Date of Award

8-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Chemical Engineering

Advisor

Bruce, David A

Committee Member

Blenner , Mark A

Committee Member

Sarupria , Sapna

Committee Member

Stuart , Steven J

Abstract

There is currently a growing interest in the catalytic synthesis of ethanol from syn-gas (2CO + 4H2 --> C2H5OH + H2O). A major challenge associated with this direct route is an inability to find a low-cost catalyst that promotes the proper combination of CO dissociation and CO insertion steps, so as to yield ethanol as the primary reaction product. Bimetallic catalysts, in which one metal promotes hydrocarbon production and the other oxygenate production, may exhibit a synergistic effect that can facilitate the formation of ethanol. Given the complexity of this reaction system, a simple trial-and-error approach to catalyst design is fraught with difficulties, which could severely limit efforts to identify an ideal catalyst material. Thus, a theoretical based investigation is essential to shed light on the complex reaction mechanism from syn-gas to ethanol, to provide guidelines for the experimental synthesis of novel catalysts, as well as conduct computational screening of potentially active and selective catalyst formulations.
Quantum mechanical simulations are used for the rational design of bimetallic catalysts that are optimally suited for the production of ethanol from syn-gas. Density Functional Theory (DFT) simulations and Brønsted-Evans-Polanyi (BEP) relations were used to map out the full reaction mechanism containing hundreds of reaction steps on several 13-atom bimetallic clusters. Microkinetic models based on the pseudo-steady-state-hypothesis (PSSH) and transition state theory were built, considering the reaction steps, the diffusion of intermediate species among different surface sites as well as the metal surface compositions. The simulation results are well matched by experimental activity tests and physical characterization studies. Moreover, key reaction descriptors and pathways for ethanol formation are identified to effectively screen promising candidates. These simulations indicate the nature and stability of the various bimetallic nanocatalysts and more importantly identify specific metal combinations, such as copper containing bimetallic systems, that are ideally suited for ethanol production.

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