Reversible hydrogenation—dehydrogenation reactions of meta-terphenyl on catalysts with various supports

Article abstract of DOI:10.1007/s11172-018-2032-8

For developing new composite systems (substrate—catalyst) for hydrogen storage, the activities of Pt and Pd catalysts on various supports were compared in reversible meta-terphenyl hydrogenation and perhydro-meta-terphenyl dehydrogenation. The microstructure of the catalysts was studied. Carbon-supported catalysts are more efficient in both reversible reactions than alumina-supported systems.

Full text of DOI:10.1007/s11172-018-2032-8

Russian Chemical Bulletin, International Edition, Vol. 67, No. 1, pp. 28—32, January, 2018
28
Reversible hydrogenation—dehydrogenation reactions of metaꢀterphenyl
on catalysts with various supports
A. N. Kalenchuk,a,b N. A. Davshan,b V. I. Bogdan,a,b S. F. Dunaev,a and L. M. Kustova,b
аDepartment of Chemistry, M. V. Lomonosov Moscow State University,
Build. 3, 1 Leninskie Gory, 119991 Moscow, Russian Federation.
Eꢀmail: akalenchuk@yandex.ru
bN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 137 2935
For developing new composite systems (substrate—catalyst) for hydrogen storage, the
activities of Pt and Pd catalysts on various supports were compared in reversible metaꢀterpheꢀ
nyl hydrogenation and perhydroꢀmetaꢀterphenyl dehydrogenation. The microstructure of the
catalysts was studied. Carbonꢀsupported catalysts are more efficient in both reversible reacꢀ
tions than aluminaꢀsupported systems.
Кey words: catalysis, hydrogenation, dehydrogenation, hydrogen storage, metaꢀterpheꢀ
nyl, perhydroꢀmetaꢀterphenyl, platinum.
In recent years, increasing attention has been paid to
in the catalytic composite systems. Here we compare the
performances of Pt and Pd catalysts on different supports
in reversible hydrogenation—dehydrogenation reactions
of metaꢀterphenyl and perhydroꢀmetaꢀterphenyl.
hydrogen as a universal energy carrier. For successful deꢀ
velopment of the environmentally benign power engineerꢀ
ing based on hydrogen fuel cells, it is important to design
efficient methods for hydrogen storage and generation.
Of considerable interest are aromatic hydrocarbons whose
hydrogen capacity exceeds 7.5 wt.%, which is higher than
that of any known storage systems.1—3 Aromatic hydroꢀ
carbons are able to undergo repeated hydrogen saturation
and evolution cycles in reversible hydrogenation—deꢀ
hydrogenation reactions without formation of COх gases
contaminating the atmosphere.4—6
The reversible hydrogenation—dehydrogenation reacꢀ
tions of aromatic compounds are usually conducted with
supported catalysts based on noble metals. The rate of
reactions is known7,8 to depend on the structure of the
metal surface and the support used; therefore, selection
of the optimal support is an important aspect of developꢀ
ment of efficient catalysts for these reactions. It was found,
for example, that multiphase catalysts on acidic supports
are often characterized by enhanced activity and selectivꢀ
ity, in particular, due to hydrogen spillover.9,10 Meanꢀ
while, acidic supports have a considerable drawback,
namely, high catalytic activity towards cracking and ring
opening reactions at dehydrogenation temperatures.11,12
One way to decrease these undesirable reactions is to use
supports with higher intertness such as activated carbon
or modern carbon materials,13,14 which bear much less
functional groups on the surface than acidic supports.
