J. Plasma Fusion Res. SERIES, Vol. 9 (2010)

Development of Pt/ASDBC Catalyst Applicable for Hydrogen Oxidationin the Presence of Saturated Water Vapor at Room Temperature
Yasunori IWAI, Katsumi SATO and Toshihiko YAMANISHI
Tritium Technology Group, Japan Atomic Energy Agency
Tokai - mura, Naka - gun, Ibaraki - ken 319-1195 Japan(Received: 27 October 2009 / Accepted: 9 April 2010)

Combined catalytic recombiner and water absorber system has been applied in a tritium handling facility toremove tritium as well as other tritiated components in the atmosphere of a containment. It has been known that thehydrogen oxidation performance of the catalyst packed in the catalytic recombiner considerably decreased at room
temperature in the case where the concentration of water vapor is very large. We have developed some hydrophobic
Pt catalysts applicable for hydrogen oxidation even in the presence of saturated water vapor at room temperature. A
new type of hydrophobic catalyst, Pt/ASDBC, has been prepared by depositing platinum on alkyl-styrene
diviyl-benzene copolymer (ASDBC). Pt/ASDBC is more hydrophobic than Pt/SDBC that is the standard catalyst
for a water detritiation system. Oxidation tests of the catalysts using 10000 ppm of hydrogen were performed in thepresence of saturated water vapor at room temperature. Hydrogen oxidation more than 99% was achieved using
Pt/ASDBC catalyst in the range of space velocity from 320 to 3300 h-1. Moreover, radiation technology was applied
to extend the pore size of catalyst. Hydrogen oxidation performance has been much improved with Pt/ASDBC
catalyst irradiated with electron beams.
Keywords: Fusion, Tritium, Detritiation, Electron beams, Pore size, SDBC, ASDBC, Hydrophobic
catalyst, Platinum, Kogel

electric insulation gas for a negative bream injector in afusion plant [7]. Negative poisoning of catalyst wasobserved in the presence of SF6. Regarding water impact,
it has been known that the hydrogen oxidation
performance of the catalyst is decreased in the case where
the concentration of water vapor is very large. The
decrease in hydrogen oxidation performance in thepresence of water vapor has been explained as the waterlayers formed on the noble metal plays the obstructionrole of hydrogen transport onto noble metal. Moreover,efficient hydrogen oxidation performance at room
temperature is strongly required taking an accident in afusion plant into consideration. The realization ofhydrophobic catalyst with an efficient hydrogen oxidation
performance at room temperature even in the presence of
saturated water vapor can also reduce the operating costof catalytic recombiner significantly. Hence, hydrophobic
catalysts have been attracted. Over 100 catalysts withhydrophobic properties have been prepared especially forthe catalysts of the hydrogen-liquid water isotopic
exchange reactions [8,9]. The conventional hydrophobic
catalysts were roughly divided into two catalysts, thatwere coating of the supported platinum catalysts (e.g. Pt/
ǩ Al2O3, Pt/Carbon) with polytetrafluoroetylene andsupporting Pt directly on styrene diviyl-benzene

1. Introduction

In a tritium handling facility, tritium or tritiatedcomponents in the atmosphere of a containment shouldbe efficiently eliminated. Combined catalytic recombiner
and water absorber system has been applied to remove
tritium as well as other tritiated components in theatmosphere of a containment [1]. The typical operating
temperatures of catalytic recombiners for the oxidationsof hydrogen and tritiated organic compounds were 473
and 773K, respectively [1]. Industrial mature designs of
the system are available for a large containment [2].
Recent investigation by Uda et al. indicated thathoneycomb types of catalyst were a viable alternative toconventional particle catalyst due to its superior
low-pressure drop characteristics [3].
Hydrogen oxidation has occurred on the catalytic
reacting surfaces coated with platinum or palladium.
Hydrogen oxidation reaction normally occurs in a wider
species concentration range and over longer times than it
would be with a gas combustion [4]. As for a possible
poisoning of catalyst, many studies have focused on thehydrogen oxidation performance in the presence of CO,
CO2, and methane [5,6]. Kobayashi et al. investigated the
poisoning of catalyst by SF6 that has been used as an
author’s e-mail:iwai.yasunori@jaea.go.jp332©2010 by The Japan Society of Plasma
Science and Nuclear Fusion Research

