Hydrogenation of alkyl-anthraquinone over hydrophobically functionalized Pd/SBA-15 catalysts

Article abstract of DOI:10.1039/c9ra07351e

Organosilane-functionalized mesoporous silica SBA-15 was prepared by the co-condensation method and then applied as a support of Pd catalysts for hydrogenation of 2-alkyl-anthraquinone (AQ, alkyl = ethyl, tert-butyl and amyl). The as-prepared Pd catalysts were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, N₂ adsorption-desorption, zeta potential, water contact angles measurement and transmission electron microscopy. By extending the pre-hydrolysis time of the silica source, the content of functional groups in the catalysts slightly increases. However, there is an initial increase in zeta potential and water contact angles up to a maximum at 2 h, followed by a decrease as the pre-hydrolysis time was further prolonged. The hydrophobicity created by organic functionalization has positive effects on AQ hydrogenation. The catalyst with the highest hydrophobicity exhibits the highest catalytic activity, with increments of 33.3%, 60.0% and 150.0% for hydrogenation of ethyl-, tert-butyl- and amyl-anthraquinone compared with the unfunctionalized one.

Full text of DOI:10.1039/c9ra07351e

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Hydrogenation of alkyl-anthraquinone over
hydrophobically functionalized Pd/SBA-15
catalysts
Cite this: RSC Adv., 2019, 9, 34581
Li Wang, Yue Zhang, Qingqing Ma, Zhiyong Pan and Baoning Zong *b
a
a
a
b
Organosilane-functionalized mesoporous silica SBA-15 was prepared by the co-condensation method and
then applied as a support of Pd catalysts for hydrogenation of 2-alkyl-anthraquinone (AQ, alkyl ¼ ethyl, tert-
butyl and amyl). The as-prepared Pd catalysts were characterized by X-ray diffraction, Fourier transform
infrared spectroscopy, thermogravimetric analysis, N
2
adsorption–desorption, zeta potential, water
contact angles measurement and transmission electron microscopy. By extending the pre-hydrolysis
time of the silica source, the content of functional groups in the catalysts slightly increases. However,
there is an initial increase in zeta potential and water contact angles up to a maximum at 2 h, followed
by a decrease as the pre-hydrolysis time was further prolonged. The hydrophobicity created by organic
functionalization has positive effects on AQ hydrogenation. The catalyst with the highest hydrophobicity
exhibits the highest catalytic activity, with increments of 33.3%, 60.0% and 150.0% for hydrogenation of
ethyl-, tert-butyl- and amyl-anthraquinone compared with the unfunctionalized one.
Received 12th September 2019
Accepted 17th October 2019
DOI: 10.1039/c9ra07351e
rsc.li/rsc-advances
catalytic performance. Tang et al. prepared an Al
extrusion method with pseudoboehmite as precursor and found
2 2
O
) is a green oxidant in line with ecological the Pd catalyst on it to be highly effective for EAQ hydrogenation
2 3
O support by
1
Introduction
Hydrogen peroxide (H
requirements and has been widely used in many domains. The due to the higher surface area and ordered pore structure.
worldwide consumption of hydrogen peroxide tends to raise yearly Chen et al. reported that large-diametered uniform mesopore of
1–3
11
12
and annual production of hydrogen peroxide reached 6 million SBA-15 was conducive to the hydrogenation of EAQ. The
4,5
tons in 2016 (based on 100% H O ). At present, the anthraqui- similar result that catalytic activity of EAQ hydrogenation
2
2
none process is almost the only industrial production method of remarkably increased with expanding the pore size of Pd/SBA-15
6
13,14
hydrogen peroxide. It involves four main processes: hydrogenation was also observed by Yuan and Wang et al.
of a 2-alkyl-anthraquinone (AQ), such as 2-ethyl-anthraquinone that the large-pored catalyst was benecial to the diffusion of
EAQ) and 2-amyl-anthraquinone (AAQ) in a nonpolar–polar both EAQ and EAQH , restraining the occurrence of deep
mixed solvent (working solution), oxidation of produced 2-alkyl- hydrogenation. Hong et al. drew the same conclusion by per-
anthrahydroquinone (AQH
), extraction of hydrogen peroxide forming hydrogenation of EAQ over anodic alumina oxide
with water from the working solution and regeneration of the supported Pd catalyst with different pore sizes.
Li et al. proposed
(
2
15
2
16
17
18
working solution. There are two routes of side reactions in hydro-
Kosydar et al. and Chen et al. reported that alkali-
genation of AQ: hydrogenation of the aromatic ring and carbonyl modication of Al
2
O
3
support could resulted in signicant
7
hydrolysis of AQH . Among the by-products formed via deep suppression of deep hydrogenation reactions. Drelinkiewicz
2
hydrogenation reactions, 2-alkyl-tetrahydro-anthraquinone is et al. proposed that the Pd catalyst on SiO
2
support was more
active and others are identied as degradation products because durable and could suppress the formation of degradation
8
19
they cannot be further oxidized to produce H
2 2
O .
products compared with that on Al
–SiO support could facilitate the
Surface area and pore size, acidity/ adsorption of EAQ molecules and thus improve the hydroge-
2 3
O . Feng et al. considered
Supported Pd-based catalysts have been widely employed in that acid sites in Al
O
3
2
2
9,10
hydrogenation of AQ.
