545384 Catalytic Methane Steam Reforming at Low Temperature By Surface Protonics

Tuesday, June 4, 2019: 3:06 PM
Texas Ballroom D (Grand Hyatt San Antonio)
Yasushi Sekine, Applied Chem., Waseda Univ., Tokyo, Japan

Generally, methane steam reforming is conducted at high temperatures (923–1123 K) with Ni catalysts because of thermodynamic equilibrium and because of methane molecule stability. However, such high reaction temperatures raise some issues such as the necessity for expensive materials that can tolerate at high temperatures, catalyst deactivation, and complex processes with multiple heat-exchangers. Lowering steam reforming temperatures not only has the potential to improve the hydrogen production efficiency, but also has high potential for waste heat recovery.

We have found that a steam reforming process in an electric field, Electreforming (ER), shows high activity even at a low temperature of 423 K. For ER, Pt or Pd catalyst supported on CeO2-based oxide are an effective catalyst. Activities increased drastically by the application of an electric field with low electric power consumption of 130 MJ/kg-H2. However, the reason why the reaction proceeded with application of the electric field was uncertain. So, the aims of this study are to elucidate the electric field effects on catalytic methane steam reforming and the reaction mechanism for Electreforming. To achieve these aims, kinetic analyses, in particular with isotopes, and operando-IR measurements were conducted with Pd catalyst supported on CeO2. Results show that the application of the electric field promoted surface protonics. Moreover, it enabled catalytic steam reforming even at the low temperature of 423 K.

Application of the electric field increased the activity drastically. To elucidate the effects of the electric field on methane steam reforming, kinetic investigations and operando-DRIFTS measurements were conducted.
Results of our kinetic analyses demonstrated that the water pressure dependency of the reaction rate increased during the application of the electric field. However, the apparent activation energy decreased with the electric field, especially at lower reaction temperatures, indicating that the reaction mechanisms with and without the electric field differ considerably.

Results of operando-DRIFTS revealed that surface proton conduction via adsorbed water on the catalyst surface occurred with the electric field, known as the Grotthuss mechanism. Furthermore, our operando analyses from the viewpoint of an inverse kinetic isotope effect revealed that methane was activated by proton collision derived from the Grotthuss mechanism. Furthermore, ER proceeds mainly at the interface between Pd and CeO2. Therefore, the surface protonics by the application of electric field serve an important role in the enhancement of catalytic methane steam reforming at a low reaction temperatures of 423 K.


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