2-(N-Methylbenzyl)pyridine: A Potential Liquid Organic Hydrogen Carrier with Fast H2 Release and Stable Activity in Consecutive Cycles

Article abstract of DOI:10.1002/cssc.201702256

The liquid organic hydrogen carrier (LOHC) 2-(N-methylbenzyl)pyridine (MBP) shows good potential for H₂ storage based on reversible hydrogenation and dehydrogenation, with an H₂ storage density of 6.15 wt %. This material and the corresponding perhydro product (H₁₂-MBP) are liquids at room temperature. Remarkably, H₂ release is much faster from H₁₂-MBP over Pd/C than from the benchmark perhydro benzyltoluene over Pt/C at lower temperatures than 270 °C, owing to the addition of N atom into the benzene ring. Since this positive effect is unfavorable to the hydrogenation reaction, more Ru/Al₂O₃ catalyst or prolonged reaction time must be applied for complete H₂ storage. Experiments with repeated hydrogenation–dehydrogenation cycles reveal that reversible H₂ storage and release are possible without degradation of the MBP/H₁₂-MBP pair. The prepared MBP satisfies the requirements for chemical stability, handling properties, and cytotoxicity testing.

Full text of DOI:10.1002/cssc.201702256

Accepted Article
Title: A potential liquid organic hydrogen carrier: 2-(n-
methylbenzyl)pyridine with fast H2 release and stable activity in
consecutive hydrogenation-dehydrogenation cycles
Authors: Jinho Oh, Kwanyong Jeong, Tae Wan Kim, Hyunguk Kwon,
Jeong Woo Han, Ji Hoon Park, and Young-Woong Suh
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10.1002/cssc.201702256
ChemSusChem
COMMUNICATION
A potential liquid organic hydrogen carrier: 2-(n-methylbenzyl)
pyridine with fast H2 release and stable activity in consecutive
hydrogenation-dehydrogenation cycles
Jinho Oh,[a] Kwanyong Jeong,[b] Tae Wan Kim,[a] Hyunguk Kwon,[c] Jeong Woo Han,[d] Ji Hoon Park,*[b]
and Young-Woong Suh*[a, e]
every H2 supply sites for energy storage. In such “chemical
storage” a favorable chemical state is liquid phase rather than
gas phase, thus named liquid organic hydrogen carrier (LOHC)
materials. LOHCs are high-boiling organic molecules that can be
easily and reversibly hydrogenated and dehydrogenated in
catalytic processes.
Abstract: For H2 storage based on reversible hydrogenation and
dehydrogenation of a liquid organic hydrogen carrier (LOHC), we
herein demonstrate a potential of 2-(n-methylbenzyl)pyridine (MBP)
with the H2 storage density of 6.15 wt%. This material and the
corresponding perhydro product (H12-MBP) exist in liquid state at
room temperature. Remarkably, H2 release is much faster from H12-
MBP over Pd/C than from the benchmark perhydro benzyltoluene
over Pt/C at lower temperatures than 270 °C due to the addition of N
atom into the benzene ring. Since this positive effect is unfavorable
to the hydrogenation reaction, more Ru/Al2O3 catalyst or prolonged
reaction time would be applied for complete H2 storage. Experiments
for repeated hydrogenation/dehydrogenation cycles reveal that
reversible H2 storage and release are possible without degradation
of the pair MBP/H12-MBP. The prepared MBP satisfies the
requirements in chemical stability, handling properties, and
cytotoxicity test.
N-ethylcarbazole (NEC) is a promising LOHC that was
suggested by the company Air Products and Chemicals.[3] H2-
lean NEC is converted to the corresponding perhydro product
(H12-NEC) by the hydrogenation reaction, where the added H2
per mol NEC are 6 mol yielding H2 storage capacity of 5.8 wt%.[4]
However, the pair NEC/H12-NEC has two main drawbacks to
complicate implementation for practical applications; a) the fully
dehydrogenated, pure NEC is a solid at room temperature due
to the melting point of 68 °C and NEC even at the hydrogenation
degrees above 10% can be solid under ambient conditions;[5] b)
the thermal stability of NEC is limited by the dealkylation to
carbazole possibly happening above 270 °C in the presence of
dehydrogenation catalysts, although the typical temperature for
H12-NEC dehydrogenation is around 230 °C. To overcome
these limitations, Wasserscheid and coworkers suggested
alternative LOHC systems using isomeric benzyltoluenes (BT)
and dibenzyltoluenes (DBT) that have been widely used as
industrial heat-transfer fluids.[6] Despite their practical
attractiveness, the dehydrogenation of H2-rich BT (H12-BT) and
DBT (H18-DBT) requires elevated temperatures compared to
H12-NEC; for instance, full dehydrogenation is achieved at
temperatures higher than 270 °C and needs prolonged exposure
to catalyst particles.
