Highly active CuZn/SBA-15 catalyst for methanol dehydrogenation to methyl formate: Influence of ZnO promoter

Article abstract of DOI:10.1016/j.mcat.2021.111514

Stable and efficient Cu/SBA-15 and xCuZn/SBA-15 (x = 5, 10 and 15) in methanol dehydrogenation to methyl formate (MF) are prepared through a double-solvent impregnation (DI) method. Among all catalysts, 10CuZn/SBA-15 shows the highest catalytic performance with selectivity to MF about 88.1 % and methanol conversion of 31.1 %, which is attributed to the well-dispersed Cu particles and high ratio of Cu°/(Cu° + Cu⁺). The proper amount of ZnO could improve dispersion of Cu because of its geometrical spacer, inhibiting growth of Cu particle, and the best dispersion is achieved in 10CuZn/SBA-15. Furthermore, the Cu°/(Cu° + Cu⁺) ratio is greatly promoted with the assistance of ZnO, attributed to Cu-ZnO interaction, which reaches maxima of 53.3 % at a Cu/Zn mole ratio of 10. Specially, the optimized catalyst shows evident suitability at high temperature for methanol dehydrogenation reactions along with high level of conversion and selectivity for 100 h. Overall, our findings reveal that modification by the appropriate amount of ZnO in Cu-based catalyst has a positive impact on obtaining MF for the methanol dehydrogenation.

Full text of DOI:10.1016/j.mcat.2021.111514

Molecular Catalysis 505 (2021) 111514
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.journals.elsevier.com/molecular-catalysis
Highly active CuZn/SBA-15 catalyst for methanol dehydrogenation to
methyl formate: Influence of ZnO promoter
,
,
,
,
,b,
Na Wanga b, Yanhong Quana b, Jinxian Zhaoa b, Haixia Lia b, Jun Rena
*
a State Key Laboratory of Clean and Efficient Coal Utilization, Taiyuan University of Technology,Taiyuan 030024, China
b Key Laboratory of Coal Science and Technology (Taiyuan University of Technology), Ministry of Education
A R T I C L E I N F O
A B S T R A C T
Keywords:
SBA-15
Stable and efficient Cu/SBA-15 and xCuZn/SBA-15 (x = 5, 10 and 15) in methanol dehydrogenation to methyl
formate (MF) are prepared through a double-solvent impregnation (DI) method. Among all catalysts, 10CuZn/
SBA-15 shows the highest catalytic performance with selectivity to MF about 88.1 % and methanol conver-
sion of 31.1 %, which is attributed to the well-dispersed Cu particles and high ratio of Cu◦/(Cu◦ + Cu+). The
proper amount of ZnO could improve dispersion of Cu because of its geometrical spacer, inhibiting growth of Cu
particle, and the best dispersion is achieved in 10CuZn/SBA-15. Furthermore, the Cu◦/(Cu◦ + Cu+) ratio is
greatly promoted with the assistance of ZnO, attributed to Cu-ZnO interaction, which reaches maxima of 53.3 %
at a Cu/Zn mole ratio of 10. Specially, the optimized catalyst shows evident suitability at high temperature for
methanol dehydrogenation reactions along with high level of conversion and selectivity for 100 h. Overall, our
findings reveal that modification by the appropriate amount of ZnO in Cu-based catalyst has a positive impact on
obtaining MF for the methanol dehydrogenation.
Methyl formate
ZnO
Cu species
Dehydrogenation
1. Introduction
unsuitable widespread in industry because of their high price and
deactivation. By comparison, Cu-based catalysts are the appropriate
Methyl formate (MF) is an important and indispensable component
of numerous chemical products in C1 chemistry, such as formic acid,
acetic acid, propionic acid, formamide, dimethyl formamide, and
ethylene glycol [1–3]. MF can be successfully synthesized by several
processes, including methanol carbonylation [4], oxidative coupling of
methanol [5], methanol dehydrogenation [6,7], direct synthesis from
CO and H2 [8] as well as hydrogenation of CO2 [9]. Among these pro-
cesses, the methanol dehydrogenation has been deemed to have great
commercial prospects on account of important merits including simple
procedures, abundant raw materials and recyclable by-product H2 [10].
