Lanthana-promoted Rh/SiO/sub 2/. II. Studies of CO hydrogenation
A study of the influence of lanthana promotion on the hydrogenation of CO over Rh/SiO/sub 2/ has been conducted. Lanthana-promoted Rh/SiO/sub 2/ exhibits higher turnover frequencies for the synthesis of CH/sub 4/, C/sub 2/-C/sub 4/ hydrocarbons, CH/sub 3/OH, and C/sub 2/ oxygenates than unpromoted Rh/SiO/sub 2/. The turnover frequency for each product goes through a maximum with increasing lanthana addition. Lanthana promotion is also found to increase the selectivity for the formation of CH/sub 3/OH, C/sub 2/ oxygenates, and C/sub 2/-C/sub 4/ hydrocarbons and to decrease the selectivity for CH/sub 4/. The selectivity for C/sub 2/ oxygenates is optimized at low levels of lanthana addition. In situ infrared observations show that lanthana promotion blocks the chemisorption of CO onto surface Rh sites. Of particular interest is the observation of a band at 1725 cm/sup -1/. This feature is assigned to CO adsorbed on a Rh site immediately adjacent to an LaO/sub x/ island. The low frequency of this vibration is attributed to a weakening of the C-O bond caused by the interaction of lanthana cations with the oxygen end of the adsorbed CO. It is postulated that the interaction of the lanthana with the CO is responsible for the enhanced rates of CO dissociation and the formation CH/sub 4/ and C/sub 2+/ products. Infrared spectroscopy also provides evidence for acyl, formate, and acetate groups on the surface of lanthana-promoted Rh/SiO/sub 2/. The possible role of these species in the synthesis of products is discussed. 26 references.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 7054847
- Journal Information:
- J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 111:2; ISSN JCTLA
- Country of Publication:
- United States
- Language:
- English
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ALCOHOLS
ALKANES
BUTANE
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISORPTION
ETHANE
HYDROCARBONS
HYDROXY COMPOUNDS
INFRARED SPECTRA
KINETICS
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
METHANATION
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METHANOL
MINERALS
ORGANIC COMPOUNDS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PROMOTERS
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RARE EARTH COMPOUNDS
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
RHODIUM COMPOUNDS
RHODIUM OXIDES
SEPARATION PROCESSES
SILICA
SILICON COMPOUNDS
SILICON OXIDES
SORPTION
SPECTRA
SURFACE PROPERTIES
TRANSITION ELEMENT COMPOUNDS