Effect of Carbon Supported Pt Catalysts on Selective Hydrogenation of Cinnamaldehyde

Article abstract of DOI:10.1155/2016/4563832

Selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) is of both fundamental and industrial interest. It is of great significance to evaluate the possible differences between different supports arising from metal dispersion and electronic effects, in terms of activity and selectivity. Herein, Pt catalysts on different carbon supports including carbon nanotubes (CNTs) and reduced graphene oxides (RGO) were developed by a simple wet impregnation method. The resultant catalysts were well characterized by XRD, Raman, N₂ physisorption, TEM, and XPS analysis. Applied in the hydrogenation of cinnamaldehyde, 3.5 wt% Pt/CNT shows much higher selectivity towards cinnamyl alcohol (62%) than 3.5 wt% Pt/RGO@SiO₂ (48%). The enhanced activity can be ascribed to the high graphitization degree of CNTs and high density of dispersed Pt electron cloud.

Full text of DOI:10.1155/2016/4563832

Hindawi Publishing Corporation
Journal of Chemistry
Volume 2016, Article ID 4563832, 9 pages
http://dx.doi.org/10.1155/2016/4563832
Research Article
Effect of Carbon Supported Pt Catalysts on Selective
Hydrogenation of Cinnamaldehyde
Qing Han, Yunfei Liu, Dong Wang, Fulong Yuan, Xiaoyu Niu, and Yujun Zhu
Key Laboratory of Functional Inorganic Material Chemistry, School of Chemistry and Materials, Heilongjiang University,
Ministry of Education, Harbin 150080, China
Correspondence should be addressed to Xiaoyu Niu; niuxiaoyu2000@126.com and Yujun Zhu; yujunzhu@hlju.edu.cn
Received 4 May 2016; Accepted 28 July 2016
Academic Editor: Ioannis D. Kostas
Copyright © 2016 Qing Han et al. is is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) is of both fundamental and industrial interest. It is of
great significance to evaluate the possible differences between different supports arising from metal dispersion and electronic effects,
in terms of activity and selectivity. Herein, Pt catalysts on different carbon supports including carbon nanotubes (CNTs) and reduced
graphene oxides (RGO) were developed by a simple wet impregnation method. e resultant catalysts were well characterized by
XRD, Raman, N physisorption, TEM, and XPS analysis. Applied in the hydrogenation of cinnamaldehyde, 3.5 wt% Pt/CNT shows
2
much higher selectivity towards cinnamyl alcohol (62%) than 3.5 wt% Pt/RGO@SiO (48%). e enhanced activity can be ascribed
2
to the high graphitization degree of CNTs and high density of dispersed Pt electron cloud.
1. Introduction
are still a challenge, which prevents their widespread appli-
cations [11]. To this end, the development of heterogeneous
catalysts on various supports provides a promising solution
because of its environment-friendly property, ability to selec-
tively hydrogenate, and simple method to recover [5, 9]. A
number of noble metal (e.g., Pt, Pd, Ir, and Ru) and nonnoble
metal (e.g., Fe, Co, Ni, and Cu) nanoparticles have been
demonstrated as effective phase for this catalytic reaction [12–
21]. A great deal of parameters, such as the nature of the
active metal, its surface structures, particle sizes, contents, the
methods of catalyst preparation, and the reaction conditions
could influence the activity and selectivity [3, 6, 22–24].
Among them, the support, which maximizes the active
surface area of metal catalysts by dispersing them over its
surface, plays a key role in both the activity and the selectivity
in the targeted selective hydrogenation due to the interaction
between the support and nanoparticles [25]. For example,
various reducible oxides such as CeO [26], MnO [27], SnO
With the rapid development of catalytic science, controlling
the reaction selectivity is particularly significant [1, 2]. As a
typical example, selective hydrogenation of ꢀ,ꢁ-unsaturated
aldehydes is of both fundamental and industrial importance
[3–5]. For instance, the hydrogenation of cinnamaldehyde
(CAL) can produce cinnamyl alcohol (COL), hydrocin-
namaldehyde (HALD), and hydrocinnamyl alcohol (HALC)
(Scheme 1) [6–8]. COL is generally considered to be the most
challenging product to obtain and is a type of important
organic intermediates for chemical synthesis, which has been
widely used in perfume, cosmetics, medicines, and fungicides
industries [3, 4]. However, the selective production of COL
is difficult because the hydrogenation of the C=C bond is
thermodynamically favored over that of the C=O group.
erefore, the development of catalysts for this class of
reactions is still challenging and highly desired.
