Nitrides and carbides of molybdenum and tungsten with high specific-surface area: their synthesis, structure, and catalytic properties
Temperature-programmed reactions between trioxides of molybdenum or tungsten and ammonia provide a new method to synthesize dimolybdenum and ditungsten nitrides with specific surface areas to two-hundred-and-twenty and ninety-one square meters per gram, respectively. These are the highest values on record for any unsupported metallic powders. They correspond to three-four nonometer particles. The reaction of molybdenum trioxide with ammonia is topotactic in the sense that one-zero-zero planes of dimolybdenum nitride are parallel to zero-one-zero planes of molybdenum trioxide. As the trioxide transforms, it passes through an oxynitride intermediate with changing bulk structure and increasing surface area and extent of reduction. The nitride product consists of platelets, pseudomorphous with the original trioxide, which can be regarded as highly porous defect single crystals. By treating small particles of dimolybdenum or ditungsten nitride with methane-dihydrogen mixtures it is possible to replace interstitial nitrogen atoms by carbon atoms, without sintering, and thus to prepare carbides of molybdenum and tungsten with very high specific surface areas. Molybdenum nitride powders catalyze ammonia synthesis. A pronounced increase in the catalytic activity with increasing particle size confirms the structure-sensitive character of this reaction.
- Research Organization:
- Stanford Univ., CA (USA)
- OSTI ID:
- 6323523
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
10 SYNTHETIC FUELS
AMMONIA
CHEMICAL REACTIONS
SYNTHESIS
MOLYBDENUM CARBIDES
CHEMICAL PREPARATION
MOLYBDENUM NITRIDES
CATALYTIC EFFECTS
MOLYBDENUM OXIDES
TUNGSTEN CARBIDES
TUNGSTEN NITRIDES
TUNGSTEN OXIDES
CARBIDES
CARBON COMPOUNDS
CHALCOGENIDES
HYDRIDES
HYDROGEN COMPOUNDS
MOLYBDENUM COMPOUNDS
NITRIDES
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
OXIDES
OXYGEN COMPOUNDS
PNICTIDES
REFRACTORY METAL COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TUNGSTEN COMPOUNDS
360201* - Ceramics
Cermets
& Refractories- Preparation & Fabrication
090320 - Inorganic Hydrogen Compound Fuels- Preparation- (1976-1989)