CHEMCATCHEM
FULL PAPERS
Characterization
Catalytic measurements
Catalytic performance was evaluated in a fixed-bed isothermal re-
actor (ꢂ0.5 K deviation) comprised of a quartz tubular reactor with
an inner diameter of 7 mm. The catalysts used for evaluation were
The pore distribution and specific surface areas of the samples
were determined by nitrogen adsorption at 77 K on a Micromeritics
ASAP-2020 analyzer. Prior to measurements, the samples were de-
gassed at 573 K for 24 h in vacuum. The specific surface areas were
calculated from the isotherms by using the BET method. The mi-
cropore volumes were obtained by the t-plot method and the
mesopore volumes were obtained by the Barrett–Joyner–Halenda
method using the desorption branches of the adsorption iso-
therms.
2
0–40 mesh. A run was initiated by loading the catalyst (1.00 g)
into the reactor. The reactant gas made up of CO (43.6%), O2
(
9.6%), methanol (18.9%), and N (27.9%) was passed over the cat-
2
3
ꢁ1
alyst at 100 cm min (STP). The reaction temperature was main-
tained at 413 K and the reaction pressure was held at 0.7 MPa. The
reaction products were analyzed online by a gas chromatograph
(
1
Agilent 7890GC) equipped with four columns: two Porapak Q 80/
00 and one Molesieve 13X 60/80 packed columns (Restek) con-
nected to a TCD for measuring CO, O , and CO ; and a DB-624 ca-
Transmission IR spectroscopy were acquired by using a Thermo
2
2
ꢁ1
Scientific Nicolet 6700 (32 scans, 4 cm ). To acquire the IR spectra,
each carbon sample was diluted to 0.1 wt.% with dry IR-quality
KBr (Fisher). Pellets (1 cm diameter) were formed from 100 mg por-
tions of the carbon-KBr powder mixture. These spectra were com-
pared on a common absorbance scale to assess the type and rela-
tive abundance of oxygen groups presented on the different
supports.
pillary column (Agilent) connected to an flame-ionization detector
for measuring methanol, DMC, and the organic byproducts. The
error margin of the GC was 1–2%. Traces of CO were detected in
2
the product, and thus the CO was not taken into consideration
2
when calculating the mass balance. MF and DMM were the only
significant byproducts detected. The carbon balance of the experi-
ments was all in range of 95–99%. The reaction and side reactions
were listed in Equations (1)–(3):
Boehm titrations were performed by placing the carbon sample
(
1.00 g) in a 50 mL volume of each of the following solutions:
[29]
2 CH OH þ CO þ 1=2 O ! CH OCOOCH þ H O
ð1Þ
ð2Þ
ð3Þ
3
2
3
3
2
sodium hydroxide, sodium carbonate, and sodium bicarbonate.
The samples were dispersed by sonicating for 20 min and then
they were heated at 373 K for 1.5 h and finally filtered. A volume
of 5 mL of the filtrate was pipetted into a flask and the excess
base was titrated with HCl. The number of acid sites was deter-
mined by using the assumptions that NaOH neutralizes carboxylic,
lactonic, and phenolic groups, Na CO neutralizes carboxylic and
2
CH OH þ O ! HCOOCH þ 2 H O
3
2
3
2
3 CH OH þ 1=2 O ! CH OCH OCH þ 2 H O
3
2
3
2
3
2
Methanol conversion was calculated from the amount of the prod-
ucts (DMC, MF, and DMM) and from the stoichiometry of Equa-
tions (1)–(3). The selectivities of DMC, MF, and DMM were deter-
mined by using Equations (4)–(6):
2
3
lactonic groups, and NaHCO neutralizes only carboxylic groups.
3
The concentrations of Cu in the samples were measured by induc-
tively coupled plasma optical emission spectroscopy (VISTA–MPX,
Virian). Before measurements, the samples were digested in HCl
and HNO3 aqueous solution assisted by microwave irradiation
2
½CH OCOOCH ꢃ
3
3
SDMC ¼ 2
ð4Þ
ð5Þ
ð6Þ
½HCOOCH ꢃ þ 3½CH ðOCH Þ ꢃ þ 2½CH OCOOCH ꢃ
3
2
3
2
3
3
(
Multiwave 3000, Anton Paar).
2½HCOOCH
3
ꢃ
SMF ¼ 2
½HCOOCH ꢃ þ 3½CH ðOCH Þ ꢃ þ 2½CH OCOOCH ꢃ
2
3
2
3
2
3
3
TEM images were recorded on a Philips TECNAI G F20 system. The
samples for TEM were prepared by placing a few drops of the
sample suspended in ethanol onto a Ni grid followed by slow
evaporation of the solvent at ambient conditions.
3½CH ðOCH Þ ꢃ
2
3 2
SDMM ¼ 2
½HCOOCH ꢃ þ 3½CH ðOCH Þ ꢃ þ 2½CH OCOOCH ꢃ
3
2
3
2
3
3
XRD measurements were performed using a Rigaku C/max-2500
diffractometer employing graphite filtered CuKa radiation (l=
Acknowledgements
1
.5406 ꢁ) at 40 kV. Diffraction data were collected by using a scan-
ning rate of 0.028 per step in the 2q range of 10–908 with a scan-
ning time of 0.3 s per step at 200 mA.
The financial support from the National Natural Science Founda-
tion of China (NSFC) (Grant No. 21325626, 20936003), the Speci-
alized Research Fund for the Doctoral Program of Higher Educa-
tion (SRFDP) (Grant No. 20090032110021) and the Program of In-
troducing Talents of Discipline to Universities (B06006) are grate-
fully acknowledged.
Raman spectroscopy analysis was performed in the range of 750–
ꢁ
1
2
200 cm at RT by using a Raman spectrometer (DXR, USA) with
a Nd:YAG laser excitation source (532 nm).
XPS analysis was performed on a PerkinElmer PHI 1600 ESCA
system operated at a pass energy of 187.85 eV for survey spectra
with an Al KR X-ray source. The acceleration voltage was 15 kV, the
2
power was 250 W, and the analysis area was 0.8 mm . Possible de-
Keywords: carbon · copper · carbonylation · supported
catalysts · surface analysis
viations from electric charges on the samples were corrected using
the C1s line at 284.6 eV as the internal standard. Multipak soft-
ware8.0 was used for data treatment.
[
[
For acidity evaluation, temperature-programmed desorption of am-
monia (NH –TPD) measurements were run on a Micromeritics Au-
3
tochem II 2920 instrument equipped with a thermal conductivity
detector. The sample (ꢀ100 mg) was pretreated at 393 K for 1 h in
a flow of Ar followed by NH adsorption at 373 K. Desorbed NH
3
3
[3] a) T. T. H. Dang, M. Bartoszek, M. Schneider, D. L. Hoang, U. Bentrup, A.
ꢁ1
was monitored at a heating rate of 10 Kmin from 373 to 753 K.
Martin, Appl. Catal. B 2012, 121, 115–122; b) S. A. Anderson, T. W. Root,
ꢀ
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 2671 – 2679 2678