(683e) Effect of Controlled Activation and Diffusion Length Manipulation On the Selective Catalytic Performance of Carbon Spheres-Based Catalyst

In this study, platinum embedded in carbon spheres was synthesized by emulsion polymerization of furfuryl alcohol in the presence of pre-formed platinum nano particles and Pluronic F-127 as the surfactant. Polyfurfuryl alcohol spheres synthesized using this approach, were pyrolyzed to form carbon spheres containing platinum nano particles as the active catalytic sites. Catalyst activity and selectivity was evaluated using hydrogenation of liquid alkenes as a probe reaction. Although the selectivity for linear and branched alkenes was significant, catalyst suffered from low activity compared to impregnated catalyst. Mass transfer limitation due to complete microprosity of the carbon spheres lowers the effectiveness factor of the catalyst for liquid phase reactions. To improve catalyst activity, different approaches were applied. To shorten the diffusion length and make more of the active sites accessible to reactant molecules, surfactant concentration was changed during synthesis. Three different sizes, 280, 220 and 170 nm of carbon spheres were synthesized and tested in hydrogenation reaction of liquid alkenes. It was found that catalyst activity is correlated with carbon spheres size (diffusion length). Decreasing the diffusion length increased the catalyst activity and led to lower selectivity in hydrogenation of linear and branched alkenes. Another approach which was used to further improve catalyst activity and retain the selectivity, was to open up the porosity in the carbon structure by controlled activation under CO₂. It is crucial to optimize the extent of carbon activation to avoid significant loss in selectivity.

Pore size distribution of the synthesized catalyst was measured by methyl chloride gas adsorption. Transmission electron microscopy was used to measure platinum nano particles size and evaluate the dispersion. Scanning electron microscopy was used to measure the average size of the carbon spheres. All the reactions were carried out in a low pressure batch Parr reactor. Samples were analyzed using a Varian GC equipped with a FID.