The addition of BaBr2 (<70 mol%) to Ho2O3 could improve considerably both theC2H6 conversion andC2H4 selectivity of theODE (oxidative dehydrogenation of ethane) reaction. The use of BaO as a modifier was not suitable because the catalyst degraded rapidly due to BaCO3 formation. At 640℃, C2H6:O2:N2D2:1:4, and space velocity=6000mL h-1 g-1, C2H6 conversion of 70.6%, C2H4 selectivity of 80.2%, and C2H4 yield of 56.6% were observed over the 50 mol% BaBr2/Ho2O3 catalyst after a reaction time of 1 h.We conclude that the addition of BaBr2 to Ho2O3 can (i) enhance oxygen activation, (ii) protect a certain amount of active basic sites from CO2 poisoning, and (iii) suppress C2H4 deep oxidation. It is possible that the presence of Br¡ ions could have induced the formation of new active sites suitable for C2H4 generation. However, we observed continuous leaching of bromine during the ODE reaction, and the 50 mol% BaBr2/Ho2O3 catalyst gradually degenerated to a somewhat aged BaO/Ho2O3 catalyst. After 40 h of reaction, the C2H6 conversion, C2H4 selectivity, and C2H4 yield diminished to 51.8, 63.8, and 33.0%, respectively.

The 30 mol% MO (MDMg, Ca, Sr, Ba)-, 30 mol% BaCO3-, and 30 mol% BaX2 (XDF, Cl, and Br)-promoted Y2O3 catalysts have been investigated for the oxidative dehydrogenation of ethane reaction. Adding BaO or BaX2 to Y2O3 could significantly enhance the C2H4 selectivity. We also found that the doping of BaX2 into Y2O3 could considerably reduce C2H4 deep oxidation. Among these catalysts, 30 mol% BaCl2/Y2O3 performed the best. It was stable within a reaction period of 40 h, giving aC2H6 conversion, aC2H4 selectivity, and a corresponding C2H4 yield of ca. 72, 74, and 53%, respectively, at 640±C and 6000 mL h-1g-1 space velocity. X-ray photoelectron spectroscopy and chemical analysis of halides indicated that the Cl- ions were uniformly distributed in 30 mol% BaCl2/Y2O3 whereas the halide ions in 30mol% BaF2/Y2O3 and 30 mol% BaBr2/Y2O3 were not. With the increase of space velocity, the C2H6 conversion decreased and the C2H4 selectivity increased at 640±C over the 30 mol% BaCl2/Y2O3 catalyst.We observed that Cl leaching was not significant in 30 mol% BaCl2/Y2O3. However, gradual Br leaching was observed over 30 mol% BaBr2/Y2O3. X-ray powder diffraction and CO2 temperature-programmed desorption (CO2-TPD) results demonstrated that the 30 mol% BaCl2/Y2O3 catalyst is durable and is resistant to CO2 poisoning whereas the 30mol% BaO/Y2O3 and BaX2 (XDF and Br)/Y2O3 catalysts are readily poisoned by CO2 due to BaCO3 formation. O2-TPD studies showed that the addition of BaO (or BaX2) toY2O3 could obviously enhance the adsorption of oxygen molecules.We consider that such enhancement is closely associated with the defects generated due to ionic exchanges between the BaO (or BaX2) and the Y2O3 phases. Among the three 30 mol% BaX2/Y2O3 catalysts calcined at 900℃, 30 mol% BaCl2/Y2O3 showed a cubic Y2O3 lattice most significantly enlarged and a BaX2 lattice most pronouncedly contracted. In situ laser raman results indicated that there were dioxygen adspecies such as O22-, O2n/2- (1<n<2), O- 2, and O2δ/2- (0<±<1) on the 30 mol% BaO/Y2O3 and 30mol% BaX2/Y2O3 catalysts. Electron paramagnetic resonance results indicated that there were monoxygen O¡ and dioxygen O2- species on Y2O3, 30 mol% BaO/Y2O3, and 30 mol% BaX2/Y2O3.We suggest that the O2- O2n/2-, O2δ/2-, and O2/2- species participate in the selective oxidation of ethane to ethene whereas the O- species were responsible for the deep oxidation of ethane.

