Combined synergetic and steric effects for highly selective hydrogenation of unsaturated aldehyde

Article abstract of DOI:10.1016/j.jcat.2019.02.022

Enhancing the selectivity to unsaturated alcohols for the hydrogenation of unsaturated aldehydes is of great importance and challenge. Herein, Pt-SnO_x@ZIF-8 catalysts with combined synergetic and steric effects were designed for the hydrogenation of 2-pentenal. The selectivity to unsaturated alcohol was enhanced from 4.3% to 61.5% by the synergetic effect between SnO_x and Pt active sites and was further enhanced to 80.9% by the steric effect of ZIF-8. In situ FTIR was used to investigate the surface reaction mode over the present catalysts. The results showed that SnO_x acted as electrophilic sites for the adsorption and activation of the C[dbnd]O bond and the apertures of ZIF-8 oriented the C[dbnd]O adsorption on the active sites.

Full text of DOI:10.1016/j.jcat.2019.02.022

Journal of Catalysis 372 (2019) 49–60
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Combined synergetic and steric effects for highly selective
hydrogenation of unsaturated aldehyde
⇑
Xiaocheng Lan, Kaizhen Xue, Tiefeng Wang
Beijing Key Laboratory of Green Reaction Engineering and Technology, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Enhancing the selectivity to unsaturated alcohols for the hydrogenation of unsaturated aldehydes is of
Received 5 December 2018
Revised 20 February 2019
Accepted 21 February 2019
great importance and challenge. Herein, Pt-SnO
effects were designed for the hydrogenation of 2-pentenal. The selectivity to unsaturated alcohol was
enhanced from 4.3% to 61.5% by the synergetic effect between SnO and Pt active sites and was further
enhanced to 80.9% by the steric effect of ZIF-8. In situ FTIR was used to investigate the surface reaction
mode over the present catalysts. The results showed that SnO acted as electrophilic sites for the adsorp-
x
@ZIF-8 catalysts with combined synergetic and steric
x
x
Keywords:
tion and activation of the C@O bond and the apertures of ZIF-8 oriented the C@O adsorption on the active
sites.
Unsaturated aldehyde
Synergetic effect
Steric effect
Ó 2019 Elsevier Inc. All rights reserved.
In situ FTIR
Selective hydrogenation
1
. Introduction
The selective hydrogenation of unsaturated organic substrates
vated on the adjacent metal active site, and the adsorbed C@O
bond was further hydrogenated by the activated H through spil-
lover. The electrophilic site can be generated from reducible metal
supports, which exhibit O-vacancy when reduced at a high temper-
containing C@O and C@C groups, such as cinnamaldehyde, 2-
pentenal and furfural, is an important step for industrial produc-
tion of fine chemicals and utilization of biomass-derived com-
pounds [1–3]. This type of reaction has attracted great interest in
fundamental research of heterogeneous catalysis [4–6]. Generally,
the hydrogenation of C@C bond was thermodynamically favored
than that of C@O over the supported group VIII metal catalysts
ature [21–23]. Some reducible supports, such as TiO
strong metal-support interactions (SMSI) effect, where the partly
reduced TiO migrated to the metal particle surface [22]. Elec-
2
, showed the
x
trophilic sites can also be generated by modifying the metal active
sites with metal oxides. For example, Tamura et al. modified Ir with
ReO
hyde, which significantly enhanced the selectivity [19]. Our previ-
ous work showed that the core-shell structure of Pt@SnO
x
to promote the adsorption of aldehyde group of crotonalde-
[
1,6]. The crucial challenge is to develop a highly selective
heterogenous catalyst for hydrogenating the C@O bond while
keeping the C@C bond.
Extensive works have been performed to design catalysts for
selective hydrogenation of unsaturated aldehydes [1,6,7]. One of
the design strategies was modifying the electronic properties of
active metal with electropositive second metals (Fe, Sn, Co) [8–
x
promoted the synergetic effect of Pt and SnO
genation of acrolein [20].
x
for the C@O hydro-
Steric effect catalysts with enhanced selectivity were produced
using the steric constriction between unsaturated organic sub-
strates and the environment of metal active sites, such as modify-
ing the active sites with microporous material (Zeolite, MOFs) [24–
26] or long-chain ligands, such as thiol and fluorous [27–29]. Gen-
erally, the steric constriction orientated the adsorption geometry of
the unsaturated aldehyde molecules, where the C@C bond was
prevented from interacting with the active sites [25]. However,
the steric effect depended on the relative sizes of the unsaturated
aldehyde molecule and the modifier. The pore sizes of Y zeolite
were commensurate with the molecular size of cinnamaldehyde
but were much larger than that of 3-prenal, thus Y zeolite encap-
sulated with Pt nanoparticles (NPs) was efficient to orient the
adsorption of C@O bond of cinnamaldehyde but was inefficient
1
4] or carbonaceous supports [15,16]. For this kind of catalysts,
electron was transfer from the second metal or support to the
active metal. The electron enriched active sites showed less hydro-
genation probability of C@C bond, which enhanced the selectivity
to unsaturated alcohols. Another design strategy was based on
the synergetic effect between metal active site and electrophilic
site [5,17–20]. The C@O bond of unsaturated aldehydes was
2
adsorbed and activated on the electrophilic site, while H was acti-
⇑
Corresponding author.
E-mail address: wangtf@tsinghua.edu.cn (T. Wang).
https://doi.org/10.1016/j.jcat.2019.02.022
021-9517/Ó 2019 Elsevier Inc. All rights reserved.
0

5
0
X. Lan et al. / Journal of Catalysis 372 (2019) 49–60
to orient that of 3-prenal [24]. Similarly, Pt NPs modified with dif-
ferent thiols showed tunable improvement in selectivity for cin-
namaldehyde but not for 3-prenal [27]. To extend the steric
effect to the selective hydrogenation of smaller unsaturated alde-
hydes, we encapsulated Pt NPs into ZIF-8, which has a commensu-
rate pore size with 3-prenal, for the hydrogenation of 3-prenal and
obtained an enhanced selectivity to unsaturated alcohol [30].
Although the selectivity has been enhanced by the developed
catalysts, it is still significant and challenging to design highly
selective catalysts for the hydrogenation of unsaturated aldehydes,
especially for simple aldehydes with small substituents on the C@C
bond [1,6]. Compared with cinnamaldehyde, smaller unsaturated
aldehydes are more difficult to be selectively hydrogenated to
unsaturated alcohols due to the substituents effect [6]. The steric
effect induced by the pore constriction requires a commensurate
pore size with molecular. ZIF-8 was a suitable porous material
for 3-prenal, but the steric hindrance of ZIF-8 for 2-pentenal was
unclear. In addition, the mechanism of the steric effect needs fur-
ther investigation. Recently, multi-effects catalysts showed signif-
icant enhanced catalyst performance [31,32]. Pt NPs modified with
aspartic acid exhibited cooperation of steric and electronic effects
for increasing the selectivity to unsaturated alcohols [32]. It is a
promising strategy to combine ZIF-8 with a more selective active
site to enhance the selectivity for the hydrogenation of 2-
strategy reported in previous work [34–36], where the Pt-Sn
NPs/methanol suspension was added into 250 mL methanol con-
taining 2.05 g 2-methyl imidazole. After ultrasonic treatment for
10 min, the solution was mixed with 250 mL methanol containing
3.67 g Zn(NO
3
)
2
ꢀ6H
2
O and kept at room temperature without stir-
ring for 24 h. The precipitated Pt-Sn@ZIF-8 was washed with
methanol three times and kept at 60 °C for 12 h to form the Pt-
SnO @ZIF-8 catalysts.
x
2.2. Catalyst characterization
The X-ray diffraction (XRD) powder patterns of the Pt and Pt-Sn
NPs were characterized on a Bruker Advance D8 X-ray diffractome-
ter with Cu Ka (k = 1.5406 Å) monochromatic radiation, where the
samples were prepared by dropping NPs/methanol solution on a
single crystal Si substrate followed by evaporation of the solvent.
The actual loadings of Pt and Sn on the catalysts were measured
by inductively coupled plasma (ICP) analysis, where the catalysts
were dissolved by boiling the catalyst powders in aquaregia. Ultra-
thin slices were prepared by ultratome (Leica- UC7 + FC7) with a
thickness of 75 nm. High-resolution transmission electron micro-
scopy (HRTEM) images and energy dispersive X-ray (EDX) analysis
of the catalysts were obtained on HRTEM (JEOL Ltd., Tokyo, Japan)
at 120 kV, where the samples were ultrasonically dispersed in
ethanol for 30 min and the solution was dropped on a carbon film
supported on a copper grid. More than 100 particles were collected
to analyze the particle size distribution of NPs. The chemistry of
the Pt and Sn was investigated by X-ray photoelectron spec-
troscopy (XPS) measurements (Thermal Scientific ESCALAB
250Xi) with a CAE: pass energy 100.0 eV analyser mode and an
x
pentenal. Our previous work showed that Pt-SnO exhibited a syn-
ergetic effect for enhancing the hydrogenation probability of the
C@O of acrolein [20]. In this work, we developed a new concept
x
Pt-SnO @ZIF-8 catalysts with combined synergetic and steric
effects for the hydrogenation of 2-pentenal. The mechanism of
the synergetic effect and steric effect were also investigated by
in situ Fourier-transformed infrared (FTIR) spectroscopy. The selec-
tivity to unsaturated alcohol was enhanced by the synergetic effect
Al K
200 °C with H
desorption isotherms were measured at ꢂ196 °C on an Autosorb-
IQ -MP-C system (Quantachrome, USA). The CO-uptake was mea-
sured by the CO chemisorption. For each measurement, 100 mg
of catalyst was pretreated in 10% H /He at 200 °C and the titration
a
X-ray source, where the samples were pre-reduced at
2
for 3 h before measurement. The N adsorption/
2
x
between SnO and Pt active sites and showed a linear relationship
with the Sn/Pt ratio. The apertures of Pt@ZIF-8 showed a steric con-
striction for C@C bond in the hydrogenation of 2-pentenal but the
ethyl group of 2-pentenal showed a lower hindrance effect than
the two methyl groups of 3-prenal. The selectivity was further
2
2
was carried out by the pulse adsorption of CO at room tempera-
ture. The FTIR spectra of CO adsorption were carried out on a
Thermo Nicolet Nexus 470 spectrometer equipped with a mercury
cadmium telluride (MCT-A) detector, by setting 64 scans for the
increased over the Pt-SnO
getic and steric effects.
x
@ZIF-8 catalyst with combined syner-
ꢂ1
samples at a resolution of 4 cm . Typically, 15 mg of the sample
2
. Experimental
.1. Catalyst preparation
The Pt-ySnO /SiO and Pt-ySnO
was pressed on a tungsten mesh and then loaded into the measure-
ment cell, which was connected to the vacuum system. The sam-
2
ples were pre-reduced at 200 °C with
H
2
for 3 h before
measurement, then the CO adsorption was performed at 11.5 kPa
x
2
x
@ZIF-8 catalysts with different
and 40 °C for 0.5 h, followed by evacuation at the same tempera-
-3
Sn/Pt molar ratios y were prepared by a two-step method. First
the Pt-Sn NPs with enriched Sn on surface were prepared by the
liquid-phase reduction method modified from the literature
ture until the pressure was below 5.0 ꢁ 10 Pa.
2.3. Catalytic evaluation
[
30,33]. Typically, 1.5 mL of H
2
PtCl
6
ꢀ6H
2
O/ethylene glycol (EG)
mL of tin(II) 2-
solution (0.015 M) and desired
a
ꢁ
The liquid phase hydrogenations of 2-pentenal were carried out
ethylhexanoate/EG solution (0.015 M) was mixed with 1.5 mL EG
at room temperature, followed by the addition of 150 mg
polyvinylpyrrolidone (PVP, MW = 58000). After being stirred for
in a stainless-steel autoclave. For each experiment, 0.3 g reactant
was added in 30 mL cyclohexane solvent. The catalyst was reduced
in hydrogen at 200 °C for 3 h prior to the reaction. The reactions
were carried out at 80 °C and 3.0 MPa hydrogen. The stirring speed
was set at 1000 r/min to exclude the effect of gas-liquid mass
transfer. Catalyst recycling experiments were carried out under
the same conditions and the spent catalyst was collected by cen-
trifugation and reused without additional treatment. The products
were analyzed by a gas chromatograph (GC 7900, Techcomp Ltd.)
3
0 min, the solution was heated to 50 °C with vigorous stirring
under N atmosphere, and then 2 mL of ethanol containing
00 mg NaBH was added dropwise into the solution. The dark
2
1
4
brown solution was kept stirring for 30 min and the obtained Pt-
Sn NPs were washed with ethanol and hexane for three times, pre-
cipitated by centrifugation and finally dispersed in methanol. For
the synthesis of Pt-ySnO
nol solution was mixed with SiO
vigorous stirring and evaporated with stirring at room tempera-
ture. Finally, the obtained Pt-ySn/SiO sample was kept at 60 °C
for 12 h to form the Pt-ySnO /SiO catalysts. The Pt-ySnO @ZIF-8
catalysts were synthesized based on the ‘‘bottle-around-a-ship”
x 2
/SiO , the as-prepared Pt-Sn NPs/metha-
equipped
with
a
super-wax
capillary
column
2
ꢂ1
2
(Alfa Aesar, 147 m g ) under
(
30 m ꢁ 0.25 mm ꢁ 0.5
l
m) and an FID detector. For the 2-
pentenal hydrogenation, the conversion and selectivity were calcu-
2
lated as:
x
2
x
Conversion ð%Þ ¼ ðNA;0 ꢂ NA;tÞ=NA;0
ð1Þ