20
basicity and hydrophilicity/hydrophobicity of support are nation activity. Yuan et al. found the selectivity of EAQ
demonstrated to be the crucial parameters affecting the hydrogenation over Pd/SBA-15 to be signicantly promoted by
incorporating Mg into SBA-15 and the rate of EAQ hydrogena-
13
tion to be accelerated by incorporating Al into SBA-15. Li et al.
observed the addition of MgO into Pd/SiO /cordierite monolith
catalyst to be favourable to the catalytic activity of EAQ hydro-
genation and attributed it to the facilitated activation and
a
Key Laboratory for Green Chemical Technology of Ministry of Education, School of
2
Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China.
E-mail: wlytj@tju.edu.cn
b
Research Institute of Petroleum Processing, SINOPEC, Beijing, 100083, China. E-mail:
21
adsorption of C]O group.
zongbn.ripp@sinopec.com
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 34581–34588 | 34581

View Article Online
RSC Advances
Paper
Polymer supports are attended by researchers as well. Bombi mixture thus obtained was transferred into a Teon-lined
ꢁ
et al. prepared resin supported Pd catalyst and achieved high stainless-steel autoclave and heated at 100 C for 48 h. The
22
activity but ordinary selectivity. Biffis et al. designed suitable solid product was obtained by ltration and then reuxed with
tailor-made resin supported Pd catalyst and improved the ethanol (GR, Real Lead Chemical Co., Ltd., China) for 24 h to
selectivity to EAQH due to the lipophilic micro-environments remove P123. Finally, the solid sample was recovered by ltra-
2
2
3
ꢁ
around Pd particles. Drelinkiewicz et al. employed polyani- tion, washed with distilled water and dried at 110 C overnight,
line (PANI) coated SiO as the support of Pd catalysts, and yielding functionalized SBA-15.
showed them to be high activity and selectivity for EAQ hydro- For comparison, a conventional SBA-15 was also synthesized
2
24
genation. In previous work, the Pd catalysts were prepared on using the same procedures and conditions as those mentioned-
SBA-15 post-graed with alkyltriethoxysilane and evaluated above, without the addition of PTES. And a calcination proce-
ꢁ
using hydrogenation of EAQ. It was found that the catalytic dure at 550 C for 6 h in air replaced the extraction with ethanol
25
activity increased with the content of carbon in the catalysts.
But it is difficult to further increase graing amount due to the
limitation of silanol groups available.
to remove P123.
2.1.2 Pd catalysts. Pd was loaded by the incipient wetness
impregnation method with the Pd loading of 1 wt%. Pd(OAc)
2
26
The co-condensation of silica source and organo- ($99.0%, Macklin Biochemical Co., Ltd., Shanghai) was used as
trialkoxysilane is another common approach of organic func- Pd source for the supports of functionalized SBA-15. 42 mg
2
tionalization of SBA-15, by which the higher functionalization Pd(OAc) was dissolved in 4.6 mL acetone. Then the solution
27
degree can be achieved. 3-Aminopropyl-triethoxysilane (APTES) was added into 2.0 g dried PTES functionalized SBA-15. Aer
ꢁ
is the most commonly used functional reagent. Chong et al. impregnating for 2 h, the sample was dried at 110 C for 12 h,
ꢁ
ꢁ
prepared APTES functionalized SBA-15 with ordered structure calcined in the air at 300 C for 4 h and reduced by H at 250 C
2
26
and uniform pore size distribution. Niu et al. found that 3- for 1 h. The resultant catalysts are denoted as Pd/P-X where X
aminopropyl functionalized SBA-15 could control the delivery of (0.5, 1, 2 and 4) means the pre-hydrolysis time of TEOS.
2
8
baicalin more efficiently than pure SBA-15. Other organic
For conventionally synthesized SBA-15 support,
$2H O ($99.0%, Macklin Biochemical Co., Ltd.,
functionalization agents are also used for the functionalization of Pd(NO
SBA-15 by the co-condensation method. Barczak et al. reported Shanghai) was used as Pd source and the resulting catalyst
3
)
2
2
2
5
the synthesis of functionalized SBA-15 by the condensation of 2- is denoted as Pd/SN.
(
2-pyridyl)ethyltrimethoxysilane (PETS) and tetraethyl orthosili-
29
cate (TEOS). Pt catalyst supported on 3-mercaptopropyle-
trimethoxysilane (MPTMS) functionalized SBA-15 was prepared
by Khan et al. and applied to the decomposition of sulfuric acid
2.2 Characterization
Powder X-ray diffraction (XRD) patterns were recorded on
0
a Philips X Pert MPD diffractometer (Cu-Ka radiation). Fourier
30
in Sulfur–Iodine cycle. Zhu et al. used aldehyde functionalized
transform infrared (FTIR) spectra were obtained on a FTIR
Bruker Equinox Vertex 70 spectrometer using a KBr wafer
SBA-15 as ammonia sensor, which exhibited excellent sensitivity,
response speed and reversibility.
