(351c) A Model Cobalt/Silica Fischer Tropsch Nanocomposite Catalyst Preparation by Surface Functionalization
Growing concerns of pollution, in addition to the rapidly depleting oil reserves, motivate research in catalytic technologies for production of clean synthetic hydrocarbon fuels such as Fischer Tropsch Synthesis (FTS). Cobalt metal is known for its FTS catalytic activity, selectivity, stability and relatively lower negative effect of water-gas shift reaction than iron-based FTS catalysts. In the quest for improvement of FTS activity, a rational strategy to achieve high throughput is to enhance cobalt dispersion and surface-to-volume ratio by decreasing the average cobalt nanoparticle size. However, literature reports on FTS activity are scattered and controversial for cobalt nanoparticles especially in the 2-12nm regime. We have focused on the synthesis of novel nanocomposite colloids such as surface modified silica supports that are decorated with nanoparticles of cobalt of different sizes. Conventional methods of preparation that rely on reduction of cobalt precursor to metallic cobalt at high temperatures (~350-700oC) and pose challenges due to catalyst deactivation from the sintering of pores of the support, agglomeration of cobalt nanoparticles, and reaction with the silica support to cobalt silicates. Cobalt nanoparticles with extended stability in solution are synthesized by thermal decomposition of a cobalt pre-cursor. The nanoparticle size can tuned by changing the reaction conditions and then be easily immobilized onto the surfaces of silica micro-particles that are surface modified with both small ligands and polymer chains. The interaction of cobalt nanoparticles with the modified silica depends upon parameters such as the functional groups of the small molecule ligands and polymer chains as well as the cobalt precursor and solvent medium that are used. Our method not only avoids the limitations of conventional impregnation techniques but also provides several benefits such as increased availability of monodisperse cobalt nanoparticles on the surface of the silica supports, ease of preparation, and manipulation of cobalt loading. Our goal is to use in situ FTIR techniques to study the impact of cobalt nanoparticle size in actual FTS reaction conditions. In this presentation, the various methods of preparation will be discussed along with the characterization of the novel nanomaterial using FTIR spectroscopy, X-ray diffraction, dynamic light scattering, electron microscopy, temperature programmed reduction and hydrogen chemisorption.