First-principles Studies Of Single Atom Catalysis In The Production Of Fine Chemicals

With the rapid development of science,technology and economy,The demand for petroleum energy is increasing,resulting in a sharp decline in the oil reserves.Meanwhile,the extensive use of petroleum energy trigger a series of the environmental problems Facing a series of energy and environmental crisis,adjusting the energy structure in the national economy and increasing the proportion of new energy and non-petroleum raw materials have become an inevitable trend.Thereby,the conversion of energy-related molecules,such as methane,nitrogen and carbon dioxide,has attracted researchers much attention.In rescent years,the reserachers found that single atom catalysts(SACs)are significantly different from the traditional bulk metal catalysts in term of geometric structure and electronic characteristics.They exhibit excellent catalystic performance and become an ideal catalyst system.Moreover,some studies found that the chemical environment of active atoms exerts a vital influence on the process of catalysis.Thus,regulating the chemical environment of the active sites and studing the effects of regulatory means on the catalytic mechanism from the atomic level,which have a positive impact on improving molecular conversion efficiency.In this thesis,using density functional theory,we studied the potential applications of single atom catalysts in the field of ammonia synthesis,methane activation,and hydrogenation reaction.The main findings of this thesis are as follows:1.We propose by density functional theory to study the catalytic performance of different transition metal single-atom embedded two-dimensional phthalocyanine framework as NRR electrocatalysts.Compared with previously reported NRR catalyst screening strategies,the dipole moment of the N?N triple bond was an efficient indicator for screening NRR catalyst.Based on the results of screening,the 2D Mo-Pc is selected as a promising NRR catalyst with a low onset potential of-0.25 V.The origin of such high catalytic performance is accounted for by the feasible donation of electrons from the Mo atom to the 2?*antibonding orbitals of N2 and thus promoting the activation of N2.Of importance,HER reactions and H2O poisoning effects can be suppressed at the active sites,indicating that the 2D Mo-Pc is highly selective for NRR.This work extends the potential applications of single-atom catalysts in the renewable energy supply.2.We studied the reaction mechanism of methane oxidation on single-atom Rh(SAs Rh-CeO2)and Rh cluster(Rh4/CeO2)doped in the cerium dioxide surface.Considering the direct oxidation of methane in H2O2 solution,we first studied the decomposition path of H2O2 molecule on the surface of SAs Rh-CeO2 and Rh4/CeO2.The results showed that H2O2 molecules are mainly decomposed into ·OH and ·OOH radicals on the surface of SAs Rh-CeO2,while it is mainly decomposed into*OH on the surface of Rh4/CeO2.The generation of OH and ·OOH radicals can promote the oxidation of CH4.By further analysis of the reaction energy of the methane oxidation path.The results indicate that SAs RhCeO2 can selectively activate CH4 to oxygenates in the presence of H2O2,while Rh4/CeO2 favor the overoxidation of CH4 to produce COx.3.The coordination environment of the single atom has a significant impact on the performance of the single atom catalysts.In view of this,we investigated the effect of Pt single atom of different coordination environments on the activity and selectivity of propyne hydrogenation.DFT calculations revealed that Pt single atoms coordinated with four oxygen on Fe2O3 support(Pt1/Fe2O3)exhibited promising selectivity in the semi-hydrogenation of propyne,while Pt single atoms coordinated with three oxygen on FeOOH support favor over-hydrogenated to form propane.This work provides a platform to investigate the structure-active relationship of catalysis.