Palladium nanoparticles supported on fibrous-structured silica nanospheres (KCC-1): An efficient and selective catalyst for the transfer hydrogenation of alkenes

Article abstract of DOI:10.1002/cctc.201402781

An efficient palladium catalyst supported on fibrous silica nanospheres (KCC-1) has been developed for the hydrogenation of alkenes and α,β-unsaturated carbonyl compounds, providing excellent yields of the corresponding products with remarkable chemoselectivity. Comparison (high-resolution TEM, chemisorption) with analogous mesoporous (MCM-41, SBA-15) silica-supported Pd nanocatalysts prepared under identical conditions, demonstrates the advantage of employing the fibrous KCC-1 morphology versus traditional supports because it ensures superior accessibility of the catalytically active cores along with excellent Pd dispersion at high metal loading. This morphology ultimately leads to higher catalytic activity for the KCC-1-supported nanoparticles. The protocol developed for hydrogenation is advantageous and environmentally benign owing to the use of HCOOH as a source of hydrogen, water as a solvent, and because of efficient catalyst recyclability and durability. The recycled catalyst has been analyzed by XPS spectroscopy and TEM showing only minor changes in the oxidation state of Pd and in the morphology after the reaction, thus confirming the robustness of the catalyst.

Full text of DOI:10.1002/cctc.201402781

DOI: 10.1002/cctc.201402781
Full Papers
Palladium Nanoparticles Supported on Fibrous-Structured
Silica Nanospheres (KCC-1): An Efficient and Selective
Catalyst for the Transfer Hydrogenation of Alkenes
Ziyauddin S. Qureshi,[a] Pradip B. Sarawade,[a, b] Matthias Albert,[d] Valerio D’Elia,*[a]
Mohamed N. Hedhili,[c] Klaus Kçhler,[d] and Jean-Marie Basset*[a]
An efficient palladium catalyst supported on fibrous silica
nanospheres (KCC-1) has been developed for the hydrogena-
tion of alkenes and a,b-unsaturated carbonyl compounds, pro-
viding excellent yields of the corresponding products with re-
markable chemoselectivity. Comparison (high-resolution TEM,
chemisorption) with analogous mesoporous (MCM-41, SBA-15)
silica-supported Pd nanocatalysts prepared under identical
conditions, demonstrates the advantage of employing the fi-
brous KCC-1 morphology versus traditional supports because
it ensures superior accessibility of the catalytically active cores
along with excellent Pd dispersion at high metal loading. This
morphology ultimately leads to higher catalytic activity for the
KCC-1-supported nanoparticles. The protocol developed for hy-
drogenation is advantageous and environmentally benign
owing to the use of HCOOH as a source of hydrogen, water as
a solvent, and because of efficient catalyst recyclability and du-
rability. The recycled catalyst has been analyzed by XPS spec-
troscopy and TEM showing only minor changes in the oxida-
tion state of Pd and in the morphology after the reaction, thus
confirming the robustness of the catalyst.
Introduction
Considerable progress has been made in the past decade in
the synthesis of mesoporous silica materials with controllable
shape, size, and pore structure.[1] The application of surfactant-
templated mesoporous silica materials with a pore size below
200 nm has been emphasized because of the potential use in
cell imaging, disease diagnosis, drug/gene/protein storage or
delivery, separations, and heterogeneous catalysis applica-
tions.[2] However, the performance, and therefore, the applica-
bility of such materials in catalysis is often hindered by the lim-
ited accessibility of the active sites within the porous structure,
which may be exasperated by factors such as clogging of the
pores and sintering of the active metal centers following ther-
mal treatment and chemical reaction.[3]
We have recently developed new, high surface area silica
nanospheres (KCC-1) with excellent textural properties (high
surface area, pore volume, and pore size), good thermal, hy-
drothermal, and mechanical properties.[1i] Remarkably, in spite
of the absence of a conventional porous structure,[4] KCC-1 dis-
plays high surface area and accessibility owing to its unprece-
dented fibrous morphology, which affords high performance
as a catalyst support.[5] In this study, we demonstrate how the
morphological properties of KCC-1 play a decisive role in en-
suring high accessibility of surface-supported Pd nanoparticles
even at high noble-metal loading and how this is reflected in
the catalytic performance of these nanocatalysts.
The reduction of CÀC multiple bonds by transition-metal-
catalyzed hydrogenation is one of the most relevant reactions
in organic chemistry.[6] Various efforts have been undertaken to
improve catalyst efficiency, selectivity, and versatility. In this
regard, complexes of transition metals such as rhodium,[7]
ruthenium,[8] palladium,[9] iridium,[10] and other metals[11] have
been used for this transformation. Among the available reduc-
tion protocols[12] catalytic transfer hydrogenation (CTH)[13] has
emerged as one of the most viable strategies because it does
not involve the use of flammable and explosive molecular hy-
drogen or metal-hydride donors. Some of the CTH methods
for the Pd-catalyzed chemoselective hydrogenation of olefinic
[a] Dr. Z. S. Qureshi, Dr. P. B. Sarawade, Dr. V. D’Elia, Prof. Dr. J.-M. Basset
Kaust Catalysis Center (KCC)
King Abdullah University of Science and Technology
Thuwal, 23955-6900 (Saudi Arabia)
E-mail: jeanmarie.basset@kaust.edu.sa
valerio.delia@kaust.edu.sa
[b] Dr. P. B. Sarawade
Department of Physics, University of Mumbai
Mumbai 400032 (India)
[c] Dr. M. N. Hedhili
Imaging and Characterization Laboratory
King Abdullah University of Science and Technology
KAUST, Thuwal 23955-6900 (Saudi Arabia)
bonds include homogeneous catalysts, such as Pd(OAc)2/
[14]
HCOONH4
and PdCl2/HCOOH (microwave).[15] However,
[d] Dr. M. Albert, Prof. Dr. K. Kçhler
Department of Chemistry
heterogeneous catalytic protocols appear more convenient
and sustainable because they allow facile product separation
and catalyst recycling. In this context, heterogeneous Pd cata-
lysts, such as Pd(OAc)2 dispersed on MCM-41,[16] Pd/C,[17] Pd/
Fe2O3,[18] and Pd-nanoparticles[19] have been used in combina-
Catalysis Research Center, Technische Universitaet Muenchen
Garching D-85748 (Germany)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201402781.
ChemCatChem 0000, 00, 0 – 0
1
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
These are not the final page numbers! ÞÞ

Full Papers
tion with various H donors for the title reaction. Nevertheless,
very few reports have appeared describing CTH promoted by
well-defined Pd nanoparticles immobilized on mesoporous
supports.[20] In continuation of our efforts on transfer hydroge-
nation by transition-metal catalysts,[21] the transfer hydrogena-
tion of alkenes and conjugated carbonyl compounds is report-
ed herein by using palladium nanoparticles supported on KCC-
1 as an efficient and recyclable catalyst, which has been ap-
plied within an environmentally benign protocol that employs
formic acid as a hydrogen donor and an aqueous medium as
a solvent.
Table 1. Physicochemical properties of the silica-supported palladium
nanocatalysts and of the precursor materials.
