Long carbon nanotubes intercrossed Cu/Zn/Al/Zr catalyst for CO/CO2 hydrogenation to methanol/dimethyl ether

Article abstract of DOI:10.1016/j.cattod.2009.05.018

Vertically aligned carbon nanotube (CNT) arrays were dispersed in Na₂CO₃ solution and co-precipitated with metal nitrite to form long CNTs (over 500 μm) intercrossed Cu/Zn/Al/Zr catalyst (CD703). The catalyst was used for methanol synthesis from CO/CO₂ hydrogenation. The space time yield (STY) of methanol on CD703 increased to 0.94 and 0.28 g/(gcat h), with an increment of 7% and 8% compared with that on the Cu/Zn/Al/Zr catalyst without CNTs for CO and CO₂ hydrogenation, respectively. Furthermore, when combined with γ-Al₂O₃ catalyst and HZSM-5, dimethyl ether (DME) was obtained with a STY of 0.90 and 0.077 g/(gcat h) at 270 °C from one step CO and CO₂ hydrogenation, respectively. Due to the phase separation, ion doping and valence compensation, hydrogen reversibly adsorption and storage on CNTs promoting hydrogen spillover, CD703 catalyst show good activity for methanol synthesis. Owing to the high thermal conductivity of CNTs, the stability of CD703 was improved. This indicated that long CNTs were a good promoter on the Cu/Zn/Al/Zr catalyst for methanol/DME production from CO/CO₂ hydrogenation.

Full text of DOI:10.1016/j.cattod.2009.05.018

Catalysis Today 150 (2010) 55–60
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Long carbon nanotubes intercrossed Cu/Zn/Al/Zr catalyst for CO/CO2
hydrogenation to methanol/dimethyl ether
Qiang Zhang, Yi-Zan Zuo, Ming-Han Han, Jin-Fu Wang, Yong Jin, Fei Wei *
Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Vertically aligned carbon nanotube (CNT) arrays were dispersed in Na CO solution and co-precipitated
2
3
Available online 23 June 2009
with metal nitrite to form long CNTs (over 500
catalyst was used for methanol synthesis from CO/CO
methanol on CD703 increased to 0.94 and 0.28 g/(gcat h), with an increment of 7% and 8% compared with
that on the Cu/Zn/Al/Zr catalyst without CNTs for CO and CO hydrogenation, respectively. Furthermore,
when combined with -Al catalyst and HZSM-5, dimethyl ether (DME) was obtained with a STY of
.90 and 0.077 g/(gcat h) at 270 8C from one step CO and CO hydrogenation, respectively. Due to the
phase separation, ion doping and valence compensation, hydrogen reversibly adsorption and storage on
CNTs promoting hydrogen spillover, CD703 catalyst show good activity for methanol synthesis. Owing to
the high thermal conductivity of CNTs, the stability of CD703 was improved. This indicated that long
m
m) intercrossed Cu/Zn/Al/Zr catalyst (CD703). The
2
hydrogenation. The space time yield (STY) of
Keywords:
Carbon nanotube
Cu/Zn/Al/Zr catalyst
2
g
2 3
O
2
CO/CO hydrogenation
0
2
Methanol synthesis
Dimethyl ether synthesis
Stability
CNTs were a good promoter on the Cu/Zn/Al/Zr catalyst for methanol/DME production from CO/CO
hydrogenation.
2
ß 2009 Elsevier B.V. All rights reserved.