X. Lan et al. / Journal of Catalysis 372 (2019) 49–60
51
Selectivity ð%Þ ¼ Ni;t=ðNA;0 ꢂ NA;t
where NA,0 was the mole of 2-pentenal in the feeding stream; NA,t
was the mole of 2-pentenal after reaction; and Ni,t was the moles
of the products.
Þ
ð2Þ
only showed the lattice space of 0.23 nm, which is the typical lat-
tice of metallic Pt (1 1 1) [37,38]. The TEM images of Pt and Pt-ySn
NPs were shown in Fig. S1. The mean size of Pt NPs was 2.1 nm.
With increasing Sn ratio, the mean particle size of Pt-ySn NPs
increased to 2.6, 2.6 and 2.8 nm at a Sn/Pt molar ratio of 0.5, 1.0
and 1.5, respectively. The particle size can be tune to small size
with the addition of PVP which limits the growth of nanoparticles.
With the protection of PVP, the particle size was only slightly influ-
enced with a further increase of the Sn content. The Sn/Pt ratio of
NPs was determined by EDS analysis and the results were summa-
rized in Table 1. Generally, the Sn/Pt atomic ratios were very sim-
ilar to the molar ratio of the precursors, suggesting that platinum
and tin were well reduced.
The TOFs were calculated as:
TOFtotal ¼ ðNA;0 ꢁ XÞ=ðt ꢁ nactive sitesÞðsꢂ1
Þ
ð3Þ
ð4Þ
ð5Þ
TOFC¼C ¼ ðNA;0 ꢁ X ꢁ ðSSAL þ SSOLÞÞ=ðt ꢁ nactive sitesÞðsꢂ1
Þ
TOFC¼O ¼ ðNA;0 ꢁ X ꢁ ðSUOL þ SSOLÞÞ=ðt ꢁ nactive sitesÞðsꢂ1
where nactive sites is the total active sites of the catalyst measured by
CO-uptake; SSAL, SUOL and SSOL are the selectivity to pentanal, pen-
tenol and pentanol, respectively; X and t is the conversion and reac-
tion time, respectively.
The in situ FTIR study on the surface hydrogenation of 2-
pentenal was performed on the same instrument as CO adsorption.
For each experiment, 15 mg of sample was loaded into the FTIR cell
Þ
The as-prepared Pt-Sn NPs were then supported on SiO2 or
encapsulated into the inner space of ZIF-8 and were further selec-
tively oxidized in air to form Pt-ySnO
where y is the Sn/Pt atomic ratio based on precursors. The
nanoparticle size was measured for Pt-ySnO /SiO (Fig. S2). Gener-
ally, compared with unsupported NPs, a similar particle size was
obtained over SiO , indicating that the particles kept unchanged
after being supported on SiO . The actual metal loadings were
x 2 x
/SiO or Pt-ySnO @ZIF-8,
x
2
2
and was pre-reduced at 200 °C under H for 3 h. Then the cell was
2
evacuated at 200 °C to remove the surface species generated dur-
ing the reduction period. The background spectrum of the bare cat-
alyst was first collected as a reference at 80 °C under evacuation.
After that, the cell was isolated from the vacuum system and
2
determined by ICP analysis and the results were listed in Table 1.
The valance states of Pt and Sn were determined by X-ray photo-
electron spectroscopy (XPS) measurements (Fig. 2). The Pt 4f and
Sn 3d peaks were deconvoluted into different valance states, as
reported in the literature [39,40]. Pt 4f7/2 showed two peaks
0
.1 kPa 2-pentenal vapor was diffused into the cell to interact with
the samples. Then, the gas phase and physically adsorbed 2-
pentenal were evacuated until the pressure decreased below
0
2+
assigned to Pt (71.2 eV) and Pt (72.2 eV), and the peak area ratio
-
3
2
+
0
5
.0 ꢁ 10 Pa and the IR spectra of the chemically adsorbed 2-
of Pt /Pt was 0.03, indicating that the platinum was mainly in
metallic state. Sn 3d5/2 was deconvoluted into Sn0 (484.6 eV),
pentenal over the catalysts were obtained. At last, high-purity
hydrogen was introduced into the cell at a timely moment and a
series of IR spectra were collected at different times on stream to
investigate the changes of the corresponding bands.
2
+
4+
Sn (486.2 eV), and Sn (487.2 eV), and the peak area ratio of
0
2+
4+
Sn /(Sn + Sn ) was 0.06, indicating that the tin was mainly in
oxidized state. The TEM images of Pt-ySnO /SiO are shown in
Fig. S2, where the NPs were evenly supported on the surface of
x
2
3
. Results
SiO
SiO
2
. The nitrogen sorption isotherms (Fig. 3) indicated that the
supported catalysts had a similar type and slightly decreased
2
3.1. Catalyst characterizations
2
surface area compared with pure SiO (Table 1). For the prepara-
tion of Pt-ySnO @ZIF-8 catalysts, the encapsulation strategy was
x
The Pt-ySn NPs with a desired Sn/Pt molar ratio y were prepared
based on our previous works [30,41]. The TEM images showed that
the NPs were distributed in the inner space of ZIF-8 and no NPs
2
+
by the liquid reduction method. It was reported that Pt was
easier to reduce than Sn2 , resulting in the formation of Pt-Sn
NPs with enriched Sn on surface [33]. Fig. 1 showed the XRD pat-
tern and HRTEM image of the as-prepared Pt-1.0Sn NPs. Compared
with Pt NPs, Pt-1.0Sn NPs showed the typical Pt diffraction peak
+
were located on the external surface of Pt-ySnO
To further confirm the distribution of NPs over the ZIF-8, ultrathin
slices of Pt-ySnO @ZIF-8 were prepared. The TEM images showed
x
@ZIF-8 (Fig. S2).
x
that NPs were dispersed inside ZIF-8 (Fig. S3). It should be noted
that the ultrathin slices contained a thickness of 75 nm which
(
Fig. 1a) without the formation of PtSn alloy. Consistently, Fig. 1b
Fig. 1. (a) XRD patterns of Pt and Pt-1.0Sn NPs; (b) HR-TEM image of Pt-1.0Sn NPs.

