Roles of phosphorous-modified Al2O3 for an enhanced stability of Co/Al2O3 for CO hydrogenation to hydrocarbons

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

“…The AlPO 4 phases can also suppress the phase transformations of cobalt oxides to less active cobalt aluminates due to the hydrophobic SiO 2 -like tridymite AlPO 4 natures. [20,21] Those synergy effects of phosphorous modification on the m-CoAl were maximized on the P(1)/m-CoAl and P(3)/m-CoAl, which was originated from the partial formation of AlPO 4 phases having higher surface hydrophobicity than alumina itself [22,23] as confirmed by XAFS and FT-IR analysis in the following section. The highly ordered mesoporous structures with a small amount of phosphorous modifier on the fresh P(3)/m-CoAl were further verified by TEM images as shown in Figure 1(C) with the magnified images in supplementary Figure S5.…”

“…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.…”

“…[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. A clearly large peak intensity at 2θ = 1.23°suggests the formation of the highly ordered mesoporous structures on the fresh m-CoAl, which were well-preserved even on the phosphorous-modified P/m-CoAl.…”

“…The highly ordered mesoporous structures with a small amount of phosphorous modifier on the fresh P(3)/m-CoAl were further verified by TEM images as shown in Figure 1(C) with the magnified images in supplementary Figure S5. The stable ordered wormhole-like mesopores with the pore size of~8 nm were clearly observed on the fresh P(3)/m-CoAl, which were mainly attributed to the preferential formation of the much denser SiO 2 -like AlPO 4 phase [19][20][21][22][23][24] on the outer surfaces of the mesoporous Co 3 O 4 À Al 2 O 3 metal oxides without significant structural collapses.…”

“…[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.…”