Microporous rare earth silicates and method of producing same

Details Microporous rare earth silicates and method of producing same Microporous rare earth silicates and method of producing same

2000-05-01

2002-04-30

Griffin, Steven P. (Department: 1754)

Chemistry of inorganic compounds

Silicon or compound thereof

Oxygen containing

C423S327100, C423S331000, C423S332000, C423S593100

Reexamination Certificate

active

06379641

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to microporous rare earth silicate compositions having a three dimensional framework structure, which contains at least silicon and one rare earth element as framework elements. The composition is represented by the empirical formula:
A
n
(M
1−z
M′
z
)
w
Si
1−y
Ge
y
O
x
.
BACKGROUND OF THE INVENTION
Microporous crystalline compositions have many industrial uses and thus are the subject of numerous research projects in both industry and academia. The first microporous compositions to be synthesized were the zeolites which are crystalline aluminosilicate compositions, and which are formed from corner sharing AlO
2
and SiO
2
tetrahedra. Zeolites are characterized by having pore openings of uniform dimensions, having a significant ion-exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal, without significantly displacing any atoms which make up the permanent zeolite crystal structure. Investigation of zeolites and their structures led to the synthesis of non-zeolitic molecular sieves which are defined as crystalline compositions which contain in their framework structure, elements other than aluminum and silicon, but which exhibit the ion-exchange and/or adsorption characteristics of zeolites. These include: 1) crystalline aluminophosphate compositions disclosed in U.S. Pat. No. 4,310,440; 2) silicon substituted aluminophosphates as disclosed in U.S. Pat. No. 4,440,871, 3) metal substituted aluminophosphates as disclosed in U.S. Pat. No. 4,853,197; and 4) metallo zinc-phosphate compositions disclosed in U.S. Pat. No. 5,302,362. Non-zeolitic molecular sieves also include crystalline metal sulfide molecular sieves as disclosed in U.S. Pat. No. 4,880,761.
There are also several reports dealing with microporous rare earth silicates. For example, J. Rocha, et al. in
Chem. Commun.,
(1997) 2103, disclosed the preparation and characterization of a composition having the bulk chemical formula of: Na
2
KYSi
8
O
19
.5H
2
O. This material was identified as AV-1 and shown to have yttrium and silicon in the framework. There are also a number of articles by S. M. Haile and co-workers in which a number of neodymium and yttrium silicates with either sodium or potassium as the alkali metal are disclosed. These articles are 1) S. M. Haile, et al., “Crystallography and Composition of Some New Potassium-Neodymium Silicates”,
Transaction of the American Crystallographic Association,
Vol. 27, (1991) 77; S. M. Haile et al., “Synthesis Structure and Ionic Conductivity of K
3
NdSi
6
O
15
”, Material Research Society Symposium Proceedings,
Vol. 210 (1991) 645; S. M. Haile et al., “Conductivity and Crystallography of New Alkali Rare Earth Silicates Synthesized as Possible Fast-Ion Conductors”,
Solid State Ionics,
53-56 (1992) 1292-1301; S. M. Haile et al., “Anisotropy in the Ionic Conductivity of K
3
NdSi
3
O
8
(OH)
2
”, Fast Ion Transports and Solids,
(1993) 315-326; S. M. Haile, et al. “Hydrothermal Synthesis of New Alkali Silicates I. Potassium Neodymium Phases”,
Journal of Crystal Growth,
131 (1993) 352-372; S. M. Haile, et al., “Hydrothermal Synthesis of New Alkali Silicates, II; Sodium Neodymium and Sodium Yttrium Phases”,
Journal of Crystal Growth,
131 (1993) 373-386; S. M. Haile et al. “Structure of Na
3
NdSi
6
O
15
.H
2
O—A Layered Silicate With Paths for Possible Fast Ion Conduction”,
Acta Cryst. (
1997), B53, 7-17. A. N. Christensen, et al. in
Acta Chemica Scandinavica,
(1997) 51: 37-43 disclosed the synthesis of rare earth disilicates, while R. D. Shannon et al., in
Phys. Chem. Minerals,
5, (1980) 245-253 disclosed the synthesis of sodium rare earth silicates which include yttrium, gadolinium, samarium, and dysprosium. Finally, R. D. Shannon et al. in
Inorganic Chemistry,
17 (4), 958-964 (1978), disclose the ionic conductivity of a Na
5
YSi
4
O
12
silicate.
