A Density Functional Study On The Adsorption And Dissociation Of Small Molecules Over ZrO₂Perfect And Supported Surfaces

Zirconia (ZrO2) is widely used as the catalyst carrier due to its high melting pointand stable chemical properties. The current theoretical studies mainly concern theinvestigation of small organic molecules (such as alcohols, hydrocarbons) adsorptionand dissociation on the cubic-ZrO2surface. However, the decomposition mechanismof small molecules on the perfect and supported surfaces is relatively in lack. In thiswork, the adsorption and decomposition mechanism of some small molecules on ZrO2(110) and (111) perfect and supported surface have been investigated, so as tounderstand the electronic structure and the catalytic mechanism of ZrO2. The maincontents we investigated in this thesis as follows:1. The adsorption of H2O, OH and O on the different sites of cubic ZrO2(110)surface has been studied with a periodic slab model by PW91approach of GGAwithin the framework of density functional theory. The results showed that H2Omolecule adsorption on cubic ZrO2(110) surface is dissociation adsorption when theadsorption model is bridge-H-up, and the H2O molecules form surface hydroxylgroups. The adsorption energy is150.5kJ/mol. The top site was found to be the moststable adsorption site for OH and O. Mulliken charge analysis shows that H2Omolecules are loss of electron donor in the adsorption state, while it is theelectron-body in the decomposition state.2. The adsorption of H2S, HS and S on the different sites of ZrO2(110) surfacewere studies. The results of geometry optimization indicate that the stable structure ofdissociation are H2S molecules adsorbed all bridge sites and parallel on the hollowsite. SH and S were found to prefer bridge sites and top sites, respectively. CompleteLST/QST methods were used to search the transition state for dissociation reaction.The results reveal that H2S dissociated on ZrO2(110) surface and form two surfacehydroxyl groups.3. The adsorption and dissociation of NO adsorption on M/ZrO2(110)(M=Ru,Rh) surface is investigated. The calculated results indicate that the hollow site isstable energetically for Ru and Rh atoms adsorption on ZrO2(110) surface with theadsorption energies of207.4and106.3kJ/mol, respectively. NO adsorption on M/ZrO2(110) surface is more stable than preface surface. Double NO has twopossible dissociation passways:(1)2NOâ†'N2(g)+2O (ads),(2)2NOâ†'N2O (g)+O (ads). The calculation results indicated that the first dissociation path is more easilythan the second.4. The adsorption of CO on Pt/ZrO2(110),(111) surface was studied. The resultsindicated that band gap were more reduced and the ability of electron transfer wasmore enhanced when Pt adsorption on ZrO2(110) surface than (111) surface. WhenCO adsorbed on ZrO2(110) surface, the adsorption energies is larger than (111)surface. CO and Pt have two electron transfer mechanism: the CO5σâ†'Pt6s of σbonding mechanism and the Pt5dâ†'CO2Ï€ of Ï€ feedback mechanism. The bondingmechanism is dominant.5. Density functional theoretical calculations were performed for N2O adsorptionand decomposition on Cu/ZrO2(111) surface. The results showed that the first step todevelop nitrogen molecule and oxygen atom is easy because of small energy barrier.