Fabrication of sheet-like HZSM-5 zeolites with various SiO2/Al2O3 and process optimization in hexane catalytic cracking

A variety of HZSM-5 zeolites with different b-axis thicknesses and SiO 2 /Al 2 O 3 were fabricated by simply modifying urea content and Al source feeding in the initial gel, respectively. Multiple characterization technologies including XRD , SEM, N 2 adsorption-desorption, NH 3 -TPD and Py-IR were employed to investigate physicochemical properties of these samples and the possible crystallization mechanism was proposed that adsorption of urea molecules on (010) facet was the key factor for fabricating thin-sheet HZSM-5 zeolites. The results of hexane cracking reaction revealed that the selectivities of light olefins reached 46.5% when controlling b-axis thickness to 340 ​nm, exceeding the control sample by 12.2%. Furthermore, the effect of SiO 2 /Al 2 O 3 under this b-axis thickness was also investigated and concluded that keeping SiO 2 /Al 2 O 3 to 200 could exhibit the optimum catalytic performance with the conversion of 95.5% and light olefins selectivities of 56.7%. The reaction conditions were optimized to be 600 ​°C at the N 2 flow rate of 25 ​mL/min and WHSV of 3 h −1 to arouse the best performance. Under this condition, the distribution of ethene and propene was quite close to that of thermodynamic equilibrium. Based on these results, the primary and secondary products were uncovered, and further the reaction pathway of hexane cracking was disclosed. This new strategy to synthesize sheet-like catalysts for enhancing the catalytic properties in hexane cracking also laid a solid foundation for the study of the catalysts on light oil cracking in industry.