5
2
X. Lan et al. / Journal of Catalysis 372 (2019) 49–60
Table 1
Characterizations of the catalysts.
a
b
c
d
2
Catalysts
Pure-SiO
Pt/SiO
Pt-0.5SnO
Pt-1.0SnO
Pt-1.5SnO
Pure-ZIF-8
Pt@ZIF-8
Pt-0.5SnO
Pt-1.0SnO
Pt-1.5SnO
Pt loading , %
Sn/Pt , mol/mol
Sn/Pt , mol/mol
Metal particle size , nm
CO-uptake,
l
mol/g
BET, m /g
2
–
–
–
–
147
136
135
137
2
0.22
0.22
0.25
0.25
–
0.58
0.56
0.54
0.53
0.00
0.53
0.90
1.31
–
0.00
0.54
0.83
1.21
0.00
0.60
1.05
1.47
–
0.00
0.60
1.05
1.47
2.1
2.6
2.6
2.8
2.16
1.40
1.24
0.90
–
3.29
2.12
1.07
0.40
x
x
x
/SiO
/SiO
/SiO
2
2
2
138
1901
1862
1829
1816
1834
2.1
2.6
2.6
2.8
x
@ZIF-8
x
@ZIF-8
x
@ZIF-8
a
b
c
Accurate Pt loading determined by ICP analysis.
Molar ratio determined by ICP analysis.
Molar ratio determined by EDS.
d
Metal particle size determined by TEM.
0
2
+
Pt
and plotted in Fig. S3, indicating that the particle size kept
unchanged when NPs were encapsulated inside ZIF-8. The ultra-
thin slices of Pt-0.5SnOx@ZIF-8 was further investigated by the
EDS mapping (Fig. S3b), confirming that the catalyst contained
Pt
(
a)
both Pt and Sn elements. The Pt and Pt-SnO
ported on the external surface of ZIF-8, which were denoted as
Pt/ZIF-8 and Pt-0.5SnO /ZIF-8, respectively. Obviously, a large
number of NPs were distributed on the surface of ZIF-8 (Fig. S2i
and 2j). The N adsorption/desorption isotherms of Pt-ySnO @-
x
NPs were also sup-
x
8
0
78
76
74
72
70
68
66
64
B.E.(eV)
2
x
ZIF-8 (Fig. 3) were of type I and identical to those of ZIF-8, indicat-
ing that the microporous structure was preserved after
encapsulating NPs.
2
+
4
+
Sn
Sn
0
To further investigate the structure of the catalysts, the adsorp-
tion of CO followed by FTIR spectroscopy was performed. The sam-
ples were exposed to 10% CO in He balance gas at 11.5 kPa and the
typical vibrations of gas phase CO and adsorbed CO were observed
Sn
(
b)
(
Fig. S4(a) and (b)). After being evaluated until the pressure was
-3
5
00
495
490
485
480
below 5.0 ꢁ 10 Pa, the gas phase CO vanished and the intensity
of adsorbed CO remained almost unchanged. The FTIR spectra of
B.E.(eV)
x 2 x
CO adsorption at 40 °C on the Pt-ySnO /SiO and Pt-ySnO @ZIF-8
catalysts are shown in Fig. 4. It was reported that the FTIR spectra
Fig. 2. XPS spectrum of Pt-1.0SnO
x
/SiO
2
(a) Pt 4f and (b) Sn 3d.
for CO adsorption on the Pt catalysts consisted of two vibration
ꢂ1
6
4
2
00
00
00
0
regions, where the wavenumber between 2000 and 2090 cm
was assigned to the linear adsorption on single Pt active sites
and the wavenumber between 1780 and 1860 cm was assigned
to the bridged adsorption on two neighboring Pt active sites
ꢂ1
(a) Pt/SiO2
(b) Pt-0.5SnO /SiO
ꢂ1
x
2
[42,43]. For Pt/SiO
2
, a strong absorption band at 2038 cm and a
(c) Pt-1.0SnO /SiO
ꢂ1
x
2
weak absorption band at 1812 cm were observed, which were
respectively assigned to linearly adsorbed CO and bridge-bonded
CO on Pt NPs. With increasing Sn/Pt ratio, the intensity of linearly
adsorbed CO decreased, indicating that the amount of exposed Pt
active sites decreased due to the surface covering SnO species.
x
In addition, the bridged adsorption of CO continuously decreased
and even vanished at a Sn/Pt ratio of 1.5. These results suggested
(d) Pt-1.5SnO /SiO
x
2
0
.0
0.2
0.4
0.6
0.8
1.0
P/P0
6
4
2
00
00
00
0
x
that the increase of surface covering SnO species destroyed the
large ensembles of Pt and isolated the adjacent Pt active sites.
For Pt based catalysts, it has been well documented that the lin-
early adsorbed CO on oxidized Pt showed IR vibration in the range
of 2080–2100 cm [42,44]. In this work, linearly adsorbed CO on
all the catalysts appeared below 2050 cm , indicating the metallic
(
a) Pt@ZIF-8
ꢂ1
(
b) Pt-0.5SnO @ZIF-8
x
(
(
c) Pt-1.0SnO @ZIF-8
ꢂ1
x
d) Pt-1.5SnO @ZIF-8
x
state of Pt, which was consistent with the XPS results.
The FTIR spectra of CO adsorption on ZIF-8 with encapsulated
metal NPs has not been reported in the literature, thus pure ZIF-
was exposed to 10% CO in He as blank experiment (Fig. S4(c)).
0
.0
0.2
0.4
0.6
0.8
1.0
P/P0
8
As expected, no band was observed after evaluation, indicating a
lack of interaction between CO and ZIF-8. In contrast, a strong band
at 2021 cm and a weak band at 1812 cm were observed on the
Pt@ZIF-8 catalyst after evaluation (Fig. S4(b)), which were respec-
tively ascribed to the linear and bridged adsorption of CO on the
Fig. 3. Nitrogen sorption isotherms of Pt-ySnO
x
/SiO
2
x
and Pt-ySnO @ZIF-8.
ꢂ1
ꢂ1
was much smaller than the whole crystal size of ZIF-8 (ꢃ500 nm),
suggesting that the visible NPs in the TEM images were encapsu-
lated inside ZIF-8. The particle size inside ZIF-8 was also measured

