Characteristic features of the selective action of platinum-doped glass fiber woven catalysts in the liquid-phase reduction of polyfunctional aromatic nitro compounds

Full text of DOI:10.1007/s10631-005-0048-8

Doklady Chemistry, Vol. 402, Part 2, 2005, pp. 111–113. Translated from Doklady Akademii Nauk, Vol. 402, No. 4, 2005, pp. 503–506.
Original Russian Text Copyright © 2005 by Wu Chuntiag, Dorokhov, Boiko, Bal’zhinimaev, Barelko.
CHEMICAL
TECHNOLOGY
Characteristic Features of the Selective Action
of Platinum-Doped Glass Fiber Woven Catalysts
in the Liquid-Phase Reduction
of Polyfunctional Aromatic Nitro Compounds
Wu Chuntiag*, V. G. Dorokhov*, G. A. Boiko*, B. S. Bal’zhinimaev**, and V. V. Barelko*
Presented by Academician A.E. Shilov January 21, 2005
Received January 25, 2005
The kinetics of liquid-phase hydrogenation of trini- investigation object. The studies cited demonstrated
trotoluene and trinitrobenzene on platinum-doped (up to that the GWC systems possess a much higher specific
0.2 wt %) glass fiber woven catalysts (SiO2 content of up catalytic activity than the traditional powder Pd/C cata-
to 98 wt %, specific surface area of 1–15 m2/g) was stud- lysts. Physicochemical studies of the glass fiber silicate
ied for the first time. Powdered carbon-supported palla- supports of the active phase led researchers [4–6] to the
dium (palladium content of 5 wt %, specific surface area conclusion that the abnormally high activity of a GWC
of up to 500 m2/g), which is a traditional catalyst for system is related to the amorphous coordinatively
these processes, was used as the reference material.
defective state of the glass template, the specific struc-
ture of the silanol groups formed in it, and the specific
mechanism of attachment of atomic clusters of catalyt-
ically active metals to the metastable glass fiber sup-
port. The technological advantages of GWCs when
used in the catalytic hydrogenation of aromatic nitro
compounds were patented [7].
The glass fiber catalysts were found to exhibit a
much higher activity than the traditional powder sys-
tems. Unexpectedly, these catalysts were found to be
exceptionally selective toward successive hydrogena-
tion of nitro groups; in particular, the first nitro group is
reduced at a rate an order of magnitude higher than the
second nitro group and, in turn, the third nitro group is
reduced more slowly than the second one by about an
order of magnitude. The hydrogenation on the tradi-
tional Pd/C powder system involves synchronously all
the nitro groups, i.e., proceeds almost nonselectively.
This paper is a next step in the study of the charac-
teristic features of reduction of nitroaromatic com-
pounds on GWC systems. Hydrogenation of polyfunc-
tional aromatic compounds, in particular, the reduction
of trinitrotoluene and trinitrobenzene to amines on plat-
inum-activated glass fiber woven catalysts, was chosen
for the investigation.
This result opens up a new way for industrial pro-
duction of complex aromatic nitroamines in a one-step
process. This process can be used as an industrial base
for utilization of nitroaromatic explosives eliminated
from normal use to obtain useful products.
The GWC samples were prepared using glass fiber
woven materials fabricated as a sparse mesh or a linen-
woven cloth as supports. The elementary fiber diameter
was 7–9 µm. These articles were manufactured from tra-
ditional silicate glasses in which the content of silicon
dioxide varied from 55 to 98 wt %, while the remaining
components were usual for glass silicate compositions of
the alumina, magnesia, calcium oxide, and boron oxide
series (glass fiber fabrics manufactured at the Polotsk
Steklovolokno Production Association were used as the
starting materials to prepare the catalysts).
