Showcasing research from Professor Katsutoshi Nagaoka’slaboratory, Department of Chemical Systems Engineering,
Graduate School of Engineering, Nagoya University,
Nagoya, Japan.

As featured in:

Nitrile hydrogenation to secondary amines under ambientconditions over palladium–platinum random
alloy nanoparticles
Palladium-platinum random alloy nanoparticles enablehydrogenation of nitriles to secondary amines without
the need for heat, pressurization, or long reaction times.
Although palladium and platinum are classically immiscible,
they were successfully alloyed through rapid chemical
reduction assisted by microwave heating. The
palladium-platinum random alloy nanoparticles exhibited
10-fold higher turnover frequency than the monometallic
palladium and platinum nanoparticles, and were able
to facilitate the conversion of various nitriles to thecorresponding secondary amines.

See Yoshihide Nishida, Katsutoshi Sato,
Katsutoshi Nagaoka et al.,Catal. Sci. Technol., 2022, 12, 4128.

rsc.li/catalysis
Registered charity number: 207890

Catalysis
Science &Technology
View Article Online

Open Access Article. Published on 01 March 2022. Downloaded on 10/15/2024 7:00:39 PM.
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.

PAPER

Cite this: Catal. Sci. Technol., 2022,
12, 4128

View Journal | View Issue

Nitrile hydrogenation to secondary amines underambient conditions over palladium–platinum
random alloy nanoparticles†
Yoshihide Nishida, ‡*a Katsutoshi Sato, *ab Chandan Chaudhari,§a
Hiroshi Yamada,a Takaaki Toriyama,c Tomokazu Yamamoto,d Syo Matsumura,cd
Susan Meñez Aspera, e Hiroshi Nakanishi, eMasaaki Haneda fg and Katsutoshi Nagaoka *a
Catalytic hydrogenation of nitriles is a cost-effective and green method for synthesizing amines and imines,
which have many industrial applications. However, this reaction generally requires harsh reaction
conditions and produces a mixture of amine and imine products due to its chemodiversity. Therefore, it isa challenge to selectively hydrogenate nitriles to a single product under ambient conditions (1 bar of H2 at
25 °C). Here, we report an effective method for selective hydrogenation of nitriles that does not require
heat, pressurization, or long reaction times. We achieved this by means of bimetalization between
palladium (Pd) and platinum (Pt) nanoparticles, which resulted in a catalyst that showed high yield of
secondary amines. Although Pd and Pt are thermodynamically immiscible, we have successfully alloyed thetwo metals by means of rapid chemical reduction assisted by microwave heating. X-ray absorption
spectroscopy suggested the formation of heteroatomic Pdδ+Ptδ− sites via charge transfer between
neighboring Pd and Pt atoms in the alloy structure. Moreover, Fourier transform IR spectroscopy andscanning transmission electron microscopy–energy-dispersive X-ray spectroscopy indicated that
decreasing the size of the PdPt (50 : 50) nanoparticles improved the degree of alloying and facilitated theReceived 19th December 2021,
Accepted 28th February 2022

formation of electron-enriched Ptδ− species. On the basis of kinetics studies and density functional theory
calculations, we concluded that cyano group activation, which was the rate-determining step overmonometallic Pd and Pt catalysts, was accelerated over the heteroatomic Pdδ+Ptδ− sites because of strong

DOI: 10.1039/d1cy02302k

back-donation from electron-enriched Ptδ− species to the carbon atom of the cyano groups. The PdPt
random alloy nanoparticles catalyzed the reactions of various aromatic and heterocyclic nitriles, and thersc.li/catalysis

corresponding secondary amines were selectively obtained in just a few hours.

aDepartment of Chemical Systems Engineering, Graduate School of Engineering,
Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.
E-mail: nishida.yoshihide@nitech.ac.jp, sato.katsutoshi@material.nagoya-u.ac.jp,
nagaoka.katsutoshi@material.nagoya-u.ac.jpbElements Strategy Initiative for Catalysts and Batteries, Kyoto University, 1-30
Goryo-Ohara, Nishikyo-ku, Kyoto 615-8245, Japanc
The Ultramicroscopy Research Center, Kyushu University, 744 Motooka, Nishi-ku,
Fukuoka 819-0395, Japand
Department of Applied Quantum Physics and Nuclear Engineering, Kyushu
University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japane
National Institute of Technology, Akashi College, 679-3 Nishioka, Uozumi, Akashi,
Hyogo 674-8501, JapanfAdvanced Ceramics Research Center, Nagoya Institute of Technology, 10-6-29
Asahigaoka, Tajimi, Gifu 507-0071, Japang
Frontier Research Institute for Materials Science, Nagoya Institute of Technology,
Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan† Electronic supplementary information (ESI) available. See DOI: 10.1039/d1cy02302k‡ (Present address) Advanced Ceramics Research Center, Nagoya Institute ofTechnology, 10-6-29 Asahigaoka, Tajimi, Gifu 507-0071, Japan.
§ (Present address) Renewable Energy Research Center, National Institute ofAdvanced Industrial Science and Technology, 2-2-9 Machiikedai, Koriyama,
Fukushima 963-0298, Japan.

4128 | Catal. Sci. Technol., 2022, 12, 4128–4137

1. Introduction
Secondary amines are versatile, indispensable intermediates
in the production of pharmaceuticals, agrochemicals, andother bioactive chemicals, as well as rubber compounds anddyes.1,2 Secondary amines are typically synthesized via Nalkylation and reductive amination,3–15 but these reactions
require expensive primary amines, toxic carbonyl compounds,
and harsh reaction conditions. In addition, over-alkylation
often occurs because of the high reactivity of amines andcarbonyl compounds. As an alternative method, nitrilehydrogenation with gaseous hydrogen has recently been
attracting attention because of its low material cost, highatom efficiency, and operational simplicity. During nitrilehydrogenation, the cyano group is sequentially hydrogenatedto a primary amine. In addition, the primary amine productcan be converted to a secondary imine or secondary amine
via in situ condensation with the primary imine intermediate(Scheme 1). This chemodiversity makes controlling theThis journal is © The Royal Society of Chemistry 2022

View Article Online

Catalysis Science & Technology

Open Access Article. Published on 01 March 2022. Downloaded on 10/15/2024 7:00:39 PM.
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.

