Low-temperature selective catalytic dehydrogenation of methylcyclohexane by surface protonics

Article abstract of DOI:10.1039/c9ra06042a

The methylcyclohexane (MCH)-toluene cycle is a promising liquid organic hydride system as a hydrogen carrier. Generally, MCH dehydrogenation has been conducted over Pt-supported catalysts, for which it requires temperatures higher than 623 K because of its endothermic nature. For this study, an electric field was applied to Pt/TiO₂ catalyst to promote MCH dehydrogenation at low temperatures. Selective dehydrogenation was achieved with the electric field application exceeding thermodynamic equilibrium, even at 423 K. With the electric field, "inverse" kinetic isotope effect (KIE) was observed by accelerated proton collision with MCH on the Pt/TiO₂ catalyst. Moreover, Pt/TiO₂ catalyst showed no methane by-production and less coke formation during MCH dehydrogenation. DRIFTS and XPS measurements revealed that electron donation from TiO₂ to Pt weakened the interaction between catalyst surface and π-coordination of toluene. Results show that the electric field facilitated MCH dehydrogenation without methane and coke by-production over Pt/TiO₂ catalyst.

Full text of DOI:10.1039/c9ra06042a

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Low-temperature selective catalytic
dehydrogenation of methylcyclohexane by surface
Cite this: RSC Adv., 2019, 9, 27743
protonics†
a
a
a
ab
c
Kent Takise, Ayaka Sato, Shuhei Ogo,
Jeong Gil Seo,
Ken-ichi Imagawa,
c
a
Shigeru Kado and Yasushi Sekine
*
The methylcyclohexane (MCH)–toluene cycle is a promising liquid organic hydride system as a hydrogen
carrier. Generally, MCH dehydrogenation has been conducted over Pt-supported catalysts, for which it
requires temperatures higher than 623 K because of its endothermic nature. For this study, an electric
2
field was applied to Pt/TiO catalyst to promote MCH dehydrogenation at low temperatures. Selective
dehydrogenation was achieved with the electric field application exceeding thermodynamic equilibrium,
even at 423 K. With the electric field, “inverse” kinetic isotope effect (KIE) was observed by accelerated
proton collision with MCH on the Pt/TiO
production and less coke formation during MCH dehydrogenation. DRIFTS and XPS measurements
revealed that electron donation from TiO to Pt weakened the interaction between catalyst surface and
p-coordination of toluene. Results show that the electric field facilitated MCH dehydrogenation without
methane and coke by-production over Pt/TiO catalyst.
2 2
catalyst. Moreover, Pt/TiO catalyst showed no methane by-
Received 4th August 2019
Accepted 26th August 2019
2
DOI: 10.1039/c9ra06042a
rsc.li/rsc-advances
2
6,7
and naphthene compounds (i.e. cycloalkanes). At hydrogen
generation sites, aromatics are converted to naphthene
Introduction
Wide distribution of high-purity hydrogen is anticipated to compounds by catalytic hydrogenation. The reverse reaction:
make it available as a clean secondary energy source: many dehydrogenation of naphthene to aromatics, is conducted at
primary energy resources can be hydrogen sources; and water is hydrogen consumption sites. Among various liquid organic
the only product of hydrogen combustion. Through the years, hydrides, the most well-known and promising system is
various hydrogen distribution systems such as compressed a methylcyclohexane (MCH)–toluene cycle (hydrogen capacity:
hydrogen, hydrogen liquefaction, and chemical storage using 6.1 wt%) by virtue of its nontoxicity and wider range of liquid
6,7
liquid compounds including ammonia and organic hydrides phase at 178–374 K.
cycloalkanes) have been examined. Nevertheless, compressed
Dehydrogenation of MCH is an endothermic reaction (as
hydrogen requires large-scale systems and high-pressure shown in eqn (1)): an energy-consuming process. This reaction
(
1
8
storage tanks. Liqueed hydrogen is unsuitable for long-term has been performed over a Pt-supported catalyst. Results show
2,3
storage because of its attendant evaporation loss (boil-off).
