Microwave treatment: A facile method for the solid state modification of potassium-promoted iron on silica Fischer-Tropsch catalysts

Abstract

Potassium-promoted (0-1.5 wt%) iron-silica catalysts for Fischer-Tropsch synthesis (FTS) have been modified using microwave radiation. Radiation produced few or no modifications in the bulk properties, but surface and catalytic behaviour were markedly changed in K promoted 10 wt% of Fe/SiO2 (10Fe/SiO2) catalysts. The effect of potassium on CO adsorption was relatively insignificant in untreated catalysts, but was large in microwave-modified catalysts. Radiation induced an increase in CH4 formation in CO + H2 temperature programmed surface reactions. Microwave treatment promoted CH4 formation from graphitic carbon in these catalysts, while decreasing CH4 formation from α- and β-carbon species, and overall favoured strong CO adsorption onto the catalyst surface. Microwave effects were catalyst particle size and treatment duration-dependent. At low alkali concentration, microwaved samples showed improved ethene selectivities, higher alpha values and lower methane and light alkene selectivities. When 0.7 wt% K was added to the 10Fe/SiO2 catalyst, the α value increased from 0.59 to 0.66 after treatment of the sample with microwave radiation in the solid state.