Previously,15—17 the terphenyl—perhydroterphenyl
pair has been shown to be promising for hydrogen storage
Experimental
Determination of the catalytic activity. Commercial γꢀaluꢀ
minaꢀsupported catalysts for benzene hydrogenation were used:
5%Pt/Al2O3, 2.5%Pd/Al2O3, and 0.12%Pd—3.8%Ni—4.3%Cr/
Al2O3. The carbonꢀsupported catalysts represented commercial
3%Pt/C (Aldrich) on the activated carbon (lot No. HI06523BT)
and 3%Pt/Sibunit. Platinum was deposited on Sibunit (Instiꢀ
tute of Hydrocarbon Processing, Siberian Branch of the Rusꢀ
sian Academy of Sciences, Omsk) by impregnating the support
to incipient wetness with an aqueous solution of [H2PtCl6] acꢀ
cording to the previously reported procedure.18 The catalyst
characteristics are summarized in Table 1.
metaꢀTerphenyl (Aldrich, 99%) (m.p. 84 °C, b.p. 379 °C,
ρ = 0.98 g cm–3) served as the starting reactant for hydroꢀ
genation. metaꢀTerphenyl was hydrogenated in an Rꢀ201
high pressure autoclave (Korea) with 100 mL inner volume at
180 °C and 70 atm. In all experiments, the substrate (50 cm3)
and the catalyst (5 cm3) were placed into the autoclave and
the reaction was carried out with stirring of the reaction
mixture at 600 rpm. The time (t/h) of complete conversion
of metaꢀterphenyl to perhydroꢀmetaꢀterphenyl served as the
key criterion for comparison of the catalysts in hydrogenaꢀ
tion. Additionally, the catalyst activity (Ag) was evaluated
using the ratio of the number of moles of the perhydroꢀmetaꢀ
terphenyl (C18H32) formed to the number of moles of the
active metal М (Pt, Pd), which was reduced to the hydrogeꢀ
ac
nation time.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 0028—0032, January, 2018.
1066ꢀ5285/18/6701ꢀ0028 © 2018 Springer Science+Business Media, Inc.

Catalyzed reactions of metaꢀterphenyl
Russ.Chem.Bull., Int.Ed., Vol. 67, No. 1, January, 2018
29
Table 1. Data on the morphology for the catalysts of metaꢀterphenyl hydrogenation and perhydroꢀmetaꢀ
terphenyl dehydrogenation
Catalyst
Bulk
density
/g cm–3
Surface
area,
SBET/m2 g–1
Metal
particle size,
R/nm
Metal
dispersion,
D (%)
5%Pt/Аl2O3*
2.5%Pd/Аl2O3*
0.12%Pd—3.8%Ni—4.3%Cr/Al2O3*
3%Pt/C («Aldrich»)
3%Pt/Sibunit
0.72
0.72
0.74
0.32
0.65
230
215
130
760
300
1.5—2
4.5—5
25—27
5—5.5
2—2.5
67
25
4
22
49
* Commercial catalysts (Redkino catalyst plant).
The product formed after hydrogenation was separated from
the catalyst and analyzed. The product containing ≥99% of the
target perhydroꢀmetaꢀterphenyl was introduced into the back
dehydrogenation reaction. A catalyst sample (6 cm3) was placed
at the center of a steel reactor of 10 mm diameter and 230 mm
length. Liquid perhydroꢀmetaꢀterphenyl was fed into the reacꢀ
tor with a HPP 5001 highꢀpressure pump and dеhydrogenation
was carried out in the flow mode at 320 °C and feed flow rate of
6 mL h–1. All piping of the flow catalytic setup was maintained
at 90 °C. At the reactor outlet, hydrogen and the reaction prodꢀ
ucts were separated. In order to obtain pure hydrogen without
other gas impurities at the outlet, a substrate cooling system
was used comprising saturators and filters, including membrane
filters.19 The conversion of perhydroꢀmetaꢀterphenyl and seꢀ
lectivity to metaꢀterphenyl in the sample accumulated after the
reaction in the flow setup during 1 h served as the major criteria
for comparison of the catalysts in dehydrogenation. In view of
the possible catalyst deactivation, samples obtained after
dehydrogenation for 4 h were compared. Since hydrogen is the
target reaction product, the catalyst activity in dehydrogenaꢀ
tion (Ad) was calculated as the ratio of the total number of
moles of hydrogen evolved upon dehydrogenation of perhydroꢀ
metaꢀterphenyl for 4 h to the number of moles of the active
metal Mac (Pt, Pd), which was reduced to the time.
