U.S. patent application number 09/767700 was filed with the patent office on 2001-06-28 for catalyst and method for the synthesis of chlorine dioxide, and method of making catalyst for the synthesis of chlorine dioxide.
Invention is credited to Ostgard, Daniel.
Application Number | 20010005499 09/767700 |
Document ID | / |
Family ID | 22767208 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010005499 |
Kind Code |
A1 |
Ostgard, Daniel |
June 28, 2001 |
Catalyst and method for the synthesis of chlorine dioxide, and
method of making catalyst for the synthesis of chlorine dioxide
Abstract
Chlorine dioxide is generated from an aqueous solution of sodium
chlorite in the presence of a catalyst having a reduced rate of
deactivation. The catalyst is preferably palladium, or palladium
together with another platinum group metal (e.g., Pd+Pt), or
palladium together with a Group IB metal (e.g., Pd+Au) deposited on
a support modified by Group IA carbonate salt (e.g.,
K.sub.2CO.sub.3) or a Group IIA carbonate salt (e.g., CaCO.sub.3)
or a magnesium salt that can be converted to MgO or a support
consisting of a Group IA carbonate salt or a Group IIA carbonate
salt or a magnesium salt that can be converted to MgO.
Inventors: |
Ostgard, Daniel; (East
Brunswick, NJ) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL, LLP
1850 M STREET, N.W., SUITE 800
WASHINGTON
DC
20036
US
|
Family ID: |
22767208 |
Appl. No.: |
09/767700 |
Filed: |
January 24, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09767700 |
Jan 24, 2001 |
|
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08206623 |
Mar 7, 1994 |
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Current U.S.
Class: |
423/477 ;
502/328; 502/330; 502/331; 502/333 |
Current CPC
Class: |
A61L 12/102 20130101;
C01B 11/024 20130101; B01J 27/232 20130101; B01J 23/52
20130101 |
Class at
Publication: |
423/477 ;
502/328; 502/330; 502/331; 502/333 |
International
Class: |
C01B 011/02 |
Claims
What is claimed:
1. A catalyst for producing chlorine dioxide having a slower rate
of deactivation, consisting essentially of a catalyst support
selected from the group consisting of a modified support modified
by a Group IA carbonate salt or a Group IIA carbonate salt or a
magnesium salt that can be converted to MgO and a support
consisting of a Group IA carbonate salt or a Group IIA carbonate
salt or a magnesium salt that can be converted to MgO, wherein the
outside edge of said catalyst support is impregnated with palladium
or palladium and another platinum group metal or palladium and a
Group IB metal.
2. The catalyst according to claim 1, wherein said another platinum
group metal is platinum.
3. The catalyst according to claim 1, wherein said Group IB metal
is gold.
4. The catalyst according to claim 1, wherein said palladium is
present in an amount of 0.1 to 20%.
5. The catalyst according to claim 2, wherein said palladium and
said platinum are present in an amount of 0.1 to 20%.
6. The catalyst according to claim 2, wherein said palladium and
said platinum are present in a ratio of Pt to Pd of 0.01:1 to
2:1.
7. The catalyst according to claim 6, wherein said palladium and
said platinum are present in a ratio of Pt to Pd of 0.2:1 to
0.8:1.
8. The catalyst according to claim 3, wherein said palladium and
said gold is present in an amount of 0.1 to 20%.
9. The catalyst according to claim 3, wherein said palladium and
said gold are present in a ratio of Au to Pd of 0.01:1 to 2:1.
10. The catalyst according to claim 9, wherein said palladium and
said gold are present in a ratio of Au to Pd of 0.2:1 to 0.8:1.
11. The catalyst according to claim 1, wherein said Group IA
carbonate salt is K.sub.2CO.sub.3.
12. The catalyst according to claim 1, wherein said Group IA
carbonate salt is CaCO.sub.3.
13. The catalyst according to claim 1 wherein said modified support
is a formed alumina modified with K.sub.2CO.sub.3 present in the
amount of 2 to 50% by weight.
14. The catalyst according to claim 1 wherein said modified support
is a high surface metallic or ceramic support.
