Microwave-assisted polyol synthesis of bimetallic RuRe nanoparticles stabilized by PVP or oxide supports (γ-alumina and silica)

Abstract

Uniform RuRe bimetallic nanoparticles (RuRe NPs) were successfully synthesized by a microwave-assisted polyol method using RuCl3 and NH4ReO4 as a precursor salts and ethylene glycol as a reducing agent. The obtained materials were characterized by UV–vis, TEM, SEM-EDS, XRD and XPS spectroscopy. Characterization by TEM showed that microwave-polyol synthesis using poly-N-vinyl-2-pyrrolidone (PVP) as a capping agent led to spherical RuRe NPs with mean size of 1.4nm or 1.6nm for the NPs with the nominal Ru/Re atomic ratio of 75:25 and 50:50, respectively, and a narrow particle size distributions (0.5–2.5nm). The size of the bimetallic NPs was slightly higher than monometallic Ru(PVP) NPs (1.3nm) prepared by the same method. XRD data confirmed small size of the obtained products. The “in situ” synthesis of γ-alumina or silica deposited NPs has been carried out without the addition of PVP, leading also to formation of bimetallic RuRe NPs. XPS analysis confirmed that the supported RuRe NPs consisted of Ru0, Re0 and oxidized Ru and Re species. However, the mean sizes and size distributions of the as-prepared bimetallic NPs depend greatly on the kind of the support used. In the case of γ-Al2O3 a narrow particle size distributions (0.5–5nm) were obtained and the mean sizes of RuRe and Ru NPs were slightly higher then for the PVP-stabilized NPs. The as-prepared silica deposited RuRe or Ru NPs were not well-dispersed and large aggregation of NPs was observed by TEM. However, diffraction data show that large agglomerates were composed from small bimetallic RuRe NPs (2.6nm) or nomometallic Ru NPs (9nm). Due to the weak interaction with silica surface, these small RuRe NPs lying very close to each other, were easily sintered during the hydrogen treatment at 400°C. In contrast, the bimetallic RuRe NPs deposited on the γ-Al2O3 under similar reducing conditions were very stable and have high activity for hydrogen chemisorption. Preliminary catalytic data show that alumina deposited RuRe nano-catalysts were more active then Ru nano-catalyst in the propane oxidation reaction.