In Situ Characterization of Catalytic Propylene Oxidation on the Pt (111) Surface

Published

January 17, 2000

Author(s)

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

Abstract

The catalytic oxidation of propylene with both propylene and oxygen in the gas phase has been characterized on the Pt(111) surface. In situ soft x-ray kinetic and spectroscopic measurements using fluorescence detection have been used to characterize this catalytic system. Catalytic In situ X-ray Absorption Spectroscopy (CIXAS) experiments clearly indicate that the dominant species on the surface during steady state propylene oxidation is propyne. This assignment is based on determination of C-H stoichiometries, C-C bond densities and detailed interpretation of spectra. Beginning with a hydrocarbon free surface at 600 K and decreasing the temperature at 0.5 K/sec, carbon uptake begins near 450 K depending upon oxygen and propylene pressure, with richer mixtures resulting in saturation of the surface with the propyne intermediate at higher temperature. The amount of adsorbed propyne at 200 K is dependent upon both oxygen and propylene pressure, with lower oxygen pressures and higher propylene pressures favoring higher surface concentrations. The initiation temperature for oxidation also depends on oxygen pressure, with higher oxygen pressures resulting in more rapid oxidation. Decreasing the temperature of the carbon free Pt(111) surface from 600 to 200 K in the presence of both propylene and oxygen results in the formation of a C3H4 propyne species as indicated by detailed in situ spectroscopic measurements. Temperature programmed measurements taken at the C-C bond to determine the number of C-C bonds indicate that intermediate adsorbs with the C-C bonds remaining intact. Upon heating, the surface intermediate remains intact until skeletal oxidation begins. In contrast to the oxidation of propylene, no dehydrogenated C3H5 intermediate is observed upon heating. Instead the surface is covered with a C3H4 propyne intermediate over the entire temperature range as observed during independent studies of propyne oxidation. In increased preassures of propylene, the surface carbon concentration increases at 200 K, consistent with coverage levels of an O(a) and propyne covered surface.

Citation

Journal of Physical Chemistry B

Volume

122

Pub Type

Journals

Keywords

intermediates, oxidation, platinum, propylene, soft x-ray, surface science

Citation

Gabelnick, A. , Capitano, A. , Burnett, D. , Fischer, D. and Gland, J. (2000), In Situ Characterization of Catalytic Propylene Oxidation on the Pt (111) Surface, Journal of Physical Chemistry B (Accessed October 5, 2024)