15. The catalyst according to claim 14 wherein said modified
support has a surface area of at least about 40 m.sup.2/g.
16. The catalyst according to claim 14 wherein said modified
support is gamma alumina, silica-alumina, silica, or titania.
17. The catalyst according to claim 1, said catalyst produced by a
method consisting essentially of preadjusting the pH of an aqueous
solution of a palladium or palladium and another platinum group
metal or palladium and a Group IB metal salt to a pH range of 1 to
6.3, adding said solution to a slurry of said catalyst support and
water, maintaining the pH of said slurry from 6 to 10 for several
minutes at a temperature of 70.degree. to 90.degree. C., and adding
a reducing agent, thereby impregnating the outside edge of said
catalyst support with palladium or palladium and another platinum
group metal or palladium and a Group IB metal.
18. A method of making a catalyst for producing chlorine dioxide
having a slower rate of deactivation, said method consisting
essentially of preadjusting the pH of an aqueous solution of a
palladium or palladium and another platinum group metal or
palladium and a Group IB metal salt to a pH range of 1 to 6.3,
adding said solution to a slurry of water and a catalyst support
selected from the group consisting of a modified support modified
by a Group IA carbonate salt or a Group IIA carbonate salt or a
magnesium salt that can be converted to MgO and a support
consisting of a Group IA carbonate salt or a Group IIA carbonate
salt or a magnesium salt that can be converted to MgO, maintaining
the pH of said slurry from 6 to 10 for several minutes at a
temperature of 70.degree. to 90.degree. C., and adding a reducing
agent, thereby impregnating the outside edge of said catalyst
support with palladium or palladium and another platinum group
metal or palladium and a Group IB metal.
19. A method for generating chlorine dioxide from a chlorine
dioxide precursor, said method comprising contacting an aqueous
medium containing a chlorine dioxide precursor with a catalyst
consisting essentially of a catalyst support selected from the
group consisting of a modified support modified by a Group IA
carbonate salt or a Group IIA carbonate salt or a magnesium salt
that can be converted to MgO and a support consisting of a Group IA
carbonate salt or a Group IIA carbonate salt or a magnesium salt
that can be converted to MgO, wherein the outside edge of said
catalyst support is impregnated with palladium or palladium and
another platinum group metal or palladium and a Group IB metal.
20. The method according to claim 19 wherein the temperature is
5.degree. to 80.degree. C.
21. The method according to claim 20 wherein the temperature is
5.degree. to 50.degree. C.
22. The method according to claim 19 wherein the pH of said aqueous
medium is 1 to 8.
23. The method according to claim 22 wherein the pH is from 4 to
8.
24. The method according to claim 19 wherein the time of the
contact between said catalyst and said chlorine dioxide precursor
ranges from 0.01 to 20 seconds.
25. The method according to claim 19 wherein said chlorine dioxide
is contacted with contact lenses for disinfecting.
26. A two component package comprising the catalyst according to
claim 1 and a chlorine dioxide precursor.
27. A method for generating chlorine dioxide from a chlorine
dioxide precursor comprising providing a multicompartment
container, a first compartment containing a chlorine dioxide
precursor, a second compartment containing the catalyst according
to claim 1, dispelling from said first compartment a quantity of
said chlorine dioxide precursor to flow into said second
compartment containing said catalyst, contacting said precursor
with said catalyst thereby forming chlorine dioxide, and ejecting
said chlorine dioxide from said container to the surface of an item
to be disinfected or treated.
Description
BACKGROUND TO THE INVENTION
[0001] The present invention relates to a catalyst for the
synthesis of chlorine dioxide and to a method of making such a
catalyst. The catalyst is preferably palladium, or palladium
together with another platinum group metal (e.g., Pd+Pt), or
palladium together with a Group IB metal (e.g., Pd+Au) deposited on
a support consisting of a Group IA carbonate salt (e.g.,
K.sub.2CO.sub.3) or a Group IIA carbonate salt (e.g., CaCO.sub.3)
or a magnesium salt that can be converted to MgO or a support
modified by Group IA carbonate salt (e.g., K.sub.2CO.sub.3) or a
Group IIA carbonate salt (e.g., CaCO.sub.3) or a magnesium salt
that can be converted to MgO. The catalysts of the present
invention has a slower rate of deactivation than catalysts
previously used for this purpose.