Methanol conversion could be promoted at the high temperature
since methanol dehydrogenation reaction to produce MF is endo-
thermic. However, the rising temperature will lead to the further
decomposition of MF to CO, resulting in the decrease of its selectivity.
Thus, the improvement of methanol conversion and MF selectivity are
not achieved at the same time, accounting for the selection and design of
catalyst is crucial. It has been demonstrated that both noble metal and
transition metal as active catalysts are used for this reaction. The noble
metal catalysts exhibit excellent catalytic performance [11], but they are
candidates for methanol dehydrogenation due to its economical and
prominent performance [12–15], in which Cu◦ as the main active spe-
cies has been got consensus on the basis of a large number of reports
[16–18]. For Cu-based catalysts, the Cu◦ facilitate dissociates the
oxygen-hydrogen of methanol to methoxyl group and further to form-
aldehyde group through dissociate carbon-hydrogen bonds, but the Cu+
sites lead to formaldehyde group decompose rapidly generate to CO and
H2 [19]. In other words, the Cu◦ is beneficial for the formation of MF,
while Cu+ is helpful to formation of CO. Thus, the control on concen-
tration of Cu◦ is one of the effective strategies promoting the catalytic
performance for methanol dehydrogenation. The previous studies
showed that adding additives such as ZnO [20–22], Be [23–25] and Ce
[26] could effectively change the ratio of Cu◦ and thus influence the
catalytic performance and stability in the reaction because of the strong
interaction between surface metals. Especially, the performance of ZnO
modified Cu-based catalysts improves significantly, thus the role of ZnO
additives has become research hotspot. Huang et al. [27] proposed that
additives of ZnO can improve the MF selectivity from 49.5 % to 79.8 %.
Besides the concentration of Cu◦, the dispersion of Cu nanoparticles
* Corresponding author.
E-mail addresses: renjun@tyut.edu.cn, 2018879598@qq.com (J. Ren).
https://doi.org/10.1016/j.mcat.2021.111514
Received 16 November 2020; Received in revised form 2 March 2021; Accepted 4 March 2021
Available online 21 March 2021
2468-8231/© 2021 Elsevier B.V. All rights reserved.

N. Wang et al.
Molecular Catalysis 505 (2021) 111514
is an important factor to consider for the dehydrogenation reaction due
to sintering easily for CuO or Cu nanoparticles during the thermal
treatments. It has been proved that SBA-15 is a good candidate as sup-
port for well dispersing Cu nanoparticles [28,29], which can be ascribed
to space limitation of its regular channels inhibiting active species from
agglomeration [30] and high specific surface area enhancing the
dispersion of Cu particles [31].
Recently, the ZnO modified Cu-based catalysts exhibit excellent
catalytic in various catalytic reactions, such as dimethyl ether steam
reforming [26], dimethyl ether synthesis, methanol synthesis [32], and
so on [33]. The role of ZnO has been focused and has increasing atten-
tion by numerous researchers. Up to now, two main hypotheses are
greatly accepted: one is that ZnO as a spacial barrier helps to increase the
Cu particles dispersion, the another one is that it acts as the active
species in the terms of Cu-Zn alloy [34]. Huang et al. [27] found that
adding ZnO is beneficial to enhance the Cu nanoparticles dispersion and
produce Cu-ZnO interaction, thus improving activity of catalyst in
methanol dehydrogenation. Besides, Cu-based catalyst modified by ZnO
possesses the superior stability to ZnO-free ones, attributing to good
dispersity of Cu nanoparticles keep in the reaction process provided by
inhibition of ZnO from Cu agglomeration. Nevertheless, systematic
research about the effect of ZnO modified Cu-based catalyst for meth-
anol dehydrogenation is seldom reported.
Fig. 1. N2 physisorption isotherms of reduced catalysts.
30 ◦C with Ar, followed by exposure to 30 % N2O/Ar keeping 30 min.
The next procedure is the same as that of the H2-TPR experiment. The
operation of CH3OH-TPD was as follows. The samples were degassed at
300 ◦C in He flow for 60 min and afterwards kept at 100 ◦C, before
methanol introduced He was used as a carrier gas. After He was used to
wash away the physical molecules on the surface, the temperature was
increased until 900 ◦C (10 ◦C minꢀ 1).
