Mesoporous-Silica-Stabilized Cobalt(II) Oxide Nanoclusters for Propane Dehydrogenation

Propane dehydrogenation is a highly efficient and selective route to produce propylene. The development of transition-metal-based catalysts, especially cobalt oxide–Co(II) for propane dehydrogenation reaction has gained momentum in the past few years. However, the formation of bulk metallic cobalt is a major drawback of cobalt oxide-based catalysts, which need to be circumvented to maintain the high propylene selectivity. In this study, a facile route is proposed to prepare stable Co(II) on a mesoporous silica matrix (Co-mSiO2) via a simple synthesis procedure using the neutral templating method. The cobalt content in the silica is varied to optimize the activity and stability during the reaction. The physicochemical properties of the catalyst measured using X-ray diffraction, N2 adsorption–desorption, and transmission electron microscopy revealed the high surface area and well-dispersed cobalt oxide present in the mesoporous silica matrix. The coordination geometry found from the UV–vis and extended X-ray absorption fine structure analysis showed that Co(II) is highly dispersed with tetrahedral coordination in the mesoporous silica. The Co-mSiO2 catalyst with the lowest cobalt content of 2 wt % tested for the propane dehydrogenation reaction at the operating temperature of 600 °C showed 36% propane conversion with 94% propylene selectivity. 2Co-mSiO2 showed the nonredox properties of Co(II) with negligible metallic cobalt formed and a lower coke deposition rate (4 mgcarbon/gcat.·h) after the reaction supported by X-ray absorption near-edge structure and thermogravimetric analysis. The source for the side reaction (coke formation) can be assigned to the strong adsorption of propylene, which was unraveled using Fourier transform infrared analysis, and a nonredox mechanism is proposed for propane dehydrogenation reaction over the 2Co-mSiO2 catalyst.