(650h) Increasing Activity, Reducing Coking, and Promoting Unexpected Reaction Pathways during Methane Steam Reforming By Applying Uniform Electric Fields in a Scalable Reactor

Authors: 
Gray, J. T., Washington State University
Ha, S., Washington State University
Che, F., University of Toronto
McEwen, J. S., Washington State University
It has been shown both computationally and in small-scale studies using STM tips for single-molecule analysis that very high electric fields can change both the kinetics and thermodynamics of chemical reactions. This could be an exciting and unexplored new area for reaction engineering, but generating uniform electric fields in a larger scale continuous flow reactor has proven to be a significant challenge. We have designed a system capable of generating uniform electric fields over Ni catalysts for methane steam reforming, which has been compared to density functional theory computations by our collaborating group in the past. This talk focuses on the experimental observations, with special focus on the properties of the catalyst itself after methane steam reforming in the presence of electric fields. We report both expected findings and a new mystery – and our attempts to unravel said mystery. On the expected side, our DFT calculations correctly predicted that, in a positive electric field, reaction rates would increase consistent with the lowering of the energy barrier of the first methane C-H bond scission; H2O would bind more readily to the surface; H2O would have a more difficult time decomposing; and that coke would have a more difficult time forming. Unexpectedly, the negative field apparently promotes alternate reaction pathways which may lead to C-C coupling reactions to form larger unsaturated hydrocarbons without coking. Both post-reaction catalysts were scrutinized using visual observations including macroscopic photographs and SEM imaging, x-ray photoelectron spectra, temperature-programmed oxidation, and x-ray diffraction patterns.
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