Temperature-programmed reduction of MoO/sub 3/ and MoO/sub 2/
The reduction of MoO/sub 3/ and MoO/sub 2/ is studied by temperature-programmed reduction (TPR). TPR patterns appear to be highly dependent on H/sub 2/O content of the reducing mixture, sample size, precalcination temperature, and heating rate. Activation energy values for reduction have been calculated from TPR series with various heating rates. A consistent interpretation of the complex TPR results is constructed, in which the extent of H/sub 2/ dissociation catalyzed by low-valent Mo atoms plays a central role. The formation of these Mo catalytic sites is found to depend on H/sub 2/O pressure, concentration of surface defects, and surface area. Reduction of MoO/sub 3/ to MoO/sub 2/ and of MoO/sub 2/ to Mo metal both can be catalyzed, in which case the rate-determining step is either H/sub 2/ dissociation, when the formation of catalytic sites is limited, or Mo-O bond breaking, when excess catalytic sites are present. Reduction of MoO/sub 3/ to MoO/sub 2/ can also take place noncatalyzed, with oxygen diffusion as rate-determining step. MoO/sub 2/ and Mo metal are also formed, as intermediates, in temperature-programmed sulfiding (TPS) of MoO/sub 3/. MoO/sub 2/ production is faster in H/sub 2//H/sub 2/S than in H/sub 2/ due to a different reduction mechanism involving H/sub 2/S as primary reactant. The formation of Mo metal is also faster, due to a higher porosity of the MoO/sub 2/ formed in situ. 48 references, 13 figures, 1 table.
- Research Organization:
- Univ. of Amsterdam, Netherlands
- OSTI ID:
- 6177537
- Journal Information:
- J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 89:21; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
CATALYSIS
CHALCOGENIDES
CHEMICAL REACTIONS
COHERENT SCATTERING
CONTROL
DATA
DIFFRACTION
ELECTRON MICROSCOPY
ELEMENTS
EXPERIMENTAL DATA
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGEN SULFIDES
INFORMATION
MICROSCOPY
MOLYBDENUM COMPOUNDS
MOLYBDENUM OXIDES
NONMETALS
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
REDUCTION
REFRACTORY METAL COMPOUNDS
SCANNING ELECTRON MICROSCOPY
SCATTERING
SULFIDES
SULFUR COMPOUNDS
TEMPERATURE CONTROL
TRANSITION ELEMENT COMPOUNDS
WATER
X-RAY DIFFRACTION