Tetraalkylammonium Functionalized Hydrochars as Efficient Supports for Palladium Nanocatalysts

Article abstract of DOI:10.1002/cctc.201902305

With the aim of preparing bio-sourced supports with enhanced properties in catalysis, we devised an original strategy allowing the immobilization of metal nanoparticles. Thus, size-controlled hydrochars with a high degree of hydroxyl functionalities, from both neat sucrose or modified with acrylic acid (10 wt.%), were derivatized with ether linkers containing ammonium groups. These non-porous carbon-based materials were used as suitable supports for the immobilization of palladium nanoparticles. The catalytic materials were synthesized by reduction of Pd(OAc)₂ to Pd(0) under H₂ atmosphere in the presence of the corresponding hydrochar, and fully characterized by standard methods. Among the different hydrochar-supported palladium materials, those functionalized with tetraalkylammonium groups afforded heterogeneous catalysts, exhibiting high activity in hydrogenations of different types of substrates (alkynes, alkenes, and carbonyl and nitro derivatives). The most efficient catalyst was recycled up to ten runs without loss of catalytic behavior, in agreement with the unchanged composite materials after catalysis (Transmission Electron Microscopy (TEM) analyses) and the lack of metal leaching in the extracted organic products (no palladium detected by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES)); these systems exhibited enhanced recyclability properties as compared to commercial Pd/C catalyst.

Full text of DOI:10.1002/cctc.201902305

Accepted Article
Title: Tetraalkylammonium functionalized hydrochars as efficient
supports for palladium nanocatalysts
Authors: Tiago A. G. Duarte, Isabelle Favier, Christian Pradel, Luísa M.
D. R. S. Martins, Ana P. Carvalho, Daniel Pla, and Montserrat
Gómez
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ChemCatChem
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Tetraalkylammonium functionalized hydrochars as efficient
supports for palladium nanocatalysts
Tiago A. G. Duarte,[a,b] Isabelle Favier,[c] Christian Pradel,[c] Luísa M. D. R. S. Martins,[a] Ana P.
Carvalho,*[b] Daniel Pla,*[c] and Montserrat Gómez*[c]
[a]
Mr. T. A. G. Duarte, Prof. L. M. D. R. S. Martins
Centro de Química Estrutural
Instituto Superior Técnico, Universidade de Lisboa
Av. Rovisco Pais, 1049-001 Lisboa, Portugal
Mr. T. A. G. Duarte, Prof. A. P. Carvalho
[b]
Centro de Química e Bioquímica e Centro de Química Estrutural
Faculdade de Ciências, Universidade de Lisboa
Campo Grande, 1749-016 Lisboa, Portugal
E-mail: apcarvalho@fc.ul.pt
[c]
Dr. I. Favier, Mr. C. Pradel, Dr. D. Pla, Prof. M. Gómez
Laboratoire Hétérochimie Fondamentale et Appliquée
Université de Toulouse 3 – Paul Sabatier, CNRS UMR 5069
118 route de Narbonne, 31062 Toulouse Cedex 9, France
E-mails: pla@lhfa.fr, gomez@chimie.ups-tlse.fr
Supporting information for this article is given via a link at the end of the document and contains general experimental procedures, materials, and
characterization of hydrochar supports and nanomaterials (Boehm titration, elemental analysis, FTIR, SEM, TEM, XPS), and selected organic compounds
(1H and 13C NMR).
Abstract: With the aim of preparing bio-sourced supports with
enhanced properties in catalysis, we devised an original strategy
allowing the immobilization of metal nanoparticles. Thus, size-
controlled hydrochars with a high degree of hydroxyl functionalities,
from both neat sucrose or modified with acrylic acid (10 wt. %), were
derivatized with ether linkers containing ammonium groups. These
non-porous carbon-based materials were used as suitable supports
for the immobilization of palladium nanoparticles. The catalytic
materials were synthesized by reduction of Pd(OAc)2 to Pd(0) under
H2 atmosphere in the presence of the corresponding hydrochar, and
fully characterized by standard methods. Among the different
hydrochar-supported palladium materials, those functionalized with
tetraalkylammonium groups afforded heterogeneous catalysts,
exhibiting high activity in hydrogenations of different types of
substrates (alkynes, alkenes, and carbonyl and nitro derivatives). The
most efficient catalyst was recycled up to ten runs without loss of
catalytic behavior, in agreement with the unchanged catalytic
materials after catalysis [Transmission Electron Microscopy (TEM)
analyses] and the lack of metal leaching in the extracted organic [no
palladium detected by Inductively Coupled Plasma-Atomic Emission
Spectrometry (ICP-AES)]; these systems exhibited enhanced
recyclability properties as compared to commercial Pd/C catalyst.
nanoparticles (PdNPs) has been intensively studied over the last
decades, with particular focus on finely control size, composition
and morphology of the as-prepared particles, having these key
parameters a direct impact on catalytic activity.[7] However, the
cost and low abundance of noble metals in the Earth’s crust
demand for robust immobilization strategies for the synthesis of
heterogeneized catalysts encompassing efficient recycling. Since
the re-use of the these high-value metal particles is a major
concern from economic and environmental point of view, different
approaches to prepare reusable PdNPs have been reported in the
literature, such as their immobilization in liquid phases, e.g. ionic
liquids,[8] water[9] and polyols,[1-2, 10] as well as on different solid
supports, e.g. mesoporous silica,[11] zeolites,[12] clays,[13]
polymers,[14] metal-organic frameworks[15] or carbon-based
materials.[7, 16] Particularly concerning the latter materials, carbon
18]
nanospheres,[17]
nanotubes,[3a,
halloysite-hydrochar
nanocomposites[19] and graphene oxide,[20] are among the most
used.
In the search of new materials with enhanced properties,
hydrothermal carbonization (HTC) methods affording non-porous
and spherically-shaped hydrochars enriched with sulfonic,[21]
amino,[22] aminopropyltriethoxysilane[23] or ethylenediamino
groups have been reported involving renewable biomass as
carbon precursors.[24] Up to now, the presence of multiple
functional groups on the surface of the hydrochars has limited
their chemoselective functionalization.[25] A glutaraldehyde cross-
linked polyethylene imine strategy has successfully been applied
for the derivatization of hydrochars,[26] but more efforts are
required for their selective functionalization.