[0002] In another aspect, the present invention concerns a method
for generating chlorine dioxide from an aqueous solution of a
precursor therefor and directing the resulting chlorine dioxide at
the material to be disinfected.
[0003] Chlorine dioxide is known to act as a disinfecting or
sterilizing agent for solutions and devices (e.g., contact lenses).
Chlorine dioxide is generally produced from a solution of a
chlorine dioxide precursor, such as sodium chlorite solutions, by
contacting the solution with a catalyst (e.g., catalysts containing
noble metals, as described for example in U.S. Pat. No. 5,008,096).
However, known catalysts have the disadvantage of becoming greatly
deactivated within a matter of days.
SUMMARY OF THE INVENTION
[0004] An object of the present invention is to provide novel
chlorine dioxide generating catalysts having a slower rate of
deactivation than known catalysts. In achieving the above and other
objects, one feature of the invention resides in a catalyst which
is composed of a support wherein the outside edge of the support is
impregnated with palladium or palladium and another platinum group
metal or palladium and a Group IB metal. The support itself is
selected from the group of supports modified by a Group IA
carbonate salt or a Group IIA carbonate salt or a magnesium salt
that can be converted to MgO. Many well known catalyst supports,
such as gamma alumina, can be used to form the modified support as
described. In another aspect, the Group IA carbonate salt (e.g.,
K.sub.2CO.sub.3) or Group IIA carbonate salt (e.g., CaCO.sub.3) or
a magnesium salt that can be converted to MgO can be formed into a
self sustaining support such as a pellet or honeycomb.
[0005] Another object of the present invention is to provide a
method of making a catalyst for producing chlorine dioxide having a
slower rate of deactivation. The method involves preadjusting the
pH of an aqueous solution of a palladium or palladium and another
platinum group metal or palladium and a Group IB metal salt to a pH
range of 1 to 6.3, adding the solution to a slurry of water and a
support selected from supports modified by a Group IA carbonate
salt or a Group IIA carbonate salt or a magnesium salt that can be
converted to MgO or a support consisting of a Group IA carbonate
salt (e.g., K.sub.2CO.sub.3) or a Group IIA carbonate salt (e.g.,
CaCO.sub.3) or a magnesium salt that can be converted to MgO,
maintaining the pH of the slurry from 6 to 10 for several minutes
at a temperature of 70.degree. to 90.degree. C., and adding a
reducing agent, thereby impregnating the outside edge of the
support with palladium or palladium and another platinum group
metal or palladium and a Group IB metal.
[0006] An additional object of the present invention is to provide
a method for generating chlorine dioxide from a chlorine dioxide
precursor. The method involves contacting an aqueous medium
containing a chlorine dioxide precursor with the above described
catalyst.
[0007] Another method for generating chlorine dioxide from a
chlorine dioxide precursor involves providing a multicompartment
container, a first compartment containing a chlorine dioxide
precursor, a second compartment containing the catalyst described
above, dispelling from the first compartment a quantity of the
chlorine dioxide precursor to flow into the second compartment
containing the catalyst, contacting the precursor with the catalyst
thereby forming chlorine dioxide, and ejecting the chlorine dioxide
from the container to the surface of an item to be disinfected or
treated.
[0008] Furthermore, there is provides a two component package
comprising the catalyst described above and a chlorine dioxide
precursor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The present invention will be further understood with
reference to the drawings, wherein:
[0010] FIG. 1 is a graph of the effect of alloying Pd with Au, Ag
or Pt on catalyst deactivation;
[0011] FIG. 2 is a graph of the effect of the support on Pd/Au
catalysts;
[0012] FIG. 3 is a graph of the effect of the support on Pd/Pt
catalysts;
[0013] FIG. 4 is a graph of the effect of the support on Pd
catalysts; and
[0014] FIG. 5 is a schematic drawing of a multicompartment
container which contains chlorine dioxide precursor and the
catalyst which generates chlorine dioxide from the precursor.
