Post-synthesis design of hierarchical ZSM-5 materials for optimal catalytic performance in the cracking of petroleum feedstock

Tóm tắt

ZSM-5 zeolites are widely used as catalysts in the oil refining and petrochemical industry due to their outstanding catalytic performance.
Despite their undisputed applications, the relative small pore size of ZSM-5 zeolites often imposes intra-crystalline diffusion limitations for reactant molecules, provoking the lower catalyst utilisation. To alleviate such limitations, in this work, an additional network of mesopores has been introduced by the post-synthesis modification. It was found that a hierarchical ZSM-5 material with the large fraction of mesopores (297m2/g) coupled to the preservation of microporous characteristics (strong Brønsted) can be optimally prepared by base treatment in 0.5M NaOH and subsequent acid washing in 0.5M HCl. The gas phase cracking of cumene, carried out at 250oC as a model reaction to test the spacious properties, revealed that the introduction of mesoporosity enhanced the utilisation of active acid sites mostly located inside the micropores of ZSM-5, consequently the superior cumene cracking activity. Thus, the advantages of ZSM-5 zeolites (strong acidity) and mesostructured materials (high accessibility) can be combined to create advanced hierarchical ZSM-5 catalysts for petroleum processing.