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), Vol. 111:2
- Country of Publication:
- United States
- Language:
- English
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CARBON MONOXIDE
METHANATION
LANTHANUM OXIDES
CATALYTIC EFFECTS
RHODIUM OXIDES
BUTANE
CATALYST SUPPORTS
CATALYSTS
CHEMICAL REACTION KINETICS
CHEMISORPTION
ETHANE
INFRARED SPECTRA
METHANE
METHANOL
PROMOTERS
PROPANE
SILICA
SURFACE PROPERTIES
ALCOHOLS
ALKANES
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
HYDROCARBONS
HYDROXY COMPOUNDS
KINETICS
LANTHANUM COMPOUNDS
MINERALS
ORGANIC COMPOUNDS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
RARE EARTH COMPOUNDS
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
RHODIUM COMPOUNDS
SEPARATION PROCESSES
SILICON COMPOUNDS
SILICON OXIDES
SORPTION
SPECTRA
TRANSITION ELEMENT COMPOUNDS
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