Catalytic dehydrogenation of formic acid over palladium nanoparticles immobilized on fibrous mesoporous silica KCC-1

Article abstract of DOI:10.1016/S1872-2067(19)63303-6

Uniform Pd nanoparticles immobilized on N-(3-trimethoxysilylpropyl)diethylenetriamine (PDETA)-functionalized fibrous silica KCC-1 (Pd/KCC-1-PDETA) were prepared with a mean Pd particle size of 2.8 nm. After characterization using powder X-ray diffraction, X-ray photoelectron spectroscopy, and N₂ adsorption-desorption isotherms, Pd/KCC-1-PDETA was used as catalyst for additive-free dehydrogenation of formic acid to produce H₂. Pd nanoparticle catalysts supported on two other mesoporous silica materials (MSF and KIT-6) were also synthesized to examine how the support affects the reaction. Among the three catalysts, Pd/KCC-1-PDETA exhibited significant catalytic activity (a turnover frequency of 332 h^?1 at 323 K and 100% selectivity towards hydrogen), owing to the unique fibrous morphology of KCC-1 and the presence of amine groups that reduced the Pd particle size and improved the access of reactant to the catalytically active Pd sites. The influence of Pd loading (2–10 wt.%), reaction temperature, and reaction time was also examined for the dehydrogenation reaction. Pd/KCC-1-PDETA was recovered easily after the reaction and showed good reusability up to five times without any significant loss in catalytic performance.

Full text of DOI:10.1016/S1872-2067(19)63303-6

Chinese Journal of Catalysis 40 (2019) 1704–1712
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article (Special Issue on Celebrating the 70th Anniversary of Dalian Institute of Chemical Physics, CAS)
Catalytic dehydrogenation of formic acid over palladium
nanoparticles immobilized on fibrous mesoporous silica KCC-1
Siqian Zhang, Yingjie Qian, Wha-Seung Ahn *
Department of Chemistry and Chemical Engineering, Inha University, Incheon 402-751, Republic of Korea
A R T I C L E I N F O
A B S T R A C T
Article history:
Uniform Pd nanoparticles immobilized on N-(3-trimethoxysilylpropyl)diethylenetriamine
(PDETA)-functionalized fibrous silica KCC-1 (Pd/KCC-1-PDETA) were prepared with a mean Pd
particle size of 2.8 nm. After characterization using powder X-ray diffraction, X-ray photoelectron
spectroscopy, and N2 adsorption-desorption isotherms, Pd/KCC-1-PDETA was used as catalyst for
additive-free dehydrogenation of formic acid to produce H2. Pd nanoparticle catalysts supported on
two other mesoporous silica materials (MSF and KIT-6) were also synthesized to examine how the
support affects the reaction. Among the three catalysts, Pd/KCC-1-PDETA exhibited significant cat-
alytic activity (a turnover frequency of 332 h−1 at 323 K and 100% selectivity towards hydrogen),
owing to the unique fibrous morphology of KCC-1 and the presence of amine groups that reduced
the Pd particle size and improved the access of reactant to the catalytically active Pd sites. The in-
fluence of Pd loading (2–10 wt.%), reaction temperature, and reaction time was also examined for
the dehydrogenation reaction. Pd/KCC-1-PDETA was recovered easily after the reaction and
showed good reusability up to five times without any significant loss in catalytic performance.
© 2019, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Received 9 December 2018
Accepted 14 January 2019
Published 5 November 2019
Keywords:
Fibrous nanosilica
KCC-1
Palladium nanoparticles
Hydrogen storage
Formic acid dehydrogenation
Published by Elsevier B.V. All rights reserved.
1. Introduction
among these, is a convenient and safe hydrogen carrier owing
to its high hydrogen content, non-toxicity, outstanding stability,
Hydrogen is one of the most promising power sources for
clean and sustainable energy supply, with the main advantages
of easy conversion to electric or mechanical energy, high ener-
gy density (3 times higher than that of fossil fuels), and pro-
ducing water as the only product after reaction with oxygen [1].
Currently, the main obstacles to commercial utilization of hy-
drogen as a power source are controllable storage and efficient
release of hydrogen. In this regard, various chemical hydrogen
storage materials including formic acid (FA), ammonia borane,
and sodium borohydride were investigated to replace the clas-
sic pressurization or low-temperature liquefaction [2]. FA,
easy regeneration, and availability (produced as a major by-
product of the biomass conversion process). FA dehydrogena-
tion reaction releases hydrogen and CO2 as a by-product (eqn.
