Novel Fe–Pd/γ-Al2O3 catalysts for the selective hydrogenation of C≡C bonds under mild conditions

Article abstract of DOI:10.1016/j.mencom.2019.05.034

Novel promising Fe–Pd/γ-Al₂O₃ catalysts for the selective liquid-phase hydrogenation of unsaturated compounds (phenylacetylene and 2-methylbut-3-yn-2-ol) under ambient conditions have been prepared. They were characterized by low temperature nitrogen adsorption, XRD, SEM, TEM, TPR-H₂ and DRIFTS-CO techniques. The presence of Pd–Fe nanoparticles led to increased reactivity and selectivity of the new catalysts in hydrogenation of the C≡C bond to the C=C one as compared to those of the Pd/Al₂O₃ system.

Full text of DOI:10.1016/j.mencom.2019.05.034

Mendeleev
Communications
Mendeleev Commun., 2019, 29, 339–342
Novel Fe–Pd/g-Al2O3 catalysts for the selective
–
–
hydrogenation of C C bonds under mild conditions
–
Anastasiya A. Shesterkina,*a Ludmila M. Kozlova,a Igor V. Mishin,a Olga P. Tkachenko,a Gennady I. Kapustin,a
Viktor P. Zakharov,b Mikhail S. Vlaskin,b Andrei Z. Zhuk,b Olga A. Kirichenkoa and Leonid M. Kustova,c
a N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian
Federation. Fax: +7 499 135 5328; e-mail: anastasiia.strelkova@mail.ru
b Joint Institute of High Temperatures, Russian Academy of Sciences, 125412 Moscow, Russian Federation
c Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation
DOI: 10.1016/j.mencom.2019.05.034
Novel promising Fe–Pd/g-Al2O3 catalysts for the selective liquid
-
CH2
phase hydrogenation of unsaturated compounds (phenyl-
acetylene and 2-methylbut-3-yn-2-ol) under ambient conditions
have been prepared. They were characterized by low tempera-
ture nitrogen adsorption, XRD, SEM, TEM, TPR-H2 and
DRIFTS-CO techniques. The presence of Pd–Fe nanoparticles
led to increased reactivity and selectivity of the new catalysts in
CH
CH
Pd–Fe/Al2O3
Selectivity 91%
Me
Me
OH
1 atm H2, 25 °C
CH2
Me
Me
200 nm
OH
–
–
hydrogenation of the C C bond to the C=C one as compared
–
Selectivity 94%
to those of the Pd/Al2O3 system.
Selective hydrogenation of C≡C to C=C bonds is a key step in
the synthesis of many important products in petrochemical
industry as well as of fine and special chemicals (i.e., vitamins A
and E, linalool, etc.).1–5 Supported Pd-containing catalysts are
usually applied for selective hydrogenation due to their unique
ability to promote adsorption of hydrogen, relative stability in air
environment, and easy recyclability.6–10 Drawbacks of this system
include high palladium loadings, deactivation, and toxicity.3,10–12,14
An addition of the second metal or metal oxide to Pd-based
catalysts and the use of some hybrid systems are known as
increasing the activity and selectivity of catalysts.15–18 The well-
known bimetallic compositions for selective alkyne hydrogena-
tion include Pd–In,19 Pd–Zn,14,17,20,21 Pd–Ag,22 and Pd–Cu.23,25
However, the Fe influence on the catalytic properties of Pd catalysts
in the mentioned reactions remains scarcely investigated. There
is increasing research interest in iron as a catalyst component
for the homogeneous and heterogeneous hydrogenation since
this transition metal is abundant in nature, cheap, non-toxic, and
potentially amenable to magnetic recovery.16,26,27 The support
material plays a crucial role in the overall catalytic performance
for achieving the high conversion and better selectivity towards the
desired products.3,28 Despite the large number of reports on the
selective hydrogenation on Pd-containing catalysts, the improve-
ments in efficiency and environmental safety of catalytic
systemsareremaininganactiveareaofresearchanddevelopment.