31
(60 mg with 1 : 50 in the mass ratio of sample to KBr and
In this work, hydrophobically functionalized SBA-15 was
synthesized by the co-condensation method with propyl-
triethoxysilane (PTES) as modication agent and supported
Pd catalyst was prepared on the as-synthesized SBA-15. The
inuences of pre-hydrolysis time of silica source on the content
and distribution of organosilane in the catalysts and thereby on
physicochemical properties and catalytic performance of cata-
lysts were investigated. The hydrogenation of AQ (2-alkyl-
anthraquinone, alkyl ¼ ethyl, tert-butyl and amyl) was selected
for performance test of catalysts.
0
.63 cm in a diameter for each measured catalyst) in an in situ
ꢀ
4
cell at a residual pressure of 10 mbar. Prior to measurement,
the powder sample was dried in a vacuum drying oven at 50 C
ꢁ
for 12 h. Elemental analysis was performed on an Elementar
Vario EL elemental analyzer with high sensitivity thermal
conductivity detector (TCD) in the mode of CHN. Thermogra-
vimetric analysis (TGA) was recorded on a TQ500 Thermal
analyzer from TA instrument under air atmosphere from room
ꢁ
ꢁ
ꢀ1
temperature to 700 C with the heating rate of 10 C min
Nitrogen adsorption–desorption measurements were carried
.
out at liquid nitrogen temperature on an APSP 2020 volumetric
adsorption analyzer, samples were pre-degassed at 200 C to
2
Experimental
ꢁ
remove water and other physical adsorbed species. Zeta
potential was measured by a Malvern Nano ZS laser granul-
ometer with a 4 mW and 633 nm He–Ne laser. Water contact
angles were measured on a Powereach JC2000D2M Drop Shape
Analyzer. The TEM images were obtained using a JEOL JEM-
2
.1 Preparation
2.1.1 SBA-15 supports. Functionalized SBA-15 was synthe-
sized by the co-condensation method. In a typical synthesis, 2 g
triblock copolymer (Pluronic P123, Sigma-Aldrich, M
¼ 5800)
was dissolved in 75 mL HCl solution with a concentration of
w
2100F transmission electron microscopy.
ꢀ1
ꢁ
1.6 mol L
and stirred at 40 C for 1 h. Then, tetraethyl
orthosilicate (TEOS, 98%, Tianjin Kermel Chemical Reagent
Corporation, China) was dropped and stirred for a certain time
2.3 Hydrogenation test
(
pre-hydrolysis time, t ¼ 0.5, 1, 2 and 4 h). Aer that, propyl- AQ hydrogenation was carried out in a batch reactor with the
triethoxysilane (PTES, AR, Aladdin Bio-Chem Technology Co., volume of 100 mL. Firstly, dried AQ (2-ethyl-anthraquinone,
Ltd., Shanghai) was added and stirred at 40 C for 24 h. The EAQ, $99.0%, Wuhan Fude Chemical Co., Ltd., China; 2-tert-
ꢁ
34582 | RSC Adv., 2019, 9, 34581–34588
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
butyl-anthraquinone, TBAQ, >98.0%, TCI Tokyo Chemical et al. on methylaminopropyl functionalized SBA-15 silica
33
Industry Co., Ltd., Japan; 2-amyl-anthraquinone, AAQ, $99.0%, synthesized by co-condensation of MAPTMS and TEOS.
Shanghai Ruisi Chemical Co., Ltd., China) was dissolved in The wide angle XRD patterns are shown in Fig. 1(b). The
a mixture solvent of 1,3,5-trimethylbenzene (TMB, 97%, Aladdin diffraction peak at 2q ¼ 22 corresponds to amorphous silica.
Industrial Corporation, China) and trioctyl phosphate (TOP, In addition, two extremely weak diffraction peaks are observed
ꢁ
34
ꢁ
ꢁ
9
8%, TCI Tokyo Chemical Industry Co., Ltd., Japan) with the at 2q ¼ 40.1 and 46.5 , indexed to (111) and (200) reections of
35
0
volume ratio of 1 : 1, yielding a working solution with the AQ palladium lattice. Among all catalysts, the signals of Pd in Pd/
concentration of 0.38 mol L . Then, 0.2 g reduced catalyst and P-0.5 can almost not be observed, which are similar to those in
ꢀ1
3
0 mL working solution were added into the reactor. N
2
was fed Pd/SN. This may be due to the slightly higher dispersion of Pd
ꢁ
36
to replace air and the reactor was heated to 60 C in a water particles in Pd/P-0.5 and Pd/SN than in others.
