Carbon species on the surface of carbon-coated catalysts and their effects on Fischer-Tropsch synthesis products

Abstract

Carbon coated cobalt core–shell catalysts with different coating thickness were prepared by acetylene dissociation at different temperatures, the carbon coating had significant cutting effects on the Fischer-Tropsch synthesis (FTS) products. Further, different carbon species remained on the surface of carbon coated catalysts with adjusting the hydrogenolysis temperature (250, 400, 600 and 700 °C, respectively). Accordingly, the catalyst structure was optimized, the selectivity of C1 ∼ C4 was reduced, while the CO conversion increased, the products in the range of C5 ∼ C12, C13 ∼ C20 and C5 ∼ C20 were obtained with high selectivity. The carbon species were discerned by elemental analysis, temperature programmed hydrogenation, Raman spectra, X-ray photoelectron spectroscopy, H2 temperature programmed reduction and H2 thermogravimetry. The roles of different carbon species in FTS were elucidated, and the relationships between carbon species and FTS products selectivity were studied in detail. The deposited carbon blocks the active center, while graphitic carbon does not block the active center, nor limit the conversion rate of CO, but only limits the diffusion of long chain products.