Elucidating the nature and role of copper species in catalytic carbonylation of methanol to methyl acetate over copper/titania-silica mixed oxides

Article abstract of DOI:10.1039/c7cy00719a

In this study, a series of copper/titania-silica mixed oxide (Cu/TS) catalysts with different copper contents were prepared by a sol-gel method. The catalytic activity was evaluated by halide-free methanol carbonylation to methyl acetate (MA). The properties of the catalysts were mainly characterized by N₂ adsorption-desorption, X-ray diffraction, dissociative N₂O chemisorption, X-ray photoelectron spectroscopy, temperature-programmed desorption of ammonia and in situ Fourier transform infrared. The results show that the crystal size and aggregation degree of Cu increase with increasing Cu content. In addition, the amount of surface Cu⁺ firstly increases and then decreases, and the maximum is 1.560 mmol g^-1 for the 10.24 Cu/TS catalyst. Both the amounts of adsorbed CO and surface Lewis acid sites are found to be proportional to the amount of surface Cu⁺ species. The catalytic performance shows that the space time yield (STY) of MA is also strongly related to the amount of surface Cu⁺ species, and the 10.24 Cu/TS catalyst has a maximum of 1.770 mol h^-1 kg_cat^-1. It is found that the surface Cu⁺ species act not only as metal sites which adsorb CO but also as Lewis acid sites which promote the adsorption of methanol (methoxy). Furthermore, the activation of CO is the major factor for the MA synthesis.

Full text of DOI:10.1039/c7cy00719a

Catalysis
Science &
Technology
View Article Online
View Journal
PAPER
Elucidating the nature and role of copper species
in catalytic carbonylation of methanol to methyl
acetate over copper/titania–silica mixed oxides†
Cite this: DOI: 10.1039/c7cy00719a
Xianjie Meng, *ab Heqin Guo,* Qiang Wang,
Bo Hou and Debao Li*
a
a
a
a
Yong Xiao, Congbiao Chen,
a
a
In this study, a series of copper/titania–silica mixed oxide (Cu/TS) catalysts with different copper contents
were prepared by a sol–gel method. The catalytic activity was evaluated by halide-free methanol carbonyl-
ation to methyl acetate (MA). The properties of the catalysts were mainly characterized by N
2
adsorption–
desorption, X-ray diffraction, dissociative chemisorption, X-ray photoelectron spectroscopy,
2
N O
temperature-programmed desorption of ammonia and in situ Fourier transform infrared. The results show
that the crystal size and aggregation degree of Cu increase with increasing Cu content. In addition, the
+
−1
amount of surface Cu firstly increases and then decreases, and the maximum is 1.560 mmol g for the
1
0.24 Cu/TS catalyst. Both the amounts of adsorbed CO and surface Lewis acid sites are found to be pro-
+
Received 20th April 2017,
Accepted 7th July 2017
portional to the amount of surface Cu species. The catalytic performance shows that the space time yield
+
(
STY) of MA is also strongly related to the amount of surface Cu species, and the 10.24 Cu/TS catalyst has
−1
cat−1
+
a maximum of 1.770 mol h kg
. It is found that the surface Cu species act not only as metal sites
DOI: 10.1039/c7cy00719a
which adsorb CO but also as Lewis acid sites which promote the adsorption of methanol (methoxy). Fur-
thermore, the activation of CO is the major factor for the MA synthesis.
rsc.li/catalysis
Previous research mainly focused on silica alumina molec-
ular sieve supported copper catalysts, such as Cu–H-MOR
1
. Introduction
As an important industrial raw material, methyl acetate (MA)
is mainly used as an organic solvent in the production pro-
cess of resin, paint, leather, etc. It is also an ideal precursor
and Cu–H-Y. Corma et al. prepared Cu–H-MOR by an ion-
exchange method and obtained about 85% MA selectivity. By
detecting the intermediate species using in situ FTIR and
MAS NMR spectroscopy, they proposed a multisite active cen-
1
–4
for the synthesis of ethanol by MA hydrogenation, which is
5
–7
+
an attractive liquid fuel. In general, MA is produced by es-
ters mechanism in which Cu activates CO and the Brønsted
8
15
terification of acetic acid and methanol, among which acetic
acid site activates methanol (methoxy) on the Cu–H-MOR.
acid is traditionally produced by the homogeneous carbonyla-
tion of methanol on a noble metal catalyst in the presence of
a halogen as a promoter. The high cost of the catalysts, cor-
Boronat et al. investigated the different carbonylation ac-
tivities of methanol in the 8MR pockets and in the main
12MR channels of mordenite using a DFT method. They
found that the Brønsted acid sites within the 8-membered
ring (8MR) channels are responsible for MA synthesis,
while those in the 12-membered ring (12MR) lead to catalyst
9
rosion to the equipment and difficult separation of the prod-
1
0
ucts limit its large-scale application.
The direct free-halide carbonylation of methanol or di-
methyl ether (DME) to MA on a solid catalyst is a promising
technology. Several types of heterogeneous catalysts, such as
1
6
deactivation. Summarizing the literature, it is incontrovert-
ible that two types of active sites, a metal site which can acti-
vate CO to form CO*, and an acid site which can activate
methanol to form methoxy, are needed for MA synthesis.
However, which valence of Cu species responsible for CO
11
12,13
14
12,15
supported rhodium, nickel,
iridium and copper,
were applied in the carbonylation of methanol. Among the
reported catalysts, the copper based catalyst showed the best
activity due to its moderate CO activation capacity.
+
activation is not clear. Corma et al. only proposed that Cu
might be the active site but did not provide evidence for the
quantitative relationship between the CO adsorption and the
a
State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese
Academy of Science, Taiyuan 030001, Shanxi, PR China.
E-mail: heqinguo@sxicc.ac.cn, dbli@sxicc.ac.cn
+
number of Cu species. On the other hand, in the carbonyla-
0
b
tion of DME, Zhan et al. declared that Cu rather than
University of Chinese Academy of Sciences, Beijing 100039, PR China
+
Cu has an enhancement effect on the conversion of DME
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
1
7
c7cy00719a
to MA.
This journal is © The Royal Society of Chemistry 2017
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
Moreover, it is arguable that the Brønsted acid sites are re-
velopment Co., Ltd, and acetylacetone (ACET) from Aladdin
Reagent Company.
sponsible for the adsorption of methanol, because the copper
species act as Lewis acid sites which can also adsorb metha-
nol. For example, in oxidative carbonylation of methanol to
dimethyl carbonate, King proposed that the adsorption and
activation of methanol proceed on the surface copper species
2 2 2
CuCl /TiO –SiO catalysts with different copper contents
were prepared by a sol–gel method. A typical process is as fol-
−
1
lows: TEOS (41.67 g) and HCl solution (15 ml, 3 mol L )
were added to ethanol (EtOH) to obtain solution A. TBOT
1
8,19
−1
rather than on the H-Y supports.
