Pd-Nanoparticles immobilized organo-functionalized SBA-15: An efficient heterogeneous catalyst for selective hydrogenation of C–C double bonds of α,β-unsaturated carbonyl compounds

Article abstract of DOI:10.1016/j.mcat.2020.111200

A novel PdNPs/SBA-NH₂-LA catalyst has been prepared by a post-synthetic grafting approach via successive anchoring of propylamine (SBA-NH₂) and lipoic acid (SBA-NH₂-LA) functional groups followed by palladium nanoparticles immobilization. The Physico-chemical properties of the catalyst were extensively investigated by XRD, N₂ adsorption-desorption, XPS, FT-IR, and TEM analysis. The PdNPs/SBA-NH₂-LA catalyst is found to be highly selective for the hydrogenation of C–C double bonds of α, β-unsaturated carbonyl compounds. Excellent conversion (95–99 %) and selectivity (>99 %) with high turn over frequency (330?1065 h^?1) achieved at room temperature under atmospheric hydrogen pressure within 30?90 min of reaction time. This kind of high activity is expected from its structural and textural integrity of the catalyst.

Full text of DOI:10.1016/j.mcat.2020.111200

Molecular Catalysis 497 (2020) 111200
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.journals.elsevier.com/molecular-catalysis
Pd-Nanoparticles immobilized organo-functionalized SBA-15: An efficient
heterogeneous catalyst for selective hydrogenation of C C double bonds of
–
α
,β-unsaturated carbonyl compounds
a,
c,
d
,
c
b
,
d
c,
Anand Narani
*, Hari Prasad Reddy Kannapu , Kishore Natte , David Raju Burri **
a
Biofuels Division, CSIR-Indian Institute of Petroleum, Haridwar Road, Mohkampur, Dehradun, 248005, Uttarakhand, India
Chemical and Material Sciences Division, CSIR-Indian Institute of Petroleum, Haridwar Road, Mohkampur, Dehradun, 248005, Uttarakhand, India
Catalysis Laboratory, I&PC Division, Indian Institute of Chemical Technology, Hyderabad, 500 007, India
b
c
d
Academy of Scientific and Innovative Research (AcSIR), Sector 19, Kamla Nehru Nagar, Ghaziabad, Uttar Pradesh, 201 00, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
A novel PdNPs/SBA-NH -LA catalyst has been prepared by a post-synthetic grafting approach via successive
2
SBA-15
anchoring of propylamine (SBA-NH
nanoparticles immobilization. The Physico-chemical properties of the catalyst were extensively investigated by
XRD, N adsorption-desorption, XPS, FT-IR, and TEM analysis. The PdNPs/SBA-NH -LA catalyst is found to be
highly selective for the hydrogenation of C C double bonds of
, β-unsaturated carbonyl compounds. Excellent
conversion (95–99 %) and selectivity (>99 %) with high turn over frequency (330ꢀ 1065 h ) achieved at room
temperature under atmospheric hydrogen pressure within 30ꢀ 90 min of reaction time. This kind of high activity
is expected from its structural and textural integrity of the catalyst.
2 2
) and lipoic acid (SBA-NH -LA) functional groups followed by palladium
Anchoring
Palladium nanoparticles
Selective hydrogenation
High TOF
2
2
–
α
ꢀ 1
Introduction
homogeneous systems have severe drawbacks like catalyst separation
and reusability, which leads to the generation of large amounts of waste
Hydrogenation is a key step in the industry for the synthesis of fine
and at the same time, manufacturing process will become costly. With
commercially available Pd/C catalyst, chemoselectivity was the major
problem [4]. To avoid these issues, Crooks [30], Kim [31], Ondruschka
[32], Stolle [33], Bhanage [34,35], Kantam [36], David [37], Mallick
[38], Shen [39] and others [40,41] [42–45], have developed supported
chemicals, fuels, and drug molecules. [1–7] Among several hydroge-
nation reactions, chemoselective hydrogenation of C C double bonds of
–
α
, β-unsaturated carbonyl compounds received enormous interest in the
fields of academia and industry because, the corresponding saturated
aldehydes/ketones have broad applications in food, fragrance, and
cosmetic industries. [8–10] Also, the hydrogenated products serve as
important intermediates for the preparation of biologically active mol-
ecules. [11,12]
Pd nanoparticles and used for hydrogenation of C
β-unsaturated carbonyl compounds in different reaction conditions.
