Nickel/titania catalysts for carbon monoxide hydrogenation: effect of potassium promoters
Nickel supported on titania (Ni/TiO/sub 2/) was studied for CO hydrogenation by temperature-programmed desorption (TPD) of CO and H/sub 2/, temperature-programmed reaction (TPR) of CO in H/sub 2/, and steady state reaction. TPD indicated that CO/sub 2/ formed when CO dissociated, and that the oxygens of CO/sub 2/ exchange with the oxygens of the TiO/sub 2/. Potassium promoter increased the activation energy for both desorption and dissociation of CO, and inhibited the recombination of C/sub a/ and O/sub a/ that occurred above 650 K. For Ni/TiO/sub 2/, the heat of adsorption from TPD was 55 kJ/mol, well below the value obtained from single crystal studies (85-90 kJ/mol). A transient adsorption state of adsorbed hydrogen was proposed. Evidence is presented indicating that this transient state exists on other support systems when TPD is done at atmospheric pressure. Potassium decreased the amount of hydrogen on the surface of 450-550 K. For both TPR and steady-state experiments, potassium decreased the site specific activity of Ni/TiO/sub 2/, and this was attributed to decreased hydrogen coverage. Potassium lowered selectivity to methane, and increased selectivity to olefins, but the chain growth probability for C/sub 4/ and C/sub 5/ hydrocarbons decreased. Potassium increased the activation energy for strong-metal interaction formation. Potassium decreased the amplitude of hydrogen desorption due to spillover hydrogen. Normalized curve treatment (NCT) was used to obtain kinetic parameters. With NCT, accurate estimates of kinetic factors were made from simulated data with noise as large as 10% of the signal and an error of less than 5% in the initial coverage.
- Research Organization:
- Colorado Univ., Boulder (USA)
- OSTI ID:
- 6073967
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
10 SYNTHETIC FUELS
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYSIS
CATALYST SUPPORTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
HYDROGENATION
METALS
NICKEL
OXIDES
OXYGEN COMPOUNDS
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS