Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
1998-10-15
2002-04-16
Griffin, Steven P. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S327000, C502S332000, C502S261000
Reexamination Certificate
active
06372687
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This invention claims priority to German application Ser. No. 19745905.6, filed Oct. 17, 1997.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to supported catalysts based on noble metal carbonyl compounds, a process for producing these catalysts and their use for the hydrogenation, dehydrogenation or oxidation of organic compounds or peroxide decomposition.
2. Description of the Related Art
There has been considerable interest in the formation, structure and catalytic use of monometallic and bimetallic nanosize particles and clusters since the excellent catalytic properties of Ru—Cu, Pt—Ir and Pt—Re systems supported on aluminum oxide in reforming processes were shown in “Bimetallic Catalysts”, Wiley, N.Y., 1983 and Int. Rev. Phys. Chem. 7, 1988,281.
Apart from the conventional ceramic catalyst supports having a broad pore radius distribution, e.g. SiO
2
, Al
2
O
3
, TiO
2
and ZrO
2
, increasing use has also been made, owing to their ready accessibility via hydrothermal synthesis, of purely mesoporous materials having pore diameters in the range from 2.5 to 10 nm as supports, as described, for example, in Current Opinion in Solid State and Material Science, 1, 1996, 76 and Current Opinion in Colloid Science, 1, 1996, 523.
Processes are also known for locating catalytically active centers within such mesopores. Nature, 378, 1995, 159, Angew. Chem. Int. Ed. Engl. 35, 1996, 2787 and Faraday Discuss. 105, 1996, 1 disclose such processes, for example the anchoring of Ti(IV) ions via Si—O bonds.
Numerous methods have been disclosed for applying noble metals and noble metal clusters to inert ceramic supports, likewise to the abovementioned mesoporous supports, in order to produce supported catalysts for hydrogenations and oxidations. Reviews may be found, for example, in Clusters and Colloids, VCH, Weinheim, 1994; Heterogeneous Catalysis, Clarendon Press, Oxford, 1987; Catalytic Chemistry, Wiley, N.Y., 1992, and Metal Clusters in Catalysis, Elsevier, Amsterdam, 1986. Although the catalysts obtained by the processes of the prior art are active in the initial phase of their use, they rapidly deactivate since the fixing of the nanosize noble metal particles and noble metal clusters to the support is unsatisfactory and the primary particles agglomerate as a result of sintering phenomena to form larger particles having only a low catalytic surface area.
OBJECT OF THE INVENTION
It is therefore an object of the present invention to provide a catalyst which still has a high activity after prolonged operating times and which has a good sintering stability, i.e. in which the noble metal clusters or nanosize particles do not agglomerate to form larger particles even after sintering. A further object of the invention is to provide a process for applying and fixing noble metal clusters to supports bearing hydroxyl groups, resulting in supported catalysts in which the metal is finely distanced and which have high activity and excellent sintering stability.
SUMMARY OF THE INVENTION
The present invention achieves this object by providing novel supported catalysts which have high catalytic activity and selectivity and also excellent sintering stability and do not have the disadvantages of the known catalysts, a process for producing these catalysts and their use in organic reactions.
BRIEF DESCRIPTION OF THE DRAWINGS
Not applicable.
DETAILED DESCRIPTION OF THE INVENTION
The present invention accordingly provides supported catalysts having a high sintering stability and comprising one or more noble metal cluster carbonyl compounds of the formula (1)
[H
a
M
b
N
c
L
d
(CO)
x
]
n−
A
n+
where
M and N
are, independently of one another, one or more metals
selected from the group consisting of Pt, Rh, Ir, Os, Ru, Ag,
Pd, Au, Ni, Fe, Co, Cu, Re, Mn;
L
is one or more neutral or anionic ligands which may be
identical or different;
(A)
n+
is one or more cations which balance the charge of the
complex;
a
is an integer from 0 to 10,
b
is an integer from 2 to 60;
c
is an integer from 0 to 30;
d
is an integer from 0 to 60;
x
is an integer from 1 to 120;
n
is the total charge of the complex which results from the
individual charges of the constituents and is greater than 0,
wherein the compounds of the formula (1) are located in the pores of a mesoporous support material.
Suitable mesoporous support materials containing hydroxyl groups are, in particular, silicon dioxide, silicon mixed oxides, aluminum oxides, zirconium oxides or titanium oxides.
Thus, according to the invention, the pore diameter when using mesoporous silicon dioxide (e.g. MCM41®, Mobil) is, for example, in the range from 2 to 50 nm, in particular in the range from 2.5 to 30 nm.
The noble metal clusters are firmly bound to the surface hydroxyl groups of The support material so as to prevent the clusters agglomerating as a result of sintering phenomena and the catalyst becoming deactivated. According to the invention, regular arrangements of noble metal clusters are formed in the pores of the support material at high metal levels, as a result of which the active metal loading can be increased significantly without any need to fear a loss of the good metal dispersions caused by agglomeration phenomena.
Thus, in the case of ruthenium, for example, the spacing of the regularly arranged noble metal cluster carbonyl compounds along the mesopore axis of the support material is, when using MCM-41, in the range from 1.0 to 5.0 nm, in particular in the range from 1.7 to 2.7. When using other support materials, the spacing of the clusters can be in the range from 0.5 to 5 nm.
The support can be impregnated with the impregnation solution by means customary in the prior art, for example by impregnation, dipping, spraying or ultrasonic dispersion. The monometal or bimetal noble metal carbonyl complexes are adsorbed from solution onto the support material. Suitable solvents are those which do not react with the noble metal carbonyl complexes. Examples of such inert solvents are aliphatic ethers, in particular diethyl ether.
In a preferred embodiment, loading of the support with the anionic clusters is achieved by the two components being slurried in ether and a small amount of a second solvent, e.g. methylene chloride, in which the cluster salt is soluble.
The noble metal M is preferably Ru, Ag, Pd, Pt, Au, Rh, Re, Ir, Co, Cu or Ni. The stoichiometric index b is in the range from 2 to 60, in particular in the range from 3 to 30.
The noble metal N is preferably Ag or Cu. The stoichiometric index c is preferably in the range from 0 to 30, in particular in the range from 0 to 15.
Apart from the noble metals and the CO groups, the noble metal carbonyl complexes may further comprise hydrogen or other ligands, but it is also possible for them to be pure carbonyl complexes without other ligands. The noble metal carbonyl complexes can comprise one, 2, 3 or 4 different chemical species as anionic, in particular strongly reducing, ligands L. These chemical species can be, for example, C, N, S, C
2
, F, Cl, Br, I, BF
4
, cyanide, isocyanide, cyanate, isocyanate, CNO, phosphines, phosphine oxides, arsines, amines, saturated or unsaturated alkyl, allyl or aryl radicals, e.g. cyclopentadienyl, which can occur in neutral form or as anions.
If the noble metal carbonyl complexes comprise one chemical species as ligand, the stoichiometric coefficient d indicates the number present. If the noble metal carbonyl complexes comprise more than one chemical species as ligands, d indicates the number present of each of them and can also be different for the individual types of ligands. For each chemical species, d is from 0 to 60, in particular from 0 to 30.
The number x of CO groups present in the complex is in the range from 1 to 120, preferably in the range from 1 to 60, in particular in the range from 5 to 50.
The total charge n of the complexes depends on the sum of the charges borne by the metals and
Dingerdissen Uwe
Hagemeyer Alfred
Johnson Brian F. G.
Kühlein Klaus
Maschmeyer T.
Frommer & Lawrence & Haug LLP
Griffin Steven P.
Hoechst Research & Technology
Nguyen Cam N.
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