Scheme 1 Nitrile hydrogenation with gaseous hydrogen.

selectivity difficult, and the industrial RANEY® Ni and Co
catalysts used for these reactions are unstable in air.16
Therefore, considerable efforts have been devoted todeveloping new catalysts with high selectivity. For example,
homogeneous Re, Ru, and Rh catalysts have been found toshow high nitrile conversion and selectivity for secondaryamines, albeit under harsh reaction conditions (60–140 °C
and 10–75 bar).17–19 In addition, heterogeneous Pd@mpgC3N4 shows good conversion and selectivity for secondaryamines at 80 °C and 10 bar,20 and a Pt nanowire catalyst was
found to convert various aromatic nitriles to theircorresponding secondary amines at 80 °C and 1 bar.21 Again,
however, most of these newly reported catalysts require hightemperature and/or hydrogen pressure, and nitrilehydrogenation under ambient conditions (room temperature
and atmospheric pressure) remains challenging.
There have been a few reports on successful conversion of
nitriles to secondary amines under ambient conditions, buthigh catalyst loads (>5 mol%) and long reaction times (24 h)
are required.22,23 The activity of catalysts can effectively be
improved by bimetallization, which results in synergistic
effects such as ligand and ensemble effects, in addition toallowing for concerted catalysis.24–26 For example, a PtMo
nanowire catalyst has been shown to be useful for converting
aromatic nitriles to their corresponding secondary amines byhydrogenation at 80 °C and 1 bar.27 A 5Pd–Ni/SiO2 catalyst
provides high conversion and selectivity for secondaryamines at 80 °C and 6 bar.28 In addition, a NiO–Pd/SiC
catalyst (ca. 1 mol%) shows remarkable performance for theselective synthesis of secondary amines under mild
conditions (30 °C and 1 bar), although a moderate reaction
time (5 h) is required.29
Chemical reduction of metal precursors in the presence of
polyvinylpyrrolidone (PVP) as a stabilizer is a simple andecofriendly method for preparing metal nanoparticles, andthe formation of well-dispersed Pd, Pt, and Pd/Pt
nanoparticles has been reported.30 PVP-stabilized bimetallic
nanoparticle catalysts also show enhanced performance
relative to that of monometallic catalysts.31,32 In addition, thehigh dispersibility of PVP in polar protic solvents such as
methanol may facilitate the diffusion of the reactants and
PVP-stabilized nanoparticle catalysts in liquid-phasereactions and improve the reaction performance. Recently,
we demonstrated for the first time that Rh nanoparticles
stabilized by PVP effectively catalyze the selective formationof secondary imines from nitriles by hydrogenation underThis journal is © The Royal Society of Chemistry 2022

Paper
ambient conditions (25 °C and 1 bar).33,34 Herein, we reportan effective method for nitrile hydrogenation that affords
secondary amines under ambient conditions over newly
developed PdPt–PVP nanoparticle catalysts. Random alloying
by chemical reduction generated PdPt–PVP nanoparticles,
despite the fact that Pd and Pt are classically immiscible
below 700 °C.35,36 Small PdPt (50 : 50)–PVP nanoparticles (3.9nm) catalyzed the conversion of various aromatic andheterocyclic nitriles to their corresponding secondary amines
in a few hours, and the turnover frequency (TOF) was up to
10 times that achieved with monometallic Pd and Pt
nanoparticles.
Experimental
andcomputational
characterization of the catalysts revealed that the cyanogroups were activated over heteroatomic Pdδ+Ptδ− sites formed
via charge transfer between neighboring Pd and Pt atoms in
the random alloy structure.

2. Experiment
Materials
Metal precursors (RuCl3·nH2O, RhCl3·3H2O, (NH4)2PdCl4,(NH4)2IrCl6, and (NH4)2PtCl4), PVP K-30, ethylene glycol (EG),diethylether, acetone, methanol (MeOH), ethanol, andactivated carbon were purchased from FUJIFILM Wako Pure
Chemical Corporation (Japan) and Sigma Aldrich (UnitedStates of America). Nitrile compounds and dodecane werepurchased from Tokyo Chemical Industry Co. (Japan). SiO2
(OX-50) was obtained from NIPPON AEROSIL (Japan). All
reagents were used as received.
Catalyst preparation
PVP-stabilized metal nanoparticles were synthesized bychemical reduction with an alcohol as a reductant. In a typical
procedure, a sealable vessel was charged with 0.25 mmol metal
precursors and 1.25 mmol PVP, and these reagents weredissolved in 20 mL of EG (Table S1†). Argon was bubbled
through the solution to remove air, and then the vessel wassealed with a cap. In a microwave synthesizer (Initiator, Biotage,
Sweden), the EG solution was rapidly heated to 165 °C and thenmaintained at that temperature for 15 min (Fig. S1†). After the
EG solution was cooled, the resulting colloidal suspension was
coagulated with diethyl ether and acetone, and the residual
solid was washed three times by repeated dispersion in waterand coagulation with diethyl ether and acetone. The washedproduct was dried under vacuum at 40 °C and crushed with anagate mortar. The morphology and particle-size distributions of
the obtained nanoparticles were determined by transmission
electron microscopy (TEM) (Fig. S2 and S3†). To vary the size of
the PdPt (50 : 50) nanoparticles, we changed the total
concentration of the metal precursors (Table S2 and Fig. S4–
S6†). To vary the composition of the PdPt nanoparticles, wechanged the ratio of the Pd and Pt precursors while keeping thetotal amount of the precursors at 0.25 mmol (Table S3 and Fig.
S7 and S8†). For IR spectroscopy and applicability studies, the
PdPt (50 : 50)–PVP nanoparticles were loaded onto SiO2 andCatal. Sci. Technol., 2022, 12, 4128–4137 | 4129

View Article Online

Paper

Catalysis Science & Technology

activated carbon supports by means of a conventional
impregnation method; the metal loading was 5 wt%.

Open Access Article. Published on 01 March 2022. Downloaded on 10/15/2024 7:00:39 PM.
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.

Hydrogenation of nitriles
Nitriles were hydrogenated in a test tube equipped with a gas
bag. In a typical reaction, 1 mmol nitrile and 1 mol% catalyst
were dispersed in 0.5 mL of MeOH. Then, the test tube wasdepressurized and filled with hydrogen gas at atmosphericpressure. The MeOH solution was stirred with a magnetic
stirrer at 1200 rpm, and the reaction was allowed to proceed
at 25 °C. Nitrile conversion and product yield were calculated
by gas chromatography with flame ionization detection anddodecane as an internal standard. The obtained secondaryamines were identified by means of gas chromatographymass spectrometry.

