FIRST-PRINCIPLES DENSITY FUNCTIONAL THEORY STUDIES OF REACTIVITIES OF HETEROGENEOUS CATALYSTS DETERMINED BY STRUCTURE AND SUBSTRATE

Author

Lei Cheng, Southern Illinois University CarbondaleFollow

Date of Award

12-2009

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Ge, Qingfeng

Abstract

In this dissertation, density functional theory (DFT) calculations were used to investigate (1)NO₂ adsorption on BaO in NO_x Storage Reduction (NSR) catalyst affected by the morphology of BaO and the γ-Al₂O₃ support, (2) energy barrier of H₂ dissociative adsorption over Mg clusters affected by its electronic structure, and (3) comparison of the activities of CeO₂ clusters affected by two different supports--monoclinic ZrO₂ and non-spinel γ-Al₂O₃. Our results showed that the electronic effect caused by the non-stoichiometry of the bare BaO clusters and surfaces improves their reactivities toward NO₂ adsorption greatly, whereas the geometric structure of the catalyst has only minor effect on the activity; we also found that the γ-Al₂O₃ substrate improves the reactivities of the supported BaO clusters and at the same time the interface between BaO and γ-Al₂O₃ provided a unique and highly reactive environment for NO₂ adsorption. Hydrogen dissociation barrier over pure Mg clusters is greatly affected by the electronic structure of the clusters--closed shell clusters such as Mg₁₀ and Mg₉2- have higher energy barrier toward H₂ dissociation; however, H₂ dissociation over clusters that are two electrons shy from the closed electronic shell are relatively easier. As substrates, neither ZrO₂(111) nor γ-Al2O3(100) affects the reactivity of the supported Ce₂O₄ toward CO₂ adsorption and CO physisorption significantly; whereas the reactivity of Ce₂O₄ toward CO reactive adsorption were found to be affected by the two substrates very differently.