The present work was aimed at the synthesis of the supported
bicomponent Fe–Pd/g-Al2O3 catalysts.† The prepared materials
were investigated by N2 adsorption–desorption measurements,
TPR-H2, XRD, DRIFTS-CO, SEM and TEM methods. Physico-
chemical properties of this system and its catalytic activity in
the selective liquid-phase hydrogenation of phenylacetylene and
2-methylbut-3-yn-2-ol (dimethylethynyl carbinol or DMEC) under
mild conditions were explored, and the influence of thermal
treatment of the samples on the activity and selectivity of the
hydrogenation processes was elucidated. 2-Methylbut-3-en-2-ol
(DMVC) obtained by selective hydrogenation of DMEC is an
important starting material for the production of vitamins A
and E. The selective hydrogenation of phenylacetylene into
styrene is of significant industrial and scientific interest, since
phenylacetylene is a poisoning impurity in styrene feedstocks,
causing deactivation of styrene polymerization catalysts.
The XRD results for the support and bimetallic PdFe catalysts
are given in Online Supplementary Materials. The peaks recorded
for the support correspond to the main diffraction peaks of
g-Al2O3 [Figure S1(a)]. The calcination in an air flow with the
subsequent reduction of the samples in H2 resulted in the forma-
tion of X-ray amorphous phases [Figure S1(b),(c)]. The formation
in flowing air at 400°C for 3 h (A), (ii) calcination in flowing N2 at
400°C for 3 h (N). All the calcined samples were reduced in H2 flow
at 400°C for 3 h and then cooled to 20°C. An organic solvent (acetone)
was introduced into the reactor with the reduced sample to exclude the
contact with oxygen inside the reactor and to prevent oxidation of Fe
nanoparticles. The reduction temperatures were selected according to the
TPR-H2 studies. The synthesized catalysts were designated as PdFe–M–H,
wherein M denotes the conditions of thermal treatment (M corresponds
to the method of calcination, and H means the reduction in H2 at 400°C).
The reduced monometallic Pd(3%)/g-Al2O3 catalysts (Pd–A–H and
Pd–N–H) were prepared similarly and used as a reference.
Catalytic properties of Pd–Fe/g-Al2O3 samples were studied in a glass
reactor at 20°C in H2 (1 atm) under vigorous shaking (600 min–1) in
ethanol (16 ml) (30 mg of catalysts, 0.13 m phenylacetylene or DMEC,
molar ratio substrate:Pd was 290:1) with undecane (for phenylacetylene)
or isoamyl alcohol (for DMEC) as an internal standard (3 ml).
†
A carrier g-Al2O3 (SBET of 240 m2 g–1, Vmesopore of 1.4 cm3 g–1
,
Vmicropore of 0.005 cm3 g–1) was obtained by a thermal decomposition
of boehmite at 600°C in air. Supported bimetallic Pd(3%)–Fe(8%)
catalysts were prepared by a simultaneous incipient wetness impregna-
tion of the g-Al2O3 carrier with aqueous solutions of [Pd(NH3)4]Cl2·H2O
(pure, 41.42% of Pd; Aurat, Russia) and (NH4)3[Fe(C2O4)3]·3H2O (pure,
98%, Acrus Organics) according to the reported procedures.29,30 The
impregnated samples were dried at 60°C for 12 h. Thermal treatment of
dry samples was carried out under different conditions: (i) calcination
© 2019 Mendeleev Communications. Published by ELSEVIER B.V.
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.
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Mendeleev Commun., 2019, 29, 339–342
of well-crystallized Pd0 nanoparticles after the treatment at 400°C
temperature above 200°C. The absorption of H2 at low tempera-
tures was decreased nearly twofold. It seems that the decomposi-
tion of ammonia complexes of precursors leads to the reduction
of Pd2+. The total calculated uptake of H2 until 850°C was
0.840 mmol g–1, i.e., almost all the hydrogen was consumed by
the reduction of iron, while about half of the palladium was
deoxidized by ammonia. This was confirmed by the XRD and
DRIFTS data.
