Raman spectroscopic evidence for the formation of silicomolybdic entities on a Mo/HY zeolite catalyst

Mo/Ze catalysts prepared by incipient wetness impregnation of a Faujasite zeolite with ammonium heptamolybdate solutions have been characterized after calcination at 500 °C and transfer in wet atmosphere. Raman spectroscopy clearly evidences the formation of [SiMo12O40]4− heteropolyanions. This formation, through extraction of Si atoms, is not observed before the calcination, the Anderson [AlMo6O24H6]3− entity being the main species formed during the impregnation-maturation.