S(i) = Σc(i)/ Σc(k)•100%,
where Σс(i) and Σc(k) is the sum of concentrations of a group of
products and all reaction products, respectively.
Study of the catalyst structure. The specific surface area
(SBET) of the catalysts was calculated from measurements of
lowꢀtemperature nitrogen sorption by the BET model.20 The
particle size R and dispersion D of active noble metals (Pt, Pd)
were determined from CO chemisorption measurements conꢀ
ducted at 35 °C on an ASAPꢀ2020 plus Micromeritics microanꢀ
alyzer (USA).21 In the calculation of R, the catalyst particles
were assumed to be spherical. The dispersion of the multicomꢀ
ponent system was estimated using the stoichiometric coeffiꢀ
cient К = 1.5, where К is the number of CO molecules per
metal atom. This coefficient takes into account different forms
of CO adsorption. The catalyst morphology was studied by field
emission scanning electron microscopy (SEM) using a Hitachi
SU8000 microscope for aluminaꢀsupported catalysts and
a JEOL JSMꢀ6390 microscope for carbonꢀsupported catalysts.
The images were recorded in the secondary electron mode at
an accelerating voltage of 2—30 kV and a working distance of
8—10 mm. EDS study of the samples was carried out using an
Oxford Instruments Xꢀmax energy dispersive spectrometer. The
sample microstructure was examined by transmission electron
microscopy (TEM) on a Hitachi HT7700 electron microscope.
The images were recorded in the light field mode at an accelerꢀ
ating voltage of 100 kV.22
Prior to hydrogenation and dehydrogenation, the catalysts
containing Pt and Pd were activated for 2 h at 320 °C in
a hydrogen flow (30 mL min–1) and Niꢀcontaining catalysts
were activated for 2 h at 500 °C.
Chromatographic analysis. The products of hydrogenation
and dehydrogenation were analyzed on a Kristaluxꢀ4000М
chromatograph equipped with a flame ionization detector with
a ZBꢀ5 capillary column (ZEBRON, USA). Analysis was carꢀ
ried out in a programmed mode at 70 to 220 °C at a heating rate
of 6 °C min–1. The partly hydrogenated and side reaction prodꢀ
ucts were identified on a FOCUS DSQ II GC/MS spectroꢀ
meter (Thermo Fisher Scientific, USA) with a TRꢀ5MS capilꢀ
lary column (Thermo, USA). The purity of the hydrogen formed
was determined by gas chromatography with a heat conductivꢀ
ity detector on a Porаpak Q packed column.
Results and Discussion
The composition and morphological data for the catꢀ
alysts used in reversible metaꢀterphenyl hydrogenation and
perhydroꢀmetaꢀterphenyl dehydrogenation reactions are
summarized in Table 1.
The specific surface areas (SBET) of the 5%Pt/Al2O3
and 2.5%Pd/Al2O3 catalysts are close. According to SEM
data, the particles of these catalysts are ∼4 μm aggregates
with a disordered structure. The SBET surface area of the
0.12%Pd—3.8%Ni—4.3%Cr/Al2O3 catalyst is smaller and
the particles are shaped like corals with tightly interlaced
arms of up to 0.4 μm length.
The conversions for both hydrogenation and dehydrogenaꢀ
tion (Х) were calculated by the formula
Х = (c0 – c)/c0•100%,
The morphology of the 3%Pt/C catalyst (Aldrich) is
typical of activated carbonꢀsupported catalysts. The SEM
image demonstrates the >2 μmꢀlarge grownꢀtogether
where c0 and с are the initial and final concentrations of the
substrate being converted. The selectivity (S) was calculated by
the equation

30
Russ.Chem.Bull., Int.Ed., Vol. 67, No. 1, January, 2018
Kalenchuk et al.
a
100 nm
50 nm
Fig. 1. TEM image of the 0.12%Pd—3.8%Ni—4.3%Cr /Al2O3
catalyst.
b
particles of various shape. Among the studied catalysts,
the activated carbonꢀsupported sample has the largest
surface area. The surface of the 3%Pt/Sibunit catalyst is
more homogeneous than that of the activated carbonꢀ
supported catalyst and the surface morphology is similar
to that of 5%Pt/Al2O3.
