Chemistry of hydrocarbon compounds – Adding hydrogen to unsaturated bond of hydrocarbon – i.e.,... – Using transition metal-containing catalyst
Reexamination Certificate
1995-06-15
2001-10-23
Langel, Wayne (Department: 1754)
Chemistry of hydrocarbon compounds
Adding hydrogen to unsaturated bond of hydrocarbon, i.e.,...
Using transition metal-containing catalyst
C423S579000, C423S580100, C564S423000, C585S269000, C585S273000
Reexamination Certificate
active
06307116
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for preparing an aerogel composed of inorganic oxides and comprising palladium, platinum, nickel, cobalt and/or copper; to homogeneously constructed, aerogel-supported transition metal catalysts produced in accordance with the process of the invention; and also to methods of using such catalysts.
Aerogel-supported metal catalysts are described by G. M. Pajonk in a review article in
Appl. Catalysis
, 72 (1991), pages 217 to 266. They are suitable for various purposes. Pt/SiO
2
aerogel catalysts, for example, catalyze the oxidation of CH
3
CHO to CH
3
COOH. Ni/SiO
2
aerogel catalysts catalyze the hydrogenation of toluene to methylcyclohexane. Cu/Al
2
O
3
aerogel catalysts catalyze the hydrogenation of cyclopentadiene to cyclopentene.
In
Appl. Catalysis
, 19 (1985), pages 339-348, the authors J. N. Armor, E. J. Carlson and P. M. Zambri describe the preparation of palladium/aluminum oxide aerogel-supported catalysts. These catalysts are suitable for the hydrogenation of nitrobenzene to aniline.
In
Appl. Catalysis
, 19 (1985), pages 327-337, the authors J. N. Armor and E. J. Carlson describe supported catalysts, namely palladium on aluminum oxide aerogel and also palladium on silicon dioxide aerogel in encapsulated form. Specific application purposes for these preparations are not indicated. However, from the context it appears that such preparations have a catalytic activity which is not more closely defined. In order to incorporate the palladium in the gel, a solution of palladium(II) acetate in warm acetone is prepared and mixed with the alkoxide precursors and an organic solvent. A problem here is that palladium(II) acetate is not readily soluble in alcohols. For this reason, in the preparation of the palladium aerogel-supported catalysts, inhomogeneous regions in the supported catalysts have to be expected.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide an improved process for producing aerogel-supported transition metal catalysts.
A further object of the invention is to provide a process for producing aerogel-supported transition metal catalysts in which the transition metal is particularly homogeneously distributed in the support material.
Another object of the invention is to provide aerogel-supported transition metal catalysts having a more uniform distribution of the transition metal in the support material.
These and other objects of the invention are achieved by providing a process for preparing an inorganic oxide aerogel containing at least one transition metal selected from the group consisting of palladium, platinum, nickel, cobalt and copper, comprising the steps of forming a mixture comprising an alkoxide precursor of the inorganic oxide, an organometal compound of said at least one transition metal, and an organic solvent; hydrolyzing the mixture with water to form a gel; and converting the gel under supercritical conditions into an aerogel, whereby the transition metal is homogeneously distributed in said aerogel; wherein the organometal compound is a chelate complex of the at least one transition metal with a chelating agent comprising Si(OR
1
)
3
anchor groups in which R
1
represents an alkyl group containing from 1 to 8 carbon atoms, and wherein the chelate complex is soluble in the organic solvent.
