10 ml H.sub.2
O and stirred for 10 minutes (Solution B). Solution B was added
to solution A dropwise while stirring. The reaction vessel was sealed
and the mixture was stirred at ambient temperature for 20 hours.
The reaction stoichiometry expressed in terms of moles per mole
Si/Al corresponded to the following:
0.20 moles TDA
198.0 moles H.sub.2 O
6.80 moles EtOH
0.79 moles HCl
0.79 moles NaOH
Si/Al=20 SiO.sub.2 /Al.sub.2 O.sub.3 =40
The resulting solid products were recovered by filtration. Surfactant
was removed from mesostructured alumina-silica by calcination at
600.degree. C. for 4 hours.
The X-ray diffraction pattern of the calcined product of Example
17 is similar to that seen in FIG. 6 and exhibits an intense peak
at low angle (2.theta.) and a broad shoulder at higher angles (2e).
As in Example 16 the X-ray diffraction pattern indicates a disordered
framework pore structure. The significant intensity of both the
primary peak and that of the shoulder results from the uniformity
of the pores and their spacing.
The N.sub.2 adsorption-desorption isotherm of the calcined product
of Example 17 are also similar to those of Example 16 (FIG. 7) and
show N.sub.2 adsorption uptakes at P/Po 0.40-0.50 and >0.9 indicating
capillary condensation within framework confined mesopores and intra-particle
textural pores, respectively.
TEM images were similar to those shown in FIGS. 8A and 8B and confirmed
both the disorder of the pore channels indicated by powder X-ray
diffraction and the uniformity of the pore diameters seen in N.sub.2
adsorption. They also confirmed the presence of small grained mesostructured
silicas that aggregate and intergrow into a sponge-like particle
with significant intra-particle textural pore volume. Observable
in the TEM images was the presence of a wormhole pore topology.
Elemental analysis confirmed the Si/Al value was equal to 20.
EXAMPLE 18
The following example demonstrates the ability to neutralize the
silicate solution with an acid after mixing the silicate solution
with the non-acidified, or protonated, polyamine solution in the
assembly of hybrid silica framework mesostructures. TDA Tallow Diamine,
C.sub.14-18 NH(CH.sub.2).sub.3 NH.sub.2 where C.sub.14-18 indicates
the range of carbon atoms in the hydrophobic chain, .about.MW 298
g/mole
TDA (0.75 g) added to 5 mL of ethanol. A 25-mL volume of H.sub.2
O was added to yield amine solution(Solution A). A 2.8-g quantity
of sodium silicate (27% SiO.sub.2 .about.14%NaOH, Aldrich)was added
to 10 ml H.sub.2 O and stirred for 10 min(Solution B). Solution
B was added to solution A dropwise while stirring. A 10-mL volume
of 1.0 M HCl was added to the silicate-amine solution with stirring.
The reaction vessel was sealed and the reaction mixture was stirred
at ambient temperature for 20 hours. The reaction stoichiometry
expressed in terms of moles per mole SiO.sub.2 correspond to the
following:
0.20 moles TDA
198.0 moles H.sub.2 O
6.80 moles EtOH
0.79 moles HCl
0.79 moles NAOH
The resulting solid products were recovered by filtration. The
Surfactant was removed from the mesostructured silica by calcination
at 600.degree. C. for 4 hours.
The X-ray diffraction pattern of the calcined product of Example
18 was similar to that seen in FIG. 6. As in Example 3 the X-ray
diffraction pattern indicated a disordered framework pore structure.
The significant intensity of both the primary peak and that of the
shoulder resulted from the uniformity of the pores and the spacing
of the pores.
The N.sub.2 adsorption-desorption isotherms of the calcined product
of Example 18 were similar to those of example 3 (FIG. 7) and showed
N.sub.2 adsorption uptakes at P/Po 0.40-0.50 and >0.9 indicating
capillary condensation within framework confined mesopores and intra-particle
textural pores, respectively.
The TEM were similar to those seen in FIGS. 8A and 8B and confirmed
both the disorder of the pore channels indicated by powder X-ray
diffraction and the uniformity of the pore diameters seen in N.sub.2
adsorption. They also confirmed the presence of small grained mesostructured
silicas that aggregate and intergrow into a sponge-like particle
with significant intra-particle textural pore volume. Observable
in the TEM images was the presence of a wormhole pore topology.
