Amorphous alloy catalysts for decomposition of flons

Highly active amorphous alloy catalysts for use in decomposing of flons into hydrofluoric acid, hydrochloric acid and carbon dioxide by the reaction of flons with water, consist of at least one element selected from the group of Ni and Co, at least one element selected from the group of Nb, Ta, Ti and Zr, which are effective for the formation of the amorphous structure by coexisting with at least one element selected from the group of Ni and Co, and at least one element selected from the group of Ru, Rh, Pd, Ir and Pt, which are necessary for the high catalytic activity. The alloys are activated by immersion into hydrofluoric acids.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to materials which are particularly suitable 
as highly active catalysts for the decomposition of chlorofluorocarbons 
(flons) to hydrofluoric acid, hydrochloric acid and carbon dioxide, and 
are characterized by being easy to produce into catalysts and providing 
for easy recovery of its catalytically useful components. 
2. Description of the Prior Art 
Investigations into methods for the decomposition of flons had previously 
been unnecessary and hence were seldom performed. It has been known that 
they decompose by burning at high temperatures, such as 800.degree. C., in 
an incinerator. According to recent investigations of the catalytic 
decomposition of flons on metal oxides, decomposition of flons occurred on 
zeolite at temperatures of from 300.degree.-500.degree. C. 
In general, ordinary alloys are crystalline in their solid state. However, 
rapid quenching of some alloys having specific compositions in the liquid 
state gives rise to the solidification of an amorphous structure. These 
alloys are called amorphous alloys. The amorphous alloys are single phase 
alloys supersaturated with various elements and have significantly high 
mechanical strength in comparison with conventional industrial alloys. 
Some amorphous alloys with specific compositions have a variety of 
superior characteristics including extremely high corrosion resistance 
that cannot be obtained in ordinary crystalline alloys. 
One of the present inventors applied the teachings of Japanese Patent 
Application No. 123111/85 regarding amorphous alloy electrode materials, 
which contain Ni, Ta and platinum group elements as essential components 
and are suitable as an anode for oxygen production by the electrolysis of 
acidic aqueous solutions because of their high activity for oxygen 
evolution. 
Japanese Patent Application No. 123111/85 discloses: 
(1) Amorphous alloy electrode materials which comprise 25 to 65 at % Ta, 
0.3 to 45 at % of at least one element selected from the group of Ru, Rh, 
Pd, Ir and Pt, and more than 30 at % Ni. 
(2) Amorphous alloy electrode materials which comprise 25 to 65 at % Ta and 
at least one element selected from the group of Ti, Zr and Nb, Ta being 
present in an amount of at least 20 at %, 0.3 to 45 of at least one 
element selected from the group of Ru, Rh, Pd, Ir and Pt, and more than 30 
at % Ni. 
Three of the present inventors have further developed surface activated 
amorphous alloy electrode materials which are suitable for the 
electrolysis of aqueous solutions and consist of Ni, very small amounts of 
platinum group metals and at least one element selected from the group of 
Ti, Zr, Nb and Ta, and their activation methods in Japanese Patent 
Application Nos. 169764/85, 169765/85 and 169767/85. They further applied 
the teachings of Japanese Patent Application No. 169766/85 regarding 
surface-activated supersaturated solid solution alloy electrode materials 
for electrolysis of aqueous solutions and their activation methods. 
Japanese Patent Application No. 169764/85 discloses: 
(1) Surface-activated amorphous alloy electrode materials consisting of 25 
to 65 at % of Nb, 0.01 to 10 at % of at least one element selected from 
the group of Ru, Rh, Pd, Ir and Pt, and the balance substantially being 
Ni, used for the electrolysis of aqueous solutions. 
(2) Surface-activated amorphous alloy electrode materials consisting of 25 
to 65 at % Nb and at least one element selected from the group of Ti, Zr 
and less than 20 at % of Ta, Nb being present in an amount of at least 10 
at %, and 0.01 to 10 at % of at least one element selected from the group 
of Ru, Rh, Pd, Ir and Pt, and the balance substantially being Ni, used for 
the was applied for electrolysis of aqueous solutions. 
