Promoting effect of a Cu-Zn binary precursor on a ternary Cu-Zn-Al catalyst for methanol synthesis from synthesis gas

Article abstract of DOI:10.1039/c4ra01583e

Small amounts of Cu-Zn binary precursor were introduced into traditional ternary Cu-Zn-Al catalysts to produce a series of modified ternary Cu-Zn-Al catalysts for the synthesis of methanol from synthesis gas with high CO content. 2 wt% Cu-Zn (Cu-Zn = 3 : 1 atomic ratio) binary precursor was found to have the most significant improvement for the catalytic performances. Physicochemical characterization of the as-prepared catalysts by TPR, in situ XRD and in situ XAES techniques indicated that the addition of a suitable amount of binary Cu-Zn precursor partially modified the structure of the catalyst, changed the particle size of Cu, copper surface area and the ratio of Cu⁺/Cu ⁰, and thus effectively improved the catalytic performances of the catalyst.

Full text of DOI:10.1039/c4ra01583e

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Promoting effect of a Cu–Zn binary precursor on a
ternary Cu–Zn–Al catalyst for methanol synthesis
from synthesis gas
Cite this: RSC Adv., 2014, 4, 30677
a
b
b
c
c
b
Wen Ding, Yingwei Liu, Fang Wang, Shuailing Zhou, Aiping Chen, Yiquan Yang
and Weiping Fang*a
Small amounts of Cu–Zn binary precursor were introduced into traditional ternary Cu–Zn–Al catalysts to
produce a series of modified ternary Cu–Zn–Al catalysts for the synthesis of methanol from synthesis
gas with high CO content. 2 wt% Cu–Zn (Cu–Zn ¼ 3 : 1 atomic ratio) binary precursor was found to
have the most significant improvement for the catalytic performances. Physicochemical characterization
of the as-prepared catalysts by TPR, in situ XRD and in situ XAES techniques indicated that the addition
of a suitable amount of binary Cu–Zn precursor partially modified the structure of the catalyst, changed
Received 23rd February 2014
Accepted 19th June 2014
DOI: 10.1039/c4ra01583e
+
0
the particle size of Cu, copper surface area and the ratio of Cu /Cu , and thus effectively improved the
www.rsc.org/advances
catalytic performances of the catalyst.
atomic ratios for methanol synthesis from synthesis gas was
1
. Introduction
investigated in this paper. The active site, the relationship
+
Methanol is a common chemical feedstock for the production between catalytic activity and the ratio of Cu /CuO were studied
of several important chemicals such as acetic acid, formalde- in detail.
1,2
hyde, and chloromethane. At present, methanol is produced
by the reaction of CO with H over a copper-based catalyst
2
2
. Experiment
(CuO–ZnO–Al
2 3
O ).
2.1 Catalyst preparation
The catalytic activity of ternary Cu–Zn–Al catalyst for meth-
3
–5
anol synthesis from syngas has achieved a high level to date.
Ternary Cu–Zn–Al catalyst precursor was prepared by reverse
1
5,16
One motivation for the ongoing research is to pursue higher precipitation method.
Firstly, a mixed solution of copper
6
–8
ꢀ1
ꢀ1
performance of the catalyst. It is widely accepted that the nitrate (1 mol l ) and zinc nitrate (1 mol l ) (volume ratio is
presence of residual precursor rosasite phase could improve the 3 : 1) was rapidly added to a solution of sodium carbonate
9–11
ꢀ1
activity of the traditional ternary catalyst.
(1 mol l ) under vigorous stirring at 343 K, then the pH was
12
13
Plyasova and Tamara et al. supposed that the presence of adjusted to 7.0–7.5. The precipitate suspension obtained was
residual carbonate in the calcined catalysts can contribute to aged at 348 K for 60 min under gentle stirring. At the same time,
14
the formation of the copper sub-oxide species. Bart et al. found aluminum emulsion prepared in advance was added to the Cu–
that the residual hydroxyl carbonates presumably facilitate the Zn precipitate suspension under stirring. Aer washing and
formation of highly active sites during reduction. However, the ltration six times, the content of Na is less than 0.1 wt&. The
research on developing a highly efficient catalyst for methanol precipitate obtained was dried at 383 K for 2 h, and then
synthesis by adding Cu–Zn binary precursor into traditional calcined at 603 K for 2 h. The composition of the ternary Cu–Zn–
ternary Cu–Zn–Al catalyst system has not been reported in Al catalyst is Cu : Zn : Al ¼ 6.75 : 2.25 : 1 in atomic ratio. The
literatures.
ternary Cu–Zn–Al sample thus prepared was molded into tablet,
The performance of a series of Cu–Zn–Al catalysts modied and then crushed into fragments, followed by screening and
with different amount of Cu–Zn precursors in different Cu–Zn collecting the particles with sizes of 40–60 mesh. The sample
0
obtained was named as Cat .
Binary Cu–Zn precursors, i.e. the mixing basic carbonate of
copper and zinc, with Cu–Zn ratio of 1 : 1, 1 : 3, 3 : 1 and 4 : 1
a
Department of Chemical and Biochemical Engineering, College of Chemistry and
Chemical Engineering, Xiamen University, Xiamen, 361005, PR China. E-mail:
wpfang@xmu.edu.cn
b
(atomic ratio) were also prepared by the reverse precipitation
Department of Chemistry, College of Chemistry and Chemical Engineering, and
ꢀ1
method. Firstly, a mixed solution of copper nitrate (1 mol l
)
National Engineering Laboratory for Green Chemical Productions of Alcohols, Ethers
ꢀ
1
and zinc nitrate (1 mol l ) (volume ratio is 1 : 1, 1 : 3, 3 : 1 and
4 : 1, respectively) was rapidly added to a solution of sodium
and Esters, Xiamen University, Xiamen, 361005, PR China
c
DaTang International Chemical Technology Research Institute Co., LTD, Beijing,
ꢀ
1
1
00070, PR China
carbonate (1 mol l ) under vigorous stirring at 343 K, the pH
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was adjusted to 7.0–7.5. The precipitate suspension generated patterns were recorded at 298, 403, 473 and 503 K, respectively,
was aged at 348 K for 60 min under gentle stirring; then the and identied according to the JCPDS data base. According to
aged precipitate suspension was washed, ltered and dried at full width at half maximum (FWHM) of Cu diffraction at 2q ¼
383 K for 2 h.
42.3, Cu average particle size was calculated from the line-
Modied ternary Cu–Zn–Al catalysts with 2 wt%, 4 wt%, 6 broading of the XRD peaks using the Scherrer equation:
wt% binary precursor (Cu–Zn atomic ratio ¼ 3 : 1) were
prepared as follows: 0.1 g, 0.2 g, 0.3 g uncalcined binary Cu–Zn
precursors (Cu–Zn atomic ratio ¼ 3 : 1) was respectively mixed
with three portions of calcined ternary Cu–Zn–Al catalyst of 5 g
each to produce three modied mixed samples, which then
were ground for 20 minutes to make them mixing evenly. The
as-prepared catalysts were named as Cat , Cat and Cat6,
d ¼ kl/(FW cos(q))
where, k is a constant generally taken as unity, l is the wave-
length of the incident radiation, FW is the full width at half
max, and q is the peak position.
Normal XRD measurements were also performed on a Pan-
alytical X'pert PRO X-ray diffractometer utilizing mono-
chromatic Cu ka radiation and in the 2q scanning range from
0 to 80 , scanning step length of 0.0167 .
The BET surface area of the catalyst was measured on the
auto Physical Chemistry adsorption test apparatus Micro-
meritics Tristar 3000, using nitrogen as adsorbate, the
isotherms were recorded at 77 K. Before each measurement, the
samples were treated under vacuum at 573 K for 3 h.