Introduction
Palladium nanoparticle-based catalysts play a pivotal role in H2-
based reactions, such as hydrodehalogenations of haloarenes[1]
and the reduction of unsaturated substrates,[2] including oxidized
nitrogen derivatives,[2a, 3] especially for the production of anilines
at industrial scale.[4] This versatile reactivity offers great potential
towards contaminated water/soil remediation via degradation of
pollutants[5] and environmentally friendly processes by means of
selective catalytic reduction approaches precluding NOx
emissions.[6] In this context, the synthesis of palladium
Hitherto, raw carbonaceous materials from biomass have been
used as supports for palladium-based nanocatalysts showing
catalytic
activity[16-17]
for
both
adsorption
and
hydrodehalogenation of chlorinated hydrocarbon pollutants.[27] In
this context, we envisioned to study the selective derivatization of
free hydroxyl groups on the carboxylic acid-free hydrochars via
1
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10.1002/cctc.201902305
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ether bond formation to graft a tetralkylammonium tail, with the
purpose of obtaining supports containing both robust linkers (high
chemical stability of ether groups) and efficient metal
nanoparticles stabilizers (ammonium moieties inducing
electrostatic stabilization).
titration results, HCh-D obtained by thermal treatment showed a
decrease of the IR absorption bands associated to carboxylic
groups, especially the band assigned to the C=O bond stretching
(Figure 4).
Taking into account our experience in the synthesis of both
hydrochars[28] and metal-based nanocatalysts,[29] we have
prepared functionalized supports for the immobilization of PdNPs,
given the promising properties of raw hydrochars as supports for
catalytic materials.[30] Herein, we describe a comparative study of
alkylammonium functionalized hydrochars versus their parent
hydrochars as supports for the immobilization of palladium
nanoparticles.
Pd@HCh-C
PdNP Synthesis
HCh-E
(mild)
Pd@HCh-E
Pd@HCh-G
Sucrose
HCh-A
HCh-B
HCh-C
HCh-G
(harsh)
HCh-F
(mild)
Sucrose
+
Acrylic acid
Pd@HCh-F
Pd@HCh-H
HCh-D
HCh-H
(harsh)
PdNP Synthesis
Results and Discussion
Pd@HCh-D
Synthesis and characterization of hydrochar-based supports
Carbon materials HCh-A and HCh-B were prepared as previously
described via hydrothermal treatment of both neat sucrose and
sucrose supplemented with acrylic acid (10 wt%), respectively, in
moderate yields (32-40%, see Figure S1 in the Supporting
Information).[31]
Figure 1. Synthesis of functionalized hydrochars and Pd@hydrochar-based
catalytic materials.
Boehm titration analyses revealed the presence of carboxylic acid,
lactone, and phenol functionalities, being phenols the most
abundant groups (57 and 54% of the total number of surface
functional groups for HCh-A and HCh-B, respectively; see Table
S1 in the Supporting Information).
Robust chemical functionalization of supports is crucial in the
rational conception of stable materials that can resist the
conditions required for catalytic applications. Actually, the stability
of the catalytic materials is a key enabling factor towards high
turnover numbers and their enhanced reusability properties. In
particular, unbranched ether bond linkages present high chemical
stability and their cleavage can only take place under strongly
acidic or extremely basic conditions.[32] To conceive a selective
functionalization strategy via ether bond formation, the carboxylic
acid residues on the hydrochars surface should be removed. Thus,
an optimized thermal treatment (340 °C for 30 min) of HCh-A and
HCh-B led to their complete decarboxylation, resulting in the new
hydrochars HCh-C and HCh-D, respectively (Figure 1). The
thermal procedure enabled not only to remove the carboxylic acid
residues, but also minimize the amount of lactonic groups present
in HCh-A and HCh-B (Figure 2). Even though the four hydrochars
are acid materials, a moderate increase of the pH at the point of
zero charge (pHPZC) was observed for the thermally treated
materials, HCh-C and HCh-D (see Table S1 in the Supporting
Information), in agreement with the decrease of the acid groups
(determined by Boehm titration).
Figure 2. Boehm titration analyses of hydrochars HCh-A, HCh-B, HCh-C, and
HCh-D.
In terms of porosity, the thermally treated HCh-C and HCh-D
presented low N2 uptake which correlated with the non-porous
nature of the starting hydrochars HCh-A and HCh-B, respectively.
The specific surface area (7 m2 g-1) and total pore volume (0.01
cm3 g-1) were determined for HCh-D which matched with the
values of the parent hydrochar HCh-B;[31] however the negligible
porosities of HCh-C and HCh-A could not be quantified by the
analytical method employed.[34] The volume of HCh-D results
from the large porosity created by the aggregation of small
hydrochar particles and proves that the thermal treatment did not
affect the surface area and total pore volume characteristics of
the material (Figure 3).
A selective functionalization of hydroxyl groups was then
envisaged via ether bond formation through different strategies
compatible with the nature of the supports. Reaction of
hydrochars with sodium hydride in an aprotic solvent (DMF) was
an efficient treatment for the deprotonation of the hydroxyl groups
Fourier Transform Infrared (FTIR) spectra of HCh-A and HCh-B
presented strong absorption bands in the range of 1585-1600 cm-
1 corresponding to aromatic C=C bond stretching. The presence
of alcohols (absorption bands at 3200-3640 and 1049-1276 cm-1)
and carboxylic acids (bands in the region 3200-3640, ca. 1690
and 1000-1250 cm-1) was also evidenced.[33] As expected, the
bands assigned to carboxylic acids are more intense in the case
of HCh-B (see Figure S2 in the Supporting Information).
into
alkoxides,
sequentially
reacting
with
the
bromoalkylammonium bromide 1 via a nucleophilic substitution
reaction (Figure 5).
The morphology of HCh-C and HCh-D did not exhibit significant
modifications in comparison to the untreated hydrochars HCh-A
and HCh-B, as observed by SEM micrographs (Figure 3 vs Figure
S1 in the Supporting Information). In accordance with the Boehm
2
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10.1002/cctc.201902305
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ammonium salt 1 was added directly to the reaction mixture.
However, when harsher reaction conditions were employed, the
supernatant was filtered out under Ar after the basic treatment,
and then the alkoxide-based hydrochar was re-suspended in a
solution containing 1 in order to avoid concomitant degradation
reactions. In both cases, the alkylation reactions were run at 90
ºC for 16 h under Ar. The resulting solids were fully characterized
by SEM, elemental analysis, solid state NMR, and FTIR.
