Synthesis and characterization of bimetallic nanocatalysts for fisher-tropsch synthesis

Abstract

Fischer-Tropsch Synthesis (FTS) enables conversion of syngas obtained from a wide variety of carbon feedstocks, to certain liquid fuels and chemicals. This synthesis is a heterogeneously catalyzed process, where cobalt (Co) and iron (Fe) are the main catalyst materials that are being used commercially. FTS is a combination of carbon monoxide (CO) reduction and a polymerization reaction. This nature of FTS causes the product spectrum to contain a wide variety of hydrocarbons and this requires post-processing to isolate desired products. As for all catalyst, FTS catalyst should have high activity, selectivity, and long operation life. To address these issues, nanocrystals with different composition, size, and geometry are being implemented as catalyst materials. The mentioned parameters play key roles in determining the type of surface sites, distribution of them and electronic structure of catalytically active atoms. This study focuses on creating a library of bimetallic core-shell nanoparticles with catalytically active shells (e.g. Fe, Co, and Fe0.5Co0.5) for FTS and tin (Sn) core. There are reasons for choosing tin as a core material: (i) tin can have oxidation states varying from +4 to -4. This property can change the behavior of shell material towards FTS since this process involves reversible oxidation steps of the catalyst. (ii) Through charge transfers between the tin core and the metal in the shell, the electronic structure of the surface would be modified. (iii) Since tin has relatively large lattice constant compared to Co and Fe, it will induce strain on the surface atoms and that would change the energetics of the surface. For the synthesis, a modified polyol process is implemented due to its simplicity, versatility, and relatively low cost. The characterizations of the synthesized nanoparticles were performed by High-Resolution Transmission Electron Microscopy (HRTEM), X-Ray Diffraction spectroscopy (XRD) and X-Ray Photoelectron Spectroscopy (XPS). At the end of the study, it is concluded that the desired nanoparticles can be synthesized by the employed synthesis method.