A mass-spectrometry study of the surface chemical activities of thorium oxide and cerium-doped thorium oxide

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1989

OSTI ID:6373254

Grabbe, A

The capacity for thorium oxide and cerium doped thorium oxide for Fischer-Tropsch catalytic activity in the 0-20 Torr pressure regime was evaluated by Quadrupole Mass Spectrometry. High surface area catalysts were prepared and characterized by adsorption isotherm measurements, scanning electron microscopy, energy dispersive x-ray spectrometry and by gas-solid oxygen isotope exchange kinetics. The oxygen exchange mechanisms were found to follow two pathways: single atom exchange between molecular oxygen and lattice oxygen (an R1 process), and a molecular exchange mechanism (an R2 process). It was found that neither process has identical Arrhenius parameters on pure ThO{sub 2} compared with 10% CeO{sub 2} doped ThO{sub 2}. Doping with ceria lowers the activation energy for both R1 and R2 exchanges by 40 KJ, the result being that exchange proceeds faster on the doped thoria than on pure thoria. Thoria doped with CeO{sub 2} has the rates of oxygen exchange altered in a non-additive way, which implies that the doped material must have the Ce completely dispersed at the surface. The product distribution for the Fischer-Tropsch reaction over the two materials indicates that the primary product is propane and methane, with small amounts of 1-butene for pure ThO{sub 2}. In the case of ThO{sub 0.9}Ce{sub 0.1}O{sub 2} catalyst, the product distribution is primarily methane, followed by propane and propene, and 2-butene. This shift in product distribution is accompanied by a 3 fold increase in the rate of consumption of CO with respect to identical conditions over pure thoria catalyst. The shift in product distribution when switching from thoria to Th{sub 0.9}Ce{sub 0.1}O{sub 2} is consistent with the redox chemistry of cerium if the synthesis is assumed to proceed by an ene-diolate intermediate.

• Research Organization: North Carolina Univ., Chapel Hill, NC (USA)
• OSTI ID: 6373254
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
010408* -- Coal
Lignite
& Peat-- C1 Processes-- (1987-)
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
ACTINIDE COMPOUNDS
ACTIVATION ENERGY
ADSORPTION ISOTHERMS
ALKANES
ALKENES
BUTENES
CATALYSTS
CATALYTIC EFFECTS
CERIUM COMPOUNDS
CERIUM OXIDES
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
CHEMICAL REACTORS
DATA ACQUISITION
DISTRIBUTION
DOPED MATERIALS
ELECTRON MICROSCOPY
ELEMENTS
ENERGY
FISCHER-TROPSCH SYNTHESIS
HYDROCARBONS
ISOTHERMS
ISOTOPIC EXCHANGE
KINETICS
MASS SPECTROSCOPY
MATERIALS
METHANE
MICROSCOPY
NONMETALS
ORGANIC COMPOUNDS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PROPANE
PROPYLENE
RARE EARTH COMPOUNDS
REACTION KINETICS
SCANNING ELECTRON MICROSCOPY
SPECTROSCOPY
SURFACE AREA
SURFACE PROPERTIES
SYNTHESIS
THORIUM COMPOUNDS
THORIUM OXIDES
X-RAY SPECTROSCOPY
YIELDS