With the aim of optimizing the catalytic performance, ZnO is used as
an additive to modify the Cu-based catalysts to obtain more effective and
stable catalysts. In this article, highly dispersed xCuZn/SBA-15 catalyst
synthesized through DI method was used to catalyze methanol dehy-
drogenation. The physical and chemical properties of samples were
investigated with the help of several characterization techniques and
their catalytic performance was studied. The structure-function rela-
tionship was explored. The role of ZnO was made detailed discussion.
2.3. Catalyst evaluations
In this study, methanol dehydrogenation to MF was conducted in a
fixed-bed reactor (500 mm × 8 mm) filled with 0.3 g catalyst sample
diluted with 3 g of quartz sand at pressure of 0.2 Mpa with reaction
temperature of 300 ◦C. Methanol was injected (0.05 mL minꢀ 1), which is
vaporized in the preheater and then fed into reactor for catalytic
dehydrogenation, using N2 as a carrier gas (30 mL minꢀ 1). After
condensation in condenser, the products were collected and then
monitored through gas chromatograph (GC-920, Shanghai Haixin) using
thermal conductivity and flame ionization detectors. The MeOH con-
version (CMeOH, %), MF selectivity (SMF, %), CO2 selectivity (SCO2, %),
CO selectivity (SCO, %) and MF yield (YMF, %) were calculated according
to the following equations:
2. Experimental
2.1. Catalyst preparation
The xCuZn/SBA-15 and Cu/SBA-15 catalysts with Cu loading of 20
wt% were synthesized by the double-solvent impregnation method. 1 g
of SBA-15 was ultrasonically dispersed in 30 mL of hexane. After adding
10 mL of aqueous solution containing certain amount of Cu(NO3)2⋅3H2O
and Zn(NO3)2⋅6H2O into the suspension, the resultant solution was
stirred at 35 ◦C for 2 h and then filtrated and dried at 80 ◦C for 12 h in
air. At last, the obtained solid was reduced by H2/N2 flow at 300 ◦C for 2
h in a tube furnace. The reduced catalysts were denoted as xCuZn/SBA-
15 (x = 5, 10 and 15), in which x means the mole ratio of Cu/Zn. The
Cu/SBA-15 catalyst (20 wt% Cu loading) was prepared by the same
procedure without the use of Zn(NO3)2⋅6H2O.
2 × nMF + nCO2 + nCO
CMeOH
=
× 100%
nMeOH + 2 × nMF + nCO2 + nCO
2 × nMF
× 100%
SMF
=
2 × nMF + nCO2 + nCO
2.2. Catalysts characterization
Table 1
Transmission electron microscopy (TEM) was obtained through a
Textural properties of Cu/SBA-15 and xCuZn/SBA-15 catalysts.
JEOL-2100
F electron microscope with X-ray energy-dispersive-
a
a
a
b
b
c
Catalysts
SBET
VP
DP
DCu
(%)
S0Cu
X0Cu
spectrometer (EDS). X-ray diffraction (XRD) was conducted on a
(m2/g)
(cm3/g)
(nm)
(m2/g)
(%)
Rigaku D/max 2500 diffraction using Cu Kα radiation with the 2θ range
SBA-15
Cu/SBA-15
15CuZn/
SBA-15
10CuZn/
SBA-15
5CuZn/SBA-
15
624
464
431
0.91
0.78
0.75
6.0
5.8
5.7
–
35.8
36.3
–
–
45.3
51.0
from 5 to 85◦. The nitrogen physisorption was determined on a Beishide
3H-2000PS2 instrument. The specific surface area (SBET), pore diameter
(DP) and pore volume (VP) were obtained through Brunauer-Emmett-
Teller (BET) and Barrett-Joyner-Halenda model. X-ray photoelectron
spectra (XPS) was collected through Thermo ESCALAB 250 spectrom-
242.2
245.5
419
347
0.72
0.65
5.8
5.7
40.1
34.7
271.5
234.7
53.3
52.1
eter with an Al Kα X-ray source. H2 temperature-programmed reduction
(H2-TPR), H2-N2O titration and CH3OH temperature-programmed
desorption (CH3OH-TPD) was tested on a XianQuan TP-5080 equip-
ment. H2-TPR were monitored by thermal conductivity detector with
pretreatment under Ar flow at 200 ◦C for 60 min before reducing by 30
% H2/Ar from 30 ◦C to 500 ◦C (10 ◦C minꢀ 1). For H2-N2O titration,
catalysts were reduced at 450 ◦C under 30 % H2/Ar and then cooled to
SiO2
347
277
1.14
1.76
13.2
25.5
–
21.7
–
–
–
–
10CuZn/
SiO2
a
The SBET, VP and DP determined by N2 adsorption-desorption.