[0015] FIG. 6 is a graph of the performance of a Pd/Au catalyst on
a K.sub.2CO.sub.3 modified alumina support.
DETAILED DESCRIPTION OF THE INVENTION
[0016] A catalyst made for the generation of chlorine dioxide in
accordance with this invention is comprised of palladium, or
palladium together with another platinum group metal (e.g., Pd+Pt),
or palladium together with a Group IB metal (e.g., Pd+Au) deposited
on a support modified by Group IA carbonate salt (e.g.,
K.sub.2CO.sub.3) or a Group IIA carbonate salt (e.g., CaCO.sub.3)
or a water soluble magnesium salt (e.g., acetate, nitrate,
carbonate, chloride) that can be converted to Mgo or a support
consisting of a Group IA carbonate salt (e.g., K.sub.2CO.sub.3) or
a Group IIA carbonate salt (e.g., CaCO.sub.3) or a water soluble
magnesium salt (e.g., acetate, nitrate, carbonate, chloride) that
can be converted to MgO. The catalytic metal must be present at a
weight % of at least 0.1 and up to 20, preferably 1 to 10, based on
the total weight of the catalyst. Palladium is preferred. Aqueous
solutions of Group VIII and Group IB metal salts (i.e., halides and
nitrates) can be used in the preparation of the catalyst. For
example, the following ranges (wt/wt) can be used: ratio of Au to
Pd, 0.01:1 to 2:1, preferably 0.2:1 to 0.8:1; ratio of Pt to Pd,
0.01:1 to 2:1, preferably 0.2:1 to 0.8:1.
[0017] The support, which is modified by Group IA carbonate salt
(e.g., K.sub.2CO.sub.3) or a Group IIA carbonate salt (e.g.,
CaCO.sub.3) or a magnesium salt that can be converted to MgO, may
be selected from many well known high surface metallic or ceramic
catalyst supports, such as gamma alumina, silica-alumina, silica,
titania, etc. Typically, such supports have a surface area of at
least about 40 m.sup.2/g, preferably 100 m.sup.2/g.*
[0018] The method of making the catalyst is illustrated with
palladium, but other platinum group metals or combinations of
palladium and another platinum group metal (e.g., Pd+Pt) or
combinations of palladium and a Group IB metal (e.g., Pd+Au) can be
substituted with comparable results. The catalyst is supported for
example on a MgO or CaCO.sub.3 or K.sub.2CO.sub.3 catalyst support
or matrix which is substantially inert when exposed to the
conditions used in the enhanced generation of chlorine dioxide from
a chlorine dioxide precursor in accordance with the present
invention. The support must be thermostable and must provide high
support area. The configuration of supports are known in the art.
The supported component may have any suitable shape or
configuration, such as sheets, rods, extrudates, tablets, pills,
irregular shaped particles, spheres, disks, pellets and the like.
Monoliths can also be used. The formation of the MgO or CaCO.sub.3
or K.sub.2CO.sub.3 inert support can be carried out by known
means.
[0019] Any of a number of conventional techniques can be employed
to deposit the platinum group metal(s), or platinum group metal and
Group IB metal, on the support material. These techniques include
impregnation, co-precipitation, ion-exchange, dipping, spraying,
vacuum deposits and the like.
[0020] The palladium or palladium and another platinum group metal
(e.g., Pd+Pt) or palladium and a Group IB metal (e.g., Pd+Au) can
be deposited on the outside edge of the MgO or CaCO.sub.3 or
K.sub.2CO.sub.3 support in a number of ways known in the art. The
preferred method is by promoting rapid hydrolysis of the water
soluble salts of the noble metals when added to a MgO or CaCO.sub.3
or K.sub.2CO.sub.3 particulate-water slurry. This can be achieved
by preadjusting the pH of the noble metal salt solution to 1 to
6.3, depending on the metal salts used, prior to addition to the
slurry. The concentration of the noble metal salt in the aqueous
solution is not critical and can vary widely. After that, the
process is continued by maintaining the pH of the slurry at 6 to 10
for several minutes at a temperature of 70.degree. to 90.degree.
