Effect of coking and propylene adsorption on enhanced stability for Co²⁺-catalyzed propane dehydrogenation

The effects of Si-additive modification on nonoxidative propane dehydrogenation (PDH) over γ-Al₂O₃ sheet-supported isolate Co²⁺ catalysts have been investigated. Si addition cannot change the nanosheet structure and tetrahedral Co²⁺ coordination of the Co catalysts; nonetheless, it introduces a number of moderate-strength acid sites by the formation of composite SiAl oxides. Promoted catalytic stability is achieved on Si-modified Si–Co–Al₂O₃ in comparison with the Si-free Co–Al₂O₃ catalyst. In spite of similar total content and H/C ratios of deposited coke species on these two spent catalysts, a relatively lower graphitization degree and a higher ratio of highly reactive coke species are observed on the Si–Co–Al₂O₃ catalyst. Furthermore, the co-feeding of C₃H₆ significantly changes the coking reaction rates but not the coke distributions on Co-based catalysts. The C₃H₆ temperature-programmed desorption profiles and in situ diffuse reflectance infrared Fourier transform spectra suggest that the interaction of C₃H₆ with Co catalysts can be affected by Si modification tuning the coking property and the catalytic stability of Co²⁺–Al₂O₃-based catalysts for the PDH reactions.