Promotional effect of Mo and Ni in plasma-synthesized Co–Fe/C bimetallic nano-catalysts for Fischer–Tropsch synthesis

Abstract

Abstract Two carbon-supported Fischer–Tropsch Synthesis (FTS) catalysts with ternary metallic formulations (10% Mo–70% Co–20% Fe and 10% Ni–70% Co–20% Fe) were synthesized through suspension plasma-spray (SPS) technology. Their average particle size determined by Transmission Electron Microscopy was 8.4 and 13.3 nm respectively and their BET specific surface areas were between 69–85 m2 g−1. As their analogous monometallic and bimetallic formulations presented in previous publications, these catalysts were both non-porous and nanometric with Scanning Electron Microscopy showing uniform metal-nanoparticle distribution in the carbon-support matrix. FTS test conditions in a 3-phase continuously stirred-tank slurry reactor operated for 24 h were: 260 °C, 2 MPa pressure, H2:CO = 2, gas hourly specific velocity = 3600 cm3 h−1 g−1 of catalyst. Basing catalyst performance on the bimetallic 80% Co–20% Fe/C catalyst, Ni-addition enhanced catalyst activity from ∼42 to 50% CO conversion, and boosted selectivity towards gasoline fraction (C5–C12) from ∼19 to 50%. Enriching the catalyst-surface acidity by Mo-promotion improved selectivity for both gasoline-fraction (19 → 33%) and the C5–C20 fraction (74 → 87%) and lowered H2O production by 30%, although at lower CO conversion (∼38%). The catalysts’ α-values were ∼0.8 in the C10+ region, and from mass balance their estimated H2 efficiency decreased in the order of Mo–Co–Fe/C >> Co-Fe/C > Ni–Co–Fe/C.