The influence of zoned Al distribution of ZSM-5 zeolite on the reactivity of hexane cracking

Abstract

A facile seed-assisted strategy was employed to synthesize ZSM-5 zeolites with different Al distribution through varying the Al content in the ZSM-5 seed and the synthetic gel, respectively. One ZSM-5 zeolite (Z1) displays Al-rich rim, synthesized by epitaxial growth on pure silica crystal seed in the Al-containing gel. The other ZSM-5 sample (Z2) has Al-homogeneous distribution obtained from Al-containing seed and pure silica gel. The both samples were determined by desilication process, XPS and 2,6-DMP adsorption IR analysis etc. Sample Z1 and Z2 perform almost the same initial conversion in n-hexane cracking reaction, but Z2 possesses the higher stability and higher olefin yield than Z1 with time on stream. There is low deactivation rate on the Z2, due to its Al-homogeneous distribution favorable for retaining channel connectivity and enhanced diffusivity, while more external coke deposit on Z1 occurs, having serious pore blocking due to its Al-rich rim.