STRUCTURE AND ACIDIC PROPERTIES OF PHOSPHATE-MODIFIED ZIRCONIA

Phosphate-modified zirconia was prepared by impregnation of Zr(OH)(4) and of m-ZrO2 with an aqueous solution of (NH4)(2)HPO4. Similar to sul fate and tungstate, phosphate shows a strong stabilizing effect on the specific surface area and the tetragonal phase of zirconia when using Zr(OH)4 as the precursor material. The adsorbed phosphate species wer e characterized by Raman, DRIFT, and P-31-MAS-NMR spectroscopies as py rophosphates, chelate-bonded orthophosphates, and oligophosphates. Onl y a distortion of the geometry of the adsorbed phosphate species was f ound after dehydration of the materials in contrast to ZrO2/SO4. FT-IR spectroscopy with CO as a probe molecule was used to characterize the acidic properties of ZrO2/PO4. New hydroxyl groups, probably P-OH gro ups with enhanced protonic acidity as compared to pure zirconia but lo wer than that of ZrO2/SO4, were observed. In addition basic Zr-OH grou ps were observed. Furthermore, strong Lewis acidic centers (cus Zr4+), comparable to ZrO2/SO4, are formed by phosphate modification of zirco nia.