Interrogating the Lewis Acidity of Metal Sites in Beta Zeolites with ¹⁵N Pyridine Adsorption Coupled with MAS NMR Spectroscopy.

ABSTRACT: The Lewis acidity of isolated framework metal sites in Beta zeolites was characterized with ¹⁵N isotopically labeled pyridine adsorption coupled with magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The ¹⁵N chemical shift of adsorbed pyridine was found to scale with the acid character of both Lewis (Ti, Hf, Zr, Nb, Ta, and Sn) and Brønsted (B, Ga, and Al) acidic heteroatoms. The ¹⁵N chemical shift showed a linear correlation with Mulliken electronegativity of the metal center in the order Ti < Hf < Zr < Nb < Ta < Sn < H⁺. Theoretical calculations using density functional theory (DFT) showed a strong correlation between experimental ¹⁵N chemical shift and the calculated metal-nitrogen bond dissociation energy, and

SUBMITTER: Gunther WR 

PROVIDER: S-EPMC5419043 | biostudies-literature | 2016 Dec

REPOSITORIES: biostudies-literature