A First Principle Study On The Ceria Nanopariticle Interaction With Small Organic Molecules

Ceria is an important material with wide applications including catalyst,electrolyte and solar cells due to its ability to accommodate varying charge states and facilitate relatively facile surface oxidation/reduction that allows it to mediate the oxygen concentration.It is well known that the concentration of Ce3+ ions increases with the reduction in the size of CeO₂ nanoparticles,and consequently oxygen exchange and redox reactions are ease to undergo.Small molecule can dissociative or molecular adsorb on the ceria surface via monodentate,bridging bidentate and chelating bidentate mode.Understanding the interaction between catatlyst and adsorbates from molecular level are of paramount importance in understanding the performance and mechanism of catalyst.Thus we carried out first principle calculations on the interaction between small molecule and ceria nanoparticle.The whole dissertation mainly includes the following three sections,1.Trimethylacetic acid adsorption on CeO₂?111?surfaceTrimethylacetic acid adsorption on the stoichiometric and oxygen-deficient CeO₂?111?surfaces was investigated using density functional theory that accounts for the on-site Coulomb interaction via a Hubbard term?DFT+U?.Both molecular state and dissociative state?TMAA ?TMA-+ H+?were identified on the stoichiometric and oxygen-deficient CeO₂?111?surfaces,respectively.TMAA/TMA-binded to surface via monodentate and bridging bidentate mode.For the stoichiometric CeO₂?111?surface,two thermodynamically favorable configurations with adsorption energies of the order of-30 kcal/mol were found;one is molecular adsorption state and the other one is dissociative state.For the oxygen-deficient CeO_2-x?111?surface,dissociative states are more favorable than molecular states.The most favorable configuration is the dissociative adsorption of TMAA with adsorption energy of the order of-77 kcal/mol.In this configuration,dissociated TMA-takes the position of oxygen vacancy,forming three Ce-O bonds.The larger absolute value of adsorption energy for TMAA/CeO₂?111?than that of TMAA/CeO_2-x?111?suggests surface oxygen defects significantly reinforce the adsorption.To evaluate the long-range dispersion interactions,we quantified the impact of van der Waals?vdW?interaction on the geometries and energies of TMAA adsorption.It is clear that the vdW correction has little effect on the geometries,whereas it is important for the adsorption energies,especially to get correct thermodynamically stable configurations.2.H₂O,CH₃OCH₃ and CH₃CH₂OH adsorption on Ce₁₉O₃₂ nanoparticle surfaceA systematic study of the interactions between Ce₁₉O₃₂ nanoparticle and small molecules consisting of H₂O,CH₃OCH₃ and CH₃CH₂OH were investigated with density functional theory.Dispersion-corrected density functional?optPBE-vdW?is also implemented in order to investigate the effects of long-range interaction of adsorbate-Ce 19O32.Both dissociative and molecular adsorption configuration of molecules binding on C19O32 were identified,and dissociated or molecular H₂O,CH₃OCH₃ and CH₃CH₂OH can bind at both corner and edge of the C19O32 nanoparticle surface.The adsorption energies of H₂O,CH₃OCH₃ and CH₃CH₂OH are in the order of-30 kcal/mol.Dissociative states at corner sites is more stable,in which charge transfer changes the Ce3+ distribution of Ce₁₉O₃₂.3.Acetic acid adsorption on CeO₂?111?and Ce₁₉O₃₂ nanoparticle surfaceForm above two sections and reference,it is seen that small molecule adsorption on CeO₂?111?surface is different form that on Ce₁₉O₃₂ surface.Acetic acid adsorption on CeO₂?111?and Ce₁₉O₃₂ nanoparticle surface was investigated using PBE+U,and the adsorption energies were verified using optPBE+U to including the vdW interaction.Both molecular state and dissociative state were identified on the CeO₂?111?,CeO_2-x?111?and Ce₁₉O₃₂ surfaces via monodentate,bidentate and chelating bidentate.Regardless of the surface structure,acetic acid dissociates on the surface is more stable than molecular adsorbs,whereas the binding modes are different from each other.For CeO_2-x?111?surface,the most stable configuration is acetate binding to surface via bridging bidentate mode;whereas for Ce₁₉O₃₂ nanoparticle surface,the most stable configuration is acetate binding to surface via chelating bidentate mode.The vdW correction is important to get correct thermodynamically stable configurations.