According to the above
(68.07 g), HCl solution (15 ml, 3 mol L ) and ACET (2 g)
literature, it is necessary to elucidate which sites on copper-
based catalysts are responsible for activating methanol and
CO. It is difficult to achieve the above goal for the reported
silica alumina molecular sieve supported copper catalysts.
This is because the silica alumina molecular sieves them-
selves have a strong ability to adsorb methanol, which may
mask the role of copper in the activation of methanol. Fur-
thermore, the acid site and metal site may change with time
due to the poor stability of these catalysts. This is bound to
increase the difficulty of the research.
were added to EtOH to obtain solution B. After the two solu-
tions were mixed together under vigorous stirring, CuCl so-
2
lution (10 wt%) was added dropwise. Subsequently, the
mixed solution was heated under reflux for 3 hours to form a
sol, which was then stored overnight with stirring until
converted into a solid gel. The obtained solid gel was firstly
dried in air at 70 °C for 10 h, then heated to 120 °C and held
for another 12 h to remove alcohol and water. Finally, the
−
1
precursor was calcined in air at 400 °C (1 °C min heating
rate) for 4 h. The loading of copper was 5–15 wt% and the ex-
act copper content was determined by ICP-OES (Table 1). The
resulting catalysts were denoted 5.45 Cu/TS, 8.15 Cu/TS,
10.24 Cu/TS, 12.64 Cu/TS and 15.76 Cu/TS, respectively. For
Mixed silica–titania oxides have good stability and weak
acidity, so they are suitable candidates for the research on
the active sites in methanol carbonylation. Above all, the
good stability of these materials is necessary for the study on
the MA synthesis mechanism. Due to their weak acidity, they
2 2
comparison, pure TiO –SiO (TS) was also prepared by the
sol–gel method, and all catalysts had the same Ti/Si molar ra-
tio (about 1).
2
0
can inhibit alcohol dehydration to ether, which is conve-
nient for studying the role of copper species in MA synthesis.
Furthermore, the presence of Ti species in the silica–titania
mixed oxides can promote the dispersion of active compo-
2.2. Characterization
2
1
nents with well-controlled surface properties. Therefore
copper can be highly dispersed on the surface. This provides
a possibility for the study on the relationship between CO ad-
Inductively coupled plasma optical emission spectroscopy
(ICP-OES) analyses were carried out on a Thermo iCAP 6300
(Thermo Fisher Scientific).
+
0
sorption and the number of Cu or Cu species.
An Autosorb-iQ2 instrument was employed to obtain ad-
sorption/desorption isotherms at −196 °C. The specific sur-
face area was evaluated by the Brunauer, Emmett and Teller
(BET) method and the pore-size distribution was calculated
by the Nonlocal Density Functional Theory (NLDFT) method
Based on the above analysis, the mixed silica–titania oxide
supported copper catalysts with different contents of copper
were prepared by a sol–gel method in the present study and
they were applied in the gas carbonylation of methanol to
MA free of halide. The copper species were characterized by
2
2–24
using the adsorption branch of the isotherm.
in situ X-ray diffraction (XRD), dissociative N
tion, and in situ X-ray photoelectron spectroscopy (XPS). The
surface acidity was analyzed by in situ temperature-
2
O chemisorp-
In situ XRD was detected using a Panalytical X'Pert3 dif-
fractometer with Mo Kα radiation over a 2θ range of 5–40° at
40 kV and 30 mA. The average particle size of Cu was calcu-
lated using the Scherrer equation d = kλ/(FW·cosIJθ)), (k = 1,
λ = 0.15406 nm, FW is the peak width of half height).
3
programmed desorption of ammonia (NH -TPD) and in situ
pyridine adsorption infrared spectroscopy (Py-IR). Their ad-
sorption properties for CO and methanol were characterized
by in situ FTIR. Through the analysis and combination of the
above date, the relationship between copper species, surface
acidity and adsorptive properties for CO and methanol as
well as activity for MA were studied. The aim of the study is
to elucidate the nature and role of Cu species in the carbonyl-
ation of methanol.
UV-vis absorption spectra of the catalysts were obtained
using a Shimadzu UV 3600 UV-vis-NIR spectrophotometer.
Temperature-programmed reduction (TPR) was recorded
on a TP-5080 chemical adsorption instrument with a thermal
conductivity detector (TCD) which was used to analyze the ef-
fluent gas. The calcined catalysts (100 mg, 60–80 mesh) were
loaded into a quartz tube and dried in an Ar stream at 100 °C
for 1 h before reduction. The catalysts were firstly reduced in
−
1
2+
CO (60 mL min ) at 230 °C for 3 h. In this process, Cu spe-
0
+
cies are reduced to Cu or Cu . Then the catalysts were
2
. Experimental
purged under Ar and cooled to 50 °C. After that, the reduced
2
.1. Catalyst preparation
copper species on the surface were oxidized in 10% N O/Ar
2
Tetraethoxysilane (TEOS), AR, was purchased from Tianjin
Kermel Chemical Reagent Co., Ltd, tetrabutyl titanate
(pulse inlet) at 50 °C for some time to guarantee the peak of
nitrogen in the effluent gas was stable. The reaction equation
is 2Cu + N O ⇌ Cu O + N . Subsequently, the catalysts were
(TBOT), AR, from Sinopharm Chemical Reagent Co., Ltd,
2
2
2
CuCl ·2H O (AR, 99%)from Tianjin Guangfu Technology De-
2
2
flushed with Ar. Finally, H -TPR was carried out (10% H /Ar,
2 2
Catal. Sci. Technol.
This journal is © The Royal Society of Chemistry 2017

View Article Online
Catalysis Science & Technology
Paper
Table 1 ICP-OES results of the investigated catalysts
Catalyst denotation TiO
2
–SiO
2
5%CuCl
2
/TiO
2
–SiO
2
8%CuCl
2
/TiO
2
–SiO
2
10%CuCl
2
/TiO
2
–SiO
2
12%CuCl
2
/TiO
2
–SiO
2
2 2 2
15%CuCl /TiO –SiO
Cu content (%)
Ti/Si (mol)
0
0.97
5.45
1.02
8.15
0.99
10.24
1.13
12.64
1.08
15.76
1.11
−
1
6
0 mL min , 50 to 700 °C with a heating rate of 10 °C
was used as a probe molecule to determine the concentration
of the Brønsted and Lewis acid sites of all reduced catalysts.
