Methanation reaction on ruthenium thin films: a mechanistic investigation. [PhD. thesis]
The kinetics of the methanation reaction were measured on thin ruthenium films in the temperature range 548 to 623K. The pressures of the reactant gases were varied over the ranges 1.5 to 1500 ..mu..m for CO and 300 to 75000 ..mu..m for H/sub 2/ to yield kinetic orders for each gas. The CO kinetic order varied from +1 at low pressures to -2 at high pressures. As the H/sub 2/ pressure was increased its kinetic order varied from +2 to -1. Both of these order plots had unusually sharp maxima. The reaction is zero order in both CH/sub 4/ and H/sub 2/O. The apparent activation energy was dependent upon temperature with a value of 21.9 kcal/mole at 573K. Auger spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) indicated that the surface was always covered with carbon. This carbon could be divided into two types based upon its reactivity toward hydrogen. Type-1 was very reactive to 3.5 torr hydrogen doses at 573K and was completely removed in less than 300 seconds. Type-2 was less reactive and required about 48 hours under the same conditions for removal. No oxygen was ever detected on the surface after methanation. Low energy electron diffraction (LEED) and XPS indicated respectively, that neither graphite nor bulk carbide was associated with the used catalyst. The deposition of up to 0.75 monolayer of carbon enhanced the rate of methanation. More carbon caused a drop in the initial rate. Methanol could be hydrogenated to methane at about the same rate as carbon monoxide. A mechanism was developed which quantitatively fits the kinetic data and qualitatively predicts all of the other observations. This mechanism involves adsorbed hydrogen interacting with non-dissociated carbon monoxide. The rate limiting step involves the interaction of Ru--H and Ru--CH/sub 3/ to form methane. A methylene carbonyl hydride is believed to act as a reversible poison at high H/sub 2/:CO ratios.
- Research Organization:
- Ames Lab., Ames, IA (United States)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 6042605
- Report Number(s):
- IS-T-871
- Resource Relation:
- Other Information: Thesis
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
FISCHER-TROPSCH SYNTHESIS
CATALYSTS
METHANATION
RUTHENIUM
CATALYTIC EFFECTS
SYNTHESIS GAS
CHEMICAL REACTION KINETICS
ACTIVATION ENERGY
AUGER ELECTRON SPECTROSCOPY
CHEMICAL REACTIONS
COAL GASIFICATION
ELECTRON DIFFRACTION
EXPERIMENTAL DATA
GRAPHS
HYDROGENATION
ISOTOPIC EXCHANGE
METHANOL
TABLES
TEMPERATURE DEPENDENCE
ALCOHOLS
COHERENT SCATTERING
DATA
DATA FORMS
DIFFRACTION
ELECTRON SPECTROSCOPY
ELEMENTS
ENERGY
FLUIDS
GASES
GASIFICATION
HYDROXY COMPOUNDS
INFORMATION
KINETICS
METALS
NUMERICAL DATA
ORGANIC COMPOUNDS
PLATINUM METALS
REACTION KINETICS
REFRACTORY METALS
SCATTERING
SPECTROSCOPY
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENTS
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