Chemical and catalytic activation of methane by metal-oxide surfaces. Annual report, September 1, 1986-August 31, 1987
The effect of reactant and product partial pressure on methane activation kinetics was examined for a series of alkali-promoted alkaline earth oxide catalysts. In the limit of vanishing oxygen partial pressure the C/sup 2 +/ product selectivity exceeded 70% (C basis) and the ethene/ethane ratio approached zero. The kinetics are consistent with the competitive gas phase dimerization and the oxidation (both homogeneous and heterogeneous) of heterogeneously produced methyl radicals. Post-reaction temperature-programmed desorption experiments following stationary-state oxidative dimerization of methane by Na-promoted CaO and Li-promoted MgO help describe a physical picture of the working catalysts. Multilayer quantities of CO/sub 2/ and fractional monolayer quantities of O/sub 2/ and H/sub 2/O were evolved by the TPD experiments suggesting that a layer of molten alkali carbonate with surface hydroxide and surface oxide is formed during the partial oxidation reaction. Surface O- species have been previously implicated as the reactive centers for methane activation by electron spin resonance (ESR) observations with quenched catalysts. However, thermally produced alkali-oxygen radical anion centers were not observed in ESR experiments to temperatures as high as 850 K with lithium-promoted MgO and sodium-promoted CaO catalysts.
- Research Organization:
- SRI International, Menlo Park, CA (USA)
- OSTI ID:
- 7040586
- Report Number(s):
- PB-88-192828/XAB
- Country of Publication:
- United States
- Language:
- English
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Chemical and catalytic activation of methane by metal oxide surfaces. Annual report, September 1, 1987-August 31, 1988
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