Process for producing hydrogen peroxide

This invention provides a process for producing hydrogen peroxide through catalytic reaction of oxygen with hydrogen in an aqueous medium in the presence of a platinum group metal catalyst, in which an organic solvent having only limited solubility with water and less hydrogen peroxide-dissolving ability compared to that of water is caused to be concurrently present in the reactor, and oxygen and hydrogen are catalytically reacted in an aqueous medium in the presence of a water- and organic solvent-insoluble, hydrophilic platinum group metal catalyst, under a low reaction pressure, to form high concentration aqueous hydrogen peroxide solution within a short time.

FIELD OF THE INVENTION 
This invention relates to an improved process for producing hydrogen 
peroxide through catalytic reaction of oxygen with hydrogen in a reaction 
medium. More specifically, the invention relates to a production process 
of hydrogen peroxide in which hydrogen peroxide concentration in the 
acquired aqueous solution is increased by the virtue of concurrent 
presence with water, which is the reaction medium, in the reactor of an 
inflammable, organic solvent having only limited solubility with water. 
PRIOR ART 
The main process for industrial production of hydrogen peroxide currently 
in use is an autoxidation process using an alkylanthraquinone as the 
medium. This process has problems in that it requires a multiplicity of 
steps such as the reduction, oxidation, separation by aqueous extraction, 
purification and concentration, etc., which render the process complex and 
increase the equipment and operation costs. Further problems reside in 
loss of alkylanthraquinone due to deterioration and degradation of 
reducing catalyst. 
Aiming at removal of those problems, a variety of production processes 
other than the above have been attempted, one of which comprises direct 
hydrogen peroxide production from oxygen and hydrogen, using a catalyst in 
a reaction medium. Already processes for making hydrogen peroxide from 
oxygen and hydrogen using platinum group metals as the catalyst have been 
proposed, with the indication that hydrogen peroxide could be formed at 
reasonably high concentration levels [Japanese Patent Publication Nos. 
47121/1981, 18646/1980 and 23401/1989; and Japanese Patent Application 
Kokai (Laid-open) No. 156005/1988]. 
These patent publications and Kokai application disclose processes for 
making aqueous hydrogen peroxide solutions by conducting the reaction 
using as the reaction medium an aqueous solution only, which contains an 
acid and/or a halogen ion. As a process other than those, also disclosed 
is the one for conducting the reaction using a mixture, in which an 
organic solvent and water are concurrently present in the reactor. That 
is, Japanese Patent Publication Nos. 17763/1986, 29363/1987 and 30122/1987 
disclose processes for producing hydrogen peroxide comprising causing 
concurrent presence of an organic solvent having a limited miscibility 
with water and water in a reactor, whereby contacting hydrogen with oxygen 
in a bi-phase liquid mixture composed of an aqueous phase and the organic 
solvent phase. The catalyst used in these processes is homogeneously 
dissolved in the organic phase, so that the hydrogen peroxide-forming 
reaction of oxygen with hydrogen is predominantly advanced in the organic 
phase. Because the hydrogen peroxide formed in the organic phase is 
extracted into the aqueous phase, eventually an aqueous solution of 
hydrogen peroxide is obtained. 
The concentration levels of hydrogen peroxide obtainable in these 
processes, however, are not sufficient for practical use. Japanese Patent 
Application Kokai No. 192710/1989 furthermore discloses a process in which 
a solvent composed of a fluorine-containing compound and water are used to 
form a bi-phase system, the reaction being advanced in the organic phase 
in the presence of a metal catalyst supported on a hydrophobic carrier to 
separate the formed hydrogen peroxide into the aqueous phase at high 
concentration levels. This process however has such defects that the 
useful kinds of the catalyst carriers are subject to the very substantial 
limitation that they must be hydrophobic, and that the selectivity of the 
reaction is not necessarily high. Whereas, application of the acid and 
promotors, whose addition to an aqueous medium is disclosed to be 
effective to improve selectivity of the reaction in prior art references 
such as Japanese Patent Application Kokai No. 156,005/1988, to the organic 
solvent is not feasible, as they render effective performance of the 
reaction difficult. U.S. Pat. No. 3,361,533 discloses a process having an 
organic solvent containing oxygen atoms concurrently present with water in 
a reactor, but the organic solvent used in said process is miscible with 
water at optional ratios, e.g., an alcohol. According to this production 
process, the resultant aqueous hydrogen peroxide solution is a mixture 
with the organic solvent. Thus the process is subject to the defect that a 
post-treament to separate and remove the organic solvent is indispensable 
after the reaction, for obtaining aqueous hydrogen peroxide solution. 
