Defect-engineered zeolite porosity and accessibility

Abstract

The study reports a simple and potentially universal strategy for post-synthetic engineering of zeolite crystals. Our strategy includes the generation of point defects in zeolite crystals by preliminary etching with oxalic acid, followed by the development of these defects by NH₄F etching. Several experimental techniques were used to measure and visualize the zeolite framework dissolution as a function of intrinsic and induced defects. It is revealed that the intrinsic defects lead to the extraction of misoriented nano domains, while those introduced by oxalic acid treatment lead further to the formation of small irregular mesopores. The resultant hierarchical zeolite shows substantially improved mesoporosity, in terms of mesopore volume and spatial distribution, and outstanding micropore acid site accessibility. These samples show superior catalytic performance in the dealkylation of a bulky molecule, 1,3,5-triisopropylbenzene. Our approach highlights the significance of chemically induced extrinsic defects, which make zeolite dissolution go beyond the limits set by the zeolite structure and synthesis chemistry.