bath. Finally, H was fed into the reactor. When the pressure
reached 0.3 MPa, the mechanical agitation was turned on and catalysts. There are four adsorption bands at 465 cm
3.1.2 FTIR measurement. Fig. 2 depicts the FTIR spectra of
2
ꢀ1
,
ꢀ
1
ꢀ1
ꢀ1
the reaction was started. H
a mass owmeter. Aer the reaction nished, the hydrogenated O deformation, SiO
working solution was completely oxidized with O at room O–Si asymmetrical stretching existed in typical SBA-15. The
temperature and atmospheric pressure and then hydrogen decreased intensities of Si–O–Si asymmetrical stretching bands
peroxide was extracted with deionized water for 4 times. H in for Pd/P-Xs might be ascribed to the co-condensation of PTES
2
consumption was measured by 800 cm , 950 cm and 1100 cm , corresponding to the O–Si–
4
tetrahedron ring, Si–OH stretching and Si–
37
2
2 2
O
the water phase was determined by titration with KMnO4
solution. The raffinate was analyzed by a gas chromatography
(
Bruker 456-GC) with DB-17 column (60 m ꢂ 0.32 mm ꢂ 0.25
mm) and FID detector.
3
Results and discussion
3
.1 Characterization of catalysts
.1.1 XRD characterization. The small angle XRD patterns
of catalysts are shown in Fig. 1(a). All catalysts have three
3
ꢁ
ꢁ
ꢁ
distinct characteristic peaks at 0.9 , 1.4 and 1.7 which can be
indexed to the (100), (110) and (200) reections associated with
32
the highly ordered hexagonal symmetry of SBA-15 structure.
With extending the pre-hydrolysis time of TEOS from 0.5 to 2 h,
the intensity of diffraction peak (100) gradually increases,
indicating increased long-range order. Among them, the peak
intensity of Pd/P-2 (the pre-hydrolysis time is 2 h) is very close to
that of Pd/SN. But, with further extension of the pre-hydrolysis
time to 4 h, the intensity of diffraction peak (100) slightly
decreases. This is in agreement with the observation by Wang
ꢀ1
ꢀ1
Fig. 2 FTIR spectra in (a) 400–1500 cm and (b) 1500–4000 cm of
Fig. 1 (a) Small angle and (b) wide angle XRD patterns of catalysts.
catalysts.
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 34581–34588 | 34583

View Article Online
RSC Advances
Paper
and Si–OH. This is in agreement with the results of small angle
XRD patterns, in which (100) diffraction peaks decrease for Pd/
ꢀ
1
ꢀ1
P-Xs. The bands at 3400 cm and 1600 cm are assigned to the
stretching and bending vibrations of physically adsorbed water,
38,39
respectively.
For Pd/P-Xs, the intensities of these two bands
signicantly weaken, indicating the decrease in hydrophilicity.
The extremely weak bands appeared in the region of 2800–
ꢀ
1
3
000 cm could be assigned to symmetric stretching vibration
ꢀ1
ꢀ1
2 3
of CH (2935 cm ) and CH (2975 cm ), asymmetric stretch-
ing vibration of CH (2858 cm ) and CH (2886 cm ), indi-
cating the presence of alkyl chain. The intensity of CH and
ꢀ1
ꢀ1 40
2
3
41
2
CH bands increase with prolonging the pre-hydrolysis time,
3
implying the incremental amount of alkyl chains.
3
.1.3 Elemental analysis and thermogravimetric analysis.
The carbon content of Pd/P-Xs obtained by elemental analysis
mcEA in Table 1) increases with prolonging the pre-hydrolysis
(
time, and reaches a maximum of 3.50% at 4 h (Pd/P-4). Fig. 3
shows the TGA curves of catalysts. The weight loss at low-
temperature (below 200 C) could be assigned to physically
Fig. 3 TGA curves of catalysts (inset: DTG curves of catalysts).
ꢁ
adsorbed water. The low-temperature weight loss of Pd/P-Xs
more distribution on the pore wall and inside pores of SBA-15 as
shown in Scheme 1. With any extension of TEOS pre-hydrolysis
time longer than 0.5 h (1 h and 2 h), the amount of hydrolyzed
TEOS increases and silanol groups gradually condense around
P123, which makes more functional groups gradually distributed
on the outer surface. At 4 h, the compact structure between P123
and silica forms, which compels functional groups to concentrate
on the channel opening. The change in distribution of functional
groups in SBA-15 with the pre-hydrolysis time of TEOS is in good
agreement with that of the pore size of Pd/P-Xs (Table 1).
(0.07–0.29%) is lower than that of Pd/SN (0.63%), being ascribed
to the lower hydrophilicity of Pd/P-Xs than Pd/SN. All the cata-
lysts (including Pd/SN) also exhibit a weight loss at high-
ꢁ
temperature (above 200 C). The high-temperature weight loss
L
of Pd/SN (1.57%, m in Table 1) is lower than that consistent
with mcEA. This indicates that the weight loss in the high
temperature is mainly caused by the decomposition of alkyl
chains.
