Seed-assisted synthesis of nanosized Beta with highly accessible mesoporosity and strong Brönsted acidity by adjusting 6-MRs formation and assembly

Abstract

A highly efficient induction focusing on the nucleation promotion and the framework elements consumption always plays a critical role in the design and synthesis of nanosized zeolitic materials. In this work, the highly crystalline nanosized Beta zeolite was hydrothermally synthesized following the seed-assisted strategy without using any additional organic structure directing agents (OSDAs) or preformed composite building units (CBUs). The physicochemical properties of the resulting nanosized zeolite Beta was strongly affected by the composition of the initial aluminosilicate gel, which can be facilely optimized just by matching the Si/Al molar ratio to the crystallization treatment. The superior mesoporous and strong acidic properties were obtained at a Si/Al ratio of ∼50. As for the framework assembly, Raman and XRD results reveal that the key factor is the continuous formation and accumulation of 6-ring structures (6-MRs) inside the aluminosilicate gel. After a 4 days and 22 h’ sufficient induction, the 5-MR and 4-MR structures were built through the bonding of 6-MR structures when fabricating the mtw, bea, and mor CBUs, and finished the assembly of Beta zeolite in 2 h. The obtained nanosized Beta zeolite exhibits a great crystallinity and a highly accessible mesopore structure that was composed solely of interparticle-type mesopores, as well as a strong Brönsted-type acidity.