In the art of producing hydrogen peroxide through catalytic reaction of 
oxygen with hydrogen in a reaction medium, it has heretofore been 
practiced, furthermore, to raise partial pressures of hydrogen and oxygen, 
with the view to obtain hydrogen peroxide at a high concentration by the 
reaction of short duration. However, in order to avoid explosion hazard of 
a gaseous mixture of hydrogen and oxygen, their blend ratio is restricted, 
and for increasing their partial pressure levels, the total pressure of 
the reaction system must be increased. When the total reaction pressure is 
thus increased, special care must be taken for operational safety. This 
simultaneously causes an economical problem that construction costs of the 
production equipments amount high. 
Problems to be Solved by the Invention 
The object of the present invention is to provide a process for producing 
hydrogen peroxide, which enables acquisition of high concentration aqueous 
hydrogen peroxide solution within a short reaction time, through a 
catalytic reaction of oxygen with hydrogen in an aqueous medium, under a 
relatively low pressure. 
In a process for catalytically producing hydrogen peroxide from oxygen and 
hydrogen, when water alone is used as the reaction medium, concentration 
of the aqueous hydrogen peroxide solution resulting from the reaction 
depends on the amount of the water which is used as the reaction medium. 
Whereas, an attempt to reduce the amount of water for the purpose of 
further increasing hydrogen peroxide concentration in the formed aqueous 
solution aggravates the mixing state within the reactor to reduce the 
reaction rate, rendering it impossible to acquire high concentration 
aqueous hydrogen peroxide solution. 
Means to Solve the Problems 
The present inventors have engaged in continuous studies in search of a 
process for catalytically producing hydrogen peroxide from oxygen and 
hydrogen, in which high concentration aqueous hydrogen peroxide solution 
can be obtained in a short reaction time under lower reaction pressure. As 
the result we discovered that the above object can be accomplished by 
causing concurrent presence in the reactor, with water which is the 
reaction medium, of an inflammable organic solvent having only limited 
solubility with water and, furthermore, having sufficiently lower hydrogen 
peroxide dissolving power compared to that of water. Based on this 
discovery the present invention has been completed. 
That is, the present invention provides a process for producing hydrogen 
peroxide through catalytic reaction of oxygen with hydrogen in an aqueous 
medium, the process being characterized in that an organic solvent having 
only limited solubility with water and less hydrogen peroxide dissolving 
ability than that of water is caused to be concurrently present with water 
in the reactor. 
According to the present invention, it is made possible to reduce the 
amount of water which is the reaction medium, while maintaining favorable 
state of mixing inside the reactor and without inviting reduction in the 
reaction rate, whereby enabling to raise concentration level of hydrogen 
peroxide in the resultant solution. According to the invention, an organic 
solvent which is inert to the reaction and has only limited solubility 
with water is added to the reactor, in an amount equalling to that of the 
reduced water, whereby maintaining the intended state of mixing within the 
reactor. A desired level of the reaction rate can consequently be 
maintained, and still more, due to the reduction of water in an amount 
corresponding to that of the added organic solvent in the reactor, the 
hydrogen peroxide concentration in the resultant aqueous solution 
increases in consequence. 
While the precise reaction mechanism is not fully known yet, presumably the 
stirring power finely divides and disperses the water or organic solvent, 
and in either of the cases the water in which the catalyst is uniformly 
dispersed in appearance flows throughout the whole reactor. Furthermore, 
because the total amount of the fluid is maintained constant, the 
favorable gas-liquid mixed state can be maintained. 
Moreover, generally solubility of hydrogen and oxygen in organic solvent is 
higher than that in water. Hence, the liquid-to-liquid migration of 
substances occurring as the hydrogen and oxygen, which are dissolved in 
the organic solvent, migrate through the interfaces with water also 
contributes to enhance the reaction rate. 
Still in addition, use of the organic solvent reduces surface tension of 
the liquid phase and minimizes bubble sizes of oxygen and hydrogen gases, 
whereby increasing the contacting efficiency of the oxygen and hydrogen 
gases with the liquid phase. 