The DCu and S0Cu on the surface calculated by N2O chemisorption.
The X0Cu calculate by Cu LMM AXES spectra.
b
c
2

N. Wang et al.
Molecular Catalysis 505 (2021) 111514
suggesting that metal compositions are effectively dispersed on the
surface of SBA-15, consistent with the findings of TEM and XRD
characterization.
For Cu-based catalysts, the Cu dispersion (DCu) is one of significant
factors affecting catalytic performance of the methanol dehydrogena-
tion to MF [27]. The Cu dispersion of the Cu/SBA-15 and xCuZn/SBA-15
catalysts is summarized in Table 1. It can be seen that the DCu value
firstly increase and then decrease with the increment of ZnO content,
and achieved the maximum of 40.1 % in the 10CuZn/SBA-15 catalyst,
which is in agreement with the TEM results. As for 15CuZn/SBA-15, the
ZnO content is too low to isolate copper particles abundantly. While, the
ZnO content is relatively high in the 5CuZn/SBA-15 catalyst, and the
copper would squeeze together and thus led to a decrease of Cu
dispersion. Combined with the TEM and N2O titration results, it is
believed that an appropriate amount of ZnO acts as a physical barrier,
isolating copper species so as to improve the Cu dispersion in the
xCuZn/SBA-15 catalysts [38].
Fig. 5 shows the H2-TPR profiles for different catalysts. The 15CuZn/
SBA-15 and 5CuZn/SBA-15 catalysts present two obvious reduction
processes specified as low-temperature peak and high-temperature
peak, which can be assigned to reduction of well-dispersed CuO nano-
particles to Cu◦ as well as bulk CuO to Cu+ and Cu◦, respectively [22,
40–42]. Nevertheless, the reduction peak of large CuO particles in
10CuZn/SBA-15 is hard to be distinguished, which might be attributed
to a more uniform distribution of copper nanoparticles as confirmed by
the TEM analysis. Thus, it can be known that the 10CuZn/SBA-15
catalyst possess a higher reducibility compared with the other cata-
lysts. With the increment of ZnO loading, the reduction peak shifts to-
wards a higher temperature, which may be due to the presence of a
specific type of Cu-ZnO interaction [21,43].
Fig. 2. XRD patterns of reduced catalysts.
nCO2
SCO2
SCO
=
× 100%
× 100%
2 × nMF + nCO2 + nCO
nCO
=
2 × nMF + nCO2 + nCO
YMF = CMeOH × SMF × 100%
3. Results and discussions
3.1. Physicochemical properties of catalysts
3.1.3. Surface chemical states
3.1.1. Textural properties
Fig. 6a shows the Cu 2p XPS results of reduced samples. Typically,
the binding energy (BE) Cu 2p3/2 peak at around 934.2 eV and the
satellite peak at 943.2 eV confirm the presence of Cu2+ species [44,45].
In Fig. 6a, only the Cu 2p1/2 BE at 952.4 eV and Cu 2p3/2 BE at 932.6 eV
belonging to Cu+ and/or Cu◦ are found [46], which indicates that high
valence state copper are reduced to low valence state [47]. From the
Fig. 6b, the asymmetrical and broad peak is detected and divided to the
two symmetric peaks center at 916.1 and 912.2 eV, assigning to Cu◦ and
Cu+, conventionally. The relative proportion of Cu◦ and Cu+ is
computed based on Cu LMM XAES spectra [48,49], and relevant data is
shown in Table 1. The Cu◦ percentage (XCu◦) first increases and then
decreases with increasing of ZnO loading, indicating it is greatly affected
by the ZnO content of this catalyst. And the 10CuZn/SBA-15 catalyst
owns the highest ratio of Cu◦/(Cu◦ + Cu+) of 53.3 %.