As shown in the DTG curves of catalysts, the maximum peak
temperature in the range of high temperature slightly decreases
with extending the pre-hydrolysis time from 0.5 to 2 h and ach-
ieves the lowest value at 2 h. Then, it rises slightly as the pre-
hydrolysis time further extended to 4 h. It can be explained by
the different distribution of organic groups. The decomposition
temperature of the organic groups distributed on the outer
surface of SBA-15 should be relatively low. At the early stage of
synthesis, a small amount of TEOS is hydrolyzed and formed
silanol groups are not yet self-assembly around the P123 micelles.
The functional groups could be dispersed homogeneously in the
mixture of TEOS and P123, which is similar to the description by
Kecht et al. in their studies on selective functionalization of CMS
3.1.4
N
2
adsorption–desorption. The
N
2
adsorption–
desorption isotherms and pore size distributions of catalysts are
displayed in Fig. 4. The calculated textural properties are listed
in Table 1. As shown in Fig. 4(a), the isotherms are all of type IV
with obvious H1 hysteresis loops at high relative pressure,
indicating the presence of uniformly ordered cylindrical mes-
43
opores. The pore size of Pd/P-Xs (5.6–6.6 nm) is smaller than
that of Pd/SN (8.0 nm), with the opposite variation in the pore
wall thickness due to the existence of organic groups. Among
Pd/P-Xs, Pd/P-2 gives the largest pore size, although its carbon
content is close to Pd/P-4 having the highest carbon content.
3.1.5 Zeta potential and water contact angle. The zeta
potential and water contact angles of catalysts are shown in
Fig. 5. The unfunctionalized catalyst has the lowest zeta
42
materials. Hence, the functional groups added at 0.5 h would
co-condense with silanol groups around P123 and a small part of
functional groups may penetrate into P123 micelles, resulting in
Table 1 Physicochemical properties of catalysts
a
b
L
c
d
2
ꢀ1
e
3
ꢀ1
f
g
h
Catalysts
mcEA (%)
m
(%)
mcGA (%)
S
BET (m g
)
V
P
(cm g
)
d
P
(nm)
t
wall/a
0
(nm)
DPd (nm)
Pd/P-0.5
Pd/P-1
Pd/P-2
Pd/P-4
Pd/SN
2.87
3.01
3.28
3.50
—
4.20
4.65
4.94
5.10
1.57
2.63
3.08
3.37
3.53
—
789
813
829
822
497
1.02
1.09
1.15
1.12
1.05
5.6
6.5
6.6
6.4
8.0
6.1/11.7
5.4/11.9
5.4/12.0
5.6/12.0
3.8/11.8
4.3
4.6
4.6
4.7
4.4
a
b
ꢁ
c
Carbon content of catalysts determined by elemental analysis. Weight loss at 200–700 C determined by thermogravimetric analysis. Difference
L
d
e
in m between Pd/P-Xs and Pd/SN. Specic surface area calculated by BET method. Total pore volume obtained at 0.9 in the relative pressure of P/
f
g
h
P
0
.
Pore size calculated from the desorption branch by BJH method. Pore wall thickness (twall ¼ a
0
ꢀ d
P
)/crystal cell parameter. Average size of
Pd particles estimated from TEM images.
34584 | RSC Adv., 2019, 9, 34581–34588
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
Scheme 1 Schematic diagram for co-condensation of PTES and
TEOS.
Fig. 5 (a) Zeta potential and (b) water contact angles of catalysts.
3.1.6 TEM. Fig. 6 shows the TEM images of catalysts and
the size distributions of Pd particles. It can be observed that all
catalysts present a regular P6mm ordered mesoporous structure,
which is consistent with the results of XRD and N adsorption–
desorption. The average sizes of Pd particles in Pd/P-0.5 and
Pd/SN are slightly smaller than those in Pd/P-1, Pd/P-2 and Pd/P-
2
Fig. 4 (a) Nitrogen adsorption–desorption isotherms and (b) pore size
distributions of catalysts.
46
4
(4.3–4.4 nm vs. 4.6–4.7 nm, Table 1).
ꢁ
potential (ꢀ3.39 mV) and water contact angle (13 ) due to the
3
.2 Catalytic test
highest hydrophilicity. Both the zeta potential and water
contact angles of functionalized catalysts increase compared
3.2.1 Hydrogenation of EAQ. The ratio of hydrogen
44
with Pd/SN, indicating the improvement of hydrophobicity. As consumption to the initial amount of EAQ (RHC, mol H2
shown in Fig. 5, zeta potential and water contact angles do not per mol AQ) over functionalized Pd/P-Xs is delineated in
monotonously vary with the carbon content, instead the Fig. 7(a). As can be seen in Fig. 7(a), RHC shows a linear increase
maximum values of zeta potential and water contact angles with the reaction time at the initial stage. Thus, the activity of
appear at 3.28%. This could be ascribed to the difference in the catalyst is described using the H initial consumption rate (r ,
2
0
distribution of organic groups, which is greatly affected by the hydrogen consumption per unit reaction time and Pd mass in
pre-hydrolysis time. Rosenholm reported that the zeta potential the linear region of RHC curve) as listed in Table 2. Pd/P-1 and
is sensitive only to functional groups on the outer surface of Pd/P-2 give the higher RHC at the same reaction time and r0
45
porous material. In comparison, functionalization groups than Pd/SN, but Pd/P-0.5 and Pd/P-4 give the opposite results.
