Dissertation
METHANE STEAM REFORMING OVER NI-BASED CATALYSTS: USING ELECTRIC FIELDS TO ENHANCE CATALYTIC PERFORMANCE
Doctor of Philosophy (PhD), Washington State University
01/2016
Handle:
https://hdl.handle.net/2376/117740
Abstract
To address some of the most common issues facing methane steam reforming (MSR) over Ni-based catalysts – such as coke poisoning and high operating temperatures – we investigate the effect of the electric field effects on the said catalytic process. Three important aspects of MSR were studied via density functional theory (DFT) calculations: (1) the coke formation over Ni surfaces (Ni(111) and Ni(211)); (2) the interaction between H2O molecules and Ni surfaces; and (3) the overall thermodynamic and kinetic properties of the MSR reaction over Ni(111). According to the results from the field-dependent microkinetic model and the corresponding experimental work, we found that, when comparing our results to those in the absence of an electric field, that a positive electric field can greatly enhance the Ni catalytic performance via: (i) impeding the coke formation over the catalytic surfaces; (ii) decreasing the initial input steam-to-methane ratio; and (iii) lowering the operating temperatures.
Furthermore, to better understand the mechanisms of sulfur and coke poisoning over the Ni-supported yttrium-stabilized-zirconia (Ni/YSZ) electrode in electrochemical cells, we elucidated the field effects on the oxygen vacancy formation at the triple phase boundary (TPB) of this catalysts via hydrogen oxidation under experimental conditions since such vacancies are active for sulfur and coke poisoning. Our results showed that both large negative and positive electric fields could lead to more active TPB vacancies of the Ni/YSZ electrode to a certain degree. This work emphasizes the significance of considering the factor of electric fields when investigating electrochemical cell systems.
Finally, we provide a 'bottom-up' fundamental insight into two debates regarding methane activation over Ni-based catalysts, including the role of a low concentration of carbon or carbide species and the role of electric fields in a fuel cell system. Our DFT results suggest that inducing a local change of the Ni oxidation states can markedly enhance methane activation. Overall, this thesis will be instructive for the design of heterogeneous reactors with tunable metal oxidation states via the modification of the surface carbon or the interface carbide complex as well as the addition of reaction environment factors (e.g., electric fields).
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Details
- Title
- METHANE STEAM REFORMING OVER NI-BASED CATALYSTS: USING ELECTRIC FIELDS TO ENHANCE CATALYTIC PERFORMANCE
- Creators
- Fanglin Che
- Contributors
- Jean-Sabin McEwen (Advisor)Su Ha (Committee Member)Aurora Clark (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- School of Chemical Engineering and Bioengineering
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 510
- Identifiers
- 99900581831101842
- Language
- English
- Resource Type
- Dissertation