Synthesis method for introducing mesoporosity in a faujasitic-like zeolite system from a sodium aluminosilicate gel composition

Abstract

We report a facile synthesis method of hierarchical faujasitic structures from a sodium aluminosilicate composition. The critical experimental variable was the removal of water via heat from the aluminosilicate gel during the synthesis process. These gels were used as starting materials for synthesis. With these partially dehydrated gels, extensive zeolite nucleation did occur, and the extent was varied both with the degree of dehydration and the temperature at which the dehydrated sample was maintained. Nanoparticles of FAU and EMT were formed that pack together resulting in external surface areas of 249-259 m 2 /g. In addition, under certain conditions of crystal growth, sheet like-structures arising from FAU-EMT intergrowths were observed. The interpenetration packing of the nanosheets lead to zeolitic particles with external surface areas in the range of 127-199 m 2 /g. The pore size distribution varied with sample preparation and ranged from 2-100 nm. These samples were characterized by N 2 adsorption, Xray diffraction and electron microscopy. The thermal and hydrothermal stability was also studied. In order to evaluate the role of the higher external surface area on a chemical reaction, the dealkylation of 1,3,5-triisopropylbenzene was examined and the product distribution did reflect the mesoporous nature of the sample.

State of the Art and Perspectives of Hierarchical Zeolites: Practical Overview of Synthesis Methods and Use in Catalysis

“…This group hydrothermally produced various types of microporous zeolite crystals with varying degrees of mesoporosity. [ 293 ] Following parameters were examined during synthesis: I) water removal during reflux, II) aging temperature, and III) aging time. Water removal led to an increased viscosity of the synthesis gel, which can induce constrained mass transport.…”

“…Unfortunately, the mesoporous materials were not completely composed of FAU, but were rather a mix of FAU and EMT phases. [ 293 ]…”

Post‐Synthetic Ensembling Design of Hierarchically Ordered FAU‐type Zeolite Frameworks for Vacuum Gas Oil Hydrocracking

“…In addition, when used with organic pore‐directing agents (PDAs) such as quaternary ammonium cations, top‐down designs such as base‐mediated desilication can offer a direct route to creating mesoporosity in high‐silica frameworks obtained by steaming [15] . In the past, numerous efforts have been made to introduce mesoporosity in zeolite frameworks by using a variety of PDAs [16–20] . The base‐mediated reorganizations were either carried out in a single step [19,21–22] or two different steps involving separate base treatment and PDA treatment [23–24] .…”

“…[15] In the past, numerous efforts have been made to introduce mesoporosity in zeolite frameworks by using a variety of PDAs. [16][17][18][19][20] The base-mediated reorganizations were either carried out in a single step [19,[21][22] or two different steps involving separate base treatment and PDA treatment. [23][24] In particular, a high degree of mesoporosity was achieved in the case of FAU-type zeolites by using PDAs such as cetyltrimethylammonium bromide (CTAB) and tetrapropylammonium salts and bases viz., NH 4 OH and NaOH.…”