(1)) in the presence of a catalyst [3]. The dehydration reaction
(eqn. (2)) can also occur to produce CO as an impurity, which is
poisonous to the novel metal catalysts in hydrogen fuel cells
[4].
HCOOH(l) → CO2(g) + H2(g), ΔG298 = –48.8 kJ mol–1 (1)
HCOOH(l) → H2O(l) + CO(g), ΔG298 = –28.5 kJ mol–1 (2)
Even though several homogeneous catalysts were reported
for FA dehydrogenation [3], heterogeneous catalysts are pre-
* Corresponding author. Tel: +82-328607466; Fax: +82-328720959; E-mail: whasahn@inha.ac.kr
This work was supported by C1 Gas Refinery Program (2015M3D3A1A01064899) by the Ministry of Science, ICT & Future Planning, and also by
Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education (Grant No.:
NRF-2015R1A4A1042434).
DOI: S1872-2067(19)63303-6 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 40, No. 11, November 2019

Siqian Zhang et al. / Chinese Journal of Catalysis 40 (2019) 1704–1712
1705
ferred due to their better reusability and recoverability for
practical applications. Some of the heterogeneous catalysts
demonstrated satisfactory catalytic activity and selectivity for
H2, and various monometallic and multi-metallic nanoparticles
such as Pd [5,6], Au [7], AgPd [8], PdNi@Ni [9], and CoAuPd
[10] have been reported so far for FA dehydrogenation reaction
at low temperatures sometimes even without using additives
(such as sodium formate, triethylamine, and others). Song et al.
[6] reported that finely-dispersed Pd nanoparticles deposited
on amine-functionalized graphene oxide exhibited a good
turnover frequency (TOF) of 3810 h–1 in a FA-sodium formate
system at room temperature. Ojeda and Iglesia [7] prepared a
Au-deposited Al2O3 catalyst for dehydrogenation of FA at 350 K,
showing better catalytic activity than Pt-deposited Al2O3. Qin
and co-workers [9] showed that the introduction of nickel
could improve the catalytic activity of Pd nanoparticles in FA
aqueous solution, and the resultant PdNi@Ni nanoparticles
gave a high TOF of 577 h–1 in a mixture of FA and sodium for-
mate at room temperature. Among the various metal nanopar-
ticles, Pd-based nanoparticles have been mostly employed as
catalyst for hydrogen release in FA dehydrogenation because of
their high catalytic activity and stability.
In addition to the selection of active metal species, the de-
sign and/or selection of a support material also strongly affect
the catalytic activity of Pd nanoparticles in FA dehydrogenation
[11]. However, only limited cases of solid-supported palladium
nanoparticle systems have been tested for FA dehydrogenation
up to now. Lee and co-workers [12] used a mesoporous silica
supported Pd-MnOx nanocatalyst system for H2 release from FA
at room temperature, and reported excellent FA decomposition
with a TOF of 540 h–1. More recently, Navlani-García and
co-workers [13] used Pd deposited on zeolite (H-BETA) but
observed a TOF value of only 64 h–1. It was envisaged that a
support with an open pore structure would help to improve the
catalytic performance of Pd catalysts by ensuring high accessi-
bility of the supported Pd nanoparticles to the reactant mole-
cules [14]. In this case, KCC-1, which possesses an open pore
structure and easy accessibility owing to its unique fibrous
morphology, was selected as a support for Pd nanoparticles
[15]. KCC-1 can be synthesized in a reverse micelle template
process in organic solvent [16]. Some papers have reported
KCC-1 as an effective catalyst support material for the transfer
hydrogenation of alkene [14], Suzuki coupling reaction [17],
reduction of 4-nitrophenol [18], and dehydration of fructose
[19] as well as working as an adsorbent for dyes [20] and CO2
capture [21].
2 wt.% Pd/KCC-1-PDETA exhibited excellent catalytic activity
with nearly 100% hydrogen selectivity towards FA dehydro-
genation.
