Catalytic Dehydrogenation Of Propane Over Transition Metal Phosphide

Propylene is a important raw material in chemical production.At present,it is the 2ⁿdd largest chemical monomer consumption next to ethylene.Propane dehydrogenation process?PDH?has become the most competitive propylene production process for the high tield,mature technique,high propane production,and reletively low cost.Pt-based and CrO_x-based catalysts are commonly used in PDH.However,both catalysts have drawback for their high cost or heavy metal contaminations.Therefore,it is particularly important to develop a cheap and pollution-free catalyst for propane dehydrogenation.Transition metal phosphides are known for their good hydrogenation property.Since hydrogenation and dehydrogenation process are reversible reactions,transition metal phosphide can theoretically be a good dehydrogenation catalyst.In this work,Ni₃P,Ni₂P,MoP and WP were immobilized on variable supports including SiO₂,Al₂O₃,ZSM-5 and activated carbon?AC?by incipient impregnation.The effects of different metal phosphides and supports on the catalytic performance of propane dehydrogenation were investigated.Among them,MoP/AC has the best activity of propane dehydrogenation reaction.MoP with different loading were prepared and characterized by means of XRD,BET,H₂-TPR,and the effects of preparation conditions?loading amount,reduction temperature?and reaction parameters?reaction temperature,feed gas composition?on the performance of catalysts were investigated.The optimal loading amount of MoP on AC is 18%,and the optimal reduction temperature of MoP/AC is 650?.Under the optimal conditions?reaction temperature of 600?,feed gas composition:n?N₂?/n?C₃H₈?=6?,the MoP/AC possesses the best catalytic performance.MoO₃/AC,P-MoO₃/AC and MoP/AC catalysts were prepared and their catalytic performance in propane dehydrogenation wew compared.The results show that MoP/AC has better performance among them.NH₃-TPD characterization showed that after reduction of P-MoO₃/AC to MoP/AC,both the acid strengh and the number of acid sites are greatly reduced,leading to the increasement of catalytic activity and selectivity of MoP/AC.The MoP/AC catalysts were further modified by adding Fe,Cu,Ce,Co,Ni and Cs as propmoter,and the AC also pretreated with HNO₃.Most of the metal ions except Ni,had posituve effect toward the selectivity of the catalyst,but the activity was reduced.HNO₃treatment has destroyed to the microporous structure of the support,thus led to the decrease of catalytic activity.