Although ammonia has been anticipated as a promising temperatures.
hydrogen carrier with a high hydrogen capacity (17.6 wt%), it tivated with coke formation and/or toluene fouling during the
high activity for dehydrogenation above 623 K of reaction
6,9–11
However, Pt-based catalysts are easily deac-
4,5
12–15
16
17
has high toxicity. Organic hydrides are more practical media reaction.
2
Recently, Ir/USY, partially reduced Mo/SiO , Pt–
for long-term storage and for mass transportation in terms of Mo/SiO (ref. 11 and 18) catalysts have been reported as effective
2
6–8
cost effectiveness and safety.
catalysts for dehydrogenation of MCH.
Using organic hydrides requires reversible hydrogenation
and dehydrogenation reactions proceeding between aromatic
0
C
7
H
14 / C
7
H
8
+ 3H
2
, DH298 ¼ 205 kJ molꢀ1
(1)
(2)
0
C
7
H
8
+ H
2
/ C
6
H
6
+ CH
4
, DH298 ¼ ꢀ42 kJ molꢀ1
a
Waseda University, Department of Applied Chemistry, 3-4-1, Okubo, Shinjuku, Tokyo,
Feasibility of the organic hydride system depends on the
product selectivity and lifetime of MCH dehydrogenation cata-
1
69-8555 Japan. E-mail: ysekine@waseda.jp
b
Myongji University, Department of Energy Science and Technology, 116 Myongji-ro,
lysts.
A side-reaction of MCH dehydrogenation, hydro-
Yongin-si, Gyeonggi-do 17058, Republic of Korea
c
R&D Center, Chiyoda Corporation, 3-13, Moriya-cho, Yokohama, Kanagawa, 221- demethylation of toluene (as shown in eqn (2)), and coking on
19–22
0
†
1
022, Japan
the catalyst are key difficulties to be overcome.
production of benzene and methane as by-products, thereby
They lead to
Electronic supplementary information (ESI) available. See DOI:
0.1039/c9ra06042a
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19
increasing the costs of hydrogen purication. Furthermore, components and coke formation amount indicated a credible
23
benzene is toxic for humans. For this study, an electric eld mass balance (almost 100%).
was applied over Pt/TiO catalyst to promote MCH dehydroge-
2
nation at lower temperatures without methane or coke by- Partial pressure dependency and isotope effects
production. This report is the rst of low-temperature and
selective catalytic dehydrogenation of MCH over Pt/TiO catalyst
2
in an electric eld.
Partial pressure dependencies of MCH, toluene, and hydrogen
on reaction rates were evaluated over Pt/TiO catalyst to eluci-
2
date the role of the electric eld. Results were obtained with and
without the electric eld at the same MCH-conversion-level i.e.
(a) at 423 K with the electric eld and (b) at 498 K without the
electric eld. For this experiment, the total feed gas ow was set
Experimental
Catalyst preparation
ꢀ
1
as 56.4 mL min at ambient pressure of 0.1 MPa. Then, the gas
ratio was modied as C
2
For catalyst preparation, platinum was supported on TiO (JRC-
7
H
14 : Ar ¼ (3.2, 6.4, 9.6, 11.3) : (53.2,
TIO-16) and CeO2 (JRC-CEO-1) using a wet-impregnation
method. Aer catalyst supports were drenched in 25 mL of
water for 120 min, Pt precursor, i.e. Pt(NH ) (NO ) (Sigma-
5
4
9
0.0, 46.8, 45.1), C H : C H : Ar ¼ 6.4 : (1.0, 2.0, 3.0,
7
14
7
8
.0) : (49.0, 48.0, 47.0, 46.0) and C H : H : Ar ¼ 6.4 : (4.0, 7.0,
7
14
2
3
4
3 2
.0, 12.0) : (46.0, 43.0, 41.0, 38.0). Reaction rates were deter-
formation rate measured using GC-TCD (GC-
A; Shimadzu Corp.).
MCH dehydrogenation was conducted by supplying isotopes of
MCH and H to investigate isotope effects with and without the
electric eld. Accordingly, the reaction gas consisted of C 14 (or
Aldrich Corp.) was added with 15 mL of diluted water and was
dissolved for 120 min in an evaporator. An adequate amount of
mined by the H
8
2
platinum precursor was introduced to make 3 wt%Pt/TiO
2
and
. The obtained solution was dried and calcined at
73 K for 120 min. The resultant catalyst powder was pressed
3
7
wt%Pt/CeO
2
2
7
H
and sieved to 355–500 mm. Prepared catalyst was used for the
reaction in the electric eld without any pre-treatment.
