The performances and characterization of BaO- and BaX{sub 2} (X = F, Cl, and Br)-promoted Y{sub 2}O{sub 3} catalysts for the selective oxidation of ethane to ethene

The 30 mol% MO (M = Mg, Ca, Sr, Ba)-, 30 mol% BaCO{sub 3}-, and 30 mol% BaX{sub 2} (X = F, Cl, and Br)-promoted Y{sub 2}O{sub 3} catalysts have been investigated for the oxidative dehydrogenation of ethane reaction. Adding BaO or BaX{sub 2} to Y{sub 2}O{sub 3} could significantly enhance the C{sub 2}H{sub 4} selectivity. The authors also found that the doping of BaX{sub 2} into Y{sub 2}O{sub 3} could considerably reduce C{sub 2}H{sub 4} deep oxidation. Among these catalysts, 30 mol% BaCl{sub 2}/Y{sub 2}O{sub 3} performed the best. It was stable within a reaction period of 40 h, giving a C{sub 2}H{sub 6} conversion, a C{sub 2}H{sub 4} selectivity, and a corresponding C{sub 2}H{sub 4} yield of ca. 72, 74, and 53%, respectively, at 640 C and 6000 mL/h g space velocity. X-ray photoelectron spectroscopy and chemical analysis of halides indicated that the Cl{sup {minus}} ions were uniformly distributed in 30 mol% BaCl{sub 2}/Y{sub 2}O{sub 3} whereas the halide ions in 30 mol% BaF{sub 2}/Y{sub 2}O{sub 3} and 30 mol% BaBr{sub 2}/Y{sub 2}O{sub 3} were not. With the increase of space velocity, the C{sub 2}H{sub 6} conversion decreased and the C{sub 2}H{sub 4} selectivity increased at 640 C over the 30 mol% BaCl{sub 2}/Y{sub 2}O{sub 3} catalyst. The authors observed that Cl leaching was not significant in 30 mol% BaCl{sub 2}/Y{sub 2}O{sub 3}. However, gradual Br leaching was observed over 30 mol% BaBr{sub 2}Y{sub 2}O{sub 3}. X-ray powder diffraction and CO{sub 2} temperature-programmed desorption (CO{sub 2}-TPD) results demonstrated that the 30 mol{degree} BaCl{sub 2}/Y{sub 2}O{sub 3} catalyst is durable and is resistant to CO{sub 2} poisoning whereas the 30 mol% BaO/Y{sub 2}O{sub 3} and BaX{sub 2} (X = F and Br)/Y{sub 2}O{sub 3} catalysts are readily poisoned by CO{sub 2} due to BaCO{sub 3} formation. O{sub 2}-TPD studies showed that the addition of BaO (or BaX{sub 2}) to Y{sub 2}O{sub 3} could obviously enhance the adsorption of oxygen molecules.