Composition-tuned oxidation levels of Pt–Re bimetallic nanoparticles for the etherification of allylic alcohols

The catalytic performance of metal nanoparticles is often affected by surface oxidation levels. Instead of post-synthesis oxidation/reduction, we propose an efficient method to modulate the oxidation levels by tuning the composition of bimetallic nanoparticles. Here we report a series of Pt–Re bimetallic nanoparticles synthesized via a facile thermal co-reduction process, with a uniform size of approximately 3 nm. The investigation of the growth of the Pt–Re nanoparticles suggests that the Re atoms were enriched on the surface, as confirmed by X-ray photoelectron spectroscopy. Furthermore, X-ray absorption spectroscopy showed that metallic Re was decreased and high-valency ReO_x species were increased in particles with higher Re/Pt ratios. In the etherification of allylic alcohols catalyzed by Pt–Re nanoparticles of different compositions under ambient conditions, particles with higher Re/Pt ratios exhibited significantly better performances. The highest mass activity of Pt–Re bimetallic nanoparticles (127 μmol·g^-1·s^-1) was more than forty times that of the industrial catalyst CH₃ReO₃ (3 μmol·g^-1·s^-1). The catalytically active sites were associated with ReO_x and could be tuned by adjusting the Pt ratio.