2
2
2
[28], TiO [29, 30], and ZnO [31] have been used as the
Recently, a large number of homogeneous catalysts such
as metal hydrides, aluminium isopropoxide, and others have
been developed for selective hydrogenation of cinnamalde-
hyde to cinnamic alcohol [9, 10]; however, efficient separation
and recovery of these advanced catalysts from reaction vessel
2
supports and were found to be able to improve the selectivity
toward COL production because of strong metal-support
interactions, which can influence the degree of reduction,
metal dispersion, and evolution of the active phase.

2
Journal of Chemistry
product was soaked in methanol/water solution (1 : 10, v/v)
for 2 h and it was repeated 4 times to remove the organic
residues in the process of modification. e resultant product
O
OH
H2
was dried at 100∘C for 24 h, marked as APTES-SiO .
Cinnamaldehyde (CAL)
Cinnamyl alcohol (COL)
H2
2
RGO@SiO2 Supports. In a typical process, APTES-SiO was
2
H2
added into graphene oxide solution. e quality ratio of
graphene oxide to APTES-SiO was kept at 1 : 9. e pH
2
OH
O
H2
value of the mixture solution was adjusted to 4.0 by NaOH
(0.1 mol/L) solution. Afer stirring for 1 h, FeCl solution was
2
slowly added to the reaction vessel. Subsequently, NaBH
4
Hydrocinnamaldehyde (HALD)
Hydrocinnamyl alcohol (HALC)
solution (1 mol/L) was added to the mixture and stirred for
10 min. Next, HCl aqueous solution was added to remove the
excess iron powders. e resultant sample was thoroughly
washed by water to remove chloride ions, which was checked
Scheme 1: Reaction pathways for cinnamaldehyde hydrogenation.
by AgNO solution (1 mol/L). en, the product was washed
3
by ethanol and dried at 80∘C for 10 h under vacuum drying,
In addition to metal oxides, owning to the unique struc-
tures and properties, various carbon materials such as carbon
nanofibers, carbon nanotubes (CNT), and reduced graphene
oxides (RGO) have also been studied as effective supports
for metal nanoparticles toward hydrogenation of unsaturated
aldehyde [32–36]. We have found that graphene-supported
Pt catalysts exhibit excellent catalytic performances in terms
of selectivity for the hydrogenation of unsaturated aldehy-
des [37]. Unfortunately, the key factor of different carbon
supports controlling the activity and selectivity still remains
unclear.
which is denoted as RGO@SiO .
2
2.2. Preparation of 3.5 wt% Pt/RGO@SiO2 and 3.5 wt%
Pt/CNTs. 3.5 wt% Pt/RGO@SiO was prepared in a typi-
2
cal process and the RGO@SiO supports (0.5 g) were first
2
suspended in deionized water (50 mL) and ultrasonicated
for 0.5 h. en, H PtCl (19.3 mmol/L) solution was added
2
6
to the slurry. Next, the mixture solution was put into ice
bath and stirred vigorously for 0.5 h. e temperature of ice
bath was kept at 2–4∘C and the pH value of the mixture
solution was adjusted to 8.0 by NaOH (0.1 mol/L) solution.
Indeed, CNTs, which are the one-dimensional (1D) tubu-
lar structure of graphite, are totally different from graphene
(2D planar structure). erefore, it would be interesting to
evaluate the possible differences between different carbon
materials arising from metal dispersion and electronic effects,
in terms of activity and selectivity. Herein, we have attempted
to address this issue through investigating Pt catalysts on dif-
ferent carbon supports including CNTs and RGO, which were
evaluated for the selective hydrogenation of CAL. 3.5 wt% Pt
nanoparticles deposited on CNTs and RGO were prepared
by the same wet impregnation method and were denoted
Aferwards, an excess of NaBH (0.4 mol/L) solution was
4
added to the mixture under vigorous stirring. Afer 3 h,
the mixture was statically placed in the ice bath for 10 h.
