Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Inorganic carbon containing
Reexamination Certificate
1997-07-16
2001-11-13
Hendrickson, Stuart L. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Inorganic carbon containing
C502S324000
Reexamination Certificate
active
06316381
ABSTRACT:
INTRODUCTION AND BACKGROUND
The present invention relates to a catalyst which contains iridium and at least one other doping element on a support for preparing substituted aromatic amines by hydrogenation of the corresponding substituted nitroaromatic compounds. In another aspect, the invention relates to the method of making the catalyst.
The hydrogenation of aromatic nitro compounds with halogen substituents, in particular chlorine, to prepare the corresponding amines has been known for some time (Ullmann, Enzyklopädie der technischen Chemie, 5th edition, vol. A2, page 46 (1985)) and is performed in the presence of metal catalysts using hydrogen as reducing agent. A serious problem in the reaction is the undesired dechlorination of the aromatic compounds, which leads to a reduction in the yield of aromatic amine compound. For this reason, many patents have dealt with processes which attempt to keep the elimination of halogens as low as possible.
Thus, the use of platinum and ruthenium on support materials as shown in U.S. Pat. No. 4,760,187 can lead to an improvement in selectivity, as does the use of platinum, palladium, rhodium, iridium, ruthenium and osmium-containing catalysts which are after-treated with acidic phosphorus compounds (DE-OS 30 06 748).
The activity and selectivity of noble metal catalysts can be affected by the presence of a co-catalyst in the reaction mixture. According to U.S. Pat. No. 5,105,012 iron powder or an iron salt can be added to the reaction mixture as a co-catalyst in addition to palladium on a carbon support as the main catalyst. U.S. Pat. No. 3,253,039 suggests adding silver nitrate to the reaction mixture in addition to a catalyst consisting of platinum on carbon. Silver is then distributed in the entire reaction mixture without being alloyed with the platinum in the catalyst. Lead, copper, nickel, bismuth and chromium nitrate have also been tried as heavy metal additives.
The activity and selectivity of hydrogenation can also be affected by specific doping of a noble metal catalyst with a variety of A and B group elements. Thus, for example, DE 42 36 203 A1 suggests using a platinum catalyst on active carbon doped with nickel and/or cobalt. According to DE 42 18 866 C1, the selectivity of hydrogenation is improved by doping a platinum catalyst on active carbon with copper. In this case, platinum and copper are deposited onto the active carbon support at the same time and then reduced.
Known hydrogenation catalysts are prepared, for example, by introducing the support material into a noble metal salt solution and evaporating the solvent. Optionally, the catalyst is then reduced. As an alternative to this, the support material may also be impregnated with the catalytically active elements by placing the support material in contact with a solution of these elements and precipitating the hydroxides of these elements in an alkaline medium. A reduction procedure may also follow this. Furthermore, it is known that a solution of the noble metal salts may be sprayed onto the support material.
The hitherto known processes for hydrogenation of substituted aromatic nitro compounds, however, still present some problems relating to activity and selectivity. Thus, the use of modifiers or promoters in combination with nitrogen-containing additives during hydrogenation leads to halogenated azobenzene and azoxybenzene derivatives (EP-OS 0 073 105). The formation of such compounds as side-products during the hydrogenation of halogenated nitroaromatic compounds should be avoided due to their toxicity.
An object of the present invention is to provide a catalyst for the hydrogenation of substituted nitroaromatic compounds which is distinguished in particular by improved selectivity as compared with known catalysts.
SUMMARY OF THE INVENTION
The above and other objects of the invention are achieved by a multimetallic catalyst which contains iridium and at least one other promoter on a support. More particularly, the catalyst of the invention features iridium doped with at least one element selected from the group consisting of manganese, cobalt, iron, nickel and ruthenium.
Suitable support materials for the catalyst of this invention are activated carbon or inorganic oxidic materials such as aluminum oxide, titanium dioxide, silicon dioxide or mixed oxides thereof. Activated carbon is preferably used. The activated carbon may be of plant or animal origin and have been activated by a variety of processes (e.g. steam, phosphoric acid, etc.). It may consist of porous and non-porous activated carbon, wherein at least 80 wt. % of the activated carbon particles have a particle size of preferably less than 100 &mgr;m. These types of activated carbon are generally obtainable from many different suppliers.
DETAILED DESCRIPTION OF INVENTION
The catalyst according to the invention contains iridium in an amount of from 0.3 to 12, preferably from 0.5 to 7 wt. %, with reference to the support material used, and at least one metal selected from the group consisting of manganese, iron, cobalt, nickel, copper and ruthenium in an amount of from 1 to 100, preferably from 5 to 50 wt. %, with reference to iridium.
To prepare the catalyst, the support as defined herein is first suspended in water and impregnated by adding aqueous salt solutions of the appropriate metals. Then the metals are reduced using a water-soluble reducing agent at temperatures from 0 to 100° C. A different sequence for adding support material, water, metal salt solutions and reducing agent may also be chosen.
Substituted nitroaromatic compounds may be hydrogenated to give the corresponding aromatic amines with high selectivity using the catalyst according to the invention. For this purpose, the nitroaromatic compounds are dissolved in suitable inert solvents and hydrogenated on the catalyst at elevated temperatures with the addition of hydrogen to give amine compounds.
Chlorine substituted aromatic nitro compounds of the formula (I) are preferred for the hydrogenation.
In formula (I), R
1
and R
2
may be identical or different and represent hydrogen, an alkyl, alkoxy, hydroxy, carboxy, carbonyl, phenyl or amino group as well as chlorine, fluorine, alkylcarbonylamido or alkyloxycarbonylamido.
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Auer Emmanuel
Freund Andreas
Gross Michael
Hartung Rolf
Degussa - AG
Hendrickson Stuart L.
Smith , Gambrell & Russell, LLP
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