The acquired data indicate that the iron reduction in the
presence of metallic Pd is already started at room temperature.
Most likely, once metallic Pd was produced, the Fe reduction
begins.
Metals states in catalysts Fe–Pd/Al2O3 were spectroscopically
estimated using DRIFTS-CO (Figure 2). Several bands are visible
in the spectrum of calcined catalyst PdFe–N [see Figure 2(a)].
The band at 2168 cm–1 characterizes linear carbonyl group at
divalent iron cations (Fe2+–CO). Upon increasing the CO desorp-
tion temperature, the position of Fe2+–CO carbonyl band does
not change, but the intensity gradually decreases (Figure S3).
After desorption of CO at room temperature, the band at
2107 cm–1 was resolved into two bands at 2128 and 2088 cm–1,
belonging to linear carbonyls at monovalent palladium cations
(Pd+–CO) and on metallic palladium (Pd0–CO), respectively. The
bands in the region of 1992–1933 cm–1 correspond to bridged
carbonyls on monovalent palladium cations (Pd+–CO–Pd+) and
metal palladium (Pd0–CO–Pd0) (Figure S3). When CO was
desorbed in vacuo at 200°C, the bands from iron and palladium
carbonyls disappear completely in the spectrum. The absence
of any shift of the band of palladium carbonyls during thermal
desorption (20–100°C) and the sufficiently high intensity of the
bridged adsorption bands indicate a low degree of dispersion of
the palladium crystallites.
in N2 flow was readily detected [Figure S1(d)]. An average size
of the primary Pd0 crystallites in the calcined bimetallic PdFe–N
catalysts was 12–13 nm. The reduction of this sample in H2 flow
at 400°C led to the formation of Pd0 nanoparticles with an
average size of 15–16 nm [Figure S1(e)], however lines from
any iron phases could not be detected. Taking into account the
XRD data, one can conclude that the phase composition and
size of primary crystallites of the supported metal depend on the
calcination conditions.
The TEM images of PdFe–N catalysts (Figure S2) confirmed
the formation of agglomerates of nanoparticles with an average
size of 20 nm. The further reduction of this sample in H2 flow at
400°C led to the formation of larger agglomerates. Due to the
complicated morphology of Al2O3 in addition to small and well-
distributed nanoparticles on the support surface in the PdFe–A
and PdFe–A–H samples, it was difficult to make any conclusion
about the size and distribution of particles.
The reducibility of the calcined samples was estimated by the
TPR method (Figure 1). The reduction of monometallic Fe2O3
supported on alumina proceeds in two steps: the conversion of
Fe3+ to Fe0 via Fe2+ at high temperatures in the range of 380–
720°C.31 The dissociative chemisorption of H2 on Pd facilitates
the reduction of ferric species at much lower temperatures.32
This trend was observed for all the bimetallic Pd–Fe catalysts in
this work. However, the TPR profiles of the calcined samples
were different.
Initial adsorption of H2 on a sample calcined in the flowing
air can be observed at –10°C. Three ranges can be recognized on
the adsorption curves: from –10 to 370, 370–630 and 630–850°C.
After 850°C, the sample was kept at Tmax until the H2 consump-
tion became negligible. The amounts of adsorbed H2 in these three
regions were 0.813, 0.108 and 0.189 mmol g–1, respectively. The
first area is related to the reduction of PdO. The total amount of
Pd in the sample was 0.282 mmol g–1. However, the H2 amount
corresponding to the first adsorption peak (maximum at 60°C) is
almost 3 (2.88) times higher than needed for the PdO reduction.
Therefore, it can be suggested that the reduction of Fe2O3 begins
at the temperature as low as ~100°C. In this region, a shoulder is
observed on the hydrogen adsorption curve. The total amount of
Fe was 1.432 mmol g–1, thus for the reduction of Fe3+ to Fe0,
2.149 mmol g–1 of H2 was required. The total amount of H2 needed
for the reduction of both iron and palladium cations to metals was
2.431 mmol g–1. At the same time, 0.998 mmol g–1 of H2 was
sufficient for processes: Fe3+ ® Fe2+ and Pd2+ ® Pd0.
