In-Situ Soft X-ray Studies of Toluene Catalytic Oxidation on the Pt(111) Surface

The catalytic oxidation of toluene on the Pt(111) surface has been characterized, in flowing oxygen pressures up to 0.01 Torr, using temperature-programmed fluorescence yield near-edge spectroscopy (TP-FYNES). During TP-FYNES oxidation experiments in flowing oxygen pressures, a dehydrogenated C 7 H 7 η 7 -phenylmethylene intermediate is formed over the 190 to 300 K temperature range. Spectroscopic (FYNES) measurements clearly indicate that C−H bond activation occurs at the methyl group and the aromatic ring remains parallel to the surface. In contrast to the intermediates formed during benzene oxidation, no rearrangement of the aromatic ring occurs, signifying that the methyl group influences the structure of intermediates formed during toluene oxidation. This η 7 -phenylmethylene intermediate dominates over the 300−370 K temperature range, but is oxidized rapidly above 370 K. Strongly adsorbed η 6 -toluene and the stable η 7 -phenylmethylene intermediate inhibit oxidation below 370 K by inhibiting oxygen adsorption. A slight increase in the rate of rapid oxidation above 370 K is observed with increasing oxygen pressures over the range of 0.0005 to 0.01 Torr. Temperature-programmed reaction spectroscopy (TPRS) indicates that the deep oxidation products on the Pt(111) surface are CO 2 and H 2 O. This combination of in-situ soft X-ray and UHV methods has provided a detailed mechanistic description of toluene catalytic oxidation on the Pt(111) surface.