Water-enhanced selective hydrogenation of cinnamaldehyde to cinnamyl alcohol on RuSnB/CeO2 catalysts

Article abstract of DOI:10.1016/j.apcata.2019.05.032

The CeO₂-supported ternary RuSnB catalysts were synthesized by incipient wetness impregnation procedures and applied in hydrogenation of cinnamaldehyde in pure water as the solvent. A synergy effect between Ru-based catalysts and water molecules has afforded the efficiently selective transformation of cinnamaldehyde to cinnamyl alcohol with the satisfactory conversion and selectivity. Structural characterization results suggested the incorporation of Ru sites into the SnO_x matrix and the electronic interaction between Ru and B additives in RuSnB/CeO₂ catalyst. The isotopic exchange studies have demonstrated that both dissociative activation of H₂ and H₂O (deuterated D₂ and D₂O) were apparently affected by the status of Ru sites. Furthermore, the kinetics tests in D₂O solvent have also revealed the co-existence of water-involved hydrogen-exchange route with the direct hydrogenation route using dissociative H₂ during the hydrogenation reaction. The optimal Ru₂Sn₁B₁/CeO₂ catalyst could afford the best H₂O-activation capability and thus accelerate the reaction rate in the H₂O-involved hydrogenation.

Full text of DOI:10.1016/j.apcata.2019.05.032

Accepted Manuscript
Title: Water-Enhanced Selective Hydrogenation of
Cinnamaldehyde to Cinnamyl Alcohol on RuSnB/CeO2
Catalysts
Authors: Yihu Dai, Xiaofang Chu, Jingjing Gu, Xing Gao,
Min Xu, Di Lu, Xiaoyue Wan, Wei Qi, Bingsen Zhang,
Yanhui Yang
PII:
S0926-860X(19)30245-5
DOI:
Reference:
https://doi.org/10.1016/j.apcata.2019.05.032
APCATA 17098
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
8 April 2019
26 May 2019
28 May 2019
Please cite this article as: Dai Y, Chu X, Gu J, Gao X, Xu M, Lu D, Wan X, Qi W,
Zhang B, Yang Y, Water-Enhanced Selective Hydrogenation of Cinnamaldehyde to
Cinnamyl Alcohol on RuSnB/CeO2 Catalysts, Applied Catalysis A, General (2019),
https://doi.org/10.1016/j.apcata.2019.05.032
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

Water-Enhanced Selective Hydrogenation of Cinnamaldehyde to Cinnamyl
Alcohol on RuSnB/CeO2 Catalysts
Yihu Daia,*, Xiaofang Chua, Jingjing Gua, Xing Gaoa, Min Xua, Di Lua, Xiaoyue Wana, Wei Qib,*,
Bingsen Zhangb, Yanhui Yanga,*
aInstitute of Advanced Synthesis, School of Chemistry and Molecular Engineering, Nanjing Tech
University, Nanjing 211816, China
bShenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese
Academy of Sciences, Shenyang 110016, China
Corresponding Author
*E-mail: ias_yhdai@njtech.edu.cn (Y. Dai)
*E-mail: wqi@imr.ac.cn (W. Qi)
*E-mail: yhyang@njtech.edu.cn (Y. Yang)
Highlights:
 RuSnB/CeO2
efficiently
catalyzes
cinnamaldehyde
1

hydrogenation to cinnamyl alcohol in water.
 Structural and electronic modification by Sn and B species
enhance catalytic property of Ru sites.
 Water-involved hydrogen-exchange route co-exists with H2-
dissociation-hydrogenation.
 H2-dissociation is not rate-limiting step whereas facile H2O-
activation accelerates reaction.
Abstract: The CeO2-supported ternary RuSnB catalysts were synthesized by incipient
wetness impregnation procedures and applied in hydrogenation of cinnamaldehyde in
pure water as the solvent. A synergy effect between Ru-based catalysts and water
molecules has afforded the efficiently selective transformation of cinnamaldehyde to
cinnamyl alcohol with the satisfactory conversion and selectivity. Structural
characterization results suggested the incorporation of Ru sites into the SnOx matrix
and the electronic interaction between Ru and B additives in RuSnB/CeO2 catalyst.
The isotopic exchange studies have demonstrated that both dissociative activation of
H2 and H2O (deuterated D2 and D2O) were apparently affected by the status of Ru
sites. Furthermore, the kinetics tests in D2O solvent have also revealed the co-
existence of water-involved hydrogen-exchange route with the direct hydrogenation
route using dissociative H2 during the hydrogenation reaction. The optimal
2

Ru2Sn1B1/CeO2 catalyst could afford the best H2O-activation capability and thus
accelerate the reaction rate in the H2O-involved hydrogenation.
Keywords: water, Ru catalyst, hydrogen exchange, selective hydrogenation, α,β-
unsaturated aldehyde and alcohol
1. Introduction
A wide variety of α,β-unsaturated alcohols serve as important fine chemicals
applied in agrochemicals, flavorings, pharmaceuticals, fragrances industrials, and
these alcohols can be manufactured through the chemoselective hydrogenation of the
carbonyls in α,β-unsaturated aldehydes and ketones [1-4]. Although such reaction
route has a high degree of atom-economy, it is still subject to the issue of
unsatisfactory hydrogenation selectivity, because C=C bonds possess lower bond
energy than C=O bonds and both thermodynamics and kinetics favor the activating
hydrogenation of C=C bonds over C=O bonds [5,6]. Different kinds of heterogeneous
metallic catalysts have been developed to accomplish the selective hydrogenation of
α,β-unsaturated aldehydes and ketones to corresponding unsaturated alcohols through
the structural optimization on active metal sites and supports as well as ligands [7-14].
With respect to focused researches of the precious metal catalysts, Pd catalysts prefer
to selectively catalyze hydrogenation of C=C moiety over C=O moiety, causing the
formation of C=C hydrogenated products [15]. On the other hand, the high-cost limits
3