DRIFT-CO spectra of the reduced PdFe–N–H catalyst contains
four bands at 2162, 2081, 2034 and 1958 cm–1 [see Figure 2(a)].
The strong band at 2162 cm–1 characterizes linear carbonyls on
divalent iron cations (Fe2+–CO). The low ones at 2081 and
2034 cm–1 correspond to linear carbonyls on two metal centers
(a)
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2162
2
1992
2168
2107
1
For the sample calcined in the flowing air, the total amount of
absorbed H2 was 1.11 mmol g–1. This allowed us to conclude that
Fe2O3 was reduced to FeO under the applied conditions (from
–100 to 850°C, 5% H2/Ar, 30 ml min–1, and heating rate of
10°C min–1).
In the case of sample calcined in the flowing N2, a decrease
in the absorption of hydrogen in the region of 0–370°C was
observed, whereas the spectra were practically coincided at the
2034
2081
1958
2400
2200
2000
1800
Wavenumber/cm–1
(b)
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
2160
PdFe–A
1
2123
2162
2062
2
1991
1963
2351
PdFe–N
2025
1958
2400
2200
Wavenumber/cm–1
2000
1800
0
200
400
T/°C
600
800
Figure 1 TPR-H2 profiles of Pd–Fe/Al2O3 samples. All data are normalized
to 1 g sample.
Figure 2 DRIFT-CO spectra of (1) calcined and (2) subsequently reduced
(a) PdFe–N and (b) PdFe–A catalysts.
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Mendeleev Commun., 2019, 29, 339–342
of palladium possessing different local environments, and the
bands near 1958 cm–1 are assigned to the bridged carbonyls on
metallic palladium (Pd0–CO–Pd0). In addition, all the bands
disappeared from the spectrum upon evacuation of the sample at
20°C (Figure S4, see Online Supplementary Materials).
Table 1 Catalytic properties of the 3Pd–8Fe/Al2O3 catalysts in selective
hydrogenation of the CºC bonds.a
99
S
r0c /molsubstrate
substrate
Entry Catalyst
Substrate Product tb/min
–1
mol
Pd
(%)
1
2
3
4
5
6
7
Lindlar
Pd–A–H
PdFe–A
PdFe–A–H
Pd–N–H
PdFe–N
Phenyl-
acetylene
Styrene 150
87
79
72
85
75
87
91
0.05
0.39
0.51
1.19
0.99
0.45
0.59
In contrast to the DRIFT-CO spectra of the PdFe–N catalyst,
those of sample PdFe–A calcined in an air flow exhibited a band
at 2351 cm–1, which can be assigned to adsorbed CO2 formed via
the reduction of Fe3+ cations by carbon monoxide, along with an
intense band at 2160 cm–1 attributed to linear carbonyl on divalent
iron cations (Fe2+–CO) [see Figure 2(b)]. The appearance of
the bands for linear carbonyls at 2123 cm–1 (Pd+–CO) and
2103 cm–1 (Pd0–CO), as well as for bridged carbonyls on mono-
valent cations of palladium (Pd+–CO–Pd+) and metal centers
of palladium (Pd0–CO–Pd0) in the region of 1991–1960cm–1
were observed in the spectra. During CO desorption in vacuo at
20–100°C, the position of the Fe2+–CO carbonyl bands did not
change, while their intensity was gradually decreased (Figure S5).
The absence of any shift of the band from the carbonyls of
palladium during thermal desorption along with a sufficiently
high intensity of the bands from the bridged adsorption forms at
the palladium centers indicate a low dispersion of the palladium
metal particles. It is consistent with the XRD results for this sample
[see Figure S1(d)]. In the spectrum of CO adsorbed on the surface
of the reduced catalyst PdFe–A–H, the band at 2351 cm–1 was
not detected, thus, all the palladium was in the metallic state. The
bands at 2062 and 2025 cm–1 belong to linear carbonyls at two
metal centers of palladium possessing different local environ-
ments, and the 1958 cm–1 band is attributed to bridged carbonyls
on metallic palladium. In addition, all the bands disappeared
during the evacuation of the sample at 20°C (Figure S6).
