MECHANISM OF THE CATALYTIC-OXIDATION OF CO WITH O-2 ON AN MO CATALYSTSUPPORTED ON SILICA AND ON BULK MOO3

The mechanism of the catalytic oxidation of CO with O-2 on an Mo catal yst supported on silica has been studied by a tracer technique using O -18(2). The supported Mo catalyst was prepared by using the ready reac tion between Mo(eta(3)C(3)H(5))(4) and the OH groups on silica. Extend ed X-ray absorption fine structure (EXAFS) spectroscopy showed that th e Mo species attached to silica are dispersed atomically and have a di oxostructure. At steady state during oxidation with CO/O-2 = 2/1, 32% of the attached Mo species were estimated to be present as Mo6+ and 68 % as Mo4+. The catalytic oxidation was accompanied by oxygen isotope e xchange between O-2 molecules. The oxidation of the oxostructure (Mo4) to the dioxostructure (Mo6+) by O-2 molecules during the catalytic o xidation produces O atoms on the silica surface. Recombination of two migrating O atoms leads to oxygen isotope exchange between O-2 molecul es. The mechanism of the catalytic oxidation of CO with O-2 on bulk Mo O3 was re-examined with reference to that elucidated on the SiO2-suppo rted Mo catalyst.