2. Experimental
2.1. Chemicals
Tetraethylorthosilicate (TEOS), cetyltrimethylammonium
bromide, 1-butanol, P123 (EO20PO70EO20, Mv = 5800), acetic
acid, ammonium fluoride, mesitylene, sodium silicate,
N-(3-trimethoxysilylpropyl)diethylenetriamine, sodium tetra-
chloropalladate(II) (Na2PdCl4), sodium borohydride, formic
acid, HCl solution (35 wt.%), toluene, and ethanol were pur-
chased from Sigma Aldrich. Urea was purchased from DUKSAN
in Korea. All the chemicals were of reagent grade and used
without further purification. Deionized water was used.
2.2. Synthesis of KCC-1
KCC-1 was prepared following the literature procedure [16]
with minor modification. Firstly, TEOS (4.7 mL) was added into
a solution of 1-butanol (2.2 mL) and toluene (51 mL). A solu-
tion of cetyltrimethylammonium bromide (1.7 g) and urea (1.1
g) in water (52 mL) was then introduced. This mixture was
vigorously stirred for 30 min at room temperature, followed by
heating at 120 °C (393 K) for 4 h. The white product was col-
lected by centrifugation, washed with water, and dried at 80 °C
(353 K) for 12 h. After that, the product was calcined at 560 °C
(833 K) for 6 h to produce template-free KCC-1.
To study the effect of the support on FA dehydrogenation,
MSF and KIT-6 were synthesized according to the methods
shown in the Supporting Information (SI).
2.3. Amine functionalization of KCC-1, MSF, and KIT-6 silica
supports
Silica-PDETA was synthesized according to the procedure
reported in the literature [24]. In a typical synthesis, KCC-1,
MSF or KIT-6 (0.5 g) was dispersed in toluene (30 mL) by son-
ication for 30 min, and PDETA (1 mmol) was added under stir-
ring at room temperature. After stirring the mixture at 80 °C
(353 K) for 24 h, the product was recovered by centrifugation,
washed with ethanol several times, and dried at 60 °C (333 K)
for 12 h. The samples are referred to as KCC-1-PDETA,
MSF-PDETA, and KIT-6-PDETA, respectively.
In this work, Pd nanoparticles with different metal loadings
on the N-(3-trimethoxysilylpropyl), diethylenetriamine
(PDETA)-functionalized KCC-1 (Pd/KCC-1-PDETA) were pre-
pared and tested for FA dehydrogenation reaction without
additives at 323 K. The catalytic performance of
Pd/KCC-1-PDETA was compared with those Pd nanoparticles
supported on mesoporous silica foam (MSF) [22] and KIT-6
[23], which have been widely applied as catalyst/support be-
cause of their promising textural properties in 3-D pore struc-
tures. The influence of reaction temperature and reaction time,
and the catalyst recyclability was also examined. The resultant
2.4. Synthesis of Pd nanoparticles immobilized on
amine-functionalized silica supports
Pd/silica-PDETA was prepared according to the procedure
reported in the literature [25]. In the typical synthesis, sili-
ca-PDETA (0.5 g) was dispersed in water (50 mL) by sonication
for 5 min followed by stirring for 10 min at room temperature.
Na2PdCl4 solution (2 mL, 0.05 mol/L in water) was introduced,
and the mixture was sonicated for 30 min followed by stirring
for 2 h at room temperature. Sodium borohydride solution (1

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Siqian Zhang et al. / Chinese Journal of Catalysis 40 (2019) 1704–1712
mL, 1 mol/L in water) was then introduced for reduction. After
stirring the mixture for 2 h, the prepared catalyst was recov-
ered by centrifugation, washed with water and ethanol several
times, and dried at 80 °C (353 K) for 16 h. These samples were
Pd/MSF-PDETA, and Pd/KIT-6-PDETA catalysts were found to
be 1.93 wt.%, 1.75 wt.%, and 1.56 wt.%, respectively (Table 1)
by ICP-OES. The actual Pd loading amounts on
Pd/KCC-1-PDETA are close to the expected loadings based on
the Pd precursors (2 wt.%) used during the preparation. The
Pd contents on MSF-PDETA and KIT-6-PDETA were somewhat
lower than the expected values due to the lower N contents
(low functionalized PDETA) on these supports as detected by
EA (Table 1).
designated as
2
wt.% Pd/KCC-1-PDETA,
2
wt.%
Pd/MSF-PDETA, and 2 wt.% Pd/KIT-6-PDETA, respectively.
