Mechanism of N2O reduction by H2 on alkali metal-activated char at low temperatures

Hydrogen-based selective catalytic reduction (H 2 -SCR) is gaining attention for its environmental benefits, in response to increasingly stringent global N 2 O emission regulations. This study investigates the catalytic performance of alkali metal-activated char (K, Ca, Na) in reducing N 2 O using H 2 at temperatures below 200℃, through theoretical calculations and experimental validation. The study reveals that K, Na, and Ca exhibit distinct behaviors in terms of loading sites. K and Na preferentially decorates at edge sites due to differences in electron conjugation and atomic population, while Ca is more inclined to load at central positions, forming strong interactions with the char. These differences lead to variations in the N 2 O reduction pathways: K/Na-char primarily engages in physical adsorption, with N 2 O reduction proceeding through higher energy barriers, whereas Ca-char facilitates chemical adsorption of N 2 O with minimal energy barriers, displaying significant catalytic activity, Despite these differences, the study identifies a common rate-determining step across all systems, predominantly involving the removal of H 2 O. Notably, Ca-char achieves a substantial reduction in activation energy to 42.1 kJ/mol, compared to the partial reduction achieved by K/Na-char to 165.4–178.3 kJ/mol, from an initial 383 kJ/mol. Experimental validation corroborates the catalytic performance of all three alkali metals.