CoOx/Silicalite-1 Tailored by Calcining Atmosphere for Oxidative Dehydrogenation of Propane With CO2.

The relatively richer reservoir and reasonable performance in activating C─H bonds make cobalt a very competitive catalyst for the oxidative dehydrogenation of propane with carbon dioxide (CO2-ODP). However, the catalytic nature of different cobalt species is ambiguous, and the development of active and selective Co-based CO2-ODP catalysts are at the very early stage. In this study, Co species on CoOx/Silicalite-1 catalysts are regulated by calcining the catalyst precursor at 500°C under Ar, Air, and H2 atmospheres, respectively. Characterization results reveal that the proportion of Co3O4 spinel, metallic Co, and tetrahedrally coordinated Co2+ species (Td-Co2+) is easily altered by changing the calcining atmosphere. Moreover, Td-Co2+ is revealed to be the active site for CO2-ODP while Co0 is active for side reactions such as cracking and reforming. As a result of the richest Td-Co2+ and diminished Co0 over the CoOx/Silicalite-1 catalyst calcined in Ar, the highest CO2-ODP performance is achieved with a propylene space-time yield of 15.88 mmol·gcat -1·h-1. Besides acting as a mild oxidant, the additional functions of CO2 are to retard the reduction of Td-Co2+ and to reduce the coke accumulation via the reverse Boudouard reaction during CO2-ODP. These understandings are important guides for optimizing with more efficient Co-based CO2-ODP catalyst.