The organic solvent useful for the present invention is subject to no 
limitation in kind, so long as it has only limited solubility with water 
and less hydrogen peroxide dissolving ability. A preferred solvent 
satisfies the following requirements, i.e., (1) it has only limited 
solubility with water; that is, the solubility of the solvent in water is 
not higher than 0.05 g-solvent/g-water, preferably not higher than 0.001 
g-solvent/g-water; and the solubility of water in the solvent is not 
higher than 0.5 g-water/g-solvent, preferably not higher than 0.01 
g-water/g-solvent: (2) its hydrogen peroxide-dissolving ability is 
sufficiently low compared to that of water; that is, the solubility of 
hydrogen peroxide is not higher than 0.5 g-H.sub.2 O.sub.2 /g-solvent, 
preferably not higher than 0.01 g-H.sub.2 O.sub.2 g-solvent: (3) it has 
viscosity not largely differing from that of water; that is, 0.2-50 
centipoise, preferably 0.5-20 centipoise: (5) it is inflammable; that is, 
it has flash point of no lower than 80.degree. C., preferably no lower 
than 120.degree. C.: and (6) it has high dissolving ability of oxygen and 
hydrogen. 
Examples of organic solvent which satisfies these requirements include 
halogenated organic compounds such as o-chlorobenzaldehyde, octyl bromide, 
1-bromo-3propane chloride. As preferred examples, hydrocarbons substituted 
with at least two halogen atoms such as fluorine, chlorine and bromine may 
be named, while still more preferred examples are hydrocarbons substituted 
with at least three halogen atoms, such as perchlorocarbon and 
perfluorocarbon compounds. Specific examples of perchlorocarbon compounds 
include trichloroethane and perchloroethylene. The most preferred are 
hydrocarbons substituted with at least three fluorine atoms, specific 
examples of which include Fluorinert.RTM. FC-77, Fluorinert.RTM. FC-43 and 
Fluorinert.RTM. FC-70, the commercial products of Sumitomo 3M Co. Ltd. 
Whereas, when the amounts of the total liquid (sum of organic solvent and 
water) and the catalyst are maintained constant while the ratio of the 
organic solvent to the water is varied, and the reaction is carried out 
under otherwise identical conditions, the total hydrogen consumption in 
the reaction is substantially unchanged. 
Hence, when the reaction medium consists of such an organic solvent and 
water at a ratio of 1:1, the hydrogen peroxide concentration in the 
solution formed after the reaction becomes about two times that in the 
case where water alone is used as the reaction medium. When the ratio 
between the organic solvent to water is 2:1 in the reaction medium, the 
hydrogen peroxide concentration in the formed aqueous solution, therefore, 
becomes about three times that in the case where water alone is used as 
the reaction medium. In practice, however, the reaction rate and 
selectivity cannot be completely free from the influence of hydrogen 
peroxide concentration in the aqueous solution, and in particular when a 
high concentration aqueous hydrogen peroxide solution is to be obtained, 
the concentration after the reaction is apt to deviate from the exact 
correspondence to the volume ratio between the organic solvent and water. 
From the standpoint of economy, therefore, the volume ratio of the organic 
solvent to water in the reactor is selected from the range of 5:95 to 
95:10, preferably 30:70 to 90:10, more preferably 50:50 to 0:20. 
According to the invention in which formation of high concentration aqueous 
hydrogen peroxide solution is intended, it is permissible to add a 
stabilizer of hydrogen peroxide to the water which is the reaction medium, 
with the view to inhibit decomposition. As the stabilizer, known 
water-soluble stabilizers can be used, specific examples including 
aminotri(methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic 
acid, methylenediaminetetra(methylenephosphonic acid) and their sodium 
salts, phosphoric acid, sulfuric acid, nitric acid, sodium pyrophosphate, 
etc. The amount of use of such a stabilizer is variable depending on the 
kind of the stabilizer selected and the concentration of aqueous hydrogen 
peroxide solution, while normal amount of addition of such a stabilizer in 
terms of its concentration in water is 1 to 1,000 ppm, preferably 5 to 100 
ppm. 
