Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Mixture is exhaust from internal-combustion engine
Reexamination Certificate
2001-07-13
2002-10-22
Sample, David (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Mixture is exhaust from internal-combustion engine
C423S213500, C423S239200
Reexamination Certificate
active
06468485
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to new crystalline zeolite SSZ-60 and processes employing SSZ-60 as a catalyst.
2. State of the Art
Because of their unique sieving characteristics, as well as their catalytic properties, crystalline molecular sieves and zeolites are especially useful in applications such as hydrocarbon conversion, gas drying and separation. Although many different crystalline molecular sieves have been disclosed, there is a continuing need for new zeolites with desirable properties for gas separation and drying, hydrocarbon and chemical conversions, and other applications. New zeolites may contain novel internal pore architectures, providing enhanced selectivities in these processes.
Crystalline aluminosilicates are usually prepared from aqueous reaction mixtures containing alkali or alkaline earth metal oxides, silica, and alumina. Crystalline borosilicates are usually prepared under similar reaction conditions except that boron is used in place of aluminum. By varying the synthesis conditions and the composition of the reaction mixture, different zeolites can often be formed.
SUMMARY OF THE INVENTION
The present invention is directed to a family of crystalline molecular sieves with unique properties, referred to herein as “zeolite SSZ-60” or simply “SSZ-60”. Preferably, SSZ-60 is obtained in its silicate, aluminosilicate, titanosilicate, vanadosilicate or borosilicate form. The term “silicate” refers to a zeolite having a high mole ratio of silicon oxide relative to aluminum oxide, preferably a mole ratio greater than 100, including zeolites comprised entirely of silicon oxide. As used herein, the term “aluminosilicate” refers to a zeolite containing both alumina and silica and the term “borosilicate” refers to a zeolite containing oxides of both boron and silicon.
In accordance with this invention, there is provided an improved process for the reduction of oxides of nitrogen contained in a gas stream in the presence of oxygen wherein said process comprises contacting the gas stream with a zeolite, the improvement comprising using as the zeolite a zeolite having a mole ratio greater than about 20 of an oxide of a first tetravalent element to an oxide of a second tetravalent element different from said first tetravalent element, trivalent element, pentavalent element or mixture thereof and having, after calcination, the X-ray diffraction lines of Table II. The zeolite may contain a metal or metal ions (such as cobalt, copper or mixtures thereof) capable of catalyzing the reduction of the oxides of nitrogen, and may be conducted in the presence of a stoichiometric excess of oxygen. In a preferred embodiment, the gas stream is the exhaust stream of an internal combustion engine.
DETAILED DESCRIPTION OF THE INVENTION
The present invention comprises a family of crystalline, large pore zeolites designated herein “zeolite SSZ-60” or simply “SSZ-60”. As used herein, the term “large pore” means having an average pore size diameter greater than about 6.0 Angstroms, preferably from about 6.5 Angstroms to about 7.5 Angstroms.
In preparing SSZ-60 zeolites, a N-ethyl-N-(3,3,5-trimethylcyclohexyl)-pyrrolidinium cation or N-ethyl-N-(2,4,4-trimethylcyclopentyl)pyrrolidinium cation is used as a crystallization template. In general, SSZ-60 is prepared by contacting an active source of one or more oxides selected from the group consisting of monovalent element oxides, divalent element oxides, trivalent element oxides, and tetravalent element oxides with the N-ethyl-N-(3,3,5-trimethylcyclohexyl)-pyrrolidinium cation or N-ethyl-N-(2,4,4-trimethylcyclopentyl)pyrrolidinium cation templating agent. SSZ-60 is prepared from a reaction mixture having the composition shown in
TABLE A
Reaction Mixture
Typical
Preferred
YO
2
/W
a
O
b
>20
30-70
OH-/YO
2
0.10-0.50
0.20-0.30
Q/YO
2
0.05-0.50
0.10-0.20
M
2
/YO
2
0.02-0.40
0.10-0.25
H
2
O/YO
2
30-80
35-45
wherein Y is silicon, germanium or a mixture thereof; W is aluminum, gallium, iron, boron, titanium, indium, vanadium or mixtures thereof; a is 1 or 2, and b is 2 when a is 1 (i.e., W is tetravalent) and b is 3 when a is 2 (i.e., W is trivalent); M is an alkali metal cation, alkaline earth metal cation or mixtures thereof; n is the valence of M (i.e., 1 or 2); and Q is a N-ethyl-N-(3,3,5-trimethylcyclohexyl)-pyrrolidinium cation or N-ethyl-N-(2,4,4-trimethylcyclopentyl)pyrrolidinium cation.
