Sum Frequency Generation Vibrational Spectroscopy of 1,3-Butadiene Hydrogenation on 4 nm PtiO sub(2), PdiO sub(2), and RhiO sub(2) Core-Shell Catalysts

1,3-Butadiene (1,3-BD) hydrogenation was performed on 4 nm Pt, Pd, and Rh nanoparticles (NPs) encapsulated in SiO sub(2) shells at 20, 60, and 100 degree C. The core-shells were grown around polyvinylpyrrolidone (PVP) coated NPs (Stober encapsulation) prepared by colloidal synthesis. Sum frequency generation (SFG) vibrational spectroscopy was performed to correlate surface intermediates observed in situ with reaction selectivity. It is shown that calcination is effective in removing PVP, and the SFG signal can be generated from the metal surface. Using SFG, it is possible to compare the surface vibrational spectrum of PtiO sub(2) (1,3-BD is hydrogenated through multiple paths and produces butane, 1-butene, and cis/trans-2-butene) to PdiO sub(2) (1,3-BD favors one path and produces 1-butene and cis/trans-2-butene). In contrast to PtiO sub(2) and PdiO sub(2), SFG and kinetic experiments of RhiO sub(2) show a permanent accumulation of organic material. Keywords: 1,3-Butadiene hydrogenation; core-shell nanoparticles; surface vibrational spectroscopy