By changing the amount of the added Na2PdCl4 solution, 5
wt.% and 10 wt.% Pd/KCC-1-PDETA were also prepared fol-
lowing the same method.
The crystalline structure of the as-prepared Pd catalysts on
different silica supports was examined by powder XRD as
shown in Figs. 1 and S1. The pristine silica materials showed a
broad peak at 2θ = 22° corresponding to their amorphous na-
ture (Figs. 1(a), S2(a-1), and S2 (b-1)). The materials after
PDETA grafting and Pd deposition showed similar XRD pat-
terns to that of the respective pristine silica supports. The
PDETA-functionalized silica supports with 2 wt.% loaded Pd
did not show any extra peak in the region of 35°–80° due to
high dispersion of Pd nanoparticles [27], but those loaded with
5 and 10 wt.% Pd showed a characteristic Pd(111) peak at
39.1° (Fig. 1(d–e)).
The morphology and particle size of the silica-supported Pd
catalysts were characterized using FE-TEM. As shown in Fig.
2(a), the Pd nanoparticles in 2 wt.% Pd/KCC-1-PDETA were
well-dispersed on KCC-1 and no coagulated Pd nanoparticles
were detected, proving a strong contact between the Pd nano-
particles and the silica support [28]. The fibrous morphology of
KCC-1 was maintained without any structural degradation after
amine functionalization and Pd loading. The Pd particle size
distribution, derived from the image in Fig. 2(a), indicates that
about 90% of Pd nanoparticles are in the size range of 2–4 nm
and the mean diameter of the Pd nanoparticles is ~2.8 nm (Fig.
2(b)). It is likely that the high nitrogen content on the KCC-1
support (Table 1) limits the mobility and the agglomeration of
the Pd particles. Pd nanoparticles deposited in 5 wt.%
Pd/KCC-1-PDETA and 10 wt.% Pd/KCC-1-PDETA had mean
particle sizes of 5.6 and 8.0 nm, respectively, and some aggre-
gated Pd nanoparticles were observed (Fig. 2(c–f)). Fig. 2(g)
and 2(i) are the FE-TEM images of the as-prepared 2 wt.%
Pd/MSF-PDETA and 2 wt.% Pd/KIT-6-PDETA, which showed
2.5. Characterization
The obtained Pd catalysts were characterized by various in-
strumentation, and the experimental details are described in SI.
2.6. Catalytic FA dehydrogenation
Catalytic performance in FA dehydrogenation was evaluated
in a 50 mL three-necked round flask with water jacket, using an
experimental set up shown in Fig. S1. In a typical experiment, a
predetermined amount of Pd catalyst (mole ratio of Pd/FA =
0.01) and water (15 mL) were added in the flask, which was
connected to a pressure-equalization funnel (containing 5
mmol FA), a gas burette, and Ar gas line. Before starting the
experiment, the reaction medium was vigorously stirred for 30
min to obtain thermal equilibrium under inert conditions. The
reaction was initiated after injecting FA (5 mmol) into the flask
under vigorous stirring. The reaction temperature was main-
tained at 323 K by using the water circulator, and the volume of
gas produced was measured by water displacement in the gas
burette.
3. Results and discussion
3.1. Catalyst characterization
The silica-PDETA supports were prepared via
a
post-synthetic functionalization method to immobilize the Pd
nanoparticles. PDETA plays the role of a tethering ligand to
bind the Pd nanoparticles with high dispersion and uniform
particle size [26]. The Pd contents in Pd/KCC-1-PDETA,
Table 1
Physicochemical properties of the silica-supported Pd catalysts.
Fraction of Pd
SBET
(m2/g) (wt.%) (wt.%)
N a Pd loading b
species c (%)
Catalyst
Pd2+
—
Pd0
—
—
70
61
60
—
—
60
—
—
65
KCC-1
KCC-1-PDETA
2 wt.% Pd/KCC-1-PDETA
5 wt.% Pd/KCC-1-PDETA
10 wt.% Pd/KCC-1-PDETA
MSF
MSF-PDETA
2 wt.% Pd/MSF-PDETA
KIT-6
520
231
168
114
90
550
290
236
714
300
248
—
—
—
1.93
4.89
9.80
—
6.13
6.13
6.13
6.13
—
—
30
39
40
—
5.04
5.04
—
—
1.75
—
—
40
—
Fig. 1. Powder X-ray diffraction patterns for (a) KCC-1, (b)
KIT-6-PDETA
4.15
4.15
—
1.56
—
35
KCC-1-PDETA, (c)
Pd/KCC-1-PDETA, and (e) 10 wt.% Pd/KCC-1-PDETA.
