Synthetic fuels from 3-φ Fischer-Tropsch synthesis using syngas feed and novel nanometric catalysts synthesised by plasma

Abstract

Nanometric carbon-supported catalysts based on cobalt and iron (Co/C, Fe/C and CoFe/C) were synthesised by plasma method for application in Fischer-Tropsch synthesis (FTS). FTS tests were conducted at reaction conditions (ca 533 K, 2 MPa) over the catalyst, in a feed stream of 60% mol fraction H2 and 30% mol fraction CO at 1.0 cm3s−1g−1 of catalyst for 24 h. Prior to this, the catalysts were pre-treated at 673 K either in pure H2 or CO flowing at 250 cm3 min−1 for 24 h. Results showed that higher temperature promoted better CO conversion; up to 100% for the Co/C catalyst at 533 K. However, lower temperatures were more conducive for the selectivity of Co/C catalyst towards gasoline (C4C12) and diesel (C13C20) fractions, since production of undesired products such as CO2 and CH4 was prevalent at higher temperatures. At 493 K, the CoFe/C bimetallics were almost inert, but at 533 K, they showed improved CO conversion. When compared to the Co/C catalyst, Fe-containing catalysts suppressed both CO2 and CH4 production. Moderated H2O production was witnessed in the CO-reduced catalysts, contrasting with catalysts pre-treated in H2 gas. Catalyst characterisation by BET surface area, XRD analysis and microscopy (SEM & TEM) showed that plasma synthesis produces catalysts with consistency, having highly dispersed nanoparticle metal moieties, interspersed with various forms of metallic, carbidic and intermetallic CoFe species in the carbon matrix support.