New insights into alkali-catalyzed gasification reactions of carbon: Comparison of N₂O reduction with carbon over Na and K catalysts

Potassium and sodium are two representative and most active catalysts for the C-NO_x reactions. The catalytic conversion of N₂O to N₂ over Na- and K-impregnated activated carbon (Na/AC and K/AC) was studied. N₂ adsorption, TPD, thermal decomposition (with TGA), and CO₂ chemisorption characterized carbon samples with different K and Na loadings at 250°C. N2O, used as a reactant, enabled the observation and analysis of the reaction mechanism of gas-carbon reactions due to its readiness for dissociative chemisorption and because the C-N₂O reaction is an elementary reaction. Potassium was more active in N₂O dissociation and oxygen transfer, yielding a much higher activity. K/C was an excellent catalyst for N₂O decomposition. A considerable amount of N₂ was produced on K/C with no carbon gasification at 150°-250°C. Significant CO₂ production occurred only at higher temperatures. The difference in activities of the two alkali metals was due to three factors, i.e., K/C was highly active for N₂O dissociation; the surface phenolate group weakened the C-C bond to facilitate gasification; and the dispersion of K₂O on carbon was higher than that of Na₂O.