Selective hydrogenation of terminal alkynes over palladium nanoparticles within the pores of amino-modified porous aromatic frameworks

Article abstract of DOI:10.1016/j.cattod.2019.05.028

Palladium catalysts, based on porous aromatic frameworks, synthesized via Suzuki cross-coupling reaction and further modified with amino groups, were prepared and tested in hydrogenation of several unsaturated compounds. Catalysts obtained were characterized by several techniques including IR spectroscopy, solid-state NMR spectroscopy, low-temperature nitrogen adsorption, transmission electron microscopy, atomic emission spectroscopy and X-ray photoelectron spectroscopy. It was shown that the amino-groups within the structure of aromatic frameworks interact with palladium nanoparticles and enhance their selectivity towards hydrogenation of terminal alkynes.

Full text of DOI:10.1016/j.cattod.2019.05.028

Accepted Manuscript
Title: Selective hydrogenation of terminal alkynes over
palladium nanoparticles within the pores of amino-modified
porous aromatic frameworks
Authors: Edward Karakhanov, Anton Maximov, Maria
Terenina, Vladimir Vinokurov, Leonid Kulikov, Daria
Makeeva, Aleksandr Glotov
PII:
S0920-5861(18)31278-1
DOI:
Reference:
https://doi.org/10.1016/j.cattod.2019.05.028
CATTOD 12204
To appear in:
Catalysis Today
Received date:
Revised date:
Accepted date:
23 August 2018
1 April 2019
14 May 2019
Please cite this article as: Karakhanov E, Maximov A, Terenina M, Vinokurov
V, Kulikov L, Makeeva D, Glotov A, Selective hydrogenation of terminal alkynes
over palladium nanoparticles within the pores of amino-modified porous aromatic
frameworks, Catalysis Today (2019), https://doi.org/10.1016/j.cattod.2019.05.028
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Selective hydrogenation of terminal alkynes over palladium nanoparticles
within the pores of amino-modified porous aromatic frameworks
Edward Karakhanova, Anton Maximova,b , Maria Tereninaa, Vladimir Vinokurovc,
Leonid Kulikova, Daria Makeevaa, Aleksandr Glotova,c*
aDepartment of Petroleum Chemistry and Organic Catalysis, Lomonosov Moscow State
University, Moscow, Russia 119991
bInstitute of Petrochemical Synthesis RAS, Moscow, Russia 119991
сPhysical and Colloid Chemistry Department, Gubkin Russian State University of Oil and Gas,
Moscow, Russia 119991
Corresponding author:
Dr. Aleksandr Glotov, e-mail: glotov.a@gubkin.ru
Postal address: Gubkin Russian State University of Oil and Gas, Physical and Colloid Chemistry
Department, 65 Leninskiy prospect, Moscow, Russia, 11999.
Graphical abstract

Highlights
 Porous aromatic frameworks stabilize palladium nanoparticles within their pores
 Amino-groups in aromatic frameworks contribute higher palladium dispersion
 Catalysts based on polymers with amino-groups convert selectively terminal alkynes
Abstract Palladium catalysts, based on porous aromatic frameworks, synthesized via Suzuki
cross-coupling reaction and further modified with amino groups, were prepared and tested in
hydrogenation of several unsaturated compounds. Catalysts obtained were characterized by
several techniques including IR spectroscopy, solid-state NMR spectroscopy, low-temperature
nitrogen adsorption, transmission electron microscopy, atomic emission spectroscopy and X-ray
photoelectron spectroscopy. It was shown that the amino-groups within the structure of aromatic
frameworks interact with palladium nanoparticles and enhance their selectivity towards
hydrogenation of terminal alkynes.
Keywords: porous aromatic frameworks; catalysis; palladium nanoparticles; selective
hydrogenation; mesoporous materials