The N2 physisorption of all reduced catalysts are illustrated in Fig. 1
and the textural properties of samples are list in Table 1. All samples
exhibit the IV isotherm with H1 hysteresis loops, which indicates mes-
oporous structure of SBA-15 is maintained in all samples after the
introduction of Cu and ZnO species. Obviously in Table 1, SBET and VP of
xCuZn/SBA-15 catalyst slowly decrease as increment of ZnO content,
implying that ZnO particles covering and clogging the pore channels of
SBA-15 supports during the process of catalyst preparation [21].
3.1.2. Crystalline phase and morphology
The XRD in Fig. 2 evidence the structures of reduced catalysts. The
wide peak is detected at 22.5◦ in all samples, which can be assigned to
the feature peak of amorphous SiO2. The sharp diffraction characteristic
at 43.1◦, 50.2◦ and 74.1◦ are attributed to metallic Cu (111, 200, 220)
[28], which may be due to the Cu2+ is reduced. In addition to this, no
obvious characteristic for zinc oxide are discovered among all catalysts
even if Cu/Zn is as low as 5, probably due to the high dispersion and
uniform distribution of the ZnO species generated by a double-solvent
impregnation method. Laugel et al. [35] proved that the DI method is
helpful to enhance the dispersion of these metal oxide nanoparticles.
Fig. 3 demonstrates the TEM pictures for four reduced samples (left)
and corresponding size distribution histograms of Cu nanoparticles
(right). All samples display well-dispersed of Cu particles on the SBA-15
supports. The notable physical difference among the four catalysts lie in
the mean size of Cu nanoparticles, which firstly decrease and then in-
crease with the increase of ZnO content, and reach a minimum value of
7.5 nm at a Cu/Zn molar ratio of 10. According to the HRTEM image
(insets in Fig. 3c), zinc oxide obviously acts as a physical spacer to
separate copper particles [36–39]. Therefore, it can be concluded that
the addition of an appropriate amount of ZnO could effectively inhibit
Cu nanoparticles from agglomeration during the preparation process of
xCuZn/SBA-15. Fig. 4 displays the corresponding element images of
reduced 10CuZn/SBA-15 catalysts. It is observed that the signal distri-
bution of Cu and ZnO species are relatively uniform and well-dispersed,
The Zn 2p XPS spectra of the xCuZn/SBA-15 catalysts are shown in
Fig. 7. The peak observed at 1022.4 eV could be assigned to Zn 2p3/2
electrons, which is greater than the value of Zn2+ (1021.2 eV) in the
reference ZnO as reported [22]. This finding indicates that the ZnO in
the xCuZn/SBA-15 catalysts should be electron-deficient compared with
pure ZnO species [50,51]. It is inferred reasonably that ZnO serves as an
electron donor promotes the transfer of electron in the reduction pro-
cess, which is beneficial to the reduction of copper and thus increase the
Cu◦ concentration as confirmed by Cu LMM XAES spectra (Table 1). In
summary, it is known that ZnO functions as both structural promoter
and electronic promoter in the xCuZn/SBA-15 catalysts. Furthermore,
the catalytic performance could be promoted through controlling of ZnO
loading, since Cu◦ as an active species and it is of great significance in
methanol dehydrogenation.
Cu◦ specific surface area (SCu◦) determines by H2-N2O titration. From
◦
Table 1, the SCu first increases, reaching the maximum value of 271.5
m2/g when the mola ratio of Cu to Zn is 10, and then decline as the ZnO
content raise. The observation indicates that the appropriate amount of
◦
ZnO could effectually enhance the Cu dispersion and thus increase SCu
,
while large Cu nanoparticles could be formed and thus result in
3

N. Wang et al.
Molecular Catalysis 505 (2021) 111514
Fig. 3. TEM patterns of reduced catalysts and the corresponding size distribution histograms of Cu particles.
decreasing of Cu◦ surface area as excess ZnO is added [22].
adsorption of CH3OH in the reaction process [19]. Obviously, the largest
desorption peak area appears in 10CuZn/SBA-15, ascribed to its largest
surface area of Cu◦ species (271.5 m2/g), which is indicative of the
strongest adsorption capacity of CH3OH. In a word, CH3OH adsorption
capacity of xCuZn/SBA-15 is capable to be enhanced greatly by surface
area of Cu◦ species results from the appropriate amount of ZnO,
conducive to promoting the catalytic performance in methanol dehy-
drogenation reaction.
3.1.4. CH3OH-TPD
Fig. 8 displays the CH3OH-TPD curves for these reduced catalysts.