Finally, the product (3.5 wt% Pt/RGO@SiO catalysts) was
2
obtained afer filtrating, washing with deionized water until
no chloride was detected, washing with ethanol, and drying
at 60∘C for 10 h. e 3.5 wt% Pt/CNTs catalyst was prepared
by following the same method.
as 3.5 wt% Pt/CNTs and 3.5 wt% Pt/RGO@SiO , respectively.
2
2.3. Catalyst Characterization. X-ray diffraction (XRD) pat-
terns were obtained with a Rigaku D/max-IIIB diffractometer
It was found that the selectivity of COL is different for the
Pt supported on different carbon. 3.5 wt% Pt/CNT shows
much higher selectivity towards cinnamyl alcohol (62%) than
˚
by using Cu-K (ꢂ = 1.5406 A) radiation. e accelerating
ꢀ
voltage and the applied current were 40 kV and 20 mA,
respectively. Raman spectra were recorded with a Jobin
Yvon HR 800 micro-Raman spectrometer at 457.9 nm. e
laser beam was focused on the sample with a 50x objec-
tive. Transmission electron microscopy (TEM) experiments
were carried out with a JOEL model JEM-2100 electron
microscope working at an acceleration voltage of 200 kV.
e samples for the TEM measurements were suspended
in ethanol and supported onto a holey carbon film on a
Cu grid. X-ray photoemission spectroscopy (XPS) studies
were carried out on a Kratos-AXIS ULTRA DLD with an
3.5 wt% Pt/RGO@SiO (48%). e effects of CNTs and RGO
2
on the properties of catalysts were investigated, indicating the
graphitization degree of support plays an important role in
the sorption of CAL and Pt species.
2. Material and Methods
2.1. Synthesis of RGO@SiO2 Supports
(3-Aminopropyl) Triethoxysilane (APTES) Modified Silica
Gel (Aladdin 200 m2/g). In a typical process, afer vacuum
drying at 110∘C for 24 h, 5.0 g silica gel was added into
APTES/toluene solution. e mole ratio of APTES to silica
gel was maintained at 1 : 2. e mixed solution was stirred
at 100∘C for 24 h. Afer cooling to room temperature, the
product was washed by using toluene 4 times (100 mL/times)
and chloroform 4 times (100 mL/time), respectively. Next, the
Al-K radiation source. Nitrogen adsorption and desorption
ꢀ
isotherms were measured at 77 K with a Micromeritics Tristar
II 3020 analyzer. e sample was degassed under vacuum at
423 K for 4 h prior to measurements. e Brunauer-Emmett-
Teller (BET) method was utilized to calculate the specific
surface areas using adsorption data in a relative pressure
range from 0.05 to 0.25.

Journal of Chemistry
3
2.4. Catalytic Performance Measurements. e catalytic per-
002
formances of 3.5 wt% Pt/RGO@SiO and 3.5 wt% Pt/CNTs
2
toward the hydrogenation of cinnamaldehyde were carried
out in a 100 mL stirred autoclave. In briefly, catalyst (50 mg)
was immersed into 15 mL of isopropanol. e trace of
dissolved oxygen was removed by flushing with nitrogen at
5 bar for 3 times and subsequently with hydrogen at 5 bar
for 3 times. en, the temperature was raised to 110∘C under
10 bar of hydrogen for 1 h, to reactivate the catalysts. en, a
mixture of cinnamaldehyde (1.0 g) and isopropanol (15 mL)
was added into the autoclave. Afer flushing with nitrogen
at 5 bar for 3 times and subsequently with hydrogen at 5
bar for 3 times, the reaction was allowed to proceed at 60∘C
under 10 bar of hydrogen. e products were analyzed on a
gas chromatography (Agilent 7820A) equipped with an FID
detector and an HP-5 capillary column (30 m × 0.32 mm ×
0.25 ꢃm). e products were further identified by GC-MS
(Agilent 6890/5973N).
111
100
200
220
110
004
(b)
(a)
10
20
30
40
50
60
70
80
2ꢀ
Graphite
Pt
Figure 1: XRD patterns of (a) 3.5 wt% Pt/RGO@SiO and (b)
2
3.5 wt% Pt/CNTs.
