Enhanced Hydrogenation Catalytic Activity of Ruthenium Nanoparticles by Solid-Solution Alloying with Molybdenum

Article abstract of DOI:10.1002/ejic.202001141

We report the hydrogenation catalytic activity application of molybdenum–ruthenium (MoRu) solid-solution alloy nanoparticles (NPs) as catalysts for the hydrogenation of 1-octene and 1-octyne. The solid-solution structure of MoRu NPs was confirmed through scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDX), and powder X-ray diffraction (PXRD) measurement. The hydrogenation catalytic activity of these NPs toward 1-octyne and 1-octene in tetrahydrofuran (THF) was tested. The hydrogenation catalytic activity of Ru was enhanced by alloying with Mo at the atomic level. An electronic modification of Ru by a charge transfer from Mo to Ru, which could induce the change in the adsorption energy of reactants resulting in enhanced catalytic activity, was observed by X-ray photoelectron spectroscopy.

Full text of DOI:10.1002/ejic.202001141

Communications
doi.org/10.1002/ejic.202001141
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
Enhanced Hydrogenation Catalytic Activity of Ruthenium
Nanoparticles by Solid-Solution Alloying with Molybdenum
[a, b]
[a]
[a]
[b]
[c]
Shinya Okazoe,
Takaaki Toriyama, Syo Matsumura,
Lena Staiger, Mirza Cokoja, Kohei Kusada, Tomokazu Yamamoto,
[c]
[c, d]
[b]
[a]
Hiroshi Kitagawa, and Roland A. Fischer*
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
We report the hydrogenation catalytic activity application of
molybdenum–ruthenium (MoRu) solid-solution alloy nanopar-
ticles (NPs) as catalysts for the hydrogenation of 1-octene and
attracted much attention because of its lower cost and higher
hydrogenation catalytic activities toward various substrates.
[
3]
To tune its catalytic activity, the alloying of Ru with other metals
has been studied. Among alloyed structures, solid-solution alloy
NPs, where constituent atoms mix at the atomic level, are well
investigated because their electronic structures can be easily
modified by changing the metal compositions or alloy
components. To date, various Ru-based solid-solution alloy NPs,
1
-octyne. The solid-solution structure of MoRu NPs was
confirmed through scanning transmission electron microscopy
(
(
STEM) coupled with energy-dispersive X-ray spectroscopy
EDX), and powder X-ray diffraction (PXRD) measurement. The
hydrogenation catalytic activity of these NPs toward 1-octyne
and 1-octene in tetrahydrofuran (THF) was tested. The hydro-
genation catalytic activity of Ru was enhanced by alloying with
Mo at the atomic level. An electronic modification of Ru by a
charge transfer from Mo to Ru, which could induce the change
in the adsorption energy of reactants resulting in enhanced
catalytic activity, was observed by X-ray photoelectron spectro-
scopy.
[4]
[5]
[6]
for example, RuÀ Pt, RuÀ Pd, and RuÀ Ni, have been synthe-
sized, and they exhibit higher catalytic activities than Ru. Most
of the reported Ru-based solid-solution alloy catalysts are
composed of late transition metals. However, Ru-based solid-
solution alloy NPs composed of early transition metals such as
[7]
[8]
Mo, W, and Cr are few reported. By contrast, PtÀ Cr, PdÀ W,
[9]
[10]
PdÀ Mo, and RhÀ W
solid-solution alloy NPs show higher
catalytic activities than monometallic catalysts. Therefore,
alloying Ru with early transition metals is challenging and might
be effective for enhancing its catalytic activities. In addition,
compared with late transition metals, in particular PGMs, early
transition metals are much cheaper and more abundant. If the
catalytic activity is enhanced by alloying with early transition
metals, this could be effective from a cost viewpoint. Recently,
we succeeded in the synthesis of solid-solution alloy NPs
The hydrogenation of unsaturated carbons is an important
reaction that is widely used in the chemical industry. From an
energy consumption viewpoint, catalysts that can effectively
promote the reaction under mild conditions are required.
Platinum group metals (PGMs), in particular Pt, Ru, Rh, and Pd,
are well known as excellent hydrogenation catalysts for
[1]
unsaturated hydrocarbons because these metals can easily
composed of Mo and Ru, and found their high catalytic activity
[2]
[[11]]
dissociate H molecules into H atoms on their surfaces. Ru has
toward the hydrogen evolution reaction.
In this study, we
2
report on the catalytic activity of MoRu solid-solution alloy NPs
for the hydrogenation of 1-octene and 1-octyne as model
substrates (Scheme 1).
[
a] S. Okazoe, L. Staiger, Dr. M. Cokoja, Prof. Dr. R. A. Fischer
Department of Chemistry and Catalysis Research Center
Technical University of Munich
Lichtenberg Straße 4, 85748 Garching, Germany
E-mail: roland.fischer@tum.de
www.department.ch.tum.de/amc/home/
b] S. Okazoe, Dr. K. Kusada, Prof. Dr. H. Kitagawa
Division of Chemistry, Graduate School of Science
Kyoto University
Kitashirakawa-Oiwakecho, Sakyo-ku, 606-8502 Kyoto, Japan
c] T. Yamamoto, T. Toriyama, Prof. Dr. S. Matsumura
The Ultramicroscopy Research Center
Ru NPs and MoRu solid-solution alloy NPs were synthesized
[11]
by thermal decomposition and denoted as Ru and Mo Ru
0.2 0.8
(see the Supporting Information, SI). The exact atomic ratio of
Mo and Ru in MoRu solid-solution alloy NPs was calculated to
be 0.19:0.81 by X-ray fluorescence (XRF) spectroscopy. The
mean diameters were 6.6�1.1 and 2.7�0.5 nm for Ru and
Mo Ru NPs, respectively (SI, Figures S1 and S2 and Table S1).
[
[
[
0
.2
0.8
The atomic distribution was determined using scanning trans-
Kyushu University
Motooka 744, Nishi-ku, 819-0395 Fukuoka, Japan
d] Prof. Dr. S. Matsumura
Department of Applied Quantum Physics and Nuclear Engineering
Kyushu University
819-0395 Fukuoka, Japan
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejic.202001141
©
2021 The Authors. European Journal of Inorganic Chemistry published by
Wiley-VCH GmbH. This is an open access article under the terms of the
Creative Commons Attribution Non-Commercial NoDerivs License, which
permits use and distribution in any medium, provided the original work is
properly cited, the use is non-commercial and no modifications or adap-
tations are made.
Scheme 1. Reaction scheme of 1-octene and 1-octyne hydrogenations.
Eur. J. Inorg. Chem. 2021, 1186–1189
1186
© 2021 The Authors. European Journal of Inorganic Chemistry
published by Wiley-VCH GmbH