2
wt.% Pd/KCC-1-PDETA, (d)
5
wt.%
2 wt.% Pd/KIT-6-PDETA
a Estimated by EA. b Estimated by ICP-OES. c Estimated by XPS.

Siqian Zhang et al. / Chinese Journal of Catalysis 40 (2019) 1704–1712
1707
sistent with the XRD and FE-TEM results.
To examine the textural properties of the as-prepared cata-
lysts, N2 adsorption-desorption measurements were made at
77 K. The obtained isotherms of KCC-1 showed a combination
of type I and IV isotherms with H1-type hysteresis (Fig. 3(a)).
The surface area of PDETA-functionalized KCC-1 decreased
from 520 m2/g (KCC-1) to 231 m2/g, confirming the successful
grafting of amine species. After the immobilization of 2, 5, and
10 wt.% Pd particles, the surface areas further decreased to
168, 114, and 90 m2/g, respectively, accompanied by the dis-
appearance of the pores around 2.2 nm in pristine KCC-1 (Fig.
3(b)). And these relatively small decreases in surface area
could be attributed to the unique fibrous structure of KCC-1, in
which the pores are not completely blocked by the introduced
amines and Pd nanoparticles owing to the open structure [25].
The same tendency was also observed in other supports used
in this study, and the surface areas of Pd/MSF-PDETA and
Pd/KIT-6-PDETA also decreased from the respective pristine
materials (see Fig. S4).
Fig. 4(a) shows the XPS spectra for
2
wt.%
Pd/KCC-1-PDETA, which confirmed the presence of Si, O, C, N,
and Pd. XPS analysis also allowed determination of the elec-
tronic states of Pd on different silica supports (Fig. 4(b–f)). The
deconvoluted Pd 3d spectrum of 2 wt.% Pd/KCC-1-PDETA (Fig.
4(b)) showed two doublet peaks: the strong peaks at 339.9 and
450
400 (a)
(1)
(2)
(3)
(4)
(5)
350
300
250
200
150
100
50
0
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (p/p0)
Fig. 2. FE-TEM images of the as-synthesized catalysts and the corre-
sponding particle size distributions of Pd NPs. (a and b) 2 wt.%
Pd/KCC-1-PDETA; (c and d) 5 wt.% Pd/KCC-1-PDETA; (e and f) 10
wt.% Pd/KCC-1-PDETA; (g and h) 2 wt.% Pd/MSF-PDETA; (i and j) 2
wt.% Pd/KIT-6-PDETA.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
(b)
(5)
(4)
(3)
that Pd nanoparticles were homogeneously dispersed on the
respective support surfaces (MSF-PDETA and KIT-6-PDETA)
with the mean particle size of 4.9 and 14.5 nm (Fig. 2(h) and
2(j)). These results clearly illustrated that the open morphology
of KCC-1 has a beneficial effect in minimizing the Pd particle
size due to highly accessible surface area [14]. HAADF-STEM
with EDX analysis and the corresponding elemental mapping
(2)
(1)
0
20
40
60
80
100
Pore size (nm)
was done to examine the composition of
2
wt.%
Fig. 3. (a) N2 adsorption-desorption isotherms at 77 K and (b) pore size
distribution curves of (1) KCC-1, (2) KCC-1-PDETA, (3) wt.%
Pd/KCC-1-PDETA, (4) 5 wt.% Pd/KCC-1-PDETA, and (5) 10 wt.%
Pd/KCC-1-PDETA.
Pd/KCC-1-PDETA. Closer inspection of the elemental mapping
image for Pd in Fig. S3(e) showed that the Pd atoms were uni-
formly distributed over the entire KCC-1 support, which is con-
2

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Siqian Zhang et al. / Chinese Journal of Catalysis 40 (2019) 1704–1712
Fig. 4. (a) XPS survey spectrum of 2 wt.% Pd/KCC-1-PDETA, and Pd 3d XP spectra of (b) 2 wt.% Pd/KCC-1-PDETA, (c) 5 wt.% Pd/KCC-1-PDETA, (d)
10 wt.% Pd/KCC-1-PDETA, (e) 2 wt.% Pd/MSF-PDETA, and (f) 2 wt.% Pd/KIT-6-PDETA.
