Fischer-Trospch Synthesis on Ordered Mesoporous Cobalt-Based Catalysts with Compact Multichannel Fixed-Bed Reactor Application: A Review

Ordered Mesoporous Co3O4−Al2O3Binary Metal Oxides for CO Hydrogenation to Hydrocarbons: Synergy Effects of Phosphorus Modifier for an Enhanced Catalytic Activity and Stability

“…A regular mesopore size of 5 nm on all the fresh P/m-CoAl was originated from the wall thickness of the hard-template of KIT-6, and a small peak intensity appeared at~14 nm in size was mainly attributed to the inter-particular pores, which was attributed to the partially disintegrated structures of the m-CoAl. [13][14][15][16][17]26] The significantly reduced surface area and pore volume as well as slightly increased average pore diameter on the fresh P/m-CoAl at a higher phosphorous content could be possibly attributed to the preferential deposition of phosphorous species on the outer surfaces of the m-CoAl, which can form the much denser SiO 2like AlPO 4 phases. [19][20][21][22][23][24] The ordered mesoporous structures of the P/m-CoAl were also verified by a small-angle X-ray scattering (SAXS) analysis, and the SAXS peaks are displayed in supplementary Figure S2.…”

“…The calculated crystallite sizes of the Co 3 O 4 using the most intense peak at 2θ = 36.9°were found to be in the range of 11.7-12.5 nm with small variations, which can be originated from the grain size of the Co 3 O 4 À Al 2 O 3 frameworks. [13][14][15][16][17]26] The possible formations of spinel-type cobalt aluminate (CoAl 2 O 4 ) on the fresh P/m-CoAl were not clearly observed due to its similar diffraction peak positions with Co 3 O 4 species. [28,29] The calculated crystallite sizes of metallic cobalt (Co 0 ) on the fresh P/m-CoAl using a volume contraction correlation of d(Co 0 ) = 0.75d(Co 3 O 4 ) [30] were found to be larger in the range of 8.7-9.4 nm than the critical sizes of 8 nm, which was well known to be a minimum size of metallic cobalt nanoparticles to show the structure insensitive natures and water resistance of the active metallic cobalt species during FTS reaction.…”

“…However, the direct applications of those ordered mesoporous transition metal oxides were so difficult for FTS reaction because of their intrinsically unstable structures by an easy phase transformation from cobalt oxides to metallic states. [6,[12][13][14] Based on our previous works, [14][15][16][17][18] the highly ordered mesoporous metal oxides structures were successfully preserved under a reductive FTS reaction condition by introducing irreducible metal oxide pillaring materials such as alumina or zirconia or by preparing binary mixed metal oxides incorporated with those irreducible metal oxides. These structural stabilities were mainly attributed to the partial formation of thermally stable spinel-type metal aluminates at an optimal molar ratio of M/Co = 0.25 (M = Al or Zr).…”

“…These structural stabilities were mainly attributed to the partial formation of thermally stable spinel-type metal aluminates at an optimal molar ratio of M/Co = 0.25 (M = Al or Zr). [13][14][15][16] In addition, the synergy effects of phosphorous species on Co/Al 2 O 3 catalysts were also reported by our previous extensive works, [19][20][21][22][23] and a superior catalytic activity on the phosphorusmodified Al 2 O 3 was observed with an improved activity and stability with less aggregation of the supported cobalt nanoparticles by partially forming hydrophobic aluminum phosphate (AlPO 4 ) species, [19][20][21] The partially formed AlPO 4 phases on the outermost γ-Al 2 O 3 surfaces inhibited the transformation of cobalt oxides to inactive cobalt aluminates due to its SiO 2 -like tridymite hydrophobic AlPO 4 surface natures by altering metal-support interactions through a stronger affinity between Al and P species than that of Al and Co species. [24] Those AlPO 4 phases can also effectively prevent the re-oxidation and aggregation of the supported cobalt nanoparticles by minimizing the phase transformations of γ-alumina to brittle boehmite (AlOOH) phase as well.…”

“…[20,21] The advantages of phosphorus incorporation on the Co/Al 2 O 3 were also reported to increase the thermal stability of active metallic cobalt nanoparticles by adjusting metalsupport interactions through a possible formation of the thermally stable spinel-type CoAl 2 O 4 phases and by enhancing the reducibility of cobalt oxide nanoparticles. [19][20][21][22][23][24] In the present study, the effects of phosphorus-modified highly ordered mesoporous Co 3 O 4 À Al 2 O 3 binary metal oxides (P/m-CoAl) during FTS reaction were investigated in terms of their structural durability [13][14][15][16][17][18]25] and outermost surface property changes to explain different catalytic activity and stability, which were not precisely reported till now as far as we know. The synergy effects of an optimal phosphorous content on the P/m-CoAl were explained by elucidating the possible phase transformations of cobalt and aluminum species as well as their positive contributions to the robust structural stability of the ordered mesoporous Co 3 O 4 À Al 2 O 3 metal oxide structures.…”