Intrinsic Kinetics of Dimethyl Ether Synthesis from Plasma Activation of CO2 Hydrogenation over Cu–Fe–Ce/HZSM-5

Article abstract of DOI:10.1002/cphc.201601283

CO₂ is activated in a plasma reactor followed by hydrogenation over a Cu–Fe–Ce/HZSM-5 catalyst, and the intrinsic kinetics of the plasma catalytic process are studied. Compared with CO₂ hydrogenation using Cu–Fe–Ce/HZSM-5 alone, the CO₂ conversion and the dimethyl ether selectivity for the plasma catalytic process are increased by 16.3 %, and 10.1 %, respectively, indicating that the CO₂ was activated by the plasma to promote hydrogenation. A study of the intrinsic kinetics shows that the activation energies of methanol formation, the reverse water–gas shift reaction, and methanol dehydration to dimethyl ether are 149.34, 75.47, and 73.18 kJ mol^?1, respectively, which are lower than if Cu–Fe–Ce/HZSM-5 is used without plasma, indicating that the activation of CO₂ in the plasma reduces the activation energy of the hydrogenation reaction and improves the yield of dimethyl ether.

Full text of DOI:10.1002/cphc.201601283

Accepted Article
Title: Intrinsic Kinetics for Dimethyl Ether Synthesis from Plasma
Activation CO2 Hydrogenation over Cu-Fe-Ce/HZSM-5
Authors: Tongming Su, Xinhui Zhou, Zuzeng Qin, and Hongbing Ji
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ChemPhysChem
10.1002/cphc.201601283
ARTICLE
Intrinsic Kinetics for Dimethyl Ether Synthesis from Plasma
Activation CO Hydrogenation over Cu-Fe-Ce/HZSM-5
2
[a]
[a]
[a]
[a, b]
Tongming Su, Xinhui Zhou, Zuzeng Qin,* and Hongbing Ji*
Abstract: The CO
2
was activated in a plasma reactor followed by
generation of complex products. This problem can be overcome
by the synergistic effect between the plasma and heterogeneous
hydrogenation over the Cu-Fe-Ce/HZSM-5 catalyst, and the intrinsic
kinetics of the plasma-catalytic process were studied. Compared with
[
5]
catalysts . Therefore, the feed gases conversion and product
selectivity can be improved by combining the plasma with
2 2
the CO hydrogenation using the Cu-Fe-Ce/HZSM-5 alone, the CO
[
6]
conversion and the dimethyl ether (DME) selectivity for the plasma-
catalytic process were increased by 16.3%, and 10.1%, respectively,
catalysts . In this way, the conversion of CO
2
hydrogenation to
DME will be affected by the plasma activation, which will improve
[
7]
indicating the CO
2
was activated by the plasma and promoted the CO
2
the DME yield from the CO
2
hydrogenation . And the excited
hydrogenation. The intrinsic kinetics study shown that the activation
energies of the methanol synthesis, the reverse water-gas shift
species (CO * or H *) can be generated in the plasma and can be
detect by the optical emission spectroscopy .
Currently, the combination of low-temperature plasma and
heterogeneous catalysis, known as plasma-catalysis, was widely
[6, 9], partial oxidation of
4 2
studied, such as reforming of CH and CO
2
2
[
8]
-
reaction, and the methanol dehydration to DME were 149.34 kJ·mol
1
-1
-1
,
75.47 kJ·mol , and 73.18 kJ·mol , respectively, which were lower
than that of using Cu-Fe-Ce/HZSM-5 without plasma, indicating that
the activation of CO in the plasma can reduce the activation energy
[
5a]
, methanol steam reforming[10], and removal of volatile
2
CH
4
organic compounds[ . These studies were almost the single-
stage plasma-catalysis systems, and synergistic effect of plasma-
catalysis can be observed in these plasma-catalytic reactions.
However, negative effect from the integration of plasma and
11]
of the hydrogenation reaction and improve the yield of DME.
Introduction
[12]
catalyst has been reported by many researchers , as well as the
reason for this phenomenon is still not clear. As we know, when
the catalyst is placed directly in the plasma area, the interactions
between plasma and catalysts are very complex in a single-stage
plasma-catalysis system. Both the chemical and physical
properties of the plasma and catalyst can be affected by each
other.
To avoid the negative effects of the plasma to the catalyst,
we use the two-stage plasma-catalysis system to study the
synergistic effect of plasma-catalysis. It was report that a two-
stage plasma-catalysis system was use for the soot oxidation and
show the synergistic effect between the plasma and the
CO
environmental pollution but also the energy shortage problem .
However, CO is very stable and extremely difficult to activate,
which prevents the conversion of CO into value-added chemicals.
Recent researches showed that the CO hydrogenation to
2
hydrogenation to dimethyl ether can alleviate not only
[
1]
2
2
2
dimethyl ether is becoming a potentially strategic important
process due to the positions of dimethyl ether as both key
[
2]
chemical platform and clean fuel , however, the CO
2
conversion
remain very low.
Plasma is the fourth state of matter, which is mainly
composed of high chemical activity particles, such as atoms,
[13]
[14]
catalyst . In the present work, Cu-Fe-Ce/HZSM-5 catalyst
was used for the synthesis of DME from CO hydrogenation in the
two-stage plasma-catalysis process. The CO was activated in
[
3]
molecules, ions, electrons, and free radicals . Low-temperature
plasma technology provides an attractive alternative to the
conventional catalytic route for converting greenhouse gases into
valuable chemicals because of its unique capacity to induce
physical and chemical reactions at low temperatures. Low-
temperature plasma has a higher electron temperature at a lower
temperature, which could overcome the thermodynamic barrier of
chemical reactions and enable thermodynamically unfavorable
2
2
the plasmas reactor, followed by hydrogenation to DME over the
Cu-Fe-Ce/HZSM-5 catalysts in the fixed bed reactor. The effects
of the discharge voltage, discharge interval, reaction temperature,
reaction pressure, and gaseous hourly space velocity (GHSV) on
2
the CO hydrogenation reaction were investigated. In addition, the
intrinsic kinetics of DME synthesis from CO
plasma-catalytic system were studied.
2
hydrogenation in the
[
4]
reactions at low temperature . Gas phase reactions can be
induced by electron collisions in the plasma, but the selectivity
toward the desired products are typically low, which lead to the
Results and Discussion
[
a]
T. Su, X. Zhou, Z. Qin, H. Ji
2
DME synthesis from CO hydrogenation in the plasma-
School of Chemistry and Chemical Engineering, Guangxi Key
Laboratory of Petrochemical Resource Processing and Process
Intensification Technology
Guangxi University
