On the surface chemistry of molybdena-alumina catalysts prepared from Mo(CO) sub 6
- Univ. of Pittsburgh, PA (USA)
Catalysts were prepared by subliming Mo(CO){sub 6} onto partially dehydroxylated (PDA) and exhaustively dehydroxylated (DA) alumina made from the same parent preparation (American Cyanamid Aero 100PHF). The chemisorption of NO and Co on these materials was studied using volumetric, chromatographic, and spectroscopic techniques. ESCA data indicated that metallic Mo crystals formed on Mo(CO){sub 6}/DA whereas on PDA both Mo{sup 4+} and some lower valence state, Mo{sup 2+} or Mo{sup 0}, were present. NO chemisorbed on both preparations at 195 K without releasing either N{sub 2}O or N{sub 2}. The chemisorption on the PDA preparations was over tenfold higher than that on the DA-supported catalysts under these conditions, but at 300 K the difference was reduced to a factor of 2. Moreover, redox chemistry occurred at this higher temperature as evidenced by the release of N{sub 2}O and N{sub 2}. The amounts of NO actually chemisorbed correlated well with the integrated IR band intensities. These data suggest that lower valence states are oxidized to Mo{sup 4+} at 300 K and that the observed IR bands stem from Mo{sup 4+}(NO){sub 2}, irrespective of the initial catalyst. Infrared spectra from residual CO remaining on decomposition of Mo(CO){sub 6} on DA and PDA showed bands which could be attributed to residual Mo(CO){sub 6} and/or to subcarbonyl species formed during decomposition. By 573 K, no residual bands could be observed. On adding-back CO at 300 K to the PDA preparation, bands at 1989 and 2170 cm{sup {minus}1} appeared, suggesting the presence of Mo{sup 4+} and residual Mo{sup 0}. Spectra from similar experiments with the DA preparation demonstrated that chemisorbed Mo(CO){sub 6} was reforming and possibly some subcarbonyl species.
- OSTI ID:
- 7128443
- Journal Information:
- Journal of Catalysis; (USA), Vol. 115:1; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ALUMINIUM OXIDES
SURFACE PROPERTIES
CARBON MONOXIDE
CHEMISORPTION
MOLYBDENUM OXIDES
NITRIC OXIDE
CARBONYLS
CATALYSTS
CHEMICAL PREPARATION
COMPLEXES
ELECTRON SPECTROSCOPY
INFRARED SPECTRA
MOLYBDENUM COMPOUNDS
REDOX REACTIONS
TEMPERATURE DEPENDENCE
ALUMINIUM COMPOUNDS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
NITROGEN COMPOUNDS
NITROGEN OXIDES
OXIDES
OXYGEN COMPOUNDS
REFRACTORY METAL COMPOUNDS
SEPARATION PROCESSES
SORPTION
SPECTRA
SPECTROSCOPY
SYNTHESIS
TRANSITION ELEMENT COMPOUNDS
020400* - Petroleum- Processing
400201 - Chemical & Physicochemical Properties