Construction and Catalytic Cracking Performance of Hollow ZSM-5 With Gradient Pore Structures
The Al-rich external and Si-rich external ZSM-5 zeolite was synthesized as parent zeolite.The hollow mesoporous ZSM-5 zeolites with the shell thickness of 80,40,20 and 10 nm were prepared using different concentrations of sodium hydroxide solutions for treatment.ZSM-5 zeolite samples were physicochemically characterized by means of XPS,XRD,TEM,SEM,NH3-TPD,Py-FTIR and N2 physical adsorption-desorption curves.Moreover,the catalytic performances of ZSM-5 zeolites in hydrocarbons cracking were investigated under the following conditions:the reaction temperature of 550 and 600 ℃,feed injection rate of 0.8 g/min,feed injection time of 150 s,and catalyst/oil mass ratio of 0.25.The results show that in the catalytic cracking reaction,HZ5-AT3 hollow zeolite with a shell thickness of 20 nm exhibits higher conversion rate and light olefin yield.This is attributed to the fact that the hollow mesoporous zeolite with a gradient distribution of micro-,meso-and macro-pores can provide rich acid centers and multi-directional diffusion paths,thus improving the accessibility of active centers,and promoting the cracking of large molecule hydrocarbons.
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