Co/Al2O3 catalysts with different Co loadings and different calcination temperatures exhibit totally various catalytic performances for ethane dehydrogenation. At lower loadings, isolated Co2+ species in the framework of CoAl2O4 formed via strong interaction between Co and alumina leads to selective activation of C–H bond and the resulting high selectivity to ethylene. While a higher Co loading with the formation of aggregated metallic Co species through the in-situ reduction of Co3O4 on the catalyst surface results in C–C bond cracking to methane. Moreover, given the results of structural characterization and activity test, the increased calcination temperature enhances the interaction between Co species and alumina and facilitates the formation of CoAl2O4 even at a relatively high Co loading of 5%, contributing to the significant improvement of the catalytic behavior from undesired C–C bond breakage to C–H bond rupture. [ABSTRACT FROM AUTHOR]