Influence of Reduction Promoters on Stability of Cobalt/g-Alumina Fischer-Tropsch Synthesis Catalysts

Abstract

This focused review article underscores how metal reduction promoters can impact deactivation phenomena associated with cobalt Fischer-Tropsch synthesis catalysts. Promoters can exacerbate sintering if the additional cobalt metal clusters, formed as a result of the promoting effect, are in close proximity at the nanoscale to other cobalt particles on the surface. Recent efforts have shown that when promoters are used to facilitate the reduction of small crystallites with the aim of increasing surface Co 0 site densities (e.g., in research catalysts), ultra-small crystallites (e.g., <2-4.4 nm) formed are more susceptible to oxidation at high conversion relative to larger ones. The choice of promoter is important, as certain metals (e.g., Au) that promote cobalt oxide reduction can separate from cobalt during oxidation-reduction (regeneration) cycles. Finally, some elements have been identified to promote reduction but either poison the surface of Co 0 (e.g., Cu), or produce excessive light gas selectivity (e.g., Cu and Pd, or Au at high loading). Computational studies indicate that certain promoters may inhibit polymeric C formation by hindering C-C coupling.

Effect of CO Concentration on the α-Value of Plasma-Synthesized Co/C Catalyst in Fischer-Tropsch Synthesis

“…For example, precious metals like Au [23], and Pt [24], or in some cases, Ru have been employed to create multi-component catalysts such as (Ru + Co + Mn/Zr/SiO 2 ) to enhance Co reducibility [25]. This alters catalyst activity and selectivity or the catalyst's preference for a specific reaction mechanism [26], although some elements acting as promoters have been observed to aggravate metal particle sintering of the metal nanoparticles [27]. Other complex catalyst formulations such as carbon-supported cobalt manganese oxide (CoMnO x ) catalysts [28], are currently being developed.…”

Lump Kinetic Analysis of Syngas Composition Effect on Fischer-Tropsch Synthesis over Cobalt and Cobalt-Rhenium Alumina Supported Catalyst

“…Compared to study by Jacobs et al [14] in Table 8, addition of 0.48%-wt rhenium promoter in 25%-wt supported alumina cobalt catalyst (0,48%Re-25%Co/Al2O3) results in product selectivity changes relatively around 0.70 to 2.60% [14]. In 0.05%Re-12%Co/Al2O3, rhenium promoter increases 1-2% reactant conversion.…”

H2-TPR, XPS and TEM Study of the Reduction of Ru and Re promoted Co/γ-Al2O3, Co/TiO2 and Co/SiC Catalysts

“…/g for TiO 2 ) were higher prior to impregnation of metals, as expected. By assuming that the total surface areas comes from the supports the addition of 20 mass % of cobalt would lead to a corresponding 20% decrease in specific surface areas , Jacobs et al, 2014. This would lead to the surface areas of 156 m The measured values are slightly below the measured surface area of the support prior to impregnation with metals, a fact that indicates some degree of pore clogging.…”