3. Results and discussion
Catalytic performance of PVP-stabilized metal nanoparticles
We began by evaluating the catalytic performance of the PVPstabilized metal nanoparticles in the hydrogenation of
benzonitrile as a model substrate by using 1 bar of hydrogenat 25 °C (Table 1). The Ru and Ir nanoparticles showed low
conversions (entries 1 and 2), probably because that the asprepared nanoparticles were relatively small, they had
inactive oxide surfaces that formed via air oxidation, and they
were barely reduced during the hydrogenation reaction. The
Rh and Pd nanoparticles showed 21% and 12% conversions
and selectively gave N-benzylidenebenzylamine (2, secondaryimine) and benzylamine (1, primary amine), respectively(entries 3 and 4). Hydrogenation over the Pt nanoparticles
gave the desired dibenzylamine (3, secondary amine) as the
major product, but the yield was only 9% (entry 5). Next, we
tried bimetallization of the Pt nanoparticles to improve theircatalytic activity, and we found that the nitrile conversion
and target product yield dramatically increased when Pd wasincorporated into the Pt nanoparticles (entry 6). The catalytic
performance of the PdPt (50 : 50) nanoparticles strongly
depended on the particle size, with the TOF increasing withdecreasing particle size (entries 7–9). Note that the TOF over
3.9 nm PdPt (50 : 50) nanoparticles was approximately 10
times the TOFs over monometallic Pd and Pt nanoparticles.
The origin of the particle-size dependence of TOF is
discussed in a subsequent section. As a comparison
experiment, we prepared physically mixed PdPt (50 : 50)
nanoparticles by co-dispersing Pd–PVP and Pt–PVP
nanoparticles, and we found that the catalytic performanceof the physical mixture was lower than that of similarly sized
bimetallic PdPt (50 : 50) nanoparticles (entry 10). This result
indicates that the PdPt (50 : 50) nanoparticles were notcomposed simply of pure Pd and Pt domains and thatbimetallization by chemical reduction was essential for thehigh catalytic performance.

Dependence of catalytic performance on the metalcomposition of PdPt nanoparticles
Next, we investigated the influence of the metal compositionof the PdPt nanoparticles on their catalytic performance(Fig. 1 and Table S4†). We prepared PdPt nanoparticles withvarious metal compositions and found that they were
spherical and well-dispersed (Fig. S7†). Notably, the sizes of
the nanoparticles and amounts of included PVP varied within
narrow ranges (Table S3 and Fig. S8†), which allowed us toeasily determine the influence of metal composition on
catalytic performance. Monometallic Pd nanoparticles
showed little in situ condensation between the primary imine
and primary amine, and then the selectivities for primary

Table 1 Hydrogenation of the model substrate benzonitrile to benzylamine (1), benzylidenebenzylamine (2), and dibenzylamine (3) under ambientconditions

Entry

Catalyst

Particle
sizea (nm)

1
2
3
4
5
6
7
8
9
10

Ru–PVP
Ir–PVP
Rh–PVP
Pd–PVP
Pt–PVP
PdPt (50 : 50)–PVP
PdPt (50 : 50)–PVP
PdPt (50 : 50)–PVP
PdPt (50 : 50)–PVP
Pd + Pt (50 : 50)–PVPe

3.2
1.8
5.0
4.9
4.3
4.6
3.9
6.8
8.4
4.9 + 4.3

Yieldb (%)
Conv. (%)

1

2

3

Dispersionc (%)

TOFd (h−1)

0
5
21
12
13
60
92
37
18
35

0
0
0
9
0
0
8
0
0
17

0
0
13
0
1
0
0
1
1
0

0
3
0
1
9
55
81
34
13
15

42
n/a
22
23
26
25
29
17
13
n/a

n/a
n/a
30 (21)20 (12)17 (13)129 (23)183 (16)98 (19)48 (18)n/abaParticle size was determined by counting 200 particles in the TEM image of each catalyst. b Conversion and yield were calculated by means ofgas chromatography with flame ionization detection using dodecane as an internal standard. c Metal dispersion was estimated according to
the equation shown in Fig. S9,† on the assumption that the nanoparticles were spherical. d TOF was calculated from the metal dispersion andthe yield of benzene rings at bracketed conversions. e Pd–PVP and Pt–PVP (entries 4 and 5) were co-dispersed in MeOH.

4130 | Catal. Sci. Technol., 2022, 12, 4128–4137

This journal is © The Royal Society of Chemistry 2022

View Article Online

Open Access Article. Published on 01 March 2022. Downloaded on 10/15/2024 7:00:39 PM.
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.

Catalysis Science & Technology

Fig. 1 Metal-composition dependence of the catalytic performance of
the PdPt nanoparticles in the hydrogenation of benzonitrile (reaction
conditions are shown in Table 1).

amine and secondary amine were 78% and 10%, respectively.
On the other hand, the Pt nanoparticles catalyzed in situ
condensation but their activity for the hydrogenation of
secondary imine was low, and then 70% selectivity forsecondary amine was obtained (Scheme 1). The selectivity of
the PdPt (90 : 10) nanoparticles for the primary amine wascomparable to that of monometallic Pd nanoparticles,
indicating that the surface of the PdPt (90 : 10) nanoparticles
was dominated by Pd species, which showed poor catalytic
activity for in situ condensation. Conversely, the desired
secondary amine was selectively obtained from reactions
catalyzed by the PdPt nanoparticles containing at least 30%
Pt, because Pt species, which facilitated the consumption of
the primary amine via in situ condensation, were exposed on
the surface of these nanoparticles. The PdPt (50 : 50)
nanoparticles showed the highest selectivity for the desired
secondary amine because they catalyzed not only in situ
condensation but also the hydrogenation of secondary imine
to secondary amine. In contrast, slightly lower secondaryPaper
amine selectivity was observed with the Pt-enriched (>50%)
nanoparticles, because their activity was insufficient tohydrogenate secondary imine to secondary amine. Moreover,themetal-composition
dependenceofbenzonitrile
conversion showed volcano-type behavior, with the highest
conversion being obtained over the PdPt (50 : 50)
nanoparticles. The time courses of substrate conversion andproduct yields over the PdPt (50 : 50) nanoparticles showedthat the intermediates, including the primary amine, wererapidly transformed (Fig. S10†); the intermediates wereundetectable even after a short reaction time, indicating thatthe hydrogenation of the cyano group was involved in therate-determining step. If isolated Pd or Pt species surroundedby Pt or Pd, respectively, were active sites, then Pt- or Pdenriched nanoparticles should show high activity.26 In otherwords, our results suggest that the active sites werecomposed of Pd and Pt pairs.
To explore the effect of bimetallization on the catalytic
activity of the PdPt (50 : 50) nanoparticles, several
characterization techniques were carried out. We usedscanning transmission electron microscopy combined withenergy-dispersive X-ray spectroscopy (STEM–EDXS) tovisualize the alloying state of the 4.6 nm PdPt (50 : 50)
nanoparticles. Fig. 2 displays the high-angle annular darkfield images and elemental maps based on the Pd-L and Pt-L
signals. In the high-resolution image, we observed the atomic
arrangements of the ABCABC… stacking corresponding to
the face-centered cubic structure (Fig. 2a). Additionally, theSTEM–EDXS maps and an overlay image showed that the PdL and Pt-L signals were randomly distributed in a single
particle, which means that the PdPt nanoparticles had arandom alloy structure (Fig. 2c and d). The phase diagram
for Pd and Pt indicates that they are thermodynamicallyimmiscible below 700 °C,35,36 but we neverthelesssuccessfully synthesized the PdPt random alloy nanoparticles
below 200 °C by chemical reduction using microwave

