Note: Descriptions are shown in the official language in which they were submitted.
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*PCT/EP99/08594 WO 00/29332
Water-soluble Nanostructured Metal-Oxide Colloids
and Method for Preparing the same
The present invention relates to mono-, bi- and multi metallic, water-
soluble metal-oxide colloids, a method for preparing the same and their
fixation on a support.
Nanostructured transition metal colloids are of great interest as catalysts
for organic reactions, as electrocatalysts in fuel cells as well as structural
elements in material science (G. Schmid, Clusters and Colloids, VCH,
Weinheim, 1994). In the literature, numerous chemical and physical
processes for the preparation of metal colloids are known, e. g., the
chemical reduction of common metal salts, as PdCl2, Pd(OAc)2. PtCl4,
RuCl3, CoCl2, NiCl2, FeCl2 or AuCl3, with a wide variety of reduction
agents, the photolytical, radiolytical or thermal decomposition or
reduction of appropriate metal precursors, or the method of metal
vaporization. Recently, electrochemical methods for the preparation of
metal colloids are being used too {M.T. Reetz, S.A. Quaiser, Angew.
Chem. 1995, 107, 2956; Angew. Chem., Int. Ed. Engl.,1995, 34,
2728). In order to prevent an undesired agglomeration of the
nanoparticles into insoluble metal powders, stabilizers, such as ligands,
polymers or surfactants are added in most cases (G. Schmid, Clusters
and Colloids, VCH, Weinheim, 1994).
Due to ecological and economical reasons water-soluble metal colloids
are of particularly great interest in industry, the synthesis of which
is ideal in an aqueous medium. The aim of preparing high concentrated,
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water-soluble, surfactant-stabilized metal colloids was achieved only in
a few cases; however, the reduction step is relatively expensive or
requires costly reduction agents, such as boron hydrides (M.T. Reetz et
al., EP 0 672 765 A1, and H. Bonnemann et al., DE 4 443 705 A1).
Furthermore, bimetallic nanoparticles are often clearly superior to the
nanometallic species for certain catalytic applications, for which reason
the selective synthesis of bimetallic metal colloids is gaining more and
more in importance (G. Schmid, Clusters and Colloids, VCH, Weinheim,
1994).
Hereby, two different metal salts are chemically or electrochemically co-
reduced in organic solvents in the presence of useful stabilizers, whereby
the degree of alloy formation of the particles generally depends from the
difference of the reduction potentials of the two metal salts used.
Therefore, not all combinations of metals are possible by this route. The
use of organic solvents and/or expensive reduction agents is also
unfavorable.
Due to high polarity and high surface tension of the water, it is
extremely difficult, just in an aqueous medium, to produce bimetallic
colloids having a high degree of alloy formation. A special challenge also
consists in alloying two metals which have a significantly different
reduction potential, e.g., a noble metal, such as platinum, with a
distinctly less noble metal, such as ruthenium, iron, cobalt or tin, in an
aqueous medium in a way as simple as possible.
Now, a surprisingly simple solution to these problems could be achieved
in an approach in which the metal salts are not reduced but condensed
in an aqueous medium and in the presence of a water-soluble stabilizer,
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whereby the corresponding nano-structured metal oxide is formed. The
stabilizer prevents the undesired formation and deposition, respectively,
of insoluble metal oxide in bulk form. Working with two metal salts
results in a co-condensation with formation of water-soluble colloidal
bimetal oxides, whereby the size of the particles is also in the
nanometer range.
The water-soluble metal-oxide colloids and bimetal-oxide colloids thus
obtained can then be characterized with the aid of appropriate physical
methods and can be processed to soluble or carrier-fixed catalysts.
Hereby, the reduction of the colloidal metal oxide may take place with
the help of reduction agents, such as hydrogen, hypophosphite or
formate, without any appreciable change of the stoichiometry or of the
particle size of the nanoparticles. The method allows an extension to
trimetal oxides and multimetal oxides, respectively.
Contrary to the corresponding metal colloids, little is known in the
literature about the preparation and the properties of metal oxide
colloids of the late transitional metals. Henglein describes the
preparation of colloidal MnOZ by radiolysis of KMn04 (C. Lume-Pereira,
et al., J. Phys. Chem. 1985, 89, 5772), Gratzel (K. Kalyanasundaram,
M. Gratzel, Angew. Chem. 1979, 91, 759) as well as Harriman (P. A.
Christensen, et al., J. Chem. Soc., Faraday Trans. 1984, 80, 1451)
obtained polymer-stabilized colloids of Ru02 from Ru04 or KRu04, and
Thomas reported colloids of Ir02 by hydrolysis of H2IrCl6 in the presence
of a polymer (A. Harriman, et al., New J. Chem. 1987, 11, 757).
Furthermore, publications by Nagy can be mentioned who obtained
colloidal particles of Re02 in microemulsions by reduction of NaRe04 with
hydrazine (J. B. Nagy, A. Claerbout, in Surfactants in Solution (K. L.
