Copper-cobalt catalysts supported on mechanically mixed HZSM-5 and γ-Al2O3 for higher alcohols synthesis via carbon monoxide hydrogenation

Article abstract of DOI:10.1039/c9ra01927h

Mechanically mixed γ-Al₂O₃ and HZSM-5 (Si/Al = 50) with different mass ratio were utilized as support for Cu-Co higher alcohol synthesis catalysts prepared through incipient wetness impregnation. The textural and structural propertie

Full text of DOI:10.1039/c9ra01927h

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Copper–cobalt catalysts supported on
mechanically mixed HZSM-5 and g-Al2O3 for higher
alcohols synthesis via carbon monoxide
hydrogenation
Cite this: RSC Adv., 2019, 9, 14592
a
a
a
a
a
a
* *
Hang Sun, Kun Dong, Yanqi Tao, Qi Wang, Yazhong Chen,
Xuan Ge,
Genlei Zhang,a Peng Cui,a Ye Wang
and Qinghong Zhangb
b
Mechanically mixed g-Al2O3 and HZSM-5 (Si/Al ¼ 50) with different mass ratio were utilized as support for Cu–
Co higher alcohol synthesis catalysts prepared through incipient wetness impregnation. The textural and
structural properties were studied using Ar low temperature adsorption and desorption, H2-temperature
programmed reduction (H2-TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS),
transmission electron microscope (TEM) and catalytic performance measurements. The results indicated that
the mechanically mixed HZSM-5 and g-Al2O3 supported copper–cobalt catalysts were superior to either g-
Al2O3 or HZSM-5 supported ones with the same metal loading. The results revealed that using HZSM-5 and
g-Al2O3 mechanically mixed benefited the dispersion of metallic phases and stronger synergetic functions
between smaller nanoparticles containing copper and/or cobalt, which is essential for HAS from CO
hydrogenation. Under working conditions of P ¼ 5.0 MPa, T ¼ 300 ꢀC, V(H2) : V(CO) : V(N2) ¼ 4 : 2 : 1 and
Received 13th March 2019
Accepted 3rd May 2019
GHSV ¼ 7200 mL gꢁ1
h
ꢁ1, mechanically mixed HZSM-5 and g-Al2O3 supported catalysts showed higher
DOI: 10.1039/c9ra01927h
catalytic activity than those over single support. For CuCo catalysts upon support containing 50.0 wt%
rsc.li/rsc-advances
HZSM-5 and 50.0 wt% g-Al2O3, the CO conversion was 21.3% and the C2+ alcohol selectivity was 41.8%.
of products and stability, attracting wide attention recently.
Copper can activate CO non-dissociatively and subsequently
1 Introduction
generate alcohols, while cobalt enables the dissociative CO
adsorption and C–C chain growth.1,2 Generally, supports for Cu–
Co catalysts include g-Al2O3, SiO2, ZrO2, TiO2, SBA-15 and ZSM-
5.9,12–16 Among them, g-Al2O3 support was widely probed. The
problems associated with the Cu–Co/g-Al2O3 catalysts such as
low CO conversion, poor selectivity and low dispersion of active
species, were found. Jovana et al.17 recently discovered that
mixed Y-zeolite and g-Al2O3 support could be combined
through extrusion, and then Pt metal was separately loaded
upon Y-zeolite or g-Al2O3. Thus, the nanoscale distance between
the acid sites and metal nanoparticle could be efficiently tuned
Catalytic conversion of syngas to long-chain hydrocarbons and
alcohols is one of the most attractive subjects in C1 chemistry.1–3
The hydrocarbons and alcohols obtained through the process
could be used as fuels, fuel additives for octane value
enhancement of gasoline or cetane value enhancement of
diesel. Also intermediates for various value-added chemicals
such as medicine, cosmetics and polyester. The most important
aspect for carbon monoxide hydrogenation is the efficient
tuning selectivity of various products through catalysts and the
working conditions. Cobalt-based catalysts are efficient for the
synthesis of long-chain paraffins using the famous Fischer–
Tropsch process,4 while copper-based catalysts are industrial-
ized for large scale methanol synthesis from syngas. Nowadays,
efficient catalysts for syngas conversion to mixed higher alco-
hols include Rh-based catalysts,5 Cu–Co bimetallic catalysts6–9
and molybdenum based catalysts.10,11 Among the non-precious
catalysts, Cu–Co bimetallic catalysts showed better selectivity
´
for hydrocarbon conversion. Lopez-Mendoza also found that
hydrodesulphurization Co–Mo–W sulde catalysts supported
upon SBA-15 and SBA-16 mechanically mixed showed better
performance than catalysts using either SBA-15 or SBA-16 as
support.18 They contributed the better performance to the
bimodal pore structure formation, which favored the diffusion
of catalyst precursors on the support and better dispersion of
the active phases. Li et al.19 utilized two types of SiO2 with
different mesopore size and HZSM-5 zeolite to prepare hybrid
supported cobalt-based catalysts for Fischer–Tropsch synthesis.
