Mesoporous carbon supported platinum nanocatalyst: Application for hydrogen production by HI decomposition reaction in S-I cycle

Article abstract of DOI:10.1166/jnn.2017.12812

Platinum supported on carbon as a catalyst is widely reported and have a wide range of applications ranging from fuel cell application to hydrogenation reactions, where structure and properties of carbon support play an important role in the functioning of the catalyst. Mesoporous carbon supported platinum nanocatalyst was synthesized by hard templating route using mesoporous silica as template. The catalyst prepared has been characterized by X-ray diffraction, Raman, SEM, TEM, XPS and BET surface area. This catalyst has been employed for liquid phase HI decomposition reaction of sulfur iodine thermochemical cycle for production of hydrogen. The catalyst was evaluated for its activity for HI decomposition reaction and stability in the reaction environment. From present study we conclude that Pt supported on mesoporous carbon is a suitable and stable catalyst for liquid phase HI decomposition reaction.

Full text of DOI:10.1166/jnn.2017.12812

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Nanoscience and Nanotechnology
Vol. 17, 2177–2184, 2017
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Mesoporous Carbon Supported Platinum Nanocatalyst:
Application for Hydrogen Production by
HI Decomposition Reaction in S–I Cycle
Deepak Tyagi, Salil Varma∗, and Shyamala R. Bharadwaj
Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
Platinum supported on carbon as a catalyst is widely reported and have a wide range of applications
ranging from fuel cell application to hydrogenation reactions, where structure and properties of car-
bon support play an important role in the functioning of the catalyst. Mesoporous carbon supported
platinum nanocatalyst was synthesized by hard templating route using mesoporous silica as tem-
plate. The catalyst prepared has been characterized by X-ray diffraction, Raman, SEM, TEM, XPS
and BET surface area. This catalyst has been employed for liquid phase HI decomposition reaction
of sulfur iodine thermochemical cycle for production of hydrogen. The catalyst was evaluated for its
activity for HI decomposition reaction and stability in the reaction environment. From present study
we conclude that Pt supported on mesoporous carbon is a suitable and stable catalyst for liquid
phase HI decomposition reaction.
IP: 95.85.71.227 On: Mon, 08 Jul 2019 12:26:19
Keywords: Pt Catalyst, Mesoporous Carbon, S–I Cycle, HI Decomposition.
Copyright: American Scientific Publishers
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1. INTRODUCTION
from water. Apparently the most straight forward method
can be direct thermal decomposition of water as shown
The search for advance materials for application in alter-
nate energy systems has been the focus of research for
materials scientists in recent time. It is due to two obvious
reasons, first the limited supply of the existing resources
which cannot meet the energy demand of future. Sec-
ond being the growing concern over environmental issues.
These two have paved the path for research in area of
alternate sources or processes with lower carbon foot print.
Hydrogen energy is considered as the best among the
other candidates which can provide clean energy. The only
requirement for this is large scale production of hydrogen
in an environment friendly methodology. In spite of being
one of the most abundant element on earth, hydrogen in
not freely available as a carrier of energy. Two most com-
mon sources for production of hydrogen can be fossil fuels
and water. Out of these two sources, hydrogen production
is primarily based on either cracking or steam reform-
ing of hydrocarbons obtained from fossil fuels. But these
technologies have their own limitation in terms of envi-
ronmental impact and the limited supply of raw materials.
Therefore the ultimate way out is production of hydrogen
below
ꢀ
H2O→H2 +0ꢁ5O2
But this is not feasible practically dueꢀ to high tem-
perature requirement in excess of 2500 C. The others
methods for production of hydrogen from water are elec-
trolysis, photo electrochemical methods, photo catalytic
methods, biological methods and thermochemical cycles
etc.1 Thermochemical cycles produce hydrogen through
a set a chemical reactions by directly using heat from
nuclear reactor or solar concentrator.2–4 Due to this direct
utilization of heat these cycles can have better efficien-
cies. Hundreds of such cycles have been proposed and
tested worldwide, with some examples being Sulfur Iodine
Cycle,5 Copper-Chlorine Cycle,6 Hybrid Sulfur Cycle etc.
