Platinum embedded within carbon nanospheres for shape selective liquid phase hydrogenation

Reactant shape selective catalysis occurs when substrates of different sizes and shapes are consumed at different rates over catalysts that combine molecular sieving transport processes with reaction. By contrast the same substrates react at nearly equivalent rates over catalysts that have large, open pores that do not induce any form of molecular sieving. Here we describe the design and synthesis of reactant shape selective catalysts for liquid phase hydrogenation reactions. Using an emulsion polymerization of furfuryl alcohol, we have made catalysts that consist of microporous carbon nanospheres within which are embedded platinum nanoparticles. The porosity of the carbon spheres was found to be a key parameter affecting catalyst activity and selectivity; porosity was varied by adding pore forming agents, such as polyethylene glycol with different molecular weights, during synthesis, or by mild oxidation of the as-synthesized catalyst using carbon dioxide. In addition to increasing porosity to reduce mass transfer limitations, a synthesis of smaller carbon spheres (<200 nm) was devised to reduce the micropore diffusion length. Decreasing the particle size of the catalyst by adjusting the surfactant composition during polymerization, improved the effectiveness factor by approximately one order of magnitude making it as active as a comparable standard metal catalyst.