2
4
respectively. Another set of catalysts Cat1/1, Cat1/3 and Cat4/1 was
prepared under the same conditions as that Cat was prepared,
only the binary Cu–Zn precursors with Cu–Zn ¼ 1 : 1, 1 : 3, and
: 1 (atomic ratio) were used, respectively. The as-prepared
2
ꢂ
ꢂ
ꢂ
1
4
catalysts were denoted as Cat1/1, Cat1/3, Cat4/1, respectively.
Obviously, the Cat sample can also be named as Cat3/1.
2
A kind of commercial catalyst (made and used in china) was
also tested for comparison, which is named as Cat307
.
0
The specic surface area (SCu) of copper (Cu ) on the cata-
lysts was measured by dissociative chemisorption of nitrous
2.2 Catalyst activity test
17,18
oxide (N
2
O-RFC) described in the literatures.
The experi-
The activity test of the as-prepared catalysts was conducted in a
stainless steel tubular ow xed-bed reactor, in which 0.5 ml of
the catalyst was lled. The composition of the feed was
ments were performed in a quartz micro reactor at 303 K to
avoid subsurface oxidation. Prior to each experiment the
15
catalysts were reduced in a mixed gas of 5 vol% H
23 K. Subsequently, the reactor was purged for 1 h with He,
then cooled down to ambient temperature. The measurement
was started by switching pure He to a mixed gas of 5 vol% N
in He, in such a way that surface Cu atoms were completely
oxidized according to the reaction Cu + N . The
2
in nitrogen at
CO : H
2
: CO
2
: N
2
(volume ratio) ¼ 14 : 76 : 5 : 5. The reaction
5
conditions were 5.0 Mpa, 498 K, and the space velocity of
ꢀ
1
1
0 000 h . The activity of the catalyst measured at 498 K is
called the original activity, which was expressed by the space-
time yield (STY) before thermal treating (Y ). The catalyst aer
reaction at 498 K was heated up to 673 K and kept it at 673 K for
h under the atmosphere of synthesis gas, then the reaction
2
O
i
O ¼ CuO + N
2
2
amount of nitrogen formed was quantied by gas chromato-
5
graph technique. The Cu surface area was calculated assuming
1
9
temperature was decreased to 498 K for reacting again, the as-
measured activity of the catalyst is called stable activity, which
was expressed by the space-time yield activity aer thermal
a molar stoichiometry of Cu/N
2
¼ 2 and a value of 1.47 ꢃ 10
copper atoms per square meter. The error in the Cu surface area
data was estimated to be less than 10%.
y y
treating (Y ), generally, Y is used to indicate the thermal
TPR characterization was performed in a stainless steel tube
reactor lled with 15 mg catalyst by using a gas mixture of 5
stability of the catalyst. The effluent gas was monitored by an
online gas chromatograph (GC950) equipped with a ame
ionization detector (FID)(GDX103 column of 2 m in length) for
methanol, methyl ether and methane analysis; and a thermal
conductivity detector (TCD) (carbon zeolite column with 1 m in
vol% H
2
in nitrogen as a carrier gas at a ow rate of 20 ml
ꢀ
1
ꢀ1
min . The heating rate was controlled at 10 K min . The
hydrogen uptake was continuously monitored using a mass-
spectrometry (MS) during the reduction.
length) for CO, CO
2
and N
2
analysis. The space-time yield (STY,
Auger electron spectroscopy (AES) experiments were carried
out by using a PHI-610 scanning Auger microprobe. A coaxial
electron gun with a single pass and 0.3% of the energy resolu-
tion selection of cylindrical mirror analyzer (CMA) was
employed. The primary electron beam energy of 3 keV and the
emission current of 0.1 mA were selected. The samples were
ꢀ
1
ꢀ1
g mlcat
h ) was dened as the mass of products per volume of
the catalyst per hour. All the activity data for methanol synthesis
are the average with error bar ꢁ3%.