No. 100 Daxue Road, Nanning 530004, P. R. China
E-mail: qinzuzeng@gmail.com
catalysis system
To investigate the synergistic effects between the plasma and the
CO hydrogenation process, the results of the DME synthesized
from CO hydrogenation by plasma alone, the CO hydrogenation
by Cu-Fe-Ce/HZSM-5 alone, and CO hydrogenation in plasma-
catalysis system were studied, the results showed in Table 1.
As shown in Table 1, from the CO hydrogenation process by
plasma alone, major product was CO, and the by-product was
2
2
2
2
[
b]
H. Ji
School of Chemistry and Chemical Engineering
Sun Yat-sen University
No. 135, Xingang Xi Road, Guangzhou, 510275, P. R. China
E-mail: jihb@mail.sysu.edu.cn
2
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ChemPhysChem
10.1002/cphc.201601283
ARTICLE
CH
with the results in the reference[15]. When CO
Cu-Fe-Ce/HZSM-5 alone, the CO conversion and the DME
selectivity were 20.9% and 63.1%, respectively. When combined
the plasma and the catalytic system, the CO conversion
increased from 20.9% to 24.3%, and the DME selectivity
increased from 63.1% to 69.5%. These results show that the CO
hydrogenation reaction was enhanced in the plasma-catalysis
process, indicating that there is a synergistic effect between
plasma and catalysis process.
4
and CH
3
OH, no DME was observed, which were consistent
catalyst to synthesize DME. In fact, only the catalytic reaction was
affected by the reaction temperature. Thus, the reaction rate
constant can be enhanced with the increasing of temperature,
which improves the reaction rate and is favorable to the synthesis
of DME. However, high temperature can lead to sintering and
crystallizing the Cu species, which will provoke a partial loss in
the catalytic activity. Therefore, the optimal reaction temperature
in the process for the synthesis of DME in the plasma-catalysis
2
hydrogenation by
2
2
2
o
system was 260 C.
Effects of the reaction pressure
The effects of the reaction pressure on the DME synthesis
Table 1 Effects of type of reaction on the CO
2
hydrogenation to DME
2
process from CO hydrogenation in the plasma-catalysis system
Y(DME) was investigated, and the results are shown in Fig. 2.
(mol%)
S (mol%)
X(CO
2
)
Reaction type
(mol%)
DME
0
CH
2.2
5.2
8.7
3
OH
CO
CH
4
Plasma aloneb
Catalyst alonea
2.9
91.7
24.8
16.8
6.1
6.8
5.9
0
20.9
24.3
63.1
69.5
13.2
16.9
Plasma + Catalystb
a
-1 -1
Reaction conditions: 260 °C (T), 3.0 MPa (P), 1500 mL·gcat ·h (GHSV),
2 2
and V(H )/V(CO ) = 4.
b
Reaction conditions: 260 °C (T), 3.0 MPa (P), 2000 mL·gcat-1·h -1 (GHSV),
3
.0 cm (d), 14.0 kV (U), and V(H )/V(CO ) = 4.
2
2
2
Fig. 2 Effects of the reaction pressure on the CO hydrogenation to DME in the
plasma-catalysis system. Reaction conditions: 2.0~4.0 MPa (P), 260 °C (T),
2000 mL·gcat-1·h -1 (GHSV), 3.0 cm (d), and 14.0 kV (U)
DME synthesis from CO
catalysis system
2
hydrogenation in the plasma-
Effects of the reaction temperature
With the reaction temperature ranging from 240 to 280 °C, the
results of CO
system are shown in Fig. 1.
2
hydrogenation to DME in the plasma-catalysis
As shown in Fig. 2, with the increasing reaction pressure from
2.0 to 2.5 MPa, the DME selectivity increased from 62.7% to
6
9.9% and then decreased from 69.9% to 57.8% when the
reaction pressure was further increased to 4.0 MPa. The CO
conversion reached a maximum value of 24.3% at 3.0 MPa and
the CH OH selectivity reached a maximum value of 11.6% at 3.5
2
3
MPa. The reaction pressure can affect the plasma area and the
catalytic reaction [16]. With the increase in the reaction pressure,
the concentration of the CO
more CO and H molecules were activated, which is favorable to
the synthesis of DME. However, when the reaction pressure was
excessive, the concentration of the CO and H molecules was
too high, which hindered the activation of CO and H molecules.
2 2
and H molecules increased, and
2
2
2
2
2
2
Fig. 1 Effects of the reaction temperature on the CO
2
hydrogenation to DME in
For the catalytic reaction, the high reaction pressure was
confirmed to be favorable to the synthesis of methanol and DME.
the plasma-catalysis system. Reaction conditions: 240~280 °C (T), 3.0 MPa (P),
-
1
-1
2
000 mL·gcat ·h (GHSV), 3.0 cm (d), and 14.0 kV (U)
Nevertheless, the CO
2
conversion and the DME selectivity
decreased when the reaction pressure was excessive. This can
be caused by the accumulation of water that cannot be removed
From Fig. 1, the CO
increased when the reaction temperature increased from 240 °C
to 260 °C, and the CO conversion and the DME selectivity
reached maximum values of 24.3% and 69.5%, respectively, at
60 °C. When the temperature was higher than 260 °C, the CO
conversion and the DME selectivity decreased. However, the
selectivity of CH OH increased with the increasing temperature.
As the plasma zone and the catalytic reaction zone are separated,
CO and H were firstly activated by energetic electrons in the
2
conversion and the DME selectivity
quickly enough in the fixed bed reactor during the process of CO
hydrogenation to DME, which will depress the catalytic activity. As
a result, CO hydrogenation to DME in the plasma-catalysis
2
2
2
system was investigated at 3.0 MPa.
Effects of the GHSV
2
2
The effects of the GHSV on the DME synthesis process from CO
2
3
hydrogenation in the plasma-catalysis system was investigated,
and the results are shown in Fig. 3.
2
2
plasma area. The active species then entered the catalytic reactor
and were catalytically hydrogenated over the Cu-Fe-Ce/HZSM-5
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ChemPhysChem
10.1002/cphc.201601283
ARTICLE
present study, when the discharge voltage was too high, more by-
products were generated in the plasma area, which weakened the
activation effect of the plasma. Therefore, the synthesis of DME
in the plasma-catalysis system was investigated at 14.0 kV.
2
Fig. 3 Effects of the GHSV on the CO hydrogenation to DME in the plasma-
-
1
-1
catalysis system. Reaction conditions: 1500~3500 mL·gcat ·h (GHSV), 260 °C
T), 3.0 MPa (P), 3.0 cm (d), and 14.0 kV (U )
(
2
Fig. 4 Effects of the discharge voltage on the CO hydrogenation to DME in the
plasma-catalysis system. Reaction conditions: 11.0~15.0 kV (U), 260 °C (T), 3.0
MPa (P), 2000 mL·gcat ·h (GHSV), and 3.0 cm (d)
-
1
-1
When the GHSV was increased from 1500 mL·gcat ·h to 2000
-1 -1
-1
-1
mL·gcat ·h , the CO
increased. When the CHSV increased to 3500 mL·gcat ·h , the CO
conversion decreased from 24.3% to 17.9%, and the DME
selectivity decreased from 69.5% to 54.8%. However, the CH OH
2
