Investigation of molecular factors governing catalytic activity and selectivity of metal-oxide nanocatalyst

Abstract

Currently, about 90% of chemical products that are widely used in real life require catalysts directly or indirectly during manufacturing process, so the catalysts are playing important roles in our daily lives. Understanding of chemical phenomena at a fundamental level along with efforts to develop eco-friendly chemical processes and to solve the energy and environmental problems that human face today is essential. For the purpose, development a new nano-catalyst with high reactivity, and selectivity as well is necessary. An understanding of the relationship between the surface structure of the catalyst and the reactivity and selectivity at the molecular level is required for a new nano-catalyst. Therefore, in this dissertation, the relationship between surface properties and catalytic properties at the molecular level is revealed. Furthermore, transition metal-based nano-catalysts are proposed to develop a new high-performance catalyst, and various surface reaction phenomena under real catalytic reaction atmosphere will be studied. Chapter 1 introduces research background. In Chapter 2, development of nickel catalyst supported on gallium oxide as an alternative catalyst for methanol synthesis, and effect of the nickel nanoparticle size on catalytic reactivity and methanol selectivity on carbon dioxide hydrogenation are introduced. Nickel catalyst on gallium oxide showed enhanced catalytic activity and methanol selectivity than those of copper-based commercial catalyst, and the methanol turnover frequency was increased as the size of the nickel nanoparticles decreased, whereas the methanol selectivity was decreased. The results suggested the possibility of the alternative methanol catalyst. In Chapter 3, effect of the platinum particle size supported on gallium oxide on the selectivity on carbon dioxide hydrogenation reaction is introduced. Recent advances in electron microscopy technology enable observation of sub-nanometer metal clusters, and as a result, interest in the catalytic activity and selectivity with sub-nanometer metal has emerged. Platinum clusters, and 10 nanometer-sized nanoparticles are dispersed on gallium oxide, respectively, and the size effect on selectivity for methane and carbon monoxide is introduced. In Chapter 4, the nature of the oxidation reaction with carbon monoxide oxidation as a model reaction is introduced using titania with controlled oxygen vacancies as a model system. Nature of the oxidation reaction with transition metal supported on titania is a long-lasting issue, however, the real oxidation mediator is still unclear. Therefore, lattice oxygen is analyzed in real time by operando techniques and quantitatively measured to prove the correlation between enhanced catalytic properties oxygen diffusion with titania having sufficient oxygen vacancies.