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F. Patcas, F.-C. Buciuman

Investigations on Formation and Structure of MnO_x/SiO₂ Catalysts

MnO_x/SiO₂ catalysts with different manganese loadings, prepared by using the pore volume impregnation technique, have been studied by using the temperature-programmed reduction (TPR) and microscopic laser-Raman spectroscopy techniques in order to characterize the dispersion of the manganese on the support and the nature and formation of the manganese oxide species.
A highly inhomogeneous distribution of manganese over the SiO₂ surface has been found, consisting of unloaded ´´white´´ surfaces, transition zones, MnO_x ´´islands´´ and well crystallized manganese oxide spots. A MnO_x-monolayer species has been identified which consisted of Mn²⁺ and Mn³⁺ cations bonded together and to the SiO₂ support by means of O-atoms. The presence of this phase in the transition zone diminished by increasing the manganese loading of the catalyst and could not be unequivocally identified on the islands and crystal spots, but at the same time the amount of dispersed and crystallized MnO₂ and Mn₂O₃ increased. A model for the formation of MnO_x -species is proposed.

Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag

Print ISSN: 0942-9352
Volume: 215, 01/2001
Pages: 029

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