Theoretical Investigation Of Catalytic Reaction On Boron Nitride Metal Nanocomposites Surface

In recent years, with the rapid development of the computer and the density functional theory electronic structure calculation, to understand the nature of materials from atomic scale and design new functional materials, implementing the first principle calculation based on density functional theory has become an important research tool. With the development of nanotechnique and characterization methods, nanomaterials has widly attracted a great attention for its novel and remarkable properties. Investigation of the catalytic activity on the surface of low dimensional nanomaterials is important to understand the catalytic mechanism and design new composite catalyst. In order to understand the catalytic activity on the surface of nanomaterials from atomic scale, implementing the first principle calculation has become an important research tool. Our work is mostly on the investigation of the catalytic activities and mechanism on the surface of h-BN/metal complex.This thesis contains5chapters, and can be divided into4parts, In the first part (the first chapter), we mainly introduce the theoretical investigation methods. In the second part, for the second chapter, we mainly introduce the investigation of the CO oxidation on single metal atom embedded h-BN monolayer. In the third part, including the third and the fourth chapter, we mainly introduce our investigation on metal substrate or metal cluster or metal wire can modulate h-BN monolayer’s or BN tube’s chemical activity toward O2activation, In the last part (last chapter), cooperated with experimental group, our work is devoted to investigation of O2activation on Pd singlet-facet nanocrystals.In the first chapter, we briefly introduce the density functional theory and transition state search methods.The density functional theory is about the the theoretical framework, application and development. Density functional theory is based on quantum mechanics, replace the wave function with particle density as the basic variable, all properties of the system can be considered to be the unique functionals of the ground state density. In practice, the practical implementation of density functional theory is through solving Kohn-Sham equation, which changes interacting multiparticle problem into non-interacting multiparticle problem. All the approximations are enclosed in the exchange correlation functional. Solve the groundstate particle density through self-consistent calculation and the corresponding system energy is the groundstate energy. The introduction of transition state search is mainly about synchronous transit method (ST) and Nudged Elastic Band Method (NEB) method. The two search methods are based on the known reactant and product.The work in the second and third chapters is about single atom catalysis for CO oxidation. In the first work, the CO oxidation behaviors on single Au atom embedded in two-dimensional h-BN monolayer are investigated on the basis of first-principles calculations, quantum Born-Oppenheim molecular dynamic simulations (BOMD) and micro-kinetic analysis. We show that CO oxidation on h-B’N monolayer supportted single gold atom prefers an unreported tri-molecular Eley-Rideal (E-R) reaction, where O2molecule is activated by two pre-adsorbed CO molecules. The formed OCOAuOCO intermediate dissociates into two CO2molecules synchronously, which is the rate-limiting step with an energy barrier of0.47eV. By using the micro-kinetic analysis, the CO oxidation following the tri-molecular E-R reaction pathway entails much higher reaction rate (1.43×105s-1) than that of bimolecular Langmuir-Hinshelwood (L-H) pathway (4.29s-1). Further, the quantum BOMD simulation at the temperature of300K demonstrates the whole reaction process in real time.In the second work, the CO oxidation behaviors on single Pt atom embedded in two-dimensional h-BN monolayer are investigated on the basis of first-principles calculations. We find that Pt anchored B vacancy of h-BN monolayer present an adsorbed CO promoting process during CO oxidation. Trimolecular reactions are much more favorable than bimolecular reactions and the most favorable reaction path is trimolecular L-H reaction. Adsorbed O2molecule reacted with one adsorbed CO molecule, to form OCOO intermediate stae, and dissociate into one CO2molecule and one remained O atom. The rate-limiting energy barrier is0.56eV, much lower than traditional bimolecular0.93eV. Situations are just the reverse for Pt anchored N vacancy of h-BN monolayer. But trimolecular coadsorptions are favorable in energy for both two species. So CO oxidation on Pt anchored B vacancy is more favorable.In the third chapter, the work is about metal substrate or cluster supported h-BN monolayer showing chemical activity toward O2activation. Perfect h-BN monolayer is very inert in chemistry. But metal substrate or cluster inject electrons into h-BN monolayer, and simultaneously reduce the work function of h-BN monolayer, which finally promote h-BN monolayer’s chemical activity. In this work, three sufaces Cu(111), Ni(111), Co(001) are choosed to support h-BN monolayer and bilayer. Results indicates, Cu(111) is the best substrate to modulate h-BN monlayer’s chemical activity toward O2activation. In practice, metal cluster can play the same role as metal surface. With the preadsobed O2molecule, CO molecule can adsorb on metal surface or cluster supported h-BN monolayer, and reacted with adsorbed O2molecule to form extraordinarily stable CO3intermediate state easily.In the fourth chapter, the work is about Ni wire encapsulated BN nanotube present catalytic activity toward O2activation and CO oxidation. Perfect BN nanotube is very inert. But metal embedded BN nanotube shows very different chemical activities. BN (8,0) and (9,0) tubes are choosed in our work. On Ni wire embedded BN (8,0) nanotube, two types of O2molecule adsorption are obserbed:superoxo and peroxo chemisorption. But on Ni wire embedded BN (9,0) nanotube, only peroxo chemisorption is observed. Peroxo chemisorbed O2molecule easily reacted with CO molecule to form very stable adsorbed CO3structure. But superoxo chemisorbed O2molecule can reacted with CO molecule to form desorbed CO2molecule. So Ni wire embedded BN (8,0) nanotube is a potential catalysis for CO oxidation.In the last chapter, cooperated with experimental group, our work is devoted to investigation of O2activation on Pd singlet-facet nanocrystals (Pd(111) and Pd(100) surface). In experiment, they synthesize Pd(100) encapsulated nanocubes and Pd(111) encapsulated octahedrons, and find singlet O2molecule is formed by probe molecules detection, and singlet O2molecule is preferentially formed on (100) surface. In theory, we investigate different O2adsorption on Pd(100) and Pd(111) surfaces. The O2molecule adsorbed on Pd(100) surface has the higher adsorption energy, longer O-O bond length and possess less local magnetic moment which indicates O2molecule is more easily adsorbed and more activated on Pd(100) surface. The inherent mechanism for O2activation is the electrons transfer from Pd surface to adsorbed O2molecules. The transferred electrons on Pd(100) surface is more than that on Pd(111) surface. The obtained electrons occupy the π*orbital of O2molecule. Since the electrons play an important role in O2activation, then we investigate how electrons density influences O2activation. In theory, we find injecting electrons into Pd slab model will ehance the adsorbed O2activation gradually and conversely injecting hole into Pd slab model will weaken the adsorbed O2activation gradually. In experiment, they synthesize Pd nanocube/TiO2hybrid structures and modulate Pd nanocube electrons density by illumination indensity. For appropriate light, electrons transfer from TiO2to metal, O2activation is enhanced. Under strong illumination, electrons transfer reverse, O2activation is weakened. So the adsorbed O2activation can be simply altered by catalysis’ electrons density.