Also, Au supported on mesostructured CeO catalyst reported for hy-
drogenation of
, β-unsaturated carbonyl compounds. [46] However,
this catalytic system was targeted for C
–
C double bonds of
α,
2
α
Considering the thermodynamics, competing for C–
O, aromatic ring
hydrogenation, and deoxygenation reactions, the chemoselective hy-
drogenation of C C double bonds of
–
–
O bond hydrogenation rather
C bond. Recently, Cu nanoparticles supported on silica
catalyst reported for selective hydrogenation of
, β-unsaturated
–
–
than the C
–
–
α
, β-unsaturated carbonyl com-
α
pounds is still remained as a challenging task. [13] In this respect,
numerous homogeneous metal complexes such as Ru [14,15], Rh [16,
carbonyl compounds in Toulene solvent. [47] Although the catalyst
displays an excellent catalytic activity and selectivity but intolerant to a
few functional groups and requires high pressures. Very recently, Yang
et al., developed biomass derived cobalt nanoparticles for chemo-
1
7], Pt [18], Ir [19–21], Pd [22,23], Ti [24] [25], Mo [26], Cu [27,28],
and Fe [29] have been employed for the selective hydrogenation of C
double bonds of
, β-unsaturated carbonyl compounds. They exhibit
high conversion with excellent selectivity. However, these
–
C
α
selective hydrogenation of
α, β-unsaturated carbonyl compounds in a
water solvent. [48] The catalyst exhibits an excellent activity and
*
Corresponding author at: Biofuels Division, CSIR-Indian Institute of Petroleum, Haridwar Road, Mohkampur, Dehradun, 248005, Uttarakhand, India.
** Corresponding author.
E-mail address: anand.narani@iip.res.in (A. Narani).
https://doi.org/10.1016/j.mcat.2020.111200
Received 7 January 2020; Received in revised form 28 August 2020; Accepted 30 August 2020
Available online 30 September 2020
2
468-8231/© 2020 Elsevier B.V. All rights reserved.

A. Narani et al.
Molecular Catalysis 497 (2020) 111200
–
afforded 61–97 % yields of C
–
C bond hydrogenated products. Despite
Preparation of catalyst
its remarkable activity and selectivity, the catalysts require high pres-
sures and long reaction times.
2
Preparation of PdNPs/SBA-NH -LA catalyst
On the other hand, mesoporous silica materials have recently
garnered interest as a catalytic supports due to their fascinating physical
and chemical properties. [49,50] Among the availability of various
mesoporous silica materials, hexagonally ordered mesoporous SBA-15
display excellent exceptional properties such as high surface area,
thermal, hydrothermal stability, thick pore walls, and larger and uni-
form pore size, which can provide the ideal environment to grow the
metal nanoparticles inside the pores of SBA-15 [51–54]. The deposition
of Pd nanoparticles into the pores of SBA-15 can be achieved by con-
ventional methods. However, leaching of the active metal centers into
the reaction media is a severe problem from an industrial perspective. In
contrast, the immobilization of active metal sites by using organic
functional groups between SBA-15 and active metal centers has emerged
as an efficient method to prepare small and isolated metal nanoparticles
Pd-Nanoparticles immobilized on lipoic acid functionalized SBA-15
has been synthesized as per the reported procedure [55], and the de-
tails are shown in Scheme 2. Initially, the mesostructured parent SBA-15
was synthesized using P123 triblock copolymer surfactant
(EO20-PO70-EO20, Aldrich, USA) as a structure-directing agent, tet-
raethylorthosilicate as silica resource using the hydrothermal process
under acidic conditions with EO20PO70EO20:2 M HCl: TEOS: H
2
O =
2:60:4.25:15 ratio. At last, the template free SBA-15 is obtained by
◦
calcination at 550 C for 6 h, and it has been used as catalyst support.