Mittal, D. O. Shah, Eds.), Plenum Press, New York, 1991, p. 363; A.
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Claerbout, J. B. Nagy in Preparation of Catalysts V (G. Poncelet, Ed.),
Elsevier, Amsterdam, 1991, p. 705).
These colloidal oxides of noble metals must be distinguished from the
publications of Matijevic, who describes metal oxides of metals, such as
iron, aluminum, chromium, titanium, nickel and cerium, made by
precipitation from homogenous solution (E. Matijevic, Langmuir 1994,
10, 8; E. Matijevic, Langmuir 1986, 2, 12), whereby the term of
"colloidal" is not appropriate in this case, since the Nm sized particles do
not remain in solution in a colloidal form. Furthermore, colloidal metal
oxides and metal sulfides may be mentioned, such as, for instance, CdS
and CoFe204, which usually are prepared in microemulsions and which
are used in the semiconductor technology as well as in magnetic liquids
(M. P. Pileni, Langmuir 1997, 13, 3266).
Another possibility for preparing metal oxide colloids consists in
oxidizing metal colloids afterwards in a specific manner, as could be
shown in the case of electrochemically prepared nanoparticles of cobalt
(M. T. Reetz, et al., Angew. Chem. 1996, 108, 2228; Angew. Chem.,
Int. Ed. Engl. 1996, 35, 2092); however, this method is not possible in
water as a medium. Therefore, neither this method nor other methods
are suitable for making available water-soluble nanoparticles of metal
or bimetal oxides in an easy way.
The new method of the controlled hydrolysis for preparing colloidal metal
oxides and bimetal oxides has the following advantages:
1) Water as an inexpensive and ecologically benign solvent.
2) A nearly complete conversion of the metal precursors into soluble
metal oxides or bimetal oxides (no loss of metal).
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3) Preparation of almost monodisperse nanoparticles in a size range
of 0,5-5 nm, which means a high dispersion of the metals.
4) Simple purification and isolation of the colloid powders by dialysis
and lyophilization.
5) Simple reduction of the metal oxides and bimetal oxides, respecti-
vely, by using hydrogen without any significant change of the
stoichiometry and the size distribution.
6) Complete re-dispersibility of the colloid powder in water with con-
centrations of up to 0.5 mole of metal per liter of water.
7) Handling of the metal-oxide colloids in air without any difficulties,
in contrast to the corresponding colloids of noble metals which are
oxidized at the surface by air.
8) Fixation on a solid support at the stage of the oxidized species.
9) Control of the stoichiometry of the bimetals within a wide range.
10) Numerous water-soluble surfactants and polymers can be used as
stabilizers.
11) The process may be extended to the preparation of trimetal oxide
colloids and multimetal oxide colloids.
According to the invention, the aqueous solution or, if possible, the
suspension of a salt of a transition metal or a mixture of two or more
metal salts is treated with the aqueous solution of a base in the
presence of a water-soluble stabilizer. This results in the hydrolysis of
the metal salts and the condensation and co-condensation, respectively,
with formation of colloidal monometal oxides or colloidally alloyed mixed
oxides.
base
MX~ + Hz0 + stabilizer > MXOY~(stabilizer)Z
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Scheme 1. Preparation of water-soluble metal-oxide colloids (MX~ _
metal salt).
In the case of preparing monometal oxides, common salts of metals of
the groups VIb, VIIb, VIII, Ib and IIb of the periodic table can be used
as precursors. In the case of preparing colloidal bimetal oxides (mixed
oxides), two common salts of metals of the groups VIb, VIIb, VIII, Ib
and/or IIb of the periodic table are used and co-condensed, respectively;
the same is possible when using one of these salts in combination with
the salt of a metal from the main group of the periodic table, whereby,
in particular, salts of tin may be used. In the case of preparing colloidal
multimetal oxides, the corresponding mixtures consisting of three or
more metal salts are chosen.
Carbonates, bicarbonates, hydroxides, phosphates or hydrogen
phosphates of alkali metals and alkaline earth metals, such as LiOH,
NaOH, KOH, LiHCOs, NaHC03, KHC03, CsHC03, LizCOs, NazC03, KZCOs,
CszCOs, Mg(OH)z, MgC03, CaC03, Li3PO4, NaZHPOa, Na3P04 or K3POa,
serve as bases. Preferred bases are LizC03, NazC03, K2C03, CszC03 or
MgC03.
