Ordered Mesoporous Co3O4-Al2O3 Binary Metal Oxides for CO Hydrogenation to Hydrocarbons: Synergy Effects of Phosphorus Modifier for an Enhanced Catalytic Activity and Stability

摘要

The synergy effects of phosphorus modifier on highly ordered mesoporous binary metal oxides of Co3O4-Al2O3, (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 SiO2-like AlPO4 phases on the outer surfaces of the m-CoAl, as well as from partially formed irreducible and thermally stable spinel-type cobalt aluminates (CoAl2O4). The hydrophobic SiO2 like tridymite AlPO4 surfaces on the ordered matrices of the P/m-CoAI also effectively prevented the heavy wax (or coke precursors) depositions. The structural instability of the P/mCoAl was observed at a higher phosphorous content above 0.5wt%P by preferentially forming the largely segregated mixed metal oxides such as Co3O4-CoAl2O4-Co-3(PO4)(2) through the phase transformations of the surface excess AlPO4.