Hydrogenation and hydroamination in the presence of catalysts based on platinum and carbon nanofibers

Article abstract of DOI:10.1134/S0965544116120100

This paper presents the data on the catalytic activity of platinum-containing carbon nanofibers in the hydrogenating amination of propanal by 4-aminobenzoic acid and the hydrogenation of nitrobenzene. The obtained data are compared with the catalytic prop

Full text of DOI:10.1134/S0965544116120100

ISSN 0965-5441, Petroleum Chemistry, 2016, Vol. 56, No. 12, pp. 1123–1127. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © N.A. Magdalinova, M.V. Klyuev, 2016, published in Nanogeterogennyi Kataliz, 2016, Vol. 1, No. 2, pp. 116–121.
Hydrogenation and Hydroamination in the Presence of Catalysts
Based on Platinum and Carbon Nanofibers
N. A. Magdalinova* and M. V. Klyuev**
Ivanovo State University, Ivanovo, Russia
*e-mail: mn2408@mail.ru,
**e-mail: klyuev@inbox.ru
Received June 5, 2016
Abstract⎯This paper presents the data on the catalytic activity of platinum-containing carbon nanofibers in
the hydrogenating amination of propanal by 4-aminobenzoic acid and the hydrogenation of nitrobenzene.
The obtained data are compared with the catalytic properties of various platinum-containing carbon nano-
materials tested under similar conditions.
Keywords: platinum, carbon nanofibers, hydrogenating amination, hydrogenation, nitrobenzene
DOI: 10.1134/S0965544116120100
Recently [1], technologies have been developed for particles and the support, increasing the degree of dis-
the anchoring of transition-metal nanoparticles with a
size of 2 to 13 nm on the surface of carbon nanomate-
rials: fullerenes, fullerene black, carbon nanotubes,
carbon nanofibers (CNFs), nanodiamonds, etc. One
of the methods to form metal particles on carbon
nanomaterials involves support treatment by various
oxidizers: HNO3 [2–4], a mixture of HNO3 and
H2SO4 [5–11], Н2О2 [12–14], О3 [12–14], HF [15], or
air. As a result, anchor functional (carboxyl, hydroxyl,
carbonyl, etc.) groups are formed on the support sur-
persion of metal sites. Similar materials may be used as
heterogeneous catalysts for various organic synthesis
reactions, including hydrogenation reactions, and
may compete with commercial catalysts, for example,
Pd/C and Pt/C.
In this study, the catalytic activity of Pt-containing
carbon nanofibers was studied in the model reactions
of hydrogenization amination of propanal by 4-ami-
nobenzoic acid (Scheme 1) and hydrogenation of
face. This facilitates better interaction between metal nitrobenzene (Scheme 2).
O
C
H
−H2O
+
CH2 CH3
NH2
HOOC
CH
HOOC
N
CH2 CH3
+H2O
H2, cat.
NH CH2 CH2 CH3
HOOC
NO2
Scheme 1.
3H2, cat.
NH2
−2H2O
Scheme 2.
The choice of the model reactions is related to their versal methods for synthesizing secondary asymmet-
practical importance as well as to the fact that the ric amines by the interaction of aliphatic and hetero-
hydrogenations of the >С=N– double bond and cyclic aldehydes with aromatic, alicyclic, or heterocy-
the nitro group may occur via different mechanisms. clic amines or their precursors. The interest in
Catalytic hydrogenating amination is one of the uni- secondary amines is associated with their peculiar
1123

1124
MAGDALINOVA, KLYUEV
chemical and biological properties that allow their use fraction analysis (XRD) of powder samples with a
for the manufacture of drugs, dyes, and fuel and oil
additives. Primary aromatic amines are employed to
manufacture dyes, vulcanization accelerators, isocya-
nates, explosives, etc. Moreover, they may be used as
original compounds in hydroamination.
ThermoARL diffractometer using CuKα radiation
with a wavelength of 1.5406 Å.
