When potassium salts such as K2CO3, KOH, CH3COOK, and K2S were added to Mo2C, the promoted catalysts showed high selectivities to alcohols and light oleflns in CO hydrogenation at 573 K and 1.0 MPa. However, K2SO4 and KCl caused only slight increase in olefin selectivity with negligible alcohol formation. These two groups of promoters showed different physical and chemical states during the reaction as observed by AES, EDS, EPMA, IR and transient reaction behavior. This difference accounted for the observed difference in selectivity