Entry Material
Surface area[a] BJH PV
BJH PS Pd loading
[nm]
[m2 gÀ1
]
[cm3 gÀ1
]
[wt%][b]
1
2
3
4
5
6
7
8
9
KCC-1
616
335
285
1005
628
572
698
286
237
1.44
0.71
0.52
0.88
0.24
0.23
0.83
0.39
0.33
9.7
7.3
7.0
2.8
2.5
2.4
5.8
4.7
4.6
KCC-1-NH2
Pd/KCC-1-NH2
MCM-41
MCM-41-NH2
Pd/MCM-41-NH2
SBA-15
13.8
16.9
13.4
SBA-15-NH2
Pd/SBA-15-NH2
The catalytic activity of the palladium particles supported on
the fibrous nanospheres (KCC-1) has been compared with that
of palladium particles supported on traditional silica-based
mesoporous supports (MCM-41, SBA-15). These catalysts have
been prepared and evaluated by using identical reaction con-
ditions as those for KCC-1. The investigation shows clearly the
decisive role of the silica morphology on the availability of the
active sites for the catalytic hydrogenation reaction, with
KCC-1 emerging as the most convenient support in virtue of
the high accessibility of Pd particles achieved even at high
metal loading (>10%).
[a] BET surface area. [b] Determined by ICP-OES elemental analysis. BJH
PV and BJH PS are the pore volume and the pore size, respectively, ac-
cording to the Barrett–Joyner–Halenda analysis.
Pd catalysts and allows a meaningful comparison of the ten-
dency towards aggregation and sintering of the Pd atoms on
the different silica supports.
A comparison of the physicochemical properties (specific
surface area, cumulative pore volume, pore size, and Pd load-
ing) of Pd/KCC-1-NH2, Pd/MCM-41-NH2, and Pd/SBA-15-NH2
and precursor materials is reported in Table 1. Not surprising-
ly,[24] the functionalization of the three supports with 3-APTES
(to yield KCC-1-NH2, MCM-41-NH2, and SBA-15-NH2) had a sig-
nificant impact on the porous structure of the silica supports
with a reduction of the pore volume by a factor of two for
KCC-1 and SBA-15 (Table 1, entries 2, 8) and by almost a factor
of four for MCM-41 (Table 1, entry 5), as an effect of the lining
of the pore walls with organic material. Accordingly, the pore
size was reduced after functionalization; for KCC-1, the support
with the largest initial pore size, this reduction was the most
pronounced (ca. 25%). 3-APTES functionalization led to
a severe decrease of the BET surface areas; after treatment,
MCM-41-NH2 still exhibits the highest surface area of
628 m2 gÀ1, but also the smallest pore volume and the smallest
pore size. The formation of Pd nanoparticles upon reduction
led to further, but less pronounced, reduction of the porosity
properties (Table 1, entries 3, 6, 9). Interestingly, in the case of
Pd/KCC-1-NH2 the reduction of pore volume upon the forma-
tion of particles was particularly marked (from 0.71 cm3 gÀ1 of
KCC-1-NH2 to 0.52 cm3 gÀ1 of Pd/KCC-1-NH2). This finding sug-
gests the formation of Pd nano-
Results and Discussion
The silica-supported Pd nanocatalysts were prepared by func-
tionalization of the supports with 3-aminopropyltrimethoxysi-
liane (3-APTES). 3-APTES acts as a tethering ligand able to bind
PdCl2 with the aim of obtaining well-spaced and uniformly dis-
persed Pd atoms on the silica surface.[22] The functionalized
materials were reacted with PdCl2 followed by reduction with
hydrogen to form supported Pd nanoparticles. This procedure
was adapted to functionalize three different silica supports
(KCC-1, MCM-41, and SBA-15) thus affording silica-supported
palladium catalysts: Pd/KCC-1-NH2, Pd/MCM-41-NH2, and Pd/
SBA-15-NH2 (Figure 1).
High Pd loadings (13.4–16.9 wt%, Table 1) could be obtained
under identical preparation conditions for all supports. The
higher metal loading obtained for Pd/MCM-41-NH2 can be at-
tributed to the larger initial surface area of MCM-41 and of its
MCM-41-NH2 derivative when compared with KCC-1 and SBA-
15 and their 3-APTES derivatives.[23] The range of loadings ob-
tained is comparable to that of many commercially available
particles directly within the
pores of the KCC-1 derivative.
The average palladium particle
size was determined by chemi-
sorption of carbon monoxide
and hydrogen, as well as by
high-resolution TEM (Table 2; the
average particle size was ob-
tained from the images in
Figure 1, see the Supporting In-
formation for particle size distri-
butions).
Figure 1. HRTEM images of a) Pd/KCC-1-NH2, b) Pd/MCM-41-NH2, and c) Pd/SBA-15-NH2 after reduction by hydro-
gen at 4008C for 15 h.
&
ChemCatChem 0000, 00, 0 – 0
www.chemcatchem.org
2
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Papers
the pore size (5.0 versus 7.0 nm), possibly allowing the major
part of Pd to be located within the fibrous network and avail-
able for chemisorption. In comparison, similar (4.6 versus
4.0 nm) or even smaller (3.7 versus 2.4 nm) average particles
size versus pore size were obtained for SBA-15 and MCM-41,
respectively. This can be interpreted as an indication of the pal-
ladium particles partially being present only the outer surface
and/or partially blocking the pores of the silica network. The
different morphologies of the three materials results, therefore,
in different accessibility of the active palladium sites formed
upon reduction.
Table 2. Average particle size of the palladium nanoparticles obtained
after reduction (4008C, 15 h, H2) as determined by H2-chemisorption
methods and HRTEM.
Material
Average particle
size by TEM
[nm]
Dispersion[a]
[%]
Average particle
size by H2 chemi-
sorption [nm][b]
Pd/KCC-1-NH2
Pd/MCM-41-NH2
Pd/SBA-15-NH2
5.0
3.7
4.0
12.4
1.4
2.8
9.0
82.1
40.7
[a] Dispersion is proportional to the amount of adsorbed hydrogen
atoms. [b] Average particle size obtained by chemisorption of carbon
monoxide shows comparable results (see the Supporting Information).
In summary, the TEM results reported can be considered as
representative of the actual size of the palladium nanoparti-
cles, whereas the chemisorption experiments reveal informa-
tion about the availability of the Pd particles, which can in turn
be more directly correlated to catalytic activity (see below).
The comparable average particle size values obtained by TEM
for all supports demonstrate that the preparation method ap-
plied here is a suitable tool to create small palladium particles
on silica supports even when higher noble-metal contents are
sought.