Amphiphilic betains, cationic, anionic and nonionic surfactants or water-
soluble polymers are possible as stabilizers. Typical examples of the
amphiphilic betains are dimethyldodecylammoniopropane sulfonate and
dimethyldodecylammoniopropane carboxylate, a typical example of the
cationic surfactant is [CICH2CH(OH)CHZN(CH3)zClsH3,]+CI-, a typical
example of the anionic tenside is sodium cocoamidoethyl-N-hydroxy-
ethyl glycinate, typical examples of the nonionic tensides are polyoxy-
ethylenelauryl ether and polyoxyethylenesorbitanmono laurate, as well
as typical examples of the water-soluble polymers are polyvinyl
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pyrrolidone) (PVP), polyethylene glycol (PEG) or alkylpoly glycoside. It
is also possible to use chiral water-soluble stabilizers such as poly-L-
aspartic acid, sodium salt. The hydrolysis and condensation,
respectively, of the metal salts in a basic, aqueous environment, and in
the presence of a stabilizer is performed in a range of temperature of
from 20 °C to 100 °C, preferably between 50 °C and 90
°C. Water
serves as a solvent and at the same time as a chemical reactant,
whereby the concentration of the aqueous solutions of the colloidal
metal oxides can amount up to 0,5 M, in relation to the metal. However,
mixtures of solvents, consisting of water and water-soluble organic
solvent, can also be used.
The particle size of the nanostructured metal-oxide colloids is normally
between 0,5 nm and 5 nm.
In the case of preparing bimetal-oxide colloids and of multimetal-oxide
colloids, the mass ratio of the metals in the product can be controlled in
an easy manner by the corresponding choice of the mass ratio of the
metal salts. The colloidal metal oxides thus obtained as well as their
reduction products with hydrogen can be characterized by means of
numerous physical methods, such as HRTEM/EDX, XRD/DFA, XPS, EXAFS
and UV spectroscopy.
For preparing heterogeneous catalysts starting from water-soluble
colloids of metals and of metal oxides, numerous oxidic and nonoxidic
solids, for example, A1203, SiOz, CaC03, MgO, La203, carbon black or
activated carbon, can be used as the solid support ("Tragerung").
For that purpose, an aqueous suspension of the solid support is treated
with an aqueous solution of the metal colloids or of the metal oxide
colloids, which causes the nanoparticles to be deposited on the solid
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support without any undesired agglomeration. It is also possible to carry
out another kind of immobilization, for instance, the inclusion in sol-gel-
materials by hydrolyzing Si(OCH3)4 or mixtures of Si(OCH3)4 and
C~H2~+1S1(OCH3)3 (n = 1-4) in the presence of the metal-oxide colloids.
With regard to the transformation of the nanoparticles of metal oxides
into the corresponding nanoparticles of metals, the various reduction
agents, particularly, hydrogen, sodium hypophosphite or sodium
formate, are suited for this. The reduction may be done at the stage of
the colloidal solutions of the metal oxides in water, or alternatively after
the fixation on the solid support and the immobilization, respectively.
The colloids of metal, bimetals or multimetal oxides described herein can
be applied as catalysts or precursors of catalysts for organic-chemical
transformations, such as hydrogenations or oxidations. The application
as electrocatalysts in fuel cells (e. g., Pt/Ru bimetal oxide) is also
evident and of particular importance in view of the low production costs.
Example 1. PtRuOx,~3.12-SB)
370 mg (5 mmole) of Li2C03 was weighed in a 250 ml three-necked flask
and dissolved in 40 ml of deionized water. 40 ml of a 0,1 M solution of
dimethyldodecylammoniopropane sulfonate (3-12-SB) in deionized water
was added thereto. A solution of 517.9 mg (1 mmole) of HzPtCl6 x 6 H20
and 235.9 mg (1 mmole) of RuCl3 x H20 in 20 ml of deionized water was
added dropwise thereto with strong stirring at room temperature for 1
hour. Hereby, the pH value of the surfactant solution decreased from
initially 11.5 to a value of 8.0, after the addition of the solution of the
metal salt was completed. The solution was tempered to 60 °C and
stirred at this temperature for ca. 20 hours. The progress of the
hydrolysis and of the condensation was followed by UV spectroscopy by
means of the decrease of the H2PtC16 absorption at 260 nm. After this
s
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_ g _
band had completely disappeared, the reaction was terminated and
cooled to room temperature. The colloidal solution was then filtered, in
order to separate any precipitated metal oxide possibly present, and was
submitted to an dialyzing process. Hereby, the colloidal metal oxide
solution was filled into a Nadir dialyzing tube and dialyzed twice against
1 I of deionized water. The change of conductivity of the permeate
monitored was conductometrically. Thereafter, the solution was filtered
once again, and the colloidal solution was lyophilized. 1.2 g of a grey
colloid powder was obtained which is completely re-dispersible in water.
Metal content: 10.70 % Pt, 5.82 % Ru (this is corresponding to a molar
ratio of 0,95:1)
TEM micrographs of the solution of the colloidal metal oxide solution
show particles having a size distribution of 1.5 ~ 0,4 nm. A individual-
particle-EDX- analysis of these particles indicates bimetal character,
since both metals always can be detected in a molar ratio between 1:2
and 2:1.
