Chemistry of inorganic compounds – Nitrogen or compound thereof – Ammonia or ammonium hydroxide
Patent
1998-10-08
2000-07-04
Griffin, Steven P.
Chemistry of inorganic compounds
Nitrogen or compound thereof
Ammonia or ammonium hydroxide
423385, 423387, 502 27, 502168, 502339, C01C 100
Patent
active
060834684
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a novel process for preparing a hydrogenation catalyst by reduction of platinum in an oxidation state of not less than two using a reducing agent in an aqueous medium in the presence of a carbon-containing support after partial poisoning.
Furthermore, the present invention also relates to a hydrogenation catalyst prepared by the process of the present invention, its use for preparing hydroxylammonium salts, a process for preparing hydroxylammonium salts and a process for regenerating hydrogenation catalysts based on platinum.
Suitable catalysts for hydrogenating organic and inorganic compounds are noble metals such as palladium, platinum or ruthenium which are applied to various supports such as silicon dioxide, aluminum oxide, graphite or activated carbon, as is known from "Katalytische Hydrierungen im organisch chemischen Laboratorium", F. Zimalkowski, Ferdinand Enke Verlag, Stuttgart (1965).
It is presumed that a high dispersion of the noble metal on the catalyst support is responsible for the activity of these catalysts. A disadvantage in terms of the process is the fact (see "Structure of Metallic Catalyst", J. R. Anderson, Academic Press (1975), pages 164ff) that under reaction conditions the particle size of the noble metal applied increases by agglomeration, the dispersion decreases and the elemental noble metal is detached from the support.
It is described in DE-C 40 22 853 that use of platinum/graphite support catalysts having a graphite particle size of 1-600 .mu.M is able to increase the selectivity in respect of hydroxylamine in the hydrogenation of nitrogen monoxide.
DE-C 956038 has disclosed supported platinum/graphite catalysts which are obtained by precipitation of platinum onto suspended graphite supports, with or without addition of poisons such as sulfur, selenium, arsenic or tellurium compounds. Such catalysts are suitable for the catalytic hydrogenation of nitrogen monoxide.
It is described in DE-C 40 22 851 that in the preparation of hydroxylamine by hydrogenation of nitrogen monoxide in the presence of supported platinum/graphite catalysts, the selectivity is related to the apparent density, the compressive strength and porosity of the graphite support.
The catalysts used in the processes of the abovementioned German patents have the disadvantage that, owing to agglomeration of the active components, only relatively short operating lives of the catalysts can be achieved.
It is an object of the present invention to provide an improved process for preparing hydrogenation catalysts which ensures longer operating lives of the catalysts used with at least the same selectivity and a high space-time yield. Furthermore, a minimization of the by-products, in particular dinitrogen monoxide, should be achieved.
We have found that this object is achieved by a process for preparing a hydrogenation catalyst by reduction of platinum in an oxidation state of not less than two using a reducing agent in an aqueous medium in the presence of a carbon-containing support after partial poisoning, wherein use is made of a compound of the general formula I ##STR2## where X, Y and Z can be identical or different and are hydrogen, C.sub.1 -C.sub.18 -alkyl, C.sub.5 -C.sub.10 -cycloalkyl, halogen, hydroxyl, C.sub.1 -C.sub.6 -alkoxy and --NR'R", where R, R' and R" can be identical or different and can be hydrogen, C.sub.1 -C.sub.18 -alkyl or C.sub.5 -C.sub.10 -cycloalkyl.
Furthermore, a hydrogenation catalyst prepared by the process of the present invention, its use for preparing hydroxylammonium salts, a process for preparing hydroxylammonium salts and a process for regenerating hydrogenation catalysts based on platinum have been found.
As C.sub.1 -C.sub.18 -alkyl radicals, preference is given to using C.sub.1 -C.sub.8 -alkyl such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-, sec-, tert-butyl, n-pentyl, neo-pentyl, n-hexyl, n-heptyl, n-octyl, particularly preferably C.sub.1 -C.sub.4 -alkyl such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-, sec- and tert-butyl.
As C.sub
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Structure of metallic Catalyst, Anderson, Academic Press, 1975, S. 164 ff.
Katalytische Hydrierung im organisch chemischen Laboratorium, F. Zinalkowski, 164 ff.
Achhammer Gunther
Heineke Daniel
Schneider Heinz-Walter
Thome Alfred
BASF - Aktiengesellschaft
Griffin Steven P.
Ildebrando Christina
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