Figure 5. Mild and harsh strategies for HCh-C and HCh-D functionalization via
ether bond formation, leading to HCh-E and HCh-G (from HCh-C), and HCh-F
and HCh-H (from HCh-D).
SEM micrographs before and after functionalization revealed that
the hydrochar derived from neat sucrose (HCh-C) was much
more sensitive to basic treatments (under both mild and harsh
conditions, HCh-E and HCh-G, respectively) than the one
containing acrylic acid as additive (HCh-D), observing broken
spheres and debris for HCh-E and HCh-G (Figure 3). In contrast,
HCh-D presenting smaller fused nanospheres was functionalized
under both basic conditions preserving the morphology, leading
to HCh-F (mild conditions) and HCh-H (harsh conditions) (Figure
3). After these observations, we focused on the characterization
of HCh-F and HCh-H.
Figure 3. SEM micrographs of hydrochars obtained by thermal treatment (HCh-
C and HCh-D) and their functionalization via ether linkages (HCh-E and HCh-
G from HCh-C; HCh-F and HCh-H from HCh-D). Note: for HCh-H, image
magnification is 3,000x; for the other images, 5,000x.
In contrast to FTIR spectra of the starting materials (the
ammonium salt 1 and HCh-D), HCh-F and HCh-H exhibited a
more intense band at ca. 1060 cm-1 that was attributed to the C–
O bond stretching of ether groups, in agreement with the reported
data (C–O bond stretching appears at 1150-1085 cm-1 for acyclic
ethers) (Figure 4).[35] Extended reaction times employed for the
preparation of HCh-H can yield ether groups on the surface
without incorporating ammonium linkers. Accordingly, the
nitrogen content determined by elemental analysis (see Table S2
in the Supporting Information) for both functionalized materials
was similar (0.88% for HCh-F and 0.92% for HCh-H); for the non-
functionalized material HCh-D, the nitrogen content was
practically negligible (0.08%).
Synthesis and characterization of Pd@hydrochar-based
supports
Figure 4. FTIR spectra (KBr pellets) of HCh-D, HCh-F, HCh-H, and the
bromoalkylammonium 1.
We prepared zero-valent PdNPs supported on the different
hydrochars following a one-step procedure. Pd(OAc)2 was
reduced under hydrogen pressure in the presence of the
corresponding hydrochar (HCh-C to HCh-H) (Figure 6), leading
to materials containing the metal particles dispersed on the
support surface as evidenced by Transmission Electron
Microscopy (TEM) (Figure 7).
Based on the quantified hydroxyl functional groups (determined
by Boehm titration), 2 and 20 equiv. of NaH were used (Figure 5).
In both cases, NaH was added to a suspension of the
corresponding hydrochar (HCh-C or HCh-D) suspended in dry
DMF under Ar; the reaction mixture was then heated to 90 ºC for
the specified time (40 min or 6 h). For the mild strategy, the
3
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Pd@HCh-H) conditions, PdNPs were efficiently adsorbed on the
supports. This might be due to the electrostatic interaction of the
nanoparticles with the ammonium groups on the surface of the
hydrochars, as this type of interaction is well-known to kinetically
stabilize metal nanoparticles avoiding their agglomeration.[36] The
particle size distribution of those PdNPs prepared from supports
functionalized under mild conditions were more homogeneous
[Pd@HCh-E (6.6 ± 2.2 nm) and Pd@HCh-F (5.4 ± 1.5 nm)] than
those obtained under harsher conditions [Pd@HCh-H (6.8 ± 2.5
nm) and Pd@HCh-G]. In particular, two populations of PdNPs
were present in Pd@HCh-G [ca. 5.0 nm (42%) and 8.0 nm (58%),
see Figure S4 in the Supporting Information]. Besides, given the
degradation of acrylic acid-free supports under basic conditions
(see above Figure 3), Pd@HCh-E and Pd@HCh-G were
discarded for further reactivity studies. Overall, Pd@HCh-F
presented the best dispersion and the smallest PdNPs among the
series of functionalized materials (see Figure S4 in the Supporting
Information for further details).
Figure 6. One-step methodology for the synthesis of PdNPs supported on
hydrochar-based supports (Pd@Hydrochar).
We also tested a sequential two-step methodology, preparing first
colloidal PdNPs in glycerol under hydrogen pressure using
polyvinylpyrrolidone (PVP) as stabilizer based on our previously
reported approach,[29c] followed by physisorption of these
preformed PdNPs on HCh-F. In this case, PVP competes with the
hydrochar as stabilizer and only partial immobilization of PdNPs
on the support was achieved as observed by TEM (see Figure S3
in the Supplementary Information).
X-ray Photoelectron Spectroscopy (XPS) analysis of Pd-based
nanomaterials derived from acrylic acid hydrochars (Pd@HCh-D,
Pd@HCh-F, and Pd@HCh-H) served to prove the presence of
Pd(0) as well as the elements coming from the support [C, O and
Br (Figure 8 for Pd@HCh-F) and Table S3 in the Supporting
Information]. Nitrogen could not be detected by this technique due
to its low content (0.43%, determined by elemental analysis),
below the limit of detection of the XPS technique (ca. 0.5%).
Pd@HCh-C
Pd@HCh-D
Pd@HCh-E
Pd@HCh-F
Pd@HCh-G
Pd@HCh-H
Figure 8. XPS analysis for Pd@HCh-F: survey spectrum (left) and high-
resolution spectrum in the Pd 3d binding energy region (right).
Figure 7. TEM images of hydrochar-supported PdNPs (Pd@HCh-C to
Pd@HCh-H).
Concerning the one-step methodology (Figure 6), the influence of
the nature of the support resulted crucial for the deposition of
PdNPs on hydrochars (Figure 7). For the materials obtained after
thermal treatment presenting hydroxyl groups on the surface
(HCh-C and HCh-D), large agglomerates of palladium were
observed for Pd@HCh-C, whereas supported and unsupported
nanoparticles were detected for Pd@HCh-D, showing a large size
distribution (6.7 ± 2.8 nm). Thus, we can conclude that the
interaction of the hydroxyl groups on the surface is not strong
enough to immobilize the nanoparticles on the carbonaceous
support in an efficient manner. In contrast, for the
tetralkylammonium functionalized hydrochars under both mild
(Pd@HCh-E and Pd@HCh-F) and harsh (Pd@HCh-G and
Figure 9. Powder X-ray diffractogram corresponding to Pd@HCh-F (red),
showing the reference patterns for fcc Pd(0) structure (blue).