There are three desorption peaks at 50ꢀ 280 ◦C, 280ꢀ 370 ◦C and
370ꢀ 500 ◦C, respectively. Nevertheless, only the medium-strong
desorption segment (280ꢀ 370 ◦C) is major concern due to the reac-
◦
tion temperature of 300 C in this work. In this range, the desorption
peak area is greatly affected from the ZnO introduction and it first in-
creases and then decreases with increasing ZnO, implying the ZnO
loading in the Cu-based catalysts have an important impact on the
CH3OH adsorption capacity. It is also found that the trend of CH3OH
adsorption capacity is consistent with that of the SCu◦, suggesting Cu◦
species provide the adsorption sites and play the significant role in
3.2. Activity of catalysts
Table 2 shows the catalytic performance of reduced Cu/SBA-15 and
xCuZn/SBA-15 catalysts for methanol dehydrogenation in 300 ◦C. Cu/
SBA-15 shows a relatively low methanol conversion (CMeOH) of 17.8 %
4

N. Wang et al.
Molecular Catalysis 505 (2021) 111514
Fig. 4. Elemental mappings of reduced 10CuZn/SBA-15: (a) STEM, (b) selection precinct, (c-f) EDS elemental mapping.
and MF selectivity (SMF) of 46.5 %. Compared with Cu/SBA-15, the
activity of xCuZn/SBA-15 is enhanced markedly at different degree
depending on the ZnO amount. Among all these catalysts, the 10CuZn/
SBA-15 shows the best catalytic performance with CMeOH of 31.1 % and
SMF of 88.1 % superior to the results reported.
is inhibited effectively through the introduction of ZnO. The possible
reaction path of methanol dehydrogenation to MF is as follows. Firstly,
–
–
H
the O H bond in CH3OH is cleavage to CH3O species. Then, the C
bond of CH3O is dissociated to produce HCHO intermediate, which is the
rate-limiting step of MF formation. Finally, MF is produced through the
CH3O species reacting with HCHO (hemiacetal route) [52] or HCHO
With increasing ZnO content, CMeOH increases until it reaches a
maximum for 10CuZn/SBA-15, and then decreases. The SMF presents a
similar trend with CMeOH, whereas the opposite trend for SCO is
observed, which implies that side reaction producing by-products of CO
dimerization (Tishchenko mechanism) [53]. During the process of
◦
–
H
methanol dehydrogenation, the Cu promote the cleavage of the O
bond in CH3OH to CH3O and further to form HCHO by promoting the
5

N. Wang et al.
Molecular Catalysis 505 (2021) 111514
Fig. 5. H2-TPR curves of unreduced catalysts.
+
–
dissociate of C H bond, whereas Cu sites cause rapid decomposition of
HCHO to CO and H2 [19]. It is confirmed that Cu◦ species contributed to
the formation of MF, while Cu+ species help to produce CO. It can
deduce that both the improvement of SMF and the declining of SCO
resulted from the increase of Cu◦ percentage through the ZnO
introduction.
It should be mentioned that the variation of CMeOH and SMF for
xCuZn/SBA-15 is consistent with the trend of Cu dispersion, the Cu◦
surface area as well as Cu◦/(Cu◦ + Cu+) ratio see from Table 1, and
opposite to the trend of Cu particles size proved by the TEM and H2-TPR
consequences, which suggests that the improvement of activity should
be corresponding closely to the physicochemical property of Cu species
derived from the introduction of moderate ZnO. According to previous
literatures, the copper dispersion and Cu◦/(Cu◦ + Cu+) ratio could be
considered as the crucial factor affecting the activity. Proved by N2O
titraotion result and TEM result, the Cu dispersion of 10CuZn/SBA-15 is
largest, which can provide more active sites (proved by Cu◦ specific
surface area) and contribute to catalytic performance. And the XPS
result shows that 10CuZn/SBA-15 with moderate amount ZnO have the
greatest ratio of Cu◦/(Cu◦ + Cu+). Based on the above analysis, it can be
concluded that ZnO acts as a physical barrier and the electron donor
generates Cu-ZnO interaction to reduce the particle size of copper and
increase the Cu◦ concentration, which further promotes the catalytic
performance of xCuZn/SBA-15 in the dehydrogenation of methanol to
MF.