Y. Iwai et al., Development of Pt/ASDBC Catalyst Applicable for Hydrogen Oxidation in the Presence of Saturated Water Vapor at Room Temperature

copolymer (Pt/SDBC). Chung et al. investigated thehydrogen oxidation performance of a Pt/SDBC catalysts
in the presence of water vapor in the temperature range
from 303 to 353K [10]. The reported conversion ratio ofhydrogen to water for the Korean Pt/SDBC catalyst at
303K was less than 10%. Hence, experiments have been
carried out especially for the development andimprovement of hydrophobic Pt/SDBC catalyst to haveefficient hydrogen oxidation performance at around room
temperature even in the presence of saturated water
vapor.
The rate-controlling step of hydrogen oxidation
reaction using a catalyst is generally pore diffusion.
Hence, radiation technology was also applied to the
Pt/SDBC and our developed Pt/ASDBC catalysts for the
purpose to extend the pore size of catalyst.
The paper describes the availability of newly
developed hydrophobic catalyst for hydrogen oxidationeven in the presence of saturated water vapor at aroundroom temperature.

Fig.1 Appearance of Pt/ASDBC catalysts

2. Experimental
Fig.2

Superior water repellence of Pt/ASDBC
catalyst
molecular structure. An appearance is shown in Fig. 1. Afeature of ASDBC was its fine mesoporosity. The
mesopore distribution of ASDBC had a keener peek thanthat of SDBC. The mesopore diameter of ASDBC at thepeek top was 163 nm. Pt/ASDBC manufactured for thistest was 0.5 wt.% Pt/ASDBC particles. The mode ofparticles’ diameter was 3.0mm. The packed density was
0.20g/mL. The specific surface area and accumulated
pore volume were 57.9m2/g and 1.49cm3/g, respectively.
The deposited platinum of the Pt/ASDBC catalyst was
1.0 g/L. This value was approximately half of the tested
commercial Pt/SDBC catalyst. Superior water repellenceof Pt/ASDBC catalyst is shown in Fig. 2.
In this study, irradiation of the 0.5 wt.% Pt/SDBC
and 0.5 wt.% Pt/ASDBC with electron beams at room
temperature up to 1500 kGy was conducted for the
purpose to extend the pore size of catalyst at theequivalent dose rate to 600 kGy/h using the electron
accelerator No.1 facility of the Cockcroft-Walton type in
Takasaki Advanced Radiation Research Institute of JAEA
under the conditions of the beam energy of 1.99 MeV andthe beam current of 2.00 mA. Each catalyst enclosed in alaminate film bag under vacuum was irradiated. A
sufficient long interval for every 50 kGy irradiation was
taken to prevent the temperature rising of the catalyst.
The Pt/SDBC irradiated to 1250KGy and Pt/ASDBC
irradiated to 1500kGy were adopted in this study.

2.1 Catalysts
Three kinds of platinum deposited catalysts havebeen developed for efficient hydrogen oxidation in thepresence of water vapor at 293K. Reactivity of thesecatalysts were compared with that of a conventional Pt /ǩAl2O3 and Pt/SDBC catalysts. Pt /ǩAl2O3 used in thistest was commercial 0.5 wt.% Pt / ǩ Al2O3 pellets
manufactured by N. E. Chemcat cooperation, Japan. A
pellet was Ǿ3mm x 3mm. A commercial Pt/SDBC usedin this test was 0.5 wt.% Pt/SDBC particles, that havebeen called Kogel catalyst, manufactured by Showa
Engineering Co. LTD., Japan [11]. The mode of particles’
diameter was 3.0mm. The packed density was 0.22g/mL.
A mercury porosimeter (Model Poresizer 9320,
Micromeritics, U.S.A.) was used for determining specificsurface area and pore size distribution of catalytic
materials. This mercury porosimeter can determine thepore size distribution from 350 microns to about 7 nm.
The specific surface area and accumulated pore volumeof 0.5 wt.% Pt/SDBC particles were 364.4m2/g and1.79cm3/g, respectively. The peak top of pore diameter
evaluated by mercury intrusion porosimetry was 61nm.
The deposited platinum of the Pt/SDBC catalyst was 1.8
g/L.
A new type of hydrophobic catalyst, Pt/ASDBC, hasbeen prepared by dipositting platinum on alkyl-styrene
diviyl-benzene copolymer (ASDBC). Pt/ASDBC is morehydrophobic than SDBC due to the intended
incorporation with hydrophobic alkyl-groups in the333