The amine-functionalized SBA-15 (SBA-NH
bilizing 3-(Aminopropyl)triethoxysilane (APTES) on pre-treated tem-
plate free SBA-15 in toluene under N atmosphere at reflux temperature.
Later, the lipoic acid (LA) has been anchored onto SBA-NH
(SBA-NH -LA) using an amide coupling agent (1-Hydroxy benzotriazole
2
) was prepared by immo-
2
2
2
with
a
narrow distribution [55–60]. Furthermore, these
(HOBT) and EDC (lipoic acid: HOBT: EDC at 1:1.1:1.5) in dichloro-
methane at room temperature for 24 h under an inert atmosphere.
Finally, Pd nanoparticles immobilized on lipoic acid-functionalized
SBA-15 achieved by reducing the Palladium acetate in methanol solu-
organo-functionalized materials will provide synergistic properties of
both organic moiety and porous structure, such as versatile functional-
ization ability for immobilization of active sites, high surface area, and
structural stability [61]. Additionally, these materials also act as het-
erogeneous catalysts to overcome the leaching problems associated with
conventional preparation methods. Recently, Esmail et al. reported
organofunctionalized mesoporous silica materials along with the depo-
sition of metal nanoparticles for a wide variety of oxidation reactions.
These catalysts are highly active and selective for the corresponding
products. Moreover, these catalysts are easily recoverable and reusable
for numerous cycles. [50,62–64]
4 2
tion using NaBH under the N atmosphere at room temperature over-
2
night. The resulted catalyst is designated as PdNPs/SBA-NH -LA.
Catalytic activity
All hydrogenation reactions were carried out in a 25 mL round
bottom flask. In a typical experiment, 1 mmol of the substrate was dis-
solved in 3 mL solvent, added 10 mg of catalyst to the reaction mixture,
Herein, for the first time, we demonstrate a novel method for the
preparation of finely dispersed Pd nanoparticles on lipoic acid func-
2
and continuously stirred at room temperature under 1 atm H atmo-
tionalized SBA-15 (PdNPs/SBA-NH
and reusable for chemoselective hydrogenation of C
, β-unsaturated carbonyl compounds (Scheme 1).
2
-LA). The catalyst is highly stable
sphere (hydrogen balloon) for a required time. After completion of the
reaction, the catalyst was separated using simple filtration and washed
with acetone followed by drying. The products were analyzed and
identified by GC–MS (QP-5050 model, M/s. Shimadzu Instruments,
Japan) equipped with ZB-5 capillary column (0.32 mm diameter and 25
m long, supplied by M/s. J & W Scientific, USA).
–
C double bonds of
α
Experimental
Materials and instrumentation
Results and discussion
Unless otherwise stated, all chemicals are purchased from Sigma-
Aldrich and used as received. Low-angle XRD patterns were recorded
As shown in Scheme 2, the PdNPs/SBA-NH -LA catalyst was syn-
2
on Ultima IV X-ray diffractometer at 40 kV and 40 mA using CuK
diation over the range 0.7_ 6 2h 6 5.0. Wide-angle X-ray diffraction
XRD) patterns of catalysts were obtained on a Bruker D8 Advance X-
α
ra-
thesized in three steps. The loading of propylamine, lipoic acid func-
tional groups, and PdNPs are determined by C, H, N, S, and ICP-MS
analysis. The propylamine loading was 2.0 mmol/g, and lipoic acid was
0.6 mmol/g. The Pd content was determined to be 1.96 wt%.