the practical application of Ir and Pt catalysts in the hydrogenation of α,β-unsaturated
aldehydes and ketones, although numerous optimization efforts have been successful
[16-22]. In consideration of affordable price and moderate catalytic hydrogenation
ability, metallic Ru heterogeneous catalysts have potentials to meet the challenges of
efficiently selective transformation of α,β-unsaturated aldehydes and ketones into α,β-
unsaturated alcohols.
There are various attempts to enhance the performance of Ru-based catalysts in
selective hydrogenation reactions of α,β-unsaturated aldehydes and ketones. Moderate
size distribution and high dispersion degree of metallic Ru nanoparticles on the
catalyst surfaces is necessary to increase the catalytic activity, however, excessively
small particle size leads to decreased hydrogenation selectivity towards the
unsaturated alcohols [23,24]. Introducing a second metal additive to form alloy
structure has also been proved as a feasible strategy to improve both catalytic
hydrogenation activity and selectivity for Ru-based catalysts [25,26]. Benefited to
electronic effects and geometric effects, satisfactory catalytic property can be gained
on those bimetallic alloy Ru-series catalysts, e.g., Ru-Fe, Ru-Pt, Ru-Pd, etc. [27,28].
In addition, an appropriate support such as SiO2, Al2O3, active carbon, carbon
nanotube and zeolite can afford specific interaction with the active Ru sites, and
consequently promote the reaction rate, the selectivity as well as the recycling
stability [29-32]. Cubic fluorite CeO2 is frequently employed as the support to
stabilize the active metallic sites by providing the strong interaction. The relatively
high lattice oxygen mobility and the superior redox ability of CeO2 support can not
4

only strongly modify the structural properties of supported metal sites, but also
specifically attract with the reaction-relevant intermediates. CeO2-supported Ru
particle has been reported as effective catalysts in hydrogenation reactions such as
CO2-to-CH4 and amides-to-alcohols [33-35], however, it has not been adopted in the
selective hydrogenation of α,β-unsaturated aldehydes and ketones into unsaturated
alcohols. Hence, a rational design strategy should be explored to preferentially
produce active and durable CeO2-supported Ru catalysts for the hydrogenation
reaction.
In addition to the structural regulation on catalysts, the catalytic hydrogenation
performances depend on the reaction conditions, especially the solvent environment.
In particularly, the utilization of water as polar solvent has attracted extensive
interests in organic synthesis in view of its substantial economic and ecological
advantages, as well as separation convenience [36,37]. However, water molecule is in
general not an innocent spectator as solvent, and it plays a critical role in the catalytic
hydrogenation cycle [38]. It has been recognized that, in contrast to a non-polar
solvent, a polar solvent could afford a facile reaction environment to achieve highly
selective hydrogenation of C=O groups and production of unsaturated alcohols with
similar polarity [39-42]. One of the reasons is identified as the preferential adsorption
of hydrophilic C=O bonds over C=C bonds on the catalyst surfaces with the aid of
dipolar water solvent [43-45]. The water molecules can coordinate with the
homogeneous complex catalysts to form hydroxo species, modifying the structural
properties of active metal sites and accelerating hydrogenation or transfer
5

hydrogenation reactions by hydrophobic effects or hydrogen-bonding interactions
with substrates [46-48]. The water molecules can also accelerate the hydrogen
diffusion across the surface of metal oxide support, determining the hydrogen
spillover process and thus affecting the catalytic hydrogenation activity [49,50].
Furthermore, our previous works have presented an active pathway of water-involved
hydrogen exchange, which is coexisted with direct hydrogenation with dissociated H2
during selective hydrogenation reaction of cinnamaldehyde to cinnamyl alcohol over
Pt-based catalysts [51]. The combining results from isotope labeling experiments and
theoretical studies have suggested that the water molecule acted as a bridge to
facilitate hydrogen exchange between the reactant substrates and the Pt sites with a
lower thermodynamic energy barrier. Therefore, water can act as green solvent or
catalytic promoter in both homogeneous and heterogeneous hydrogenation reactions,
however, great progress in more advantageous use of water remains to be done.
In present work, we finely tune the chemical structure of active Ru sites
supported by CeO2 via the co-modification with tin and boride additives. The
Ru/CeO2-series catalysts with low Ru loadings are applied in the chemoselective
hydrogenation reaction of cinnamaldehyde to cinnamyl alchol with pure water as
solvent instead of commonly used organic solvents. In addition, a series of detailed
characterizations are performed to verify the structural information of Ru-based
catalysts. The isotopic experiments of H2-D2 and H2-D2O exchange as well as D2O-
involved kinetics tests are also carried out for illustrating the catalytic effects of water
molecules in the Ru-catalyzed hydrogenation reactions.
6

2. Experimental
2.1 Materials
Ruthenium chloride hydrate (RuCl3·xH2O, 35.0-42.0% in Ru basis), tin chloride
dihydrate (98.0-103.0%), boric acid (99.8%), cerium oxide (99.9%), dodecane (98%),
ethyl acetate (99.8%), cyclohexane (99.7%), and toluene（99.5%）were purchased
from Aladdin Reagent Corp. (Shanghai, China). Cinnamaldehyde (99.0%),
phenylpropyl aldehyde (95.0%), cinnamyl alcohol (98.0%), 3-phenylpropanol
(99.0%) and isopropanol (99.9%) were obtained from Sigma-Aldrich (Shanghai,
China). D2O (deuteration degree >99.8%) was provided by J&K Scientific (Shanghai,
China). H2 (99.999%), Ar (99.999%) were supplied by Nanjing Special Gas Factory
(Nanjing, China). D2 (99.999%, deuteration degree >99.8%) was obtained from
Suzhou Changyou Gas Co., LTD. (Suzhou, China).
2.2. Catalyst preparation
All Ru-based catalysts were prepared by the incipient wetness impregnation
method and dry commercial CeO2 particles were employed as the support. A series of
CeO2-supported Ru, Sn or/and B catalysts with the theoretical molar ratios were
synthesized using RuCl3, SnCl2 and H3BO3 as the precursors. The ethanol solution
containing certain amounts of the precursor salts was incipient impregnated into 1.0 g
of the CeO2 support. After impregnation, the sample was maintained at room
temperature for 2 h and then dried overnight in an oven at 100 oC. The catalyst was
finally obtained after reduction process in a tube furnace under 60 mL of 15 vol.%
H2/Ar flow at 350 oC for 3 h with a heating rate of 2 oC/min. The accurate loading
7