Sulfur Iodine Cycle (S–I Cycle) is one of the most promis-
ing processes for large scale production of hydrogen from
water. It decomposes water into hydrogen and oxygen
through the three reactions as shown in Figure 1.
As one can see from Figure 1, HI decomposition into
Hydrogen and iodine is an integral part of the S–I cycle.
This reaction is also an integral step of some other
iodine based cycles like Magnesium Iodine Cycle etc.7ꢂ8
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2017, Vol. 17, No. 3
1533-4880/2017/17/2177/008
doi:10.1166/jnn.2017.12812
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Mesoporous Carbon Supported Platinum Nanocatalyst: Application for Hydrogen Production
Tyagi et al.
For the synthesis of catalyst 2 g of the prepared silica
template was mixed with 2 g of sucrose and 4.2 ml chloro-
platinic acid (1% solution) in 5.8 ml of water in a round
bottom flask and stirred for 6 h and left overnight. The
ꢀ
paste obtained in this process was fiꢀrst dried at 100 C
for 6 h and then carbonized at 160 C for another 6 h.
The powder thus obtained was mixed with 1.6 g sucrose
in 10 ml of water. After which the process of stirring and
drying was repeated. The powder so obtained was heated
at 800 ꢀC under Nitrogen flow for 3 h. Subsequently noble
metal was reduced by heating under hydrogen flow at
300 ꢀC for 3 h. After reduction of noble metal, removal of
silica was carried out by suspending the mixture in 20 ml
of 40% hydrofluoric acid and stirring overnight at room
temperature. The final product was filtered, washed thor-
Figure 1. Schematic presentation of S–I Cycle.
ꢀ
oughly several times and dried at 80 C.
HI decomposition reaction is thermodynamically limited
reaction and it requires a catalyst to achieve workable reac-
tion rates.9
2.2. Characterization
The powder X-ray diffraction patterns of fresh as well as
used catalysts were recorded on Philips Analytical Diffrac-
tometer in the range 20 to 70ꢀ 2ꢃ values (Using Ni fil-
tered Cu Kꢄ radiation). The surface morphologies and
particle size were studied using Seron AIS 2100 and Zeiss
Scanning electron microscope and Transmission Electron
Microscope. The BET surface area of the catalysts by
N2 adsorption method and noble metal dispersion by
CO chemisorption was determined by using Micromerit-
Presence of iodine in HI makes the process even less
efficient. To improve overall efficiency of the process vari-
ous options have been tried. Some typical examples are use
of phosphoric acid,10 electro–electro dialysis concentration
method,11ꢂ12 use of silica membrane reactor13 and reactive
distillation method.14 For decomposition of HI after any of
the above process, a noble metal based catalyst is required.
Metals like Ni15ꢂ16 and Pd has also been used for this
reaction but mainly Pt based catalysts have been used for
HI decomposition, with oxides like alumina,17 ceria,18ꢂ19
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ics ASAP 2010 Surface Area and Porosity Analyser. Sur-
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ceria-zirconia,20 zirconia21 and carbon supports. Delivered by Ingenta
22ꢂ23
face characterisation was carried out using XPS system by
SPECS, Germany, employing Al X-ray source for excita-
Platinum is one of the most used metals as catalyst,
but its cost is very high. Therefore it is desirable to
disperse small amount of platinum in form of nanoparti-
cles on a high surface area support to increase the activ-
ity of the catalyst and minimize its cost. Supported Pt
nanocatalysts have wide range of applications like proton
exchange membrane fuel cell (PEMFC),24 dehydrogena-
tion of hydrocarbons,25–27 automobile exhaust conversion,
carbon monoxide oxidation28 etc.