1.
Introduction
At present, olefins are one of the most important materials in petrochemistry. They are used
not only for polymerization processes, but also in the industrial organic synthesis of detergents,
lubricants and other chemical reagents [1,2]. Industrial synthesis of alkenes includes such processes
as thermal, steam or catalytic cracking of petroleum alkanes and dehydrogenation of ethylbenzene.
However, after these processes not only desirable products are obtained, but also small amounts of
highly unsaturated compounds, which poison the catalysts of the further polymerization and
contribute to formation of byproducts in various processes. Traditional method for the removal of
such impurities is the selective hydrogenation of highly unsaturated compounds in alkene streams,
because it is the most economic and energy effective process [3–5].
It is well-known, that palladium catalysts are proved to be one of the most active, selective
and durable with respect to the target alkene [6–8]. To increase their selectivity, catalysts could be
modified with nitrogen-containing additives (aliphatic amines, pyridine, etc.). It is believed, that
these additives occupy acid sites on the support surface and inhibit the oligomerization which
occurs there. Moreover, they interact not only with the support, but also with active Pd sites, and
weaken the palladium affinity to an alkene to a greater extent than to an alkyne, which facilitates
desorption of the alkene from the reaction sites and inhibits side hydrogenation to saturated
hydrocarbons [6,9].
Nowadays catalysts based on transition metal nanoparticles seem to be promising for many
important processes in organic synthesis and petrochemistry due to their high activity provided by
incredibly high specific surface area, and possibility of regeneration [10–16]. Unfortunately,
nanoparticles are prone to aggregation, which leads to the growth of the particles size and,
consequently, to the decrease of the total surface area and to the reduction of catalytic activity.
One of the ways to prevent this process is to incorporate nanoparticles in rigid matrixes, for
example, porous aromatic frameworks (PAFs), which could stabilize them [17–20]. The most
known example of PAFs is PAF-1 (Fig. 1), synthesized by Ben et al. [21] via the Yamamoto cross-
coupling reaction. This material with an exceptionally high BET surface area of 5600 m2/g
possesses thermal and chemical stability. Also advantages of PAFs are their regular rigid structure
and simplicity of methods of their functionalization [22]. After PAF-1, numerous studies were
devoted to synthesis, modification with functional groups, metal complexes and nanoparticles and
application of the obtained materials in the fields of gas separation, adsorption, energy conversion
and storage, catalysis [23–29]. The structure of PAF can influence on the shape and size of
nanoparticles formed in its pores, the selectivity of process and catalytic behavior of active centers.
Thus, several PAFs with mesoporous structure were synthesized via Suzuki-Miyaura cross-
coupling reaction [30–35], and materials with bigger pore sizes were more active in catalytic
processes or adsorption of bulky molecules.
Fig. 1. Example of structure of Porous aromatic frameworks with diamond-like structure [21].