amounts of Ru, Sn and B in the catalysts were verified with the ICP-OES analyses
and the data were summarized in Table 1. The Ru weight loadings were fixed at
approximately 0.7 wt.%, while the molar ratios of Sn and B to Ru were approaching
1:2 for Ru2Sn1/CeO2, Ru2B1/CeO2 and Ru2Sn1B1/CeO2 catalysts.
2.3. Catalyst characterization
Inductively coupled plasma-optical emission spectrometry (ICP-OES, Perkin
Elmer, Avio 200) was used to measure the Ru, Sn and B loadings in different
catalysts. X-ray diffraction (XRD) patterns were recorded on a Bruker AXS D8 Focus
diffractrometer in the 2θ range of 15° to 75° at 40 kV and 40 mA operating
conditions. Transmission electron microscope (TEM) images were acquired on a
Hitachi HT7700 TEM operated at 120 kV. X-ray photoelectron spectroscopy (XPS)
was performed on an Escalab250Xi electron spectrometer (Thermo Scientific) with a
monochromatic 150 W Al Kα radiation source. The Brunauer-Emmett-Teller (BET)
specific surface areas were obtained from the N2 adsorption-desorption measurements
performed at -196 oC on a Quantachrome Autosorb-iQ3 adsorption analyzer. The
samples were first degassed under vacuum at 200 oC for 8 h. The Raman spectra were
recorded on a Horiba HR Evolution spectrometer with 532 nm excitation laser source.
Temperature programmed reduction (TPR) was performed on a chemical
adsorption analyzer (AutoChem 2920, Micromeritics) with a U-shaped quartz tube.
80 mg of catalyst was loaded and then pretreated in 30 mL/min of Ar flow for 1.5 h at
300 oC. After cooling down to room temperature and reaching a steady state, the
reduction TCD signal was started to record with heating sample to 550 oC in 20
8

mL/min 10 vol.% H2/Ar at a specific rate of 10 oC.
The diffuse reflectance infrared fourier transform spectroscopy (DRIFTs) of CO
adsorption was performed on a Nicolet iS10 FTIR spectrometer equipped with a
Harrick diffuse reflection cell and a liquid nitrogen-cooled MCT/A detector. The
sample was pretreated at 300 oC for 90 min and cooled down to 25 oC in 30 mL/min
of Ar flow before CO adsorption experiment. The background spectrum was collected
after 60 min in 30 mL/min of Ar gas, followed by introducing 10 mL/min of CO flow
to start the chemisorption. After the CO adsorption lasting for 30 min, the sample was
further purged with 30 mL/min of Ar flow for 30 min and then the spectrum was
acquired. Accumulating 16 scans and a spectral resolution of 4 cm-1 were set for all
recorded spectra.
2.4. Catalytic hydrogenation reaction
The cinnamaldehyde hydrogenation reaction was proceeded in a 50 mL Hastelloy
batch reactor (NS-50-C276, Anhui Kemi Machinery Technology Co., Ltd.) with a
Teflon liner. Catalyst (20 mg), and CALD (200 μL) in solvent (10 mL) were added
into the reactor. The residual air inside the reactor was removed by repeatedly
pressurizing and releasing H2 gas. The reaction was performed at 60 or 100 oC under
1 or 20 bar of H2. For eliminating the external mass transfer limitation, 700 rpm of
stirring speed was used in all the reactions. After the reaction was completed, the
reactor was cooled to room temperature and the high-pressure H2 was released. The
catalyst powder was separated by 1400 rpm centrifugation. All the liquid products
were analyzed using a flame ionization detector (FID)-equipped gas chromatograph
9

(GC, Agilent, 7890B). A CP-WAX 52 CB column (30 m × 0.25 mm × 0.25 μm) was
armed in the GC for products separation. The byproducts were identified by a gas
chromatography-mass spectrometry (GC-MS, Agilent, 6890N-5973). Tetradecane
was served as the internal standard and the carbon balance was kept >99% in all the
hydrogenation reactions. For recycling tests, the reused catalyst was hot filtrated and
washed with ethanol several times after each reaction run, and then kept drying before
next reaction run. The catalytic reaction data were calculated based on the the
following formulas:
Conversion = [ Nin(CALD) - Nout(CALD) ] / Nin(CALD)  100%
Selectivity(i) = Nout(i) / iNout(i)  100%
Carbon balance = [ Nout(CALD) + iNout(i) ] / Nin(CALD)  100%
Specific reaction rate = [ Conversion  Nin(CALD) ] / [ Time  Ntotal(Ru) ]
Where i represented hydrogenation products; Nout(i) was the molar amount of
corresponding product i; Ntotal(Ru) was the molar number of total Ru atoms in
employed catalyst.
The experimental CALD concentration as a function of time were plotted
according to a rate law of first order with respect to CALD. The reaction rate constant
k was calculated by the linear fitting method with the following formula:
ln (Ct / C0) = - k  t
where Ct represented the CALD concentration at reaction time t, and C0 was the
initial CALD concentration.
2.5. Isotope labeling measurement
10

H2-D2 exchange experiments were performed in a fixed-bed reactor with a quartz
tube (8 mm in inner diameter). A 10 mg portion of catalyst was loaded in the reactor
and the feeding gases consisted of 8 mL/min of H2, 8 mL/min of D2 and 36 mL/ min
of Ar balance gas. Prior to the exchange reaction, the sample was pretreated in Ar
flow at 120 oC for 30 min. After cooling to 40 oC, the gas flow was switched to H2-
D2-Ar mixture to start the H2-D2 exchange reaction. The exchange reaction-relevant
gases of H2, HD and D2 were analyzed with a mass spectrometer (MS, QGA, Hiden
Analytical Ltd.).
H2-D2O exchange measurements were performed in a batch reactor operated at
100 oC and 20 bar of H2. The loading amount of Ru-based catalyst was 20 mg and the
exchange reaction was lasted for 2 h. After the reaction was completed and the reactor
was cooled down, the gaseous mixture inside the reactor, including H2, D2 and HD,
was collected with a gas bag and then was analyzed on the MS.
Isotope-labeling kinetic studies were also performed in a batch reactor. The
reaction conditions were similar to the regular catalytic hydrogenation reaction tests
except of using D2O to replace H2O as solvent. The certain conditions were 20 mg of
Ru-based catalyst, 200 μL of CALD, 10 mL of D2O solvent, 60 or 100 oC, 1 or 20 bar
of H2, and 2 h of time duration. The liquid products containing deuterated molecules
were analyzed on the GC-MS. The reference experiments were also carried out to
clarify the exchange degrees between three kinds of primary hydrogenated products
(CALA, HCALD and HCALA) and pure D2O in the absence of the Ru catalysts. The
reference experiment of exchange between D2 and products was further performed in
11

