Unusual 1,2-dichloroethane dehydrochlorination over ruthenium-oxychloride catalyst

Article abstract of DOI:10.1016/j.catcom.2015.04.005

This communication presents the data on the unusual conversion of 1,2-dichloroethane over ruthenium-oxychloride catalyst. It was found that dichloroethane was dehydrochlorinated at moderate temperatures with release of ethylene and, unexpectedly, the products of destructive oxidation, namely CO and CO₂.

Full text of DOI:10.1016/j.catcom.2015.04.005

Catalysis Communications 67 (2015) 95–97
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Unusual 1,2-dichloroethane dehydrochlorination over
ruthenium-oxychloride catalyst
N.V. Testova a, A.S. Shalygin a, T.S. Glazneva a,b, , E.A. Paukshtis a,b,c, V.N. Parmon a,b,c
⁎
a
Boreskov Institute of Catalysis, Pr. Akademika Lavrentieva, 5, Novosibirsk 630090, Russia
Novosibirsk State University, Pirogova Str., 2, Novosibirsk 630090, Russia
National Research Tomsk State University, Pr. Lenina, 36, Tomsk 634050, Russia
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
This communication presents the data on the unusual conversion of 1,2-dichloroethane over ruthenium-
oxychloride catalyst. It was found that dichloroethane was dehydrochlorinated at moderate temperatures with
release of ethylene and, unexpectedly, the products of destructive oxidation, namely CO and CO2.
© 2015 Elsevier B.V. All rights reserved.
Received 16 January 2015
Received in revised form 27 February 2015
Accepted 1 April 2015
Available online 8 April 2015
Keywords:
1,2-Dichloroethane
Ruthenium oxychloride
Dehydrochlorination
1. Introduction
reaction. It was shown that K4[Ru2OCl10]/TiO2 catalyst was more active
in Deacon reaction than RuO2, and it was superior to all known catalysts
It is known that the thermal dehydrochlorination (pyrolysis) of 1,2-
dichloroethane (DCE) is used to produce vinyl chloride:
for activity and selectivity in oxychlorination of methane and ethane [4].
The aim of the present work was to study the dehydrochlorination of
1,2-dichloroethane on K4[Ru2OCl10]/TiO2 catalyst, since its high activity
was expected at low temperatures, when the formation of acetylene is
thermodynamically impossible.
С2Н4Сl2→CH2 ¼ CHCl þ HCl:
Pyrolysis is performed at 450–520 °C and 2 MPa when it occurs via a
radical chain mechanism. This process is accompanied by undesirable
side reaction of acetylene formation:
2. Experimental
K4[Ru2OCl10]/TiO2 catalyst was prepared by incipient wetness im-
pregnation of titania (Degussa P-25 with a specific surface of 57 m2/g
and a pore volume of 0.36 cm3/g) with an aqueous hydrochloric acid so-
lution of K4[Ru2OCl10] (Aurat, Russia) (pH = 1) at 90 °C followed by
drying at 110 °C and calcination in air at 350 °C for 2 h. The ruthenium
content in the sample determined by atomic emission spectroscopy
with inductively coupled plasma using an Optima 4300 DV PerkinElmer
spectrometer was 0.28 wt.%.
CH2 ¼ CHCl→С2Н2 þ HCl:
To reduce the formation of acetylene, the temperature reduction is
necessary. The natural way of lowering the temperature of the process
is the application of a catalyst [1], but the catalysts effective for dehydro-
chlorination have not been found so far.
The catalysts based on ruthenium show a good performance in
reactions involving chlorine such as Deacon reaction [2,3] and
oxychlorination of methane and ethane [4]. It can be assumed that the
high reactivity of these catalysts is due to the high affinity of ruthenium
to chlorine, namely, due to the ability to form oxychlorides of various
compositions which are stable in aqueous solutions [5]. In particular,
Shalygin and co-authors [4] have suggested that (RuO2 − xClx) rutheni-
um oxychloride is the active site of RuO2/TiO2 catalyst in Deacon
XPS study of the catalyst showed that the charge of ruthenium atom
is 4+, and the oxygen and chlorine atoms possess the same properties
as those in a bulk K4[Ru2OCl10]. UV–Vis DR spectroscopy data showed
the presence of [Ru2OCl10]
4− anions in the catalyst with the bridging
oxygen in this anion being of electrophylic nature [6]. The active compo-
nent of the catalyst is supposed to be ruthenium oxychloride [4,7].
The temperature of catalyst calcination was set to 350 °C since the
calcination in air at higher temperatures leads to destruction of the ac-
tive component of the catalyst due to chlorine removal. However, HCl
which is formed during the reaction maintains the existence of Cl5Ru-
⁎
Corresponding author at: Boreskov Institute of Catalysis, Pr. Akademika Lavrentieva, 5,
Novosibirsk 630090, Russia.
E-mail address: glazn@catalysis.ru (T.S. Glazneva).
http://dx.doi.org/10.1016/j.catcom.2015.04.005
1566-7367/© 2015 Elsevier B.V. All rights reserved.

