Palladium-containing graphene-like materials: Preparation and application as hydrogenation catalysts

Article abstract of DOI:10.1134/S0965544116060025

The preparation of palladium-containing graphene-like materials modified with amines is described. The structure of the resulting materials is studied by a complex of physicochemical methods. The materials are tested as hydrogenation and hydrodehalogenati

Full text of DOI:10.1134/S0965544116060025

ISSN 0965ꢀ5441, Petroleum Chemistry, 2016, Vol. 56, No. 6, pp. 503–509. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © P.A. Kalmykov, A.A. Arbuzov, N.A. Magdalinova, B.P. Tarasov, M.V. Klyuev, 2016, published in Nanogeterogennyi Kataliz, 2016, Vol. 1, No. 1, pp. 43–49.
PalladiumꢀContaining GrapheneꢀLike Materials:
Preparation and Application as Hydrogenation Catalysts
a
b
a
b
a,
P. A. Kalmykov , A. A. Arbuzov , N. A. Magdalinova , B. P. Tarasov , and M. V. Klyuev *
a
Ivanovo State University, Ivanovo, Russia
b
Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, Russia
*
eꢀmail: klyuev@inbox.ru, k_p.a@mail.ru
Received September 21, 2015
Abstract—The preparation of palladiumꢀcontaining grapheneꢀlike materials modified with amines is
described. The structure of the resulting materials is studied by a complex of physicochemical methods. The
materials are tested as hydrogenation and hydrodehalogenation catalysts. It is shown that the characteristics
of these catalysts are superior to those of the commercial counterpart, viz., palladiumꢀcontaining activated
carbon.
Keywords: grapheneꢀlike materials, catalysts, palladium, hydrogenation, hydrodechlorination
DOI: 10.1134/S0965544116060025
Carbon nanomaterials (fullerene black, nanofiꢀ hydrogenation and hydrodechlorination catalysts are
bers, nanotubes, and nanodiamonds) that contain described.
transition metals have been extensively studied as catꢀ
alysts for various organic and petrochemical synthesis
reactions, particularly hydrogenation [1–5].
EXPERIMENTAL
The unique properties of graphene and grapheneꢀ
like materials have aroused the interest of scientists
Graphite Oxide (GO) Synthesis
GO was prepared by a modified Hammers–Offeꢀ
man method [6, 21]. Twenty grams of natural graphite
around the world and triggered vigorous research.
2
Graphene is a twoꢀdimensional material in which sp
ꢀ
GKꢀ1 and 10 g of NaNO were placed in a 2 L threeꢀ
3
hybridized carbon atoms form a hexagonal lattice.
Graphene can be modified by the introduction of varꢀ
ious functional groups, particularly those that can
neck flask equipped with a mechanical stirrer and a
thermometer; 550 mL of concentrated H SO was
poured into the flask. The resulting mixture was
2
4
bind the atoms of transition metals. These metalꢀconꢀ heated in a water bath to 318 K under continuous stirꢀ
taining grapheneꢀlike materials are used as catalysts ring until the blue color of graphite bisulfate occurred.
for various conversions of organic compounds, such as The resulting suspension was cooled in an ice bath to
2
83 K; 66 g of KMnO was slowly added to it, while
hydrogenation processes. Prefunctionalization subꢀ
stantially decreases the aggregation of graphene sheets
4
maintaining the temperature of the reaction mixture
below 293 K. After the addition of KMnO , the ice
[
6], and increases the number of growth centers of
metallic nanocrystals due to the presence of amino
groups on the surface In particular, many examples of
4
bath was removed; the temperature of the mixture was
allowed to rise no higher than 313 K. After thickening
of the mixture, the stirring was stopped for ~8 h. The
mixture was cooled in an ice bath to 283 K; 1 L of bidꢀ
istilled water was slowly added to the mixture, while
maintaining the temperature of the mixture below
.
