Process for the preparation of molecular sieve silicas

Details Process for the preparation of molecular sieve silicas Process for the preparation of molecular sieve silicas

2001-04-13

2003-08-19

Sample, David (Department: 1755)

Chemistry of inorganic compounds

Silicon or compound thereof

Oxygen containing

C423S329100, C423S335000

Reexamination Certificate

active

06607705

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the preparation of molecular sieve silicas, particularly calcined silicas. In particular the present invention relates to the use of water soluble silicates and non-ionic polyoxyethylene oxide PEO based surfactants for the preparation of the silicas which have thermal stability.
2. Description of Related Art
Mesoporous silicas are useful in a variety of applications. Calcined silicas are useful in refining if they are stable at temperatures between 600° C. to 800° C.
Mesoporous molecular sieve silicas with wormhole framework structures (e.g., MSU-X (Bagshaw, S. A., et al.,
Science
269 1242 (1995); Bagshaw, S. A., et al.,
Angwen. Chem., Int. Ed. Engl.,
35 1102 (1996); and 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)), SBA-3 (Huo, Q., et al.,
Nature
368 317 (1994)), and SBA-15 (Zhao, D., et al.,
J. Am. Chem. Soc.,
120 6024 (1998)). 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 (Zhang, W., et al.,
Stud. Surf. Sci. Catal.,
117 23 (1998); Reddy, J. S., et al.,
J. Chem. Soc., Chem. Commun.,
1059 (1994); Reddy, J. S., et al.,
J. Chem. Soc., Chem. Commun.
2231 (1995); Sayari, A.,
Chem. Mater.
8 1840 (1996); Mokaya, R., et al.,
J. Catal.,
172 211 (1997); and Kloetstra, K. R., et al.,
J. Chem. Soc., Chem. Commun.,
228 (1997)). All of the wormhole framework structures reported to date have been prepared through supramolecular S°I° (Tanev, P. T., et al.,
Science
267 865 (1995)) and N°I° (Bagshaw, S. a., et al.,
Science
269 1242 (1995); Bagshaw, S. A., et al.,
Angwen. Chem. Int. Ed. Engl.,
35 1102 (1996); and Prouzet, E., et al., Angwen. Chem. Int. Ed. Engl., 36 516 (1997)) assembly pathways where I° is an electrically neutral silica precursor (typically, tetraethylorthosilicate, TEOS), S° is a neutral amine surfactant, and N° 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 may be anticipated if a more efficient approach to either S°I° or N°I° assembly could be 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). Related patents are: U.S. Pat. Nos. 5,622,684, 5,795,559, 5,800,799 and 6,027,706 to Pinnavaia et al.
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, a N° surfactant (Sierra, L., et al.,
Adv. Mater.,
11(4) 307 (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.
There is a need for mesostructures structurally stable to calcination temperatures in excess of 600° to 800° C.


REFERENCES:
patent: 5622684 (1997-04-01), Pinnavaia et al.
patent: 5795559 (1998-08-01), Pinnavaia et al.
patent: 5800799 (1998-09-01), Pinnavaia et al.
patent: 5840271 (1998-11-01), Carrazza et al.
patent: 6106802 (2000-08-01), Lujano et al.
patent: 6190639 (2001-02-01), Guth et al.
patent: 2003/0031615 (2003-02-01), Satou et al.
patent: WO-200010916 (2000-03-01), None
Zhou, et al., “Nonionic Triblock and Star Diblock Copolymer and Oligomeric Surfactant Synthesis of Highly Ordered, Hydrothermally Stable, Mesoporous Silica Structures,” J. Am. Chem. Soc., 120, pp. 6024-6036, 1998.

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