This study is focused on the synthesis of two palladium catalysts, based on mesoporous
aromatic frameworks with diamond-like structure, constructed from tetraphenylmethane
molecules: PAF-20 and its derivative PAF-20-NH2, functionalized with amino-groups. Catalysts
Pd-PAF-20 and Pd-PAF-20-NH2 were tested in hydrogenation of different unsaturated
compounds.
2.
Experimental
2.1. Materials
Following materials were used as substrates: styrene (Arcos Organics, 97%);
phenylacetylene (Aldrich, 98%); octene-1 (Aldrich, 98%); octyne-1 (Aldrich, 97%); octyne-4
(Aldrich, 99%); 2,5-dimethylhexadiene-2,4 (Aldrich, 96%). HNO3 (Component-Reaktiv, high-
purity grade) and SnCl2 (Aldrich, 98%) were used for synthesis of modified PAF. Methanol (Arcos
Organics, 99+%); ethanol (Irea 2000, analytical grade); tetrahydrofuran (THF) (Khimmed, high-
purity grade); trifluoroacetic acid (Aldrich, ReagentPlus®) were used as solvents.
Solvents were purified according to standard methods. PAF-20 was synthesized by the
procedure previously described in [36]. Material was then modified with amino groups in two
steps. Firstly, support PAF-20 was nitrated by mixture of nitric and trifluoroacetic acids to obtain
PAF-20-NO2; nitro groups were further reduced by tin(II) chloride in the THF media to prepare
PAF-20-NH2 [31]. To deliver metals into the pores of material, the support were impregnated with
palladium(II) chloride (Aurat, high-purity grade) in its methanol solution, which was subsequently
reduced with an alcoholic solution of hydrazine hydrate.
2.2. Instruments and investigation procedures
IR spectroscopy. IR spectra were taken with a Nicolet IR2000 (Thermo Scientific) instrument
using multiple distortion of the total internal reflection method with multi-reflection HATR
accessories, containing a 45˚ ZnSe crystal for different wavelengths with a resolution of 4 cm-1 in
the range of 4000–400 cm-1. All spectra were taken by averaging 100 scans.
Solid-state NMR spectroscopy. Analysis by solid-state CP-MAS 13C NMR spectroscopy was
carried out on a Varian NMR Systems instrument with an operating frequency of 125MHz in the
pulsed operation mode with a rotation frequency of 10 kHz.
Low-temperature nitrogen adsorption. Nitrogen adsorption/desorption isotherms were recorded
at 77 K on a Micromeritics Gemini VII 2390 instrument. Before measurements, samples were out-
gassed at 110°C for 6 h. The surface area (SBET) was calculated by the Brunauer–Emmett–Teller
(BET) method based on adsorption data in a range of relative pressures P/P0 = 0.05–0.2. Pore volume
and pore size distribution were determined from the adsorption branches of isotherms using the
Barrett–Joyner–Halenda (BJH) model. Total pore volume (Vtot) was determined from the amount of
nitrogen adsorbed at a relative pressure of P/P0 = 0.995.
Transmission electron microscopy (TEM). TEM analysis was carried out on a LEO912c AB
OMEGA microscope with electron tube voltage of 100 kV. The processing of the micrographs and
the calculation of the average particle size were conducted using the ImageJ software program.
Atomic emission spectroscopy. The quantitative determination of palladium and platinum in the
samples was performed with inductively coupled plasma atomic emission spectroscopy (ICP AES)
on an IRIS Interpid II XPL instrument (Thermo Electron Corp., United States) with radial and
axial viewing at wavelengths of 310 and 95.5 nm.
X-ray photoelectron spectroscopy (XPS). XPS studies were performed on
a
PHI5500VersaProbeII instrument using excitation with Al Kα X-ray radiation at 1486.6 eV. The
calibration of photoelectron peaks was based on the Au 4f line with a binding energy of 84 eV and