Firstly, each catalyst (∼15 mg) was pressed into a 13 mm wa-
fer, weighed, then placed into a catalyst holder and loaded
−
1
min ) to reduce the surface Cu O to metal copper. The reac-
tion equation is Cu
sumption in this TPR was denoted X (mol). The dispersion
2
2 2 2
O + H ⇌ 2Cu + H O. Hydrogen con-
(
D) of Cu and exposed Cu surface area (S) were calculated
into an in situ cell with CaF windows. Secondly, the catalysts
2
2
5,26
through the equations as follows.
were pretreated at 230 °C for 3 h under CO and then cooled
to 50 °C under vacuum. The background spectra were
obtained at this time. Thirdly, the catalysts were exposed to
pyridine vapor for 30 min and evacuated for 30 min to elimi-
nate physically adsorbed pyridine. Finally, 150 °C was set as
the desorption temperature and the spectra were collected in
−
1
the range 4000–1100 cm by averaging 32 scans at a resolu-
−
1
tion of 4 cm . The Brønsted and Lewis acid concentrations
2
7
were calculated according to the literature.
In situ FTIR was carried out to probe the adsorption of CO
and methanol. The catalysts were heated at 120 °C in Ar for 1
h to remove the water on the surface. Then the catalysts were
reduced by CO at 230 °C for 3 h and purged by Ar. After that,
the catalysts were exposed to CO at 50 °C for 0.5 h. Subse-
quently, the CO-saturated catalysts were purged by an Ar flow
again in order to remove the gas phase CO molecules. Fi-
nally, the spectra were collected by averaging 64 scans at 4
In these equations, nCu is the molar quantity of copper,
N
av is Avogadro's constant, MCu is the relative atomic mass of
−
1
19
copper (63.46 g mol ) and 1.4 × 10 is the number of copper
atom per square meter where the average surface area of a
−
2
2
copper atom is assigned to be 7.11 × 10 nm .
XPS and Auger electron spectroscopy (XAES) were
performed on a Kratos AXIS ULTRA DLD electron spectrome-
ter with 75 W Al K
α
(hv = 1486.6 eV) radiation. The catalysts
−1
cm resolution. Subtraction of the spectra from those before
were compressed into a pellet of 2 mm thickness and then
mounted on a catalyst holder by utilizing double-sided adhe-
sive tape for XPS analysis. The catalysts were reduced by CO
at 230 °C for 3 h and then transferred into the XPS chamber
probe molecule adsorption shows bands due to adsorbed
species. The adsorption of methanol was carried out at 50 °C
after the adsorption of CO. In particular, methanol was dosed
using a saturator with flowing Ar.
Energy Dispersive X-Ray Fluorescence (EDXRF) was ap-
plied on an UX220 to trace the chloride ion during the reac-
tion including pretreatment and carbonylation.
−
8
without exposure to air and evacuated (<10 Torr) overnight.
Finally, the catalyst holder was transferred to the analysis
chamber for XPS study. The base pressure inside the analysis
−
10
chamber was usually maintained at better than 10
Torr.
The binding energies were referenced to the C1s line at 284.6
eV from adventitious carbon (ESI† Fig. S2). The curve
deconvolution of the obtained spectra was performed by
using the XPS peak fitting program (XPSPEAK41, Chemistry,
CUHK).
2
.3. Carbonylation reaction
Catalytic measurements were carried out in a continuous
flow fixed-bed containing 2.0 g of the catalysts (20–40 mesh).
Before reaction, the catalysts were reduced by pure CO for 3
h at 230 °C, and then methanol was introduced into the reac-
tor through a constant-flux pump. The flow rate of the gas
was controlled by mass-flow controllers and the liquid rate
was controlled by the pump. The feed composition was meth-
anol: CO = 15 v/85 v. The reaction products were analyzed by
on-line gas chromatography (GC-950) using a Propack T col-
umn and a TDX-01 column equipped with a TCD. The separa-
tion of methanol, DME, methyl formate (MF) and MA was
carried out on a capillary column HP-Plot/Q. The product se-
lectivity was calculated on a carbon molar base: S = Y n /
NH -TPD was performed to determine the acidity of the
3
catalysts. The catalysts (0.1 g, 60–80 mesh) were firstly heated
−
1
in an Ar or CO flow (flow rate, 60 mL min ) at 230 °C for 3
h, and then cooled to 50 °C. After that, the catalysts were ex-
posed to NH
3
until saturation, and purged by Ar for 2 h in or-
der to eliminate the physically adsorbed NH . Finally, TPD
3
−
1
was conducted (50 to 650 °C, 10 °C min ) and the NH in
3
the effluent was detected and recorded by the Online CDMC
chromatography workstation (Shanghai). The stripped off
−
1
ammonia was collected using 0.01 mol L HCl solution,
followed by acid base titration to measure the acid content.
i
i i
P
i i i
Y n × 100%, where i is the reaction product, S is the selec-
FTIR was employed using
a
Thermo Nicolet 7000
tivity to product i, Y is the number of carbon atoms of prod-
uct i, and n is the number of moles of product i.
i
connected to a gas-dosing and evacuation system. Pyridine
i
This journal is © The Royal Society of Chemistry 2017
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
Table 2 Apparent dispersions and crystal sizes of Cu in the catalysts
3
. Results and discussion
a
3
.1. Structure and textural properties of the catalysts
2
N -adsorption–desorption
XRD dp (nm)
2
−1
3
−1
Catalysts
TS
S
BET (m g
)
V
pore (cm g
)
d (nm) Cu100
2
The N adsorption–desorption isotherms and the pore distri-
bution of the catalyst are shown in Fig. 1. All the catalysts
present typical type I isotherms which indicate the existence
242.5
233.2
233.0
0.109
0.099
0.103
0.102
0.103
0.100
1.91
1.79
1.78
1.79
1.78
1.78
—
5.45 Cu/TS
15.6
18.4
22.4
28.6
39.5
2
8
8.15 Cu/TS
of micropores. All the pores are smaller than 2 nm, and the
introduction of copper leads to a rapid decrease of the
amount of pores of about 1.6 nm and an increase of the
amount of pores of between 1.0 to 1.5 nm. The calculated tex-
tural properties of the catalysts are shown in Table 2. The
copper content has little influence on the pore diameter and
surface area (SBET). This confirms that there is no intensive
destruction or blockage of the support. From these results,
it can be concluded that the highly dispersed copper centers
are expected to be prevalently exposed on the walls of the
micropores.
1
1
0.24 Cu/TS 232.4
2.64 Cu/TS 232.2
15.76 Cu/TS 231.4
a
Calculated using the Scherrer equation from XRD data after
reduction.
2
9
on the reduced catalysts is also calculated using the Scherrer
equation (see Table 2). As the copper content increases, the
size also increases from 15.6 nm to 39.5 nm, which indicates
the aggregation of copper.
The crystal structure properties of the catalysts before and
after CO reduction are verified by XRD characterization (see
Fig. 2). It can be seen that, all the catalysts before reduction
exhibit a similar peak around 2θ = 12° due to the presence of
In view of the insensitivity of XRD to the copper species in
the fresh catalysts, diffuse reflectance UV-vis absorption is
applied to characterize the dispersion of copper (see Fig. 3).
For the TS catalyst, only one type of band in the range 200–
400 nm (6.2–3.1 eV) can be seen in the plot, which is
assigned to the ligand-to-metal charge-transfer (LMCT) band.