3. Results and Discussion
2D band
D band
G band
Due to the poor dispersion of RGO support, RGO was
dispersed on SiO to obtain the RGO@SiO support. us,
2
2
3.5 wt% Pt/RGO@SiO and 3.5 wt% Pt/CNTs were prepared
2
by reduction of H PtCl using NaBH and used to research
2
6
4
the effect of different carbon supported Pt catalysts on
selective hydrogenation of cinnamaldehyde.
3.1. XRD Analysis. A sharp and strong diffraction peak
at 27∘ in 3.5 wt% Pt/CNTs was assigned to (002) facet of
graphite, suggesting the ordered structure and high graphite
degree of CNTs support (Figure 1). A weak and broad peak
3.5wt% Pt/CNTs
1000
1500
2000
2500
3000
at 22.1∘ in 3.5 wt% Pt/RGO@SiO can be assigned to the
Raman shifs (cm−1
)
2
characteristic structure of RGO due to restacking effects,
indicating the graphene oxide has been reduced to a certain
degree. e results illustrate that the CNTs support has
Figure 2: Raman spectra of 3.5 wt% Pt/RGO@SiO and 3.5 wt%
2
Pt/CNTs.
a higher graphitization degree than RGO@SiO support.
2
Additional diffraction peaks were observed in the patterns
of both catalysts at 39.7, 46.4, and 67.5∘, which correspond
to the (111), (200), and (220) crystalline planes of the face-
centered cubic (fcc) Pt, respectively [38]. e average particle
sizes of Pt nanoparticles are about 4.0 and 4.4 nm for 3.5 wt%
0.82, respectively (Table 1). It indicates that CNTs have a
higher degree of graphitization than RGO support, which
is in agreement with the XRD analysis. e ꢅ2D/ꢅ ratio of
G
3.5 wt% Pt/CNTs is 0.70, suggesting that the tube wall of
Pt/RGO@SiO and 3.5 wt% of Pt/CNTs, respectively, which
CNTs support is thin. In contrast, the intensity of 2D peak
2
are calculated by using the full width at half maximum of Pt
(111) reflection based on Scherrer’s equation [39].
of 3.5 wt% Pt/RGO@SiO catalyst is relatively weak, which is
2
possibly caused by the reunion of RGO.
3.2. Raman Spectroscopy. Raman is one of the useful tools
for providing detailed structures of carbon materials, such
as disorder and defect structure. Figure 2 shows the Raman
3.3. TEM Analysis. e morphology of 3.5 wt% Pt/
RGO@SiO and 3.5 wt% Pt/CNTs was investigated by TEM
2
measurements, as shown in Figure 3. e structure of
different carbon supports can be clearly distinguished. TEM
spectra of 3.5 wt% Pt/RGO@SiO and 3.5 wt% Pt/CNTs. In
2
the Raman spectroscopy of both catalysts, the appearance
of two prominent peaks, D (1368 cm−1) and G (1590 cm−1)
bands, is usually assigned to the breathing mode of ꢄ-point
phonons of A1g symmetry and the E2g phonons of sp2 carbon
atoms, respectively [40, 41]. It is well known that the increase
images of 3.5 wt% Pt/RGO@SiO and 3.5 wt% Pt/CNTs
2
catalysts show that a number of Pt nanoparticles were well
dispersed on 1D intertwined CNTs and 2D planar RGO
support, respectively (Figures 3(a) and 3(c)). Figures 3(e) and
3(f) show the particle size distribution of Pt nanoparticles,
respectively. e mean particle size of Pt nanoparticles
in the intensity ratio of D/G (ꢅ /ꢅ ) accounts for a low
G
crystalline degree of graphite maDterials. e ꢅ /ꢅ values
for the 3.5 wt% Pt/CNTs and 3.5 wt% Pt/RGO@SiO is
around 3.8 nm and 3.1 nm, respectively. e results match
G
2
of 3.5 wt% Pt/RGO@SiO and 3.5 wt% Pt/CNTsDare 1.2 and
2

4
Journal of Chemistry
Table 1: Physicochemical properties of 3.5 wt% Pt/CNTs and 3.5 wt% Pt/RGO@SiO .
