Reduction of carbon dioxide by hydrogen on metal–carbon catalysts under supercritical conditions

Article abstract of DOI:10.1134/S0036024416120050

The reduction of carbon dioxide with hydrogen on metal–carbon (Ru, Rh, Ir) catalysts is investigated under supercritical conditions for the first time. High selectivity (close to 100%) toward methanation with good stability of catalytic activity is observed for Ru- and Rh-containing catalyst, while the preferred reduction to CO is observed for Ir/C catalyst.

Full text of DOI:10.1134/S0036024416120050

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2016, Vol. 90, No. 12, pp. 2352–2357. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © V.I. Bogdan, A.E. Koklin, D.O. Kozak, L.M. Kustov, 2016, published in Zhurnal Fizicheskoi Khimii, 2016, Vol. 90, No. 12, pp. 1785–1790.
CHEMICAL KINETICS
AND CATALYSIS
Reduction of Carbon Dioxide by Hydrogen on Metal–Carbon
Catalysts under Supercritical Conditions
a,b
a
a
a,b
V. I. Bogdan , A. E. Koklin , D. O. Kozak , and L. M. Kustov *
a
Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia
b
Department of Chemistry, Moscow State University, Moscow, 119991 Russia
*e-mail: lmk@ioc.ac.ru
Received December 1, 2015
Abstract—The reduction of carbon dioxide with hydrogen on metal–carbon (Ru, Rh, Ir) catalysts is investi-
gated under supercritical conditions for the first time. High selectivity (close to 100%) toward methanation
with good stability of catalytic activity is observed for Ru- and Rh-containing catalyst, while the preferred
reduction to CO is observed for Ir/C catalyst.
Keywords: carbon dioxide, reduction, carbon monoxide, methane, supercritical CO , metal nanoparticles,
2
rhodium, ruthenium, iridium
DOI: 10.1134/S0036024416120050
INTRODUCTION
Ru/C. The efficiency of a catalyst is thus largely deter-
mined by the metal–support interaction. In the case of
Ru/C, the carbon support partially blocks the surfaces
of metal particles, thereby reducing their activity.
The recycling of carbon dioxide as a major green-
house gas via its conversion into valuable products
(
including СО, СН , СН ОН, and НСООН) is a high
4 3
priority of modern catalytic chemistry. The reaction of
All known studies were performed at pressures up
CO reduction is particularly important as the first to 20 atm, and usually at atmospheric pressure. Only a
2
stage in the activation of CO in order to conduct the few examples of CO reacting with H and amines to
2
2
2
subsequent processes based on the obtained products: produce formamides in supercritical CO (at pressures
2
greater than 75 atm) are known [10–13]. At the same
CO + H = CO + H O,
2
2
2
time, there are no data from studying the reaction of
CO hydrogenation in supercritical CO .
(1)
(2)
(3)
ΔH298 K = 41.2 kJ/mol,
2
2
CO + 4H = CH + 2H O,
In this work, CO hydrogenation was investigated on
2
2
4
2
2
metal–carbon catalysts for the first time in order to
ΔH298 K = –252.9 kJ/mol,
identify the benefits of the process in supercritical CO .
2
CO + 3H = CH OH + H O,
2
2
3
2
ΔH298K = –49.5 kJ/mol.
EXPERIMENTAL
There are a variety of metal-containing catalysts for
Catalysts Ru/C, Rh/C, and Ir/C with metal con-
tents of 10 wt % were prepared via successive impreg-
nations with metal chloride solutions, followed by
reduction at 400–500°C for 5 h.
CO reduction, showing different efficiencies and
2
selectivities in the carbon dioxide conversion into the
above products [1–7]. However, there are no works in
which this transformation was observed under super-
critical conditions.
The interaction between CO and H was investi-
2
2
It is known that some precious (Ru, Pd, Pt) and
gated in a flow-type reactor. The experimental condi-
tions are shown in Table 1. Liquid carbon dioxide was
fed through a syringe pump; hydrogen, using a gas
flow controller. The pressure was adjusted with a dia-
non-noble (Ni) metals are active in the conversion of
CO to CH , and that the noble metals are generally
2
4
more active than nickel [8].
The effect the support and dispersion of metal have phragm valve. Analysis was performed on LKhM-80
on the catalytic properties of ruthenium nanoparticles chromatograph with a thermal conductivity detector.
in this reaction was investigated in [9]. It was shown on The columns were packed with Porapak Q and CaA.
3
the basis of activity that the catalysts could be arranged The amounts of the loaded catalyst were 0.5–2 cm .
in the order Ru/Al O > Ru/MgAl O > Ru/MgO > The reaction temperatures were 50–450°C, and the
2
3
2
4
2352