After the introduction of copper, the LMCT band shifts to the
range 200–500 nm (6.2–2.5 eV). In addition, another band in
the range 500–800 nm (2.5–1.55 eV) is observed, which is at-
tributed to the d–d transition bands. With increasing Cu con-
tent, the band at 260 nm is always present while the band at
360–410 nm gradually forms especially when the copper con-
tent is higher than 10.45%. The band centered around 260
2
1
amorphous silicon dioxide. No peaks for crystalline tita-
nium and copper were found, implying their high dispersion.
After reduction by CO at 230 °C for 3 h, the typical diffraction
0
peaks of Cu at 2θ = 19.59, 22.66, 32.23 and 37.94° are
detected on all Cu/TS catalysts. Nevertheless, the diffraction
+
peaks for Cu do not appear on the XRD patterns. It is proba-
+
bly because the Cu particles are too small to be detected.
0
With increasing copper content, the intensity of the Cu dif-
fraction peaks increases which indicates the increasing crys-
0
2+
2−
tal size of Cu . Simultaneously, there is a shift in 2θ from
nm is characteristic of highly dispersed (isolated) Cu –O in
3
2
1
9.59° to 19.45° which indicates that the interaction between
octahedral coordination and the band at 360–410 nm is
3
0,31
33
copper and the support weakens.
The crystal size of Cu
characteristic of oligomers of type Cu–O–Cu.
This
Fig. 1 Nitrogen adsorption/desorption isotherms of the catalysts previously outgassed at 150 °C (A); pore distribution calculated from the
nitrogen adsorption/desorption isotherms (curves are shifted) (B): (a) TS, (b) 5.45 Cu/TS, (c) 8.15 Cu/TS, (d) 10.24 Cu/TS, (e) 12.64 Cu/TS and (f)
1
5.76 Cu/TS.
Catal. Sci. Technol.
This journal is © The Royal Society of Chemistry 2017

View Article Online
Catalysis Science & Technology
Paper
Fig. 2 XRD patterns of the catalysts before (A) and after (B) reduction by CO: (a) TS, (b) 5.45 Cu/TS, (c) 8.15 Cu/TS, (d) 10.24 Cu/TS, (e) 12.64 Cu/
TS and (f) 15.76 Cu/TS.
+
+
0
phenomenon indicates that the copper dispersion decreases,
which is consistent with the XRD results.
To further gain quantitative information about the metal
dispersion and surface composition of the catalysts, TPR
culate the Cu /(Cu + Cu ) ratio from the Cu LMM XAES spec-
tra (see Table 3). It is found that this value increases from
36.66% to 60.41% when the Cu loading is increased, which is
possibly because the increase of crystal size promotes incom-
2
+
+
characterization after dissociative N O chemisorption is car-
plete reduction of Cu to Cu (see XRD and UV-vis). Com-
bined with the TPR and ICP results, the amounts of different
copper species including Cu and Cu are calculated (see
Table 3). It is found that the amount of Cu firstly increases
and then declines as the copper content increased, and the
2
ried out (see Table 3). It is found that the dispersion of cop-
per on the reduced catalysts decreases with increasing copper
content, and the minimum is only 10.25% for the 15.76 Cu/
TS catalyst. The surface area of copper also decreases from
+
0
+
2
−1
−1
2
88.46 to 69.34 m g . These trends are in line with those of
10.24 Cu/TS catalyst has a maximum of 1.560 mmol g . The
0
the XRD and UV-vis results. This may be because the interac-
tion between copper and the support is strong when the cop-
per loading is low, which is favorable to stabilize the copper
amount of Cu exhibited the same change trend, but the 8.15
−
1
Cu/TS catalyst achieves a maximum of 1.701 mmol g . In the
carbonylation of methanol and DME, CO was proposed to be
activated on reduced copper sites.
Cu and Cu on the catalyst surface may be associated with
their adsorption capacity for CO, and then influence the syn-
thesis of MA.
3
4
15,17
particles and resist their fast aggregation. With further in-
creasing copper content, the weak interaction between copper
and the support leads to the increase of crystal size and for-
mation of oligomers species.
Hence, the amounts of
+
0
3
.2. Analysis of Cu species in Cu/TS
3.3. Acidity generated by copper species
In situ XPS and XAES are carried out to determine the valence
states of the Cu species on the surface of catalyst. As shown
in Fig. 4, only two peaks centered at 932.5 and 952.3 eV are
observed on the reduced catalysts. They are attributed to
Cu2p3/2 and Cu2p1/2, respectively. The disappearance of the
Cu2p satellite peak centered at 942–944 eV (see Fig. S2 in the
The acidity of the catalyst before and after reduction is char-
acterized using NH -TPD technology (see Fig. 6A and B). The
3
TS catalyst is spread in the temperature range 150–350 °C, at-
tributed to the weakly adsorbed ammonia. There is no posi-
tional change of the desorption peak when copper is intro-
duced which illustrates that copper before reduction does
not change the acid strength. With increasing copper con-
tent, the number of acid sites decreases which may be due to
2
+
ESI†) indicates that all Cu species have been transformed
0
+
35–37
into Cu or Cu during the reduction process.
+
0
2+
In order to quantitatively distinguish Cu from Cu , the
Cu LMM XAES spectra (see Fig. 5) are analyzed. As can be
seen, all catalysts exhibit two obvious overlapping peaks at
the coverage of Cu replacing the H of hydroxyl groups.
3
8
The TS catalyst shows similar features of NH desorption
3
before and after reduction by CO. For the reduced Cu/TS cat-
0
+
5
66 and 571 eV, which correspond to Cu and Cu , respec-
alysts, another desorption peak of NH at about 344 °C due
3
3
9,40
tively.
Then overlapping peak resolving is applied to cal-
to middle strong acid sites appears. This may be generated
This journal is © The Royal Society of Chemistry 2017
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
Fig. 3 Diffuse reflectance UV-vis absorption spectra of all catalysts. Inset plots are the enlarged view from 300–500 nm: (a) TS, (b) 5.45 Cu/TS, (c)
.15 Cu/TS, (d) 10.24 Cu/TS, (e) 12.64 Cu/TS and (f) 15.76 Cu/TS.
8
Table 3 Cu components in the surface of reduced Cu/TS catalysts
N
2
O-TPR
Binding energy(eV)
+
0
+c
0d
Cu /(Cu
Total surface
Cu (mmol g
Cu
Cu
2
Cu−1
0
+
+ a
b
−1
−1
−1
Catalyst
DCu (%)
S
Cu (m g
)
Cu
Cu
+ Cu ) (%)
)
(mmol g
)
(mmol g )
5
8
1
1
1
.45 Cu/TS
.15 Cu/TS
0.24 Cu/TS
2.64 Cu/TS
5.76 Cu/TS
42.64
38.09
27.79
13.81
10.25
288.46
257.68
187.99
93.42
565.66
565.63
565.60
565.81
565.51
570.37
569.81
570.28
570.32
570.18
36.66
45.20
54.82
58.83
60.41
2.324
3.104
2.846
1.745
1.615
0.852
1.403
1.560
1.027
0.976
1.472
1.701
1.286
0.718
0.639
69.34
a
b
c
+
+
0
+
d
0
Calculated based on Cu LMM XAES deconvolution. Total surface Cu = ICP × DCu
.