C., prior to the addition of a reducing agent.
[0021] The result of following these reaction conditions is that
the finely divided MgO or CaCO.sub.3 or K.sub.2CO.sub.3 particles
have the catalytically active metal, e.g., palladium (or Pd+Pt or
Pd+Au), deposited on the exterior surface of the particle. The MgO
or CaCO.sub.3 or K.sub.2CO.sub.3 particle can range from 0.01 to 4
mm in size, preferably 0.3 to 4 mm, though the upper limit is not
critical. The penetration of the palladium (or Pd+Pt or Pd+Au) into
the MgO or CaCO.sub.3 or K.sub.2CO.sub.3 particle can be determined
by transmission electron microscopy.
[0022] Broadly, the method for enhancing generation of chlorine
dioxide according to the present invention involves contacting an
aqueous medium containing a chlorine dioxide precursor with a
catalyst formed of Pd (or Pd+Pt or Pd+Au) deposited on a MgO or
CaCO.sub.3 or K.sub.2CO.sub.3 inert support. The temperature at
which the aqueous medium is maintained during contact of the
chlorine dioxide precursor with the catalyst can vary widely.
Preferably, the temperature is in the range of 5.degree. C. to
80.degree. C., and preferably 5.degree. C. to 50.degree. C.
Typically the process is carried out at ambient temperature. The pH
of the aqueous medium is usually in the range of 1 to 8, preferably
4 to 8. Generally, the catalyst contact time with the chlorine
dioxide precursor ranges from 0.01 to 20 seconds.
[0023] Chlorine dioxide precursors which may be employed in the
practice of the present invention are those compounds capable of
generating, releasing or being converted to chlorine dioxide when
contacted with a catalyst formed of Pd (or Pd+Pt or Pd+Au)
deposited on a MgO or CaCO.sub.3 or K.sub.2CO.sub.3 support under
the reaction conditions previously described. Any metal chlorite
salt capable of generating chlorine dioxide can be utilized as the
chlorine dioxide precursor. Preferably, alkali metal chlorites are
used, especially sodium chlorite in an aqueous medium. The amount
of chlorine dioxide precursor present in the aqueous medium can
vary widely and will be dependent upon the amount of chlorine
dioxide to be generated. For example, it has been found that the
amounts of chlorine dioxide precursor present in the aqueous medium
can range from 0.0001 to 30 weight %, preferably 0.0005 to 10
weight %. Preferably, a chlorine dioxide complex sold by Bio-Cide
International, Inc. of Norman, Okla. under the trademark
Purogene.sup.R, is used (described in U.S. Pat. No. 5,008,096,
incorporated by reference in its entirety).
[0024] In order to be able to control the chlorine dioxide formed
in the course of the catalytic reaction and to direct the flow of
the chlorine dioxide, it is desirable to conduct the reaction in a
space where the catalyst and precursor solution are kept separate
until it is desired to generate the chlorine dioxide. Thus, for
marketing the product, a two component package can be provided with
suitable separation means and dispenser means to direct the flow of
chlorine dioxide to the surface, object or material to be
disinfected.
[0025] All kinds of contact lenses may be disinfected by utilizing
chlorine dioxide produced by the catalysts of the present invention
in a manner known in the art.
[0026] In accordance with a further embodiment of the present
invention there is provided a two component package which
separately contains the catalyst and the chlorine dioxide
precursor.
[0027] As shown in FIG. 5, there can be provided a device for
dispensing chlorine dioxide 10 containing a compartment 12 for
holding the aqueous precursor. The device also has a compartment 20
for holding the catalyst 14 separate and apart from the aqueous
precursor. A tube or other device 16 is arranged so as to permit
contact of the aqueous precursor with the catalyst. A dispenser of
any convenient design 18 can be arranged in the device 10 for
delivery of the chlorine dioxide generated in the upper compartment
20.