2.3 Catalyst characterization
reduced by a gas mixture of 5 vol% H in nitrogen, and pro-
2
The in situ XRD experiments were performed on a Panalytical
X'pert PRO X-ray diffractometer utilizing monochromatic Cu ka
tected by N
2
, and then the glass tubes were sealed. All the
ꢂ
ꢂ
operations were carried out in a glove box.
radiation and in the 2q scanning range from 10 to 80 , scan-
ꢂ
ning step length of 0.0167 . The experiment conditions were
2 2
under reducing atmosphere (5%H /95%N ), ow rate of 15 ml
min , heating rate of 10 K min , and in the temperature range
from 298 to 503 K. The experiments were conducted for 2 h at
3
. Results and discussion
ꢀ
1
ꢀ1
3.1 Catalytic activity and stability
the temperatures of 298, 403, 473 and 503 K, respectively. Aer The activity data of the catalysts are shown in Table 1, in which
0 min when the preset temperatures reached, the diffraction BET surface area and pore sizes of the catalysts are also
3
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a
Table 1 Activities and BET data of different catalysts
STY of methanol
ꢀ
1
ꢀ1
(g mlcat
h )
BET surface area
Cu surface area
(m per g Cu)
Pore width
(nm)
CO conv.
(%)
Particle size
(nm) Cu
2
ꢀ1
2
Catalysts
Cat307
(m g
)
Y
i
Y
y
108
110
101
99
96
95
91
101
93
31.5
29.8
36.8
34.5
32.8
30.4
29.5
36.8
31.0
7.2
6.8
7.4
7.6
7.8
7.2
7.0
7.4
6.8
74.4
72.5
77.8
72.1
71.4
70.6
73.2
77.8
72.2
1.83
1.76
1.96
1.85
1.80
1.75
1.91
1.96
1.88
1.56
1.55
1.65
1.60
1.57
1.60
1.65
1.65
1.60
4.0
4.0
3.5
4.2
4.1
3.9
4.5
3.5
3.7
Cat
Cat
Cat
Cat
0
2
4
6
Cat1/3
Cat1/1
Cat3/1 (Cat
Cat4/1
2
)
a
ꢀ1
Reaction conditions: 5.0 MPa, 10 000 h , V(CO) : V(H2) : V(CO2) : V(N2) ¼ 15 : 75 : 5 : 5, 498 K.
presented. In Table 1, the activity sequence of the catalysts Cat
Cat and Cat is found to be Cat > Cat > Cat . Obviously, the industrial application. Catalytic activity as a function of reaction
activity of modied ternary Cu–Zn–Al catalysts with binary Cu– time for the Cat and Cat catalysts is displayed in Fig. 1. It can
Zn precursor was decrease with increasing in the percentage of be seen from Fig. 1 that both Cat and Cat exhibited very stable
2
,
The long-term stability and activity of the catalyst is vital for
4
6
2
4
6
2
0
0
2
the binary Cu–Zn precursor doped. In comparison with activity at 493 K during 500 h reaction. However, aer 200 h
unmodied ternary Cu–Zn–Al catalyst Cat , all the modied reaction, the space-time yield (STY) of methanol over Cat was
0
2
ternary Cu–Zn–Al catalysts exhibit higher Y
sequence of the catalysts Cat1/1, Cat1/3, Cat3/1 (Cat
Cat3/1 (Cat ) > Cat1/1 > Cat4/1 > Cat1/3. Obviously, Cat
i
and Y
y
. The activity found to be higher than that over Cat
) and Cat4/1 is is relatively small, indicating that the Cat
0
, although, the difference
2
2
catalyst is more
2
2
(Cat3/1 promising one for use to catalyze the synthesis of methanol
)
exhibits more excellent catalytic performance for the reaction. from synthesis gas.