Fig. 2 (a) High-resolution high-angle annular dark-field image and (b) high-angle annular dark-field image. (c) Pd-L and (d) Pt-L maps obtained by
STEM–EDXS analysis of the 4.6 nm PdPt (50 : 50) nanoparticles. (e) Overlay of the images in panels c and d.

This journal is © The Royal Society of Chemistry 2022

Catal. Sci. Technol., 2022, 12, 4128–4137 | 4131

View Article Online

Open Access Article. Published on 01 March 2022. Downloaded on 10/15/2024 7:00:39 PM.
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.

Paper
heating. As a comparison experiment, we prepared the PdPt
(50 : 50) nanoparticles under the conditions used for the
preparation of the 4.6 nm sample, except that we employed amantle heater, which allows for slow heating (1 °C min−1,
Fig. S11a†). The STEM–EDXS maps of the resulting
nanoparticles showed that the Pd-L and Pt-L signals werelocalized at the interior and exterior of the particles,
respectively (Fig. S11b–f†), which indicates the formation of a
Pd-rich core and a Pt-rich surface phase. Furthermore, thesmall particles produced by heterogeneous heating from the
mantle heater34 were composed mainly of Pt species. On thebasis of these experimental results, we propose that thealloying mechanism involves rapid and simultaneous
reduction of the readily reducible [PdCl4]2− and [PtCl4]2− ionsby microwave heating.
Next, we performed X-ray absorption spectroscopy at theSPring-8 synchrotron radiation facility. Fig. 3 shows the Pd Kand Pt L3-edge X-ray absorption near-edge structure (XANES)
spectra and the k 3-weighted Fourier transform (FT) extended
X-ray absorption fine-structure (EXAFS) spectra of the PdPt
nanoparticles with various metal compositions. The EXAFS
oscillations before FT are also shown in Fig. S12.† In the
XANES region, the white-line intensity of the Pt L3-edge andthe position of the Pd K-edge reflect the electronic states of
the tested samples.37,38 The Pd K- and Pt L3-edge XANESCatalysis Science & Technology
spectra of the PdPt nanoparticles were similar to those of Pd
and Pt foil, suggesting that at all metal compositions, thenanoparticles were composed of metallic Pd and Pt species(Fig. 3a and b). Notably, the white-line intensity of the Pt L3edge spectra decreased with increasing Pd content, whichconverted the Pt species to electron-enriched Ptδ− species(Fig. 3b and S13†). In contrast, there was no significant
change in the Pd K-edge XANES spectra with increasing Pt
content, and evaluating the change in the electronic state of
the Pd species with respect to the Pt content was difficult(Fig. 3a). This difficulty was probably due to the fact that theenergy resolution at the Pd K-edge (24.4 keV) is lower thanthat at the Pt L3-edge (11.5 keV).39 However, density
functional theory calculations described later in the paper
suggest that the electron density of the Pd species decreased
when the Pd atoms were replaced with Pt atoms, whichmeans that the Pd species donated electrons to the Pt species
in the PdPt nanoparticles. Additionally, the Pd K- and Pt L3edge FT EXAFS spectra, which provide information about the
local coordination structure, depended on how much of thesecond element was introduced (Fig. 3c and d). The split
peaks at 2–3 Å in the Pd K- and Pt L3-edge spectra were
attributed to the heteroatomic Pd–Pt bond,40,41 whichindicates that the PdPt nanoparticles had an alloy structure.
In the X-ray diffraction analysis of the PdPt nanoparticles

Fig. 3 (a) Pd K-edge and (b) Pt L3-edge XANES spectra of the PdPt nanoparticles with various metal compositions. (c) Pd K-edge and (d) Pt L3edge FT EXAFS spectra of the PdPt nanoparticles with various metal compositions.

4132 | Catal. Sci. Technol., 2022, 12, 4128–4137

This journal is © The Royal Society of Chemistry 2022

View Article Online

Open Access Article. Published on 01 March 2022. Downloaded on 10/15/2024 7:00:39 PM.
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.

Catalysis Science & Technology
with various metal compositions (Fig. S14†), diffraction
patterns attributed to a face-centered cubic structure wereobserved for all samples, which is consistent with the resultsof STEM–EDXS analysis (Fig. 2a). On the basis of the metalcomposition dependence of the catalytic performance,
STEM–EDXS analysis, and X-ray absorption spectroscopy, we
propose that the hydrogenation of benzonitrile was promoted
over heteroatomic Pdδ+Ptδ− sites that formed via chargetransfer between neighboring Pd and Pt atoms in the random
alloy structure. Alloying equal amounts of Pd and Pt atoms
maximized the number of heteroatomic Pdδ+Ptδ− sites,
resulting in excellent catalytic activity.