As the catalyst to be used in the invention, platinum group metals such as 
palladium, platinum etc. are preferred. The form of the catalyst is not 
critical so long as it is substantially hydrophilic, which may be pellet 
or powder. The term, hydrophilic catalyst, to be used in the invention 
signifies that the catalyst has the property to predominantly disperse in 
an aqueous phase, when it is added to a reaction system wherein two 
phases, viz., aqueous phase and organic phase, are present. The 
hydrophilic catalyst includes a sole platinum group metal catalyst and, 
preferably, a platinum group metal catalyst supported on a hydrophilic 
carrier. Such a catalyst supported on a hydrophilic carrier is prepared by 
supporting a platinum group metal such as palladium or platinum on 
commonly used catalyst carrier, for example, silica, titania, alumina, 
magnesia, zirconia, celia, zeolite or activated carbon, etc. in their 
commonly used form. Also a platinum group metal such as palladium or 
platinum on a resin carrier, e.g., styrene-divinylbenzene copolymer resin, 
vinyl chloride-vinyl acetate copolymer resin or porous Teflon resin, which 
has a hydrophilic surface can be used. The resin carrier is given the 
hydrophilic surface in advance of the reaction through a treatment 
comprising immersing the catalyst in a water-soluble organic solvent such 
as methyl alcohol, ethyl alcohol, etc. and thereafter substituting the 
solvent with water. The catalyst to be used in the present invention may 
comprise 0.01 to 30%, preferably 0.1 to 10% platinum group metal supported 
on a carrier such as alumina, silica, titania, magnesia, zirconia, celia, 
zeolite, activated carbon, etc. The amount of the catalyst for use is 
normally 1 to 300 grams, preferably 2 to 150 grams, per liter of the 
reaction medium. It is necessary that the catalyst be insoluble in both 
the organic solvent and water. Because the reaction takes place in 
water-phase according to the present invention, a promotor (e.g. halogen 
ion) or an acid such as sulfuric or hydrochloric acid, which are effective 
for increasing selectivity of the reaction can be added to the water, 
which is the reaction medium, at an optional ratio. In consequence of such 
an addition, high concentration aqueous hydrogen peroxide solution can be 
effectively obtained through the process of this invention. That is, the 
present invention is applicable also to those various processes which have 
heretofore been developed for catalytic production of hydrogen peroxide 
from oxygen and hydrogen, in which system water is used as the reaction 
medium. By applying the process of this invention, high concentration 
aqueous hydrogen peroxide solution can be effectively obtained. 
As the reaction apparatus for practicing the present invention, generally 
an agitation type reactor is used, but bubbling column or fluidized 
bed-type reactor or the like can also be used without limitation, so long 
as the apparatus can provide the power to sufficiently disperse the 
organic solvent and water. The hydrogen peroxide production according to 
the present invention, furthermore, is normally practiced by contacting 
oxygen and hydrogen with the catalyst, in the optional presence of an 
inert gas such as nitrogen which has no adverse effect on the intended 
reaction, under the conditions as reaction pressure ranging from 
3.times.10.sup.7 -1.5.times.10.sup.9 Pa (3-150 kg/cm.sup.2.G), preferably 
5.times.10.sup.7 -1.times.10.sup.9 Pa (5-100 kg/cm.sup.2.G), most 
preferably 8.times.10.sup.7 -5.times.10.sup.8 Pa (8-50 kg/cm.sup.2.G), at 
reaction temperature of 0.degree. C. -80.degree. C., preferably 
5.degree.-50.degree. C., and for a time ranging from 30 minutes to 6 
hours. 
Effect of the Invention 
According to the invention, a process for producing hydrogen peroxide is 
provided, which enables acquisition of high concentration aqueous hydrogen 
peroxide solution through a reaction for only a short time in which oxygen 
and hydrogen are allowed to catalytically react in an aqueous medium at a 
low reaction pressure. Consequently, the construction cost for the 
equipment is reduced, and it is made possible to effectively produce 
hydrogen peroxide.

EXAMPLES 
Hereinafter the invention is explained in further details with reference to 
working Examples and Comparative Examples, in which the reacted amount of 
hydrogen is determined by chromatographic analysis of composition of the 
gas at the exit of the reactor used. Furthermore, concentration of 
hydrogen peroxide in the reaction medium is measured by titration method 
with potassium permanganate solution which is rendered acidic by addition 
of sulfuric acid. 
Example 1 
A reaction for producing hydrogen peroxide from oxygen and hydrogen was 
conducted in the following manner. 