C D ; denoted as MCH ) : H (or D ) : Ar ¼ 6.4 : 4.0 : 46.0. The
7
14
D
2
2
ꢀ1
total gas ow rate was 56.4 mL min . Reaction rates were assessed
by the formation rates of H , HD, and D .
2
2
Catalytic activity tests
2
A xed-bed ow type reactor was packed with 200 mg of Pt- DRIFTS measurements during toluene feed over Pt/TiO and
supported catalysts to conduct MCH dehydrogenation. An Pt/CeO
electric eld was applied using two stainless steel electrodes set
2
DRIFTS (diffuse reectance for infrared Fourier transform
on upper side and bottom side of the catalyst bed. Catalytic
dehydrogenation in the electric eld was performed by appli-
cation of 3.0 mA of constant current between two electrodes.
The reaction temperature was set between 423 to 773 K with and
without the electric eld. A thermocouple was placed on the
catalyst bed for monitoring the real temperature of the catalyst
because Joule heat is expected to increase the catalyst temper-
ature during dehydrogenation in the electric eld. Ttc stands for
the real catalyst temperature measured by the thermocouple.
spectroscopy) measurements were conducted to investigate
toluene adsorption over Pt/TiO and Pt/CeO catalysts using
2 2
a Fourier transform infrared spectrometer (FT/IR-6100; Jasco
Corp.). Teon-made DRIFTS cells were packed with sieved
catalyst, on which two stainless steel electrodes were set to apply
the electric eld. Detailed information related to the apparatus
24
of DRIFTS measurement is presented elsewhere. Although the
electric eld was stabilized over Pt/TiO in a xed-bed ow-type
2
reactor, electrical discharge has occurred all the time over
The reaction gas consisted of C
7
H
14 : Ar ¼ 6.4 : 30 (total gas ow
packed Pt/TiO
with the electric eld was performed only over Pt/CeO
reasons. Toluene gas was introduced into the measurement
chamber for 30 min. Subsequently, in the case of Pt/CeO , the
2
in the DRIFTS cell. Therefore, the experiment
ꢀ
1
rate: 36.4 mL min ) at ambient pressure of 0.1 MPa. Reactions
were conducted in a kinetic region, i.e. diffusion is not a rate-
determining factor. The gaseous products of the reaction were
analyzed using GC-TCD (GC-8A; Shimadzu Corp.) and GC-FID
2
for safety
2
feed gas was switched to argon. Then an electric eld was
applied for 30 min. Subsequently, purge treatment was con-
ducted to extract toluene gas from the chamber atmosphere.
The DRIFTS spectra were obtained aer each process.
(
GC-8A; Shimadzu Corp.). The hydrogen yield was dened
ꢀ1
2
using the MCH feed rate (mmol min ) and H formation rate
ꢀ
1
(mmol min ).
Hydrogen yield (%) ¼ rH2/(C
7
H14 feed rate ꢁ 3) ꢁ 100
(3)
Characterization of catalysts
2
The apparent activation energy was estimated over Pt/TiO from The metallic surface area of Pt metal was evaluated using CO
Arrhenius plots during MCH dehydrogenation with and without the pulse measurements (Autosorb iQ; Quantachrome Instru-
electric eld. Reaction rates were estimated in kinetic control. The ments). For vaporizing adsorbed water on the catalyst, pre-
reaction rates were calculated from the H
same manner as that used for activity tests.
2
formation rate in the treatment was conducted at 673 K in helium. In addition,
STEM images and EDX mapping results were obtained from
Deposited coke amounts were evaluated using temperature scanning transmission electron microscopy (STEM; HF-2210;
programmed oxidation (TPO) measurements estimating CO or Hitachi Ltd.) to conrm the state of Pt over catalytic supports.