2
C1s content (%)
Pt species content (%)/BE (eV)d
c
Pt size (nm)b
Catalysts
ꢅ /ꢅ
ꢆ
a (m2/g)
D
G
BET
C-C
64.2
16.5
C=O
-COO
Pt0/BE
58.6/71.6
19.0/71.4
PtII/BE
25.9/72.8
65.6/72.4
PtIV/BE
15.5/75.1
15.4/74.9
3.5 wt% Pt/CNTs
3.5 wt% Pt/RGO@SiO
147
152
4.0
4.4
0.82
1.2
28.1
7.7
69.7
11.7
2
aValues calculated from catalysts corrected mass (i.e., without mass induced by metal loading).
bPt particle sizes were calculated from XRD patterns based on Scherrer’s equation, respectively.
cCalculated from the Raman results using the intensities of D and G peaks.
dCaculated from the XPS results.
Table 2: e catalytic performances of various catalysts toward the hydrogenation of cinnamaldehyde.
Selectivity (%)
Conversion (%)
Catalysts
HALD
HALC
COL
62
48
Othersa
3.5 wt% Pt/CNTsb
39
38
73
23
35
8
9
11
6
6
6
4
b
3.5 wt% Pt/RGO@SiO
2
3.5 wt% Pt/grapheneb [37]
82
a includes 1-(3-propoxyprop-1-enyl)benzene, cinnamyl formate, cinnamic acid, benzyl, cinnamate, 4,4-diphenylcyclohexa-1,5-dienyl acetate, and other
condensation products that could not be identified by GC-MS because of their large molecular weights.
bReaction conditions: 10 bar H , 60 C, and 2 h.
∘
2
well with the XRD analysis. Figures 3(b) and 3(d) are the
corresponding high-resolution TEM (HRTEM) images.
HRTEM images of Pt nanoparticles in both 3.5 wt% Pt/CNTs
their deconvolution into three spin-split states [42–44], as
summarized in Table 1.
In terms of quantitation of the composition of the Pt
nanoparticles, the contents of the surface Pt0, PtII, and PtIV
and 3.5 wt% Pt/RGO@SiO catalysts display the well-defined
2
lattice fringes.
species in 3.5 wt% Pt/CNTs and 3.5 wt% Pt/RGO@SiO cata-
2
e measured lattice spacing values from the insertion
of HRTEM images are 0.233 nm and 0.253 nm, which can be
well assigned to the (111) planes of the face-centered cubic Pt.
HRTEM image of CNTs displays the (002) graphite planes
with interlayer spacing of 0.34 nm mostly parallel to the tube
axis (Figure 3(e)). In addition, Figure 3(f) also shows the well-
defined lattice fringes of RGO. e lattice spacing values were
calculated to be 0.287 nm, which is corresponding to the
(002) planes of graphite.
lysts were estimated to be 58.6/25.9/15.5% and 19.0/65.6/
15.4%, respectively. Interestingly, the amount of Pt0 in 3.5 wt%
Pt/CNTs catalyst (58.6%) is much higher than that of 3.5 wt%
Pt/RGO@SiO (19.1%).
2
3.5. Catalytic Performances. e effect of different carbon
supports for Pt nanoparticles on the selective hydrogenation
of CAL was investigated and the results were summarized in
Table 2. When the reaction time is 2 h, the conversion of CAL
is 39% over 3.5 wt% Pt/CNTs, which is comparable to that
3.4. X-Ray Photoelectron Spectroscopy. XPS was used to study
of 3.5 wt% Pt/RGO@SiO (38%). e selectivity to COL for
2
the surface nature and structure of 3.5 wt% Pt/CNTs and
3.5 wt% Pt/CNTs is 62%, which is much better than that of
3.5 wt% Pt/RGO@SiO (Figure 4). e high-resolution C1s
3.5 wt% Pt/RGO@SiO (48%). e selectivity to HALD and
2
2
spectra of the 3.5 wt% Pt/CNTs and 3.5 wt% Pt/RGO@SiO
HALC is 35% and 11% over 3.5 wt% Pt/RGO@SiO , respec-
2
2
could be deconvolved into three peaks at 284.6, 287.3,
and 290.2 eV, which were assigned to the C element in
C-C, C=O, and -COO groups, respectively, as shown in
Figures 4(a) and 4(c). e content of C-C bond in 3.5 wt%
Pt/CNTs reached 64.2%, and the half peak width is 0.62 eV,
indicating that the CNTs have better graphitization degree,
which is in agreement with the Raman and XRD results.