conversion and DME selectivity slightly
-
1
-1
2
Effects of the discharge interval
The Cu-Fe-Ce/HZSM-5 catalyst and plasma activation were
used to investigate the effects of a range of discharge intervals
3
selectivity increased with the GHSV. The space velocity can affect
the plasma area and the catalytic reaction. For the plasma area, the
from 3.0 to 6.0 cm on the synthesis of DME from CO
hydrogenation, and the results were shown in Fig. 5.
2
residence time of CO
2
and H
space velocity . A decrease in the space velocity might possibly
extend the residence time of the CO /H mixing gases, allowing the
CO and H to be sufficiently activated and more active species to
2
can be affected by the change of
[9]
2
2
2
2
be created. However, when the space velocity was too low, the
active species will take more time to reach the catalytic reactor, and
some of the active species will be annihilated on the way to the
catalytic reaction zone, so these species cannot be used to
synthesize DME. For the catalytic reaction, the residence time of
the reactant over the catalyst surface is increased by decreasing
the space velocity, leading to sufficient contact between the
reactant and the active sites of the catalysts, which can increase
the DME yield. However, when the space velocity is too high, some
of the methanol rapidly leaves the fixed-bed reactor and cannot
promptly dehydrate to DME on the surface of the HZSM-5 catalyst,
which will increase the methanol selectivity. These results suggest
that the optimal GHSV for the synthesis of DME in the plasma-
catalysis system is 2000 mL·gcat ·h .
Effects of the discharge voltage
With discharge voltages ranging from 11.0 to 15.0 kV, the
influences of the voltage on the CO hydrogenation to DME in the
2
plasma-catalysis system was investigated, the results were
shown in Fig. 4.
As shown in Fig. 4, the selectivity of DME and CH OH
3
increased with the discharge voltage increasing from 11.0 to 14.0
kV. At a discharge voltage greater than 14.0 kV, the selectivity of
2
Fig. 5 Effects of the discharge interval on the CO hydrogenation to DME in the
plasma-catalysis system. Reaction conditions: 3.0~6.0 cm (d), 260 °C (T), 3.0
-1 -1
MPa (P), 2000 mL·gcat ·h (GHSV), and 14.0 kV (U)
Fig. 5 shows that the CO
2
conversion, DME selectivity and
-1
-1
CH
3
OH selectivity all decreased with the increasing discharge
interval, achieved the maximum value at 3.0 cm. Modifying the
discharge interval can change the size of the plasma zone, which
can then change the energy density of the plasma area. The
energy density of plasma area increased with the discharge
interval, which increased the amount of active species activated
by the plasma and improved the DME yield. The optimal
discharge interval for the synthesis of DME in the plasma-
catalysis system was 3.0 cm.
3 2
DME and CH OH decreased. The CO conversion increased with
The intrinsic kinetics for dimethyl ether synthesis from
CO /H in the plasma-catalysis system
2 2
Excluding the internal and external diffusion
the increasing discharge voltage. The discharge voltage can only
affect the plasma area[17]. The energy density of the plasma area
increased with the discharge voltage, which increases the density
The Cu-Fe-Ce/HZSM-5 catalyst was used for the catalytic
of energetic electrons and the probability of energetic electrons
hydrogenation of CO
the effects of the amount of catalyst (1.0 and 2.0 g) and the
residence time on the catalytic CO hydrogenation were
investigated, and the results are shown in Fig. 6A.
2
to DME in the plasma-catalysis system, and
2 2 2 2
colliding with CO and H and H
molecules[ . Thus, more CO
10]
molecules can be activated by plasma, and generate more
excited CO and H molecules (expressed as CO * and H *),
which is favorable to the synthesis of DME. However, in the
2
2
2
2
2
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ChemPhysChem
10.1002/cphc.201601283
ARTICLE
of CH
4
18]
is considered balanced in the CO
2
hydrogenation to
DME[ . To investigate the intrinsic kinetics of the DME synthesis
from CO /H in the plasma-catalysis system, the methanol
2
2
synthesis reaction, the methanol dehydration reaction, and the
reverse water-gas shift reaction should be considered, which are
shown in Eqs. 1-3.
Reverse water-gas shift reaction:
CO
Methanol synthesis reaction:
CO + 3H ⇋ CH OH + H
Methanol dehydration reaction:
CH OH ⇋ CH OCH + H
2
+ H
2
⇋ CO + H
2
O
∆H298= 41.17 kJ·mol-1
(1)
∆H298= −49.46 kJ·mol-1 (2)
∆H298= −23.51 kJ·mol-1 (3)
2
2
3
2
O
2
3
3
3
2
O
The reverse water-gas reaction (Eq. 1) and methanol
synthesis (Eq. 2) reacted over the Cu-Fe-Ce catalyst, and the
methanol dehydration to DME (Eq. 3) occurred on the HZSM-5
component of the catalyst.
The reaction rate of methanol synthesis reaction was less than
methanol dehydration reaction. Therefore, the reaction of methanol
synthesis and methanol dehydration are consecutive exothermic.
Methanol dehydration can be affected by the formation of methanol.
Furthermore, methanol synthesis reaction and the reverse water-
gas shift reaction are mutually parallel reactions, and methanol
formation was affected by the formation of CO.
Fig. 6 Effects of the residence time (A) and catalyst particle sizes (B) on the CO
conversion
2
In the plasma area, the collision of energetic electrons with CO
and H molecules can generate a series of active species, such as
excited CO , H molecules, hydrogen radicals, oxygen radicals, etc.,
2
2
2
2
which are shown in Eqs. 4-7. Because the plasma area and the
catalytic reactor are separated, some of the hydrogen radicals,
oxygen radicals and other active species will react with each other,
-
3
When the residence time is less than 1.33×10 h, the GHSV
-1
-1
is greater than 1500 mL·gcat ·h , and the CO
overlapped when either 1.0 g or 2.0 g catalyst was used, which
indicated that CO conversion was not affected by the gas mass
flow rate. Therefore, when the GHSV is faster than 1500 mL·gcat-
1·h -1, the influence of the mass-transfer resistance of the external
2
conversion curves
so they will not reach the catalytic reactor to participate in the CO
hydrogenation reaction, as shown in Eqs. 8-10.
2
2
CO
CO
2
+ e* → CO +O+e
+ e* →CO * + e
(4)
(5)
2
2
diffusion can be ignored.
H
2
+ e* → H + H + e
+ e* →H *+ e
+H → CO + OH
OH + H → H
O + H + H → H
With plasma alone, a very small amount of CH
(6)
(7)
(8)
(9)
(10)
Once the external diffusion was excluded as a relevant factor,
H
2
2
the influence of the Cu-Fe-Ce/HZSM-5 particle size on CO
conversion was investigated, and the results are shown in Fig. 6B.