CO formation caused by the oxidation of coke. The tempera- The specic surface area of catalysts was examined using
2
ꢀ
1
ture was increased from 298 K to 1173 K at 10 K min in the gas nitrogen adsorption with the BET method (Gemini VII; Micro-
composition of O
ꢀ
1
2
: He ¼ 10 : 90 (mL min ). The product meritics Instrument Corp.). For this experiment, pre-treatment
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was conducted at 473 K in nitrogen atmosphere for 120 min.
Additionally, the electric state of Pt was investigated using XPS
measurements (VersaProbe2; ULVAC-PHI, Inc.) without an
exposure to air. Orbital 4f7/2 and 4f5/2 of Pt were measured. For
this experiment, X-ray source was Al Ka. The binding energies
were referenced to the C 1s peak at 284.8 eV.
Results and discussion
Promotion effects of electric elds on catalytic activity during
MCH dehydrogenation
Aer various screening tests, we performed MCH dehydroge-
nation over Pt/TiO
temperatures from 423 K to 773 K with and without an electric
eld (3 mA of constant current). The resultant catalytic activities
2
catalyst as an optimal catalyst at several
Fig. 1 Arrhenius plots of Pt/TiO
EF).
2
with and without the electric field
(

are presented in Table 1. Although the applied electric eld
produced little Joule heat, the increase of the catalyst bed
partial pressure dependencies of MCH, toluene, and hydrogen.
Generally speaking, the catalytic MCH dehydrogenation is
a reversible endothermic reaction. The MCH dehydrogenation
reaction rate is assumed as the following equation using MCH,
toluene, and hydrogen partial pressures.
temperature (thermocouple temperature, T ) was no more than
tc
1
0 K during the reaction. Additionally, the electric eld appli-
cation drastically improved the catalytic activity. The electric
eld effect was more remarkable at lower temperatures. Espe-

cially at 423 K, the catalytic activity was 17.9%, even in a kinetic
condition. That activity exceeded the equilibrium limitation
a
b
c
rdehydrogenation ¼ k[MCH] [Toluene] [H ]
2
(4)
(5%) at this temperature.
The values of apparent activation energy were evaluated with
and without the electric eld to elucidate the promoted catalytic
performance of Pt/TiO
catalyst by the electric eld. Fig. 1 shows MCH partial pressure similarly in both cases: a was 0.49 with
Arrhenius plots over Pt/TiO
catalyst during MCH dehydroge- the electric eld and 0.47 without the electric eld. As results
nation with (lled plots) and without (blank plots) the electric over Pt/TiO catalyst, the toluene partial pressure was unrelated
eld. According to these results, the respective values of to the dehydrogenation rate; b was zero with and without the
The dehydrogenation rate was correlated positively with the
2
2
2

ꢀ
1
apparent activation energy were 26.9 and 60.7 kJ mol with and electric eld. This tendency found for the toluene partial pres-
without the electric eld. Such experimental data indicate that sure, which differs from the well-known Pt catalyst supported
25
the applied electric eld facilitated the MCH dehydrogenation, on alumina, has been reported for Pt/TiO
and changed the reaction mechanism.
catalyst. Accord-
ingly, Pt catalyst supported on TiO is more tolerant of inhibi-
2
2
tion by toluene adsorption during MCH dehydrogenation.
Regarding results of hydrogen partial pressures found with and
without the electric eld, the MCH dehydrogenation rate was
Kinetic analysis and isotope effect during MCH
dehydrogenation in the electric eld
To investigate the role of the applied electric eld, partial
pressure dependencies were evaluated. Fig. 2 presents results of
Table 1 Catalytic activity during MCH dehydrogenation with/without
a
the electric field
Reaction
With EF
tc/K
Without EF
2
tc/K H yield/%
Temperature/K
T
H
2
yield/%
T
4
4
4
5
5
6
6
7
7
23
73
98
23
73
23
73
23
73
432
475
—
523
573
623
673
723
773
17.9
31.7
—
58.2
78.1
94.4
99.6
100.0
99.9
423
473
498
523
573
623
673
723
773
1.2
10.9
19.0
32.6
63.9
76.1
88.3
94.5
98.8
Fig. 2 Partial pressure dependences of (a) methylcyclohexane, (b)
toluene, and (c) hydrogen over Pt/TiO for MCH dehydrogenation.
2
Reaction temperature 423 K (with EF), 498 K (without EF), and input
current 3 mA.
a
Ttc: catalyst-bed temperature measured with a thermocouple.