In this respect, the substitution with nitrogen in aromatic
rings is worth being considered, as demonstrated in the
NEC/H12-NEC pair. Crabtree described that nitrogen atoms
have a positive effect on thermodynamic properties concerning
their use as hydrogen carriers.[7] Müller et al. also confirmed the
potential of nitrogen-containing aromatic compounds to
experience enthalpy changes during hydrogenation and thereby
favor the dehydrogenation reaction.[2c] Thus, we examined the
enthalpy of dehydrogenation reaction (ΔHdehydro) by density
functional theory (DFT) calculations (details in Supporting
Information), when the perhydro product of diphenylmethane is
modified by N substitution and CH3 addition. Figure 1 clearly
shows that the substitution of N atom into the aromatic ring
makes the release of hydrogen thermodynamically favorable by
reducing the overall dehydrogenation enthalpy while it
decreases H2 storage capacity in relatively small extents
(marked by blue arrows). The addition of methyl group is also
effective in the reduction of the dehydrogenation enthalpy but
lowers H2 storage capacity by at least 0.41 wt% per methyl
group. Since the enthalpy of dehydrogenation for the
heterocyclic ring is lower than that for the homocyclic ring, the
materials containing at least one N-containing heterocycle like 2,
4, 5, 6, and 7 have lower overall dehydrogenation values
compared to benchmark H12-BT (3). However, some problems
were found for the materials 2, 4, and 6; 1) the opening of the N-
containing ring was observed in the dehydrogenation of the
material 2 over Pd/C at 270 °C; 2) it was hard to technically
prepare the dehydrogenation product of the materials 4 and 6 as
liquid state due to strong intermolecular interaction of N atoms.
Since the theoretical H2 storage capacity of the material 7 is
below 6 wt%, the material 5 (marked by a red star) was selected
for this communication and demonstrated for the first time as a
potential LOHC material.
The hydrogen economy is based on three elements such as
production, storage, and utilization of hydrogen as an energy
carrier.[1] H2 is currently produced by steam reforming of fossil
fuels, and future H2 production is likely based on the electrolysis
of water using electricity generated from renewable energy
resources. The produced hydrogen can be utilized, for example,
in fuel cells or in internal combustion engines while fuel cells
available at a lower cost are being developed. However, there
are a number of issues to be addressed for efficient hydrogen
storage. Among three types of conversion to overcome storage
limitations associated with elemental hydrogen, reversible H2
storage by means of chemical bonds (i.e., hydrogenation and
dehydrogenation) is proposed to be a promising solution.[2] In
this concept a H2-lean molecule is hydrogenated at a site
supplying abundant, cheap hydrogen into the corresponding H2-
rich molecule that can be stored for extended periods and
transported using present energy transport infrastructures. H2 is
finally released at energy demand sites via catalytic
dehydrogenation and then H2-lean molecule can go back to
[a] J. Oh, T. W. Kim, Prof. Dr. Y.-W. Suh
Department of Chemical Engineering
Hanyang University
Wangsimni-ro 222, 04763 Seoul (Republic of Korea)
E-mail: ywsuh@hanyang.ac.kr
[b] K. Jeong, Dr. J. H. Park
Carbon Resources Institute
Korea Research Institute of Chemical Technology
Gajeong-ro 141, Yuseong-gu, 34114 Daejeon (Republic of Korea)
E-mail: jihpark@krict.re.kr
[c] H. Kwon
Department of Chemical Engineering
University of Seoul
Seoulsiripdae-ro 163, Dongdaemun-gu, 02504 Seoul (Republic of Korea)
[d] Prof. Dr. J. W. Han
Department of Chemical Engineering
Pohang University of Science and Technology (POSTECH)
Cheongam-Ro 77, Nam-Gu, 37673 Pohang (Republic of Korea)
[e] Prof. Dr. Y.-W. Suh
Research Institute of Industrial Science
Hanyang University
Wangsimni-ro 222, 04763 Seoul (Republic of Korea)
Supporting information and the ORCID identification number(s) for the
author(s) of this article can be found under: https://doi.org/10.1002/
ccsc.xxxxxxxxx.