4
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Powder X-Ray Diffraction (PXRD) of Pd@HCh-F revealed the
presence of crystalline Pd(0) showing the expected fcc structure
(Figure 9). A broad band centered on 24° (2) points to the
presence of amorphous material due to the carbon-based support.
With the aim of determining the support structure, Raman
analyses were carried for HCh-D, HCh-F, Pd@HCh-D, and
Pd@HCh-F. However, any absorption corresponding to graphite
(G) or diamond (D) bands was observed, as reported for sucrose-
derived biochars obtained by pyrolysis at relative low temperature
(215 ºC).[37]
In order to evidence the functionalization of the support, solid
state NMR analyses were performed by means of 13C Cross-
Polarization Magic Angle Spinning (CP MAS) NMR experiments.
The 13C CP MAS NMR spectrum of Pd@HCh-F exhibited a peak
in the aliphatic region around 30 ppm, analogously to HCh-F, but
not present for HCh-D; this resonance could be attributed to the
N-functionalization of the hydrochar (Figure 10).
Table 1. Hydrogenation of 1-phenyl-1-propyne catalyzed by PdNP supported
on functionalized hydrochars.a
Entry Catalyst
Time
(h)
pH2
(bar) (%)b
Conv. Selectivity (%)b
1c
2d
3
Pd@HCh-D
2
2
1
1
3
3
1
1
>99
>99
34
>99 (2H)
Pd@HCh-F
Pd@HCh-D
Pd@HCh-F
>99 (2H)
91% (cis-2H’) + 9% 2H
4
>99
8% trans-2H’
+ 72%
cis-2H’ + 20% 2H
a Reaction conditions: 1 mmol of 1-phenyl-1-propyne (2), 0.5 mol% of Pd, 1 mL
of heptane at 50 ˚C. b Determined by GC using dodecane as internal standard.
c After the first run, TEM analysis evidenced the agglomeration of PdNPs (see
Figure S5a in the Supporting Information); its recycling gave only 70%
conversion. d After the first run, PdNPs were not modified (see Figure S5b in the
Supporting Information).
Then, we applied the most active catalyst, i.e. Pd@HCh-F, in the
hydrogenation of di-, tri- and tetra-substituted alkenes under 1 bar
H2 pressure (entries 1-4, Table 2). The cyclic conjugated alkene
3 led selectively to the corresponding hydrogenated compound
3H, even at 0.1 mol% Pd (entry 1, Table 2). Internal alkenes are
more challenging substrates; 2,3-dimethyl-but-2-ene (4) gave the
reduced compound under higher pressure (3 bar H2; entry 2,
Table 2). The geminal alkene 2,3-dimethyl-but-1-ene (5) mainly
led to the isomerization product (4, 65%) together with 2,3-
dimethylbutane (35%) (entry 3, Table 2). In accordance to these
results, the hydrogenation of (R)-limonene ((R)-6) mainly afforded
the product corresponding to the hydrogenation of the exocyclic
C=C bond (entry 4, Table 2).

Figure 10. 13C CP MAS NMR spectra of HCh-D, HCh-F, and Pd@HCh-F.
denotes signals probably due to residual DMF adsorbed on the surface.[38]
Consequently, Pd@HCh-F was the selected material for catalytic
studies; Pd@HCh-D (hydrochar bearing hydroxyl groups) and
commercial Pd/C (10 mol%) were used for control purposes.
4-Phenyl-3-buten-2-one (7) led selectively to the formation of 4-
phenylbutan-2-one (7H),
a common skeleton present in
fragrances (entry 5, Table 2). For this reaction, the catalyst was
reused ten consecutive runs preserving its catalytic behavior
(Figure 11); for all 10 runs, no palladium was detected by ICP-
AES for the extracted organic products (less than 0.05 ppm Pd,
limit of detection). TEM analyses after the 5th and 10th runs did not
show any morphological change in relation to the starting catalytic
material (see Figures S6 and S7 in the Supporting Information).
Thus, the functionalization by grafting tetraalkylammonium
groups via ether bond linkages allows the recyclability of the
supported nanocatalyst Pd@HCh-F for hydrogenation processes.
The performance of Pd@HCh-F was benchmarked to commercial
Pd/C. This commercial material gave quantitative conversions up
to three recyclings under the same reaction conditions (50 ºC, 30
min and 0.5 mol% catalyst loading), but the conversion decayed
to 36% in the fourth cycle. The efficient recycling capabilities of
Pd@HCh-F in comparison to Pd@HCh-D and commercial Pd/C
validate our mild functionalization strategy towards the design and
synthesis of robust hydrochar-supported catalysts which could be
of interest for other carbonaceous raw supports.[30, 40]
Pd-catalyzed hydrogenations
In this study, we chose the hydrogenation of 1-phenyl-1-propyne
as benchmark reaction, using both catalysts, Pd@HCh-D
(ammonium-free support) and Pd@HCh-F (ammonium-
functionalized support) under low H2 pressure (1 and 3 bar) and
moderate temperature (50 ºC), in the presence of 0.5 mol% Pd
loading. Both systems gave full conversion under 3 bar H2 for 2 h
(entries 1-2, Table 1). Under smoother conditions (1 h and 1 bar
H2 pressure), Pd@HCh-F kept its activity, while Pd@HCh-D led
to only 34% conversion (entries 3-4, Table 1). High chemo- and
stereoselectivity towards the formation of the cis-alkene was
obtained with both catalysts (entries 3-4, Table 1). TEM analyses
after hydrogenation (entries 1-2, Table 1) evidenced clear
differences between both catalytic materials: while Pd@HCh-F
was not modified, Pd@HCh-D showed agglomeration (see Figure
S5 in the Supporting Information), in accordance with the activity
loss when Pd@HCh-D was recycled (entry 1, Table 1). In contrast
to metal-based catalysts for the semihydrogenation of alkynes,[29e,
39]
the catalytic behavior of Pd@HCh-D and Pd@HCh-F proved
that the hydrochar supports did not passivate the palladium
surface, thus favoring the adsorption of alkenes.
5
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10.1002/cctc.201902305
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FULL PAPER
this
catalytic
system
only hydrogenates
conjugated
Table 2. Pd@HCh-F catalyzed hydrogenation of different functional groups.a
tetrasubstituted alkenes.
