Monolayer molybdena an alumina: vapor pressure measurement
The common monolayer model of MoO/sub 3/ on Al/sub 2/O/sub 3/ implies a decrease in free energy when a monolayer is formed from a crystallite of MoO/sub 3/. The increased stability of the monolayer should be reflected in a decrease in MoO/sub 3/ vapor pressure above MoO/sub 3/-Al/sub 2/O/sub 3/, by comparison with unsupported (bulk) MoO/sub 3/. This prediction confirmed: the apparent vapor pressure above MoO/sub 3/-Al/sub 2/O/sub 3/ is at least an order of magnitude less than that above unsupported MoO/sub 3/, at comparable temperatures. The vapor pressure has been studied for two alumina supports (Houdry 200 S and Davison 10867-18), two particle sizes, several MoO/sub 3/ loadings as a function of temperature, carrier gas velocity, and time of experiments. For MoO/sub 3/ on Houdry 200 S alumina, particle size has little effect, suggesting that the values are not limited by the rate of diffusion through pores. But for MoO/sub 3/ on Davison 10867-18 alumina, particle size shows an appreciable effect. Loading is an important variable, probably reflecting energetic heterogeneity of the sites on the alumina surface. The apparent vapor pressures are highest in the initial period of measurement; experiments with pre-dried samples and with addition of water vapor to the feed establish that this behavior is probably caused by evolution of water vapor, by surface dehydroxylation of the alumina, at the beginning of a run.
- Research Organization:
- State Univ. of New York, Buffalo (USA)
- OSTI ID:
- 6800696
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CATALYST SUPPORTS
CHALCOGENIDES
COMPARATIVE EVALUATIONS
ENERGY
FLOW RATE
FLUID FLOW
FLUIDS
FREE ENERGY
GAS FLOW
GASES
LAYERS
MOLYBDENUM COMPOUNDS
MOLYBDENUM OXIDES
OXIDES
OXYGEN COMPOUNDS
PARTICLE SIZE
PHYSICAL PROPERTIES
QUANTITY RATIO
REFRACTORY METAL COMPOUNDS
SIZE
STABILITY
TEMPERATURE DEPENDENCE
THERMODYNAMIC PROPERTIES
TIME DEPENDENCE
TRANSITION ELEMENT COMPOUNDS
VAPOR PRESSURE
VAPORS
WATER VAPOR