Y. Iwai et al., Development of Pt/ASDBC Catalyst Applicable for Hydrogen Oxidation in the Presence of Saturated Water Vapor at Room Temperature

space velocity, SV (h-1), was defined by the following
equation:
SV = Q/Vcat(2)
where Vcat and Q were the volume of catalyst (cm3) andthe volumetric flow rate (cm3-STP/h), respectively.

2.2 Hydrogen Oxidation Performance Test
The experimental apparatus is shown in Fig. 3. Anexperimental gas mixture containing approximately
10000ppm of hydrogen in dry air (21%O2 and 79% N2)
was fed to the reactor packed platinum catalysts. The
water vapor concentration of the experimental gas was
negligibly small. The flow rate of a gas was controlledwith a gas flow controller (8300MC, KOFLOC, Japan).
The inner diameter and length of the catalytic reactor
were 56.5mm and 150mm, respectively. The catalytic
reactor was not thermally insulated. The temperature ofcatalyst was monitored with a thermocouple. The
oxidation tests were carried out at room temperaturearound 293K. The pressures at the inlet and outlet of thereactor were measured with Baratron pressure gauges(Type 626, MKS, Japan). The water concentration at the
inlet of the reactor was measured with a capacitance-type
dew point hygrometer (M Series [dew point: 213-293 K],
Panametrics, Japan). The process gases were sampled at
the inlet and outlet of the reactor and the concentrationsof hydrogen were measured using a micro gas
chromatograph with a thermal conductivity detector(Micro-GC CP-2002, CHROMPACK, Holland). The
detectable sensitivity of hydrogen with the micro gas
chromatograph was more than 10ppm. When thereactivity of a platinum catalyst in the presence of water
was investigated, an experimental gas with saturated
water vapor was made by passing the experimental gas
through two water bubblers and a water mist trap in series.
In this case, the water vapor in the process gas discharged
from the reactor was removed by passing two silica gel
absorbers in series prior to the sampling of process gas.
The conversion factor of hydrogen oxidation, CF (-),
was defined by the following equation:

2.3 Thermal Stability Test
Thermogravimetric analysis (TGA) of catalytic
materials was carried out on a TG-DTA-2000S analyzer(Mac Science, Japan). Since the non-repeatable results
due to combustion of the catalysts in air obscured thedifference of thermal stability, helium atmosphere wasselected to prevent any combustion of the sample and any
adsorption of moisture. The repeatable results obtained ina helium atmosphere showed clearly the difference ofthermal stability between Pt/SDBC and Pt/ASDBC. An
aluminum pan was used for each sample, and it was
flamed prior to each analysis. The weight of a sample
was approximately 6.0 mg. The temperature ramp rate
was 1 K/min.

3. Results and Discussion
3.1 Hydrogen Oxidation Performance of Pt/ASDBC
catalyst
The CF v.s. SV for tested platinum catalysts in theabsence of water vapor in the experimental gas at 293K
was shown in Table 1. The CF for hydrophilic Pt /ǩ
Al2O3 catalyst was quite low even in the absence of water
vapor at 293K. The gradual decrease in reactivity wasobserved for Pt /ǩAl2O3 catalyst. The low reactivity wasobserved especially at approximately 250 h-1 of SV. At
the low SV, it was pointed out that the laminar layer
resistance decreased in reactivity [12]. Moreover, thedeactivation by adsorption of produced water moleculeson platinum surface should be considered. Small part of
the adsorbed water molecules was purged from theplatinum surface with a dry air. However in the light ofour previous study on the water desorption from porousaluminate materials, it is quite difficult to remove most ofadsorbed water molecules from platinum surface with a
dry air of low SV [13, 14]. The heat of reaction led to thetemperature increase of up to 3 K in the Pt /ǩAl㧞O㧟
catalyst bed. The CFs for Pt/SDBC and Pt/ASDBC
were more than 1000. The CF more than 1000 indicated

