Density Functional Theory Study On Catalytic Oxidation Of Isopropanol At Normal Temperature

The efficient abatement of volatile organic compounds（VOCs）is one of the frontier research issues in the environmental field.Normal Temperature Catalytic Oxidation technology（NTCO）with low energy consumption and high safety coefficient will become an important development direction of VOCs treatment.To reveal the microscopic reaction mechanism of VOCs at normal temperature will greatly promote the improvement of NTCO,which has important scientific value and far-reaching significance.The structural model of Pt/TiO₂ and Pt/Na-TiO₂ catalysts were built based on TEM,XAFS characterization and density functional theory（DFT）.The reaction mechanism for degradation of isopropanol at normal temperature was investigated.The main research contents were as follows:The Pt element is supported on anatase TiO₂（101）of Pt/TiO₂and Pt/Na-TiO₂in the form of single atom.Pt element on Pt/TiO₂is adsorbed on the bridge site between two two-coordination oxygen atoms in the outermost layer on TiO₂（101）.The coordination number of adjacent O,Ti,Na atoms and Pt atom in Pt/Na-TiO₂ all is 4.The reaction path of O₃ or H₂O to generate hydroxyl groups at the most stable adsorption site and the sub-stable adsorption site on Pt/TiO₂ and Pt/Na-TiO₂ catalysts,respectively,were calculated by DFT with dispersion correction,zero-point vibration energy correction and enthalpy,entropy,Gibbs free energy correction.The nature cause of the different efficiency in catalytic isopropanol degradation between Pt/TiO₂ and Pt/Na-TiO₂（66%and 100%,respectively）was revealed.For Pt/Na-TiO₂,the most stable configuration of H₂O is easily decomposed into OH*,then the H atom in OH*is captured byO₃ to form HO₃·and finally genarated·OH andO₂.Thegeneration of OH*on Pt/TiO₂ is mainly through the decomposition of the sub-stable configuration ofO₃.The generated O*byO₃ decomposition combined with Pt and Ti atoms to form Pt-O-Ti site,over which H₂O is decomposed into OH*,then the H atom in OH*is captured byO₃ to form HO₃·and finally genarated·OH andO₂.Considering the oxidation reaction of·OH,addition reaction and C-C bond breaking reaction,the mechanism of·OH mineralizing isopropanol at normal temperature was proposed.The formed（CH₃）₂CHO·by the clevage of O-H bond of isopropanol could break the C-C bond to generate methyl and acetaldehyde.The intermediates for·OH mineralizing methyl is determined to be methanol,formaldehyde,formic acid.And the intermediates for acetaldehyde mineralization by·OH is found to be glyoxylic acid.The interaction between the supported metal and the oxide support of single atom catalyst,the electronic interaction between the adsorbed molecule and the single atom catalyst,and the physicochemical properties of the single atom catalyst were analyzed by projected state density,d-band center,crystal orbital Hamiltonian population,natural bond orbital theory,charge density difference,spin density,band decomposed charge density,electrostatic potential,electron localization function.Most of the anti-bonding orbits generated by the interaction between Na-3s and O-2s orbits,as well as the interaction between Na-3s and O-2px orbits in Pt/Na-TiO₂ is not occupied by electrons.And only a little part of orbits is occupied,the energy of which is below the Fermi level,indicating the orbit interaction of large amount of Na and O atoms on Pt/Na-TiO₂significantly contributed to the stability of the system.So the reactant molecules are much easier to adsorb on Na site of Pt/Na-TiO₂ was much compared with the Pt site of Pt/TiO₂.