The catalytic oxidation of toluene on the Pt(111) surface has been characterized, in flowing oxygen pressures up to 1.33 Pa, using fluorescence yield near-edge spectroscopy (FYNES). During temperature-programmed (TP-FYNES) oxidationexperiments in flowing oxygen, a dehydrogenatedh7-phenymethylene surfaceintermediate is formed between 190 and 300 K. Spectroscopic measurements clearly indicate that C-H bond activation occurs at the methyl group since 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. Thish7-phenymethylene intermediate dominates over the 300 to 370 K temperature range, but is oxidized rapidly above 370 K. Strongly-adsorbedh6-toluene and the stable,h7-phenymethylene intermediate inhibit oxidation below 370 K by inhibiting oxygen adsorption. A slight decrease in the activation energy is observed with increasing oxygen pressures over the range of 0.067 to 1.33 Pa. Temperature-programmed reaction spectroscopy (TPRS) indicates that the deep oxidation products on Pt(111) are carbon dioxide and water. This combination of temperature-programmed UHV and soft x-ray fluorescence experiments has provided a detailed mechanistic description of toluene catalytic oxidation on the Pt(111) surface.
Citation: Journal of Physical Chemistry B
Pub Type: Journals
catalysis, NEXAFS, orientation, oxidation, soft x-ray