For microstructure analysis, thin sections of the cataꢀ
lyst were studied by TEM. Considering the TEM image
of the 0.12%Pd—3.8%Ni—4.3%Cr/Al2O3 sample (Fig. 1),
one can see that the microstructure of alumina comprises
needleꢀlike crystallites with an average size of ∼20—30 nm.
On the surface of some of them, particles of the active
component are located. The gaps between the microꢀ
blocks of needle crystals form micropores (0.6—1.5 nm)
and mesopores (<45 nm).23
50 nm
Fig. 2. TEM images of the 3%Pt/C (Aldrich) (a) and
3%Pt/Sibunit (b) catalysts.
The TEM images of the carbonꢀbased catalysts (Fig. 2)
show that the microstructure of the 3%Pt/C catalyst supꢀ
ported on activated carbon consists of irregularly shaped
aggregates, whereas the 3%Pt/Sibunit catalyst has a globꢀ
ular microstructure. The porous structure of activated carꢀ
bon mainly consists of microꢀ and macropores. The
Sibunit carbon support is mainly a mesoporous material.23
It follows from comparison of the TEM images that the
Pt particles in the 3%Pt/C catalyst on activated carbon
are distributed homogeneously, whereas in the Sibunitꢀ
supported catalyst, they are mainly located on the surface
of globules. It can be seen that the average Pt particle size
in the catalyst on activated carbon is greater than that for
the catalyst on Sibunit, which is correlated with the CO
chemisorption data (see Table 1).
Data on the metaꢀterphenyl hydrogenation and perꢀ
hydroꢀmetaꢀterphenyl dehydrogenation are summarized
in Table 2.
The reversible hydrogenation of metaꢀterphenyl (1,3ꢀ
diphenylbenzene, C18Н14) and dehydrogenation of perꢀ
hydroꢀmetaꢀterphenyl (1,3ꢀdicyclohexylcyclohexane,
C18Н32) can be represented as general Scheme 1.
The target product of metaꢀterphenyl hydrogenation
is perhydroꢀmetaꢀterphenyl and the reverse reaction of
Table 2. Catalyst activity in metaꢀterphenyl hydrogenation and perhydroꢀmetaꢀterphenyl dehydrogenation
Catalyst
SBET/m2 g–1
Hydrogenation
Dehydrogenation
Х (%)
t/h
Аg
X (%)
S (%)
Аd
5%Pt/Аl2O3
2.5%Pd/Аl2O3
0.12%Pd—3.8%Ni—4.3%Cr/Al2O3
3%Pt/C (Aldrich)
3%Pt/Sibunit
230
215
130
760
300
199
173
186
100
199
15
20
16
14
15
0.06
0.04
1.10
0.80
0.32
43
35
26
92
91
38
90
85
94
95
10.5
10.9
17.2
12.8
11.4

Catalyzed reactions of metaꢀterphenyl
Russ.Chem.Bull., Int.Ed., Vol. 67, No. 1, January, 2018
31
Scheme 1
cal decrease in the initial granules does not have a noticeꢀ
able effect.