The average CO conversion rate is equal over the average
catalyst particle size range of 0.15-0.25 mm, which shows that in
this size range CO conversion is not affected by the catalyst
particle size. Therefore, the influence of mass-transfer resistance
of the internal diffusion on the reaction can be ignored when the
particle size is smaller than 0.25 mm.
2
CO
2
2
O
2
2
O
3
OH and CH
4
2
were detected in the reaction products. The formation of CH
and CH are shown in Eqs. 11-17.
Formation of CH OH:
CO + H → HCO
HCO + H → CH
3
OH
4
3
(11)
(12)
(13)
(14)
In the plasma-catalysis system, when the GHSV is more than
500 mL·gcat-1·h -1 and the particle size is smaller than 0.25 mm,
CO hydrogenation to DME in the plasma-catalysis system is not
2
2
O
1
CH
CH
2
O + H → CH
O + H → CH
3
O
OH
3
3
affected by mass-transfer resistance from external or internal
diffusion and instead is controlled by intrinsic kinetic processes.
Suggested mechanism
hydrogenation to DME in the plasma-catalysis
molecules were firstly activated by energetic
electrons at plasma area, and then, the active species entered the
catalytic reactor and reacted to synthesize DME over the Cu-Fe-
Ce/HZSM-5 catalyst. The target product was DME, and the
Formation of CH
OH + CH
4
:
3
OH → H
2
O + CH
+ OH
2
OH
(15)
(16)
(17)
CH
CH
2
OH + H → CH
+ H → CH
3
In the CO
2
3
4
system, CO and H
2
2
Therefore, in the plasma area, we assume that:
1) The hydrogen radicals, oxygen radicals and other active
(
species with high activity are produced in the plasma area, which
can react with each other, and therefore do not reach the catalytic
byproducts were CH
barrier of the CH formation was less than that of the methanol
synthesis, methanol dehydration, and reverse water-gas
reactions. However, the CH yield is still very low, so the synthesis
3 4
OH, CO, and CH , because the energy
reactor to participate in the CO
of these active species can be ignored in the CO
reaction.
2
hydrogenation. Thus, the influence
4
2
hydrogenation
4
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ChemPhysChem
10.1002/cphc.201601283
ARTICLE
(
2) The collision of energetic electrons with CO
2
and H
2
HCOOHσσ + Hσ⇋ H
2
COσσ + OHσ
COσ + 2σ
OHσ+ σ
OH + σ
Oσ + σ
O + σ
Methanol dehydration to DME reaction:
(29)
(30)
(31)
(32)
(33)
(34)
molecules can generate excited CO
expressed as CO
reaction area for the synthesis of DME over Cu-Fe-Ce/HZSM-5
catalysts.
2
and
H
2
molecules
H
2
COσσ + Hσ⇋ H
COσ+ Hσ⇋ CH
OHσ ⇋ CH
Hσ + OHσ⇋ H
Oσ ⇋ H
3
(
2
* and H
2
*), which can reach the catalytic
H
3
3
CH
3
3
2
(
3) The products CO, CH
3
OH and CH
4
are present in the
H
2
2
plasma area in very small amounts, so to simplify the process,
these products are ignored.
CH
3
OH + HX ⇋ HXCH
3
OH
X + HXH
(35)
(36)
+
-
Previous studies have shown that the concentration of the
plasma-generated active species can be considered directly
proportional to the energy density of plasma area[19]. Because the
cross-sectional area of the plasma reactor is constant, the
discharge volume is considered directly proportional to the
HXCH
3
OH + HX ⇋ CH
3
2
O
+
CH3
O
(37)
+
-
-
CH3 X + HXCH OH HXCH3
H + X
3
+
CH
3
-
(38)
HXCH3
O
H + X
HXCH3
O
CH + HX
3
discharge interval. The concentration of CO
in Eqs. 18 and 19, respectively.
2
* and H
2
* are shown
HXCH
H + X ⇋ HX
3
-
—O—CH
3
⇋ CH
3
OCH
3
+ HX
(39)
(40)
+
U 1
U
p
CO*2
=a
P=b
P
(18)
(19)
The treatment of intrinsic kinetic experimental data
The experimental data obtained in the present study were the
conversion and the selectivity of CO, CH OH, and DME, and
d 5
d
U 4
d 5
U
p
*
=c
P=d
P
H2
d
CO
2
3
where a, b, c and d are constant, P is the total pressure, U is
the discharge voltage, and d is the discharge interval.
In the catalytic CO hydrogenation reaction, the Cu-Fe-Ce
2
catalyst was used for the methanol synthesis. Cu species are
generally thought to be the main center of activity for the methanol
these data were converted to the concentration of each
component. The methanol dehydration and reverse water-gas
shift reactions are equimolar molecular reactions, and the
reaction molecularity of each remains constant before and after
the reaction. However, the CO hydrogenation to CH OH will
2 3
cause the reaction molecularity to decrease, so the reaction
molecularity will decrease for the whole process. The fraction of
synthesis process[20]
.
Extensive density functional theory
calculations were performed to map out the entire reaction
network of CO hydrogenation to methanol on the Cu (111)
2 2
V(H )/V(CO ) in the system is 4, and the composition before and
2
surface [21], and the formate pathway is one of the reaction
mechanisms. Based on previous studies[20c], the formate pathway
was considered the methanol synthesis reaction mechanism in
after the reaction can be described as follows:
0
0
CO
The composition before the reaction:
F : F  4:1
H
2
2
Total molar flow before the reaction:
0
CO
5
F
the present work. In this way, CO
2
is hydrogenated to form HCOO,
CO via formic acid
HCOOH) intermediates, followed by two consecutive
2
2
According to the CO conversion and the selectivity and yield
of each product, the composition of products can be calculated,
and the HCOO is then converted into H
2
(
as shown in Eqs. 41-44.
3
hydrogenation steps to form H CO, and methanol. However, the
0
FCO  F (1 XCO2
)
(41)
(42)
(43)
(44)
CO
HOCO and HCOO, which may affect the whole reaction process.
The suggested reaction mechanism of CO hydrogenation to
CH OH is shown in Eqs. 20-34, where σ indicates single atomic
2
2
* and H * activated by the plasma can affect the formation of
CO
2
2
0
FCO  F YCO
CO2
2
0
FCH3OH  F YCH3OH
CO2
3
0
FDME  0.5F YDME
adsorption, and σσ represents diatomic adsorption.
CO2
Methanol dehydration to DME occurs over the HZSM-5
component of the catalyst. The adsorbed methanol obtains a
proton (H) adsorbed at the acid sites of HZSM-5, and then
Based on the conservation of mass and reaction equilibrium,
the molar flow of H O and H in the products can be obtained, and
the calculation formulas are shown in Eqs. 45 and 46.
2
2
0
dissociates into a positive carbon ion and water, and
neighbouring, undissociated methanol combines with the carbon
cation as This reaction
nucleophile, forming DME[22]
a
FH2O  FCO (YCO YCH OH 1.5YDME
)
(45)
(46)
2
3
0
0
FH2  F  F (YCO 3YCH3OH 3YDME
)
H2
CO2
a
.
Summing of Eqs. 41-46, the total molar flow of the products
can be obtained as shown in Eq. 47.
mechanism can be described in Eqs. 35-40, where HX represents
HZSM-5.
6
0
Methanol synthesis and reverse water-gas shift reactions:

