Date of Award

2016

Document Type

Open Access Dissertation

Department

Chemical Engineering

Sub-Department

College of Engineering and Computing

First Advisor

Andreas Heyden

Abstract

This dissertation augments the field of computational catalysis with uncertainty quantification. An efficient tool to describe the energetics and structure of atomistic systems is density functional theory (DFT). DFT may be used to understand how catalysts work although DFT is inexact in nature due to approximations necessary for computational tractability. These approximations in DFT cause uncertainty in microkinetic model results for catalytic systems. Therefore, reliable model results gained from DFT include a quantification of uncertainty. The case study to examine a systematic framework for uncertainty quantification is water-gas shift (WGS CO+H2O⇌CO2+H2) reaction by Pt/TiO2 catalyst.

Uncertainties are represented with probabilities and a latent variable model is developed that account for errors and correlations in DFT energies. This probabilistic model is further constrained to known reaction thermodynamics, and then propagated to quantities of interest such as turnover frequency (TOF), apparent activation barrier, and reaction orders. DFT energies are obtained using four separate functionals PBE, RPBE, HSE, and M06L that each have their own justification for being appropriate for this study. Although the uncertainty in model results spans orders of magnitude, a new approach is introduced to identify the dominant catalytic cycle under uncertainty. Next three active sites of the Pt/TiO2 catalyst are compared using uncertainty and Bayesian statistics to find which active site best explains experiments. Of the three active sites, two involve the oxide support (TiO2) in the mechanism of reaction. The third active site models only the metal with Pt(111). The two active sites involving the oxide support both explain the experimental data far better than the terrace Pt(111) active site. Therefore, it is concluded that the oxide support plays a mechanistic role in the WGS reaction. The selected active site is verified with separate experiments at separate pressure and temperature conditions

Share

COinS