The Catalytic Reaction Mechanism Research Of CO₂ And H₂O On TiO₂ Surface

Carbon dioxide?CO₂?is both the greenhouse gas need to be dealed with and rich,safety,renewable resource of C1,a variety of compounds were made form CO₂ which as a raw material through the formation of C-C,C-H,C-N,C-O bonds.Water?H₂O?is the most abundant resources of H in nature,CO₂ and H₂ O can react and produce CH3 OH,CH4,CH3CH₂ OH,syngas compounds and so on.Therefore,it is necessary to give a theoretical research to CO₂ and H₂ O catalytic reaction on perfect and with oxygen vacancy titanium dioxide surface using quantum chemical calculations.Thus,it can deepen people's knowledge of microscopic mechanism of CO₂ and H₂ O catalytic reaction on perfect and with oxygen vacancy titanium dioxide surface and provide theory clues to design and imptovement of high efficient novel catalyst.First,we systematically studied the CO₂ and H₂ O catalytic reaction on perfect anatase?101?surface by use of self-consistent periodic density functional?DFT?.We put emphasis on all reaction intermediates involved in catalytic reaction and found that: H atom like to adsorb on 2cO atom and 3cO atom on TiO₂?101?surface.CO₂ and TiO₂?101?surface interaction is weak,belongs to the physical adsorption.CH₂ OH through C atoms adsorbs at TiO₂?101?surface 2cO atoms,but its suitable adsorption structure for the reaction is physical adsorption.The other intermediates through O atoms interact with 5cTi atom on TiO₂?101?surface and the adsorption energy are small.Through the optimization of possible intermediates calculations,we choose suitable initial state and final state to find the reaction transition state,we finally confim the most likely mechanism of the reaction: H₂ O ? H + OH;H + CO₂ ? HCOO;HCOO + H ? HCOOH;HCOOH + H ? CH₂OOH;CH₂OOH ? CH₂ O + OH;CH₂O + H ? CH₂OH;the five hydrogenation reaction step,CH₂ OH adsorption with H form product of CH3 OH.The primitive reaction H + CO₂ ? HCOO and HCOOH + H ?CH₂OOH reaction energy barrier is bigger and the reaction is difficult.Then,we make a study of CO₂ and H₂ O catalytic reaction on anatase?101?surface with oxygen vacancy.We put emphasis on all reaction intermediates involved in catalytic reaction and found that: H atom like to adsorb on 2cO atom on TiO₂?101?surface with oxygen vacancy,the adsorption energy is smaller than that is on perfect TiO₂?101?surface.CO₂ and TiO₂?101?surface with oxygen vacancy interaction is stronger than perfect TiO₂?101?surface.The other intermediates through O atom or C atom interact with 4cTi atom or 5cTi atom on TiO₂?101?surface with oxygen vacancy and the adsorption energy are larger,which is mainly due to the intermediate structures filling oxygen vacancy position that result in large changes in the basal energy before and after adsorption.Through the optimization of possible intermediates calculations,we choose suitable initial state and final state to find the reaction transition state,we mainly studied the initial decomposition reaction of H₂ O and the first step of CO₂ hydrogenation,in the study we found that the existence of oxygen vacancy inhibited the initial decomposition reaction of H₂ O and promote the first step of CO₂ hydrogenation reaction.