Industrial & Engineering Chemistry Research, Vol.41, No.1, 37-45, 2002
Ethane oxidative dehydrogenation over halogenated Bi2Sr2CaCu2O8-delta catalysts
The layered oxide Bi2Sr2CaCu2O8-delta (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 degreesC, a C2H6/O-2/N-2 molar ratio of 2/1/3.7, and a contact time of 1.67 x 10(-4) h g mL(-1), Bi2Sr2CaCu2O7.811F0.366 (Bi-2212-F) showed 70.8% C2H6 conversion, 72.5% C2H4 selectivity, and 51.3% C2H4 yield; Bi2Sr2CaCu2O7.901Cl0.394 (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 Bi2212-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 O-18/O-16 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.