Based on TEM results, KCC-1 presents fully loaded fibers cov-
ered by well-dispersed Pd nanoparticles with an average size
of 5.0 nm (see the tomography in the Supporting Information),
whereas H2-chemisorption data led to a slightly larger estimat-
ed average particle size of 9 nm. Large differences were ob-
served for the results obtained by the two techniques (chemi-
sorption and electron microscopy) for the particle size of Pd/
MCM-41-NH2 and Pd/SBA-15-NH2 highlighting the limitations
of both methods when taken singularly. TEM measurements
provide an average particle size obtained by counting several
hundreds of clusters on comparatively small areas, which are
not necessarily representative for the whole sample. Chemi-
sorption measurements involve a bulk amount of material pro-
viding more statistically reliable results and catalytically rele-
vant information that depends on the accessibility of the palla-
dium sites. The palladium particle sizes of the three samples
obtained by chemisorption methods range from small particles
of 9 nm on Pd/KCC-1-NH2 to large particles of 41 nm on Pd/
SBA-15-NH2 and up to very large particles of about 82 nm on
Pd/MCM-41-NH2. These values were verified by two different
probe molecules (hydrogen and carbon monoxide, see the
Supporting Information, Table S1), leading to comparable re-
sults. The particle sizes measured by TEM, however, are much
smaller than those obtained by chemisorption experiments
(average diameter between 3.7 nm for Pd/MCM-41-NH2 and
5.0 nm for Pd/KCC-1-NH2). Very similar size distributions were
observed for the different materials with the dimension of the
vast majority of the nanoparticles being between 2 and 7 nm
(See the Supporting Information).
The silica-supported Pd nanocomposites have been exam-
ined as chemoselective catalysts for the transfer hydrogenation
of olefins and conjugated carbonyl compounds by selecting
1,3-diphenyl-2-propen-1-one (1a) as a benchmark substrate.
The influence of various reaction parameters, such as the
choice of catalyst, solvent and hydrogen source, temperature,
catalyst loading, and reaction time have been investigated
(Table 3). Pd/KCC-1-NH2 proved to be an excellent catalyst for
Table 3. Application of the Pd nanocomposites for the catalytic hydroge-
nation of 1,3-diphenyl-2-propen-1-one 1a.[a]
Entry Catalyst
Solvent
Conversion Selectivity[b] 2a/3a
[%][b]
[%]
1
2
3
4
5
6
7
Pd/KCC-1-NH2
toluene
THF
CH2Cl2
H2O
MeOH
H2O/MeOH 99
47
59
63
13
68
93:7
Pd/KCC-1-NH2
Pd/KCC-1-NH2
Pd/KCC-1-NH2
Pd/KCC-1-NH2
Pd/KCC-1-NH2
94:6
89:11
92:8
95:5
100:0
98:2
Differences of one order of magnitude between the two
methods indicate that the probe molecules could not likely
adsorb on a large portion of the palladium deposited on Pd/
MCM-41-NH2 and Pd/SBA-15-NH2. This might be due either to
the incomplete reduction of the particle surfaces to the metal-
lic state or to their inaccessibility for the probe gases as an
effect of clogged pores. Interestingly, the amount of chemisor-
bed hydrogen follows the same trend as pore size and
volume, with the highest values measured for KCC-1 and the
lowest for MCM-41, for which the number of active sites is
about one order of magnitude lower than on KCC-1-NH2.
Considering the average particle size measured by HRTEM
for the supports employed, it is possible to observe that only
for Pd/KCC-1-NH2 is the average particle clearly smaller than
Pd/MCM-41-NH2 H2O/MeOH 61
8
Pd/SBA-15-NH2
Pd/KCC-1-NH2
Pd/KCC-1-NH2
Pd/KCC-1-NH2
Pd/KCC-1-NH2
Pd/KCC-1-NH2
Pd/KCC-1-NH2
Pd/KCC-1-NH2
H2O/MeOH 38
H2O/MeOH 33
H2O/MeOH 52
H2O/MeOH 28
H2O/MeOH 86
H2O/MeOH 89
H2O/MeOH 99
H2O/MeOH 73
99:1
9[c]
10[d]
11[e]
12[f]
13[g]
14[h]
15[i]
88:12
90:10
100:0
99:1
100:0
100:0
100:0
[a] Reaction conditions: 1a (1 mmol), HCOOH (1.5 mmol), solvent (5 mL;
for entries 6–15 the H2O/MeOH ratio was set to 3:2 v/v), catalyst (50 mg,
6.5 mol% Pd for Pd/KCC-1-NH2) at 1008C for 24 h. [b] Conversions of 1a
determined by GC-MS analysis. [c] HCOONa as hydrogen source.
[d] HCOONH4 as hydrogen source. [e] 0.6 mmol of triethylamine was
added [f] At 808C. [g] Using 25 mg (3.25 mol% Pd) Pd/KCC-1-NH2.
[h] 12 h. [i] 6 h.
ChemCatChem 0000, 00, 0 – 0
www.chemcatchem.org
3
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ

Full Papers
the quantitative and selective conversion of conjugated olefin
1a to the corresponding carbonyl compound (2a). The nature
of the solvent was found to strongly affect the yield and selec-
tivity of the reaction (Table 3, entries 1–6).
pore clogging and it is ultimately detrimental to the catalytic
performance. The type of support did not have an influence
on the chemoselectivity of the reaction, but lower selectivity
towards 2a was observed in organic solvents (Table 3, en-
tries 1–6). The use of alternative H sources, such as HCOONa or
HCOONH4 and the addition of triethylamine (triethylamine/
formic acid 2:5),[25] had no beneficial effects and instead led to
lower substrate conversion and selectivity (Table 3, entries 9,
10, and 11).
In nonpolar media, such as toluene, only moderate conver-
sion was observed (Table 3, entry 1). More polar and aprotic
solvents, such as THF (59%) and CH2Cl2 (63%), provided good
to moderate conversion towards hydrogenation product 2a
(Table 3, entries 2, and 3). Slightly higher conversion was ob-
tained by using a polar and protic solvent, such as MeOH,
whereas the reaction in pure water was sluggish because of
poor substrate solubility (Table 3, entries 4, and 5). However,
a mixture of MeOH and water (MeOH/water=2:3 v/v) provided
an ideal reaction medium allowing quantitative conversion of
1a and absolute chemoselectivity (Table 3, entry 6). Further op-
timization of the reaction conditions showed that the high cat-
alytic activity of Pd/KCC-1-NH2 allows the reaction temperature
to be reduced to 808C (Table 3, entry 12), the palladium con-
centration to be reduced by half (Table 3, entry 13), and the re-
action time to be significantly reduced (Table 3, entries 14, and
15) without, or with only minor, effects on the catalytic effi-
ciency. A reaction time of 12 h proved to be sufficient to
achieve full conversion of the starting material.
Alternative reducing agents, such as hydrazine[26] and an
amino borane,[27] have also been tested under the same reac-
tion conditions (see the Supporting Information, Table S-3).
