Chemistry of hydrocarbon compounds – Adding hydrogen to unsaturated bond of hydrocarbon – i.e.,...
Reexamination Certificate
2000-11-30
2002-11-19
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Adding hydrogen to unsaturated bond of hydrocarbon, i.e.,...
C585S259000, C585S261000, C585S267000, C585S269000, C585S275000
Reexamination Certificate
active
06482997
ABSTRACT:
The present invention relates conversion reaction of organic compounds employing to supported metallic catalysts containing at least one metal, at least one support and optionally an alkali or alkaline-earth metal, which has particles of an average size greater than approximately 1 nm, and more than 80% of particles, the size of which is comprised in the range D±(D.O.2) where D represents the average size of the particles.
DESCRIPTION OF THE PRIOR ART
The properties of supported metallic catalysts, i.e. catalysts constituted by a metal or by several metals, deposited on a support chosen from refractory oxides, carbon, polymers or any other material, are conditional on a set of parameters highly dependent on the preparation method and treatment conditions chosen to obtain the finished catalyst.
With regard to the supported metallic catalysts, there are a large number of examples in the literature showing the influence of the size of metallic crystallites on the activity of the final catalyst. This aspect has been described in extensive detail in Catalysis by Metals and Alloys, V. Ponec, E. Bond, Study in Surface Science and Catalysis, Volume 95, page 280, 1995.
The reactions included within the scope, i.e. for which the activity of the metallic atoms situated on the surface of the particles is dependent on the size of these particles, are called structure-sensitive.
Among the reactions in which the catalyst according to the invention can be used, for example, hydrogenation reactions of compounds having acetylenic, dienic, olefinic, aromatic, ketone, aldehyde, acid or nitro functions, the hydrogenation of carbon monoxide into C1-C6 alcohols, into methanol or into dimethyl ether, isomerization or hydroisomerization reactions, hydrogenolysis, and in general manner reactions involving breaking or forming a carbon-carbon bond can be mentioned.
For all these reactions, it is necessary to have available a simple method of preparation which allows catalysts having a controlled metallic particle size to be obtained in order to fully optimize catalyst activity.
The conventional preparation processes for supported metallic catalysts consist of depositing a metallic salt or a co-ordination complex on the support, then carrying out an activation stage consisting of thermal treatments carried out under air and/or under hydrogen.
They allow catalysts to be obtained for which the particle sizes are small (less than approximately 1 nm) and for which a significant proportion of the metal (more than 80%) is accessible to the molecules to be converted (J. P. Boitiaux, J. Cosyns, S. Vasudevan, Scientific Bases for the Preparation of Heterogeneous Catalysts, G. Poncelet et al. Editor, pages 123-134, Elsevier, 1983).
Such catalysts can be used in certain reactions (dehydrogenation of paraffins, for example) but do not lead to higher activites for other reactions (hydrogenation of diolefines or acetylenic compounds, for example). For these reactions, it is advantageous to have a supported metallic catalyst for which the metallic particles have a size greater than approximately 1 nm, less than 80% of the metal involved therefore being accessible to the molecules to be converted.
To achieve particle sizes greater than approximately 1 nm by conventional methods, it is usually necessary to treat the catalyst under severe conditions (increase in activation temperature, treatment in the presence of water vapour), which leads to a sintering of the particles, i.e. to their enlargement (J. P. Boitiaux, J. Cosyns, S. Vasudevan, Applied Catalysis, Vol 6, Pages 41 to 51, 1983).
However, with this technique, the enlargement of the particles is not well controlled. The catalysts thus obtained are composed of particles, the size of which can vary within a large range. These catalysts have a proportion of particles of a size less than the size of the desired particles and the atoms situated at the surface of which are less active in the reaction considered. They also contain particles of larger size having only a low proportion of metallic atoms accessible and thus a low overall activity.
The said conventional preparation processes, i.e. the processes in which a metallic salt or a co-ordination complex is deposited on a support, then subjected to an activation procedure (cf. Z. Karpinski, Adv. Catal., Vol.37, p.45, 1990), are thus not satisfactory as they do not allow catalysts having particles of larger size, i.e. greater than approximately 1 nm with a restricted distribution of particle size to be obtained.
In order to improve the activity of the catalysts, it is thus advantageous to have a preparation method available which allows supported metallic catalysts to be obtained the particle size of which is on average greater than approximately 1 nm and having a restricted distribution as regards size.
More fundamental studies on supported metallic catalysts reported in the literature show that the interaction between the metal or metals comprising the catalyst and the support used also affect the activity of the catalyst (cf. Z. Karpinski, Adv. Catal., Vol.37, p.45, 1990).
It is generally acknowledged that for reactions, such as for example, hydrogenation reactions, detachment or carbon-carbon bond formation, a strong interaction between the metal and the support leads to a decrease in catalyst activity. This strong interaction between the metal and the support is generally conditional upon the method of preparing the catalyst and, there again, it is necessary to have a preparation method for limiting the interaction between the metal and support.
This interaction between the metal and the support can be characterized by a set of characterization techniques known to a person skilled in the art. For example, programmed thermoreduction which consists of determining the reduction temperature of the supported metal oxide can be mentioned. In fact, it has been shown that the more the reduction temperature of the metal oxide is increased, the more the interaction between the metal and the support is increased.
Another method, more difficult to implement but giving a direct response, is EXAFS. In this method, the identification of the number of neighbouring oxygen atoms around the reduced metal allows comparison of the interaction between the metal and the support for two catalysts having similar metallic particle sizes, but produced by different preparation methods, and thus the quantification of the interaction between the metal and the support.
SUMMARY OF THE INVENTION
The present invention relates to a catalyst which can be used in a process involving conversion reactions for organic compounds, comprising at least one support and at least one metal, and characterized in that it has particles the average size of which is greater than approximately 1 nm, and more than 80% of the particles size of which is comprised in a range D±(D.0.2), i.e. comprised between D−(D.0,2) and D±(D.0,2) where D represents the average size of the particles.
A new preparation process for supported metallic catalysts has also been discovered, allowing the size of the particles of the finished catalyst to be better controlled. The process according to the invention consists of preparing a colloidal suspension, in aqueous phase, of the oxide of the metal or metals to be supported, then depositing this suspension on a support, drying the product obtained and optionally reducing the oxide or oxides thus supported.
DETAILLED DESCRIPTION OF THE INVENTION
The catalyst according to the invention comprises at least one support, preferably of oxide type, and at least one metal, preferably chosen from the metals of groups 5 to 12, i.e. from the groups 5,6,7,8,9,10,11 and 12 of the new periodic classification (Handbook of Chemistry and Physics, 76
th
edition, 1995-1996. inside front cover), preferably from the following elements: V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, more preferably from the metals of groups 6 to 10 of said classification and very preferably from the following meta
Didillon Blaise
Petit-Clair Carine
Uzio Denis
Griffin Walter D.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Nguyen Tam M.
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