The space-time yields (STY) of methanol before and aer
ꢀ
1
ꢀ1
thermal treating for Cat are found to be 1.96 g ml
h
and
2
cat
3.2 Pore distribution
ꢀ1
ꢀ1
1.65 g mlcat
h , higher than those of the commercial catalyst
Cat307 by about 7.1% (Y ) and 5.7% (Y ), and higher than those
0
Fig. 2 illustrates the pore size distribution of the catalysts Cat ,
i
y
2 4 6
Cat307, Cat , Cat and Cat . The pore size distribution of all the
over the catalyst Cat
0
i y
by about 11.4% (Y ) and 6.4% (Y ),
catalysts ranges from 2 to 15 nm, suggesting that all the cata-
lysts possess typical mesoporous structure.
shows that the pores of the sample Cat enlarged due to the
addition of the binary Cu–Zn precursor.
respectively. Under the conditions of 5.0 MPa and 493 K, the
binary precursor-modied catalyst Cat shows the highest CO
conversion of 77.8%, being higher than the commercial catalyst
307 by about 4.6% and the traditional catalyst Cat by about
.3%. The addition of suitable amount of binary precursor
19–21
This gure also
2
2
C
5
(
0
0 2
The different pore distributions of Cat and Cat may depend
on the fact that the added material blocked smaller pores with
the sizes ranging from 2 to 6 nm in the catalysts, while the pore
enlargement is caused by the decomposition of the binary
precursors.
2 wt%) and suitable Cu–Zn ratio (Cu–Zn ¼ 3 : 1) of binary
precursor can modulate the surface structure of the Cu–Zn–Al
Catalyst. Our experiment results show that the copper surface
area increased at rst then decrease with increasing the amount
10
of the binary precursor (Cu–Zn ¼ 3 : 1). Baltes et al. believed
3.3 XRD characterization
that the presence of carbonate residues presumably delayed the
fragmentation of the catalyst structure before the reduction of Fig. 3 shows the in situ XRD patterns arising from the samples of
the copper species began. As a result, smaller copper particles pure ternary precursor, and the Cat , Cat , Cat catalysts. The
2
0
307
ꢂ
were formed. Further more, higher copper surface area was peak at 2q ¼ 34.2 is assigned to aurichalcite phase (Cu,
ꢂ
found in Cat . The role of the binary precursor was found to be Zn) (CO ) (OH) . The peak at 2q ¼ 35.4 is ascribed to rosasite
2
5
3 2
6
ꢂ
similar as that the carbonate residues play. It could be assumed phase (Cu, Zn)
2
CO
3
(OH)
CO
2
. The peak at 2q ¼ 31.8 belongs to
that the main function of suitable amount of binary precursor (2 malachite phase Cu
2
3
(OH)
6
. The peaks at 2q ¼ 43.1, 50.1,
ꢂ
wt%) is to stabilize active sites by attenuating the agglomeration 73.9 are assigned to metal Cu.
of Cu particles. It can be found from Table 1 that Cat
2
(Cu–Zn ¼
2
The in situ XRD patterns arising from Cat and the binary Cu–
3
: 1) had the smallest particles size of Cu and highest Cu Zn precursor (Cu–Zn ¼ 3 : 1 atomic ratio) are shown in Fig. 4(A)
surface area. Table 1 also shows the total BET surface areas and and (B), respectively. It can be found that the crystal of rosasite
copper surface areas of the catalysts. The BET surface area of still exists in both samples at 503 K; and that for the ternary Cu–
Cat2 exhibits a little smaller than those of Cat307 and Cat0. Zn–Al precursor the peak due to Cu appear at 473 K. The rosasite
Meanwhile, the pore size of Cat
and Cat
2
is larger than those of Cat307 crystal phase didn't completely decompose during the reduction
process. According to the XRD results, the non decomposed
0
.
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0 2
Fig. 1 Catalytic performance of Cat (A) and Cat (B) as a function time.