(
Ray Powder Diffractometer using Ni filtered Cu Ka radiation at a scan
◦
speed of 2 min-1. X-ray photoelectron spectroscopy (XPS) analysis of
the catalyst was carried out by a Kratos analytical spectrophotometer,
with Mg Ka monochromated excited radiation (1253.6 eV). The residual
pressure in the analysis chamber was around 10ꢀ 9m bar. The binding
energy (BE) measurements were corrected for charging effects con-
cerning the C 1s peak of the adventitious carbon (284.6 eV). Infrared
spectra were recorded on a Bruker Alpha-T, FT-IR system, in the scan
Catalyst characterization
N2 adsorption-desorption analysis
The structure and textural properties of SBA-15, SBA-NH , SBA-NH -
2
2
LA, and PdNPs/SBA-NH -LA are determined by N2 adsorption-
2
ꢀ 1
range of 4000–400 cm . A Philips Tecnai F12 FEI transmission electron
microscope (TEM) operating at 80–100 kV was used to record TEM
images.
desorption analysis, and the corresponding isotherms are displayed in
Fig. 1. All four samples exhibit type-IV isotherm with H1 hysteresis loop,
[65,66] representing the intact of the ordered mesoporous structure of
parent SBA-15 after the successive functionalization of propylamine,
lipoic acid groups, and deposition of Pd nanoparticles. Inset (Fig. 1)
shows the pores are distributed between 4.6–7.10 nm. The BET surface
2
area of SBA-15 is 713 m /g, and a decrease in the surface area (429
2
m /g) was observed after successive functionalization with propylamine
2
and lipoic acid. Further, the BET surface area is reduced to 398 m /g
after the immobilization of Pd nanoparticles. A similar trend was
monitored in the case of pore volume and pore diameter, indicating the
partial blockage of pores by the introduction of propylamine, lipoic acid
groups, and Pd nanoparticles on the surface of the parent SBA-15
(Table 1).
Scheme 1. Selective hydrogenation of C
–
C double bonds of
α,β-unsaturated
carbonyl compounds over PdNPs/SBA-NH
2
-LA catalyst.
2

A. Narani et al.
Molecular Catalysis 497 (2020) 111200
2
Scheme 2. Schematic representation of PdNPs/SBA-NH -LA catalyst.
XRD analysis
The low-angle X-ray diffraction analysis of SBA-15, SBA-NH
-LA, and PdNPs/SBA-NH -LA catalysts is shown in Fig. 2. All the
catalysts exhibited three well-resolved diffracted peaks. The intense
2
, SBA-
NH
2
2
◦
◦
◦
peak at 0.95–1.01 and two weak peaks at 1.67ꢀ 1.71 , 1.91ꢀ 1.96 are
corresponding to (100), (110), and (200) planes, representing the
characteristics of ordered Mesoporous structure. [67] The XRD results
suggest that the 2D structure of mesoporous SBA-15 has not been
changed during the preparation of the PdNPs/SBA-NH
However, the decrease in the intensity of (100) and (110), (200) planes
of SBA-NH , SBA-NH -LA, and PdNPs/SBA-NH -LA might be due to the
2
-LA catalyst.
2
2
2
loss of some uniformity in the 2D hexagonal structure of SBA-15 by filled
with propylamine and lipoic acid functional groups.
2
The wide-angle XRD pattern of the PdNPs/SBA-NH -LA catalyst is
◦
◦
displayed in Fig. 3. The diffracted peaks observed at 40.11 , 46.74 and
◦
6
8.1 on the 2θ scale are contributions from (111), (200) and (220)
planes of palladium in the metallic state, which is being by the reported
values (JCPDS file No.87-0639).
Fig. 1. N
2
adsorption-desorption isotherms of PdNPs/SBA-NH
2
-LA samples (a)
SBA-15, (b) SBA-NH
2
, (c) SBA-NH
2
-LA, and (d) PdNPs/SBA-NH -LA.
2
Table 1
Structural and textural properties of SBA-15, SBA-NH
2
, SBA-NH
2
-LA, and
PdNPs/SBA-NH
2
-LA.
Catalysts
S
BET
2
V
t
D
BJH
d
100
a
o
t
3
[c]
[d]
[e]
[f]
(
m /
(cm /
[b]
(nm)
(nm)
(nm)
(nm)
[
a]
g)
g)
SBA-15
713
468
429
1.01
0.87
0.82
6.99
6.86
6.01
9.29
8.92
8.83
10.73
10.30
10.19
5.63
5.19
5.09
SBA-NH
SBA-NH
LA
2
2
-
PdNPs/SBA-
NH -LA
398
0.79
5.98
8.74
10.09
4.99
2
[
a] BET surface area. [b] Total pore volume. [c] BJH pore diameter. [d] d(100)
spacing. [e] Unit cell parameter (a
= 2 x d(100)/√3). [f] Pore wall thickness (t
– pore size).
o
=
a
o
2 2
Fig. 2. Low angle XRD pattern of (a) SBA-15, (b) SBA-NH , (c) SBA-NH -LA,
and (d) PdNPs/SBA-NH -LA.