In this work, we report the preparation of platinum
based catalyst supported on mesoporous carbon which was
derived by mesoporous silica template using hard tem-
plating route. The catalyst was evaluated for its catalytic
activity and stability for HI decomposition reaction.
tion. The amount of noble metal in the reflux was deter-
mined by using Horiba Jobin Vyon JY 2000 ICP-AES
instrument.
2.3. Catalyst Activity and Stability Test
The prepared catalyst was evaluated for its catalytic activ-
ity for liquid phase HI decomposition reaction. For carry-
ing out the reaction a reflux setup as shown in Figure 2
was used. First of all 250 mg of the catalyst was taken
in the round bottom flask along with 50 ml of 27% of
hydriodic acid. The mixture was heated under reflux con-
ditions. The reactor is chosen with the objective that the
unreacted HI as well as iodine is condensed back into
the flask and only hydrogen can escape. During the reac-
tion gas coming out from the reactor is passed through
two traps containing starch solution and silver nitrate solu-
tion. There was no colour change in either of the trap,
which confirms that gas coming out is neither iodine nor
HI vapours. This gas was collected in an inverted column
and taken out by a syringe through a septum at the top
of the column. It was analysed using a gas chromatograph
(Chromatography and Instruments company, GC 2011)
equipped with molecular sieve 5 Å column and thermal
conductivity detector and the gas was identified to be
hydrogen.
2. EXPERIMENTAL DETAILS
2.1. Synthesis of Catalyst
For preparation of catalyst, the synthesis of meso-
porous silica was carried out first. Synthesis of template
i.e., mesoporous silica was carried out by using follow-
ing chemicals. Pluronic P123, Cetyl trimethylammonium
bromide (CTAB) and Tetra ethyl ortho silicate (TEOS)
employing the methodology as described in literature.29
The mesoporous silica hence prepared was washed thor-
oughly and dried.
2178
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Tyagi et al.
Mesoporous Carbon Supported Platinum Nanocatalyst: Application for Hydrogen Production
Figure 4. Adsorption isotherm of (a) fresh and (b) used Pt/ C catalysts.
Figure 2. Experimental setup for catalytic activity evaluation.
Another advantage of liquid phase HI decomposition is
that in this case the energy required for vaporization in
case of vapour phase decomposition is not required, hence
resulting in overall increase in efficiency of the process.
After carrying out the reaction for desired interval, the
resulting solution was filtered and the filtrate was analysed
for concentrations of H+ and I− ions. The decrease in con-
centrations of H+ and I− ions was used to calculate the
percentage conversion. The conversion was also calculated
by mass balance against increase in iodine concentration.
The concentrations of H+ and I− ions were determined by
The equilibrium constant equation for decomposition of
HI to H2 and I2 can be illustrated as given below:
PI0ꢁ5PH0ꢁ5
2
2
Kp =
(1)
PHI
It is evident from this equation that at a given pressure
of HI, lowering of I2 partial pressure is required for higher
yield of H2. This means that a sink of iodine is required
to drive the reaction in forward direction. This sink for
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iodine can be provided by the reactant HI itself because I−
Copyright: American Scientific Publishers
forms polyiodide species in presence of iodine. Thus the
iodine formed gets dissolved in HI in form of polyiodides
and doesn’t get deposited on the catalyst surface. There-
fore the active sites of the catalyst surface remain free
for the reaction. Therefore in case of liquid phase decom-
position reaction, dissolution of the I2 formed at catalyst
surface into the HI solution and continued intimate con-
tact between HI and catalyst maintains high reactivity lev-
els with generation of gaseous H2 even in presence of I2.