Communications
doi.org/10.1002/ejic.202001141
mission electron microscopy (STEM) and energy dispersive X-
ray (EDX) spectroscopy. high-angle annular dark-field
HAADF)-STEM image, the corresponding Mo-L and Ru-L EDX
maps, and an overlay of Mo and Ru maps of Mo Ru NPs are
shown in Figure 1a–d. The EDX maps clearly show the Mo and
Ru atoms to be homogeneously distributed in each NP,
indicating a solid-solution alloy structure. In addition, we also
confirmed a solid-solution structure through STEM-EDX line
analysis (Figure S3). The crystal structure of the synthesized NPs
was examined using powder X-ray diffraction (PXRD) (SI,
Figure S4), and the patterns were refined by the Le Bail method
the comparable size of NPs could not be prepared by the
thermal decomposition.
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
A
(
The time dependence of catalytic conversion of 1-octene at
60°C is presented in Figure 2a. 1-octene was converted to n-
octane on Ru and Mo Ru NPs within 15 min. Mo Ru NPs
0
.2
0.8
0
.2
0.8
0.2
0.8
showed a catalytic activity comparable or slightly higher than
Ru NPs, and the same tendency was observed at 30°C
(Figure 2b). Small amounts of the isomers cis-2-octene and
trans-2-octene were also observed during hydrogenation; the
time-dependent concentration of C8 species is shown in
Figure S8 and Figure S9. These isomers were also converted to
n-octane in the end.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
(SI, Figures S5 and S6). The calculated lattice constants of
Mo Ru NPs (a=2.7706 Å, c=4.3289 Å for a hcp structure, a=
We further performed hydrogenation of 1-octyne under
3 bar H2 at 60°C. The concentrations of 1-octyne, 1-octene,
trans-2-octene, cis-2-octene, and n-octane normalized without
oligomers are shown in Figure 3a and Figure 3b, and the final
concentration of the solution is shown in Table 1. Full
conversion of 1-octyne over Ru NPs reached at 60 min, whereas
that over Mo Ru NPs reached at 45 min. Mo Ru showed a
0.2
0.8
3
.8530 Å for a fcc structure) were slightly larger than those of
Ru NPs (a=2.7109 Å, c=4.2879 Å for a hcp structure, a=
.8202 Å for a fcc structure), which indicates alloying Ru with
3
Mo which has a larger atomic radius. These results support the
formation of a solid-solution alloy with lattice parameters that
[11]
are larger than those of Ru, as previously reported.
0
.2
0.8
0.2
0.8
These NPs were applied in the catalytic hydrogenation of
unsaturated hydrocarbons (1-octene and 1-octyne) (Scheme 1).
Hydrogenation tests were performed with 1 mol% NPs toward
the substrates in 2.4 mL of tetrahydrofuran (THF). A 0.05 mL
substrate and 0.05 mL n-dodecane as an internal standard were
much higher catalytic activity for 1-octyne than Ru, which
demonstrated that alloying Ru with early transition metal is also
effective in enhancing the hydrogenation catalytic activity of
added to the solutions. Next, H was introduced into the reactor
2
under a pressure of 1 or 3 bar. The concentrations of substrates
and products were determined by gas chromatography. The
details of the catalytic tests are described in SI. In general, the
size of NPs is one of the factors to determine the catalytic
activity, and comparable sizes of NPs should be used for a fair
comparison. However, we used different sizes of NPs because
2
Figure 2. Time dependence of 1-octene conversion under 3.0 bar H at (a)
60°C and (b) 30°C. The conversions over Ru and Mo0.2Ru0.8 are represented
by circles and squares, respectively. The lines are shown as a guide for the
eyes.
Figure 3. Time-dependent concentration of 1-octyne and the products at 60
°C with (a) Ru and (b) Mo0.2Ru0.8. The concentrations of 1-octyne, 1-octene,
trans-2-octene, cis-2-octene, and n-octane are represented by red, green,
blue, purple, and brown dots, respectively. The concentrations were
normalized without oligomers. The lines are shown as a guide for the eyes.
Figure 1. (a) HAADF-STEM image, (b) Mo-L, (c) Ru-L EDX maps, and (d)
overlay image of Mo0.2Ru0.8
.
Eur. J. Inorg. Chem. 2021, 1186–1189
www.eurjic.org
1187
© 2021 The Authors. European Journal of Inorganic Chemistry published
by Wiley-VCH GmbH