XPS examinations of these colloids showed that ruthenium is present in
the oxidation state of IV, whereas two equal parts of platinum are
incorporated into the colloid in the oxidation states of II and IV, respecti-
vely.
The XRD spectrum of the sample which was reduced in a stream of HZ
at 120 °C shows a scatter curve, from which an average peak distance
of 2.73 ~ can be calculated (bulk PtRu: 2.71 ~, bulk Pt: 2.774 ~, bulk
Ru: 2.677 ~). As a result, the average particle size was found to be 1.2
nm. Principally, Mis-icosahedra as well as decahedra contribute to the
DFA simulation of the scatter curve, whereas the proportion of larger
particles of the fcc type being relatively small.
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Example 2. PtRu0,;~1.12-CB)
370 mg (5 mmole) of l_i2COs were weighed in a 250 ml three-necked
flask and dissolved in 20 ml of deionized water. 60 ml of a 0,1 M
solution of dimethyldodecylammonio acetate (1-12-CB) in deionized
water was added thereto. A solution of 517.9 mg (1 mmole) of H2PtC16
x 6 H20 and 235.9 mg (1 mmole) of RuCl3 x H20 in 20 ml of deionized
water was added dropwise thereto with strong stirring at room
temperature for 1 hour. Hereby, the pH value of the surfactant solution
decreased from initially 12.0 to a value of 8.5, after the addition of the
solution of the metal salt was completed. The solution was tempered to
60 °C and stirred at this temperature for ca. 20 hours. The progress of
the hydrolysis and the condensation were observed by UV spectroscopy
by means of the decrease of the H2PtC16 absorption at 260 nm. After this
band had completely disappeared, the reaction was terminated and
cooled to room temperature. The colloidal solution was then filtered, in
order to separate any precipitated metal oxide possibly present, and
submitted to an dialyzing process. Hereby, the colloidal solution of the
metal oxide was filled into a Nadir dialyzing tube and dialyzed twice
against 1 I of deionized water. The change of the conductivity of the
permeate was monitored conductometrically. Thereafter, the solution
was filtered once again, and the colloidal solution was lyophilized. 1.5
g of a grey colloid powder was obtained which is completely re-
dispersible in water.
Metal content: 13.27 % Pt, 4,85 % Ru (this is corresponding to a molar
ratio of 1.42:1)
TEM: 1.4 nm
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Example 3. PtRuO_ PVP
370 mg (5 mmole) of LizC03 as well as 3 g of polyvinyl pyrrolidone)
(PVP) were weighed in a 250 ml three-necked flask and dissolved in 80
ml of deionized water. A solution of 517.9 mg (1 mmole) of HZPtCl6 x
6 H20 and 235.9 mg (1 mmole) of RuCl3 x H20 in 20 ml of deionized
water was added dropwise thereto with strong stirring at room
temperature for 1 hour. Hereby, the pH value of the polymer solution
decreased from initially 11,5 to a value of 7.5, after the addition of the
solution of the metal salt was completed. The solution was tempered to
60 °C and stirred at this temperature for ca. 20 hours. The progress of
the hydrolysis and the condensation was monitored by UV spectroscopy
by means of the decrease of the H2PtC16 absorption at 260 nm. After this
band had completely disappeared, the reaction was terminated and
cooled to room temperature. Subsequently, the colloidal solution was
filtered, in order to separate any precipitated metal oxide present, and
submitted to an dialyzing process. Hereby, the colloidal solution of the
metal oxide was filled into a Nadir dialyzing tube and dialyzed twice
against 1 I of deionized water. The change of conductivity of the
permeate was monitored conductometrically. Thereafter, the solution
was filtered once again, and the colloidal solution was lyophilized. 2.9
g of a grey colloid powder was obtained which is completely re-
dispersible in water, MeOH, EtOH and DMF.
Metal content: 6.78 % Pt, 3.15 % Ru (this is corresponding to a molar
ratio of 1.11:1)
TEM: 1.6 nm
Example 4. PtRuOY f3-12-SBA, Pt/Ru = 4:1
370 mg (5 mmole) of Li2C03 was weighed in a 250 ml three-necked flask
and dissolved in 40 ml of deionized water. 40 ml of a 0,1 M solution of
dimethyldodecylammoniopropane sulfonate (3-12-SB) in deionized water
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was added thereto. A solution of 828.6 mg (1,6 mmole) of H2PtC16 x
6 H20 and 94.4 mg (0.4 mmole) of RuCl3 x H20 in 20 ml of deionized
water was added dropwise thereto with strong stirring at room
temperature for 1 hour. Hereby, the pH value of the surfactant solution
decreased from initially 11.5 to a value of 8.0, after the addition of the
solution of the metal salt was completed. The solution was tempered to
80 °C and stirred at this temperature for ca. 6 hours, whereby the
progress of the hydrolysis and the condensation was followed by UV
spectroscopy by means of the decrease of the HZPtCl6 absorption at 260
nm. After termination of the reaction, the colloidal solution was filtered,
in order to separate any precipitated metal oxide possibly present, and
submitted to an dialyzing process. Hereby, the colloidal solution of the
metal oxide was filled into a Nadir dialyzing tube and dialyzed twice
against 1 I of deionized water. The change of conductivity of the
permeate was monitored conductometrically. Thereafter, the solution
was filtered once again, and the colloidal solution was lyophilized. 1.2
g of a grey colloid powder was obtained which is completely re-
dispersible in water.