1
. Introduction
conventional Cu/Zn/Al methanol synthesis catalysts. Some works
sought to improve the dispersion of the conventional Cu/Zn/Al
catalyst by using complicated preparation procedures. Other
works sought to improve the catalyst by adding additives other
than Al to Cu/Zn crystallites or Cu/Zn/Al composites, e.g., Melian-
Cabrera reported the use of Cr, Zr, V, Ce, Ti, Ga, and Pd to modify Cu/
ZnO-based catalysts [13–16]. Some additives, such as Ce, Ga, Pd,
were quite expensive. Recently, we found that the catalyst
performance can be enhanced by the catalyst structure modulation
with doping Zr [17]. By using a well controlled co-precipitation
procedure, Cu/Zn/Al/Zr catalyst with high activity for both CO and
It is
hydrogenation in industry on Cu/Zn/Al catalyst [1–4]. To promote
the methanol synthesis process, CO was always added into the
reactant for methanol synthesis [5–7]. Recently, the greenhouse
effect is a threat to the living environment of mankind. The
a long history for methanol production from CO
2
transformation of CO
2
into useful chemicals, e.g. methanol,
dimethyl ether (DME), is an attractive way to protect global
environment. However, the conventional Cu/Zn/Al catalyst is a
porous solid catalyst with low thermal conductivity. The reaction
heat is difficult to be transferred and the diameter of single tube of
the reactor has to be limited to several centimeters in order to
control the temperature of the hot spots in the fixed bed.
Meanwhile, the Cu/Zn/Al catalyst is not as active for methanol
2
CO hydrogenation was developed. Furthermore, the object to
obtain a catalyst with high activity and stability is still a goal. The
viewpoint of enhancing heat transfer on Cu/Zn-based catalyst to
promote methanol synthesis is still less mentioned.
synthesis from a H
2
/CO
2
mixture at temperatures below 250 8C
Carbon nanotubes (CNTs) were found to possess excellent
thermal conduction property. For example, the axial thermal
conductivity of CNTs was found to be extremely high, about
2000 W/m K or more than 3000 W/m K for multi-walled CNTs and
even higher for single-walled CNTs [18,19], and the thermal
conductivities of CNT-in-oil suspensions and CNT-in-polymer
composites were observed to be significantly improved. For
example, a 150% increase at 1% volume fraction of CNTs [20,21].
Some trials have been done on CNTs-Cu/Zn/Al catalyst [12,22].
Although short agglomerated CNTs wherein the nanotubes are
randomly entangled with each other were used in previous
research, the CNT promotion effect was remarkable on Cu/Zn/Al
[
2,4], even though it is now accepted that methanol synthesis from
syngas actually proceeds through CO
active and stable catalyst is needed.
The Cu/Zn/Al catalysts for methanol synthesis are agglomerated
nanoparticles [8–10]. The good Cu/Zn dispersion is believed to be a
key factor for a high-performance methanol synthesis catalyst
2
hydrogenation. A highly
[
2,4,11,12]. Most researches are concerned on modifications of
*
Corresponding author. Tel.: +86 10 62784654; fax: +86 10 62772051.
E-mail address: weifei@flotu.org (F. Wei).
0920-5861/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2009.05.018

5
6
Q. Zhang et al. / Catalysis Today 150 (2010) 55–60
catalyst for methanol synthesis [12]. Now, millimeter vertically
aligned CNT arrays were large-scaled produced on ceramic spheres
as-treated CNTs was over 500
into the Na CO solution by high speed shearing in liquid phase.
Furthermore, the solution of Cu(NO O, Zn(NO ꢀ6H O,
ꢀ6H
Al(NO O and ZrOCl with a concentration of 0.6 mol/L were
ꢀ6H
mixed with ratio of 6:3:0.5:0.5, then the mixture was
precipitated with the CNTs/Na CO solution at 80 8C with strong
mm, which can be dispersed easily
2
3
[
23–25]. They are easily to be dispersed into fluffy CNTs by high
3
)
2
2
3
)
2
2
speed shearing [26]. CNTs also showed amazing applications in
catalysis [27–29]. With larger aspect ratio, the CNTs showed better
performance in heat transfer. Till now, the performance of long
3
)
3
2
2
a
2
3
CNTs intercrossed Cu/Zn/Al/Zr catalyst for CO/CO
is still an open question.
2
hydrogenation
stirring for 1.0 h. After filtration and washing, the catalyst was
dried at 120 8C for 12.0 h and calcined at 300 8C for 4.0 h to get the
long CNTs intercrossed Cu/Zn/Al/Zr catalyst (CD703).