on the Cu2p3/2 line (932.6 eV). The transmission energy of the energy analyzer was 117.4 eV
(survey scans) and 23.5 eV (individual lines).
Gas-liquid chromatography. Analysis of the reaction mixture was carried out on a ChromPack
CP9001 chromatograph equipped with a flame-ionization detector and a 30 m × 0.2 mm column
(SE-30 grafted phase). Helium was carrier gas with a flow rate of 30 mL/min. Chromatograms
were recorded and analyzed using the Maestro 1.4 software program. Conversion (%) was
determined from changes in the relative peak areas of the substrate and the products. The analysis
conditions are given in Table 1.
Table 1. Gas–liquid chromatography analysis conditions
Octene, octyne,
dimethylhexadiene
Substrates
Styrene, phenylacetylene
Detector temperature, ˚C
Injector temperature, ˚C
Initial column temperature, ˚C
Final column temperature, ˚C
Column heating rate, ˚C/min
Initial time, min
250
250
60
220
10
10
5
45
165
5
10
5
Final time, min
2.3. Catalysts preparation
The catalysts were synthesized by impregnating the support material with solution of
palladium(II) chloride in methanol, which was subsequently reduced with hydrazine hydrate. The
calculated amount of metal was 5 wt %.
A typical procedure for synthesis of Pd–PAF catalysts includes drying of 200 mg of the
support in a vacuum at 60˚C for 1 h and its subsequent impregnation with 17.5 mg of palladium(II)
chloride in 30 ml of methanol in a round-bottom flask equipped with a magnetic stirrer anchor and
a reflux condenser at room temperature under continuous stirring for 12 h. After that, 0.5 ml of
hydrazine hydrate was added dropwise to the resulting suspension. In the end, the catalyst was
filtrated; the precipitate was washed with water and alcohol several times. After drying in a vacuum,
the resulting product had the form of a light-grey powder.
2.4. Catalytic testing procedure
The calculated amounts of the catalyst and a substrate were placed in a thermostatically
controlled steel autoclave equipped with a glass test-tube and a magnetic stirrer anchor; all
catalytic reactions were performed without solvents. The autoclave was sealed, filled with
hydrogen to a pressure of 1 MPa, and exposed at 60˚C for 30 minutes; after that, the autoclave was
cooled down to the room temperature and depressurized.
Catalytic tests were repeated twice for all substrates with a deviation of the obtained results
lower than 5%. The catalyst activity for each reaction was calculated according to [37] as the
amount of the substrate reacted per time and per mole of the metal on the particle surface.
In catalysts recycling experiments, after the first run, the used catalyst was recovered by
centrifugation and washed with diethyl ether, followed by centrifugation. The process was
repeated twice, and the resulted solid was directly used for the next run with the same amount of
the substrate.
3.
Results and discussion

3.1. Characterization of PAF-20 and PAF-20-NH2
PAF-20 was synthesized via Suzuki cross-coupling reaction between tetrakis[p-
bromophenyl] methane and p-phenylenediboronic acid as previously described in [36]. PAF-20
was then modified with nitro groups, using nitric acid in the presence of trifluoroacetic acid, which
were then reduced with tin(II) chloride in THF [31] (Fig. 2).
Fig. 2. Schematic synthesis of PAF-20-NH2 from PAF-20.
The obtained materials were described by means of IR spectroscopy, solid state NMR
spectroscopy and low-temperature adsorption-desorption of nitrogen. The IR spectrum of PAF-20-
NO2 displayed strong absorption bands peaking at 1529 and 1344 cm-1, which correspond to nitro
groups (Fig. 4). They disappear after reduction of nitro groups into amino groups. It also should be
underlined, that absorption bands characteristic for the B–OH and C–Br bonds weren’t observed in
the regions of 3100–3600 and 1076 cm-1, thus cross-coupling reaction has proceeded completely.
NO2
NH2
PAF-20-NH2
PAF-20-NO2
PAF-20
3800
3600
3400
3200
3000
2800
2600
2400
2200
2000
1800
1600
1400
1200
1000
800
600
Wavenumber (cm-1)
Fig. 3. IR spectra of PAF-20, PAF-20-NO2 and PAF-20-NH2.
The 13C NMR spectrum of PAF-20 exhibits signals in the region of 120-150 ppm for sp2-
hybridized carbon atoms of aromatic fragments and at 65 ppm, corresponding to sp3-hybridized
carbon atoms in the bundles of tetraphenylmethane pieces (Fig. 4). The spectrum of synthesized
material does not display a CAr-Br signal at 120 ppm characteristic of tetrakis[p-
bromophenyl]methane; this fact also confirms the completeness of Suzuki reaction. The PAF-20-
NH2 spectrum displays strong signal in the region of 144-146 ppm and a shoulder at 115 ppm, which
are absent in PAF-20 spectrum. The first signal could be attributed to carbon atoms, bonded with
amino groups, and the second one characterizes centers in o- and p-positions to amino groups.