Metal content: 14.87 % Pt, 2,97 % Ru (this is corresponding to a molar
ratio of 2,59:1)
TEM: 1.5 nm
Example 5. PtRu0x~3-12-SBA,, Pt/Ru = 1:4
370 mg (5 mmole) of l-i2C03 was weighed in a 250 ml three-necked flask
and dissolved in 40 ml of deionized water. 40 ml of a 0,1 M solution of
dimethyldodecylammoniopropane sulfonate (3-12-SB) in deionized water
was added thereto. A solution of 207.2 mg (0.4 mmole) of H2PtCl6 x
6 HZO and 377.4 mg (1.6 mmole) of RuCl3 x H20 in 20 ml of deionized
water was added dropwise thereto at room temperature for 1 hour.
Hereby, the pH value of the surfactanr solution decreased from initially
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11.5 to a value of 8.0, after the addition of the solution of the metal salt
was completed. The solution was tempered to 80 °C and stirred at this
temperature for 6 hours, whereby the progress of the hydrolysis and the
condensation was monitored by UV spectroscopy by means of the
decrease of the H2PtC16 absorption at 260 nm. After termination of the
reaction, the colloidal solution was filtered, in order to separate any
precipitated metal oxide possibly present, and submitted to an dialyzing
process. Hereby, the colloidal solution of the metal oxide was filled into
a Nadir dialyzing tube and dialyzed twice against 1 I of deionized water.
The change of conductivity of the permeate was monitored conducto-
metrically. Thereafter, the solution was filtered once again, and the
colloidal solution was lyophilized. 1.2 g of a grey colloid powder was
obtained which is completely re-dispersible in water.
Metal content: 9.67 % Pt, 11.27 % Ru (this is corresponding to a molar
ratio of 1:2.26)
TEM: 1.5 nm
Examele 6. PtOz (3-12-SB)
296 mg (4 mmole) of Li2COs and 674 mg (2 mmole) of PtCl4 were
weighed in a 250 ml three-necked flask and dissolved in 160 ml of
deionized water. 40 ml of a 0,1 M solution of dimethyldodecylammonio-
propane sulfonate (3-12-SB) in deionized water was added thereto. The
solution was stirred at 80 °C for 24 hours, whereby a discoloration
from
yellow orange to red brown occurred. After termination of the reaction,
the colloidal platinum dioxide solution was filtered, and, subsequently,
the solution was dialyzed twice against 1.5 I of deionized water in a
Nadir dialyzing tube. The change of conductivity of the permeate was
monitored conductometrically. Thereafter, the solution was filtered once
again, and the colloidal solution was lyophilized. 1.3 g of a grey colloid
powder was obtained which is completely re-dispersible in water.
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Metal content: 22.41 % Pt
TEM: 1.7 nm
Example 7. PtRuO_-colloid havincLa chiral tenside as stabilizer
370 mg (5 mmole) of Li2C03 was weighed in a 250 ml three-necked flask
and dissolved in 20 ml of deionized water. 60 ml of a 0,1 M solution of
3-(N,N-dimethyldodecylammonio-2-(S)-hydroxy butyrate (3-12-CB*) in
deionized water was added thereto. A solution of 517.9 mg (1 mmole)
of H2PtCl6 x 6 H20 and 235.9 mg (1 mmole) of RuCl3 x Hz0 in 20 ml of
deionized water was added thereto dropwise with strong stirring at room
temperature for 1 hour. Hereby, the pH value of the surfactant solution
decreased from initially 12 to a value of 8.0, after the addition of the
solution of the metal salt was completed. The solution was tempered to
80 °C and stirred at this temperature for 26 hours, whereby the
progress
of the hydrolysis and the condensation was followed by UV spectroscopy
by means of the decrease of the H2PtCl6 absorption at 260 nm. After
termination of the reaction, the colloidal solution was filtered, in order
to separate any precipitated metal oxide possibly present, and submitted
to an dialyzing process. Hereby, the colloidal solution of the metal oxide
was filled into a Nadir dialyzing tube and dialyzed twice against 1 I of
deionized water. The change of conductivity of the permeate was
followed conductometrically. Thereafter, the solution was filtered once
again, and the colloidal solution was lyophilized. 1.5 g of a grey colloid
powder was obtained which is completely re-dispersible in water.
