A Study On The Catalytic Mechanisms Of CeO₂,Hf-MOF,COPs And Bi₂MoO₆ Systems

With the rapid industrial development,various environmental pollution problems have become more and more severe,causing serious problems to human life.Catalysts are needed to eliminate industrial pollution.Due to wide band gaps,it is difficult for the effective transition of photogenerated electrons to occur in traditional semiconductor catalysts.This results in their poor catalytic efficiency,which makes it necessary to modify their structure micro-scopically.Doping is one of the most important methods for developing new and efficient catalysts.Cerium-based,Metal-organic frameworks（MOFs）,Conjugated organic polymers（COPs）,bismuth-based catalysts are the focus of this research.This paper use first-principle density functional theory（DFT）computations to explore electronic structure of the materials:Cu-doped CeO₂,Hf-MOF,COP-X（X=O,N,S）,Ti-doped Bi₂MoO₆and Bi₂WO₆.The research content mainly includes the following parts:1.First principles density functional theory computation is performed to study the effect of Cu²⁺doping on the formation of oxygen vacancies and adsorption of SO₂on the CeO₂（111）surface.The results indicate that Cu²⁺doping reduces the formation energy of oxygen vacancies on the CeO₂（111）crystal surface,especially those surface vacancies closer to Cu²⁺.The SO₂adsorption capacity of the Cu²⁺area on the surface to is significantly improved,and the adsorption energy becomes more negative.This indicates that SO₂ tends to be adsorbed in the Cu-rich region,which protects the catalytically active sites in the Ce-rich region.2.The reduction mechanism of cyclohexanone catalyzed by Hf-MOF is calculated.The results show that during the reaction,the H atom on the hydroxyl group of isopropanol is gradually transferred to theμ-OH atom connected to Hf（IV）,and the O atom on the hydroxyl group are coordinated to Hf（IV）forming Hf-O bond.This helps promote H transfer.We used the multi-coordinate driven method to drive the reactant to the product.The maximum energy on the reaction path appears at rc≈0.65,and the corresponding structure provides an approximate transition state.The energy barrier is about 45.4 kcal/mol.3.The electronic structure and CO₂ reduction process of COP-X materials are simulated.Density of states（DOS）and band results confirm that the substitution of S leads to the reduced band gap of COP-S,which is believed to be beneficial for the production of photogenerated carriers.The electron onating capacity of O,N and S atoms is revealed by the calculated total charge density distribution on the periodic polymer frameworks.The S substitution renders the electron to spread to the peripheral scaffold,in contrast,the electron density is mainly concentrated on O and N in COP-O and COP-N,respectively.The calculation of the Gibbs free energy based on the plausible CO₂reduction pathways on COP-X shows that COP-S presents the lowest energy barrier of CO₂adsorption.The formation of*COOH can be considered as the rate-determining step during the photoconversion of CO₂ on of these COPs.COP-S exhibits the best CO₂ reduction ability.4.In order to determine the influence of Ti doping on the electronic structure of Bi₂MoO₆and Bi₂WO₆,the electronic properties are calculated by density functional theory,including:DOS,band gap,differential charge density.The study of the DOS shows that after doping,the DOS of the conduction band and the valence band moves to a lower energy direction as a whole,which promotes the generation of photogenerated electrons.The decrease of the band gap indicates that doping can expand the absorption of visible light.In addition,Ti doping induces the distortion of intrinsic electric density and the internal electric field.