Herein, super long CNTs were dispersed into Cu/Zn/Al/Zr
catalyst. The improved catalyst was used for direct CO/CO
hydrogenate into methanol. It was combined with -Al or
HZSM-5 for DME production from CO/CO hydrogenation.
2
As a reference catalyst, the Cu/Zn/Al/Zr catalyst (CD503) with a
ratio Cu:Zn:Al:Zr of 6:3:0.5:0.5 was synthesized by co-precipita-
tion methods [17]. Also a commercial catalyst code named COM
that had been successfully used in many plants in China for
producing methanol from syngas was used. There have been many
generations of commercial catalysts for methanol synthesis, and
this is perhaps the most commonly used industrial catalyst in
China at present [17,31].
g
2 3
O
2
2
. Experimental
The vertically aligned CNT arrays with a length of 5.0 mm were
obtained through a floating catalyst process (Fig. 1a) [30]. They are
with good alignment as shown in Fig. 1b. It was dispersed by high
speed shearing [26] and then mild acid treatment. The length of the
For DME synthesis from CO,
dehydrated catalyst. While for DME synthesis from CO
g
-Al
2
O
3
was used as the methanol
, HZSM-5
2
Fig. 1. (a) Large amount of vertically aligned CNT arrays. (b) SEM images of CNTs in the array with good alignment. (c)–(e) SEM images, (f) TEM image and (g) high-resolution
TEM images of long CNT intercrossed Cu/Zn/Al/Zr catalyst (CD703).

Q. Zhang et al. / Catalysis Today 150 (2010) 55–60
57
with a Si/Al ratio of 39 was used for methanol dehydration. The
bifunctional DME synthesis catalysts were physical mixtures of
methanol synthesis catalyst and dehydrated catalyst with the ratio
of 2.0.
The catalytic reaction on the COM/CD503/CD703 catalyst was
carried out in a fixed bed reactor. The reactor is with a diameter
of 12.0 mm and a length of 500 mm. Before the reaction started,
2 2
the catalyst was reduced with a 5% H /95% N mixture at
atmospheric pressure by raising the temperature slowly to the
reaction temperature over 10.0 h. Then the reduction gas was
switched to the reaction gas and the pressure was raised to the
reaction pressure 4.0 MPa to start the reaction. The space
velocity was 6000 mL/(gcat h). The first sample of the effluent
was taken 2.0 h after steady reaction conditions were estab-
lished, and then samples were taken every 30 min for online
analysis of the effluent composition. The reaction temperature
was controlled by furnace heating device and the pressure was
controlled by the feeding rate. For CO hydrogenation into
Fig. 2. XRD patterns of COM, CD503 and CD703 catalyst.
methanol, the ratio of H
the temperature was 230 8C. For CO
methanol, the ratio of H to CO was 3.0, the temperature
was 240 8C. DME can be obtained from CO hydrogenation using
CD703 combined with -Al catalyst, the ratio of H to CO was
.0. DME synthesis can also be synthesized from CO hydro-
genation using CD703 combined with HZSM-5 catalyst. The ratio
of H to CO was 3.0, the pressure was 5.0 MPa.
2
to CO (5% CO
2
was included) was 2.0,
2
hydrogenation into
2
2
long CNTs were interwoven into a 3D network in the catalyst
agglomerates. The long CNTs were coated by the Cu/Zn/Al/Zr
catalyst, and a necklace-like hybrid structure was shown in Fig. 1c.
The size of Cu/Zn/Al/Zr agglomerates was just 300–600 nm in
diameter. As shown in Fig. 1d and e, the Cu/Zn/Al/Zr nanoparticles
were dispersed among CNTs networks. As can been seen in TEM
images of CD703 catalyst (Fig. 1f and g), although some large Cu/
Zn/Al/Zr agglomerates are formed on the CNT network during
sonication process, a majority of catalyst particles distributed
along CNTs possessed a size of 12–16 nm. The reference catalysts
are nanoparticle agglomerates, the morphology of which can be
found in Supplementary material. The XRD patterns of COM,
CD503, CD703 catalysts were shown in Fig. 2. The CD703 pattern
showed low signal–noise ratio and weak peak intensity. CuO peak
and MWCNT peak can be detected. The weak peaks in CD503 XRD
pattern are assigned to CuO. For COM catalyst, the peak patterns
were assigned to CuO and ZnO with good crystalline. The high peak
intensity of COM catalyst was high and small half-peak width
indicated the relatively large crystalline size of CuO and ZnO.