Fig. 4. Solid-state 13C CP-MAS NMR spectra of frameworks PAF-20 and PAF-20-NH2
The low-temperature nitrogen adsorption–desorption studies of the porosity of the
synthesized supports showed a steep absorption of nitrogen at low pressures (P/P0 = 0 – 0.05),
which indicates the presence of micropores in the material structure (Fig. 5). In addition, in a
relative pressure region of P/P0 = 0.2–0.9, the nitrogen adsorption curve gradually ascends without
exhibiting a plateau, hysteresis loop between the adsorption and desorption curves is observed; all
these facts confirm the mesoporous nature of the materials obtained. The insertion of amino groups
leads to the decrease of the support’s specific surface area, total pore volume and pore volume of
mesopores. This also could be seen by decrease of the loop between adsorption and desorption curves
in case of PAF-20-NH2 material. Also, the average pore size increased, which may indicate a partial
destruction of the porous structure of PAF-20 during nitration. It should be noted, that by the IV type
of N2 adsorption isotherms, the synthesized supports can be classified as hierarchically porous
materials [38,39]. The textural characteristics of PAF-20 and PAF-20-NH2 (Table 2) correlate with
the previously published data [31].
Table 2. Results of low-temperature nitrogen adsorption–desorption for PAF-20 and PAF-20-NH2
Specific surface
Total pore
Pore volume of
Average pore
size, nm
Material
area by BET, m2/g
volume, cm3/g
mesopores, cm3/g
PAF-20
PAF-20-NH2
523
376
0.35
0.3
0.21
0.15
3.3
3.9
Fig. 5. N2 adsorption isotherms of PAF-20 (left) and PAF-20-NH2 (right) measured at 77 K.

3.2. Catalysts characterization
Both the Pd–PAF-20 and Pd–PAF-20-NH2 catalysts were synthesized by the immobilization
of metal nanoparticles in pores of the support. The resulting materials were characterized by atomic
emission spectroscopy and TEM. The results of atomic emission spectroscopy showed that the metal
content in Pd–PAF-20 was 4.7 wt%, and in Pd–PAF-20-NH2 – 3.15 wt%.
Fig. 6 shows microphotographs of the catalysts and particle size distribution for the
resulting materials. Particle size distribution curve for Pd–PAF-20-NH2 is close to normal
(Gaussian) and exhibit a maximum at 2.9 nm. In contrast Pd-PAF-20 demonstrates bimodal
particle size distribution. Smaller particles with the average size of 3 nm are encapsulated in the
pores of the carrier, while larger particles with the average diameter of 10.8 nm are distributed on
the external surface. This demonstrates that the size of metal nanoparticles within the pores of
aromatic framework is determined by the size of the material pores. Also, it is clearly seen, that
modification of PAF-20 structure with amino-groups is crucial for effective diffusion of palladium
into the pores of support and its uniform distribution is due to polarity increasing of the material
[40].
Fig. 6. TEM microphotographs and particle size distribution for Pd–PAF-20 (A-C) and Pd–PAF-
20-NH2 (D-F)