Seen from the Table 2, the 10CuZn/SBA-15 catalyst shows a rela-
tively higher methanol conversion of 31.1 % with the MF selectivity of
88.1 % in comparison to 10CuZn/SiO2 (17.0 % CMeOH and 59.2 % SMF).
This may be due to the fact that the uniformly ordered pore channels of
SBA-15 facilitate the dispersion of copper, resulting in smaller particles
and more exposed active sites so as to improve the catalytic performance
of xCuZn/SBA-15. (Detailed explanations are given in the supporting
information).
Fig. 9 shows the stability of 10CuZn/SBA-15 and displays the rela-
tively stable trend of CMeOH and SMF with about 31 % and 89 % indi-
vidually during a 100 h. The reason may be associated with prevention
Fig. 6. (a) Cu 2p XPS and (b) Cu LMM XAES spectra of reduced catalysts.
6

N. Wang et al.
Molecular Catalysis 505 (2021) 111514
Fig. 7. Zn 2p XPS spectra of reduced catalysts.
Fig. 8. CH3OH-TPD profiles of reduced catalysts.
Table 2
The catalytic performance of reduced Cu/SBA-15 and xCuZn/SBA-15 catalysts.
Catalysts
CMeOH (%)
SMF (%)
SCO (%)
SCO2 (%)
YMF (%)
Cu/SBA-15
17.8
23.0
31.1
24.6
17.0
16.7
18.9
46.5
55.8
88.1
70.9
59.2
88.1
78.9
52.4
42.5
10.5
27.1
39.1
5.5
1.1
1.7
1.4
2.0
1.7
2.4
3.8
8.3
12.8
27.4
17.4
10.1
–
15CuZn/SBA-15
10CuZn/SBA-15
5CuZn/SBA-15
10CuZn/SiO2
Cu5MgO5 [54]
CuO-Al2O3 [18]
8.6
–
Reaction conditions: mcat=0.3 g, T=300 ◦C, PN2 = 0.2 MPa, LHSVMeOH=7.9 hꢀ 1
,
10 h.
from growth of Cu particle and the strong interaction between ZnO and
Cu provided by ZnO additives, reducing the risk of catalyst deactivation
and exhibiting a high thermal stability in the process of reaction.
Fig. 9. Evaluation results of 10CuZn/SBA-15 stability.
which also displays satisfactory stability for longer than 100 h. The most
excellent activity of 10CuZn/SBA-15 is attributed to the best dispersion
of Cu particles as well as the highest Cu◦/(Cu◦ + Cu+) ratio primarily.
The present work sheds light on the influence of ZnO amount in physical
and chemical properties in Cu-based catalysts and highlights the
importance of introduction of ZnO as a promoter to improve catalytic
performance in the MF production.
4. Conclusions
The ordered mesoporous xCuZn/SBA-15 and Cu/SBA-15 catalysts
are synthesized through DI method for methanol dehydrogenation to
MF. It is found that appropriate amount of ZnO would take an active
influence on Cu dispersion and Cu◦/(Cu◦ + Cu+) ratio in the Cu-based
catalyst. Furthermore, the methanol conversion and MF selectivity in-
creases with increasing amount of ZnO until the ratio Cu/Zn of 10, and
they are highest of 31.1 % and 88.1 % respectively for 10CuZn/SBA-15,
7

N. Wang et al.
Molecular Catalysis 505 (2021) 111514
[18] S. Sato, M. Iijima, T. Nakayama, T. Sodesawa, F. Nozaki, Vapor-phase
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Na Wang: Conceptualization, Formal analysis, Investigation,
Writing - original draft. Yanhong Quan: Formal analysis, Writing - re-
view & editing. Jinxian Zhao: Writing - review & editing. Haixia Li:
Conceptualization, Methodology. Jun Ren: Supervision, Project
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Declaration of Competing Interest
[22] X. Wang, K. Ma, L. Guo, Y. Tian, Q. Cheng, X. Bai, J. Huang, T. Ding, X. Li, Cu/
ZnO/SiO2 catalyst synthesized by reduction of ZnO-modified copper phyllosilicate
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to ethanol over boron doped carbon aerogels supported Cu catalyst,
ChemistrySelect 5 (2020) 11517–11521.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgement
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This work was funded by the National Natural Science Foundation of
China (21776194 and 21808154).
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Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2021.111514.
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