Hierarchical zeolites stabilized cobalt(II) as propane dehydrogenation catalyst: Enhanced activity and coke tolerance via alkaline post-treatment

Transition metal cobalt exhibits strong activation capabilities for alkanes, however, the instability of Co sites leads to sintering and coke deposition, resulting in rapid deactivation. Hierarchical zeolites, with their diverse pore structures and high surface areas, are used to effectively anchor metals and enhance coke tolerance. Herein, a post-treatment method using an alkaline solution was employed to synthesize meso‑microporous zeolite supports, which were subsequently loaded with Co species for propane dehydrogenation catalyst. The results indicate that the application of NaOH, an inorganic base, produces supports with a larger mesopore volume and more abundant hydroxyl nests compared to TPAOH, an organic base. UV–vis, Raman, and XPS analyses reveal that Co in the 0.5Co/SN-1–0.05 catalyst is mainly in the form of tetrahedral Co²⁺, which effectively activates CH bonds. In contrast, the 0.5Co/S-1 catalyst contains mainly Co₃O₄ species. Co²⁺ supported on hierarchical zeolites shows better propane conversion (58.6 %) and propylene selectivity (>96 %) compared to pure silica zeolites. Coke characterization indicates that hierarchical zeolites accumulate more coke, but it is mostly in the form of easily removable disordered carbon. The mesopores in the microporous zeolite support help disperse the active Co metal and facilitate coke removal during dehydrogenation, effectively preventing deactivation from sintering and coke coverage.