tively, which is corresponding to 23% and 9% for 3.5 wt%
Pt/CNTs. It indicates that 3.5 wt% Pt/CNT is more favor of
the hydrogenation of C=O bond of cinnamaldehyde. In both
cases, a minor quantity of acetal by-product was detected.
e recycling experiments were carried out over 3.5 wt%
Pt/CNTs and 3.5 wt% Pt/RGO@SiO catalysts and shown
2
in Figures 5 and 6, respectively. e catalysts were reused
directly without any treatment afer being precipitated and
separated from the reaction solution. Afer four cycles,
the activity of 3.5 wt% Pt/CNTs was a slight decrease, the
conversion of CAL declined only from 39% to 32%, and the
selectivity to COL decreased from 62% to 53% (Figure 5).
In contrast, 3.5 wt% Pt/RGO@SiO displays a weak sharp
2
peak at 284.6 eV that only accounted for 16.5% of total
carbon. And the half peak width is 0.79 eV, much wider
than that of 3.5 wt% Pt/CNTs catalyst. ese results suggest
that the graphene oxide can be partly reduced into RGO.
e more content of C=O and -COO bonds in 3.5 wt%
Pt/RGO@SiO may be resulting from the SiO substrate,
And, for 3.5 wt% Pt/RGO@SiO catalyst, the conversion
2
to CAL and selectivity to COL afer four catalytic cycles
decreased to 26% and 34%, respectively (Figure 6). In general,
the catalytic stability of 3.5 wt% Pt/CNTs is higher than that
2
2
which decrease the reducibility of graphene oxide. e Pt4f
XPS spectra of 3.5 wt% Pt/CNTs and 3.5 wt% Pt/RGO@SiO
2
are shown in Figures 4(b) and 4(d), respectively, together with
of 3.5 wt% Pt/RGO@SiO catalyst.
2

Journal of Chemistry
5
CNT (002)
0.371nm
Pt (111)
0.233nm
5nm
100 nm
(a)
(b)
RGO (002)
0.287 nm
Pt (111)
0.253nm
50nm
5nm
(c)
(d)
40
35
30
25
20
15
10
5
18
16
14
12
10
8
6
4
2
0
0
2
3
4
5
2
3
4
Particle size (nm)
Particle size (nm)
(e)
(f)
Figure 3: TEM images of (a, b) 3.5 wt% Pt/CNTs and (c, d) 3.5 wt% Pt/RGO@SiO catalysts; Pt particle size distributions of (e) 3.5 wt%
2
Pt/CNTs and (f) 3.5 wt% Pt/RGO@SiO ; the insets in panel (b and d) are the corresponding HRTEM images of CNT, Pt nanoparticle, and
2
reduced graphene oxides (RGO).
e difference in selectivity for 3.5 wt% Pt/CNTs and
values were obtained for 3.5 wt% Pt/CNTs and 3.5 wt%
3.5 wt% Pt/RGO@SiO with same conversion may be
Pt/RGO@SiO synthesized here, but high selectivity was seen
2
2
attributed to the Pt species and supports. According to
above characterization results, similar mean particle size
only with the 3.5 wt% Pt/CNTs sample. It is seen that other
factors may account for the good selectivity to COL with

6
Journal of Chemistry
290
285
280
80
78
76
74
72
70
68
Binding energy (eV)
Binding energy (eV)
(a)
(b)
294
292
290
288
286
284
282
280
80
78
76
74
72
70
68
Binding energy (eV)
Binding energy (eV)
(c)
(d)
Figure 4: C 1s (a, c) and Pt 4f (b, d) high-resolution XPS spectra of (a, b) 3.5 wt% Pt/CNTs and (c, d) 3.5 wt% Pt/RGO@SiO .