the hydrogenation of a variety of aromatic nitro comꢀ
pounds [7–13] and compounds containing multiple
bonds [14–19] have been described. Previously, the
use of an ethylenediamineꢀmodified palladiumꢀconꢀ
3
23 K. The thoroughly stirred suspension was transꢀ
taining grapheneꢀlike material as a hydrogenation catꢀ ferred into a 3 L beaker; 70 mL of 30% H O was
2
2
alyst has been patented [20]. In this study, the preparaꢀ added dropwise under stirring. The resulting bright
tion of amineꢀmodified palladiumꢀcontaining yellow suspension of GO was diluted with bidistilled
grapheneꢀlike materials, the findings of their examiꢀ water to 40 L and washed by decantation until the negꢀ
2–
4
nation by a complex of physicochemical analysis ative reaction of the mother liquor for SO
methods, and the results of testing of these materials as respect to BaCl ).
ions (with
2
503

504
KALMYKOV et al.
GO Functionalization
Functionalized GO (FGO) was prepared using the
160 mL of a 5% aqueous solution of lithium formate
heated to 328 K was added to the resulting mixture.
Synthesis was conducted at 328 K. After 15–20 min,
the reaction mixture was heated to 343 K, cooled to
room temperature, and allowed to settle for 24 h. After
settlement, it was subjected to decantation with disꢀ
tilled water 3–4 times at 24 h intervals. After the final
following
amines:
ethylenediamine
diethylenetriamine
triethylenetetramine
H NCH CH NH ,
2
2
2
2
(
(
H NCH CH ) NH,
2
and
2
2 2
NH CH CH NHCH ) .
2
2
2
2 2
FGO was prepared from GO as follows: 0.5 g of decantation, the catalyst was airꢀdried at room temꢀ
dried GO was dispersed in 200 mL of butanolꢀ1 in an perature.
ultrasonic bath for 3 h to obtain a homogeneous mass
of the exfoliated GO; 50 mL of the respective amine
was added to the mass; the resulting mixture was
Investigation Procedures
The resulting materials were studied by a complex
refluxed for 3 h. The products were filtered off, washed
with ethanol to remove excess amine, and dried in a of physicochemical methods (FTIR spectroscopy,
vacuum at 353 K.
Raman spectroscopy, Xꢀray diffraction (XRD) analyꢀ
sis, and scanning electron microscopy (SEM) using a
PerkinElmer Spectrum 100 FTIR spectrometer with a
Catalyst Synthesis Procedure
–1
resolution of 0.5 cm , a Horiba Jobin Yvon T64000
To prepare the Ktꢀ2 catalyst, a 300 mg weighed spectrometer with a 514.5 nm argon laser line, and a
portion of sample 2 (Table 1) was suspended in 40 mL Zeiss LEO SUPRA 25 fieldꢀemission scanning elecꢀ
of ethanol in a roundꢀbottom flask and held at 318 K tron microscope with the EDX function. The vacuum
–
10
in an ultrasonic bath (VUꢀ09ꢀYaꢀFPꢀ03) at a freꢀ in the working chamber was 6.0
×
10
kPa. The
quency of 22 kHz for 15 min. An alcohol solution of accelerating voltage was 10 kV, the current density was
palladium chloride, as required for the preparation of 0.16 nA to 0.25 pA, the working distance was 9.8–
a catalyst containing 5 wt % of the metal, was then 10.2 mm, and the magnification was 25000
×
to
slowly poured into the resulting suspension heated to a 35000×. XRD analysis was conducted on a DRONꢀ2
temperature of 318 K. To this end, a 25 mg weighed instrument in an angle range of 2
= 5°–70° with a
θ
portion of PdCl was dissolved in 10 mL of ethanol step of 0.03°; CHNS/O elemental analysis was conꢀ
2
acidified with 0.6 mmol of hydrochloric acid. The ducted using the Vario Micro cube software package by
resulting composition was stirred with a magnetic stirꢀ combustion at 1423 K in the presence of pure oxygen
rer for 45 min. The reactor was then purged with and subsequent reduction of oxides and separation on
hydrogen; the attached metal was reduced with a chromatographic column. Determination of eleꢀ
sodium tetrahydroborate (100 mg) in a hydrogen ments was based on the content of CO and H O in the
2
2
atmosphere. The reduction was conducted in a therꢀ combustion products. The signal of each oxide was
mostated glass reactor at a temperature of 318 K under recorded using a thermal conductivity detector. The
continuous stirring with a magnetic stirrer with a thermal properties of the samples were characterized
Teflon anchor for 30 min. The suspension was then filꢀ by thermogravimetry on a NETZSCH STA 409 C
tered through an ashless paper filter (FILTRAK blue Luxx thermoanalyzer in an argon or air atmosphere at
ribbon) and washed with distilled water and ethanol a temperature of 303–1273 K and a heating rate of
until the mother liquor gave a negative test for chlorine 10 K/min.