In the reverse dehydrogenation of perhydroꢀmetaꢀterꢀ
phenyl carried out with three aluminaꢀsupported cataꢀ
lysts, the conversion increases with increasing content of
the active metal (see Table 2). The conversion in the
dehydrogenation catalyzed by 5%Pt/Al2O3 is markedly
lower than the conversions on either of the 3%Pt/C
catalysts. The 2.5%Pd/Al2O3 and 0.12%Pd—3.8%Ni—
4.3%Cr/Al2O3 catalysts show higher selectivities to metaꢀ
terphenyl than the 5%Pt/Al2O3 platinum catalyst. The
conversions of perhydroꢀmetaꢀterphenyl and the selectivꢀ
ities to metaꢀterphenyl obtained on both Pt/C catalysts
are similar, although the surface areas (SBET), disperꢀ
sions (D), and active component particle sizes (R) differ
for these catalysts. In both cases, the evolved hydrogen
was of high purity, as shown by chromatography. In the
dehydrogenation, the longest continuous operation withꢀ
out deactivation was found for the 3%Pt/C catalyst with
activated carbon.19
Examination of the data of Table 2 converted to the
amount of noble metal (Pt, Pd) indicates that the highest
Ag and Ad values in both reversible reactions were shown
by the modified 0.12%Pd—3.8%Ni—4.3%Cr/Al2O3 catꢀ
alyst. However, for hydrogen storage applications, most
important is the system capacity for saturation and evoꢀ
lution of the highest amount of hydrogen rather than the
activity per unit metal. From this standpoint, the best
conversion and activity balance for hydrogenation and
dehydrogenation reactions is attained with both Pt/C catꢀ
alysts. Meanwhile, both these values are higher for the
catalyst with activated carbon, but the Sibunit catalyst is
more processable, especially for dehydrogenation carried
out in a flow reactor.
Thus, the obtained experimental data on metaꢀterꢀ
phenyl hydrogenation and perhydroꢀmetaꢀterphenyl deꢀ
hydrogenation in the presence of various Pt and Pd cataꢀ
lysts demonstrate that the catalysts on carbon supports
are more efficient in both reversible reactions than alumiꢀ
naꢀsupported systems. It was also found that Pt catalysts
provide higher conversion in both reactions than the Pd
catalysts. It was demonstrated that the content of the
noble metal can be reduced by modifying the noble metal
by other metals, which is important for the design of less
expensive hydrogen storage catalytic composite systems.
perhydroꢀmetaꢀterphenyl dehydrogenation gives, on the
contrary, metaꢀterphenyl. 3ꢀCyclohexylbiphenyl and
1,3ꢀdiphenylcyclohexane with one saturated ring
(C18Н20) and phenylꢀ1,3ꢀbicyclohexane and 3ꢀphenylbiꢀ
cyclohexane with two saturated rings (C18Н26), respecꢀ
tively, are formed as intermediate products.15,17
Comparison of the experimental data (see Table 2)
indicates that complete saturation of metaꢀterphenyl with
hydrogen during hydrogenation is markedly faster with
Pt/C catalysts than with aluminaꢀsupported catalysts. The
differences can be attributed to the diffusion restrictions
caused by pore clogging with coke, which is typical of
reactions involving large molecules and catalyzed by
aluminaꢀbased catalysts.24 Hydrogenation time is virtuꢀ
ally the same for both Pt/C catalysts, despite the fact that
the 3%Pt/Sibunit surface area is almost twice smaller
than that of the 3%Pt/C catalyst on activated carbon.
Possibly, in the activated carbonꢀbased catalyst, some Pt
is blocked in micropores, which reduces the fraction of
the accessible surface of the active metal.
While comparing Pdꢀcontaining catalysts, one can see
that the modified 0.12%Pd—3.8%Ni—4.3%Cr/Al2O3
catalyst exhibits higher activity towards hydrogenation of
metaꢀterphenyl than the 2.5%Pd/Al2O3 catalyst containꢀ
ing more Pd. The mechanical grinding of the initial
0.12%Pd—3.8%Ni—4.3%Cr/Al2O3 catalyst granules leads
to increase in the conversion up to 99% with hydrogenaꢀ
tion time decreasing to 12 h, whereas similar mechanical
treatment of the 2.5%Pd/Al2O3 catalyst does not change
the activity towards metaꢀterphenyl hydrogenation.
Apparently, the forced disconnection of the coral arms
in the modified Pd catalyst promotes an increase in
the active surface area, whereas in the case of extensive
surface of the 2.5%Pd/Al2O3 catalyst, the mechaniꢀ
This work was financially supported by the Russian
Science Foundation (Project No. 14ꢀ50ꢀ00126).
