The effect of carbon and oxygen on the surface chemistry of tungsten carbides

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1989

OSTI ID:6900211

Ribeiro, F H.L.A.

Two phases of tungsten carbide, WC and {beta}W{sub 2}C, were prepared with 30 and 100 m{sup 2}/g{sup {minus}1} respectively. The {beta}W{sub 2}C was synthesized by the temperature programmed reaction (TRP) of WO{sub 3}, in NH{sub 3} followed by carburization of the product {beta}W{sub 2}N with a mixture of CH{sub 4} and H{sub 2}. The WC phase was made from WO{sub 3} with a mixture of CH{sub 4} and H{sub 2}. Under the experimental conditions chosen, CH{sub 4} also decomposed to form a carbonaceous deposit on the surface. This deposit was removed as CH{sub 4} by flowing H{sub 2} over the samples at 973 K. Following this treatment the samples are designated fresh samples. The surface of tungsten carbides was probed by the catalytic reactions of 2,2-dimethylpropane and n-hexane in H{sub 2}. Samples exposed to O{sub 2} were found to behave very differently from the fresh samples. Fresh samples catalyzed only the breaking of carbon-carbon bonds. With the samples exposed to O{sub 2}, isomerization of n-hexane to 2- and 3-methylpentane and of 2,2-dimethylpropane to isopentane was also observed, the latter reaction having been previously reported on low S{sub g} samples than had been also exposed inadvertently to O{sub 2}. The main conclusion of the work is that surface oxygen is a key component in the isomerization of hydrocarbons over tungsten carbide. The role of oxygen in the isomerization of neopentane may be the same as the currently proposed role of oxygen in the metathesis of alkenes over tungsten oxides. By contrast, for the isomerization of n-hexane, oxygen may simply provide the acidic sites available on the alumina of supported platinum in the typical bifunctional mechanism of alkane isomerization.

• Research Organization: Stanford Univ., CA (USA)
• OSTI ID: 6900211
• Country of Publication: United States
• Language: English

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ALKANES
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
AMMONIA
CARBIDES
CARBON
CARBON COMPOUNDS
CARBURIZATION
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CATALYTIC REFORMING
CHALCOGENIDES
CHEMICAL PREPARATION
CHEMICAL REACTIONS
COMPARATIVE EVALUATIONS
CONTROL
DEPOSITION
ELEMENTS
HARDENING
HEXANE
HYDRIDES
HYDROCARBONS
HYDROGEN
HYDROGEN COMPOUNDS
ISOMERIZATION
METALS
METHANE
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
ORGANIC COMPOUNDS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PLATINUM
PLATINUM METALS
REFORMER PROCESSES
REFRACTORY METAL COMPOUNDS
SURFACE AREA
SURFACE HARDENING
SURFACE PROPERTIES
SURFACE TREATMENTS
SYNTHESIS
TEMPERATURE CONTROL
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
TUNGSTEN CARBIDES
TUNGSTEN COMPOUNDS
TUNGSTEN OXIDES