Committee Chair:  

Professor Giannis Mpourmpakis 

Department of Chemical and Petroleum Engineering, University of Pittsburgh 

Committee Members:

Professor Götz Veser

Chemical and Petroleum Engineering, University of Pittsburgh

Professor Mohammed Masnadi

Chemical and Petroleum Engineering, University of Pittsburgh

Professor Peng Liu

Department of Chemistry, University of Pittsburgh

Title:

“Catalyst Design for Dehydrogenation of Light Alkanes to Olefins”

Abstract

Light olefins are one of the most important compounds used as building blocks in the chemical industry for the production of a variety of chemicals. Currently, there is a rapidly increasing gap between global demand and supply for olefins. Taking advantage of the low cost of light alkanes and their abundance in the Marcellus and Utica shale reserves, catalytic nonoxidative dehydrogenation (DH) of alkanes is an attractive route to produce olefins. The discovery of active catalysts plays a key role in reducing the energy input required in DH processes. Metal oxides (MOs) exhibiting Lewis acid−base surface functionalities have shown promise as DH catalysts. However, the DH mechanisms on MOs are debated in the literature and can vary with the catalyst type and the nature of active sites present. In addition, the discovery of efficient DH catalysts has traditionally relied on chemical intuition and/or “trial-and-error” experimentation. Alternatively, developing structure-activity relationships (SARs) based on first-principles calculations can accelerate the discovery of active and selective catalysts for the production of olefins.

The main objective of this proposal is to develop and apply SARs for the discovery of active and stable DH catalysts. Initial efforts from this thesis have focused on (i) understanding the mechanistic aspects of the DH of ethane (EDH), propane (PDH), and isobutane (iBDH) on pristine and gallium-doped γ-Al₂O₃ using Density Functional Theory (DFT) calculations and (ii) developing SARs based on fundamental properties of the catalyst and reacting hydrocarbons. In addition to MOs, metal nitrides (MNs) exhibit intrinsic Lewis acid-base functionalities that can activate the C-H bond of alkanes, showing potential as DH catalysts. Preliminary throughput catalyst screening of several MNs using our developed SARs revealed aluminum nitride (AlN) as a promising DH catalyst. Moving forward, we specifically aim to 1: Investigate PDH mechanisms on pristine AlN. Although AlN possesses many attractive catalytic features, it has not yet been utilized as a DH catalyst and our understanding of the exact DH mechanism is very limited. DFT calculations will be used to examine potential PDH mechanisms on AlN. 2: Address the catalytic activity and selectivity of heterometal doped AlN. Tuning the electronic structure of AIN via heterometal doping can enhance its catalytic activity by altering the Lewis acid-base properties of the catalyst. Reactivity and selectivity descriptors can aid the screening of heterometal doped AlN systems towards PDH reaction. 3: Construct a detailed microkinetic modeling (MKM) for PDH on pristine and heterometal doped AlN. Although the DFT-calculated reaction energies and barriers provide valuable information about the relative activity of the PDH mechanisms, MKM is needed to solve the steady-state at reaction conditions based on the calculated kinetic and thermodynamic information. Through the development of a first-principles-based MKM, we aim to accurately describe the DH reaction kinetics.

With the successful completion of the above aims, we will have an advanced understanding of the dominant DH reaction mechanisms on pristine and heterometal doped AlN systems. Importantly, this work will guide experimental efforts toward the discovery of highly active and selective DH catalysts for industrial applications. Moreover, it will establish a computational framework combining catalyst screening tools, such as the developed SARs, and multiscale simulations for the discovery of highly active DH catalysts.