96
N.V. Testova et al. / Catalysis Communications 67 (2015) 95–97
O-RuCl5 structure, and the temperature of catalytic experiment can be
raised up to 450 °C.
30
20
10
0
3
Catalytic experiments were performed in a tubular flow reactor
(quartz tube with a length of 200 mm and an internal diameter of
7 mm) with a fixed catalyst bed at atmospheric pressure and at a tem-
perature in the range of 150–450 °C. The catalyst in the amount of
0.30 g prepared as a fraction of 0.25–0.5 mm was placed in the reactor.
1,2-Dichloroethane in a stream of argon (Sibtekhgaz, purity of 99.998%)
at a concentration of 3.5–4% was passed through a catalyst bed. The total
c
2
1
space velocity of the gas mixture was varied from 1300 to 28,600 h−1
.
250
300
350
400
400
400
450
The analysis of the product composition was performed after achieving
steady activity at a given temperature. The reaction products were ana-
lyzed using a specially designed capillary column (20 m × 0.32 mm)
with a stationary DVB-PLOT phase and flame ionization detector on
Tsvet-570 chromatograph. The reaction products such as CO, CO2, and
HCl were analyzed by Infrared spectroscopy using an FTIR-8300
Shimadzu spectrometer and a gas cell with NaCl windows and an opti-
cal path of 18.5 cm. Material balances for carbon and chlorine were cal-
culated according to the equations:
100
80
60
40
20
0
3
2
b
1
in
Cbalance ¼ ðCeth þ Cvch þ 1=2CСОþСО þ СDCEoutÞ=СDCE
;
250
300
350
450
2
100
80
60
40
20
0
1
ꢀ
ꢁ
out
in
Clbalance
¼
Cvch þ CНСl þ 2СDCE
=2СDCE ;
2
a
3
in
out
where С
and С
are the concentrations of 1,2-dichloroethane at the
DCE
DCE
reactor inlet and outlet (vol.%), respectively, and Сeth, Сvch, СНСl, and
ССО + СО are the concentrations of ethylene, vinyl chloride, HCl, and car-
2
bon oxides, respectively (vol.%).
250
300
350
450
Temperature,oC
3. Results and discussion
Fig. 1 shows the temperature dependence of 1,2-dichloroethane
conversion over K4[Ru2OCl10]/TiO2 catalyst and the corresponding se-
lectivity of major product formation at three feed rates of the reaction
mixture. Dehydrochlorination of 1,2-dichloroethane was observed at
temperatures above 250 °C. The following compounds were chromato-
graphically detected at the exit of the reactor: C2H4 and C2H3Cl. Besides
these products, IR spectroscopic study revealed the formation of HCl
and, unexpectedly, CO and CO2.
Fig. 1. Conversion degree of dichloroethane (a) and the selectivity of ethylene (b) and
vinyl chloride (c) formation in dehydrochlorination depending on the reaction tempera-
ture and a space velocity (3.75 0.25% DCE in Ar) of: 1–1300 h−1, 2–12,000 h−1, and
3–28,600 h−1
.
It is possible to assume the following sequence of transformations of
1,2-dichloroethane:
The conversion of 1,2-dichloroethane and the composition of reac-
tion products essentially depend on the space velocity of the reaction
mixture. At low feed gas rates (1300 h−1), the conversion of 1,2-dichlo-
roethane reached 94% even at 300 °C (Fig. 1a), with the ethylene being
the main product (Fig. 1b). Acetylene formation was not revealed in any
experiment. Selectivity to vinyl chloride (Fig. 1c) did not exceed 3% and
further decreased with an increase in the temperature. The total selec-
