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. N-2 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 degrees C, a propane conversion of approximately 8% is observed for Co-Al with a >80% propylene selectivity, which corresponds to a turnover frequency of 5.1h(-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 degrees C. Continuous deactivation of the catalyst is observed for Co-Al at this elevated temperature. Insitu 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.