2
the 3.5 wt% Pt/CNTs catalyst. Firstly, there is the effect of
the Pt electron structure. In our previous reports [37, 45–
47], it has been found that the Pt0 species plays a key role
in the selectivity to COL in the selective hydrogenation of
cinnamaldehyde, and there is a linear correlation between
the amount of Pt0 and the selectivity. e more the surface
Pt0 content catalyst has, the higher selectivity to COL it
exhibits. We have brought out that there is the special effect
of carbon support on the amount of Pt0 species [37]. Here,
the amount of Pt0 species is 58.6% and 19.0% on the surface
in the selective hydrogenation of CAL. e Raman results
shown in Table 1 indicate that the value of ꢅ /ꢅ is 0.82
D
and 1.2 for 3.5 wt% Pt/CNTs and 3.5 wt% Pt/RGGO@SiO ,
2
respectively, which is much higher than that of 3.5 wt%
Pt/graphene (0.29) [37]. It suggests that the graphitization
degree of support is listed as follows: graphene > CNTs
> RGO@SiO , meaning there are more amounts of the
2
disordered sp2-bonded carbon such as various -COH and
-COOH groups, on the surface of 3.5 wt% Pt/CNTs and
3.5 wt% Pt/RGO@SiO . ese groups derived from the low
2
crystallinity degree of the carbon support. Secondly, property
of supports can influence the sorption of CAL. According
to literatures [9], the worse the crystallinity degree of the
carbon support is, the weaker the adsorption of CAL is on
its surface. e much lower graphitization degree of support
is disadvantage for the weak ꢇ-ꢇ interactions between CAL
and the surface sp2-bonded carbon support, which results
in the low conversion of CAL. Moreover, the weak ꢇ-ꢇ
interactions can favor the contact of C=C with Pt species due
to CAL structure, which leads to the decrease in selectivity to
COL and increase in selectivity to HALD. e graphitization
degree of 3.5 wt% Pt/CNTs is much higher than that of
of 3.5 wt% Pt/CNTs and 3.5 wt% Pt/RGO@SiO (Figure 4,
2
Table 1), respectively, which responds to the selectivity of
COL (Table 2). e amount of Pt0 species on the surface of
3.5 wt% Pt/CNTs and 3.5 wt% Pt/RGO@SiO is the important
2
reason for the selectivity of COL. Furthermore, it is noticed
that the amount of Pt0 species for 3.5 wt% Pt/CNTs is similar
to that of 3.5 wt% Pt/graphene (61%) [37]; however, the
selectivity to COL is much lower compared with 3.5 wt%
Pt/graphene (82%) [37]. It is obvious that there is not a
linear correlation between selectivity to COL and Pt0 species
for 3.5 wt% Pt/CNTs, 3.5 wt% Pt/RGO@SiO , and 3.5 wt%
Pt/graphene. us, we think that the carbon support itself
2
3.5 wt% Pt/RGO@SiO ; thus, the high selectivity to COL may
be partly attributed to the better graphitization degree. e
2
plays other roles besides effect on the formation of Pt0 species

Journal of Chemistry
7
70
60
50
40
30
20
10
4. Conclusion
In summary, different carbon materials including CNTs and
RGO were evaluated as support for Pt nanoparticles. TEM
images showed that Pt nanoparticles dispersed well on CNTs
and RGO surface with a size of about 4 nm. Compared
with 3.5 wt% Pt/RGO@SiO , 3.5 wt% Pt/CNT shows better
2
selectivity for the hydrogenation of C=O bonds. e unique
catalytic performance can be attributed to not only the high
graphitization degree of CNTs, which facilitate the adsorption
of CAL and improve the selectivity of COL, but also the high
density of dispersed Pt electron cloud, which benefit for the
COL production.
0
1
2
3
4
Cycle
Competing Interests
Conversion
Selectivity
e authors declare that there is no conflict of interests
regarding the publication of this paper.
Figure 5: Stability test for 3.5 wt% Pt/CNTs shown as perfor-
mance versus number of recycling runs. Reaction conditions: 50 mg
3.5 wt% Pt/CNTs, 1.00 g CAL, 30 mL isopropanol, 10 bar H , 60∘C,
2
Acknowledgments
and 2 h.
is work was supported by Natural Sciences Fund of
Heilongjiang Province (B2015009), Postdoctoral Science-
Research Developmental Foundation of Heilongjiang
Province of China (LBH-Q12022), the Scientific Research
Foundation for the Returned Overseas Chinese Scholars,
State Education Ministry (2013-1792), and Ministry of
Human Resources and Social Security (2013-277).
60
50
40
30
20
10
0
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