Theoretical Study On The Adsorption And Dissociation Of Water On Flat And Stepped Co(0001) Surfaces

Cobalt-based catalysts have been shown to be the most promising in Fischer-Tropsch synthesis?FTS?,due to its high catalytic and chain growth capacity.It is important to reduce the consumption of the catalyst and improve the catalyst activity.Some experimental studies have shown that by-product water in FTS,may passivate the catalyst,while other work indicates that it can increase catalyst activity of cobalt catalysis or have no effect.However,from the literature reports it is known that little attention has been focused on the interaction of water with Co?0001?surface.In this work,we have studied water and dimer dissociation by oxygen-assisted on flat-and stepped-Co?0001?surfaces using first-principles calculations.The main results are summarized as following:In this work,we first studied water molecule adsorption and dissociation on the flat-Co?0001?surface.Present results demonstrate that single water molecule prefers top site and weakly binds to the surface,which is feasible to desorption from the clean surface.In contrast,the interaction between water molecule and cobalt atom has been significantly enhanced in the presence of pre-adsorbed oxygen atom,and the oxygen atom significantly promotes water dissociation into hydroxyl.In addition,the additional H₂ O molecule in dimer can also effectively decrease the energy barrier of water dimer partial dissociation.Specifically,the rate-determining step for the reaction of 2H₂ O + O ? 3OH + H is predicted with an activation energy of 0.97 eV on Co?0001?,considerably lower than that of 1.7 eV on Pt?111?.Secondly,the theoretical study on water dissociation on stepped-Co?0001?surface has been studied.Present results indicate that molecular water molecule always prefers step-top site with a higher adsorption energy than that on flat Co?0001?surface.Moreover,the presence of pre-adsorbed oxygen atom can stabilize water molecule,and make great contribution to water dissociation.In addition,the additional H₂ O molecule in dimer has a significant promotion effect on water dimer partial dissociation,while it is feasible for dissociation via the reaction of 2H₂ O + O ? 3OH + H with an activation energy of 1 eV.Actually,the defects play an important role for water dissociation on O-covered Co?0001?.