High‐temperature Fischer–Tropsch synthesis for the production of short‐chain olefins over iron catalysts supported on multiwalled carbon nanotubes (CNTs) was investigated under industrially relevant conditions (340 °C, 25 bar, H2/CO=1) to elucidate the influence of nitrogen and oxygen functionalization of the CNTs on the activity, selectivity, and long‐term stability. Surface functionalization of the CNTs was achieved by means of a gas‐phase treatment using nitric acid vapor at 200 °C for oxygen functionalization (O‐CNTs) and ammonia at 400 °C for the subsequent nitrogen doping (N‐CNTs). Ammonium iron citrate impregnation followed by calcination was applied for the deposition of iron nanoparticles with particle sizes below 9 nm. Subsequent to reduction in pure H2 at 380 °C, the Fe/N‐CNT and Fe/O‐CNT catalysts were applied in Fischer–Tropsch synthesis, in which they showed comparable initial conversion values with an excellent olefin selectivity [S(C3–C6)>85 %] and low chain growth probability (α≤0.5). TEM analysis of the used catalysts detected particle sizes of 23 and 26 nm on O‐CNTs and N‐CNTs, respectively, and Fe5C2 was identified as the major phase by using XRD, with only traces of Fe3O4. After 50 h time on stream under steady‐state conditions, an almost twofold higher activity compared to the Fe/O‐CNT catalysts had been maintained by the Fe/N‐CNT catalysts, which are considered excellent Fischer–Tropsch catalysts for the production of short‐chain olefins owing to their high activity, high selectivity to olefins, low chain growth probability, and superior long‐term stability.

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The adsorption of carbon monoxide on an either unpromoted or potassium-promoted bulk iron catalyst was investigated at 303 K and 613 K by means of pulse chemisorption, adsorption calorimetry, temperature-programmed desorption and temperature-programmed surface reaction in hydrogen. CO was found to adsorb mainly molecularly in the absence of H(2) at 303 K, whereas the presence of H(2) induced CO dissociation at higher temperatures leading to the formation of CH(4) and H(2)O. The hydrogenation of atomic oxygen chemisorbed on metallic iron was found to occur faster than the hydrogenation of atomically adsorbed carbon. At 613 K CO adsorption occurred only dissociatively followed by recombinative CO(2) formation according to C(ads) + 2O(ads)→ CO(2(g)). The presence of the potassium promoter on the catalyst surface led to an increasing strength of the Fe-C bond both at 303 K and 613 K: the initial differential heat of molecular CO adsorption on the pure iron catalyst at 303 K amounted to 102 kJ mol(-1), whereas it increased to 110 kJ mol(-1) on the potassium-promoted sample, and the initial differential heat of dissociative CO adsorption on the unpromoted iron catalyst at 613 K amounted to 165 kJ mol(-1), which increased to 225 kJ mol(-1) in the presence of potassium. The calorimetric CO adsorption experiments also reveal a change of the energetic distribution of the CO adsorption sites present on the catalyst surface induced by the potassium promoter, which was found to block a fraction of the CO adsorption sites.

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