(3) Surface-activated amorphous alloy electrode materials consisting of 25 
to 65 at % of Nb, 0.01 to 10 at % of at least one element selected from 
the group consisting of Ru, Rh, Pd, Ir and Pt, less than 7 at % of P and 
the substantial balance of Ni, used for the electrolysis of aqueous 
solutions. 
(4) Surface-activated amorphous alloy electrode materials consisting of 25 
to 65 at % Nb and at least one element selected from the group consisting 
of Ti, Zr and less than 20 at % of Ta, Nb being present in an amount of at 
least 10 at %, and 0.01 to 10 at % least one element selected from the 
group of Ru, Rh, Pd, Ir and Pt, less than 7 at % of P and the balance 
substantially being Ni, used for the electrolysis of aqueous solutions. 
(5) A method for activating amorphous alloys for electrodes characterized 
by the immersion of the above-mentioned amorphous alloy electrode 
materials into corrosive solutions for surface enrichment of platinum 
group elements as a result of preferential dissolution of Ni, Nb, Ta, Ti 
and Zr. 
Japanese Patent Application No. 169765/85 discloses: 
(1) Surface-activated amorphous alloy electrode materials consisting of 25 
to 65 at % of Ta, 0.01 to 10 at % of at least one element selected from 
the group consisting of Ru, Rh, Pd, Ir and Pt, less than 7 at % of P and 
the balance substantially being 20 at % or more Ni, used for electrolysis 
of aqueous solutions. 
(2) Surface-activated amorphous alloy electrode materials consisting of 25 
to 65 at % Ta and at least one element selected from the group of Ti, Zr 
and Nb, Ta being present in an amount of at least 20 at %, 0.01 to 10 at % 
of at least one element selected from the group of Ru, Ph, Pd, Ir and Pt, 
less than 7 at % of P and the substantial balance being 20 at % or more 
Ni, used for the electrolysis of aqueous solutions. 
(3) A method for activating amorphous alloys for electrodes characterized 
by the immersion of the above-mentioned amorphous alloy electrode 
materials into corrosive solutions for surface enrichment of platinum 
group elements as a result of preferential dissolution of Ni, Nb, Ta, Ti 
and Zr. 
Japanese Patent Application No. 169767/85 discloses: 
(1) Surface-activated amorphous alloy electrode materials consisting of 25 
to 65 at % Ta and at least one element selected from the group of Ti and 
Zr, Ta being present in an amount of from 5 to less than 20 at %, and 0.01 
to 10 at % of at least one element selected from the group of Ru, Rh, Pd, 
Ir and Pt, the substantial balance being Ni, used for the electrolysis of 
aqueous solutions. 
(2) Surface-activated amorphous alloy electrode materials consisting of 25 
to 65 at % Ta and at least one element selected from the group of Ti and 
Zr, Ta being present in an amount of from 5 to less than 20 at %, and 0.01 
to 10 at % of at least one element selected from the group of Ru, Rh, Pd, 
Ir and Pt, less than 7 at % of P and the balance substantially being 20 at 
% or more Ni, used for the electrolysis of aqueous solutions. 
(3) A method for activating amorphous alloys for electrodes characterized 
by immersing the above-mentioned amorphous alloy electrode materials into 
corrosive solutions for surface enrichment of platinum group elements as a 
result of the preferential dissolution of Ni, Ta, Ti and Zr. 
Japanese Patent Application No. 169766/85 discloses: 
(1) Surface-activated supersaturated solid solution alloy electrode 
materials consisting of 20 to less than 25 at % of at least one element 
selected from the group of Nb and Ta, 0.01 to 10 at % of at least one 
element selected from the group of Ru, Rh, Pd, Ir and Pt and the balance 
substantially being Ni, used for the electrolysis of aqueous solutions. 
(2) Surface-activated supersaturated solid solution alloy electrode 
materials consisting of 20 to less than 25 at % of at least one element 
selected from the group of Nb and Ta, 0.01 to 10 at % of at least one 
element selected from the group of Ru, Rh, Pd, Ir and Pt, less than 7 at % 
of P and the substantial balance being Ni, used for the electrolysis of 
aqueous solutions. 