REDUCTION OF CARBON DIOXIDE BY HYDROGEN ON METAL–CARBON
2353
Table 1. Catalysts and experimental conditions (P = 80 atm) The selectivity of product formation is calculated
using the formula
V , cm3
Catalyst
H : CO2
T, C
2
cat
S(i) = n(i)/∑nj,
Ru/C
Ru/C
Ru/C
Ru/C
Ru/C
Rh/C
Ir/C
1 : 1
2 : 1
1 : 1
1 : 1
1 : 1
1 : 1
1 : 1
2
2
2
0.5
1
50–180
50–200
180
180–350
80–350
50–400
50–400
where n(i) is the amount of the ith product at the out-
let, ∑n is the total number of all products containing
j
carbon (ethane has a coefficient of 2, since it is formed
from two molecules of CO ). Substituting n = cV, we
2
obtain the formula for calculating selectivity:
1
1
S(i) = с(i)/∑сj.
The theoretical conversion of hydrogen was also cal-
culated, based on the conversion of carbon dioxide
and the selectivity of the products:
pressure of the reaction mixtures of CO and H was
0 atm.
2
2
8
Kcalc(H ) = K(CO )(S(CO) + 4S(CH )
2
2
4
The data from chromatographic analysis of the
+
3S(CH OH) + 7S(C H ))/100.
3 2 6
reaction products were used as primary data. The con-
centration of water was calculated from the concentra-
tions of CO, CH , CH OH, and C H , using the above
4
3
2
6
RESULTS AND DISCUSSION
reaction equations:
The interaction between carbon dioxide and
hydrogen on the investigated catalysts was accompa-
nied by the formation of CO, hydrocarbons (mainly
methane), and oxygenates (methanol):
c
(
H O
)
= c
(
CO
)
+ 2c
(
CH4
)
2
+ c CH OH + 4c C H ,
( ) ( )
3 2 6
where c(i) is the concentration of the ith component.
The concentrations of all components were then nor-
malized.
1
CO + H O
2
2
CO + H
CH + H O
2
2
4
2
The conversion of CO and H was calculated using
2
2
the formula
3
CH OH + H O
3
2
K = [(n – n )/n ] × 100,
in
out
in
Scheme.
where n and n are the amounts of CO and H at
in
out
2
2
The main routes of carbon dioxide and hydrogen
interactions are:
the inlet and outlet of the reactor;
n = cV,
route 1
where c is concentration and V is gas flow.
CO + H → CO + H O;
2
2
2
In maintaining the carbon balance,
route 2
n (CO ) + n(CO) + n(CH ) + n(CH OH)
out
2
4
3
CO + H → CO + H O,
2 2 2
+
2n(C H ) = n (CO ),
2
6
in
2
CO + 3H → CH + H O,
2
4
2
n(i) is the amount (mol or volume) of the ith compo-
nent; this corresponds to
−−−−−−−−−−−−−−−−−−−−
CO + 4H → CH + 2H O;
2
2
4
2
cout
(
CO2
)
Vout + c
Vout + 2c
V and V is the gas flow at the inlet and outlet of the
(
CO
)
Vout + c
(
CH4
)
Vout
route 3
+
c
(
CH OH
)
(
C H
)
Vout = cin
(
CO2
)
V ,
3
2
6
in
CO + H → CO + H O,
2
2
2
in
out
reactor, and c and c are the initial and final con-
CO + 2H → CH OH,
2 3
out
in
centrations of CO .
2
−−−−−−−−−−−−−−−−−−−−
To calculate conversion using the above formula,
we must determine V and V . Because these values
CO + 3H → CH OH + H O.
in
out
2
2
3
2
3
are unknown, we assume that V = 100 cm /min.
According to the last equation, V is then
in
Data on the composition of the reaction mixture
are shown in Table 2. The data on the conversion of
carbon dioxide in the reaction with hydrogen and the
selectivities toward main products on different cata-
lysts are summarized in the Table 3. The catalyst Ru/C
out
Vout = cin
(
CO2
)
/(cout
(
)
CO2
+ 2c
)
(
+ c
(
CO
)
+ c
(
CH4
)
+
c
(
CH OH
C H
)
)V .
3
2
6
in
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 90 No. 12 2016