the presence of catalyst (conditions: 20 mg of Ru2Sn2B1/CeO2 catalyst, 60 μL of
product, 10 mL of n-dodecane, 100 oC, 1 bar of D2, and 12 h of time duration).
3. Results and discussion
3.1. Catalytic performance of Ru catalysts in water
These CeO2-supported Ru catalysts with various compositions were applied in
the selective hydrogenation of cinnamaldehyde (CALD) to cinnamyl alcohol (CALA)
at a relatively low temperature (60 oC) with pure water as the solvent. For evaluating
the specific reaction rate under a comparable level, the CALD conversion in each test
was kept at approximately 40% through reregulating the reaction time duration and/or
catalyst amount. As presented in Fig. 1A, monometallic Ru/CeO2 catalyst displayed
an unsatisfactory hydrogenation selectivity towards CALA at 60.2% and a lower
specific reaction rate of 11.0 h-1 (consumed CALD moles derived by total Ru mole in
the catalyst per hour). The modification with B additive in Ru2B1/CeO2 catalyst led to
a decreased CALA selectivity at 47.7%, however, it caused near two times
improvement in the reaction rate to 29.3 h-1, as compared to Ru/CeO2 catalyst. For
Sn-modified bimetallic Ru2Sn1/CeO2 catalyst, both the reaction rate and CALA
selectivity further increased up to 118.2 h-1 and 71.8%, respectively. In contrast to
monometallic and binary Ru-based catalysts, ternary Ru2Sn1B1/CeO2 catalyst
exhibited a significantly promoted catalytic hydrogenation performance that its
specific reaction rate and the CALA selectivity could reach up to 223.2 h-1 and 89.7%,
respectively.
The CALD hydrogenation reaction was performed in the kinetic region to further
12

compare the catalytic properties of Ru2Sn1/CeO2 and Ru2Sn1B1/CeO2 catalysts. The
reaction rate constants (k) over these two catalysts were measured in the initial
reaction stages, and the linear dependence of ln(Ct/C0) as a function of reaction time
suggested that the catalytic reaction followed psudo first-order with respect to CALD
reactant, as shown in Fig. 1B. The Ru2Sn1B1/CeO2 catalyst displayed a k value of
0.289 h-1, which was two times as high as that of Ru2Sn1/CeO2 catalyst (k=0.133 h-1).
In addition, the CALA selectivity of Ru2Sn1/CeO2 catalyst was always less than 80%
during the whole reaction stages, whereas Ru2Sn1B1/CeO2 catalyst can maintain a
superior CALA selectivity beyond 90% in the hydrogenation reaction. These results
indicated that the CeO2-supported Ru catalyst jointly decorated with Sn and B species
could efficiently catalyze the selective hydrogenation reaction of CALD to CALA in
water solvent.
The solvent effect cannot be ignored in the heterogeneous catalysis, especially in
the catalytic hydrogenation of α,β-unsaturated aldehydes and ketones to α,β-
unsaturated alcohols [42,51]. The optimized Ru2Sn1B1/CeO2 catalyst was employed to
verify the superior catalytic properties in pure water over varieties of organic solvents
in CALD hydrogenation reactions. With same reaction conditions and time durations,
poor CALA selectivity at less than 50% and low CALD conversion at less than 30%
were obtained in those common organic solvents such as ethyl acetate, cyclohexane,
n-dodecane and toluene, as shown in Fig. 2A. Specifically, isopropanol has been
served as the most frequently used solvent in the hydrogenation reaction of
unsaturated aldehydes, nonetheless, the CALA selectivity and the CALD conversion
13

of Ru2Sn1B1/CeO2 catalyst with isopropanol as solvent were only 75.0% and 24.0%,
respectively, which were still dramatically inferior to that with water as the solvent
(93.9% for CALA selectivity and 96.0% for CALD conversion). When small amount
of water was added into isopropanol (molar ratio of water to isopropanol=5:100,
10:100), obvious increase of conversion (29.5% and 33.0%) was observed, suggesting
the acceleration effect of water molecules in the hydrogenation reactions. The first
order reaction rate constants (k) in water and isopropanol solvents were further
measured in the kinetic reaction regions. The k value of 0.289 h-1 was observed in
water, which was over five times higher than that of 0.051 h-1 obtained in isopropanol
solvent, as shown in Fig. 2B. These results clearly demonstrated that water solvent
molecules played a critical role in enhancing both catalytic activity and hydrogenation
selectivity in CALD hydrogenation reaction. The catalytic effects of water would be
worth more detailed discusses in the following sections.
The catalytic stability and reusability of the optimal ternary Ru2Sn1B1/CeO2
catalyst was also investigated by repeated reaction tests in water solvent, and the
performances were presented in Fig. 3. After each recycling reaction run, the catalyst
was hot filtrated and washed with ethanol several times, and then kept drying
overnight till the next cycle run. Both the CALD conversion and the CALA
selectivity were maintained approaching 90% in six-cycle runs, suggesting great
catalytic and structural stabilities of the Ru2Sn1B1/CeO2 catalyst in aqueous phase
selective hydrogenation of CALD to CALA.
3.2 Structure characterization of CeO2-supported Ru catalysts
14

A series of CeO2-supported Ru catalysts were prepared by the incipient wetness
impregnation method. The dry commercial CeO2 nanoparticles (NPs) were employed
as the support and the Ru loadings were fixed at approximately 0.7 wt.% for all the
Ru-based catalysts, which were confirmed by the ICP-OES analyses results as listed
in Table 1. The molar ratios of Ru:Sn and Ru:Sn:B were approaching 2:1 and 2:1:1
for Ru2Sn1/CeO2 and Ru2Sn1B1/CeO2 catalysts, respectively (Table 1). Since these Ru
catalysts exhibited distinctly different catalytic performances in the CALD
hydrogenation reactions, their composition and structure were carefully characterized
to gain a clear physical chemical insight on the relevance between the catalytic
activity and the catalyst structure, namely the nature in structure-function relations.
The powder XRD patterns in Fig. 4A revealed that only the standard diffraction
peaks of the cubic fluorite CeO2 phase were observed on either pure CeO2 support or
the Ru-based catalyst. The legible peaks at 28.4o, 32.9o, 47.3o, 56.2o and 58.9o were
corresponding to the (111), (200), (220), (311), and (222) planes of CeO2,
respectively. Neither metallic Ru nor RuO2 phase was observed in these supported Ru
catalysts. In addition, the diffraction peaks of SnO2, Sn or B-related phases were not
found in the XRD patterns of Sn or B-containing catalysts, possibly due to the
relatively low loading amounts or high dispersion of Ru, Sn and B species on CeO2
surfaces. The nitrogen adsorption isotherms exhibited similar specific BET surface
areas for the catalysts (approximately 20 m2/g, Table 1), suggesting that the
impregnated deposition of Ru, Sn or B species cannot apparently vary the surface area
of CeO2 NP supports. The visible (532 nm) Raman spectra of the CeO2-supported
15

