Defects tune the acidic strength of amorphous aluminosilicates

Area of Science:

• Materials Science
• Catalysis
• Solid-State Chemistry

Background:

• Crystalline zeolites offer high acidity but suffer from limited porosity.
• Mesoporous amorphous aluminosilicates possess better porosity but insufficient acidity.
• A significant gap exists between these two material classes for catalytic applications.

Purpose of the Study:

• To investigate defect engineering for fine-tuning the acidity of amorphous acidic aluminosilicates (AAS).
• To synthesize and characterize defective amorphous acidic aluminosilicates (D-AAS) by introducing oxygen vacancies.
• To evaluate the impact of these defects on acidity and catalytic behavior.

Main Methods:

• Synthesis of defective amorphous acidic aluminosilicates (D-AAS) via defect engineering.
• Solid-state nuclear magnetic resonance (NMR) spectroscopy (¹H, ²⁷Al, ¹⁷O) to study structural changes and acidity.
• X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy to analyze chemical environment modifications.
• In-situ FTIR to probe reaction mechanisms and reactant activation.

Main Results:

• Oxygen vacancies were successfully introduced into AAS, creating D-AAS.
• NMR, XPS, and FTIR studies confirmed that defects localized structural changes and altered the chemical environment of acidic sites.
• D-AAS exhibited enhanced performance in four acid-catalyzed reactions, demonstrating improved reactant activation.
• In-situ FTIR provided molecular-level insights into the role of defects in catalysis.

Conclusions:

• Defect engineering is a viable strategy to tune the acidity of amorphous aluminosilicates.
• D-AAS effectively bridge the porosity-acidity gap between zeolites and amorphous aluminosilicates.
• This approach offers a promising route for designing advanced catalytic materials.