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10.1002/cssc.201702256
ChemSusChem
COMMUNICATION
Scheme 1. Synthesis protocol for MBP starting from 2-methylpyridine.
The molecular weights of the as-prepared MBP and its
perhydro product, 2-[(n-methylcyclohexyl)-methyl]piperidine
isomers (H12-MBP), were measured to be 183.1124 (calcd.
183.1126 for C13H13N) and 195.2064 (calcd. 195.2065 for
C13H25N) by high-resolution mass spectra, respectively (Figure
S2). This represents the theoretical H2 storage capacity of 6.15
wt% similar to the pairs toluene/methylcyclohexane (6.12 wt%)
and BT/H12-BT (6.22 wt%). The melting points of MBP and
H12-MBP were measured to be in the range −50.1 to −46.2 °C
and −19.3 to −18.0 °C, respectively (Figure S3), indicating that
they both exist in liquid state at room temperature. Their boiling
points were estimated to be ca. 291–293 °C. These thermal
properties are comparable to those of the pair BT/H12-BT and
clearly fulfill thermal requirement for reversible LOHC materials.
Therefore, the process conditions for H2 storage and release will
be nearly similar with both pairs.
Figure 1. Effect of N substitution and CH3 addition to dicyclohexylmethane on
the calculated dehydrogenation enthalpy value and theoretical hydrogen
storage capacity. The value in parentheses indicates the difference of
ΔHdehydro between the molecules in each arrow.
Next, we examined catalytic H2 release from H12-MBP
with supported Pt and Pd catalysts (metal/reactant (M/R) = 0.1
mol%) at 270 °C typical for the dehydrogenation of H12-BT
(Table 1). In the dehydrogenation of H12-MBP, supported Pd
catalysts on carbon and alumina were more active than Pt
analogues on the same supports, where Pd/C showed nearly
100% efficiency in H2 release. This is contrary to the results in
the dehydrogenation of H12-BT; consistent with Wasserscheid
et al.,[6] our activity results identified the superior performance of
supported Pt to Pd. Further tests at 230 and 250 °C confirmed
the higher dehydrogenation activities of Pd/C in the conversion
Since the material 5 is not commercially available, the
synthesis protocol for acquiring in bulk quantity was investigated
at first. In preliminary tests, the Friedel-Crafts alkylation of
toluene with 2-chloromethyl pyridine over aluminum chloride
showed a higher product yield (>90%) than coupling reactions
using Grignard reagent, organozinc halide or metal catalyst with
special ligands. However, since the production cost largely
depends on the price of 2-chloromethyl pyridine, we developed
the synthesis protocol starting from 2-methylpyridine (Scheme 1), of H12-MBP. In order to validate experimental results, we are
which was described in Supporting Information. The final
product identified by 13C NMR spectrum (Figure S1) was 2-(n-
methylbenzyl)pyridine isomers (hereafter referred to as MBP).
Since the proposed synthesis needs relatively simple work-up
and cheap raw materials, MBP could be prepared cheaply; for
instance, the material cost approximately amounts to US $8 to
$9 per kilogram when calculated from bulk quote of raw
materials. Note that the retail price of technically available BT
(e.g., Marlotherm® LH as a registered trademark of Sasol
Germany GmbH) ranges in US $7 to $8 per kilogram. We are
now pursuing to secure a cheaper synthesis protocol at several
tons scale based on the direct chlorination of 2-methylpyridine.[8]
making DFT calculations as examined for catalytic behaviors of
Pt and Pd in the dehydrogenation of decalin to naphthalene,[9]
which will be reported later.