catalysts in Fig. 4B-C were dominated by a strong peak at 461 cm-1 with a weak band
at 1172 cm-1, which were corresponding to the F2g symmetry vibrational mode and the
second-order longitudinal optical (2LO) mode of the fluorite CeO2 lattice,
respectively [52]. Neither defect-induced band at ca. 590 cm-1 nor bands of surface
oxygen species at 830, 890 or 1139 cm-1 was observed on these catalysts, indicating
that there was no abundant oxygen-vacancies and adsorbed oxygen species on the
catalyst surfaces [53,54]. In addition, the typical peaks of A1g and B2g vibration modes
of Sn-O bonds in crystalline SnO2 (at ca. 632 and 724 cm-1, respectively) were absent
on the Raman spectra, suggesting the absence of bulk SnO2 species in Sn-containing
catalysts [54-56]. The TEM images in Fig. 5 illustrated that the Ru nanoparticles
could highly disperse on the CeO2 support in all Ru-based catalysts. For CeO2-
supported monometallic Ru NPs, the average particle size was comparatively small,
2.3±0.7 nm as shown in Fig. 5A-B. The modification of Sn or B additives could not
cause obvious changes in the particle size distributions. As shown in Fig. 5C-F, the
similar particle sizes were observed at 2.1±0.7 and 2.6±0.8 nm for Ru2Sn1/CeO2 and
Ru2Sn1B1/CeO2 catalyst, respectively.
XPS measurements in Fig. 6 presented the electronic states of Ru and Sn species
on the Ru-based catalysts surfaces. Since the signal of Ru 3d 3/2 orbit overlapped
with that of C 1s orbit, the Ru 3d 5/2 peak was used to determine the chemical states
of Ru species in all the catalysts. The metallic Ru0 and oxidative Ruδ+ surface species
were confirmed to be coexisted in monometallic Ru/CeO2 catalyst, which both
metallic Ru0 peak at 280.1 eV in binding energy (BE) and oxidative Ruδ+ peak at
16

281.6 eV were presented in the spectrum in Fig. 6A [57,58]. The peak corresponding
to Ru0 surface species disappeared on bimetallic Ru2Sn1/CeO2 catalyst, however, the
peak of Ruδ+ species was distinguishable in the XPS spectrum (Fig. 6B). In the case
of the ternary Ru2Sn1B1/CeO2 catalyst, two peaks of Ru0 and Ruδ+ species appeared in
parallel, as shown in Fig. 6C. The calculated atomic ratios of Ru0/Ruδ+ in the Ru-
based catalysts were summarized in Table 1, which the values were 80/20, 0/100 and
26/74, for Ru/CeO2, Ru2Sn1/CeO2 and Ru2Sn1B1/CeO2 catalyst, respectively. XPS
results also provided the distributions of surface Sn-related species, and the coexisted
metallic Sn0 and oxidative SnOx species were observed on all Sn-containing catalysts,
as presented in Fig. 6D-F. Furthermore, SnOx species dominated over metallic Sn0,
which the ratios of Sn0/Sn2+/4+ were 10/90 and 24/76, for Ru2Sn1/CeO2 and
Ru2Sn1B1/CeO2 catalyst, respectively (Table 1). According to the XPS analyses
results, the addition of SnOx species led to the disappearance of metallic Ru0 surface
species in Ru2Sn1/CeO2 catalyst, might due to full coverage of SnOx on Ru atoms or
incorporation of Ru into SnOx matrix. The further modification with B species in
Ru2Sn1B1/CeO2 catalyst allowed the partial exposure of metallic Ru0 and Sn0 sites on
the surface, possibly attributed to the electric neutrality demanding in the presence of
positive B3+ species [57,59].
To investigate the structural redox properties of various phases on the catalyst
surface and their interactions, H2-TPR analyses were performed on these series of Ru
catalysts. As presented in Fig. 7, only one prominent peak at ca. 460 oC was observed
on pure CeO2 support, which was assigned to the reduction of surface oxygen species
17

on CeO2 [60]. A wide hydrogen-absorption reduction region at 180-450 oC with a
peak at 250 oC was attributed to the reduction of SnOx species with strong interactions
with the CeO2 support for the Sn/CeO2 (Sn: 0.4 wt.%) catalyst. A peak of CeO2-
stabilized RuOx species at 65 oC was observed on the monometallic Ru/CeO2 catalyst.
Modification of Sn additive on Ru in the Ru2Sn1/CeO2 catalyst exhibited two
overlapping peaks at 100 and 160 oC, located in the middle of each reduction peaks of
RuOx and SnOx surface species. The enhanced anti-reduction ability reflected the
formation of SnOx matrix-immobilized RuOx structure with strong interactions
between these two components. Ru2Sn1B1/CeO2 catalyst with further B modifications
revealed a similar H2-TPR pattern except of a slightly shifted reduction peak at 100
oC. In addition, the individual reduction behavior of RuOx species was evidently
distinguishable, compared to that in Ru2Sn1/CeO2 catalyst, suggesting that the B
additives could effectively introduce migration of Ru atoms inside SnOx matrix into
the surface. This result was also conformed to the varying tendency of Ru0/Ruδ+ ratio
from XPS spectral results.
The DRIFT spectra of the chemisorption of CO probe molecules provided
sensitive structural information of the Ru sites on the catalyst surface as well as the
synergistic effect of RuSnB ternary species. The experiments were carried out at 25
oC and the in-situ DRIFT spectra were recorded after CO desorption in the Ar flow.
The spectra in Fig. 8 were displayed in Kubelka-Munk (K-M) unit and fitted with five
types of the chemisorption configurations of CO on Ru sites, as summarized in Table
2. Two distinct peaks at relatively higher frequencies (HF) of 2140 and 2088 cm-1 and
18

three peaks at lower frequencies (LF) of 2055, 2017 and 1969 cm-1 could be precisely
fitted with three Ru catalysts. The LF peak at 1969 cm-1 was assigned to the bridge-
bonded CO on the metallic Ru0 atoms, and the LF peaks at 2017 and 2055 cm-1 were
associated with the adsorption of dicarbonyl CO species on oxidative Ru2+ site and on
the metallic Ru0 site, respectively [61-63]. Two HF peaks at 2088 and 2140 cm-1 were
corresponding to the adsorption models of CO species on the oxidative Ruδ+ sites,
including dicarbonyl, tricarbonyl and linear models [61-63].
The CO-adsorption DRIFT spectral features clearly indicated different
distributions of metallic Ru0 and oxidative Ruδ+ surface sites in these three Ru-based
catalysts. The ratios of Ruδ+/Ru0 in Ru/CeO2, Ru2Sn1/CeO2 and Ru2Sn1B1/CeO2
catalysts were 12.3/87.7, 84.9/15.1 and 84.6/15.4, respectively, according to the fitted
peak areas. Dramatically reduced amount of metallic Ru0 surface sites in
Ru2Sn1/CeO2 and Ru2Sn1B1/CeO2 catalysts compared to that in Ru/CeO2 catalyst was
in accord with the H2-TPR results that part of Ru atoms were incorporated into the
SnOx matrix. It also agreed with the H2-TPR results that B-modified Ru2Sn1B1/CeO2
catalyst had a slightly increased proportion of metallic Ru0 surface sites than
Ru2Sn1/CeO2 catalyst. Furthermore, the role of B additive in the electronic
modification of Ru was evidenced by the blue-shift of the CO-adsorption
characteristic peaks [64, 65]. For instance, either bridge-bonded CO-Ru0 peak or
dicarbonyl CO-Ru2+ peak shifted towards higher frequencies over Ru2Sn1B1/CeO2
catalyst in contrast with Ru2Sn1/CeO2 catalyst (1969 to 1971 cm-1 and 2017 to 2022
cm-1, respectively). Therefore, these combined characterization results presented that
19

