Comprehensive IR study on acid/base properties of metal oxides Original Research Article

Acid/base properties (type, strength, number) of a wide range of metal oxides were studied by IR (infra-red) spectroscopy. Ammonia, pyridine and CD3CN were used as probe molecules for acidity measurement. CO2, CHCl3, benzaldehyde and nitrobenzene were used for basicity measurement. Pyridine for the nature and number of acid sites, CD3CN for the strength of acid sites, CHCl3 for the strength of basic sites and nitrobenzene for the number of basic sites were found to be suitable probes. The absorption coefficients of pyridine for acidic sites and nitrobenzene for basic sites, estimated for various metal oxides by IR coupled with mass spectrometry, were within ±10% of the average value, which indicates that the integrated molar extinction coefficients could be used for semi-quantification of acid/base sites of various oxides samples. The comprehensive IR results in this study will be available to characterize properties of Lewis and Brønsted acid sites and basic sites on metal oxides by a simple IR experiment.