Exploring the Structure and Function of Rare-earth Elements Incorporated into Zeolite Catalysts

Rare-earth element (REE) incorporation into zeolites has been shown to catalyze a variety of selective oxygenate transformations including ethanol to olefins, yet the structure and function of REE-based Lewis acid zeolites remain unclear. In this study, we proposed five Y acid sites and constructed 91 hypothetical Y-deAlBeta structures and evaluated them based on experimental physicochemical characterization including X-ray absorption spectroscopy and pyridine FTIR. We demonstrated the kinetic relevance of these proposed sites for catalytic turnovers by comparing ethanol dehydration kinetics on our site structures with experimentally measured kinetics. Our analysis identified three fundamental site motifs—defect-open, dehydrated defect-open, and geminal hydroxyl—stabilized by adjacent silanol defects and hydroxyl groups that agreed with spectroscopic characterization and dehydration kinetic measurements. These representative Y sites were extended to 13 other REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) to explore trends in Lewis acid strength, assessed via pyridine adsorption energies and supported by experimentally measured pyridine FTIR. A linear correlation between Lewis acid strength and HOMO+LUMO energies was established, offering a predictive framework for understanding structure–function relationships in REE incorporated Beta zeolites. These findings provide molecular-level insight into REE incorporation and its role in tuning Lewis acid strength for selective catalytic transformation of biomass-derived oxygenates into chemicals and liquid fuels.