ions in reaction with a 10% silver nitrate solution.
Next, the catalyst was dried in a thermostatted oven at
Catalytic Testing Procedure
a temperature of 318 K for 2 h to obtain a black powder
Ktꢀ2). A similar procedure was used to prepare cataꢀ
(
The testing of materials based on palladium and
FGO (Pd/FGO) as catalysts for the hydrogenation of
nitrobenzene and cyclohexene and the hydrodehaloꢀ
lysts based on samples 3 and 4 (Ktꢀ3 and Ktꢀ4, respecꢀ
tively).
Catalytic properties were compared using pallaꢀ genation of chlorobenzene was conducted as follows.
diumꢀcontaining activated carbon M200 (Pd/C). This Thirty milligrams of the catalyst was placed into a glass
catalyst was prepared as follows. Prior to the deposiꢀ reactor, which was equipped with a jacket for thermoꢀ
tion of palladium, 10 g of activated carbon was susꢀ statting and a magnetic stirrer, under a solvent layer
pended in 100 mL of water in a roundꢀbottom flask at (10 mL of ethanol) and subjected to activation in a
3
(
2
13–323 K for 15 min and held in the ultrasonic bath hydrogen atmosphere for 10 min. Next, 1 mmol of the
VUꢀ09ꢀYaꢀFPꢀ03) at 318 K and a frequency of substrate was introduced in the flow of hydrogen;
2 kHz for 15 min. An aqueous solution of palladium hydrogenation was conducted at = 318 K and PH2
T
=
chloride required for the preparation of a catalyst conꢀ 0.1 MPa. During the entire test, the reaction mixture
taining 1 wt % of the metal was then slowly poured into was stirred at a constant speed of 1250 revolutions of
the resulting suspension heated to a temperature of the magnetic stirrer anchor per minute; this speed is
3
18 K. A 166.7 mg weighed portion of PdCl was disꢀ sufficient for the occurrence of the process in the
2
solved in 30 mL of 1 M hydrochloric acid. Next, kinetic region as experimentally determined for the
PETROLEUM CHEMISTRY Vol. 56
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PALLADIUMꢀCONTAINING GRAPHENEꢀLIKE MATERIALS
505
studied conditions using the model reaction of
nitrobenzene hydrogenation over the tested catalysts
an example of the dependence, as derived for the
Vabs H , mL/min
2
4
3
3
2
.0
.5
.0
.5
(
reaction in the presence of Pd/C, is shown in Fig. 1).
The reaction rate was measured in the kinetic
region by the volumetric method according to hydroꢀ
gen absorption. The true catalytic activity of heterogeꢀ
neous catalysts should be related to the number of
active sites of the catalyst, which is difficult to estiꢀ
mate. Therefore, the catalytic activity of the studied
objects under similar conditions was compared in
2.0
.5
.0
1
–1
terms of the turnover number (TON, min ), which
shows the number of substrate moles converted per
mole of metal per minute. Under the studied condiꢀ
tions, the reactions are zero order with respect to the
substrate and first order with respect to the catalyst and
hydrogen. To confirm the occurrence of the processes
1
0.5
0
200 400 600 800 1000 1200 1400 1600 1800 2000
v, rpm
in the kinetic region, the Thiele criterion (
used:
Φ
) was
Fig. 1. The hydrogen absorption rate as a function of the
number of revolutions of the stirrer anchor.
