YBa₂Cu₃O_7-δX_σ (X=F and CI): Highly Active and Durable Catalysts for the Selective Oxidation of Ethane to Ethene

The catalytic performance and characterization of YBa₂Cu₃O_7-δ and YBa₂Cu₃O_7-δX_σ for the oxidative dehydrogenation of ethane (ODE) to ethene have been investigated. Under the reaction conditions of temperature=680°C, C₂H₆/O₂/N₂ molar ratio=2/1/3.7, and contact time=1.67×10^-4 h g ml^-1, YBa₂Cu₃O_7-0.21F_0.16 showed 84.1% C₂H₆ conversion, 81.8% C₂H₄ selectivity, and 68.8% C₂H₄ yield; YBa₂Cu₃O_7-0.18Cl_0.13 showed 92.5% C₂H₆ conversion, 72.0% C₂H₄ selectivity, and 66.6% C₂H₄ yield. The sustainable performance during a period of 40 h on-stream reaction at 680°C demonstrated that the F- and Cl-doped catalysts are durable. X-ray powder diffraction results indicated that the undoped YBa₂Cu₃O_7-δ and halide-doped YBa₂Cu₃O_7-δX_σ were of triple-layered oxygen-deficient perovskite-type orthorhombic structure. The results of the X-ray photoelectron spectroscopy, thermal treatment, thermogravimetric analysis, and ¹⁸O₂-pulsing studies indicated that the incorporation of halide ions into the YBa₂Cu₃O_7-δ lattice enhanced the activity of lattice oxygen. According to the O₂ temperature-programmed desorption and temperature-programmed reduction results, we conclude that the oxygen species desorbed at 610-710°C are active for the selective oxidation of ethane and those desorbed below 610°C are active for the total oxidation of ethane; a suitable oxygen nonstoichiometry and Cu³⁺ concentration in YBa₂Cu₃O_7-δX_σ are required for the best catalytic performance of the catalysts.