References
1. M. Taube, D. Rippin, D. Cresswell, W. Knecht, Int. J.
Hydrogen Energy, 1983, 8, No. 3, 213.
2. Y. Saito, Cat. Cat., 2005, 47, 137.
3. R. B. Biniwale, S. Rayalu, S. Devotta, M. Ichikawa, Int. J.
Hydrogen Energy, 2008, 33, No. 1, 360.

32
Russ.Chem.Bull., Int.Ed., Vol. 67, No. 1, January, 2018
Kalenchuk et al.
4. K. Oda, K. Akamatsu, T. Sugawara, P. Kikuchi, A. Segaꢀ
wa, S. Nakao, Ind. Eng. Chem. Res., 2010, 49, 11287.
5. S. Hodoshima, A. Hiroshi, T. Shigeki, S. Yasukazu, Int. J.
Hydrogen Energy, 2003, 28, 1255.
17. A. N. Kalenchuk, V. I. Bogdan, S. E. Bogorodskii, Russ. J.
Phys. Chem. A., 2016, 90, 1921.
18. A. N. Kalenchuk, V. I. Bogdan, L. M. Kustov, Catal. in
Industry, 2015, 7, 60.
6. N. Kariya, A. Fukuoka, M. Ichikawa, Appl. Catal. A: General,
2002, 233, 91.
19. A. N. Kalenchuk, V. I. Bogdan, L. M. Kustov, Russ. J.
Chem. Bull. A, 2015, 89, 16.
7. F. Roessner, U. Roland, J. Mol. Catal. A: Chem., 1996,
112, 401.
20. A. L. KlyachkoꢀGurvich, Bull. Acad. Sci. USSR, Div. Chem.
Sci., 1961, 10, 1884.
8. H. Chen, H. Yang, O. Omotogo, L. Ding, Y. Briker,
Y. Zheng, Z. Ring, Appl. Catal. A: General, 2009, 358, 103.
9. V. V. Rozanov, O. V. Krylov, Russ. Chem. Rev., 1997,
66, 117.
10. C. M. Lu, Y. M. Lin, I. Wang, Appl. Catal. A: General, 2000,
198, 223.
21. P. A. Webb, C. Orr, Analytical Methods in Fine Particle
Technology, 1st ed., Micromeritics Instrument, Norcross,
USA, 1997.
22. V. V. Kachala, L. L. Khemchyan, A. S. Kashin, N. V. Orꢀ
lov, A. A. Grachev, S. S. Zalesskii, V. P. Ananikov, Russ.
Chem. Rev., 2013, 82, 648.
11. M. Jacquin, D. J. Jones, J. Roziere, S. Albertazzi, A. Vacꢀ
cari, M. Leranda, L. Storaro, R. Ganzerla, Appl. Catal. A:
General, 2003, 251, 131.
12. L. M. Kustov, A. L. Tarasov, J. Sung, D. Y. Godovsky,
Focus Article. Mendeleev Commun., 2014, 24, 1.
13. P. Li, Y. L. Huang, D. Chen, J. Zhu, T. J. Zhao, X. G.
Zhou, Catal. Commun., 2009, 10, 815.
23. A. P. Karnaukhov, Adsorbtsiya. Tekstura Dispersnykh i
Poristykh Materialov [Adsorption. Texture of Dispersed and
Porous Materials], Nauka, Novosibirsk, 1999, 470 pp.
(in Russian).
24. S. Van Donk, A. H. Janssen, J. H. Bitte, K. P. De Jong,
Catal. Rev., 2003, 45, 297.
14. F. RodriguezꢀReinoso, Carbon, 1998, 36, 159.
15. A. N. Kalenchuk, V. I. Bogdan, S. E. Bogorodskii, L. M.
Kustov, Kinet. Catal., 2016, 57, 219.
Received August 4, 2017;
in revised form December 4, 2017;
accepted December 5, 2017
16. A. N. Kalenchuk, A. E. Koklin, V. I. Bogdan, L. M. Kusꢀ
tov, Russ. Chem. Bull., 2017, 66, 1208.