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a
2
Table 2 Isotope effect during MCH dehydrogenation over Pt/TiO
ꢀ1
Condition
T
tc/K
H
2
production rate/mmol min
H
2
yield/%
D H
k /k /—
With EF (423 K)
MCH
MCH
MCH
MCH
MCH
MCH
MCH
MCH
H
/H
/D
/H
/D
/H
/D
/H
/D
2
437
435
434
433
496
495
497
496
109
134
135
160
169
182
111
117
13.8
17.1
17.1
20.3
21.5
23.2
14.2
14.9
—
H
2
1.24
1.24
1.47
—
1.08
0.66
0.69
D
D
2
2
Without EF (498 K)
H
H
2
2
D
D
2
2
a
Ttc: catalyst-bed temperature measured with a thermocouple.
hydrogen partial pressure was positively correlated with the
MCH dehydrogenation rate in the electric eld, c, was 0.15,
which differs from common results. In earlier studies, such
positive values of hydrogen partial pressure dependence are
+
apparent if proton (H ) hopping occurs on the catalyst
2
6–28
surface.
electric eld, protons hopped on Pd/CeO
facilitated methane activation by proton collision with
In the case of methane steam reforming in the
2
catalyst surface and
Fig. 3 Mechanism scheme of MCH dehydrogenation over Pt/TiO
2
in
the electric field.
24,26
methane.
Therefore, protons can function as a reaction
promoter during MCH dehydrogenation in the electric eld. In
the low temperature and low conversion region, toluene and
hydrogen, which were products of dehydrogenation had no
negative inuence on dehydrogenation rate. Therefore, dehy-
drogenation might proceed with an irreversible process.
To elucidate the role of proton species, isotope effects were
conrmed by supplying isotopic MCH and D during MCH
D 2
dehydrogenation with and without the electric eld (Table 2).
Here, isotope effects were expressed by the ratio of rate
Fig. 4 Results of catalytic activity tests in the electric field over Pt/TiO
2
2 4
and Pt/CeO at 423 K: (a) hydrogen yield and (b) CH by-production
rate.
negatively correlated by hydrogen without the electric eld, c
was ꢀ0.21. One can infer that hydrogen promoted reverse
toluene hydrogenation without the electric eld. However, the
Fig. 5 Spectra of in situ DRIFTS measurements of (a) Pt/TiO
Pt/CeO in various conditions at 423 K.
2
and (b) Fig. 6 XPS analysis of the Pt 4f7/2 and 4f5/2: (a) Pt/TiO
2
as made, (b) Pt/
2
TiO after EF, (c) Pt/CeO as made, and (d) Pt/CeO after EF.
2
2
2
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Table 3 Electronic state of Pt on TiO
2
and CeO
2
from XPS measurement
Binding energy/eV
Relative peak area/%
0
2+
4+
0
2+
4+
Catalyst
Condition
As made
Aer reaction with EF (423 K)
As made
Pt
Pt
Pt
Pt
Pt
Pt
3
3
3
3
wt% Pt/TiO
wt% Pt/TiO
wt% Pt/CeO
wt% Pt/CeO
2
70.8
70.9
70.9
70.8
72.4
72.5
72.4
72.5
74.2
74.3
74.2
74.3
22.9
43.5
16.5
39.8
52.2
27.1
74.8
50.0
24.9
29.5
8.8
2
2
2
Aer reaction with EF (423 K)
10.3
constants (k) with/without isotope, i.e. k /k ratio. Generally, k /
DRIFTS measurements were conducted over Pt/TiO and Pt/
2
D
H
D
kH is a value lower than 1 because chemical bonding of heavier CeO2 catalysts supplying toluene on the catalyst surface, as
2
9
isotopes is more stable (lower zero-point energy: ZPE).
