Enhanced catalytic performance of nanosheet ZSM-5 zeolites for methane-propane co-aromatization: Structural engineering via controlled desilication-recrystallization

A facile desilication-recrystallization strategy is developed to fabricate b-axis oriented hollow nanosheet ZSM-5 zeolites. • Optimal catalyst achieves 94.4% propane conversion, 8.2% methane conversion and 80.1% aromatic selectivity in MPC reaction. • The catalyst exhibits a 100 h catalytic lifetime (10-fold that of commercial ZSM-5) with excellent regeneration stability. • In-situ IR and DFT calculations reveal the synergistic mechanism of methane-propane co-aromatization. A nanosheet ZSM-5 (∼100 nm thick) was synthesized via a facile desilication-recrystallization approach using silicalite-1 as a precursor for methane and propane co-aromatization (MPC). The Si/Al feed ratio was tuned by varying NaAlO 2 dosage to direct the structural evolution of the zeolite. The acid strength and acid amount gradually increased with decreasing the Si/Al ratio from 100 to 25. Under the suitable Si/Al ratio of 50, the resulting Zn-bZSM-5(50) catalyst possessed the proper acidity and the largest average pore diameter of 6.16 nm, which endowed it with optimal catalytic performance: achieving 94.4% propane conversion, 8.2% methane conversion, 80.1% total aromatics selectivity, and an extended catalytic lifetime of 100 h. Additionally, the catalyst displayed outstanding regeneration stability, with no significant decline in reactant conversion and aromatics selectivity after five consecutive reaction-regeneration cycles. The exceptional stability originated from the chemical anchoring of Zn species as isolated [ZnOH] + sites within the framework, which effectively suppressed Zn volatilization. In-situ infrared spectroscopy analysis revealed that the presence of methane, combined with the acidity and Zn species, promoted the formation of adsorbed reaction intermediates, thereby improving the reaction performance. Control experiments with varied feed compositions further confirmed the synergistic effect between methane and propane. Density functional theory (DFT) calculations demonstrated that the co-aromatization of methane and propane was more thermodynamically favorable for the conversion of methane, corroborating the experimental observations. These findings establish a rational design strategy for developing nanosheet ZSM-5 zeolites with the superior performance and a long lifetime for MPC reaction. Download: Download high-res image (269KB) Download: Download full-size image