The hydrogenating amination reaction was con-
ducted as follows. Twenty milligrams of the catalyst
was placed into a glass reactor equipped with a tem-
perature-controlled jacket and a magnetic stirrer in a
hydrogen stream under a layer of solvent (5 mL of eth-
anol and 10 mg of NaBH4) and activated by hydrogen
EXPERIMENTAL
Carbon nanofibers were obtained at the Labora-
tory of Hydrogen-Accumulating Materials, Institute for 10 or 60 min. After that, a solution that was pre-
of Problems of Chemical Physics, Russian Academy
of Sciences, by the pyrolysis of gas mixture C2H4 : H2 :
Ar = 1.5 : 3 : 1 in a quartz flow gas reactor at an atmo-
spheric pressure at 700°C using Ni/MgO as a catalyst
(hereinafter, CNF(0)) [16]. A similar technique was
used for the synthesis of carbon nanofibers in the pres-
ence of H2O (CNF(W)), C2H5OH (CNF(E)),
NH4OH (CNF(N)), and HCl (CNF(Cl)) vapors.
A MgO powder (analytical grade) was used as a cat-
alyst support for obtaining carbon nanofibers. On the
surface of the MgO powder, Ni was precipitated from
an aqueous Ni(NO3)2 solution followed by drying in
air at 150°C for an hour. The reduction of metal was
conducted immediately during pyrolysis without pre-
liminary holding in a hydrogen atmosphere. In accor-
dance with elemental analysis, the content of nickel in
the catalyst Ni/MgO was 5 wt %.
pared by mixing 2 mmol of 4-aminobenzoic acid and
2 mmol of propanal in 20 mL of ethanol was intro-
duced into the reactor in a hydrogen stream and
hydrogenation was conducted at Т = 45°C and
=
PH
2
0.1 MPa. The reaction of nitrobenzene hydrogenation
was run as follows. Twenty milligrams of the catalyst
and 10 mg of NaBH4 were placed into the reactor
under a layer of solvent (10 mL of ethanol), activation
was conducted for 60 min, and 1 mmol of nitroben-
zene was added in a hydrogen stream. When the
hydrogenation of one nitrobenzene portion was com-
pleted (Т = 45°С and
= 0.1 MPa), another portion
PH
2
was added in a hydrogen stream and hydrogenation
was conducted under the same conditions. In total,
five nitrobenzene portions were added sequentially.
The reaction rate was measured by the volumetric
method according to hydrogen absorption. It is known
that the true catalytic activity of heterogeneous cata-
lysts should be related to the number of active sites of
the catalyst, whose estimation presents a problem.
Under similar reaction conditions, the catalytic activ-
The composition of the gas phase was varied by a
change in the volume velocities of gas streams. Gas-
phase additives were introduced into the reaction zone
by passing an argon stream through a bubbler filled
with a liquid volatile component. When the synthesis
was completed, carbon nanofibers were sonificated in ity of the test objects may be compared in terms of the
turnover number (TON, min–1), which shows the
number of substrate molecules converted per mole of
platinum per minute.
concentrated hydrochloric acid at 70°C for an hour
and a half to remove the catalyst.
Platinum clusters were supported as follows [17,
18]: a weighed portion of carbon nanofiber was placed
in an alkaline solution (pH 11) of ethylene glycol, in
which the calculated amount of H2PtCl6 was dis-
solved; after that, dispersing was conducted in an
ultrasonic bath for an hour, platinum was reduced
under microwave radiation at a power of 800 W for 1–
2 min, and the resulting samples were rinsed with dis-
tilled water and air dried at 90°C for 6 h.
