Temperature-programmed studies of alkali-promoted Ni/SiO/sub 2/ catalysts
The role of potassium as an alkali promoter in the methanation and Fischer-Tropsch synthesis has been studied. Promoted catalysts were prepared in a manner such that the potassium present on the catalytic metal could be distinguished from that present on the support. Potassium addition had the effect of decreasing the steady-state rate of methane formation as well as higher hydrocarbon formation. The activation energy for methanation increased upon potassium promotion. However, significant increases in the selectivity for higher hydrocarbon and olefin formation occurred as the potassium coverage of the nickel metal was increased. The role of potassium in bringing about the above effects was investigated through temperature-programmed studies. Temperature -programmed desorption studies showed that the bonding strength of hydrogen to nickel decreased upon promotion. Also, the activation energy for CO dissociation decreased and the bonding strength of active surface carbon to nickel increased upon promotion. Temperature-programmed surface reaction studies indicated a depression of the rate of hydrogenation of active surface carbon as a result of the addition of potassium. It was therefore concluded that active surface carbon hydrogenation was rate-determining for methanation on nickel. The active surface carbon species could be transformed into an inactive carbon species, which deactivated the nickel catalysts. Potassium promotion slowed the transformation of active to inactive carbon, thereby prolonging the effective lifetime of the Ni/SiO/sub 2/ catalyst.
- Research Organization:
- Georgia Inst. of Tech., Atlanta (USA)
- OSTI ID:
- 6975871
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
010408* -- Coal
Lignite
& Peat-- C1 Processes-- (1987-)
ACTIVATION ENERGY
ADDITIVES
ALKALI METALS
ALKANES
ALKENES
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYSIS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DEACTIVATION
ELEMENTS
ENERGY
FISCHER-TROPSCH SYNTHESIS
GAS YIELDS
HYDROCARBONS
KINETICS
METALS
METHANATION
METHANE
NICKEL
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
POTASSIUM
PROMOTERS
REACTION KINETICS
SERVICE LIFE
TEMPERATURE EFFECTS
TRANSITION ELEMENTS
YIELDS