Iron-manganese catalyst supported on silicalite 1 was prepared by impregnation. The catalyst preparation was followed by X-ray diffraction, temperature-programmed reduction and Mossbauer spectroscopy. Hydrogenation of CO was studied in a high pressure reactor by varying CO:H-2 ratio, temperature, and pressure. The silicalite supported catalyst shows very high selectivity for C-2-C-4 alkenes. When acidic ZSM-5 having the same structure as silicalite 1 was used as the support, the product had very little alkenes. Addition of 0.2% potassium improves the alkene selectivity of the Fe-Mn on the silicalite catalyst.