Hole-Doped La1.85Sr0.15CuO4–δXσ(X=F, Cl) and Electron-Doped Nd1.85Ce0.15CuO4–δXσ Halo-Oxide Catalysts for the Selective Oxidation of Ethane to Ethene

The catalytic performance and characterization of Ln1.85A0.15CuO4–δ and Ln1.85A0.15CuO4–δXσ (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; La1.85Sr0.15CuO3.930Cl0.053 showed 82.8% C2H6 conversion, 73.2% C2H4 selectivity, and 60.6% C2H4 yield; Nd1.85Ce0.15CuO3.981F0.092 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 Ln1.85A0.15CuO4–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 O2− 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 Ln1.85A0.15CuO4–δXσ are required for the best catalytic performance of the catalysts.