Nanoparticles of Rh confined and tailored by LaFeO3–La2O3 on SiO2 for direct ethanol synthesis from syngas

Abstract

A catalyst with a novel composition for direct ethanol synthesis from syngas was prepared and investigated in this work, which is Rh nanoparticles (NPs) highly dispersed on La₂O₃ modified LaFeO₃, and the Rh NPs/La₂O₃–LaFeO₃ was loaded on SiO₂ with high surface area. The catalyst was prepared by using LaFe_1−xRh_xO₃ in the perovskite phase as the precursor, which was transformed to Rh/La₂O₃–LaFeO₃/SiO₂ after reduction. The results showed that, compared to Rh–La₂O₃/SiO₂, the activity and selectivity to ethanol were improved markedly, which was ascribed to the well-matched catalyzing process by the active sites of Rh⁰, Rh⁺ (or Rh^δ+) and the oxygen vacancies on the surface of LaFeO₃; of those, Rh⁰ dissociatively adsorbed CO and the latter two associatively adsorbed CO. Moreover, the interaction of La₂O₃ and LaFeO₃ donated electrons to rhodium, which effectively adjusted the ratio of CO adsorbed associatively and dissociatively, and thus improved the selectivity to ethanol and lowered the selectivity to methanol. The catalyst also exhibited excellent resistance to the sintering of Rh NPs and to carbon deposition, which was attributed to the confinement of Rh NPs by La₂O₃ and LaFeO₃, the eliminating effect of La₂O₃ and LaFeO₃ and the very high dispersion of Rh NPs.