Ethane oxidative dehydrogenation over halogenated Bi₂Sr₂CaCu₂O₈-δ catalysts

The layered oxide Bi₂Sr₂CaCu₂O₈-δ (Bi-2212) and halogenated Bi-2212 have been investigated as catalysts for the oxidative dehydrogenation of ethane to ethylene. By introducing a small amount of fluoride or chloride ions into the Bi-2212 lattice, one can enhance the catalytic performance significantly. At a temperature of 680 °C, a C₂H₆/O₂/N₂ molar ratio of 2/1/3.7, and a contact time of 1.67 × 10^-4 h g mL^-1, Bi₂Sr₂CaCu₂O_7.811 F_0.366 (Bi-2212-F) showed 70.8% C₂H₆ conversion, 72.5% C₂H₄ selectivity, and 51.3% C₂H₄ yield; Bi₂Sr₂CaCu₂O_7.901 Cl_0.394 (Bi-2212-Cl) showed 77.2% C₂H₆ conversion, 76.6% C₂H₄ selectivity, and 59.1% C₂H₄ yield. During 60 h of on-stream reaction at 680 °C, the two halogenated materials exhibited stable catalytic performance. We observed a remarkable reduction in deep ethylene oxidation over the halogenated catalysts. X-ray powder diffraction results indicated that Bi-2212 and the halogenated Bi-2212 oxides were single-phase and tetragonal in structure. The results of Cu and Bi oxidation state chemical analyses and X-ray photoelectron spectroscopic investigations revealed the presence of Cu³⁺, Cu²⁺, and Bi³⁺ in Bi-2212 and Cu⁺, Cu²⁺, Bi⁵⁺, and Bi³⁺ in Bi-2212-F and Bi-2212-Cl. Oxygen temperature-programmed desorption and temperature-programmed reduction studies indicated that the halogenation of Bi-2212 promoted the activity of lattice oxygen; such a promotional effect was confirmed by the results of ¹⁸O/¹⁶O exchange experiments. We conclude that, by modifying the oxygen nonstoichiometry and copper and bismuth oxidation states via halogenation, one can convert the Bi-2212 oxide to catalysts active and selective for the oxidation of ethane to ethylene.