Density Functional Theory Study Of The Adsorption Behavior Of Carbochlorination On TiO₂?110?surface

The preparation of titanium tetrachloride?TiCl₄?by carbochlorination of TiO₂ is an important intermediate step in the production of titanium dioxide and sponge titanium,adding carbon could significantly improve the chlorination reaction rate of TiO₂,which is the precondition for the industrial application of this method.A large number of studies have been conducted on the mechanism of carbochlorination of TiO₂ at home and abroad,the main viewpoints included stepwise reduction reaction,reduction of oxygen partial pressure,formation of intermediate compounds and auto-catalytic mechanism,etc,but the essence of this macro phenomenon has not been revealed although they complement each other.In this paper,the first-principle method based on density functional theory was adopted to explore the co-adsorption reaction of both carbon/CO and Cl₂ onto the TiO₂?110?surface which was perfect and with defect of bridge oxygen vacancy,respectively.The behavior mechanism of adding carbon to promote the chlorination process of TiO₂ was revealed using the calculation of the adsorption structure,adsorption energy,charge density and density of states?DOS?of the system,which laid a theoretical foundation for further research on the catalytic reaction mechanism of adding carbon to titanium oxide.The main conclusions were as follows:?1?The adsorption of carbon or CO with Cl₂ on the TiO₂?110?surface was mutually promoting.carbon or C atom in CO promoted the bonding of chlorine with surface Ti atoms by binding to O atoms on the TiO₂?110?surface.O?2c?atom was relatively active on the TiO₂?110?surface,which was easier to capture carbon and CO.The binding of carbon or CO to the surface was the trigger point of chemisorption of Cl₂ on the surface.?2?The C atom in carbon or CO and the Ti?5c?atom on TiO₂?110?surface appeared sp and sd³ orbitals hybridization to form C-O and Ti-Cl bonds before adsorption,respectively.Meanwhile,the electron transfer channel in the direction of C/C₄/CO?TiO₂?110??Cl₂ was formed on the surface.?3?The strength of Ti-O bond on the surface and inside of TiO₂?110?was weakened by the formation of C-O bond and Ti-Cl bond,which activated the surface Ti,O atom,and promoted the fracture of partial Ti-O bond,making preparation for the formation of the next Cl-Ti bond and C-O bond.?4?The dissociation of CO or CO₂ from the TiO₂?110?surface was an exothermic reaction.If a certain amount of reaction energy was provided in the chlorination process,the dissociation reaction could occur,resulting in the formation of O vacancy defects on the surface,which provided a new adsorption site for the next Cl₂ molecule.?5?The presence of bridge oxygen vacancy increased the surface activity of TiO₂?110?,and the adsorption sites of Cl₂ on the reduced TiO₂?110?surface tended to occupy the bridge oxygen vacancy.