Compared with COM catalyst, the CuZn dispersion in CD703 is
much better [32].
g
2
O
3
2
2
2
2
2
The morphology of the catalyst was characterized by a JSM
401F scanning electron microscope (SEM) operated at 5.0 kV and
7
a JEM 2010 high-resolution transmission electron microscope
TEM) operated at 120.0 kV. The sample for the TEM observation
(
was prepared using a common sonication method. The structure of
the catalyst was identified by the X-ray powder diffractometer
(
XRD, D8-Advance, Bruker, Germany) using Cu K radiation, a fixed
a
power source (40.0 kV, 40.0 mA), and an aligned silicon detector.
The reactor was connected to an online GC 7890II gas
chromatograph with a thermal conductivity detector, and a
Porapak T (5.0 m) column connected in parallel with a TDX-01
2
(3.0 m) column. CO, CO conversion, the space time yields (STYs) of
DME and MeOH, which gave the amounts of DME and MeOH
produced per gram catalyst per second, were defined as follows:
nCO;in ꢁ nCO;out
X
X
CO
¼
(1)
(2)
n
CO;in
3.2. The activity of methanol synthesis from CO/CO
2
hydrogenation
hydrogena-
nCO2;in ꢁ nCO ;out
2
CO2
¼
n
Methanol synthesis was tested from CO or CO
2
2
CO ;in
tion and the typical results were shown in Table 1. On CD503
catalyst, the CO conversion was 0.509, and the STY of
methanol was about 0.877 g/(gcat h). When long CNTs were
added, the CO conversion and STY of methanol increased to
n
DME;out
STYDME
¼
ꢂ SVCO=CO2 ꢂ MDME
nCO=CO2;in
ꢂ 0:001 ðkg=gÞ=22:4 ðL=molÞ=2
(3)
(4)
0
.545 and 0.939, respectively. Compared with CO conversion on
CD503 catalyst and COM catalyst, there was a 7% and 33.5%
increment. For CO hydrogenation, the CO conversion was just
.215 when CD703 catalyst served as catalyst for methanol
synthesis. Compared with CO hydrogenation on CD503 and
COM catalyst, CO conversion was increased by a 4.8% and
n
3
CH OH;out
STYMeOH
¼
ꢂ SVCO=CO2 ꢂ MMeOH
2
2
nCO=CO2;in
0
ꢂ 0:001 ðkg=gÞ=22:4 ðL=molÞ
2
2
where nDME, nCO and nCO were the molar flow rates of DME, CO,
31.2%, respectively.
2
2 2
and CO , respectively; SVCO=CO was the space velocity of CO or CO ;
2
and MDME and MMeOH were the molar mass of DME and MeOH,
respectively.
Table 1
Methanol synthesis from CO or CO
2
hydrogenation on various catalysts.
CO2 hydrogenation
3
. Results and discussion
Catalyst
CO hydrogenation
CO conversion
STY g/(gcat h)
CO
2
conversion
STY g/(gcat h)
3.1. The morphology of CNTs intercrossed Cu/Zn/Al/Zr catalyst
COM
0.408
0.509
0.545
0.707
0.877
0.939
0.163
0.205
0.215
0.151
0.261
0.282
CD503
CD703
After co-precipitation process, a CNT (15 wt%) intercrossed Cu/
Zn/Al/Zr catalyst (CD703) was obtained. As shown in Fig. 1c, the

5
8
Q. Zhang et al. / Catalysis Today 150 (2010) 55–60
3
.3. The activity of DME synthesis from CO/CO
2
hydrogenation
deactivation of CuZn-based catalyst. Cu/Zn particles will cluster
into large particles through Ostwald ripening or migration, and the
activity for methanol synthesis decreases gradually [2,4,7,34,35].
