Fischer-Tropsch synthesis on potassium-modified Fe₃O₄ nanoparticles

Synthesized magnetite (Fe₃O₄) nanoparticles, with an average crystallite size of 8 and 22 nm, were investigated for Fischer-Tropsch synthesis reaction to clarify the effects of iron crystallite size and a potassium promoter. The larger crystallite size of Fe₃O₄ without the potassium promoter showed an increased CO conversion with a lower selectivity of C₅+ and olefinic hydrocarbons. This was mainly attributed to the enhanced reduction degree and an abundance of active edge sites of cube-like morphology. However, a modification of Fe₃O₄ nanoparticles with the potassium promoter significantly changed the product distribution by increasing C₅+ and olefinic hydrocarbons with much higher CO conversions. The enhanced activity on the large crystallite size of K-modified Fe₃O₄ was mainly attributed to an enhanced secondary reaction of olefins formed on the active iron carbide sites. The positive effect of the potassium promoter was much significant on the larger Fe₃O₄ nanoparticles due to an abundant presence of potassium promoter on the outer surface of the large Fe₃O₄ nanoparticles with a bigger inter-particular pore diameter for an easy mass transport.