The first studies of the mechanism and kinetics of
liquid-phase hydrogenation of nitroaromatic com-
pounds on new-generation catalytic systems, namely,
glass fiber woven catalysts (GWCs) doped by platinum
group metals, were carried out only several years ago
[1−3]. The simplest monofunctional nitroaromatic
compound, nitrobenzene, which is catalytically
reduced by hydrogen to aniline, was chosen as the basic
The catalytically active component (in this study,
platinum) was introduced into the glass fiber template
via ion exchange processes during impregnation of the
support in aqueous solutions of platinum-containing
salts followed by drying and heat treatment of the sam-
ples. The platinum content in the samples ready for
experiments varied from 0.1 to 0.2 wt %. The catalyst
porosity (the degree of development of the internal sur-
* Institute of Problems of Chemical Physics,
Russian Academy of Sciences, Chernogolovka,
Moscow oblast, 142432 Russia
** Boreskov Institute of Catalysis, Siberian Division,
Russian Academy of Sciences, pr. Akademika Lavrent’eva 5,
Novosibirsk, 630090 Russia
0012-5008/05/0006-0111 © 2005 Pleiades Publishing, Inc.

112
Degree of hydrogen conversion, η
WU CHUNTIAG et al.
H2 absorption rate V
, mL/min
H2
1
2
3
0.1% Pt (1 m2/g)
1.0
0.8
0.6
0.4
0.2
4
0.1% Pt (5 m2/g)
0.1% Pt (15 m2/g)
Pd/C – 5% (500 m2/g)
20
10
0
3
2
3
4
1
2
1
2
3
4
0.1% Pt (1 m2/g)
0.1% Pt (5 m2/g)
0.1% Pt (15 m2/g)
Pd/C – 5% (500 m2/g)
4
1
0
20 40 60 80 100 120 140 160
0.2
0.4
0.6
0.8
1.0
Time t, min
Degree of hydrogen conversion, η
Fig. 1. Degree of hydrogen conversion vs. transformation
time during the TNT hydrogenation.
Fig. 2. Rate of hydrogen absorption vs. degree of hydrogen
conversion during the TNT hydrogenation.
face) ranged from 1 m2/g (for samples manufactured
from silica fabrics) to 15 m2/g (for samples manufac-
tured from alumina–borosilicate glass fiber fabrics).
The specified value of this parameter was ensured by
preliminary dosed leaching of the starting glass fiber
materials in acid media.
nitrotoluene (2HA4ANT), 2,4-diamino-6-nitrotoluene
(2,4DANT), 2,4-diamino-6-nitrosotoluene (2,4DANST),
2,4-diamino-6-hydroxylaminotoluene (2,4DAHAT),
and 2,4,6-triaminotoluene (TAT).
To compare the key parameters of trinitrotoluene
(trinitrobenzene) hydrogenation on GWC systems with
the process parameters of hydrogenation on a dispersed
Pd/C catalyst under standard conditions, control exper-
iments were carried out. Catalyst samples resembling
industrial catalysts in their characteristics were pre-
pared: a carbon powder with a particle size of 100–
200 µm, an internal surface area of 500 m2/g, and a Pd
content of 5 wt %.
The experiments were carried out in static (nonflow)
setups in 50- to 200-mL laboratory glass reactors. The
reaction medium was formed as a 1–3% solution of
trinitrotoluene (trinitrobenzene) in isopropanol. A reac-
tor with a shaking device that ensured stirring of the
reaction mixture through the to-and-fro motion of the
whole reaction vessel was used. The rocking amplitude
was 8–10 cm and the frequency was 500 swings per
minute. Hydrogen was supplied through a nonflow cir-
cuit from a calibrated receiver with a water seal. This
allowed us to record the kinetics of transformation of
the nitroaromatic compound by measuring the rate of
hydrogen absorption with time. A piece of the woven
glass fiber catalyst was situated in the reactor in the free
(nonfastened) state and was in active contact with the
liquid due to the turbulent conditions created in the
reactor by the shaker. The weight of the catalyst loaded
into the reactor was about 0.08–0.1 g per milliliter of
the working solution.
Figure 1 presents experimental data characterizing
the hydrogen absorption dynamics during hydrogena-
tion of trinitrotoluene (TNT) over various catalysts (the
dynamic course of trinitrobenzene reduction is qualita-
tively similar).
