Oxidative dehydrogenation of ethane over BaF2 promoted SmO3-LaF3 catalysts

Abstract

Oxidative dehydrogenation of ethane (ODE) was investigated on Sm2O3-LaF3 and BaF2 promoted Sm2O3-LaF3 catalysts. Under the reaction conditions: 973 K, reactant mixture (C2H6:O-2:N-2=2:1:7) flow rate 40 ml/min, 89.7% ethene selectivity with 22.1% ethane (C2H6) conversion was obtained on Sm2O3-LaF3 catalyst (molar ratio 1 : 1) The addition of BaF2 significantly improved the catalytic performance. On 16.7 mol% BaF2/Sm2O3-LaF3 (molar ratio 1.1), 83.9% ethene selectivity with 42.0% ethane conversion was obtained. XRD measurement revealed that partial cation or anion substitution occurred between Sm2O3 and LaF3 phases (for Sm2O3-LaF3 catalysts) as well as Sm2O3-LaF3 and BaF2 phases (for BaF2/Sm2O3-LaF3 catalysts). Structure defects such as anionic vacancies, O- and F-center might be formed by the substitution Rhombohedral Sm2/3La1/3OF was the main component in catalysts of Sm2O3-LaF3 (molar ratio 1:1) and 16.7 mol% BaF2/Sm2O3-LaF3 (molar ratio 1:1). The formation of this kind of binary rare earth oxyfluoride might be one of the factors that are responsible for the high C2H4 selectivity. XPS results that the binding energies of La3d(5/2) and Sm3d(5/2) in catalysts of Sm2O3-LaF3 are 0.5-1.5 eV negative shifts compared with the standard binding energies of La3d(5/2) and Sm3d(5/2) in La2O3, LaF3 and Sm2O3 show that the electron donating ability of Sm2O3-LaF3 catalysts is higher than pure La2O3, LaF3 and Sm2O3. Adding 16.7 mol% BaF2 to Sm2O3-LaF3 catalysts, although the binding energy of La3d(5/2) varied little compared with that in Sm2O3-LaF3, the difference between the binding energies of La3d(5/2) and La3d(3/2) decreased slightly. The contraction of cubic BaF2 and the decrease of the difference of the binding energy of La3d(5/2) and La3d(5/2) suggested that the isomorphous substitution between BaF2 and LnOF (Ln=La and/or Sm) lattice took place and more structure defects were formed. These might be the cause of the improvement of ethane conversion.