F
i
FCO2 (5 2XCO2  2YCO
)
(47)
i1
H
H
CO
CO
2
+ 2σ ⇋ 2Hσ
* + 2σ ⇋ 2Hσ
(20)
(21)
(22)
(23)
(24)
(25)
(26)
(27)
(28)
The mole fraction of each composition of the products is
2
shown in Eq. 48.
2
+ Hσ + σ ⇋ HOCOσσ
* + Hσ + σ ⇋ HOCOσσ
6
2
y  F / Fi

(48)
i
i
i1
HOCOσσ⇋ COσ + OHσ
COσ ⇋ CO + σ
CO
CO
The experimental intrinsic kinetic data for CO
2
hydrogenation
to DME in the plasma-catalysis system are shown in Table 2.
For comparison, the intrinsic kinetic data for CO
2
+ Hσ + σ ⇋ HCOOσσ
* + Hσ + σ ⇋ HCOOσσ
2
2
hydrogenation to DME with catalysis alone are shown in Table 3.
HCOOσσ+ Hσ⇋ HCOOHσσ + σ
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ChemPhysChem
10.1002/cphc.201601283
ARTICLE
2
Table 2 Intrinsic kinetic data of the CO hydrogenation to DME in the plasma-catalysis system
T
P
W
cat/φ
V
U
d
p
CO
p
CO2
p
DME
p
CH OH
3
p 2
H
pH2O
oC)
(MPa)
(gcat.·h·m )
-3
(kV)
(cm)
(
(MPa)
(MPa)
(MPa)
(MPa)
(MPa)
(MPa)
240
240
240
240
240
250
250
250
250
250
260
260
260
260
260
270
270
270
270
270
280
280
280
280
280
260
260
260
260
260
260
260
260
260
260
260
260
260
260
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
2.0
2.5
3.0
3.5
4.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3333
2500
2000
1667
1429
3333
2500
2000
1667
1429
3333
2500
2000
1667
1429
3333
2500
2000
1667
1429
3333
2500
2000
1667
1429
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
2500
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
14.0
11.0
12.0
13.0
14.0
15.0
14.0
14.0
14.0
14.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
4.0
5.0
6.0
0.0185
0.0152
0.0167
0.0188
0.0230
0.0248
0.0221
0.0217
0.0221
0.0240
0.0298
0.0261
0.0234
0.0237
0.0254
0.0323
0.0264
0.0246
0.0242
0.0258
0.0309
0.0252
0.0249
0.0255
0.0270
0.0202
0.0213
0.0263
0.0197
0.0202
0.0268
0.0236
0.0260
0.0261
0.0280
0.0261
0.0276
0.0230
0.0216
0.5246
0.5221
0.5295
0.5354
0.5374
0.5094
0.5042
0.5145
0.5216
0.5253
0.4952
0.4928
0.5067
0.5166
0.5201
0.4981
0.4964
0.5092
0.5169
0.5209
0.5053
0.5031
0.5139
0.5209
0.5242
0.3462
0.4207
0.4932
0.5853
0.6816
0.5046
0.5015
0.4977
0.4928
0.4903
0.4928
0.4961
0.5026
0.5053
0.0304
0.0328
0.0262
0.0222
0.0207
0.0420
0.0466
0.0381
0.0333
0.0307
0.0516
0.0550
0.0420
0.0340
0.0311
0.0417
0.0450
0.0364
0.0318
0.0294
0.0354
0.0380
0.0311
0.0273
0.0254
0.0235
0.0405
0.0546
0.0549
0.0499
0.0441
0.0472
0.0508
0.0550
0.0537
0.0550
0.0516
0.0466
0.0436
0.0048
0.0059
0.0063
0.0088
0.0126
0.0069
0.0087
0.0100
0.0125
0.0167
0.0110
0.0128
0.0148
0.0170
0.0175
0.0112
0.0148
0.0138
0.0147
0.0166
0.0174
0.0190
0.0176
0.0172
0.0177
0.0038
0.0073
0.0129
0.0198
0.0185
0.0078
0.0090
0.0111
0.0128
0.0122
0.0128
0.0114
0.0096
0.0082
2.3073
2.3047
2.3196
2.3208
2.3086
2.2591
2.2479
2.2700
2.2762
2.2706
2.2167
2.2095
2.2489
2.2660
2.2699
2.2483
2.2415
2.2685
2.2782
2.2768
2.2564
2.2563
2.2767
2.2842
2.2847
1.5117
1.8600
2.2102
2.6160
3.0417
2.2499
2.2444
2.2251
2.2095
2.2147
2.2095
2.2195
2.2457
2.2608
0.1144
0.1194
0.1017
0.0941
0.0977
0.1578
0.1705
0.1459
0.1343
0.1327
0.1957
0.2038
0.1642
0.1427
0.1361
0.1685
0.1760
0.1475
0.1342
0.1305
0.1546
0.1584
0.1358
0.1248
0.1210
0.0946
0.1501
0.2029
0.2043
0.1882
0.1669
0.1743
0.1894
0.2038
0.2012
0.2038
0.1938
0.1725
0.1605
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ChemPhysChem
10.1002/cphc.201601283
ARTICLE
2
Table 3 Intrinsic kinetic data of the CO hydrogenation to DME by catalysis alone
T
P
W
cat/φ
V
U
(kV)
d
(cm)
p
CO
p
CO2
p
DME
p
3
CH OH
oC)
(MPa)
(gcat.·h·m )
-3
(
(MPa)
(MPa)
(MPa)
(MPa)
240
240
240
240
240
250
250
250
250
250
260
260
260
260
260
270
270
270
270
270
280
280
280
280
280
260
260
260
260
260
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
2.0
2.5
3.0
3.5
4.0
3333
2500
2000
1667
1429
3333
2500
2000
1667
1429
3333
2500
2000
1667
1429
3333
2500
2000
1667
1429
3333
2500
2000
1667
1429
2500
2500
2500
2500
2500
0.0144
0.0152
0.0154
0.0136
0.0109
0.0197
0.0221
0.0228
0.0204
0.0170
0.0331
0.0326
0.0301
0.0272
0.0244
0.0265
0.0276
0.0277
0.0233
0.0204
0.0242
0.0255
0.0257
0.0219
0.0192
0.0136
0.0249
0.0331
0.0302
0.0301
0.5433
0.5483
0.5518
0.5555
0.5577
0.5279
0.5327
0.5361
0.5400
0.5433
0.5049
0.5170
0.5236
0.5282
0.5307
0.5119
0.5195
0.5247
0.5301
0.5331
0.5172
0.5239
0.5287
0.5326
0.5355
0.3520
0.4231
0.5049
0.5997
0.6971
0.0232
0.0190
0.0161
0.0139
0.0126
0.0313
0.0253
0.0220
0.0195
0.0180
0.0421
0.0323
0.0274
0.0239
0.0224
0.0311
0.0265
0.0236
0.0215
0.0204
0.0249
0.0213
0.0192
0.0179
0.0170
0.0187
0.0334
0.0421
0.0409
0.0402
0.0034
0.0036
0.0041
0.0048
0.0058
0.0046
0.0050
0.0057
0.0068
0.0082
0.0069
0.0068
0.0069
0.0082
0.0107
0.0101
0.0096
0.0099
0.0107
0.0126
0.0145
0.0137
0.0131
0.0132
0.0142
0.0025
0.0045
0.0069
0.0094
0.0143
2.3285
2.3381
2.3448
2.3524
2.3581
2.2985
2.3121
2.3190
2.3273
2.3343
2.2467
2.2751
2.2927
2.3053
2.3094
2.2904
2.3000
2.3054
2.3158
2.3192
2.3057
2.3124
2.3171
2.3257
2.3297
1.5410
1.8845
2.2467
2.6573
3.0533
0.0873
0.0758
0.0678
0.0599
0.0547
0.1181
0.1029
0.0944
0.0859
0.0791
0.1663
0.1362
0.1193
0.1071
0.1024
0.1300
0.1168
0.1085
0.0986
0.0943
0.1135
0.1031
0.0962
0.0887
0.0844
0.0722
0.1296
0.1663
0.1625
0.1650
Derivation of the intrinsic kinetics model
The catalytic reaction was the main process for CO
reactions and chemical adsorption and desorption occur
exclusively on these two active sites.
2
hydrogenation to DME in the plasma-catalysis system, and the
plasma activation played a subsidiary role, which can be regarded
as a plug flow system. According to the dynamic Langmuir-
Hinshelwood chemisorption model[23], we assume that:
(2) The concentrations of the gaseous forms of each
component present in the reaction system reach equilibrium, and
the gases behave as ideal gases.
(3) The rate-limiting steps of the reverse water-gas shift,
methanol synthesis and methanol dehydration reactions are Eqs.
22, 29 and 37, respectively. Moreover, the non-rate-controlling
steps reach equilibrium.
(
1) Cu species act as the active sites for the methanol
synthesis and reverse water-gas shift reactions, and HZSM-5 is
the active site for the methanol dehydration reaction. Surface
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ChemPhysChem
10.1002/cphc.201601283
ARTICLE
According to these assumptions, the intrinsic kinetic models of
hydrogenation to DME in the plasma-catalysis system were
established, and the kinetic equations are shown in Eqs. 49-51.
respectively, indicating that plasma activation can reduce the
activation energy of the reaction and improve the yield of DME.
CO
2
Table 4 Intrinsic kinetic parameters of the CO
plasma-catalysis system
2
hydrogenation to DME in the