Cu = total surface Cu × Cu /(Cu + Cu ). Cu = total
+
surface Cu − Cu .
by the reduced copper species on the surface of the catalyst.
Then these two peaks are deconvoluted to calculate the acid-
acid sites during reduction, CO is used as reducing gas in-
4
4
stead of a H
2
atmosphere. The FTIR spectra of pyridine
ity of each peak according to the desorbed amount of NH
see Table 4). With increasing copper content, the amount of
3
adsorbed on the catalysts are shown in Fig. 7. Typical bands
−
1
(
attributed to Brønsted acid sites (∼1540 and ∼1630 cm )
−
1
weak acid sites decreases rapidly and eventually disappears
which may be attributed to the coverage of copper. Mean-
while, the amount of middle strong acid sites decreases
slowly when the copper content is low but then decreases sig-
nificantly which could possibly be due to the copper cations
on the surface. Combined with the UV-vis and XPS result, it
can be deduced that the copper cations create new acid sites,
which is consistent with the dispersion information.
and Lewis acid sites (∼1450 and ∼1610 cm ) are observed.
When the copper is loaded, the characteristic band at 1446
−
1
−1
cm corresponding to Lewis acid sites shifts to 1450 cm .
+
This phenomenon demonstrates that Cu species create
Lewis acid sites.
As far as we know, the critical diameters of Py and NH3
are 0.6 nm and 0.26 nm, respectively, which are much
smaller than the average pore size (1.78–1.91 nm) obtained
In order to further explore the nature of the relationship
between the copper content and the surface acidity, pyridine
is employed to characterize both Brønsted and Lewis acid
from N adsorption–desorption characterization. As a conse-
quence, it can be assumed that the acid site amounts
2
3
obtained from NH -TPD and Py-IR are equal. The areas of the
4
1–43
−1
−1
sites by in situ FTIR spectroscopy.
The results of NH3-
bands at ∼1540 cm and ∼1446 cm are corrected using
the corresponding molar extinction coefficients of pyridine
adsorbed on each type of acid site. The ratios of Lewis acid
to Brønsted acid sites are calculated by this method. Com-
TPD suggest that there are no strong acid sites in the surface
of the catalysts, so a low desorption temperature (150 °C) is
set to identify the Brønsted acid sites and Lewis acid sites of
the reduced catalysts. To avoid the regeneration of Brønsted
3
bined with the total amount of acid sites calculated by NH -
Catal. Sci. Technol.
This journal is © The Royal Society of Chemistry 2017

View Article Online
Catalysis Science & Technology
Paper
Fig. 4 Cu2p XPS spectra of the reduced Cu/TS catalysts: (a) 5.45 Cu/TS, (b) 8.15 Cu/TS, (c) 10.24 Cu/TS, (d) 12.64 Cu/TS and (e) 15.76 Cu/TS.
Fig. 5 Cu LMM XAES spectra of the reduced Cu/TS catalysts: (a) 5.45 Cu/TS, (b) 8.15 Cu/TS, (c) 10.24 Cu/TS, (d) 12.64 Cu/TS and (e) 15.76 Cu/TS.
TPD, the amount of Lewis and Brønsted acid sites are
obtained and shown in Table 4. With increasing copper con-
tent, the amount of Brønsted acid sites decreases dramati-
cally and completely disappears when the copper content
reaches 12.64%. This clearly indicates that the protons are
gradually exchanged by Cu cations as the copper content in-
creases. In contrast, the amount of Lewis acid sites increases
firstly and then decreases, which reaches the maximum
ing trend of the Lewis acid sites is similar to that of the
amount of surface Cu species. This phenomenon indicates
that there is a strong relationship between them.
+
3.4. Adsorption of CO and methanol
In situ FTIR for CO chemisorption is applied to differentiate
the location and state of Cu species on the Cu/TS catalysts. It
−
1
+
(0.457 mmol g ) on the 10.24 Cu/TS catalyst. Combined with
is known that CO adsorption on Cu cations is preferential,
4
5
the ICP, TPR and XPS results, it can be seen that the chang-
strong and irreversible. The reason is that the strong ligand
This journal is © The Royal Society of Chemistry 2017
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
3
Fig. 6 NH -TPD profiles of the catalysts before (A) and after (B) reduction.
3
Table 4 Acid strength distribution of the catalysts calculated using the results of NH -TPD and Py-FTIR
−3
−1
3
NH -TPD (×10 mmol g )
After reduction
Total acid sites
−3
−3
Before
reduction
L (×10
B (×10
−
1
−1
Catalysts
TS
Weak acid sites
Medium-strong acid sites
L/B
mmol g
)
mmol g )
584
455
354
248
125
101
584
583
512
472
349
289
584
65
54
27
10
0
0
518
458
445
339
289
1.37
3.17
8.39
31.26
∞
338
443
454
457
349
289
246
139
54
15
0
5.45 Cu/TS
8.15 Cu/TS
10.24 Cu/TS
12.64 Cu/TS
15.76 Cu/TS
∞
0
interactions between the support and the copper species ren-
exposed to methanol and the FTIR spectra of methanol
adsorbed on different catalysts at 50 °C are shown in
Fig. 9. All spectra are recorded after pretreatment and the
background spectra of the respective pretreated catalysts
are subtracted.
+
der the central Cu cations more electron-rich and favor the
4
6–48
insertion of CO.
All catalysts are reduced by CO at 230 °C
for 3 h prior to CO adsorption at 50 °C for 1 h.
As shown in Fig. 8, there is no adsorption peak for the TS
catalyst but all the reduced Cu/TS catalysts exhibit one
−
1
As shown in Fig. 9, two bands at 2955 and 2849 cm are
observed on all catalysts which are assigned to the CH va-
lence vibrations. Also, there is a CH deformation vibration
−
1
overlapping band at ∼2129 cm , which is attributed to CO
+
−1
adsorbed on Cu . The weak shoulder peak at ∼2120 cm can
+
−1
be seen for the catalysts, which may be due to the Cu –CO
complexes in different sites on the surface.
band at around 1456 cm . According to the previous litera-
4
9–51
53
−1
With increas-
ture, the couple of bands at 2955 and 2848 cm is very typi-
cal for CH stretching of methoxide species. Furthermore, the
ing copper content, the peak strength increases firstly and
then decreases and the maximum is obtained for the 10.24
Cu/TS catalyst. This trend is perfectly in keeping with the
−
1
broad low intensity band around 2570 cm can be assigned
to the combination of υ (CO) and δ (CH ) indicating indi-
3
+
amount of surface Cu species. Notably, there is no shift for
rectly the formation of methoxide. These bands indicate the
formation of methoxy species on all catalysts. By comparison
of the band intensities, it can be concluded that Cu/TS cata-
the CO adsorption band frequencies. This indicates that the
structure of the copper particles is not changed. This is
guided by the results of Dejong et al., who attributed frequen-
lysts adsorb much more methoxy species than the bare TS
−
1
−1
cies of adsorbed CO above 2120 cm to atomically rough
copper surfaces exposing a large number of coordinatively
support. Splitting of the ν(CH
3
) mode (2955/2923 cm and
−
1
2848/2825 cm ) can be observed when copper is loaded. It
may result from adsorbed methoxy species at different cop-
per species.