Under the studied conditions, the test reactions
have the zero order with respect to the substrate and
the first order with respect to the catalyst and hydro-
gen [19]. The occurrence of processes in the
kinetic region was confirmed using the Thiele crite-
rion (Ф) [20]:
W
CD
The as-prepared samples were analyzed at the
Institute of Problems of Chemical Physics, Russian
Academy of Sciences. Elemental analysis was con-
ducted by a semi-micromethod. The specific surface
of the catalysts was studied by thermogravimetry and
differential scanning combustion calorimetry on a
NETZSCH STA-409 PC Luxx thermal analyzer cou-
pled with a QMS-403 C mass spectrometer; measure-
ments were conducted in the linear heating mode at a
rate of 10°C/min from room temperature to 1000°C in
air. The average sizes of metal particles were calculated
by the Selyakov–Scherrer equation according to dif-
Φ = R
,
where R is the average diameter of catalyst particles,
cm; W is the rate of reaction, on the linear
portion of the kinetic curve to a 10% conversion from
the theoretically calculated value for each substrate,
mol/(L s); С is the substrate concentration, mol/L;
and D is the diffusion coefficient, 10–5 cm2/s. In
experiments, the Thiele criterion was found to be
much smaller than unity (Ф = 2.0 × 10–6–2.1 × 10–5).
This fact provides unambiguous evidence that the
fractograms that were registered by X-ray powder dif- reaction occurs in the kinetic region.
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HYDROGENATION AND HYDROAMINATION IN THE PRESENCE
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Table 1. Elemental analysis of carbon nanofibers
Sample C, wt % H, wt % N, wt % O, wt %
CNF(0)
CNF(W)
CNF(E)
CNF(N)
CNF(Cl)
CNF(E) nitrogen is absent (Table 1). The content of
oxygen is approximately 1% (Table 1).
The anchoring of platinum was conducted from an
aqueous solution of H2PtCl6. For all the samples, the
calculated amount of platinum was 20 wt %, but in
81.96
80.88
75.91
68.61
78.22
0.527
0.536
0.000
0.438
0.413
0.240
0.170
0.000
1.940
0.150
0.621
1.025
0.698
0.773
1.028
accordance
with
thermogravimetry,
sample
Pt/CNF(0) contained 19 wt % platinum. The highest
amount of platinum (23 wt %) was found in sample
Pt/CNF(N). The lowest amount of metal (16 wt %)
was in the sample prepared using water vapor. The
samples prepared with the addition of hydrochloric
acid and alcohol vapors contained 17 and 21 wt % Pt,
respectively (Table 2, entries 1–5).
RESULTS AND DISCUSSION
The elemental composition of the carbon nanofi-
bers obtained by the pyrolysis of gas mixture C2H4 : H2 :
Ar = 1.5 : 3 : 1 (CNF(0)) and in the presence of H2O
The diameter of nanofibers was 20–40 nm. The
sizes of Pt crystallites calculated for the Pt(220) line of
diffractograms via the Selyakov–Scherrer equation
were 5–7 nm for all the samples. However, as evi-
denced by electron microscopy data (Fig. 1), the sizes
of Pt particles were somewhat different and ranged
from 2–3 nm to large agglomerates with a size of 20–
30 nm.
The catalytic activity of the test Pt/CNF samples
was studied in model reactions: the hydrogenating
amination of propanal by 4-aminobenzoic acid
and the hydrogenation of nitrobenzene. Table 2
(CNF(W)),
C2H5OH
(CNF(E)),
NH4OH
(CNF(N)), and HCl (CNF(Cl)) vapors is shown in
Table 1. The content of carbon is varied from 68 to
82%. The largest amounts of carbon, 81.96 and
80.88%, respectively, are contained in CNF(0) and
CNF(W), while the lowest amount of carbon is con-