pCO pH2O



0
.5 0.5
0.5
K1
k1 pCO2
U
P
/ d 1(
)
KP1
0.5
p
0.5
CO2

UP/d


(49)
r1 
Kinetic constant
Value
Kinetic constant
E (kJ·mol-1
Value
75.47
0.5
0.75 0.75
0.75
2
(
1 KCO pCO  KH2O pH2O  K U
P
/ d  K U
P
/ d
)
2
3

K4 pCH3OH pH2O

k1(mol·cm0.5·h -1·MPa-1.5·kV-0.5·g cat-1
)
9.73×10
2
)
2
2
2
1
k U P / d 1(
)
2

4


KP2 (UP / d)

(50)
(51)
r2 
(mol·cm ·h ·MPa ·kV ·g cat-1)
2
-1
-2
-2
2.03×103
(kJ·mol-1)
E
2
0.5
0.5
0.5
0.75 0.75
0.75
3
k
2
149.34
73.18
(
1 KCO pCO  KH2O pH2O  K U
P
/ d  K U
P
/ d
)
2
3
2
k  p
/ pH2O (K / K )p

k3(mol· h-1·MPa-1·g cat-1
4
E (kJ·mol-1
3
)
3

CH3OH
5
P3
DME

)
2.62×10
r3 
'
2
(
1 KCH3OH pCH3OH  K pH2O )
H2O
(kV·cm-1)
3.51×102
(kJ·mol-1)
K
1
ΔH
1
-113.23
-46.27
93.26
i i
The equilibrium constants k or K corresponding to each
reaction temperature were substituted into the Arrhenius equation
and the Van’t Hoff equations were transformed into Eqs. 52 and
K
2
(cm0.5·MPa-0.5·kV-0.5
)
3.83×10-6
ΔH
2
(kJ·mol-1)
(cm0.75·MPa-0.75·kV-0.75
6.51×10-9
(kJ·mol-1)
3
K
3
)
ΔH
5
3, respectively.
4
2
-4
4.58×10-4
(kJ·mol-1)
Ei
K
4
(kV ·MPa ·cm )
ΔH
4
43.96
ki  ki ，0 exp[
]
(52)
(53)
RT

