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

摘要

Nanometric carbon-supported catalysts based on cobalt and iron (Co/C, Fe/C and Co-Fe/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 H_2 and 30% mol fraction CO at 1.0 cm~3s~(-1)g~(-1) of catalyst for 24 h. Prior to this, the catalysts were pre-treated at 673 K either in pure H_2 or CO flowing at 250 cm~3 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 (C4-C12) and diesel (C13-C20) fractions, since production of undesired products such as CO_2 and CH_4 was prevalent at higher temperatures. At 493 K, the Co-Fe/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 CO_2 and CH_4 production. Moderated H_2O production was witnessed in the CO-reduced catalysts, contrasting with catalysts pre-treated in H_2 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 inter-metallic Co-Fe species in the carbon matrix support.