Halide-doped perovskite-type AMn_1-xCu_xO_3-δ (A = La_0.8Ba_0.2) catalysts for ethane-selective oxidation to ethene

The undoped and halide-doped perovskite-type oxide AMn_1-xCu_xO_3-δ (A = La_0.8Ba_0.2) catalysts have been investigated for the oxidative dehydrogenation of ethane (ODE) to ethene. Under the reaction conditions of temperature = 680°C, C₂H₆/O₂/N₂ molar ratio = 2/1/3.7, and space velocity = 6000 mlh^-1 g^-1, AMn_0.7Cu_0.3O_2.808F_0.124 showed 49.2% C₂H₆ conversion, 66.8% C₂H₄ selectivity, and 32.9% C₂H₄ yield; AMn_0.7Cu_0.3O_2.817Cl_0.114 showed 73.0% C₂H₆ conversion, 69.5% C₂H₄ selectivity, and 50.8% C₂H₄ yield. The sustainable performance during a period of 48 h on-stream reaction at 680°C demonstrated that the F- and Cl-doped catalysts are durable. We also observed that the addition of halide ions to the perovskites could reduce deep ethene oxidation. X-ray powder diffraction results indicated that at x = 0.3 the undoped AMn_1-xCu_xO_3-δ and halide-doped AMn_1-xCu_xO_3-δX_σ (X = F, Cl) were single-phase and cubic in structure; when the x value exceeded 0.7, there were trace amounts of La₂CuO₄ and/or CuO phases besides the perovskite phase. The results of Mn oxidation state titration and X-ray photoelectron spectroscopic studies showed that (i) the surface and bulk compositions of AMn_0.7Cu_0.3O_2.808F_0.124 and AMn_0.7Cu_0.3O_2.817Cl_0.114 are rather similar and (ii) there were Mn⁴⁺, Mn³⁺, and Cu²⁺ in the catalysts. Oxygen temperature-programmed desorption studies illustrated that the doping of halide would result in the disappearance of oxygen adspecies and the promotion of lattice oxygen activity. The results of ¹⁸O/¹⁶O isotopic exchange indicated that the incorporation of halide ions into the AMn_1-xCu_xO_3-δ lattice enhanced the activity of lattice oxygen. The outcome of C₂H₆- and C₂H₆/O₂/N₂-pulsing investigations demonstrated that adsorbed oxygen species are prone to induce ethane complete oxidation, while lattice oxygen species are active for ethane selective oxidation.