7.86×10-5
(kJ·mol-1)
K
K
K
K
5
(a.u.)
ΔH
5
-60.51
-50.38
-81.43
-26.16
-32.83
Hi
K  K exp[
]
i
i，0
CO (MPa-1
)
5.28×10-3
(kJ·mol-1)
RT
.3.5 Parameter estimate
According to atomic matrix method, three independent
reactions were involved in the CO hydrogenation to DME in the
plasma-catalysis system, and the CO , CO and DME were
HCO
3
-1
1.76×10-6
(kJ·mol-1)
HCH3OH
CH3OH(MPa )


HH2O
H2O (MPa-1)
3.64×10-7
(kJ·mol-1)
2
2
'
H O
MPa-1)
2.39×10-12
(kJ·mol-1)
H
H2O
(
'
K
considered the key components. Eqs. 54-56 were obtained on the
basis of the chemical reaction equations and the mass balance[24]
2
.
For comparison, based on the intrinsic kinetics of model 3 in
ref [20c], the optimized model parameters of the intrinsic kinetics of
CO hydrogenation to DME with Cu-Fe-Ce/HZSM-5 catalysts
d[(yCO2 , in  yCO2 , out )P/RT]
r

 r  r2
(54)
(55)
(56)
CO2
1
d(W / )
2
cat
V
d(yCO, out P/RT)  r1
alone are shown in Table 5.
r

CO
d(Wcat /V )
Table 5 Intrinsic kinetic parameters of the CO2 hydrogenation to DME with
catalysis alone
d(yDME, out P/RT)  2r3
rDME

d(W / )
cat
V
Kinetic constant
Value
8.37
Kinetic constant
Value
i i 1 2 3
where y=p/P, and r , r , r were substituted by Eqs. 49, 50, 51,
(mol·h ·MPa-1.5·g cat-1)
-
1
E
(kJ·mol-1)
E (kJ·mol-1
121.67
162.39
k
1
1
respectively. The square residual of the experimental values and
the calculated values of the partial pressure for each key
component were used for the optimized objective function, as
k2 (mol·h-1·MPa-1·g cat-1
3
)
1.28×10
2
)
(mol· h ·MPa ·g cat-1)
-
1
-1
3.69×103
2.63×104
4.27×10-7
E
3
(kJ·mol-1)
86.51
k
3
shown in Eq. 57.
M
2
2
2
S 
[(PCO 2 , exp  PCO 2 , cal )  (P
 PCO, cal )  (P
 PDME, cal ) ]

CO, exp
DME, exp
(57)
(kJ·mol-1)
K
1
(a.u.)
ΔH
1
-57.36
j1
The Runge-Kutta-Philberg algorithms were used to obtain
(MPa0.5
(kJ·mol-1)
K
K
K
K
K
2
3
)
ΔH
ΔH
2
3
-39.53
-106.62
-37.83
-67.18
-46.95
-27.82
the optimal solution to the ordinary differential Eqs. 54-56. The
optimization algorithm was established using 1stOpt program
(a.u.)
1.92×10-8
7.25×10-2
5.42×103
(kJ·mol-1)
(
7D-Soft High Technology Inc.， China). The optimized model
CO (MPa-1
)
ΔHCO(kJ·mol-1)
ΔHCH3OH(kJ·mol-1)
ΔHH2O(kJ·mol-1)
parameters of the intrinsic kinetics of CO hydrogenation to DME
in the plasma-catalysis system are shown in Table 4.
2
-
1
CH3OH (MPa )
Table 4 shows that the activation energies of the methanol
synthesis, reverse water-gas shift reaction, and methanol
dehydration to DME were found to be 149.34, 75.47, and 73.18
kJ·mol , respectively. With catalytic hydrogenation alone[20c], the
activation energies of the methanol synthesis, reverse water-gas
shift reaction, and methanol dehydration to DME were found to be
-
1
3.86×10-9
2.39×10-3
H2O (MPa )
'
(MPa-1
)
'
(kJ·mol-1
)
K
H
H2O
H2O
-1
Validation of the intrinsic kinetics model
The F-test was used to validate the intrinsic kinetics model.
F was the ratio of the sum of mean square to the sum of mean
square of the residual, and ρ is a coefficient of determination
calculated by Eqs. 58 and 59, respectively.
-1
162.39, 121.67, and 86.51 kJ·mol , respectively. The activation
2
[25]
,
-1
-
energies of the three reactions were 13.05 kJ·mol , 46.20 kJ·mol
1,
5
and 13.33 kJ·mol-1 lower than those using the Cu-Fe-Ce/HZSM-
catalyst alone, respectively. In the results of Table 1, the CO
M
M






2
2
p

(pj, exp  pj, cal
)
/ Mp
2

j, exp

j1
j1
conversion and DME selectivity increased by 16.3%, and 10.1%
for the CO hydrogenation to DME in the plasma-catalysis system,
F 
M
(58)
2
(
pj, exp  pj, cal ) / (M  M )
p

2
j1
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ChemPhysChem
10.1002/cphc.201601283
ARTICLE
M
M
2
2
2
j, exp
kinetic model was established. The main conclusions of this work
are the following:

