Induced Active Sites by Adsorbate in Zeotype Materials

Area of Science:

• Materials Science
• Catalysis
• Solid-State Chemistry

Background:

• Zeolites are crucial for industrial applications, with active sites traditionally considered fixed.
• The dynamic creation of active sites by adsorbates in zeotype materials is largely unexplored.
• Lewis acidic sites (LASs) and Lewis basic sites (LBSs) are accepted active sites in pristine zeolites.

Purpose of the Study:

• To experimentally observe the establishment of induced active sites in silicoaluminophosphate (SAPO) by adsorbates.
• To challenge the conventional understanding of fixed active sites in zeotype materials.
• To investigate the dynamic interactions between adsorbates and zeotype frameworks.

Main Methods:

• High-resolution magic-angle-spinning solid-state NMR
• Synchrotron X-ray diffraction
• Neutron powder diffraction
• In situ diffuse reflectance infrared Fourier transform spectroscopy
• Ab initio molecular dynamics

Main Results:

• Direct experimental evidence of induced active sites in SAPO by adsorbates was obtained.
• A transformation from Brønsted acid sites (Al(OH)Si) to induced frustrated Lewis pair (FLP) structures was observed.
• Induced FLPs, comprising three-coordinated framework Al (LAS) and SiOH (LBS), transiently favor heterolytic molecular binding.

Conclusions:

• The study demonstrates the dynamic establishment of active sites in zeotype materials.
• Induced active sites can be created by molecular bombardment, challenging the fixed site paradigm.
• This finding opens new avenues for understanding adsorption and catalysis in zeolitic structures.