10.1002/cssc.201801937
ChemSusChem
FULL PAPER
was raised under nitrogen flow (6.6 mL min–1 per reactor). After reaching
the respective pressure and a temperature of 250 °C, the N2 flow was
replaced by a flow of CO2:H2:C2H4/C3H6:N2=4:2:1:1 for activation. Then
the tests were performed at 200°C using various feeds
CO2:H2:C2H4/C3H6:N2 (1:1:1:1; 1:2:4:1, and 1:3:3:1). The contact time
was 43 gcat min L–1. The feed components and the reaction products
were analyzed by an on-line GC (Varian CP-3800).
and the following gas mixtures were successively dosed each for 60 min:
C2H4/N2, H2/C2H4/N2, and CO2/H2/C2H4/N2 (10 vol% of each gas in N2,
respectively). At the end of the experiment, the cell was flushed with N2
while the pressure was lowered to 1 bar.
A
TAP-2 (temporal analysis of products) reactor operating at
52, 53]
microsecond time resolution[50,
was applied to investigate the
interaction of CO2, CO, C2H4, and H2 with fresh and used (270 h on
stream at 200 - 250°C using various feeds containing CO2, H2 and C2H4)
catalysts. The catalyst sample (70 mg) was filled into the isothermal zone
of the quartz reactor (i.d.=6 mm, length=40 mm) for each measurement.
The catalyst bed was fixed between two quartz particle (grain size=250-
350 μm) layers. Fresh catalysts were treated in a flow of H2 (3 mL·min-1)
and Ar (9 mL·min–1) for 1 h at 250 °C prior to evacuation (10-5 Pa) and
cooling to 200°C. Used catalysts were only heated in vacuum (10-5 Pa)
for 30 min at 200°C before pulsing of a 1:1 mixture of reactant and argon
at 200°C. The pulse size was adjusted to approximately 1015 Ar atoms.
This guarantees that only interactions between reactants and catalyst
surface are analysed. Each pulse was repeated 10 times for each atomic
mass unit improved the signal to noise ratio. The analysis of gas phase
components was carried out with a quadrupole mass spectrometer (HAL
RC 301, Hiden Analytical).
The yield of propanol, propanal, butanol, butanal, propane, butane and
CO was calculated on the basis of CO2 or feed olefin using equation 1
taking into account that one C3 hydrocarbon/oxygenate molecule in tests
with ethylene is formed from one CO2 and one C2H4 while one C4
hydrocarbon/oxygenate molecule in tests with propene is formed from
one CO2 and one C3H6. In order to ensure high precision in determining
low degrees of CO2, C2H4 and C3H6 conversion, it was calculated from
the yields of reaction products formed from these feed components (eq.
2). Selectivity was calculated according to equation 3.
ꢃ
ꢅ
ꢀ ꢂ
ꢈ 100%
(1)
ꢁ
ꢃ
ꢆ,ꢇ
∑
ꢉꢊ ꢂ ꢁ ꢀ
(2)
(3)
ꢁ
ꢌ
ꢅ
ꢋꢁ ꢂ ꢍ ꢈ 100%
ꢆ
Acknowledgements
where ꢎꢊ and ꢎꢁ stand for mole flows of feed components and reaction
products, respectively. Subscript 0 is used for inlet mole flows.
The authors gratefully thank Christine Rautenberg for carrying
out the CO adsorption experiments, Dr. Marga-Martina Pohl for
assistance in recording STEM images, and Anja Simmula for the
ICP-OES analysis.
For the characterization of the Au NP´s CO was used as probe molecule.
The measurements in transmission mode were carried out on a Nicolet
iS10 spectrometer (Thermo Scientific) equipped with a heatable, coolable,
and evacuable homemade reaction cell with CaF2 windows connected to
a gas-dosing and evacuation system. The sample powders were pressed
into self-supporting wafers with a diameter of 20 mm and a weight of
50 mg. Before CO adsorption, the samples were pretreated in the
reaction cell in He (20 mL min-1) at 200°C for 30 min or
10%CO2/10%H2/He (20 mL min-1) at 250°C for 60 min. Used and
external pretreated samples were pretreated in He (20 mL min-1) at
200°C for 30 min. After cooling down to room temperature, the reaction
cell was closed and further cooled down to the adsorption temperature of
-160°C, and a background spectrum of the sample was recorded. Then,
a 5% CO/He mixture was dosed in pulses until saturation, which was
controlled by inspecting the band intensities. Before recording the CO
adsorbate spectrum the physisorbed CO was removed by evacuating the
cell. Subsequently, the CO desorption under vacuum was followed by
continuous heating the sample and measuring a spectrum every 10°C.
Generally, subtracted spectra were evaluated obtained by subtraction of
the background spectrum measured at -160°C from the respective CO
adsorbate spectrum.
Keywords: CO2 conversion • Au catalyst • reverse water-gas
shift • hydroformylation • in situ FTIR
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