Furthermore, it is found that the Cu –CO band shifts from
2129 to 2115 cm as methanol is present. This indicates that
5
2
unsaturated surface atoms.
To see in which manner the admixture of CO and meth-
anol adsorb at the surface and which is the active adsorp-
tion site, the catalysts are pre-adsorbed with CO and then
+
−
1
Catal. Sci. Technol.
This journal is © The Royal Society of Chemistry 2017

View Article Online
Catalysis Science & Technology
Paper
Fig. 7 FTIR spectra of pyridine absorbed on the reduced catalysts: (a) TS, (b) 5.45 Cu/TS, (c) 8.15 Cu/TS, (d) 10.24 Cu/TS, (e) 12.64 Cu/TS and (f)
5.76 Cu/TS.
1
CO and methanol are able to adsorb on the same Cu sites.
With increasing copper content, the peak intensity of Cu –
CO shows the same trend with that in single adsorption of
CO. But the peak intensity of methoxy increases firstly and
then remains constant. So the key role in catalytic perfor-
mance will be discussed in the upcoming section.
chlorine in the 10.24 Cu/TS catalyst during the reaction on
stream. The variation of methanol conversion and the STY of
MA with reaction time have also been compared (see Fig. S3
and Table S1†).
It is found that the atomic ratio of Cl/Cu and the Cl con-
tent on the catalysts decreases rapidly with reaction time on
stream. Simultaneously, the peak of Cl in the XPS spectra ap-
parently decreases after 24 h reaction, indicating that the Cl
anions are lost during the carbonylation reaction. However,
the STY of MA increases firstly and then becomes stable. This
trend indicates that there is no direct relationship between
+
3
.5. Catalytic performance
To rule out the effect of chlorine in the catalytic reaction pro-
cess, the XPS and EDXR technologies are used to characterize
Fig. 8 In situ DRFTIR spectra of CO adsorbed on the Cu/TS catalysts: (a) TS, (b) 5.45 Cu/TS, (c) 8.15 Cu/TS, (d) 10.24 Cu/TS, (e) 12.64 Cu/TS and (f)
5.76 Cu/TS.
1
This journal is © The Royal Society of Chemistry 2017
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
Fig. 9 FTIR spectra of methanol adsorbed on the x Cu/TS catalysts after CO adsorption: (a) TS, (b) 5.45 Cu/TS, (c) 8.15 Cu/TS, (d) 10.24 Cu/TS, (e)
2.64 Cu/TS and (f) 15.76 Cu/TS.
1
Cl and MA synthesis. In other words, chlorine does not par-
ticipate in the reaction directly.
have similar adsorption capacities for methanol when the
copper content is higher than 8.15%. However, the selectivity
and yield of MA show great variations. That is to say, the ad-
sorption of methanol is not the key factor for MA synthesis.
Combining the results of Py-IR and CO adsorption FTIR, it is
found that the adsorption capacity for CO and the amount of
Lewis acid sites have the same variation tendencies as the
STY of MA. All of them achieved the peak values on the 10.24
Cu/TS catalyst. This suggests that the MA synthesis is
positively related to these two factors. In other words,
the Cu/TS catalyst having more Lewis acid sites and stronger
adsorption ability for CO is favorable for MA production. Fur-
thermore, by associating with the copper species, it can be
concluded that the adsorption strength of CO and the
amount of Lewis acid sites are proportional to the amount of
Then the catalytic performance of TS and Cu/TS catalysts
is shown in Table 5. On the TS catalyst, the methanol conver-
sion is 29.81% and DME is the only product. For the Cu/TS
catalysts, the conversion of methanol displays little variation
but the products are different from the TS catalyst, which are
DME, MA and MF.
With increasing copper content, the selectivity and STY of
MA increases firstly and then declines. Their maximum
values are obtained on the 10.24 Cu/TS catalyst being
−
1
−1
5
0.133% and 1.770 mol h kgcat , respectively. The different
catalytic performance of the catalyst is closely related to the
5
4
physical and chemical surface properties of the catalysts. By
comparing the adsorption performance of all catalysts to the
reagents, it is found that the adsorption ability for CO and
methanol is the significant requirement for MA synthesis,
which is in good accordance with that reported in the litera-
+
surface Cu species. By inference, the synthesis of MA has a
+
close relationship with the surface Cu species. In order to
provide further evidence for this relationship, the variation of
1
5
0
+
ture. Besides, the FTIR results indicate that Cu/TS catalysts
the STYMA is plotted as a function of the amount of Cu and Cu ,
Table 5 Catalytic performance for methanol carbonylation on the different catalysts
(mol%)
S
i
X
Methanol
STYMF (mol
STYMA (mol
STYDME (mol
h
−
1
−1
kgcat
−1
−1
kgcat
−1
−1
kgcat )
Catalyst
(%)
MA
MF
DME
h
)
h
)
TS
29.805
28.842
30.415
29. 215
26.147
24.473
0
0
100
0
0
3.313
1.422
1.061
0.988
1.494
1.580
5
8
1
1
1
.45 Cu/TS
.15 Cu/TS
0.24 Cu/TS
2.64 Cu/TS
5.76 Cu/TS
28.435
40.197
50.133
35.219
32.709
27.200
28.414
22.992
19.372
16.008
44.365
31.389
26.875
45.409
51.283
0.873
0.962
0.747
0.564
0.436
0.913
1.636
1.770
1.185
1.126
cat−
1
−1
cat−1 −1
h ; time on stream = 24 h; X:
Reaction conditions: T = 230 °C; P = 1.0 Mpa; GHSVCO = 1800 L kg
conversion, S: selectivity and STY: space time yield.
h
; LHSVmethanol = 0.9 L kg
Catal. Sci. Technol.
