Factors affecting activity and selectivity during cyclohexanone hydrogenation with colloidal platinum nanocatalysts

The hydrogenation of cyclohexanone was carried out with 100% selectivity to cyclohexanol by utilizing 1–10 nm size poly(vinylpyrrolidone)-capped colloidal platinum nanocatalysts dispersed in the aqueous-phase. Particle sizes for these synthesized nanocatalysts were determined by transmission electron microscopy (TEM), and open adsorption sites on the metal nanoparticle surface were established through attenuated total reflectance infrared (ATR-IR) spectroscopic studies of chemisorbed carbon monoxide. The effect of the reaction conditions (temperature, hydrogen pressure, and cyclohexanone concentration) on turnover frequencies (TOFs) was examined to calculate apparent activation energies and reaction orders. In addition, platinum nanoparticle size and PVP molecular weight were varied to investigate effects of nanocatalyst properties on catalytic activity and reaction selectivity. In situ ATR-IR spectroscopy was used to verify adsorbed cyclohexanone as being present on the nanocatalyst surface during the reaction. Combining kinetic parameters with identification of adsorbed species is essential for developing a molecular-level mechanism for the reaction, thereby allowing factors controlling activity and selectivity in these aqueous-phase hydrogenations to be elucidated. Taken together, these results permit the ingredients essential for a highly active and selective catalyst to be discerned.

Figure optionsDownload high-quality image (85 K)Download as PowerPoint slideResearch highlights▶ Catalytic activity for the aqueous-phase hydrogenation of cyclohexanone using colloidal platinum nanocatalysts increases with reaction temperature, reactant concentration, hydrogen pressure, and nanoparticle size. ▶ Catalytic activity for the aqueous-phase hydrogenation of cyclohexanone using colloidal platinum nanocatalysts does not depend on the capping agent molecular weight, regardless of nanoparticle size. ▶ Under these mild conditions, the reaction proceeds via a Langmuir-Hinshelwood mechanism with 100% selectivity to cyclohexanol.