Dehydrogenation of ethane over perovskite oxide catalysts was investigated using the redox of perovskites and H 2 O as an oxidizing agent. The La 0.8 Ba 0.2 MnO 3−δ (LBMO) perovskite showed a high catalytic activity for dehydrogenation of ethane. Periodic dry (without H 2 O)−wet (with H 2 O) operation tests revealed that dehydrogenation of ethane in the presence of H 2 O over LBMO proceeded via the Mars−van Krevelen (MvK) mechanism. Under the wet condition with D 2 O instead of H 2 O, D 2 formation was verified, demonstrating that reactive lattice oxygens in LBMO contributed to the dehydrogenation reaction and that they were regenerated by water. Isotopic transient tests with H 2 18O and in situ X-ray absorption fine structure measurements revealed that the reduction and oxidation of Mn in LaMnO 3 and LBMO occurred under the reaction atmosphere and that the partial replacement of the La sites with Ba improved the redox ability of Mn, resulting in its high activity. Furthermore, temperature-programmed reduction under H 2 elucidated that the reduction of Mn 3+ to Mn 2+ was promoted by Ba doping. The LBMO perovskite showed the very high activity for dehydrogenation of ethane in the presence of H 2 O via the MvK mechanism by virtue of the high redox properties of Mn.
For effective utilization of ethane in natural gas, catalytic dehydrogenation of ethane is a promising option that offers better efficiency than ethane cracking to produce ethylene, the most important fundamental chemical. Recently, it was reported that catalytic dehydrogenation of ethane proceeds effectively on doped perovskite oxide via the Mars–van Krevelen (MvK) mechanism. For this work, the reaction mechanism was investigated using density functional theory calculations. Results demonstrated that ethane activation over perovskite (La1–x Ba x MnO3−δ) proceeds at the surface lattice oxygen coordinated with Ba, resulting in a low energy barrier of the C–H bond activation. Based on Bader charge analysis, the electron-deficient surface lattice oxygen, which is favorable for hydrogen abstraction from light alkanes, forms around Ba. In addition, the electronic charges of the surface lattice oxygen are important for H2 desorption. The electronic charge depends on hydrogen coverage: electron-rich surface lattice oxygen, which is favorable for H2 desorption, forms at high hydrogen coverage. Therefore, a part of the surface lattice oxygens of perovskite would be covered with hydrogen atoms under the reaction atmosphere, leading to effective H2 desorption and the proceeding catalytic cycle via the MvK mechanism.
We studied dehydrogenation catalysts to improve the performance of the ethane cracking tube. Ga, Ge, In, and Sn were studied as dehydrogenation catalysts. Catalytic activity tests showed that the Ga catalyst has the best performance among them. Although the Ga catalyst supported on α-Al2O3 calcined at 1323 K deactivated with time on stream, the Ga catalyst supported on γ-Al2O3 calcined at 1323 K showed high ethylene yield and stability. Analyses of BET, XRD, EDX, and XANES were conducted to elucidate the differences of their performances. Ga catalyst supported on γ-Al2O3 calcined at 1323 K showed high catalytic activity and stability because Ga was supported as a highly dispersed β-Ga2O3-like structure thanks to high specific surface area of the γ-Al2O3 support.
Introducing a catalyst for dehydrogenation of ethane (EDH) for steam cracking represents a promising solution with high feasibility to realize efficient ethylene production. We investigated EDH over transition-metal-doped CeO 2 catalysts at 873 K in the presence of steam. Ce 0.8 Co 0.2 O 2 exhibited high EDH activity and selectivity to ethylene (ca. 95%). In the absence of H 2 O, the catalytic activity dropped rapidly, indicating the promotive effect of H 2 O on ethylene formation. Catalytic experiments with water isotopes (D 2 O and H 2 18 O) demonstrated that EDH over Ce 0.8 Co 0.2 O 2 proceeds through the Mars−van Krevelen (MvK) mechanism in which the reactive lattice oxygen in Ce 0.8 Co 0.2 O 2 contributes to EDH. The consumed lattice oxygen was subsequently regenerated with H 2 O. X-ray diffraction and in situ X-ray absorption fine structure spectroscopy revealed that cobalt species were mainly present as CoO under EDH conditions and that redox between Co 2+ and Co 0 proceeded concomitantly with EDH. In contrast with Ce 0.8 Co 0.2 O 2 , no contribution of the lattice oxygen of CoO to EDH was verified in the case of CoO supported on α-Al 2 O 3 , which exhibited lower activity than Ce 0.8 Co 0.2 O 2 . Therefore, Co−CeO 2 interactions are expected to play a crucially important role in controlling the characteristics of the reactive lattice oxygen suitable for EDH via the MvK mechanism.
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