Chemistry Department Colloquium

Probe Active Site Structures in Metal-Containing Zeolites of Varied Complexity James W. Harris Associate Professor, Hewson Engineering Faculty Fellow The University of Alabama, Chemical and Biological Engineering Understanding the structure of primary binding sites in heterogeneous catalysts, as well as the role of their local environment, is essential to developing complete molecular-scale descriptions of the chemistry occurring over these sites. In this seminar, I will present two examples of catalysis over metal-containing zeolites of varying complexity. In the first example, I will discuss our efforts to use molecular complexes dispersed on zeolites as structural models for metal–nitrogen-doped carbons (M-N-Cs) that catalyze oxidation reactions. Because M-N-Cs contain a distribution of M species that varies with the synthesis protocol, it is difficult to compare reactivity across M-N-Cs with different metal identities. Metal phthalocyanine complexes (MPCs) share the same M-N4 local coordination as the most reactive sites in M-N-Cs and are readily available with a range of metal identities. Through a series of in situ and operando X-ray absorption spectroscopy (XAS) measurements, we show that the structures of FePCs remain intact after encapsulation within, or dispersal upon, faujasite zeolites. FePC and Fe-N-C catalysts were tested in propane hydroxylation with N2O, a reaction not previously reported over either class of catalyst. We show that the apparent activation energy for Fe reduction, determined from transient XANES measurements, is comparable to that obtained from steady-state kinetic measurements. This indicates that reduction of adsorbed oxygen species via propane C–H bond activation has a high degree of rate control, consistent with prior computational studies. This work advances our efforts to better understand the reactivity of M-N-Cs and to use these earth-abundant materials in thermal catalysis. In the second example, I will discuss our contributions to the production of sustainable aviation fuel (SAF) from renewable alcohols. This conversion proceeds over multifunctional copper-, zinc-, and rare-earth-element (REE)-containing dealuminated Beta zeolites via a series pathway requiring dehydrogenation, aldol condensation, hydrogenation, and dehydration steps in a precise sequence. We have quantified the number of Lewis acid sites in these materials via ex situ and in situ chemical titrations and find evidence for multiple types of REE Lewis acid sites that collectively catalyze dehydration, aldol condensation, and Meerwein–Ponndorf–Verley (MPV) reduction. The kinetics of C–C coupling from ethanol–acetaldehyde mixtures over monometallic REE-containing dealuminated Beta zeolite catalysts with differing Lewis acid site strengths (e.g., Y/deAlBeta and La/deAlBeta) are comparable, whereas product selectivities differ. These results suggest a minimal impact of REE identity on the rate of C–C coupling, but predictable differences in selectivity to secondary products over REE sites as a function of their Lewis acid site strength. These findings support our ongoing efforts to reduce the cost and carbon footprint of SAF production. Biographical Information: James W. Harris received a B.S. in Chemical Engineering from the University of Virginia in 2012 and a Ph.D. in Chemical Engineering from Purdue University in 2017. Harris joined the Department of Chemical and Biological Engineering at The University of Alabama (UA) as an Assistant Professor in Fall 2019, and was promoted to Associate Professor (with tenure) in Fall 2026. His research group is involved in projects related to the responsible use of energy carriers for production of fuels and chemicals. Professor Harris is particularly interested in catalysis occurring over metal surfaces whose properties evolve as a function of their environment, and over