CF = Cin/Cout(1)
where Cin and Cout were the hydrogen concentrations at
the inlet and the outlet of the reactor, respectively. The
T
P
HM
Catalytic
ReactorDry line
Wet line

H2: 10000ppm + Air

MFC

HM
P

Water
Mist
Bubbler Separator

Dehumidifier(Silica gel)
Gas sampling line
Gas sampling line
Micro-GC Analyzer

Table 1 Conversion factor v.s. space velocity in theabsence of water vapor at 293K

MFC: Gas flow controller, P: Pressure gauges, HM: Hygrometer, T:
Temperature monitor, Micro-GC: Micro gas chromatograph with athermal conductivity detector

Catalyst
Pt /ǩAl2O3
Pt/SDBC
Pt/ASDBC

Fig. 3 Experimental apparatus for Hydrogen Oxidation
Performance Test

334

SV=294 h-1
9.51
>1000

Conversion Factor
SV=588 h-1 SV=1176 h-1
4.53
4.69
>1000
>1000
>1000

SV=2941 h-1
3.75
>1000

Y. Iwai et al., Development of Pt/ASDBC Catalyst Applicable for Hydrogen Oxidation in the Presence of Saturated Water Vapor at Room Temperature

3.2 Effect of Irradiation on the Hydrogen Oxidation
Performance of Pt/ASDBC
Figure 4 shows the CF v.s. SV for irradiatedplatinum catalysts in the presence of saturated water
vapor in the experimental gas at 293K. The validity ofradiation technology was well demonstrated. Radiation
technology was applied to extend the pore size of catalyst,
since the rate-controlling step of hydrogen oxidation
reaction is generally pore diffusion. Hydrogen oxidation
performance has been much improved with Pt/ASDBC
catalyst irradiated with electron beams. Figure 5 shows
the pore size distribution of unirradiated catalytic
materials measured by mercury porosimeter. A feature ofthat the hydrogen was practically not detected in thesample gas from the outlet of the catalytic reactor by amicro gas chromatograph. The key factor to achieve sucha large CF was the water repellence of the polymers. The
deactivation by adsorption of produced water moleculeson platinum surface was negligibly small. The heat ofreaction led to the temperature increase of up to 10 K in
the Pt/SDBC and Pt/ASDBC catalyst beds due to highreactivity.
The CF v.s. SV for tested platinum catalysts in thepresence of saturated water vapor in the experimental gas
at 293K is shown in Table 2. In the presence of water
vapor, the CF for hydrophilic Pt /ǩAl2O3 catalyst wasconsiderably low. The increase of temperature was notobserved in the Pt /ǩAl㧞O㧟 catalyst bed. Pt /ǩAl2O3
catalyst cannot be applied as hydrogen oxidation catalyst
for a catalytic recombiner operated at room temperature.
On the other hand, Pt/SDBC and Pt/ASDBC maintain alarge CF even in the presence of saturated water vapor.
Although the deposited platinum used to prepare
Pt/ASDBC catalyst was reduced to 1.0 g/L which value
was approximately half of a commercial Pt/SDBC
catalyst, hydrogen oxidation more than 99% wasachieved using Pt/ASDBC catalyst in the range of SV
from 320 to 3300 h-1.The increase in CV was evaluatedespecially for Pt/SDBC catalyst even as the SV wasincreased. The CF is generally decreased as the SV isincreased. The primary consideration in understanding
this increase of CV should be the thermal effect. The
increase in CV must be due to the temperature rising byheat of reaction, since the Pt/SDBC and Pt/ASDBC
catalyst have high reactivity. The increase in temperature
was measured as the SV was increased. At the SV=1290
h-1, the temperature increase reached 12 K in the
Pt/SDBC catalyst bed. ASDBC is more hydrophobic than
SDBC and has superior water repellence. Hence, the CF
of Pt/ASDBC at the lower SV was significantly improved
as expected. The decrease in adsorption of produced
water molecules on platinum surface was achieved. This
result reveals our developed Pt/ASDBC is a promisingcatalyst for a catalytic recombiner operated at room
temperature.

