Synthetic Control of the Defect Structure and Hierarchical Extra-Large-/Small-Pore Microporosity in Aluminosilicate...

Area of Science:

• Materials Science
• Catalysis
• Nanotechnology

Background:

• Zeolites are crucial microporous materials in catalysis.
• Controlling zeolite porosity is key to optimizing catalytic performance.
• STA-30 (SWY-type aluminosilicate zeolite) synthesis offers opportunities for structural tuning.

Purpose of the Study:

• To investigate the impact of synthesis parameters on STA-30 zeolite's defect chemistry and solid acidity.
• To understand how different organic structure-directing agents influence STA-30's porosity and properties.
• To explore the creation of hierarchical porosity in STA-30 via direct synthesis.

Main Methods:

• Synthesis of STA-30 using varied gel aging, Al source, and organic structure-directing agents.
• Powder X-ray diffraction for structural characterization.
• Isopentane adsorption and FTIR of adsorbed pyridine for porosity and acidity analysis.
• High-resolution scanning transmission electron microscopy for visualizing pore structure.

Main Results:

• Different synthesis routes yielded STA-30 with similar Si/Al ratios but varying crystal morphology, porosity, and silanol concentration.
• STA-30 templated with diDABCO-C8²⁺ exhibited hierarchical microporosity with extra-large (13 Å) noncrystallographic pores.
• This hierarchical structure increased pore volume by up to 30%, enhanced silanol concentration, and reduced Brønsted acid sites (BASs) accessibility.
• High accessibility (77%) of BASs was observed in the hierarchically porous STA-30.

Conclusions:

• STA-30 can be synthesized as a hierarchically porous zeolite through direct synthesis by controlling crystallization conditions.
• The choice of organic structure-directing agent significantly influences the development of noncrystallographic porosity and silanol content.
• Hierarchical porosity in STA-30 offers a route to tailor its properties for catalytic applications.