The hybrid supported catalysts showed higher performance and
it was believed that mesopores provided quick mass transfer
aAnhui Province Key Laboratory of Advanced Catalytic Materials and Reaction
Engineering, School of Chemistry and Chemical Engineering, Hefei University of
Technology, Hefei 230009, China. E-mail: wangqi@hfut.edu.cn; chenyazhong@hfut.
edu.cn; Fax: +86-551-62901450; Tel: +86-551-62901450
bState Key Laboratory of Physical Chemistry of Solid Surface, College of Chemistry and
Chemical Engineering, Xiamen University, Xiamen 361005, China
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channels, while the micropores contributed to high metal
X-ray powder diffraction (XRD) was used to determine the
dispersion and accelerated hydrocracking/hydroisomerization phase composition and particle size of the catalysts before and
reaction rate. Generally, using dual supports with different aer reduction. The XRD measurements were performed on
pore structure could signicantly alter the dispersion of active a Rigaku D/MAX2500VL/PC using nickel ltered Cu-Ka radia-
species during catalyst preparation and diffusion of reagents, tion (l ¼ 0.1541 nm), operating voltage of 40 kV and current of
reaction pathways or intermediates for complex reactions such 40 mA. The intensity was measured by step scanning in the 2q
as higher alcohol synthesis (HAS) and Fischer–Tropsch range between 10ꢀ and 90ꢀ, with a 2q step of 0.02ꢀ. The average
synthesis.20 Thus, in this work, we prepared copper–cobalt crystallite sizes were calculated using the peak width at half
catalysts supported upon mechanically mixed g-Al2O3 and peak height and the Debye–Scherrer equation aer background
HZSM-5 with different mass ratio to probe the pore structure subtracting and correction for instrumental broadening.
evolution and their inuences upon catalytic performance of
HAS from CO hydrogenation.
Transmission microscopy microscope images were obtained
using a JEM-2100F operated at 200 kV. TEM samples were
prepared by the ultrasonic dispersion of slightly ground catalyst
samples in ethanol for 30 min, and then a drop of the
suspension was applied onto a holey carbon grid. The particle
size distribution was calculated on monolayer particles by using
SigmaScan soware.
2 Experimental
2.1 Catalyst preparation
The g-Al2O3 was supplied by Liaoning Haitai Technology Incor-
poration. HZSM-5 (Si/Al ¼ 50) powder (Nanjing University Catalyst
Factory) were mixed together according to the desired mass ratio,
then put into a planetary ball mill QM-3SP04 (Nanjing University
Instrument Plant) at a certain rate of ball milling for 4.0 h. Thus,
obtained powders were pressed into disks and then crushed,
sieved to collect the grains of 60–80 mesh in size. The supports
were described as ZaAb according to the mass ratio of HZSM-5 and
g-Al2O3 (a : b). For comparison, According to the above experi-
mental steps, g-Al2O3, HZSM-5 support with grain size of 60–80
mesh was also prepared. HZSM-5 + g-Al2O3 support was described
as a simple physical mixing of HZSM-5 and g-Al2O3 aer ball
milling with a mass ratio of 1 : 1, and then obtained powders were
pressed into disks and then crushed, sieved to collect the grains of
60–80 mesh in size. The copper–cobalt catalysts for HAS were
prepared through incipient wetness impregnation process. The
total metal nitrate loading was kept at 15.0 wt%, while the Cu/Co
molar ratio was kept at 0.4. Typically, a certain amount of
Co(NO3)2$6H2O and Cu(NO3)2$3H2O of analytical grade,
purchased from Sinopharm Chemical Reagent Co., Ltd. and used
without further purication, were weighed with an electronic
balance, dissolving in a certain deionized water, then as prepared
support such as ZaAb, HZSM-5 + g-Al2O3, g-Al2O3 and HZSM-5 were
put into the solution for 24.0 h at ambient temperature. Then, the
samples were dried at 100 ꢀC for 6.0 h. Aer drying, the samples
were put into a muffle furnace for calcination with a temperature
ramp rate of 2 ꢀC minꢁ1 from 100 ꢀC to 500 ꢀC and kept for 5.0 h.
