Title:

Understanding the Interplay of Metal and Oxide Phases in COx Reduction Chemistries

Abstract:

COx hydrogenation technologies have attracted tremendous interest due to their potential to convert CO2, the main anthropogenic greenhouse gas (GHG), into value-added C1 and C2+ products, often powered by renewable energy sources. In this context, photo-, thermo- and electro-catalytic processes have been proposed, with many technologies currently in pilot and demonstration stages, and a few already in commercialization. Typically, COx hydrogenation processes involve heterogeneous catalysts due to their potential to bypass catalyst-product separations. Nonetheless, despite the great technological progress of the past two decades, the nature of the catalytic active sites in many processes remains a topic of debate, hindering further advances. Two such examples are the electroreduction of CO2 (CO2RR) and the thermocatalytic hydrogenation of CO via the Fischer-Tropsch synthesis (FTS). In both cases, different active phases have been proposed, including metals, oxides, and partially reduced oxide surfaces. Yet, it is probable that there is no single active phase, but rather an interplay between oxidized and metallic surfaces that determines the activity at the atomic level.

The main objective of this proposal is to provide a better understanding of the role of different phases in CO2RR and FTS, as well as to shed light on the factors that might drive phase changes. Preliminary efforts from this work have used density functional theory (DFT) calculations to (1) unravel the promotion effects of Ru isolated surface atoms on Co-based FTS, specifically, on enhancing the reducibility of the Co host; (2) understand the role of site coordination in driving the surface oxidation of Cu nanoparticles under CO oxidation conditions. Following this line of work and motivated by the pressing climate change crisis, we aim to: (1) improve the performance of CO2 electrochemical reduction catalysts, and (2) screen effective catalysts for the thermocatalytic reduction of CO via FTS. Specifically in aim 1 we will focus on understanding the role of different oxidation states and inlet CO2 concentrations in shifting the product selectivity in gas-fed flow electrolyzers, as well as understanding how catalyst promoter loadings can be tuned to optimize product selectivity. For aim 2, we will extend our work on isolated Ru atoms by screening other promoters in order to improve the activity and selectivity toward C5+ products. Additionally, we will investigate how promoters might induce catalyst oxidation by increasing the affinity towards O or H2O.

 Successful completion of the above aims will provide us with a deeper understanding of the factors inducing phase transformations of active sites under reaction conditions. Moreover, it will set a computational framework for the effective screening of catalysts that encompasses different oxidation states, promoter effects, and chemical ordering.

Committee Chair:

Dr. Giannis Mpourmpakis

Department of Chemical and Petroleum Engineering

University of Pittsburgh

Committee Members:

Dr. James McKone

Department of Chemical and Petroleum Engineering

University of Pittsburgh

Dr. John Keith

Department of Chemical and Petroleum Engineering

University of Pittsburgh

Dr. Marc D. Porosoff

Department of Chemical Engineering

University of Rochester