In practice, SSZ-60 is prepared by a process comprising:
(a) preparing an aqueous solution containing sources of at least one oxide capable of forming a crystalline molecular sieve and a N-ethyl-N-(3,3,5-trimethylcyclohexyl)-pyrrolidinium cation or N-ethyl-N-(2,4,4-trimethylcyclopentyl)pyrrolidinium cation having an anionic counterion which is not detrimental to the formation of SSZ-60;
(b) maintaining the aqueous solution under conditions sufficient to form crystals of SSZ-60; and
(c) recovering the crystals of SSZ-60.
Accordingly, SSZ-60 may comprise the crystalline material and the templating agent in combination with metallic and non-metallic oxides bonded in tetrahedral coordination through shared oxygen atoms to form a cross-linked three dimensional crystal structure. The metallic and non-metallic oxides comprise one or a combination of oxides of a first tetravalent element(s), and one or a combination of a second tetravalent element(s) different from the first tetravalent element(s), trivalent element(s), pentavalent element(s) or mixture thereof. The first tetravalent element(s) is preferably selected from the group consisting of silicon, germanium and combinations thereof. More preferably, the first tetravalent element is silicon. The second tetravalent element (which is different from the first tetravalent element), trivalent element and pentavalent element is preferably selected from the group consisting of aluminum, gallium, iron, boron, titanium, indium, vanadium and combinations thereof. More preferably, the second trivalent or tetravalent element is aluminum or boron.
Typical sources of aluminum oxide for the reaction mixture include aluminates, alumina, aluminum colloids, aluminum oxide coated on silica sol, hydrated alumina gels such as Al(OH)
3
and aluminum compounds such as AlCl
3
and Al
2
(SO
4
)
3
. Typical sources of silicon oxide include silicates, silica hydrogel, silicic acid, fumed silica, colloidal silica, tetra-alkyl orthosilicates, and silica hydroxides. Boron, as well as gallium, germanium, titanium, indium, vanadium and iron, can be added in forms corresponding to their aluminum and silicon counterparts.
A source zeolite reagent may provide a source of aluminum or boron. In most cases, the source zeolite also provides a source of silica. The source zeolite in its dealuminated or deboronated form may also be used as a source of silica, with additional silicon added using, for example, the conventional sources listed above. Use of a source zeolite reagent as a source of alumina for the present process is more completely described in U.S. Pat. No. 5,225,179, issued Jul. 6, 1993 to Nakagawa entitled “Method of Making Molecular Sieves”, the disclosure of which is incorporated herein by reference.
Typically, an alkali metal hydroxide and/or an alkaline earth metal hydroxide, such as the hydroxide of sodium, potassium, lithium, cesium, rubidium, calcium, and magnesium, is used in the reaction mixture; however, this component can be omitted so long as the equivalent basicity is maintained. The templating agent may be used to provide hydroxide ion. Thus, it may be beneficial to ion exchange, for example, the halide for hydroxide ion, thereby reducing or eliminating the alkali metal hydroxide quantity required. The alkali metal cation or alkaline earth cation may be part of the as-synthesized crystalline oxide material, in order to balance valence electron charges therein.
The reaction mixture is maintained at an elevated temperature until the crystals of the SSZ-60 zeolite are formed. The hydrothermal crystallization is usually conduct
Chevron U.S.A. Inc.
Sample David
Sheridan Richard J.
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