Effect of Mg/Al Ratio on Catalytic Behavior of Fischer–Tropsch Cobalt-Based Catalysts Obtained from Hydrotalcites Precursors

Layered double hydroxides of the hydrotalcite (HT)-type materials have been considered as promising supports for Co-based Fischer–Tropsch synthesis (FTS) catalysts. In this work the effect of the Mg/Al ratio on the catalytic behavior of cobalt-based catalysts obtained from HTs precursors have been studied. Cobalt supported on Mg–Al oxides obtained from HTs Mg–Al precursors were prepared by wet impregnation method and calcined at 300 °C. The textural, structural and reducibility properties of the samples were characterized using different techniques. FTS was evaluated in a down-flow fixed-bed reactor at 20 bar, 250 °C and H₂/CO ≈ 2 molar ratio. All catalysts were active and stable during 72 h testing time. The stability was improved by the presence of magnesium in the alumina support; however the CO conversion was negatively affected by increasing the Mg/Al ratio. The reducibility of cobalt decreased as the Mg/Al ratio increased, probably due to the strong Co–O–Mg interaction as evidenced by the formation of Co_xO_y–MgO mixed oxide. Furthermore, the activity of the catalysts was correlated with the H₂-chemisorption measurements. The results suggest that HTs as Co-based catalysts were highly stable in FTS.