Experimental study of the oscillatory behavior of CO oxidation on Pt/Al/sub 2/O/sub 3/ by in situ infrared transmission spectroscopy
The dynamic behavior of CO oxidation on Pt/..gamma..-Al/sub 2/O/sub 3/ catalysts was studied in an all Pyrex flow reactor under isothermal conditions and atmospheric pressures with infrared transmission spectroscopy as a tool for in situ characterization of intermediate species on the catalyst surface. The catalysts were made by impregnation of the support with H/sub 2/PtCl/sub 6/.H/sub 2/O solution and were characterized by H/sub 2/ and CO chemisorption and by Transmission Electron Microscopy (TEM). CO was found to be chemisorbed on Pt at three different surface states. At equilibrium coverage, 80% of the surface was covered by the linear state and the rest was equally shared by the bridge and twin states. The stability of these states to thermal desorption and oxidation is as follows: twin > linear > bridge. Self-sustained oscillations in the reaction rate and in linearly chemisorbed CO were observed with the same frequencies in a true kinetic regime. The region of oscillations was found to be intricately dependent on the system external variables such as gas phase temperature, inlet CO concentration in air, P/sub CO//P/sub O/sub 2// ratio in the inlet stream, and Pt surface to catalyst geometrical area ratio. Three distinctive reactor states were observed and were characterized as follows: time-invariant stable states, oscillatory states with well-defined periods and aperiodic or chaotic states. Oscillations were found to last for days without any catalyst deactivation effects. The oscillations were always observed around a region of maximum CO coverage. It is suggested that the competitive behavior around in the reaction steps through a Langmuir-Hinshelwood reaction mechanism could provide a driving mechanism for the oscillations.
- OSTI ID:
- 5640731
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CARBON MONOXIDE
CHEMISORPTION
OXIDATION
CATALYSTS
INFRARED SPECTRA
TRANSMISSION ELECTRON MICROSCOPY
PLATINUM
CATALYTIC EFFECTS
ALUMINIUM OXIDES
OSCILLATIONS
PLATINUM CHLORIDES
REACTION KINETICS
ALUMINIUM COMPOUNDS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
CHLORIDES
CHLORINE COMPOUNDS
ELECTRON MICROSCOPY
ELEMENTS
HALIDES
HALOGEN COMPOUNDS
KINETICS
METALS
MICROSCOPY
OXIDES
OXYGEN COMPOUNDS
PLATINUM COMPOUNDS
PLATINUM METALS
SEPARATION PROCESSES
SORPTION
SPECTRA
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
400800* - Combustion
Pyrolysis
& High-Temperature Chemistry