Theoretical Study Of CO₂ Hydrogenation To Methanol On The Surface Of Pt-doped In₂O₃

The synthesis of methanol by hydrogenation of CO₂ can use greenhouse gas as a resource to convert it into clean energy or platform compounds,and achieve"waste into treasure".At present,copper-based catalysts are mainly used in industry,of which activity are relatively high,but prone to inactivation,resulting in a low methanol yield.The economy needs to be improved.Th erefore,it is necessary to find and design more efficient catalysts.In this paper,the reaction mechanismsfor CO₂ hydrogenation to produce methanol on two Pt-doped In₂O₃catalyst surfaces and Pt In alloy surface were studied using density functional theory（DFT）,in order to promote the development and application of Pt-doped In₂O₃ catalysts in the field of catalysis.First of all,the effect of Pt bonding doping on the generation of oxygen vacancieswas studied on the surface of In₂O₃ catalyst,the adsorption and dissociation of CO₂ and H₂ on the Pt-In₂O₃surface wasexplored,and the main reaction path and rate control steps were analyzed for CO₂hydrogenation to methanol.Secondly,the main reaction path and rate control steps on the surface of Pt₄/In₂O₃ were studied for CO₂ hydrogenation to methanol via theoretical calculations,and the influence s of H coverage and H₂O on the hydrogenation process and the structural change for Pt₄ cluster were analyzed.Finally,on the surface of alloy Pt In,the main reaction path and rate control steps for CO₂ hydrogenation to methanol were studied to determine whether CO₂hydrogenation could be carried out successfully.The main conclusions are as follows:1.On the Pt bonded In₂O₃（110）surface,it is more difficult to form an oxygen vacancy through the reduction of H₂and CO.The Pt-O bond is strong and plays the role of fixing O.The doping of Pt also improves the strength of the nearby In-O bonds,avoidthe surface overreduction and thereby enhances the catalyst stability.Comparing the adsorption energy of CO₂ on the catalyst surface before and after Pt doping,it is found that Pt doping can not only strength the adsorption and activation of CO₂on the In₂O₃ surface,it can but also enhance the dissociation and adsorption of H₂,and the closer it is to the position of Pt,the easier to dissociate H2.CO₂ in the O_v3 oxygen vacancy on the Pt-In₂O₃（110）surface is hydrogenated through the formate（HCOO）path to form methanol.An Oatom of CO₂ will fill the oxygen vacancy during the reaction process to turn the defective Pt-In₂O₃（110）surface into a perfect surface,which is once again reduced by H₂ to adsorb CO₂ for hydrogenation.The surface changes in such a cycle,which promotes the occurrence of reaction.2.The doping of Pt₄ cluster to the In₂O₃（110）surface is a strong exothermic process.Under its strong interaction with In₂O₃,the Pt₄ cluster configuration is expanded from a regular tetrahedron to a butterfly structure.The formation of OH in the CO₂ hydrogenation reaction makesthe Pt₄ cluster configuration returnto the regular tetrahedron.After OH hydrogenation to produce H ₂O,the Pt₄ cluster structure will expand again.The configuration of Pt₄ cluster changes in this regular cycle in the CO₂ hydrogenation reaction.CO₂ is mainly adsorbed and activated at the Pt₄/In₂O₃ interface.H₂ is easy to beadsorbed and dissociated at the Pt ₄ cluster.The synergy between Pt₄ cluster and In₂O₃ promotes the CO₂ hydrogenation reaction;CO₂ is hydrogenated to produce methanol on the surface of Pt₄/In₂O₃through the formate pathway,and the high Hatom coverage and the participation of H₂O can promote the reaction.3.The hydrogenation of CO₂ on the surface of Pt In（110）is not inhibited,and methanol can be synthesized through the formate path.The interaction between Pt and In has no negative impact on the production of methanol.4.Comprehensive analysis and comparison of Pt-In₂O₃（110）,Pt₄/In₂O₃（110）and Pt In（110）shows that CO₂ is difficult to dissociate into CO and O on al l thethree surfaces,thus avoiding catalyst poisoning.CO ₂ hydrogenation to methanol followsthe HCOO pathway on thethree surfaces.The defective Pt-In₂O₃（110）surface exhibitsthe strongest ability to dissociate H ₂ and adsorb CO₂,the energy level for CO₂ hydrogenation to methanol as a whole is the lowest.The defective Pt-In₂O₃（110）surface is the most conducive to CO₂ hydrogenation to synthesize methanol.