[0028] Furthermore, the present invention concerns a method for
generating chlorine dioxide from a chlorine dioxide precursor which
utilizes the multicompartment container shown in FIG. 5. In order
to generate chlorine dioxide, the container, for example, can be
inverted and the compartment containing the chlorine dioxide
precursor is squeezed in order to flow at least a portion of the
chlorine dioxide precursor into the compartment which contains the
catalyst. The resulting chlorine dioxide is ejected from the
container via an opening to the surface of the item (e.g., contact
lenses) to be disinfected or treated. The compartment which
contains the catalyst is separated from the compartment containing
the chlorine dioxide precursor by a catalyst retention means (e.g.,
a filter). The compartment which contains the catalyst is separated
from the opening by a catalyst retention means (e.g., a
filter).
EXAMPLES
[0029] The following examples are further illustrative of the
present invention:
Example 1
Effect of Alloying Pd on Catalyst Activity
[0030] As shown in Table 1 and FIG. 1, the alloying of Pd with Pt,
Ag or Au decreases the rate of deactivation (in comparison to a
catalyst containing only Pd).
[0031] Catalyst K was prepared by suspending 48.3 grams of
Rhone-Poulenc Chemie spheralite 532, a gamma alumina containing
1.3% La.sub.2O.sub.3 and 0.5% Nd.sub.2O.sub.3 and ground to a
particle size range of 75 to 212 microns, in 250 ml of deionized
water. To this 25 suspension was added an aqueous solution of
palladium nitrate containing 2.5 grams of Pd. The pH of the Pd
solution had been adjusted to 1.0 with sodium carbonate. After
heating this suspension at 80.degree. C. for 15 min., while
maintaining the pH at approximately 6-7 with sodium carbonate, a
solution of sodium hydroxide and formaldehyde was added and the
mixture stirred for another 15 min. The alumina containing 4.9 wt %
reduced palladium was filtered, washed with DI water, and dried
overnight at 120.degree. C.
[0032] Catalyst L was prepared by suspending 94.7 grams of
Rhone-Poulenc Chemie spheralite 532, a gamma alumina containing
1.3% La.sub.2O.sub.3 and 0.5% Nd.sub.2O.sub.3 and ground to a
particle size range of 75 to 212 microns, in 500 ml of deionized
water. To this suspension was added an aqueous solution of
palladium nitrate and tetrachloro auric acid. This precious metal
solution consisted of 5.0 grams of Pd and 2.0 grams of Au, and its
pH had been adjusted to 1.0 with sodium carbonate. After heating
this suspension at 80.degree. C. for 15 min., while maintaining the
pH at approximately 9-10 with sodium carbonate, a solution of
sodium hydroxide and formaldehyde was added to the mixture stirred
for another 15 min. The alumina containing 4.9 wt % reduced
palladium and 2.0 wt % reduced gold was filtered, washed with DI
water, and dried overnight at 120.degree. C.
[0033] Catalyst M was made in the same manner as catalyst L except
that the final catalyst consisted of 4.9% Pd and 3.0% Au. 25
Catalyst N was prepared by suspending 94.7 grams of Rhone-Poulenc
Chemie spheralite 532, a gamma alumina containing 1.3%
La.sub.2O.sub.3 and 0.5% Nd.sub.2O.sub.3 and ground to a particle
size range of 75 to 212 microns, in 500 ml of deionized water. To
this suspension was added an aqueous solution of palladium nitrate
and platinum nitrate. This precious metal solution consisted of 5.0
grams of Pd and 2.0 grams of Pt, and its pH had been adjusted to
1.0 with sodium carbonate. After heating this suspension at
80.degree. C. for 15 min., while maintaining the pH at
approximately 6-7 with sodium carbonate, a solution of sodium
hydroxide and formaldehyde was added and the mixture stirred for
another 15 min. The alumina containing 4.9 wt % reduced palladium
and 2.0 wt % reduced platinum was filtered, washed with DI water,
and dried overnight at 120.degree. C.