Entry Substrate Product
Pd
t
pH2
Conv. Selectivity
Exploration of the hydrogenation substrate scope Pd@HCh-F
revealed that both nitro and aldehyde groups can be reduced
under mild reaction conditions. In particular, benzaldehyde (9,
entry 7, Table 2) and nitrobenzene derivatives (10 and 11, entries
8-9, Table 2) were efficiently reduced; for 11, no
hydrodehalogenation was observed under these reaction
conditions. However, acetophenone and indole were not
hydrogenated by Pd@HCh-F even under harsher conditions (40
bar H2 and 50 ºC for 16 h).
(mol%) (h) (bar) (%)b
(%)b,c
0.5
(0.1)
1
1
>99
(98)
100
(100)
1d
(1) (1)
3
3H
2e
0.5
0.5
1
1
3
3
50
100
4H
4H
4
5
35 (4H)
65 (4)
3e
>99
100
80
60
40
20
0
4
0.5
1
3
>99
85 (6H)f
(R)-6
6H
7H
>99
(Run
10: >99)
5
6
0.5
0.5
0.5
1
3
100
100
7
49
(Run 2:
90,g
1
2
3
4
5
6
7
8
9
10
Recycling cycle
1
Run 3:
>99h)
Conversion
4-phenyl-2-butanone selectivity
8
8H
Figure 11. Recycling of hydrogenation of 4-phenyl-3-buten-2-one catalyzed by
Pd@HCh-F.
15
(1) (3)
3
>99
(30)
100
(100)
7d
0.5
9
9H
The slower hydrogenation of aldehydes compared to nitro groups
permitted to carry out a reductive amination in one pot procedure
starting from nitrobenzene and benzaldehyde to yield N-
benzylaniline (11) in 57% isolated yield (Figure 12). The reaction
proceeds via condensation of the formed aniline with the
unreacted aldehyde to form the corresponding benzylideneaniline
which undergoes hydrogenation much easily than the parent
aldehyde. Reaction by-products arising from reduction of the
aldehyde [i.e. aniline (32%), the condensation intermediate
(phenylmethylidene)aniline (8%), and also benzyl alcohol (9%)],
were detected by 1H NMR. The reaction conditions were not
further optimized.
0.5
(0.1)
0.5
(1) (1)
1
>99
(<5)
100
(100)
8d
10
10H
9
0.5
1
3
>99
100
11
11H
a
Reaction conditions: 1 mmol of substrate, 1 mL of heptane at 50 ˚C using
Pd@HCh-F as catalyst. b Determined by GC-MS analyses using dodecane as
internal standard. c Characterization of the product by NMR. d Data in brackets
correspond to 0.1 mol% catalyst loading. e Dodecane as solvent and heptane
as internal standard. f Menthane and isomerization products of menthene were
also detected. g after 6 h. h after 15 h.
With the aim of proving the high activity of Pd@HCh-F, we studied
the hydrogenation of a tetrasubstituted compound, 1,2,3,4,5-
pentamethylcyclopentadiene (entry 6, Table 2). At short time (1 h
under 3 bar H2), 49% conversion was achieved leading
exclusively to 1,2,3,4,5-pentamethylcyclopentene. The catalyst
was recycled and reused under the same conditions but at longer
times, giving full conversion after 15 h of reaction (after 6 h of
reaction, 90% conversion was attained). These results show that
Figure 12. Pd@HCh-F catalyzed one-pot reductive amination.
6
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10.1002/cctc.201902305
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To tune the surface chemistry properties of the synthesized hydrochars,
the materials were thermally modified. Thermal treatments were
performed in a vertical Thermoline 2100 furnace using a fixed bed quartz
reactor. HCh-A and HCh-B (1.0 and 1.5 g, respectively) were introduced
in the furnace at ambient conditions, heated to 290 °C (leading to HCh-C’
and HCh-D’) or 340 °C (leading to HCh-C and HCh-D) for 30 min, and
then cooled. The treatments were carried out under N2 flow (5 cm3/s) and
the temperature was increased at a 10 °C/min rate.
Conclusion
With the aim of synthesizing selectively functionalized hydrochar
supports derived from a naturally occurring sugar (sucrose), a
thermal treatment of HCh-A and HCh-B precursors afforded
enriched carbonaceous materials with hydroxyl groups exhibiting
no traces of carboxylic acids on the surface, together with little to
negligible porosity properties. Taking advantage of the chemical
stability of the ether bond linkages, a series of functionalized
Synthesis of functionalized hydrochars
tetraalkylammonium hydrochars were prepared enabling
a
comparative study towards the use of these materials as both
supports and stabilizers for the synthesis of palladium
nanoparticles. The ammonium groups prompted an electrostatic
stabilization and in consequence an efficient adsorption of the
metal nanoparticles on the hydrochars.
Two different functionalization conditions were employed for the
derivatization of carboxylic acid-free hydrochars HCh-C and HCh-D
(named mild and harsh, Figure 1).
General procedure under mild reaction conditions: NaH (2 equiv.) was
added to a suspension of the corresponding hydrochar (1 equiv. of OH
function as determined by Boehm titration for HCh-C or HCh-D) in dry
DMF (60 mL/mmol) under Ar. The reaction mixture was then heated to 90
ºC for 40 min. At that time, the ammonium salt 1 (6 equiv.) was added in
one solid portion and the reaction mixture was maintained at 90 ºC for 16
h under Ar. The solid was recovered by vacuum filtration and washed with
DMF (3 x 10 mL), HBr/MeOH (1/3 vol. ratio) (3 x 10 mL), MeOH (3 x 10
mL) and acetone (3 x 10 mL). The functionalized material was then dried
under reduced pressure to provide HCh-E (from HCh-C) and HCh-F (from
HCh-D).
These catalytic materials were straightforwardly prepared in a
one-pot procedure, by in-situ reduction of Pd(OAc)2 in the
presence of the corresponding support under hydrogen
atmosphere. Among these as-prepared materials, Pd@HCh-D
and Pd@HCh-F were chosen for catalytic evaluation due to the
exhibited stability of supports during the synthesis of the catalytic
materials (as evidenced by SEM analyses). These
heterogeneous catalysts were tested in the hydrogenation of
different unsaturated functional groups, revealing high selectivity.
Pd@HCh-F was highly efficient towards the full hydrogenation of
alkyne and alkene substrates under mild conditions. Moreover,
aldehyde and nitro groups were also hydrogenated. The
enhanced recyclability of Pd@HCh-F was proven, being reused
10 consecutive runs preserving the catalytic reactivity; no metal
leaching was detected in the extracted organic phases. Under the
same reaction conditions, the activity of commercial Pd/C
decayed after the third catalyst recycling, giving only a 36%
conversion in the fourth run.