Without the electric eld, the results follow these general trends be stable and applicable in the DRIFTS system because of the
when isotope MCH was introduced, k /k was 0.66 with cell structure. Therefore, in situ DRIFTS with the electric eld
MCH /H and k /k was 0.69 with MCH /D . Accordingly, the was conducted over Pt/CeO instead of Pt/TiO . Regarding the
kinetic isotope effect (KIE) was conrmed without the electric Pt/CeO catalyst, toluene adsorption was observed both with
eld. Nevertheless, with the electric eld, k /k increased as and without the electric eld (C–H stretching around
a larger proportion of deuterium was introduced into the 3000 cm ).
shown in Fig. 5. In the case of Pt/TiO , the electric eld cannot
2
D
D
H
D
2
D
H
D
2
2
2
2

D
H
ꢀ
1
35,36
However, the IR peaks for toluene are barely
reactor, as shown in Table 2. This inverse KIE has been observed visible over Pt/TiO catalyst, even under a toluene atmosphere.
2
when C–H–H conguration was formed through proton colli- Furthermore, the peaks disappeared completely aer purge
24
24,30–34
sion, explained by the ZPE discrepancy on isotopes.
2
treatment. These results demonstrate that Pt/TiO catalyst can
During MCH dehydrogenation in the electric eld, inverse KIE suppress toluene adsorption and methane by-production
are observed by the collision of accelerated proton with H (or D)- during MCH dehydrogenation.
+
atoms of MCH to form [H (or D)–H (or D)–C
7
H
13] over Pt/TiO
2
Fig. 6 and Table 3 present results of XPS measurements for Pt
and Pt/CeO . The XPS peaks for 4f7/2 and 4f5/2
orbitals are divisible into three states: Pt , Pt , and Pt . Here,
catalyst, to advance the reaction of MCH dehydrogenation over Pt/TiO
further. Aer dehydrogenation, the resultant state of C H
H has much lower energy level than the three-atom transition Pt was assumed as embedded Pt with strong metal and
2
2
+
0
2+
4+ 37
+
7
13
4
+
2
and the initial physisorption state (Fig. 3). In this case, reverse support interaction (SMSI). As SMSI is known to occur readily
hydrogenation has larger activation energy, making it difficult between Pt and TiO
to proceed.
2
(ref. 25) because Pt is highly dispersed and
Thereby, results suggest that the applied not aggregated (shown in ESI Fig. S2†), it might be the reason
electric eld promoted proton hopping and MCH dehydroge- why Pt/TiO showed lower surface area than Pt/CeO did (ESI
nation to show higher catalytic activity beyond the equilibrium Table S2†). Larger amounts of Pt might be embedded inside the
24,31,32,34
2
2
limitation (Fig. 3).
TiO
Pt/TiO and Pt/CeO from the ratio of (Pt + Pt )/Pt . Pt on TiO
2
showed more peak area for Pt even aer the reaction in the
2
support. Pt reducibility was estimated and compared over
0
2+
4+
2
2
4
+
Methane by-production suppression and the electric state of
platinum on Pt/TiO catalyst
2
4
+
electric eld, so the reducibility of Pt in/on TiO seems low
2
2
+
0
due to the SMSI. On the other hand, comparing Pt and Pt , Pt
on Pt/TiO is more metallic aer the reaction in the electric
eld. It has been described in earlier reports that supported Pt
is more easily reduced in the electric eld, and TiO can
2
donate electrons to Pt. The interaction between Pt and p-
Methane by-production rate and coke deposition over Pt/TiO2
catalyst were investigated during MCH dehydrogenation at 423
K in the electric eld. Only slight to no coke deposition occurred
in this catalyst system (ESI Table S1†). Also, the structure of
catalyst was not changed even aer the reaction in the electric
2

38
25
25
coordination of toluene can be weakened over reductive Pt.

eld (ESI Table S2†). Fig. 4 presents results of the catalytic
Consequently, reductive Pt over Pt/TiO catalyst is important for
2
activity and methane by-production rate during 120 min of
dehydrogenation. For better comparison, results over Pt/CeO2
catalyst are also presented in Fig. 4. Results show that Pt/TiO2
had no methane by-production aer 10–25 min of dehydroge-
nation as the applied electric eld being stabilized. According to
high tolerance against toluene inhibition and methane by-
production.
