Chemistry and Chemical Biology ETDs

Publication Date

Fall 11-17-2020

Abstract

Diesel oxidation catalysts deactivate due to Pt sintering, a major problem in automotive industries. To make sure they operate effectively throughout the lifetime of the vehicle, automotive industries are putting an excessive amount of Pt. There is a need to develop a catalyst that serves long term performance with minimal use of Pt. Jones et al.1 demonstrated that ceria traps Pt atoms. His work generated some logical and valid questions such as what is the mechanism for the formation of anomalously large Pt particles? What is the upper limit of Pt metal loading in the form of single atoms in ceria? What are the sites responsible for the atom trapping? Where does the Pt atom locate: the surface or subsurface of the ceria? Does a non-reducible oxide support trap Pt atom? Is it possible to modify the nucleation of Pt using atom trapped ceria as support? The fundamental understanding of these questions was the focus of this dissertation.

Energy Dispersive X-ray Spectroscopy (EDX) was used for the quantification of Pt. Multiple characterization techniques such as X-ray Diffraction (XRD), Low Energy Ion Scattering (LEIS), X-ray Photoelectron Spectroscopy (XPS), Diffuse Reflectance Infrared Fourier Transmission Spectroscopy (DRIFTS), Aberration Corrected Scanning Transmission Electron Microscopy (AC-STEM), X-ray Absorption Spectroscopy (XAS), CO oxidation reactivity, and Density functional theory (DFT) were used to understand the state and nature of the Pt species.

The experimental evidence suggests Pt particle grow anomalously large due to vapor phase assisted catalyst sintering when subjected to accelerated aging. Ceria can trap 3wt% Pt metal in the form of single atoms which corresponds to 1atom/nm2. The trapped single-atom Pt binds to the ceria (111) step edges strongly and prevents its emission to the vapor phase. Spinel (MgAl2O4) can stabilize Pt atoms with the aid of K additive. By anchoring Pt ions on the catalyst support, the morphology of the deposited phase can be modified causing the formation of 2-D rafts instead of 3-D metal nanoparticles.

In conclusion, trapping of mobile species (PtO2) into ceria support via high-temperature vapor-phase synthesis restricts the anomalous growth of Pt, slows down the emission of Pt from the catalyst system, and allows 100% atom efficiency. Strongly bounded Pt atoms on ceria modify the morphology of the deposited phase to 2-D rafts.

Keywords

single-atom catalysis, thermal stability, ionic Pt, catalyst preparation, atom trapping, Sintering of Pt, Volatilization of Pt, Diesel oxidation catalysts, PdO 2D-raft, Nucleation site

Document Type

Dissertation

Degree Name

Chemistry

Level of Degree

Doctoral

Department Name

Department of Chemistry and Chemical Biology

First Committee Member (Chair)

Abhaya K. Datye

Second Committee Member

Hua Guo

Third Committee Member

Adrian Brearley

Fourth Committee Member

Eric J. Peterson

Download

Share

COinS