A 6-liter capacity SUS 316 stainless steel autoclave with a cooling jacket 
was charged with 2075 ml of Fluorinert.RTM. FC-77 (commercial name of a 
perfluoro hydrocarbon manufactured by Sumitomo 3M Co. Ltd.) as a perfluoro 
hydrocarbon. Then 692 ml of an aqueous solution, in which sodium brominate 
concentration was adjusted to 0.5 mmol/liter and sulfuric acid 
concentration, to 0.1 mol/liter, and 5 grams of a commercial 5 wt. % 
Pd-on-titania catalyst (manufactured by N. E. Chemcat Corp.) was 
suspended, was added to the autoclave, to make the total amount of the 
reaction medium 2767 ml. The autoclave was closed, and air was introduced 
thereinto at a rate of 959 Nl/hr. The pressure inside the autoclave was 
thus raised up to 9.times.10.sup.7 Pa (9 kg/cm.sup.2.G) with a pressure 
control valve. While continuously passing the air, agitation was started 
to a rate of 1500 rpm, while maintaining the reaction pressure of 
9.times.10.sup.7 Pa (9 kg/cm.sup.2.G) and the reaction temperature, at 
10.degree. C. After the reaction conditions were stabilized, gaseous 
hydrogen was passed at a rate of 60 Nl/hr for 30 minutes, to effect the 
reaction. After the 30 minutes' reaction, the hydrogen peroxide 
concentration in water was 2.48% by weight, total amount of reacted 
hydrogen was 0.71 mol, and the hydrogen selectivity was 71%. The hydrogen 
selectivity was calculated by the equation below: 
EQU Hydrogen selectivity (%)=[(amount of hydrogen peroxide formed of the 
reaction mol)-(theoretical amount of hydrogen peroxide to be formed from 
the hydrogen consumption mol)].times.100 
Fluorinert.RTM. FC-77 has solubility in water not higher than 0.01 
mg/g-water, dissolving power of hydrogen peroxide not higher than 0.015 
mg-H.sub.2 O.sub.2 / g-solvent, a viscosity of 1.4 centipoise, and has no 
flash point. 
Example 2 
Example 1 was repeated except that the amount of Fluorinert FC-77 was 
reduced to 1845 ml and that 922 ml of an aqueous solution of identical 
composition with that used in Example 1, containing as suspended therein 5 
g of a commercial 5 wt. % Pd-on-titania catalyst (manufactured by N. E. 
Chemcat Corp.) was used. After 30 minutes' reaction, hydrogen peroxide 
concentration in the water was 1.99% by weight, total amount of reacted 
hydrogen was 0.74 mol, and the hydrogen selectivity was 73%. 
Example 3 
Example 1 was repeated except that the amount of Fluorinert FC-77 was 
reduced to 1384 ml and that 1384 ml of an aqueous solution of identical 
composition with that used in Example 1, containing as suspended therein 5 
g of a commercial 5 wt. % Pd-on-titania catalyst (manufactured by N. E. 
Chemcat Corp.) was used. After 30 minutes' reaction, hydrogen peroxide 
concentration in the water was 1.42% by weight, total amount of reacted 
hydrogen was 0.76 mol, and the hydrogen selectivity was 76%. 
Comparative Example 1 
Example 1 was repeated except that Fluorinert FC-77 was not used and that 
2767 ml of an aqueous solution of identical composition with that used in 
Example 1, containing as suspended therein 5 g of a commercial 5% by 
weight Pd-on-titania catalyst (manufactured by N. E. Chemcat Corp.) was 
used. After termination of 30 minutes' reaction, hydrogen peroxide 
concentration in the water was 0.78% by weight, total amount of reacted 
hydrogen was 0.80 mol, and the hydrogen selectivity was 80%. 
Example 4 
Example 1 was repeated except that 20 g of a commercial 5 wt. % 
Pd-on-alumina catalyst (manufactured by N. E. Chemcat Corp.) was used. 
After termination of the 30 minutes' reaction, hydrogen peroxide 
concentration in the water was 2.37% by weight, total amount of reacted 
hydrogen was 0.70 mol, and the hydrogen selectivity was 69%. 
Comparative Example 2 
Example 4 was repeated except that Fluorinert FC-77 was not used and that 
2767 ml of an aqueous solution of identical composition with that used in 
Example 4, containing 20 g of a commercial 5 wt. % Pd-on-alumina catalyst 
(manufactured by N. E. Chemcat Corp.) was used. After termination of 30 
minutes' reaction, the hydrogen peroxide concentration in the water was 
0.79 wt. %, total amount of reacted hydrogen was 0.79 mol, and the 
hydrogen selectivity was 81%. 
Example 5 
Example 1 was repeated except that the amount of Fluorinert FC-77 was 
increased to 3458 ml to make the total amount of the reaction medium 4150 
ml. After termination of the 30 minutes' reaction, hydrogen peroxide 
concentration in the water was 3.51% by weight, the total amount of 
reacted hydrogen was 1.05 mols, and the hydrogen selectivity was 68%. 