Particle-size dependence of the TOF over the PdPt (50 : 50)
nanoparticles
To investigate the origin of the particle-size dependence of
the TOF over the PdPt (50 : 50) nanoparticles (Table 1), wecharacterized the PdPt (50 : 50) nanoparticles by means ofvarious methods. TEM showed that all the nanoparticle
samples were well-dispersed with no aggregation, whichindicates that any differences in the catalytic activity of the
PdPt (50 : 50) nanoparticles could be attributed to thedifferences between their structures and electronic states.
The surface states of the PdPt (50 : 50) nanoparticles, as well
as monometallic Pt and Pd nanoparticles, were analyzed by
FT-IR spectroscopy with carbon monoxide (CO) as a probe
molecule (Fig. 4). The monometallic Pd nanoparticles showeda strong absorption peak assignable to CO adsorbed on
bridge sites and three-fold hollow sites composed of metallic
Pd species (Pd0–CObridge and Pd0–COhollow, respectively) ataround 1750–1950 cm−1.24,42 Unfortunately, distinguishing
between the Pd0–CObridge and Pd0–COhollow peaks wasdifficult because of the broadness of the peak. The
monometallic Pt nanoparticles showed a strong peak at 2048
cm−1 and a weak peak at around 1750–1900 cm−1; thesepeaks were assigned to CO adsorbed on linear and bridge
sites composed of metallic Pt species, respectively (Pt0–

Paper
COlinear and Pt0–CObridge).43,44 In contrast, the spectrum of
the 3.9 nm PdPt (50 : 50) nanoparticles showed two
representative absorption peaks: one at 2035 cm−1 andanother at around 1750–1950 cm−1. The former peak was
assigned to Pt0–COlinear, and because the latter peak islocated between the peaks observed for the monometallic Pd
and Pt nanoparticles, it can probably be assigned to CO
adsorbed on bridge and three-fold hollow sites composed ofboth Pd0 and Pt0 species. In other words, both Pd and Pt
species were exposed and adjacent on the surface of the 3.9
nm PdPt (50 : 50) nanoparticles. Moreover, the wavenumberof the peak attributed to Pt0–COlinear (2035 cm−1) was much
lower than that observed for the monometallic Pt
nanoparticles (2048 cm−1), suggesting that the exposed Pt
species were in an electron-enriched state owing to chargetransfer from neighboring Pd species. However, the intensityof the peak at around 1750–1950 cm−1 gradually decreased as
the size of the PdPt (50 : 50) nanoparticles increased, and the
IR spectrum of CO adsorbed on the 8.4 nm PdPt (50 : 50)
nanoparticles was quite similar to that of CO adsorbed on
the monometallic Pt nanoparticles. These results suggest that
increasing the size of the PdPt (50 : 50) nanoparticles reduced
the degree of alloying, formed Pt-rich surfaces, andsuppressed charge transfer. In other words, decreasing theparticle size contributed to the formation of electronenriched Pt species via random alloying, which in turnincreased the catalytic activity and TOF.
To visualize the particle-size dependence of the degree ofalloying, we performed STEM–EDXS analysis of the smallest(3.9 nm) and largest (8.4 nm) PdPt (50 : 50) nanoparticles. As
expected, the homogeneous and heterogeneous distributionsof the Pd-L and Pt-L signals were detected in the 3.9 nm
sample (Fig. 4b–d) and the 8.4 nm sample (Fig. 4e–g),respectively. Particularly in the 8.4 nm sample, the Pd-L and
Pt-L signals were localized at the interior and exterior of theparticles, respectively, indicating the formation of a Pd-richcore and a Pt-rich surface phase (Fig. 4e–g). To improve thevisibility of the structural differences between the 3.9 and 8.4

Fig. 4 (a) FT-IR spectra of CO adsorbed on the SiO2-supported PdPt (50 : 50) nanoparticles of various sizes. (b) Pd-L and (c) Pt-L maps obtainedby STEM–EDXS analysis of the 3.9 nm PdPt (50 : 50) nanoparticles. (d) Overlay of the images in panels b and c. (e) Pd-L and (f) Pt-L maps obtainedby STEM–EDXS analysis of the 8.4 nm PdPt (50 : 50) nanoparticles. (g) Overlay of the images in panels e and f.

This journal is © The Royal Society of Chemistry 2022

Catal. Sci. Technol., 2022, 12, 4128–4137 | 4133

View Article Online

Open Access Article. Published on 01 March 2022. Downloaded on 10/15/2024 7:00:39 PM.
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.

Paper
nm samples, we also recorded the line-scan profiles of the
Pd-L and Pt-L signals. For the 3.9 nm sample, the Pd-L and
Pt-L signals were randomly distributed around 50 at%
regardless of the distance from the center of the particle,
suggesting the formation of a random alloy structure (Fig.
S15a†). In contrast, for the 8.4 nm sample, the Pd-L signals
were higher at the particle interior than at the exterior and
the Pt-L signals were higher at the exterior than at theinterior (Fig. S15b†), meaning that increasing the size of the
PdPt (50 : 50) nanoparticles led to the formation of particles
with a Pd-rich core and a Pt-rich surface phase. Furthermore,
we obtained the X-ray absorption spectra of the PdPt (50 : 50)
nanoparticles of various sizes (Fig. S16 and S17†). The Pt L3edge XANES spectra showed that the particle size had no
significant effect on the electronic state of bulk Pt species(Fig. S16b†), which suggests that changing the particle size
did not affect the electron density of bulk Pt species. The
results of XANES analysis cannot be compared with theresults of FT-IR analysis, which provide information about
the electronic state of the metal surface (Fig. 4). In addition,
we observed no particle-size dependence in the Pd K-edge
spectra because the energy resolution at the Pd K-edge islower than that at the Pt L3-edge (Fig. S16a†).39 In the Pd Kand Pt L3-edge FT EXAFS spectra, the split peaks attributed
to the heteroatomic Pd–Pt bond were observed at 2–3 Å forall samples.40,41 These experimental results show that
increasing the particle size of the PdPt (50 : 50) nanoparticles
resulted in structural changes at the particle surface rather
than in the bulk. Considering that the size of the PdPt (50 :50) nanoparticles changed when the concentration of themetal precursors was changed, we reasoned that thedifference in the alloying degree arose from the collision andgrowth of the nanoparticles. That is, particle growth resulting
from multiple collisions probably generated pure Pd and Pt
domains under thermodynamic control.35,36

Mechanism of nitrile activation
To understand the reaction between benzonitrile andhydrogen over the 3.9 nm PdPt (50 : 50) random alloy andmonometallic nanoparticles, we determined the influence ofbenzonitrile concentration and hydrogen pressure on theinitial reaction rate (Fig. 5a and b). When the reaction was
carried out over the monometallic Pd and Pt nanoparticles,
the rate increased with increasing benzonitrile concentration
and with increasing hydrogen pressure, and the obtained
positive reaction orders for benzonitrile and hydrogen meanthat their activation was involved in the rate-determining
step. At a nitrile concentration higher than the original
concentration, a negative reaction order was obtained overthe Pt nanoparticles, suggesting that benzonitrile wasstrongly adsorbed on the surface of the Pt nanoparticles. In
contrast, the reaction rate over the PdPt (50 : 50)
nanoparticles was independent of nitrile concentration but
strongly dependent on hydrogen pressure. These data
demonstrate that the rate-determining step shifted from