ꢂ
aurichalcite phase ((Cu, Zn)
3
5
(CO
3
)
2
(OH)
6
); the peaks at 2q ¼ 18.9 ,
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
1.7 , 32.6 , 35.4 , 42.2 , 47.6 , 58.3 , 62.8 are ascribed to mal-
ꢂ
ꢂ
ꢂ
achite phase (Cu
4
2
CO
3
(OH)
2
); the peaks at 2q ¼ 14.7 , 17.3 , 29.6 ,
ꢂ ꢂ
3.9 , 48.6 belong to rosasite phase ((Cu, Zn) CO (OH) ).
2 3 2
22–25
ꢂ
From Fig. 5 we can see that the peak at 2q ¼ 13.0 is the strongest
ꢂ
one, which can be ascribed to aurichalcite; the peaks at 2q ¼ 17.3
ꢂ
and 31.7 are strong peaks, which are specic to rosasite and
malachite, respectively. There is no rosasite phase in binary
precursor of Cu–Zn ¼ 1 : 1 and Cu–Zn ¼ 1 : 3 in Fig. 5. These
results conrm that more rosasite phase in catalyst precursors
26–30
can promote the activity of the catalyst.
That is because the
sosoloid of CuO and ZnO generated by decomposition of rosasite
phase is the main active phase of the catalyst. The Cu–Zn ratio will
majorly inuence the content of rosasite phase. The higher the
copper ratio, the more the rosasite phase in the binary precursors.
Fig. 2 Pore distributions of the catalysts Cat
Cat
0 2 4
, Cat307, Cat , Cat and
6
.
3.4 TPR
TPR proles of all the samples are shown in Fig. 6. It can be seen
from Fig. 6 that each of the catalysts has one TPR peak, which
occurs at 485 K for Cat
0
2
and at 491 K for Cat . The higher
reduction temperature of Cat
2
illustrates that there may be some
31
specic type of CuO strongly interacting with ZnO lattice. The
original TPR prole can be deconvoluted into two peaks, i.e. a
low temperature reduction peak and a high temperature
reduction peak. These two reduction peaks can be ascribed to
the reduction of dispersed and isolated copper oxides on the
3
2,33
Fig. 3 In situ XRD patterns of binary precursor, Cat
03 K.
0
, Cat
2
and Cat307 at surface of alumina and bulk ZnO, respectively.
Herman
5
30
+
et al. reported that Cu ion dissolved in ZnO matrix is active
site of the catalyst for methanol synthesis. It was also believed
+
that the solid solution of Cu /ZnO has an important promoting
rosasite crystal phase could suppress the aggregation of metal
Cu, leading to the improvement of the stability of the catalyst.
Fig. 5 shows the XRD patterns arising from binary Cu–Zn
precursors with different Cu–Zn ratios. There mainly exit three
crystal phases in the precursors of the four catalysts. The peaks at
effect on the catalytic activity and the intermediate products
+
bonded with Cu are hydroxyl, formate, formyl and methoxy
22
8
0
d+
species. Arena et al. proposed that the “mix” of Cu , Cu and
oxide basic sites concurred to cause the adsorption/activation of
H , CO and CO . Our experiment results indicate that the suit-
2 2
able amount (2 wt%) of binary precursor (Cu–Zn ¼ 3 : 1) may
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
2q ¼ 13.0 , 24.1 , 27.9 , 34.2 , 38.4 , 41.9 , 50.1 are assigned to
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Fig. 4 In situ XRD patterns due to the Cat
2
and binary precursor sample (Cu–Zn ¼ 3 : 1) at different reducing temperatures.
Fig. 5 XRD patterns of the different Cu–Zn binary precursors. (a)
Cu : Zn ¼ 1 : 1 (b) Cu : Zn ¼ 1 : 3 (c) Cu : Zn ¼ 3 : 1 (d) Cu : Zn ¼ 4 : 1.
