Molecular Mechanisms of Propyne Oxidation on the Pt(111) Surface: In Situ Soft X-Ray Studies in Pressures of Oxygen

Published

August 1, 2001

Author(s)

A M. Gabelnick, D J. Burnett, J L. Gland, Daniel A. Fischer

Abstract

Oxidation of preadsorbed propyne has been characterized on the Pt(111) surface in oxygen pressures up to 1.2 Pa. using fluorescence yield ultra-soft X-ray adsorption methods above the carbon K edge. A combination of temperature programmed reaction spectroscopy (TPRS) and temperature programmed fluorescence yield near edge spectroscopy (TP-FYNES) experiments indicate that similar oxidation pathways occur both for coadsorbed oxygen and pressures of oxygen. Soft x-ray spectroscopy indicates that propyne adsorbs nearly parallel to this surface with a saturation coverage of 1.45 x 10¹⁵ C atoms/cm². Oxidation of small propyne coverages with coadsorbed oxygen results in simultaneous CO₂ and H₂O peaks at 320 and 420 K, as seen in TPRS. Oxidation of higher propyne coverages with coadsorbed oxygen results in a broad oxidation peak over the 350-420 K temperature range. Oxidation of a saturated propyne monolayer in oxygen pressures (TP-FYNES) results in a rapid decrease in carbon coverage over the same temperature range suggesting similar mechanisms. Isothermal oxidation in oxygen atomospheres indicates that propyne oxidation is 1st order in propyne coverage and has an activation energy of 7.1 kJ/mol for high coverages. Deviations from first order behavior suggest that a second process may become important at lower coverages in oxygen atmospheres. Regardless of coverage and initial conditions, both TPRS and TP-FYNES indicate oxydehydrogenation and skeletal oxidation occur simultaneously and the oxidation proceeds with a fixed C₃H₄ stoichiometry. Taken together these results give a molecular picture of propyne oxidation on the Pt(111) surface.

Citation

Journal of Physical Chemistry B

Volume

105

Issue

No. 32

Pub Type

Journals

Keywords

intermediates, oxidation, platinum, propyne, soft x-ray

Citation

Gabelnick, A. , Burnett, D. , Gland, J. and Fischer, D. (2001), Molecular Mechanisms of Propyne Oxidation on the Pt(111) Surface: In Situ Soft X-Ray Studies in Pressures of Oxygen, Journal of Physical Chemistry B (Accessed October 13, 2024)