Applicants have now synthesized crystalline microporous rare earth silicates, which are different from those enumerated above. These compositions can be described by the empirical formula:
A
n
(M
1−z
M′
z
)
w
Si
1−y
Ge
y
O
x
.
where A is a cation selected from the group consisting of alkali metals, alkaline earth metals, hydronium ion and mixtures thereof, “n” is the mole fraction of A and varies from about 0.5 w to about 4 w, M is at least one element selected from the group of rare earth elements, except that when “z” is zero, M is not neodymium or yttrium, “z” is the mole fraction of M′ and varies from 0 to about 0.99, M′ is a metal having a valence of +2, +3, +4 or +5, “w” is the mole fraction of the sum of M and M′ and varies from about 0.1 to about 0.5, “y” is the mole fraction of germanium and varies from 0 to about 0.99 and “x” has a value such that it satisfies the valence of the framework elements. As will be shown in detail, the members of the family of rare earth silicates synthesized and characterized by applicants either have crystal structures which are different from those previously disclosed or contain rare earth elements in the structure which have not been synthesized before.
SUMMARY OF THE INVENTION
As stated, this invention relates to a new family of crystalline microporous rare earth silicates and a method of preparing them. Accordingly, one embodiment of the invention is a crystalline microporous composition having a three dimensional framework structure of at least silicon tetrahedral oxide units and at least one M oxide unit and having an empirical formula on an anhydrous basis of:
A
n
(M
1−z
M′
z
)
w
Si
1−y
Ge
y
O
x
.
where A is a cation selected from the group consisting of alkali metals, alkaline earth metals, hydronium ion and mixtures thereof, “n” is the mole fraction of A and varies from about 0.5 w to about 4 w, M is at least one element selected from the group of rare earth elements, except when “z” is zero, M is not neodymium or yttrium, “z” is the mole fraction of M′ and varies from 0 to about 0.99, M′ is a metal having a valence of +2, +3, +4 or +5, “w” is the mole fraction of the sum of M and M′ and varies from about 0.1 to about 0.5, “y” is the mole fraction of germanium and varies from 0 to about 0.99 and “x” has a value such that it satisfies the valence of the framework elements.
Another embodiment of the invention is a process for preparing the rare earth silicates described above. The process comprises forming a reaction mixture containing reactive sources of A, M, silicon, optionally M′ and optionally germanium, at a temperature and a time sufficient to form the crystalline composition, the mixture having a composition expressed in terms of mole ratios of oxides of:
a
A
2/m
O:1−
b
MO
h/2
:b
M′O
g/2
:1−
c
SiO
2
:c
GeO
2
:d
H
2
O
where “a” has a value of about 1 to about 50, “m” is the valence of A and has a value of +1 or +2, “b” has a value from 0 to less than 1.0, “g” has a value of +2, +3, +4 or +5, “h” has a value of +3 or +4, “c” has a value from zero to less than 1.0 and “d” has a value from about 30 to about 2000.
These and other objects and embodiments will become more apparent after the following detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Applicants have prepared crystalline and microporous rare earth silicates by a hydrothermal synthesis at a relatively low temperature and a relative high pH. Several of these rare earth silicates are characterized by x-ray diffraction patterns which are not associated with any known structures. The rare earth silicates have a three-dimensional framework structure of at least silicon tetrahedral oxide units and at least one rare earth oxide unit. The rare earth metals have a valence of +3 or +4 and a coordination number of 6, 7 or 8. These compositions are described on an anhydrous basis by the empirical formula:
A
n
(M
1−z
M′
z
)
w
Si
1−y
Ge
y
O
x
.
I

Affiliated with

Also associated with

Rating

Microporous rare earth silicates and method of producing same does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Microporous rare earth silicates and method of producing same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Microporous rare earth silicates and method of producing same will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2890636