the optimal Ru2Sn1B1/CeO2 catalyst might consist of RuSn alloy phase encapsulated
by SnOx-matrix on CeO2 support. The Sn additives largely modify the surface
electron density of active Ru sites for improving the adsorption and reactivity of the
C=O bond, while the geometric effect of intermetallic RuSn-encapsulated SnOx
species can play a part in the suppression of C=C bond adsorptive hydrogenation [66-
68]. The electronic and catalytic properties of Ru could be further modified by their
interaction with Sn and B promoters for most promising hydrogenation catalysts
based on ternary RuSnB compositions [57-59, 64, 69].
3.3. Ru site-determined H2 dissociation
Detailed kinetic studies have presented that the reaction rates of metal-catalyzed
direct hydrogenation of α,β-unsaturated aldehydes obeyed the Langmuir-Hinshelwood
kinetic law [70]. Consequently, the dissociative activation ability of H2 molecules
adsorbed on the Ru catalyst surface should be one of the most critical factor to
consider. The H2-D2 exchange reaction rates over three Ru-based catalysts were
measured at 25 oC with an online MS. As shown in Fig. 9, the exchange product HD
could be steadily produced with the co-feeding of 1:1 (in vol.%) H2 and D2, however,
significantly different rates of HD generation were observed on three Ru catalysts.
Specifically, the HD generation rate of the monometallic Ru/CeO2 catalyst was 13.5
and 4.4 times as high as that of Ru2Sn1/CeO2 and Ru2Sn1B1/CeO2 catalysts,
respectively, possessing the superior ability of H2 dissociation. The weaker H2
dissociation ability of Sn-modified Ru2Sn1/CeO2 catalyst might be ascribed to
reduced metallic Ru sites exposed on the catalyst surface. This result was associated
20

with the coverage of surface Ru atoms by the SnOx species, which was also in
agreement with the CO-adsorption DRIFT spectrum and H2-TPR pattern.
Furthermore, the modification of B additive in Ru2Sn1B1/CeO2 catalyst led to higher
exposure degree of Ru atoms and thus higher H2 dissociation rate compared to
Ru2Sn1/CeO2 catalyst.
On the other hand, the monometallic Ru/CeO2 catalyst showed the greatest H2
dissociation ability among three Ru-based catalysts, nonetheless, it showed the lowest
CALD conversion in the high-pressure hydrogenation reaction, indicating that H2
dissociative activation should not be the rate-limiting step in Ru-catalyzed CALD
hydrogenation reaction. This result was also verified by the fact that the
hydrogenation activity was still in the consequence of Ru/CeO2 (15.0 h-1) <
Ru2Sn1/CeO2 (37.6 h-1) < Ru2Sn1B1/CeO2 (43.3 h-1), when ambient pressure (1 bar) of
H2 was adopted in the hydrogenation reactions. These observations were in line with
the previous report that the hydrogenation reactions of unsaturated aldehydes and
ketones ordinarily followed a near first-order reaction kinetics with respect to H2,
involving the dissociated H species weakly bonding on the metal surface [71-73].
3.4. H2O-involved hydrogenation
As described in above section, the utilization of water as solvent could facilitate
selective hydrogenation of CALD to CALA over Ru-based catalysts. In addition to
afford a polar reaction environment, water has also been demonstrated to induce a
water-mediated hydrogen-exchange reaction route for accelerating the CALD
hydrogenation reaction on alloyed PtFe catalysts, which was coexisted with direct H2
21

dissociative hydrogenation route [51]. It could be expected that water-involved
reaction pathway occurred in the Ru-catalyzed hydrogenation of CALD. Therefore,
pure deuterium oxide (D2O) was employed instead of H2O to further study the
catalytic role of water in the reactions.
The control experiments of exchange between the relevant reactants and D2O
were first carried out in the absence of the Ru catalysts. No MS signals of the
deuterated molecules through H-D exchange were emerged for CALA, HCALD and
HCALA, suggesting that alkenyl and aldehyde as well as hydroxyl groups could not
interact with D2O molecules. The intensity ratio of the peak at m/z=M+1
(M=molecular weight) to the molecular ion peak at m/z=M were extremely low
(<0.2) for all three hydrogenation products in the reference tests, as shown in Fig.
10A-C. The control experiments of exchange between the main products and D2 gas
were further performed in the presence of Ru2Sn1B1/CeO2 catalyst. The MS spectra
displayed that the peak intensity ratio of m/z=M+1 to m/z=M did not obviously
increase as compared to that of pristine molecules, suggesting that almost no product
molecule has exchanged with D species dissociated from D2 on the Ru2Sn1B1/CeO2
catalyst surfaces. However, the peak intensity ratio of m/z 135:134 for the primary
product CALA was remarkably increased up to 1.1 after Ru2Sn1B1/CeO2-catalyzed
hydrogenation reaction at 100 oC in D2O solvent, as shown in Fig. 10D, suggesting
that a large number of the deuterated CALA molecules has produced during the
reaction. This result demonstrated that the D atom in the deuterated CALA product
could derive from the D2O-involved hydrogenation reaction process rather than a
22

simple H-D exchange process between D2O and formed CALA molecules. In
addition, the deuteration of both HCALD and HCALA that served as the C=C
hydrogenated product and the full hydrogenated product, respectively, was also
observed after the reaction. The peak intensity ratio of m/z 135:134 for HCALD and
the ratio of m/z 137/136 for HCALA reached to 1.7 and 2.4, respectively, as
presented in Fig. 10E-F, greatly higher than the values (0.1-0.2) obtained in reference
tests. These observations proved that D2O was involved not only in the C=O
hydrogenation, but also in the C=C hydrogenation during Ru2Sn1B1/CeO2-catalyzed
reaction. Furthermore, such D2O-mediated reaction pathway could occur even under
varied reaction temperature and H2 pressure. For CALA, HCALD and HCALA
products in the hydrogenation reaction at 60 oC under 1 bar of H2, their peak intensity
ratios of m/z (M+1)/M were 0.9, 1.2 and 0.9, respectively, which were still obviously
larger than the ratios observed in the reference tests.
Fig. 11 presented the signals of deuterated molecules in the MS spectra for all of
three kinds of products (CALA, HCALD and HCALA) in the CALD hydrogenation
reactions catalyzed by monometallic Ru/CeO2 and bimetallic Ru2Sn1/CeO2 catalysts,
evidencing that the D2O-involved D-exchange could serve as a crucial pathway that
coexisted with the direct H2 dissociative hydrogenation pathway in the Ru-catalyzed
reactions (Scheme 2). Either of these two pathways could definitely influence the
whole hydrogenation reaction, and it is reasonable to expect that the H2O-involved H-
exchange (as well as D-exchange for D2O) process should be determined by the Ru
sites.
23

