Characterization of Alumina and Silica Sol-Gel Encapsulated Fe/Co/Ru Nanocatalysts in Microchannel Reactors for F-T Synthesis of Higher Alkanes

Abstract

We have been investigating conversion of syngas (CO: H₂) to higher alkanes [Fischer-Tropsch (F-T) Process] in 5 μm and 25 μm channel microreactors coated with sol-gel encapsulated Fe/Co-nanocatalysts. These nano-metal-catalysts were incorporated into the sol-gel matrix by two methods: 1) metal nitrate solutions; 2) metal oxide nanoparticles. Characterization of these catalysts containing Co and Fe in alumina and silica sol-gel has been carried out by several techniques. The surface area measurements by BET method show an average specific surface area of 285 m²/g for alumina and 300 m²/g for silica sol-gel encapsulated catalysts. In order to optimize the sol-gel preparation and deposition in the microchannels, the elemental composition of sol-gel encapsulated catalyst was examined by EDX. The SEM and AFM images of the reactors before and after deposition of the catalysts have also been studied. Hydrogenation-reduction efficiency of the activated Fe-Co catalysts and the level of poisoning after the reaction were estimated using a vibrating sample magnetometer (VSM). The result suggests more efficient reduction in the case of the nano-particle metal oxides compared to that derived from metal nitrate solutions. In overall, 85% of the catalyst is poisoned after 25 hrs of catalytic reaction. The surface area and the syngas conversion results indicate that silica sol-gel matrix may be a better catalyst support. For alumina sol-gel support, higher conversion of syn-gas is observed with 25 μm microreactor channels. For silica sol-gel, syngas conversion as high as 73% has been achieved by adding Ru as a promoter to the Fe/Co catalyst mixture.