Nitrogen Reduction by Nanostructure‐Supported Ruthenium Catalysts
Rami Doukeh, Maria Lehene, Cezara Zagrean‐Tuza, Augustin C. Mot, Radu Silaghi‐Dumitrescu, Codruta Sarosi, Carmen Ioana Fort, Graziella Liana Turdean, Gheorghe Borodi, Sofia Oleinic, Cașen PanaitescuABSTRACT
Reported here are the synthesis, characterization, and photocatalytic evaluation of two zero‐valent ruthenium catalysts supported on multi‐walled carbon nanotubes (Ru 0 @CNTs) and on graphitic carbon nitride (Ru 0 @g‐C 3 N 4 ), prepared by wet impregnation of RuCl 3 followed by thermal reduction under hydrogen. The materials were comprehensively characterized by XRD, SEM‐EDS, TGA‐DTG, BET surface area analysis, UV–vis diffuse reflectance spectroscopy, XPS, and ESR. Ru 0 @CNTs displayed a substantially higher specific surface area (73.5 m 2 g − 1 ) and pore volume (0.367 cm 3 g − 1 ) relative to Ru 0 @g‐C 3 N 4 (21.4 m 2 g − 1 ; 0.015 cm 3 g − 1 ), and exhibited broader visible‐light absorption associated with the narrower bandgap of the CNT support (1.82 eV vs. 2.71 eV for g‐C 3 N 4 ). In photocatalytic nitrogen reduction experiments, Ru 0 @CNTs yielded 183.2 ± 3.7 µmol NH 3 g − 1 alongside 31.3 ± 0.6 µmol g − 1 of the hydrazine intermediate, outperforming Ru 0 @g‐C 3 N 4 (150.4 ± 4.4 and 17.6 ± 1.0 µmol g − 1 , respectively); the ammonia yields increased by ∼20% at pH 3 for both catalysts. Electrochemical linear sweep voltammetry confirmed that NRR onset for Ru 0 @CNTs occurs at a substantially more positive potential (−0.3 V vs. Ag/AgCl) than for Ru 0 @g‐C 3 N 4 (−1.5 V), where competing hydrogen evolution dominates. DFT calculations rationalize the observed reactivity trends.