A kinetic study on the adsorption and reaction of hydrogen over silica-supported ruthenium and silver-ruthenium catalysts during the hydrogenation of carbon monoxide
The simultaneous adsorption and reaction of hydrogen with preadsorbed carbon monoxide was investigated over a series of silica-supported ruthenium and silver-ruthenium bimetallic catalysts to elucidate the role of site sensitivity on hydrogen adsorption and methane formation. The specific rate of methane synthesis, which is a direct measure of the catalyst activity toward the Fischer-Tropsch synthesis, measured at 460 Torr and temperatures from 400 to 500 K, varied from 0.01 x 10{sup {minus}3} to 3 x 10{sup {minus}3}S{sup {minus}1}. As little as 3% Ag reduced the methanation rate of Ru by 80%. The temperature dependence of the turnover frequency showed that the apparent activation energy for methanation dropped from 24 kcal/mol for the monometallic ruthenium case to 18 kcal/mol for the bimetallic case. Since silver does not adsorb or react with either hydrogen or carbon monoxide, these results show that silver does not act merely as a dilutant in the bimetallic system. These observations are elucidated in terms of a new model for surface-sensitive hydrogen adsorption, termed portal site mediated adsorption, where low-coordination edge and corner sites on the catalyst surface act as sinks for rapid, dissociative adsorption of weakly bound, highly mobile surface hydrogen. In situ {sup 1}H-NMR measurements of surface hydrogen coverages during reaction were used to confirm the kinetic model treatment of the reaction data.
- Research Organization:
- Iowa State Univ., Ames, IA (US)
- Sponsoring Organization:
- USDOE; National Science Foundation (NSF)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 20003857
- Journal Information:
- Journal of Catalysis, Vol. 188, Issue 1; Other Information: PBD: 15 Nov 1999; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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