[0034] Catalyst O was prepared by suspending 95.2 grams of
Rhone-Poulenc Chemie spheralite 532, a gamma alumina containing
1.3% La.sub.2O.sub.3 and 0.5% Nd.sub.2O.sub.3 and ground to a
particle size range of 75 to 212 microns, in 500 ml of deionized
water. To this suspension was added an aqueous solution of
palladium nitrate and silver nitrate. This precious metal solution
consisted of 5.0 grams of Pd and 1.1 grams of Ag, and its pH had
been adjusted to 1.0 with sodium carbonate. After heating this
suspension at 80.degree. C. for 15 min., while maintaining the pH
at approximately 9-10 with sodium carbonate, a solution of sodium
hydroxide and formaldehyde was added and the mixture stirred for
another 15 min. The alumina containing 4.9 wt % reduced palladium
and 4.9 wt % reduced palladium and 1.1 wt % reduced silver was
filtered, washed with DI water, and dried overnight at
120.degree..
[0035] Experiments were performed using catalysts K, L, M, N and O
to determine their activity and stability to generate chlorine
dioxide from an aqueous solution of sodium chlorite. In these tests
50 mg portions of the catalyst were held in a cylindrical cell at
room temperature. An aqueous solution of sodium chlorite (150 ppm)
was passed over the catalyst at a rate of approximately 1 ml/sec.
The steady state concentration of ClO.sub.2 generated in the outlet
stream was measured each day over a three minute period. The
concentration of ClO.sub.2 was measured using an ultraviolet
spectrometer in a manner known in the art.
1TABLE 1 Effect of Alloying Pd with Pt, Ag and Au on Catalyst
Activity Catalyst K L M N O Palladium, wt % 4.9 4.9 4.9 4.9 4.9
Gold, wt % -- 2 3 -- -- Platinum, wt % -- -- -- 2 -- Silver, wt %
-- -- -- -- 1.1 Support Designation 532 532 532 532 532 ClO.sub.2
Conc. (ppm): Initial 2.75 2.99 2.81 3.39 2.54 Day 15 0.75 1.49 1.78
2.01 1.38 Day 30 0.4 1.03 1.55 1.32 0.94 Deactivation, %: Day 15
72.7 50.2 36.7 40.7 45.7 Day 30 85.5 65.6 44.8 61.1 63
[0036] By substituting Cu for Au or Ag (as shown in the preparation
of catalysts L or M or O in Table 1), comparable results are
obtained.
Example 2
Effect of Different Supports on Catalyst Activity
[0037] Catalyst P was made in the same manner as catalyst K except
that the support was Aldrich 24,338-8, a commercially available
source of MgO.
[0038] Catalyst Q was made in the same manner as catalyst L except
that the support was Aldrich 24,338-8, a commercially available
source of MgO.
[0039] Catalyst R was made in the same manner as catalyst N except
that the support was Aldrich 24,338-8, a commercially available
source of MgO.
[0040] Catalyst S was made in the same manner as catalyst M except
that the support was Sturcal F, a commercially available source of
CaCO.sub.3 from Sturge Chemicals.
[0041] Catalyst T was made in the same manner as catalyst N except
that the support was Sturcal F, a commercially available source of
CaCO.sub.3 from Sturge Chemicals.
[0042] The experiments to determine the activity and stability of
catalysts P, Q, R, S and T for the generation of chlorine dioxide
from sodium chlorite were performed in the same manner as described
above.
[0043] Table 2 describes the Mgo or CaCO.sub.3 supports used for
this catalytic system:
2TABLE 2 Example 2 Support Descriptions Support Designation
24,338-8 Sturcal F 532 Material MgO CaCO.sub.3 Gamma
Al.sub.2O.sub.3 La2O3, wt % -- -- 1.3 Nd2O3, wt % -- -- 0.5
Particle Size Range, g <200 <200 75-212 Pore Volume, cc/g 1.7
E-2 1.7 E-2 7.2 E-1 Surface Area, m.sup.2/g 6.1 5.7 112
[0044] Table 3 describes the activity of these catalysts:
3TABLE 3 Effect of Different Supports on Catalyst Activity Catalyst
P Q R S T Palladium, wt % 5 5 5 4.9 4.9 Gold, wt % -- 2 -- 3 --
Platinum, wt % -- -- 2 -- 2 Support MgO MgO MgO CaCO.sub.3
CaCO.sub.3 ClO.sub.2 Conc. (ppm): Initial 0.69 0.92 0.92 1.12 1.38
Day 15 0.29.sup.A 0.72 0.89 0.98 1 Day 30 -- 0.37.sup.B 0.6 0.8
0.69 Deactivation, %: Day 15 58.0.sup.A 21.7 3.3 12.5 27.5 Day 30
-- 59.8.sup.B 34.8 28.6 50 .sup.AThis measurement was taken on day
14. .sup.BThis measurement was taken on day 28.
