N₂O Decomposition over Fe-ZSM-5: A Systematic Study in the Generation of Active Sites

We have carried out a systematic investigation of the critical activation parameters (i.e., final temperature (673-1273 K), atmosphere (He vs. O₂/He), and final isothermal hold (1 min-15 h) on the generation of "α-sites", responsible for the direct N₂O decomposition over Fe-ZSM-5 (Fe content = 1200-2300 ppm). The concentration of α-sites was determined by (ia) transient response of N₂O and (ib) CO at 523 K, and (ii) temperature programmed desorption (TPD) following nitrous oxide decomposition. Transient response analysis was consistent with decomposition of N₂O to generate (i) "active" α-oxygen that participates in the low-temperature CO→CO₂ oxidation and (ii) "non-active" oxygen strongly adsorbed that is not released during TPD. For the first time, we were able to quantify the formation of α-sites, which requires a high temperature (>973) treatment of Fe-ZSM-5 in He over a short period of time (<1 h). In contrast, prolonged high temperature treatment (1273 K) and the presence of O₂ in the feed irreversibly reduced the amount of active sites.