10
11
5.5
4.6
11
8
PdFe–N–H
8
9
10
Lindlar
Pd–N–H
PdFe–N–H
DMEC
DMVC 32
89
80
94
0.09
0.87
0.78
6
9.5
a Reaction conditions: Csubstrate = 0.13 mol dm–3, mcatalyst = 0.03 g, H2 (1 atm),
room temperature, nsubstrate:nPd = 290:1. bTime required for the complete
conversion of the substrate. c Initial hydrogenation rate calculated at the
conversion of the substrate not exceeding 10%.
(91%) was observed for the sample PdFe–N–H (see Table 1,
entry 7).
The catalytic properties of the sample PdFe–N–H were studied
in the hydrogenation of the C≡C bond in an unsaturated alcohol.
The selectivity towards DMVC on this catalyst under mild
reaction conditions was 95% at the complete DMEC conversion
at a high rate of hydrogenation (see Table 1, entry 10).
The reduced Pd–Fe/Al2O3 samples demonsrated promising
magnetic properties and were easily separated from the reaction
solution with a permanent magnet (Figure 3). The catalytic activity
and the selectivity remained high even after four successive
catalytic recycles (Figure 4). In addition, no metal leaching
occurred during the cyclic operation after four cycles.
In conclusion, the novel Pd–Fe/Al2O3 catalysts for the selective
hydrogenation of alkynes into alkenes were prepared. The catalytic
properties of the bimetallic catalysts depend on the conditions of
thermal treatment of their precursors. The calcination process
has significantly affected the palladium dispersion. The presence
of Fe in Pd–Fe/Al2O3 catalyst modifies the catalytic behavior of Pd.
The formation of Pd–Fe bimetallic phase in the samples promotes
their reactivity and selectivity. The best results on the selective
styrene formation (91% at the 100% conversion of phenyl-
acetylene) and DMVC (95% at the 100% conversion of DMEC)
were observed for the sample calcined in N2 flow at 400°C and
The summarized results of the DRIFT-CO experiments for
the calcined catalysts are given in Online Supplementary
Materials (Figure S7). Thus, the comparison of the DRIFT-CO
spectra of the Pd–Fe/Al2O3 catalysts prepared under various
conditions suggests the formation of different bimetallic phase
in the samples.
Catalytic activity of the prepared Pd and Pd–Fe samples in
liquid-phase hydrogenation of unsaturated compounds (phenyl-
acetylene and 2-methylbut-3-yn-2-ol) under ambient conditions
is summarized in Table 1. The monometallic iron samples (both
calcined and reduced in a H2 flow at 400°C) were catalytically
inactive under the reaction conditions. The activities of synthesized
monometallic catalysts Pd–A–H and Pd–N–H were 15 and
25 times higher than that of the Lindlar catalyst (5% Pd/CaCO3
inhibitedbytheleadcomplexes)inthereactionofphenylacetylene
hydrogenation, respectively. However, the selectivity towards
styrene was lower than that of the Lindlar catalyst (see Table 1,
entry 2), while the Pd–N–H sample was more active than the
monometallic sample calcined in an air flow. The modification
of monometallic palladium samples with iron has significantly
changed their catalytic properties. Catalytic performance of
bimetallic Pd–Fe/Al2O3 catalysts in the hydrogenation of phenyl-
acetylene depends primarily on the calcination procedure and
hence on the nature of active sites and the particle size. Comparing
the calcined Pd–Fe/Al2O3 samples, one may conclude that at a
similar initial rate of hydrogenation, the maximum selectivity to
styrene (87%) at the complete conversion of phenylacetylene was
observed in the case of PdFe–N sample (see Table 1, entry 6).