Curve 1 describes the absorption of hydrogen in
TNT hydrogenation on a GWC sample with a specific
surface area of 1 m2/g. The dashed line designates the
integral amount of absorbed hydrogen, which corre-
sponds to the complete stoichiometric reduction of the
three nitro groups to amino groups. The data presented
in Figure 1 demonstrate that the kinetic curve is step-
wise: after absorption of one-third of the hydrogen
(complete reduction of the first nitro group, with a char-
acteristic time of 30 min), hydrogenation is sharply
retarded; then the second nitro group starts to be hydro-
genated, and this process lasts for 3 h. This is followed
by hydrogenation of the third nitro group, which devel-
ops much more slowly than the second step.
In addition to the recording of the dynamics of
hydrogen absorption, the kinetics of hydrogenation was
measured by taking samples of the working fluid from
the reactor. The samples were analyzed for reactants
and products (nitroamines and amines). The intermedi-
ate compounds and the reaction products, as well as
1
their elemental composition, were identified by H
NMR using a Bruker AC-200P spectrometer (1H,
200 MHz). The analytical procedure used in the work
allowed us to detect the following transformation prod-
These macrokinetic regularities identified using the
ucts: 4-hydroxylamino-2,6-dinitrotoluene (4HADNT), integral volumetric recording of the reaction dynamics
2-amino-4,6-dinitrotoluene (2ADNT), 4-amino-2,6- were confirmed by NMR monitoring of the composi-
dinitrotoluene (4ADNT), 2-amino-4-hydroxylamino-6- tion of the reaction medium. The interpretation of the
nitrotoluene (2A4HANT), 2-hydroxylamino-4-amino-6- NMR spectra showed that, after the first step of hydro-
DOKLADY CHEMISTRY Vol. 402 Part 2 2005

CHARACTERISTIC FEATURES OF THE SELECTIVE ACTION
113
gen absorption (~2.3 mol, which makes up one-third of ized inside a pore, resulting in equalization of the coor-
the whole amount of hydrogen needed for complete dination factor for all nitro groups.
reduction of the three nitro groups), the reaction mix-
For experimental verification of this hypothesis, we
ture contains only 4HADNT, 2ADNT, and 4ADNT.
prepared GWC samples with developed surfaces, 5 and
15 m2/g. The kinetics of TNT hydrogenation on these
catalyst samples is shown by curves 2 and 3 (Figs. 1, 2).
The experiment confirmed qualitatively the assump-
tion; i.e., the selectivity coefficients decrease with an
increase in the specific surface area. On passing from
the 1 m2/g GWC sample to the 15 m2/g GWC, the selec-
tivity coefficients for the second nitro group decrease
from 6–7 to 2–3, while those for the third nitro group
decrease from 60–70 to 25–35. However, the porous
GWC still remains highly selective compared to the tra-
ditional powder catalysts, which have much more
developed surfaces (500 m2/g).
This study represents the first stage in investigating the
mechanism of hyperselectivity discovered in hydrogena-
tion of polyfunctional nitroaromatic compounds on glass
fiber woven catalysts doped with platinum group metals.
It is necessary to study the specific features of action of
GWCs activated by various metals and metal composi-
tions for different contents of these metals in the glass tem-
plate (Pt, Pd, Rh, Ru). It is important to study in more
detail the role of the specific surface area of the GWC in
the hydrogenation of nitroaromatic compounds. Neverthe-
less, the practical value of this study, which opens the way
for one-step synthesis of complex nitroamines, is already
obvious. Moreover, this process should be regarded as the
foundation for the development of industrial processes for
utilization of nitroaromatic explosives to give useful prod-
ucts for civilian purposes.
The compounds identified after the second hydrogena-
tion step (~6.11 mol of hydrogen) were 2,4DANT,
2A4HANT, 2HA4ANT, 2,4DANST, and 2,4DAHAT.
