| Abstrakt: |
IR spectra of quinoline have been measured following adsorption on and subsequent desorption from SiO2, TiO2, ZrO2, niobic acid, SiO2-Al2O3, H-mordenite, and sepiolite. There is clear evidence from the IR spectra of three modes of adsorption: (i) hydrogen bonding to surface hydroxyl groups, (ii) electron transfer at Lewis acidic surface sites, and (iii) proton transfer at Brønsted acidic surface sites. Protonation of quinoline occurred with adsorption on niobic acid, SiO2-Al2O3, and H-mordenite, indicating the presence of Brønsted acidic sites with pKa values ≤4.90. Hydrogen bonding and interaction with Lewis acid sites was observed for each of the oxides studied. The results establish that the adsorption of quinoline can provide useful information regarding the nature of surface acidity on oxides which is complementary to that obtained from other probe molecules such as NH3 and pyridine. |