㪐㪐㩼



㪐㪇㩼

㪇㩼











Fig. 4 Conversion factor v.s. space velocity forirradiated platinum catalysts in the presence of
saturated water vapor at 293K.

ً; Pt/ǩAl2O3 [Pt:5.3g/L],
٨; Pt/SDBC [Pt:1.8g/L],
٤; Pt/SDBC (Irradiated to 1250kGy with EBs)[Pt:1.8g/L],‫ ;ع‬Pt/ASDBC [Pt:1.0g/L],‫ ;غ‬Pt/ASDBC(Irradiated to 1500kGy with EBs)[Pt:1.0g/L].

Intrusion volume [cc/g]

6Conversion Factor
SV=1290 h-1
SV=3226 h-1
1.08
1.27
130.70228.75202.40127.00Pt/ASDBC

5
Pt/SDBC

4
3
Pt/SDBC

2

Pt/ASDBC

1
0

1

10

100

1000

Pore diameter [nm]Differential pore volume [cc/g log A]

Pt /ǩAl2O3
Pt/SDBC
Pt/ASDBC

SV=323 h-1
1.70
37.00
91.45





Table 2 Conversion factor v.s. space velocity in thepresence of saturated water vapor at 293K
Catalyst

Hydrogen
Oxidation
Efficiency
㪐㪐㪅㪐㩼

10000

Fig. 5 Pore size distribution of unirradiated catalytic
materials measured by mercury porosimeter.

335

Y. Iwai et al., Development of Pt/ASDBC Catalyst Applicable for Hydrogen Oxidation in the Presence of Saturated Water Vapor at Room Temperature

ASDBC is similar to that of SDBC. It is reasonable tosuppose that the degradation in mechanical strength ofirradiated ASDBC is similar to that of SDBC. The resultof degradation in mechanical strength of irradiated SDBC
strongly supports that radiation technology is applicable
to improve the hydrogen oxidation performance of
Pt/SDBC and Pt/ASDBC catalysts.

Table 3 Specific surface area and pore size distributionof catalytic materials
Catalyst

Irradiation

unirradiated1250kGy
unirradiatedPt/ASDBC
1500kGy
Pt/SDBCSpecific
Surface[m2/g]
364.4
77.2
57.9
43.4

Peak Top Accumulated
Diameter Pore Volume[nm][mL/g]
61
1.79
240
1.84
163
1.49
170
1.55

Load at break [N]unirradiated Pt/ASDBC catalyst is a designed fine poresize distribution and larger peak top pore diameter thanthat of unirradiated Pt/SDBC. The peak-top pore diameterof unirradiated Pt/ASDBC catalyst can be controlled to
be in the range from 100 to 220 nm. The manufacturingof ASDBC beads needs a lot of know-how. We haveestablished the fabrication technology of ASDBC beads
ranged from 1.0 to 5.0mm in diameter. Specific surface
area and pore size distribution of catalytic materials areshown in Table 3. It is clear that irradiation of Pt/SDBC
catalyst with electron beams caused a considerable
enlargement of peak-top pore diameter and the following
decrease in specific surface area. Though unirradiatedPt/ASDBC has originally fine pore size distribution andlarger peak top pore diameter than that of unirradiatedPt/SDBC, enlargement of peak top pore diameter and thefollowing decrease in specific surface area of irradiatedPt/ASDBC was also measured as expected. The
rate-controlling step of hydrogen oxidation reaction is
generally pore diffusion. The improvement of hydrogenoxidation performance of irradiated Pt/SDBC andirradiated Pt/ASDBC was due accordingly to theenlargement of pore size by irradiation.
The degradation in mechanical strength of irradiated
SDBC series catalysts is a debatable point that should becleared. Figure 6 shows the result of compression test ofirradiated Pt/SDBC catalyst based on Japanese Industrial
Standard K 6254-1993 using a PC-controlled Strograph
VE5D (Toyoseiki Co. Ltd., Japan). The crosshead speed
adopted was 10mm/min. SDBC beads with 5.0mm ofdiameter was selected. Multiple measurements using
more than 5beads were made on all conditions. SDBC
beads with 5.0mm of diameter had an increase inmechanical strength with increase in radiation dose. Bothchain scission and bridging were admittedly competingfor the structural change of the beads by irradiation. The
reason for the increase in load at break is that the bridgesof the polymer were predominant over chain scission on
the structural change of polystyrene divinyl- benzene
beads by irradiation. The degradation in mechanicalstrength of irradiated ASDBC beads was not tested withthe same method due to the insufficient amount of
catalyst available for the test. The backbone structure of

