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

• Main Authors: Bryan Bromley, Chiara Pischetola, Linda Nikoshvili, Fernando Cárdenas-Lizana, Lioubov Kiwi-Minsker
• Format: Article
• Language: English
• Published: MDPI AG 2020-08-01
• Series: Molecules
• Subjects: FeZSM-5 activation; N₂O decomposition; <i>α</i>-sites formation; transient response; NO and O₂ temperature programmed desorption
• Online Access: https://www.mdpi.com/1420-3049/25/17/3867

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 “<i>α</i>-sites”, responsible for the direct N₂O decomposition over Fe-ZSM-5 (Fe content = 1200–2300 ppm). The concentration of <i>α</i>-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” <i>α</i>-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 <i>α</i>-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.