Temperature programmed reduction in H2 (H2-TPR) experi-
ments were conducted on a self-made microreactor-gas chro-
matograph (GC) system using a 5% H2–95% Ar atmosphere. The
sample (20.0 mg) was heated from room temperature to 100 ꢀC
under 30.0 mL minꢁ1 Ar ow and kept at 100 ꢀC for at least
30 min, and then cooled down to room temperature. Then Ar
was switched to 30.0 mL minꢁ1 5% H2–95% Ar gas, and the
sample was hꢀeated with a linear temperature rise from 50 ꢀC to
700 C at 10 C minꢁ1. H2 consumption was measured online
ꢀ
with a thermal conductivity detector (TCD).
The surface species of the catalysts were detected using X-ray
induced Auger electron spectroscopy (ESCALAB250Xi, Thermo
Fisher). The spectrum was recorded with Al-Ka1 as the exciting
source (hl ¼ 1486.6 eV). The binding energy or kinetic energy
values for the Auger electron were calibrated using the C 1s peak
of 284.7 eV as the reference.
2.3 Catalytic performance
The catalytic performance of each catalyst was evaluated using
a stainless-steel tubular reactor. 5.0 mL catalyst was charged
into the reactor. Then, the catalyst was activated in a hydrogen
ux with a GHSV of 3000 hꢁ1 at 400 ꢀC for 12.0 h with
a temperature ramp rate of 10 ꢀC minꢁ1 from ambient
temperature. Then the temperature was lowered to 300 ꢀC,
a feeding gas mixture with a composition of N2 : H2 : CO ¼
4 : 2 : 1 was delivered to reactor with a total GHSV of 7200 hꢁ1
.
The reaction pressure was maintained at 5.0 MPa through
a backpressure regulator. The products were online monitored
2.2 Catalyst characterizations
The specic surface areas of catalysts were determined through through a gas chromatograph (GC-2000 III) equipped with TCD
Ar adsorption at using Micromeritics ASAP 2020 M. Prior to and FID detectors. N2, CO, CH4, CO2 in products were separated
adsorption, the samples were degassed at 80 ꢀC for 2.0 h to with 2.0 m TDX-01 carbon molecular sieve column using
remove physically adsorbed components under vacuum. The hydrogen as carrier gas and detected by TCD. Hydrocarbons and
surface area was determined from the linear portion (P/P0
¼
alcohols were separated with 15.0 m ꢂ 25 mm ꢂ 0.25 mm KB-
0.05–0.30) of the Brunauer–Emmett–Teller (BET) equation. The Plot Q capillary column using N2 as carrier gas and detected
mesopore volume and pore size distribution were calculated by FID. Conversion of CO was calculated using N2 as internal
using the BJH model, while the micropore volume and pore size standard according to the TCD analysis results. The selectivity
distribution were calculated using HK model. The pore diam- to hydrocarbons and alcohols and their space time yields were
eter distribution was calculated by the BJH method using the calculated using carbon normalization method. Data with
adsorption branch of the isotherms.
carbon balance and oxygen balance over 95% were utilized.
