In situ UV-VIS diffuse reflectance spectroscopy of reduction-reoxidation of heteropoly compounds by methanol and ethanol: a correlation between spectroscopic and catalytic data
J. Melsheimer et al., In situ UV-VIS diffuse reflectance spectroscopy of reduction-reoxidation of heteropoly compounds by methanol and ethanol: a correlation between spectroscopic and catalytic data, CATAL LETT, 60(3), 1999, pp. 103-111
The degree of reduction/oxidation of H4PVMo11O40 (HPA) and Cs2H2PVMo11O40 (
CsPA) was studied during reduction and reoxidation by methanol, ethanol and
mixtures with oxygen, respectively. The peak intensity of the intervalence
charge transfer (IVCT) band, the apparent band gap energy (E-g*) and catal
ytic data were obtained by in situ UV-VIS diffuse reflectance spectrosccopy
(UV-VIS-DRS) and on-line gas chromatography (GC), respectively. The peak i
ntensity of the IVCT band and E-g* increase during the reduction of heterop
oly compounds by the alcohols. The spectroscopic and catalytic data (conver
sion, selectivity) correlate in the transient state during the reoxidation
process. It is shown that isolated Keggin anions act as precursors for the
active states of the catalysts, which molecular structure cannot be deduced
from UV-VIS spectroscopy alone. UV-VIS spectroscopy, however, can serve as
a tool to determine the degree of reduction in future combined in situ UV-
VIS/Raman/XRD studied.