Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1998-09-01
2000-06-27
Griffin, Steven P.
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
502345, 502344, 502343, 502330, 502337, 502326, 502353, 502305, 502336, 502349, 502347, 502355, 502340, 502439, B01J 2370, B01J 2104, B01J 2302, B01J 2358, B01J 2300
Patent
active
060806990
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for producing a heterogeneous catalyst, which is comprised of at least one catalytically active component and at least one catalytically inert component, whereby the components are dispersed in one another.
The "mean particle diameter" or the "particle size" mentioned in this application is understood to be the d.sub.50 value. This value is so defined that 50% of the particles in question have a smaller particle or grain diameter then the given d.sub.50 value.
BACKGROUND OF THE INVENTION
In the production of industrially used heterogeneous catalysts, two types can be differentiated, namely supported catalysts and massive catalysts. With supported catalysts, the catalytically active material, for example, metal salts or metal oxides are applied to a catalytically inactive support, for example, aluminum oxide, by immersion or impregnation. The form and size of the support, for example, balls or tablets with dimensions of 10 to 50 mm, determine in this case, the shape and size of the finished catalyst. By contrast thereto, the massive catalyst is comprised of a powder mixture of a catalytically active and an inert mass. It has a shape and size determined by the subsequent shaping of the mixture, for example, by extruding or pelletizing.
The invention relates to massive catalysts. They are produced according to the state of the art by precipitation of a metal salt solution, filtration, drying, calcining and subsequent shaping and optionally reduction, e.g. with hydrogen.
The activity, selectivity and life of a catalyst for a given chemical composition depends to a considerable extent upon its physical structure. One understands physical structure to refer to the dispersity, the surface structure and the pore structure. Correspondingly, for many applications, a fine grained catalyst finely divided within the finished shape of the catalyzer, with a high specific surface area, is preferred.
To obtain an especially high dispersity and surface area of the massive catalyst, it is known in the art to precipitate the catalytically active metal salts together with catalytically inert components. Such catalysts are not supported catalysts but rather are considered massive catalyst which are produced by a so-called "mixed precipitation".
An example of such mixed precipitation is found in DE 39 30 298 A1. Here, a massive copper-zinc-silicate catalyst is produced by addition of a solution of copper nitrate and zinc nitrate to a solution of sodium silicate with vigorous agitation.
It is important with such mixed precipitation that there be a higher solubility product of the active component than that of the inert component at the given pH value. In this case, the inert component precipitates initially in a fine particle size, typically about 500 nm, upon which the smaller particles of the active component can grow. The larger inert particles with the smaller active particles deposited thereon, enable a fine distribution of the active component in the massive catalyst. These particles have, in addition, a high mechanical stability so that the particles of the active component cannot be readily separated from the inert component under customary conditions.
On the contrary, what is unwanted is the opposite ratio of the solubility products. In this case, initially the active components precipitate in the form of relatively large particles upon which the inert fine grained particles deposit. On the one hand, the catalytically effective surface is partly covered by the inert particles. On the other, there is a further drawback in the experimentally determinable reduction in the adhesion of the active particles on the inert particles in the mixed particles mass.
The mixed precipitation under the above mentioned desirable conditions, has several drawbacks. One is the fact that a satisfactory difference of the solubility products of active and inert components corresponding to the aforedescribed requirements only occurs in a limited range of pH values. However, th
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Donley Cynthia M
Dubno Herbert
Griffin Steven P.
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