improvement in the reactivity, selectivity and stability of supported metal nanocatalysts: computational study

Abstract

Nanoparticles of late transition metals have been widely used as a catalyst for energy technology, pol-lution prevention, or environmental cleanup. Improvement of the reactivity, selectivity and long-term stability are the key to develop a new nanocatalyst. These catalytic properties can be explained by a complicated combination of various factors such as the size, the composition, the structure and the charge state of a nanoparticle. However, the exact nature of their relationship and priority is still debatable. For understanding the details on a fast and complicate chemical reaction, atomic scale calculations are so useful. This thesis is based on density functional theory (DFT) calculations and a modified kinetic model.

In chapter 2, I focused on the effect of the charge state of a nanoparticle on the catalytic reactivity and structural stability. Small nanoparticles supported on the metal oxide surface exhibit unique catalytic properties. The electronic interaction of the metal nanoparticles with the oxide support induces a change in the charge state of the supported nanoparticle and the catalytic property. I considered carbon monoxide (CO) oxidation on the positively and negatively charged bare Ag13 nanoparticle with different initial structures, icosahedron (Ih) and cuboctahedron (COh). As the expansion of this study, I considered the real system which consists of many molecules under working conditions. CO poisoning has been issued as a crucial problem. In chapter 3, CO poisoning effect on the CO oxidation reactivity of Pt nanoparticles is analyzed with varying the particle size. A difference between adsorption energies of CO and O2 molecules which are reactant gases of CO oxidation is considerably great. Strong adsorption of CO molecules induces the poisoning effect and diminishes the catalytic reactivity. I investigated enhancement of the O2 selectivity and a change in the entire reactivity by substituting Au atoms for some Pt atoms. In the practica...