50
45
40
35
30
25
20
15
10
5
0

0

500

1000

1500

2000

2500

Dose [kGy]Fig.6 Result of compression test of irradiatedPt/SDBC catalyst

3.3 Thermal Stability of Irradiated Pt/ASDBC
Catalyst
The intended incorporation with hydrophobic
alkyl-groups in the molecular structure of ASDBC
suggests the degradation in thermal stability of
Pt/ASDBC catalyst by comparison with Pt/SDBC catalyst.
Figure 7 shows the result of thermogravimetric analysis
of catalytic materials in a helium atmosphere. Slightdecrease in thermal stability was observed for Pt/ASDBC
catalyst by comparison with Pt/SDBC catalyst as
expected. Unirradiated Pt/SDBC is the standard catalyst
100

TG [%]

80

60

40

Pt/SDBC - unirradiatedPt/SDBC -1250 kGy

20

Pt/ASDBC - unirradiatedPt/ASDBC - 1500 kGy

0
473

523

573

623

673

723

773

Temperature [K]Fig. 7 Result of thermogravimetric analysis of
catalytic materials.

336

Y. Iwai et al., Development of Pt/ASDBC Catalyst Applicable for Hydrogen Oxidation in the Presence of Saturated Water Vapor at Room Temperature

for a water detritiation systemnormallyoperated at 343 K.
The thermal stability of unirradiated Pt/SDBC has been
acceptable for the use in a tritium facility. Hence, it isreasonable to suppose that such a slight decrease inthermal stability of irradiated Pt/ASDBC is not a
debatable issue against its validity as a promising catalyst
for a catalytic recombiner operated at room temperature.
Moreover, negligible decrease in thermal stability wasobserved for irradiated catalyst by comparison withunirradiated catalyst. This result strengthens ourunderstanding that irradiated catalysts are also promisingcatalysts for a catalytic recombiner operated at room
temperature.

(2005).
[10] H. Chung et al., Fusion Sci. Technol. 56, 141 (2009).
[11] Y. Iwai et al., Fusion Sci. Technol. 41, 1126 (2002).
[12] M. Kinoshita et al.,”Preliminary Design Study ofcatalytic Oxidation Reactor in Tritium Removal System”,
JAERI-M 8612 (1979), Japan Atomic Energy ResearchInstitute.
[13] Y. Iwai et al., Journal of Physics and Chemistry of Solids
70, 881 (2009).
[14] Y. Iwai et al., J. Nucl. Sci.Technol. 45, 532 (2008).

4. Conclusions

We have developed some hydrophobic Pt catalysts
applicable for hydrogen oxidation in the presence of
saturated water vapor at room temperature. A new typeof hydrophobic catalyst, Pt/ASDBC, has been preparedby dipositting platinum on alkyl-styrene diviyl-benzene
copolymer (ASDBC). Pt/ASDBC is more hydrophobic
than Pt/SDBC that is a promising catalyst for a water
detritiation system. The deposited platinum used toprepare Pt/ASDBC catalyst was 1.0 g/L. The value wasapproximately half of a commercial Pt/SDBC catalyst.
Oxidation tests of the catalysts using 10000 ppm ofhydrogen were performed in the presence of saturated
water vapor at room temperature. Hydrogen oxidation
more than 99% was achieved using Pt/ASDBC catalyst in
the range of space velocity from 320 to 3300 h-1.
Moreover, radiation technology was applied to extend thepore sizeof catalyst, since the rate-controlling step ofhydrogen oxidation reaction is pore diffusion. Hydrogenoxidation performance has been much improved with
Pt/ASDBC catalystirradiated with electron beams.

Acknowledgments

Part of this work has been carried out through the funding
support from MEXT/Japan for 2 years of FY2009-2010(KAKENHI; Grant-in-Aid for Young Scientist (B),No.21760699). The authors wish to acknowledge thisfunding support.
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337