AN EXAMINATION OF THE ACID SITES IN SAPO-5

We have examined a series of SAPO-5 materials using temperature-programmed desorption and thermogravimetric analysis (TPD-TGA) of isopropylamine, n-propylamine, ammonia, propene, and 2-propanol and compared the results to those for AIPO-5. For isopropylamine and n-propylamine, desorption of propene and ammonia was observed from well-defined features in the TPD-TGA curves, features which were not observed on AIPO-5. These desorption features appear to be due to simple Brønsted-acid sites, and the concentration of sites determined by both amines was the same. For low Si concentrations, there appears to be one acid site per framework Si. The differences between AIPO-5 and SAPO-5 materials could also be observed with propene, which oligomerized at 300 K in SAPO-5 but not in AIPO-5. While differences were observed between AIPO-5 and the SAPO-5s for TPD-TGA of ammonia and 2-propanol, desorption from sites present in AIPO-5 were difficult to distinguish from the stronger sites present in the SAPO-5s. The results suggest that adsorption of simple amines may be very useful for characterization of acid sites in silica aluminophosphate molecular sieves. © 1991.