Communications
doi.org/10.1002/ejic.202001141
Table 1. Final concentration of products after 1-octyne hydrogenation.
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
Entry
Catalyst
Temperature [°C]
H
2
pressure [bar]
Time
Conversion [%]
n-Octane [%]
Oligomerization [%]
1
2
3
4
5
Ru
60
60
30
30
30
3
3
3
1
1
60 min
45 min
120 min
24 h
100
100
100
47
86
86
87
32
85
14
14
13
1
Mo0.2Ru0.8
Mo0.2Ru0.8
Ru
Mo0.2Ru0.8
24 h
100
15
Ru. 1-octene and n-octane were observed in the initial period
with both NPs. This indicates that hydrogenation of 1-octene
was subsequently promoted following that of 1-octyne. There-
fore, both Ru and Mo Ru NPs have low selectivity for
MoRu solid-solution alloy NPs were synthesized by thermal
decomposition and characterized by STEM-EDX and PXRD.
Enhancement of the hydrogenation catalytic activity of Ru NPs
toward 1-octene and 1-octyne by solid-solution alloying with
Mo, which is an early transition metal, was observed. This study
suggests that atomic-level mixing with early transition metals
has the potential to improve the catalytic properties of PGM.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
0
.2
0.8
semihydrogenation. This process would be caused by the
similar adsorption energies of 1-octyne and 1-octene on the
NPs. Because Mo Ru NPs showed better catalytic activity, we
0.2
0.8
further tested 1-octyne hydrogenation at 30°C, which is a
milder condition. As shown in Figure S10, 1-octyne and 1-
octene were fully reduced within 120 min. Moreover, only Acknowledgements
Mo Ru NPs showed 100% conversion at 30°C even under
0.2
0.8
1
bar H2 condition, although Ru NPs showed only 47%
This work was supported by ACCEL from the Japan Science and
Technology Agency (JST), Grant Number JPMJAC1501, Grant-in-
Aid for Specially Promoted Research 20H05623, and JSPS KAKENHI
Grant Number 19 J15102, Japan. STEM observations were
performed as part of a program conducted by the Advanced
Characterization Nanotechnology Platform sponsored by The
Ministry of Education, Culture, Sports, Science and Technology
(MEXT), Japan. The authors thank the Deutsche Forschungsge-
meinschaft (DFG) for financial support of this work in the frame of
the DFG-project (project no. Fi 502/32-2). Open access funding
enabled and organized by Projekt DEAL.
conversion (see Table 1, entries 3 and 4). As another substrate,
we selected phenylacetylene (Scheme S1 in SI) and performed
their hydrogenation tests. We also confirmed the enhanced
hydrogenation catalytic activity of Ru toward phenylacetylene
(Table S2 in SI).
Catalytic activities are strongly affected by the electronic
structure of the catalyst surface. To investigate the electronic
structure of Mo Ru NPs, X-ray photoelectron spectroscopy
0.2
0.8
(XPS) analysis was performed. As shown in Figure 4, Ru 3p
peaks of Mo Ru NPs shifted to slightly lower energy
0.2
0.8
compared with those of Ru (SI, Table S2), indicating that a
charge transfer from Mo to Ru occurred. It was assumed that