(3) Surface-activated supersaturated solid solution alloy electrode 
materials consisting of 20 to less than 25 at % of at least one element 
selected from the group of Ti and Zr and 5 at % or more of at least one 
element selected from the group of Nb and Ta, 0.01 to 10 at % of at least 
one element selected from the group of Ru, Rh, Pd, Ir and Pt and the 
balance substantially being Ni, used for the electrolysis of aqueous 
solutions. 
(4) Surface-activated supersaturated solid solution alloy electrode 
materials consisting of 20 to less than 25 at % of at least one element 
selected from the group of Ti and Zr and 5 at % or more of at least one 
element selected from the group of Nb and Ta, 0.01 to 10 at % of at least 
one element selected from the group of Ru, Rh, Pd, Ir and Pt, less than 7 
at % of P and the balance substantially being Ni, used for the 
electrolysis of aqueous solutions. 
(5) A method for activating supersaturated solid solution alloys for 
electrodes characterized by immersing the above-mentioned supersaturated 
solid solution alloy electrode materials into corrosive solutions for 
surface enrichment of platinum group elements as a result of the 
preferential dissolution of Ni, Nb, Ta, Ti and Zr. 
Furthermore, the present inventors presented surface-activated amorphous 
alloys for methanol fuel cell in Japanese Patent Application No. 
154570/86. 
Japanese Patent Application No. 154570/86 discloses: 
(1) Surface-activated amorphous alloys for methanol fuel cells, consisting 
of 20 to 80 at % of at least one element selected from the group of Ti and 
Zr, 0.5 to 20 at % of Pt and the balance substantially being 10 at % or 
more of at least one element selected from the group of Ni and Co. 
(2) Surface-activated amorphous alloys for methanol fuel cells consisting 
of 20 to 80 at % of at least one element selected from the group of Ti and 
Zr, 0.5 to 20 at % of Pt, at most 10 at % (at most the same at % as Pt if 
Pt is at most 10 at %) of at least one element selected from the group of 
Ru, Rh, Pd, Ir, Tl, Si, Ge, Sn, Pb and Bi and the balance substantially 
being 10 at % or more of at least one element selected from the group of 
Ni and Co. 
(3) Surface-activated amorphous alloys for methanol fuel cells, consisting 
of 20 to 70 at % of at least one element selected from the group of Nb and 
Ta, 0.5 to 20 at % of Pt, and the balance substantially being at least one 
element selected from the group of Ni and Co. 
(4) Surface-activated amorphous alloys for methanol fuel cells, consisting 
of 20 to 70 at % of at least one element selected from the group of Nb and 
Ta, 0.5 to 20 at % of Pt, at most 10 at % (at most the same at % as Pt if 
Pt is at most 10 at %) of at least one element selected from the group of 
Ru, Rh, Pd, Ir, Tl, Si, Ge, Sn, Pb and Bi, and the balance substantially 
being 10 at % or more of at least one element selected from the group of 
Ni and Co. 
(5) Surface-activated amorphous alloys for methanol fuel cells consisting 
of 20 to 80 at % of at least one element selected from the group of Ti and 
Zr and at most 70 at % of at least one element selected from the group of 
Nb and Ta, 0.5 to 20 at % of Pt, and the balance substantially being 10 at 
% or more of at least one element selected from the group of Ni and Co. 
(6) Surface-activated amorphous alloys for methanol fuel cell, consisting 
of 20 to 80 at % of at least one element selected from the group of Ti and 
Zr and at most 70 at % of at least one element selected from the group of 
Nb and Ta, 0.5 to 20 at % of Pt, at most 10 at % (at most the same at % as 
Pt if Pt is at most 10 at %) of at least one element selected from the 
group of Ru, Rh, Pd, Ir, Tl, Si, Ge, Sn, Pb and Bi, and the balance 
substantially being 10 at % or more of at least one element selected from 
the group of Ni and Co. 
In order to overcome the high operation temperatures of catalysts 
consisting of platinum group elements supported on ceramics used in the 
purification of exhaust gases from plants and vehicles, in addition to the 
difficulty of recovering platinum group elements, three of the present 
inventors investigated catalysts capable of operating at low temperatures, 
such as the beginning of combustion, in addition to being easy to recover, 
and invented catalysts for the purification of exhaust gases by the 
reaction of carbon monoxide with nitrogen oxides in exhaust gases as 
Japanese Patent Application No. 262986/89. 
