REDUCIBILITY AND SPECTROSCOPIC BEHAVIOR OF THE (NH4)4[H6CUMO6O24].4H2O ANDERSON PHASE

The vibrational spectrum of (NH4)4[H6CuMo6O24].4H2O was analyzed and i s discussed on the basis of the different Mo-O bond lengths in the lat tice. The temperature-programmed reduction (TPR) process was also stud ied by means of several techniques, such as X-ray diffraction, scannin g electron microscopy, and infrared, Raman and electron spin resonance (ESR) spectroscopies. The results revealed that the MoO2 oxide, toget her with Cu metal, is formed at almost-equal-to 385-degrees-C, while t he final reduction to Mo0 occurs at 783-degrees-C. These reduction ste ps for molybdenum are at almost-equal-to 350 and almost-equal-to 70-de grees-C, respectively, below those observed for ammonium heptamolybdat e. The presence of Mo(V) and Cu(I) species was also suggested in the c ourse of the thermal reduction by ESR spectroscopy. The TPR data of so me other Anderson phases have been used for purposes of comparison. Th e effect of the redox potential of the heteroatom on the stability of these phases has been analyzed. The presence of metallic copper seems to increase the capability of the reducing agent to form Mo0.