Design High Activity Catalysts Through Electronic Structure Regulation And Their Catalytic Applications

In the chemical industry and industrial research,catalysis plays an important role in modern society,such as petroleum refining,synthesis of ammonia and vehicle exhaustion conversion.With the population growth,the depletion of fossil fuels and the deterioration of the global environment,rational design and synthesis of catalysts with high activity,selectivity and stability are the ultimate goal of green catalysis.The catalytic activity of the catalyst depends on its electronic structure,the spatial and energy distribution of valence electrons at the catalyst surface determine the activation energy barrier and the reaction pathways in the catalytic reaction.Therefore,in this dissertation we have designed highly e:fficient catalysts by engineering its electronic structure and explored the structure-activity relationships and the catalytic mechanism through combining experiment and theory.The details are as follows:1.The interface plays an increasingly crucial part in heterogeneous catalysis due to its unique electronic structure.However,the design of interfacial catalyst with high activity remains a challenge,because the nature of the active site and the origin of the catalytic role that interface plays still remain unclear.Herein,we combined experiment and density functional theory calculations to unravel the reaction mechanism for CO oxidation by constructing CeO2/Co3O4 and Ru/Co3O4 interface structures.CeO2/Co3O4 interface structure exhibited higher catalytic activity for CO oxidation compared with CeO2 and Co3O4,it could achieve complete oxidization of CO to CO2 at 110?.Similarly,Ru/C03O4 interface structure also show remarkable catalytic activity for CO oxidation,it could catalyze the complete oxidation of CO to CO2 at 75 ?,which was better than pure Ru and bare Co3O4.Density functional theory calculations indicated that there was a strong interaction between CeO2 or Ru with Co3O4,and electron transfer from CeO2 or Ru to Co3O4,consequently tuning the reactivity of interface structures.We also calculated the reaction pathway of CO oxidation on Ru/Co3O4 interface structures,and the calculated results showed that compared with pure Ru and bare Co3O4,the Ru/C03O4 interface structures could significantly reduce activation energy for CO oxidation reaction,thus resulting in its high catalytic activity for CO oxidation.2.Carbon materials are electrochemically inert toward the hydrogen evolution reaction(HER)as the neutral carbon atoms have poor adsorption strength of H.Nevertheless,the incorporation of heteroatoms(such as N)can modulate electronic structure of carbon,turning inert C atom into electrocatalytic HER active site.Although heteroatom-doped carbon materials can catalyze HER,the catalytic activity is still far lower than commercial 20%Pt/C as heteroatom has limited ability to tune electronic structure of carbon.Herein,with a similar electronic structure as Pt-group metals,MoP was successfully encapsulated into N doped porous carbon frameworks(MoP@NC)as an electrocatalyst for HER.The MoP@NC exhibited high activity with an overpotential of only 121 mV at 10 mA/cm2 in 0.5 M H2SO4 electrolyte,and it also showed high activity in 1M KOH electrolyte,especially at high current density with an overpotential of 277 mV at 100 mA/cm2,which was better than that of commercial 20%Pt/C catalyst.Density functional theory calculations indicated that the electronic structure of the outer carbon layer could be modified by the encapsulated MoP core,which effectively enhancing the adsorption strength of*H on C atom,and thus decreasing ?G*H,thereby accelerating overall HER process.3.Graphene,with a zero band gap,consisting of a single layer of sp2-hybridized carbon is inert in the oxygen evolution reaction(OER).Interestingly,heteroatom(e.g.,B,N,or S)incorporation can adjust the electronic structure of graphene,changing inert C atom into electrocatalytic OER active site.However,the overall catalytic activity of heteroatom doped graphene for OER is still much lower than commercial IrO2 catalyst.Herein,we successfully constructed FeNiIr ternary alloys encapsulated into N doped graphene(FeNiIr@NG)as an electrocatalyst for OER.The FeNiIr@NG exhibited high OER activity with only 271 mV overpotential at 10 mA/cm2 in 1 M KOH electrolyte,which was better than that of commercial IrO2 catalysts.Density functional theory calculations indicated that the FeNiIr ternary alloys could maneuver the electronic structure of graphene by transferring their valence electrons to graphene,which effectively optimized the adsorption strength of oxygen-bearing intermediates(*O,*OH and*OOH),and decreased the energy barrier of OER,thus reducing overpotential for OER.4.With a half filled d-electron shell,molybdenum(Mo)plays an important role as catalysts in the petrochemical industry.However,Mo is generally regarded as not catalytically active for oxygen reduction reaction(ORR)compared with other transition metals such as Fe and Co.Inspired by molybdoenzymes,herein,we successfully tune Mo into highly active electrocatalytic site for ORR by tailoring its d-band center through engineering N and O as the nearest coordinated atoms.This bio-inspired ORR electrocatalyst consists of atomically dispersed nitrogen/oxygen-coordinated Mo cofactors embedded in porous carbon frameworks(Mo-N/O-C),demonstrating prominent ORR catalytic capability and durability compared to those of the state-of-the-art Pt/C under alkaline condition.The extraordinary performance of Mo-N/O-C electrocatalyst is also demonstrated in zinc-air batteries as an air cathode.Density functional theory calculations reveal that changing local geometry of the nearest coordinated N and O atoms could tune the position of d-band center of Mo,subsequently tailoring its binding capability with oxygen-bearing intermediates.Remarkably,the Mo-N2O2 cofactor is demonstrated the fastest ORR kinetics due to the maneuvering of d-band center to a reasonable position,which facilitated the rate-limiting desorption of*OH,thereby accelerating overall ORR process.