RII Track-4:NSF: Design of zeolite-encapsulated metal phthalocyanines catalysts enabled by insights from synchrotron-based X-ray techniques

Heterogeneous catalysts are used in a wide range of industries, including the chemicals and automotive sectors, to enable reactions to proceed under milder conditions with higher selectivity towards desired products. These materials have complex structures that are difficult to define, and therefore difficult to further improve. In this project, model catalysts will be developed that have well defined structures, in order to determine which aspects of these materials are beneficial for catalysis.

Using state-of-the-art X-ray techniques available only at a handful of laboratories in the world (known as synchrotrons), the research team will precisely determine the structures of these materials during reaction. These measurements are not possible in university laboratories. Through this project, a graduate student and a professor will gain expertise in performing these measurements and analyzing the resultant data, allowing the researchers to share their knowledge with diverse collaborators across the state of Alabama.

Through those efforts, this project will increase access to synchrotron-based X-ray techniques for researchers in Alabama, allowing the state to be increasingly competitive in attracting federal funding and private investment in scientific research. This Research Infrastructure Improvement Track-4 EPSCoR Research Fellows project will provide a fellowship to an Assistant Professor and training for a graduate student at the University of Alabama Tuscaloosa.

This work would be conducted in collaboration with researchers at the SLAC National Accelerator Laboratory.

Development of structure function relationships necessary for rational design of heterogeneous catalysts requires detailed knowledge of the structure of inorganic solids at the atomic level, including of the electronic structures of metal atoms and the local connectivity between atoms as a function of process conditions. Laboratory-scale techniques can quantify the number of metal binding sites but cannot identify and quantify their structural features (oxidation states, coordination numbers, and metal-ligand bond distances) during reaction.

The best technique for these measurements is operando synchrotron-based X-ray absorption spectroscopy (XAS), wherein quantitative XAS data are collected over a working catalyst while reaction rates are measured simultaneously. The project will develop a fundamental understanding of the structure of zeolite-encapsulated metal-phthalocyanine complexes (MPCs) and the chemistries they mediate by taking extended visits to the Stanford Synchrotron Radiation Lightsource (SSRL) at SLAC National Accelerator Laboratory (SLAC).

Combining XAS with in situ wide angle x-ray scattering (WAXS) and infrared spectroscopy measurements allows monitoring of the structure of both the primary binding sites, the structure of the zeolitic pores that confine them, and the intermediates present during catalysis. The research team will gain expertise in XAS and WAXS by working with recognized experts in these techniques.

The materials characterized in this proposal avoid heterogeneities in local configurations of primary binding sites that are unavoidable for many other zeolite-, doped-carbon-, and MOF-based catalysts. These catalysts will be more stable than analogous MPC complexes in solution, allowing for gas-phase chemistry over single-site catalysts. This will be the first use of faujasite zeolite encapsulated MPC complexes, to our knowledge, for gas-phase oxidation reactions with N2O, and thus the first measurements of in situ or operando XAS spectra of these catalysts during this reaction.

By gaining an understanding of the structure and stability of these materials under reaction conditions, we will describe catalysis over heterogeneous single-atom complexes without distractions from variation in the local configuration of the primary binding sites and the pores that confine them.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.