Hole-Doped La_1.85Sr_0.15CuO_4-δX _σ(X=F, Cl) and Electron-Doped Nd_1.85Ce_0.15CuO_4-δX_σ Halo-Oxide Catalysts for the Selective Oxidation of Ethane to Ethene

The catalytic performance and characterization of Ln_1.85A_0.15CuO_4-δ and Ln_1.85A_0.15CuO_4-δX_σ (Ln=La, Nd; A=Sr, Ce; X=F, Cl) for the oxidative dehydrogenation of ethane (ODE) to ethene have been investigated. The hole-doped catalysts performed better than the electron-doped ones. Under the reaction conditions of temperature, 660°C; C₂H₆/O₂/N₂ molar ratio, 2/1/3.7; and contact time, 1.67×10^-4 h g mL^-1; La_1.85Sr_0.15CuO_3.930Cl_0.053 showed 82.8% C₂H₆ conversion, 73.2% C₂H₄ selectivity, and 60.6% C₂H₄ yield; Nd_1.85Ce_0.15CuO_3.981F_0.092 showed 72.1% C₂H₆ conversion, 61.8.0% C₂H₄ selectivity, and 44.6% C₂H₄ yield. The sustainable performance during a period of 60 h on-stream reaction at 660°C demonstrated that the F- and Cl-doped catalysts are durable. The results of X-ray powder diffraction indicated that the Sr-substituted cuprates were of T structure whereas the Ce-doped cuprates were of T^′ structure. The results of X-ray photoelectron spectroscopic (XPS) studies revealed that there were Cu²⁺ and Cu³⁺ in the Sr-doped cuprate catalysts and Cu⁺ and Cu²⁺ in the Ce-doped cuprate catalysts. The results of the XPS, thermogravimetric analysis (TGA), and ¹⁸O₂-pulsing studies demonstrated that the incorporation of halide ions into the Ln_1.85A_0.15CuO_4-δ lattice promoted the activity of lattice oxygen. By comparing the results of XPS, TGA, and O₂ temperature-programmed desorption with the catalytic performance of the catalysts, we conclude that (i) lattice O^2- species at the surface are active for the selective oxidation of ethane; (ii) in excessive amount, O^- species accommodated in oxygen vacancies are prone to induce the total oxidation of ethane; and (iii) a suitable Cu³⁺ or Cu⁺ concentration and/or oxygen nonstoichiometry in Ln_1.85A_0.15CuO_4-δX_σ are required for the best catalytic performance of the catalysts.