Solid-State 1H NMR Studies of Aluminum Oxide Hydroxides and Hydroxides
journal contributionposted on 05.06.1996, 00:00 by Gilberto Piedra, John J. Fitzgerald, Neal Dando, Steven F. Dec, Gary E. Maciel
1H CRAMPS (Combined Rotation and Multiple Pulse Spectroscopy) investigations have been used to identify the protons of Al−OH groups associated with low-surface-area aluminum oxide hydroxide and hydroxide materials. The 1H CRAMPS spectrum of boehmite (γ-AlOOH) shows a single peak at 8.8 ppm due to protons associated with Al2OH groups containing six-coordinate aluminum and three-coordinate oxygen, whereas the 1H CRAMPS spectrum of diaspore (α-AlOOH) depicts a sharp peak at 10.8 ppm that is assigned to the protons associated with Al3OH groups containing six-coordinate aluminum and four-coordinate oxygen. The 1H CRAMPS spectra of aluminum hydroxides show three 1H NMR peaks, in approximate 3:2:1 ratios, that are attributed to the protons associated with three different types of Al2OH groups. In gibbsite (γ-Al(OH)3), these 1H NMR peaks appear at 5.8, 4.3, and 2.9 ppm and are assigned to protons (a) H(3), H(5), and H(6), (b) H(1) and H(4), and (c) H(2), respectively, on the basis of X-ray diffraction and neutron diffraction data. In bayerite (α-Al(OH)3), these resonances are at 5.0, 4.3, and 2.9 ppm and are assigned to protons (a) H(1), H(2), and H(3), (b) H(4) and H(6), and (c) H(5), respectively. Dipolar dephasing experiments indicate that the protons associated with Al2OH groups containing three-coordinate oxygens are involved in stronger 1H−1H dipolar interactions than the protons associated with the Al3OH groups containing four-coordinate oxygens.