Metal content: 6.24 % Pt, 3.92 % Ru (this is corresponding to a molar
ratio of 0.82:1)
TEM: 1.6 nm
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Example 8. PtRuO_-colloid having a chiral polvmer as stabilizer
37 mg (0.5 mmole) of Li2C03 as well as 500 mg of poly-L-aspartic acid,
sodium salt were weighed in a 50 ml two-necked flask and dissolved in
ml of deionized water. A solution of 51.8 mg (0.1 mmole) of HZPtCl6
x 6 H20 and of 23.6 mg (0.1 mole) of RuCl3 x Hz0 in 5 ml of deionized
water was added dropwise thereto with strong stirring over a period of
10 minutes at room temperature. Hereby, the pH value of the polymer
solution decreased from initially 11,5 to a value of 7.5 after the addition
of the solution of the metal salt was completed. The solution was
tempered to 60 °C and stirred at this temperature for 26 hours. The
progress of the hydrolysis and the condensation was followed by UV
spectroscopy by means of the decrease of the H2PtCl6 absorption at 260
nm. After this band had completely disappeared, the reaction was
terminated and cooled to room temperature. Subsequently, the colloidal
solution was filtered, in order to separate any precipitated metal oxide
possibly present, and submitted to an dialyzing process. Hereby, the
colloidal solution of the metal oxide was filled into a Nadir dialyzing tube
and dialyzed twice against 1 I of deionized water. The change of
conductivity of the permeate was followed conductometrically.
Thereafter, the solution was filtered once again, and the colloidal
solution was lyophilized. 500 m g of a grey colloid powder was obtained
which is completely re-dispersible in water, MeOH, EtOH and DMF.
Metal content: 3.78 % Pt, 1.98 % Ru (this is corresponding to a molar
ratio of 0.98:1)
TEM: 1.6 nm
Example 9. PtSn0,;~3-12-SBA
74 mg (1 mmole) of LiZCOs as well as 103.6 mg (0.2 mmole) of H2PtCls
x 6 H20 were weighed in a 100 ml three-necked flask, and the solution
was dissolved in 20 ml of a 0,1 M solution of dimethyldodecylammonio-
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propane sulfonate (3-12-SB) in deionized water. A solution of 37.8 mg
(0.2 mmole) of SnCIZ x 2H20 in 5 ml of deionized water was added
dropwise thereto with strong stirring at room temperature for 30
minutes. The solution was tempered to 70 °C and stirred at this
temperature for 10 hours, whereby the progress of the hydrolysis and
the condensation was followed by UV spectroscopy by means of the
decrease of the H2PtCl6 absorption at 260 nm. After termination of the
reaction, the colloidal solution was filtered, in order to separate any
precipitated metal oxide and submitted to an dialyzing process. Hereby,
the colloidal solution of the metal oxide was filled into a Nadir dialyzing
tube and dialyzed twice against 0,5 I of deionized water. The change of
conductivity of the permeate was followed conductometrically.
Thereafter, the solution was filtered once again, and the colloidal
solution was lyophilized. 0,6 g of a grey colloid powder was obtained
which is completely re-dispersible in water.
Metal content: 6.79 % Pt, 2.67 % Sn (this is corresponding to a molar
ratio of 1.55:1)
TEM: 1.5 nm
The EDX analysis of the particles indicates a bimetal character.
Example 10. PtFeOx,~3-12-SB)
74 mg (1 mmole) of Li2C03 as well as 103.6 mg (0.2 mmole) of H2PtCl6
x 6 H20 were weighed in a 100 ml three-necked flask, and the solution
was dissolved in 20 ml of a 0,1 M solution of dimethyldodecyl-
ammoniopropane sulfonate (3-12-SB) in deionized water. A solution of
39.8 mg (0.2 mmole) of FeCl2 x 4 H20 in 5 ml of deionized water was
added dropwise thereto with strong stirring at room temperature for 30
minutes. The solution was tempered to 70 °C and stirred at this
temperature for 10 hours, whereby the progress of the hydrolysis and
the condensation was followed by UV spectroscopy by means of the
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decrease of the H2PtCl6 absorption at 260 nm. After termination of the
reaction, the colloidal solution was filtered, in order to separate any
precipitated metal oxide possibly present, and submitted to an dialyzing
process. Hereby, the colloidal solution of the metal oxide was filled into
a Nadir dialyzing tube and dialyzed twice against 0,5 I of deionized
water. The change of conductivity of the permeate was followed
conductometrically. Thereafter, the solution was filtered once again, and
the colloidal solution was lyophilized. 0,6 g of a grey colloid powder was
obtained which is completely re-dispersible in water.
Metal content: 6.12 % Pt, 1.24 % Fe (this is corresponding to a molar
ratio of 1.42:1)
TEM: 1.5 nm
The EDX analysis of the particles indicates a bimetal character.