General procedure under harsh reaction conditions: NaH (20 equiv.) was
added to a suspension of the corresponding hydrochar (1 equiv. of OH
function as determined by Boehm titration for HCh-C or HCh-D) in dry
DMF (60 mL/mmol) under Ar; the reaction mixture was heated to 90 ºC for
6 h. The supernatant was filtered out under Ar and discarded. Then, a
solution of the ammonium salt 1 (6 equiv.) in DMF (60 mL/mmol) was
added to the hydrochar residue and the reaction mixture was heated to 90
ºC for 16 h under Ar. The mixture was then filtered out and the hydrochar
residue was washed with DMF (3 x 10 mL), HBr/MeOH (3 x 10 mL), MeOH
(3 x 10 mL) and acetone (3 x 10 mL). The resulting solid was then dried
under reduced pressure to provide HCh-G (from HCh-C) and HCh-H (from
HCh-D). The as-prepared hydrochars were characterized by elemental
analysis, FTIR, and SEM. For a description of the characterization
techniques employed, see Section A in the Supporting Information.
Overall, the low porosity of HCh-D and derived hydrochars might
help against deleterious diffusion pathways through the catalyst
support itself, thus enabling milder reaction conditions than for
micro- and mesoporous catalytic materials.[12a, 12c] In contrast to
unfunctionalized supports such as Pd@HCh-D and those
40]
reported
in
the
literature,[30,
tetraalkylammonium
Synthesis of Pd@hydrochar-based supports
functionalization enables the recyclability of the catalytic material
Pd@HCh-F mainly thanks to the robustness of the support and
Pd-support electrosteric interactions.
Palladium acetate (5 mg, 0.022 mmol) was mixed with 0.100 g of the
corresponding hydrochar (HCh-C, HCh-D, HCh-E, HCh-F, HCh-G, HCh-
H) in 10 mL of ethanol (99.8%) in a Fisher-Porter bottle. The mixture was
then pressurized with 3 bar of H2 at 75 °C, and stirred overnight. The solid
was recovered by vacuum filtration, washed with ethanol 99.8% (3 x 10
mL) and dried under reduced pressure. All Pd@hydrochar materials were
characterized by Transmission Electron Microscopy (TEM). Pd@HCh-D
and Pd@HCh-F were further characterized by different techniques (see
section 3): solid state Nuclear Magnetic Resonance (ssNMR), elemental
analysis, SEM, FTIR, Raman, XPS, and ICP-AES.
Experimental Section
For general procedures, materials, and instruments, see Section A in the
Supporting Information.
Synthesis of (10-bromodecyl)triethylammonium bromide
Pd-catalyzed hydrogenation reactions
(10-Bromodecyl)triethylammonium bromide (1) was prepared in a solvent-
free approach from 1,10-dibromodecane and NEt3 at 90 ºC for 16 h as a
white solid (highly hygroscopic, 93% yield); see Section C in the
Supporting Information for further experimental and characterization data.
Substrate (1 mmol) in 1 mL of heptane and in the presence of 0.5 mol%
Pd of the corresponding catalytic material (Pd@HCh-D, Pd@HCh-F) was
pressurized at the convenient pressure (from 1 to 40 bar) and temperature,
and stirred for the appropriate time. After depressurization and cooling
down at room temperature, the liquid phase was recovered by micro-
filtration and the catalytic material washed with heptane (3 x 1 mL). The
combined heptane fractions were evaporated under reduced pressure and
the organic products were analyzed by Gas Chromatography coupled
Mass Spectrometry (GC-MS) and 1H NMR, using dodecane as internal
standard, unless otherwise stated.
Preparation of hydrochars
The hydrochars HCh-A and HCh-B have been recently reported[31] and
prepared based on the procedure reported by Demir-Cakan et al.[41] (see
Section B in the Supporting Information).
7
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10.1002/cctc.201902305
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FULL PAPER
M. Giraud, F. Mammeri, J. Peron, J. Y. Piquemal, L. Sicard, G. Viau,
Chem. Soc. Rev. 2018, 47, 5187.
[11] a) G. Budroni, A. Corma, H. García, A. Primo, J. Catal. 2007, 251,
345; b) B. Karimi, M. Khorasani, H. Vali, C. Vargas, R. Luque, ACS
Catal. 2015, 5, 4189.
Despite the different porosity characteristics (specific surface area of 759
m2g-1 and total pore volumes of 0.23 and 0.31 cm3g-1),[34] palladium
supported on activated carbon (Pd/C, 10 mol%) was tested as catalyst
control.
[12] a) S. Mandal, D. Roy, R. V. Chaudhari, M. Sastry, Chem. Mater.
2004, 16, 3714; b) M. Navlani-García, M. Martis, D. Lozano-Castelló,
D. Cazorla-Amorós, K. Mori, H. Yamashita, Catal. Sci. Technol. 2015,
5, 364; c) J. Zhang, L. Wang, Y. Shao, Y. Wang, B. C. Gates, F. S.
Xiao, Angew. Chem., Int. Ed. 2017, 56, 9747.
[13] D. Divakar, D. Manikandan, V. Rupa, E. L. Preethi, R.
Chandrasekar, T. Sivakumar, J. Chem. Technol. Biotechnol. 2007, 82,
253.
Catalytic recycling
The catalyst was recovered after hydrogenation by filtration, washed with
heptane (5 x 10 mL) and dried under vacuum for 2 h before to be used in
the subsequent hydrogenation reaction.
[14] a) H. P. Hemantha, V. V. Sureshbabu, Org. Biomol. Chem. 2011,
9, 2597; b) V. L. Budarin, J. H. Clark, R. Luque, D. J. Macquarrie, R.
J. White, Green Chem. 2008, 10, 382.
Acknowledgements
[15] a) L. Chen, H. Chen, R. Luque, Y. Li, Chem. Sci. 2014, 5, 3708;
b) J. Hermannsdörfer, R. Kempe, Chem. Eur. J. 2011, 17, 8071.
[16] S.-F. Jiang, L.-L. Ling, Z. Xu, W.-J. Liu, H. Jiang, Ind. Eng. Chem.
Res. 2018, 57, 13055.
[17] X. Sun, Y. Li, Angew. Chem., Int. Ed. 2004, 43, 597.