The third step (~8.4 mol of hydrogen absorbed) yields
TAT and 2,4DANT. These results indicate that the reduc-
tion of trinitrotoluene on platinum-activated GWCs pro-
ceeds by a complex stepwise mechanism involving suc-
cessive hydrogenation of the nitro groups.
This conclusion becomes more evident when the
results are presented in the coordinates current transfor-
mation rate–specific fraction of hydrogen absorbed
(Fig. 2). It can be seen that the GWC sample with a spe-
cific surface area of 1 m2/g (curve 1) reduces the first
nitro group at a rate 6–7 times higher than it reduces the
second nitro group and 60–70 times higher than the
third nitro group is reduced to an amino group. These
data indicate unambiguously that the selectivity of TNT
hydrogenation on GWC systems is extremely high and
allows one-step preparation of any combination of
amines and nitroamines according to a specified task.
For comparison, Figs. 1 and 2 (curves 4) show the
kinetics of reduction of TNT nitro groups on traditional
5% Pd/C powder catalysts (the experimental conditions
and the specific amount of the catalytic metal in the
experiments shown by curves 1 and 4 are identical).
The pattern of TNT transformation on 5% Pd/C and the
data of NMR analysis of the reduction products on this
catalytic system demonstrate substantial differences:
the powder catalyst accomplishes an almost nonselec-
tive reduction of TNT, the three nitro groups being
hydrogenated almost synchronously up to complete
transformation into amino groups.
ACKNOWLEDGMENTS
The authors are grateful to the Polotsk Steklovolo-
kno Production Association for providing the glass
fiber fabric materials used to prepare GWC samples.
This work was supported by the NATO scientific
foundation Science for Peace, project no. SfP 971897.
When analyzing the possible mechanism of the
hyperselectivity discovered for the GWC system in
TNT hydrogenation, we put forward a hypothesis relat-
ing this effect to the presence of two different valence
states of platinum, Pt0 and Pt2+, in the GWC. There are
grounds for assuming that this composition of active
sites can ensure selective coordination of trinitrotolu-
ene adsorbed on the GWC surface. In the case of tradi-
tional powder catalysts, only Pt0 participates in the pro-
cess. This results in planar TNT adsorption, which
ensures equal accessibility of all three nitro groups for
the reaction with hydrogen. A role of the substantial
difference between the specific surface areas of the new
and the traditional catalytic systems (1 m2/g for the
GWC and 500 m2/g for the powder catalyst) in the high
selectivity of TNT hydrogenation also cannot be ruled
out. This version implies that the steric factor is more
pronounced on the catalyst with the small surface area,
and, hence, the coordination of the TNT nitro groups in
the adsorbed state is highly differentiated. In the cata-
lyst sample with the developed surface, the TNT mole-
cule penetrates into the near-surface layer and is local-
REFERENCES
1. Dorokhov, V.G., Barelko, V.V., Bal’zhinimaev, B.S.,
et al., Khim. Prom-st., 1999, no. 8, pp. 44–48.
2. Barelko, V., Dorokhov, V., Fomin, A., et al., Abstracts of
Papers, IV Eur. Congr. on Catalysis (EUROCAT-4), Flo-
rence, 1999, P/II/290, p. 828.
3. Dorokhov, V.G., Barelko, V.V., and Balzhinimaev, B.S.,
Abstracts of Papers, III Int. Symp. on Catalysis in Mul-
tiphase Reactors, Naples, 2000, pp. 367–373.
4. Simonova, L.G., Barelko, V.V., Bal’zhinimaev, B.S.,
et al., Kinet. Katal., 2001, vol. 42, no. 5, pp. 762–772.
5. Simonova, L.G., Barelko, V.V., Bal’zhinimaev, B.S.,
et al., Kinet. Katal., 2001, vol. 42, no. 6, pp. 907–916.
6. Bal’zhinimaev, B.S., Simonova, L.G., Barelko, V.V.,
et al., Kinet. Katal., 2001, vol. 42, no. 6, pp. 917–927.
7. RF Patent No. 2156654, Byull. Izobret., No. 27 (2000).
DOKLADY CHEMISTRY Vol. 402 Part 2 2005