Mechanism of the catalytic oxidation of CO with O2 on an Mo catalyst supported on silica and on bulk MoO3
Abstract
The mechanism of the catalytic oxidation of CO with O2 on an Mo catalyst supported on silica has been studied by a tracer technique using 18O2. The supported Mo catalyst was prepared by using the ready reaction between Mo(η3-C3H5)4 and the OH groups on silica. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that the Mo species attached to silica are dispersed atomically and have a dioxostructure. At steady state during oxidation with CO/O2= 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 exchange between O2 molecules. The oxidation of the oxostructure (Mo4+) to the dioxostructure (Mo6+) by O2 molecules during the catalytic oxidation produces O atoms on the silica surface. Recombination of two migrating O atoms leads to oxygen isotope exchange between O2 molecules. The mechanism of the catalytic oxidation of CO with O2 on bulk MoO3 was re-examined with reference to that elucidated on the SiO2-supported Mo catalyst.