Dr. Andy Marsh, along with several LVC students, published two research articles which utilized platinum nanocatalysts: Synthesis, Characterization, and Reaction Studies of a PVP-Capped Platinum Nanocatalyst Immobilized on Silica & Factors Affecting Activity and Selectivity during Cyclohexanone Hydrogenation with Colloidal Platinum Nanocatalysts.
The research in this funded project was aimed at comprehending how catalyst structure (particle size, polymer molecular weight, and immobilization) and reaction conditions (temperature, pressure, and concentration) affect activity and selectivity in the aqueous-phase hydrogenation of cyclohexanone using colloidal platinum nanocatalysts. The project goals were accomplished through a combination of nanocatalyst synthesis and characterization, catalytic reaction studies, and spectroscopic identification of adsorbed surface species. PVP-stabilized Pt nanocatalysts were synthesized in the 1-10 nm size range using published literature methods, and then characterized using transmission electron microscopy (TEM) and infrared (IR) spectroscopy.
After characterization, hydrogenations were performed using a Parr 4566 mini benchtop batch reactor, and we monitored product formation by gas chromatography/mass spectrometry (GC/MS). In all reactions carried out, 100% selectivity was observed for cyclohexanol formation; no side products from dehydrogenation reactions were found. Measured turnover frequencies were found to increase with increasing particle size, but showed no trend with regards to polymer molecular weight. From the results of our temperature studies, calculated apparent activation energies indicate the rate of reaction increases with temperature for each particle size. Pressure studies indicate the reaction order with respect to hydrogen is 0.3, whereas concentration studies indicate the reaction order with respect to cyclohexanone is 0.8. The rate law incorporating these orders is consistent with a Langmuir-Hinshelwood mechanism in which both molecules have low adsorption and one of the molecules (hydrogen) exhibits dissociative adsorption. Results from ATR-IR experiments performed during hydrogenation support our determined rate law. The effect of immobilizing the nanocatalysts on an oxide surface on the catalytic activity for cyclohexanone hydrogenation was investigated. Catalytic activity of this material for the hydrogenation of cyclohexanone was found to be greater than that of colloidal PVP-capped platinum nanocatalysts. In addition, the immobilized nanocatalyst displayed no change in activity after being recycled.
Our findings have shown that nanocatalyst properties (particle size and support) and reaction conditions (temperature) may be tuned to control catalytic activity. In addition it has been shown that it is possible to perform liquid-phase hydrogenation reactions in a "green" solvent such as water with high activity and selectivity.