Integrated Theoretical and Empirical Studies for Probing Substrate-Framework Interactions in Hierarchical Catalysts

Area of Science:

• Materials Science
• Catalysis
• Nanotechnology

Background:

• Soft templating with siliceous surfactants is key for synthesizing hierarchically porous silicoaluminophosphates (HP SAPOs).
• HP SAPOs exhibit improved mass transport properties, crucial for catalytic applications.
• Enhanced performance of HP SAPOs in the Beckmann rearrangement of cyclohexanone oxime to $\epsilon$-caprolactam motivates further investigation.

Purpose of the Study:

• To investigate the catalytic potential of the siliceous mesopore network in HP SAPOs.
• To understand the substrate-framework interactions within HP (Si)AlPOs.
• To elucidate the role of micro- and mesopore interconnectivity in catalytic activity.

Main Methods:

• Integrated theoretical and empirical study.
• Inelastic neutron scattering (INS) for studying substrate-framework interactions.
• Spectroscopic analyses: FTIR spectroscopy, MAS NMR spectroscopy.
• Computational analyses.

Main Results:

• INS studies provided unique insights into substrate-framework interactions, allowing study of reactive species.
• Spectroscopic and computational analyses revealed cooperativity between silanol and Brønsted acid sites.
• The interconnectivity of micro- and mesopores in organosilane-templated SAPO facilitates cyclohexanone oxime protonation.

Conclusions:

• The siliceous mesopore network in HP SAPOs plays a critical role in their catalytic performance.
• Cooperative action between different acid sites within the hierarchical pore structure enhances catalytic efficiency.
• This study provides a fundamental understanding of HP SAPO catalysis for nylon-6 precursor synthesis.