334.6 eV correspond to Pd(0) 3d3/2 and 3d5/2, respectively [29],
and the low intensity peaks at 337.5 and 342.8 eV were at-
tributed to Pd(2+) 3d3/2 and 3d5/2, respectively [29]. These
results indicate that 2 wt.% Pd/KCC-1-PDETA still has almost
30% of Pd2+ ion (Table 1). The existence of Pd2+ species here
indicates that some of the Pd precursor interacted strongly
with the electron-enriched nitrogen on KCC-1 support due to
the strong complexing ability of nitrogen species, and that it
was difficult to reduce all the Pd2+ ions [30]. The positions of
the Pd 3d peaks and the amount of Pd2+ species for all other
samples are shown in Fig. 4 and Table 1, respectively. The
amounts of Pd2+ ions in the other as-prepared catalysts were
higher than that in 2 wt.% Pd/KCC-1-PDETA.
3.2. Dehydrogenation of HCOOH
The catalytic performance of the Pd-supported silica cata-
lysts towards FA decomposition in the absence of additives was
examined, and the obtained results are given in Fig. 5. Fig. 5(a)
shows the total volume of the generated gas (CO2 + H2) versus
reaction time in the FA aqueous solution (5 mmol FA, nPd/nFA
=
0.01, 15 mL H2O) in the presence of 2 wt.% Pd/KCC-1-PDETA, 2
Fig. 5. Total gas volume (CO2+H2) versus time (5 mmol FA, nPd/nFA = 0.01, 15 mL water, 323 K) catalyzed by (a) 2 wt.% Pd/KCC-1-PDETA (1), 2 wt.%
Pd/MSF-PDETA (2), and 2 wt.% Pd/KIT-6-PDETA (3), and (b) 2 wt.% Pd/KCC-1-PDETA (1), 5 wt.% Pd/KCC-1-PDETA (2), and 10 wt.%
Pd/KCC-1-PDETA (3).

Siqian Zhang et al. / Chinese Journal of Catalysis 40 (2019) 1704–1712
1709
reported for FA decomposition reaction (Table 2). By compari-
son, the gas production profiles of 2 wt.% Pd/MSF-PDETA and
2 wt.% Pd/KIT-6-PDETA catalysts showed lower catalytic ac-
tivities, although H2 was steadily released from the reaction
mixture. The TOF of 2 wt.% Pd/MSF-PDETA and 2 wt.%
Pd/KIT-6-PDETA up to 20% conversion of FA were only 147
Table 2
TOF values for FA decomposition over various heterogeneous catalysts
without any additives.
Temperature (K) TOF (h–1) Reference
Catalyst
2 wt.% Pd/KCC-1-PDETA
323
313
303
298
323
323
323
323
323
323
323
323
323
323
323
313
337
298
298
298
298
298
298
298
298
296
332 a
197
151
122 a
147a
97 a
242 a
222 a
1300 a
525
382
252
230
59
This work
This work
This work
This work
This work
This work
This work
This work
[40]
and 97 h–1, respectively, and the TOF of
2 wt.%
Pd/KCC-1-PDETA was almost 2 and 3 times higher than that of
2 wt.% Pd/MSF-PDETA and 2 wt.% Pd/KIT-6-PDETA, respec-
tively. This difference is possibly due to the higher amount of
the electron-rich nitrogen, smaller Pd particle size, and fibrous
structure of KCC-1 that allowed more FA to access the catalyti-
cally active Pd sites [23,31–34]. The nPd/nFA was kept close to
0.01 in all three catalysts, and therefore the Pd loading differ-
ence is not a factor when comparing the catalytic activities.
Since some other researchers had used far higher Pd load-
ings than 2 wt.% [12,31,35], Pd/KCC-1-PDETA with 5 wt.% and
10 wt.% Pd were also prepared to investigate how the Pd
loading affects the catalytic activity of Pd/KCC-1-PDETA. FA
decomposition tests were carried out using these catalysts at
the same FA concentration and temperature as mentioned
above, and the gas evolution profiles are presented in Fig. 5(b).