The Japanese Patent Application No. 262986/89 discloses: 
(1) Surface-activated catalysts for purifying exhaust gases, consisting of 
20 to 70 at % of at least one element selected from the group of Nb and 
Ta, 0.5 to 20 at % of at least one element selected from the group of Ru, 
Rh, Pd, Ir and Pt, and the balance substantially being at least one 
element selected from the group of Ni and Co. 
(2) Surface-activated catalysts for the purification of exhaust gases, 
consisting of 20 to 80 at % of at least one element selected from the 
group of Ti and Zr, 0.5 to 20 at % of at least one element selected from 
the group of Ru, Rh, Pd, Ir and Pt, and the balance substantially being at 
least 10 at % of at least one element selected from the group of Ni and 
Co. 
(3) Surface-activated catalysts for the purification of exhaust gases, 
consisting of 20 to 80 at % of at least one element selected from the 
group of Ti and Zr and at most 70 at % of at least one element selected 
from the group of Nb and Ta, 0.5 to 20 at % of at least one element 
selected from the group of Ru, Rh, Pd, Ir and Pt and the balance 
substantially being at least 10 at % of at least one element selected from 
the group of Ni and Co. 
Until the year 2000, the production and use of the 5 worst flons, which 
destruct ozonosphere and induce the greenhouse effect, will be prohibited. 
They may be substituted by other flons. Current industries are using large 
amounts of different flons. It is, therefore, necessary to develop a 
technique by which used flons can be converted to hydrofluoric acid, 
hydrochloric acid and carbon dioxide for re-use without consumption of a 
large amount of energy. 
In view of the above discussion, there has been a strong demand for highly 
active and easily recoverable catalysts for converting flons at low 
temperatures and with a low consumption of energy. 
SUMMARY OF THE INVENTION 
It is an objective of the present invention to provide highly active and 
easily producible and recoverable catalysts by which the reaction of flons 
with water to form hydrofluoric acid, hydrochloric acid and carbon dioxide 
can be conducted at relatively low temperatures close to ambient 
temperatures. 
The objective of the invention has been achieved by finding that some 
amorphous alloys have a high catalytic activity for the conversion of 
flons. The present invention is directed to catalytically active and 
easily producible and recoverable alloys consisting of at least one 
element selected from the group of Co and Ni, and valve metals which form 
an amorphous structure by being alloyed with at least one element selected 
from the group of Ni and Co, and a very small amount of platinum group 
elements, which are effective as the catalyst for the reaction of flons 
with water, the alloys being activated by hydrofluoric acid treatment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In order to obtain easily producible and recoverable catalysts with a 
selectively high catalytic activity for a specific reaction, it is more 
convenient to use alloys containing necessary amounts of effective 
elements rather than using platinum group elements supported by alumina, 
titania, silica, etc. However, when conventionally processed crystalline 
alloys are used, the additions of large amounts of various elements often 
lead to the formation of multiple phases of different chemical properties 
and to poor mechanical strength, and it is difficult to obtain materials 
with a large specific surface area necessary for effective catalysts. 
On the other hand, the amorphous alloys of the present invention are 
prepared to prevent localization of alloy constituents due to rapid 
quenching of the melt of the above-mentioned compositions and, hence, they 
are highly homogeneous and mechanically strong and tough. When these 
alloys are treated by immersion in hydrofluoric acids, alloy constituents 
not necessary for catalytic activity are dissolved into the hydrofluoric 
acids with the subsequent formation of highly active catalysts with a 
remarkable large surface area enriched in catalytically active platinum 
group elements. During this treatment, hydrogen evolution occurs violently 
on the platinum group elements in the alloys, since the platinum group 
elements act as the cathode in the amorphous alloys composed of a 
chemically homogeneous single phase solid solution. Since the hydrogen 
evolution provides dissolution of alloy constitutents not necessary for 
catalytic activity, violent hydrogen evolution on the homogeneous alloys 
results in the rapid and uniform dissolution of alloy constituents not 
necessary for the catalytic activity. This leads to the formation of 
highly active catalysts with a large surface area enriched in 
catalytically active platinum group elements. 