1
( pj, exp  pj, cal ) /
p


(59)
j1
j1
where, M is the number of the experiments and M
p
is the number
of variables in the equation of model; pj, cal and pj, exp are the
calculated model values and experimental values of the partial
pressures of CO , CO, and DME, respectively. The results of the
2
statistical significance test are shown in Table 6.
Table 6 Statistical test of the intrinsic kinetic model
Equation
M
p
M-M
p
ρ2
F
p p
10F0.05(M ,M-M )
a
r
r
r
r
r
r
CO2
13
13
8
26
26
31
21
21
22
0.9958
0.9945
0.9924
0.9977
0.9974
0.9962
475.6
360.1
507.1
854.9
775.9
1005.0
21.5
21.5
22.7
23.7
23.7
24.0
a
CO
a
DME
b
CO2
9
b
CO
9
b
DME
8
aThe results of plasma activation combined with the hydrogenation process;
bThe results of catalysis alone.
2
In general, if ρ > 0.9 and F> 10F0.05, the intrinsic kinetic model
is reliable at α = 0.05. Table 6 shows that all the F-values
(
360.1~1005.0) were larger than the 10F0.05 (21.5~24.0) values,
which indicated that these two kinetic models for the plasma
activation combined hydrogenation process and the catalysis
alone are both reasonable. The greater are the decisive index and
F-value, the more reliable is the intrinsic kinetic model. Table 6
illustrates that the experimental results predicted by the intrinsic
kinetic model were reasonable at α = 0.05. However, the F-value
for the catalysis alone was greater than that of the combined
plasma activation and hydrogenation process, which indicates
that the intrinsic kinetic model for the catalysis system alone is
more reliable. This result can be explained to that when the
plasma was added to the reaction system, more parameters was
Fig. 7 Comparison between the calculated and experimental value of CO
CO (B), DME (C) pressure in the CO hydrogenation reaction
2
(A),
2
considered, which affected the intrinsic kinetics of the CO
hydrogenation reaction.
2
2
(1) CO conversion and DME selectivity in the plasma-
catalysis system were increased by 16.3% and 10.1% compared
with that of the Cu-Fe-Ce/HZSM-5 catalyst alone, respectively,
2
The experimental values of the partial pressures of CO , CO,
and DME in the plasma-catalysis system were plotted against the
values calculated by the intrinsic kinetic model, and the results
were compared with catalysis alone, which is shown in Fig. 7. In
the analysis diagram, the points are evenly distributed on both
sides of the diagonal for both reaction systems, indicating that the
calculated value is reasonable, which supports the reliability of the
intrinsic kinetic model.
indicating that the catalytic CO
promoted by the plasma activation.
(2) When the Cu-Fe-Ce/HZSM-5 catalysts with 3.0 wt% CeO
were used in the plasma-catalysis system for CO hydrogenation
to DME at 14.0 kV, 3.0 cm, 260 °C and 3.0 MPa with GHSV =
2
hydrogenation process can be
2
2
-1
-1
2
2000 mL·gcat ·h , the CO conversion was 24.3%, and the DME
selectivity was 69.5%.
(
3) The intrinsic kinetics study found that the activation
energy of the methanol synthesis, the reverse water-gas shift
reaction and the methanol dehydration to dimethyl ether were
Conclusions
-1
-1
-1
149.34 kJ·mol , 75.47 kJ·mol , 73.18 kJ·mol , respectively. By
comparison, the activation energy of the three reactions could be
decreased after the plasma activation was introduced, which
indicated that plasma activation can reduce the activation energy
of the reaction to improve the yield of dimethyl ether.
The synergistic effect of plasma activation and catalytic
hydrogenation for CO
addition, the intrinsic kinetics of DME synthesis from CO
plasma-catalysis system was investigated, and the intrinsic
2
hydrogenation to DME were studied. In
2
in a
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ChemPhysChem
10.1002/cphc.201601283
ARTICLE
-
1
-1
R: gas constant, J·mol ·K
S: residual square sum
Experimental Section
i
S: selectivity of component i, mol%
2
Cu-Fe-Ce/HZSM-5 with 3.0 wt% CeO was used as the catalyst to
T: temperature, °C
U: discharge voltage, kV
V: volume, m3
2
synthesize DME from CO hydrogenation in a plasma-catalysis system.
The experimental apparatus consisted of a fixed-bed reactor and a plasma
reactor (Fig. 8). The plasma reactor consists of a quartz tube with an inner
diameter of 4 cm, a pin electrode (copper wire with the diameter of 1 mm)
and a plate electrode (copper plate with the diameter of 3.5 cm). The length
of plasma reactor is 25 cm, and the discharge zone can be adjusted in the
range of 1~20 cm. A high-voltage alternating current in the range of 16 kV
W
cat: weight of the catalyst, g
: conversion of component i, mol%
: mole fraction of component i, mol%
: yield of component i, mol%
ΔH: adsorption enthalpy increment, kJ·mol
X
i
y
i
Y
i
-
1
(
50 kHz) was applied to create plasma. The fixed-bed reactor is a
3
-1
V
φ : volumetric flow rate, m ·h
stainless-steel reaction tube (inner diameter 10 mm and a length of 300
mm). A total of 1.0 g Cu-Fe-Ce/HZSM-5 catalyst was placed in the fixed-
2
ρ : determinant index
Subscripts
bed reactor and was reduced at 300 °C for 4 h by H
rate of 30 mL·min-1 before the CO
hydrogenation reaction. After the
catalyst was reduced, the temperature was lowered to 100 °C, the inflow
of H was replaced with a mixture of H and CO (4:1 mol ratio), and the
CO hydrogenation to DME in the plasma-catalysis system was carried out
at 11.0-15.0 kV, 240-280 °C and 2.0-4.0 MPa with a discharge zone length
2
(99.999%) at a flow
cal: calculation value
cat: catalyst
exp: experimental value
i: the ith component
in: inflow
2
2
2
2
2
out: outflow
-
1
-1
of 3.0-4.0 cm, and a GHSV of 1500-3500 mL·gcat ·h . Under steady-state
conditions, the products were analysed using an Agilent 4890D gas
chromatograph with a thermal conductivity detector.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (21366004, 21425627), Natural Science
Foundation of Guangxi Province (2016GXNSFFA380015,
2015GXNSFDA139005), and the Open Project of Guangxi Key
Laboratory of Petrochemical Resource Processing and Process
Intensification Technology (2015K004).
2
Keywords: CO hydrogenation • dimethyl ether • plasma
activation • intrinsic kinetics • Cu-based catalyst
2
Fig. 8 Experimental apparatus for CO hydrogenation in the plasma-catalysis
system. (1, 5 stop valve; 2, 6 constant pressure valve; 3, 7 mass flowmeter; 4
plasma reactor; 8 triple valve; 9 fixed-bed reactor; 10 back pressure valve; 11
six-way valve; 12 gas chromatograph)
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Table of Contents
ARTICLE
Tongming Su, Xinhui Zhou, Zuzeng
Qin,* Hongbing Ji*
Page No. – Page No.
Intrinsic Kinetics for Dimethyl Ether
Synthesis from Plasma Activation
CO
Ce/HZSM-5
2
Hydrogenation over Cu-Fe-
The kinetic model for the plasma-catalysis system and catalysis system are both
reasonable. And the activation energies of the methanol synthesis, reverse water-
gas shift reaction, and methanol dehydration to DME for the plasma-catalysis system
were 13.05 kJ·mol , 46.20 kJ·mol , and 13.33 kJ·mol lower than that of the
catalysis system.
-1
-1
-1
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