This journal is © The Royal Society of Chemistry 2017

View Article Online
Catalysis Science & Technology
Paper
0
+
Fig. 10 The correlation of STYMA with Cu (A) and Cu (B) for the reduced catalysts.
respectively (see Fig. 10A and B). A significant positive corre-
results show that the Brønsted acid sites are not replaced
completely by copper species when the copper content is
lower than 10.24%. With decreasing amount of Brønsted acid
sites, the selectivity to DME decreases. That is to say, the
Brønsted acid sites are responsible for the formation of DME
when the copper content is lower than 10.24%. Meanwhile,
there are no Brønsted acid sites when the copper content is
higher than 10.24%, but the selectivity to DME increases sig-
nificantly. This indicates that the Lewis acid sites can also
+
lation is found between the STYMA with the amount of Cu
0
rather than Cu , and the 10.24 Cu/TS catalyst has a maxi-
−
1
−1
+
mum of 1.770 mol h kgcat . In conclusion, the surface Cu
species is the dominant factor for MA synthesis.
Combined with the characterization results and related ex-
periments, it is surmised that CO and methanol co-adsorb on
+
the Cu sites proceeding to undergo a carbonylation reaction
+
to produce MA. The Cu species act not only as metal centers
6
0–62
to activate CO but also as Lewis acid sites responsible for ac-
tivating methanol (methoxy). Obviously, the activation of CO
is a major factor. It may be because the attack of CO at the
methoxy group to form C–C band is the rate-determining step
promote the formation of DME.
However, the selectivity
to DME is not proportional to the amount of Lewis acid sites.
It may be because DME is an intermediate product that par-
6
3
ticipates in the carbonylation reaction.
5
5
of the carbonylation reaction.
Methyl formate (MF), as an important by-product, is pro-
duced on the Cu/TS catalysts. As shown in the Table 5, with
increasing copper content, the selectivity and STY of MF in-
creases firstly and then decreases. Their maximum values are
obtained on the 8.15 Cu/TS catalyst, 28.414% and 0.962 mol
4
. Conclusions
In summary, the carbonylation of methanol to MA is success-
fully conducted over Cu/TS catalysts. With increasing copper
content, the highest MA selectivity of 50.13% and maximum
STYMA of 1.770 mol h kgcat are obtained over the 10.24
Cu/TS catalyst. By analyzing the surface properties of the cat-
alysts and reaction results, the better catalytic performance is
−
1
−1
h
kgcat , respectively. It is found from the previous studies
−
1
−1
that MF is produced mainly by dehydrogenation of methanol
5
6,57
over copper-containing catalysts.
tions among the STY of MF with the amount of Cu and Cu
are shown in the ESI† (see Fig. S4). The STY of MF is found
Therefore, the correla-
+
0
+
closely related to the amount of surface Cu rather than that
0
+
0
+
to be proportional to the amount of Cu rather than Cu , and
the 8.15 Cu/TS catalyst exhibited a maximum of 0.962 mol
of Cu . Furthermore, the role of the Cu species is investi-
gated and summarized as the following two points: firstly,
they act as metal sites to activate CO which is the key factor
for MA synthesis. Secondly, they generate new Lewis acid
sites to promote the adsorption of methoxy. In addition, the
dehydration of methanol to DME occurs preferentially on
Brønsted acid sites. When it occurs in the Lewis acid sites, it
will compete with the carbonylation reaction. As another by-
product, MF is produced by dehydrogenation of methanol
−
1
−1
0
h
kgcat . Thus, it can be deduced that the surface Cu spe-
cies are responsible for MF synthesis.
For the formation of DME, the TS support exhibited the
highest catalytic activity. But on the Cu/TS catalysts, its yield
decreased firstly and then increased with increasing copper
content, and the minimum was obtained on the 10.24 Cu/TS
catalyst. It is known that DME is produced by methanol dehy-
5
8,59
0
dration, which occurs mainly in the acid sites.
The Py-IR
and surface Cu species are responsible for MF synthesis.
This journal is © The Royal Society of Chemistry 2017
Catal. Sci. Technol.

View Article Online
Paper
Catalysis Science & Technology
Acknowledgements
24 A. V. Neimark, P. I. Ravikovitch, M. Grun, F. Schuth and
K. K. Unger, J. Colloid Interface Sci., 1998, 207, 159–169.
This work is part of the project “Study on The New Type of
Catalytic System in The Halide-free Carbonylation of Metha-
nol to Methyl Acetate”, supported by the National Natural Sci-
ence Foundation of China (Grant No.21303241).
2
2
5 C. J. G. Vandergrift, A. F. H. Wielers, B. P. J. Joghi, J.
Vanbeijnum, M. Deboer, M. Versluijshelder and J. W. Geus,
J. Catal., 1991, 131, 178–189.
6 A. Gervasini and S. Bennici, Appl. Catal., A, 2005, 281,
1
99–205.
2
2
7 C. A. Emeis, J. Catal., 1993, 141, 347–354.
8 T. Tago, D. Aoki, K. Iwakai and T. Masuda, Top. Catal.,
2009, 52, 865–871.
References
1
2
3
K. Fujimoto, T. Shikada, K. Omata and H. Tominaga, Chem.
Lett., 1984, 2047–2050, DOI: 10.1246/cl.1984.2047.
A. G. Stepanov, M. V. Luzgin, V. N. Romannikov and K. I.
Zamaraev, J. Am. Chem. Soc., 1995, 117, 3615–3616.
B. Ellis, M. J. Howard, R. W. Joyner, K. N. Reddy, M. B.
Padley and W. J. Smith, in 11th International Congress on
Catalysis - 40th Anniversary, Pts a and B, ed. J. W. Hightower,
W. N. Delgass, E. Iglesia and A. T. Bell, Elsevier Science Bv,
Amsterdam, 1996, vol. 101, pp. 771–779.
29 M. Richter, M. J. G. Fait, R. Eckelt, E. Schreier, M. Schneider,
M. M. Pohl and R. Fricke, Appl. Catal., B, 2007, 73, 269–281.
30 Y. Wang and R. A. Caruso, J. Mater. Chem., 2002, 12,
1442–1445.
31 Y. Zhu, Y. Zhu, G. Ding, S. Zhu, H. Zheng and Y. Li, Appl.
Catal., A, 2013, 468, 296–304.
32 W. M. H. Sachtler and Z. C. Zhang, Adv. Catal., 1993, 39,
129–220.
4
Q. Xu, S. Inoue, N. Tsumori, H. Mori, M. Kameda, M.
Tanaka, M. Fujiwara and Y. Souma, J. Mol. Catal. A: Chem.,
33 J. J. Bravo-Suárez, B. Subramaniam and R. V. Chaudhari,
J. Phys. Chem. C, 2012, 116, 18207–18221.
2
001, 170, 147–153.
34 F. Dong, G. Ding, H. Zheng, X. Xiang, L. Chen, Y. Zhu and Y.
Li, Catal. Sci. Technol., 2016, 6, 767–779.
35 J. Toyir, P. R. r. d. l. Piscina, J. L. G. Fierro and N. s. Homs,
Appl. Catal., B, 2001, 34, 255–266.
36 J. Toyir, P. R. r. d. l. Piscina, J. L. G. Fierro and N. s. Homs,
Appl. Catal., B, 2001, 29, 207–215.
