Halo-oxide ACuO_2-δX_σ (A = Sr_0.63Ca_0.27, X = F, Cl) catalysts active and durable for ethane selective oxidation to ethene

The catalytic performance and characterization of ACuO_2-δ (A = Sr_0.63 Ca_0.27) and ACuO_2-δX_σ (X = F, Cl) catalysts have been investigated for the oxidative dehydrogenation of ethane (ODE) to ethene. The results of X-ray diffraction indicated that the three catalysts are single-phase and tetragonal infinite-layer in structure. The incorporation of fluoride or chloride ions in the ACuO_2-δ lattice can significantly enhance C₂H₆ conversion and C₂H₄ selectivity. At C₂H₆/O₂/N₂ molar ratio = 2/1/3.7 and space velocity = 6000 ml h^-1 g^-1, we observed 73.5% C₂H₆ conversion, 67.2% C₂H₄ selectivity, and 49.4% C₂H₄ yield at 660°C over ACuO_1.901F_0.088, and 87.4% C₂H₆ conversion, 74.4% C₂H₄ selectivity, and 65.0% C₂H₄ yield at 680°C over ACuO_1.950Cl_0.036. With the decrease in C₂H₆/O₂ molar ratio, C₂H₆ conversion increased, whereas C₂H₄ selectivity decreased. Within 48 h of on-stream ODE reaction, the two halide-doped materials exhibited sustainable catalytic performance. Based on the results of X-ray photoelectron spectroscopy, O₂ temperature-programmed desorption, and C₂H₆ and C₂H₆/O₂/N₂ (2/1/3.7 molar ratio) pulse studies, we conclude that (i) the incorporation of halide ions into the ACuO_2-δ lattice could enhance lattice oxygen activity, and (ii) in excessive amount, the O^- species accommodated in oxygen vacancies and desorbed below 600°C tend to induce ethane complete oxidation, whereas the lattice oxygen species desorbed above 600°C are active for ethane selective oxidation to ethene. By regulating the oxygen vacancy density and Cu³⁺ population in the halo-oxide catalyst, one can generate a durable catalyst with good performance for the ODE reaction.