The generality of the optimized protocol was assessed by
using a variety of substrates (Table 4). The catalyst exhibited
high activity for the hydrogenation of differently substituted
double bonds and the desired products were afforded in quan-
titative yields (Table 4, entries 1–7). (E)-Stilbene was poorly
soluble in the MeOH/H2O mixture, however the reaction was
carried out successfully by using THF as a solvent (Table 4,
entry 4). The reaction protocol allowed the facile and selective
hydrogenation of functionalized unsaturated compounds, such
as nitriles and amides (Table 4, entries 8, 9). When 3-nitrostyr-
ene was used as a substrate, the products of hydrogenation at
only one of the reducible functionalities (mostly at the double
bond) along with the product of complete hydrogenation (3-
ethylaniline) were observed. By employing three equivalents of
formic acid under the same reaction conditions the exclusive
and quantitative formation of 3-ethylaniline was observed,
thus showing that Pd/KCC-1-NH2 can efficiently reduce both
functionalities, albeit not selectively (Table 4, entry 10, 11). The
hydrogenation of 4-bromostyrene was also studied (Table 4,
entry 12). This substrate did not afford the expected hydroge-
nation product; the formation of a product generated by the
Heck coupling of two molecules of 4-bromostyrene was de-
tected as the main reaction product (see the Supporting Infor-
mation). The chemoselectivity of the catalyst was investigated
for the reduction of additional conjugated carbonyl com-
pounds. The reduction of ethyl cinnamate and of cinnamic
acid (Table 4, entries 13, and 14) worked smoothly affording
high yields of the desired products with total chemoselectivity
towards the hydrogenation of the double bond. Dibenzylide-
neacetone proved to be a more challenging substrate, yielding
a mixture of the products of partial and complete hydrogena-
tion in low to moderate yields under the optimized reaction
conditions (Table 4, entry 15). We further explored the hydro-
A comparison of the catalytic activity of Pd/KCC-1-NH2 with
the Pd nanoparticles supported on the other porous silica ma-
terials (Pd/MCM-41-NH2, Pd/SBA-15-NH2) reveals the higher cat-
alytic activity of Pd/KCC-1-NH2. Although Pd/MCM-41-NH2 pres-
ents a higher Pd loading and almost double the surface area
(Table 1) compared with Pd/KCC-1-NH2, lower conversion (61%
in 24 h, Table 3, entry 7) was observed for this catalyst under
the same reaction conditions. Pd/SBA-15-NH2, with a Pd load-
ing comparable to that of Pd/KCC-1-NH2, did not perform well
as a catalyst for the hydrogenation of 1a (Table 3, entry 8).
Very similar particle size distributions have been determined
by HRTEM analysis for all the materials under identical prepara-
tive conditions, therefore, the higher catalytic activity of KCC-
1 can be attributed to the higher amount of accessible active
sites on the support surface, as highlighted by the chemisorp-
tion experiments. In addition, the particular morphology of Pd/
KCC-1-NH2 can support faster mass transfer because of the
larger pore size (Table 1). For the other two supports, the situa-
tion appears more complex. The pore size and pore volume of
Pd/SBA-15-NH2 are larger than that of Pd/MCM-41-NH2. Larger
pores should enhance mass transfer and accelerate the reac-
tion, that is, the activity of Pd/SBA-15-NH2 should be higher
than that of Pd/MCM-41-NH2. However, this is not the case.
Moreover, the accessible Pd surface area is found to be clearly
smaller for Pd/MCM-41-NH2 (Table 2), which indicates a complex
superimposition of site accessibility, sorption effects, and mass
transfer. Interestingly, an hydrothermally prepared Pd catalyst
(2.8 wt% Pd) supported on MCM-41[16] proved to be an excel-
lent catalyst for the transfer hydrogenation of olefins and con-
jugated carbonyl compounds at 708C in methanol; in this
case, the catalyst was reported to display a BET surface area of
970 m2 gÀ1 and a pore volume of 0.78 cm3 gÀ1. This result con-
firms that for the case of MCM-41 the preparation of a high
loading of 3-APTES-stabilized Pd nanoparticles can lead to
genation of
a cyclic enone, such as 2-cyclohexen-1-one
(Table 4, entries 16, and 17); this reaction afforded a mixture of
cyclohexanone and phenol. The formation of phenol can be at-
tributed to the aerobic dehydrogenation of the cyclohexenone
moiety and this reaction has been reported to be promoted
by molecular Pd complexes[28] or by Pd/C;[29] the involvement
of Pd nanoparticles in this process has been proposed.[30] Inter-
estingly, cyclohexanone is also formed in the absence of formic
acid, with phenol being the main product in this case. There-
fore, 1-cyclohex-2-enone can behave as the hydrogen donor
for the reduction of the double bond of another molecule of
the same compound. Increasing the amount of formic acid
&
ChemCatChem 0000, 00, 0 – 0
www.chemcatchem.org
4
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Papers
the hydrogenation of nonconjugated olefins, such as styrene,
towards which Pd/KCC-1-NH2 showed high activity. Moreover,
they are reported to lose activity, and in some case chemose-
lectivity,[19a] upon recycling much more rapidly than was ob-
served (see below) for Pd-KCC-1-NH2.[32] The higher robustness
and recyclability degree of our catalyst may be attributed to
the easier recoverability of the silica-supported nanoparticles
and to the anchoring function of 3-APTES.
Table 4. Hydrogenation of model substrates by using Pd/KCC-1-NH2 and
HCOOH.[a]
Entry
1
Substrate
Product
Yield [%][b]
99 (95)[c]
2
3
4
100 (97)[c]
100
99[d] (92)[c]
Pd/KCC-1-NH2 proved to be a recyclable catalyst for the
benchmark hydrogenation of 1,3-diphenyl-2-propen-1-one
(1a). After completion of the first reaction (1008C, 12 h) to
yield the corresponding ketone, the catalyst was recovered by
centrifugation, washed sequentially with methanol and ace-
tone, and finally dried under vacuum at 658C for 4 h. The re-
covered catalyst was recycled four times under the same reac-
tion conditions and was found to retain high activity and selec-
tivity (Figure 2) with only a minor decline in catalytic per-
5
6
100
99
7
8
9
100
95 (88)[c]
100 (91)[c]
10
45[e]
11[f]
12
100 (94)[c]
0[g]
13
14
15
89
77[h]
36[i,f]
16
(62:38)[j]
(38:62)[j]
17[k]
Figure 2. Recycling study of Pd/KCC-1-NH2 for the hydrogenation of 1,3-di-
phenyl-2-propen-1-one. The conversion dropped to 94% after five catalytic
cycles.
[a] Substrate (1 mmol), Pd/KCC-1-NH2 (50 mg, 6.5 mol%), HCOOH
(1.5 mmol), H2O (3 mL), MeOH (2 mL), at 1008C for 12 h. [b] Yield of the
main hydrogenation product as determined by GC-MS; unless otherwise
specified, no additional products were observed. [c] Isolated yields after
extraction with EtOAc from the reaction mixture. [d] THF (5 mL) as sol-
vent. [e] The product contains 32% of unreacted starting material, 19%
of 3-ethylnitrobenzene and 2% of 3-vinylaniline (see chromatogram in
the Supporting Information). [f] 3 equiv. of formic acid. [g] A product of
the Heck coupling between two molecules of 4-bromostyrene was de-
tected. [h] The product contains 23% of the methyl ester of the carboxyl-
ic acid product (methyl 3-phenylpropanoate). [i] 10% of the product of
hydrogenation at both double bonds (1,5-diphenylpentan-3-one) was
found. [j] cyclohexanone/phenol ratio, no starting material detected.
[k] No formic acid was added.
formance observed (94% yield at the fifth cycle). This decline
was mostly owing to handling loss of catalyst that occurred
during the iterations. In four additional runs (1008C, 6 h), recy-
cled Pd/KCC-1-NH2 provided a performance very close to that
observed in Table 1, entry 15, thus confirming the robustness
of the catalyst (see also Table S-2 in the Supporting Informa-
tion). TEM images of the fresh and used catalyst (Figure 3) con-
firm that the Pd nanoparticles supported on fibrous nanosilica
remained mostly unchanged after five catalytic cycles, indicat-
ing no significant, or only minor, particle agglomeration, thus
employed to three equivalents did not have any effect on im-
proving the selectivity towards cyclohexanone. In spite of the
high potential utility of this process, it exceeds the scope of
the current study and it has not been explored further.