37 J. Gong, H. Yue, Y. Zhao, S. Zhao, L. Zhao, J. Lv, S. Wang
and X. Ma, J. Am. Chem. Soc., 2012, 134, 13922–13925.
38 M. J. V. A. M. Lyons, E. M. Pearce and J. V. Waszczak,
Macromolecules, 1988, 21, 3125–3134.
5
6
7
8
9
D. Wang, G. H. Yang, Q. X. Ma, Y. Yoneyama, Y. S. Tan, Y. Z.
Han and N. Tsubaki, Fuel, 2013, 109, 54–60.
Y. Zhang, X. G. San, N. Tsubaki, Y. S. Tan and J. F. Chen,
Ind. Eng. Chem. Res., 2010, 49, 5485–5488.
Z. J. Zuo, L. Wang, L. M. Yu, P. D. Han and W. Huang,
J. Phys. Chem. C, 2014, 118, 12890–12898.
S. Wang, W. Guo, L. Zhu, H. Wang, K. Qiu and K. Cen,
J. Phys. Chem. C, 2015, 119, 524–533.
J. H. Jones, Platinum Met. Rev., 2000, 44, 94–105.
1
1
0 D. Forster, J. Am. Chem. Soc., 1976, 98, 846–848.
1 J. Hjortkjaer, Y. Chen and B. Heinrich, Appl. Catal., 1991, 67,
39 K. Sun, W. Lu, F. Qiu, S. Liu and X. Xu, Appl. Catal., A,
2003, 252, 243–249.
2
69–278.
40 L. Chen, P. Guo, M. Qiao, S. Yan, H. Li, W. Shen, H. Xu and
K. Fan, J. Catal., 2008, 257, 172–180.
41 R. Buzzoni, S. Bordiga, G. Ricchiardi, C. Lamberti, A.
Zecchina and G. Bellussi, Langmuir, 1996, 12, 930–940.
42 J. A. Lercher, C. Grundling and G. EderMirth, Catal. Today,
1996, 27, 353–376.
1
1
2 F. Peng and F. Xiao-Bao, Catal. Today, 2004, 93-95, 451–455.
3 Q. Zhang, H. Wang, G. Sun, K. Huang, W. Fang and Y. Yang,
Catal. Commun., 2009, 10, 1796–1799.
1
4 G. Zehl, S. Bischoff and B. Lucke, Catal. Lett., 1993, 19,
2
47–255.
1
5 T. Blasco, M. Boronat, P. Concepcion, A. Corma, D. Law
43 G. Busca, Phys. Chem. Chem. Phys., 1999, 1, 723–736.
44 D. Berthomieu and G. Delahay, Catal. Rev.: Sci. Eng.,
2006, 48, 269–313.
and J. A. Vidal-Moya, Angew. Chem., Int. Ed., 2007, 46,
3
938–3941.
1
1
6 M. Boronat, C. Martinez and A. Corma, Phys. Chem. Chem.
Phys., 2011, 13, 2603–2612.
7 H. Zhan, S. Huang, Y. Li, J. Lv, S. Wang and X. Ma, Catal.
Sci. Technol., 2015, 5, 4378–4389.
45 K. Hadjiivanov and H. Knözinger, Phys. Chem. Chem. Phys.,
2001, 3, 1132–1137.
46 Y. C. Jun-Cheng Hu, P. Yang, J.-F. Deng and K.-N. Fan,
J. Mol. Catal. A: Chem., 2002, 185, 1–9.
1
1
2
8 S. T. King, J. Catal., 1996, 161, 530–538.
47 M. M. Volker Raab and J. Sundermeyer, J. Mol. Catal. A:
Chem., 2001, 175, 51–63.
9 S. T. King, Catal. Today, 1997, 33, 173–182.
0 B. Bonelli, M. Cozzolino, R. Tesser, M. Diserio, M.
Piumetti, E. Garrone and E. Santacesaria, J. Catal.,
48 Y. Cao, J. C. Hu, P. Yang, W. L. Dai and K. N. Fan, Chem.
Commun., 2003, 908–909, DOI: 10.1039/b301375h.
49 G. T. Palomino, S. Bordiga, A. Zecchina, G. L. Marra and C.
Lamberti, J. Phys. Chem. B, 2000, 104, 8641–8651.
50 P. Rejmak, M. Sierka and J. Sauer, Phys. Chem. Chem. Phys.,
2007, 9, 5446–5456.
51 J. Howard and J. M. Nicol, Zeolites, 1988, 8, 142–150.
52 K. P. Dejong, J. W. Geus and J. Joziasse, Appl. Surf. Sci.,
1980, 6, 273–287.
2
007, 246, 293–300.
1 J. Ren, Z. Li, S. Liu, Y. Xing and K. Xie, Catal. Lett.,
008, 124, 185–194.
2 P. B. Balbuena and K. E. Gubbins, Langmuir, 1993, 9,
801–1814.
3 C. Lastoskie, K. E. Gubbins and N. Quirke, J. Phys. Chem.,
993, 97, 4786–4796.
2
2
2
2
1
1
Catal. Sci. Technol.
This journal is © The Royal Society of Chemistry 2017

View Article Online
Catalysis Science & Technology
Paper
5
3 J. Engeldinger, C. Domke, M. Richter and U. Bentrup, Appl.
Catal., A, 2010, 382, 303–311.
59 Y. Xu, P. Yang, H. Zhang and Z. Deng, Synth. React. Inorg.,
Met.-Org., Nano-Met. Chem., 2011, 41, 1033–1038.
60 J. M. Campelo, F. Lafont, J. M. Marinas and M. Ojeda, Appl.
Catal., A, 2000, 192, 85–96.
61 V. Vishwanathan, H. S. Roh, J. W. Kim and K. W. Jun, Catal.
Lett., 2004, 96, 23–28.
62 H. Jo, H. Jung, J. Park and K.-D. Jung, Bull. Korean Chem.
Soc., 2017, 38, 307–312.
63 T. Blasco, M. Boronat, P. Concepcion, A. Corma, D. Law
and J. A. Vidal-Moya, Angew. Chem., Int. Ed., 2007, 46,
3938–3941.
5
5
4 S. Zhang, G. Fan and F. Li, Green Chem., 2013, 15, 2389.
5 P. Cheung, A. Bhan, G. J. Sunley and E. Iglesia, Angew.
Chem., Int. Ed., 2006, 45, 1617–1620.
5
5
5
6 S. P. Tonner, M. S. Wainright, D. L. Trimm and N. W. Cant,
Appl. Catal., 1984, 11, 93–101.
7 A. Bakhtyari, M. Parhoudeh and M. R. Rahimpour, J. Nat.
Gas Sci. Eng., 2016, 28, 31–45.
8 Z. Hosseini, M. Taghizadeh and F. Yaripour, J. Nat. Gas
Chem., 2011, 20, 128–134.
This journal is © The Royal Society of Chemistry 2017
Catal. Sci. Technol.