The structure-activity relations in the alumina-supported cobalt catalysts are studied at the realistic conditions of Fischer-Tropsch synthesis using in situ time-resolved XRD and catalytic measurements. Cobalt sintering during the first 3-5 h of the reaction and cobalt carbidisation at a longer time on stream (>8 h) coincide with catalyst deactivation.

A three-step sintering mechanism is proposed for Co-based catalysts under Fischer–Tropsch reaction conditions. This mechanism includes an intermediate formation of oxide layer on cobalt metal nanoparticles in the presence of water. The partially reversibly oxidized surface accelerates sintering by both reducing the surface energy and enhancing the diffusion rates of cobalt particles. The proposed mechanism is then employed for a fixed-bed unsteady state reactor. The effect of particle growth on the catalytic activity was analyzed within a diverse range of operating conditions (syngas ratio = 1.5–4, water co-feed ratio = 0–6, inert co-feed ratio = 0–6). It is found that, at the same gas space velocity, sintering proceeds faster at higher H2/CO ratios. At the same initial conversion, a low H2/CO syngas ratio increases sintering severity, i.e., catalyst deactivation due to the crystallite growth, as it brings about higher relative water partial pressure. Dilution of syngas with different amounts of inert gas does not affect the cobalt sintering rate. Cobalt sintering proceeds more rapidly if water is co-fed during the reaction.

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Strong bifunctional performance was observed on a ZSM-5 seed-grafted SBA-15 supported cobalt catalyst reacted at 260 °C in FTS.

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Carbon materials have attracted increasing attention as supports for metal catalysts. Ironcontaining carbon nanotubes often promoted with copper have found application in Fischer-Tropsch synthesis, which provides an alternative way for conversion of renewable feedstocks to chemicals and fuels. In carbon nanotubes, the active phase can be nanoconfined inside the channels or localized on the outer surface. In most of previous work, the distribution of metal nanoparticles inside or outside carbon nanotubes is considered to be immobile during the catalyst activation or catalytic reaction.In this paper, we uncovered remarkable mobility of both iron and copper species in the bimetallic catalysts between inner carbon nanotube channels and outer surface, which occurs in carbon monoxide and syngas, while almost no migration of iron species proceeds in the monometallic catalysts. This mobility is enhanced by noticeable fragility and defects in carbon nanotubes, which appear on their impregnation with the acid solutions of metal precursors and precursor decomposition. Remarkable mobility of iron and copper species in bimetallic catalysts affects the genesis of iron active sites, and enhances interaction of iron with the promoter. In the bimetallic iron-copper catalysts, the major increase in the activity was attributed to higher reaction turnover frequency over iron surface sites located in a close proximity with copper.

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Mesoporous cellular silica foams (MCF) have 3D pore networks in which large spherical cell pores interconnect with small window pores. This novel characteristic provides an open pore structure that favors the accessibility of reactants and mass transfer in reactions. In this work, MCF was functionalized by assembling ZSM‐5 seeds to improve the acidity and the ZSM seed was found to disperse in the MCF structure homogeneously (MCF‐Z). The obtained MCF‐Z materials showed high surface acidity and were then used as supports for cobalt Fischer–Tropsch synthesis (FTS) bifunctional catalysts (20 wt % Co). Compared with Co/MCF catalyst, the Co/MCF‐Z catalysts showed higher CO conversion and improved durability in FTS at 260 °C and 1.0 MPa. Moreover, on increasing the amount of ZSM‐5 seed, the activity of Co/MCF‐Z catalysts gradually increased and then decreased. Co/MCF‐Z catalyst assembled with the highest amount of ZSM‐5 seed (Al/Si=1.5 %, molar ratio) exhibited the lowest deactivation rate, which was owing to the superior stability of the MCF‐Z support and an increased interaction between cobalt and MCF‐Z. The Co/MCF‐Z bifunctional catalyst showed higher iso‐paraffin/n‐paraffin ratios, higher olefin/paraffin ratios as well as lower C2–C4 alcohol selectivity in comparison to Co/MCF catalyst. For the Co/MCF‐Z catalyst, the decrease in space velocity led to hydrocarbon selectivity shifting toward middle distillate products.