Controllable Synthesis of Hollow Mesoporous ZSM-5 with Improved Catalytic Performance for Tetralin Hydrocracking to Light Aromatics

Traditional ZSM-5 zeolite with a microporous structure suffers from diffusion limitations for large molecules and poor accessibility to active centers, resulting in low catalytic activity and rapid deactivation via coking. Herein, we designed and prepared ZSM-5 with hollow cavity and uniform mesopores in the shell through one-step alkali treatment using mixed alkali of tetrapropylammonium hydroxide (TPAOH) and sodium carbonate (Na2CO3). The size of mesopores in the shell could be controlled in the range of 2-12 nm by simply changing the concentration of Na2CO3. The effects of alkali treatment time, Si/Al ratio of parent ZSM-5, and zeolite/solution ratio on the formation of mesopores were systematically investigated. The construction of hollow mesoporous structure for ZSM-5 led to a significant improvement of catalytic activity in the conversion of tetralin to benzene, toluene, ethylbenzene, and xylene (BTEX). The tetralin conversion and BTEX yield for hollow mesoporous ZSM-5 achieved 99.6% and 49.2%, respectively, while those of solid ZSM-5 were 94.0% and 41.6%, respectively. Moreover, the lifespan of hollow mesoporous ZSM-5 was significantly prolonged compared with solid ZSM-5. The enhanced catalytic performance of hollow mesoporous ZSM-5 could be attributed to reduced diffusional resistance and increased accessibility to acid sites as well as improved tolerance capacity of coke species. This study provides a facile and effective strategy for the preparation of zeolite catalysts with uniform and tunable mesopores and also exhibits the advantages of mesoporous zeolites in the reactions related to large molecules.