To show the stability of the CNTs intercrossed catalyst, a 160-h test
For DME one-step synthesis from CO/CO
independent stoichiometric reactions, namely,
2
and H
2
, there are four
2 3
for CO hydrogenation on CD703 + g-Al O catalyst with a reaction
ꢃ
ꢃ
ꢃ
ꢃ
Methanol synthesis from CO hydrogenation:
pressure of 5.0 MPa was carried out. As comparison, CD503 with no
CNTs was taken as reference. As shown in Fig. 5, during the initial
OH ꢁ 90:4 kJ molꢁ1
CO þ 2H
2
¼ CH
3
(5)
(6)
(7)
(8)
8.0 h, the CO conversion and DME STY were higher on the CD503
Methanol synthesis from CO
2
hydrogenation:
catalyst than those on CD703 catalyst. However, the deactivated
rate on the CD503 was fast. Then, CO conversion and STY of DME
turn opposite position after 8.0-h reaction. CO conversion
decreased by 5% and 2%; STY of DME decreased by 13% and 2%
on CD503 and CD703 catalyst, respectively. The stability of DME
synthesis on the CD703 catalyst was improved when long CNTs
were added.
ꢁ 49:3 kJ molꢁ1
CO
2
þ 3H
2
¼ CH
3
OH þ H
2
O
Water gas shift reaction:
ꢁ41:0 kJ molꢁ1
CO þ H
2
O ¼ CO
2
þ H
2
DME synthesis from methanol dehydration:
1
2
CH
3
OH ¼ CH
3
OCH
3
þ H
2
O
ꢁ 23:4 kJ molꢁ
2
3.5. The promotion of long CNTs on CO/CO hydrogenation
Cu/Zn-based catalyst served as catalyst in methanol synthesis
process as shown in (5) and (6). DME can be easily obtained by
methanol dehydration with -Al or HZSM-5 as catalyst [33].
Here, we mixed -Al and CD703 catalyst, and tested DME
synthesis from CO hydrogenation. To show the effect of the
addition of CNTs, a CD503 catalyst combined with -Al catalyst
was also tested. Fig. 3 shows curve of the CO conversion, STY of
methanol, and DME vs reaction temperature from CO hydrogena-
tion. The CO conversion and STY of DME increased with higher
temperature. The methanol produced on CD703 exhibited the
highest yield at a temperature of 230 8C. The CO conversion, STY of
methanol and DME all increased when 15 wt% CNTs were added
into the Cu/Zr/Al/Zr catalyst. At low temperature, there were
increases of CO conversion and STY of methanol. When the
reaction temperature became higher, the increment of CO
conversion and methanol STY became smaller.
Long CNTs were added into the Cu/Zn/Al/Zr catalyst for
methanol synthesis. In CD703, with the addition of long CNTs,
as indicated by the XRD pattern as shown in Figs. 1 and 2, a Cu/Zn/
Al/Zr catalyst with high Cu/Zn dispersion was formed with the
contribution of heterogeneous nucleation. Liu et al. reported that
g
2 3
O
g
2 3
O
4
+
g
2
O
3
the Zr dissolved in ZnO crystal caused the formation of positive
ion defects on the surface of Cu–ZnO. These defects can form and
0
+
2+
stabilize more active sites, Cu –Cu –O–Zn , on the catalyst
+
surface by adsorbing Cu [36] and the Cu/Zn dispersion was
thereby improved by Zr doping. Furthermore, there were phase
separation effect originated from the CNT intercrossed Cu/Zn/Al/Zr
particles. As reported by Dong et al., the addition of CNTs can
increase specific surface area, especially Cu surface area of the
catalyst, and CNTs can reversibly adsorb and store a considerably
greater amount of hydrogen [12]. The above mentioned feature
was beneficial for generating microenvironments with high
stationary-state concentration of active hydrogen adspecies on
the surface of the CNT promoted Cu/Zn/Al/Zr catalyst [12]. Here,
the CNTs from arrays with large aspect ratio and good dispersion
were intercrossed among the methanol synthesis catalysts, and the
highly conductive CNTs might promote hydrogen spillover from
the Cu sites to the Cu/Zn interfacial active sites [12]. These
Using CD703 + HZSM-5 catalyst, DME can be obtained from CO
hydrogenation. As shown in Fig. 4, with higher reaction
temperature, the conversion of CO and STY of DME and methanol
simultaneously increased. There was about 1% increment for the
CO conversion during all the temperature range.