4134 | Catal. Sci. Technol., 2022, 12, 4128–4137

Catalysis Science & Technology

Fig. 5 Dependence of the initial reaction rate on (a) benzonitrile
concentration and (b) hydrogen pressure over the 3.9 nm PdPt (50 :50), 4.9 nm Pd, and 4.3 nm Pt nanoparticles. The reactions were
performed under ambient conditions.

nitrile activation when the reaction was carried out over Pd
and Pt to a step involving hydrogen when the reaction was
carried out over a random alloy containing equal amounts of
Pd and Pt atoms; that is, nitrile activation was strongly
promoted over the PdPt (50 : 50) random alloy nanoparticles.
We carried out density functional theory calculations toclarify the mechanism of benzonitrile activation over the
PdPt (50 : 50) nanoparticles. Fig. S18† shows a slab model ofthe nanoparticles and the corresponding histogram of theatomic charges. Clearly, the Pd species donated an electron
to the Pt species; the average charges of the Pd and Pt atoms
were +0.108e and −0.108e, respectively, which is consistent
with the X-ray absorption spectroscopy and FT-IR results.
Next, we calculated the benzonitrile adsorption sites on the
111 surface of the nanoparticles and found that in the stable
adsorbed state, the cyano group was adsorbed on the bridge
site and the plane of the aromatic ring was parallel to the
111 surface. In addition, the bridge-site dependence of theenergy of adsorption on the PdPt (50 : 50) nanoparticles
demonstrated that in the most stable state, the nitrogen andcarbon atoms of the cyano group were located on the Pdδ+and Ptδ− atoms (labeled 02 in Fig. S19†); the atomic
configuration of the most stable adsorbed benzonitrile
molecule on the 111 surface of the PdPt (50 : 50)
nanoparticles is shown in Fig. 6a. On the basis of theplausible adsorption configuration of benzonitrile on the 111
surface, we calculated the difference between the number ofvalence electrons on the carbon atom of the cyano group ofadsorbed benzonitrile and the number on the carbon atomof gas-phase benzonitrile (Fig. 6b). In all the tested samples,
the number of valence electrons increased owing to electron
donation from the metal to the carbon atom (i.e., backdonation), and the PdPt (50 : 50) random alloy nanoparticles
showed the largest change in the number of valence
electrons. Note that the reaction orders for benzonitrile

This journal is © The Royal Society of Chemistry 2022

View Article Online

Open Access Article. Published on 01 March 2022. Downloaded on 10/15/2024 7:00:39 PM.
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.

Catalysis Science & Technology

Paper

Fig. 6 (a) Most stable atomic configuration of benzonitrile adsorbed on the 111 surface of the PdPt (50 : 50) random alloy nanoparticles. Blue andyellow balls indicate the surface Pd and Pt atoms. Gray, brown, and white balls indicate nitrogen, carbon, and hydrogen atoms. The adsorption siteis labeled 02 in Fig. S19.† The atoms were rendered using VESTA.45 (b) The number of valence electrons on the carbon atom of the cyano group in
the adsorbed benzonitrile compared with the number on the carbon atom in gas-phase benzonitrile. The numbers of valence electrons were
determined by means of the Bader charge analysis.46

shown in Fig. 5 decreased with increasing the contribution ofback donation (i.e., nitrile activation). These results suggestthat the back donation from the Ptδ− atom of theheteroatomic Pdδ+Ptδ− sites was strongly enhanced, which
weakened the CN bond and thus enhanced the reactivity of
the cyano group with dissociated hydrogen.

Reusability and applicability of 3.9 nm PdPtĲ50 : 50)
nanoparticles
The reusability of the best-performing carbon-supported PdPt
(50 : 50) nanoparticles (i.e., the 3.9 nm nanoparticles) was
evaluated in the hydrogenation of benzonitrile underambient conditions. After the reaction for 3 h, the catalyst
was collected by coagulation and centrifugation, washed withethanol and diethylether, dried under vacuum at 40 °C, andthen reused. These experiments revealed that the activity of
the catalyst decreased with repeated use but the activity
degradation slowed down after five uses (Fig. S20a†).
Benzonitrile conversion stopped when the catalyst wasremoved from the reaction mixture by coagulation andcentrifugation, which means that the active metal did notleach into the solution, and the catalytic reaction proceeded
heterogeneously (Fig. S20b†). On the other hand,thermogravimetric analysis of the fresh and used carbonsupported catalysts showed that the metal loading decreased
from 5.7 wt% to 4.2 wt% with repeated use (Fig. S21†), which
may be due to the release of the metal particles from thecarbon support by heavy stirring and shaking during catalyst
washing. Additionally, TEM and STEM–EDXS analyses wereused to directly observe the morphology of the catalyst before
and after the reaction. Before the reaction, spherical
nanoparticles were well-dispersed on the carbon support (Fig.
S22a†). In contrast, after five uses, aggregates of the primaryparticles were observed although the size of the primaryparticles remained essentially unchanged (Fig. S22b and cThis journal is © The Royal Society of Chemistry 2022

and S23†). These results suggest that the decrease in catalytic
activity with repeated use was due to a reduction in thenumber of exposed metal atoms (i.e., available active sites) as
a result of reduced metal loading and aggregate formation.
Fortunately, the EDXS maps of the Pd-L and Pt-L signals
clearly overlapped, indicating that the alloying state of the
PdPt (50 : 50) nanoparticles was unchanged even after fiveuses (Fig. S22c–f†). In addition, the PdPt (50 : 50)
nanoparticles that had been used five times showed better
catalytic activity than the smaller Pd and Pt nanoparticles,
owing to the alloying effect described in the above sections(Fig. S24†).
Next, we explored the applicability of the carbon-supported
3.9 nm PdPt (50 : 50) nanoparticles by carrying out reactions ofvarious benzonitriles under ambient conditions (Table 2).
Benzonitrile was successfully converted to its corresponding
secondary amine in 96% yield after the reaction for 3 h (entry
1). Benzonitriles bearing an electron-withdrawing group (–CF3,–F, or –COCH3) afforded moderate to high yields of thecorresponding secondary amines in only 2 h (entries 2–4),
probably because the cyano groups in these substrates werestrongly polarized by the electron-withdrawing functionalgroup, which would favor the interaction with the heteroatomic
Pdδ+Ptδ− sites. In addition, benzonitriles with an electrondonating group (–OCH3 or –CH3) were transformed into
secondary amines in 2–3 h (entries 5–7), which indicates thatthe interaction between the cyano group and the heteroatomic
Pdδ+Ptδ− sites was facilitated not only by electron-withdrawing
functional groups but also by resonance structures involving
the aromatic ring. Heterocyclic nitriles smoothly gave moderate
to high yields of secondary amines (entries 8 and 9). In
contrast, because of the lack of resonance effects, an aliphatic
nitrile (isobutyronitrile) did not react completely even if thereaction time was prolonged (entry 10). It is notable that these
newly developed PdPt (50 : 50) random alloy nanoparticles had
higher catalytic activity for the hydrogenation of aromatic and