The important finding is much faster H2 release from H12-
MBP over Pd/C compared to the benchmark H12-BT over Pt/C
at 230, 250, and 270 °C (Figure 2a). The addition of N atom into
the benzene ring is beneficial to the dehydrogenation reaction,
similar to the dehydrogenation performance of Pd catalysts for
H12-NEC.[10] However, catalyst deactivation cannot be ruled out
because the catalytic dehydrogenation of H12-MBP became
saturated at 230 and 250 °C by preferential adsorption of the
pyridine ring. As the piperidine ring is dehydrogenated much
Table 1. Activity results in the dehydrogenation of H12-MBP and H12-BT for 4 h.
Catalyst
Temperature
[°C]
M/R
Conversion
Selectivity to MBP or BT
[mol%][b]
H2 yield
H2 volume
[cm3][c,d]
[mol%, wt%][a]
[mol%][b]
[mol%][b]
H12-MBP conversion
Pt/C (1 wt%)
270
270
270
270
250
230
250
230
230
0.1, 0.100
0.1, 0.100
0.1, 0.054
0.1, 0.054
0.1, 0.054
0.1, 0.054
0.2, 0.109
0.4, 0.217
0.6, 0.326
62.8
58.9
98.7
92.2
60.4
37.3
94.4
73.6
86.7
78.3
79.8
99.9
99.2
90.9
54.7
98.4
92.7
97.6
55.9
53.0
98.7
91.8
57.7
28.8
93.6
70.9
85.7
643.1 (56.7)
605.6 (53.4)
1132.4 (99.9)
1045.7 (92.2)
662.3 (58.4)
342.5 (30.2)
1082.0 (95.4)
824.5 (72.7)
968.6 (85.4)
Pt/Al2O3 (1 wt%)
Pd/C (1 wt%)
Pd/Al2O3 (1 wt%)
Pd/C (1 wt%)
Pd/C (1 wt%)
Pd/C (1 wt%)
Pd/C (1 wt%)
Pd/C (1 wt%)
H12-BT conversion
Pt/C (1 wt%)
Pt/Al2O3 (1 wt%)
Pd/C (1 wt%)
Pd/Al2O3 (1 wt%)
Pt/C (1 wt%)
Pt/C (1 wt%)
Pt/C (1 wt%)
270
270
270
270
250
230
250
230
230
0.1, 0.100
0.1, 0.100
0.1, 0.054
0.1, 0.054
0.1, 0.100
0.1, 0.100
0.2, 0.200
0.4, 0.400
0.6, 0.600
99.9
95.0
60.8
49.1
61.1
26.9
98.1
47.5
79.2
98.6
97.2
85.1
86.3
80.0
93.7
92.2
88.3
86.3
99.2
93.7
56.2
45.7
55.0
26.1
94.2
44.7
73.8
1132.4 (99.9)
1079.7 (95.2)
646.5 (57.0)
543.3 (47.9)
641.9 (56.6)
299.4 (26.4)
1102.4 (97.2)
514.9 (45.4)
822.3 (72.5)
Pt/C (1 wt%)
Pt/C (1 wt%)
[a] M/R = Metal-to-reactant ratio. [b] Calculated by GC results. [c] Measured by gas burette at the end of the experiment. [d] The values in parenthesis indicate
calculated H2 yields (unit: %) on the basis of H2 volume (1134.2 cm3) expected upon complete dehydrogenation of the reactant.
