Model vanadium-phosphorus-oxygen catalysts for the selective oxidation of C/sub 4/ hydrocarbons to maleic anhydride
Two model vanadium-phosphorus-oxygen catalysts, ..beta..-VOPO/sub 4/ and (VO)/sub 2/P/sub 2/O/sub 7/, were investigated for the selective oxidation of C/sub 4/ hydrocarbons to maleic anhydride. In situ laser Raman spectroscopy was used. Complementary techniques including x-ray powder diffraction and x-ray photoelectron spectroscopy were used for characterization of the fresh and used catalytic materials. The direct observation of phase stability and the participation of lattice oxygen during catalysis was possible using the in situ Raman technique. In particular, ..beta..-VOPO/sub 4/ and (VO)/sub 2/P/sub 2/O/sub 7/ demonstrated bulk structural integrity during n-butane oxidation. The relatively greater reducing capacity of 1-butene induced the ..beta..-VOPO/sub 4/ to (VO)/sub 2/P/sub 2/O/sub 7/ phase transformation. Direct structural identification of catalytically active centers for paraffin and olefin oxidation were investigated using an /sup 18/O-enriched ..beta..-VOPO/sub 4/ phase catalyst. Active sites responsible for complete combustion (Site I) and selective oxidation (Site II) were identified. The selective route for 1-butene oxidation involved predominantly Site II centers, while Site I centers were associated with complete combustion. In contrast, n-butane oxidation required the highly active Site I centers for initial activation and for the formation of an intermediate containing two oxygen atoms. Raman band assignments indicated these oxygen sites were associated with PO/sub 4/ units in the ..beta..-VOPO/sub 4/ lattice. Maleic anhydride conversion was particularly sensitive to the catalytic phase present. Significant combustion activity was observed when maleic anhydride was fed directly to an integral flow reactor charged with model catalysts. The combustion activity was least for (VO)/sub 2/P/sub 2/O/sub 7/, nominally a V(IV) phase. The ..beta..-VOPO/sub 4/ catalyst, nominally a V(V) phase, resulted in increased conversions of maleic anhydride.
- Research Organization:
- Ames Lab., IA (USA)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 6510309
- Report Number(s):
- IS-T-1307; ON: DE87010935
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360603 -- Materials-- Properties
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALKANES
ALKENES
ANHYDRIDES
BUTANE
BUTENES
CARBOXYLIC ACIDS
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTIONS
CONVERSION
DICARBOXYLIC ACIDS
HYDROCARBONS
LASER SPECTROSCOPY
MALEIC ACID
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PHOSPHORUS COMPOUNDS
PHOSPHORUS OXIDES
RAMAN SPECTROSCOPY
SPECTROSCOPY
TRANSITION ELEMENT COMPOUNDS
VANADIUM COMPOUNDS
VANADIUM OXIDES