trends to distribute on the outer surface of catalyst at the pre- The high activity of Pd/P-2 and Pd/P-1 can be explained by
hydrolysis time of 2 h.
combination of high hydrophobicity and relatively large pore
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 34581–34588 | 34585

View Article Online
RSC Advances
Paper
have higher hydrophobicity than Pd/SN, the obviously small
pore size of Pd/P-0.5 and Pd/P-4 limit the diffusion of EAQ
molecules, rendering the lower activity than the latter. As for
between Pd/P-0.5 and Pd/P-4, the smaller size of Pd particles in
Pd/P-0.5 than Pd/P-4 is responsible for its relatively higher
16
activity.
The selectivity to target product 2-ethyl-anthrahydroquinone
EAQH ) and by-products detected including 2-ethyl-anthrone
EAN), 2-ethyl-5,6,7,8-tetrahydroanthraquinone (H EAQ), and
-ethyl-1,2,3,4-tetrahydroanthraquinone (iso-H EAQ) at about
(
(
2
4
2
0
4
22
.95 in RHC are shown in Table 2. Bombi et al. and Biffis
23
et al. reported that the lipophilic catalysts could reduce the
probability of deep hydrogenation, improving the selectivity. In
this work, however, the selectivity to EAQH
2
is very close
(approximately 95%). This might be ascribed to the low polarity
2
of EAQH . Moreover, the hydrophobicity of Pd/P-Xs is much
lower than that of lipophilic supports used in their work. Under
this circumstance, the improvement effect of hydrophobicity
created by organic functionalization on the selectivity is slight
and it is easy to be neutralized by the negative effects of
decreased pore size of functionalized catalysts on the selectivity.
3.2.2 Hydrogenation of TBAQ and AAQ. Fig. 7(b) and Table
2
show RHC, r and selectivity of the TBAQ and AAQ hydroge-
0
nation over Pd/SN and Pd/P-2. It is found that Pd/P-2 gives
higher activity than Pd/SN, regardless of the reactants. More-
over, the positive effects of hydrophobicity on the rate of AQ
hydrogenation enhance with the alkyl-chain length. To be
specic, the initial hydrogenation rate of AAQ, TBAQ and EAQ
increases by 150.0%, 60.0% and 33.3%, respectively. In addi-
tion, it can be observed that the rate of EAQ hydrogenation is
more rapid than that of TBAQ, which is in its turn more rapid
than that of AAQ. The results are accordant with those reported
Fig. 6 TEM images of (a) Pd/P-0.5, (b) Pd/P-1, (c) Pd/P-2, (d) Pd/P-4
and (e) Pd/SN (insets: size distributions of Pd particles).
diameter. The high hydrophobicity benets the adsorption of
EAQ molecules on the catalyst surface from the organic solu-
tion. And larger pore diameter could facilitate the diffusion of
49
by Yuan et al.
For hydrogenation of TBAQ and AAQ, the by-products
detected in this work are only corresponding H AQ (2-tert-
4
47,48
EAQ molecules to active sites.
Although Pd/P-0.5 and Pd/P-4
Fig. 7 Ratio of hydrogen consumption to the initial amount of AQ (RHC) for (a) EAQ hydrogenation and (b) TBAQ and AAQ hydrogenation
ꢀ1
ꢀ1
ꢁ
(
reaction conditions: catalyst amount: 6.7 g L , concentration and volume of AQ solution: 0.38 mol L and 30 mL, temperature: 60 C,
pressure: 0.3 MPa).
34586 | RSC Adv., 2019, 9, 34581–34588
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
Table 2 Initial hydrogen consumption rate and selectivity of AQ hydrogenation
b
S , %
a
Catalysts
Reactants
r
0
(mol H
2
per g Pd per min)
AQH
2
H
4
AQ
EAN
4
iso-H EAQ
Pd/P-0.5
Pd/P-1
Pd/P-2
Pd/P-4
Pd/SN
Pd/P-2
Pd/SN
Pd/P-2
Pd/SN
EAQ
EAQ
EAQ
EAQ
EAQ
TBAQ
TBAQ
AAQ
AAQ
0.14
0.16
0.20
0.13
0.15
0.08
0.05
0.05
0.02
94.9
95.1
95.3
94.6
94.3
93.2
93.3
92.9
93.1
3.6
3.5
3.4
3.8
4.1
6.4
6.4
6.7
6.6
1.3
1.2
1.1
1.4
1.4
0.4
0.3
0.4
0.3
0.2
0.2
0.2
0.2
0.2
—
—
—
—
a
Initial hydrogen consumption rate dened as hydrogen consumption per unit reaction time and Pd mass in the linear region of RHC curve (Fig. 7).