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Fig. 2 showed the high resolution TEM images of copper–
cobalt catalysts supported on various carriers aer reduction
and passivation. The particle size distribution was also pre-
sented. From the results, it could be seen that the particle size of
copper–cobalt bimetal possessed narrower distribution and
smaller average particle sizes supported on HZSM-5 and g-Al2O3
mechanically mixed than those supported either on HZSM-5 or
on g-Al2O3. The existence states of copper, cobalt species aer
reduction were found very complex, including forms such as
metallic Cud+ (d ¼ 0–1) and Co0, Cu–Co alloy,8 core–shell
structures such as Cu@Co or Co@Cu, and mixed nano-
particles.15 At the same time, complete reduction of copper and
cobalt species was hardly realized. Thus, a fraction of Cu+ and
Cu2+ also existed. Likewise, part of Co2+ also existed in the
reduced catalysts, as revealed by XPS characterization in this
work. The average particle size was estimated to be 2.87 nm for
g-Al2O3 supported catalyst and 2.78 nm for HZSM-5 supported
catalyst (Fig. 2A). While for the mixed support, the average
particle size decreased to 1.76 nm for catalyst supported on
Z1A1. We ascribed the phenomenon to the fact that due to the
mesopore modication by nanosized HZSM-5 during ball
milling. As the pore size of HZSM-5 was only 0.5 nm, diffusion
of catalyst precursor into the pore structure of HZSM-5 is diffi-
cult. Thus, only a small fraction of copper and cobalt species
existed in the pore structure of HZSM-5, while a large fraction of
copper and cobalt species existed outside the pore structure of
HZSM-5. While for g-Al2O3 supported copper–cobalt catalyst,
the relative larger average pore size and wider distribution of
pore size makes the nano-connement effect smaller than those
on mixed support with smaller average pore size and narrower
3 Results and discussion
3.1 Physiochemical properties
The texture properties of HZSM-5, Z1A1, HZSM-5 + g-Al2O3 and g-
Al2O3 supports including BET surface areas, micropore volume,
mesopore volume and micropore surface areas were displayed in
Table 1 and Fig. 1. HZSM-5 support showed higher specic
surface area and abundant micropore structure, while g-Al2O3
support showed lower specic surface area and only mesopore
structure. Supports on Z1A1 and HZSM-5 + g-Al2O3 showed the
specic areas between those of HZSM-5 and g-Al2O3. For Z1A1 and
HZSM-5 + g-Al2O3 supports, the micropore surface areas,
micropore volumes and mesopore volumes all showed only
a physical mixture of separate phase, ball milling and simple
physical mixing did not change the texture of each phase. Thus,
the texture properties are combinations of each phase according
to the mass ratio. The experimentally determined values are very
close to the calculated ones. Fig. 1 showed the pore size distri-
bution of mechanically mixed HZSM-5 and g-Al2O3 using H–K or
BJH models. In Fig. 1a, the HK model revealed that HZSM-5
showed very typical micropore structure of 0.5 nm, while g-
Al2O3 did not show micropore structure. For example, Z1A1
showed most probable pore size of 6.0 nm. HZSM-5 showed most
probable pore size of 4.7 nm with small pore volume, suggesting
the formation of secondary pore due to the packing of nano-
particles of HZSM-5 generated from ball milling and CuCo/ZaAb
is almost 70–80% respect to the original support surface area,
which is indicative of the high dispersion of the active phases on
the support and the possible formation of clusters of oxides of
transition metals which occlude smaller pores.
Table 1 The texture properties of various carriers
Micropore
Micropore
Mesopore
BET (m2 gꢁ1
Support
)
area (m2 gꢁ1
)
volume (cm3 gꢁ1
)
volume (cm3 gꢁ1
)
Sample
Catalyst
Support
Catalyst
Support
Catalyst
Support
Catalyst
HZSM-5
Z1A1
g-Al2O3
HZSM-5 + g-Al2O3
392.3
296.4
292.6
342.1
271.0
217.7
161.9
229.5
265.6
149.0
—
254.0
132.4
—
0.125
0.103
—
0.11
0.060
—
—
—
0.37
0.74
0.43
0.16
0.41
0.23
160.2
146.5
0.134
0.083
Fig. 1 The pore size distribution of supports: (A) HK model (B) BJH model.
