EFFECT OF PRECIPITATION MEDIUM AND THERMAL-TREATMENT ON STRUCTURE ANDTEXTURAL PROPERTIES OF CHROMIUM ORTHOPHOSPHATES

The effect of the precipitation agent on the structure and textural pr operties of CrPO4 (Cr/P=1) catalYsts has been studied. Catalysts obtai ned in propylene oxide-aqueous ammonia exhibited higher thermal stabil ity and, hence, greater surface areas and pore volumes than catalysts obtained in propylene oxide or aqueous ammonia exclusively. The former also showed a small,surface area decrease on increasing calcination t emperature up to 1073 K. Nevertheless, calcination at 1273 K develops in all cases crystalline CrPO4, showing the beta-structure. Moreover, CrPO4 catalysts thermally treated below 1273 K only exhibited hydrogen bonded hydroxy groups (nu(O-H) congruent-to 3450 cm-1).