Consequently, catalysts for production of hydrofluoric acid, hydrochloric 
acid and carbon dioxide by the reaction of flons with water can be 
obtained by the alloys of the present invention, after being subjected to 
activation treatment by immersion in hydrofluoric acids. 
The components and compositions of the alloys of the present invention are 
specified as above for the following reasons: 
In the alloys of the present invention, Ni and Co are the basic components 
which form the amorphous structure when they coexist with one or more 
elements selected from the group of Nb, Ta, Ti and Zr. Therefore, in order 
to form the amorphous structure, the alloys may consist of at least one 
element selected from the group of Ni and Co and at least one element 
selected from Nb and Ta should contain 20 to 70 at % of at least one 
element selected from the group of Nb and Ta. The amorphous structure can 
also be obtained when the alloys consist of at least one element selected 
from the group of Ni and Co and at least one element selected from Ti and 
Zr, with at least 20 to 80 at % of at least one of Ti and Zr being 
present. 
Furthermore, in the alloys consisting of at least one element selected from 
the group of Ni and Co, at least one element selected from Ti and Zr, and 
at least one element selected from Nb and Ta, the amorphous structure can 
be obtained if the alloys contain 20 to 80 at % of at least one element 
selected from the group of Ti and Zr with at most, 70 at % of at least one 
of Nb and Ta being present. 
The platinum group elements Ru, Rh, Pd, Ir and Pt are all effective for 
high catalytic activity and, hence, the catalytic activity requires that 
one or more of these platinum group elements should be present in an 
amount of 0.5 at % or more. However, the addition of large amounts of 
platinum group elements make the alloys quite expensive and are rather 
detrimental for both the increasing of the catalyst surface area and 
surface enrichment of the platinum group elements since the beneficial 
effect of preferential dissolution of elements not necessary for catalytic 
activity decreases by the excessive addition of platinum group elements. 
Therefore, the content of platinum group elements should not exceed 20 at 
%, and the most suitable contents are from 1 to 10 at %. 
The preparation of the amorphous alloys of the present invention can be 
carried out by any kind of method for the preparation of amorphous alloys, 
such as rapid quenching from the liquid state. 
One embodiment of an apparatus for preparing the amorphous alloys of the 
present invention is shown in the accompanying drawing. This is called the 
rotating wheel method. The apparatus is placed in a vacuum chamber 
indicated by a dotted rectangle. In the figure, a quartz tube 2 has a 
nozzle 3 at its lower end, and raw materials 4 and an inert gas for 
preventing oxidation of the raw materials are fed from an inlet 1. A 
heating furnace 5 is placed around the quartz tube 2 so as to heat the raw 
materials 4. A high speed wheel 7 is placed below the nozzle 3 and is 
rotated by a motor 6. 
For the preparation of the amorphous alloys, the raw materials 4 of the 
prescribed compositions are placed in the quartz tube 2 and the vacuum 
chamber is evacuated up to about 10.sup.-5 torr. After the evacuated 
vacuum chamber is filled with argon gas of about 1 atm, the raw materials 
4 are melted by the heating furnace 5. The molten alloy impinges under the 
pressure of the inert gas onto the outer surface of the wheel 7, which is 
rotated at a speed of 1,000 to 10,000 rpm, whereby an amorphous alloy is 
formed as a long thin plate, which may for example have a thickness of 
0.01 mm, a width of 10 mm and a length of several meters. 
The amorphous alloys of the present invention will be further illustrated 
by certain examples which are provided only for purpose of illustration 
and are not intended to limit the present invention. 
EXAMPLE 1 
A raw alloy was prepared by argon arc melting of a mixture of commercial 
metals so as to form Ni-40 at % Nb-2 at % Rh. After remelting of the raw 
alloy under an argon atmosphere, amorphous alloy ribbons were prepared by 
the rotating wheel method using the apparatus shown in the figure. The 
amorphous alloys thus prepared were 0.01-0.05 mm thick, 1-3 mm wide and 
3-20 m long ribbons. The formation of an amorphous structure was confirmed 
by X-ray diffraction. 
