Insight of the effect of Fe content in Fe/biochar on the conversion of syngas to olefins via Fischer-Tropsch synthesis

Herein, a series of Fe-based biochar catalysts (xFe/WSBC) were synthesised via impregnation using wheat straw as a carbon precursor and applied to the Fischer–Tropsch synthesis of olefins (FTO) from syngas. Various characterisations of fresh catalysts demonstrated that Fe content significantly affected the dispersion of iron particles and the surface distribution of Fe 3 + /Fe 2+ . Among the samples, 5Fe/WSBC exhibited the highest surface Fe 3+ /Fe 2+ ratio and thus the lowest surface electron density, which enhanced the adsorption and activation of H 2 . In addition, an appropriate amount of the Fe additive (5 wt%) significantly decreased the Fe 3 O 4 particle size, which promoted the continuous reduction and carbonisation processes during FTO to generate iron carbide phases, which boosted CO activation and the subsequent C–C coupling. Therefore, 5Fe/WSBC exhibited the highest CO conversion (46.9 %) and iron time yield (348.9 μmol CO ·g Fe −1 ·s −1 ) as well as the major enhancement of selectivity to light olefins (C 2 = –C 4 = ). The results for the used catalysts demonstrated that 5 wt% Fe clearly inhibited the sintering of iron particle size and improved the catalytic stability of FTO.