Highly Active Pt–Co Bimetallic Nanoparticles on Ionic Liquid-Modified SBA-15 for Solvent-Free Selective Hydrogenation of Cinnamaldehyde

Small Pt–Co bimetallic nanoparticles were prepared on ionic liquid-functionalized SBA-15. The prepared 2Pt–2Co/IL@SBA-15 showed high activity and selectivity in cinnamaldehyde hydrogenation to form cinnamyl alcohol under solvent-free conditions. The reaction proceeded efficiently without any addition of solvent with simple product recovery. 2Pt–2Co/IL@SBA-15 exhibited superior activity compared to the monometallic catalysts and Pt–Co on unmodified SBA-15, with 97.1% conversion and 96.2% selectivity to cinnamyl alcohol. The formation of small Pt–Co bimetallic nanoparticles and the presence of an ionic liquid are the keys to its high activity. XAFS analysis and STEM EDS mapping revealed that Pt–Co bimetallic nanoparticles were formed with both Pt and Co exposed on the surface of the nanoparticles. The charge transfer from Co to Pt on the surface of bimetallic nanoparticles results in a high selectivity for cinnamyl alcohol formation. The ionic liquid assisted the formation of small Pt–Co nanoparticles inside the pores of SBA-15 and acted as an "immobilized solvent" allowing the hydrogenation reaction to proceed efficiently without the need for an additional solvent. Moreover, the ionic liquid is strongly bonded to SBA-15, preventing aggregation of bimetallic nanoparticles, resulting in high durability and stability that allows the catalyst to be used six times without significant activity loss.