A comparison with other recently published Pd nanocata-
lysts, such as the aqueous Pd nanoparticles reported by Bagal
and Bhanage[19a] and especially the polymer-supported nano-
particles reported by Mahato et al.,[19b] shows that the applica-
tion of the latter catalysts is advantageous upon Pd/KCC-1-NH2
in terms of turnover frequency for the hydrogenation of conju-
gated carbonyl compounds and for their efficacy and selectivi-
ty towards halogenated substrates.[31] However, these catalysts
have not been tested[19a] or are reported to be inactive[19b] for
Figure 3. TEM images of Pd/KCC-1-NH2 nanocatalysts a) before reaction and
b) after five catalytic cycles.
ChemCatChem 0000, 00, 0 – 0
www.chemcatchem.org
5
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ

Full Papers
confirming the high stability and durability of the catalyst. The
leaching of palladium into the reaction media was analyzed by
inductively coupled plasma–optical emission spectrometry
(ICP-OES) of the product at the end of the reaction after cata-
lyst separation. The palladium concentration in the solution
phase was found to be lower than the detectable level of
0.01 ppm, which implies no significant leaching of palladium
and negligible contamination of products. This finding can be
attributed to the presence of the APTES-3 amino groups on
the surface of KCC-1 that act as “anchors” for the metal parti-
cles, preventing leaching and agglomeration.[33]
additional peak located at 336.7 eV can be attributed to Pd
(Pd2+) from PdO.[31c,38] The PdO formed after the reaction rep-
resents just 4% of the total palladium. We can, therefore, con-
clude that following the reaction the chemical state of palladi-
um did not change significantly and that palladium remained
dominantly in its metallic form.
Conclusions
Finely dispersed Pd nanoparticles supported on fibrous silica
nanospheres KCC-1 have been prepared and have performed
as efficient, robust, and chemoselective catalysts for the trans-
fer hydrogenation of C=C bonds. A systematic comparison be-
tween the palladium nanoparticles supported on KCC-1 and
those prepared under identical conditions on traditional meso-
porous silica materials (MCM-41, SBA-15) has been carried out
to understand the importance of the morphology of the silica
supports in terms of particle size, distribution and, in particular,
accessibility of the palladium nanoparticles formed. TEM- and
chemisorption-based comparison between the various nano-
catalysts revealed excellent Pd particle dispersion and accessi-
bility to the probe molecules on the fibrous branches of KCC-
1. Comparable particle sizes, but limited accessibility to the
probe molecules, were observed under the same preparative
conditions for the other supports. This can be interpreted as
an effect of different surface mobility, of pore clogging, and fi-
nally of the particular fibrous morphology of Pd/KCC-1-NH2 on
granting superior availability of the active catalytic centers
when compared with the traditional porous supports. In agree-
ment with these results and interpretation, Pd/KCC-1-NH2 ex-
hibited the highest catalytic activity for the hydrogenation of
1,3-diphenyl-2-propen-1-one (1a) of the nanocomposites pre-
pared. The sustainable protocol that employs formic acid as
a hydrogen donor could be extended to the efficient and se-
lective hydrogenation of a variety of substrates. The catalyst
could be recovered and reused several times without signifi-
cant loss of its catalytic activity. No significant catalyst degrada-
tion or leaching of palladium to the organic layer and product
could be observed at the end of the reaction. This finding is
supported by TEM, ICP-OES, and XPS measurements.
To determine whether the catalytic activity originated from
Pd/KCC-1-NH2 or from homogeneous palladium traces leached
during the reaction, a hot-filtration test was performed.[34] The
Pd/KCC-1-NH2 catalyst was filtered off after a reaction time of
one hour and the filtrate was allowed to react further with no
additional conversion of the substrate observed.[35]
XPS spectra obtained for Pd/KCC-1-NH2 before and after the
reaction show four major peaks corresponding to Si (Si2p), Pd
(3d), O (O1s), and C (C1s) elements (Figure S4 and S5). High-
resolution XPS spectra of the Pd3d core level before (Figure 4)
and after four catalysis cycles (Figure S6) were also obtained.
Figure 4. High-resolution XPS spectra of Pd core level of Pd/KCC-1-NH2
before reaction; see the Supporting Information (Figure S6) for the spectra
obtained after four catalytic cycles showing an additional peak at 336.7 eV.
Experimental Section
The Pd3d core level contains four doublets (Pd3d5/2
–
Pd3d3/2) with a fixed area ratio equal to 3:2 and doublet sepa-
ration at 5.27 eV. Before application in catalysis, Pd3d5/2 was
composed of two components located at 335.1 and 337.8 eV.
The dominant peak representing 98% of the total palladium
was observed at 335.1 eV binding energy and corresponds to
metallic Pd (Pd0),[36] whereas the peak located at 337.8 can be
assigned to Pd in Pd(OH)2 or/and PdO.[36c,37] The additional
doublet observed at 342.2–347.5 eV, corresponding to plasmon
loss structures from metallic palladium, was added to fit the
Pd3d core level.[36b] The XPS spectra measured for fresh Pd/
MCM-41-NH2 and Pd/SBA-15-NH2 are identical to that of fresh
Pd/KCC-1-NH2 showing a nearly complete reduction of the
PdCl2 precursor. After the reaction, the Pd3d5/2 was composed
of three components located at 335.1, 336.7, and 337.8 eV. The
General information, particle size distribution, tomography screen-
shots, copies of XPS and NMR spectra, and chromatographic analy-
sis of the reaction products can be found in the Supporting Infor-
mation.
Preparation of monodispersed fibrous-structured silica
nanospheres (KCC-1)
KCC-1 was synthesized by modification of a previously reported[1i]
procedure by template-mediated hydrolysis–polycondensation of
tetraethyl orthosilicate (TEOS). In a typical synthesis, TEOS (35 mL)
was dissolved in a solution of cyclohexane (300 mL) and pentanol
(20 mL). A solution of cetyltriammonium bromide (CTAB) (13.33 g)
in water (500 mL) was then added. This mixture was stirred for
30 min at RT and then heated in a microwave at 1208C for 30 min.
&
ChemCatChem 0000, 00, 0 – 0
www.chemcatchem.org
6
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Papers
The white precipitated product was washed with water and air
dried. The residual template was removed by calcination at 5508C
for 6 h in a continuous flow of air. The material obtained is desig-
nated as KCC-1.
Keywords: chemoselectivity
hydrogenation · nanocatalysis · palladium
·
fibrous
nanosilica
·
MCM-41[39] and SBA-15[40] were prepared according to reported
procedures.
[1] a) C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli, J. S. Beck, Nature
1992, 359, 710–712; b) P. T. Tanev, T. J. Pinnavaia, Science 1995, 267,
865–867; c) D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F.
Chmelka, G. D. Stucky, Science 1998, 279, 548–552; d) N. R. Shiju, A. H.
Alberts, S. Khalid, D. R. Brown, G. Rothenberg, Angew. Chem. Int. Ed.
