Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 9: Oxides and Insulators: Adsorption I
O 9.6: Vortrag
Montag, 26. März 2007, 12:30–12:45, H42
Influence of Mo coordination on oxygen activation in hetero and homogeneous molybdena catalysts. DFT cluster model studies. — •Renata Tokarz-Sobieraj and Malgorzata Witko — Institute of Catalysis and Surface Chemistry, PAS, ul. Niezapominajek 8, 30 239 Krakow, Poland
Activation of the molecular oxygen may be caused by bonding it to the transition metal center in metal complex (homogeneous process) or to the metal center present at the solid surface (heterogeneous reaction). The electronic properties of the bonded molecular oxygen, and what follows, its reactivity depend on the character of bonding defined by the type of metal and its surrounding ligand(s) or surface atom(s). The aim of present studies is to examine O2 activation process in molybdenum porphyrin (homogeneous systems) and molydbenum trioxide (heterogeneous catalysts) using quantum chemical DFT methods within GGA-RPBE functional. The preference to form superoxo or peroxo structure for each of the systems and their possible further transformed forms that are hydroperoxo or oxo species is considered. It is found that in any system the direct consequence of O2 binding to the molybdenum ions is its activation expressed by the elongation and weakening of the O-O bond. The adsorption of the H atom on the O2 species leads to the further weakening of the O-O bond. The second H atom undergoes adsorption and water species is formed. The later may desorb leading to the oxygen atom doubly bonded to the molybdenum ion. As the result the high valent oxo porphyrin complex or molybdenyl bond at the oxide surface is formed.