A comparative study on different regeneration processes of Pt-Sn/γ-Al_2O_3 catalysts for propane dehydrogenation

摘要

Three different regeneration processes including hydrogen or nitrogen purging and coke-burning treatment were used to restore the Pt-Sn/γ-Al_2O_3 catalysts, through which propane dehydrogenation reaction was performed in a consecutive reaction-regeneration mode. It was found that the catalyst using hydrogen regeneration showed the best stability compared with those regenerated by nitrogen purging and coke-burning treatment, suggesting that hydrogen regeneration is an effective approach for maintaining the performance of Pt-Sn/γ-Al_2O_3 catalysts in propane dehydrogenation reaction. The effect of different regeneration atmospheres on the metal active center and the coke deposition was investigated by XRD,TEM, N_2-physisorption, TPO, TG and Raman technologies, and the results revealed that hydrogen or nitrogen regeneration resulted in little impact on the size and structure of metal active center, retaining the effective Pt Sn phase over the catalyst. Moreover, hydrogen regeneration not only removed the low dense components of the coke, but also altered the property of the residual coke through hydrogenation, leading to a higher mobility of coke, and thus a higher accessibility of the metal active centers. Whereas nitrogen regeneration only removed the low dense components of the coke. Although coke-burning regeneration caused a thorough coke removal, the catalyst subjected to repeated redox exhibited poor stability due to metal agglomeration, phase segregation and the resulting large Pt_3Sn particle and core-shell structure with a Sn-rich surface.