2011, 50, 9615–9619; Angew. Chem. 2011, 123, 9789–9793; e) J. N. Cha,
G. D. Stucky, D. E. Morse, T. J. Deming, Nature 2000, 403, 289–292; f) T.
Yokoi, Y. Sakamoto, O. Terasaki, Y. Kubota, T. Okubo, T. Tatsumi, J. Am.
Chem. Soc. 2006, 128, 13664–13665; g) Q. He, X. Cui, F. Cui, L. Huo, J.
Shi, Microporous Mesoporous Mater. 2009, 117, 609–616; h) P. B. Sara-
wade, J. K. Kim, A. Hilonga, H. T. Kim, J. Hazard. Mater. 2010, 173, 576–
580; i) V. Polshettiwar, D. Cha, X. Zhang, J. M. Basset, Angew. Chem. Int.
Ed. 2010, 49, 9652–9656; Angew. Chem. 2010, 122, 9846–9850; j) P. B.
Sarawade, J. K. Kim, A. Hilonga, D. V. Quang, H. T. Kim, Appl. Surf. Sci.
2011, 258, 955–961.
Functionalization of silica supports (KCC-1, MCM-41 and
SBA-15) with amino groups
Anhydrous toluene (150 mL), silica support (10.00 g) and 3-amino-
propyltriethoxysilane (3-APTES, 40 mL, 171 mmol) were mixed in
a 250 mL round-bottom flask and heated at reflux temperature for
48 h. The solution was filtered, the white precipitate was washed
with acetone and chloroform, and then the solid cake was dried
overnight at 608C in an oven.
[2] a) S. Gai, P. Yang, P. Ma, D. Wang, C. Li, X. Li, N. Niu, J. Lin, J. Mater.
Chem. 2011, 21, 16420–16426; b) P. B. Sarawade, J. K. Kim, A. Hilonga,
H. T. Kim, Powder Technol. 2010, 197, 288–294; c) M. E. Davis, Nature
2002, 417, 813–821; d) A. J. Gellman, N. Shukla, Nat. Mater. 2009, 8,
87–88; e) G. J. Hutchings, J. Mater. Chem. 2009, 19, 1222–1235; f) S. H.
Joo, J. Y. Park, C. K. Tsung, Y. Yamada, P. Yang, G. A. Somorjai, Nat. Mater.
2009, 8, 126–131; g) M. T. Reetz in Nanoparticles and Catalysis (Eds.: D.
Astruc), Wiley-VCH, Weinheim, 2008, pp. 255–279.
[3] a) R. Schlçgl, S. B. A. Hamid, Angew. Chem. Int. Ed. 2004, 43, 1628–1637;
Angew. Chem. 2004, 116, 1656–1667; b) V. V. Khatko, R. E. Soltis, J. R.
McBride, K. E. Nietering, Sens. Actuators B 2001, 77, 548–554.
[4] KCC-1 does not present a porous, but rather a fibrous structure, howev-
er, the spaces and channels between the fibers can be assimilated to
pseudo-pores (and are treated herein as such).
[5] a) M. Bouhrara, C. Ranga, A. Fihri, R. R. Shaikh, P. Sarawade, A. H. Emwas,
M. N. Hedhili, V. Polshettiwar, ACS Sustainable Chem. Eng. 2013, 1,
1192–1199; b) V. Polshettiwar, J. Thivolle-Cazat, M. Taoufik, F. Stoffel-
bach, S. Norsic, J. M. Basset, Angew. Chem. Int. Ed. 2011, 50, 2747–2751;
Angew. Chem. 2011, 123, 2799–2803; c) H. G. Peng, L. Xu, H. Wu, K.
Zhang, P. Wu, Chem. Commun. 2013, 49, 2709–2711.
[6] a) J. G. de Vries, C. J. Elsevier, Hand book of Homogeneous Hydrogena-
tion, Wiley-VCH, Weinheim, 2007; b) Z. Wu, E. Borretto, J. Medlock, W.
Bonrath, G. Cravotto, ChemCatChem 2014, 6, 2762–2783.
Preparation of Pd nanoparticles supported on silica
A 100 mL Schlenk flask was charged with functionalized silica sup-
port (KCC-1-NH2, MCM-41-NH2 or SBA-15-NH2) material (1 g), PdCl2
(0.5 g), and deionized water (40 mL), and the whole mixture was
then sonicated for 2 h. The suspension obtained was continuously
stirred at room temperature for 24 h. The solid product was col-
lected by centrifugation, washed several times with water, metha-
nol, and acetone, respectively, and dried overnight in an oven at
658C. The reduction of palladium was performed in a fixed-bed
continuous-flow reactor. 200 mg of material was placed in a stain-
less-steel tabular reactor with an internal diameter of 9 mm and re-
duced in a stream of hydrogen (30 mLminÀ1) at 4008C for 15 h.
The temperature in the reactor was controlled by using a PID tem-
perature controller connected to a thermocouple placed inside the
catalyst bed. The Pd content in the final material was determined
by using ICP-elemental analysis.
[7] a) X. Li, L. Li, Y. Tang, L. Zhong, L. Cun, J. Zhu, J. Liao, J. Deng, J. Org.
Chem. 2010, 75, 2981–2988; b) Z. Baꢂn, Z. Finta, G. Keglevich, I. Her-
mecz, Green Chem. 2009, 11, 1937–1940.
[8] a) Y. Sasson, J. Blum, Tetrahedron Lett. 1971, 12, 2167–2170; b) Y.
Sasson, J. Blum, J. Org. Chem. 1975, 40, 1887–1896; c) G. Descotes, D.
Sinou, Tetrahedron Lett. 1976, 17, 4083–4086; d) T. Doi, T. Fukuyama, J.
Horiguchi, T. Okamura, I. Ryu, Synlett 2006, 721–724; e) C. Mebi, R. Nair,
B. Frost, Organometallics 2007, 26, 429–438; f) A. Indra, P. Maity, S. Bha-
duri, G. K. Lahiri, ChemCatChem 2013, 5, 322–330.
[9] a) C. Schmçger, A. Stolle, W. Bonrath, B. Ondruschka, T. Keller, K. D.
Jandt, ChemSusChem 2009, 2, 77–89; b) S. Ganji, S. Mutyala, C. K. P.
Neeli, K. S. R. Rao, D. R. Burri, RSC Adv. 2013, 3, 11533–11538; c) A. M.
Raspolli Galletti, C. Antonetti, M. Bertoldo, F. Piccinelli, Appl. Catal. A
2013, 468, 95–101; d) O. Verho, A. Nagendiran, C.-W. Tai, E. V. Johnston,
J.-E. Bꢃckvall, ChemCatChem 2014, 6, 205–211; e) A. mori, Y. Miyakawa,
E. Ohashi, T. Haga, Org. Lett. 2006, 8, 3279–3281; f) H. Otsuka, E. Shira-
Experimental procedure for the reduction of alkenes
The nanocatalyst (50 mg) was stirred in a mixture of water (3 mL)
and methanol (2 mL). The reduction substrate (1 mmol) and
HCOOH (1.5 mmol) were then added. The resulting reaction mix-
ture was stirred at 1008C for 12 h in a 50 mL flask equipped with
a reflux condenser and capped by a CaCl2 valve. The progress of
the reaction was monitored by GC-MS. Upon completion, the mix-
ture was cooled to RT and the catalyst was separated by centrifu-
gation. The products were extracted with ethyl acetate (3ꢁ5 mL)
and dried over Na2SO4 and the solvent was evaporated under
vacuum to yield the crude product. The crude product was ana-
lyzed by gas-chromatographic techniques to determine yield and
chemoselectivity.
