New insights into alkali-catalyzed gasification reactions of carbon: Comparison of N{sub 2}O reduction with carbon over Na and K catalysts
Catalytic conversion of N{sub 2}O to N{sub 2} over Na- and K-impregnated activated carbon (Na/AC and K/AC) was investigated. K and Na are two representative and most active catalysts for the C-NO{sub x} reactions. Carbon samples with different K and Na loadings were characterized by N{sub 2} adsorption, thermal decomposition (with TGA), TPD, and CO{sub 2} chemisorption at 250 C. CO{sub 2} chemisorption at 250 C proved to be effective for the measurement of potassium dispersion but not for sodium. Using N{sub 2}O as the reactant facilitated the observation and analysis of the reaction mechanism of gas-carbon reactions due to its readiness for dissociative chemisorption and also because the C-N{sub 2}O reaction is an elementary reaction. Based on isothermal reactions and TPR, potassium was found to be more active in both N{sub 2}O dissociation and oxygen transfer thus gave rise to a much higher activity. It was found that K/C was an excellent catalyst for N{sub 2}O decomposition. In the low-temperature range of 150--250 C, a significant amount of N{sub 2} was produced on K/C with no carbon gasification. Significant CO{sub 2} production occurred only at higher temperatures. The fundamental reason for the difference in activities of the two alkali metals is a combination of three factors. First, K/C is highly active for N{sub 2}O dissociation. The O atoms thus produced would form active surface intermediates, most likely the epoxy intermediate which significantly weakened the surface C-C bonds for gasification (which is the basis of the unified mechanism of Chen and Yang). Second, the surface phenolate group also weakened the C-C bond to facilitate gasification, but the weakening was more pronounced by the -C-O-K group than by the -C-O-Na group. Third, the dispersion of K{sub 2}O on carbon was higher than that of Na{sub 2}O.
- Research Organization:
- Univ. of Queensland (AU)
- OSTI ID:
- 20076095
- Journal Information:
- Journal of Catalysis, Vol. 192, Issue 1; Other Information: PBD: 15 May 2000; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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