A series of silica doped alumina (SDA) [Si-Al2O3] having high surface area and narrow pore size distribution are synthesized with varying amount of silica and used as a support material to facilitate incorporation of Co, Mg and Zr into it. These supported Co-Mg-Zr/SDA materials are used as catalysts for selective synthesis of middle distillate through Fischer-Tropsch synthesis (FTS) reaction. Trace quantity (similar to 0.05 wt %) of ruthenium (Ru) has also been used as a promoter for Co -Mg-Zr/SDA catalyst to improve the reducibility, selectivity towards middle distillate and increasing the catalyst life. The detail characterizations of catalysts indicate that Ru promotion and narrow pore size distribution facilitate CO conversion and middle distillate selectivity. Synthetic syngas of composition (H-2 = 28.63%, CO = 14.27%, CO2 = 9.25%, CH4 = 1.0%, and N-2 = 46.85%), which may be obtained after coal gasification and H-2 enrichment process by water gas shift (WGS) reaction has been used as a reactant for middle distillate synthesis. The role of Ru and silica proportion on Co-Mg-Zr/SDA is investigated through Low Temperature Fischer-Tropsch (LTFT) synthesis at 220 degrees C temperature and 30 bar pressure. The surface acidity of the Ru/Co-Mg-Zr/SDA catalyst plays an important role for middle distillate selectivity and CO conversion. To determine the durability of catalysts, 300 h continuous experimental run has been conducted at Gas Hourly Space Velocity (GHSV) of 500 h(-1). Among the catalysts in the present study, Ru/Co-Mg-Zr/SDA(7.5) catalyst shows highest CO conversion (94.2%) with 85% selectivity of C-6-C-19 hydrocarbon.