To prove this view, H2-D2O exchange experiments were performed on three types
of CeO2-supported Ru catalysts. The yields of gaseous HD and D2 products during the
exchange reactions were displayed in Fig. 12. The Ru2Sn1B1/CeO2 catalyst showed
higher generation rates of HD and D2 than monometallic Ru/CeO2 catalyst, while the
bimetallic Ru2Sn1/CeO2 catalyst showed the lowest rates among three Ru catalysts.
The relatively poor H2-dissociation ability of Ru2Sn1/CeO2 catalyst, which was
clarified by previously discussed H2-D2 exchange results, possibly caused the lowest
H2-D2O exchange reaction rate. On the other hand, in view of that the efficiency of
the H2 dissociative activation of Ru2Sn1B1/CeO2 catalyst has been demonstrated lower
than that of Ru/CeO2 catalyst, reflecting that Ru2Sn1B1/CeO2 catalyst was more
capable of efficiently achieving water dissociative activation compared to Ru/CeO2
catalyst. Therefore, Ru2Sn1B1/CeO2 catalyst could maximum the formation rates of
these deuterated hydrogenation products as compared with Ru/CeO2 and
Ru2Sn1/CeO2 catalysts, under similar deuteration degrees of the primary products in
the D2O-involved hydrogenation reactions.
4. Conclusions
In summary, the co-modification of Sn and B additives on CeO2-supported Ru
sites by geometric and electronic effects can afford significantly enhanced catalytic
properties with respect to both activity (the specific reaction rate reaches 223 h-1 ) and
selectivity (90%) in aqueous phase hydrogenation reaction of CALD to CALA. The
detailed characterization results reveal that the ternary Ru2Sn1B1/CeO2 catalyst is
composed of SnOx-encapsulated RuSn alloy on CeO2 surface. The isotopic labeling
24

kinetic experiments demonstrate that water-mediated hydrogen-exchange route is
coexisted with direct hydrogenation route with dissociated H2 during Ru-catalyzed
hydrogenation reactions. The performances in H2-D2 and H2-D2O exchange reactions
suggest that the activation of H2 molecules is not the rate-limiting step, nonetheless,
the activation of water molecules can determine the water-involved hydrogenation
process. This work shows a promising strategy of synergetic effect between structural
modification and water assistance for metal-catalyzed hydrogenation reactions of α,β-
unsaturated aldehydes and ketones into unsaturated alcohols.
Acknowledgements
NJTech group appreciates the financial support from the National Natural
Science Foundation of China (21802070, and the support from the Jiangsu Provincial
Department of Education and Natural Science Foundation (17KJB150021 and
BK20170986). IMR group thanks the National Natural Science Foundation of China
(91645114, 21573256, 21761132010) for the financial support. We are grateful for
the support from Nanjing Technology Innovation Fund for Overseas Talents.
References
[1] P. Gallezot, D. Richard, Selective hydrogenation of α,β-unsaturated aldehydes,
Catal. Rev. 40 (1998) 81-126.
[2] Y. Yuan, Y. Siyu, W. Mengnan, L. Shujie, Y. Ning, Recent progress in
chemoselective hydrogenation of alpha,beta-unsaturated aldehyde to unsaturated
25

alcohol over nanomaterials, Curr. Org. Chem. 17 (2013) 400-413.
[3] P. Claus, Selective hydrogenation of α,β-unsaturated aldehydes and other C=O and
C=C bonds containing compounds, Top. Catal. 5 (1998) 51-62.
[4] P. Mäki-Arvela, J. Hájek, T. Salmi, D.Y. Murzin, Chemoselective hydrogenation
of carbonyl compounds over heterogeneous catalysts, Appl. Catal. A-Gen. 292 (2005)
1-49.
[5] J.W. Medlin, Understanding and controlling reactivity of unsaturated oxygenates
and polyols on metal catalysts, ACS Catal. 1 (2011) 1284-1297.
[6] M.S. Ide, B. Hao, M. Neurock, R.J. Davis, Mechanistic insights on the
hydrogenation of α,β-unsaturated ketones and aldehydes to unsaturated alcohols over
metal catalysts, ACS Catal. 2 (2012) 671-683.
[7] B. Wu, H. Huang, J. Yang, N. Zheng, G. Fu, Selective hydrogenation of
alpha,beta-unsaturated aldehydes catalyzed by amine-capped platinum-cobalt
nanocrystals, Angew. Chem. Int. Ed. 51 (2012) 3440-3443.
[8] G. Kennedy, L.R. Baker, G.A. Somorjai, Selective amplification of C=O bond
hydrogenation on Pt/TiO2: catalytic reaction and sum-frequency generation
vibrational spectroscopy studies of crotonaldehyde hydrogenation, Angew. Chem. Int.
Ed. 53 (2014) 3405-3408.
[9] M. Zhao, K. Yuan, Y. Wang, G. Li, J. Guo, L. Gu, W. Hu, H. Zhao, Z. Tang, Metal-
organic frameworks as selectivity regulators for hydrogenation reactions, Nature 539
(2016) 76-80.
[10] Y. Zhu, H. Qian, B. A. Drake, R. Jin, Atomically Precise Au25(SR)18
nanoparticles as catalysts for the selective hydrogenation of α,β-unsaturated ketones
and aldehydes, Angew. Chem. Int. Ed. 49 (2010) 1295-1298.
[11] Y. Dai, Y. Wang, B. Liu, Y. Yang, Metallic nanocatalysis: an accelerating
26