tivity towards destructive oxidation of 1,2-dichloroethane – carbon
oxide and dioxide – was about 73%. It is important to indicate that the
content of oxygen in argon used as the carrier gas did not exceed
10 ppm.
С2Н4Сl2→CH2 ¼ CHCl→CH2 ¼ CH2 þ HCl→СО þ СО2:
According to thermodynamic data, the formation of ethylene from
vinyl chloride is only possible in the reaction with molecular hydrogen
(ΔH = −61.8 kJ/mol). Direct experimental proofs of ethylene production
from DCE with the selectivity higher than 90% were published in [8,9]. The
process occurs in the presence of hydrogen (hydrodechlorination) which
is not the case in our study.
However, the question arises as to how the hydrogen for vinyl chlo-
ride conversion into ethylene and oxygen for the destructive oxidation
1,2-Dichloroethane conversion decreased at an increase in the feed
rate of the gas mixture up to 12,000 and 28,600 h−1 and reached values
of 75 and 54%, respectively, at 450 °C. The highest selectivity to vinyl
chloride was found in the case of the highest feed rate of the reaction
stream. Table 1 shows the results obtained at the highest conversion
of 1,2-dichloroethane, as well as the data on carbon and chlorine
balance.
Table 1
Dichloroethane conversion and product formation selectivity in dehydrochlorination re-
action at 450 °C depending on a space velocity.
V, h−1 XDCE
%
,
Selectivity, mol%
CHCl
%
,
Balance
CH4 C2H4 C2H3Cl C2H2Cl2
*
CO +
CO2
C
Cl
The balance data lead to the conclusion that instead of the expected
dehydrochlorination, the following gross-transformation proceeded in
all cases:
1300
12,000 74.7 0.6
28,600 53.9
94.1 1.4
21.9
49.6
76.6 13.5
0.2
1.6
–
3.8 72.5
1.7 46.2
7.6
6.0
4.3
0.95 0.97
1.05 1.08
1.02 1.03
0.2
–
–
–
9.0
Water vapors were added to the reaction flow (С2Н4Сl2:Н2О = 1:1)
52,100 53.8 92.9 2.0 4.3
–
–
–
–
0.99 1.03
С2Н4Сl2→ð1−хÞCH2 ¼ CH2 þ хðСО þ СО2Þ þ 2HCl:
* — Unidentified products.

N.V. Testova et al. / Catalysis Communications 67 (2015) 95–97
97
appears in the system. The answer to the second part of the question
Acknowledgments
may follow from the known fact that the electrophilic oxygen is present
in [RuO2 − xClx]4− ruthenium oxychloride [5,6]. But in this case, one
could expect rapid deactivation of the catalyst due to consumption of
electrophilic oxygen. However, at least for 8 h, no change in catalyst ac-
tivity was observed. In addition, we cannot ignore the fact that the sup-
port (TiO2) may also be involved in the reaction process under the
conditions of an aggressive environment.
The only source of both oxygen and hydrogen is molecular water
appearing in the reaction mixture as a result of chlorination of titania
surface at elevated temperatures with hydrogen chloride formed in
the basic reaction of 1,2-dichloroethane dehydrochlorination. It was re-
cently discovered that molecular water decomposed at low tempera-
tures over ruthenium complexes supported on TiO2 under the
influence of visible light [10]. The process involved ruthenium (III)
ions. Several Ru-containing catalysts active in water oxidation process
were also reported [11–14].
Ministry of Education and Science of the Russian Federation is grate-
fully acknowledged for supporting the research.
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