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10.1002/cssc.201702256
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COMMUNICATION
perhydro isomers was studied at 150 °C and 50 bar of H2 over
supported Ru catalysts, where the reaction condition is similar to
that in Wasserscheid et al.[6] When the M/R value of 0.08 mol%
and the reaction time of 2 h were used, H2 loading was less
efficient for MBP than for BT over a commercial 5 wt% Ru/Al2O3
(Table 2). Note that the pyridine ring is hydrogenated earlier
than the benzene ring (identified by 1H NMR spectra and GC
chromatograms in Figure S5), as found in the synthesis of 2-
and 4-substituted benzylpiperidines.[11] Even with 0.23 mol%
M/R value and more active Ru catalysts demonstrated in the
hydrogenation of benzylpyridine,[12] 100% selectivity to H12-MBP
was not obtained at 2 h though the conversion of MBP reached
100%. This is due to an adverse effect of introducing N atom
into the aromatic ring on the Gibbs free energy of hydrogenation
reaction. Nevertheless, such limitation could be circumvented by
applying a prolonged reaction time (e.g., 4 h) or by adding more
catalyst amount relative to the MBP amount (e.g., M/R of 0.30
mol%). When considering a much lower price of Ru (US $65 per
troy oz. in September 2017) than other noble metals (Pt and Pd:
US $979 and $943 per troy oz., respectively), the latter option
(i.e., more catalyst) would be recommended for practical
application.
Under the best conditions for the hydrogenation and
dehydrogenation reactions, the reversibility of only the pair
MBP/H12-MBP was tested (Figure S6). In the first cycle, the H2
storage efficiency of the as-prepared MBP was estimated to be
100% over Ru/Al2O3 and the measured H2 yield released from
the hydrogenation product H12-MBP was also 100 mol% over
Pd/C. The same values of H2 storage efficiency and H2 yield
were achieved in the second and third cycles. When the gas
chromatograms of the product mixtures obtained in the three-
cycle test were compared, no decomposition products were
found in the liquid phase (Figure 3). Also, light boiling
decomposition products were not detected in the gas phase
(Figure S7), which will be investigated more accurately in our
further work. Therefore, the pair MBP/H12-MBP can be used
reversibly. Notably, the hydrogenation and dehydrogenation
products obtained from the experiments were used repeatedly,
for example, at least fifty times due to difficulty in the consistent
supply of fresh MBP.
Figure 2. a) Time-dependent H2 release curves for H12-MBP over Pd/C (filled
symbols) and for H12-BT over Pt/C (open symbols) at 230, 250, and 270 °C,
where the M/R value was 0.1 mol%. b) H2 release curves at 230 °C for H12-
MBP over Pd/C (blue symbols) and for H12-BT over Pt/C (red symbols),
where the M/R value was 0.4 mol% (circles) or 0.6 mol% (triangles). The
horizontal lines represent the isothermal region in the experiments.
The stability of H2-lean MBP was also tested under three
different conditions. As listed in Table S1, MBP was very stable
under air at 100 °C and under N2 at 270 °C for 72 hours, similar
to BT under identical conditions. This indicates that MBP can be
stored at ambient temperature and even at high temperatures if
inert atmosphere is applied. However, the test in the presence of
a typical dehydrogenation catalyst Pd/C (M/R = 0.2 mol%) under
N2 at 270 °C showed the formation of decomposition products
whose amount was slightly higher than from BT with Pt/C, which
is similar to the NEC case.[6] Such formation could be
significantly reduced at a lower temperature of 250 °C showing
nearly complete dehydrogenation of H12-MBP.
faster than the cyclohexane ring, 2-[(n-methylcyclohexyl)-
methyl]pyridine isomers were only detected as the reaction
intermediate (identified by 1H NMR spectra and GC
chromatograms in Figure S4). In order to prevent this trouble,
more active metals relative to the amount of H12-MBP are
required; for instance, 95.4% of theoretical H2 volume was
attained at 250 °C with Pd/C with the M/R value of 0.2 mol%
(Table 1). It is more remarkable that at 230 °C the
dehydrogenation of H12-MBP over Pd/C is faster and, at the
same time, more efficient than that of H12-BT over Pt/C, where
the M/R value is sufficiently high at 0.4 and 0.6 mol% (Figure 2b).
Since H2 release is more facile from H12-MBP than from H12-
BT, we can use milder conditions for the dehydrogenation of the
former material.
Additionally, the MBP properties relevant to practical
transportation and storage were investigated. First, the apparent
viscosity of H2-lean MBP was measured in the temperature
Next, the hydrogenation of MBP into the corresponding
Table 2. Catalytic H2 storage of H2-lean BT and MBP at 150 °C and 50 bar over Ru/Al2O3
Reactant
(20 ml)
Catalyst
M/R
Time
[h]
Conversion
[mol%][b]
Selectivity to H12-BT or H12-MBP
[mol%][b]
H2 storage eff.
