title: Redox properties of manganese-containing zirconia solid solution catalysts analyzed by in situ UV-vis spectroscopy and crystal field theory.
abstract: The optical absorption spectra of manganese-promoted sulfated zirconia, a highly active alkane isomerization catalyst, were found to be characterized by oxygen-to-manganese charge-transfer transitions at 300-320 nm and d-d transitions of manganese ions at 580 and 680 nm. The latter were attributed to Mn(4+) and Mn(3+) ions, which are known to be incorporated in the zirconia lattice. The oxygen surroundings of these ions were modeled assuming a substitutional solid solution. The crystal field splittings, vibronic coupling constants, and oscillator strengths of the manganese ions were calculated on the basis of a cluster model that considers the manganese center as a complex with the adjacent ions of the lattice as ligands. The ratio of Mn(3+) to Mn(4+) ions was determined using the spectra and the model, and the relative concentrations of Mn(2+), Mn(3+), and Mn(4+) ions were determined with the help of the average valence known from X-ray absorption data in the literature. The redox behavior of manganese-promoted sulfated zirconia in oxidizing and inert atmosphere was elucidated at temperatures ranging from 323 to 773 K.
authors: Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany. klokishner@yahoo.com
authors: Sophia I
authors: SI
authors: Klokishner
authors: Oleg
authors: O
authors: Reu
authors: Carine E
authors: CE
authors: Chan-Thaw
authors: Friederike C
authors: FC
authors: Jentoft
authors: Robert
authors: R
authors: Schlögl