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Fig. 2 TEM images of different catalysts and their particle size distribution ((a) Cu–Co/HZSM-5; (b) Cu–Co/Z1A1; (c) Cu–Co/g-Al2O3).
pore size distribution.21–24 According to the HAS mechanism 5, Z1A1 and g-Al2O3 supported catalysts were 1.39, 1.59 and 1.41
over copper-modied Fischer–Tropsch synthesis catalyst, respectively. Mixed support beneted the reduction of surface
metallic Cu0 absorbs CO associatively for the CO insertion Cu2+ into Cud+. The Co2p XPS spectrum suggested the presence
reactions to form alcohols, while metallic Co0 absorbs CO dis- of Co0 and Co2+ in the reduced catalysts,5 which corresponded
sociatively to increase the carbon chains.24 The close interaction to the binding energy of 778.3 eV and 780.2 eV, respectively. The
between copper and cobalt species, are essential for structure specic ratio of Co0/Co2+ ratios over HZSM-5, Z1A1 and g-Al2O3
sensitivity HAS reactions.
were 1.48, 0.94 and 1.34. It seemed that using Z1A1 support
Fig. 3 and 4 presented the XPS spectra of Cu2p and Co2p in beneted the reduction of copper oxide species while to some
reduced catalysts. The binding energies, peak areas and specic extent hindered the reduction of cobalt species into Co0.
ratio of surface species were listed in Tables 2 and 3. The Cu2p
Fig. 5 showed H2-TPR proles of copper–cobalt catalysts on
spectrum, aer peak splitting, identication and deconvolution various supports. It was found that both copper and cobalt
analysis, suggested the presence of Cud+ (d ¼ 0–1) and Cu2+
,
species could be reduced and their reduction could be interacted.
which corresponded to the binding energy of 932.5 eV and Wang et al.25 found that for 5Cu15Co supported on g-Al2O3,
933.5 eV, respectively. The Cud+/Cu2+ specic ratios over HZSM- composite oxides such as CuCo2O4 and CuxCo3ꢁxO4 spinel with
Fig. 3 XPS spectra of Cu 2p region for catalysts on various supports Fig. 4 XPS spectra of Co 2p region of catalysts on various supports ((a)
((a) Cu–Co/HZSM-5; (b) Cu–Co/Z1A1; (c) Cu–Co/g-Al2O3).
Cu–Co/HZSM-5; (b) Cu–Co/Z1A1; (c) Cu–Co/g-Al2O3).
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Table 2 XPS data of Cu 2p region of catalysts on various supports
Peak areas (AU)
Position (eV)
Cu–Co/HZSM-5
Cu–Co/Z1A1
Cu–Co/g-Al2O3
Cud+ (932.5 eV) 7628.9 (58.14%) 7029 (61.44%) 6328.6 (58.50%)
Cu2+ (933.5 eV) 5492.8 (41.86%) 4412 (38.56%) 4488.8 (41.50%)
Cud+/Cu2+
1.39
1.59
1.41
high structure similarity with Co3O4 could be formed, thus the
reduction temperature for cobalt species could be decreased. The
peak temperature around 250 ꢀC was ascribed to the reduction of
CuO, while peak temperature around 290 ꢀC was ascribed to the
reduction of CuCo2O4. For Co3O4, peak reduction temperature
was around 370 ꢀC. In this work, the peak reduction temperature
all shied to higher ones than those reported by Wang due to the
lower content of copper and cobalt species and nano-
connement effect of pore structure. For Cu–Co/HZSM-5 cata-
lyst (Fig. 6a), two reduction peak temperatures, one at 300 ꢀC and
the other one at 420 ꢀC, were observed. The 300 ꢀC reduction
peak corresponded to the reduction of CuO, while the 420 ꢀC
reduction peak temperature was attributed to the reduction of
CuCo2O4. For Cu–Co/g-Al2O3 catalyst (Fig. 5c), the peak temper-
Fig. 5 H2-TPR profiles for CuCo catalysts on different supports ((a)
Cu–Co/HZSM-5; (b) Cu–Co/Z1A1; (c) Cu–Co/g-Al2O3).
