Halide-doped perovskite-type AMn1−xCuxO3−δ (A = La0.8Ba0.2) catalysts for ethane-selective oxidation to ethene Original Research Article

The undoped and halide-doped perovskite-type oxide AMn1−xCuxO3−δ (A=La0.8Ba0.2) 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 ml h−1 g−1, AMn0.7Cu0.3O2.808F0.124 showed 49.2% C2H6 conversion, 66.8% C2H4 selectivity, and 32.9% C2H4 yield; AMn0.7Cu0.3O2.817Cl0.114 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 AMn1−xCuxO3−δ and halide-doped AMn1−xCuxO3−δXσ (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 AMn0.7Cu0.3O2.808F0.124 and AMn0.7Cu0.3O2.817Cl0.114 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 AMn1−xCuxO3−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.