Enhanced ammonia dehydrogenation over Ru/La(x)-Al2O3 (x = 0–50 mol%): Structural and electronic effects of La doping

Abstract

Ru (1.0 wt% loaded)-based catalysts supported on La(x)-Al2O3 (x = 0, 1, 5, 10, and 50 mol%) were synthesized and characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) measurement, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and temperature programmed reduction (TPR). The as-prepared La(x)-Al2O3 materials were found to have increased amounts of the LaAlO3 phase as the La doping level (x) increased from 0 to 50 mol%. In addition to metal-to-support interactions between Ru and Al2O3, the newly formed LaAlO3 phase in the Ru catalysts was proposed to interact strongly with Ru active sites based on the XRD, H2-TPR and XPS results. The Ru/La(x)-Al2O3 catalysts were active for the dehydrogenation of ammonia, and among them, the Ru/La(10)-Al2O3 and Ru/La(50)-Al2O3 (or Ru/LaAlO3) catalysts exhibited superior performance with >96% conversions of ammonia at 550 °C. When an increased Ru content (2.0 wt%) was impregnated onto La(10)-Al2O3, the dehydrogenation activity was significantly improved with nearly 100% conversion (>95%) of ammonia at 500 °C. This catalyst further displayed an enhanced thermal stability towards ammonia decomposition with the GHSVNH3 of 10,000 mL/gcat h at 550 °C for >120 h. The incorporated element La is thought to play an important role in enhancing metal-support interaction, ultimately facilitating ammonia dehydrogenation even at low temperatures.