Catal. Sci. Technol., 2022, 12, 4128–4137 | 4135

View Article Online

Paper

Catalysis Science & Technology

Table 2 Substrate scope of nitrile hydrogenation over the carbonsupported 3.9 nm PdPt (50 : 50) nanoparticles

Time (h)Conv.a (%)

Yielda (%)

1

3

99

96

2

2

99

90

Open Access Article. Published on 01 March 2022. Downloaded on 10/15/2024 7:00:39 PM.
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.

Entry

Substrate

species, and thus enhanced catalytic activity. The
nanoparticles could be used to transform various aromaticand heterocyclic nitriles into their corresponding secondaryamines in just a few hours under ambient conditions. Ourfindings can be expected to facilitate the development of a
new class of catalysts that will enable moleculartransformations without the need for heat, pressurization, orlong reaction times.

Author contributions
3

2

99

95

4

2

92

62

5

3

99

89

6

2

96

82

7

3

99

81

8

2

99

45

9

3

91

81

10

8

71

54

Yoshihide Nishida: designing of research, data collection, andwriting-editing.
KatsutoshiSato:coordinationofcharacterization, conducting X-ray absorption spectroscopy,
and editing. Chandan Chaudhari and Hiroshi Yamada: data
curation and validation. Takaaki Toriyama, Tomokazu
Yamamoto and Syo Matsumura: STEM–EDXS analysis. Susan
Meñez Aspera and Hiroshi Nakanishi: density functional theory
calculation. Masaaki Haneda: FT-IR analysis. Katsutoshi
Nagaoka: designing of research and writing-editing.

Conflicts of interestaConversion and yield were calculated by gas chromatography withflame ionization detection using dodecane as an internal standard.

heterocyclic nitriles to the corresponding secondary amines
than any previously reported catalysts (Table S5†).17–23,27–29

4. Conclusions
We found that benzonitriles can be effectively hydrogenatedunder ambient conditions over the newly developed
bimetallic PdPt nanoparticles. Rapid chemical reduction
assisted by microwave heating enabled us to randomly alloyclassically immiscible Pd and Pt atoms, resulting in amarkedly enhanced catalytic activity relative to that ofmonometallic Pd and Pt catalysts; nitrile hydrogenation
reactions catalyzed by the alloyed catalysts selectively
producedsecondaryamines.
Experimental
andcomputational studies revealed that the hydrogenation
reaction was accelerated over heteroatomic Pdδ+Ptδ− sites
because of strong back-donation. In addition, alloying equalamounts of Pd and Pt atoms and decreasing the size of thenanoparticles maximized the number of heteroatomic Pdδ+Ptδ− sites, resulting in the formation of electron-enriched Ptδ−

4136 | Catal. Sci. Technol., 2022, 12, 4128–4137

There are no conflicts to declare.

Acknowledgements
This research was supported by the ACCEL program, Japan
Science and Technology Agency (JST), JPMJAC1501 and theJapan Society for the Promotion of Science (JSPS) KAKENHI,
20J13035. STEM observations were performed as a part of aprogram conducted by the Advanced Characterization
Nanotechnology Platform Japan, sponsored by the Ministry of
Education, Culture, Sports, Science and Technology (MEXT),
Japan
(No.
JPMXP09A20KU0356).
X-ray
absorption
measurements were performed at the BL01B1 facilities ofSPring-8 at the approval of the Japan Synchrotron Radiation
Research Institute (JASRI) (Nos. 2019A1703 and 2020A1692).
K. Sato thanks the Program for Elements Strategy Initiative
for Catalysts & Batteries (ESICB) commissioned by MEXT. We
acknowledge Dr. K. Kusada and Dr. H. Asakura (Kyoto
University) for fruitful discussions concerning X-ray
diffraction and X-ray absorption analysis.

References
1 C. Su, R. Tandiana, J. Balapanuru, W. Tang, K. Pareek, C. T.
Nai, T. Hayashi and K. P. Loh, J. Am. Chem. Soc., 2015, 137,
685–690.
2 P. P. Zhao, X. F. Zhou, J. J. Dai and H. J. Xu, Org. Biomol.
Chem., 2014, 12, 9092–9096.
3 R. N. Salvatore, A. S. Nagle, S. E. Schmidt and K. W. Jung,
Org. Lett., 1999, 1, 1893–1896.
4 G. Marzaro, A. Guiotto and A. Chilin, Green Chem., 2009, 11,774–776.
5 M. C. Lubinu, L. De Luca, G. Giacomelli and A. Porcheddu,
Chem. – Eur. J., 2011, 17, 82–85.

This journal is © The Royal Society of Chemistry 2022

View Article Online

Open Access Article. Published on 01 March 2022. Downloaded on 10/15/2024 7:00:39 PM.
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.