Fig. 7. XPS measurements for Pd–PAF-20 (left) and Pd–PAF-20-NH2 (right).
XPS analysis demonstrates that both Pd–PAF-20 and Pd–PAF-20-NH2 do not contain any
traces of boron and bromine, but small amounts of phosphorus remained from cross-coupling
reaction catalyst were detected (Table 3). It should be noted, that the amounts of palladium, detected
by the XPS and ICP-AES techniques for Pd-PAF-20-NH2, were comparable. This confirms the
uniform distribution of palladium by support. In contrast, there is a big difference between results of
XPS and ICP-AES data for Pd-PAF-20 catalyst. This difference may occur when palladium is
located predominantly at near-to-surface area of support material, which means poor metal diffusion
into the pores of non-modified PAF-20. In both spectra two sets of peaks corresponding to Pd0 and
PdOx/Pd (Pd 3d5/2 and Pd 3d3/2) are observed (Fig. 7), confirming incorporation of palladium into
pores of material. PdOx/Pd peaks for Pd–PAF-20-NH2 are more intense and, moreover, have lesser
binding energy, which confirms the influence of amino-groups on electron density of palladium
(Table 4). The similar effect of interaction between palladium and nitrogen-containing materials was
reported in several studies, devoted to synthesis and characterization of properties of palladium
catalysts based on triazolyl-containing porous aromatic polymers [41–43]: due to a stronger
interaction between Pd NPs and nitrogen atoms, a greater shift of N 1s peak toward higher energies
and of Pd 3d5/2 and 3d3/2 peaks toward lower energies was observed.
Table 3. Components of the XPS spectra.
Element
C
O
Pd
N
P
85.8 at. %
81.3 wt.%
7.4 at. %
8.4 wt.%
0.4 at. %
3.1 wt.%
5.9 at. %
6.1 wt.%
0.5 at. %
1.1 wt.%
Pd–PAF-20-NH2
90.9 at. %
69.1 wt.%
4.6 at. %
4.3 wt.%
4.2 at. %
26.0 wt.%
0.3 at. %
0.6 wt.%
Pd–PAF-20
-
Table 4. Peak parameters for XPS spectra of Pd-PAF-20 and Pd-PAF-20-NH2 catalysts
Catalyst
Parameter
Binding energy, eV
Content, %
Pd0
PdOx
Pd 3d5/2, 334.2 eV
Pd 3d3/2, 339.6 eV
85.3 %
Pd 3d5/2, 336.4 eV
Pd 3d5/2, 341.8 eV
14.7 %
Pd-PAF-20
Pd 3d5/2, 334.2 eV
Pd 3d3/2, 339.2 eV
32.4 %
Pd 3d5/2, 335.8 eV
Pd 3d3/2, 340.8 eV
67.6 %
Binding energy, eV
Content, %
Pd-PAF-20-NH2

3.3. Catalytic Tests
Both Pd–PAF-20 and Pd–PAF-20-NH2 were tested as catalysts in the hydrogenation of
different olefins, alkynes and dienes. The main results are demonstrated in Fig. 8 and Table 5.
Fig. 8. Hydrogenation of unsaturated compounds over the Pd–PAF-20 and Pd–PAF-20-NH2
catalysts. Reaction conditions: 1 mg of catalyst, substrate:metal = 27000:1 (mol), 60 ˚C, 1 MPa H2,
30 min.
In cases for all substrates Pd–PAF-20 was more active, than Pd–PAF-20-NH2, but on the
other hand, Pd–PAF-20-NH2 was more selective towards needed olefins, for example, this catalyst
didn’t demonstrate any significant activity for octene-1 or 2,5-dimethylhexadiene-2,4 (Fig. 9).
This fact can be explained considering the modification with amino groups, which interact with
palladium particles and, on the one hand, block active sites on their surface reducing the activity
of the catalyst [44] and, on the other hand, weaken the palladium affinity to an alkene by increasing
electron density on the palladium and facilitating alkene desorption from the surface [45], which
increases the selectivity of the catalyst.
Table 5. Distribution of reaction products in hydrogenation of unsaturated compounds over Pd–
PAF-20 and Pd–PAF-20-NH2.
Product yield, %
Substrate
Styrene
Reaction products
Pd–PAF-20
Pd–PAF-20-NH2
Ethylbenzene
Styrene
54
59
3
24
30
1
Phenylacetylene
Ethylbenzene
Octene-1
Octane
66
2
26
4
Octyne-1
Octyne-4
Octene-4
73
8
4
trans-octene-2
cis-octene-2
<1
<1
2
Octene-1
8.2
21
8
Octane
2,5-dimethylhexene-2
2,5-dimethylhexane
2
2,5-
dimethylhexadiene
32
<1

