Theoretical Study Of H₂ Adsorption And Dissociation On Iron-Sulfide System

The adsorption and dissociation of H₂ on metals is of great improtance in catalytic reactions.Understanding the nature of catalytic reactions is significant to provide theoretical guidance of coal direct hydrogenation liquefaction and catalytic hydropyrolysis by studying the adsorption and dissociation of H₂ on the iron-sulfur system.Moreover,the interaction between H₂ and iron-sulfur systems are investigated for providing improtant theoretical knowledge and solve practical problems of indusrical catalytic.Therefore,the adsorption and dissociation of H₂ on?FeS?_n^0/+?n=1-6?,Fe_n S_m^0/+?n+m=5?clusters,and the most stable 100,substable 110 surfaces of pyrite were studied using density functional theory.The main conclusions are as follows:?1?When the iron-sulfur ratio is 1:1,H₂ preferentially bind to the Fe atom of?FeS?_n^0/+?n=1-6?clusters and the electrons transfers from H₂ to the?FeS?_n clusters.The result shows that the neutral?FeS?_n clusters interacts with H₂ more strongly at n=1,5,and the adsorption energy are 0.30 eV and 0.44 eV,respectively.The adsorption energy of H₂ on the cationic FeS⁺,?FeS?₄⁺,?FeS?₅⁺clusters are higher?0.40-0.43 eV?.Generally,compared with neutral clusters,cationic?FeS?_n⁺clusters is the most advantageous to H₂ adsorption.H₂ dissociation also happens on Fe atoms,and the two H atoms in the product are located on the Fe and adjacent S atoms,respectively.The dissociation process of H₂ on the neutral?FeS?_n clusters are the most favorable at n=1,and the energy barrier is 0.50 eV.It was found that the cationic?FeS?₃⁺cluster possesses the lowest energy barrier?0.42 eV?compared to the others.?2?Whereas the iron-sulfur ratio is different,the most favorable adsorption site of H₂ is on the Fe atom of Fe_nS_m^0/+?n+m=5?clusters.And the Fe_nS_m clusters accepts electrons from hydrogen.The adsorption energy of H₂ on the neutral Fe_nS_m clusters are higher?0.41-1.50 eV?at n=2,4,5 and on the cationic Fe_nS_m⁺clusters are greater at n=2,4?0.36 eV,0.36 eV?.H₂ dissociation process of on Fe_nS_m^0/+?n+m=5?clusters takes place on Fe atom.When the iron-sulfur ratio is close to 1:1,the two H atoms in the dissociation product tend to locate on the Fe atom and adjacent S atom,respectively.And while the iron-sulfur ratio relatively large or small,the two H atoms are located on Fe atoms.It is most advantageous to the dissociation process of H2 on the neutral Fe4S,Fe₅ and cationic FeS₄⁺clusters,and the energy barrier is between 0.01 eV and 0.07 eV.?3?H₂ prefers to attach to Fe atoms for the pyrite FeS₂?100?and?110?surfaces.And the adsorption energy of the FeS₂?100?and?110?surface are 0.48 eV and 0.45 eV,respectively.During dissociation process,the two H atoms in dissociation product are bind to Fe atom and S atom,respectively.In additon,the reaction enenrgy of hydrogen on the?100?surface is greater than?110?surface?0.87 eV and 0.58 eV,respectively?.And the energy barrier on the iron-sulfur clusters is smaller than the FeS₂?100?and?110?surfaces.Furthermore,it's not conducive to H₂ dissociation for the most stable?100?and substable?110?surfaces of pyrite FeS₂.There are 45 figures,8 tables and 118 references in this thesis.