In accordance with a further aspect of the invention, the objects are also achieved by providing a supported transition metal catalyst consisting of an inorganic oxide aerogel support having a transition metal selected from the group consisting of platinum, nickel, cobalt and copper homogeneously distributed therein, produced by a process comprising the steps of forming a mixture comprising an alkoxide precursor of the inorganic oxide, a chelate complex of the at least one transition metal with a chelating agent comprising Si(OR
1
)
3
anchor groups in which R
1
represents an alkyl group containing from 1 to 8 carbon atoms, and an organic solvent in which the chelate complex is soluble; hydrolyzing the mixture with water to form a gel; and converting the gel under supercritical conditions into an aerogel.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process of the invention for the preparation of an aerogel based on inorganic oxides and comprising a transition metal selected from among palladium, platinum, nickel, cobalt and copper, an alkoxide precursor of the inorganic oxide and also an organic palladium, platinum, nickel, cobalt and/or copper compound being mixed with an organic solvent, the precursor being hydrolyzed and the resulting gel being converted under supercritical conditions into an aerogel comprising the transition metal, is characterized in that the transition metal is used in the form of a chelate complex, which is soluble in the organic solvent, with a chelating agent having Si(OR
1
)
3
anchor groups, where R
1
is alkyl having from 1 to 8 carbon atoms. The chelating agent may comprise one or more anchor groups. The complex comprises conventional inorganic or organic anions, preferably acetylacetonate. It is important for the process of the invention that the chelate complex of palladium, platinum, nickel, cobalt or copper which is used be soluble in the organic solvent which is used. The solubility of a given chelate complex (for example, a complex between palladium
2+
and the chelating agent having Si(OR
1
)
3
anchor groups) in an intended solvent can be readily determined by persons of ordinary skill in the art through simple experiments.
If desired, one or more additional alkoxide precursors of base metal oxides can be additionally used and hydrolyzed. Mixed inorganic oxides are then formed.
Preferred organic solvents are alcohols having from 1 to 4 carbon atoms. Alcohols having from 1 to 3 carbon atoms are particularly preferred. It is also possible to use liquid carbon dioxide as the solvent. Other suitable solvents include lower-alkyl monoethers of glycol, for example glycol monomethyl ether.
It is within the scope of the invention to prepare aerogel-supported catalysts which contain only a single transition metal or to prepare aerogel-supported catalysts which contain two or more of the recited transition metals.
Preferred chelate complexes are those with diamine compounds. Such diamine chelating agents comprise two primary, secondary or tertiary amino groups and also the Si(OR
1
)
3
anchor group or groups mentioned.
It is preferred to use chelate complexes of Pt
2+
, Ni
2+
, Co
2+
, Cu
2+
and particularly Pd
2+
with a compound of the formula (I)
R
2
R
3
N—(CHR
4
)
a
—N(R
5
)—(CHR
6
)
b
—Si(OR
1
)
3
(I),
where R
1
has the above meaning,
R
2
and R
3
can be identical or different and are hydrogen, alkyl having from 1 to 4 carbon atoms, phenyl or phenyl substituted by 1 or more C1 or C2 alkyl groups,
R
4
and R
5
are identical or different and are hydrogen or alkyl having from 1 to 4 carbon atoms,
R
6
is hydrogen or alkyl having from 1 to 6 carbon atoms,
a is an integer from 1 to 4, and
b is an integer from 1 to 8. The preferred anion is acetylacetonate.
It is particularly preferred to use a compound corresponding to the general formula (I), where
R
1
is alkyl having from 1 to 4 carbon atoms,
R
2
, R
3
, R
4
and R
5
can be identical or different and are, independently of one another, hydrogen, methyl or ethyl,
R
6
is hydrogen or alkyl having from 1 to 4 carbon atoms,
a is an integer from 1 to 3, and
b is an integer from 1 to 4.
Chelate complexes of Pt
2+
, Ni
2+
, Co
2+
, Cu
2+
and especially of Pd
2+
with N-[3-(trimethoxysilyl)propyl]-1,2-ethanediamine, N-[3- (triethoxysilyl)propyl]-1,2-ethanediamine and N-[3-(tripropoxysilyl)propyl]-1,2-ethanediamine are particularly suitable.
The invention will be described in further detail with reference to a preferred embodiment relating to the preparation of aerogel-supported palladium catalysts. It should be understood, however, that this description is merely a represen
Heinrichs Benoî ;t
Pirard Jean-Paul
Pirard Rene
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