Nature and Consequences of Al – Al Pairing in SSZ-13 Zeolite

William  Schneider, University of Notre Dame

The location of Al in the SSZ-13 framework influences the amount and nature of Cu ion exchange and potentially the stability of the zeolite framework itself. In this work we use first-principles density functional theory calculations to examine the relative energy of Al pair sites in silica-rich SSZ-13. We show that the energies are a strong function of the counter-ions. Al-O-Al linkages are stabilized when charge-compensated as Brønsted acid sites, potentially promoting dealumination.  In contrast, Cu(II) ion exchange destabilizes these same linkages and favors instead interactions with two Al in the same 6-membered-ring. The results may help rationalize the apparent stabilization of SSZ-13 imparted by Cu ion exchange.