According to the XRD, TEM and TPR-H2 analyses, calcination
in a N2 flow at 400°C led to the formation of well-crystallized
Pd0 nanoparticles with the size of 15 nm, whereas the sample
calcined in air (PdFe–A) was X-ray amorphous and consisted
mainly of the Pd0 and Fe3+ and Fe2+ oxides. A further reduction
of all the calcined samples in an H2 flow at 400°C increased their
selectivity to styrene and activity. However, the highest selectivity
separation
Figure 3 The magnetic separation of the reduced PdFe–N–H catalyst from
the reaction solution.
1.0
0.8
0.6
0.4
0.2
0.0
100
80
60
40
20
0
1
2
3
4
Figure 4 Reusability of the PdFe–N–H catalyst in four consecutive cycles
of phenylacetylene hydrogenation.
– 341 –

Mendeleev Commun., 2019, 29, 339–342
16 V. P.Ananikov, D. B. Eremin, S.A.Yakukhnov,A. D. Dilman,V.V. Levin,
then reduced in H2 flow at 400°C. Thus, our stable magnetic
Pd–Fe/Al2O3 catalysts are a good alternative to the traditional
toxic Lindlar catalyst in the selective alkyne hydrogenation under
mild conditions.
M. P. Egorov, S. S. Karlov, L. M. Kustov, A. L. Tarasov, A. A. Greish,
A. A. Shesterkina, A. M. Sakharov, Z. N. Nysenko, A. B. Sheremetev,
A. Yu. Stakheev, I. S. Mashkovsky, A. Yu. Sukhorukov, S. L. Ioffe,
A. O. Terent’ev, V. A. Vil’, Yu. V. Tomilov, R. A. Novikov, S. G. Zlotin,
A. S. Kucherenko, N. E. Ustyuzhanina, V. B. Krylov, Yu. E. Tsvetkov,
M. L. Gening and N. E. Nifantiev, Mendeleev Commun., 2017, 27, 425.
17 Z. Wang, L.Yang, R. Zhang, L. Li, Z. Cheng and Z. Zhou, Catal. Today,
2016, 264, 37.
18 E. A. Redina, O. A. Kirichenko, A. A. Greish, A. V. Kucherov, O. P.
Tkachenko, G. I. Kapustin, I. V. Mishin and L. M. Kustov, Catal. Today,
2015, 246, 216.
19 I. S. Mashkovsky, N. S. Smirnova, P.V. Markov, G. N. Baeva, G. O. Bragina,
A. V. Bukhtiyarov, I. P. Prosvirin andA.Yu. Stakheev, Mendeleev Commun.,
2018, 28, 603.
Electron microscopy characterization was performed at the
Department of Structural Studies of N. D. Zelinsky Institute
of Organic Chemistry of the Russian Academy of Sciences.
A. Shesterkina is grateful to Haldor Topsøe A/S for the financial
support in the framework of PhD student support programme.
The authors are grateful to E. Shuvalova for the assistance in
conducting the experiments.
20 M. Crespo-Quesada, M. Grasemann, N. Semagina, A. Renken and
L. Kiwi-Minsker, Catal. Today, 2009, 147, 247.
21 I. S. Mashkovsky, P.V. Markov, G. O. Bragina, G. N. Baeva,A.V. Rassolov,
A. V. Bukhtiyarov, I. P. Prosvirin, V. I. Bukhtiyarov and A.Yu. Stakheev,
Mendeleev Commun., 2018, 28, 152.
22 A.V. Rassolov, P.V. Markov, G. O. Bragina, G. N. Baeva, I. S. Mashkovskii,
I. A.Yakushev, M. N. Vargaftik andA.Yu. Stakheev, Kinet. Catal., 2016,
57, 853 (Kinet. Katal., 2016, 57, 857).
Online Supplementary Materials
Supplementary data associated with this article can be found
in the online version at doi: 10.1016/j.mencom.2019.05.034.
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Received: 3rd October 2018; Com. 18/5709
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