Abstract: A large amount of SO_2 and a small amount of SO_3 are emitted from coal-fired power plants.The generation of SO_3 is not only harmful to the environment,but also dangerous to the safe operation of the power plant.Current studies show that Fe_2O_3 contained in the fly ash and the boiler wall have a significant catalytic effect on the SO_3formation.However,the research on the path and mechanism of SO_3catalytic formation by Fe_2O_3 is not deep enough.In this paper,theα-Fe_2O_3(001) surface was established firstly,and the adsorption configuration of SO_2and O_2onα-Fe_2O_3(001) surface was studied by density functional theory(DFT).The stable adsorption configuration of SO_2 and the dissociation pathway of O_2on Fe_2O_3(001) surface were obtained.The reaction path and energy barrier of catalytic formation of SO_3 onα-Fe_2O_3 surface were studied by using transition state search method.Then the energy barrier of catalytic formation of SO_3 in gas phase reaction were compared.The results show that the most stable adsorption configuration of SO_2 is that O and S atom in SO_2 are adsorbed above Fe atoms onα-Fe_2O_3,while S atom is not easy to be adsorbed above lattice oxygen ofα-Fe_2O_3 crystal.The adsorption energy of O_2 onα-Fe_2O_3 surface is greater than the maximum adsorption energy of SO_2,which means that O_2 is more easily adsorbed onα-Fe_2O_3 surface.In addition,O_2 is easy to dissociate and form O atom on the defect Fe_2O_3 surface with oxygen vacancy,which indicates thatα-Fe_2O_3 with oxygen vacancy is easier to promote the dissociation of O_2 and the generation of adsorbed oxygen on the surface.The L-H mechanism of SO_3 formation is that SO_2 and O atoms in the gas phase are adsorbed firstly on theα-Fe_2O_3 surface,and then combine to form SO_3,and the reaction energy barrier is 231.65 kJ/mol.The E-R mechanism is that SO_2in the gas phase reacts with adsorbed oxygen onα-Fe_2O_3surface to form SO_3while the reaction energy barrier is 24.82 k J/mol,which is less than that of L-H mechanism and far less than that of SO_3formation in gas phase reaction.The above results confirm that Fe_2O_3has a significant catalytic effect on the formation of SO_3,and the E-R mechanism is the dominant reaction mechanism.The existence of oxygen vacancy promotes the dissociation of O_2on the surface ofα-Fe_2O_3,and the surface adsorbed oxygen plays an important role in the catalytic process.