A study of the morphology of silica-supported MoO sub 3
Molybdenum based catalysts have ample applications in hydrotreating and hydrocracking of petroleum feedstock and for hydro-processing of coal liquids and hydrogenation of coal-derived gases. It is the purpose of this thesis to examine the interaction of the hexagonal and orthorhombic phases of MoO{sub 3} with silica and to exploit its behavior for improved control of silica supported MoO{sub 3} morphology. The effect of preparation on the structure of MoO{sub 3} on silica support is studied by varying the air calcination-temperature, time; and loading of precursor; and by adding either HNO{sub 3} or NH{sub 4}OH. Characterization methods used are (XRD) in conjunction with (XPS), and TEM. It is concluded that thermodynamically stable large orthorhombic crystallites are formed at 500C from (a) pure precursor, (b) supported precursor in absence of acid or base at {ge}8.8 wt% loading, and (c) hexagonal MoO{sub 3}. Rhombic crystallites spread in time in presence of ammonia and support at low temperature. A metastable equilibrium state of well dispersed hexagonal crystallites is formed at 300C, when excess ammonia is present. The final morphology is independent of pH and nearly independent of calcination temperature. The morphology can be controlled as follows: (a) large hexagonal crystallites can be produced with acid impregnated precursor at room temperature and with a 300C calcination, (b) small, well dispersed hexagonal crystallites are formed with or without base upon calcination at 300C, (c) large orthorhombic crystallite are always formed by calcination at 500C, and (d) smaller orthorhombic crystallites may be produced from a short calcination of the dispersed hexagonal phase.
- Research Organization:
- Illinois Univ., Chicago, IL (United States)
- OSTI ID:
- 6069210
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
AIR
AMMONIA
AMMONIUM COMPOUNDS
AMMONIUM HYDROXIDES
CALCINATION
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL REACTIONS
COAL GAS
COAL LIQUIDS
COHERENT SCATTERING
CRACKING
CRYSTAL STRUCTURE
DECOMPOSITION
DIFFRACTION
ELECTRON MICROSCOPY
ELECTRON SPECTROSCOPY
ENERGY SOURCES
FLUIDS
FOSSIL FUELS
FUELS
GASES
HYDRIDES
HYDROCRACKING
HYDROGEN COMPOUNDS
HYDROGENATION
HYDROXIDES
INORGANIC ACIDS
LIQUIDS
LOADING RATE
MICROSCOPY
MINERALS
MOLYBDENUM COMPOUNDS
MOLYBDENUM OXIDES
MORPHOLOGY
NITRIC ACID
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PETROLEUM
PH VALUE
PHOTOELECTRON SPECTROSCOPY
PROCESSING
PYROLYSIS
REFINING
REFRACTORY METAL COMPOUNDS
SCATTERING
SILICA
SILICON COMPOUNDS
SILICON OXIDES
SPECTROSCOPY
SYNTHESIS
TEMPERATURE DEPENDENCE
THERMOCHEMICAL PROCESSES
TIME DEPENDENCE
TRANSITION ELEMENT COMPOUNDS
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY