Influence of the rare earth (R) element in Ru-supported RScSi electride-like intermetallic catalysts for ammonia synthesis at low pressure: insight into NH3 formation mechanism

Charlotte Croisé (1) , Khaled Alabd (2) , Sophie Tencé (2) , Etienne Gaudin (2) , Antoine Villesuzanne (2) , Xavier Courtois (1) , Nicolas Bion (1) , Fabien Can (1)

1 IC2MP [Poitiers] - Institut de chimie des milieux et matériaux de Poitiers [UMR 7285]
2 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux

This study investigates the influence of the rare-earth (R) element in Ru/RScSi electride-like intermetallic catalysts for ammonia synthesis under mild conditions (300–450 °C; 1–5 bar). All materials present poor specific surface area and the grain size impacts the ammonia yield. The catalytic performances follow the La to Gd lanthanides series (Ru1.7/LaScSi=Ru1.7/CeScSi=Ru1.7/PrScSi>Ru1.7/NdScSi>Ru1.5/SmScSi>Ru1.3/GdScSi) and appear correlated with the formation of the hydride phase. Ru1.7/CeScSi shows remarkable catalytic activity under moderate condition (0.58 mmolNH3/h/g at 300 °C, 1 bar) associated with its reversible hydrogen storage–release properties. It is evidenced that RScSi materials assist the N2 dissociation in agreement with their electride character and that the hydrogen for NH3 formation mainly comes from gaseous hydrogen and not primarily from the hydride phase. It is suggested that NHX formation could be the rate determining step rather than the N2 cleavage over these catalysts.

Mots clés: hydride; intermetallic; NH3; ruthenium; transient experiments

Domaines: Catalyse

Charlotte Croisé, Khaled Alabd, Sophie Tencé, Etienne Gaudin, Antoine Villesuzanne, et al.. Influence of the rare earth (R) element in Ru-supported RScSi electride-like intermetallic catalysts for ammonia synthesis at low pressure: insight into NH3 formation mechanism. ChemCatChem, 2023, 15 (3), e202201172 (12 p.). ⟨10.1002/cctc.202201172⟩. ⟨hal-03992609⟩