2
2
2
3.4. The stability of DME synthesis from CO hydrogenation
characteristics were favorable for increasing the rate of the CO/CO
2
hydrogenation into methanol (Table 1). With faster rate of
methanol production on CD703, DME was also available with
high STY (Figs. 3 and 4).
The stability is a key issue for one step DME synthesis from
syngas. Usually, the sintering was
a main factor for the
2 3
Fig. 3. (a) CO conversion and (b) STY yield of methanol and DME on CD503/CD703 + g-Al O catalyst.

Q. Zhang et al. / Catalysis Today 150 (2010) 55–60
59
Fig. 4. (a) CO
2
conversion and (b) STY yield of methanol and DME on CD503/CD703 + HZSM-5 catalyst.
The stability of the CD703 is another key issue, especially for
DME production. It is an important issue for industrial applica-
tions. When CD703 catalyst used in the fixed bed, it should be
granulated into cylindrical, trefoil or spherical particles. If the
temperature was higher than 400 8C, the Cu/Zn would sinter into
large catalyst particles and the deactivation is irreversible. To
estimate the heat transfer phenomena in a single particle, the heat
transfer in a control volume of the present catalyst can be
described by:
where
l
P
is thermal conductivity of the catalyst,
D
H is the enthalpy
of methanol synthesis. After deduction on the homogeneous
spherical catalyst particles, Eq. (9) can be transformed into:
2
d T 2 dT
DH
l
P
m
þ
¼ C
(10)
dr2 r dr
The boundary condition can be further described by:
dT
r ¼ 0;
¼ 0
(11)
(12)
dr
r ¼ R; T ¼ Ts
ꢀ
ꢁ
2
d
dT
r2
dT
dr
r2drk
4p
ðr þ drÞ
l
P
T þ dr dr ꢁ 4
p
l
P
¼ 4p
v
C
D
H
(9)
dr
Thus, the highest temperature difference in a single particle can
be expressed by:
D
H ꢀ D
e
T ꢁ T
s
¼
ðC
A
ꢁ CAs
Þ
(13)
l
The highest temperature difference is obtained by the
assumption that the concentration was zero in the particles. From
Eq. (13), it is indicated that the temperature rise in the single
particle is inversely proportion to the conductivity of the catalyst.
For CD503, the porous catalyst similar to traditional Cu/Zn/Al
catalyst, the thermal conductivity was about 0.4 W/m K [37]. In
CD703, CNTs were long and woven into a continuous phase. With
previous model by Nan et al. [38,39], the thermal conductivity was
estimated to be 20 W/m K. This was similar to the results obtained
in CNTs/ceramic or CNTs polymer system in the literature [40–42].
With a high thermal conductive supports, the heat produced by the
reaction can be removed quickly and the maximum temperature
e
rise decreased from 50 to 1 8C (in CO hydrogenation with D of
ꢁ
6
2
6
.2 ꢂ 10 m /s [37]) in CD703. Furthermore, the catalyst nano-
particles in CD703 are distributed among CNT network (Fig. 1) and
the sinter of Cu/Zn particles on CD703 was thereby suppressed
compared with COM or CD503 catalyst (Fig. 5). By the design of
hierarchical structure of the catalyst, a high thermal conductive
catalyst with high Cu/Zn dispersion was obtained (Fig. 5), leading
to the relatively high activity and stability in the reaction.
4. Conclusions
By co-precipitation methods, long CNTs from vertically aligned
CNT arrays were dispersed and intercrossed into Cu/Zn/Al/Zr
catalyst (CD703) for methanol/DME production through CO/CO
hydrogenation. The CNTs were coated by Cu/Zn/Al/Zr catalyst
2 3
Fig. 5. Comparison of CD503/CD703 + g-Al O catalyst for CO hydrogenation into
DME.
