Comparisons of Propylene and Propyne Catalytic Oxidation on a 10 Angstrom Pt/Al2O3 Thin Film Using In-Situ Soft X-Ray Fluorescence Methods

Published

March 1, 2004

Author(s)

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

Abstract

Propyne and propylene oxidation have been studied on a 1 0 nm Pt/A 1₂0₃ thin film catalyst using a combination of synchrotron basedsoft x-ray techniques for oxygen pressures up to 1.3 Pa. In-situ temperature-programmed and isothermal kinetic experiments were useto evaluate reaction mechanisms and energetics. Propyne oxidation on the thin film occurs in a simple, one-step process with a C₃H₄(propyne) intermediate. Propylene oxidation on this surface is more complex. Initial propylene desorption and oxydehydrogenationresults in the formation of a C₃H₅ intermediate (I -methylvinyl). As skeletal oxidation begins with further increases in temperature,additional oxydehydrogenation results in the formation of a C₃H₄ (propyne) intermediate. Thus, as observed previously on the Pt(111)surface, skeletal oxidation of both propyne and propylene above 370 K proceed through a propyne intermediate. Even for this complexsupported Pt thin film sample, the oxidation mechanisms for propyne and propylene remain stable over the entire oxygen pressure rangstudied. The propyne and propylene oxidation temperatures on the Pt film are quite similar to the Pt(111) surface. Propyne adsorbs onthe 10 nm Pt/Al₂O₃ thin film through the π system nearly parallel to the surface, in a manner very similar to the Pt(111) surface.However, molecular adsorption of propylene on the Pt film surface is more complex. A new weakly adsorbed bonding mode is observedon the Pt film in addition to a strongly adsorbed form similar to propylene bonding on the Pt(111) surface. This weakly bound speciesdesorbs between 200 and 270 K, while the more tightly bound propylene species remains on the surface undergoes oxydehydrogenationand skeletal oxidation as outlined above.

Citation

Surface Science

Volume

553

Issue

No. 1-3

Pub Type

Journals

Keywords

alkenes, alkynes, catalysis, NEXAFS, oxidation, platinum, thin film

Citation

Burnett, D. , Gabelnick, A. , Marsh, A. , Fischer, D. and Gland, J. (2004), Comparisons of Propylene and Propyne Catalytic Oxidation on a 10 Angstrom Pt/Al₂O₃ Thin Film Using In-Situ Soft X-Ray Fluorescence Methods, Surface Science (Accessed April 23, 2024)