Molecule Modeling Of Pd/M-OMS-2 Catalyze Material

Cryptomelane type manganese oxide octahedral molecular sieves?noted as OMS-2?is well acknowledged for efficient atomic utilization in its synthesis,high activity of its lattice oxygen and favorable dielectric properties.OMS-2 based materials have engaged much attention for its potential application in industrial catalyzing,energy storage and photoelectric devices.In its practice of catalyzing,OMS-2 is superiors at its high ratio of atomic utilization during the synthesis,appreciable efficiency of catalytic oxidation and united size of poles.Several intrinsic particles can exist in the tunnels of OMS-2 and it is known that these particles are found to contribute to the favorable catalytic activity and thermal stability of OMS-2.At present,experimental researches on the catalytic oxidation of reductive molecules on the surfaces of OMS-2 have gained remarkable progress,but the details of the catalytic process has not yet been fully revealed and demands more research efforts.In this thesis,the physical and chemical properties of OMS-2 crystal and the oxidation mechanism on the surface of OMS-2 is investigated utilizing first principle density functional theory computations.The main theme includes:The structure,the synthesis method and the catalytic performance of manganese oxide OMS serial materials is introduced and a brief review of current theoretical investigation towards OMS-2 materials and relevant experimental progress is provided.An introduction about fundamental concepts in density functional theory computations is provided and a discussion of how the parameters were selected is also included.The crystal structural models of OMS-2 and K-OMS-2 are constructed and are investigated utilizing density functional theory computations.The results showed that the tunnel potassium ions could help strengthening the structural stability of OMS-2 crystals,it is also noted that two types of electronic structure is found among the lattice oxygen.The following computation on Ag-OMS-2 materials located the most stable site of Ag atom in the OMS-2 tunnel structure.The energy calculations of Ag-OMS-2 materials in different sites indicated that the energy barrier for Ag to move across the tunnel structure is ca.0.35eV.The calculation results of Pd loaded OMS-2 catalytic materials showed that the adsorption of Pd on the?1 1 0?Miller index facet of OMS-2 could enhance the electronegativity of the nearby surface lattice oxygen atoms.This effect could possibly leads to the better adsorption rate of some reductive molecules with a positive charged center,and hence the better performance for catalytic oxidation.A detailed insight into the physicochemical properties catalytic mechanism of Pb doped OMS-2 material is rendered in the fourth chapter.The analysis in depth on the electronic structure and charge distribution of the lattice showed that the average oxidation state of Mn and the energies required for lattice oxygen vacancy formation are reduced after the incorporation of Pb atoms.The energy computations of the oxidation mechanism of CO on the?1 1 0?facet of OMS-2 and Pb-OMS-2 demonstrated that the existence of Pb in the tunnels of OMS-2 could reduce energies required for the surface lattice oxygen migration.In the end,a H₂ temperature programmed reduction test is performed on the as synthesized OMS-2 and PbOMS-2 materials and it is verified the increased chemical activity among the lattice oxygen after the doping of Pb.The results showed that modified OMS-2 materials have a promising potential for industrial catalyzing.