tained in CNF(N) (68.61%). The content of hydrogen
in all the samples is almost the same (0.4–0.5%). The
exception is provided by sample CNF(E), containing
no hydrogen (Table 1). The content of nitrogen in the
samples is 0.01–0.2%, except nanofibers obtained (entries 1–5) lists the reaction rates for the hydroge-
with the addition of ammonia vapor (1.94%), while in nating amination of propanal by 4-aminobenzoic acid
Table 2. Rates of amine formation in hydrogenation and hydrogenating amination reactions (entries 6–15 [21]*)
Hydrogenating amination Nitrobenzene hydrogenation
Metal
Entry
Catalyst
L**, nm
W × 105,
W × 104,
TON,
min–1
TON,
min–1
content, wt %
mol/(L s)
mol/(L s)
1
2
3
4
5
Pt/CNF(0)
Pt/CNF(W)
Pt/CNF(E)
Pt/CNF(N)
Pt/CNF(Cl)
19
16
21
23
17
5–7
5–7
5–7
5–7
5–7
5.3
3.1
8.4
1.5
7.4
4.1
2.8
5.9
1.0
6.4
7.7
5.6
7.3
6.3
8.8
23.7
17.3
22.5
19.6
27.2
6
7
8
Pt/CNF(1)
(d*** = 20–40 nm)
Pt/CNF(2)
(d = 100–200 nm)
Pt/CNF(3)
(d = 100–200 nm)
Pt/CNT(1)
Pt/CNT(2)
Pt/ND(1)
Pt/ND(2)
Pt/ND(3)
26.6
6–8
6–8
6–8
1.6
1.0
2.3
0.6
2.0
0.9
2.0
4.5
5
–
–
24.1
3.2
7.7
9
10
11
12
13
14
15
4.4
22.6
15
20
25
10
20
6–8
6–8
5
5
5
4–5
2.5
0.8
2.5
0.5
0.9
1.8
1.6
3.8
1.7
1.1
1.7
2.5
3.9
1.6
1.8
1.1
1.9
3.1
3.0
3.0
–
14.6
4.9
42.2
32.2
25.7
–
Pt/FB
Pt/C (Е-ТЕK)
3.8
11.2
* Reaction conditions [21]: Т = 45°C,
= 0.1 MPa, 30 mg of catalyst, 10 mg NaBH ; hydrogenating amination: 25 mL of ethanol;
4
P
H2
2 mmol of propanal, 2 mmol of 4-aminobenzoic acid; hydrogenation: 10 mL of ethanol and 1 mmol of nitrobenzene.
** L is the average size of metal particles calculated by the Selyakov–Scherrer equation according to X-ray powder diffraction patterns.
*** d is the diameter of carbon nanofibers.
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1126
MAGDALINOVA, KLYUEV
(b)
(а)
(c)
100 nm
100 nm
100 nm
(d)
(e)
100 nm
100 nm
Fig. 1. Micrographs of Pt/CNF samples [18]: (а) 19 wt % Pt/CNF(0), (b) 16 wt % Pt/CNF(W), (c) 21 wt % Pt/CNF(E),
(d) 23 wt % Pt/CNF(N), and (e) 17 wt % Pt/CNF(Cl).
and the hydrogenation of nitrobenzene together with Pt/CNF(E) (Table 2). The lower the content of the
the values of activity (TON, min–1) of Pt/CNFs in
these reactions. Certainly, it is unknown how many
active sites are involved in catalysis, i.e., active sites
interacting with substrate molecules, and how many
platinum atoms are incorporated into the composition
of each site. However, the studied reactions are distin-
guished only by the nature of substrate molecules;
therefore, the use of this expression for catalyst activity
seems to be quite reasonable. As is clear from Table 2,
in the hydroamination reaction, the lowest reaction
rates and turnover numbers are observed for the cata-
lyst Pt/CNF(N), containing the highest amount of
the metal (23 wt %). The sample containing the lowest
amount of the metal (16 wt % Pt/CNF(W)) was
more active; namely, its TON was higher by a factor
of ≈3 compared with Pt/CNF(N). A high catalytic
activity was exhibited by the samples obtained from
CNFs in the presence of 21 wt % alcohol Pt/CNF(E)
and 17 wt % hydrochloric acid Pt/CNF(Cl) (TON =
5.9 and 6.4 min–1, respectively); as regards activity,
these catalysts surpassed Pt/CNF(N) by ≈6 and
6.5 times. In this series of catalysts, Pt/CNF(0) takes
the middle position in terms of both platinum content
and catalytic activity (Table 2, entries 1–5). The rate
of the hydroamination reaction mediated by
Pt/CNF(0) also takes a medium value.
metal in the sample, the higher its activity.