W
Φ = R
,
CD
is the average diameter of the catalyst partiꢀ
is the reaction rate in the linear portion of
where
cles, cm;
R
dreds of square micrometers. During the reduction of
GO, the graphene planes are united into stacks comꢀ
posed of a large number of sheets [22]. The aliphatic
moieties attached to the GO surface during functionꢀ
alization prevent agglomeration of graphene sheets in
W
the kinetic curve to a 10% conversion from the theoꢀ
retically calculated value for each substrate, mol/(L s);
C
is the substrate concentration, mol/L; and D is the
–5
2
diffusion coefficient, 10 cm /s. In the experiments, the reduction process.
the Thiele criterion was significantly lower than unity
Thermogravimetry analysis in an argon atmoꢀ
sphere showed that the amineꢀmodified GO are more
stable than unmodified GO. The decomposition temꢀ
peratures of samples 2, 3, and 4 were 403, 443, and
05 K, respectively (Table 1), while the decomposition
temperature of GO was 373–383 K.
(
Φ
= 0.01–0.1); this finding undoubtedly indicates
the occurrence of the reaction in the kinetic region.
To study the stability of the catalysts, upon the
completion of the conversion of a portion of the subꢀ
strates, another portion was introduced without sepaꢀ
rating the catalyst and isolating the target products
from the reaction mixture.
4
The elemental analysis data for unmodified and
The products of hydrogenation and hydrodechloriꢀ modified GOs are listed in Table 1, which shows that
nation reactions were analyzed using a 3700 Series gas the modification of GO with amines leads to a
chromatograph equipped with a flame ionization decrease in the weight fraction of oxygen in the samꢀ
detector, a TsvetKhromꢀ8 generator with a hydrogen ples; this finding indicates the occurrence of deoxyꢀ
purity of 99.999% as a hydrogen source, and a 3
×
genation during the reaction.
2
000 mm chromatographic glass column packed with
The amount of palladium attached to the Ktꢀ2,
Ktꢀ3, and Ktꢀ4 samples was determined by oxidative
thermogravimetry according to the amount of the
noncombustible residue (Table 2). The table shows the
elemental analysis data for the Ktꢀ2, Ktꢀ3, and Ktꢀ4
samples before reaction, after one hydrogenation
cycle, and after five cycles of substrate hydrogenation
Lucopren Gꢀ1000 (5%) on Chromaton NꢀAWꢀ
DMCS (carrier gas, nitrogen; evaporation temperaꢀ
ture, 363–503 K; column temperature, 333–453 K;
carrier gas flow rate, 1.8
rate, 40 mL/min; and injected sample volume, 0.1–
.0 L).
±
0.02 L/h; hydrogen flow
2
μ
(
five portions of cyclohexene were consecutively
RESULTS AND DISCUSSION
Characterization of the Synthesized Materials
added without separating the catalyst from the reacꢀ
tion mixture). It is evident that the amount of pallaꢀ
dium attached to the support corresponds to the calꢀ
The analysis results showed that the amination of culated value (with allowance for the measurement
graphene was effective (the absorption band at error of the instrument). The metal is reliably attached
560 cm that occurred in the IR spectrum correꢀ to the support; it is not washed off during hydrogenaꢀ
–1
1
sponds to the N–H inꢀplane stretching vibrations). tion. The C/H ratio also remains unchanged; this feaꢀ
The SEM micrographs (Fig. 2) show that GO is comꢀ ture suggests that the catalyst is chemically stable
posed of distorted planes with an area of a few hunꢀ under the test conditions.
