On the Way to a More Open Porous Network of a Co–Re/Al2O3 Catalyst for Fischer–Tropsch Synthesis: Pore Size and Particle Size Effects on Its Performance

Abstract

Five different c-alumina supports were used, one commercial and four prepared in a macro-mesoporosity range of 7-1000 nm by different preparation methods. A simple method was used to obtain a macromesoporous alumina support by modification of an initial commercial mesoporous alumina with a pore generating agent. Supports were used to prepare Fischer-Tropsch synthesis (FTS) catalysts. Supports and catalysts were characterized by several techniques and tested in a labscale fixed-bed reaction unit in the FTS at 493 K and 2 MPa, with small (\63 lm) and large (500-710 lm) catalyst particle size (PS). Catalytic results showed that with small catalyst PS, the behavior is similar among them. With large catalyst PS, C 5? selectivity considerably decreased and CH 4 selectivity increased for all catalysts due to diffusional restrictions. Nevertheless, the effect of diffusion limitations of reactants and products through catalyst pores were lower for catalysts with a higher mesoporosity (20-50 nm), and much lower for the catalyst obtained when the support was modified to add macroporosity between 100 and 1000 nm. These macropores improve the transport of reactants and heavy hydrocarbons produced between the gaseous phase and the active sites. As a consequence, a better performance of the catalyst is attained, reducing the non-desirable effects of a diffusionlimited regime.

Fischer–Tropsch synthesis over a 3D foamed MCF silica support: Toward a more open porous network of cobalt catalysts

“…1). These novel pore structures minimize the mass transfer limitation of reactants during catalyst preparation and reactions, which improves the metal dispersion and the contact frequency between reactants and active sites, leading to improved catalytic performance [20]. Mass transfer limitation is an important factor affecting catalyst performance (activity and hydrocarbon selectivity) in FTS because a CO/H 2 ratio gradient may exist due to the different diffusion rates of CO and H 2 along a long, small pore channel.…”

Effects of macropores on reducing internal diffusion limitations in Fischer–Tropsch synthesis using a hierarchical cobalt catalyst

“…However, the effects of the diffusion limitations were much lower for the catalyst obtained when the support was modied to add macropores between 100 and 1000 nm. 17 T. Witoon et al also obtained similar results using meso-macroporous silica-supported cobalt catalysts. 18 They found that with large catalyst particles (650 to 850 mm), the C 5+ selectivity of cobalt supported on meso-macroporous silica was much higher than that on unimodal mesoporous silica.…”

The interplay of polyoxyethylene (40) stearate surfactant concentration and aging time on the Mesoporous γ-alumina synthesis and appraisal of its catalytic activity

“…1 [17]. The similarity in the diffractogram indicates that the alumina phase is not considerably influenced by the PS amount [29]. Nevertheless, a slight improvement in crystallinity with increasing PS concentration is observed.…”