The Fabrication Of (Ga,Cr)/ZSM-5 Hollow Fibers For Efficient Catalytic Conversion Of N-Butane

Light olefins are important basic chemical raw materials,and catalytic cracking of C4 alkanes into light olefins is of great significance.Catalyst is one of the key factors for catalytic cracking process.n-buatne,as an important component of C4 alkanes,is difficult to be cracked and exhibits low selectivity to light olefins due to its high stability.Metal/ZSM-5 bifunctional catalysts,combining the dehydrogenation of metal and the cracking function of ZSM-5,can activate n-butane and are expected to obtain high yield of light olefins.Hence,this paper aims at the study of highly efficient bifunctional catalytic cracking catalysts.Firstly,nano-ZSM-5 zeolite was modified by Ga element,and a series of Ga₂O₃/ZSM-5 catalysts with different Ga₂O₃ loadings were prepared by incipient-wetness impregnation method.Then,Ga₂O₃/ZSM-5 was used as the building blocks to prepare Ga₂O₃/ZSM-5 hollow fibers via coaxial electrospinning.The physicochemical features of the as-prepared catalysts were characterized and their performances for the catalytic conversion of n-butane were investigated.The results indicate that the as-prepared Ga₂O₃/ZSM-5 hollow fibers possess neat morphology,uniform diameter and macro-meso-microporosity structure.And,the conversion of n-butane and yield of C2=,C3=,C4= plus BTX on the as-prepared catalysts are high,which are attributed to the good banlance of the cracking function of ZSM-5 and the dehydrogenation of Ga₂O₃,and also the synergetic effect of bifunctionality and hierarchical porosity.The conversion of n-butane is close to 100% at 575 oC,and the yield of C2=,C3=,C4= plus BTX reach to 87.6% at 600 oC,which is 56.3%,24.6%,and 13.3% higher than that of ZSM-5,ZSM-5 zeolite fibers,and Ga₂O₃/ZSM-5,respectively.Then,nano-ZSM-5 were modified by Cr element through the in-situ synthesis and incipient-wetness impregnation methods,respectively.The effect of different preparation methods on the catalytic performance of the as-prepared catalysts was investigated.Furthermore,the in-situ Cr-modified nano-ZSM-5 was used as building blocks to prepare Cr/ZSM-5 hollow fibers via coaxial electrospinning.The results show that the as-prepared Cr/ZSM-5 hollow fibers possess neat morphology and continuous hierarchical structure.And the fibers show excellent catalytic cracking performances of n-butane.The conversion of n-butane and yield of ethane plus propene reach to 98.1% and 55.8% at 625 oC,respectively.Superior catalytic performances are attributed to the cooperation of the suitable acidity of ZSM-5 zeolite,the highly dispersed and isolated active sites of framework Cr and the excellent mass transfer performance of hierarchical hollow fibers.