Ordered Mesoporous Co ₃ O ₄ −Al ₂ O ₃ Binary Metal Oxides for CO Hydrogenation to Hydrocarbons: Synergy Effects of Phosphorus Modifier for an Enhanced Catalytic Activity and Stability

The synergy effects of phosphorus modifier on highly ordered mesoporous binary metal oxides of Co ₃ O ₄ −Al ₂ O ₃ (m-CoAl), prepared by nanocasting method using a hard template of KIT-6, were observed by an enhanced catalytic and structural stability of the m-CoAl during CO hydrogenation to hydrocarbons. The enhanced structural stability of the ordered mesoporous structures on the phosphorous-modified m-CoAl at an optimal amount of phosphorous modifier below 0.3 wt%P (P(3)/m-CoAl) was attributed to the partial formation of thermally stable metal phosphates under a reductive Fischer-Tropsch synthesis (FTS) reaction condition. The positive effects of the phosphorous modifier were originated from the partially formed SiO ₂ -like AlPO ₄ phases on the outer surfaces of the m-CoAl, as well as from partially formed irreducible and thermally stable spinel-type cobalt aluminates (CoAl ₂ O ₄ ). The hydrophobic SiO ₂ -like tridymite AlPO ₄ surfaces on the ordered matrices of the P/m-CoAl also effectively prevented the heavy wax (or coke precursors) depositions. The structural instability of the P/m-CoAl was observed at a higher phosphorous content above 0.5wt%P by preferentially forming the largely segregated mixed metal oxides such as Co ₃ O ₄ −CoAl ₂ O ₄ −Co ₃ (PO ₄ ) ₂ through the phase transformations of the surface excess AlPO ₄ .