Selectivity at RHC of about 0.95.
b
butyl- and 2-amyl-5,6,7,8-tetrahydroanthraquinone, H TBAQ
4
References
and H AAQ) and AN (2-tert-butyl- and 2-amyl-anthrone, TBAN
4
and AAN). As can be seen in Table 2, the selectivity to the target
products and by-products over functionalized and unfunction-
alized catalysts is very close, which is similar to the results of the
EAQ hydrogenation. Moreover, the selectivity of TBAQ and AAQ
hydrogenation is also very close.
1 R. Guan, X. Yuan, Z. Wu, L. Jiang, Y. Li and G. Zeng, Chem.
Eng. J., 2018, 339, 519–530.
2 R. Ciriminna, L. Albanese, F. Meneguzzo and M. Pagliaro,
ChemSusChem, 2016, 9, 3374–3381.
3 Y. Guo, C. Dai and Z. Lei, Chem. Eng. Process., 2019, 136, 211–
225.
4
S. Yang, A. Verdaguer-Casadevall, L. Arnarson, L. Silvioli,
ˇ
´
4
Conclusions
V. Colic, R. Frydendal, J. Rossmeisl, I. Chorkendorff and
I. E. L. Stephens, ACS Catal., 2018, 8, 4064–4081.
H. Li, B. Zheng, Z. Pan, B. Zong and M. Qiao, Front. Chem.
Sci. Eng., 2017, 12, 124–131.
PTES functionalized SBA-15 was synthesized by the co-
condensation method and used as the support for prepara-
tion of Pd catalyst. The hydrophilicity/hydrophobicity and
pore size of catalysts were shown to be greatly affected by the
pre-hydrolysis time of TEOS. The organic functional groups
in SBA-15 support synthesized at the pre-hydrolysis time of
5
6
7
8
9
H. Yao, C. Shen, Y. Wang and G. Luo, RSC Adv., 2016, 6,
23942–23948.
A. Drelinkiewicz and A. Waksmundzka-G ´o ra, J. Mol. Catal. A:
Chem., 2006, 246, 167–175.
R. Kosydar, A. Drelinkiewicz and J. P. Ganhy, Catal. Lett.,
2
h trend to distribute on its outer surface and the Pd catalyst
prepared on it (Pd/P-2) has the highest hydrophobicity and
largest pore size. The combination of the high hydropho-
bicity and largest pore size benets the activity of catalyst.
The highest initial hydrogen consumption rate for the EAQ
2010, 139, 105–113.
E. Yuan, C. Wu, X. Hou, M. Dou, G. Liu, G. Li and L. Wang, J.
Catal., 2017, 347, 79–88.
1
0 R. E. Albers, M. Nystr ¨o m, M. Siverstr ¨o m, A. Sellin,
A.-C. Dellve, U. Andersson, W. Herrmann and T. Berglin,
Catal. Today, 2001, 69, 247–252.
hydrogenation (0.2 mol H
over Pd/P-2.
2
per g Pd per min) was obtained
The positive effect of support hydrophobicity on catalyst
activity increases with the length of alkyl side chain in 2-alkyl-
anthraquinone. The initial hydrogen consumption rate for the
AAQ hydrogenation obtained over Pd/P-2 increased by 150.0%
compared with that over the catalyst prepared on unfunction-
alized SBA-15 support.
1
1
1
1
1 P. Tang, Y. Chai, J. Feng, Y. Feng, Y. Li and D. Li, Appl. Catal.,
A, 2014, 469, 312–319.
2 X. Chen, S. Wang, J. Zhuang, M. Qiao, K. Fan and H. He, J.
Catal., 2004, 227, 419–427.
3 E. Yuan, C. Wu, G. Liu, G. Li and L. Wang, J. Ind. Eng. Chem.,
2
018, 66, 158–167.
4 N. Wang, Q. Ma, E. Yuan and L. Wang, Trans. Tianjin Univ.,
019, 25, 595–602.
15 X. Li, H. Su, G. Ren and S. Wang, RSC Adv., 2015, 5, 100968–
00977.
6 R. Hong, J. Feng, Y. He and D. Li, Chem. Eng. Sci., 2015, 135,
74–284.
2
Conflicts of interest
1
There are no conicts to declare.
1
1
1
2
7 R. Kosydar, A. Drelinkiewicz, E. Lalik and J. Gurgul, Appl.
Catal., A, 2011, 402, 121–131.
8 H. Chen, D. Huang, X. Su, J. Huang, X. Jing, M. Du, D. Sun,
L. Jia and Q. Li, Chem. Eng. J., 2015, 262, 356–363.
Acknowledgements
This work is supported by nancial support from the National
Natural Science Foundation of China (21676184).
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 34581–34588 | 34587

View Article Online
RSC Advances
Paper
1
2
2
2
2
2
2
2
2
2
9 A. P. A. Drelinkiewicz, R. Kangas and R. Laitinen, Catal. Lett., 35 F. Ulusal, E. Er u¨ nal and B. G u¨ zel, J. Nanopart. Res., 2018, 20,
004, 94, 157–170. 219.