X. Lan et al. / Journal of Catalysis 372 (2019) 49–60
53
(
II), and further hydrogenation of the above intermediate products
Linear adsroption
Pt/SiO2
to saturated alcohol (III and IV). The saturated alcohol can also be
directly produced through simultaneous hydrogenation of C@O
and C@C bonds (V). In addition, the decarbonylation reaction to
produce CO and hydrocarbon was reported in some reaction condi-
tions (VI). Generally, the decarbonylation reaction to produce CO
occurred in the gas phase hydrogenation [6] or some surface
science experiments with lower coverage of unsaturated aldehyde
molecules [4,5], but did not proceed in the liquid phase
hydrogenation.
Pt-0.5SnO /SiO2
x
Pt-1.0SnO /SiO2
x
Pt-1.5SnO /SiO2
x
Bridged adsroption
Catalytic evaluations of 2-pentenal (UAL) hydrogenation were
carried out in the liquid phase, and the selectivity comparison of
the present catalysts was based at a similar conversion of ꢃ10%
(Table S1). Consistently, only three products of pentanal (SAL),
(
a)
pentenol (UOL) and pentanol (SOL) were produced and no decar-
bonylation reaction was detected. Since the hydrogenation of
2
200
2100
2000
1900
1800
ꢂ1
C@C bond (35 KJ mol ) is thermodynamically favored than that
-
1
Wavenumber, cm
ꢂ1
of C@O bond (40 KJ mol ) over group VIII metals [1], the selectiv-
ity to unsaturated alcohol was always below 10% in the hydrogena-
tion of small unsaturated aldehyde, such as acrolein and
crotonaldehyde, over non-modified Pt catalysts [6,20]. With the
Pt@ZIF-8
Linear adsroption
Pt-0.5SnO @ZIF-8
x
Pt-1.0SnO @ZIF-8
present Pt/SiO
alcohol was only 4.3% and most of the reactant was hydrogenated
to saturated aldehyde (87.9%). With the Pt-0.5SnO /SiO catalyst,
the selectivity increased to 21.4%. In addition, the selectivity con-
tinuously increased with increasing amount of SnO species. To
further confirm the effect of SnO , the Pt-1.0SnO /SiO catalyst
was reduced with H at 400 °C for 3 h. In the subsequent reaction
evaluation, Pt-1.0SnO
tivity than Pt-1.0SnO
2
catalyst (Fig. 5(a)), the selectivity to unsaturated
x
Pt-1.5SnO @ZIF-8
x
x
2
Bridged adsroption
x
x
x
2
2
x
/SiO
2
-HT showed lower activity and selec-
(Table S1). The TEM images (Fig. S5)
x
/SiO
2
showed that the metal particle size increased after the high tem-
perature reduction. In addition, the nanoparticles showed a lattice
space of 0.30 nm, which was larger than any orientation of the
metallic Pt and was indexed to the orientation of PtSn alloy. These
(
b)
2
200
2100
2000
Wavenumber, cm
1900
1800
x
results indicated that SnO favored the C@O hydrogenation rate
-
1
and thereby led to the higher selectivity to unsaturated alcohol.
However, it should be noted that it is difficult to completely
Fig. 4. FTIR spectra of CO adsorption at 40 °C on (a) Pt-ySnO
ySnO @ZIF-8 catalysts.
x
/SiO
2
and (b) Pt-
0
exclude the effect of a small fraction of Sn on the catalyst, which
x
could also contribute to the enhanced selectivity.
Previously, we found that the selectivity to unsaturated alcohol
was enhanced for the hydrogenation of 3-prenal after encapsulat-
ing Pt NPs inside ZIF-8 [30]. The enhanced selectivity over Pt@ZIF-8
was ascribed to the steric effect of the micropores of ZIF-8, where
the apertures around the Pt NPs surface oriented linearly adsorp-
tion of 3-prenal molecules on Pt active sites through the C@O bond
while the C@C bond was prevented from interacting with active
sites by the two methyl groups at the terminal of C@C bond. This
kind of steric effect was related to the structure of unsaturated
aldehyde molecules, for example the C@C bond of acrolein without
the hindrance of substituents could be adsorbed on active sites,
thus the steric effect was inefficient for the selective hydrogenation
of acrolein [30]. Herein, 2-pentenal had an ethyl group at the ter-
minal of C@C bond and the selectivity to unsaturated alcohol
increased to 31.0% over Pt@ZIF-8 compared with 4.3% over Pt/
encapsulated Pt NPs. With the addition of SnO
the intensity of both linear and bridged adsorption of CO decreased
Fig. 4(b)). In addition, the bridged adsorption of CO almost disap-
peared over Pt-1.5SnO @ZIF-8. These results indicated that, over
the Pt-ySnO @ZIF-8 catalysts, the adjacent Pt active sites were sep-
arated by the surface covering SnO species. It is notable that the
band of linear adsorption of CO on Pt-ySnO @ZIF-8 showed a slight
, which could be ascribed to
x x
(Pt-ySnO @ZIF-8),
(
x
x
x
x
x 2
red shift compared with Pt-ySnO /SiO
the ZIF-8 support effect.
CO-chemisorption was used to measure the amount of surface
Pt atoms (Table 1). Although there are two types of CO adsorption
modes over the Pt sites, the percentage of bridge adsorbed CO on Pt
is very low, therefore a 1.0 stoichiometric ratio of CO/metal was
widely used for Pt or PtSn catalysts in the literature [9,38]. This
was also verified in our CO-FTIR experiments that only slight
2
SiO (Table S1). However, there is still 52.7% of 2-pentenal hydro-
bridged adsorption of CO was found in Pt/SiO
Fig. 4). In accordance with the CO-FTIR results, the CO-uptake val-
ues decreased with the increase of Sn/Pt ratio, indicating that the
SnO covered the surface of Pt NPs.
2
and Pt@ZIF-8
genated to saturated aldehyde, indicating that the ethyl group of 2-
pentenal showed a lower hindrance effect than the two methyl
groups of 3-prenal. The selectivity to unsaturated alcohol over
(
x
the Pt-ySnO
increasing the SnO
x
@ZIF-8 catalysts was continuously enhanced with
species (Fig. 5(b)), where the selectivity was
x
3.2. Hydrogenation reaction results
enhanced to 48.5%, 62.0% and 80.9% at the Sn/Pt ratio of 0.5, 1.0
and 1.5, respectively. With increasing Sn/Pt ratio, the selectivity
The hydrogenation of unsaturated aldehydes has been exten-
to saturated alcohol was kept at ꢃ10% over Pt-ySnO
decreased from 16% to 1% over Pt-ySnO @ZIF-8. Pt/ZIF-8 and Pt-
0.5SnO /ZIF-8 were also evaluated for the hydrogenation of 2-
pentenal. Compared with Pt/ZIF-8, the addition of SnO in Pt-
x 2
/SiO but
sively investigated and the reaction pathways were summarized
in Scheme 1, including hydrogenation of the C@O bond to unsatu-
rated alcohol (I), hydrogenation of C@C bond to saturated aldehyde
x
x
x

5
4
X. Lan et al. / Journal of Catalysis 372 (2019) 49–60
+
CO
HO
(III)
(VI)
(I)
pentenol(UOL)
(V)
HO
pentanol(SOL)
O
2-pentenal (UAL)
(
IV)
(II)
O
pentanal(SAL)
Scheme 1. Reaction pathway of 2-pentenal hydrogenation.
1
00
1
00
Selectivity
UOL
SOL
SAL
8
6
4
0
0
0
80
60
40
20
0
Conversion
20
0
(a)
(b)
2
2
2
2
/
SiO
/SiO
/SiO
x
IF-8
@Z
x
x
@
ZIF-8
@
ZIF-8
Pt/SiO
x
x
x
Pt@ZIF-8
Pt-0.5SnO
Pt-1.0SnO
Pt-1.5SnO
.5SnO
1
Pt-0.5SnO
/SiO
Pt-1.0SnO
Pt-
Fig. 5. Product distribution for 2-pentenal hydrogenation over (a) Pt-ySnO
x
2
and (b) Pt-ySnO
x
@ZIF-8 at a conversion of ꢃ10%.
0
.5SnO
x
/ZIF-8 increased the selectivity to unsaturated alcohol. It is
showed a lower selectivity
hydrogenation of C@O [1,6]. With the addition of SnO
higher TOFC@O (0.18–0.26 s ) was obtained over Pt-ySnO
x
, a much
/SiO
ꢂ1
notable that NPs supported on SiO
2
x
2
.
than that supported on the external surface of ZIF-8, which was
ascribed to the supported effect. Compared with Pt@ZIF-8 (31%)
It can be inferred that new active sites different from Pt were gen-
erated for the hydrogenation of C@O. The surface enriched SnO
x
and Pt-0.5SnO
.5SnO /ZIF-8 (31.6%) showed a lower selectivity to UOL, respec-
tively (Table S1). The TEM images indicated that the Pt and Pt-
SnO NPs were deposited on the external surface of bare ZIF-8
and these NPs of ꢃ2.6 nm were difficult to migrate inside ZIF-8.
For Pt@ZIF-8 and Pt-0.5SnO @ZIF-8, the TEM images of ultrathin
slices indicated that Pt-SnO NPs located inside the ZIF-8. The
smaller apertures, surrounding the surface of Pt-SnO , oriented
the C@O to be adsorbed on the Pt-SnO active sites and thereby
x
@ZIF-8 (48.5%), both the Pt/ZIF-8 (15.4%) and Pt-
acted an electrophilic site for the adsorption of C@O, and the acti-
vated C@O was further hydrogenated through H spillover. These
0
x
results also indicated that the structure of Pt-ySnO
alysts was benefit for the synergetic effect between SnO
x
NPs in the cat-
and Pt,
x
x
leading to enhanced selectivity. For the hydrogenation of C@C
bond, the TOFC@C based on CO uptake reflects the intrinsic proper-
ties of Pt active sites. The catalyst characterizations indicated that
x
x
x
the SnO
PtSn alloy was formed in the catalysts, electron transfer could
occur from SnO to the adjacent Pt atoms [45,46]. It has been
reported that electron enriched Pt showed less hydrogenation
probability of C@C bond [1]. With the increasing amount of SnO
more Pt active sites were modified by the SnO , thus a much lower
x
was enriched on the surface of Pt. Although no obvious
x
enhanced the selectivity to unsaturated alcohol.
The TOFs were calculated based on the CO chemisorption, as
listed in Table 2. The hydrogenation of C@C only occurred on the
x
x
,
Pt sites, while the C@O can also be hydrogenation on SnO
x
through
x
ꢂ1
H-spillover, thus the hydrogenation activities of C@C (TOFC@C) and
C@O (TOFC@O) were calculated based on the selectivity. For the
TOFC@C was obtained over Pt-1.0SnO
x
/SiO
2
(0.249 s ) and Pt-
ꢂ1
ꢂ1
1.5SnO
x
/SiO
2
(0.099 s ). The Pt/SiO
2
(0.525 s ) exhibited a much
ꢂ1
hydrogenation of C@O, Pt/SiO
2
exhibited much low TOFC@O of
higher TOFtotal than Pt-ySnO
x
@ZIF-8 (ꢃ0.052 s ) while the TOFC@O
ꢂ1
0
.063 s , which was consistent with the well documented results
for the hydrogenation of C@O bond over these catalysts were sim-
ilar. For Pt/SiO , the hydrogenation results revealed the intrinsic
that the Pt metal exhibits a poor intrinsic property for the selective
2