2

6
0
Q. Zhang et al. / Catalysis Today 150 (2010) 55–60
[
[
10] R.T. Figueiredo, A. Martinez-Arias, M.L. Granados, J.L.G. Fierro, J. Catal. 178 (1998)
46.
11] U.R. Pillai, S. Deevi, Appl. Catal. B: Environ. 65 (2006) 110.
particles. With the effect of phase separation, ion doping and
valence compensation, hydrogen reversibly adsorption and
storage on CNTs promoting hydrogen spillover, the CNT promoted
catalyst showed high performance for methanol synthesis. For CO/
1
[12] X. Dong, H.B. Zhang, G.D. Lin, Y.Z. Yuan, K.R. Tsai, Catal. Lett. 85 (2003) 237.
[
[
[
13] J.P. Shen, C.S. Song, Catal. Today 77 (2001) 89.
14] I. Melian-Cabrera, M.L. Granados, J.L.G. Fierro, J. Catal. 210 (2002) 273.
15] J. Agrell, H. Birgersson, M. Boutonnet, I. Melian-Cabrera, R.M. Navarro, J.L.G. Fierro,
J. Catal. 219 (2003) 389.
CO
.94 and 0.28 g/(gcat h), with an increment of 7% and 8% compared
to Cu/Zn/Al/Zr catalyst without CNTs (CD503). When CD 703 was
combined with -Al catalyst and HZSM-5, DME was obtained
with a STY of 0.90 and 0.077 g/(gcat h) at 270 8C from one step CO
hydrogenation and CO hydrogenation. Meanwhile, the thermal
2
hydrogenation, the STY of methanol on CD703 increased to
0
[16] R.Q. Yang, X.C. Yu, Y. Zhang, W.Z. Li, N. Tsubaki, Fuel 87 (2006) 443.
[
[
[
17] X. An, J.L. Li, Y.Z. Zuo, Q. Zhang, D.Z. Wang, J.F. Wang, Catal. Lett. 118 (2007) 264.
18] R.S. Ruoff, D.C. Lorents, Carbon 33 (1995) 925.
19] S. Berber, Y.K. Kwon, D. Tomanek, Phys. Rev. Lett. 84 (2000) 4613.
g
2 3
O
[20] H. Huang, C.H. Liu, Y. Wu, S.S. Fan, Adv. Mater. 17 (2005) 1652.
2
[
[
[
21] C.H. Liu, H. Huang, Y. Wu, S.S. Fan, Appl. Phys. Lett. 84 (2004) 4248.
22] B.S. Shen, X.M. Wu, H.B. Zhang, G.D. Lin, X. Dong, Acta Chim. Sin. 62 (2004) 1721.
23] Q. Zhang, J.Q. Huang, M.Q. Zhao, W.Z. Qian, Y. Wang, F. Wei, Carbon 46 (2008)
1152.
conductivity increased from 0.4 to 20 W/m K, and thus the hot spot
in the catalyst was eliminated, preventing the catalyst from
deactivation. The long CNT was an extraordinary promoter when it
was intercrossed into Cu/Zn/Al/Zr catalyst for methanol synthesis.
[
[
[
[
[
24] Q. Zhang, J.Q. Huang, F. Wei, G.H. Xu, Y. Wang, W.Z. Qian, D.Z. Wang, Chin. Sci. Bull.
52 (2007) 2896.
25] R. Xiang, G. Luo, W. Qian, Y. Wang, F. Wei, Q. Li, Chem. Vapor Depos. 13 (2007)
Acknowledgements
533.
26] Q. Zhang, G.H. Xu, J.Q. Huang, W.P. Zhou, M.Q. Zhao, Y. Wang, W.Z. Qian, F. Wei,
Carbon 47 (2009) 538.
27] X.L. Pan, Z.L. Fan, W. Chen, Y.J. Ding, H.Y. Luo, X.H. Bao, Nat. Mater. 6 (2007)
507.
