Proximity Matters: Catalytic Consequences and Control of Active Site Proximity in Zeolites
William F. Schneider
University of Notre Dame
Catalytic activity in zeolites is often associated with extralattice ions that charge compensate a minority of Al3+ ions on a lattice primarily populated by Si4+. The density of those Al3+ ions (generally expressed as a silicon-to-aluminum ratio, or SAR) determines the total concentration of exchangeable sites, but the proximity of the Al3+ ions can exert influence over the reactivity and even the chemical identity of the extralattice ions at those exchange sites. While it can be difficult to interrogate these proximity effects in the laboratory, computational (density functional theory) models provide perfect control over atom locations and an ability to ask and answer questions about how this proximity influences ion exchange and reactivity. In this presentation I will describe our work to understand the relationship between Al proximity, ion exchange, and reactivity in the context of Cu-SSZ-13 zeolites (Science 2017, 357, 898) used commercially for the selective catalytic reduction of NOx and Fe-SSZ-13 zeolites (ACS Catal. 2018, 8, 10119) of interest for partial methane oxidation. I will also discuss the use of computational models to discover approaches to develop reporters of Al proximity and even to control that proximity under synthetic conditions. The work highlights the role of proximity as a key design parameter in zeolite catalysis.