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Medientyp:
E-Artikel
Titel:
Direct Synthesis of Ammonia from N2 and H2O on Different Iron Species Supported on Carbon Nanotubes using a Gas‐Phase Electrocatalytic Flow Reactor
Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Green NH<jats:sub>3</jats:sub> production by direct electrocatalytic synthesis from N<jats:sub>2</jats:sub> and H<jats:sub>2</jats:sub>O is still a challenging reaction, which requires us to better understand the nature of the active materials. We show here that iron oxide (Fe<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>) nanoparticles (supported over carbon nanotubes, CNTs) become more active than the corresponding samples after reduction to form Fe‐ or Fe<jats:sub>2</jats:sub>N‐supported nanoparticles, both indicated as active species in the thermal catalytic reduction of N<jats:sub>2</jats:sub> to ammonia. Characterization data, however, indicate that even for these Fe‐ and Fe<jats:sub>2</jats:sub>N−CNT samples, obtained from Fe<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>−CNT by reduction in H<jats:sub>2</jats:sub> or NH<jats:sub>3</jats:sub> at 500 °C, the active species responsible for N<jats:sub>2</jats:sub> reduction reaction (NRR) at low applied potential (−0.5 V vs RHE) are the same, that is, small (<1–2 nm) iron oxide nanoparticles that are not detected by XRD, but evidenced by XPS and which amount could be correlated to the rate of ammonia formation. This species is stable for at least 24 h of electrocatalytic flow tests. However, at higher applied potentials, sintering/transformation of this species occurs, with loss of the electrocatalytic activity, and Fe<jats:sub>2</jats:sub>N nanoparticles may also be reduced in situ, forming ammonia, but with irreversible deactivation.</jats:p>