Comparative Example 3 
Example 5 was repeated except that Fluorinert FC-77 was not used and that 
4150 ml of an aqueous solution of identical composition with that used in 
Example 5, containing as suspended therein 5 g of a commercial 5 wt. % 
Pd-on-titania catalyst (manufactured by N. E. Chemcat Corp.) was used. 
After the 30 minutes' reaction, hydrogen peroxide concentration in the 
water was 0.80% by weight, the total amount of reacted hydrogen was 1.19 
mols and the hydrogen selectivity was 82%. 
Example 6 
Example 5 was repeated except that the reaction was continued for 1.5 
hours. After termination of 1.5 hours' reaction, hydrogen peroxide 
concentration in the water was 7.66% by weight, the total amount of 
reacted hydrogen was 2.84 mols, and the hydrogen selectivity was 55%. 
Comparative Example 4 
Example 6 was repeated except that Fluorinert FC-77 was not used, and that 
4150 ml of an aqueous solution of identical composition with that used in 
Example 6, containing as suspended therein 5 g of a commercial 5 wt. % 
Pd-on-titania catalyst (manufactured by N. E. Chemcat Corp.) was used. 
After the 1.5 hours' reaction, hydrogen peroxide concentration in the 
water was 1.92% by weight, the total amount of reacted hydrogen was 3.01 
mols and the hydrogen selectivity was 78%. 
Example 7 
Example 1 was repeated except that aminotri (methylenephosphonic acid) was 
added to the aqueous solution at a concentration of 75 ppm. After the 30 
minutes' reaction, hydrogen peroxide concentration in the water was 2.62% 
by weight, the total amount of reacted hydrogen was 0.65 mol, and the 
hydrogen selectivity was 82%. 
Example 8 
Example 1 was repeated except that Fluorinert FC-77 was replaced by 
perchloroethylene (manufactured by Kanto Kagaku K. K.). After the 30 
minutes' reaction, hydrogen peroxide concentration in the water was 2.44% 
by weight, the total amount of reacted hydrogen was 0.68 mol, and the 
hydrogen selectivity was 73%. 
The perchloroethylene used has a solubility in water not higher than 0.01 
mg/g-water, a dissolving power of hydrogen peroxide not higher than 0.015 
mg-H.sub.2 O.sub.2 / g-solvent, a viscosity of 0.88 centipoise, and has no 
flash point. 
Example 9 
An aromatic adsorbent resin manufactured and sold by Mitsubishi Kasei Kogyo 
Corp. under the commercial name of HP20 (styrene-divinylbenzene copolymer; 
particle size, 0.2-1 mm; specific surface area, 605 m.sup.2 /g; true 
specific gravity, 1.01; water content, 56.3 wt. %) was washed with 
methanol and 30% aqueous hydrogen peroxide solution, and dried in vaquo. 
The dried resin was swollen with chloroform, impregnated with palladium 
acetate/chloroform solution, vacuum-dried, and reduced with hydrogen in 
gaseous phase at 100.degree. C. to provide a hydrophobic 1% Pd/HP20 
catalyst. The catalyst was rendered hydrophilic by the following method: 
the hydrophobic 1% Pd/HP20 was washed with methanol, causing sufficient 
swelling to wet inside of the pores; then the methanol was substituted 
with a large quantity of water and the system was filtered to provide a 
hydrophilic 1% Pd/HP20 catalyst. 
Example 1 was repeated except that 40 g of the above catalyst was used 
instead of the Pd-on-titania catalyst. The catalyst before initiation of 
the reaction dispersed in the aqueous phase. After the 30 minutes' 
reaction, hydrogen peroxide concentration in the water was 2.04% by 
weight, the total amount of reacted hydrogen was 0.50 mol, and the 
hydrogen selectivity was 83%. After termination of the reaction, the 
catalyst still remained in the aqueous phase. 
Comparative Example 5 
Example 9 was repeated except that the hydrophobic 1% Pd/HP20 catalyst as 
prepared by the method described in Example 9 was used without the 
preceding treatment for rendering it hydrophilic. The catalyst before 
initiation of the reaction dispersed in the Fluorinert FC-77 phase. After 
the 30 minutes' reaction, hydrogen peroxide concentration in the water was 
0.62% by weight, the total amount of reacted hydrogen was 0.35 mol, and 
the hydrogen selectivity was 36%.