Investigation Of Non-noble Metals Co And Fe Based Catalysts Preparation And Catalytic Performancein Propane Dehydrogenation

As an important basic chemical raw material,the demand for propylene has maintained rapid growth,while the traditional steam cracking and catalytic reforming process for producing propylene cannot meet the market demand.With the rise of the shale gas revolution,the production of propane has greatly increased.Propane dehydrogenation,as an important targeted propylene production technical route,has gradually attracted widespread attention.At present,Pt-based and Cr-based catalysts are commercial propane dehydrogenation catalysts,but the expensive cost of Pt and environment harmfulness of Cr limit their further promotion and application.The transition metals Co and Fe have excellent ability in C-H bond activation with low price and environmental friendliness which show good prospects.In this thesis,Co-based catalysts with different supports were prepared by impregnation method,and introduced into propane dehydrogenation.Co/Silicalite-1showed the best propane dehydrogenation activity with propylene space-time yield（STY）reaching at 1.5 kg（C₃H₆）·h^-1·kg^-1,which is higher than most of the reported Co based catalysts,and can even achieve comparable activity to some commercial Pt-based catalysts.In addition,the apparent activation energies for different supported Co catalysts are in the sequence of Co/Al₂O₃>Co/HMS>Co/ZSM-5>Co/S-1,indicating that Co/Silicalite-1 has a strong propane activation ability.With investigation using UV-Vis,Raman,XPS and H₂-TPR,it could be found that the Co species on Silicalite-1 are mainly in the form of tetracoordinated Co²⁺species.Meanwhile,compared with other supported Co-based catalysts,the enhanced interaction between Co and Silicalite-1 and the appropriate support acid property are the most important factors influencing the catalyst reactivity and product selectivity.In addition,a series of modified Fe-based catalysts were prepared by nitrogen doped carbon material modification and applied to propane dehydrogenation.The reaction results showed that the modified Fe@NC/Si O₂has an initial propane conversion of 14.9%,which is nearly three times to that of unmodified Fe/Si O₂（5.1%）.And compared with Fe@NC/Si O₂,the initial selectivity to propylene Fe@NC/Si O₂also increased from 52.3%to 73.3%,which shows obvious advantage.The preparation parameters of nitrogen doped carbon modification process were further investigated by varying the supports,nitrogen doped carbon precursors and Fe precursors.The results showed that the introduction of nitrogen doped carbon can effectively improve the propane molecules activation ability on Fe-based catalysts.Combining with XRD,TEM and XPS characterizations,it could be illustrated that the N species in nitrogen doped carbon are mainly in the form of pyridine N,which can effectively provide electrons for Fe species.Besides,nitrogen doped carbon can increase the dispersion and enhance the anti-sintering ability of Fe.This method significantly improves the propane conversion and propylene selectivity,and suppresses the formation of by-products which could provide significance in modification for non-noble metal based dehydrogenation catalysts.