Solid-State 1H MAS NMR Characterization of γ-Alumina and Modified γ-Aluminas

Abstract

1H single pulse MAS and CPMG T2/CSA-filter NMR experiments have been performed in order to characterize the hydroxyl structure of γ-alumina, as well as fluoride- and phosphate-modified γ-alumina materials. We have shown that problems associated with the strong homonuclear dipole-dipole interactions between protons of neighboring OH groups can be overcome by isotopic dilution of the alumina surface protons by deuterium exchange. Partially deuterated γ-alumina yields resonances at around −0.3, 0.3, 1.5, 2.4, 4.0, 5.0, 6.5, 7.1, and 7.8 ppm. CPMG T2/CSA-filter NMR experiments performed on alumina calcined at 700°C show that five different types of hydroxyl groups are present. CPMG T2/CSA-filter NMR of deuterated F/Al2O3 produces a resonance at 11.5 ppm in addition to a range of resonances between −0.2 and 7 ppm. NMR data for calcined P/Al2O3 and P-Mo(12)/Al2O3 (Wt% P = 0.0-10.0) show that polymeric orthophosphates produce a resonance at 3.4 ppm, while the monomeric orthophosphate species gives rise to a resonance at 1.2 ppm.