Study of the redox properties of bismuth-molybdate and uranium-antimonate catalysts
The oxidation/reduction properties of various bismuth molybdates, molybdenum trioxide, bismuth oxide, uranium antimonate, and iron antimonate have been studied in an effort to correlate them to their catalytic properties. The temperature at which ..gamma..-phase bismuth molybdate is prereduced plays an important role in the behavior the catalyst exhibits under reoxidation conditions. The overall behavior of ..gamma..-phase bismuth molybdate under catalytic conditions may be divided into two temperature regimes: below 360/sup 0/C the catalyst shows a higher rate of propylene adsorption than product desorption, and above 360/sup 0/C where produced desorption is dominant. This temperature is the same at which the Arrhenius plot for the reaction has a break. Several reduction of ..gamma..-bismuth molybdate results in the formation of clusters of bismuth metal and crystallites of molybdenum dioxide. This is irreversible. The reoxidation of the bismuth molybdate catalysts shows the presence of two oxygen incorporation temperatures. The ratios of the areas under these peaks are not the same for the three catalysts. Uranium antimonate shows a lesser degree of lattice oxygen participation. During several reduction the catalyst decomposes partially and an excess of antimony is evident. The isothermal reduction profiles of the catalysts permitted their classification into either of two reduction models: (A) ..cap alpha..-, ..beta..-, ..gamma..-phase bismuth molybdates, molybdenum trioxide, bismuth oxide, and the equimolar mixture follow the nucleation model, (B) uranium antimonate, and iron antimonate following the shrinking sphere model. These models have been correlated to certain characteristics of these catalysts. Group A catalysts show a high degree of lattice oxygen participation (migration of bulk oxygen to surface nuclei). In contrast in group B catalysts only a few layers of oxygen are peeled off during catalysis.
- Research Organization:
- Wisconsin Univ., Milwaukee (USA)
- OSTI ID:
- 5015333
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ANTIMONATES
CATALYTIC EFFECTS
REDOX REACTIONS
BISMUTH COMPOUNDS
IRON COMPOUNDS
MOLYBDATES
MOLYBDENUM OXIDES
URANIUM COMPOUNDS
ACTINIDE COMPOUNDS
ANTIMONY COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
MOLYBDENUM COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
REFRACTORY METAL COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
400702* - Radiochemistry & Nuclear Chemistry- Properties of Radioactive Materials
400201 - Chemical & Physicochemical Properties