seamless integration with nanotechnology, Small 11 (2015) 268-289.
[12] H. Lin, J. Zheng, X. Zheng, Z. Gu, Y. Yuan, Y. Yang, Improved chemoselective
hydrogenation of crotonaldehyde over bimetallic AuAg/SBA-15 catalyst, J. Catal. 330
(2015) 135-144.
[13] K.H. Dostert, C.P. O'Brien, F. Ivars-Barcelo, S. Schauermann, H.J. Freund,
Spectators control selectivity in surface chemistry: acrolein partial hydrogenation over
Pd, J. Am. Chem. Soc. 137 (2015) 13496-13502.
[14] Q. Hu, S. Wang, Z. Gao, Y. Li, Q. Zhang, Q. Xiang, Y. Qin, The precise
decoration of Pt nanoparticles with Fe oxide by atomic layer deposition for the
selective hydrogenation of cinnamaldehyde, Appl. Catal. B-Environ. 218 (2017) 591-
599.
[15] M. Lashdaf, A.O.I. Krause, M. Lindblad, M. Tiitta, T. Venäläinen, Behaviour of
palladium and ruthenium catalysts on alumina and silica prepared by gas and liquid
phase deposition in cinnamaldehyde hydrogenation, Appl. Catal. A-Gen. 241 (2003)
65-75.
[16] W.O. Oduro, N. Cailuo, K.M.K. Yu, H. Yang, S.C. Tsang, Geometric and
electronic effects on hydrogenation of cinnamaldehyde over unsupported Pt-based
nanocrystals, Phys. Chem. Chem. Phys. 13 (2011) 2590-2602.
[17] J. Shi, M. Zhang, W. Du, W. Ning, Z. Hou, SnO2-isolated Pt3Sn alloy on reduced
graphene oxide: an efficient catalyst for selective hydrogenation of C=O in
unsaturated aldehydes, Catal. Sci. Technol. 5 (2015) 3108-3112.
[18] Z. Guo, C. Xiao, R.V. Maligal-Ganesh, L. Zhou, T.W. Goh, X. Li, D. Tesfagaber,
A. Thiel, W. Huang, Pt Nanoclusters confined within metal-organic framework
cavities for chemoselective cinnamaldehyde hydrogenation, ACS Catal. 4 (2014)
1340-1348.
27

[19] F. Ammari, An emergent catalytic material: Pt/ZnO catalyst for selective
hydrogenation of crotonaldehyde, J. Catal. 221 (2004) 32-42.
[20] S. Bhogeswararao, D. Srinivas, Intramolecular selective hydrogenation of
cinnamaldehyde over CeO2-ZrO2-supported Pt catalysts, J. Catal. 285 (2012) 31-40.
[21] E. Gebauerhenke, J. Grams, E. Szubiakiewicz, J. Farbotko, R. Touroude, J.
Rynkowski, Pt/Ga2O3 catalysts of selective hydrogenation of crotonaldehyde, J. Catal.
250 (2007) 195-208.
[22] X. Hong, B. Li, Y. Wang, J. Lu, G. Hu, M. Luo, Stable Ir/SiO2 catalyst for
selective hydrogenation of crotonaldehyde, Appl. Surf. Sci. 270 (2013) 388-394.
[23] A.J. Plomp, H. Vuori, A.O.I. Krause, K.P. de Jong, J.H. Bitter, Particle size
effects for carbon nanofiber supported platinum and ruthenium catalysts for the
selective hydrogenation of cinnamaldehyde, Appl. Catal. A-Gen. 351 (2008) 9-15.
[24] G.C.S. Galvagno, G. Neri, A. Donato, R. Pietropaolo, Hydrogenation of
cinnamaldehyde over Ru/C catalysts: effect of Ru particle size, J. Mol. Catal. 64
(1991) 237-246.
[25] G. Neri, L. Mercadante, C. Milone, R. Pietropaolo, S. Galvagno, Hydrogenation
of citral and cinamaldehyde over bimetallic Ru-Me/Al2O3 catalysts, J. Mol. Catal. A-
Chem. 108 (1996) 41-50.
[26] T.-N. Ye, J. Li, M. Kitano, M. Sasase, H. Hosono, Electronic interactions
between a stable electride and a nano-alloy control the chemoselective reduction
reaction, Chem. Sci. 7 (2016) 5969-5975.
[27] J. Teddy, A. Falqui, A. Corrias, D. Carta, P. Lecante, I. Gerber, P. Serp, Influence
of particles alloying on the performances of Pt-Ru/CNT catalysts for selective
hydrogenation, J. Catal. 278 (2011) 59-70.
[28] J. Qiu, X.Wang, H. Han, C. Liang, C. Li, Selective hydrogenation of
28

cinnamaldehyde over carbon nanotube supported Pd-Ru catalyst, React. Kinet. Catal.
Lett. 88 (2006) 269-275.
[29] A. Jung, A. Jess, T. Schubert, W. Schütz, Performance of carbon nanomaterial
(nanotubes and nanofibres) supported platinum and palladium catalysts for the
hydrogenation of cinnamaldehyde and of 1-octyne, Appl. Catal. A-Gen. 362 (2009)
95-105.
[30] H. Shen, H. Tang, H. Yan, W. Han, Y. Li, J. Ni, Geometric effect of
Ru/HSAG@mSiO2: a catalyst for selective hydrogenation of cinnamaldehyde, RSC
Adv. 4 (2014) 30180-30185.
[31] N. Mager, P. Libioulle, S. Carlier, S. Hermans, Water-soluble single source
precursors for homo- and hetero-metallic nanoparticle catalysts supported on
nanocarbons, Catal. Today 301 (2018) 153-163.
[32] Y. Yan, Q. Wang, C. Jiang, Y. Yao, D. Lu, J. Zheng, Y. Dai, H. Wang, Y. Yang,
Ru/Al2O3 catalyzed CO2 hydrogenation: oxygen-exchange on metal-support
interfaces, J. Catal. 367 (2018) 194-205.
[33] F. Wang, C. Li, X. Zhang, M. Wei, D.G. Evans, X. Duan, Catalytic behavior of
supported Ru nanoparticles on the {100}, {110}, and {111} facet of CeO2, J. Catal.
329 (2015) 177-186.
[34] Y. Guo, S. Mei, K. Yuan, D.-J. Wang, H.-C. Liu, C.-H. Yan, Y.-W. Zhang, Low-
temperature CO2 methanation over CeO2-Supported Ru single atoms, nanoclusters,
and nanoparticles competitively tuned by strong metal-support interactions and H-
spillover effect, ACS Catal. 8 (2018) 6203-6215.
[35] M. Tamura, S. Ishikawa, M. Betchaku, Y. Nakagawa, K. Tomishige, Selective
hydrogenation of amides to alcohols in water solvent over a heterogeneous CeO2-
supported Ru catalyst, Chem. Commun. 54 (2018) 7503-7506.
29