[0045] In comparing tables 1 and 3 it is obvious that the MgO and
CaCO.sub.3 supported catalysts, when compared to those on the
Rhone-Poulenc Chemie spheralite 532, have lower levels of activity,
but they deactivate less. Therefore, the MgO and CaCO.sub.3
supported catalysts would be more desirable when low constant
levels of ClO.sub.2 generation are needed over an extended period
of time. FIGS. 2, 3, and 4 show the effect of the different
supports on the stability of the various Pd/Au, Pd/Pt, and Pd
catalysts respectively.
Example 3
The Use of K.sub.2CO.sub.3 Modified {fraction (1/32)}" Alumina
Spheres as a Support
[0046] Table 4 and FIG. 6 demonstrate that a suitable catalyst can
also be made on a K.sub.2CO.sub.3 modified fixed bed support. A 500
gram portion of the Condea {fraction (1/32)}" alumina spheres was
modified by spraying on a solution that contained 10 g of
K.sub.2CO.sub.3 and 215 grams of water. This was followed by a
drying step at 100.degree. C. in a rotating drum and an air
calcination at 950.degree. C. for one hour. As shown in Table 5,
this modification has no noticeable effects on physical properties
of the support.
4TABLE 4 The performance of the K.sub.2CO.sub.3 modified {fraction
(1/32)}" alumina spheres as a catalyst support Catalyst U Palladium
wt % 5 Gold, wt % 3 Amount of K.sub.2CO.sub.3 Added, wt % 2
ClO.sub.2 Conc. (ppm): Initial 1.09 Day 13 1.09 Deactivation Day
13, % 0
[0047]
5TABLE 5 The effects of the K.sub.2CO.sub.3 modification on the
physical properties of the {fraction (1/32)}" alumina spheres
Amount of K.sub.2CO.sub.3, Added, wt % 0 2 Surface Area, m.sup.2/g
97.9 95.3 Total Pore Volume, cc/g 0.33 0.32 Average Pore Diameter,
.ANG. 133.5 133.7
[0048] Catalyst U was prepared by spraying 110.4 grams of the above
mentioned K.sub.2CO.sub.3 modified Condea alumina {fraction
(1/32)}" spheres with a 28.5 ml precious metal solution containing
6 grams of palladium as palladium chloride, 3.6 grams of gold as
tetrachloroauric acid, 5ml of 20% Na.sub.2CO.sub.3 solution. The
catalyst was then reduced in a 20 ml comprised of 29.3% sodium
formate and 2% hydrazine at 25.degree. C. for 30 minutes. The
catalyst was then filtered, washed with DI water, and dried
overnight at 120.degree. C.
[0049] The experiments to determine the activity and stability of
catalyst U for the generation of chlorine dioxide from sodium
chlorite was performed in the same manner as described in examples
1 and 2 except that 0.2003 grams of catalyst U was used. The
cylindrical cell used to contain catalyst U during the experiments
had the diameter of 4 mm and the height of 19 mm, while the
cylindrical cell used for the catalysts of examples 1 and 2 had the
diameter of 15 mm and the height of 1 mm.
[0050] Further variations and modifications of the invention will
become apparent to those skilled in the art from the foregoing and
are intended to be encompassed by the claims appended hereto.
[0051] U.S. Pat. Nos. 5,008,096; 4,731,192; and 4,362,707 are
incorporated by reference in their entirety. Our copending U.S.
patent application Ser. No. 08/008,971, filed on Jan. 26, 1993, is
incorporated by reference in its entirety.
* * * * *