(758d) DFT Investigations for the Influence of the Framework Topology in Cu2+ Exchange and Siting Preference in Zeolites

Ion-exchanged zeolites are widely used as heterogenous catalysts. In particular, Cu-SSZ-13 (CHA) is the on-board catalysts for NO_X selective catalytic reduction (SCR) with NH₃. Previous works have shown Cu²⁺ is exchanged in CHA as ZCuOH, Z₂Cu or oxo dimer, where Z indicates a framework Al.¹ Both computational and experimental results show ZCuOH in CHA resides in the large 8-membered-ring (8MR) openings, and Z₂Cu in CHA prefers to coordinate with 2^ndand 3^rd nearest neighbor Al pairs in 6MR.¹ Since CHA has 3-dimensional pore openings and only 1 symmetry-distinct T-site, how the Cu²⁺ speciation and siting preference will differ for frameworks with more symmetry-distinct T-site and less dimensional pore openings are still unclear. In this work, we performed plane-wave-based Density Functional Theory (DFT) supercell calculations to investigate the Cu²⁺ exchange and siting preference in 4 different frameworks. We choose other zeolite frameworks with different dimensional pore openings and numbers of T-sites to be compared with CHA to compare ZCuOH, Z₂Cu and Cu dimer exchange energies and siting preferences in those frameworks. We improved a previous reported variable charge model to correlate the Z₂Cu exchange energies with descriptors by including symmetry-related factors.² This work can help the predictions of Cu²⁺ exchange in other zeolite frameworks to choose a specific zeolite framework for a particular Cu²⁺ exchange functionality.

[1] Paolucci, Christopher, et al. Journal of the American Chemical Society 138.18 (2016): 6028-6048.

[2] Li, Sichi, et al. The Journal of Physical Chemistry C 122.41 (2018): 23564-23573.