ˇ
kawa, T. Hayashi, Chem. Commun. 2007, 1819–1821; g) V. Jurcꢄk, S. P.
Nolan, C. S. J. Cazin, Chem. Eur. J. 2009, 15, 2509–2511.
[10] a) C. Hammond, M. T. Schꢅmperli, S. Conrad, I. Hermans, ChemCatChem
2013, 5, 2983–2990; b) S. Sakaguchi, T. Yamaga, Y. Ishii, J. Org. Chem.
2001, 66, 4710–4712; c) J. Blum, Y. Sasson, S. Iflah, Tetrahedron Lett.
1972, 13, 1015–1018; d) Y. Himeda, N. Onozawa-Komatsuzaki, S. Miya-
zawa, H. Sugihara, T. Hirose, K. Kasuga, Chem. Eur. J. 2008, 14, 11076–
11081; e) W.-J. Lu, Y.-W. Chen, X.-L. Hou, Angew. Chem. Int. Ed. 2008, 47,
10133–10136; Angew. Chem. 2008, 120, 10287–10290.
[11] a) B. M. Trost, Z. T. Ball, T. Jçge, J. Am. Chem. Soc. 2002, 124, 7922–7923;
b) V. Jurkauskas, J. P. Sadighi, S. L. Buchwald, Org. Lett. 2003, 5, 2417–
2420; c) T. Ikawa, K. Hattori, H. Sajiki, K. Hirota, Tetrahedron 2004, 60,
Recyclability study
Upon reaction completion the reaction mixture was allowed to
cool to RT. The catalyst was recovered by centrifugation and
washed vigorously with methanol (5ꢁ10 mL) and acetone (5ꢁ
10 mL) to remove all traces of product or reactant present and
centrifuged again. The catalyst was dried at 658C under reduced
pressure and kept at this temperature for a period of 4 h before
the subsequent cycle.
ChemCatChem 0000, 00, 0 – 0
www.chemcatchem.org
7
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ

Full Papers
ˇ
6901–6911; d) V. Jurcꢄk, S. P. Nolan, C. S. J. Cazin, Chem. Eur. J. 2009, 15,
[26] a) A. Dhakshinamoorthy, S. Navalon, D. Sempere, M. Alvaro, H. Garcia,
Chem. Commun. 2013, 2359–2361; b) J. Lin, J. Chen, W. Sua, Adv. Synth.
Catal. 2013, 355, 41–46; c) A. Dhakshinamoorthy, M. Alvaro, H. Garcia,
Adv. Synth. Catal. 2009, 351, 2271–2276.
[27] a) X. Yang, T. Fox, H. Berke, Org. Biomol. Chem. 2012, 10, 852–860; b) M.
Yurderi, A. Bulut, M. Zahmakirana„ M. Gꢅlcana, S. ꢆzkar, Appl. Catal. B
2014, 160–161, 534–541.
[28] a) Y. Izawa, D. Pun, S. S. Stahl, Science 2011, 333, 209–213; b) Y. Izawa,
C. Zheng, S. S. Stahl, Angew. Chem. Int. Ed. 2013, 52, 3672–3675;
Angew. Chem. 2013, 125, 3760–3763.
2509–2511; e) P. Four, F. Guibe, Tetrahedron Lett. 1982, 23, 1825–1827.
[12] a) A. Kosal, B. Ashfeld, Org. Lett. 2010, 12, 44–47; b) E. Keinan, D. Perez,
J. Org. Chem. 1987, 52, 2576–2580; c) D. Hays, M. Scholl, G. Fu, J. Org.
Chem. 1996, 61, 6751–6752.
[13] a) J. Kaspar, R. Spogliarich, A. Cernogoraz, M. Graziani, J. Organomet.
Chem. 1983, 255, 371–376; b) M. Node, K. Nishide, Y. Shigeta, H. Shiraki,
K. Obata, J. Am. Chem. Soc. 2000, 122, 1927–1936; c) J. S. Bajwa, J.
Slade, O. Repic, Tetrahedron Lett. 2000, 41, 6025–6028; d) Y. Ukisu, T.
Miyadera, Appl. Catal. B 2003, 40, 141–149.
[29] M. Sutter, R. Lafon, Y. Raoul, E. Mꢇtay, M. Lemaire, Eur. J. Org. Chem.
2013, 5902–5916.
[14] Z. Baꢂn, Z. Finta, G. Keglevich, I. Hermecz, Tetrahedron Lett. 2005, 46,
6203–6204.
[30] D. Pun, T. Diao, S. S. Stahl, J. Am. Chem. Soc. 2013, 135, 8213–8221.
[31] According to Ref. [19a], the hydrogenation of 1a by the aqueous Pd
nanoparticles (1 mol%) takes place at 1008C affording 99% conversion
to 2a within 8 h. The TOF (turnover frequency) can be estimated as
TON/h (TON: mmol product/mmol Pd) and is equal to 12.4 hÀ1. Accord-
ing to Ref. [19b] the TOF for the hydrogenation of 1a in refluxing meth-
anol by the polymer-supported nanoparticles is as high as 1463 hÀ1. Ac-
cording to our experimental results, the TOF for the hydrogenation of
1a by Pd/KCC-1-NH2 as displayed in Table 3, entry 14 (conversion: 73%,
[15] A. Sharma, V. Kumar, A. K. Sinha, Adv. Synth. Catal. 2006, 348, 354–360.
[16] P. Selvam, S. U. Sonavane, S. K. Mohapatra, R. V. Jayaram, Tetrahedron
Lett. 2004, 45, 3071–3075.
[17] a) R. Liua, Y. Wang, H. Cheng, Y. Yu, F. Zhao, M. Arai, J. Mol. Catal. A
2013, 366, 315–320; b) H. Wu, L. Hintermann, Synthesis 2013, 45, 888–
892; c) H. S. P. Rao, K. S. Reddy, Tetrahedron Lett. 1994, 35, 171–174.
[18] D. Scholz, C. Aellig, I. Hermans, ChemSusChem 2014, 7, 268–275.
[19] a) D. B. Bagal, B. M. Bhanage, RSC Adv. 2014, 4, 32834–32839; b) S. K.
Mahato, R. Ul Islam, C. Acharya, M. J. Witcomb, K. Mallick, ChemCatChem
2014, 6, 1419–1426; c) C. Batarseh, Z. Nairoukh, I. Volovych, M.
Schwarz, R. Schomꢃcker, M. Fanun, J. Blum, J. Mol. Catal. A 2013, 366,
210–214; d) K. Mennecke, R. Cecilia, T. N. Glasnov, S. Gruhl, C. Vogt, A.
Feldhoff, M. A. Larrubia Vargas, C. O. Kappe, U. Kunz, A. Kirschning, Adv.
Synth. Catal. 2008, 350, 717–730.