Pt/CNF(N) and Pt/CNF(W) also exhibit lower cata-
lytic activity in the hydrogenation of nitrobenzene in
the tested sequence.
The above data are compared with the results
reported for platinum-containing carbon nanofibers
(Pt/CNFs), carbon nanotubes (Pt/CNTs), nanodia-
monds (Pt/NDs), fullerene black (Pt/FB), and the
commercial catalyst on carbon (Pt/C) of the E-TEK
brand that contain different amounts of the metal
(Table 2, entries 6–15) [21]. All the catalysts have
close average sizes of platinum particles. It is seen that
all the test samples (Table 2, entries 1–5) surpass
Pt/CNF in reaction rates and activities in both hydro-
genating amination and hydrogenation (Table 2,
entries 6–8), while Pt/CNF(Cl), Pt/CNF(0), and
Pt/CNF(E) showed the highest activity among all the
compared catalysts based on carbon nanomaterials. In
the hydrogenation of nitrobenzene, the tested catalysts
(Table 2, entries 1–5) are inferior to platinum-con-
taining nanodiamonds solely in terms of activity
(Table 2, entries 11–13), although turnover numbers
for 17 wt % Pt/CNF(Cl) are higher than turnover
numbers for 25 wt % Pt/ND (Table 2, entries 5, 13).
In the hydrogenation of nitrobenzene, the stability
of the studied Pt/CNFs was examined in five sequen-
tial cycles of nitro group full reduction (Fig. 2). The
time of one cycle was 15–20 min depending on the
catalyst. Figure 2 shows that, in the third to fourth
cycle, the rate of hydrogenation decreases by 11–20%;
in the case of Pt/CNF(0), the rate of hydrogenation
Note that the hydrogenation of nitrobenzene pro-
ceeds at a higher rate than hydrogenating amination.
It appears that the nitro group is more accessible to
catalytic sites than multiple bond >C=N– screened by
ethyl and 4-carboxyphenyl groups. The highest values
of hydrogenation rate and TON are observed in the
presence of Pt/CNF(Cl), Pt/CNF(0), and decreases by almost one-third; and in subsequent
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HYDROGENATION AND HYDROAMINATION IN THE PRESENCE
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uglerodnykh nanomaterialov (Hydrogenation Catalysts
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Fig. 2. Stability of Pt/CNF in the hydrogenation of five
sequential nitrobenzene portions.
cycles, it remains constant within the experimental
error.
Thus, the introduction of organic and inorganic
additive vapors in the synthesis of carbon nanofibers
affects both the physical and catalytic characteristics
of the related platinum-containing materials.
Pt/CNFs were catalytically active in the hydrogenat-
ing amination of propanal by 4-aminobenzoic acid
and the hydrogenation of nitrobenzene. The highest
activity in the hydroamination reaction is observed for
samples Pt/CNF(W), Pt/CNF(Cl), and Pt/CNF(E);
in the hydrogenation of nitrobenzene, for samples
Pt/CNF(Cl), Pt/CNF(0), and Pt/CNF(E). The ca-
talysts containing a high amount of platinum are less
efficient than samples containing a small amount of
platinum. The tested Pt/CNFs are rather stable and
may be used repeatedly.
ACKNOWLEDGMENTS
We are grateful to the staff of the Laboratory of
Hydrogen-Accumulating Materials, Institute of Prob-
lems of Chemical Physics, Russian Academy of Sci-
ences, Chernogolovka, and personally to the head of
this laboratory B.P. Tarasov for supplying us with the
samples of platinum-containing carbon nanofibers
and E.A. Reikhardt for her help in experiments.
This work was supported by the Ministry of Educa-
tion and Science of the Russian Federation (state
order, agreement no. 114121750070).
REFERENCES
1. Klyuev,
M.V.,
Magdalinova,
N.A.,
and
Translated by T. Soboleva
Kalmykov, P.A., Katalizatory gidrogenizatsii na osnove
PETROLEUM CHEMISTRY Vol. 56 No. 12 2016