The highly active metallic catalyst was obtained by the surface activation 
treatment of this alloy by immersion in 46.5% HF for 300-900 sec at 
ambient temperature. The reactor tube was prepared by placing 0.5 g of the 
metallic catalysts of 5 cm length in a glass tube of 8 mm inner diameter 
into an electric furnace. The reactant gas mixture of CFC-12 flon and 
water obtained by bubbling CFC-12 flon through warm water was passed 
through the reactor tube. The amounts of CO.sub.2 and remaining CFC-12 
flon in the gas passing through the reactor tube were analyzed by gas 
chromatography. HF and HCl were dissolved in water and determined. 
Table 1 shows the reaction temperature and conversion. 
TABLE 1 
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Mass of CFC-12 flon converted by 1 g 
Reaction of rhodium in the amorphous alloy 
Temperature catalyst for 1 h 
.degree.C. g 
______________________________________ 
250 1.2 
300 2.6 
350 12.5 
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EXAMPLE 2 
Raw alloys, whose nominal compositions are shown in Table 2, were prepared 
by argon arc melting of mixtures of commercial metals. After remelting of 
the raw alloys under an argon atmosphere, amorphous alloys were prepared 
by the rotating wheel method by the apparatus shown in the figure. The 
amorphous alloys thus prepared were 0.01-0.05 mm thick, 1-3 mm wide and 
3-20 m long ribbons. The formation of an amorphous structure was confirmed 
by X-ray diffraction. 
The highly active metallic catalysts were obtained by the surface 
activation treatment of these alloys by immersing then in 2-46% HF 
solutions for 300-900 sec at ambient temperature. The reactor tube was 
prepared by placing 0.5 g of the metallic catalysts of 5 cm length in a 
glass tube of 8 mm inner diameter and into an electric furnace. 
The reactant gas mixture of CFC-12 flon and water obtained by bubbling 
CFC-12 flon through warm water was passed through the reactor tube. The 
amounts of CO.sub.2 and remaining CFC-12 flon in the gas passed through 
the reactor tube were analyzed by gas chromatography. HF and HCl were 
dissolved in water and determined. 
Table 2 shows the reaction temperature and conversion. 
TABLE 2 
______________________________________ 
Mass of CFC-12 flon 
converted by 1 g of 
platinum group 
elements in the 
amorphous alloy 
catalysts for 1 h (g) 
Alloy Reaction Temperature 
(at %) 150.degree. C. 
200.degree. C. 
______________________________________ 
Ni--30Ta--2Rh 1.0 8.0 
Ni--30Ta--2Pt 0.2 2.2 
Ni--30Ta--2Ir 0.5 2.0 
Ni--30Ta--2Pd 0.3 1.8 
Ni--30Ta--2Ru 0.2 2.0 
Ni--30Ta--3Rh 1.0 3.1 
Ni--40Nb--2Rh 1.1 3.2 
Ni--40Nb--2Ru 0.3 2.0 
Ni--40Ta--30Nb--10Rh 1.2 3.5 
Ni--10Ta--10Nb--0.5Rh 
1.0 2.9 
Ni--20Ta--20Nb--10Rh--10Ru 
1.2 3.5 
Ni--20Co--30Ta--10Nb--2Rh 
1.1 3.1 
Co--40Nb--3Rh 1.1 3.1 
Ni--70Ti--0.5Ru 0.2 2.0 
Ni--40Zr--0.25Rh--0.25Pt 
1.1 3.2 
Ni--20Zr--1Pt 0.3 1.8 
Ni--40Ti--40Zr--3Ir 0.3 1.9 
Co--20Zr--5Pd 0.2 1.6 
Co--20Ti--20Pd 0.3 1.9 
Ni--20Co--40Zr--1Pd-1Rh--1Ru-0.5Pt 
1.0 2.0 
Ni--70Ta--10Ti--1Pd 0.2 1.9 
Ni--10Ta--30Nb--20Zr--1Pd 
0.2 1.9 
Ni--10Ta--10Nb--20Ti--20Zr--3Ru 
0.2 1.8 
Co--30Nb--10Zr--3Ir 0.3 2.0 
Ni--30Co--10Ta--10Nb--10Ti--10Zr-- 
0.9 2.8 
0.25Ir--0.25Rh 
______________________________________ 
Consequently, the amorphous alloy catalysts of the present invention have 
very high activities for the decomposition of flons to hydrofluoric acid 
and carbon dioxide by the reaction of flons with water.