The controlled dispersion of silica supported MoO sub 3 : The role of ammonia

Journal Article · Wed Jan 01 04:00:00 EST 1992 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1016/0021-9517(92)90186-L· OSTI ID:7141462

Datta, A K; Ha, Jinwook; Regalbuto, J R ^[1]

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1. Univ. of Illinois, Chicago (United States)

The morphology of silica supported catalysts, prepared by impregnation of ammonium heptamolybdate and for various weight loadings up to 35 wt%, was studied using X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy, In addition to the orthorhombic phase, the behavior of the rarely studied hexagonal phase was fully characterized. All morphologies of silica supported MoO{sub 3} appear to be thermodynamically driven. At low loadings there appeared one stable dispersion, independent of initial precursor dispersion. For high loaded catalysts there appeared three states: a metastable sintered hexagonal state and a well dispersed hexagonal state at moderate temperature calcinations (300 C), and the sintered orthorhombic state at high temperature (500 C). Whereas the sintered orthorhombic phase is detected by XRD at loadings in excess of 1.1 atom Mo/nm{sup 2}, the well dispersed hexagonal phase is not evident until 4.0 atoms Mo/nm{sup 2}. It is possible to produce the well dispersed hexagonal phase from the sintered orthorhombic phase with an ammonia impregnation and subsequent calcination at 300 C. The apparently higher dispersion of the hexagonal phase may arise from some role of ammonia which results in a stronger MoO{sub 3}-surface interaction.

• OSTI ID: 7141462
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 133:1; ISSN 0021-9517; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360602 -- Other Materials-- Structure & Phase Studies
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
AMMONIA
CALCINATION
CATALYST SUPPORTS
CATALYSTS
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL REACTIONS
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DECOMPOSITION
DIFFRACTION
DISTRIBUTION
ELECTRON MICROSCOPY
ELECTRON SPECTROSCOPY
FABRICATION
HEXAGONAL LATTICES
HYDRIDES
HYDROGEN COMPOUNDS
IMPREGNATION
MICROSCOPY
MOLYBDENUM COMPOUNDS
MOLYBDENUM OXIDES
MORPHOLOGY
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
OXIDES
OXYGEN COMPOUNDS
PHASE STUDIES
PHOTOELECTRON SPECTROSCOPY
PYROLYSIS
QUANTITY RATIO
REFRACTORY METAL COMPOUNDS
SCATTERING
SILICON COMPOUNDS
SILICON OXIDES
SINTERING
SPECTROSCOPY
SURFACE PROPERTIES
SYNTHESIS
TEMPERATURE DEPENDENCE
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENT COMPOUNDS
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY