First-principle Investigations Of Molecular Dissociation And Cyclization On Metal Surface

In recent years,the excellent catalytic performance of surface and interface have attracted wide attentions.Understanding the reaction mechanism on surface and interface is crucial for designing new catalysts and optimizing the existing catalysts.First principle calculations based on density functional theory were carried out,to investigate reaction mechanism of hydrogen dissociation at organic molecule-metal interface and porphyrin derivatives cyclization on surface.Catalytic models based on the surface of metal and low dimensional materials were designed,and a variety of modulation strategies have been proposed.In the first part,the theoretical investigations on an paradigm of molecular dissociation--a“quantum nutcracker”for H₂ dissociation,are provided.The two nutcracker jaws are transition-metal phthalocyanine and a metal substrate such as Cu?111?or Au?111?,all of which are relatively inert on their own.Density-functional-theory calculations demonstrate that,when a H₂ molecule enters the channel between the jaws,it splits into two H atoms by quantum interactions and a gentle mechanical squeeze.Au-based nutcrackers are predicted to operate at room-temperature,while less-expensive Cu-based ones are predicted to be active at a slightly elevated temperature.Indirect experimental evidence is consistent with the present predictions.Such in silico design holds promise for inexpensive,high-performance heterogeneous catalysts for H₂ dissociation and may inspire new approaches to other complex reactions.In the second part,the intramolecular cyclization reactions of iron?II?meso-tetrakis?pentafluorophenyl?porphyrin molecule on Au?111?is investigated combining scanning tunneling microscopy with density-functional-theory calculations.In the experimental observation,the selectivity for one particular product is as high as 90%,which constructs a regular self-assemble chrial structure.Theoretical calculations indicate that intermolecular steric constraint in the self-assembly structure of the adsorbed precursors as well as surface confinement effect are response for the high selectivity of reaction.Comparing the relative energy of intermediate products of two different reaction pathways,we find that the selectivity is increased obviously by intermolecular interaction.By controlling the coverage and heating rate,the single product yield can be achieved from 20%to 90%.The intramolecular cyclization reaction mechanism will bring new inspirations to the area of catalyst design.In the third part,the wide band gap tunability of hybrid TMD double-wall nanotubes?DWNTs?is predicted.The electronic property of hybrid X-Mo-Y nanotubes with different components?X=O and S,inside a tube.Y=S and Se,outside a tube?ranges from metal to semiconductor.Density-function theory?DFT?with HSE06hybrid functional gives a reliable band gap,that all the single wall nanotubes?SWNTs?are semiconductors with the band gap larger than 0.5 eV.Theoretical calculations indicates that the double-wall nanotubes?DWNTs?which are constructed using hybrid X-Mo-Y SWNTs,are either metallic or semiconducting with a band gap ranging from zero to that of inner nanotube.Electronic property of DWNTs depends both on electronegativity difference and diameter difference.If there is no difference in electron negativity between inner atoms?X?of outer tube and outer atoms?Y?of inner tube,the band gap of DWNTs is the same as that of the inner one.If there is a significant electronegativity difference,the electronic property of DWNTs ranges from metallic to semiconducting,depending on diameter differences.The results provide alternative ways for the band gap engineering of TMD nanotubes.