Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Patent
1997-01-21
1999-01-12
Trinh, Ba K.
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
549533, 502 66, 502262, C07D30106, C07D30112, B01J 2906
Patent
active
058592652
DESCRIPTION:
BRIEF SUMMARY
This application is 371 application of PCT/EP95/02651, dated Jul. 7, 1995.
The present invention relates to a novel oxidation catalyst based on a titanium or vanadium silicalite having a zeolite structure and containing platinum metals, a process for its preparation and various oxidation processes using this oxidation catalyst.
Platinum-containing titanium ailicalites are known to be oxidation catalysts. For example, J.Chem. Soc., Chem.Commun. (1992), 1446-1447 (1) describes the hydroxylation of benzene and hexane over palladium-containing titanium silicalites. Japanese Preliminary Published Application 92/352771 (2) relates to the preparation of propylene oxide from propene, hydrogen and oxygen using a palladium-containing titanium silicalite catalyst.
However, such prior art oxidation catalysts have disadvantages. In many cases, the catalysts are suitable only for a narrow range of intended uses. The selectivity, conversion, space-time yield and life are also often unsatisfactory parameters.
It is an object of the present invention to provide a universally applicable, efficient oxidation catalyst which is easy to prepare and no longer has the disadvantages of the prior art.
We have found that this object is achieved by an oxidation catalyst based on a titanium or vanadium silicalite having a zeolite structure and containing from 0.01 to 20% by weight of one or more platinum metals selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium and platinum, wherein the platinum metals are each present in at least two different bond energy states.
For the purpose of the present invention, it is of decisive importance that, before it is used, the oxidation catalyst contains the platinum metals in the stated special modification comprising the mixture of different bond energy states. The different bond energy states correspond formally to different oxidation states of the metals. In a preferred embodiment, two, three, four or five different bond energy states are present.
Where two different bond energy states are present, this can represent, for example, a mixture of species of the oxidation states 0 and +1, 0 and +2, 0 and +3 or 0 and +4. The two species are usually present in a ratio of from 5:95 to 95:5, in particular from 10:90 to 90:10.
Where three different bond energy states are present, this can represent, for example, a mixture of species for the oxidation states 0, +1 and +2 or 0, +2 and +3 or 0, +2 and +4 or 0, +1 and +3 or 0, +1 and +4 or 0, +3 and +4. The three species are usually present in a ratio of (0.05-20):(0.05-20):1, in particular (0.1-10):(0.1-10):1.
Furthermore, mixtures of four or more different oxidation states may also be present, for example of 0, +1, +2 and +3 or 0, +1, +2 and +4 or 0, +2, +3 and +4 or 0, +1, +3 and +4 or 0, +1, +2, +3 and +4. Here, the species are present in weight ratios similar to those in the case of the mixtures of 2 or 3 different oxidation states.
The palladium is preferred among the platinum metals. In a particularly preferred embodiment, the palladium is present in two or three different bond energy states.
The bond energy states at the surface of the catalyst may be most simply characterized by X-ray photoelectron spectroscopy (XPS). For example, in a typical mixture of three palladium species, the corresponding values for the energies of the Pd-3d.sub.5/2 state is 335.0-335.4 eV, 336-336.6 eV and 337.1-337.9 eV, which formally corresponds to the oxidation states Pd.sup.0, Pd.sup.1+ and Pd.sup.2+.
In the case of the novel oxidation catalysts, it is particularly advantageous to apply the platinum metals in a manner such that no metal-metal bonds are effective and metal-zeolite bonds predominate. In particular, X-ray fine structure investigations (EXAFS) reveal that, with the presence of palladium, an important feature is that virtually exclusively palladium-oxygen bond distances of 2.02.+-.0.02 .ANG. occur and palladium-palladium distances of 2.74.+-.0.02 .ANG., as in expanded palladium metal or palladium agglomerates, and palladium
Bassler Peter
Dembowski Jurgen
Eller Karsten
Fischer Martin
Harder Wolfgang
BASF - Aktiengesellschaft
Trinh Ba K.
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