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titrating them against 0.1N NaOH and 0.1N AgNO3 solu-
tions. The H+ and I− titrations were carried out using an
auto titrator, Model Titra from Lab India with glass elec-
trode and silver–silver chloride potentiometric electrodes
respectively. Iodine concentration was determined by titrat-
ing the solution against thiosulphate using starch as an
indicator. The used catalyst was analysed by XRD and
SEM to see if any structural and morphological changes
are there after HI decomposition reaction. The stability
Figure 3. XRD pattern of the Pt/C catalyst.
Figure 5. Pore size distribution of (a) fresh and (b) used Pt/C catalysts.
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Mesoporous Carbon Supported Platinum Nanocatalyst: Application for Hydrogen Production
Tyagi et al.
Figure 6. SEM images of Pt/C catalyst.
of catalyst against noble metal leaching was determined
by analysing platinum content in the HI phase using ICP-
AES, model JY 2000 from HORIBA Jobin Yvon.
Where ꢆ is the wavelength of radiation, ꢃ is the angle
of the diffraction peak, and b is the full width at half
maximum of the diffraction peak (in radian). The cal-
culated crystallite size of the platinum was found to be
nearly 6 nm.
3. RESULTS AND DISCUSSION
3.1. Characterization
3.1.1. X-ray Diffraction
3.1.2. N2 Adsorption Measurements
Nitrogen adsorption isotherms for fresh as well as used
The X-ray diffraction patterns were recorded in 10 to
70ꢀ 2ꢃ range on Philips Analytical Diffractometer (using
Ni-filtered Cu-Kꢄ radiation). Figure 3 shows the XRD
pattern of the catalyst which has a broad peak cen-
tring at 23ꢀ, which is characteristic of amorphous carbon.
The XRD pattern also exhibits a peak at 39.7ꢀ conform-
ing to platinum metal (JCPDS No. 04-0802). Crystal-
lite size D of platinum was calculated from the Scherrer
formula
ꢀ
samples were recorded at −196 C temperature. Before
recording of the isotherm, both ꢀthe samples were subjected
to in situ evacuation at 300 C temperature. The BET
surface area of the catalyst was found to be as high as
1122 m2g−1 and pore volume was 0.893 cm3g−1
.
Figures 4 and 5 shows the adsorption desorption
isotherm and pore size distribution curve for both the
samples along with the silica template used respectively.
Figure 4 shows a hysteresis loop (Type-IV) which is a
characteristic of mesoporous materials.
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D = ꢅ0ꢁ9 ꢆꢇ/ꢅb ·cosꢃꢇ
(2)
Figure 7. FEG-SEM images of Pt/C catalyst.
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Tyagi et al.
Mesoporous Carbon Supported Platinum Nanocatalyst: Application for Hydrogen Production
Figure 10. SAED pattern of the catalyst.
Figure 8. TEM images of Pt/C catalyst.
micrographs suggests that the Platinum particles are almost
spherical.
Figure 9 shows the particle size distribution where diam-
Pore size distribution curve for the silica shows that it
contains pores of around 9 nm size, while the catalyst pre-
pared by using this template has presence of pores around
4 nm, which again corresponds to presence of mesopores.
eter was measured for than 150 randomly selected particles
in enlarged TEM images. It shows that most of the parti-
cles (>80%) are in the range of 4 to 7 nm with an average
of around 6 nm which is in very good agreement with the
size calculated from XRD. Figure 10 shows the SAED pat-
tern of platinum particle which is indexed as (111), (200)
reflections of fcc structure of platinum.
3.1.3. Scanning Electron Microscopy
Surface morphology of the catalyst was observed using
Scanning Electron Microscopy (SEM). Figure 6 shows the
SEM images of Pt/C catalyst which show rough surface
with open pores and a few loose particles over it. Figure 7
shows high resolution FEG-SEM micrograph, it clearly
3.1.5. X-ray Photoelectron Spectroscopy
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Surface composition of the catalyst was analyzed using
X-ray Photoelectron spectroscopy. The XPS measurements
for Pt/C were carried out in constant analyzer energy mode
using Al Kꢄ radiation (1486.6 eV). The survey scan of
the sample shows peaks only in the spectral regions cor-
responding to carbon, platinum and oxygen.