2
3

A. Narani et al.
Molecular Catalysis 497 (2020) 111200
2
Fig. 3. Wide-angle XRD pattern of PdNPs/SBA-NH -LA catalyst.
1
3
Fig. 5. Solid-state C CP-MAS NMR spectra of SBA-NH
2 2
and SBA-NH -
XPS analysis
XPS analysis has been carried out to determine the oxidation state of
Pd in the prepared PdNPs/SBA-NH -LA catalyst, and the corresponding
spectra is shown in Fig. 4. The survey XPS spectra of PdNPs/SBA-NH -LA
Inset, Fig. 4) disclose the presence of Pd, Si, and Oxygen in the catalyst.
LA samples.
2
2
(
As shown in Fig. 4, the Pd 3d peak fitted into two peaks, the binding
energy at 335.9 eV is attributed to 3d5/2, and the energy band centered
at 342.1 eV is associated with 3d3/2 of Pd in zero oxidation state. No
+
2
evidence of Pd presence was observed, indicating the palladium is in
the reduced form [68] (Fig. 4).
Solid-state 13C CP-MAS NMR analysis
The functionalization of 3-(Aminopropyl)triethoxysilane (APTES)
followed by anchoring of lipoic acid on the surface of SBA-15 has been
confirmed by solid-state 1 C CP-MAS NMR analysis (Fig. 5). As shown in
3
Fig. 5, three peaks observed at 13.2, 24.3, and 45.6 ppm respectively for
sample, corresponding to 1C, C, and 3C of 3-(Aminopropyl)
2
SBA-NH
2
triethoxysilane (APTES), confirming the immobilization of propylamine
group on the surface of SBA-15. [69] After treating of SBA-NH with
lipoic acid, the –C = O peak of pure lipoic acid (182 ppm) [70] shifted to
67.5 ppm (SBA-NH -LA), representing the amide bond formation be-
tween –NH and ꢀ COOH groups of SBA-NH and lipoic acid. [70] In
addition, SBA-NH -LA shows the new peaks in the aliphatic region
2
2 2
Fig. 6. FT-IR spectra of (a) SBA-15, (b) SBA-NH , (c) SBA-NH -LA samples.
1
2
2
2
ꢀ 1,
NH
2
-LA. All samples exhibited broadband between 3650ꢀ 3100 cm
2
which arise from the combination of ꢀ OH stretching and intermolecular
(
10ꢀ 55 ppm); however, these peaks are merged with the of SBA-NH
2
hydrogen bonding vibrations. New bands appeared in the range of
signals.
-1
-1
2
937ꢀ 2860 cm and 1494ꢀ 1383 cm for SBA-NH
samples, attributed to ꢀ CH stretching and bending vibrations of
anchored propyl amine, lipoic acid groups on the surface of SBA-15.
2 2
and SBA-NH -LA
2
FT-IR analysis
Fig. 6 shows the FT-IR spectra of (a) SBA-15, (b) SBA-NH
2
(c) SBA-
-1
Further, SBA-NH
bending vibration of –NH
appeared for the SBA-NH
-LA sample at 1520 cm-1 and 1648 cm ,
O stretching frequency in amide (II) group and
2
shows the band at 1566 cm , which is due to the
2
group. [71,72] Two additional bands
-1
2
–
C
–
–
allocated to
bending vibrations of –NH group, [55,73] representing the formation
amide bond between –NH and ꢀ COOH groups of propylamine and
2
lipoic acid on SBA-15.