X. Lan et al. / Journal of Catalysis 372 (2019) 49–60
55
Table 2
Activities of the present catalysts for 2-pentenal hydrogenation.
ꢂ1
ꢂ1
ꢂ1
Catalyst
Pt/SiO
Pt-0.5SnO
Pt-1.0SnO
Pt-1.5SnO
Pt@ZIF-8
Pt-0.5SnO
Pt-1.0SnO
Pt-1.5SnO
TOFtotal, s
TOFC=C, s
TOFC=O, s
TOFC=O/TOFC=C
2
0.525
0.723
0.421
0.256
0.121
0.034
0.052
0.052
0.502
0.568
0.249
0.099
0.084
0.018
0.020
0.010
0.063
0.252
0.217
0.182
0.057
0.020
0.034
0.043
0.13
0.44
0.87
1.84
0.69
1.13
1.75
4.28
x
x
x
/SiO
/SiO
/SiO
2
2
2
x
@ZIF-8
x
@ZIF-8
x
@ZIF-8
properties of Pt that the C@C bond was thermal dynamically
favored over C@O. Most of the unsaturated aldehyde were hydro-
genated to saturated aldehyde with unreacted C@O bond, thus the
x x
the synergetic effect between SnO and Pt active sites, where SnO
acted as electrophilic sites for adsorption and activation of the C@O
bond. With the Pt@ZIF-8 catalyst, the steric effect increased the
TOFC=O was much lower than TOFC@C over Pt/SiO
, the steric constriction limited the internal diffusion [1,25,26]
and the total reaction activity TOFtotal over Pt-SnO @ZIF-8 was
lower than that over Pt/SiO . With the steric effect constriction of
2
. For Pt-SnO
x
@ZIF-
selectivity by 26.7% compared with non-modified Pt/SiO
ingly, the selectivity was further enhanced by about 20% at each
Sn/Pt ratio when the Pt-SnO particles were encapsulated inside
ZIF-8. The Pt-ySnO @ZIF-8 catalysts were also used for the hydro-
2
. Interest-
8
x
x
2
x
ZIF-8 channels, the C@C bond was prevented from interacting with
metal actives while the C@O bond was oriented to be adsorbed on
the active sites, thus a much lower TOFC@C while a similar TOFC@O
genation of 3-prenal. The two methyl groups of 3-prenal showed a
higher hindrance effect than the ethyl group of 2-pentenal, thus
96.0% selectivity was obtained over the Pt@ZIF-8 catalyst at a sim-
ilar conversion. In addition, the selectivity was further enhanced to
were obtained over Pt-SnO
the synergetic effect and steric effect were combined over the Pt-
ySnO @ZIF-8 catalyst. The ratio of TOFC@O/TOFC@C was calculated
in Table 2. The Pt/SiO only gave a low ratio of 0.13 because the
hydrogenation rate of C@C was much higher than that of C@O.
The addition of SnO activated the C@O bond and the synergetic
effect between Pt and SnO further enhanced the hydrogenation
rate of C@O, thus the ratio of TOFC@O/TOFC@C increased from 0.13
to 1.84 over the Pt-ySnO /SiO catalysts. For the Pt-ySnO @ZIF-8,
x x
@ZIF-8. With the addition of SnO ,
x
98.6% over the Pt-0.5SnO @ZIF-8 catalyst. The above results indi-
x
cated that the selectivity to unsaturated alcohol can be further
increased by combining the synergetic and steric effects. Recycling
experiments were performed to evaluate the stability of Pt-
2
x
1.5SnO
x
@ZIF-8 catalyst (Fig. S6). For each reaction, a ꢃ80% selectiv-
x
ity to UOL was obtained and the activities were similar without
significant loss. The slight decrease of activity could be ascribed
to the loss of catalysts during the reusing process. The spent Pt-
x
2
x
the ratio of TOFC=O/TOFC=C increased from 0.69 to 4.28 when the
Sn/Pt ratio increase from 0 to 1.5, indicating that the hydrogena-
tion rate of C@C bond was significantly decreased by the steric con-
striction of ZIF-8 channels.
x
1.5SnO @ZIF-8 catalyst was characterized by TEM and XRD
(Fig. S7). The results indicated that ZIF-8 kept the crystallization
structure and no NPs migrated to the external surface. The ultra-
thin slices of the spent Pt-SnOx@ZIF-8 were prepared for TEM char-
The selectivity to UOL was plotted as a function of the Sn/Pt
molar ratio (Fig. 6). The selectivity over both series of catalysts con-
tinuously increased with the increase of Sn/Pt ratio, in consistent
acterization, showing that the Pt-SnO
dispersed inside the ZIF-8. ZIF-8 exhibits a good stability even at
300 °C under air flow [41]. The Pt-SnO NPs encapsulated inside
x
NPs were still well
x
with the relative activity ratio (TOFC@O/TOFC@C). Over the Pt-ySnO
x
/
ZIF-8 were protected by the stable structure of ZIF-8.
SiO catalysts, the selectivity to UOL increased from 4.3% to 21.4%,
2
4
1
0.8% and 61.5% when the Sn/Pt increased from 0 to 0.5, 1.0 and
.5, respectively. This enhanced selectivity could be ascribed to
3.3. In situ FTIR spectrum for surface reaction
To better understand the mechanism by which the synergetic
and steric effects enhanced the selectivity to unsaturated alcohol,
in situ FTIR spectroscopy was employed to determine the surface
adsorption modes and surface reaction pathways.
80
60
40
20
0
Pt-ySnO /SiO
The FTIR spectra of gas phase UAL and SAL were firstly collected
and shown in Fig. S8. UAL and SAL spectra showed two similar fea-
x
2
Pt-ySnO @ZIF-8
x
ꢂ1
ꢂ1
tures in the ranges of 2700–3000 cm
which were assigned to the vibrations of ʋ(CAH) in the aldehyde
group and d(ACH ) in the methyl group, respectively [44,47,48].
and 1350–1500 cm ,
3
Differently, the typical ʋ(C@O) vibration of SAL molecule showed
ꢂ1
a single band centered at 1745 cm , while this vibration in the
ꢂ1
ꢂ1
spectrum of UAL showed two bands at 1726 cm and 1713 cm
ꢂ1
due to the conjugation effect of ʋ(C@C) (1646 cm ) [44]. Then
the catalyst sample was loaded into the FTIR cell followed by the
injection of UAL vapor (0.1 KPa). As shown in Fig. S9, the typical
ꢂ1
ꢂ1
ʋ(C@O) vibrations of gas phase UAL (1726 cm and 1713 cm
)
emerged and diminished when the FTIR cell was continuously
evacuated. After the gas phase and physically absorbed UAL were
-3
removed (P < 5.0 ꢀ 10 Pa), a steady IR spectrum of chemically
0
.0
0.5
1.0
1.5
adsorbed UAL was obtained. The spectrum of UAL adsorbed on
ꢂ1
ꢂ1
SiO
1
2
surface exhibited bands at 1708 cm
,
1660 cm
,
and
Sn/Pt (molar ratio)
ꢂ1
619 cm (Fig. S10(a)). The first two bands were ascribed to the
Fig. 6. Effect of Sn/Pt ratio on the selectivity to UOL.
2
C@O frequencies of UAL coordinated on SiO surface, as indicated

5
6
X. Lan et al. / Journal of Catalysis 372 (2019) 49–60
Table 3
Vibration of the functional groups of 2-pentenal (UAL) and pentanal (SAL).
Support
UAL
(C@O), cm
SAL
(C@O), cm
ꢂ1
ꢂ1
ꢂ1
ꢂ1
ʋ
1
2
ʋ (C@O), cm
ʋ(C@C), cm
ʋ
1
SiO
ZIF-8
2
1708
1727
1660
1703
1619
1638
1708
1727
by the red-shifts from the corresponding frequencies of gaseous
UAL. The band at 1619 cm was assigned to the vibration of ʋ
The typical bands of adsorbed UAL and SAL molecules are sum-
ꢂ1
marized in Table 3 based on the above arguments. Subsequently,
in situ FTIR spectrum was used to monitor the changes of these
bands during UAL hydrogenation at 353 K. In each experiment,
the sample was first treated with 2-pentenal at 353 K. After the
sample was fully chemisorbed with 2-pentenal molecules, the
gas phase and physically adsorbed 2-pentenal were removed
(
C@C) [19]. The spectrum of UAL adsorbed on ZIF-8 also showed
ꢂ1
ꢂ1
ꢂ1
three bands centered at 1727 cm , 1703 cm , and 1638 cm
Fig. S10(b)), which were ascribed to the vibrations of ʋ (C@O),
(C@O), and ʋ(C@C), respectively. The corresponding bands in
the spectrum of UAL on ZIF-8 showed quite different shift com-
pared with that of UAL on SiO . To further confirm the assignments
of C@C and C@O vibrations of adsorbed UAL molecule in the IR
spectra, SAL molecules were adsorbed on SiO and ZIF-8 followed
by FTIR detection (Fig. S9). Compared with the spectrum of UAL,
no vibrations of ʋ(C@C) appeared and a strong band (SiO
(
ʋ
1
2
2
under continuous evacuation. Then 11.5 KPa of H
followed by in situ FTIR detection. Blank experiments using bare
SiO and ZIF-8 were firstly carried out under the same conditions
(Fig. S11). For ZIF-8 with chemisorbed UAL, the introduction of
hydrogen did not weaken or change the bands of ʋ (C@O),
(C@O), and ʋ(C@C). For SiO with chemisorbed UAL, the bands
of ʋ (C@O) and ʋ(C@C) kept unchanged, while the vibration of
2
was introduced
2
2
2
:
1
ꢂ1
ꢂ1
1
708 cm , ZIF-8: 1727 cm ) attributed to ʋ(C@O) of adsorbed
ʋ
2
2
SAL was observed.
1
2(
C=O)
0
.08
.06
.04
.02
(C=C)
(
a)
(
c)
2(C=O)
1(
C=O)
1(
C=O)
(C=C)
Pt-CO
0
.06
Pt-CO
0
0.5 min
0
.5 min
0.04
0
5
min
10 min
2
0 min
30 min
0 min
0 min
0 min
70 min
0
5 min
0
0
.02
.00
1
0 min
0 min
0 min
4
2
3
5
6
0
.00 40 min
5
0 min
6
0 min
0 min
7
-
0.02
2
200
2000
1800
1600
1400
2
200
2000
1800
1600
1400
-
1
Wavenumber, cm
-
1
Wavenumber, cm
(b)
2(C=O)
2(C=O)
(C=C)
(d)
0
0
0
0
.06
.04
.02
.00
0.08
(C=C)
1(C=O)
Pt-CO
1(C=O)
0
.06
0
.5 min
min
0 min
0 min
0 min
0 min
0 min
0 min
70 min
5
1
0
.5 min
0.04
5
min
2
3
4
10 min
20 min
3
0 min
0
0
.02
.00
40 min
50 min
60 min
70 min
5
6
2
200
2000
1800
1600
1400
2200
2000
1800
Wavenumber, cm
1600
1400
-
1
-1
Wavenumber, cm
2 x 2 x 2 x 2
Fig. 7. In situ FTIR for the hydrogenation of UAL over (a) Pt/SiO , (b) Pt-0.5SnO /SiO , (c) Pt-1.0SnO /SiO , and (d) Pt-1.5SnO /SiO .