2354
BOGDAN et al.
Table 2. Data on the composition of the gas mixture after the hydrogenation of CO (P = 80 atm)
2
Concentration in the gas mixture after the reaction, vol %
Catalyst
T, °C
H2
CO
CH4
CO2
H O
CH OH
C H
2
3
2
6
Ru/C
H : CO = 1 : 1
Vcat = 2 cm
100
120
140
41.8
36.6
5.8
0.9
0.2
56.2
55.7
59.7
56.1
0.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.4
1.4
0.0
2.6
3.5
7.7
6.8
0.7
4.1
17.4
25.4
25.8
0.0
0.2
0.5
6.2
47.0
48.2
64.8
62.0
62.3
32.3
35.6
31.6
30.5
46.8
44.2
54.0
66.6
75.8
75.1
73.9
74.5
74.3
74.0
74.2
73.5
71.7
72.0
65.1
81.3
78.2
79.6
57.6
73.8
65.9
69.7
66.0
78.4
41.8
40.8
51.3
51.5
52.6
66.7
65.2
50.4
47.9
48.4
47.5
56.6
1.4
8.1
34.8
50.8
51.5
0.0
0.4
1.0
12.4
102.4
98.4
0.6
17.1
46.3
48.4
48.6
48.8
48.0
47.9
47.5
47.3
49.4
52.3
1.4
15.6
37.1
33.6
0.0
5.7
6.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.2
0.2
0.2
0.2
0.2
0.2
0.1
0.2
0.0
0.0
0.2
0.2
0.0
0.0
0.0
0.1
0.1
0.6
0.4
0.3
2
2
3
160
1
80
Ru/C
100
120
140
H : CO = 2 : 1
2
2
3
Vcat = 2 cm
1
60
80
00
1
2
51.2
49.2
0.3
0.2
Ru/C
180
45.5
24.6
0.5
H : CO = 1 : 1
2
2
8.6
3
Vcat = 2 cm
23.1
24.2
24.2
24.3
23.9
23.9
23.7
23.5
24.6
26.1
0.7
0.1
0.4
0.7
0.8
1
.0
.3
.9
.4
.0
1
1
1
1
Ru/C
H : CO = 1 : 1
180
250
300
32.3
8.0
0.7
2
2
7.8
3
Vcat = 0.5 cm
18.5
16.7
0.0
2.9
3.1
4.3
4.6
16.6
11.8
12.9
0.0
0.5
1.6
10.7
11.2
0.0
0.3
0.8
1.2
8.3
350
0.4
Ru/C
120
180
200
42.4
23.3
30.5
24.3
27.2
1.6
H : CO = 1 : 1
2
2
3
Vcat = 1 cm
250
280
300
320
350
8.6
9.4
33.9
24.1
26.1
0.0
1.0
3.1
24.4
25.3
0.0
0.3
24.5
48.7
47.6
44.6
18.1
18.8
49.6
45.8
45.7
42.0
23.6
Rh/C
H : CO = 1 : 1
200
250
300
0.0
0.0
0.0
0.4
0.4
0.0
0.0
0.0
0.0
0.4
2
2
3
Vcat = 1 cm
3
4
50
00
Ir/C
250
300
320
H : CO = 1 : 1
2
2
3.1
5.1
10.0
24.9
3
Vcat = 1 cm
3
4
50
00
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REDUCTION OF CARBON DIOXIDE BY HYDROGEN ON METAL–CARBON
2355
Table 3. Data on conversion and selectivity toward the main products of CO reduction (P = 80 atm)
2
Selectivity, vol %
Conversion
Catalyst
T, °C
100
CO , %
2
CO
CH4
CH OH
other products
3
Ru/C
H : CO = 1 : 1
1
8
21
29
29
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
99
99
99
99
99
99
99
99
0
2
2
3
Vcat = 2 cm
120
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
1
1
1
40
60
80
1
1
Ru/C
100
120
140
1
2
H : CO = 2 : 1
2
2
3
Vcat = 2 cm
17
52
53
1
11
23
24
1
60
80
00
1
2
Ru/C
180
H : CO = 1 : 1
2
2
3
Vcat = 2 cm
25
25
24
24
24
24
26
27
1
9
100
100
99
Ru/C
180
250
300
H : CO = 1 : 1
19
18
0
2
2
3
Vcat = 0.5 cm
99
350
Ru/C
120
180
200
4
5
6
7
18
23
24
0
0
0
0
0
0
0
0
100
100
99
98
97
H : CO = 1 : 1
0
0
1
2
3
3
2
2
2
3
Vcat = 1 cm
250
280
300
320
350
97
98
Rh/C
200
250
300
1
3
15
16
0
0
0
11
10
100
100
83
H : CO = 1 : 1
0
0
6
6
2
2
3
Vcat = 1 cm
350
00
84
4
Ir/C
250
300
320
6
8
16
21
21
91
82
87
43
43
9
18
13
53
53
H : CO = 1 : 1
0
0
0
5
2
2
3
Vcat = 1 cm
350
00
4
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 90 No. 12 2016

