Tailoring Multiple Porosities of Hierarchical ZSM-5 Zeolites by Carbon Dots for High-Performance Catalytic Transformation

A simple and high-efficiency method is proposed to synthesize hierarchical ZSM-5 zeolites with micropore and multistage mesopores by adopting water-soluble carbon dots (CDots) with various size distributions, such as 1-stage size distribution of CDots-1 of around 23 nm, 2-stage size distribution of CDots-2 of 6 and 9 nm, 3-stage size distribution of CDots-3 of 5, 8, and 18 nm. The abundant -OH and -COOH groups on the surface of CDots provide high solubility in water. The characterization techniques confirmed that the dual-porous h-ZSM-5 (MIcro-mEsopores) and multi-porous h-ZSM-5 (MIcro-mEso-mEsopores), h-ZSM-5 (MIcro-mEso-mEso-mEsopores, M-IEEE) catalysts are obtained. Notably, the hierarchical ZSM-5(M-IEEE) catalyst with micropore of 0.55 nm, two small mesopores of 4.8 and 7.4 nm, and one large mesopore of 17.5 nm show excellent catalytic performance with the highest 1,3,5-triisopropylbenzene (TIPB) cracking conversion (97.3%) and high stability. Similarly, the h-ZSM-5(M-IEEE) shows the high ethanol to olefins conversion (100%). The improved catalytic activity can be attributed to the more efficient diffusion of reactants and products in the crystals with the help of multistage mesopores, improved anti-coking stability, combined with the effect of suitable acidity, and the increased accessibility of the acid sites.

Automated summary

A high-efficiency method for synthesizing hierarchical ZSM-5 zeolites with micropore and multistage mesopores using water-soluble carbon dots of various size distributions has been proposed. The obtained catalysts showed excellent catalytic performance and stability, attributed to improved reactant and product diffusion, anti-coking stability, suitable acidity, and increased accessibility of acid sites facilitated by multistage mesopores.