Synthesis of BiRh Nanoplates with Superior Catalytic Performance in the Semihydrogenation of Acetylene

Highly uniform and well-crystallized nanoparticles of the intermetallic compound BiRh were obtained by low-temperature synthesis at 240 degrees C using the microwave-assisted polyol process. In this time- and energy-efficient reaction the polyol acts as solvent, reducing agent, and surfactant, while the microwave radiation leads to fast and homogeneous nucleation and crystal growth. Electron microscopy studies confirmed the presence of pseudohexagonal nanoplates with a primary particle diameter of 60 nm and high crystallinity. As indicated by high-resolution transmission electron microscopy, the plate normal is generally not parallel to [001] but coincides with [421]. Powder X-ray diffraction and energy dispersive X-ray spectroscopy revealed the single-phase nature and the equimolar composition. The specific surface area (0.54 m(2) g(-1)) and the particle size distribution were measured by fractional sedimentation. According to the analysis of the chemical bonding by means of quantum chemical calculations, 0.62 electrons are transferred from Bi to Rh. Covalent homoatomic Rh-Rh as well as heteroatomic three-center Rh-Bi-Rh bonds define a three-dimensional bonding network. Unsupported BiRh nanoparticles exhibit an extraordinary high selectivity of 88 to 93% in the semihydrogenation of acetylene, which makes them an interesting model compound as well as a promising candidate for the application as an industrial catalyst.