Research On Fe₂O₃-graphene Catalyzed Hydrolysis Of COS And CS₂ Reaction Mechanism

The existence of COS and CS₂ in the reducing atmosphere such as yellow phosphorous tail gas and the airtight carbide furnace not only affects the quality of the chemical products,but also corrodes the pipe,which leads to the poisoning of the downstream catalyst.At present,the removal methods of COS and CS₂ roughly can be classificated into dry and wet method.Due to the high catalytic selectivity,low operating temperature and mild reaction conditions,the low temperature catalytic hydrolysis method in dry method has been paid more attention by researchers.The more mature of these studies are activated-carbon based materials loaded with metal oxides as catalysts for removal of COS and CS₂ in tail gas.According to the hydrolysis rate of COS and CS₂ active components and the oxidation rate of H₂S,Fe has better catalytic activity,but the catalyst deactivation causes COS and CS₂ catalytic hydrolysis reaction efficiency lower,this is the main factor of limiting the catalyst performance.In order to solve the above-mentioned problems,we need to figure out the catalytic hydrolysis process and mechanism of COS and CS₂.At present,the catalytic hydrolysis reaction mechanism of the activated carbon based catalyst on COS and CS₂ is still in the exploratory stage,and the relevant reports are less.In order to solve the existing problems,the graphene is selected as a simplified model of activated carbon,and all possible adsorption structure of COS,CS₂ and hydrolysis reactant H₂O on the graphene are calculated generally from the point of view of quantum chemistry density functional theory.It is concluded that the most stable adsorption structure for COS is COS（f）,while the COS is parallel to the graphene surface and adsorbs in the Top sit,and the adsorption can be-0.830eV.H₂O is a non-linear symmetric molecule.For H₂O molecules,when H₂O presents the"down V"structure on the graphene surface,the adsorption energy is the largest,while H₂O adsorbs in the Hollow position.In order to explore the bonding between the three molecules and the graphene surface,the corresponding partial density of states（PDOS）and the Mulliken net charge for the most stable structure are also calculated.The results show that there is a charge transfer between COS,CS₂ and H₂O and graphene,that is,there are the formation of chemical bonds between the two ones.In order to explore the catalytic hydrolysis of COS and CS₂ on the active components of the catalyst,this paper investigate the role of theα-Fe₂O₃ and COS and CS₂.However,the hydrolysis of COS and CS₂ involves the adsorption process of H₂O,so the interaction between H₂O and COS is explored,and H₂O preadsorption is obtained before the interaction with the COS.The process of H₂O separate adsorption and dissociation is also studied in this paper,and the maximum adsorption energies of O,OH and H₂O on the surface ofα-Fe₂O₃（001）are:-430.268,-390.230,-332.246 kcal/mol,and all of them are chemical adsorption.Moreover,it is known that H₂O tends to dissociate adsorption on the surface ofα-Fe₂O₃（001）.Based on this,COS inα-Fe₂O₃（001）surface in the process of catalytic hydrolysis enclosed for:COS inα-Fe₂O₃ adsorption mechanism of（001）surface is H₂O to disintegrate after surface adsorption,OH and H after dissociation attack C and S atoms of COS,respectively.The H atoms in the OH continue to attack S atoms,causing the C-S bond to break and the formation of H₂S.The bonding between O atoms and C on the surface ofα-Fe₂O₃（001）will eventually form CO₂ and dissociate from the surface.The catalytic hydrolysis of CS₂ on theα-Fe₂O₃（001）surface was studied from"one-step method"and"two-step method"respectively obtaining two different reaction paths.The former one is considering two H₂O and CS₂ reaction at the same time,generating two H₂S molecules and CO₂.While the latter one is considered COS as the hydrolysis intermediate of CS₂,and the hydrolysis process of CS₂ is divided into two steps:CS₂ is firstly hydrolyzed to COS,then COS forms H₂S and CO₂.Comparing the energy of the two reaction paths,the"one-step method"is more advantageous than the“two-step method”on theα-Fe₂O₃（001）surface.And for both reactions,the H₂O attack on C=S is a crucial step in the reaction.This paper elucidate the catalytic hydrolysis mechanism of COS and CS₂ on the surface ofα-Fe₂O₃（001）,and H₂S is the common product after the reaction,which is also the main cause of the catalystic inactivation.The adsorption and dissociation process of H₂S on theα-Fe₂O₃（001）surface is studied and is found to be similar to H₂O.H₂S will adsorb on theα-Fe₂O₃（001）surface firstly,and then S atoms bond with top-Fe atom.Then H₂S will take the first step to dissociate,and the solution will be SH and H,and the dissociation energy is 7.04kcal/mol.After the dissociation,SH is going to be followed by the second step,and then the S will continue to bond with the Fe forming the FeS finally.