Material constituted by ultrafine metallic and oxide particles

Details Material constituted by ultrafine metallic and oxide particles Material constituted by ultrafine metallic and oxide particles

2001-08-16

2003-12-30

Nguyen, Cam N. (Department: 1754)

Chemistry of hydrocarbon compounds

Adding hydrogen to unsaturated bond of hydrocarbon, i.e.,...

Hydrocarbon is aromatic

C585S266000, C585S270000, C585S275000, C585S276000, C585S277000, C502S306000, C502S307000, C502S308000, C502S309000, C502S311000, C502S312000, C502S313000, C502S314000, C502S315000, C502S316000, C502S317000, C502S318000, C502S322000, C502S323000, C502S327000, C502S328000, C502S329000, C502S330000, C502S331000, C502S332000, C502S333000, C502S334000, C502S335000, C502S336000, C502S337000, C502S338000, C502S339000, C502S342000, C502S346000, C502S348000, C502S351000, C502S354000

Reexamination Certificate

active

06670515

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a material constituted by ultrafine metallic particles and by ultrafine oxide particles, a process for its preparation, and its utilization, particularly for catalysis.
2. Description of the Related Art
Materials constituted by fine metallic particles are known for diverse applications, particularly in catalysis. Various processes for preparing them have been described.
L. K. Kurihara et al. (Nanostructured Materials, Vol. 5, No. 6, 607-613, 1995) describe the preparation of nanometric metal particles of a metal by a so-called “polyol” process, used for various easily reducible metals such as, for example, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Sn, Re, W, Pt, alone or as a mixture. Such a process consists of dissolving or suspending a precursor of the said metal in a polyol, then heating under reflux to obtain a precipitate of metallic particles. The particles obtained can be nanometric. They are polymetallic when the reaction medium contains salts of different metals. The production of nanometric Cu—Co particles by the polyol process is described in L. K. Kurihara et al., J. Mat. Res., Vol. 10, No. 6, June 1995.
Nanometric particles containing aluminum can be prepared by reducing a salt with LiAlH
4
. Thus the preparation of nanocrystalline Ti/Al and Ni/Al particles from a chloride of the corresponding metal in the presence of LiAlH
4
is described by J. A. Haber et al., Advanced Materials, 1996, 8, No. 2. The reaction mechanism of this process is the following:
M
n+
+n
LiAlH
4
→n
Li
+
+M+
n
AlH
3
+n
/2H
2′
n
AlH
3
→3
n
/2H
2′
,
the content of Al having an upper limit corresponding to the valence of the associated metal.
The preparation of nanometric intermetallic particles by means of borohydrides is furthermore known. S. T. Schwab et al., Materials Science and Engineering, A204 (1995) 197-200, describe the preparation of intermetallic particles by the reduction of a mixture of salts of different metals by a borohydride (for example, TiCl
4
+AlCl
3
+lithium triethyl borohydride). This process enables intermetallic particles to be obtained without limitations on the content of the respective metals. It requires a heat treatment at 1,000° C. to decompose the products obtained by the reaction of the salts with the borohydride and to obtain the metallic forms.
The preparation is likewise known of fine monometallic particles by the reaction of a metal salt with sodium hydride in solution in an organic solvent and in the presence of an alcoholate. Such a process has been described for nickel particles and for zinc particles (Paul Caubere et al., J. Am. Chem Soc., 1982, 104, 7130; P. Gallezot, C. Leclercq, Y. Fort, P. Caubére, Journal of Molecular Catalysis, 93 (1994) 79 83, pp. 80-83; Brunet et al., Journal of Organic Chemistry 1980, Vol. 45, pp. 1937-1945). The particles obtained have a crystallite dimension of nm order and are particularly useful as a catalyst for heterogeneous catalysts. When they are prepared in the presence of a phosphine or 2,2′-bipyridine ligand, they lose their reducing properties and behave as a coupling agent (Lourak et al., Journal of Organic Chemistry, 1989, Vol. 54, pp. 4840-4844).
An analogous process has likewise been described for the preparation of monometallic particles of Pd, which can be used as a catalyst for the hydrogenation of acetylene (J. J. Brunet and P. Caubére, J. Org. Chem., 1984, 49, 4058-4060).
