Revisiting the use of 2,6-dimethylpyridine adsorption as a probe for the acidic properties of metal oxides

To check if the adsorption/desorption of 2,6-dimethylpyridine (2,6-DMP) is a suitable probe for the surface acidity of oxides, and to assign a band of controversial interpretation often observed upon 2,6-DMP adsorption, the a mbient temperature uptake of 2,6-DMP on several oxidic systems was carried out. SiO2 was observed to yield a plain H-bonding interaction, characterize d by an 8a band of adsorbed 2,6-DMP that is typical of silanols. Several (s pinel) transition aluminas and the corundum alpha -alumina phase were exami ned and allowed to test the suitability of 2,6-DMP in distinguishing differ ent types of surface Lewis acidity. Sulfated alumina and a beta -zeolite in its H-form were used to check the sensitivity of 2,6-DMP uptake toward eit her induced or intrinsic Bronsted acidity and the possibility of observing (weak) Lewis-coordinated 2,6-DMP also in the presence of (strong) Bronsted- bound 2,6-DMP.