The capability to activate light alkanes at mild temperature and selectively control the oxidation reactions are defined the characteristic of an efficient catalyst for the direct oxidation of light alkanes to value-added products. IrO2 (110) surface, which possesses coordinativedly unsaturated iridium and oxygen atoms, is expected to be a potential catalyst to activate light alkanes at mild temperature. In this thesis, density functional theory (DFT) calculations were employed to explore the activation of methane and ethane on the IrO2 (110) surface. The possible reaction pathways of methane and ethane on the IrO2 (110) surface were also investigated. Furthermore, the adsorption characeristics of CHx (x=1-4) and C2H6 on the IrO2 (110) surface were studied using the analyses of density of states (DOS) and electron density difference (EDD) contours.
The calculated results indicate that CH4 and C2H6 adsorb on the IrO2 (110) surface by the agostic interaction between C-H bonds and coordinativedly unsaturated Ir atoms of surface. In addition to the agostic interaction, dispersion interaction also plays an important role in the interaction of CH4 and C2H6 with IrO2 (110) surface. Both of the agostic and dispersion interaction facilitate molecular-mediated mechanism for the first C–H bond cleavage of these alkanes with a low kinetic barriers of 0.25 eV and 0.50 eV which are likely to occur at mild temperature condition. The dehydrogenation reactions of methane and ethane on the IrO2 (110) surface are occurred by the transfer of hydrogen atoms to Obr and Otop sites. Among the dehydrogenation reactions of methane, CH2 dissociation into CH has highest activation energy, making CH2 the most significant monomeric building block on the IrO2 (110) surface. Based on our DFT calculations, the direct conversion of methane to formaldehyde is a possible route on the IrO2 (110) surface via selective CH4 dehydrogenation reactions to CH2 and then the coupling reaction of CH2 with the Otop atom. The energetics for ethane dehydrogenation to ethylene are accessible. However, since the adsorption energy of ethylene is rather high on the IrO2 (110) surface, ethylene prefers undergoing further reactions than desorption from the surface. Therefore, the production of ethylene is infeasible on the IrO2 (110) surface. Instead, the coupling reaction ethylene with Otop to form oxametallacycle is favorable on the IrO2 (110) surface. DFT calculations predict that 1, 2-H shift reaction of oxametallacycle intermediate towards the formation of acetaldehyde is more favorable than ring closure of oxametallacycle to the formation of ethylene oxide. The density functional theory calculations from this work provide an initial basis for understanding and designing efficient catalyst for the direct conversion of light alkanes to the value-added chemicals under mild temperature.

The capability to activate light alkanes at mild temperature and selectively control the oxidation reactions are defined the characteristic of an efficient catalyst for the direct oxidation of light alkanes to value-added products. IrO2 (110) surface, which possesses coordinativedly unsaturated iridium and oxygen atoms, is expected to be a potential catalyst to activate light alkanes at mild temperature. In this thesis, density functional theory (DFT) calculations were employed to explore the activation of methane and ethane on the IrO2 (110) surface. The possible reaction pathways of methane and ethane on the IrO2 (110) surface were also investigated. Furthermore, the adsorption characeristics of CHx (x=1-4) and C2H6 on the IrO2 (110) surface were studied using the analyses of density of states (DOS) and electron density difference (EDD) contours.
The calculated results indicate that CH4 and C2H6 adsorb on the IrO2 (110) surface by the agostic interaction between C-H bonds and coordinativedly unsaturated Ir atoms of surface. In addition to the agostic interaction, dispersion interaction also plays an important role in the interaction of CH4 and C2H6 with IrO2 (110) surface. Both of the agostic and dispersion interaction facilitate molecular-mediated mechanism for the first C–H bond cleavage of these alkanes with a low kinetic barriers of 0.25 eV and 0.50 eV which are likely to occur at mild temperature condition. The dehydrogenation reactions of methane and ethane on the IrO2 (110) surface are occurred by the transfer of hydrogen atoms to Obr and Otop sites. Among the dehydrogenation reactions of methane, CH2 dissociation into CH has highest activation energy, making CH2 the most significant monomeric building block on the IrO2 (110) surface. Based on our DFT calculations, the direct conversion of methane to formaldehyde is a possible route on the IrO2 (110) surface via selective CH4 dehydrogenation reactions to CH2 and then the coupling reaction of CH2 with the Otop atom. The energetics for ethane dehydrogenation to ethylene are accessible. However, since the adsorption energy of ethylene is rather high on the IrO2 (110) surface, ethylene prefers undergoing further reactions than desorption from the surface. Therefore, the production of ethylene is infeasible on the IrO2 (110) surface. Instead, the coupling reaction ethylene with Otop to form oxametallacycle is favorable on the IrO2 (110) surface. DFT calculations predict that 1, 2-H shift reaction of oxametallacycle intermediate towards the formation of acetaldehyde is more favorable than ring closure of oxametallacycle to the formation of ethylene oxide. The density functional theory calculations from this work provide an initial basis for understanding and designing efficient catalyst for the direct conversion of light alkanes to the value-added chemicals under mild temperature.

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