Preparation of hierarchical ZSM-5 zeolites and their catalytic performance in thiophene alkylation

ZSM-5 zeolites were treated by Na₂CO₃ solutions with different concentrations and characterized by XRD, XRF, SEM, N₂ sorption and NH₃-TPD techniques; the influence of Na₂CO₃ treatment on their pore structure, acidity and performance in thiophene alkylation was investigated. The results showed that the BET surface area, external surface area and mesoporous volume of the ZSM-5 zeolites were enhanced through Na₂CO₃ treatment and the acidity was also modulated without altering the microporous structure of ZSM-5 zeolites. The activity and the selectivity to alkylates of the ZSM-5 zeolites in thiophene alkylation are also improved after Na₂CO₃ treatment. With the increase of Na₂CO₃ solution concentration, the thiophene conversion over the hierarchical ZSM-5 zeolites increases gradually, while the selectivity to alkylates increases first, reaches a maximum and then decreases along with the Na₂CO₃ solution concentration. When the Na₂CO₃ concentrations are 2 and 3 mol/L the thiophene conversions and alhylation selectivities are 81.26%, 73.15% and 90.57%, 72.59%, respectively.