10.1002/cctc.201801988
ChemCatChem
FULL PAPER
water. Finally, the cake was dried at 110 °C for 12 h, followed by
calcination in muffle overnight at 350 °C for 4 h. Obtained sample was
denoted as CuZnZr(CP) catalyst.
of the analysis chamber was maintained at < 10−6 Torr. Radiation energy
of Ar ion beam is 2 k eV.
The bulk analytical composition of the catalysts was determined by
XRF measurements, using a Bruker AXS-S4 Explorer spectrometer,
equipped with a Rhodium X-ray source (Rh anode and 75 μm Be-
window), a LiF 220 crystal analyzer and a 0.12o divergence collimator.
Raman scattering spectroscopy was measured using a diode-pumped
solid state laser of wavelength 533 nm with a power of 50mW.
CuZnZr(VPT) catalyst. Vapor-phase-treatment process was operated in
an autoclave containing the Teflon liner. In a typical process, the
powdered CuZnZr(CP) sample was placed on Teflon liner with a Teflon
interlayer, and the aqueous solution of vapor-phase-treatment reagent
was added into the bottom of the Teflon liner. In our experiments, the
quantity of the treatment reagents is equaled to that of CuZnZr(CP)
catalyst. The treatment is operated at 180 °C for 2 days. The obtained
sample was dried at 110 oC for 12 h, and then calcined at 550 °C for 4 h.
Wherein, the CuZnZr catalysts treated with no any vapor-phase reagent
but deionized water was denoted as CuZnZr-H2O and the CuZnZr
catalysts treated by TPABr were denoted as CuZnZr-TPABr, respectively.
Otherwise, the CuZnZr(CP) catalyst was also treated with TPABr for 1 ,3
and 4 days respectively, and the obtained catalysts were denoted as
CuZnZr-TPABr-1d, CuZnZr-TPABr-3d and CuZnZr-TPABr-4d, wherein,
above-mentioned CuZnZr-TPABr catalyst is equivalent to CuZnZr-
TPABr-3d catalyst. As comparison and reference, some additional TPABr
treated catalysts with different vapor-phase-treatment temperature were
prepared in our experiments. Wherein, treatment temperature is 120 °C,
140 °C, 160 °C, 180 °C, 200 °C, respectively. The obtained samples
were dried at 110 °C for 12 h, and then calcined at 550 °C for 4 h. Other
operation conditions/parameters are similar with that for preparing
CuZnZr-TPABr-3d catalyst.
Catalytic evaluation of catalysts
The CO2 hydrogenation was performed in a fixed bed stainless steel
tubular reactor (with 15.5 mm in inner diameter, 500 mm in length). In a
typical experiment, the 3 g catalyst was packed in the reactor. The pre-
reduction was conducted using a stream of diluted hydrogen (10% H2 in
N2) at 300 °C for 10 h. After pre-reduction, the reaction was run at
temperature 250 °C and pressure 5.0 MPa, using
a feed gas
(H2/CO2/N2=69/23/8) at a space velocity of 3000 mL/gcat/h. The effluent
products were kept in gaseous state by electronic heater and analyzed
online by a gas chromatograph with thermal conductivity detector (TCD),
using carbon molecular sieve column for hydrogen, carbon monoxide
and methane. The selectivity of hydrocarbon products was measured
online by another gas chromatograph with a hydrogen flame ionization
detector (FID), using GDX-403 column for hydrocarbons, methanol and
dimethyl ether. N2 was used as the internal standard for chromatographic
analysis. The analytical results from different gas chromatographs were
correlated by methane concentration.
Characterization methods
Powder X-ray diffraction patterns (XRD) were recorded over the 2θ
range from 5o to 80o using a Rigaku MiniFlex II X-ray diffractometer,
which was operated at 40 kV and 40 mA with Cu Kα radiation (k =
0.15418 nm).
Acknowledgements
This work was supported by the Key Science and Technology
Program of Shanxi Province, China (MD2014-10), National
Natural Science Foundation of China (21573269, 21603258),
and Natural Science Foundation of Shanxi Province
(201601D202015), China.
H2-temperature-programmed reduction (H2-TPR) was performed to
investigate the reducibility of the catalysts using
a chemisorption
instrument (TP-5080). The catalyst (50 mg) was pretreated at 300 °C
under a flow of N2 (30 ml/min) for 1 h and then cooled to 50 °C; after
cooling, the flow was switched to a H2/N2= 0.09 mixture (35 ml/min). The
temperature-programmed reduction was performed from 100 °C to
600 °C with a heating rate of 10 °C/min.
CO2 temperature programmed desorption (CO2-TPD) measurements
were carried out on an AMETEK mass spectrometer to monitor the
desorption of CO2. In each experiment, the sample was reduced at
300 °C for 4 h with diluted hydrogen (10% H2 in N2). After cooling down
to 50 °C, the catalyst was exposed on CO2 flow for 1 h, and then flushed
with Ar until the baseline is stable. The CO2 desorption was performed
from 50 °C to 600 °C with a heating rate of 10 °C/min and the signal was
recorded by thermal conductivity detector (TCD).
Keywords: CO2 hydrogenation • methanol • vapor-phase-
treatment • CuZnZr catalyst
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