Abstract: The reaction sequence of the direct synthesis of acetic acid by CH4/CO2 two -step reaction on binary Co/Pd catalysts under isothermal conditions, which is favored in thermodynamics, goes through as follows: first, Co activates CH4 le ading to CHxCo (x=0,1); then， the overfall of CHx f r om Co to Pd generating CHyPd (y=1-3); last, CO 2 inserts into CHyPd forming acetic acid.

Key words: carbon species, cobalt, palladium, thermodynamics, mechanism, density functional theory, methane, carbon dioxide, acetic acid