Computational Catalyst Design for Hydrocarbon Partial Oxidation Processes

Abstract

Chemical conversions in catalytic selective oxidation processes of light hydrocarbons are responsible for the production of numerous industrial chemicals, plastics, and intermediates. These processes are relatively expensive to perform, and are typically operated at high thermodynamic inefficiency, so the development of novel, highly efficient catalysts designed under process intensification (PI) would prove to be very cost effective. Specifically, the selective oxidation of ethylene to ethylene oxide (EO) will be the focus of our study. EO is mainly used to produce ethylene glycol, and it is produced commercially via an exothermic, vapor-phase reaction of ethylene and oxygen over Ag catalysts. There exists a strong driving force toward unselective reaction to complete combustion, and conversion must be kept low to ensure high selectivity to EO. The research on the most commonly used silver catalysts is needed to understand the micro- and macroscopic factors which affects the behaviors of EO production process.

In Chapter 2, we focused on surface catalytic mechanisms of the ethylene oxide (EO) formation process. Periodic plane-wave Density Functional Theory (DFT) methods were used to analyze related reaction mechanisms on the Ag(111) surface facet with low coverage. Then, the structures of the various crystal planes, Ag(100), Ag(110) and Ag(111), on the catalytic performance of silver-based catalysts in the ethylene oxidation system were studied in Chapter 4 to determine the geometric and electronic effects. Metallic promoters like cesium and rhenium were introduced into the current reaction system on Ag(110) surface to figure out how the microscopic interactions among atoms influence the macroscopic performance of reaction processes. Energetic changes of related species and pathways were calculated. Key surface species are identified to suggest the key factors for the selectivity during EO formation. Our results are consistent with previous kinetic modeling efforts in the literature which did not employ DFT analysis. Lastly, our study demonstrates how fundamental theoretical investigations and multi-scale modeling techniques are currently impacting the advancement of rational catalyst design in the light hydrocarbon processing industry.

In the possible future studies, an overall theoretical system of the ethylene oxidation process on the silver-based catalysts will be developed, which will greatly aid in the process intensification efforts of catalytic partial oxidation reactors.