For the 5 wt.% and 10 wt.% Pd loadings on KCC-1-PDETA, the
volumes of released gas mixture were 205 and 175 mL with the
TOF of 242 and 222 h–1, respectively (Fig. 5(b-2) and (b-3)).
The decreased catalytic activity with increased Pd loading on
KCC-1-PDETA seems to be a consequence of the bigger particle
size and agglomeration of Pd nanoparticles [30] as shown in
Fig. 2. Also, Fig. 4 and Table 1 show that at higher Pd loadings,
the portion of the unreduced Pd2+ against Pd0 was higher,
which contributes to a lower catalytic activity [36]. Therefore, 2
wt.% Pd loaded on KCC-1-PDETA was used for further experi-
ments in FA dehydrogenation reaction.
2 wt.% Pd/MSF-PDETA
2 wt.% Pd/KIT-6-PDETA
5 wt.% Pd/KCC-1-PDETA
10 wt.% Pd/KCC-1-PDETA
Pd MnOx/NH2-SiO2
PdAg/NH2-UiO-66
PdAg/C
[31]
[8]
Ag@Pd/C
PdAu/C
Pd/zeolite
Pd/MCTP-1
PdAgMn/NH2-SiO2
PdAg/resin
[41]
[42]
[13]
[43]
52
1430 a
820
1269 a
90
98 a
89
85
80 a
12
53
[44]
[45]
[46]
[47]
[48]
[49]
[50]
Pd/NH2-KIE-6
PdAg/C
PdMn/NH2-KIE-6
Au@Pd/N-rGO
CoAuPd/DNA-rGO
CoAuPd/C
[10]
[51]
[52]
[53]
NiAuPd/C
AuPd-CeO2/N-rGO
Pd-poly(allyl-amine)
46
a TOF is calculated using the first 20% conversion of FA.
wt.% Pd/MSF-PDETA, and 2 wt.% Pd/KIT-6-PDETA at 323 K.
Clearly, 2 wt.% Pd/KCC-1-PDETA was the most active catalyst
among these three (Fig. 5(a–1)) and 245 mL of gas mixture
(CO2 + H2) evolved within 40 min, corresponding to complete
dehydrogenation of FA as calculated by eqn. (S1). The TOF
(eqn. (S2)) during the first 20% conversion of FA was calculat-
ed to be 332 h−1 without any additives at 323 K, which is com-
parable to the best palladium-based heterogeneous catalysts
The influence of temperature on FA dehydrogenation over 2
wt.% Pd/KCC-1-PDETA is shown in Fig. 6(a). An increase in the
volume of liberated gas from 110 to 245 mL was observed
when the temperature was increased from 298 to 323 K, illus-
trating that a higher reaction temperature promotes FA dehy-
drogenation. However, since the FA boiling point is 373 K, the
Fig. 6. (a) Total gas volume (CO2+H2) versus time from the reactant solution (5 mmol FA, nPd/nFA = 0.01, 15 mL water) catalyzed by 2 wt.%
Pd/KCC-1-PDETA at different temperatures and (b) the corresponding Arrhenius plot.

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Siqian Zhang et al. / Chinese Journal of Catalysis 40 (2019) 1704–1712
FA will evaporate at above 323 K, which limits the practical
application of hydrogen generation [37]. The rate constant k at
different temperatures was determined from the slope of the
linear portion of each plot in Fig. 6(a). The Arrhenius plot of lnk
vs. 1/T for 2 wt.% Pd/KCC-1-PDETA is shown in Fig. 6(b). The
obtained activation energy (Ea) is 37.15 kJ/mol, which is com-
parable to those of other previously reported catalysts
[5,35,38].
To confirm the absence of poisonous CO produced during
the reaction, the evolved gas was treated with a trap (5 mol/L
NaOH solution) at 323 K to remove CO2 (Fig. 7). The gas volume
decreased to half after the NaOH treatment, indicating that
practically CO-free hydrogen was evolved from FA dehydro-
genation over the 2 wt.% Pd/KCC-1-PDETA catalyst. GC analy-
sis detected only the signals of H2 and CO2 without CO (detec-
tion limit: ~10 ppm CO), which also confirmed the H2 selectivi-
ty of the catalyst for formic acid dehydrogenation.
Fig. 8. Recycle test of 2 wt.% Pd/KCC-1-PDETA in FA dehydrogenation
(5 mmol FA, nPd/nFA = 0.01, 15 mL water, 323 K).