Fig. 7 XAES spectra of Cu LMM for reduced catalysts.
0
+
3
2
change the ratio of Cu to Cu and strengthen the interaction of 914–920.6 eV are deconvoluted into two peaks; the one at
+
+
Cu and ZnO, which is conrmed to be responsible for the about 916.2 eV is attributed to Cu , and the other at about
improvement of the activity.
0
918.4 eV is ascribed to Cu .
+
+
0
Table 2 shows the relative atomic ratios of Cu to (Cu + Cu )
which are calculated from the relative areas of Cu and Cu .
+
0
3
.5 In situ XAES
Fig. 7 shows Cu LMM XAES spectra of the samples Cat
Cat and Cat . The original spectra arising from the catalysts at
When the amount of binary precursor (Cu–Zn ¼ 3 : 1) is 2 wt%,
+
+
0
the Cu to (Cu + Cu ) ratio of the catalyst is the highest. Some
researchers believed that the activity of the catalyst for
0
2
, Cat ,
4
6
Fig. 6
2
H -TPR profiles of all the samples.
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Table 2 Surface Cu component of reduced catalysts based on Cu
LMM deconvolution
8 F. Arena, G. Italiano, K. Barbera, S. Bordiga, G. Bonura and
L. Spadaro, Appl. Catal., A, 2008, 350, 16–23.
a
b
ꢀ1
9 J. Toyir, P. R. Piscina, J. Llorca, J. R. Fierro and N. Homs,
Phys. Chem. Chem. Phys., 2001, 3, 4837–4845.
K. E. /eV
A. P. /eV
B. E. of Cu
2p3/2/eV
+
0
+
0
cu+c/% 10 C. Baltes, S. Vukojevic and F. Schuth, J. Catal., 2008, 258,
Catalyst
Cu
Cu
Cu
Cu
X
3
34–345.
Cat
Cat
Cat
Cat
0
2
4
6
916.3
916.4
916.3
916.4
918.4
918.4
918.4
918.3
1890.0
1848.9
1890.0
1848.9
1851.1
1851.0
1851.1
1851.1
932.7
932.7
932.7
932.7
25.4
36.2
27.5
26.3
1
1 W. Q. Xia, H. D. Tang, S. D. Lin, Y. Q. Cen and H. Z. Liu, Chin.
J. Catal., 2009, 30, 879–883.
12 L. M. Plyasova, T. M. Yur'eva, T. A. Kriger, O. V. Makarova,
a
b
c
+
+
V. A. Zaikovskii, L. P. Soloveva, et al., Kinet. Catal., 1995,
Kinetic energy. Auger parameter. Intensity ratio of Cu to (Cu
+
0
36, 425–443.
Cu ) by deconvolution of Cu LMM XAES spectra.
13 M. Y. Tamara, M. P. Lyudmila, I. Z. Vladimir, P. M. Tatyana,
B. Alfred and C. Johannes, Phys. Chem. Chem. Phys., 2004, 6,
4522–4534.
methanol synthesis is related linearly to the copper surface area; 14 J. C. J. Bart and R. P. A. Sneeden, Catal. Today, 1987, 2,
3
3
and the metallic copper is the active species. The others
1–14.
+
insisted that the amount of Cu determined the methanol 15 F. Wang, Y. Liu, Y. Gan, W. Ding, W. Fang and Y. Yang, Fuel
In addition, it was claimed by Jones' group
that both Cu and Cu species are essential for methanol 16 L. Wang, L. Yang, Y. Zhang, W. Ding, S. Chen, W. Fang and
formation and the ratio of Cu /Cu determines the specic
activity. We propose that Cu /Cu ratio is crucial for catalytic 17 C. Yang and Z. Y. Ma, Catal. Today, 2006, 116, 222–
34,35
synthesis activity.
Process. Technol., 2013, 110, 190–221.
+
0
+
0
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30682 | RSC Adv., 2014, 4, 30677–30682
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