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showed well dispersed particles of platinum (white dots)
over the support.
3.1.4. Transmission Electron Microscopy
Figure 11 shows the intensity versus binding energy
data obtained for spectral region corresponding to Pt 4f .
It can be deconvoluted into only one doulet (4f5/2 and
4f7/2) with respective binding energies of 71.3 and 74.6 eV
using CasaXPS software. These binding energy values cor-
respond to metallic state of platinum.30ꢂ31 Thus XPS study
Pt particles were seen clearly through Transmission Elec-
tron Microscopy. Figure 8 shows the TEM image of the
Pt/C sample, which clearly shows highly dispersed plat-
inum particles over the support. The analysis of TEM
Figure 9. Particle size distribution.
Figure 11. XPS spectra of Pt-4f spectral region.
J. Nanosci. Nanotechnol. 17, 2177–2184, 2017
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Mesoporous Carbon Supported Platinum Nanocatalyst: Application for Hydrogen Production
Tyagi et al.
Table I. Catalytic activity of Pt/C catalyst for HI decomposition
reaction.
S. no.
Reaction time (hr)
% Conversion (%)
1.
2.
3.
4.
5.
1
2
2
3
4
9.6
15.2
2.9 (without catalyst)
21.4
28.2
graphite exhibits a peak at 1580 cm−1 corresponding to
sp2 hybridized carbon called as G band. Appearance of
another broad peak at around 1300 cm−1 is due to disor-
dered carbon structure.
Figure 13 shows the Raman spectra of the Pt/C catalyst,
which shows two peaks at around 1310 and 1590 cm−1
.
These two peaks are assigned as D band and G band
respectively. D band here is very broad and it contains
contributions from both sp3 hybridized carbon as well
as disordered carbon structure. Thus Raman spectroscopy
results indicate that the carbon contains disordered car-
bon in addition to graphitized carbon.32–34 The width and
relative intensities of both G and D lines (IG/ID) is also
used for characterization of carbon materials. IG/ID ratios
for the Pt/C catalyst is 1.15, which is in good agreement
with similar mesoporous carbon materials as reported in
literature.35ꢂ36 These results and IG/ID ratio are in good
corroboration with the XPS results and sp2/sp3 ratio as
reported by Tai et al.37
Figure 12. XPS spectra of C-1s spectral region.
reveals that platinum present here is in zero oxidation state
which is essential for its catalytic activity.
Figure 12 shows the spectral region corresponding to
C-1s spectral region; it can be fitted to three peaks with
binding energy 284.3, 285.4 and 287.9 eV. These peaks
correspond to sp2, sp3 and CO (Carbon bonded to oxy-
gen, C–O or C O) types of carbon.31 Therefore the oxy-
gen present is associated with carbon and not platinum.
Also presence of sp2 hybridized carbon confirms the pres-
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ence of rolled graphene like structure which is very mush
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required for formation of mesoporous structures of carbon.
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3.2. Activity Measurement
3.1.6. Raman Spectroscopy
The catalyst was evaluated for its activity for liquid phase
HI decomposition reaction. Reaction was carried out at
Raman spectroscopy is a very powerful tool for the
characterization of different carbon materials. Two crys-
talline forms of carbon i.e., diamond and graphite has
entirely different Raman spectra. Raman spectra of dia-
mond have a band at 1332 cm−1 which is a character-
istic of sp3 hybridized carbon, while Raman spectra of
ꢀ
120 C for different time intervals. After the reaction the
solution was filtered and the eluent was analysed for con-
centrations of H+, I− and I2 present in it. The concentra-
tions of H+ and I− ions was determined by titrating this
eluent solution against 0.1 N NaOH and 0.1 N AgNO3
Figure 13. Raman spectrum of the catalyst.
Figure 14. XRD pattern of the used Pt/C catalyst.