The usefulness of ultrafine polymetallic particles as catalysts for various reactions is known. The French patent application No. 97.11814 describes a process which enables ultrafine polymetallic particles to be obtained containing aluminum having good purity, with any given aluminum content. The process consists of reducing a mixture of salts in solution in an organic solvent by means of a hydride of an alkali metal or alkaline earth metal, at a temperature lower than or equal to the reflux temperature of the solvent, the mixture of salts in solution comprising at least one salt of a metal having a standard oxidation potential E
0
(M
n+
/M) at 25° C. greater than −1.18 V. The material obtained by this process is constituted by nanometric polymetallic particles which have a mean crystallite dimension less than 4 nm, in which the various metals present are intimately associated, and which are constituted by at least one metal chosen from the group constituted by Ni, Co, Fe, Cu, Zn, Cd, Cr, Mn, Pd, Ag, Pt, Au, Bi and Sb, and at least one metal chosen from the group constituted by V, Zr, Ce, Ti, Hf and Al. Such a material can be used as a catalyst for diverse reactions, particularly for the hydrogenation of olefins and for the direct coupling of aromatic halogenated derivatives.
SUMMARY OF THE INVENTION
The present inventors have now found a process permitting the preparation of metallic particles which have improved catalytic performance.
The present invention thus has as its object a material constituted by ultrafine metallic particles and by ultrafine oxide particles, a process for its preparation, and also its utilization as a catalyst.
The material which is the object of the present invention comprises at least one metallic element M of degree of oxidation 0 having catalytic properties, and at least one metallic element M′ having a standard oxidation potential less than that of the element M, at least a portion of the M′ atoms being in an oxidized form; and it is characterized in that:
it is in the form of particles having a mean dimension less than 50 nm, at least 80% by number of the particles having a mean dimension less than 10 nm;
a particle of the material is constituted by
at least one metallic element M of degree of oxidation 0, or by
at least one metallic element M′ in oxidized form, or by
at least one metallic element M′ of degree of oxidation 0, or by
the combination of at least two species chosen from the three preceding species, it being understood that the mean content of the element M of degree of oxidation 0 in the material is greater than 25% by number of atoms with respect to the whole of the material, the mean total content of the element M′ is at most equal to 75% by number of atoms with respect to the whole of the material, and the mean content of the element M′ in the oxidized form is greater than 10% by number of atoms with respect to the total content of the element M′.
A metal M′ which has a standard oxidation potential less than that of a metal M is a metal which is easier to oxidize than the metal M.
An element M or M′ of degree of oxidation 0 will hereinafter be respectively denoted by M(0) or M′(0).
A material according to the invention can furthermore contain the element M in oxidized form, under the condition that the proportion of the oxidized element M is not greater than 10% by number of atoms with respect to the total quantity of the element M.
The element M is a metal having catalytic properties. It is advantageously chosen from among Pd, Pt, Rh, Ir, Ni, Co, V, Mo, Zn, Cd, Cu, Ag, Au and Fe.
The element M′ is chosen from among V, Zr, Ce, Ti, Hf, Al, Ni, Co, Fe, Ru, Cu, Zn, Cd, Cr, Mn, Bi, Sb and Si. The choice of the element M′ is made such that the standard oxidation potential of the selected element M′ is less than that of the element M with which it is associated. The pairs (M, M′) such as (Ni, Fe), (Ni, Al), (Pd, Cu), (Pd, Ni) or (Pd, Al) are particularly preferred.
When M is Ni, Co, or Fe, the mean dimension of the particles constituting the material of the invention is ≦10 nm, 80% by number of the particles having a mean dimension less than 5 nm.
The material of the present invention can be obtained by subjecting to an oxidation, polymetallic particles containing at least one element M(0) having catalytic properties and at least one element M′(0) having a lower standard oxidation potential than that of the metal M, the said particles having a mean dim

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