[18] a) B. Cornelio, G. A. Rance, M. Laronze-Cochard, A. Fontana, J.
Sapi, A. N. Khlobystov, J. Mater. Chem. A 2013, 1, 8737; b) B.
Cornelio, A. R. Saunders, W. A. Solomonsz, M. Laronze-Cochard, A.
Fontana, J. Sapi, A. N. Khlobystov, G. A. Rance, J. Mater. Chem. A
2015, 3, 3918.
The Centre National de la Recherche Scientifique (CNRS) and
the Université de Toulouse 3 – Paul Sabatier are gratefully
acknowledged for their financial support. The work was also
supported by the Foundation for Science and Technology (FCT)
through projects UID/Multi/00612/2019 to Centro de Química e
Bioquímica,
ERQ/1648/2014
UID/QUI/00100/2019
and CATSUS
and
PhD
PTDC/QEQ-
fellowship
(PD/BD/105993/2014) to T. A. G. D. The authors thank Yannick
Coppel for helpful discussions concerning the solid state NMR
studies, and S. Mallet-Ladeira and L. Vendier for X-ray diffraction
analyses.
[19] S. Sadjadi, M. Akbari, B. Léger, E. Monflier, M. M. Heravi, ACS
Sustainable Chem. Eng. 2019, 7, 6720.
[20] a) M. Nasrollahzadeh, S. Mohammad Sajadi, A. Rostami-
Vartooni, M. Alizadeh, M. Bagherzadeh, J. Colloid Interface Sci. 2016,
466, 360; b) S. I. El-Hout, S. M. El-Sheikh, H. M. A. Hassan, F. A.
Harraz, I. A. Ibrahim, E. A. El-Sharkawy, Appl. Catal., A. 2015, 503,
176.
Keywords: Hydrochar, Palladium nanoparticles, Hydrogenation,
[21] Y. Chen, X. Ai, B. Huang, M. Huang, Y. Huang, Y. Lu, Cellulose
2017, 24, 2743.
Support functionalization, Recycling.
[22] Y. Chen, J. Chen, S. Chen, K. Tian, H. Jiang, J. Mater. Chem. A
2015, 3, 9843.
[23] J. Vieillard, N. Bouazizi, R. Bargougui, N. Brun, P. Fotsing
Nkuigue, E. Oliviero, O. Thoumire, N. Couvrat, E. Djoufac Woumfo,
G. Ladam, N. Mofaddel, A. Azzouz, F. Le Derf, Chem. Eng. J. 2018,
342, 420.
[24] a) N. Tran Hai, F.-C. Huang, C.-K. Lee, H.-P. Chao, Green
Process. Synth. 2017, 6, 565; b) H. Wang, L. Ma, K. Cao, J. Geng, J.
Liu, Q. Song, X. Yang, S. Li, J. Hazard. Mater. 2012, 229-230, 321; c)
D.-P. Yang, Z. Li, M. Liu, X. Zhang, Y. Chen, H. Xue, E. Ye, R. Luque,
ACS Sustainable Chem. Eng. 2019, 7, 4564.
[25] A. Dieguez-Alonso, A. Funke, A. Anca-Couce, A. Rombolà, G.
Ojeda, J. Bachmann, F. Behrendt, Energies 2018, 11, 496.
[26] Y. Shi, T. Zhang, H. Ren, A. Kruse, R. Cui, Bioresour Technol.
2018, 247, 370.
[1] A. Reina, A. Serrano-Maldonado, E. Teuma, E. Martin, M. Gómez,
Catal. Commun. 2018, 104, 22.
[2] a) I. Favier, D. Pla, M. Gómez, Chem. Rev. 2019, doi:
10.1021/acs.chemrev.9b00204; b) A. Bouriazos, C. Vasiliou, A.
Tsichla, G. Papadogianakis, Catal. Today 2015, 247, 20; c) S. Bulut,
Z. Fei, S. Siankevich, J. Zhang, N. Yan, P. J. Dyson, Catal. Today
2015, 247, 96; d) D. J. Gavia, Y.-S. Shon, ChemCatChem 2015, 7,
892; e) M. R. Knecht, D. B. Pacardo, Anal. Bioanal. Chem. 2010, 397,
1137.
[3] a) A. B. Dongil, L. Pastor-Perez, J. L. G. Fierro, N. Escalona, A.
Sepulveda-Escribano, Appl. Catal., A 2016, 513, 89; b) K. Duan, Z.
Wang, C. Hardacre, Z. Liu, S. Chansai, C. Stere, Catal. Today 2019,
332, 69; c) G. C. Mondragon Rodriguez, B. Saruhan, O. Petrova, W.
Gruenert, Top. Catal. 2009, 52, 1723; d) M. Y. Smirnov, E. I. Vovk, A.
V. Kalinkin, A. V. Pashis, V. I. Bukhtiyarov, Kinet. Catal. 2012, 53, 117.
[4] T. Kahl, K. Schröder, F. R. Lawrence, W. J. Marshall, H. Höke, R.
Jäckh, in Ullmann's Encyclopedia of Industrial Chemistry, 2011.
[5] a) B. Hosseinkhani, T. Hennebel, S. Van Nevel, S. Verschuere, M.
M. Yakimov, S. Cappello, M. Blaghen, N. Boon, Environ. Sci. Technol.
2014, 48, 550; b) M. M. Khin, A. S. Nair, V. J. Babu, R. Murugan, S.
Ramakrishna, Energy Environ. Sci. 2012, 5, 8075; c) B.-Z. Wu, H.-Y.
Chen, S. J. Wang, C. M. Wai, W. Liao, K. Chiu, Chemosphere 2012,
88, 757; d) B. Kumari, D. P. Singh, Ecol. Eng. 2016, 97, 98.
[6] J. Bassil, A. AlBarazi, P. Da Costa, M. Boutros, Catal. Today 2011,
176, 36.
[7] A. Balanta, C. Godard, C. Claver, Chem. Soc. Rev. 2011, 40, 4973.
[8] a) T. Dang-Bao, D. Pla, I. Favier, M. Gómez, Catalysts 2017, 7,
207; b) J. D. Scholten, B. C. Leal, J. Dupont, ACS Catal. 2012, 2, 184;
c) C. Janiak, in Ionic Liquids (ILs) in Organometallic Catalysis (Eds.:
J. Dupont, L. Kollár), Springer Berlin Heidelberg, Berlin, Heidelberg,
2015, pp. 17.