Example 11. PtW0,~3-12-SB)
74 mg (1 mmole) of t-iZC03 as well as 103.6 mg (0.2 mmole) of HZPtCl6
x 6 H20 were weighed in a 100 ml three-necked flask, and the solution
was dissolved in 20 ml of a 0,1 M solution of dimetnyiaoaecyi-
ammoniopropane sulfonate (3-12-SB) in deionized water. A solution of
66.0 mg (0.2 mmole) of Na2W0a in 5 ml of deionized water was added
dropwise thereto with strong stirring at room temperature for 30
minutes. The solution was tempered to 70 °C and stirred at this
temperature for 10 hours, whereby the progress of the hydrolysis and
the condensation was followed by UV spectroscopy by means of the
decrease of the H2PtCl6 absorption at 260 nm. After termination of the
reaction, the colloidal solution was filtered, in order to separate any
precipitated metal oxide present and submitted to an dialyzing process.
Hereby, the colloidal solution of the metal oxide was filled into a Nadir
dialyzing tube and dialyzed twice against 0,5 I of deionized water. The
change of conductivity of the permeate was followed conductometrically.
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Thereafter, the solution was filtered once again, and the colloidal
solution was lyophilized. 0.5 g of a grey colloid powder was obtained
which is completely re-dispersible in water.
Metal content: 4.61 % Pt, 0.78 % W (this is corresponding to a molar
ratio of 5.5:1)
TEM: 1.5 nm
The EDX analysis of the particles indicates a bimetal character.
Example 12. PtRuWOx (3.12-SB)
370 mg (5 mmole) of Li2C03 was weighed in a 250 ml three-necked flask
and dissolved in 20 ml of deionized water. 60 ml of a 0,1 M solution of
dimethyldodecylammoniopropane sulfonate (3-12-SB) in deionized water
was added thereto. A solution of 517.9 mg (1 mmole) of H2PtC16 x 6 H20
and 141.5 mg (0.6 mmole) of RuCl3 x H20 and of 66.0 mg (0.2 mmole)
of Na2W04 in 20 ml of deionized water was added dropwise thereto with
strong stirring at room temperature for 3 hours. Hereby, the pH value
of the tenside solution decreased from initially 11.4 to a value of 9.8,
after the addition of the solution of the metal salt was completed. The
solution was tempered to 60 °C and stirred at this temperature for ca.
22 hours, whereby the progress of the hydrolysis and the condensation
was followed by UV spectroscopy by means of the decrease of the
H2PtC16 absorption at 260 nm. After termination of the reaction, the
colloidal solution was filtered and submitted to an dialyzing process.
Hereby, the colloidal solution of the metal oxide was filled into a Nadir
dialyzing tube and dialyzed twice against 1 I of deionized water. The
change of conductivity of the permeate was followed conductometrically.
Thereafter, the solution was filtered once again, and the colloidal
solution was lyophilized. 1.8 g of a grey colloid powder was obtained
which is completely re-dispersible in water.
Metal content: 8.31 % Pt, 2.91 % Ru, 0.73 % W
~s
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TEM: 1.5 nm
Example 13: Reduction of the colloidal metal oxide solution
1 g of the isolated and purified PtRuOX (3-12-SB) colloid prepared in
accordance to example 1 was dissolved in 100 ml of deionized water in
a Schlenck vessel under protective gas. After an ultrasonic treatment for
30 min, the Schlenck vessel was subjected to a slight evacuation for a
short while, a gas balloon filled with hydrogen was connected therewith,
and the solution was then stirred in a H2 atmosphere at room
temperature for 24 hours. The initially dark green to brown solution
changes its color to deep black during this time. The colloidal solution
can be lyophilized or can directly be processed on a carrier material for
fixation.
TEM micrographs of the colloidal solution of PtRu show particles having
a size distribution of 1,7~0,4 nm. A EDX individual particle analysis of
these particles indicates an almost complete formation of an alloy.
XPS examinations with these colloids showed that both platinum and
ruthenium are present in a metallic form.
Example 14' Fixation of a PtRu colloid on Vulcan as the solid support
3.552 g Vulcan XC-72R of the Cabot Company was weighed in a 1 I
three-necked flask and suspended in 200 ml of a buffer solution (Citrate
buffer, 50 mM, pH 4.7). 300 ml of an aqueous solution of PtRu(3-12-SB)
(888 mg of noble metal) prepared according to specification of example
13 was added dropwise thereto under a protective gas at 50 °C for 3
hours. Subsequently, the suspension was stirred at 50 °C for 40 hours
and stirred for another 16 hours at 100 °C. After cooling, the black
suspension was centrifuged, the supernatant solution was decanted, the
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catalyst was washed twice with 200 ml of methanol, respectively, and
dried in vacuum at 40 °C.
Metal content: 8.00 % Pt, 4.62 % Ru
Particle sizes: colloid without carrier: 2.2~0.6 nm
colloid with carrier: 2.3~0.6 nm
HRTEM micrographs of the catalyst show a homogenous distribution of
the PtRu nanoparticles on the solid support.
