Halide-doped perovskite-type AMn_(1-x)Cu_xO_(3-##delta) (A = La_(0.8)Ba_(0.2)) catalysts for ethane-selective oxidation to ethene

摘要

The undoped and halide-doped perovskite-type oxide AMnvxCUxO3~~l (A Lao.sBao.2) catalysts have heen investigated for the oxidative dehydrogenation of ethane (ODE) to ethene. Under the reaction conditions of temperature 680CC, C21-161O2/N2 molar ratio = 2/1/3.7, and space velocity 6000m1hi g’, AMno.7Cuo.302.sotFo.i24 showed 49.2% C2H6 conversion, 66.8% C2H4 selectivity, and 32.9% C2H4 yield; AMnO-,Cuo.302.si7Clo.i14 showed 73.0% C21-16 conversion, 69.5% C2H4 selectivity, and 50.8% C2H4 yield. The sustainable performance during a period of 48 h on-stream reaction at 6800C 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 AMnv~Cu~O3—~ and halide-doped ~ (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 CuG 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 AMno.7Cuo.302.sosFOj24 and AMnogCuo302.8i7Clo.i 14 are rather similar and (ii) there were Mn4250L? Mn3±, and Cu> 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 i801160 isotopic exchange indicated that the incorporation of halide ions into the AMn1 —x Cu.r O3~ lattice enhanced the activity of lattice oxygen. The outcome of C2H6- and C2116/02/N2-pulsing investigations demonstrated that adsorbed oxygen species are prone to induce ethane complete oxidation, while lattice oxygen species are active for ethan~ selective oxidation.