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

Rare-earth element (REE) incorporation into dealuminated zeolites has been shown to catalyze a variety of selective oxygenate transformations, including ethanol to olefins, yet the structure and function of REE-incorporated Lewis acid zeotypes remain unclear. In this study, we proposed five yttrium acid site configurations and evaluated each against experimental physicochemical characterization techniques including X-ray absorption spectroscopy and pyridine Fourier transformed infrared spectroscopy (FTIR). 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. By comparing ethanol dehydration kinetics, we identified that interconvertible defect-open and dehydrated defect-open sites are kinetically relevant for catalytic turnovers. The three yttrium open site structural motifs from Y/deAlBeta were extended to 14 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 highest occupied molecular orbital + lowest unoccupied molecular orbital energies was established, offering a predictive framework for understanding structure–function relationships in REEs incorporated into dealuminated Beta zeotypes. These findings provide molecular-level insight into REE incorporation and its role in tuning Lewis acid strength for the selective catalytic transformation of biomass-derived oxygenates into chemicals and liquid fuels.