The catalytic performance and characterization of perovskitetype halo-oxide La1¡xSrxFeO3-δXσ (XDF, Cl) as well as La1-x SrxFeO3-δ(x=0-0.8) for the oxidative dehydrogenation of ethane (ODE) to ethene have been investigated. XRD results indicate that the catalysts had oxygen-deficient perovskite structures and TGA results demonstrated that the F-and Cl-doped perovskites were thermally stable. Under the reaction conditions of C2H6/O2/N2D 2/1/3.7, temperature=660℃C, and space velocityD6000 mL h¡1 g¡1, C2H6 conversion, C2H4 selectivity, and C2H4 yield were, respectively, 55.3, 45.1, and 24.9% over La0.6Sr0.4FeO3¡0.048; 76.8, 62.1, and 47.7% over La0.8Sr0.2FeO3¡0.103F0.216; and 84.4, 68.4, and 57.6% over La0.6Sr0.4FeO3¡0.103Cl0.164. Over the two halo-oxide catalysts, with an increase in space velocity, C2H6 conversion decreased, whereas C2H4 selectivity increased. Both La0.8Sr0.2FeO3-δ0.103F0.216 and La0.6Sr0.4FeO3-0.103Cl0.164 were durable within 40h of onstream ODE reaction. XPS results suggested that the presence of halide ions in the perovskite lattices promotes lattice oxygen mobility. It is apparent that the inclusion of For Cl-ions in La1¡xSrxFeO3-δ can reduce the deep oxidation of C2H4 and thus enhance C2H4 selectivity. Based on the results of O2-TPD and TPR studies, we suggest that the oxygen species that desorbed at temperatures ranging from 590 to 700℃ over the La0.8Sr0.2FeO3-0.103F0.216 and La0.6Sr0.4FeO3-0.103Cl0.164 catalysts are active for the selective oxidation of ethane to ethene.Byregulating the oxygen vacancy density and the oxidation states of B-site cations by implanting halide ions into oxygen vacancies in perovskite-type oxides (ABO3), one may obtain catalysts that are durable and selective for the ODE reaction.

The catalytic performance and characterization of YBa2Cu3O7-δ and YBa2Cu3O7-δXσ for the oxidative dehydrogenation of ethane (ODE) to ethene have been investigated. Under the reaction conditions of temperature=680℃, C2H6/O2/N2 molar ratioD2/1/3.7, and contact timeD1.67£10¡4hgml¡1, YBa2Cu3O7¡0.21F0.16 showed 84.1% C2H6 conversion, 81.8% C2H4 selectivity, and 68.8% C2H4 yield; YBa2Cu3O7¡0.18Cl0.13 showed 92.5% C2H6 conversion, 72.0% C2H4 selectivity, and 66.6% C2H4 yield. The sustainable performance during a period of 40h on-stream reaction at 680℃ demonstrated that the F- and Cl-doped catalysts are durable. X-ray powder diffraction results indicated that the undoped YBa2Cu3O7-δ and halide-doped YBa2Cu3O7-δXσ were of triple-layered oxygen-deficient perovskite-type orthorhombic structure. The results of the X-ray photoelectron spectroscopy, thermal treatment, thermogravimetric analysis, and 18O2-pulsing studies indicated that the incorporation of halide ions into the YBa2Cu3O7-δ lattice enhanced the activity of lattice oxygen. According to the O2 temperature-programmed desorption and temperature-programmed reduction results, we conclude that the oxygen species desorbed at 610-710℃ are active for the selective oxidation of ethane and those desorbed below 610℃ are active for the total oxidation of ethane; a suitable oxygen nonstoichiometry and Cu3C concentration in YBa2Cu3O7-δXσare required for the best catalytic performance of the catalysts.

The catalytic performance and characterization of Ln1.85A0.15 CuO4–± and Ln1.85A0.15CuO4–±X¾ (LnDLa, Nd; ADSr, Ce; XDF, 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 T0 structure. The results of X-ray photoelectron spectroscopic (XPS) studies revealed that there were Cu2C and Cu3C in the Sr-doped cuprate catalysts and CuC and Cu2C 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–± 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 Cu3C or CuC concentration and/or oxygen nonstoichiometry in Ln1.85A0.15CuO4-±X¾ are required for the best catalytic performance of the catalysts.