SYNTHESIS AND CHARACTERIZATION OF VAPSO-44 AND VAPSO-5

Aluminophosphate molecular sieves of structures 5 (AFI) and 44 (CHA) h ave been prepared with different vanadium contents. The crystallizatio n was performed by means of a mcirowave power system. The crystallinit y of the samples was checked by X-ray diffraction (XRD), thermal analy sis and adsorption measurements, and compared with the data for the co rresponding SAPO molecular sieves. The acidity was studied by calorime tric measurements of the differential molar heat of NH3 sorption and b y temperature-programmed desorption (TPD) of ammonia.Electron paramagn etic resonance (EPR) spectra indicate the presence of isolated immobil e VO2+ species in square-pyramidal symmetry. VO2 clusters were also fo und in samples with higher vanadium content. On calcination V4+ is par tially oxidized to V2O5. Only a small amount of VO2+ (<1 atom%) may be stabilized on the inner surface of the pore system. The incorporation of V4+ into tetrahedrally coordinated framework positions can be excl uded from the EPR results. It follows from IR measurements that VO2+ i ons are fixed on the inner surface via a condensation process with hyd roxy groups.