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Tyagi et al.
Mesoporous Carbon Supported Platinum Nanocatalyst: Application for Hydrogen Production
Figure 15. SEM images of the used Pt/C catalyst.
respectively using an autotitrator. The titrants NaOH and
AgNO3 were standardized by their titration against Potas-
sium Hydrogen Phthalate (KHP) and NaCl respectively.
The decrease in H+ and I− ions with respect to their con-
centrations in original solutions was used to calculate the
percentage conversion. These two values were found to be
in good agreement. The concentration of iodine in solution
was determined by titrating it against Sodium thiosulphate
using starch as an indicator. There was increase in the
concentration of iodine after the reaction which was also
used to calculate the percentage conversion of HI. This
value was in agreement with that of calculated by the ion
concentrations. The % conversion values thus obtained are
shown below in Table I. The % conversion values increase
The eluent solution was analysed for presence of plat-
inum by ICP-AES to evaluate how much platinum is being
leached out into the solution. The ICP-AES analysis of the
solution shows that only 0.018% of initial loading plat-
inum leaches out into the solution. This number indicates
that the platinum has good retention in the mesoporous
carbon matrix.
4. CONCLUSION
Mesoporous carbon supported platinum nano catalyst was
successfully synthesized by hard templating route. Plat-
inum was present in form of uniformly distributed particles
of 4–7 nm size over the mesoporous carbon support. This
catalyst was used for the liquid phase HI decomposition
IP: 95.85.71.227 On: Mon, 08 Jul 2019 12:26:19
with increasing reaction time. Also when compared to
blank run (without catalyst) for 2 hours there is significant
increase in the % conversion value upon using the catalyst.
Also these values of percentage conversion are compara-
ble to our earlier reported Pt/Zirconia catalyst21 and better
than some of previous Pt/carbon catalysts.22
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reaction of the Sulphur-Iodine process. In presence of the
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catalyst the conversion of HI to hydrogen increase signif-
icantly as compared to the blank run. The catalyst was
found to be stable in terms of structure of supports as well
as in terms of noble metal retention under the reaction
conditions.
This type of material has a potential to be used in HI
decomposition reaction of Sulphur-Iodine cycle for hydro-
gen production as well as other applications which requires
highly dispersed Pt nanocatalyst on a carbon support.
3.3. Stability
The stability of the catalyst in terms of its structural
integrity and platinum leaching was studied after atypical
study of 2 hours. After 2 hour run of the reaction, the used
catalyst was removed from the solution by filtering. It was
washed thoroughly and dried. This catalyst was analysed
by several techniques like XRD, SEM, N2 sorption etc.
Figure 14 shows the XRD pattern of the used catalyst.
Here, there is no shift in peaks corresponding to carbon as
well as platinum, which means there is no major change in
the structure of catalyst during the course of the reaction.
Figure 15 shows the SEM images of the used catalyst,
these also indicate that there are no major morphologi-
cal changes when compared with the fresh catalyst SEM
images. The adsorption desorption isotherm and the pores
size distribution curve for the used catalyst are given in
Figures 4 and 5 along with the fresh catalyst. These two
also indicate that the mesoporous structure of the catalyst
remain stable. All these facts imply that the catalyst was
stable the harsh conditions of liquid phase HI decomposi-
tion reaction.
Acknowledgments: The authors are thankful to
Dr. Pushan Ayyub, TIFR for providing FEG-SEM and
TEM facility and Dr. W. D. Einicke and Dr. R. Gläser,
Institute of Chemical Technology, Universität Leipzig,
Leipzig, Germany for N2 adsorption measurements.
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IP: 95.85.71.227 On: Mon, 08 Jul 2019 12:26:19
Copyright: American Scientific Publishers
Received: 10 September 2015. Accepted: 4 February 2016.
Delivered by Ingenta
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J. Nanosci. Nanotechnol. 17, 2177–2184, 2017