Finally, the catalyst cycling experiment was conducted with
2 wt.% Pd/KCC-1-PDETA catalyst in the additive-free dehy-
drogenation of FA at 323 K (Fig. 8). At the end of each reaction
cycle, the Pd catalyst was recovered by filtration, washed with
water several times, and dried at 60 °C (333 K) for 12 h before
reuse. After the fifth run, the recovered catalyst showed about
7% decline in catalytic activity (Fig. 8), which can be ascribed to
a reduced number of active sites due to the Pd particles grown
in size from 2.8 nm (fresh) to 3.3 nm (reused) (Fig. S5) [39].
ICP-OES analysis after the first run showed no Pd leaching (de-
tection limit: ~0.01 ppm for Pd) into the solution.
under the same conditions. The Pd/KCC-1-PDETA exhibited the
best catalytic activity, with a TOF value of 332 h–1
and 100% of
H2 selectivity for FA dehydrogenation. This can be attributed to
the unique fibrous morphology of KCC-1, which helps to in-
crease the FA accessibility to the catalytically active palladium
nanoparticle sites in smaller size. The influence of Pd loading in
the FA dehydrogenation was also investigated, showing that a
sufficiently low loading of Pd resulted in smaller deposited Pd
nanoparticles on KCC-1-PDETA, which led to the production of
more H2 gas. Additionally, 2 wt.% Pd/KCC-1-PDETA could
maintain its catalytic activity after several recycles.
4. Conclusions
In summary, finely dispersed 2 wt.% Pd nanoparticles de-
posited on KCC-1 were successfully prepared with a mean par-
ticle size of 2.8 nm. The prepared sample was used as an effi-
cient, robust, and selective catalyst for FA decomposition
without additives at 323 K. The catalytic performance of Pd
nanoparticles deposited on KCC-1 was systematically evaluated
and compared with that of the Pd nanoparticles deposited on
conventional mesoporous silica materials (MSF and KIT-6)
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Graphical Abstract
Chin. J. Catal., 2019, 40: 1704–1712 doi: S1872-2067(19)63303-6
Catalytic dehydrogenation of formic acid over palladium nanoparticles
immobilized on fibrous mesoporous silica KCC-1
HCOOH
Pd/KCC-1-PDETA
Siqian Zhang, Yingjie Qian, Wha-Seung Ahn*
Inha University, Republic of Korea
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纤维状中孔硅胶KCC-1负载的钯纳米颗粒上甲酸催化脱氢反应
Siqian Zhang, Yingjie Qian, Wha-Seung Ahn *
仁荷大学化学与化学工程系, 仁川402-751, 韩国
摘要: 在N-(3-三甲氧基硅丙基)二乙烯三胺(PDETA)功能化的纤维状硅胶KCC-1上负载了均一的、平均粒径为2.8 nm的Pd
纳米粒子(Pd/KCC-1-PDETA), 采用粉末X射线衍射、X射线光电子能谱和N2吸附-脱附等温线对其进行了表征, 并将其作为
催化剂用于无添加剂的甲酸脱氢制H2的反应中. 同时还制备了另外两个中孔硅胶材料(MSF和KIT-6)负载的Pd纳米粒子,
以考察反应中催化剂的载体效应. 结果表明, Pd/KCC-1-PDETA催化剂表现出很高的催化性能(323 K时TOF值为332 h−1, 氢
气选择性100%). 这归结为KCC-1独特的纤维状形貌和胺基基团的存在, 从而降低了Pd颗粒尺寸, 促进了反应物与催化活
性 位 Pd 的 接 触 . 还 考 察 了 Pd 负 载 量 (2–10 wt%) 、 反 应 温 度 和 反 应 时 间 对 脱 氢 反 应 性 能 的 影 响 . 反 应 结 束 后 ,
Pd/KCC-1-PDETA催化剂容易回收, 可重复使用5次而催化性能未见明显下降, 表现出较好的重复使用性能.
关键词: 纤维状纳米硅胶; KCC-1; 钯纳米颗粒; 储氢; 甲酸脱氢
收稿日期: 2018-12-09. 接受日期: 2019-01-14. 出版日期: 2019-11-05.
*通讯联系人. 电话: +82-328-607466; 传真: +82-328-720959; 电子信箱: whasahn@inha.ac.kr
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).