Kinetic insights into the reduction of ceria facilitated via the partial oxidation of methane
| Autor: | Jonathan R. Scheffe, Kent J. Warren |
|---|---|
| Rok vydání: | 2018 |
| Předmět: |
Materials science
Renewable Energy Sustainability and the Environment Materials Science (miscellaneous) Diffusion Energy Engineering and Power Technology 02 engineering and technology Activation energy Partial pressure 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences Methane 0104 chemical sciences Chemical kinetics Reaction rate chemistry.chemical_compound Fuel Technology Nuclear Energy and Engineering chemistry Chemical engineering Partial oxidation 0210 nano-technology Syngas |
| Zdroj: | Materials Today Energy. 9:39-48 |
| ISSN: | 2468-6069 |
| DOI: | 10.1016/j.mtener.2018.05.001 |
| Popis: | A kinetic relaxation study of the partial oxidation of methane over ceria in the absence of gas-phase oxygen, a promising pathway for syngas production, was performed under atmospheric pressure between 750 °C and 1100 °C. Using a thermogravimetric analyzer, the effect of cyclability, gas/solid diffusion, reactant/product composition, and surface contaminants on the measured rate of ceria reduction was addressed. Reaction kinetics were described by an apparent activation energy that was extracted from Arrhenius-type plots as a function of composition. Determined via two isoconversional methods, apparent activation energy was shown to vary with reaction extent between 20 kJ mol −1 and 80 kJ mol−1, increasing mostly for large reduction extents (δ > 0.15). Interestingly, this range is lower than the discrete values presented in literature and supports the idea that reaction rates are not limited by bulk diffusion. Further, although deposited carbon was not experimentally detected, evidence of surface adsorbates , such as carbonates and hydroxyls, was observed, as the reaction rate was impacted by the length of subsequent oxidation in O 2. The reaction rate was also proportional to the methane partial pressure and weakly inhibited by additional hydrogen (only at large nonstoichiometries), in agreement with equilibrium thermodynamic predictions. Experimental repeatability upon isothermal cycling increased with increasing operating temperature, contrary to higher-temperature, ceria-based thermochemical cycles. Overall, this work provides new experimental insights that affect the partial oxidation of methane over ceria and help guide the immediate development of larger scale systems. |
| Databáze: | OpenAIRE |
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