Example 15: Fixation of a PtRuOx colloid on Vulcan as the solid support
3.552 g Vulcan XC-72R of the Cabot Company which previously was
surface oxidized with a solution of NaOCI was weighed in a 1 I three-
necked flask and suspended in 200 ml of water. Then, 300 ml of an
aqueous solution of PtRuOX (3-12-SB) (888 mg of noble metal) prepared
according to specification of example 1 was added dropwise thereto at
60 °C for 3 hours. Then, 0,1 M HCI was added dropwise there, until the
solution reached a pH value of 2.5, and the suspension was stirred at 50
°C for 40 hours. After cooling, the black suspension was centrifuged,
the
supernatant solution was decanted, the catalyst was washed twice with
200 ml of methanol, respectively, and dried in vacuum at 40 °C.
Metal content: 14.32 % Pt, 8.45 % Ru
Example 16: Fixation of a PtRuO.{ colloid on activated carbon as the
solid support
5.7 g of activated carbon was weighed into a 500 ml three-necked flask
and suspended in 200 ml of deonized water. 100 ml of an aqueous
solution of PtRuOX (3-12-SB) (300 mg of noble metal) which was
prepared according to specification of example 1 was dropped thereto
within 1 hour at 50 °C. Subsequently, the solution was stirred at 50
°C
for 24 hours. After cooling and allowing to stand, the supernatant clear
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solution was decanted, the catalyst was washed three times with 200 ml
methanol, respectively, and dried in vacuum at 40 °C.
Metal content: 2.72 % Pt, 1.26 % Ru
Example 17' Fixation of a PtRu colloid on alumina as the solid support
5.7 g of A120s was weighed in a 500 ml three-necked flask and suspen-
ded in 200 ml of deonized water. 100 ml of an aqueous solution of PtRu
(3-12-SB) (300 mg of noble metal) prepared according to specification
of example 13 was added dropwise thereto under a protective gas at 50
°C within 1 hour . Subsequently, the suspension was stirred at 50
°C for
24 hours. After cooling and allowing to stand, the catalyst was filtered,
washed three times with 200 ml methanol, respectively, and dried in
vacuum at 40 °C.
Metal content: 2.91 % Pt, 1.70 % Ru
Example 18: Fixation of a PtRuOX colloid on La 03 as the solid support
5.7 g of La203 was weighed in a 500 ml three-necked flask and suspen-
ded in 200 ml of deonized water. 100 ml of an aqueous solution of
PtRuOX (3-12-SB) (300 mg of noble metal) prepared according to
specification of example 1 was added dropwise thereto at 50 °C within
1 hour. Subsequently, the suspension was stirred at 50 °C for 24 hours.
After cooling and allowing to stand, the catalyst was filtered, washed
three times with 200 ml of methanol, respectively, and dried in vacuum
at 40 °C.
Metal content: 2.83 % Pt, 1.88 % Ru
Example 19: Immobilization of a PtRuOx colloid in sol gel-materials
1.2 ml (8 mmole) of tetramethoxy silane (TMOS) was initially added to
a 2 ml polypropylene vessel, and 0,5 ml of an aqueous solution of a
PtRuOX (3-12-SB) colloid (10 mg of noble metal; 20 g/I), prepared accor-
21
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ding to the specification of example 1, and 50 NI of a 0,1 M solution of
NaF was pipetted thereto. Subsequently, the vessel was sealed and
agitated on a Vortex mixer at room temperature for 10 seconds. After a
heating up has become evident, the black mixture was allowed to stand,
whereupon a gelation of the solution occurred ca. 10 seconds later. Now,
the gel was submitted to an ageing process in a sealed vessel at room
temperature, for 24 hours and then dried at 37 °C in a drying oven for
3 days. To wash out the stabilizer, the gel was refluxed in 30 ml of
ethanol for 3 days, centrifuged and washed again with 30 ml of ethanol,
centrifuged again and finally dried in a drying oven at 37 °C for 4
days.
630 mg of a grey powder is obtained.
Metal content: 0.92 % Pt, 0.56 % Ru
ExamJ~le 20: Hydrogenation of cinnamic ethyl ester
250 mg of a PtRuO,~/activated carbon (10 mg of noble metal) catalyst,
prepared according to example 16, was weighed in a glass reactor which
is equipped with a high speed stirrer. The reactor was sealed, connected
to a thermostat and tempered to 25 °C. Following repeated processes of
evacuation and argonization of the reactor, 60 ml of absolute methanol
was added thereto, and the vessel was repeatedly evacuated for a short
time at an agitator power of 2000 rpm. After stirring for 60 min in an
atmosphere of H2, 2 ml of cinnamic ethyl ester was injected, and the
initial activity of the hydrogenation was determined by means of the
time-dependant change of the H2-level of the buret.
Activity: 150 ml of Hz/(g of noble metal~min). Under the same
conditions, the classical Adams-catalyst showed a lower activity: 38 ml
of Hz/(g of noble metal~min).
22