ꢀ
ature around 310 C was ascribed to the reduction of CuO, the
asymmetric reduction peak temperature overlapped in the range
of 400–500 ꢀC were ascribed to the reduction of CuCo2O4 and
Co3O4. For the mixed supports (Fig. 5b), the hydrogen
consumption peak temperatures became complex. The rst peak
reduction temperature appeared at 350 ꢀC, the reduction of CuO
became more difficult in comparison with both HZSM-5 and g-
Al2O3 supported catalysts. For the HZSM-5 supported catalysts,
copper and cobalt species mainly existed on the outside of the
surface although it showed larger surface area and micropore
surface area due to its 0.5 nm pore size. Thus, the reduction
temperature shied to lower ones due to its smaller particle size
and weaker interaction with the support. For the mixed supports,
the peak reduction temperatures all shied to lower ones, due to
the smaller particle sizes of CuO and CuCo2O4 due to nano-
connement effect. The smaller of the pore size, the lower peak
temperature for reduction were observed on CuCo catalysts on
mixed supports. The modication of nano pore structure resul-
ted in ner CuO and CuCo2O4 particles, showing different
reduction behaviors.
Fig. 6 XRD patterns for copper–cobalt catalysts supported over
different supports ((a) Cu–Co/HZSM-5; (b) Cu–Co/Z1A0.5; (c) Cu–Co/
Z1A1; (d) Cu–Co/Z1A2; (e) Cu–Co/Z1A4; (f) Cu–Co/g-Al2O3).
very small or existed in an amorphous state.19 XRD diffraction
peaks for HZSM-5 with 2 theta values of 23.2ꢀ, 24.0ꢀ and 24.6ꢀ
(Fig. 6a) or g-Al2O3 with 2 theta values of 36.9ꢀ, 44.9ꢀ and 59.2ꢀ
(Fig. 2f) were found. With the increase of g-Al2O3 content in the
support, the intensities for XRD peaks corresponding to HZSM-5
decreased, while those for g-Al2O3 phase increased. No novel
phase formation occurred during ball milling.
Fig. 6 showed the XRD patterns of copper–cobalt catalysts
supported on various supports in oxidation state. The results
indicated that both copper species and cobalt species were highly
dispersed, no XRD diffraction peaks was found for the copper or
cobalt species, suggesting that CuO or Co3O4 particle size was
Table 3 XPS data of Co 2p region of catalysts on various supports
Peak areas
Position (eV)
Cu–Co/HZSM-5
Cu–Co/Z1A1
Cu–Co/g-Al2O3
Co0 (778.3 eV)
Co2+ (780.2 eV)
Co0/Co2+
6031.90 (59.62%)
4085.78 (40.38%)
1.48
5706.48 (48.49%)
6062.03 (51.51%)
0.94
3849.10 (57.34%)
2864.01 (42.66%)
1.34
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Table 4 Catalytic performances of catalysts on various supports in terms of CO conversion and carbon-based selectivity of productsa
Selectivity products (C%)
Catalysts
CO conversion (%)
Hydrocarbons
Methanol
C2–8 alcohols
CO2
Cu–Co/HZSM-5
Cu–Co/Z1A0.5
Cu–Co/Z1A1
Cu–Co/Z1A2
Cu–Co/Z1A4
Cu–Co/g-Al2O3
Cu–Co/HZSM-5+ Cu–Co/g-Al2O3 (1 : 1)
Cu–Co/HZSM-5 + g-Al2O3
2.73
20.15
21.31
18.16
16.71
16.47
9.42
49.28
41.71
28.68
35.11
42.72
36.56
41.82
35.24
25.55
17.98
21.30
18.87
17.01
23.99
21.40
22.34
18.45
33.87
41.80
38.13
33.39
34.25
30.35
35.45
6.72
6.44
8.22
7.89
6.88
5.20
6.43
6.97
17.78
a
Working conditions: T ¼ 300 ꢀC, P ¼ 5.0 MPa, GHSV ¼ 7200 hꢁ1
.
a portion of micropore into the catalyst. Secondly, the smaller
mesopore of support beneted the dispersion of copper and
cobalt species due to the nano-connement effect, thus, smaller
mixed nanoparticles of core–shell structure or Cu–Co alloy
essential for HAS could be obtained. Thirdly, mesopore is very
important for reagents diffusion to active sites, while micropore
were important to grantee the formation of normal paraffin and
straight carbon chain alcohols. Proper micropore volume to
mesopore volume ratio was found closely related with CO
conversion and selectivity to higher alcohols.