[%][c]
[mol%, wt%][a]
BT
BT
5 wt% Ru[d]
5 wt% Ru[d]
5 wt% Ru[d]
5 wt% Ru[d]
5 wt% Ru[e]
1 wt% Ru[e]
1 wt% Ru[e]
1 wt% Ru[e]
0.05, 0.03
0.08, 0.05
0.08, 0.05
0.23, 0.13
0.23, 0.13
0.23, 0.13
0.23, 0.13
0.30, 0.17
2
2
2
2
2
2
4
2
100.0
100.0
21.0
100.0
100.0
100.0
100.0
100.0
77.6
100.0
0.0
44.2
66.8
77.7
100.0
100.0
88.8
100.0
10.5
72.1
83.4
88.8
100.0
100.0
MBP
MBP
MBP
MBP
MBP
MBP
[a] M/R = Metal-to-reactant ratio. [b] calculated by GC results. [c] H2 storage efficiency = (full hydrogenation product [mol] × 6H2 + single-ring hydrogenation
product [mol] × 3H2)/(reactant [mol] × 6H2) × 100%. [d] 5 wt.% Ru/Al2O3 (Alfa Aesar) used after reduction by H2 at 250 °C for 4 h. [e] 1 and 5 wt% Ru/γ-Al2O3
prepared by H2 activation of Al2O3-supported Ru3(CO)12 precursor at 500 °C for 5 h.
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10.1002/cssc.201702256
ChemSusChem
COMMUNICATION
MBP should be evaluated; although the cytotoxicity test showed
that MBP-treated cells are more viable than BT-treated ones
(Figure S11), the ecotoxicity against aquatic environments would
be studied in near future.
Acknowledgements
This work was financially supported by the Korea Institute of
Energy Technology Evaluation and Planning under the Ministry
of Trade, Industry & Energy, Republic of Korea (KETEP-2015-
3030041160) and by the Basic Science Research Program
through the National Research Foundation of Korea under the
Ministry
of
Education,
Republic
of
Korea
(NRF-
2016R1A6A1A03013422). The authors are grateful to Dr. G. O.
Lee for her help in the cytotoxicity test at the Jeollanamdo
Institute of Natural Resources (JINR) research center.
Conflict of interest
The authors declare no conflict of interest.
Keywords: sustainable chemistry • hydrogen storage •
Figure 3. GC chromatograms of the product mixtures obtained thorough
three cycles of MBP hydrogenation over 1 wt% Ru/Al2O3 (reaction condition:
M/R = 0.3 mol%, 150 °C, 50 bar, 2 h) and H12-MBP dehydrogenation over 1
wt% Pd/C (reaction condition for H2 release: M/R = 0.1 mol%, 270 °C, 4 h).
For GC analysis, the oven program A (presented in Supporting Information)
was used.
dehydrogenation • N-containing heterocycles
[1]
[2]
P. Preuster, C. Papp, P. Wasserscheid, Acc. Chem. Res. 2017, 50, 74–
85.
a) D. Teichmann, W. Arlt, P. Wasserscheid, R. Freymann, Energy
Environ. Sci. 2011, 4, 2767–2773; b) D. Teichmann, K. Stark, K. Müller,
G. Zöttl, P. Wasserscheid, W. Arlt, Energy Environ. Sci. 2012, 5, 9044–
9054; c) K. Müller, J. Völkl, W. Arlt, Energy Technol. 2013, 1, 20–24; d)
M. Markiewicz, Y. Q. Zhang, A. Bosmann, N. Bruckner, J. Thoming, P.
Wasserscheid, S. Stolte, Energy Environ. Sci. 2015, 8, 1035–1045.
a) G. P. Pez, A. R. Scott, A. C. Cooper, H. Cheng, (Air Products and
Chemicals Inc.), US7101530 B2, 2006; b) M. Arnende, C. Gleichweit, K.
Werner, S. Schernich, W. Zhao, M. P. A. Lorenz, O. Höfert, C. Papp, M.
