Properties Modification of Nanosized Hollow Zeolite Crystals by Desilication

A strategy to modify the properties of hollow zeolite was developed by leaching the parent zeolite in alkaline solution. A systematic study was performed to identify the effect of both the synthesis conditions of parent zeolite and the leaching conditions on the properties of hollow zeolite. Fine-tuning the leaching conditions, i.e. the concentration of sodium hydroxide solution, allows control over the degree of hollowness of the zeolite, achieving the introduction of larger voids in different locations of individual crystals, which is a key factor if the crystals are to be used for catalytic applications. In addition, a hypothesis was proposed to explain the formation of hollow ZSM-5 crystals. By replacing part of tetrapropylammonium hydroxide (TPAOH) with tetrapropylammonium bromide (TPABr) as the structure-directing agent (SDA), the parent zeolites obtained were less stable in alkaline solution and formed hollow structures more easily. The size of hollow zeolite crystals could be easily controlled by adjusting the water content of the synthesis gel. Finally, crystals with double shells were prepared by a method involving two consecutive crystallizations followed by base leaching. Overall, fine-tuning of zeolite synthesis and post-synthesis conditions leads to control of the structure of hollow zeolite crystals.