Study On The Effect Of Catalyst Support In Propane Dehydrogenation

A large amount of propane with relatively low price is more readily available due to the shale gas revolution,providing high quality and stable source of raw materials for propylene production.With the growing demand for propylene,propane dehydrogenation to propylene has been attracted much attention in the market in recent years.The study on propane dehydrogenation catalyst not only meets the market demand but also meets the national planning for mastering the core technology strategy.However,in the current Pt-based catalysts for propane dehydrogenation,the coke deposition and metal sintering lead to a rapid deactivation.Therefore,adjusting the surface characteristics of the catalysts to improve the selectivity and stability,in turn prolong the lifetime of the catalyst is the main research interest in propane dehydrogenation.This work is devoted on the application of Pt/BN and Pt/GaAlO_x catalysts in propane dehydrogenation,focusing on the effect of the catalyst pretreatments and the reaction feeds on the structure and performance of the catalysts,which are shown as follows:1.The Pt/BN catalyst was prepared by the incipient wetness impregnation method.The effects of calcination and reduction treatment on the catalyst activity during the pretreatment of the catalyst were investigated.It was found that the surface of the Pt size without calcination,but reduction was smaller,the side reaction is more likely to occur,and the excessive formation of coke in the early stage of the reaction leads to a rapid decrease in the activity of the catalyst.The particle size of the Pt after calcination and reduction is relatively larger.the addition of a small amount of H₂ can effectively suppress the side reactions,and the lack of acidic sites on the surface of BN,so that the side reactions of aromatization are inhibited.Other,the coke of the low C/H ratio modifies the active center.These factors make the propylene selectivity of the catalyst approaches 99%,the catalyst exhibits high selectivity and stability.Further research on the regeneration of the catalyst revealed that the catalyst could be directly regenerated by 2%O₂/N₂ at 550oC to recover more than 95%of the activity.It is further inferred that the BN edge can effectively anchor the Pt particles and prevent it from being oxidized,so less agglomeration of Pt particles.2.The gallium-aluminum solid solution?GaAlO_x?was synthesized by hydrothermal method.The Pt/GaAlO_x catalyst prepared by the incipient wetness impregnation was application in the propane dehydrogenation.The effect Ga/Al ratio on the dehydrogenation activity of propane Pt/GaAlO_x was investigated.The Pt/GaAlO_x catalyst exhibited the highest activity at Ga/Al=1:32.Based on this result,the effect of pretreatment on activity was further studied.Calcination at 500°C-800°C has no significant change in the crystal form of support.However,the higher the calcination temperature of the support,the faster the catalyst is deactivated.The calcination temperature after impregnation is optimal at 700°C.Combined with the literature,this is closely related to the formation of tetracoordinate Ga³⁺and Pt dispersion at different calcination temperature.The catalyst was reduced under different temperature,and it was found that the catalyst without reduction was more active.Although there was no obvious reduction peak in the catalyst in the H₂-TPR test,which proved that the precursor Pt?NH?₄?NO₃?₂ after decomposition,Pt⁰ is formed at high temperature and the Ga-Al is too stable to be reduced at these conditions,even in the presence of Pt.Further tests of different Pt loadings were carried out.It was found that the GaAlO_x itself also had certain activity,and the activity of the catalyst was increased by nearly 4 times after the addition of0.1wt%Pt.Increasing both conversion and selectivity can be explained by geometric effect and electronic effect.In experiments with different C₃H₈/H₂ ratio in feed,the addition of a small amount of H₂ can inhibit the rapid accumulation of cook,while the excessive H₂ partial pressure increases the side reactions,which may be related to the free H coverage concentration on the catalyst surface.