X. Lan et al. / Journal of Catalysis 372 (2019) 49–60
57
ʋ
2
(C@O) was unusually strengthened with the reaction time and
returned to its original intensity after evacuating the H . The above
results indicated that pure SiO and ZIF-8 were inert for the hydro-
genation of C@C and C@O bonds
In situ FTIR spectra for the Pt-ySnO
Fig. 7. Several changes occurred in the relative peak intensities as
the spectra evolved with time on stream. For Pt/SiO with chemi-
ʋ
2
(C@O) decreased with time on stream while that of ʋ
1
(C@O) kept
x
species
2
unchanged. In our previous work, we found that the SnO
acted as adsorption sites for activation of C@O bond of acrolein,
and the adsorbed C@O on SnO was further hydrogenated by the
activated H spilled from Pt sites [20]. In this work, the characteri-
zation results showed that the SnO
on the surface of Pt. The increased amount of SnO
vided more sites for activation of C@O, resulting in a faster decre-
ment of ʋ (C@O) with time on stream.
It has been reported that the Pt(CO) gem-dicarbonyl species
2
2
x
x
2
/SiO catalysts are shown in
x
species of Pt-SnO
x
was located
2
ꢂ1
x
species pro-
sorbed UAL (Fig. 7a), the band intensity of 1619 cm ʋ(C@C) grad-
ually decreased upon the introduction of hydrogen and meanwhile
the band intensity of 1708 cm
2
ꢂ1
1
ʋ (C@O) increased, probably aris-
ing from the hydrogenation of C@C bond corresponding to the con-
was found on small clusters and showed typical double bands at
version of adsorbed UAL to adsorbed SAL. The prominent band
the IR range of CO linearly adsorption [43,52]. As shown in Fig. 7
ꢂ1
ꢂ1
appeared at ꢃ2020 cm in the region for CO adsorbed on Pt. The
(b) and (c), double adsorption bands at 2035 cm
and
/SiO
ꢂ1
intensity of this band increased with the reaction time, which
was ascribed to the decarbonylation reaction of UAL (pathway
VI). Several adsorption modes were reported for the hydrogenation
of unsaturated aldehydes [4,49–51], and the decarbonylation reac-
2058 cm occurred on the Pt-0.5SnO
x
/SiO
2
and Pt-1.0SnO
x
2
catalysts. The CO-FTIR results indicated that the increased SnO
species isolated the large ensembled Pt sites, resulting in the for-
mation of exposed Pt cluster. Therefore, the Pt(CO) gem-
x
2
tion occurred mainly through
g
4
(C@C, C@O) adsorption mode,
dicarbonyl species was formed during the decarbonylation reac-
tion of UAL and presented the unique double bands in IR spectra.
Differently, no obvious CO-Pt species was observed in the Pt-
which required more adjacent Pt atoms for the interaction of
C@C and C@O bonds. The irreversibly adsorbed CO poisoned the
Pt active sites and the adsorbed C@O could not be further hydro-
genated due to the lack of active H [40,48], thus the intensity of
1.5SnO
tion reaction was suppressed. These results indicated that the
exposed adjacent Pt atoms were inadequate for the adsorption
mode at an increased amount of surface SnO species.
x 2
/SiO catalyst (Fig. 7(d)), suggesting that the decarbonyla-
2
band ʋ (C@O) only slightly decreased over the Pt/SiO
2
catalyst.
g
4
With the increase of Sn/Pt ratio (Fig. 7(b)–(d)), the intensity of
x
x x x
Fig. 8. In situ FTIR for the hydrogenation of UAL over (a) Pt@ZIF-8, (b) Pt-0.5SnO @ZIF-8, (c) Pt-1.0SnO @ZIF-8, and (d) Pt-1.5SnO @ZIF-8.

5
8
X. Lan et al. / Journal of Catalysis 372 (2019) 49–60
The intensity of ʋ(C@C) over all the catalysts decreased with
time on stream, but the mechanism was different. The decrease
of ʋ(C@C) can be ascribed to the following main reasons: the
CO-species over Pt-ySnO
than that over the Pt-0.5SnO
surface in the Pt-ySnO @ZIF-8 catalysts was modified by the aper-
tures of ZIF-8, which oriented the surface adsorption of UAL mole-
cules. Thus, the decarbonylation reaction through the mode was
inhibited by the stereoconfinment of apertures on the surface of
Pt-SnO particles of the Pt-ySnO @ZIF-8 catalyst. Over the Pt-
1.5SnO @ZIF-8 catalyst (Fig. 8(d)), the intensity of C@C vibration
was almost unchanged and only a slight decrease of ʋ (C@O) was
observed. In conjunction with the high selectivity to unsaturated
alcohol over Pt-1.5SnO @ZIF-8, it can be inferred that the com-
x
@ZIF-8 (y = 0.5 and 0.1) was much lower
x
/SiO (y = 0.5 and 0.1). The Pt-SnO
2
x
x
hydrogenation of C@C forming adsorbed SAL (D
lation reaction forming adsorbed CO (D ), and the hydrogenation
of C@O adsorbed on SnO followed by desorption of unsaturated
alcohol (D ). For Pt/SiO without the modification of SnO , only
and D proceeded upon the introduction of H . With the
increase of Sn/Pt ratio (0.5 and 1.0), the SnO species on the Pt sur-
face provided new active sites for the process of D . For Pt-1.5SnO
SiO , the exposed adjacent Pt atoms became inadequate for the
1
), the decarbony-
2
g
4
x
3
2
x
x
x
D
1
2
2
x
x
1
3
x
/
2
x
decarbonylation reaction and the D
1
and D
3
reactions, resulted in
bined synergetic and steric effects can effectively prevent C@C
the decrease of ʋ(C@C).
from interacting with Pt active sites.
The intensity of the corresponding bands over the pure ZIF-8
was about 4 times higher than that over the pure SiO (Fig. S11).
This was because the surface area of ZIF-8 (1900 m /g) was much
2
2
4
. Discussion
2
higher than that of SiO
cules were adsorbed on the ZIF-8 surface. For better comparison,
the spectra over Pt-ySnO @ZIF-8 at 0.5 min and 70 min were com-
pared in Fig. 8 to investigate the corresponding bands. For Pt@ZIF-
, an obvious Pt-CO species was obtained when introducing H
2
(147 m /g), and much more reactant mole-
The selectivity to unsaturated alcohol was significantly
x
enhanced in the hydrogenation of unsaturated aldehyde over the
designed dual effect catalysts. Based on the above results, this
enhancement in selectivity was ascribed to both the synergetic
and steric effects, and the reaction modes in the liquid phase
8
2
,
indicating that decarbonylation reaction occurred (Fig. 8(a)). How-
ever, the intensity of the CO-Pt species over Pt@ZIF-8 was lower
2
hydrogenation were hypothesized in Scheme 2. For Pt/SiO , the
than that over Pt/SiO
tion of UAL by steric constriction of ZIF-8 channels. Compared with
Pt/SiO (Fig. 7(a)), an obvious decrement in ʋ (C@O) was observed
over Pt@ZIF-8 (Fig. 8(a)), suggesting that the steric effect oriented
the (C@O) adsorption on Pt. For the Pt-ySnO @ZIF-8 catalysts
Fig. 8(b)–(d)), the intensity of CO-Pt species in IR spectra
decreased with increasing Sn/Pt ratio and even no CO-Pt species
was observed over Pt-1.5SnO @ZIF-8, because the Pt active sites
were separated by the surface covering SnO . The intensity of
2 4
, which was ascribed to inhibited g adsorp-
adequate assemble Pt atoms showed a strong linear adsorption
and an obvious bridged adsorption of CO. The TEM results indi-
cated that the Pt NPs had a mean size of 2.08 nm, which favored
the
through
duced CO formed the CO-Pt species as indicated in the IR spectra.
Different from the IR surface reaction, the decarbonylation path-
way did not proceed in the liquid phase hydrogenation. Thus, in
the liquid phase hydrogenation reaction, UAL was adsorbed on Pt
2
2
g
4
(C@C, C@O) adsorption mode [53]. The adsorbed UAL
mode proceeded the decarbonylation, and the pro-
g
x
g
4
(
x
x
2 x 2 x
Scheme 2. Reaction modes over different catalysts. (a) Pt/SiO , (b) Pt-SnO /SiO , (c) Pt@ZIF-8, and (d) Pt-SnO @ZIF-8.