The work was supported by the Foundation for Natural
Scientific Foundation of China (Nos. 20736004 and 20736007),
China National program (No. 2006CB932702). We thank Dr. Xin
An, Jia-Qi Huang, and Guang-Hui Xu for the helpful discussion.
28] D.S. Su, X.W. Chen, X. Liu, J.J. Delgado, R. Schlogl, A. Gajovic, Adv. Mater. 20 (2008)
3597.
[
[
29] J. Zhang, X. Liu, R. Blume, A.H. Zhang, R. Schlogl, D.S. Su, Science 322 (2008) 73.
30] Q. Zhang, W.P. Zhou, W.Z. Qian, R. Xiang, J.Q. Huang, D.Z. Wang, F. Wei, J. Phys.
Chem. C 111 (2007) 14638.
31] S.M. Zhao, S.Z. Chen, F.S. Hu, Ind. Catal. 11 (2003) 26.
32] Y.Z. Zuo, X. An, M.H. Han, J.F. Wang, D.Z. Wang, Y. Jin, Chin. J. Catal. 29 (2008)
1266.
Appendix A. Supplementary data
[
[
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.cattod.2009.05.018.
[
[
33] X. An, Y.Z. Zuo, Q. Zhang, D.Z. Wang, J.F. Wang, Ind. Eng. Chem. Res. 47 (2008)
6547.
34] H.H. Kung, Catal. Today 11 (1992) 443.
References
[35] A.T. Aguayo, J. Erena, I. Sierra, M. Olazar, J. Bilbao, Catal. Today 106 (2005) 265.
[36] R.C. Liu, Y.Q. Yang, Y.Z. Yuan, Z.Y. Lin, C. Li, H. Yuang, Q. Wang, H.B. Zhang, J. Nat.
[
[
[
[
[
[
[
[
[
1] G.H. Graaf, E.J. Stamhuis, A. Beenackers, Chem. Eng. Sci. 43 (1988) 3185.
2] A.Y. Rozovskii, G.I. Lin, Top. Catal. 22 (2003) 137.
3] J.P. Lange, Catal. Today 64 (1999) 3.
4] X.M. Liu, G.Q. Lu, Z.F. Yan, J. Beltramini, Ind. Eng. Chem. Res. 42 (2003) 6518.
5] C. Busetto, G. Delpiero, G. Manara, F. Trifiro, A. Vaccari, J. Catal. 85 (1984) 260.
6] X. An, F. Ren, J.L. Li, J.F. Wang, Chin. J. Catal. 26 (2005) 729.
7] J.P. Lange, Catal. Today 64 (2001) 3.
8] J.L. Li, X.G. Zhang, T. Inui, Appl. Catal. A: Gen. 147 (1996) 23.
9] J.T. Li, W.D. Zhang, L.Z. Gao, P.Y. Gu, K.Q. Sha, H.L. Wan, Appl. Catal. A: Gen. 165
Gas Chem. 10 (2001) 308.
[37] G.H. Graaf, H. Scholtens, E.J. Stamhuis, A. Beenackers, Chem. Eng. Sci. 45 (1990)
773.
[38] F. Deng, Q.S. Zheng, L.F. Wang, C.W. Nan, Appl. Phys. Lett. 90 (2007) 021914.
[39] C.W. Nan, Z. Shi, Y. Lin, Chem. Phys. Lett. 375 (2003) 666.
[40] Y.A. Kim, S. Kamio, T. Tajiri, T. Hayashi, S.M. Song, M. Endo, M. Terrones, M.S.
Dresselhaus, Appl. Phys. Lett. 90 (2007) 093125.
[41] L. Kumari, T. Zhang, G.H. Du, W.Z. Li, Q.W. Wang, A. Datye, K.H. Wu, Compos. Sci.
Technol. 68 (2008) 2178.
(1997) 411.
[42] X. Liu, Y. Zhang, A.M. Cassell, B.A. Cruden, J. Appl. Phys. 104 (2008) 084310.