Tracking Coordination Environment and Reaction Intermediates in Homogeneous and Heterogeneous Epoxidation Catalysts...

Area of Science:

• Catalysis
• Materials Science
• Spectroscopy

Background:

• Titanium (Ti)-based molecules and materials are crucial in homogeneous and heterogeneous catalysis.
• Understanding the electronic structure of Ti active sites is key for structure-property relationships.
• X-ray absorption spectroscopy (XAS) offers elemental selectivity and sensitivity to local symmetry.

Purpose of the Study:

• To demonstrate the utility of Ti L2,3-edge spectroscopy for characterizing Ti-based epoxidation catalysts.
• To establish molecular-level structure-property relationships by linking spectroscopic signatures to electronic structures.
• To develop a computational approach for interpreting Ti L2,3-edge spectra.

Main Methods:

• Creation of a spectral library of molecular Ti reference compounds with diverse coordination environments and ligands.
• Implementation of a computational methodology using multiplet ligand field theory and maximally localized Wannier orbitals.
• Benchmarking the computational method against the established spectral library.

Main Results:

• Ti L2,3-edge spectroscopy provides unique information on five- and six-coordinated Ti species, complementary to K-edge XAS.
• A validated computational approach allows for the interpretation of Ti L2,3-edge spectroscopic signatures.
• Spectroscopic signatures were successfully linked to electronic structures for various Ti species.

Conclusions:

• Ti L2,3-edge spectroscopy is a powerful tool for characterizing Ti-based homogeneous and heterogeneous catalysts.
• The developed computational methodology enables accurate prediction and tracking of catalytically relevant intermediates.
• This work facilitates the rational design of improved Ti-based epoxidation catalysts.