CO hydrogenation over clean and oxidized rhodium foil and single crystal catalysts. Correlations of catalyst activity, selectivity, and surface composition

Journal Article · Mon Dec 01 04:00:00 EST 1980 · J. Catal.; (United States)

DOI:https://doi.org/10.1016/0021-9517(80)90030-5· OSTI ID:6662182

Castner, D B; Blackadar, R L; Somorjai, G A

CO hydrogenation at 6 atm over Rh polycrystalline foil and single (111) catalysts was investigated in a system where the surface structure and composition of the catalysts could be characterized both before and after the reaction. The reaction conditions (H/sub 2/:CO ratio, reaction temperature, surface pretreatment, and gas phase additives) were systematically varied to determine the conditions necessary for the formation of oxygenated hydrocarbons. Initially clean Rh catalysts showed no structure sensitivity, primarily produced methane (90 wt%) at an initial rate of 0.15 molecules site/sup -1/ sec/sup -1/ at 300/sup 0/C, and did not produce detectable amounts of oxygenated hydrocarbons. Preoxidation of the Rh (800 Torr O/sub 2/, 600/sup 0/C, 30 min) resulted in dramatically increased initial rates, a larger fraction of higher molecular weight hydrocarbons in the product distribution, formation of methanol, ethanol, and acetaldehyde, and some structure sensitivity. The different Arrhenius methanation preexponential factors and activation energies over the clean and preoxidized Rh foils indicate the methanation mechanism is different on these two surfaces. Decreasing the reaction temperature or H/sub 2/:CO ratio increased the C/sub 2/H/sub 4/ to C/sub 2/H/sub 6/ ratio and shifted the product distribution toward the higher molecular weight hydrocarbons. The addition of 1 mole% of CH/sub 3/OH, CH/sub 3/CH/sub 2/OH, or C/sub 2/H/sub 4/ to the H/sub 2/:CO reaction mixture caused a small increase in the fraction of higher molecular weight hydrocarbons. 10 figures, 3 tables.

• Research Organization: Lawrence Berkeley Lab., CA
• OSTI ID: 6662182
• Journal Information: J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 66:2; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

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400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ACETALDEHYDE
ALCOHOLS
ALDEHYDES
ALKANES
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYSIS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTIONS
COMPARATIVE EVALUATIONS
ELEMENTS
ETHANOL
HYDROCARBONS
HYDROGEN
HYDROXY COMPOUNDS
KINETICS
MEDIUM PRESSURE
METALS
METHANATION
METHANE
METHANOL
NONMETALS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PLATINUM METALS
REACTION KINETICS
REFRACTORY METALS
RHODIUM
SURFACE PROPERTIES
TRANSITION ELEMENTS