PETROLEUM CHEMISTRY Vol. 56
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506
KALMYKOV et al.
1
1
м
µ
к
m
м
1
1
0
0
0
0 нм
n
m
(
a)
(b)
(б)
(
а)
1
00 nm
20 nm
20 нм
1
00 нм
(
(
в
c
)
)
г)
(d)
Fig. 2. SEM images of (a) GO, (b) reduced GO, and (c, d) FGO.
Figure 3 shows a highꢀresolution micrograph of the mechanisms of hydrogenation of the double >C=C<
Ktꢀ2 sample. It is evident that the catalyst has a flaky bond and the nitro group or to steric hindrances that
structure with a varying number of layers. The metal arise during the hydrogenation of the internal double
particles are uniformly attached to the surface of the bond in cyclohexene compared with a more accessible
support flakes and generally have a spherical structure nitro group of nitrobenzene.
and a size of 3–10 nm.
The stability of the catalysts prepared according to
the same procedure in the hydrogenation of five porꢀ
Examination of the Activity of Catalysts Based
on Palladium and FGO in Hydrogenation Processes
tions of the substrate (nitrobenzene and cyclohexene)
was studied. Examination of the stability of the synꢀ
thesized catalysts shows (Fig. 4) that the repeated use
The synthesized Pd/FGO samples were studied in
model hydrogenation reactions using two substrates of the catalysts leads to the “catalystꢀconditioning”
that differ in the nature of the unsaturated portion, effect. After introduction of the next portions of the
viz., the nitro group and the double multiple bond, substrate without isolating the reaction products and
and in the hydrodechlorination of chlorobenzene.
separating the catalyst, the reaction rate slightly
The test results for the catalysts are shown in increases. After the hydrogenation of a few substrate
Table 3. It is evident that the hydrogenation rate of portions (the amount depends on the nature of the
nitrobenzene is 1.5–2.8 times higher than that of substrate), the reaction rate achieves a maximum value
cyclohexene. This fact is attributed either to different and then does not change, at least for 3 h.
Table 1. Elemental analysis of unmodified and modified GOs
Elemental composition, wt %
Sample
C/O
C
H
N
O
1
2
3
4
GO
49.3
74.1
75.6
69.3
2.4
2.6
3.1
3.9
0.0
13.6
9.2
45.1
7.4
1.46
GO + Ethylenediamine
GO + Diethylenetriamine
GO + Triethylenetetramine
7.5
13.8
4.2
4.1
14.4
12.5
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PALLADIUMꢀCONTAINING GRAPHENEꢀLIKE MATERIALS
Table 2. The contents of carbon, hydrogen, and palladium in Pd/FGO
507
Elemental composition, wt %
After one cyclohexene
hydrogenation cycle
After five cyclohexene
hydrogenation cycles
Catalyst
initial
C
H
Pd
C
H
Pd
C
H
Pd
Ktꢀ2
Ktꢀ3
Ktꢀ4
68.1
66.5
64.5
2.7
3.5
4.0
5.4
5.1
4.4
68.5
66.7
63.9
3.1
3.1
3.9
5.3
5.0
4.5
69.0
67.1
64.0
2.9
3.3
3.7
5.3
5.1
4.9
Table 3. The results of testing of the Pd/FGO samples in model reactions*
Nitrobenzene
Cyclohexene
reaction rate
turnover
reaction rate
W × 10 ,
Catalyst
turnover
number TON,
rate constant
L/(mol s)
k
,
4
rate constant
L/(mol s)
k
,
4
W
×
10 ,
number TON,
–1
–1
min
mol H /(L s)
min
mol H /(L s)
2
2
Ktꢀ2
Ktꢀ3
Ktꢀ4
13.3
14.5
19.5
76.7
84.3
3.3
3.4
4.6
5.7
6.9
9.0
33.9
40.7
51.8
1.4
1.6
2.1
115.9
*
The error in determining the rate constant and turnover number values does not exceed 5–7%.