[9] a) S. Noël, B. Léger, A. Ponchel, K. Philippot, A. Denicourt-Nowicki,
A. Roucoux, E. Monflier, Catal. Today 2014, 235, 20; b) A. Denicourt-
Nowicki, A. Roucoux, in Nanomaterials in Catalysis (Eds.: P. Serp, K.
Philippot), Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, 2013,
pp. 55; c) J. Yang, J. Y. Lee, J. Y. Ying, Chem. Soc. Rev. 2011, 40,
1672.
[27] a) H. Choi, S. R. Al-Abed, S. Agarwal, D. D. Dionysiou, Chem.
Mater. 2008, 20, 3649; b) F. He, D. Zhao, Environ. Sci. Technol. 2005,
39, 3314.
[28] a) M. Nunes, I. M. Rocha, D. M. Fernandes, A. S. Mestre, C. N.
Moura, A. P. Carvalho, M. F. R. Pereira, C. Freire, RSC Adv. 2015, 5,
102919; b) D. M. Fernandes, A. S. Mestre, A. Martins, N. Nunes, A.
P.
Carvalho,
C.
Freire,
Catal.
Today
2019,
doi:
10.1016/j.cattod.2019.02.048; c) A. S. Mestre, E. Tyszko, M. A.
Andrade, M. Galhetas, C. Freire, A. P. Carvalho, RSC Adv. 2015, 5,
19696.
[29] a) L. Rodríguez-Pérez, E. Teuma, A. Falqui, M. Gómez, P. Serp,
Chem. Commun. 2008, 4201; b) E. Castillejos, M. Jahjah, I. Favier, A.
Orejon, C. Pradel, E. Teuma, A. M. Masdeu-Bulto, P. Serp, M. Gómez,
ChemCatChem 2012, 4, 118; c) I. Favier, M.-L. Toro, P. Lecante, D.
Pla, M. Gómez, Catal. Sci. Technol. 2018, 8, 4766; d) F. Chahdoura,
C. Pradel, M. Gómez, Adv. Synth. Catal. 2013, 355, 3648; e) A. Reina,
I. Favier, C. Pradel, M. Gómez, Adv. Synth. Catal. 2018, 360, 3544; f)
T. Dang-Bao, C. Pradel, I. Favier, M. Gómez, Adv. Synth. Catal. 2017,
359, 2832.
[30] a) C. W. A. Chan, Y. Xie, N. Cailuo, K. M. K. Yu, J. Cookson, P.
Bishop, S. C. Tsang, Chem. Commun. 2011, 47, 7971; b) P. Burguete,
A. Corma, M. Hitzl, R. Modrego, E. Ponce, M. Renz, Green Chem.
2016, 18, 1051.
[10] a) A. Reina, C. Pradel, E. Martin, E. Teuma, M. Gómez, RSC Adv.
2016, 6, 93205; b) F. Fiévet, S. Ammar-Merah, R. Brayner, F. Chau,
[31] T. A. G. Duarte, A. P. Carvalho, L. M. D. R. S. Martins, Catal.
Today 2019, doi: 10.1016/j.cattod.2019.04.044.
8
This article is protected by copyright. All rights reserved.

10.1002/cctc.201902305
ChemCatChem
FULL PAPER
[32] J. Clayden, N. Greeves, S. Warren, Organic Chemistry, OUP
Oxford, 2012.
[33] a) T. J. Bandosz, C. O. Ania, in Interface Science and Technology,
Vol. 7 (Ed.: T. J. Bandosz), Elsevier, 2006, pp. 159; b) H. Marsh, F.
Rodríguez-Reinoso, in Activated Carbon, Elsevier Science Ltd,
Oxford, 2006; c) J. L. Figueiredo, M. F. R. Pereira, M. M. A. Freitas, J.
J. M. Órfão, Carbon 1999, 37, 1379.
[34] M. Thommes, K. Kaneko, A. V. Neimark, J. P. Olivier, F.
Rodriguez-Reinoso, J. Rouquerol, K. S. Sing, Pure Appl. Chem. 2015,
87, 1051.
[35] E. Pretsch, P. Bühlmann, M. Badertscher, Structure
Determination of Organic Compounds: Tables of Spectral Data,
Springer Berlin Heidelberg, 2009.
[36] J. Durand, E. Teuma, M. Gómez, Eur. J. Inorg. Chem. 2008, 2008,
3577.
[37] T. Reed, J. Fournier, G. Nelson, Raman Characterization of
Biochar
Bonding,
2009.
https://www.peaklab.net/peaklab-
reports/raman-characterization-of-biochar-bonding/.
[38] The use of cross-polarization excitation techniques 13C CP MAS
permits to suppress signals from solvent molecules due to their
relative mobility properties. However, signals of adsorbed DMF
cannot be excluded.
[39] a) v. H. Lindlar, Helv. Chim. Acta 1952, 35, 446; b) P. T. Witte, P.
H. Berben, S. Boland, E. H. Boymans, D. Vogt, J. W. Geus, J. G.
Donkervoort, Top. Catal. 2012, 55, 505; c) P. Gallois, J. J. Brunet, P.
Caubere, J. Org. Chem. 1980, 45, 1946; d) D. Savoia, E. Tagliavini,
C. Trombini, A. Umani-Ronchi, J. Org. Chem. 1981, 46, 5340; e) M.
Zhao, Chem. Asian J. 2016, 11, 461.
[40] M. Oregui-Bengoechea, N. Miletić, W. Hao, F. Björnerbäck, M. H.
Rosnes, J. S. Garitaonandia, N. Hedin, P. L. Arias, T. Barth, ACS
Sustain. Chem. Eng. 2017, 5, 11226.
[41] R. Demir-Cakan, N. Baccile, M. Antonietti, M.-M. Titirici, Chem.
Mater. 2009, 21, 484.
9
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Entry for the Table of Contents
Tetraalkylammonium functionalized hydrochars as efficient supports for palladium nanocatalysts.
Tiago A. G. Duarte, Isabelle Favier, Christian Pradel, Luísa M. D. R. S. Martins, Ana P. Carvalho,* Daniel Pla,* and Montserrat
Gómez*
Tetraalkylammonium-functionalized hydrochars outperform classical Pd on carbon supports for catalyst heterogenization in terms of
morphology-controlled palladium nanoparticle synthesis, efficient immobilization and recyclability towards hydrogenation.
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