Graphene-Supported, Iron-Based Nanoparticles for Catalytic Production of Liquid Hydrocarbons from Synthesis Gas: The Role of the Graphene Support in Comparison with Carbon Nanotubes

Fischer-Tropsch synthesis (FTS) is a potentially attractive technology for the production of clean liquid fuels from synthesis gas. The efficiency and selectivity of FTS can be enhanced by the design of new active catalyst systems with improved selectivity for long-chain hydrocarbons and low methane production. In this paper, we introduce a new class of FT catalysts supported on the high surface area graphene nanosheets and report on their high activity and selectivity for the production of long-chain hydrocarbons. The chemical reduction of graphene oxide in water in the presence of the metal salts under microwave irradiation allows the deposition of well-dispersed surface-oxidized metal nanoparticles on the defect sites of the graphene nanosheets. The Fe-K-nanoparticle catalyst supported on graphene exhibits high activity and selectivity toward C-8 and higher hydrocarbons with excellent stability and recyclability. In comparison with other carbon supports, such as carbon nanotubes, the graphene support shows a unique tendency for minor formation of the low-value and undesirable products methane and carbon dioxide, respectively. The water-gas shift activity is reduced on the graphene support as compared with CNTs, and as a result, the formation of CO2 is significantly reduced. Evidence is presented for the formation of the active Fe5C2 iron carbide phase during the FTS on the graphene-supported Fe catalysts. The high activity and selectivity of the catalysts supported on graphene are correlated with the presence of defects within the graphene lattice that act as favorable nucleation sites to anchor the metal nanoparticles, thus providing tunable metal support interactions. Given the activity, selectivity, and stability of the new graphene-supported, Fe-based nanoparticle catalysts, their industrial application appears to be promising. Controlling the nature and density of the defect sites in graphene could lead to improved understanding of the catalyst graphene interactions and to further enhancement of the performance of these catalysts for the production of liquid fuels.