DFT Study On The Electronic Structure For NiO Solid And Its Adsorption Reaction On Surface

NiO is an important catalyst for the oxidation, dehydrogenation and coupling of organic substances, the exact description of its electronic structure has been a disputable notable problem. Theoretical studies on the electronic structure of NiO solid and its surface reactions will be good for understanding special structure, catalytic activity and bonding mechanism of NiO bulk and its surface reaction, these studies will also promote the theoretical research for the post transition metal oxides. In this paper, we study the electronic structures of NiO bulk, surfaces and some of its important adsorption reactions with DFT method by combining the cluster model and slab model, and we have studied the properties of these electronic structures in nature of orbital interaction. The main results of this paper are list as following: 1. The studies on the band structures of NiO bulk and surfaces have been carried out by periodically UB3LYP method. There is no band gap for the NiO(001) and (111) surface, and the band gap is 1.44eV for NiO bulk. The energy calculation results indicate that NiO (001) is stable with small surface energy while the NiO(111) is unstable with large surface energy, which is consistent with the experimental result. The analyses of orbital interaction based on energy bands and DOSs indicate that there is obvious covalent interaction between Ni-O. The electronic migration from bulk to surface is been found and it is more obvious in O-vacancy surface. 2. Our studies for the adsorption of CO and NO on NiO(001) surfaces indicate that the favorite adsorption manner for CO is that CO adsorbs on the Ni site with C-end perpendicularly and for NO is that NO adsorbs N atom down ontop a Ni atom with a N-O bond tilting away from the surface normal by 59.1o, which are both consistent with the experimental results. The vibration frequencies of C-O and N-O exhibit blue shift and red shift after adsorption respectively, we first give the mechanism of charge transfer and σbond bend to explain the situation. 3. In the studying of adsorption of BF₃ on NiO (001) surface and F₂ on BF₃/NiO(001) surface, we get the adsorption energy and the stable adsorption figuration. The activation energy for the dissociation of F₂ on BF₃/NiO(001) system was calculated to be only 11.0kJ/mol, much lower that the bond energy of F-F in F₂, which indicated that the BF₃/NiO(001) system can catalyze both acid-base type reaction and redox reaction. 4. The mechanism of oxidative coupling of methane on NiO(001) surface was studied in this paper, the activation energies for the dehydrogenation of methane and the migration of methyl on NiO(001) surface are both obtained, the interaction mechanism between methyl and NiO (001) surface was also interpreted in the nature of orbitals. 5. The study on NiO(111) shows that there is a two orbital-four electrons interaction between (1×1) NiO(111) and CO molecule, which leads strong adsorption. The study on the catalytic decomposition of formic acid on NiO(111) surface shows that there is O-interchange between formic acid O atom and lattice O atom in dehydration producing H2O+CO, while in dehydrogenation producing H2+CO2, there is no O-interchange, we first explain this experimental result based on our calculation.