Scalable and mesoporogen-free synthesis of a highly oriented nanorod-assembled ZSM-5 zeolite for efficient benzene alkylation with ethanol

Abstract

Hierarchical ZSM-5 zeolites with intercrystalline mesopores are crucial for improving the mass transport and accessibility of active sites. Traditional synthesis methods often require organic structure-directing agents with complicated design and/or environmentally harmful additives while involving tedious synthetic procedures. To streamline the method for constructing hierarchical ZSM-5 zeolites, we herein propose a seed-induced approach free of any additives to efficiently synthesize oriented nanorod-assembled hierarchical ZSM-5 zeolites (NA-ZSM-5) with abundant intercrystalline mesopores. By systematically examining the parameters of the seed on the resultant ZSM-5, we found that a seed with high crystallinity is a prerequisite for constructing the oriented aggregation of nanorods while the length of the nanorods can be finely controlled from ∼180 nm to ∼600 nm via adjusting the seed dosage. Importantly, the seed functions as a dynamic template on which aluminosilicate precursors gradually deposit and further evolve to c-axis oriented nanorods. The resulting NA-ZSM-5 zeolite demonstrates a relatively better catalytic lifetime of 200 h, with benzene conversion constantly higher than 53.3% and ethyl selectivity remaining above 92.4% in the benzene alkylation with ethanol. Additionally, this synthetic procedure can be successfully scaled up in 1 L and 3 L autoclaves with product yields of above 94%. This work demonstrates an efficient and scalable approach to producing hierarchical ZSM-5 zeolites with abundant intercrystalline mesopores for value-added conversion of the benzene series.