Koch, P. Wasserscheid, M. Laurin, H.-P. Steinrück, J. Libuda, ACS
Catal. 2014, 4, 657–665; c) M. Amende, C. Gleichweit, S. Schernich, O.
Höfert, M. P. A. Lorenz, W. Zhao, M. Koch, K. Obesser, C. Papp, P.
Wasserscheid, H.-P. Steinrück, J. Libuda, J. Phys. Chem. Lett. 2014, 5,
1498–1504.
range −5 to 50 °C (details in Supporting Information). The values
are higher than those of BT at all temperatures (Figure S8), but
the difference at 25 °C is only 2.1 cP (3.8 cP for BT vs. 5.9 cP
for MBP). When compared with DBT (ca. 37.8 cP) and ethylene
glycol (16.1 cP) at 25 °C, MBP is much less viscous. Next, the
corrosion rate of MBP and H12-MBP was evaluated by the
copper strip corrosion test (ASTM D130-12) to visually compare
with the Copper Strip Corrosion Standards a color of Cu strips
obtained after immersion in a solution at 100 °C specific for
diesel fuels for 3 h, (Figure S9).[13] In the tests with fresh H12-
MBP and MBP solutions at 100 °C, the corrosion rate was
estimated to be 1a or 1b (“slight tarnish”), as shown in Figure
S10. The similar corrosion rate was examined with the MBP
solution obtained after the third dehydrogenation in the three-
cycle test at 100 °C and even at the elevated temperature of
270 °C, which was also observed in the tests with BT at 100 and
270 °C. Therefore, MBP can be transported through existing
pipelines without difficulty.
[3]
[4]
a) K. M. Eblagon, D. Rentsch, O. Friedrichs, A. Remhof, A. Zuettel, A. J.
Ramirez-Cuesta, S. C. Tsang, Int. J. Hydrogen Energy 2010, 35,
11609–11621; b) K. M. Eblagon, K. Tam, K. M. K. Yu, S.-L. Zhao, X.-Q.
Gong, H. He, L. Ye, L.-C. Wang, A. J. Ramirez-Cuesta, S. C. E. Tsang,
J. Phys. Chem. C 2010, 114, 9720–9730.
In summary, we examined the potential of the pair
MBP/H12-MBP as a possible LOHC material, where the melting
points of both molecules are lower than 0 °C and their boiling
points are ca. 291–293 °C. Overall, this pair showing H2 storage
density of 6.15 wt% fairly satisfies the requirements in chemical
reversibility without decomposition, chemical and thermal
stability, and handling property. Particularly, the full
dehydrogenation of H12-MBP could be performed at lower
temperatures with faster rates than that of the benchmark BT
used as a heat transfer fluid, which is the favorable effect of N
atom present in the pyridine ring. Although this effect influenced
the hydrogenation reaction adversely, it could be overcome
simply by more addition of supported Ru catalyst because Ru is
much cheaper than other noble metals. Consequently, the pair
MBP/H12-MBP is evaluated to contain LOHC properties
comparable to or even better than the pair BT/H12-BT.
Nevertheless, additional works would be done to address the
possibility of our LOHC material in practical use, including the
matters related with the hydrogenation and dehydrogenation
reactions (typically, the preparation of more active
hydrogenation and dehydrogenation catalysts (now under study)
and the development of efficient reactors for H2 storage and
release). Particularly, toxicological aspects of MBP and H12-
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10.1002/cssc.201702256
ChemSusChem
COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
Boost up H2 economy: A new liquid
organic hydrogen carrier is designed
by adding N atom into the benzene
ring of a benchmark heat transfer
fluid. The crossover between H2-lean
and H2-rich forms of the title material
is successfully reversible in repeated
runs. Notably, H2 release is very fast
owing to a reduced dehydrogenation
enthalpy by the presence of N atom.
Our approach can contribute to an
efficient H2 storage system.
J. Oh, K. Jeong, T. W. Kim, H. Kwon,
J. W. Han, J. H. Park,* Y.-W. Suh*
Page No. – Page No.
A potential liquid organic
hydrogen carrier: 2-(n-
methylbenzyl)pyridine with fast H2
release and stable activity in
consecutive hydrogenation-
dehydrogenation cycles
This article is protected by copyright. All rights reserved.