Catalysis Science & Technology
6 M. H. S. A. Hamid, P. A. Slatford and J. M. J. Williams, Adv.
Synth. Catal., 2007, 349, 1555–1575.
7 C. Chiappe and D. Pieraccini, Green Chem., 2003, 5, 193–197.
8 O. Saidi, A. J. Blacker, M. M. Farah, S. P. Marsden and J. M.
Williams, Chem. Commun., 2010, 46, 1541–1543.
9 O. Saidi, A. J. Blacker, M. M. Farah, S. P. Marsden and J. M.
Williams, Angew. Chem., Int. Ed., 2009, 48, 7375–7378.
10 T. T. Dang, B. Ramalingam, S. P. Shan and A. M. Seayad, ACS
Catal., 2013, 3, 2536–2540.
11 B. Emayavaramban, P. Chakraborty, E. Manoury, R. Poli and
B. Sundararaju, Org. Chem. Front., 2019, 6, 852–857.
12 R. Apodaca and W. Xiao, Org. Lett., 2001, 3, 1745–1748.
13 S. Hoffmann, M. Nicoletti and B. List, J. Am. Chem. Soc.,
2006, 128, 13074–13075.
14 A. F. Abdel-Magid, K. G. Carson, B. D. Harris, C. A.
Maryanoff and R. D. Shah, J. Org. Chem., 1996, 61,
3849–3862.
15 J. S. Sapsford, D. J. Scott, N. J. Allcock, M. J. Fuchter, C. J.
Tighe and A. E. Ashley, Adv. Synth. Catal., 2018, 360,
1066–1071.
16 T. Mitsudome, M. Sheng, A. Nakata, J. Yamasaki, T.
Mizugaki and K. Jitsukawa, Chem. Sci., 2020, 11, 6682–6689.
17 K. Rajesh, B. Dudle, O. Blacque and H. Berke, Adv. Synth.
Catal., 2011, 353, 1479–1484.
18 S. Saha, M. Kaur, K. Singh and J. K. Bera, J. Organomet.
Chem., 2016, 812, 87–94.
19 Y. Sato, Y. Kayaki and T. Ikariya, Organometallics, 2016, 35,
1257–1264.
20 Y. Li, Y. Gong, X. Xu, P. Zhang, H. Li and Y. Wang, Catal.
Commun., 2012, 28, 9–12.
21 S. Lu, J. Wang, X. Cao, X. Li and H. Gu, Chem. Commun.,2014, 50, 3512–3515.
22 A. Galan, J. De Mendoza, P. Prados, J. Rojo and A. M.
Echavarren, J. Org. Chem., 1991, 56, 452–454.
23 Y. Monguchi, M. Mizuno, T. Ichikawa, Y. Fujita, E.
Murakami, T. Hattori, T. Maegawa, Y. Sawama and H. Sajiki,
J. Org. Chem., 2017, 82, 10939–10944.
24 N. Toshima and T. Yonezawa, New J. Chem., 1998, 22,
1179–1201.
25 Y. Nakagawa and K. Tomishige, Catal. Commun., 2010, 12,
154–156.
26 H. Miura and T. Shishido, Chem. Lett., 2021, 50, 346–352.
27 S. Lu, P. Xu, X. Cao and H. Gu, RSC Adv., 2018, 8, 8755–8760.
28 H. Wang, Q. Luo, W. Liu, Y. Lin, Q. Guan, X. Zheng, H. Pan,
J. Zhu, Z. Sun, S. Wei, J. Yang and J. Lu, Nat. Commun.,
2019, 10, 4998–5006.

This journal is © The Royal Society of Chemistry 2022

Paper
29 Z.-F. Jiao, J.-X. Zhao, X.-N. Guo, X.-L. Tong, B. Zhang, G.-Q.
Jin, Y. Qin and X.-Y. Guo, Catal. Sci. Technol., 2019, 9,
2266–2272.
30 M. Yamauchi, H. Kobayashi and H. Kitagawa,
ChemPhysChem, 2009, 10, 2566–2576.
31 K. Kusada, H. Kobayashi, R. Ikeda, Y. Kubota, M. Takata, S.
Toh, T. Yamamoto, S. Matsumura, N. Sumi, K. Sato, K.
Nagaoka and H. Kitagawa, J. Am. Chem. Soc., 2014, 136,
1864–1871.
32 C. Song, A. Tayal, O. Seo, J. Kim, Y. Chen, S. Hiroi, L. S. R.
Kumara, K. Kusada, H. Kobayashi, H. Kitagawa and O.
Sakata, Nanoscale Adv., 2019, 1, 546–553.
33 Y. Nishida, C. Chaudhari, H. Imatome, K. Sato and K.
Nagaoka, Chem. Lett., 2018, 47, 938–940.
34 Y. Nishida, Y. Wada, C. Chaudhari, K. Sato and K. Nagaoka,
J. Jpn. Pet. Inst., 2019, 62, 220–227.
35 S. R. Bharadwaj, A. S. Kerkar, S. N. Tripathi and S. R.
Dharwadkar, J. Less-Common Met., 1991, 169, 167–172.
36 G. Rakhtsaum, Platinum Met. Rev., 2013, 57, 202–213.
37 C. Sarkar, P. Koley, I. Shown, J. Lee, Y.-F. Liao, K. An, J.
Tardio, L. Nakka, K.-H. Chen and J. Mondal, ACS Sustainable
Chem. Eng., 2019, 7, 10349–10362.
38 L. S. R. Kumara, O. Sakata, H. Kobayashi, C. Song, S.
Kohara, T. Ina, T. Yoshimoto, S. Yoshioka, S. Matsumura
and H. Kitagawa, Sci. Rep., 2017, 7, 14606.
39 H. Miura, K. Endo, R. Ogawa and T. Shishido, ACS Catal.,
2017, 7, 1543–1553.
40 N. Toshima, M. Harada, T. Yonezawa, K. Kushihashi and K.
Asakura, J. Phys. Chem., 1991, 95, 7448–7453.
41 C. Cong, S. Nakayama, S. Maenosono and M. Harada, Ind.
Eng. Chem. Res., 2018, 57, 179–190.
42 J. Prinz, R. Gaspari, Q. S. Stöckl, P. Gille, M. Armbrüster, H.
Brune, O. Gröning, C. A. Pignedoli, D. Passerone and R.
Widmer, J. Phys. Chem. C, 2014, 118, 12260–12265.
43 E. S. Gutterød, S. Øien-Ødegaard, K. Bossers, A.-E.
Nieuwelink, M. Manzoli, L. Braglia, A. Lazzarini, E.
Borfecchia, S. Ahmadigoltapeh, B. Bouchevreau, B. T.
Lønstad-Bleken, R. Henry, C. Lamberti, S. Bordiga, B. M.
Weckhuysen, K. P. Lillerud and U. Olsbye, Ind. Eng. Chem.
Res., 2017, 56, 13206–13218.
44 M. J. Hossain, M. M. Rahman and M. Jafar Sharif, NanoscaleAdv., 2020, 2, 1245–1252.
45 K. Momma and F. Izumi, J. Appl. Crystallogr., 2011, 44,
1272–1276.
46 G. Henkelman, A. Arnaldsson and H. Jónsson, Comput.
Mater. Sci., 2006, 36, 354–360.

Catal. Sci. Technol., 2022, 12, 4128–4137 | 4137