Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Reexamination Certificate
2001-01-18
2004-10-05
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
C502S063000
Reexamination Certificate
active
06800266
ABSTRACT:
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
+
) and anionic water-soluble silicates (I
−
). 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
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. 6,143,879 (1992)).
The syntheses of HMS materials rely on H-bonding interactions between the neutral amine surfactant (S
o
) assemblies and molecular silica precursors (I
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. 6,143,879 (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
o
I
o
(Tanev, P. T., et al., Science 267 865 (1995) and N
o
I
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
o
is an electrically neutral silica precursor (typically, tetraethylorthosilicate, TEOS), S
o
is a neutral amine surfactant, and N
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
o
I
o
or N
o
I
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
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° C., but the complete removal of the surfactant at 600° 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° 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. 5,800,799, 6,027,706, 5,622,684, 5,795,559, 5,855,864, 5,672,556, 5,840,264, 5,800,800, 5,785,946, and 5,712,402, 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
Kim Seong-Su
Pauly Thomas R.
Pinnavaia Thomas J.
Board of Trustees of Michigan State University
Johnson Edward M.
McLeod Ian C.
Silverman Stanley S.
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