Uniform catalytic site in Sn-beta-zeolite determined using X-ray absorption fine structure

Area of Science:

• Materials Science
• Catalysis
• Inorganic Chemistry

Background:

• Tin-beta zeolite is an efficient heterogeneous catalyst for Baeyer-Villiger oxidations.
• Understanding the precise location of tin within the zeolite framework is crucial for optimizing catalytic performance.

Purpose of the Study:

• To determine the specific crystallographic sites occupied by tin (Sn) in the beta-zeolite structure.
• To correlate the tin site location with the observed catalytic selectivity in Baeyer-Villiger oxidations.

Main Methods:

• Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to analyze the local structure around tin.
• Multishell fitting analysis of EXAFS data was employed to precisely locate the tin atoms.

Main Results:

• Tin atoms are not randomly distributed but occupy specific, identical T5/T6 crystallographic sites within the beta-zeolite.
• Tin is substituted in pairs on opposite sides of the six-membered rings.
• This uniform site occupancy leads to consistent catalytic activity and high selectivity.

Conclusions:

• The specific and uniform crystallographic location of tin in beta-zeolite is responsible for its high catalytic selectivity.
• The observed enzyme-like selectivity in Baeyer-Villiger oxidations is attributed to these uniform active sites.
• A symbiotic relationship between the structure-directing agent and tin heteroatoms during synthesis is proposed.