2356
BOGDAN et al.
CO conversion, %
2
6
0
0
0
0
0
0
2
5
4
3
2
1
1
3
4
0
120
160
200
240
280
320
360
Т, °C
3
3
Fig. 1. CO conversion on the Ru/C catalyst: (1) H : CO = 1 : 1, V = 2 cm ; (2) H : CO = 2 : 1, V = 2 cm ; (3) H :
2
2
2
cat
2
2
cat
2
3
3
CO = 1 : 1, V = 1 cm ; (4) H : CO = 1 : 1, V = 0.5 cm .
2
cat
2
2
cat
1
00
0
100
80
60
40
20
0
Rh/C
S, %
24 K, %
Ir/C
24
20
16
12
3
1
8
20
1
6
2
1
60
3
2
1
4
2
0
0
8
4
0
8
4
0
0
2
4
400
240
280
320
360
240
280
320
360
400
Т, °C
Т, °C
Fig. 2. Dependence of (1) CO conversion and selectivity to (2) CO, (3) CH , and (4) C H in the reaction of CO and H on
2
4
2
6
2
2
3
Rh/C and Ir/C catalysts. H : CO = 1 : 1, V = 2 cm .
2
2
was studied most throughly in the hydrogenation of these experiments (Fig. 1, curves 1–4), the residual
CO . Figure 1 shows the dependence of the conversion hydrogen concentration was less than 1% at maximum
2
of CO on the process temperature.
temperature (hydrogen conversion was 99–100%).
2
The data show that methane was produced upon
Selectivity differed considerably for the Rh/C and
CO and H interaction on the Ru/C catalyst through- Ir/C catalysts, even though both displayed similar
2
2
activity in CO conversion (Fig. 2). At low tempera-
out the investigated range of temperatures (T = 100–
2
3
2
60°C). Selectivity was 100% at a catalyst loading of tures (250–300°C), only methane formed on Rh/C.
3
cm and 97–100% at smaller loadings, while the As the temperature rose, selectivity fell slightly to 83–
selectivity toward methanol was 1–3%. At the ratio 84%, and CO and C H were also present in the prod-
2
6
H : CO = 1 : 1, maximum CO conversion was 25%; ucts. In contrast, methane selectivity grew from 9 to
2
2
2
at the ratio 2 : 1, it was 50%. On the Ru/C catalyst in 53% on Ir/C as the temperature rose from 300 to
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
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REDUCTION OF CARBON DIOXIDE BY HYDROGEN ON METAL–CARBON
ACKNOWLEDGMENTS
CO conversion, %
2357
2
3
3
2
2
5
0
5
0
This work was supported by the RF Ministry of
Education and Science, project no. RFME-
FI61615X0041.
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(
The process of CO hydrogenation to methane pro-
2
ceeds with high selectivity on metal–carbon catalysts.
6
Ru/C catalyst has the highest selectivity toward CH .
4
The catalytic reaction could be used for the recycling
1
of CO via its conversion into useful products, and for
2
the purification of certain high-temperature gas mix-
tures containing CO .
Translated by A. Pashigreva
2
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 90 No. 12 2016