A Mesoporous Cobalt Aluminate Spinel Catalyst for Nonoxidative Propane Dehydrogenation

A mesoporous CoAl₂O₄ spinel (Co-Al) is synthesized by a one-step evaporation-induced self-assembly (EISA) method. N₂ physisorption and TEM are used to demonstrate the presence of mesopores within the Co-Al material. The spinel crystal structure of Co-Al, in which Co occupies tetrahedral (T_d) sites, is confirmed by using XRD and UV/Vis spectroscopy. In nonoxidative propane dehydrogenation at 550 °C, a propane conversion of approximately 8 % is observed for Co-Al with a >80 % propylene selectivity, which corresponds to a turnover frequency of 5.1 h⁻¹ based on an estimation of the number of active Co sites by using NH₃ temperature-programmed desorption. A much higher propane conversion rate and a circa 80 % propylene selectivity is observed upon reaction at 600 °C. Continuous deactivation of the catalyst is observed for Co-Al at this elevated temperature. In situ X-ray absorption spectroscopy results suggest that Co remains as a T_d Co²⁺ species under the reaction conditions. The T_d Co²⁺ sites within the Co-Al material are thus proposed to act as Lewis acidic active sites; this acidity is verified using IR spectroscopy with pyridine as a probe molecule.