It should be noted that the yield of the hydrogenaꢀ genation of five portions of nitrobenzene, the total
tion reaction target products is close to the quantitaꢀ decrease in the reaction rate was more than 30%
tive yield; it is 96–98% for cyclohexene and 98–99% (Fig. 4), whereas in similar experiments in the presꢀ
for nitrobenzene (determined by GLC).
ence of Pd/FGO, no decrease in the rate was observed
The tested catalysts were compared with the comꢀ (Fig. 4).
mercial Pd/C (using activated carbon M200). It was
The Ktꢀ3 and Ktꢀ4 catalysts were tested in the
shown that Pd/FGO exhibits a significantly higher hydrodechlorination of chlorobenzene (Table 4); both
activity than that of the counterpart based on activated catalysts exhibited activity in this reaction. The quanꢀ
carbon in the studied model hydrogenation reactions. titative analysis of the hydrodechlorination reaction
Thus, the hydrogenation reaction rate over Pd/FGO is products, as conducted by GLC, showed that within
2
.5 times higher than that over Pd/C in the case of 90 min the benzene yields were 80 and 88% in the
nitrobenzene and 30% higher in the case of cyclohexꢀ cases of Ktꢀ3 and Ktꢀ4, respectively. This value is comꢀ
ene. Another advantage of Pd/FGO over Pd/C is that parable to that provided by Pd/C (93%); however, the
the reaction rate over Pd/C, unlike Pd/FGO, graduꢀ reaction rate over this catalyst is almost 3 times lower
ally decreases in the hydrogenation of each consecuꢀ than that in the presence of Ktꢀ3 or Ktꢀ4. The high
tive portion of the substrate; for example, in the hydroꢀ yield of the target product in the hydrodechlorination
(a)
(b)
100 nm
20 nm
Fig. 3. SEM images of the Ktꢀ2 sample after a cycle of hydrogenation of 5 mmol of cyclohexene with a resolution of (a) 100 and
b) 20 nm.
(
PETROLEUM CHEMISTRY Vol. 56
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2016

508
KALMYKOV et al.
Wabs H × 10 , mol/(L s)
4
2
Pd/C
Kt-2
Kt-3
Kt-4
5
4
3
2
1
0
1
2
3
4
5
Number of substrate portion
Fig. 4. The stability of the catalyst samples in model nitrobenzene hydrogenation reactions.
Table 4. Results of testing of the Pd/FGO samples in the hydrodechlorination of chlorobenzene*
Turnover number
TON, min–1
Rate constant
L/(mol s)
k,
Reaction rate W ×
104,
Catalyst
Benzene yield, %
mol H /(L s)
2
Ktꢀ3
Ktꢀ4
5.5
5.6
32.0
32.7
1.3
1.3
80
88
*
The error in determining the rate constant and turnover number values does not exceed 5–7%.
of chlorobenzene suggests that these catalysts are
promising for use in hydrodehalogenation reactions.
This assumption requires further study.
ACKNOWLEDGMENTS
This work was supported by the Ministry of
Education (no. 114121750070) and Science of the
Russian Federation (state order, agreement
Thus, the proposed catalysts based on palladium
and GO are of considerable interest for use in hydroꢀ no. 14.604.21.0124,
genation reactions. The structure of both GO and the RFMEFI60414X0124).
GOꢀbased catalysts has been studied by a complex of
unique
identifier
physicochemical methods. It has been shown that the
synthesized samples exhibit high activity and stability
in the model reactions of hydrogenation of nitrobenꢀ
zene and cyclohexene and the hydrodechlorination of
chlorobenzene under mild conditions (T = 318 K; solꢀ
vent, ethanol; and PH2 = 0.1 MPa). The target product
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Translated by M. Timoshinina
PETROLEUM CHEMISTRY Vol. 56
No. 6
2016