EXAMPLE 19
The following example are presented to demonstrate the ability
to assemble hybrid silica framework mesostructures by initially
mixing the silicate and amine solutions at low pH (<4) and then
titrating with a base to raise the pH to the preferred value (6.0-8.5)for
precipitation of the products. TDA Tallow Diamine, C.sub.14-18 NH(CH.sub.2).sub.3
NH.sub.2 where C.sub.14-18 indicates the range of carbon atoms
in the hydrophobic chain, .about.MW 298 g/mole
TDA (0.75 g) was added to 5 mL of ethanol. A 25-mL volume of 1.0
M HCl was then added to yield the acidified amine solution(Solution
A). A 2.8-g quantity of sodium silicate (27% SiO.sub.2 .about.14%NaOH,
Aldrich) was added to 10 ml H.sub.2 O and stirred for 10 min(Solution
B). Solution B was added to solution A dropwise while stirring.
15 mL of 1.0 M NaOH was added to the silicate-amine solution with
stirring, yielding a final pH of 6.0-8.5. The reaction vessel was
sealed and the mixture was stirred at ambient temperature for 20
hours. The reaction stoichiometry expressed in terms of moles per
mole Si/Al corresponded to the following:
0.20 moles TDA
198.0 moles H.sub.2 O
6.80 moles EtOH
1.98 moles HCl
1.98 moles NaOH
The resulting solid products were recovered by filtration. The
surfactant was removed from the mesostructured silica by calcination
at 600.degree. C. for 4 hours.
The X-ray diffraction pattern of the calcined product of Example
19 was similar to that seen in FIG. 6. As in Example 3 the X-ray
diffraction pattern indicated a disordered framework pore structure.
The significant intensity of both the primary peak and that of the
shoulder resulted from the uniformity of the pores and their spacing.
The N.sub.2 adsorption-desorption isotherm of the calcined product
of Example 19 were similar to those of example 3 (FIG. 7) and showed
N.sub.2 adsorption uptakes at P/Po 0. 40-0.50 and >0.9 indicative
of capillary condensation within framework confined mesopores and
intra-particle textural pores respectively.
The TEM images were similar to those seen in FIGS. 8A and 8B and
confirmed both the disorder of the pore channels indicated by powder
X-ray diffraction and the uniformity of the pore diameters evidenced
by N.sub.2 adsorption. They also confirmed the presence of small
grained mesostructured silicas that aggregate and intergrow into
a sponge-like particle with significant intra-particle textural
pore volume. Observable in the TEM images was the presence of a
wormhole pore topology.
EXAMPLE 20
The following example is presented to demonstrate the ability to
substitute an organo-silicate solution for an inorganic sodium silicate
solution in the assembly of hybrid silica framework mesostructures.
TDA Tallow Diamine, C.sub.14-18 NH(CH.sub.2).sub.3 NH.sub.2 where
C.sub.14-18 indicates the range of carbon atoms in the hydrophobic
chain, .about.MW 298 g/mole TMAOH Tetramethylammonium hydroxide
A 0.76-g quantity of fumed silica (Cab-O-Sil) was added to 15 mL
of H.sub.2 O and then 2.76 g of TMAOH was added. The mixture was
heated to 40.degree. C. for 72 h (Solution A).
TDA (0.75 g) was added to 5 mL of ethanol. A 25-mL volume of 1.0
M HCl and 5 mL of H.sub.2 O was added to yield an acidified amine
solution(Solution B). Solution A was added to solution B dropwise
while stirring. The reaction vessel was sealed and stirred at ambient
temperature for 20 hours. The reaction stoichiometry expressed in
terms of moles per mole Si/Al corresponded to the following:
0.20 moles TDA
198.0 moles H.sub.2 O
6.80 moles EtOH
2.0 moles HCl
2.0 moles TMAOH
The resulting solid products were recovered by filtration. The
surfactant was removed from the mesostructured silica by calcination
at 600.degree. C. for 4 hours.
The X-ray diffraction pattern of the calcined product of Example
20 were similar to that seen in FIG. 6. As in Example 3 the X-ray
diffraction pattern indicated a disordered framework pore structure.
The significant intensity of both the primary peak and that of the
shoulder results from the uniformity of the pores and their spacing.
The N.sub.2 adsorption-desorption isotherm of the calcined product
of Example 20 were similar to those of example 3 (FIG. 7) and showed
N.sub.2 adsorption uptakes at P/Po 0.40-0.50 and >0.9 indicating
capillary condensation within framework confined mesopores and intra-particle
textural pores respectively.
The TEM images were similar to those seen in FIGS. 8A and 8B and
confirmed both the disorder of the pore channels indicated by powder
X-ray diffraction and the uniformity of the pore diameters indicated
by N.sub.2 adsorption. They also confirmed the presence of small
grained mesostructured silicas that aggregate and intergrow into
a sponge-like particle with significant intra-particle textural
pore volume. Observable in the TEM images was the presence of a
wormhole pore topology.
It is intended that the foregoing description be only illustrative
of the present invention and that the present invention be limited
only by the hereinafter appended claims. |