Heteropolyoxotungstates containing a wide catalytic target: reducibility and thermal stability

The potassium salts of complex heteropolyoxotungstates K10[(PW9O34)2M4(H2O)2]·20H2O containing tetranuclear clusters (MO6)4 with M = Co, Zn and Mn were synthesized and characterized by means of X-ray Powder Diffraction Analysis (XRD), Vibrational Spectroscopy (FTIR and Raman), Diffuse Reflectance Spectroscopy (DRS) and Scanning Electron Microscopy (SEM and EDAX). The thermal decomposition of these species in air atmosphere (DTA-TGA) and in reducing conditions (H2-N2) by Temperature Programmed Reduction (TPR) was analyzed and discussed on the basis of the characterization of intermediate and pyrolysis products. Additional thermal treatments were made by means of X-ray Powder Diffraction “in situ” technique. Besides, as the FTIR and Raman vibrational spectra of pure samples are poorly described in literature, the reassignment was included.