60
50
40
30
20
10
0
Pd-PAF-20
Pd-PAF-20-…
Run
1
2
3
4
5
6
Fig. 9. Reusability of Pd-PAF-20 and Pd-PAF-20-NH2. Reaction conditions: 1 mg of catalysts, 1.3
ml of phenylacetylene, 60˚C, 1 MPa H2, 30 min.
Recyclability tests were also performed for both catalysts. As shown in Fig. 9, Pd-PAF-20-
NH2 can be used at least six times without significant loss of activity. In the case of Pd-PAF-20
conversion of phenylacetylene decreased dramatically after the first run. TEM images (Fig. 10)
demonstrate that for both catalysts after the third run the quantity of palladium nanoparticles within
the pores of PAFs per unit of the surface hadn’t changed, however, the average diameter of
nanoparticles slightly increased for both of them and amounted to 3.7 nm for Pd-PAF-20 and to
3.6 nm for Pd-PAF-20-NH2. The first loss of activity for Pd-PAF-20 may be explained by the
washing out of some large agglomerates of palladium particles from the surface of grains of the
carrier. Further decrease of catalyst activity could be related to metal leaching from the pores of
PAF-20. In contrast, no significant decrease in catalytic activity was observed for Pd-PAF-20-NH2.
30
25
20
15
10
5
0
2.5
3
3.5
4
4.5
5
5.5
6
d, nm
30
25
20
15
10
5
0
2
2.5
3
3.5
4
4.5
5
5.5
6
d, nm
Fig. 10. TEM microphotographs and particles size distributions for Pd–PAF-20 (a) and Pd–
PAF-20-NH2 (b) after the third run.

Catalytic activities of Pd–PAF-20 and Pd–PAF-20-NH2 were compared with previously
described catalysts (Table 6). Phenylacetylene was chosen as the substrate for comparison. Catalysts
based on PAFs show better activity in comparison with industrial Lindlar catalyst, while keeping
selectivity at 95–98% [46]. They are also more selective than common Pd-catalysts based on
activated carbon and SiO2.
Table 6. Comparison of Pd-catalysts based on different supports for hydrogenation of
phenylacetylene.
Catalyst
Reaction conditions
Conv.,% Select.,% Reference
1 mg catalyst, 1.3 ml phenylacetylene,
Substrate:Pd = 27000:1 (mol)
Pd–PAF-20
(4.7% Pd)
62
31
5
95
98
This study
This study
[46]
60˚C, 1 MPa H2, 30 min
1 mg catalyst, 1.3 ml phenylacetylene,
Substrate:Pd = 27000:1 (mol)
Pd–PAF-20-NH2
(3.15% Pd)
60˚C, 1 MPa H2, 30 min
10 mg catalyst, 0.6 ml phenylacetylene,
Substrate:Pd = 5800:1 (mol)
Pd/Lindlar
(1% Pd)
> 99
88
30˚C, atmospheric H2, 270 min
13 mg catalyst, 0.5 ml phenylacetylene,
Substrate:Pd = 3700:1 (mol)
Pd/carbon
(1% Pd)
85
51
[46]
50˚C, 0.2 MPa H2, 15 min
0.2 g catalyst, 1 ml phenylacetylene,
Substrate:Pd = 480:1 (mol)
Pd/SiO2
(1% Pd)
96
[47]
30˚C, 0.1 MPa H2, 1 h
4.
Conclusions
Highly selective catalysts for the hydrogenation of terminal alkynes based on the
nanoparticles of Pd immobilized in porous aromatic frameworks were developed. Catalytic
characteristics were investigated in the hydrogenation of different alkenes and alkynes. High
selectivity for alkenes (to 99%) was achieved. Pd–PAF-20 was more active, but Pd–PAF-20-NH2
proved to be more selective towards needed olefins. Synthesized catalysts were comparable in
selectivity with industrial ones, but also found to be more active.
5.
Acknowledgments
The study was supported by the Russian Science Foundation within a framework of Project N 15-
19-00099.
6.
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