Atomic-scale insights into rare earth Oxo-Cation stabilization in HY zeolites: A periotic DFT study

Abstract

This study systematically investigates the stabilization mechanisms and structural-electronic modulation of rare earth cations (La³⁺, Ce³⁺, Y³⁺) at distinct crystallographic sites (SI’, SII, SIII) in HY zeolites using density functional theory (DFT) calculations. It is revealed that the stability of rare earth oxo-cations (REO⁺) strongly depends on their occupied positions and ionic radii. At the SI’ sites, LaO⁺, with a larger ionic radius (1.16 Å), exhibits the lowest formation energy (ΔE < 0) and preferentially stabilizes within the 6-membered rings (6-MR) of sodalite cages through strong interactions with framework oxygen atoms, while Y³⁺ (0.90 Å) induces localized lattice distortions and migrates to SII/SIII sites due to spatial constraints. Structural analyses demonstrate that REO⁺ incorporation synergistically regulates zeolite stability via geometric effects (e.g., 6-MR contraction and supercage expansion) and electronic effects (weakened Al-O bond polarization and enhanced RE-O charge transfer). Specifically, La³⁺ strengthens covalent bonding through d-orbital-mediated directional charge transfer, whereas Ce³⁺ induces asymmetric charge redistribution via 4f-orbital participation, which is also proofed by the COHP and DOS analysis. This work elucidates the atomic-scale site selectivity and stabilization mechanisms of RE cations in zeolites, providing theoretical insights for designing highly stable RE-modified HY zeolite catalysts with tailored acidity. These findings hold significant implications for industrial applications such as petroleum cracking and environmental catalysis.