Concepts of the surface excess energy in the present work have been applied to explain the methane formation in Fischer-Tropsch synthesis by iron catalysts. A series of iron oxide particles doped by adding copper and lanthanum were prepared as a catalyst via precipitation by microemulsion method. Size dependent kinetic expressions for methane formation were derived and evaluated using experimental results. Experimental results show that the methane formation is increased by decreasing the catalyst particle size. The value of surface tension energy (σ) for iron catalyst is calculated in range of 0.047-0.015 J/m2 in methane formation mechanism. This value is lower than iron metal and is referred to the presence of iron carbide and gas phase in this catalytic reaction. With a series of complicated mechanisms, methane is produced on the surface of catalyst and in the gas phase as well, this would be elaborated by following paragraphs, thus we can conclude that surface tension of catalyst has less effect on these reactions.

Keywords