IN-SITU DETERMINATION OF BRONSTED LEWIS ACIDITY ON CATION-EXCHANGED CLAY MINERAL SURFACES BY ATR-IR/

Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spe ctroscopy has been used to determine the nature of acid sites present in Na+-, Ni2+- and Al3+-exchanged montmorillonite using the diagnostic base, pyridine. The pyridine additions were performed in situ at 25 d egrees C in the presence of liquid benzene or deuterated 1,4-dioxan to ascertain whether the acidity profile was influenced by the presence of either the non-polar or oxygenated solvent. Pyridine treated Ni2+-m ontmorillonite exhibited absorption bands characteristic of Lewis boun d base in both benzene and deuterated 1,4-dioxan indicating that the L ewis acid sites were present at low temperature and were accessible in both solvents. The presence of a strong 1537 cm(-1) band in pyridine- saturated Al3+-montmorillonite confirmed that this clay acted as a Bro nsted acid in benzene. However, this diagnostic band was significantly reduced in the presence of deuterated 1,4-dioxan.