Stabilization of iron by manganese promoters in uniform bimetallic FeMn Fischer–Tropsch model catalysts prepared from colloidal nanoparticles

Abstract

A systematic study was carried out to investigate the response of monodisperse supported Fe and FeMn nanoparticles to treatments in O2, H2 and H2/CO at temperatures between 270 and 400°C. Uniform size (7–14 nm), Fe and mixed FeMn nanoparticles were synthesised by applying thermal decomposition of Fe- and Mn-oleate complexes in a high boiling point solvent. By combining X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) analysis, the phase composition and morphology of the model catalysts were studied. Energy-dispersive X-ray analysis shows that the catalyst particles have the expected composition of Fe and Mn. Well-defined crystallite phases [maghemite (γ-Fe2O3) and mixed FeMn-spinel] were observed after calcination at 350°C in Ar/O2 using XPS analysis. Upon subsequent treatments in H2 and H2/CO the crystal phases changed from maghemite (γ-Fe2O3) to metallic Fe, Fe carbide and graphitic C. Using Mn as a promoter influences the nanoparticle size achieved during the fabrication of Fe nanoparticles and improves their stability against morphological change and agglomeration during reduction and Fischer–Tropsch synthesis conditions.