Hydroxyl Groups as Bronsted Acids and Lewis Bases

3 Hydroxyl Groups as Bronsted Acids and Lewis Bases 

4 Spectroscopic Methods of Detecting Lewis Acidity/Basicity and Bronsted Acidity/Basicity 

Many methods have been developed to detect the Lewis acidity/basicity and Bronsted acid-ity/basicity. Liquid- or gas-phase titration, UV spectroscopy, and calorimetry are some of the non-spectroscopic methods of detecting acidity and basicity of an oxide material.26 However, we shall confine our discussion to the spectroscopic methods of detecting the acidity and basicity of an oxide material. IR, Raman, and NMR are the common spectroscopic techniques used to quantify the acidity or basicity of an oxide material. 

Two types of probe molecules have been used for the detection of Lewis and Bronsted acid sites. The first involves the adsorption of relatively strong basic molecules such as pyridine, ammonia, quinoline, and diazines. The second kind involves the adsorption of weak base molecules such as CO, NO, acetone, acetonitrile, and olefins. The pioneering works of Parry27 and Hughes and 

White28 indicated that the adsorption of pyridine molecule can be used to determine the concentration of Bronsted and Lewis acid sites. When IR is used in conjunction with thermal desorption, an estimation of the acid strength distribution can be obtained. 

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