Detection and Estimation of Brønsted Acidities in Alkali Metal Cation Exchanged X and Y Zeolites

An “indicator titration” method that can identify the acidity of a zeolite is presented. This method is particularly useful when the zeolite possesses acidity that is below the detection limit of conventional techniques such as MAS NMR. However, this technique underestimates the extent of acidity of zeolites that contain a large number of acidic sites such as in CaY and HY. On the basis of this technique, the commonly available alkali metal exchanged Y zeolites are estimated to contain one acidic site per ∼116 aluminums. In contrast to Y, the alkali metal exchanged X zeolites do not contain enough Brønsted acid sites to be detected by this technique.