Skip to Main Content
 

Global Search Box

 
 
 
 

Files

File List


Diss_final.pdf (2.77 MB)

ETD Abstract Container

Abstract Header

First-Principles Studies of the Reactivity of Transition Metal Oxide Surfaces

Pan, Li
http://rave.ohiolink.edu/etdc/view?acc_num=osu1448910602

Abstract Details

2015, Doctor of Philosophy, Ohio State University, Chemical Engineering.
Transition metals such as platinum and palladium are important oxidation catalysts used in processes such as exhaust-gas treatment (e.g. catalytic converters) and power generation (e.g. gas turbines). Often these catalysts operate under oxygen-rich conditions and a variety of oxygen phases may potentially form. The formed oxide surfaces may dramatically alter catalytic performance. As an example, PdO has been shown to have a high activity in the catalytic combustion of methane. We have investigated the reaction chemistry of the PdO(101) surface using Density Functional Theory (DFT) and compared our results with surface science experiments. The philosophy behind our approach is to examine individual processes that occur during the more complex catalytic reaction conditions. This approach allows us to establish a fundamental understanding of these underlying processes and ultimately will help in assembling a full picture of catalyst behavior under reaction conditions. First we studied the oxygen vacancy evolution during thermal reduction of the PdO(101) surface. Thermal reduction allows for the examination of the evolution of O vacancy formation without the complexity of chemical reduction (e.g. reduction by CO). Our DFT results show that the existence of oxygen vacancies on the surface activates neighboring lattice oxygen atoms promoting long vacancy chains on the atomic surface, an observation that matches scanning tunneling microscopy (STM) images. We next examined O2 adsorption on the unreduced PdO(101) surface with the goal of understanding how this important reactant interacts with the surface. However, the Perdew-Burke-Ernzerhof (PBE) calculations overestimate the bonding energy of O2 on the PdO(101) surface because DFT-PBE predicts a strong interaction between the unfilled O2 molecular orbitals and Pd d bands. The Heyd-Scuseria-Ernzerhof (HSE) functional reduces this interaction and the calculated adsorption energy using DFT-HSE agrees well with temperature programmed desorption (TPD) experiments. This result shows the importance of characterizing elementary processes with both DFT and surface science experiments. The adsorption and oxidation of CO, NO, and propane on PdO(101) were also investigated. According to DFT-HSE calculations, CO molecules can only adsorb on top of Pdcus site and react with adjacent lattice Ocus atoms. After reduction, the formed oxygen vacancies strongly stabilize the neighboring CO adsorption, so the remaining CO tend to diffuse to the vacancy sites. If the surface is contaminated with water, the CO oxidation is promoted because water forms a hydrogen bond and stabilizes the carboxyl intermediate during the oxidation. Unlike CO, the adsorption of NO has various configurations and NO can also bond on Pd4f sites. At low coverages, the Pdcus bridge site is preferred as well as there is a flat-lying configuration. When the coverage increases to 0.35 ML, all the NO diffuse to the atop Pdcus sites and further NO adsorbs on Pd4f sites until it reaches saturation. In DFT, no facile oxidation pathways were found. Finally we studied the activation of propane on PdO(101) and demonstrate that the existence of alkane σ-complexes has possible impact in our expectation of the temperature range where alkanes can be activated and potentially opens up opportunity for selective alkane chemistry.
Aravind Asthagiri (Advisor)
Lisa Hall (Committee Member)
Isamu Kusaka (Committee Member)
125 p.
Chemical Engineering
DFT; PdO; Oxidation

Recommended Citations

Citations

  • Pan, L. (2015). First-Principles Studies of the Reactivity of Transition Metal Oxide Surfaces [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1448910602

    APA Style (7th edition)

  • Pan, Li. First-Principles Studies of the Reactivity of Transition Metal Oxide Surfaces. 2015. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1448910602.

    MLA Style (8th edition)

  • Pan, Li. "First-Principles Studies of the Reactivity of Transition Metal Oxide Surfaces." Doctoral dissertation, Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1448910602

    Chicago Manual of Style (17th edition)

osu1448910602
548
© 2015, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.