0 J.-T. Feng, H.-Y. Wang, D. G. Evans, X. Duan and D.-Q. Li, 36 L. Li, L.-X. Zhang, J.-L. Shi, J.-N. Yan and J. Liang, Appl.
Appl. Catal., A, 2010, 382, 240–245. Catal., A, 2005, 283, 85–89.
1 X. Li, H. Su, G. Ren and S. Wang, Appl. Catal., A, 2016, 517, 37 T. Ji, C. Ma, L. Brisbin, L. Mu, C. G. Robertson, Y. Dong and
68–175. J. Zhu, Appl. Surf. Sci., 2017, 399, 565–572.
2 G. Bombi, S. Lora, M. Zancato, A. A. D'Archivio, K. Jerabek 38 R. He, Z. Wang, L. Tan, Y. Zhong, W. Li, D. Xing, C. Wei and
and B. Corain, J. Mol. Catal. A: Chem., 2003, 194, 273–281. Y. Tang, Microporous Mesoporous Mater., 2018, 257, 212–221.
3 A. Biffis, R. Ricoveri, S. Campestrini, M. Kralik, K. Jeroea¡bek 39 M. M. Abolghasemi, S. Hassani and M. Bamorowat,
and B. Corain, Chem.–Eur. J., 2002, 8, 2962–2967. Microchim. Acta, 2015, 183, 889–895.
4 A. Drelinkiewicz, A. Waksmundzka-G ´o ra, J. W. Sobczak and 40 J. Huang, M. Ye, Y. Qu, L. Chu, R. Chen, Q. He and D. Xu, J.
J. Stejskal, Appl. Catal., A, 2007, 333, 219–228. Colloid Interface Sci., 2012, 385, 137–146.
5 Q. Ma, N. Wang, G. Liu and L. Wang, Microporous 41 H. Yang, F. Li, C. Shan, D. Han, Q. Zhang, L. Niu and
Mesoporous Mater., 2019, 279, 245–251. A. Ivaska, J. Mater. Chem., 2009, 19, 4632–4638.
6 A. S. M. Chong and X. S. Zhao, J. Phys. Chem. B, 2003, 107, 42 J. Kecht, A. Schlossbauer and T. Bein, Chem. Mater., 2008, 20,
2650–12657. 7207–7214.
7 D. Rath, S. Rana and K. M. Parida, RSC Adv., 2014, 4, 57111– 43 T. Krajnovic, D. Maksimovic-Ivanic, S. Mijatovic, D. Draca,
2
1
1
5
7124.
K. Wolf, D. Edeler, L. A. Wessjohann and
G. N. Kaluderovic, Nanomaterials, 2018, 8, 322.
44 Y. Xia, Z. Yang, R. Zhang, Y. Xing and X. Gui, Fuel, 2019, 239,
145–152.
8 X. Niu, X. Zhou, Z. Lv, Y. Gao, J. Zhang and H. Wang, Mater.
Res. Innovations, 2016, 20, 151–155.
9 M. Barczak, J. Solid State Chem., 2018, 258, 232–242.
2
3
0 H. A. Khan, A. Jaleel, P. Natarajan, S. Yoon and K.-D. Jung, 45 J. M. Rosenholm and M. Lind ´e n, Chem. Mater., 2007, 19,
Int.
J.
Hydrogen
Energy,
2019,
DOI:
10.1016/
5023–5034.
j.ijhydene.2019.05.139.
1 Y. Zhu, Z. Cheng, Q. Xiang, Y. Zhu and J. Xu, Sens. Actuators,
B, 2018, 256, 888–895.
46 H. G. Hosseini, E. Doustkhah, M. V. Kirillova, S. Rostamnia,
G. Mahmoudi and A. M. Kirillov, Appl. Catal., A, 2017, 548,
96–102.
3
32 Z. Zhang, Y. Luo, Y. Guo, W. Shi, W. Wang, B. Zhang, 47 X. Chen, J. Catal., 2003, 220, 254–257.
R. Zhang, X. Bao, S. Wu and F. Cui, Chem. Eng. J., 2018, 48 A. Drelinkiewicz, A. Waksmundzkagora, W. Makowski and
344, 114–123.
J. Stejskal, Catal. Commun., 2005, 6, 347–356.
3
3
3 X. Wang, Y.-H. Tseng, J. C. C. Chan and S. Cheng, 49 E. Yuan, X. Ren, L. Wang and W. Zhao, Front. Chem. Sci. Eng.,
Microporous Mesoporous Mater., 2005, 85, 241–251.
4 J. Sun, J. Zhang, H. Fu, H. Wan, Y. Wan, X. Qu, Z. Xu, D. Yin
and S. Zheng, Appl. Catal., B, 2018, 229, 32–40.
2017, 11, 177–184.
34588 | RSC Adv., 2019, 9, 34581–34588
This journal is © The Royal Society of Chemistry 2019