Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1992-10-13
1995-05-09
Pal, Asok
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
4232135, 502334, 502339, B01J 2344
Patent
active
054139848
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a method of preparing multimetal catalysts.
Multimetal catalysts are frequently used in refining, petrol chemistry, fine chemistry and catalytic combustion and post-combustion, in order to accelerate chemical reactions. They normally have the advantage over monometallic catalysts of being more selective; this is illustrated in Hydrocarbon Technology, 1990, 12, 20-43, by the improvement in selectivity in the formation of toluene during catalytic reforming of n-heptane on a catalyst based on platinum and iridium, compared with the same reaction on a catalyst based on platinum only. In catalytic combustion or post-combustion, catalysts based on platinum and palladium or based on platinum and rhodium are preferred to catalysts based on platinum only, since they broaden the range of operating conditions under which the catalysts can be used.
For metal catalysts to have good catalytic activity, the metal particles must be in a highly divided state. The principle which is most widely applied to obtain this state is deposition of the metals on a porous carrier. Porous carriers have a large specific surface area, on which the metals can be deposited in the form of very small particles. Multimetal catalysts are obtained on the same principle.
The porous carriers used are selected according to their texture, resistance to high-temperature fritting and chemical properties. Those most commonly used are aluminas, silica, silica-aluminas, zeolites, oxides of titanium, cerium, chromium or zirconium, mixed oxides of aluminium and magnesium or aluminium and nickel, carbides, nitrides, borides and activated carbons. Porous carriers may be impregnated with metals by several methods which are well known in the art. Ch. Marcilly and J. P. Franck have drawn up a list of such methods (Revue Institut Francais du Petrole, 1984, 3, 337-364). The most frequently used are impregnation by exchange and dry impregnation. The first method exploits the cation or anion exchange properties of porous carriers. It comprises dipping the porous carrier in an aqueous or organic solution of metal precursors with a controlled pH. The ionic metal precursors in solution are exchanged with surface locations of the carrier. The second method comprises preparing an aqueous or organic solution of metal precursors and impregnating the porous carrier with a volume of solution equal to its pore volume.
These techniques can be applied not only to the preparation of monometallic catalysts but also to the preparation of multimetal ones. In the latter case the solutions of metal precursors simultaneously contain the precursors of the various metals with which the carrier is to be impregnated. The technique is then described as the co-impregnation method.
SUMMARY OF THE INVENTION
In seeking to improve the catalytic properties of multimetal catalysts, Applicants have found that catalysts can be prepared by a method comprising two impregnation stages, and further comprising at least one treatment in a reducing medium after the first impregnation stage. This method increases the stability of catalytic performance.
The invention thus concerns a method of preparing multimetal catalysts in which the active phase comprises at least two metals A and B belonging to Groups VIII and IB of the Periodic Table, deposited on a porous carrier, characterised in that: at least one precursor of metal A: atmosphere at a temperature from 120.degree. to 800.degree. C., followed by activation in a reducing medium at a temperature from 0.degree. to 800.degree. C.; partly impregnated with the precursor of metal A is impregnated with at least one precursor of metal B; and atmosphere at a temperature of 120.degree. to 800.degree. C., possibly followed by activation in a reducing medium at 0.degree. to 800.degree. C.
In preparing catalysts by the method of the invention, the porous carrier may be selected according to the application envisaged, from the group mentioned above. Some examples of the aluminas are ro, gamma, eta, delta, the
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Barbier Jacques
Durand Daniel
Mabilon Gil
Marecot Patrice
Prigent Michel
Institut Francais du Pe'trole
Pal Asok
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