this electronic structure change influences the adsorption Conflict of Interest
energies of substrates on solid-solution alloy NPs, resulting in
the enhancement of the catalytic activity of Mo Ru . We
The authors declare no conflict of interest.
0
.2
0.8
confirmed the change of the adsorption sites by alloying
through CO-DRIFTS (Figures S10–S12 in SI). This also may
attribute to the enhancement of catalytic activity. In summary,
Keywords: Alloys
Nanoparticles · Ruthenium
·
Hydrogenation
·
Molybdenum
·
[1] a) G. C. Bond, P. B. Wells, J. Catal. 1965, 5, 65–73; b) G. C. Bond, P. B.
Wells, J. Catal. 1965, 4, 211–219; c) G. C. Bond, G. Webb, P. B. Wells, J.
Catal. 1968, 12, 157–165; d) A. S. Al-Ammar, G. Webb, J. Chem. Soc.
Faraday Trans. 1 1979, 75, 195–205.
[2] a) H. Conrad, G. Ertl, E. E. Latta, Surf. Sci. 1974, 41, 435–446; b) K.
Christmann, G. Ertl, T. Pignet, Surf. Sci. 1976, 54, 365–392; c) J. A.
Schwarz, Surf. Sci. 1979, 87, 525–538; d) J. T. Yates, P. A. Thiel, W. H.
Weinberg, Surf. Sci. 1979, 84, 427–439.
[3] a) A. Nowicki, Y. Zhang, B. Leger, J. P. Rolland, H. Bricout, E. Monflier, A.
Roucoux, Chem. Commun. 2006, 296–298; b) M. Aygün, C. T. Stoppiello,
M. A. Lebedeva, E. F. Smith, M. d. C. Gimenez-Lopez, A. N. Khlobystov,
T. W. Chamberlain, J. Mater. Chem. A 2017, 5, 21467–21477.
[4] a) M. Liu, W. Yu, H. Liu, J. Zheng, J. Colloid Interface Sci. 1999, 214, 231–
2
37; b) J. N. G. Stanley, F. Heinroth, C. C. Weber, A. F. Masters, T.
Maschmeyer, Appl. Catal. A 2013, 454, 46–52.
[5] M. Tang, S. Mao, M. Li, Z. Wei, F. Xu, H. Li, Y. Wang, ACS Catal. 2015, 5,
3100–3107.
Figure 4. XPS spectra of Ru and Mo0.2Ru0.8 NPs. The observed spectra, sum of
fitting peaks, and backgrounds are represented by gray dots, red, and black
solid lines, respectively. The fitting components of metallic and oxide are
represented by blue and green lines, respectively.
[
6] G. Chen, S. Desinan, R. Rosei, F. Rosei, D. Ma, Chem. Eur. J. 2012, 18,
7
925–7930.
Eur. J. Inorg. Chem. 2021, 1186–1189
www.eurjic.org
1188
© 2021 The Authors. European Journal of Inorganic Chemistry published
by Wiley-VCH GmbH

Communications
doi.org/10.1002/ejic.202001141
[
7] H. Yang, N. Alonso-Vante, J.-M. Leger, C. Lamy, J. Phys. Chem. B 2004,
08, 1938–1947.
[8] A. Sarkar, A. V. Murugan, A. Manthiram, J. Mater. Chem. 2009, 19, 159–
65.
9] A. Sarkar, A. V. Murugan, A. Manthiram, J. Phys. Chem. C 2008, 112,
2037–12043.
[10] W. Zhang, L. Wang, H. Liu, Y. Hao, H. Li, M. U. Khan, J. Zeng, Nano Lett.
017, 17, 788–793.
[11] S. Okazoe, K. Kusada, D. Wu, T. Yamamoto, T. Toriyama, S. Matsumura, S.
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
1
Kawaguchi, Y. Kubota, H. Kitagawa, Chem. Commun. 2020, 56, 14475–
14478.
1
[
1
Manuscript received: December 21, 2020
Revised manuscript received: February 20, 2021
Accepted manuscript online: February 22, 2021
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
Eur. J. Inorg. Chem. 2021, 1186–1189
www.eurjic.org
1189
© 2021 The Authors. European Journal of Inorganic Chemistry published
by Wiley-VCH GmbH