Acidity of sulfated tin oxide and sulfated zirconia: A view from solid-state NMR spectroscopy

Acidic properties of ZrO2, SO42-/ZrO2, SnO2, and SO42-/SnO2 were studied by solid-state NMR spectroscopy. 1H MAS NMR indicated that SO42- was able to react with the hydroxyl groups of ZrO2 and SnO2, leading to the formation of new acid sites. 1H, 13C, and 31P MAS NMR spectra of adsorbed probe molecules indicated that both Brönsted and Lewis acid sites were present on SO42-/ZrO2, but only Brönsted acid site existed on SO42-/SnO2. Acid strength of SO42-/SnO2 was stronger than that of SO42-/ZrO2. Both of them were slightly stronger than that of HZSM-5, but still weaker than that of 100% H2SO4.