TEM analysis
2
The structure and morphology of the PdNPs/SBA-NH -LA catalyst
were analyzed by TEM analysis, and the corresponding image is shown
in Fig. 7. The particle size distribution graph is shown in Fig. 7 as an
inset. The TEM analysis results reveal that the Pd nanoparticles are
spherical and homogeneously distributed throughout the SBA-15 ma-
trix. The average diameter of Pd nanoparticles determined to be around
1
2ꢀ 13 nm with a narrow distribution.
Hydrogenation of C C double and triple bonds
2
The catalytic performance of the PdNPs/SBA-NH -LA catalyst was
–
Fig. 4. XPS spectra of PdNPs/SBA-NH
2
-LA catalyst.
4

A. Narani et al.
Molecular Catalysis 497 (2020) 111200
Table 3
Hydrogenation of 1,3-Diphenyl-2-propen-1-one over different catalysts.
Entry
Catalyst
Time
h)
Conversion
(%)
Selectivity
(%)
TOF
ꢀ
1 a
(
(h
)
1
2
3
4
5
SBA-15
24
–
–
–
–
SBA-NH2
Pd/SBA-15
24
–
–
1.5
1.5
1.5
25
53
98
>99
>99
>99
92.6
SBA-NH
PdNPs/SBA-
NH -LA
2
-Pd
196.3
355.0
2
hydrogenation of the C
–
C double bond of various alkenes with different
functional groups was evaluated over Pd/SBA-NH
2
-LA catalyst, and the
results are depicted in Table 4. Styrene and methyl-substituted styrene
underwent complete conversion with excellent selectivity for desired
products (Table 4, Entry 1 and 2). When –NH
2
group present on the
aromatic ring at m-position (Table 4, Entry 3), the reaction took a long
time for completion. In the case of 4-Bromostyrene, only double bond
was hydrogenated, and no dehalogenated product was observed
2
Fig. 7. TEM image of PdNPs/SBA-NH -LA catalyst.
(
Table 4, entry 4). Different aromatic and cyclic
α
,β-unsaturated com-
O, ꢀ COOH, and ꢀ OH (Table 4, Entry 5–10)
functional groups were selectively hydrogenated at C C double bonds,
and the conversions are ranging between 96–99 %. However, these re-
–
C
–
–
evaluated for the selective hydrogenation of C
atmospheric H pressure at room temperature. 1,3-Diphenyl-2-propen-
-one was chosen as a model substrate since it has two different func-
tional groups and easy to monitor the activity and selectivity for the
–
C double bonds under
pounds were having
–
2
1
–
–
C O, ꢀ COOH
–
actions were completed in 90 min. reaction time. The
–
and ꢀ OH moieties were untouched during the reaction.
hydrogenation of the C
–
C double bond over C O bond. In order to
optimize the reaction parameters, the reaction was performed in
different solvents, and the results are summarized in Table 2. With non-
polar toluene solvent, only 65 % conversion obtained (Table 2, entry 1),
while the aprotic polar THF solvent produced 80 % conversion (Table 2,
entry 2). Significant improvement in conversion is observed with protic
polar methanol and ethanol solvents (85 % and 90 %, Table 2, entry
Leaching and reusability studies
In order to confirm the no leaching of palladium nanoparticles from
PdNPs/SBA-NH -LA catalyst, a hot filtration experiment was conducted
2
for the hydrogenation of 1,3-Diphenyl-2-propen-1-one for 1 h under
standard reaction conditions (1 mmol 1,3-Diphenyl-2-propen-1-one, 10
3
,4). Highest conversion (98 %) with 99 % selectivity attained in
acetonitrile solvent within 90 min. of reaction time (Table 2, entry 5).
