Abstract <p>A series of alumina-supported cobalt catalysts promoted with palladium, platinum, and ruthenium were investigated for the synthesis of hydrocarbons from CO and H₂. The addition platinum-group metals facilitated the reduction of cobalt and significantly enhanced catalytic activity. At high CO conversion levels, the CO₂ content in the gaseous products increased considerably, most likely due to a shift in the water–gas equilibrium toward the right. At a low synthesis temperature (210°C), the 0.15%Ru–15%Co/Al₂O₃ catalyst demonstrated the highest performance: it exhibited the greatest selectivity toward C₅₊ hydrocarbons (84.6%) alongside the lowest methane selectivity (8.6%), at CO conversion of 31.0%. However, at 240°C, when CO conversion increased to 86–89%, the selectivity advantages of the Ru- and Pt-promoted catalysts diminished. Under these same conditions, the Pd-promoted catalyst maintained a sufficiently high C₅₊ selectivity (72.3%), and the content of the valuable diesel fraction (C₁₁–C₁₈) in the synthesized hydrocarbons reached its highest level, accounting for 52% of the total C₅₊ products.</p>