| As an important transition metal-oxide, zirconium oxide (ZrO2) possesses particular properties different from other metal oxides, such as unique acidity, basis sites sustentation, tolerance high temperature stability and heat insulation. Therefore, zirconium oxide (ZrO2) has been widely applied to toughening ceramic materials, gas-sensitive sensors and catalysts. In this thesis, the structures and adsorption performances of (ZrO2)n clusters are investigated using the density functional theory methods (DFT) in the GaussianO3 package. The main and important conclusions are summarized as follows:1 To obtain the lowest-energy structures of (ZrO2)n (n=3-6) clusters, a number of possible structures have been taken into account. The calculated results of the total binding energies, the total binding energy gaps and the second derivative energies (Δ2En), indicate that (ZrO2)5 cluster are of relatively higher stability. According to IR active vibration spectra analysis, the Zr-O stretching motion from terminal oxygen atoms appear at between 900 and 1000cm-1, the Zr-O-Zr-0 four-membered rings give rise to the IR active modes between 600 and 700cm-1, in addition, and the bands around 800cm-1 result from the motion of Zr-O-Zr-O-Zr-O bond at the cage structure. By analyzing Mulliken and NBO charges in (ZrO2)n clusters, it is indicate that Zr-O bonds are ionic bonds. In addition, the 4d orbital of Zr atoms and the 2p orbital of O atoms take an active role in the bonding. The calculated HOMO-LUMO gaps exhibit an even-odd alternating pattern with increasing cluster size, which means that the higher chemical stability is found at n=3,5.2 The adsorption behaviors and relative characters of H2 molecules toward (ZrO2)n (n=1-6) clusters have been investigated by using density functional theory. The calculated adsorption energies illustrate that these adsorption processes are the chemisorption, and one H2 molecule can be easily absorbed on (ZrO2)n (n=1-6) clusters by binding to the top Zr atom. The analyses of vibrational frequency and charge transfer have a deep view of H-O and Zr-H bonds formed in different sized ZrnO2nH2 clusters. To investigate the dissociation mechanism of H2 on (ZrO2)n clusters, we explore the pathway related to H2 dissociation on (ZrO2)n (n=4-6) clusters. These pathways over the potential energy surfaces are obtained through the intrinsic reaction coordinate (IRC) analyses from positive and negative direction of imaginary frequency of their transition states. With the increasing number of H2 molecule adsorption, the adsorption of H2 molecule exhibits two tendencies. The first tendency is that H2 molecule prefers to approach to the low coordinative sites. The second tendency is that these adsorption modes are all do their best to keep symmetry to minimize the system energy.3 The structure, energy, charge transfer and HOMO-LUMO gaps of Ni on (ZrO2)n (n=1-6) clusters have been studied by using the density functional theory. The HOMO-LUMO gaps show that Ni-(ZrO2)n (n=1-6) clusters have larger chemical stabilities than (ZrO2)n (n=1-6) clusters. Therefore, the adsorption behavior of CO2 gaseous molecules on Ni-(ZrO2)n (n=1-6) clusters have been considered. The CO2 molecules adsorption on Ni atoms sited on the Ni-(ZrO2)n (n=1-6) clusters are thermodynamically favored by obtaining the adsorption energies, bonding parameters and vibrational frequency. In these modes, the sorption on Ni-(ZrO2)6 cluster is more favorable than others. |
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