Next, we compare the activity of PdNPs/SBA-NH -LA with different
catalysts, and the results are shown in Table 3. The reaction did not
proceed with parent SBA-15 and SBA-NH (Table 3, entry 1,2), indi-
cating the need for active metal for C C double bond hydrogenation of
,3-Diphenyl-2-propen-1-one. Only 25 % conversion with the turn over
2 2
mg PdNPs/SBA-NH -LA catalyst, 3 mL acetonitrile, 1 atm H , room
temperature). After 1 h of reaction time, the catalyst was recovered by
hot filtration from the reaction mixture. Then, 1 mmol of 1,3-Diphenyl-
2
2
-propen-1-one was added to the filtrate and continued the reaction. No
2
–
further hydrogenation of Diphenyl-2-propen-1-one was observed,
demonstrating no leaching of palladium nanoparticles into the solution
mixture during the reaction. In addition, the filtrate was further
analyzed by ICP-MS analysis and found no traces of palladium nano-
particles in the solution. Evaluate the activity and stability of the used
catalyst; the catalyst was collected by simple filtration and washed
several times with ethanol solvent. The separated catalyst was dried at
room temperature under vacuum and reused five times. The obtained
results were displayed in Fig. 8. No significant drop in the activity of the
catalyst was noticed as the C–C double bond hydrogenated product was
obtained in 96 % yield with 99 % selectivity even after the 5th run. The
Pd content in the used catalyst was determined to be 1.94 wt%.
1
ꢀ 1
frequency (TOF) value 92.5 h
observed with Pd/SBA-15 catalyst
(
Table 3, entry 3), while the conversion and TOF increased to 53 %,
ꢀ 1
1
92.6 h when the reaction was performed with SBA-NH -Pd catalyst
2
(
Table 3, entry 4). The maximum conversion (98 %) and selectivity (99
ꢀ 1
%
) with as high as TOF value were 355 h achieved with PdNPs/SBA-
-LA catalyst (Table 3, entry 5) using atmospheric H pressure in
acetonitrile solvent at room temperature for 90 min.. The remarkable
catalytic activity of the Pd/SBA-NH -LA catalyst is due to the formation
NH
2
2
2
of small size PdNPs and stabilization of PdNPs through the strong
interaction between -SH groups and PdNPs.
Reaction conditions: 1,3-Diphenyl-2-propen-1-one (1 mmol),
catalyst (10 mg), acetonitrile (3 mL), 1 atm H
2
, room temperature, 90
Conclusions
a
min. TOF = turnover frequency, moles of product/moles of catalyst
ꢀ
1)
(
h
In conclusion, we have prepared a novel PdNPs/SBA-NH
lyst by a post-synthetic grafting approach using propylamine (SBA-NH
and lipoic acid (SBA-NH -LA) functional groups with a particle size of
2ꢀ 13 nm. This novel catalyst exhibits an excellent activity for che-
moselective hydrogenation of C C double bonds of
2
-LA cata-
With the optimized reaction conditions in hand, selective
2
)
2
1
–
α, β-unsaturated
Table 2
Effect of solvent on the hydrogenation of 1,3-Diphenyl-2-propen-1-one over
carbonyl compounds to saturated carbonyl compounds at room tem-
2
PdNPs/SBA-NH -LA catalyst.
perature under atmospheric hydrogen pressures with high TOF values
ꢀ 1
ꢀ
1
(330ꢀ 1065 h ) Moreover, various functional groups were untouched
during the reaction. Moreover, the catalyst is easily recovered and
reused five times without losing its activity and selectivity.
Entry
Solvent
Conversion (%)
Selectivity (%)
TOF (h )
1
2
3
4
5
Toluene
THF
65
80
85
90
98
>99
>99
>99
>99
>99
240.7
296.3
314.8
333.3
355.0
Methanol
Ethanol
Acetonitrile
Author contribution
Reaction conditions: 1, 3-Diphenyl-2-propen-1-on (1 mmol), catalyst (10 mg),
solvent (3 mL), 1 atm H , room temperature, 90 min.
Dr. Anand Narani and Dr. David Raju Burri initiated, designed and
developed the project. Dr. Anand Narani performed all the experiments
2
5

A. Narani et al.
Molecular Catalysis 497 (2020) 111200
Table 4
Selective hydrogenation of different
α
,β-unsaturated carbonyl compounds over PdNPs/SBA-NH
2
-LA catalyst.
Reaction conditions: substrate (1 mmol), catalyst (10 mg), acetonitrile (3 mL), 1 atm H
catalyst). bTOF = turnover frequency, moles of product/moles of catalyst (hꢀ 1).
2
, room temperature. TON = turnover number (moles of product/moles of
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Declaration of Competing Interest
The authors report no declarations of interest.
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