3.2 Catalytic performances
The catalytic performances in terms of CO conversion and
selectivity to products were shown in Table 4. In order to
investigate the effect of ball milling, catalyst containing 1 : 1
weight ratio of CuCo/HZSM-5 and CuCo/g-Al2O3 were prepared
and evaluated. The reaction products include C1–C8 straight
alcohols and C1–C10 normal paraffins and a small fraction of
CO2. The reaction products agreed with the Anderson–Schulz–
Flory distribution. From Table 4, it could be seen that the
catalytic performance of CuCo/HZSM-5 was unsatisfactory,
conversion of CO was only 2.73%, and the selectivity to higher
alcohols was only 18.45%. The catalytic performance of CuCo/g-
Al2O3 was better than CuCo/HZSM-5, with CO conversion of
16.47% and selectivity to higher alcohols of 43.25%. Interest-
ingly, catalyst containing 1 : 1 weight ratio of CuCo/HZSM-5 and
CuCo/g-Al2O3 showed catalytic performance in terms of CO
conversion and selectivity to higher alcohols just the same as
the weighted mean performance of CuCo/HZSM-5 and CuCo/g-
Al2O3. No interaction between the two catalysts occurred.
However, CuCo catalyst over mixed supports showed superior
performance than both CuCo/HZSM-5 and CuCo/g-Al2O3.
Among them, CuCo/Z1A1 showed best performance under
4 Conclusions
Ball milling HZSM-5 and g-Al2O3 mixture altered the pore
structure of g-Al2O3, retaining part of pore volume but
decreasing the most probable pore size. CuCo bimetallic cata-
lysts over the mixed supports showed smaller average particle
size and better dispersion of cobalt and copper species, as evi-
denced by the TEM characterization. Due to the nano-
connement effects of nano pore, better performances were
observed for CuCo catalysts over mixed supports. H2-TPR
results suggested copper and cobalt species in the smaller
mesopores of supports were easier to reduction, increasing
Cud+/Cu2+ ratio while decreasing the Co0/Co2+ ratio (a factor
closely related with the carbon chain growth). Thus, higher CO
conversion and selectivity to higher alcohols were obtained.
Over CuCo/Z1A1 catalyst, CO conversion could reach 21.3% and
selectivity to higher alcohols of 41.80%. Through the pore
modication and nano connement effects, smaller nano-
particles for copper and cobalt species with close interaction
could be obtained, which were supposed to be very important
for higher alcohols synthesis from CO hydrogenation.
ꢀ
working conditions of T ¼ 300 C, P ¼ 5.0 MPa and GHSV ¼
7200 hꢁ1. Conversion of CO reached 21.3% and selectivity to
higher alcohols was 41.80%. The catalytic activity of CuCo/Z1A1
was higher than that of CuCo/HZSM-5 + g-Al2O3, which indi-
cated that the composite support of ball milling was more
advantageous to the catalytic activity than the simple physical
composite support. Further increase the g-Al2O3 content in ZaAb
supports resulted in poorer performance. The Ar physical
adsorption results indicated that with the increase of g-Al2O3
content in ZaAb supports, the ratios between the mesopore
volumes and micropore volumes increased, from at the same
time, the pore size also increased. The increased pore size
favored the growth of metallic particles during reduction and
reaction. Thus, poorer performance could be predicted, as
revealed in Table 4. CuCo/g-Al2O3 showed highest mesopore
volume and largest most probable pore size, while its catalytic
performance was poorer than the CuCo catalysts using ZaAb
supports. The reasons were ascribed to the following factors.
Firstly, ball milling of HZSM-5 and g-Al2O3 resulted in smaller
mesopore size of ZaAb supports, at the same time introduced
Conflicts of interest
There are no conicts to declare.
Acknowledgements
This work is nancially supported by Open Project of State Key
Laboratory of Physical Chemistry of Solid Surfaces (201412).
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 14592–14598 | 14597

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14598 | RSC Adv., 2019, 9, 14592–14598
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