X. Lan et al. / Journal of Catalysis 372 (2019) 49–60
59
active sites through the
to produce the main product of saturated aldehyde (Scheme 2a).
The synergetic effect between TiO and Pt has been demon-
strated by Kennedy et al. [5] that a crotyl-oxy surface intermediate
was obtained over the Pt/TiO , which exhibited a 52% selectivity to
C@O bond hydrogenation. Here in, the synergetic effect between Pt
and SnO was applied in the selective hydrogenation of UAL. The
characterization results showed that the SnO species mainly cov-
g
4
mode and the C@C was hydrogenated
selectivity to unsaturated alcohol and the TOFC@O/TOFC@C ratio
increased with increasing amount of SnO . Compared with C@C
bond, the hydrogenation probability of C@O was enhanced due
to the addition of SnO . The higher amount of SnO provided more
electrophilic sites for the adsorption of C@O and the adsorbed C@O
was further hydrogenated by the H activated by adjacent Pt, result-
ing in the positive relationship between selectivity and Sn/Pt ratio.
x
x
x
x
x
x
x
x
The decarbonylation reaction was suppressed due to the SnO and
ered the Pt surface and divided the large assembled Pt sites, which
decreased the linear CO-Pt adsorption and vanished the bridged CO
the apertures of ZIF-8, thus no CO-species was observed in the IR
spectra. These dual effects resulted in a highly selective adsorption
adsorption. The coverage effect of SnO
x
was further confirmed by
of C@O on SnO
x
and a high selectivity to UOL (Scheme 2d).
in situ FTIR, where the CO-Pt species formed through the decar-
bonylation of UAL decreased with increasing Sn/Pt ratio. The IR
5
. Conclusions
spectra showed that the intensity of ʋ
on stream over the Pt-ySnO /SiO catalyst, indicating that the C@O
bond was activated by the SnO . These results were consistent with
the TOF values that a much higher TOFC=O was obtained over the
Pt-ySnO /SiO catalyst. Thus, SAL and UOL were the main products
in the liquid phase hydrogenation of UAL over Pt-ySnO /SiO cata-
lysts. Based on the above discussion, it could be inferred that two
reaction processes occurred over the SnO modified Pt catalyst in
2
(C@O) decreased with time
x
2
Synergetic and steric effects were applied to design highly
selective catalysts for the hydrogenation of unsaturated aldehydes.
The surface enriched SnO in Pt-SnO and the encapsulation of Pt-
SnO inside ZIF-8 were confirmed by catalyst characterizations.
Compared with Pt/SiO , the surface enriched SnO on the Pt-ySnO
SiO catalyst isolated the assembled Pt atoms and suppressed the
formation of CO-Pt species produced form the decarbonylation
reaction in the FTIR experiments. In addition, the SnO species
acted as electrophilic sites for the adsorption and activation of
the C@O bond, resulting in the decrease of ʋ (C@O) vibration. Thus,
the selectivity to unsaturated alcohol was enhanced by the syner-
getic effect between SnO and Pt active sites and showed a positive
linear relationship with the Sn/Pt ratio. The channel of ZIF-8
showed steric constriction in the hydrogenation of unsaturated
aldehydes by orienting the C@O adsorption on the Pt active sites.
The two methyl groups of 3-prenal showed a higher hindrance
effect than the ethyl group of 2-pentenal and a much higher selec-
tivity was obtained over the hydrogenation of 3-prenal. For the
hydrogenation of 2-pentenal, the selective was only enhanced to
x
x
x
x
2
x
x
2
2
x
x
/
2
x
the liquid phase hydrogenation (Scheme 2b): one is the adsorption
of C@C on Pt that results in the formation of SAL, and the other is
the adsorption of C@O on SnO followed by hydrogenation with
x
spilled hydrogen to form UOL.
x
2
The steric effect was firstly reported for the hydrogenation of
cinnamaldehyde, where the phenyl group showed steric hindrance
for the C@C adsorption in some cases [1]. This steric effect can be
induced by large metal particles that exhibit flat surface. The steric
repulsion of the aromatic ring hindered the parallel adsorption of
the planar cinnamaldehyde molecule on a flat metal surface [54].
Ligands and porous materials were used to modify the metal active
sites, which also showed steric hinderance of C@C due to the inter-
action between phenyl group and modified metal surface [25,27].
Compared with Pt/C, the selectivity to cinnamyl alcohol was
increased from 33% to 74% when Pt NPs were encapsulated in zeo-
lite Y [24]. However, the steric effect was mostly applied in the
hydrogenation of unsaturated aldehyde with large substituents at
the C@C bond, and was found ineffective for those with the small
substituents [24,27]. Over the present Pt@ZIF-8 catalyst, ZIF-8 with
a channel size of 0.34 nm was combined with Pt active sites for the
hydrogenation of UAL. The TEM images of ultrathin slices con-
firmed that the Pt NPs were encapsulated into the ZIF-8 internal
structure. The Pt surface was modified by the apertures of ZIF-8
and the UAL molecules were oriented by the aperture to linearly
interact with Pt active sites. This steric effect increased the C@O
adsorption of UAL on Pt and enhanced the C@O hydrogenation
selectivity (Scheme 2c). It should be noted that the steric effect
x
3
1% over the Pt@ZIF-8 but was further increased to ꢃ80% by encap-
sulating Pt-SnO into ZIF-8. The synergetic and steric effect was
combined over the Pt-SnO @ZIF-8 to prevent the C@C adsorption
x
x
and inhibit the C@C hydrogenation.
Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (No. 21676155).
Appendix A. Supplementary material
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.jcat.2019.02.022.
cannot completely prevent the
the CO-Pt species formed in the decarbonylation reaction were
detected in the IR spectra. In the liquid phase reaction, this
adsorption mode resulted in the formation of saturated aldehyde,
4
g (C@C, C@O) adsorption because
References
g
4
[
1] P. Gallezot, D. Richard, Selective hydrogenation of
Catal. Rev. 40 (1998) 81–126.
a, b-unsaturated aldehydes,
thus a certain amount of SAL was also produced through the
mode over Pt@ZIF-8 (Scheme 2c).
g
4
[2] M. Zhao, K. Yuan, W. Yun, G. Li, J. Guo, G. Lin, W. Hu, H. Zhao, Z. Tang, Metal–
organic frameworks as selectivity regulators for hydrogenation reactions,
Nature 539 (2016) 76–80.
In fact, the steric effect cannot completely prevent the C@C
bond from interacting with active sites due to the defect or flexibil-
ity of the steric constriction. Thus, the selectivity of steric effect
catalysts was also affected by the active metal. Pt NPs with highly
intrinsic selectivity to C@O hydrogenation showed a 74% selectiv-
ity to cinnamyl alcohol when encapsulated into zeolite Y, while the
selectivity was only increased from 30% to 63% for Ru-Y and from
[
3] X. Li, P. Jia, T. Wang, Furfural: A promising platform compound for sustainable
production of C4 and C5 chemicals, ACS Catal. 6 (2016) 7621–7640.
[
4] C.J. Kliewer, M. Bieri, G.A. Somorjai, Hydrogenation of the
a, b-unsaturated
aldehydes acrolein, crotonaldehyde, and prenal over Pt single crystals: a
kinetic and sum-frequency generation vibrational spectroscopy study, J. Am.
Chem. Soc. 131 (2009) 9958–9966.
[5] G. Kennedy, L.R. Baker, G.A. Somorjai, Selective amplification of C=O bond
hydrogenation on Pt/TiO : catalytic reaction and sum-frequency generation
2
vibrational spectroscopy studies of crotonaldehyde hydrogenation, Angew.
Chem. Int. Ed. 126 (2014) 3473–3476.
0
% to 16% for Rh-Y compared with the corresponding metal sup-
ported on carbon [24,25]. In this work, Pt-SnO NPs supported
non-porous SiO exhibited the synergetic effect for enhancing the
selectivity to C@O hydrogenation. The synergetic and steric effects
were further combined over the Pt-SnO @ZIF-8 catalysts. The
[6] P. Mäki-Arvela, J. Hajek, T. Salmi, D.Y. Murzin, Chemoselective hydrogenation
of carbonyl compounds over heterogeneous catalysts, Appl. Catal. A-Gen. 292
x
2
(
2005) 1–49.
[
7] T. Chen, V.O. Rodionov, Controllable Catalysis with nanoparticles: bimetallic
alloy systems and surface adsorbates, ACS Catal. 6 (2016) 4025–4033.
x

