IR microspectroscopic investigation of the acid sites in metal substituted AIPO₄-5 molecular sieves: Part 1. Sorption of benzene and strong bases

The functional groups of metal substituted aluminophosphate (MeAPO-5) materials and their interactions with probe molecules were investigated by in situ IR microspectroscopy. All metal substituted samples showed IR bands which can be assigned to the bridging hydroxy groups. Their acid strength determined from the perturbation of the bands by sorption of benzene decreased in the sequence SAPO-5 > MgAPO-5 > BeAPO-5 > CoAPO-5. Sorption of strong bases (ammonia and pyridine) induced the cleavage of at least one bond between the framework metal cation and oxygen at the bridging hydroxy groups leading to strong coordinative interactions of the base molecules with the framework metal cations.