Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1999-04-14
2000-11-28
Dunn, Tom
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
502325, 502337, 502338, 502339, 502345, B01J 2500, B01J 2502, B01J 2504, B01J 2300, B01J 2370
Patent
active
061535540
DESCRIPTION:
BRIEF SUMMARY
The subject of the invention is the preparation of supported, non-pyrophoric, skeleton catalysts containing catalytically active metal(s), preferably nickel, cobalt, chromium, copper, manganese, iron, palladium and/or platinum.
The skeleton-metal (or Raney-metal) catalysts are made of alloys that contain catalytically active metal or metals (e.g.: Ni, Co, Fe, Cu, Pd, etc.) and easily dissolvable, catalytically inactive component or components (e.g.: Al, Si, Mg, Zn). In the alloy the active metal is "dissolved", i.e. it is finely dispersed. The inactive component is removed from the alloy using a solvent (generally aqueous alkali solution) not attacking the active metal. The active metal is left over as a catalyst in the form of fine particles. The activity of the catalysts made this way is greater than the one produced from the appropriate metal oxide with reduction. Their importance and wide-spread application are explained by the exceptionally high activity.
Skeleton catalysts were first patented by Raney (Raney, M.: U.S. Pat. Nos.: 1,563,787 (1925); 1,628,191 (1927); 1,915,473 (1933)).
From the alloy normally containing about 50% active metal and about 50% inactive component, the latter component is generally dissolved in two steps (Schroter, R.: Neuere Methoden der praparativen organischen Chemie, Verlag Chemie GmbH, Berlin, 1943, p. 78; Beregi, L.: Magyar Kemikusok Lapja 9, 234 (1954) Csros, Z., Petro, J. and Voros, J.: MTA Km. Tud. Oszt. Kozl. 9, 433 (1957)): The steps are the following:
The initial alkaline wash is generally carried out by adding the alloy to a 15-25 wt % alkali solution which amounts to four times the weight of the alloy (it is normally added slowly because of the intensive hydrogen development and the exothermic reaction). Then the mixture is heated until the hydrogen development is finished. The alloy to alkali solution--and the alloy to alkali hydroxide ratios, which are characteristic on this step, are given in weight-parts of the alloy, on the basis of the data of related references (Katalysatoren nach Raney, Merkblatt, Degussa (1967) p. 7):
______________________________________ NaOH solution Solution/alloy
Alloy/NaOH
wt % wt. ratio wt. ratio
______________________________________
13 12 2
20 4-5 0.8-1.0
25 4 1.0
______________________________________
When the initial alkaline wash is finished, the solution is separated by decantation and generally the suspension left is heated again with a fresh alkali solution using the same amount as for the initial alkaline wash, in order to complete the dissolution process.
The above process steps are in accordance with the present general practice. In modem industrial and commercial reviews generally above process descriptions can be found (Die Wirksamkeit spezieller Raney-Nickel-Katalysatoren mit definierte Eigenschaften fur chemische Reaktionen. Informationen, DODUCO (1967).2.0).
The catalytic features of the catalyst made from a given alloy are decisively influenced by the conditions of the alkaline wash or washes described above. For example when dissolving a nickel-aluminium alloy the crystal system of the alloy containing the aluminium is rearranged. The way and extent of rearrangement changes with the time and temperature of the operation and with the amount of alkali (Wagner, H., Schwab, G. and Stolger, I.: Z. phys. Chem. B. 27, 439 (1934)). As a consequence the method of dissolving the alloy is decisive on the catalytic features of the product.
According to the U.S. Pat. No. 3,809,658, the starting alloy powder is decomposed first, in a wet solid phase using water and a small amount of alkali hydroxide, and then the process is finished with a following intensive dissolving treatment using concentrated alkali hydroxide solution at a temperature around 100.degree. C.
As it is obvious from the related literature dozens of process variations have been tried in this field. All of them, with no-exception, are characterised by a first step wherein 20-30 wt % aqueous alkaline was used in an amount which was at
REFERENCES:
patent: Re32104 (1986-04-01), Gray
patent: 3809658 (1974-05-01), Csuros et al.
patent: 4375003 (1983-02-01), Allain et al.
Dunn Tom
Nguyen Cam N.
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