6
0
X. Lan et al. / Journal of Catalysis 372 (2019) 49–60
[
8] J.C. Wu, T.-S. Cheng, C.-L. Lai, Boron nitride supported PtFe catalysts for
selective hydrogenation of crotonaldehyde, Appl. Catal. A-Gen. 314 (2006)
33–239.
9] A.-R. Rautio, P. Mäki-Arvela, A. Aho, K. Eränen, K. Kordas, Chemoselective
C=O bond for
a, b-unsaturated aldehydes and the C=C bond for a, b-
unsaturated ketones, Catal. Sci. Technol. 6 (2016) 7386–7390.
2
[30] X. Lan, N. Huang, J. Wang, T. Wang, Geometric effect in the highly selective
hydrogenation of 3-methylcrotonaldehyde over Pt@ ZIF-8 core-shell catalyst,
Catal. Sci. Technol. 7 (2017) 2601–2608.
[31] F. Yang, D. Liu, H. Wang, X. Liu, J. Han, Q. Ge, X. Zhu, Geometric and electronic
effects of bimetallic Ni–Re catalysts for selective deoxygenation of m-cresol to
toluene, J. Catal. 349 (2017) 84–97.
[32] H. Liu, Q. Mei, S. Li, Y. Yang, Y. Wang, H. Liu, L. Zheng, P. An, J. Zhang, B. Han,
Selective hydrogenation of unsaturated aldehydes over Pt nanoparticles
promoted by the cooperation of steric and electronic effects, Chem.
Commun. 54 (2018) 908–911.
[
hydrogenation of citral by Pt and Pt-Sn catalysts supported on TiO
nanoparticles and nanowires, Catal. Today 241 (2015) 170–178.
2
[
[
[
[
10] A.B. Merlo, B.F. Machado, V. Vetere, J.L. Faria, M.L. Casella, PtSn/2 catalysts
prepared by surface controlled reactions for the selective hydrogenation of
cinnamaldehyde, Appl. Catal. A-Gen. 383 (2010) 43–49.
11] A. Huidobro, A. Sepúlveda-Escribano, F. Rodrıguez-Reinoso, Vapor-phase
hydrogenation of crotonaldehyde on titania-supported Pt and PtSn SMSI
catalysts, J. Catal. 212 (2002) 94–103.
12] E. Galloway, M. Armbrüster, K. Kovnir, M.S. Tikhov, R.M. Lambert, Bromine-
promoted PtZn is very effective for the chemoselective hydrogenation of
crotonaldehyde, J. Catal. 261 (2009) 60–65.
[33] M. Liu, W. Tang, Z. Xie, H. Yu, H. Yin, Y. Xu, S. Zhao, S. Zhou, Design of highly
efficient Pt-SnO
2
hydrogenation nanocatalysts using Pt@Sn core-shell
nanoparticles, ACS Catal. 7 (2017) 1583–1591.
13] J. Silvestre-Albero, F. Coloma, A. Sepúlveda-Escribano, F. Rodríguez-Reinoso,
[34] G. Lu, S. Li, Z. Guo, O.K. Farha, B.G. Hauser, X. Qi, Y. Wang, X. Wang, S. Han, X.
Effect of the presence of chlorine in bimetallic PtZn/CeO
vapor-phase hydrogenation of crotonaldehyde, Appl. Catal. A-Gen. 304 (2006)
59–167.
14] Z. Tian, Q. Li, J. Hou, Y. Li, S. Ai, Highly selective hydrogenation of
2
catalysts for the
Liu, Imparting functionality to a metal–organic framework material by
controlled nanoparticle encapsulation, Nature Chem. 4 (2012) 310–316.
[35] P. Hu, J.V. Morabito, C.-K. Tsung, Core–shell catalysts of metal nanoparticle
core and metal–organic framework shell, ACS Catal. 4 (2014) 4409–4419.
[36] L. Chen, R. Luque, Y. Li, Controllable design of tunable nanostructures inside
metal-organic frameworks, Chem. Soc. Rev. 46 (2017) 4614.
1
[
a, b-
unsaturated aldehydes by Pt catalysts supported on Fe-based layered double
hydroxides and derived mixed metal oxides, Catal. Sci. Technol. 6 (2016) 703–
7
07.
15] X. Ji, X. Niu, B. Li, Q. Han, F. Yuan, F. Zaera, Y. Zhu, H. Fu, Selective
hydrogenation of cinnamaldehyde to cinnamal alcohol over
platinum/graphene catalysts, ChemCatChem 6 (2014) 3246–3253.
[37] X. Wang, L. Altmann, J.R. Stöver, V. Zielasek, M. Bäumer, K. Al-Shamery, H.
Borchert, J.R. Parisi, J. Kolny-Olesiak, Pt/Sn intermetallic, core/shell and alloy
nanoparticles: colloidal synthesis and structural control, Chem. Mater. 25
(2012) 1400–1407.
[
[
16] F.A. Armstrong, A.M. Bond, H.A.O. Hill, I.S. Psalti, C.G. Zoski, A microscopic
model of electron transfer at electroactive sites of molecular dimensions for
reduction of cytochrome c at basal-and edge-plane graphite electrodes, J. Phys.
Chem. 93 (1989) 6485–6493.
[38] N. Chen, Y. Ren, E.W. Qian, Elucidation of the active phase in PtSn/SAPO-11 for
hydrodeoxygenation of methyl palmitate, J. Catal. 334 (2016) 79–88.
[39] C.D. Wagner, G. Muilenberg, Handbook of X-ray Photoelectron Spectroscopy,
Perkin-Elmer, 1979.
[
17] B. Campo, M. Volpe, S. Ivanova, R. Touroude, Selective hydrogenation of
[40] H. Rong, Z. Niu, Y. Zhao, H. Cheng, Z. Li, L. Ma, J. Li, S. Wei, Y. Li, Structure
evolution and associated catalytic properties of Pt-Sn bimetallic nanoparticles,
Chem.-Eur. J. 21 (2015) 12034–12041.
[41] X. Lan, N. Huang, J. Wang, T. Wang, A general and facile strategy for precisely
controlling the crystal size of monodispersed metal-organic frameworks via
separating the nucleation and growth, Chem. Commun. 54 (2018) 584–587.
[42] B. Qiao, A. Wang, X. Yang, L.F. Allard, Z. Jiang, Y. Cui, J. Liu, J. Li, T. Zhang, Single-
crotonaldehyde on Au/HSA-CeO
18] S. Bhogeswararao, D. Srinivas, Intramolecular selective hydrogenation of
cinnamaldehyde over CeO -ZrO -supported Pt catalysts, J. Catal. 285 (2012)
1–40.
2
catalysts, J. Catal. 242 (2006) 162–171.
[
2
2
3
[
[
[
[
[
[
[
[
19] M. Tamura, K. Tokonami, Y. Nakagawa, K. Tomishige, Selective hydrogenation
of crotonaldehyde to crotyl alcohol over metal oxide modified Ir catalysts and
mechanistic insight, ACS Catal. 6 (2016) 3600–3609.
atom catalysis of CO oxidation using Pt
641.
1 x
/FeO , Nature Chem. 3 (2011) 634–
x 2
20] X. Lan, T. Wang, X. Li, N. Huang, J. Wang, Pt@SnO /SiO catalysts with
enhanced selectivity to allyl alcohol for acrolein hydrogenation, Catal. Sci.
Technol. 6 (2016) 7703–7707.
[43] Y. Zhu, Z. An, J. He, Single-atom and small-cluster Pt induced by Sn (IV) sites
confined in an LDH lattice for catalytic reforming, J. Catal. 341 (2016) 44–54.
[44] J. Ryczkowski, IR spectroscopy in catalysis, Catal. Today 68 (2001) 263–381.
[45] P.V. Samant, M.F.R. Pereira, J.L. Figueiredo, Mesoporous carbon supported Pt
and Pt–Sn catalysts for hydrogenation of cinnamaldehyde, Catal. Today 102
(2005) 183–188.
21] J.C. Serrano-Ruiz, J. Luettich, A. Sepúlveda-Escribano, F. Rodríguez-Reinoso,
Effect of the support composition on the vapor-phase hydrogenation of
crotonaldehyde over Pt/Ce
22] A.M. Ruppert, T. Paryjczak, Pt/ZrO
x
Zr1-x
O
2
catalysts, J. Catal. 241 (2006) 45–55.
/TiO catalysts for selective hydrogenation
2
2
of crotonaldehyde: Tuning the SMSI effect for optimum performance, Appl.
Catal. A-Gen. 320 (2007) 80–90.
2
[46] A.B. Merlo, B.F. Machado, V. Vetere, J.L. Faria, M.L. Casella, PtSn/SiO catalysts
prepared by surface controlled reactions for the selective hydrogenation of
cinnamaldehyde, Appl. Catal. A-Gen. 383 (2010) 43–49.
23] E. Gebauer-Henke, J. Grams, E. Szubiakiewicz, J. Farbotko, R. Touroude, J.
Rynkowski, Pt/Ga
2
O
3
catalysts of selective hydrogenation of crotonaldehyde, J.
[47] A. Dandekar, M.A. Vannice, Crotonaldehyde hydrogenation on Pt/TiO
2
and Ni/
Catal. 250 (2007) 195–208.
TiO SMSI Catalysts, J. Catal. 183 (1999) 344–354.
2
24] P. Gallezot, A. Giroir-Fendler, D. Richard, Chemioselectivity in cinnamaldehyde
hydrogenation induced by shape selectivity effects in Pt-Y zeolite catalysts,
Catal. Lett. 5 (1990) 169–174.
[48] 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.
25] D.G. Blackmond, R. Oukaci, B. Blanc, P. Gallezot, Geometric and electronic
[49] L.E. Murillo, J.G. Chen, A comparative study of the adsorption and
effects in the selective hydrogenation of
a, b-unsaturated aldehydes over
hydrogenation of acrolein on Pt (111), Ni (111) film and Pt–Ni–Pt (111)
bimetallic surfaces, Surf. Sci. 602 (2008) 919–931.
[50] J. Haubrich, D. Loffreda, F. Delbecq, P. Sautet, A. Krupski, C. Becker, K. Wandelt,
zeolite-supported metals, J. Catal. 131 (1991) 401–411.
26] 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
Adsorption of
a, b-Unsaturated Aldehydes on Pt (111) and Pt-Sn Alloys: II.
Crotonaldehyde, J. Phys. Chem. C 113 (2009) 13947–13967.
(
2014) 1340–1348.
[51] D.I. Jerdev, A. Olivas, B.E. Koel, Hydrogenation of crotonaldehyde over Sn/Pt
(111) alloy model catalysts, J. Catal. 205 (2002) 278–288.
[
[
[
27] K.R. Kahsar, D.K. Schwartz, J.W. Medlin, Control of metal catalyst selectivity
through specific noncovalent molecular interactions, J. Am. Chem. Soc. 136
[52] J.C. Matsubu, V.N. Yang, P. Christopher, Isolated metal active site concentration
(
2013) 520–526.
and stability controls catalytic CO
(2015) 3076–3084.
2
reduction selectivity, J. Am. Chem. Soc. 137
28] K.B. Vu, K.V. Bukhryakov, D.H. Anjum, V.O. Rodionov, Surface-bound ligands
modulate chemoselectivity and activity of a bimetallic nanoparticle catalyst,
ACS Catal. 5 (2015) 2529–2533.
29] W. Li, Y. Wang, P. Chen, M. Zeng, J. Jiang, Z. Jin, Thermoregulated phase-
transfer iridium nanoparticle catalyst: highly selective hydrogenation of the
[53] M. Englisch, A. Jentys, J.A. Lercher, Structure sensitivity of the hydrogenation of
crotonaldehyde over Pt/SiO and Pt/TiO , J. Catal. 166 (1997) 25–35.
2
2
[54] A. Giroir-Fendler, D. Richard, P. Gallezot, Chemioselectivity in the catalytic
hydrogenation of cinnamaldehyde. Effect of metal particle morphology, Catal.
Lett. 5 (1990) 175–181.