[20] O. Verho, A. Nagendiran, E. V. Johnston, C.-W. Tai, J.-E. Bꢃckvall, Chem-
CatChem 2013, 5, 612–618.
[21] D. B. Bagal, Z. S. Qureshi, K. P. Dhake, S. R. Khan, B. M. Bhanage, Green
Chem. 2011, 13, 1490–1494.
[22] a) Z. Dong, X. Le, X. Li, W. Zhang, C. Dong, J. Ma, Appl. Catal. B 2014,
158–159, 129–135; b) A. Fihri, M. Bouhrara, U. Patil, D. Cha, Y. Saih, V.
Polshettiwar, ACS Catal. 2012, 2, 1425–1431.
in 6 h at 1008C using 6.5 mol% of Pd) is 1.9 hÀ1
.
[32] According to Ref. [19a], the activity of the aqueous Pd nanoparticles
drops after four recycling experiments to 89% conversion and 91% se-
lectivity from initial 99% conversion and 99% selectivity. According to
Ref. [19b], the activity of the polymer-supported nanoparticles for the
hydrogenation of 1a is reported to drop to 84% yield from initial 96%
within just three catalytic cycles; in this case, the catalyst-recovery oper-
ation is reported to be difficult because of the nature of catalyst and
a considerable Ostwald ripening is observed. Conversely, the recovery
of Pd/KCC-1-NH2 proceeded smoothly by centrifugation and the cata-
lyst was observed to lose just 7% of the initial catalytic activity for the
hydrogenation of 1a after nine cycles (see Table S-2 and Table 3,
entry 14) with no detrimental effects on selectivity.
[23] According to the work described by M. Ide, M. El-Roz, E. De Canck, A.
Vicente, T. Planckaert, T. Bogaerts, I. Van Driessche, F. Lynen, V. Van Spey-
broeck, F. Thybault-Starzyk, P. Van Der Voort, Phys. Chem. Chem. Phys.
2013, 15, 642–650, MCM-41 and SBA-15 contain a comparable amount
of bulk silanols (3.6 and 3.5 mmolgÀ1, respectively). However, in virtue
of its much higher surface area (similar values as for our MCM-41 and
SBA-15 materials (Table 1) were reported: 1144 m2 gÀ1 for MCM-41 and
656 m2 gÀ1 for SBA-15), MCM-41 displays a slightly higher absolute
number of surface silanols available for reaction with probe silanes (2.2
versus 1.8 mmolgÀ1 of SBA-15). Therefore, it is expected that a higher
amount of 3-APTES will be grafted on MCM-41 and that this would cor-
respond, in the end, to a higher Pd loading. Interestingly, the ratio be-
tween the available surface silanols in MCM-41 and SBA-15 (2.2/1.8=
1.22) as obtained by Ide et al. correspond approximately to the ratio of
the Pd loadings obtained by us on MCM-41 and SBA-15 (16.9/13.4=
1.26).
[24] a) M. Tagaya, T. Ikoma, Z. Xu, J. Tanaka, Inorg. Chem. 2014, 53, 6817–
6827; b) A. L. Doadrio, J. M. Sanchez-Montero, J. C. Doadrio, A. J. Salinas,
A. M. Vallet-Regi, Microporous Mesoporous Mater. 2014, 195, 43–49; c) S.
Jabbari, H. Mahdav, M. Nikoorazm, A. Ghorbani-Choghamarani, Res.
Chem. Interm. 2014, DOI: 10.1007/s11164-014-1690-x; d) U. Patil, A. Fihri,
A.-H. Emwas, V. Polshettiwar, Chem. Sci. 2012, 3, 2224–2229; e) N. Gart-
mann, D. Brꢅhwiler, Materials 2011, 4, 1096–1103; f) J. Trissa, M. Hart-
mann, S. Ernst, S. B. Halligudi, J. Mol. Catal. A 2004, 207, 131–137.
[25] a) C. Wang, A. Pettman, J. Bacsa, J. Xiao, Angew. Chem. Int. Ed. 2010, 49,
7548–7552; Angew. Chem. 2010, 122, 7710–7714; b) W. Leitner, J. M.
Brown, H. Brunner, J. Am. Chem. Soc. 1993, 115, 152–159.
[33] V. Polshettiwar, M. N. Nadaguada, R. S. Varma, Chem. Commun. 2008,
6328–6320.
[34] H. E. B. Lempers, R. A. Sheldon, J. Catal. 1998, 175, 62–69.
[35] However, the limitations of this test are well known as it is not exclud-
ed that the leached palladium species might not agglomerate, precipi-
tate, and deactivate following the removal of the support under the re-
ducing reaction conditions applied; see: N. T. S. Phan, M. Van Der Sluys,
C. W. Jones, Adv. Synth. Catal. 2006, 348, 609–679.
[36] a) C. D. Wagner, A. V. Naumkin, A. Kraut-Vass, J. W. Allison, C. J. Powell,
J. R. Rumble Jr., NIST X-ray Photoelectron Spectroscopy Database, NIST
Standard Reference Database 20, Version 3.2 (Web Version), 2000;
b) M. C. Militello, S. J. Simko, Surf. Sci. Spectra 1994, 3, 387–394; c) E.
Smolentseva, B. T. Kusema, S. Beloshapkin, M. Estrada, E. Vargas, D. Y.
Murzin, F. Castillon, S. Fuentes, A. Simakov, Appl. Catal. A 2011, 392, 69–
79.
[37] K. S. Kim, A. F. Grosman, N. Winograd, Anal. Chem. 1974, 46, 197–200.
[38] a) L. P. Haack, K. Otto, Catal. Lett. 1995, 34, 31–40; b) T. Pillo, R. Zimmer-
mann, P. Steiner, S. Hufner, J. Phys. Condens. Matter 1997, 9, 3987–
3999; c) R. S. Monteiro, D. Zemlyanov, J. M. Storey, F. H. Ribeiro, J. Catal.
2001, 199, 291–301.
[39] S. A. Idris, C. M. Davidson, C. McManamon, M. A. Morris, P. Anderson,
L. T. Gibson, J. Hazard. Mater. 2011, 185, 898–904.
[40] J. Wang, Q. Liu, Microporous Mesoporous Mater. 2005, 83, 225–232.
Received: September 29, 2014
Published online on && &&, 0000
&
ChemCatChem 0000, 00, 0 – 0
www.chemcatchem.org
8
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

FULL PAPERS
Break the tradition: Pd-Nanoparticles
supported on fibrous KCC-1 nanospheres
perform as an efficient and recyclable
catalyst for the transfer hydrogenation
of alkenes and conjugated carbonyl
compounds. A systematic comparison
with Pd nanoparticles supported on tra-
ditional porous supports (MCM-41, SBA-
15) demonstrates the pivotal role of the
fibrous morphology in ensuring en-
hanced accessibility of the active metal
centers.
Z. S. Qureshi, P. B. Sarawade, M. Albert,
V. D’Elia,* M. N. Hedhili, K. Kçhler,
J.-M. Basset*
&& – &&
Palladium Nanoparticles Supported on
Fibrous-Structured Silica Nanospheres
(KCC-1): An Efficient and Selective
Catalyst for the Transfer
Hydrogenation of Alkenes
ChemCatChem 0000, 00, 0 – 0
www.chemcatchem.org
9
ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