The active surface species in alkali-catalyzed carbon gasification: Phenolate (C-O-M) groups vs clusters (particles)
- State Univ. of New York, Buffalo, NY (United States)
The activities and catalytic roles of different species of potassium in the gasification reactions of graphite by H[sub 2]O and CO[sub 2] are investigated. TEM techniques are used to measure the rates of monolayer edge recession (uncatalyzed and C-O-K catalyzed) and rates of monolayer channeling (catalyzed by particles) on the basal plane of graphite reacting with 21 Torr H[sub 2]O at 700[degrees]C. The turnover frequencies for carbon gasification are: 0.08 s[sup -1] (catalyzed by C-O-K groups), and 7.8 s[sup -1] (catalyzed by particles). Thus the particles have a high activity, whereas the C-O-K groups have only a small activity. TGA and literature results using mixtures of carbon and alkali salts show a sigmoidal dependence of gasification rates on catalyst loading. This is the result of catalyst dispersion and competition between the C-O-K groups and alkali particles. A CNDO semi-empirical molecular orbital calculation is performed on model graphite substrates with -O and -O-K groups bonded to the (10[bar 1]l) zigzag face and (11[bar 2]l) armchair face. On the zigzag face, the carbon atom bridging two C-O-K groups gains a large negative charge (-0.486) and hence is a favorable site for binding an O atom. The surface C-C bonds in this structure are substantially weakened by adding O atoms on the bridging C atoms, leading to CO the alkali particles being more active than the C-O-M (where M = alkali) groups is that the particles can dissociate H[sub 2]O and CO[sub 2] at higher rates, by providing either more active sites or higher activities. The CNDO results also predict that the C-O-K groups have an inhibiting effect on the armchair face. 47 refs., 6 figs., 4 tabs.
- OSTI ID:
- 5990033
- Journal Information:
- Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 141:1; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALKALI METAL COMPLEXES
CARBON
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON MONOXIDE
CARBON OXIDES
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL ANALYSIS
COMPLEXES
ELECTRON MICROSCOPY
ELEMENTAL MINERALS
ELEMENTS
GASIFICATION
GRAPHITE
GRAVIMETRIC ANALYSIS
HYDROGEN COMPOUNDS
MATHEMATICAL MODELS
MICROSCOPY
MINERALS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PARTICLES
POTASSIUM COMPLEXES
QUANTITATIVE CHEMICAL ANALYSIS
SUBSTRATES
THERMAL ANALYSIS
THERMAL GRAVIMETRIC ANALYSIS
THERMOCHEMICAL PROCESSES
TRANSMISSION ELECTRON MICROSCOPY
WATER