Conclusions
2
the partial pressure dependency of toluene, Pt/TiO catalyst
showed high tolerance against inhibition by toluene adsorption Dehydrogenation of methylcyclohexane (MCH) was conducted
during MCH dehydrogenation both with and without the elec- over Pt/TiO catalyst by applying an electric eld. The electric
2
tric eld. Methane by-production reportedly occurs with hydro- eld promoted the reaction to achieve 17.9% hydrogen yield,
demethylation of produced toluene during MCH dehydroge- even at 423 K and a kinetic condition, under which the catalytic
nation. Consequently, the toluene behavior over Pt/TiO2 is activity exceeded the equilibrium limitation (5%). Despite the
regarded as related to the methane by-production rate during reversibility of dehydrogenation, the reaction rate was positively
dehydrogenation.
correlated with the partial pressure of hydrogen with the electric
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
eld application. Additionally, an inverse kinetic isotope effect 14 G. Maria, A. Marin, C. Wyss, S. Muller and E. Newson, Chem.
KIE) was observed with isotope MCHD (C D ) and D in the Eng. Sci., 1996, 51, 2891–2896.
electric eld. These results indicate that hydrogen-derived 15 W. Wang, L. Miao, K. Wu, G. Chen, Y. Huang and Y. Yang,
species, i.e. protons, promoted the abstraction of H-atoms Int. J. Hydrogen Energy, 2019, 44, 2918–2925.
from MCH for dehydrogenation. Furthermore, Pt/TiO cata- 16 D. K. Cromwell, P. T. Vasudevan, B. Pawelec and
lyst, different from other catalysts, showed neither methane nor J. L. G. Fierro, Catal. Today, 2016, 259, 119–129.
coke by-production during MCH dehydrogenation in the elec- 17 N. Boufaden, R. Akkari, B. Pawelec, J. L. G. Fierro, M. Said
tric eld at 423 K. DRIFTS measurements revealed that toluene Zina and A. Ghorbel, Appl. Catal., A, 2015, 502, 329–339.
was only slightly adsorbed over Pt/TiO
catalyst. XPS measure- 18 N. Boufaden, B. Pawelec, J. L. G. Fierro, R. Guil L ´o pez,
(
7
14
2
2
2
ments demonstrated that Pt on TiO was more metallic aer
R. Akkari and M. Said Zina, Mater. Chem. Phys., 2018, 209,
188–199.
2
applying the electric eld. Actually, TiO is known to be capable
2
of donating electrons to the empty orbital of Pt. Therefore, we 19 A. Nakano, S. Manabe, T. Higo, H. Seki, S. Nagatake, T. Yabe,
inferred that more metallic Pt on TiO
interaction between Pt and p-coordination of toluene. In
conclusion, results show that Pt/TiO
2
support weakened
S. Ogo, T. Nagatsuka, Y. Sugiura, H. Iki and Y. Sekine, Appl.
Catal., A, 2017, 543, 75–81.
2
catalyst promotes MCH 20 Y. Sugiura, T. Nagatsuka, K. Kubo, Y. Hirano, A. Nakamura,
dehydrogenation selectively at low temperatures by virtue of
proton hopping in the electric eld.
K. Miyazawa, Y. Iizuka, S. Furuta, H. Iki, T. Higo and
Y. Sekine, Chem. Lett., 2017, 46(11), 1601–1604.
2
2
2
2
2
2
2
2
2
3
3
3
1 S. Manabe, T. Yabe, A. Nakano, S. Nagatake, T. Higo, S. Ogo,
H. Nakai and Y. Sekine, Chem. Phys. Lett., 2018, 711, 73–76.
2 F. Alhumaidan, D. Tsakiris, D. Cresswell and A. Garforth, Int.
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3 W. F. Greenlee, J. D. Sun and J. S. Bus, Toxicol. Appl.
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4 S. Okada, R. Manabe, R. Inagaki, S. Ogo and Y. Sekine, Catal.
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5 S. Nagatake, T. Higo, S. Ogo, Y. Sugiura, R. Watanabe,
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6 R. Manabe, S. Okada, R. Inagaki, K. Oshima, S. Ogo and
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8 R. Inagaki, R. Manabe, Y. Hisai, Y. Kamite, T. Yabe, S. Ogo
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Conflicts of interest
There are no conicts to declare.
Acknowledgements
This study was supported by JST-CREST JPMJCR1423 and JSPS
Grants-in-Aid for Scientic Research – KAKENHI.
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