In situ assembly of ZSM-5 nanocrystals into micro-sized single-crystal-like aggregates via acid-catalyzed hydrolysis of tetraethylorthosilicate

ZSM-5 aggregates were synthesized with the silica source tetraethylorthosilicate (TEOS) being hydrolyzed at acidic conditions to produce siliceous precursors, followed by the addition of aluminum sulfate and tetrapropyl ammonium bromide (TPABr), and with the resulting gel mixture being hydrothermally crystallized at basic conditions. The obtained products were characterized by XRD, SEM, and N2 adsorption. Well crystallized ZSM-5 can be successfully synthesized through the sulfuric acid-catalyzed hydrolysis of TEOS within a short crystallization time 35 h. The thus produced micro-sized single-crystal-like zeolite ZSM-5 aggregates (10 μm) are made of uniformly distributed nanocrystals with sizes of about 200 nm. Moreover, by adjusting the hydrothermal reaction parameters, such as increasing the crystallization temperature, the TPABr/SiO2 ratio and the pH value of reaction solution, the crystallization is accelerated substantially. Also, the moderate H2O/SiO2 molar ratio of 20–60 in the synthesis mixture can lead to pure ZSM-5, and yet the optimal ratio is 40.